Ammonites from the lower and middle Toarcian (Jurassic) in the Cantabrian Range (Asturias and Basco-Cantabrian Basin, Northern Spain). Chronostratigraphy, biotic events and correlations with other Iberian basins

Ammonites from the lower and middle Toarcian (Jurassic) in the Cantabrian Range (Asturias and Basco-Cantabrian Basin, Northern Spain). Chronostratigraphy, biotic events and correlations with other Iberian basins | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Ammonites from the lower and middle Toarcian (Jurassic) in the Cantabrian Range (Asturias and Basco-Cantabrian Basin, Northern Spain). Chronostratigraphy, biotic events and correlations with other Iberian basins Antonio Goy, Maria Jose Comas-Rengifo, José Carlos García-Ramos, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4224858/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Oct, 2024 Read the published version in Journal of Iberian Geology → Version 1 posted 5 You are reading this latest preprint version Abstract The present paper studies the ammonite associations from the terminal Pliensbachian (Spinatum Zone, Hawskerense Subzone) and from the lower-middle Toarcian (Tenuicostatum to Variabilis Zones) in two areas of the Cantabrian Range, situated in the Asturian Basin (AB) and in the Basco-Cantabrian Basin (BCB). The outcrops examined in the AB were situated on the coast, between Villaviciosa and Ribadesella and those of the BCB were located inland, in the provinces of Cantabria and Palencia. The lower boundary of the Toarcian was accurately established with the first record of the genus Dactylioceras in both basins. In the Cantabrian Range, we characterised all the standard zones and subzones of the Toarcian Stage. In order to establish the chronostratigraphic horizons, we considered the evolution of the Dactylioceratidae (Dactylioceratinae) in the Tenuicostatum Zone, of the Hildoceratidae (Harpoceratinae) in the Serpentinum Zone, of the Hildoceratidae (Hildoceratinae) from the last horizon of the Falciferum Subzone to the end of the Bifrons Zone, and of the Phymatoceratidae (Phymatoceratinae) in the Variabilis Zone. We identified the following main regional or global biotic events: 1) the mass extinction of the Amaltheidae Family in the upper part of the Hawskerense Subzone; 2) the expansion of the Dactylioceratinae Subfamily as from the base of the Tenuicostatum Zone; 3) the extinction of practically all the late Arieticeratinae ( Emaciaticeras , Canavaria , Tauromeniceras ), of the Lioceratoides and of the Dactylioceras ( Eodactylites ) in the boundary between the Paltum/Mirabile and Semicelatum subzones; 4) the final extinction of the aforementioned groups, and of the Neolioceratoides , Protogrammoceras ( Paltarpites ) and almost all the Dactylioceras ( Orthodactylites ) in the boundary between the Tenuicostatum and Serpentinum zones, coinciding with the final stage of the Jenkyns Event. When the factors that caused this event came to an end, at regional or global scale there occurred a recovery of the Dactylioceratinae, Harpoceratinae and Hildoceratinae within a short time interval, with significant radiations of these subfamilies. The Phymatoceratinae subsequently radiated from the Bifrons Zone. Lower Jurassic Pliensbachian-Toarcian boundary ammonite zonal chronostratigraphy extinction ammonoid provincialism Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction The ammonoids from the interval between the Upper Pliensbachian (Spinatum Zone, Hawskerense Subzone) and the Upper Toarcian (Thouarsense Zone, Bingmanni Subzone) are well represented in the Cantabrian Range, where the Lower Jurassic successions continue, though not continuously, extend for over 300 km, from Avilés in Asturias to the Aralar Mountains in Navarre. For the chronostratigraphic study of the abovementioned interval, we selected several sections of the Asturian Basin (AB) and of the Basco-Cantabrian Basin (BCB). Noteworthy among these are, in the AB, the W Rodiles (WR), Santa Mera (SM) and Lastres (LA) sections, and in BCB, the Salinas de Pisuerga (Sl), San Andrés (SA), Camino (CM), San Miguel de Aguayo (SMA), Tudanca (TU) and Castillo Pedroso (CP) sections (Fig. 1 ). The Toarcian Stage, proposed by d’Orbigny (1949, 1952), commences with the appearance of Dactylioceras ( Eodactylites ) shortly after the mass extinction of the Amaltheidae Hyatt Family, 1867. This Stage was subdivided by Buckman ( 1910 ) into the Whitbian and Yeovilian Stages, on a lithostratigraphic basis, which includes the Variabilis Zone within the Whitbian. Subsequently, M.K. Howarth (in: Dean et al., 1961 ) redefined the Whitbian, situating the boundary between the two substages at the base of the Variabilis Zone. Other authors employing a binary division are Ohmert ( 1976 ), Knitter & Ohmert (1983), Etzold et al. 1989 , Howarth (1991, 1992) and Page ( 2003 ). On the contrary, some authors have chosen to use a ternary division (Monestier, 1931 ; Gabilly et al., 1971 ; Guex, 1972 ; Suárez Vega, 1974 ; Elmi et al., 1974 , 1989 , 1994 , 1997 ; Gabilly, 1973 , 1976a , b ; Goy, 1974 , 1985 ; Goy et al., 1988 , 2010 ; Fauré, 2002 ; Page, 2003 ; Bécaud, 2006 , Salazar-Ramírez et al., 2020 ). The lithostratigraphic units where the ammonoids studied were recorded are the Rodiles Fm, Santa Mera Mb, in the AB (Valenzuela et al., 1986 ; Valenzuela Fernández, 1988 ) and the terminal part of the Camino Fm and the lower part of the Castillo Pedroso Fm in the BCB (Robles et al., 2002 , 2004 ). The stratigraphic distribution of the Toarcian ammonoids in the AB was investigated by Dubar & Mouterde ( 1957 ) and in particular by Suárez Vega ( 1974 ) in the second half of the XX century, and by Gómez et al. ( 2008 ), Goy et al. ( 2010 )d mez & Goy (2011) in the early years of the XXI century. In the BCB, the ammonites were studied by Dahm ( 1966 ), Braga et al. ( 1985 , 1988 ), Comas-Rengifo et al. ( 1988 ), Bernad ( 1993 ), Goy et al. ( 1994 , 2006b ), Gómez & Goy ( 2011 ) and Salazar-Ramírez et al. ( 2020 ). The present paper enhances the available information on the succession of the ammonoids, characterises the choronostratigraphic units, based upon the evolution of this group of fossils; moreover, a comparison is made between the record obtained and that of the standard scales established by other authors. Another interesting aim of our paper involves correlating the chronostratigaphic succession obtained with that of the Subboreal, Submediterranean and Mediterranean subprovinces ( sensu Page, 2003 ), between the Tenuicostatum and Bifrons zones and that of the NW of Europe and the Mediterranean province in the Variabilis Zone and, in particular, with other Iberian basins, such as the Iberian Range, the W of Portugal (LB) and the Betic Range. The chronostratigraphic succession obtained should be employed to correlate the principal events that took place in this period in the Cantabrian Range with those identified in the NW of Europe and in the N of África. 2 Location and Geological setting The lithostratigraphic succession of the lower Toarcian presents a thickness of 14 m and that of the middle Toarcian has a thickness of 17.5 m in the AB. It comprises an alternation of limestones and marly limestones with marls, of a grey-black colour, in which no significant discontinuities can be observed. It is arranged in transgressive-regressive cycles, which display transgressive maxima in the Tenuicostatum Zone (Paltum/Mirabile Subzone) and in the Bifrons Zone (Bifrons Subzone). The former coincides with a section of marls rich in organic material, and the latter, which is the most noteworthy of the whole Lower Jurassic, coincides with the maximum deepening of this basin (Gómez & Goy, 2000 ; Gómez et al., 2008 ). In the AB, three sections were studied; these are situated from W to E along the coast: 1) WR (Spinatum Zone p.p . to Bifrons Zone), 2) SM (Variabilis Zone to Thouarsense Zone, Bingmanni Subzone) and 3) LA (Spinatum Zone to Serpentinum Zone). The complete reference stratigraphic succession can be seen in the first two sections: WR and SM (Fig. 2 ) where all the layers of the lower and middle Toarcian exhibit a continuous outcrop. Both of them were thoroughly sampled; a noteworthy lateral continuity can be observed in the levels identified and which can be recognised from the Villaviciosa inlet to Lastres beach. In the BCB, the lithostratigraphic succession of the lower Toarcian presents a thickness of 17 m, and that of the middle Toarcian, 24 m. Moreover, the same main T-R cycles as in the AB can be observed (Quesada et al. 2005 ). We conducted an in-depth study of the SMA sections (Spinatum Zone, Hawskerense Subzone to the Bifrons Zone p.p .) and the SA section (Bifrons Zone, Bifrons Subzone p.p . to the Thouarsense Zone, Bingmanni Subzone). The Tudanca (TU ) and Castillo Pedroso (CP) sections of this basin are also very important due to being situated in the depocentre and to exhibiting, as a whole, the greatest thicknesses (Comas-Rengifo et al. 1988 ; Quesada et al., 2005 ; Gómez & Goy, 2011 ). Although these are inland outcrops, the complete succession was accurately reconstructed with the use of detailed samples in the SMA sections (Fig. 3 ) and SA (Fig. 4 ). 3 Materials In the present paper we employed the ammonoids from the period investigated; these are deposited in the Museo del Jurásico de Asturias (Asturias Jurassic Museum - MUJA), and the “Suárez Vega Collection” can be found, which includes the specimens studied and cited by Suárez Vega ( 1974 ). The Spanish material from the “Mouterde Collection” has also been examined; this was provided by the Facultades Católicas de Lyon (Lyon catholic faculties) and are housed at the Geology Faculty of Madrid’s Complutense University. Moreover, we used the specimens collected during the research by Braga et al. ( 1985 , 1988 ), Bernad ( 1993 ), Goy et al. ( 1994 , 2010 ), Gómez et al. ( 2008 ), Comas-Rengifo & Goy ( 2010 ), Gómez & Goy ( 2011 ), Comas-Rengifo et al. ( 2016 ), Gómez et al. ( 2016a ), Salazar-Ramírez et al. ( 2020 ), Comas-Rengifo et al. (in litt.). Exceptionally, we made use of the specimens of the lower Toarcian obtained by Comas-Rengifo ( 1982 ) in the Muro de Aguas section (Peña Isasa Massif, Logroño); it is associated with the BCB from a sedimentary perspective. These collections have been completed with the ammonoids obtained by the authors of the present paper over the last few years in expanded sections that were thoroughly sampled. Therein, we detected no relevant discontinuities that could be appraised with the available chronostratigraphy, with the exception of a hiatus identified in the Bifrons Subzone of the BCB sections and a stratigraphic gap affecting the base of the Upper Toarcian, in the same basin, and which affects the Bingmanni and Thouarsense subzones. Whatever the case may be, apart from the aforementioned exceptions, none of the discontinuities comprise more than one zone. 4 Results Figs. 2-4 show the stratigraphic distribution of the index species in the zones, subzones and horizons identified in the AB (WR and SM sections) and the BCB (SMA and SA sections), as well as that of other species of interest which facilitate the correlation with the standard scales and with other Iberian basins, such as the Iberian Range, the LB and the Betic Range in the interval between the Pliensbachian and the middle Toarcian. Figs. 5-9 present the most representative species in the interval considered in relation to the aforementioned standard scales and the Iberian basins. 4.1.1 Upper Pliensbachian ( p.p. ) Spinatum ZoneOppel, 1856 Index species : Pleuroceras spinatum (Bruguière) In the AB, the Spinatum Zone commences with the first record of the genus Pleuroceras ( P . salebrosum ) in ER614 (Comas-Rengifo et al., 2016, and in litt.). In the Apyrenum Subzone the following species occur: P . cf. salebrosum , P . transiens and P. solare , which is associated with other species of Pleuroceras ( P. spinatum , P. paucicostatum , P. apyrenum , P . cf. yeovilense ), Amauroceras ( A . ferrugineum ) and Amaltheus ( A. margaritatus ). In the BCB, the first level containing Pleuroceras ( P. transiens ) was identified, in almost the same position as in the Castillo Pedroso and Camino sections (Braga et al., 1985: CP64; 1988: CM153). The species P. salebrosum was recorded in levels (CP68) that were slightly more recent that the one contained in the first P. transiens . Hawskerense SubzoneBuckman, 1922, emend . Howarth, 1955 Index species : Pleuroceras hawskerense (Young & Bird) The Hawskerense Subzone commences with the first record of P. elaboratum in level LA39, followed by the index species of the subzone in level LA40 (equivalent to level WR16i). It might be associated with P. spinatum and with A. ferrugineum , as well as with scarce Lioceratoides and with N. expulsus . Subsequent to the Hawskerense Horizon, the extinction occurred of the Amaltheidae Family, with the exception of the genus Amaurocera s, which persisted up to the first levels of the Toarcian. Above the last Pleuroceras ( P. spinatum and P. gigas ), we recorded some Arieticeratinae, such as E. emaciatum (WR19, WR20), C. cf. gregalis (WR23, WR24) and T. elisa (LA49i), these characterise the Emaciatum and Elisa horizons. Associated with the Arieticeratinae, Lioceratoides and N. expulsus were found only on rare occasions. In the BCB in the upper part of the Hawskerense Subzone, P . hawskerense P. spinatum and forms close to P. apyrenum were replaced by Hildoceratidae (Arieticeratinae) such as E. imitator and C. zancleana , followed by E. emaciatum , and C. peloritana , in Camino (Braga et al., 1988; Comas-Rengifo et al., 2016) and by T. nerina in the last levels of the Pliensbachian in the CP (Comas-Rengifo et al., 1988). In the Hawskerense Subzone, the following four chronostratigraphic horizons were characterised. The supplementary data provide further relevant information, such as the list of species cited in the text, as well as the first level at which the index species was recorded and which marks the beginning of each horizon in the AB and BCB. Elaboratum Horizon Dommergues et al., 1997 Index species : Pleuroceras hawskerense forma elaboratum (Simpson) Hawskerense Horizon Buckman 1922, emend . Dommergues et al. 1997 Index species : Pleuroceras hawskerense (Young & Bird) (Fig. 5a) Emaciatum Horizon Braga, 1982 Index species : Emaciaticeras emaciatum (Catullo) (Fig. 5b) Elisa Horizon Braga, 1982 Index species : Tauromeniceras elisa (Fucini) (Fig. 5c) 4.1.2 Lower Toarcian The Toarcian Working Group was created in 1984 during the 1st International Symposium on Jurassic Stratigraphy held in Erlangen (Germany) following a debate on the best criterion for establishing the GSSP of the base of the Toarcian Stage. Numerous meetings held from 1984 and 2012 in Erlangen, Lisbon, Poitiers, Mendoza, Nuévalos-Friburgo, Vancouver, Palermo, Peniche, Krakov, Sheong of Suining, Jaipur, etc. resulted in an agreement to commence this stage, with the first record of Dactylioceras ( Eodactylites ) being established some years later, when the Peniche section (Portugal) was chosen as the GSSP (Rocha et al., 2016). Tenuicostatum ZoneBuckman, 1910 Index species : Dactylioceras ( Ortodactylites ) tenuicostatum (Young & Bird) It starts with the first layer containing D . ( Eodactylites ) simplex followed by D . ( E .) mirabile-polymorphum associated with A. ferrugineum , Neolioceratoides in both basins and, exceptionally, with Lioceratoides . Following the extinction of the Amaltheidae Family in the upper non-terminal part of the Hawskerense Subzone, carbon cycle perturbations affected the marine and terrestrial environments (Jenkyns & Clayton, 1986; Jenkyns, 1988; Hesselbo et al., 2000, 2007; Wignall et al., 2005: Bodin et al., 2010; Müller et al., 2017, 2020 ; Reolid, 2014; Fantasia et al., 2019;Rodrigues, 2020, 2021; Reolid et al., 2021; Silva et al., 2021; Gambacorta et al., 2023).These are likely related to extinction bioevents that caused a staggered extinction of the ammonoids and other groups of organisms (brachiopods, bivalves, foraminifera, ostracods, calcareous nannoplankton, palynomorphs, etc., etc.) in numerous basins of the western Tethys (Arias et al., 1992; Arias, 2013;Herrero, 1994, 2008, 2014; Little & Benton, 1995; Comas-Rengifo et al., 1996, 1999, 2010a;Goy et al., 1996, 1998; Barrón et al., 1999, 2013;Aberhan & Fürsich, 2000; García Joral & Goy, 2000; Macchioni & Cecca, 2002; Cecca & Macchioni, 2004; Gómez et al., 2008;Mattioli et al., 2008, 2009; Bilotta et al., 2010; Dera et al., 2010; Gómez & Arias, 2010; García Joral et al., 2011, 2018, 2022;Gómez & Goy, 2011; Kovács, 2011; Sandoval et al., 2012; Fraguas et al., 2012, 2021;Reolid et al., 2014a, b, 2019, 2023; Baeza-Carratalá et al., 2015, 2017, 2018; Rita et al., 2016;Duarte et al., 2018a, b; Rosales et al., 2018;Danise et al., 2019; Martínez & García Joral, 2020; Salazar-Ramírez et al., 2020 ; De Baets et al., 2021; Fernández-Martínez et al., 2021, 2023; Rodríguez-Tovar, 2021 ; Reolid & Ainsworth, 2022). The Tenuicostatum Zone has frequently been subdivided into two subzones. A lower one, Paltum (in the Subboreal and northern Sub-Mediterranean provinces) or Mirabile Subzone (in the Mediterranean and southern Submediterranean provinces), and an upper one, Semicelatum Subzone, which is common in the three abovementioned provinces. The horizons of these subzones were established considering the evolution of the Dactylioceratinae species. Paltum Subzone Howarth, 1973/Mirabile Guex, 1973 Index species : Protogrammoceras ( Paltarpites ) paltum Buckman and Dactylioceras ( Eodactylite s) mirabile (Fucini), respectively. The Paltum Subzone was used mainly in the NE of England and Scotland (Howarth, 1973, 1992; Page, 2003) and in the northern part of the Submediterranean Province: Centre-West and N of France (e.g. Elmi et al., 1997; Rulleau, 1993; Bécaud, 2006). It includes one single horizon (Paltum Horizon), which is approximately similar to the Simplex and Mirabile horizons, pertaining to the Mirabile Subzone, in LB in the Peniche and Rabaçal sections (Rocha et al., 2016; Duarte et al., 2018a, b; Paredes et al., 2018), in the Iberian Range (Comas-Rengifo, 1982; Goy, 1985; Goy et al., 1988; Goy & Martínez, 1990; Comas-Rengifo et al., 2010a, b), in the BCB (Braga et al., 1985, 1988; Bernad, 1993; Goy et al., 1994) and in the Pyrenean Range (Fauré, 2002). The Mirabile Subzone is typical of the Mediterranean Province: Betic Range, Apennines, Sicily, Hungary, N of Africa, Alpine Areas, etc. (Fucini, 1935; Gèczy, 1967a, b; Rivas, 1972; Guex, 1973; Elmi et al., 1974, 1997, 2007a , 2009; Wiedenmayer, 1980; Jiménez & Rivas, 1981, 1991, 1992; Benshili, 1989; Goy et al., 1988; Faraoni et al. 1995; Venturi & Ferri, 2001; Macchioni, 2002; Cecca & Macchioni, 2004; Elmi, 2006; Bilotta et al., 2010; Ettaki et al., 2011; Boulila et al., 2019; Benzaggagh et al., 2022; Benzaggagh, 2024). In the BCB, which generally presents more affinities with the Submediterranean Province than with the Mediterranean Province, the index species of both subzones are frequently recorded. As in the Iberian Range, for the last forty years (Braga et al., 1985, 1988; Goy, 1985) the Tenuicostatum Zone has usually been subdivided into the Mirabile and Semicelatum subzones. On the contrary, in the AB, until several years ago the Mirabile Subzone (Goy et al., 2010; Comas-Rengifo et al., 2016) had not usually been used. Simplex HorizonHillebrandt & Schmidt-Effing, 1981, emend . Goy & Martínez, 1990 Index species : Dactylioceras ( Eodactylites ) simplex Fucini (Fig. 5d) Other Ammonoids: AB : A. ferrugineum ; N . cf. expulsus , N. hoffmanni , N. schopeni ; BCB : Canavaria sp., P. ( Protogrammoceras ) veliferum , Lioceratoides sp., N. expulsus , N. hoffmanni . Mirabile Horizon Colo, 1961, emend . Goy & Martínez, 1990 Index species : Dactylioceras ( Eodactylites ) mirabile Fucini (Fig. 5f) Other Ammonoids: AB : D. ( Eodactylites ) polymorphum (Fig. 5e), P. ( Paltarpites ) paltum , N. cf. expulsus , N. hoffmanni , N. schopeni ; BCB : D. ( Eodactylites ) polymorphum , P . (Paltarpites ) paltum , N. hoffmanni , N. schopeni . SemicelatumSubzone Howarth, 1973 Index species : Dactylioceras ( Orthodactylites) semicelatum (Simpson) The Paltum/Mirabile Subzone is followed by the Semicelatum Subzone in the Subboreal and Submediterranean provinces, (Howarth, 1973; Elmi et al., 1989, 1997; Fauré, 2002; Rocha et al., 2016), as well as in some areas of the Tethys (Elmi et al., 1997, 2009; Macchioni, 2002; Cecca & Macchioni, 2004). It is characterised by the expansion of the D. ( Orthodactylites ), which do not become totally extinct during the Jenkyns Event. Howarth (1978) describes D . ( Orthodactylites ) semiannulatum in the Exaratum Subzone of Northamptonshire (England), and Jiménez & Rivas (1991) D . ( Orthodactylites ) andaluciensis in the Striatus and Levisoni subzones of the CB. In the N of Iberia, Duarte et al. (2018a, b) cite both species in the Levison Subzone and Salazar-Ramírez et al. (2020) in the Elegantulum Subzone of the BCB. In this subzone, three species of D . ( Orthodactylites ), D . ( O ) crosbeyi, D . ( O .) tenuicostatum and D. ( O ) semicelatum succeed in the Subboreal Province and in some basins of the Submediterranean Province. According to Howarth (1992), in the NE of England, D . ( O.) crosbeyi is recorded in a slightly older level than the one containing D . ( O .) clevelandicu m . In the GSSP in Peniche, however, the distributions of both species would appear to overlap (Rocha et al., 2016; Duarte et al., 2018a, b); the same thing occurs in the N of the LB and in the BCB (Duarte et al., 2018b; Salazar-Ramírez et al., 2020). D . ( O .) tenuicostatum is a species typical of the Subboreal Province and of the northern sector of the Submediterranean Province (Dean et al., 1961; Howarth, 1973; Gabilly, 1976; Rulleau, 1993; Elmi et al., 1997; Page, 2003); it has a poor record in the Submediterranean Province (Goy & Martínez, 1990; Salazar-Ramírez et al., 2020) and is absent from the Mediterranean Province (Jiménez, 1976; Elmi et al., 1994, 1997; Macchioni, 2002; Bilotta et al., 2010). Moreover, D . ( O. ) semicelatum is frequent in the Subboreal Province throughout most of the Submediterranean Province. In the N of Iberia, it is usually associated with P. ( Paltarpites ) madagascariense (Goy et al., 1994, 1996; Comas-Rengifo et al., 1996, 1999; Fauré, 2002) and in the Iberian Range and the LB, several species of the genus Bouleiceras have also been occasionally recorded (Mouterde, 1953; Behmel & Geyer, 1966; Goy, 1974; Mouterde & Rocha, 1981; Mouterde & Elmi, 1991; Rulleau et al., 2003; Martínez & García Joral, 2020). Some of them become extinct and others persist during the Elegantulum Subzone or they originate following the Jenkyns Event. Nonetheless, this genus has never been found in the Cantabrian Range or in the Pyrenees. In the upper part of the Semicelatum Subzone, Page (2003) characterised an antiquum Biohorizon, due to the habitual presence of T. antiquum . This species is rare outside the Subboreal Province and the N of the Submediterranean Province. In the Cantabrian Range, some specimens of Tiltoniceras are known to exist in the Tudanca, San Miguel de Aguayo and W Rodiles sections (Gómez & Goy, 2011: TU31; Salazar-Ramírez et al., 2020: SM57i; Comas-Rengifo, et al., in litt.: WR43.2); these are situated in a position equivalent to that of T . antiquum . Furthermore, in the basins in the N of Iberia, such as the Cantabrian Range and the Pyrenees, in the Crosbeyi Horizon, the D. ( Eodactylites ) and the Lioceratoides become extinct or were already extinct; the Neolioceratoides ( N . hoffmanni and N. schopeni ) are rare and the P . ( Protogrammoceras ) and Arieticeratinae ( Canavaria and Tauromeniceras ) are practically non-existent, although they persist until the upper part of the Semicelatum Subzone in some areas of the Tethys, such as the Betic Range and in the Apennines (Braga et al., 1982; Macchioni & Meister, 2003). The P . ( Paltarpites ) become extinct at the end of the Jenkyns Event (Goy et al., 1996; Ferreti, 2002; Bécaud, 2006). Crosbeyi HorizonGoy & Martínez,1990 Index species : Dactylioceras ( Orthodactylites ) crosbeyi (Simpson) (Fig. 5g) Other ammonoids: AB : P. ( Paltarpites ) paltum , P. ( Paltarpites ) madagascariense , Neolioceratoides hoffmanni , Neolioceratoides schopeni ; BCB : D . ( Orthodactylites ) clevelandicum, P . ( Paltarpites ) cf. paltum, N. schopeni . Tenuicostatum Horizon Goy & Martínez, 1990 Index species : Dactylioceras ( Orthodactylites ) tenuicostatum (Young and Bird) (Fig. 5h) Other ammonoids: AB y BCB : P. ( Paltarpites ) madagascariense. Semicelatum Horizon Goy & Martínez, 1990 Index species Dactylioceras ( Orthodactylites) semicelatum (Simpson) (Fig. 5i) Other ammonoids: AB : D. ( Orthodactylites ) tenuicostatum (en la base), P. ( Paltarpites) madagascariense , Tiltoniceras sp.; BCB : D. ( Orthodactylites ) ernsti P. (Paltarpites) madagascariense - Serpentinum Zone Oppel, 1856 Index species: Harpoceras serpentinum (Schlotheim) (Fig. 5k) H. serpentinum is a difficult species to base on the illustration of the specimen type because it was often considered to belong to the genera Hildoceras (Buckman, 1919), Hildaites (Mouterde, 1967; Rivas, 1972; Goy, 1974; Riegraf, 1984; Jiménez, 1986), Harpoceratoides (Gabilly et al., 1971; Suárez Vega, 1974) or Hildoceratoides (Elmi et al., 1974). Based on the research of Howarth (1992) it was usually included in the Harpoceras Genus (Rulleau, 1993; Goy et al., 1994; Comas-Rengifo et al., 1996; Elmi et al., 1997; Page, 2003; Bécaud, 2006, etc.). The Serpentinum Zone, which commences with the first record of E. elegantulum (Fig. 5j) in the AB (WR43.4, LA69.4) and in the BCB (CM246, SM58), is related to an episode with Black Shales presenting a thickness of 1 to 3 m. In the AB they are approximately 1.7 m thick and in the BCB the minimum values (1.1 m) are close to Salinas de Pisuerga; the maxima (approx. 3 m) are close to Tudanca in the depocentre of the basin (Comas-Rengifo et al., 1988; Bernad, 1993; Goy et al., 1994; Gómez & Goy, 2011; Fraguas et al., 2020; Salazar-Ramírez et al., 2020). In accordance with Elmi et al. (1997), the zone has been subdivided into the Elegantulum and Falciferum subzones. For the subdivision of both into horizons, we considered the evolution of four Harpoceratinae species, followed by O. douvillei , which is present throughout the range. ElegantulumSubzoneGabilly, 1976a Index species : Eleganticeras elegantulum (Young and Bird) (Fig. 5j) Other ammonoids: AB : H. wrighti (Fig. 9a) In the boundary between the Semicelatum-Elegantulum subzones, the Tiltoniceras and the P . ( Paltarpites ) become extinct, with a notable decrease in the D . ( Orthodactylites ). Additionally, the expansion starts of the Eleganticeras, Cleviceras , Harpoceras and Hildaites . (Gabilly, 1976, Howarth, 1992; Bécaud, 2006), as well as that of other groups affected by the extinction event (Arias et al., 1992; Herrero, 2008; Mattioli, 2008; Gómez & Arias (2010); García Joral, et al., 2011; Gómez & Goy, 2011; Fraguas et al., 2012, 2023; Baeza Carratalá et al., 2017; Reolid et al., 2023). The Exaratum Horizon, equivalent to the Exaratum Subzone of Etzol et al. (1989), is characteristic of the Subboreal Province, and has also been used in the Cantabrian Range (Goy et al. 2010, Comas-Rengifo et al., in litt . and in the present research), whereas in the more southern areas of the Submediterranean Province, the Strangewaysi Horizon (Gabilly, 1976; Elmi et al., 1994, 1997; Fauré, 2002, Bécaud, 2006) is more often employed. In the Mediterranean Province, the correlations with the standard scales are complex and tend to be inaccurate (Jiménez, 1986; Macchioni, 2002; Bilota et al., 2010). Thus, for instance, the Exaratum/Strangewaysi horizons would roughly correspond to the AndalucienseHorizon of the Betic Range ( Jiménez, 1986), to the E. iblanenseHorizon of theMediterranean (Macchioni, 2002) and to the fasciculatus & fortiundicosta Biohorizon of the Apennines (Bilota et al., 2010). Characterisation of a Serpentinum Horizon in the upper part of the Elegantulum Subzone is infrequent in the Submediterranean Province. In the Cantabrian Range, however, following the first Harpoceras species ( H. strangewaysi ) the index species of this horizon is relatively abundant, persisting up to the start of the Falciferum Subzone (in the AB: Gómez et al., 2008; Goy et al., 2010; in BCB: Gómez & Goy, 2011; Salazar-Ramírez et al., 2020). Elegantulum Horizon Gabilly, 1976a Index species : Eleganticeras elegantulum (Young & Bird) (Fig. 5j) Other ammonoids: AB : D. ( Orthodactylites ) semicelatum , P. ( Paltarpites ) madagascariense , H. wrighti ; BCB : D. ( Orthodactylites ) semicelatum , H . strangewaysi , H. wrighti. Exaratum Horizon Page, 2003 (as Biohorizon) Index species : Cleviceras exaratum (Young and Bird) (Fig. 5k) Other ammonoids: AB : D. ( Orthodactylites ) gr. semiannulatum , H. strangewaysi (Fig. 5l) , H. forte ; BCB : D. ( Orthodactylites ) andaluciensis , H. strangewaysi , H. levisoni (Fig. 9b), H. forte . Serpentinum Horizon nov. Index species : Harpoceras serpentinum (Schlotheim) (Fig. 6a) Other ammonoids: AB : C. exaratum , H. levisoni ; BCB : D. ( Orthodactylites ) semiannulatum , N. crassoides , C. elegans , H. levisoni . Falciferum SubzoneHaug, 1885 Index species : Harpoceras falciferum (J. Sowerby) (Fig. 7a) This subzone was employed by Elmi (1967) and Howarth (1992), including the whole range of the index species, which, in its upper part is associated with H. sublevisoni , so that the Bifrons Zone started with the first record of D. commune . In the last few years, many authors have chosen to place the lower boundary of the Bifrons Zone at the first record of the genus Hildoceras (Mouterde, 1967; Gabilly et al., 1971; Guex, 1972; Rivas, 1972; Schmidt-Effing, 1972; Gabilly, 1976; Elmi et al. 1974, 1989, 1994, 1997; Suárez Vega, 1974; Goy, 1974; Comas-Rengifo, 1982; etc.). In the standard scales of the Subboreal Province, two Biohorizons can be distinguished, pseudoserpentinum and falciferum ; in the Submediterranean Province, two Horizons (or Zonules), Pseudoserpentinum and Douvillei; however, the Mediterranean Province is not subdivided (Elmi et al., 1997; Page, 2003). The Pseudoserpentinum Horizon, in the AB and the BCB, is characterised by the index species, associated with H. subserpentinus and with scarce Dactylioceratidae, such as Nodicoeloceras and D . ( Dactylioceras ). The Douvillei Horizon presents a broad distribution throughout numerous basins in Europe and the N of Africa. It has been cited in the Subboreal Province by Buckman (1923, as O. orthus ) and Howarth (1992); in the Sub-mediterranean Province by Elmi (1967, as O. orthus ), Gabilly (1973, 1976), Goy (1974, as O. orthus ), Goy et al. (1988, 1994, 1996, 2010), Goy & Martínez (1990), Bernad (1993), Rulleau (1993), Comas-Rengifo et al. (1996), Elmi et al. (1997), Fauré (2002), Neige & Rouget (2002), Duarte et al. (2018b), etc. In the Mediterranean Province they refer to the type species of this horizon: Gèczy (1971, as O . cf. douvillei ), Guex (1973, as O. intermedius ), Elmi et al. (1974), Jiménez (1986), Goy et al. (1988), Jiménez & Rivas (1992), Cresta et al. (1995), Macchioni & Venturi (1996), Macchioni (2002) and Bilota et al. (2010), among others. Pseudoserpentinum Horizon Gabilly, 1976a Index species : Harpoceras pseudoserpentinum Gabilly (Fig. 6b) Other ammonoids: AB : H. subserpentinum (Fig. 9c); BCB : Nodicoeloceras sp., D. ( Dactylioceras ) sp. Douvillei Horizon Goy &Martínez, 1990 Index species : Orthildaites douvillei (Haug) (Fig. 6c) Other ammonoids: AB : Nodicoeloceras sp., Dactylioceras ( Dactylioceras ) sp., Harpoceras falciferum , P. pluricostatus 4.1.3 Middle Toarcian Some authors (Dean et al., 1961; Howarth, 1973, 1978, 1992; Page, 2003) subdivided the Toarcian into two substages, the lower and upper ones, which do not exactly coincide with the Whitbian and Yeovilian described with a lithostratigraphic base by Buckman (1910), Under this supposition, the Upper Toarcian commences at the base of the Variabilis Zone. In addition, according to Elmi et al., (1997), as from the “Colloque du Jurassique de Luxembourg” numerous authors have employed a ternary division for the Toarcian Stage, situating the Middle Toarcian–Upper Toarcian boundary in the base of the Thouarsense Zone (Elmi 1967; Guex, 1972, 1975; Elmi et al., 1974, 1989, 1994, 1997; Gabilly, 1973, 1976; Goy et al., 1988 ; C omas-Rengifo et al., 1996; Bécaud, 2006; Gèczy & Szente, 2007; Gómez et al., 2008, among others).It comprises theBifrons and Variabilis zones and commences starts with the first record of the genus Hildoceras Hyatt, 1867, corresponding to the first layer containing H. sublevisoni Fucini. Bifrons Zone Reynès, 1868 Index species : Hildoceras bifrons (Bruguière) For the subdivision of this zone the evolution of the Hildoceras species was considered and in accordance with Elmi et al. (1997), it was subdivided into two subzones: Sublevisoni and Bifrons which, in turn, were subdivided into three horizons each (see Figs. 2-3) Sublevisoni SubzoneDonovan, 1958 Index species : Hildoceras sublevisoni Fucini In this subzone, the following species succeed in time: H. sublevisoni , H. tethysi and H. lusitanicum . In the lower part, Harpoceratinae persist, as do H. falciferum , although there is an unequivocal dominance of H. sublevisoni , which is associated with scarce Dactylioceratidae, such as D. ( Dactylioceras ) and Peronoceras . In the upper part, H. lusitanicum is associated with Peronoceras , H. subplanatum and with the first Pseudolioceras . a Horizonte Sublevisoni Gabilly, 1976a Especie índice : Hildoceras sublevisoni Fucini (Fig. 6d) Otros ammonoideos: AB : H. falciferum ; BCB , H. falciferum , O. douvillei (sólo en la base), H. caterinii , D . ( Dactylioceras ) sp., Peronoceras sp. Horizonte Tethysi Elmi et al., 1991 Especie índice : Hildoceras tethysi Gèczy (Fig. 6e) Otros ammonoideos: AB y BCB : H. sublevisoni (sólo en la base); BCB : H . crassum . Horizonte LusitanicumGabilly, 1976a Especie índice : Hildoceras lusitanicum Meister (Fig. 6f) Otros ammonoideos: AB: H. tethysi (sólo en la base); BCB : H . subplanatum , Pseudolioceras sp. (cf. lithense / cf. bulbiense ), Peronoceras sp. Bifrons SubzoneGabilly et al., 1971 Index species : Hildoceras bifrons (Bruguière) As in the previous subzone, in the Bifrons Subzone, three Hildoceras species se succeed, H. apertum , H. bifrons and H. semipolitum . The Hildoceratinae continue to dominate, although as a whole, the species diversity is greater than in the rest of the Bifrons Zone. Specifically recorded in the Bifrons Horizon are: Harpoceratinae ( H. subplanatum ), Dactylioceratidae ( Peronoceras , Zugodactylites , Porpoceras ), Phymatoceratidae ( Phymatoceras ) and Mercaticeratinae ( Arctomercaticeras ). Apertum Horizon Elmi et al., 1991 Index species : Hildoceras apertum Gabilly (Fig. 6g) Otros ammonoideos: AB: P . cf. fimbriatum , P. narbonense ; BCB: Catacoeloceras sp. Bifrons Horizon Elmi, 1967 Index species : Hildoceras bifrons (Bruguière) (Fig. 7b) Other ammonoids: AB: P. cf. fibulatum , P. vortex , Zugodactylites sp., Z. braunianus , H . cf. subplanatum , P. lythense , H. apertum , Ph. narbonense , Ph . aff. robustum ; BCB: P . cf. vortex , P. narbonensis . Semipolitum Horizon Elmi, 1967 Especie índice : Hildoceras semipolitum (Buckman) (Fig. 7c) Other ammonoids: AB: C. crassum , Mucrodactylites sp., A. dilatum ; BCB: H. cf . subplanatum , O . ( Pseudopolyplectus ) cf. loev e, A. cf. dilatum . Variabilis ZoneGabilly, 1976a (= XII Horizon) Index species : Haugia variabils (d’Orbigny) In the Cantabrian Range the sediments of the Variabilis Zone present relatively high thicknesses, which reach 10 m in the Santa Mera section and 18 m in the San Andrés section (Figs. 1 and 3). The base of this zone is marked by the first record of the genus Haugia , which usually corresponds to H. evoluta or H. navis. In order to subdivide it, we considered the evolution of the species of the genus, H. navis , H. variabilis and H. jugosa in the Variabilis Subzone, H. illustris and H. phillpsi in the Illustris Subzone and H. vitiosa in the Vitiosa Subzone. The specimens of this genus are relatively scarce and are rarely found complete (Comas-Rengifo et al., 1988; Goy et al. 1994, 2010). Variabilis SubzoneGabilly et al. 1971 Index species : Haugia variabilis (d’Orbigny) Guex (1972) situates H. navis in the lower part of the Variabilis Subzone of the Causses; according to Gabilly (1976, 1990), in the lower part of the Variabilis Zone of Vandée forms of Haugia are recorded which exhibit straight ribs and a poorly marked projection in the Saint-Nicolas section (Jard-sur-mer, Vendée), where the sediments of this zone are somewhat more expanded than in other sections of the Thouars region. The forms of Haugia indicate that H. evoluta is situated in the basal part of the Variabilis Subzone, followed by Haugia of the jugosa group (such as H . jugosa and H. ogerieni , which are recorded in the same level. With the data subsequently obtained in the Lyon region (Lafargue quarries, Belmont) by Roulleau (1993), Elmi et al. (1997) define a Navis Horizon and a Jugosa Horizon in the Variabilis Subzone. In the AB and the BCB, the succession recorded involves H. navis , H. variabilis y H. gr. jugosa . With regard to the latter species, also found in the same level are the morphotypes jugosa and ogerieni just below the position of H. illustris and P. aratum. Oher elements of interest for the correlations are C. gemma (Fig. 9e), P. sternale and P. helveticum (Goy & Martínez, 2009; Goy et al., 2010). Navis Horizon Elmi et al., 1997 Index species : Haugia navis (Dumortier) (Fig. 7d) Other ammonoids: AB : H. semipolitum , H. evoluta , B . cf. lehmanni ; BCB: Catacoeloceras sp., Collina sp., H. semipolitum , P. sternale . VariabilisHorizon Gabilly, 1990 Index species : Haugia variabilis (d’Orbigny) (Fig. 7g) Other ammonoids: AB : C. cf. gemma , C . cf. confectum , M . cf. gracilis , P. sternale , B . cf. lehmann i, D. malagna ; BCB : P. sternale , P. helveticum , A . cf. dilatum , P. cf. frantzi . JugosaHorizon Elmi et al., 1997 Index species : Haugia jugosa (Sowerby) (Fig. 8a, b) Goy et al. (2010) characterise an ogerieni Biohorizon (Index species: Haugia ogerieni (Dumortier, 1874) presenting a similar duration in the Santa Mera section (Asturias). Other ammonoids: AB : C . cf. confectum , C. linae , M . cf. gracilis , P. sternale , P. helveticum , P. primaria , H. jugosa morp. ogerieni , D . cf. rudis, Lytoceras sp.; BCB : P . helveticum , H . cf. jugosa, Denckmannia sp., Alocolytoceras sp. Illustris Subzone Gabilly et al., 1971 Index species : Haugia Illustris (Denkmann) In this subzone Haugia , with flexuose ribs and a poorly marked peripheral projection, is usually classified as H. illustris and H. beani , followed by Haugia with flexuose ribs up to the body chamber, clearly showing a forward projection of the whorls (Gabilly, 1976). In the Cantabrian Range, there is a record of similar forms that can be associated, in the lower part of the subzone with P. aratum , a ubiquitist species that is frequent in the NW European Province and that is also known in the Mediterranean Province (Goy et al., 1988). In the upper part of the subzone, forms close to H. phillipsi and H. metallaria are situated; these can be associated with P. bodei , a species that has been cited in Causses, Germany, the Iberian Range and the Cantabrian Range (Guex, 1975; Ohmert, 1976; Goy et al., 1990, 1994). In this subzone, the first Gèczyceras are also recorded; these constitute important elements for correlating with different areas of the Mediterranean Province (Martínez, 1992; Martínez et al., 2015; Elmi et al., 2007b). Illustris Horizon Gabilly, 1990 Index species : Haugia illustris (Denkmann) Other ammonoids: AB : C . cf. raquinianum , O . bicarinatum , H. aff. illustris , B. primaria, P . subregale (Fig. 9f), P. aratum (Fig. 9g) , G. costatum ; BCB : O. bicarinatum , Osperlioceras spp. , Haugia sp. (Fig. 7e), P. subregale, P. aratum, P. discoides, G. cf . costatum. Phillipsi Horizon Gabilly, 1990 Index species : Haugia phillipsi (Simpson) (Fig. 9d) Other ammonoids: AB : B. primaria , H . cf. phillipsi , H. cf. metallaria , Haugia sp., D. tumefacta , P . cf. struckmanni , P . aff. bingmanni , P . bodei , G . cf. costatum ; BCB: Osterlioceras sp., P. discoides , H. cf. phillipsi , G . cf. costatum. Vitiosa Subzone Gabilly et al., 1971 Index species : Haugiella vitiosa (Buckman) In this subzone, apart from the index species, there are several species of Pseudogrammoceras ( P. muelleri , P . aff. bingmanni ) and Gèczyceras ( G. costatum, G. clausum ). In adjacent basins, Fauré (2002) describes two new species of Haugiella in the Pyrenean Range and Goy & Martínez (1990) cite, apart from Gèczyceras , P. discoides, Haugia sp. and D. tumefacta. Vitiosa Horizon Gabilly, 1976 Index species : Haugiella vitiosa (Buckman) (Fig. 7h) Other ammonoids: AB : P . muelleri , P . aff. bingmanni, G. clausum , G. aff. c ostatum ; BCB : G. costatum . 4.1.4 Upper Toarcian The lower boundary of the upper Toarcian is marked by the presence of P. bingmanni in the base of the Thouarsense Zone. ThouarsenseZone Brasil, 1896 Index species : Grammoceras thouarsense (d’Orbigny) Although this zone is traditionally considered to commence with the first record of P. bingmanni (Denckmann), this species poses several problems with regard to its use as an indicator of the start of the upper Toarcian. On one hand, it presents great variability and is associated with forms displaying a morphology that is very close to the standard type of P. bingmanni (Gabilly, 1976; Roulleau, 1989); on the other hand, in Causses it was found from the start of the Vitiosa Subzone (Guex, 1975) and on the platforms of the IB there is evidence that it also coexisted with Haugiella in the upper part of the Variabilis Zone (Comas-Rengifo et al., 1996). Bingmanni Subzone Gabilly, 1976 Index species : Pseudogrammoceras bingmanni (Denckmann) It is conserved as the first subzone of the upper Toarcian in order to maintain the nomenclatural stability; however, perhaps it would be preferable to commence the substage with the first record of the genus Grammoceras Hyatt, 1867, including “ Pseugogrammoceras. doerntense Denckmann, 1887”, a species that some authors consider to be a Grammoceras (Gèczy, 1967a; Guex, 1975; Schlegelmilch, 1976). In the standard scale of the NW European Province, in the Thouarsense Subzone, two horizons have been defined, the Doertense Horizon and the Thouarsense Horizon . In the AB, this subzone is very thin and is consequently difficult to distinguish from the Bingmanni Subzone. Currently, taxonomic records have been recognised for P . bingmanni , P . cf. doerntense and P . cf. thouarsense , below the first Esericeras . In the BCB the Thouarsense Subzone is affected by a discontinuity which reaches the Fascigerum Subzone. 5 Discussion and Correlations 5.1 Sequential stratigraphy and Palaeobiogeography The Interval studied comprises the terminal part of the T4-R4 cycle and the T5-R5 cycle (p.p.) described by Quesada et al. ( 2005 ) in the BCB, which is equivalent to the LJ-3 cycle of de Gómez & Goy ( 2005 ) in the Iberian Range. Specifically, it ranges from the regressive part of the LJ3-1 subcycle (Spinatum Zone, Hawskerense Subzone) to the terminal part of the LJ3-3 subcycle (Variabilis Zone, Vitiosa Subzone). In the Spinatum Zone, following a cold episode, which occurred in the Apyrenum Subzone, where the water temperature is 10.5–11º on average (Rosales et al., 2004 ; Gómez et al., 2008 ), the tendency changes and the temperature rises, reaching approximately 17.5º towards the end of the regressive part of the LJ3-1cycle, a fact that coincides with the extinction of the Amaltheidae Family. From this time onwards (sub-cycle LJ3-2), oceanic palaeotemperatures display remarkable fluctuations, with an increasing tendency to rise, which significantly affected the ammonoids and other groups of benthic and planktonic organisms, giving rise to extinction events in the Tenuicostatum Zone (boundary between the Mirabile and Semicelatum subzones) and the boundary between the Semicelatum y Elegantulum subzones of the Serpentinum Zone. (Jenkyns Event). During the LJ3-3 subcycle, the average temperature continued to rise up to the upper part the Bifrons Zone, surpassing the average temperature (27º) in the east of the Iberian Peninsula (Gómez et al., 2008 ). This transgressive general episode appears to have caused significant provincialism in the in the W of Europe and in the N of Africa, with three palaeobiogeographic provinces: Subboreal, Submediterranean and Mediterranean, defined by Page 2003 ), which include the epicontinental seas in the NW of Europe, the basins of France, Germany and the N of Iberia and the truly Tethysic basins of the Betic Range, Apennines, Hungary and the N of Africa, among others. During the Variabilis Zone, which corresponds to the regressive part of the LJ-3 cycle, it is difficult to differentiate the Submediterranean Province; consequently, it is usually decided to differentiate a NW European Province and a Mediterranean Province (Elmi et al., 1997 , Page, 2003 ). After the Variabilis Zone, the first two subzones of the Thouarsense Zone are quite thin throughout the Cantabrian Range where, as a whole, the thickness is less than 1 m (Goy et al., 1994 ; Gómez et al., 2008 ). Figures 2 – 3 and 9 refer to both subzones since, at least in the AB there is a taxonomic record of the index species (Goy et al., 2010 ). However, in the boundary between the Variabilis-Thouarsense zones, there is evidence of small discontinuities in the AB and in the Santa Mera section, and of noteworthy discontinuities in the BCB, which can be seen in the Salinas de Pisuerga, San Andres, Camino and Castillo Pedroso sections (Comas-Rengifo et al., 1988 ; Bernad, 1993 , Goy et al.; 1994 ). In basins close to those studied, such as the northern part of the Iberian Range, in the Ricla section, where the first two subzones are also thin (1.5 m), the Bingmanni and Thouarsense subzones have been characterised; they are separated by a small discontinuity (Goy & Martínez, 1990 ). 5.2 Correlation with the standard scale and with other Iberian basins For the reasons given in subchapter 5.1, in order to correlate the basins of the Cantabrian Range (AB and BCB) with others on the Iberian Peninsula, on one hand we considered the horizons recognised between the Hawskerense Subzone and the Bifrons Subzone (Figs. 2 – 3 and 6 – 7 ), where three different palaeobiogeographic provinces have been differentiated; on the other hand, the horizons recognised in the Variabilis Zone (Figs. 4 – 5 and 8 – 9 ) were taken into account; therein, only two provinces were differentiated, NW Europea and Mediterranea. For the correlation with the standard scales for the provinces cited, as well as for the IB, LB and BB (Fig. 10 – 11 ), we used as reference studies (Howarth, 1955 , 1973 , 1978 , 1992; Dean et al., 1961 ; Mouterde, 1967 ; Guex, 1972 , 1975 ; Gabilly, 1976; Comas-Rengifo, 1982 ; Goy et al. 1988 , 1990, 1994 , 2006b , 2010 ; Elmi et al., 1994 , 1997 , 2007; Comas-Rengifo et al., 1996 , 2010a ; Fauré, 2002 , 2013 ; Page, 2003 , 2004 ; Bécaud, 2006 ; Gómez et al., 2008 ; Gómez & Goy, 2011 ; Rocha et al., 2016 ; Duarte et al., 2018a , b ; Salazar-Ramírez et al., 2020 ). However, in the Mediterranean Tethysic areas and in the Atlantic sector of Morocco, we considered as reference studies (Gèczy, 1967a, b; Rivas, 1972 ; Guex, 1973 ; Elmi et al., 1974 ; Jiménez & Rivas, 1981 , 1991, 1992; Braga, 1982 ; Braga et al., 1982 ; Jiménez, 1986 ; Goy et al., 1988 ; Benshili, 1989 ; Mouterde & Elmi ( 1991 ), Cresta et al., 1995 ; Macchioni, 2002 ; Rakus & Guex, 2002 ; Fauré et al., 2007 ; Lachkar et al., 2007 ; Bilotta et al., 2010 ; Ettaki et al., 2011 , Kováks, 2011; Reolid et al., 2012a , b , 2018 , 2023 ). In the terminal Pliensbachian (Spinatum Zone, Hawskerense Subzone) and the Toarcian (Tenuicostatum to Bifrons zones), the succession of horizons characterised in the AB and the BCB is very similar to that displayed by the standard scale of the Submediterranean Province and, in most cases, the horizons are the same as those of the aforementioned scale. Only the occasional difference is observed in the Interval corresponding to the Hawskerense and Paltum subzones, as a result of the greater abundance of Mediterranean species recorded in the Cantabrian Range. Correlation with the standard scale of the Subboreal Province initially appears to be more difficult, because we employed different methodologies to define the zones; different indices are frequently used to denominate the chronostratigraphic units established. Additionally, different classification systems have been used, one based upon the succession of biohorizons and another one based on the succession of chronohorizons. Nonetheless, in most cases, the ammonoids used as a reference in the subboreal areas were also recorded in the Submediterranean areas, such as the AB and the BCB. Moreover, Page ( 2003 , Fig. 6 ) established a correlation between both standard scales which facilitates comparison with other basins. The succession of the IB is practically identical to the zones and subzones characterised; only the horizons exhibit some differences, and there are also some elements of correlation which minimise the inaccuracies. In the LB, above all in the BB, the differences existing are more noteworthy both in the subzones and in the horizons. The difficulties involved in correlating the Toarcian in the IB and in the BB were previously described by Goy et al. ( 1988 ). In the middle Toarcian (Variabilis Zone), the sedimentary changes that occurred as from the base of this zone modified the conditions of the epicontinental basins of W Europe in such a way that, in the Cantabrian Range, with slight changes, the succession obtained is very similar to that of the standard scale (Gabilly, 1990 ; Elmi et al., 1997 ) (Fig. 11 ) and the same can be said for the PB (Fauré, 2002 ). As for the IB, the succession presents quite a few analogies and some differences with respect to the basins of the Cantabrian Range. Interestingly, P. aratum , a frequent species in the IB, constitutes a good element of correlation with our study area, and with the LB and the BB; moreover, the Alticarinatus/Bodei Horizon in the IB occupies a position similar to that of the Phillipsi Horizon of the AB-BCB. With regard to the LB, until the end of the Bifrons Zone, the succession established is similar to that of the basins of the Submediterranean Province, showing few differences in relation to the basins of the Cantabrian Range. Nonetheless, as from the base of the Variabilis Zone (in the NW European Province) or Gradata Zone (in the Mediterranean Province), the succession of ammonoids presents a clear difference, to the extent that there is only one good element of correlation, P. aratum , throughout the Variabilis/Gradata Zone. Other taxa have been recorded in the aforementioned basins, among which the following ones can be highlighted: P. sternale and Collina , which can be found sporadically in the lower part of the Gemma Subzone, P. subregale , which are located in the upper part of the same subzone and below the Alticarinatus Subzone, and G. costatum , to be found in the upper part of the Gradata Zone. The index species of the Alticarinatus Subzone is relatively frequent in the LB, rare in the IB, and has not been cited in the Cantabrian Range. 6 Conclusions The sections studied are generally quite well expanded, with no significant discontinuities, with the exception of the boundary between the Variabilis Zone and the Thouarsense Zone in the Basque-Cantabrian Basin. The lower Toarcian presents a thickness of 12 m and the middle Toarcian is approximately 23 m thick. As a whole, between the Tenuicostatum and Variabilis zones, in the Asturian Basin, over 120 successive levels containing ammonoids have been identified. In the same Interval of the Basque-Cantabrian Basin, 110 successive levels have been identified. The associations recorded have enabled the characterisation of six zones (Spinatum, Tenuicostatum, Serpentinum, Bifrons, Variabilis, Thouarsense p.p .), eleven subzones (Hawskerense, Paltum/Mirabile, Semicelatum, Elegantulum, Falciferum, Bifrons, Semipolitum, Variabilis, Illustris, Vitiosa, Bingmanni) and twenty-six horizons (or zonules); all these are described in detail in Chap. 4.1.1 and are compared with the standard scales (Dean et al., 1961 , Dommergues et al., 1997 , Elmi et al., 1997 , Page, 2003 ). The lower boundary of the Toarcian is situated in levels WR27 and LA50s (Asturias) and in level SM33 (Cantabria). The start of the Toarcian is marked by the first appearance of Dactylioceras ( Eodactylites ) Schmidt-Effing, 1972 , above levels containing Emaciaticeras Fucini, 1931 and Tauromeniceras , Mouterde, 1967 ; these succeeded the last levels with Pleuroceras Hyatt, 1867, in the Spinatum Zone of the Pliensbachian, in a similar manner to what occurs in the Peniche (Portugal) and Almonacid de la Cuba sections (E of Spain), where the GSSP and the ASP of the Toarcian Stage are situated (Comas-Rengifo et al., 2010a , b ; Rocha et al. 2016 ). In relation to the ammonoids, three significant extinction events have been detected. The first of these is situated in the terminal part of the Hawskerense Subzone and affects practically the whole Amaltheidae Family at regional or global scale. The second took place in the boundary between the Mirabile/Paltum Subzone and the lower part of the Semicelatum Subzone; it is a staggered event that affects genera and species of the subfamilies Dactylioceratinae, Arieticeratidae, Harpoceratinae and Hildoceratinae. The third extinction event occurred in the boundary between the Semicelatum and Elegantulum subzones; it is likely at global scale and significantly affects the subfamilies Dactylioceratinae, Arieticeratinae and Harpoceratinae, as well as some species of Bouleiceratinae. The ammonoids obtained are typical of the Submediterranean Province up to the end of the Bifrons Zone and of the NW European Province in the Variabilis Zone. The associations recorded are similar to those found in the Iberian Range; they present a noteworthy similarity to the successions of the NE of England, France and, to a lesser extent, the Lusitanian Basin and the Betic Range. On the contrary, the elements typical of the Mediterranean Province are limited to the intervals coinciding with transgressive episodes, such as the interval between the terminal part of Hawskerense Subzone and the Paltum/Mirabile Subzone and in the Bifrons Zone. Declarations Supplementary information The online version contains supplementary material available Acknowledgements: Our sincere thanks to those responsible for the Jurassic Museum of Asturias (MUJA) who for twenty years have given us their support and facilitated research on ammonoids and other Jurassic fossil groups in the Cantabrian Mountains and, in particular, in Asturias. To colleagues from the University of Granada, Profs. J.C. Braga and P. Rivas, as well as Prof. A. Jiménez, with whom numerous field campaigns were carried out between 1981 and 1988, which, besides being enjoyable, provided us with important stratigraphic and palaeontological data related to this article. To Profs. J.J. Gómez, C. Herrero, G. Martínez, L.C. Suárez Vega and S. Ureta, who participated in the papers that constitute the main background of the present work, in 1994 and 2010, we are very grateful for their valuable contributions. To other members of the research teams of the aforementioned projects, specialists in groups other than ammonoids: C. Arias, E. Barrón, M. Canales, L.V. Duarte, A. Fraguas, F. García Joral, N. Perilli, and A. Rodrigo, we thank them for their contributions and comments for a better understanding of the extinction events studied here. Data for this article was collected with the projects CGL2008-03112/BTE, CGL2011-25894, CGL2015-66604-R of the Spanish Ministry of Economy and Competitiveness, developed in the Department of Geodynamics, Stratigraphy and Palaeontology (Complutense University of Madrid). This work is a contribution to Research Group 910431 “Mesozoic Biotic Processes” of the Complutense University of Madrid. We are grateful to Gema Martín (Palaeontology Area of the Geological Science Faculty) for their excellent photographic works, to Cormac de Brun for reviewing the English version. Funding Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Financial support for L. Piñuela and J.C. García-Ramos was provided by Sociedad Pública de Gestión y Promoción Turística y Cultural del Principado de Asturias (Board of Tourism and Culture Management and Promotion of the Principality of Asturias). Statements and declarations We declare that this manuscript is original, has not been published before and is not currently being considered for publication elsewhere. Conflicts of interest We know of no conflicts of interest associated with this publication, and there has been no significant financial support for this work that could have influenced its outcome. 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Changes in benthic microfossil assemblages before, during and after the early Toarcian biotic crisis in the Portland-Wigth Basin (Kerr McGee 97/12-1 well, offshore southern England). Palaeogeography, Palaeoclimatology, Palaeoecology , 599, 111044. https://doi.org/10.1016/j.palaeo.2022.111044 Reolid, M., Copestake, P. & Johnson, B. (2019). Foraminiferal assemblages, extintions and appearances associated with the Early Toarcian Oceanic Anoxic Event in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, United Kingdom. Palaeogeography, Palaeoclimatology, Palaeoecology , 532 , 109277 https://doi.org/10.1016/j.palaeo.2019.109277 Reolid, M., Marok, A. & Sèbane, A. (2014a). Foraminiferal assemblages and geochemistry for interpreting the incidence of Early Toarcian environmental changes in North Gondwana palaeomargin (Traras Mountains, Algeria). Journal of African Earth Sciences, 95 , 105–122. https://doi.org/10.1016/j.jafrearsci.2014.03.004 Reolid, M., Mattioli, E., Duarte, L. V. & Ruebsam, W. (2021). The Toarcian Oceanic Anoxic Event: Were do we stand? In: Reolid, M., Duarte, L.V., Mattioli, E., Ruebsam ((Eds.). Carbon Cycle and Ecosystem Response to the Jenkyns Event in the Early Toarcian (Jurassic). Geological society, London, Special Publication, 514 , 1–11. https://doi.org/10.1144/SP514-2021-74 Reolid, M., Mattioli, E., Nieto, L. M. & Rodríguez-Tovar, F. J. (2014b). The Early Toarcian Oceanic Anoxic Event in the External Subbetic (Southiberian Palaeomargin, Westemmost Tethys): Geochemistry, nannofossils and ichnology. Palaeogeography, Palaeoclimatology, Palaeoecology , 411 , 79–94. https://doi.org/10.1016/j.palaeo.2014.06.023 Reolid, M., Molina, J. M., Nieto, L. M. & Rodríguez-Tovar, F. J. (2018). The Toarcian Oceanic Anoxic Event in the South Iberian Palaeomargin . Springer Briefs in Earth Sciences. Doi: 10.1007/978-3-319-67211.3 Reolid, M., Rodríguez-Tovar, F. J., Marok, A. & Sebane, A. (2012a). The Toarcian oceanic anoxic event in the Western Saharan Atlas, Algeria (North African paleomargin): Role of anoxia and productivity. Geological Society of America Bulletin , 124 (9-10), 1646–1664. https://doi.org/10.1130/B30585.1 Reolid, M., Sebane, A., Rodríguez-Tovar, F. J. & Marok, A. (2012b). Foraminiferal morphogroups as a tool to approach the Toarcian Anoxic Event in the Western Saharan Atlas (Algeria). Palaeogeography, Palaeoclimatology, Palaeoecology , 323-325 , 87–99. https://doi.org/10.1016/j.palaeo.2012.01.034 Reolid, M., Soussi, M., Ruebsam, W., Taher, I. B. H., Mattioli, E., Saidi, M. & Schwark, L. (2023). Ecosystem recovery after the Early Jurassic T-OAE in the Châabet El Attaris section of the Tunisian Atlas. Palaeogeography, Palaeoclimatology, Palaeoecology , 631, 111832. https://doi.org/10.1016/j.palaeo.2023.111832 Riegraf, W. (1984). Mikrofauna, biostratigraphie und fazies im unteren Toarcium Südwestdeutchlands und Vergleiche mit benachbarten Gebieten. Tubinger Mikropaläontologische Mitteilungen, 3 , 1–232. Rita, P., Reolid, M., Duarte, L.V. (2016). Benthic foraminiferal assemblages record major environmental perturbations during the Late Pliensbachian-Early Toarcian interval in the Peniche GSSP, Portugal. Palaeogeography, Palaeoclimatology, Palaeoecology , 454 , 267–281. https://doi.org/10.1016/j.palaeo.2016.04.039 Rivas, P. (1972) . Estudio paleontológico-estratigráfico del Lias (Sector Central de las Cordilleras Béticas). Tesis Doctoral, Universidad de Granada, 2 vols. 254 + 242 p. (inédita). Publicaciones de la Universidad de Granada,77 p. Robles, S., Quesada, S., Rosales, I., Aurell, M., Meléndez, G. & Bádenas, B. (2002). Jurassic. Basque-Cantabrian basin. In: W. Gibons & T. Moreno (Eds). The Geology of Spain . Geological Society , London, 215–221. Robles, S., Quesada, S., Rosales, I., Aurell, M. & García-Ramos, J.C. (2004): El Jurásico marino de la Cordillera Cantábrica. In: J.A. Vera (Ed.), Geología de España . SGE-IGME, pp. 279–285. Rocha, R. B., Mattioli, E., Duarte, L. V., Pittet, B., Elmi, S., Mouterde, R., Cabral, M. C., Comas-Rengifo, M. J., Gómez, J. J., Goy, A., Hesselbo, S. P., Jenkyns, H. C., Littler, K., Mailliot, S., Oliveira, L. C. V., Osete, M. L., Perilli, N., Pinto, S., Ruget, C. & Suan, G. (2016). Base of the Toarcian Stage of the Lower Jurassic defined by the Global Boundary Stratotype Section and Point (GSSP) at the Peniche section (Portugal). Episodes , 39(3), 460–481. https://doi.org/10.18814/epiiugs/2016/v39i3/99741 Rodrigues, B., Silva, R. L., Mendoça Filho, J. G., Comas-Rengifo, M. J., Goy, A. & Duarte, L. V. (2020). Kerogen assemblages and δ 13 C of kerogen the uppermost Pliensbachian-lower Toarcian succession of the Asturias Basin (northern Spain). International Journal of Coal Geology , 229, 103573. https://doi.org/10.1016/j.coal.2020.103573 Rodrigues, B., Silva, R. L., Mendoça Filho, J. G., Reolid, M., Sadki, D., Comas-Rengifo, M. J., Goy, A. & Duarte, L. V. (2021). The Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian. In: M. Reolid, L. V. Duarte, E. Mattioli, & W. Ruesbsam, (Eds). Carbon Cycle and Ecosystem Response to the Jenkyns Event in the Early Toarcian (Jurassic). Geological Society, London , 514 , 291–307. https://doi.org/10.1144/SP514-2020-271 Rodríguez-Tovar, F. J. (2021). Ichnology of the Toarcian Oceanic Anoxic Event: an underestimated tool to nassesspalaeoenvironmental interpretation. Earth Sci. Rev. , 216 (7-9), 103579. https://doi.org/10.1016/j.earscirev.2021.103579 Rosales, I., Barnolas, A., Goy, A., Sevillano, A., Armendáriz, M. & López-García, J. M. (2018). Isotope records (C-O-Sr) of late Pliensbachian-early Toarcian environmental perturbations in the westernmost Tethys (Majorca Island, Spain). Palaeogeography, Palaeoclimatology, Palaeoecology , 497 , 168–185. https://doi.org/10.1016/j.palaeo.2018.02.016 Rosales, I., Quesada, S. & Robles, S. (2004). Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, Northen Spain. Palaeogeography, Palaeoclimatology, Palaeoecology , 203 , 253–275. https://doi.org/10.1016/S0031-0182(03)00686-2 Rulleau, L. (1989). Les Grammoceratinae du Toarcien supérieur de la región lyonnaise. Section géologie et paléontologie du Comité d’Établissiements des ciments Lafarge, Lozanne , France, 1–11. Rulleau, L. (1993). Les ammonites du Toarcien inférieur et moyen de la région lyonnaise. Section géologie et paléontologie du Comité d’Établissiements des ciments Lafarge, Lozanne , France, 1–15. Rulleau, L., Bécaud, M. & Neige, P. (2003). Les ammonites traditionnellement regroupées dans la sous-famille des Bouleiceratinae (Hildoceratidae, Toarcien): aspects phylogénétiques, biogéographiques et systématiques. Geobios , 36 , 317–348. DOI: 10.1016/S0016-6995(03)00034-2 Salazar-Ramírez, R. W., Herrero, C. & Goy, A. (2020). Lower Toarcian ammonites and foraminífera assemblages in the San Miguel de Aguayo Section (Basque-Cantabrian Basin, Spain). Journal of Iberian Geology , 46 , 39–60. https://doi.org/10.1007/s41513-019-00118-8 Sandoval, J, Bill., M., Aguado, R., O'Dogherty, L., Rivas, P., Morard, A. & Guex, J. (2012). The Toarcian in the Subbetic basin (southern Spain): Bio-events (ammonite and calcareous nannofossils) and carbon-isotope stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology , 342–343 , 40–63. https://doi.org/10.1016/j.palaeo.2012.04.028 Schmidt-Effing, R. (1972). Die Dactylioceratidae, eine Ammoniten-Familie des unteren Jura (Systematik, Stratrigraphie, Zoogeographie, Phiylogenie mit besonderer Berücksichtigung spanischen Materials). Zur Paläonlogie jurassischer Invertebraten. Münstersche Forschungenzur Geologie Paläontologie, 25/26 , 1–255. Silva, R. L., Ruhl. M., Barry, C., Reolid, M., Ruebsam, W. (2021). Pacing of late Pliensbachian and early Toarcian carbon cycle perturbations and environmental change in the westernmost Tethys (La Cerradura Section, Subbetic zone of the Betic Cordillera, Spain). Geological Society, London, Special Publications , 514 , 387–408. https//doi.org/10.1144/SP514-2021-27 Suárez Vega, L. C. (1974). Estratigrafía del Jurásico en Asturias. Cuadernos de Geología Ibérica, 3, 1–369. Valenzuela Fernández, M. (1988). Estratigrafía, sedimentología y paleogeografía del Jurásico de Asturias . Tesis Doctoral, Facultad de Geología, Universidad de Oviedo (inédita). Valenzuela, M., García-Ramos, J. C., Suárez de Centi, C. (1986). The Jurassic sedimentation in Asturias (N Spain). Trabajos de Geología, 16 , 121–132. Venturi, F. & Ferri, R. (2001). Ammoniti Liassici dell’Appennino Centrale , Tibergraph, Città di Castello (Perugia), 271 p. Wignall, P. B, Newton, R. J. &Little, T. S. (2005). The timing of paleoenvironmental change and cause-and-effect relationships during the Early Jurassic mass extinction in Europe. American Journal of Science , 305( 10).1014–1032. https://doi.org/10.2475/ajs.305.10.1014 Wiedenmayer, F. (1980). Die Ammoniten der mediterranen Provinz im Pliensbachian und unteren Toarcian aufgrund neuer Untersuchungen im Generoso-Becken (Lombardische Alpen). Mémoires de la Société helvétique des Sciences naturelles , 93, 1–197. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4224858","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":291846456,"identity":"868e4cd6-b309-45bc-af59-f74d9ee66a5a","order_by":0,"name":"Antonio Goy","email":"","orcid":"","institution":"Complutense University of Madrid: Universidad Complutense de Madrid","correspondingAuthor":false,"prefix":"","firstName":"Antonio","middleName":"","lastName":"Goy","suffix":""},{"id":291846457,"identity":"cc11a124-f69b-4ab6-9f3b-650770f5f7db","order_by":1,"name":"Maria Jose Comas-Rengifo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyklEQVRIiWNgGAWjYFCCA2BSjnQtxqTbldhAtFLdxsMPH92oqUuf7958gJmnZhsDP/8B/FrMDhwzNs45djh345ljCcw8x24zSM5IIKTlDJt0DtuB3I0zcgyYeRtuMxjcIOAwiJZ/demG899AtNifJ+gwoJbcNuYEeQkeqC0MBB0G9Etu32HDDTxpCQfnHLvNI3GDkJYbhx8+zvlWJy/ffvjggzc1t+X4+wk4jEECqsDgACRWeQioBwL+Bggt30BY7SgYBaNgFIxQAAAI+0c0n2+SYQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-6593-3798","institution":"Complutense University of Madrid: Universidad Complutense de Madrid","correspondingAuthor":true,"prefix":"","firstName":"Maria","middleName":"Jose","lastName":"Comas-Rengifo","suffix":""},{"id":291846458,"identity":"51524ba1-9438-4f60-8582-9a4e9564bb8a","order_by":2,"name":"José Carlos García-Ramos","email":"","orcid":"","institution":"Museo del Jurásico de Asturias (MUJA). San Juan de Duz. 33328 Coluga (Asturias) Soain Rasa de San Telmo, s/n","correspondingAuthor":false,"prefix":"","firstName":"José","middleName":"Carlos","lastName":"García-Ramos","suffix":""},{"id":291846459,"identity":"c6d70c30-cc09-455c-a896-fe88be1ee5e2","order_by":3,"name":"Laura Piñuela","email":"","orcid":"","institution":"Museo del Jurásico de Asturias. Rasa de San Telmo, s/n. San Juan de Duz, 33328 Colunga (Asturias). Spain San Telmo, s/n. San Juan de Duz","correspondingAuthor":false,"prefix":"","firstName":"Laura","middleName":"","lastName":"Piñuela","suffix":""}],"badges":[],"createdAt":"2024-04-05 21:22:30","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4224858/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4224858/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s41513-024-00252-y","type":"published","date":"2024-10-09T15:57:46+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54975618,"identity":"8b0c8ade-4336-41e8-bd5e-f89460ee6283","added_by":"auto","created_at":"2024-04-19 12:45:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":185204,"visible":true,"origin":"","legend":"\u003cp\u003eMap of the Lower Jurassic outcrops of the Cantabrian and Iberian Ranges. Abbreviations: WR WRodiles. SM Santa Mera. LA Lastres. TU Tudanca. CM Camino. SMA San Miguel de Aguayo. CP Castillo Pedroso, SP Salinas de Pisuerga. SA San Andrés. MA Muro de Aguas. RI Ricla.\u003c/p\u003e","description":"","filename":"Figures1111.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/f893373f4486daa2b9cd2ddf.png"},{"id":54975617,"identity":"f3ac94eb-f89d-4f85-8ed7-76e1075b8b48","added_by":"auto","created_at":"2024-04-19 12:45:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1081493,"visible":true,"origin":"","legend":"\u003cp\u003eLithological sections in the outcrops of the Rodiles W (WR) and Santa Mera (SM) in the Asturian Basin with the stratigraphical distributions of the ammonites species\u003cdel\u003e \u003c/del\u003e(after Gómez et al., 2008; Comas-Rengifo \u0026amp; Goy, 2010; Goy et al., 2010; Gómez et al., 2016a, b). Abbreviations: A Index species. B\u003cstrong\u003e \u003c/strong\u003especies of interest for correlation. Z Zone. SZ Subzone. Hz Horizon. THO Thouarsense. HW Hawskerense. PA/MI Paltum/Mirabile. SE Semicelatum. EL Elegantulum. FA Falciferum. SU Sublevisoni. BI Bifrons. VA Variabilis. IL Illutris. BI Vitiosa. BN Bingmanni. Hw Hawskerense. Em Emaciatum. Es Elisa. Si Simplex. Mi/Po Mirabile/Polymorphum. Cr Crosbeyi. Te Tenuicostatum. Se Semicelatum. El Elegantulum. Ex Exaratum. Sr Serpentinum. Sr Strangewaysi. Ps Pseudoserpentinum. Do Douvillei. Su Sublevisoni. Te Tethysi. Lu Lusitanicum. Ap Apertum. Bi Bifrons. Se Semipolitum. Na Navis. Va Variabilis. Ju Jugosa. Il Illustris. Pi Phillipsi. Vi Vitiosa.\u003c/p\u003e","description":"","filename":"Figures1112.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/2642fa1720c489c0c8d80bfc.png"},{"id":54976268,"identity":"1096ecca-9a21-49cd-a372-fccafd9a3ff8","added_by":"auto","created_at":"2024-04-19 12:53:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":448192,"visible":true,"origin":"","legend":"\u003cp\u003eLithological section in the outcrop of the San Miguel de Aguayo (SMA) in the Basque-Cantabrian Basin with the stratigraphical distributions of the ammonites species (after Salazar-Ramírez et al., 2020). Abreviations: AIndex species. B\u003cstrong\u003e \u003c/strong\u003especies of interest for correlation. Z Zone. SZ Subzone. Hz Horizon. HW Hawskerense. PA/MI Paltum/Mirabile. SE semicelatum. EL Elegantulum. FA Falciferum. SU Sublevisoni. BI Bifrons. Hw Hawskerense. Em Emaciatum. Es Elisa. Si Simplex. Mi/Po Mirabile/ Polymorphum. Cr Crosbeyi. Te Tenuicostatum. Se Semicelatum. El Elegantulum. Ex Exaratum. Sr Serpentinum. Sr Strangewaysi. Ps Pseudoserpentinum. Do Douvillei. Su Sublevisoni. Te Tethysi. Lu Lusitanicum. Ap Apertum. Bi Bifrons.\u003c/p\u003e","description":"","filename":"Figures1113.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/376a65815ac7b1365b61671e.png"},{"id":54975620,"identity":"004eb0f0-9d48-438c-8536-f9506d7a5ebe","added_by":"auto","created_at":"2024-04-19 12:45:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":471922,"visible":true,"origin":"","legend":"\u003cp\u003eLithological section of the middle Toarcian in two outcrops at San Andrés (SA) in the Basque-Cantabrian Basin with the stratigraphical distributions of the ammonites species. 1SA partial section of Bifrons and Variabilis zones, and 2SA partial section of Varibialis Zone (after Goy et al., 1994). Abbreviations: AIndex species, B\u003cstrong\u003e \u003c/strong\u003especies of interest for correlation Z Zone. SZ Subzone. Hz Horizon. THO Thouarsense. SU Sublevisoni. BI Bifrons. BN Bingmanni. Lu Lusitanicum. Ap Apertum. Bi Bifrons. Se Semipolitum. Na Navis. Va Variabilis. Ju Jugosa. Il Illustris. Pi Phillipsi. Vi Vitiosa.\u003c/p\u003e","description":"","filename":"Figures1114.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/a534f211e557f9100e59819b.png"},{"id":54976270,"identity":"d801ae11-b875-4f26-9f99-afa37a8d88ab","added_by":"auto","created_at":"2024-04-19 12:53:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":6553457,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003cem\u003e Pleuroceras hawskerense \u003c/em\u003eHowarth CM191, Hawskerense Sz, Hawskerense Hz, refigured from Comas-Rengifo et al., 2016, Fig. 3.9. \u003cstrong\u003eb\u003c/strong\u003e \u003cem\u003eEmaciaticeras emaciatum\u003c/em\u003e (Catullo) CM205, Hawskerense Sz, Emaciatum Hz, refigured from Comas-Rengifo et al., 2016, Fig. 4.4. \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eTauromeniceras elisa\u003c/em\u003e (Fucini) LS49i, Hawskerense Sz, Elisa Hz. \u003cstrong\u003ed\u003c/strong\u003e \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003esimplex\u003c/em\u003e Schmidt-Effing SMA31 (+0,7 m from the base), Paltum/Mirabile Sz, Simplex Hz, refigured from Salazar-Ramírez et al., 2020, fig. 3H. \u003cstrong\u003ee\u003c/strong\u003e \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003epolymorphum \u003c/em\u003eFucini MA293, Paltum/Mirabile Sz, Mirabile Hz. \u003cstrong\u003ef \u003c/strong\u003e\u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003emirabile \u003c/em\u003eFucini MA293, Paltum/Mirabile Sz, Mirabile Hz. \u003cstrong\u003eg \u003c/strong\u003e\u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003ecrosbeyi\u003c/em\u003e (Simpson) WR38s, Semicelatum Sz, Crosbeyi Hz. \u003cstrong\u003eh\u003c/strong\u003e \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003etenuicostatum \u003c/em\u003e(Young \u0026amp; Bird) SM52.1, Semicelatum Sz, Tenuicostaum Hz, refigured from Salazar-Ramírez et al., 2020, fig. 3L. \u003cstrong\u003ei \u003c/strong\u003e\u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003esemicelatum \u003c/em\u003e(Simpson), SMA56.7, Semicelatum Sz, Semicelatum Hz, refigured from Salazar-Ramírez et al., 2020, fig. 3K. \u003cstrong\u003ej\u003c/strong\u003e \u003cem\u003eEleganticeras elegantulum\u003c/em\u003e (Young \u0026amp; Bird) SMA60.1, Serpentinum Sz, Elegantulum Hz,\u003cstrong\u003e \u003c/strong\u003erefigured from Salazar-Ramírez et al., 2020, fig. 4A. \u003cstrong\u003ek\u003c/strong\u003e \u003cem\u003eCleviceras exaratum\u003c/em\u003e (Young \u0026amp; Bird) WR43.6, Serpentinum Sz, Exaratum Hz. \u003cstrong\u003el \u003c/strong\u003e\u003cem\u003eHarpoceras strangewaysi\u003c/em\u003e Sowerby LS47s, Serpentinum Sz, Elegantulum Hz, x0.7. All photographs natural size, except Fig. l. Scale bar = 2 cm.\u003c/p\u003e","description":"","filename":"Figures1115.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/6e7b164cd7859f9a788b8cc0.png"},{"id":54976272,"identity":"b79f7880-6b85-4453-8372-fb428fd4bfa9","added_by":"auto","created_at":"2024-04-19 12:53:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1875718,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e \u003cem\u003eHarpoceras serpentinum \u003c/em\u003e(Schlotheim) WR49, Elegantulum Sz, Serpentinum Hz, x0.5. \u003cstrong\u003eb\u003c/strong\u003e \u003cem\u003eHarpoceras pseudoserpentinum \u003c/em\u003e(Gabilly) WR58, Falciferum Sz, Pseudoserpentinum Hz, x0.5. \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eOrthildaites douvillei \u003c/em\u003e(Haug) SMA91s.5, Falciferum Sz, Douvillei Hz, refigured from Salazar-Ramírez et al., 2020, fig. 4G\u003cem\u003e.\u003c/em\u003e \u003cstrong\u003ed \u003c/strong\u003e\u003cem\u003eHildoceras sublevisoni\u003c/em\u003eFucini 1CM258, Sublevisoni Sz, Sublevisoni Hz, refigured from Goy et al., 1994, lám. 1, fig. 4. \u003cstrong\u003ee\u003c/strong\u003e \u003cem\u003eHildoceras tethysi \u003c/em\u003eGèczy WR84, Sublevisoni Sz, Tethysi Hz.\u003cem\u003e \u003c/em\u003e\u003cstrong\u003ef\u003c/strong\u003e \u003cem\u003eHildoceras lusitanicum \u003c/em\u003eMeister 1SA76, Sublevisoni Sz, Lusitanicum Hz, refigured from Goy et al., 1994, lám. 1, fig. 5. \u003cstrong\u003eg\u003c/strong\u003e \u003cem\u003eHildoceras apertum \u003c/em\u003eGabilly SMA122s, Bifrons Sz, Apertum Hz, refigured from Salazar-Ramírez et al., 2020, fig. 4K. All photographs natural size, except Figs. a and b. Scale bar = 2 cm.\u003c/p\u003e","description":"","filename":"Figures1116.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/3750259209560c0560e64bdc.png"},{"id":54976874,"identity":"735148b1-bda1-4552-87fa-1175cd5ba61b","added_by":"auto","created_at":"2024-04-19 13:01:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":6062060,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003e\u003cem\u003eHarpoceras falciferum \u003c/em\u003eHaug WR70, Falciferum Sz, Douvillei Hz, x0.7. \u003cstrong\u003eb \u003c/strong\u003e\u003cem\u003eHildoceras bifrons\u003c/em\u003e\u003cstrong\u003e \u003c/strong\u003e(Bruguière) WR100, Bifrons Sz, Bifrons Hz. \u003cstrong\u003ec \u003c/strong\u003e\u003cem\u003eHildoceras semipolitum\u003c/em\u003e Buckman 1SA98, Bifrons Sz, Semipolitum Hz. \u003cstrong\u003ed \u003c/strong\u003e\u003cem\u003eHaugia navis\u003c/em\u003e (Dumortier) CM320, Variabilis Sz, Navis Hz. \u003cstrong\u003ee \u003c/strong\u003e\u003cem\u003eHaugia \u003c/em\u003esp. 1SA81, Variabilis Sz, Vitiosa Hz. \u003cstrong\u003ef\u003c/strong\u003e \u003cem\u003eHaugia illustris\u003c/em\u003e (Denckmann) 2SA74, Variabilis Sz. Hz Illustris. \u003cstrong\u003eg\u003c/strong\u003e \u003cem\u003eHaugia variabilis\u003c/em\u003e (d´Orbigny) 2SA64, Variabilis Sz, Variabilis Hz, refigured from Goy et al., 1994, fig. 7, x0.5.\u003cstrong\u003e h\u003c/strong\u003e \u003cem\u003eHaugiella vitiosa\u003c/em\u003e (Buckman) 2SA74, Variabilis Sz, Phillipsi Hz. All photographs natural size, except Figs. a and g. Scale bar = 2 cm.\u003c/p\u003e","description":"","filename":"Figures1117.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/211af5c93611086b2361bd9a.png"},{"id":54975622,"identity":"196fd16f-f7ab-4435-9028-a5894cb953f8","added_by":"auto","created_at":"2024-04-19 12:45:12","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1419224,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e \u003cem\u003eHaugia jugosa \u003c/em\u003e(Sowerby) SM27, Variabilis Sz, Jugosa Hz. \u003cem\u003eHaugia jugosa \u003c/em\u003e(Sowerby) morphotype\u003cem\u003e Haugia ogerieni \u003c/em\u003e(Dumortier) SM27, Variabilis Sz, Jugosa Hz.\u003c/p\u003e","description":"","filename":"Figures1118.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/237fb9ff7c3fffffde273649.png"},{"id":54975628,"identity":"8df61f75-e850-451a-a22d-6d8f1aeb3e13","added_by":"auto","created_at":"2024-04-19 12:45:12","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":6503620,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003e\u003cem\u003eHildaites wrighti\u003c/em\u003eSpath WR43.7, Elegantulum Sz, Elegantulum Hz. \u003cstrong\u003eb \u003c/strong\u003e\u003cem\u003eHildaites levisoni \u003c/em\u003e(Simpson) 1CM246, Falciferum Sz, Strangewaysi Hz, refigured fromGoy et al., 1994, fig. 6, x0.7\u003cstrong\u003e. c\u003c/strong\u003e\u003cem\u003e. Hildaites subserpentinum \u003c/em\u003eBuckman WR64, Falciferum Sz, Pseudoserpentinum Hz. \u003cstrong\u003ed\u003c/strong\u003e \u003cem\u003eHaugia \u003c/em\u003ecf. \u003cem\u003ephillipsi \u003c/em\u003e(Simpson) ME80, Variabilis Sz, Phillipsi Hzx0.5. \u003cstrong\u003ee \u003c/strong\u003e\u003cem\u003eCollina gemma\u003c/em\u003e Bonarelli ME29s, Variabilis Sz, Variabilis Hz. \u003cstrong\u003ef \u003c/strong\u003e\u003cem\u003ePseudogrammoceras subregale \u003c/em\u003ePinna ME43, Illustris Sz, Illustris Hz. \u003cstrong\u003eg\u003c/strong\u003e\u003cem\u003e Pseudogrammoceras aratum \u003c/em\u003e(Buckman) ME44i, Illustris Sz, Illustris Hz. All photographs natural size, except Figs. b and d. Scale bar = 2 cm.\u003c/p\u003e","description":"","filename":"Figures1119.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/fc5f496c896f1fb47d2105a2.png"},{"id":54975626,"identity":"bb00aaf8-7229-4ee1-937d-fd5ab1dcbe57","added_by":"auto","created_at":"2024-04-19 12:45:12","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":857186,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of scales of the lower and middle Toarcian (Bifrons Zone) of the Iberian basins \u003cstrong\u003e1\u003c/strong\u003ePage, 2003. \u003cstrong\u003e2\u003c/strong\u003eGabilly, 1976. \u003cstrong\u003e3\u003c/strong\u003e Elmi et al., 1997. \u003cstrong\u003e4\u003c/strong\u003e Goy et al., 1994. \u003cstrong\u003e5\u003c/strong\u003e Goy et al., 2010. \u003cstrong\u003e6 \u003c/strong\u003eSalazar-Ramírez et al\u003cem\u003e.\u003c/em\u003e, 2020. \u003cstrong\u003e7\u003c/strong\u003e Comas-Rengifo, 1982. \u003cstrong\u003e8\u003c/strong\u003e Goy et al., 1988. \u003cstrong\u003e9\u003c/strong\u003e Comas-Rengifo, et al., 1996.\u003cstrong\u003e10\u003c/strong\u003e Elmi et al., 2006. \u003cstrong\u003e11\u003c/strong\u003e Rocha et al., 2016. \u003cstrong\u003e12\u003c/strong\u003e Comas-Rengifo, et al., 2018a, b. \u003cstrong\u003e13\u003c/strong\u003e Braga, 1982. \u003cstrong\u003e14\u003c/strong\u003e Jiménez, 1986. \u003cstrong\u003e15\u003c/strong\u003e Goy et al., 1988. Abbreviations: SUBZ Subzone. HW Hawskerense. PA Paltum. CL Clevelandicum. TE tenuicostatum. SE Semicelatum. EX Exaratum. EL Elegantulum. FA Falciferum. CO Crosbeyi. FI Fibulatum. CR Crassum. SU Sublevisoni. BI Bifrons.\u003c/p\u003e","description":"","filename":"Figures11110.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/eb05f5c65d65f602fd40fae6.png"},{"id":54976269,"identity":"945840f1-8b32-4466-a892-afea9cd24ec9","added_by":"auto","created_at":"2024-04-19 12:53:12","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":285016,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of scales of the middle Toarcian (Variabilis Zone) of the Iberian basins. \u003cstrong\u003e1\u003c/strong\u003e Gabilly, 1976. \u003cstrong\u003e2\u003c/strong\u003eElmi et al., 1997. \u003cstrong\u003e3\u003c/strong\u003e Page, 2003. \u003cstrong\u003e4\u003c/strong\u003e Goy et al., 1994. \u003cstrong\u003e5\u003c/strong\u003e Gómez et al., 2008. \u003cstrong\u003e6\u003c/strong\u003e Goy et al., 2010. \u003cstrong\u003e7 \u003c/strong\u003eGoy et al., 1988. \u003cstrong\u003e8\u003c/strong\u003e. Comas-Rengifo, et al., 1996\u003cstrong\u003e. 9 \u003c/strong\u003eGoy et al., 1996. \u003cstrong\u003e10\u003c/strong\u003e Elmi et al., 1997. \u003cstrong\u003e11\u003c/strong\u003eElmi et al., 2007. \u003cstrong\u003e12\u003c/strong\u003e García-Gómez \u0026amp; Rivas, 1981. \u003cstrong\u003e13\u003c/strong\u003e Goy et al., 1988. Abbreviations: SUBZ Subzone THO Thouarsense. BON. Borarelli. FAL Fallaciosum. VA Variabilis. IL Illutris. BI Vitiosa. BN Bingmanni. GE Gemma. AL Alticarinatus. GR Gradata. ME Mediterraneum.\u003c/p\u003e","description":"","filename":"Figures11111.png","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/62c6567e15b11a7d0ce18491.png"},{"id":66597243,"identity":"b16eaf4e-68f1-4cfb-af12-ddc18d253519","added_by":"auto","created_at":"2024-10-14 16:08:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":33282664,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/004c4d12-7dda-4b7d-9aef-c8658d8ec34c.pdf"},{"id":54975621,"identity":"174a358e-4460-49df-8385-821b699be0cd","added_by":"auto","created_at":"2024-04-19 12:45:12","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":21707,"visible":true,"origin":"","legend":"","description":"","filename":"Suplementarydata.docx","url":"https://assets-eu.researchsquare.com/files/rs-4224858/v1/79f99ee65823975a85a4a5a7.docx"}],"financialInterests":"","formattedTitle":"Ammonites from the lower and middle Toarcian (Jurassic) in the Cantabrian Range (Asturias and Basco-Cantabrian Basin, Northern Spain). Chronostratigraphy, biotic events and correlations with other Iberian basins","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe ammonoids from the interval between the Upper Pliensbachian (Spinatum Zone, Hawskerense Subzone) and the Upper Toarcian (Thouarsense Zone, Bingmanni Subzone) are well represented in the Cantabrian Range, where the Lower Jurassic successions continue, though not continuously, extend for over 300 km, from Avil\u0026eacute;s in Asturias to the Aralar Mountains in Navarre. For the chronostratigraphic study of the abovementioned interval, we selected several sections of the Asturian Basin (AB) and of the Basco-Cantabrian Basin (BCB). Noteworthy among these are, in the AB, the W Rodiles (WR), Santa Mera (SM) and Lastres (LA) sections, and in BCB, the Salinas de Pisuerga (Sl), San Andr\u0026eacute;s (SA), Camino (CM), San Miguel de Aguayo (SMA), Tudanca (TU) and Castillo Pedroso (CP) sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Toarcian Stage, proposed by d\u0026rsquo;Orbigny (1949, 1952), commences with the appearance of \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eEodactylites\u003c/em\u003e) shortly after the mass extinction of the Amaltheidae Hyatt Family, 1867. This Stage was subdivided by Buckman (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1910\u003c/span\u003e) into the Whitbian and Yeovilian Stages, on a lithostratigraphic basis, which includes the Variabilis Zone within the Whitbian. Subsequently, M.K. Howarth (in: Dean et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1961\u003c/span\u003e) redefined the Whitbian, situating the boundary between the two substages at the base of the Variabilis Zone. Other authors employing a binary division are Ohmert (\u003cspan citationid=\"CR145\" class=\"CitationRef\"\u003e1976\u003c/span\u003e), Knitter \u0026amp; Ohmert (1983), Etzold et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1989\u003c/span\u003e, Howarth (1991, 1992) and Page (\u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). On the contrary, some authors have chosen to use a ternary division (Monestier, \u003cspan citationid=\"CR137\" class=\"CitationRef\"\u003e1931\u003c/span\u003e; Gabilly et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e1971\u003c/span\u003e; Guex, \u003cspan citationid=\"CR102\" class=\"CitationRef\"\u003e1972\u003c/span\u003e; Su\u0026aacute;rez Vega, \u003cspan citationid=\"CR182\" class=\"CitationRef\"\u003e1974\u003c/span\u003e; Elmi et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1974\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e1989\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1994\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Gabilly, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e1973\u003c/span\u003e, \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e1976a\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003eb\u003c/span\u003e; Goy, \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1974\u003c/span\u003e, \u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Goy et al., \u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e1988\u003c/span\u003e, \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Faur\u0026eacute;, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Page, \u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; B\u0026eacute;caud, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, Salazar-Ram\u0026iacute;rez et al., \u003cspan citationid=\"CR178\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe lithostratigraphic units where the ammonoids studied were recorded are the Rodiles Fm, Santa Mera Mb, in the AB (Valenzuela et al., \u003cspan citationid=\"CR184\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Valenzuela Fern\u0026aacute;ndez, \u003cspan citationid=\"CR183\" class=\"CitationRef\"\u003e1988\u003c/span\u003e) and the terminal part of the Camino Fm and the lower part of the Castillo Pedroso Fm in the BCB (Robles et al., \u003cspan citationid=\"CR167\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, \u003cspan citationid=\"CR168\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe stratigraphic distribution of the Toarcian ammonoids in the AB was investigated by Dubar \u0026amp; Mouterde (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e1957\u003c/span\u003e) and in particular by Su\u0026aacute;rez Vega (\u003cspan citationid=\"CR182\" class=\"CitationRef\"\u003e1974\u003c/span\u003e) in the second half of the XX century, and by G\u0026oacute;mez et al. (\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), Goy et al. (\u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2010\u003c/span\u003e)d mez \u0026amp; Goy (2011) in the early years of the XXI century. In the BCB, the ammonites were studied by Dahm (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1966\u003c/span\u003e), Braga et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1985\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1988\u003c/span\u003e), Comas-Rengifo et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1988\u003c/span\u003e), Bernad (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1993\u003c/span\u003e), Goy et al. (\u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e1994\u003c/span\u003e, \u003cspan citationid=\"CR101\" class=\"CitationRef\"\u003e2006b\u003c/span\u003e), G\u0026oacute;mez \u0026amp; Goy (\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) and Salazar-Ram\u0026iacute;rez et al. (\u003cspan citationid=\"CR178\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe present paper enhances the available information on the succession of the ammonoids, characterises the choronostratigraphic units, based upon the evolution of this group of fossils; moreover, a comparison is made between the record obtained and that of the standard scales established by other authors. Another interesting aim of our paper involves correlating the chronostratigaphic succession obtained with that of the Subboreal, Submediterranean and Mediterranean subprovinces (\u003cem\u003esensu\u003c/em\u003e Page, \u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), between the Tenuicostatum and Bifrons zones and that of the NW of Europe and the Mediterranean province in the Variabilis Zone and, in particular, with other Iberian basins, such as the Iberian Range, the W of Portugal (LB) and the Betic Range. The chronostratigraphic succession obtained should be employed to correlate the principal events that took place in this period in the Cantabrian Range with those identified in the NW of Europe and in the N of \u0026Aacute;frica.\u003c/p\u003e"},{"header":"2 Location and Geological setting","content":"\u003cp\u003eThe lithostratigraphic succession of the lower Toarcian presents a thickness of 14 m and that of the middle Toarcian has a thickness of 17.5 m in the AB. It comprises an alternation of limestones and marly limestones with marls, of a grey-black colour, in which no significant discontinuities can be observed. It is arranged in transgressive-regressive cycles, which display transgressive maxima in the Tenuicostatum Zone (Paltum/Mirabile Subzone) and in the Bifrons Zone (Bifrons Subzone). The former coincides with a section of marls rich in organic material, and the latter, which is the most noteworthy of the whole Lower Jurassic, coincides with the maximum deepening of this basin (G\u0026oacute;mez \u0026amp; Goy, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; G\u0026oacute;mez et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the AB, three sections were studied; these are situated from W to E along the coast: 1) WR (Spinatum Zone \u003cem\u003ep.p\u003c/em\u003e. to Bifrons Zone), 2) SM (Variabilis Zone to Thouarsense Zone, Bingmanni Subzone) and 3) LA (Spinatum Zone to Serpentinum Zone). The complete reference stratigraphic succession can be seen in the first two sections: WR and SM (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) where all the layers of the lower and middle Toarcian exhibit a continuous outcrop. Both of them were thoroughly sampled; a noteworthy lateral continuity can be observed in the levels identified and which can be recognised from the Villaviciosa inlet to Lastres beach.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the BCB, the lithostratigraphic succession of the lower Toarcian presents a thickness of 17 m, and that of the middle Toarcian, 24 m. Moreover, the same main T-R cycles as in the AB can be observed (Quesada et al. \u003cspan citationid=\"CR151\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). We conducted an in-depth study of the SMA sections (Spinatum Zone, Hawskerense Subzone to the Bifrons Zone \u003cem\u003ep.p\u003c/em\u003e.) and the SA section (Bifrons Zone, Bifrons Subzone \u003cem\u003ep.p\u003c/em\u003e. to the Thouarsense Zone, Bingmanni Subzone). The Tudanca (TU\u003cem\u003e)\u003c/em\u003e and Castillo Pedroso (CP) sections of this basin are also very important due to being situated in the depocentre and to exhibiting, as a whole, the greatest thicknesses (Comas-Rengifo et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Quesada et al., \u003cspan citationid=\"CR151\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; G\u0026oacute;mez \u0026amp; Goy, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Although these are inland outcrops, the complete succession was accurately reconstructed with the use of detailed samples in the SMA sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) and SA (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3 Materials","content":"\u003cp\u003eIn the present paper we employed the ammonoids from the period investigated; these are deposited in the Museo del Jur\u0026aacute;sico de Asturias (Asturias Jurassic Museum - MUJA), and the \u0026ldquo;Su\u0026aacute;rez Vega Collection\u0026rdquo; can be found, which includes the specimens studied and cited by Su\u0026aacute;rez Vega (\u003cspan citationid=\"CR182\" class=\"CitationRef\"\u003e1974\u003c/span\u003e). The Spanish material from the \u0026ldquo;Mouterde Collection\u0026rdquo; has also been examined; this was provided by the Facultades Cat\u0026oacute;licas de Lyon (Lyon catholic faculties) and are housed at the Geology Faculty of Madrid\u0026rsquo;s Complutense University.\u003c/p\u003e \u003cp\u003eMoreover, we used the specimens collected during the research by Braga et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1985\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1988\u003c/span\u003e), Bernad (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1993\u003c/span\u003e), Goy et al. (\u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e1994\u003c/span\u003e, \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), G\u0026oacute;mez et al. (\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), Comas-Rengifo \u0026amp; Goy (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), G\u0026oacute;mez \u0026amp; Goy (\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), Comas-Rengifo et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), G\u0026oacute;mez et al. (\u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2016a\u003c/span\u003e), Salazar-Ram\u0026iacute;rez et al. (\u003cspan citationid=\"CR178\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), Comas-Rengifo et al. (in litt.). Exceptionally, we made use of the specimens of the lower Toarcian obtained by Comas-Rengifo (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1982\u003c/span\u003e) in the Muro de Aguas section (Pe\u0026ntilde;a Isasa Massif, Logro\u0026ntilde;o); it is associated with the BCB from a sedimentary perspective.\u003c/p\u003e \u003cp\u003eThese collections have been completed with the ammonoids obtained by the authors of the present paper over the last few years in expanded sections that were thoroughly sampled. Therein, we detected no relevant discontinuities that could be appraised with the available chronostratigraphy, with the exception of a hiatus identified in the Bifrons Subzone of the BCB sections and a stratigraphic gap affecting the base of the Upper Toarcian, in the same basin, and which affects the Bingmanni and Thouarsense subzones. Whatever the case may be, apart from the aforementioned exceptions, none of the discontinuities comprise more than one zone.\u003c/p\u003e"},{"header":"4 Results","content":"\u003cp\u003eFigs. 2-4 show the stratigraphic distribution of the index species in the zones, subzones and horizons identified in the AB (WR and SM sections) and the BCB (SMA and SA sections), as well as that of other species of interest which facilitate the correlation with the standard scales and with other Iberian basins, such as the Iberian Range, the LB and the Betic Range in the interval between the Pliensbachian and the middle Toarcian. \u003c/p\u003e\n\u003cp\u003eFigs. 5-9 present the most representative species in the interval considered in relation to the aforementioned standard scales and the Iberian basins.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003e4.1.1 Upper Pliensbachian (\u003cem\u003ep.p.\u003c/em\u003e)\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eSpinatum ZoneOppel, 1856\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003ePleuroceras spinatum\u003c/em\u003e (Brugui\u0026egrave;re)\u003c/p\u003e\n\u003cp\u003eIn the AB, the Spinatum Zone commences with the first record of the genus \u003cem\u003ePleuroceras \u003c/em\u003e(\u003cem\u003eP\u003c/em\u003e. \u003cem\u003esalebrosum\u003c/em\u003e) in ER614 (Comas-Rengifo et al., 2016, and in litt.). In the Apyrenum Subzone the following species occur: \u003cem\u003eP\u003c/em\u003e. cf. \u003cem\u003esalebrosum\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. \u003cem\u003etransiens\u003c/em\u003e and \u003cem\u003eP. solare\u003c/em\u003e, which is associated with other species of \u003cem\u003ePleuroceras \u003c/em\u003e(\u003cem\u003eP. spinatum\u003c/em\u003e, \u003cem\u003eP. paucicostatum\u003c/em\u003e, \u003cem\u003eP. apyrenum\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. cf. \u003cem\u003eyeovilense\u003c/em\u003e), \u003cem\u003eAmauroceras\u003c/em\u003e (\u003cem\u003eA\u003c/em\u003e. \u003cem\u003eferrugineum\u003c/em\u003e) and \u003cem\u003eAmaltheus\u003c/em\u003e (\u003cem\u003eA. margaritatus\u003c/em\u003e). In the BCB, the first level containing \u003cem\u003ePleuroceras\u003c/em\u003e (\u003cem\u003eP. transiens\u003c/em\u003e) was identified, in almost the same position as in the Castillo Pedroso and Camino sections (Braga et al., 1985: CP64; 1988: CM153). The species \u003cem\u003eP. salebrosum\u003c/em\u003e was recorded in levels (CP68) that were slightly more recent that the one contained in the first \u003cem\u003eP. transiens\u003c/em\u003e. \u003c/p\u003e\n\n\u003cp\u003eHawskerense SubzoneBuckman, 1922, \u003cem\u003eemend\u003c/em\u003e\u003cstrong\u003e. \u003c/strong\u003eHowarth, 1955\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003ePleuroceras hawskerense\u003c/em\u003e (Young \u0026amp; Bird)\u003c/p\u003e\n\u003cp\u003eThe Hawskerense Subzone commences with the first record of \u003cem\u003eP. elaboratum\u003c/em\u003e in level LA39, followed by the index species of the subzone in level LA40 (equivalent to level WR16i). It might be associated with \u003cem\u003eP. spinatum\u003c/em\u003e and with \u003cem\u003eA. ferrugineum\u003c/em\u003e, as well as with scarce \u003cem\u003eLioceratoides\u003c/em\u003e and with \u003cem\u003eN. expulsus\u003c/em\u003e. Subsequent to the Hawskerense Horizon, the extinction occurred of the Amaltheidae Family, with the exception of the genus \u003cem\u003eAmaurocera\u003c/em\u003es, which persisted up to the first levels of the Toarcian. Above the last \u003cem\u003ePleuroceras \u003c/em\u003e(\u003cem\u003eP. spinatum\u003c/em\u003e and \u003cem\u003eP. gigas\u003c/em\u003e), we recorded some Arieticeratinae, such as \u003cem\u003eE. emaciatum\u003c/em\u003e (WR19, WR20), \u003cem\u003eC.\u003c/em\u003e cf. \u003cem\u003egregalis\u003c/em\u003e (WR23, WR24) and \u003cem\u003eT. elisa\u003c/em\u003e (LA49i), these characterise the Emaciatum and Elisa horizons. Associated with the Arieticeratinae, \u003cem\u003eLioceratoides\u003c/em\u003e and \u003cem\u003eN. expulsus\u003c/em\u003e were found only on rare occasions.\u003c/p\u003e\n\u003cp\u003eIn the BCB in the upper part of the Hawskerense Subzone, \u003cem\u003eP\u003c/em\u003e. \u003cem\u003ehawskerense\u003c/em\u003e \u003cem\u003eP. spinatum\u003c/em\u003e and forms close to \u003cem\u003eP. apyrenum\u003c/em\u003e were replaced by Hildoceratidae (Arieticeratinae) such as \u003cem\u003eE. imitator\u003c/em\u003e and \u003cem\u003eC. zancleana\u003c/em\u003e, followed by \u003cem\u003eE. emaciatum\u003c/em\u003e, and \u003cem\u003eC. peloritana\u003c/em\u003e, in Camino (Braga et al., 1988; Comas-Rengifo et al., 2016) and by \u003cem\u003eT. nerina\u003c/em\u003e in the last levels of the Pliensbachian in the CP (Comas-Rengifo et al., 1988). In the Hawskerense Subzone, the following four chronostratigraphic horizons were characterised. \u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eThe supplementary data\u003c/strong\u003e provide further relevant information, such as the list of species cited in the text, as well as the first level at which the index species was recorded and which marks the beginning of each horizon in the AB and BCB. \u003c/p\u003e\n\n\u003cp\u003eElaboratum Horizon Dommergues et al., 1997\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003ePleuroceras hawskerense\u003c/em\u003e forma \u003cem\u003eelaboratum \u003c/em\u003e(Simpson)\u003c/p\u003e\n\u003cp\u003eHawskerense Horizon Buckman 1922, \u003cem\u003eemend\u003c/em\u003e. Dommergues et al. 1997\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003ePleuroceras hawskerense \u003c/em\u003e(Young \u0026amp; Bird) (Fig. 5a)\u003c/p\u003e\n\u003cp\u003eEmaciatum Horizon Braga, 1982\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eEmaciaticeras emaciatum\u003c/em\u003e (Catullo) (Fig. 5b)\u003c/p\u003e\n\u003cp\u003eElisa Horizon Braga, 1982\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eTauromeniceras\u003c/em\u003e \u003cem\u003eelisa \u003c/em\u003e(Fucini) (Fig. 5c)\u003c/p\u003e\n\n\u003cp\u003e4.1.2 Lower Toarcian\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eThe Toarcian Working Group was created in 1984 during the 1st International Symposium on Jurassic Stratigraphy held in Erlangen (Germany) following a debate on the best criterion for establishing the GSSP of the base of the Toarcian Stage. Numerous meetings held from 1984 and 2012 in Erlangen, Lisbon, Poitiers, Mendoza, Nu\u0026eacute;valos-Friburgo, Vancouver, Palermo, Peniche, Krakov, Sheong of Suining, Jaipur, etc. resulted in an agreement to commence this stage, with the first record of \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eEodactylites\u003c/em\u003e) being established some years later, when the Peniche section (Portugal) was chosen as the GSSP (Rocha et al., 2016).\u003c/p\u003e\n\n\u003cp\u003eTenuicostatum ZoneBuckman, 1910\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eDactylioceras \u003c/em\u003e(\u003cem\u003eOrtodactylites\u003c/em\u003e) \u003cem\u003etenuicostatum\u003c/em\u003e (Young \u0026amp; Bird)\u003c/p\u003e\n\u003cp\u003eIt starts with the first layer containing \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003esimplex\u003c/em\u003e followed by \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eE\u003c/em\u003e.) \u003cem\u003emirabile-polymorphum \u003c/em\u003eassociated with \u003cem\u003eA. ferrugineum\u003c/em\u003e, \u003cem\u003eNeolioceratoides\u003c/em\u003e in both basins and, exceptionally, with \u003cem\u003eLioceratoides\u003c/em\u003e. \u003c/p\u003e\n\u003cp\u003eFollowing the extinction of the Amaltheidae Family in the upper non-terminal part of the Hawskerense Subzone, carbon cycle perturbations affected the marine and terrestrial environments (Jenkyns \u0026amp; Clayton, 1986; Jenkyns, 1988; Hesselbo et al., 2000, 2007; Wignall et al., 2005: Bodin et al., 2010; M\u0026uuml;ller et al., 2017, 2020\u003cstrong\u003e; \u003c/strong\u003eReolid, 2014; Fantasia et al., 2019;Rodrigues, 2020, 2021; Reolid et al., 2021; Silva et al., 2021; Gambacorta et al., 2023).These are likely related to extinction bioevents that caused a staggered extinction of the ammonoids and other groups of organisms (brachiopods, bivalves, foraminifera, ostracods, calcareous nannoplankton, palynomorphs, etc., etc.) in numerous basins of the western Tethys (Arias et al., 1992; Arias, 2013;Herrero, 1994, 2008, 2014; Little \u0026amp; Benton, 1995; Comas-Rengifo et al., 1996, 1999, 2010a;Goy et al., 1996, 1998; Barr\u0026oacute;n et al., 1999, 2013;Aberhan \u0026amp; F\u0026uuml;rsich, 2000; Garc\u0026iacute;a Joral \u0026amp; Goy, 2000; Macchioni \u0026amp; Cecca, 2002; Cecca \u0026amp; Macchioni, 2004; G\u0026oacute;mez et al., 2008;Mattioli et al., 2008, 2009; Bilotta et al., 2010; Dera et al., 2010; G\u0026oacute;mez \u0026amp; Arias, 2010; Garc\u0026iacute;a Joral et al., 2011, 2018, 2022;G\u0026oacute;mez \u0026amp; Goy, 2011; Kov\u0026aacute;cs, 2011; Sandoval et al., 2012; Fraguas et al., 2012, 2021;Reolid et al., 2014a, b, 2019, 2023; Baeza-Carratal\u0026aacute; et al., 2015, 2017, 2018; Rita et al., 2016;Duarte et al., 2018a, b; Rosales et al., 2018;Danise et al., 2019; Mart\u0026iacute;nez \u0026amp; Garc\u0026iacute;a Joral, 2020; Salazar-Ram\u0026iacute;rez et al., 2020\u003cstrong\u003e; \u003c/strong\u003eDe Baets et al., 2021; Fern\u0026aacute;ndez-Mart\u0026iacute;nez et al., 2021, 2023; Rodr\u0026iacute;guez-Tovar, 2021\u003cstrong\u003e; \u003c/strong\u003eReolid \u0026amp; Ainsworth, 2022).\u003c/p\u003e\n\u003cp\u003eThe Tenuicostatum Zone has frequently been subdivided into two subzones. A lower one, Paltum (in the Subboreal and northern Sub-Mediterranean provinces) or Mirabile Subzone (in the Mediterranean and southern Submediterranean provinces), and an upper one, Semicelatum Subzone, which is common in the three abovementioned provinces. \u003c/p\u003e\n\u003cp\u003eThe horizons of these subzones were established considering the evolution of the Dactylioceratinae species.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003ePaltum Subzone Howarth, 1973/Mirabile Guex, 1973\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eProtogrammoceras\u003c/em\u003e (\u003cem\u003ePaltarpites\u003c/em\u003e)\u003cem\u003e paltum\u003c/em\u003e Buckman and \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eEodactylite\u003c/em\u003es) \u003cem\u003emirabile\u003c/em\u003e (Fucini), respectively.\u003c/p\u003e\n\u003cp\u003eThe Paltum Subzone was used mainly in the NE of England and Scotland (Howarth, 1973, 1992; Page, 2003) and in the northern part of the Submediterranean Province: Centre-West and N of France (e.g. Elmi et al., 1997; Rulleau, 1993; B\u0026eacute;caud, 2006). It includes one single horizon (Paltum Horizon), which is approximately similar to the Simplex and Mirabile horizons, pertaining to the Mirabile Subzone, in LB in the Peniche and Raba\u0026ccedil;al sections (Rocha et al., 2016; Duarte et al., 2018a, b; Paredes et al., 2018), in the Iberian Range (Comas-Rengifo, 1982; Goy, 1985; Goy et al., 1988; Goy \u0026amp; Mart\u0026iacute;nez, 1990; Comas-Rengifo et al., 2010a, b), in the BCB (Braga et al., 1985, 1988; Bernad, 1993; Goy et al., 1994) and in the Pyrenean Range (Faur\u0026eacute;, 2002). \u003c/p\u003e\n\u003cp\u003eThe Mirabile Subzone is typical of the Mediterranean Province: Betic Range, Apennines, Sicily, Hungary, N of Africa, Alpine Areas, etc. (Fucini, 1935; G\u0026egrave;czy, 1967a, b; Rivas, 1972; Guex, 1973; Elmi et al., 1974, 1997, 2007a\u003cstrong\u003e,\u003c/strong\u003e 2009; Wiedenmayer, 1980; Jim\u0026eacute;nez \u0026amp; Rivas, 1981, 1991, 1992; Benshili, 1989; Goy et al., 1988; Faraoni et al. 1995; Venturi \u0026amp; Ferri, 2001; Macchioni, 2002; Cecca \u0026amp; Macchioni, 2004; Elmi, 2006; Bilotta et al., 2010; Ettaki et al., 2011; Boulila et al., 2019; Benzaggagh et al., 2022; Benzaggagh, 2024).\u003c/p\u003e\n\u003cp\u003eIn the BCB, which generally presents more affinities with the Submediterranean Province than with the Mediterranean Province, the index species of both subzones are frequently recorded. As in the Iberian Range, for the last forty years (Braga et al., 1985, 1988; Goy, 1985) the Tenuicostatum Zone has usually been subdivided into the Mirabile and Semicelatum subzones. On the contrary, in the AB, until several years ago the Mirabile Subzone (Goy et al., 2010; Comas-Rengifo et al., 2016) had not usually been used.\u003c/p\u003e\n\n\u003cp\u003eSimplex HorizonHillebrandt \u0026amp; Schmidt-Effing, 1981, \u003cem\u003eemend\u003c/em\u003e. Goy \u0026amp; Mart\u0026iacute;nez, 1990\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eDactylioceras \u003c/em\u003e(\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003esimplex\u003c/em\u003e Fucini (Fig. 5d)\u003c/p\u003e\n\u003cp\u003eOther Ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eA. ferrugineum\u003c/em\u003e; \u003cem\u003eN\u003c/em\u003e. cf. \u003cem\u003eexpulsus\u003c/em\u003e, \u003cem\u003eN.\u003c/em\u003e \u003cem\u003ehoffmanni\u003c/em\u003e, \u003cem\u003eN. schopeni\u003c/em\u003e; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eCanavaria\u003c/em\u003e sp., \u003cem\u003eP. \u003c/em\u003e(\u003cem\u003eProtogrammoceras\u003c/em\u003e) \u003cem\u003eveliferum\u003c/em\u003e, \u003cem\u003eLioceratoides \u003c/em\u003esp., \u003cem\u003eN. expulsus\u003c/em\u003e, \u003cem\u003eN.\u003c/em\u003e \u003cem\u003ehoffmanni\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eMirabile Horizon Colo, 1961, \u003cem\u003eemend\u003c/em\u003e. Goy \u0026amp; Mart\u0026iacute;nez, 1990\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003emirabile\u003c/em\u003e Fucini (Fig. 5f)\u003c/p\u003e\n\u003cp\u003eOther Ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003epolymorphum\u003c/em\u003e\u003cem\u003e \u003c/em\u003e(Fig. 5e), \u003cem\u003eP. \u003c/em\u003e(\u003cem\u003ePaltarpites\u003c/em\u003e) \u003cem\u003epaltum\u003c/em\u003e, \u003cem\u003eN. \u003c/em\u003ecf. \u003cem\u003eexpulsus\u003c/em\u003e, \u003cem\u003eN. hoffmanni\u003c/em\u003e, \u003cem\u003eN. schopeni\u003c/em\u003e; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eEodactylites\u003c/em\u003e) \u003cem\u003epolymorphum\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. \u003cem\u003e(Paltarpites\u003c/em\u003e) \u003cem\u003epaltum\u003c/em\u003e, \u003cem\u003eN. hoffmanni\u003c/em\u003e, \u003cem\u003eN. schopeni\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eSemicelatumSubzone Howarth, 1973\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eOrthodactylites) semicelatum \u003c/em\u003e(Simpson)\u003c/p\u003e\n\u003cp\u003eThe Paltum/Mirabile Subzone is followed by the Semicelatum Subzone in the Subboreal and Submediterranean provinces, (Howarth, 1973; Elmi et al., 1989, 1997; Faur\u0026eacute;, 2002; Rocha et al., 2016), as well as in some areas of the Tethys (Elmi et al., 1997, 2009; Macchioni, 2002; Cecca \u0026amp; Macchioni, 2004). It is characterised by the expansion of the \u003cem\u003eD.\u003c/em\u003e (\u003cem\u003eOrthodactylites\u003c/em\u003e), which do not become totally extinct during the Jenkyns Event. Howarth (1978) describes \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003esemiannulatum\u003c/em\u003e in the Exaratum Subzone of Northamptonshire (England), and Jim\u0026eacute;nez \u0026amp; Rivas (1991) \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003eandaluciensis\u003c/em\u003e in the Striatus and Levisoni subzones of the CB. In the N of Iberia, Duarte et al. (2018a, b) cite both species in the Levison Subzone and Salazar-Ram\u0026iacute;rez et al. (2020) in the Elegantulum Subzone of the BCB.\u003c/p\u003e\n\u003cp\u003eIn this subzone, three species of \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e),\u003cem\u003e D\u003c/em\u003e. (\u003cem\u003eO\u003c/em\u003e) crosbeyi, D\u003cem\u003e. \u003c/em\u003e(\u003cem\u003eO\u003c/em\u003e.)\u003cem\u003e tenuicostatum \u003c/em\u003eand\u003cem\u003e D. \u003c/em\u003e(\u003cem\u003eO\u003c/em\u003e)\u003cem\u003e semicelatum\u003c/em\u003e succeed in the Subboreal Province and in some basins of the Submediterranean Province. According to Howarth (1992), in the NE of England, \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eO.) crosbeyi\u003c/em\u003e is recorded in a slightly older level than the one containing \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eO\u003c/em\u003e.) \u003cem\u003eclevelandicu\u003c/em\u003e\u003cem\u003em\u003c/em\u003e. In the GSSP in Peniche, however, the distributions of both species would appear to overlap (Rocha et al., 2016; Duarte et al., 2018a, b); the same thing occurs in the N of the LB and in the BCB (Duarte et al., 2018b; Salazar-Ram\u0026iacute;rez et al., 2020).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eO\u003c/em\u003e.) \u003cem\u003etenuicostatum\u003c/em\u003e is a species typical of the Subboreal Province and of the northern sector of the Submediterranean Province (Dean et al., 1961; Howarth, 1973; Gabilly, 1976; Rulleau, 1993; Elmi et al., 1997; Page, 2003); it has a poor record in the Submediterranean Province (Goy \u0026amp; Mart\u0026iacute;nez, 1990; Salazar-Ram\u0026iacute;rez et al., 2020) and is absent from the Mediterranean Province (Jim\u0026eacute;nez, 1976; Elmi et al., 1994, 1997; Macchioni, 2002; Bilotta et al., 2010). \u003c/p\u003e\n\u003cp\u003eMoreover, \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eO.\u003c/em\u003e) \u003cem\u003esemicelatum\u003c/em\u003e is frequent in the Subboreal Province throughout most of the Submediterranean Province. In the N of Iberia, it is usually associated with \u003cem\u003eP.\u003c/em\u003e (\u003cem\u003ePaltarpites\u003c/em\u003e) \u003cem\u003emadagascariense\u003c/em\u003e (Goy et al., 1994, 1996; Comas-Rengifo et al., 1996, 1999; Faur\u0026eacute;, 2002) and in the Iberian Range and the LB, several species of the genus \u003cem\u003eBouleiceras\u003c/em\u003e have also been occasionally recorded (Mouterde, 1953; Behmel \u0026amp; Geyer, 1966; Goy, 1974; Mouterde \u0026amp; Rocha, 1981; Mouterde \u0026amp; Elmi, 1991; Rulleau et al., 2003; Mart\u0026iacute;nez \u0026amp; Garc\u0026iacute;a Joral, 2020). Some of them become extinct and others persist during the Elegantulum Subzone or they originate following the Jenkyns Event. Nonetheless, this genus has never been found in the Cantabrian Range or in the Pyrenees. In the upper part of the Semicelatum Subzone, Page (2003) characterised an \u003cem\u003eantiquum\u003c/em\u003e Biohorizon, due to the habitual presence of \u003cem\u003eT. antiquum\u003c/em\u003e. This species is rare outside the Subboreal Province and the N of the Submediterranean Province. In the Cantabrian Range, some specimens of \u003cem\u003eTiltoniceras\u003c/em\u003e are known to exist in the Tudanca, San Miguel de Aguayo and W Rodiles sections (G\u0026oacute;mez \u0026amp; Goy, 2011: TU31; Salazar-Ram\u0026iacute;rez et al., 2020: SM57i; Comas-Rengifo, et al., in litt.: WR43.2); these are situated in a position equivalent to that of \u003cem\u003eT\u003c/em\u003e. \u003cem\u003eantiquum\u003c/em\u003e. \u003c/p\u003e\n\u003cp\u003eFurthermore, in the basins in the N of Iberia, such as the Cantabrian Range and the Pyrenees, in the Crosbeyi Horizon, the \u003cem\u003eD.\u003c/em\u003e (\u003cem\u003eEodactylites\u003c/em\u003e) and the \u003cem\u003eLioceratoides\u003c/em\u003e become extinct or were already extinct; the \u003cem\u003eNeolioceratoides\u003c/em\u003e (\u003cem\u003eN\u003c/em\u003e. \u003cem\u003ehoffmanni\u003c/em\u003e and \u003cem\u003eN. schopeni\u003c/em\u003e) are rare and the \u003cem\u003eP\u003c/em\u003e. (\u003cem\u003eProtogrammoceras\u003c/em\u003e) and Arieticeratinae (\u003cem\u003eCanavaria\u003c/em\u003e and \u003cem\u003eTauromeniceras\u003c/em\u003e) are practically non-existent, although they persist until the upper part of the Semicelatum Subzone in some areas of the Tethys, such as the Betic Range and in the Apennines (Braga et al., 1982; Macchioni \u0026amp; Meister, 2003). The \u003cem\u003eP\u003c/em\u003e. (\u003cem\u003ePaltarpites\u003c/em\u003e) become extinct at the end of the Jenkyns Event (Goy et al., 1996; Ferreti, 2002; B\u0026eacute;caud, 2006).\u003c/p\u003e\n\n\u003cp\u003eCrosbeyi HorizonGoy \u0026amp; Mart\u0026iacute;nez,1990 \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003ecrosbeyi \u003c/em\u003e(Simpson) (Fig. 5g)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eP.\u003c/em\u003e (\u003cem\u003ePaltarpites\u003c/em\u003e) \u003cem\u003epaltum\u003c/em\u003e, \u003cem\u003eP. \u003c/em\u003e(\u003cem\u003ePaltarpites\u003c/em\u003e) \u003cem\u003emadagascariense\u003c/em\u003e, \u003cem\u003eNeolioceratoides hoffmanni\u003c/em\u003e, \u003cem\u003eNeolioceratoides schopeni\u003c/em\u003e; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003eclevelandicum,\u003c/em\u003e \u003cem\u003eP\u003c/em\u003e. (\u003cem\u003ePaltarpites\u003c/em\u003e) cf. \u003cem\u003epaltum,\u003c/em\u003e \u003cem\u003eN. schopeni\u003c/em\u003e. \u003c/p\u003e\n\u003cp\u003eTenuicostatum Horizon Goy \u0026amp; Mart\u0026iacute;nez, 1990\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003etenuicostatum \u003c/em\u003e(Young and Bird) (Fig. 5h)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB y BCB\u003c/strong\u003e: \u003cem\u003eP. \u003c/em\u003e(\u003cem\u003ePaltarpites\u003c/em\u003e) \u003cem\u003emadagascariense. \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eSemicelatum Horizon Goy \u0026amp; Mart\u0026iacute;nez, 1990\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species Dactylioceras \u003c/em\u003e(\u003cem\u003eOrthodactylites) semicelatum \u003c/em\u003e(Simpson) (Fig. 5i)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003etenuicostatum\u003c/em\u003e (en la base), \u003cem\u003eP. \u003c/em\u003e(\u003cem\u003ePaltarpites)\u003c/em\u003e \u003cem\u003emadagascariense\u003c/em\u003e, \u003cem\u003eTiltoniceras\u003c/em\u003e sp.; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003eernsti P. (Paltarpites) madagascariense\u003c/em\u003e\u003cem\u003e-\u003c/em\u003e\u003c/p\u003e\n\n\u003cp\u003eSerpentinum Zone Oppel, 1856\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species:\u003c/em\u003e \u003cem\u003eHarpoceras serpentinum\u003c/em\u003e (Schlotheim) (Fig. 5k)\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eH. serpentinum\u003c/em\u003e is a difficult species to base on the illustration of the specimen type because it was often considered to belong to the genera \u003cem\u003eHildoceras\u003c/em\u003e (Buckman, 1919), \u003cem\u003eHildaites\u003c/em\u003e (Mouterde, 1967; Rivas, 1972; Goy, 1974; Riegraf, 1984; Jim\u0026eacute;nez, 1986), \u003cem\u003eHarpoceratoides \u003c/em\u003e(Gabilly et al., 1971; Su\u0026aacute;rez Vega, 1974) or \u003cem\u003eHildoceratoides\u003c/em\u003e (Elmi et al., 1974). Based on the research of Howarth (1992) it was usually included in the \u003cem\u003eHarpoceras\u003c/em\u003e Genus (Rulleau, 1993; Goy et al., 1994; Comas-Rengifo et al., 1996; Elmi et al., 1997; Page, 2003; B\u0026eacute;caud, 2006, etc.).\u003c/p\u003e\n\u003cp\u003eThe Serpentinum Zone, which commences with the first record of \u003cem\u003eE. elegantulum\u003c/em\u003e (Fig. 5j) in the AB (WR43.4, LA69.4) and in the BCB (CM246, SM58), is related to an episode with Black Shales presenting a thickness of 1 to 3 m. In the AB they are approximately 1.7 m thick and in the BCB the minimum values (1.1 m) are close to Salinas de Pisuerga; the maxima (approx. 3 m) are close to Tudanca in the depocentre of the basin (Comas-Rengifo et al., 1988; Bernad, 1993; Goy et al., 1994; G\u0026oacute;mez \u0026amp; Goy, 2011; Fraguas et al., 2020; Salazar-Ram\u0026iacute;rez et al., 2020). In accordance with Elmi et al. (1997), the zone has been subdivided into the Elegantulum and Falciferum subzones. For the subdivision of both into horizons, we considered the evolution of four Harpoceratinae species, followed by \u003cem\u003eO. douvillei\u003c/em\u003e, which is present throughout the range. \u003c/p\u003e\n\n\u003cp\u003eElegantulumSubzoneGabilly, 1976a\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eEleganticeras elegantulum\u003c/em\u003e (Young and Bird) (Fig. 5j)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eH. wrighti\u003c/em\u003e (Fig. 9a) \u003c/p\u003e\n\u003cp\u003eIn the boundary between the Semicelatum-Elegantulum subzones, the \u003cem\u003eTiltoniceras\u003c/em\u003e and the \u003cem\u003eP\u003c/em\u003e. (\u003cem\u003ePaltarpites\u003c/em\u003e) become extinct, with a notable decrease in the \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eOrthodactylites\u003c/em\u003e). Additionally, the expansion starts of the \u003cem\u003eEleganticeras,\u003c/em\u003e \u003cem\u003eCleviceras\u003c/em\u003e, \u003cem\u003eHarpoceras\u003c/em\u003e and \u003cem\u003eHildaites\u003c/em\u003e. (Gabilly, 1976,\u003cem\u003e \u003c/em\u003eHowarth, 1992; B\u0026eacute;caud, 2006), as well as that of other groups affected by the extinction event (Arias et al., 1992; Herrero, 2008; Mattioli, 2008; G\u0026oacute;mez \u0026amp; Arias (2010); Garc\u0026iacute;a Joral, et al., 2011; G\u0026oacute;mez \u0026amp; Goy, 2011; Fraguas et al., 2012, 2023; Baeza Carratal\u0026aacute; et al., 2017; Reolid et al., 2023).\u003c/p\u003e\n\u003cp\u003eThe Exaratum Horizon, equivalent to the Exaratum Subzone of Etzol et al. (1989), is characteristic of the Subboreal Province, and has also been used in the Cantabrian Range (Goy et al. 2010, Comas-Rengifo et al., \u003cem\u003ein litt\u003c/em\u003e. and in the present research), whereas in the more southern areas of the Submediterranean Province, the Strangewaysi Horizon (Gabilly, 1976; Elmi et al., 1994, 1997; Faur\u0026eacute;, 2002, B\u0026eacute;caud, 2006) is more often employed. In the Mediterranean Province, the correlations with the standard scales are complex and tend to be inaccurate (Jim\u0026eacute;nez, 1986; Macchioni, 2002; Bilota et al., 2010). Thus, for instance, the Exaratum/Strangewaysi horizons would roughly correspond to the AndalucienseHorizon of the Betic Range\u003cstrong\u003e (\u003c/strong\u003eJim\u0026eacute;nez, 1986), to the E. iblanenseHorizon of theMediterranean (Macchioni, 2002) and to the \u003cem\u003efasciculatus\u003c/em\u003e \u0026amp; \u003cem\u003efortiundicosta\u003c/em\u003e Biohorizon of the Apennines (Bilota et al., 2010).\u003c/p\u003e\n\u003cp\u003eCharacterisation of a Serpentinum Horizon in the upper part of the Elegantulum Subzone is infrequent in the Submediterranean Province. In the Cantabrian Range, however, following the first \u003cem\u003eHarpoceras\u003c/em\u003e species (\u003cem\u003eH. strangewaysi\u003c/em\u003e) the index species of this horizon is relatively abundant, persisting up to the start of the Falciferum Subzone (in the AB: G\u0026oacute;mez et al., 2008; Goy et al., 2010; in BCB: G\u0026oacute;mez \u0026amp; Goy, 2011; Salazar-Ram\u0026iacute;rez et al., 2020).\u003c/p\u003e\n\u003cp\u003eElegantulum Horizon Gabilly, 1976a \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e:\u003cem\u003e Eleganticeras elegantulum\u003c/em\u003e (Young \u0026amp; Bird) (Fig. 5j)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003esemicelatum\u003c/em\u003e, \u003cem\u003eP.\u003c/em\u003e (\u003cem\u003ePaltarpites\u003c/em\u003e) \u003cem\u003emadagascariense\u003c/em\u003e, \u003cem\u003eH. wrighti\u003c/em\u003e; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003esemicelatum\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003estrangewaysi\u003c/em\u003e, \u003cem\u003eH. wrighti.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eExaratum Horizon Page, 2003 (as Biohorizon)\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eCleviceras exaratum\u003c/em\u003e (Young and Bird) (Fig. 5k)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eOrthodactylites\u003c/em\u003e) gr. \u003cem\u003esemiannulatum\u003c/em\u003e, \u003cem\u003eH. strangewaysi \u003c/em\u003e(Fig. 5l)\u003cem\u003e, H. forte\u003c/em\u003e;\u003cem\u003e \u003c/em\u003e\u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003eandaluciensis\u003c/em\u003e,\u003cem\u003e H. strangewaysi\u003c/em\u003e, \u003cem\u003eH. levisoni \u003c/em\u003e(Fig. 9b), \u003cem\u003eH. forte\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eSerpentinum Horizon\u003cem\u003enov.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHarpoceras serpentinum\u003c/em\u003e (Schlotheim) (Fig. 6a)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eC. exaratum\u003c/em\u003e, \u003cem\u003eH. levisoni\u003c/em\u003e;\u003cem\u003e \u003c/em\u003e\u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eOrthodactylites\u003c/em\u003e) \u003cem\u003esemiannulatum\u003c/em\u003e, \u003cem\u003eN. crassoides\u003c/em\u003e, \u003cem\u003eC. elegans\u003c/em\u003e, \u003cem\u003eH. levisoni\u003c/em\u003e.\u003c/p\u003e\n\n\u003cp\u003eFalciferum SubzoneHaug, 1885\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e:\u003cem\u003eHarpoceras falciferum\u003c/em\u003e (J. Sowerby) (Fig. 7a)\u003c/p\u003e\n\u003cp\u003eThis subzone was employed by Elmi (1967) and Howarth (1992), including the whole range of the index species, which, in its upper part is associated with \u003cem\u003eH. sublevisoni\u003c/em\u003e, so that the Bifrons Zone started with the first record of \u003cem\u003eD. commune\u003c/em\u003e. In the last few years, many authors have chosen to place the lower boundary of the Bifrons Zone at the first record of the genus \u003cem\u003eHildoceras\u003c/em\u003e (Mouterde, 1967; Gabilly et al., 1971; Guex, 1972; Rivas, 1972; Schmidt-Effing, 1972; Gabilly, 1976; Elmi et al. 1974, 1989, 1994, 1997; Su\u0026aacute;rez Vega, 1974; Goy, 1974; Comas-Rengifo, 1982; etc.).\u003c/p\u003e\n\u003cp\u003eIn the standard scales of the Subboreal Province, two Biohorizons can be distinguished, \u003cem\u003epseudoserpentinum\u003c/em\u003e and \u003cem\u003efalciferum\u003c/em\u003e; in the Submediterranean Province, two Horizons (or Zonules), Pseudoserpentinum and Douvillei; however, the Mediterranean Province is not subdivided (Elmi et al., 1997; Page, 2003).\u003c/p\u003e\n\u003cp\u003eThe Pseudoserpentinum Horizon, in the AB and the BCB, is characterised by the index species, associated with \u003cem\u003eH. subserpentinus\u003c/em\u003e and with scarce Dactylioceratidae, such as \u003cem\u003eNodicoeloceras\u003c/em\u003e and \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eDactylioceras\u003c/em\u003e). \u003c/p\u003e\n\u003cp\u003eThe Douvillei Horizon presents a broad distribution throughout numerous basins in Europe and the N of Africa. It has been cited in the Subboreal Province by Buckman (1923, as \u003cem\u003eO. orthus\u003c/em\u003e) and Howarth (1992); in the Sub-mediterranean Province by Elmi (1967, as \u003cem\u003eO. orthus\u003c/em\u003e), Gabilly (1973, 1976), Goy (1974, as \u003cem\u003eO. orthus\u003c/em\u003e), Goy et al. (1988, 1994, 1996, 2010), Goy \u0026amp; Mart\u0026iacute;nez (1990), Bernad (1993), Rulleau (1993), Comas-Rengifo et al. (1996), Elmi et al. (1997), Faur\u0026eacute; (2002), Neige \u0026amp; Rouget (2002), Duarte et al. (2018b), etc. In the Mediterranean Province they refer to the type species of this horizon: G\u0026egrave;czy (1971, as \u003cem\u003eO\u003c/em\u003e. cf. \u003cem\u003edouvillei\u003c/em\u003e), Guex (1973, as \u003cem\u003eO. intermedius\u003c/em\u003e), Elmi et al. (1974), Jim\u0026eacute;nez (1986), Goy et al. (1988), Jim\u0026eacute;nez \u0026amp; Rivas (1992), Cresta et al. (1995), Macchioni \u0026amp; Venturi (1996), Macchioni (2002) and Bilota et al. (2010), among others. \u003c/p\u003e\n\n\u003cp\u003ePseudoserpentinum Horizon Gabilly, 1976a\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHarpoceras pseudoserpentinum\u003c/em\u003e Gabilly (Fig. 6b)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eH. subserpentinum \u003c/em\u003e(Fig. 9c); \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eNodicoeloceras\u003c/em\u003e sp., \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eDactylioceras\u003c/em\u003e) sp.\u003c/p\u003e\n\u003cp\u003eDouvillei Horizon Goy \u0026amp;Mart\u0026iacute;nez, 1990 \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eOrthildaites douvillei\u003c/em\u003e (Haug) (Fig. 6c)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eNodicoeloceras\u003c/em\u003e sp., \u003cem\u003eDactylioceras \u003c/em\u003e(\u003cem\u003eDactylioceras\u003c/em\u003e) sp., \u003cem\u003eHarpoceras falciferum\u003c/em\u003e, \u003cem\u003eP. pluricostatus\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003e4.1.3 Middle Toarcian\u003c/p\u003e\n\n\u003cp\u003eSome authors (Dean et al., 1961; Howarth, 1973, \u003cstrong\u003e1978,\u003c/strong\u003e 1992; Page, 2003) subdivided the Toarcian into two substages, the lower and upper ones, which do not exactly coincide with the Whitbian and Yeovilian described with a lithostratigraphic base by Buckman (1910), Under this supposition, the Upper Toarcian commences at the base of the Variabilis Zone. \u003c/p\u003e\n\u003cp\u003eIn addition, according to Elmi et al., (1997), as from the \u0026ldquo;Colloque du Jurassique de Luxembourg\u0026rdquo; numerous authors have employed a ternary division for the Toarcian Stage, situating the Middle Toarcian\u0026ndash;Upper Toarcian boundary in the base of the Thouarsense Zone (Elmi 1967; Guex, 1972, 1975; Elmi et al., 1974, 1989, 1994, 1997; \u003cstrong\u003eGabilly, 1973,\u003c/strong\u003e 1976; Goy et al., 1988\u003cstrong\u003e; C\u003c/strong\u003eomas-Rengifo et al., 1996; B\u0026eacute;caud, 2006; \u003cstrong\u003eG\u0026egrave;czy \u0026amp; Szente, 2007;\u003c/strong\u003e G\u0026oacute;mez et al., 2008, among others).It comprises theBifrons and Variabilis zones and commences starts with the first record of the genus \u003cem\u003eHildoceras\u003c/em\u003e Hyatt, 1867, corresponding to the first layer containing \u003cem\u003eH. sublevisoni\u003c/em\u003e Fucini. \u003c/p\u003e\n\n\u003cp\u003eBifrons Zone Reyn\u0026egrave;s, 1868 \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHildoceras bifrons\u003c/em\u003e (Brugui\u0026egrave;re)\u003c/p\u003e\n\u003cp\u003eFor the subdivision of this zone the evolution of the \u003cem\u003eHildoceras\u003c/em\u003e species was considered and in accordance with Elmi et al. (1997), it was subdivided into two subzones: Sublevisoni and Bifrons which, in turn, were subdivided into three horizons each (see Figs. 2-3) \u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eSublevisoni SubzoneDonovan, 1958\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHildoceras sublevisoni\u003c/em\u003e Fucini \u003c/p\u003e\n\u003cp\u003eIn this subzone, the following species succeed in time: \u003cem\u003eH. sublevisoni\u003c/em\u003e, \u003cem\u003eH. tethysi\u003c/em\u003e and \u003cem\u003eH. lusitanicum\u003c/em\u003e. In the lower part, Harpoceratinae persist, as do \u003cem\u003eH. falciferum\u003c/em\u003e, although there is an unequivocal dominance of \u003cem\u003eH. sublevisoni\u003c/em\u003e, which is associated with scarce Dactylioceratidae, such as \u003cem\u003eD. \u003c/em\u003e(\u003cem\u003eDactylioceras\u003c/em\u003e) and \u003cem\u003ePeronoceras\u003c/em\u003e\u003cem\u003e. \u003c/em\u003eIn the upper part, \u003cem\u003eH. lusitanicum\u003c/em\u003e is associated with \u003cem\u003ePeronoceras\u003c/em\u003e, \u003cem\u003eH. subplanatum\u003c/em\u003e and with the first \u003cem\u003ePseudolioceras\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003cp\u003eHorizonte Sublevisoni Gabilly, 1976a\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEspecie \u0026iacute;ndice\u003c/em\u003e: \u003cem\u003eHildoceras sublevisoni\u003c/em\u003e Fucini (Fig. 6d)\u003c/p\u003e\n\u003cp\u003eOtros ammonoideos: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eH. falciferum\u003c/em\u003e; \u003cstrong\u003eBCB\u003c/strong\u003e, \u003cem\u003eH. falciferum\u003c/em\u003e, \u003cem\u003eO. douvillei\u003c/em\u003e (s\u0026oacute;lo en la base), \u003cem\u003eH. caterinii\u003c/em\u003e, \u003cem\u003eD\u003c/em\u003e. (\u003cem\u003eDactylioceras\u003c/em\u003e) sp., \u003cem\u003ePeronoceras\u003c/em\u003e sp.\u003c/p\u003e\n\u003cp\u003eHorizonte Tethysi Elmi et al., 1991\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEspecie \u0026iacute;ndice\u003c/em\u003e: \u003cem\u003eHildoceras tethysi\u003c/em\u003e G\u0026egrave;czy (Fig. 6e)\u003c/p\u003e\n\u003cp\u003eOtros ammonoideos: \u003cstrong\u003eAB y BCB\u003c/strong\u003e: \u003cem\u003eH. sublevisoni\u003c/em\u003e (s\u0026oacute;lo en la base); \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ecrassum\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eHorizonte LusitanicumGabilly, 1976a\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEspecie \u0026iacute;ndice\u003c/em\u003e: \u003cem\u003eHildoceras lusitanicum\u003c/em\u003e Meister (Fig. 6f)\u003c/p\u003e\n\u003cp\u003eOtros ammonoideos: AB: \u003cem\u003eH. tethysi\u003c/em\u003e (s\u0026oacute;lo en la base); \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eH\u003c/em\u003e. \u003cem\u003esubplanatum\u003c/em\u003e, \u003cem\u003ePseudolioceras\u003c/em\u003e sp. (cf. \u003cem\u003elithense\u003c/em\u003e / cf. \u003cem\u003ebulbiense\u003c/em\u003e), \u003cem\u003ePeronoceras\u003c/em\u003e sp.\u003c/p\u003e\n\n\u003cp\u003eBifrons SubzoneGabilly et al., 1971\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHildoceras bifrons\u003c/em\u003e (Brugui\u0026egrave;re)\u003c/p\u003e\n\u003cp\u003eAs in the previous subzone, in the Bifrons Subzone, three \u003cem\u003eHildoceras \u003c/em\u003especies se succeed, \u003cem\u003eH. apertum\u003c/em\u003e, \u003cem\u003eH. bifrons\u003c/em\u003e and \u003cem\u003eH. semipolitum\u003c/em\u003e. The Hildoceratinae continue to dominate, although as a whole, the species diversity is greater than in the rest of the Bifrons Zone. Specifically recorded in the Bifrons Horizon are: Harpoceratinae (\u003cem\u003eH. subplanatum\u003c/em\u003e), Dactylioceratidae (\u003cem\u003ePeronoceras\u003c/em\u003e, \u003cem\u003eZugodactylites\u003c/em\u003e, \u003cem\u003ePorpoceras\u003c/em\u003e), Phymatoceratidae (\u003cem\u003ePhymatoceras\u003c/em\u003e) and Mercaticeratinae (\u003cem\u003eArctomercaticeras\u003c/em\u003e).\u003c/p\u003e\n\n\u003cp\u003eApertum Horizon Elmi et al., 1991\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHildoceras apertum\u003c/em\u003e Gabilly (Fig. 6g)\u003c/p\u003e\n\u003cp\u003eOtros ammonoideos: AB: \u003cem\u003eP\u003c/em\u003e. cf. \u003cem\u003efimbriatum\u003c/em\u003e, \u003cem\u003eP. narbonense\u003c/em\u003e; BCB: \u003cem\u003eCatacoeloceras\u003c/em\u003e sp.\u003c/p\u003e\n\u003cp\u003eBifrons Horizon Elmi, 1967\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHildoceras \u003c/em\u003e\u003cem\u003ebifrons\u003c/em\u003e (Brugui\u0026egrave;re) (Fig. 7b)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: AB: \u003cem\u003eP.\u003c/em\u003e cf. \u003cem\u003efibulatum\u003c/em\u003e, \u003cem\u003eP. vortex\u003c/em\u003e, \u003cem\u003eZugodactylites\u003c/em\u003e sp., \u003cem\u003eZ. braunianus\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. cf. \u003cem\u003esubplanatum\u003c/em\u003e, \u003cem\u003eP. lythense\u003c/em\u003e, \u003cem\u003eH. apertum\u003c/em\u003e, \u003cem\u003ePh. narbonense\u003c/em\u003e, \u003cem\u003ePh\u003c/em\u003e. aff. \u003cem\u003erobustum\u003c/em\u003e; BCB: \u003cem\u003eP\u003c/em\u003e. cf. \u003cem\u003evortex\u003c/em\u003e, \u003cem\u003eP.\u003c/em\u003e \u003cem\u003enarbonensis\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eSemipolitum Horizon Elmi, 1967\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEspecie \u0026iacute;ndice\u003c/em\u003e: \u003cem\u003eHildoceras semipolitum \u003c/em\u003e(Buckman) (Fig. 7c)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: AB: \u003cem\u003eC. crassum\u003c/em\u003e, \u003cem\u003eMucrodactylites \u003c/em\u003esp., \u003cem\u003eA. dilatum\u003c/em\u003e; BCB: \u003cem\u003eH. \u003c/em\u003ecf\u003cem\u003e. subplanatum\u003c/em\u003e,\u003cem\u003e O\u003c/em\u003e. (\u003cem\u003ePseudopolyplectus\u003c/em\u003e) cf. \u003cem\u003eloev\u003c/em\u003ee, \u003cem\u003eA. \u003c/em\u003ecf.\u003cem\u003e dilatum\u003c/em\u003e.\u003c/p\u003e\n\n\u003cp\u003eVariabilis ZoneGabilly, 1976a (= XII Horizon)\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia variabils\u003c/em\u003e (d\u0026rsquo;Orbigny)\u003c/p\u003e\n\u003cp\u003eIn the Cantabrian Range the sediments of the Variabilis Zone present relatively high thicknesses, which reach 10 m in the Santa Mera section and 18 m in the San Andr\u0026eacute;s section (Figs. 1 and 3).\u003c/p\u003e\n\u003cp\u003eThe base of this zone is marked by the first record of the genus \u003cem\u003eHaugia\u003c/em\u003e, which usually corresponds to \u003cem\u003eH. evoluta\u003c/em\u003e or \u003cem\u003eH. navis.\u003c/em\u003e In order to subdivide it, we considered the evolution of the species of the genus, \u003cem\u003eH. navis\u003c/em\u003e, \u003cem\u003eH. variabilis\u003c/em\u003e and \u003cem\u003eH. jugosa\u003c/em\u003e in the Variabilis Subzone, \u003cem\u003eH. illustris\u003c/em\u003e and \u003cem\u003eH. phillpsi\u003c/em\u003e in the Illustris Subzone and \u003cem\u003eH. vitiosa\u003c/em\u003e in the Vitiosa Subzone. \u003c/p\u003e\n\u003cp\u003eThe specimens of this genus are relatively scarce and are rarely found complete\u003cem\u003e \u003c/em\u003e(Comas-Rengifo et al., 1988; Goy et al. 1994, 2010).\u003c/p\u003e\n\n\u003cp\u003eVariabilis SubzoneGabilly et al. 1971\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia variabilis\u003c/em\u003e (d\u0026rsquo;Orbigny)\u003c/p\u003e\n\u003cp\u003eGuex (1972) situates \u003cem\u003eH. navis\u003c/em\u003e in the lower part of the Variabilis Subzone of the Causses;\u003cs\u003e \u003c/s\u003eaccording to Gabilly (1976, 1990), in the lower part of the Variabilis Zone of Vand\u0026eacute;e forms of \u003cem\u003eHaugia\u003c/em\u003e are recorded which exhibit straight ribs and a poorly marked projection in the Saint-Nicolas section (Jard-sur-mer, Vend\u0026eacute;e), where the sediments of this zone are somewhat more expanded than in other sections of the Thouars region. The forms of \u003cem\u003eHaugia \u003c/em\u003eindicate that \u003cem\u003eH. evoluta\u003c/em\u003e is situated in the basal part of the Variabilis Subzone, followed by \u003cem\u003eHaugia\u003c/em\u003e of the \u003cem\u003ejugosa\u003c/em\u003e group (such as \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ejugosa\u003c/em\u003e and \u003cem\u003eH. ogerieni\u003c/em\u003e, which are recorded in the same level. With the data subsequently obtained in the Lyon region (Lafargue quarries, Belmont) by Roulleau (1993), Elmi et al. (1997) define a Navis Horizon and a Jugosa Horizon in the Variabilis Subzone. \u003c/p\u003e\n\u003cp\u003eIn the AB and the BCB, the succession recorded involves \u003cem\u003eH. navis\u003c/em\u003e, \u003cem\u003eH. variabilis\u003c/em\u003e y \u003cem\u003eH. \u003c/em\u003egr. \u003cem\u003ejugosa\u003c/em\u003e. With regard to the latter species, also found in the same level are the morphotypes \u003cem\u003ejugosa\u003c/em\u003e and \u003cem\u003eogerieni \u003c/em\u003ejust below the position of \u003cem\u003eH. illustris\u003c/em\u003e and \u003cem\u003eP. aratum.\u003c/em\u003e Oher elements of interest for the correlations are \u003cem\u003eC. gemma \u003c/em\u003e(Fig. 9e), \u003cem\u003eP. sternale \u003c/em\u003eand \u003cem\u003eP. helveticum\u003c/em\u003e (Goy \u0026amp; Mart\u0026iacute;nez, 2009; Goy et al., 2010). \u003c/p\u003e\n\n\u003cp\u003eNavis Horizon Elmi et al., 1997\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia navis\u003c/em\u003e (Dumortier) (Fig. 7d)\u003c/p\u003e\n\u003cp\u003eOther ammonoids:\u003cem\u003e \u003c/em\u003e\u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eH. semipolitum\u003c/em\u003e, \u003cem\u003eH. evoluta\u003c/em\u003e, \u003cem\u003eB\u003c/em\u003e. cf. \u003cem\u003elehmanni\u003c/em\u003e; \u003cstrong\u003eBCB:\u003c/strong\u003e \u003cem\u003eCatacoeloceras\u003c/em\u003e sp., \u003cem\u003eCollina\u003c/em\u003e sp., \u003cem\u003eH. semipolitum\u003c/em\u003e, \u003cem\u003eP. sternale\u003c/em\u003e. \u003c/p\u003e\n\u003cp\u003eVariabilisHorizon Gabilly, 1990\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia variabilis \u003c/em\u003e(d\u0026rsquo;Orbigny) (Fig. 7g)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eC.\u003c/em\u003e cf. \u003cem\u003egemma\u003c/em\u003e, \u003cem\u003eC\u003c/em\u003e. cf. \u003cem\u003econfectum\u003c/em\u003e, \u003cem\u003eM\u003c/em\u003e. cf. \u003cem\u003egracilis\u003c/em\u003e, \u003cem\u003eP. sternale\u003c/em\u003e, \u003cem\u003eB\u003c/em\u003e. cf. \u003cem\u003elehmann\u003c/em\u003ei, \u003cem\u003eD. malagna\u003c/em\u003e; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eP. sternale\u003c/em\u003e, \u003cem\u003eP. helveticum\u003c/em\u003e, \u003cem\u003eA\u003c/em\u003e. cf. \u003cem\u003edilatum\u003c/em\u003e, \u003cem\u003eP. \u003c/em\u003ecf. \u003cem\u003efrantzi\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eJugosaHorizon Elmi et al., 1997 \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia \u003c/em\u003e\u003cem\u003ejugosa\u003c/em\u003e (Sowerby) (Fig. 8a, b)\u003c/p\u003e\n\u003cp\u003eGoy et al. (2010) characterise an \u003cem\u003eogerieni\u003c/em\u003e Biohorizon (Index species: \u003cem\u003eHaugia ogerieni\u003c/em\u003e (Dumortier, 1874) presenting a similar duration in the Santa Mera section (Asturias).\u003c/p\u003e\n\u003cp\u003eOther ammonoids:\u003cem\u003e \u003c/em\u003e\u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eC\u003c/em\u003e. cf. \u003cem\u003econfectum\u003c/em\u003e, \u003cem\u003eC. linae\u003c/em\u003e, \u003cem\u003eM\u003c/em\u003e. cf. \u003cem\u003egracilis\u003c/em\u003e, \u003cem\u003eP. sternale\u003c/em\u003e, \u003cem\u003eP. helveticum\u003c/em\u003e, \u003cem\u003eP.\u003c/em\u003e \u003cem\u003eprimaria\u003c/em\u003e, \u003cem\u003eH.\u003c/em\u003e \u003cem\u003ejugosa\u003c/em\u003e morp. \u003cem\u003eogerieni\u003c/em\u003e, \u003cem\u003eD\u003c/em\u003e. cf. \u003cem\u003erudis, Lytoceras\u003c/em\u003e sp.; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eP\u003c/em\u003e. \u003cem\u003ehelveticum\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. cf. \u003cem\u003ejugosa,\u003c/em\u003e \u003cem\u003eDenckmannia\u003c/em\u003e sp., \u003cem\u003eAlocolytoceras\u003c/em\u003e sp.\u003c/p\u003e\n\n\u003cp\u003eIllustris Subzone Gabilly et al., 1971\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia Illustris \u003c/em\u003e(Denkmann)\u003c/p\u003e\n\u003cp\u003eIn this subzone \u003cem\u003eHaugia\u003c/em\u003e, with flexuose ribs and a poorly marked peripheral projection, is usually classified as \u003cem\u003eH. illustris\u003c/em\u003e and \u003cem\u003eH. beani\u003c/em\u003e, followed by \u003cem\u003eHaugia\u003c/em\u003e with flexuose ribs up to the body chamber, clearly showing a forward projection of the whorls (Gabilly, 1976). In the Cantabrian Range, there is a record of similar forms that can be associated, in the lower part of the subzone with \u003cem\u003eP. aratum\u003c/em\u003e, a ubiquitist species that is frequent in the NW European Province and that is also known in the Mediterranean Province (Goy et al., 1988). In the upper part of the subzone, forms close to \u003cem\u003eH. phillipsi\u003c/em\u003e and \u003cem\u003eH. metallaria\u003c/em\u003e are situated; these can be associated with \u003cem\u003eP. bodei\u003c/em\u003e, a species that has been cited in Causses, Germany, the Iberian Range and the Cantabrian Range (Guex, 1975; Ohmert, 1976; Goy et al., 1990, 1994). In this subzone, the first \u003cem\u003eG\u0026egrave;czyceras\u003c/em\u003e are also recorded; these constitute important elements for correlating with different areas of the Mediterranean Province (Mart\u0026iacute;nez, 1992; Mart\u0026iacute;nez et al., 2015; Elmi et al., 2007b).\u003c/p\u003e\n\n\u003cp\u003eIllustris Horizon Gabilly, 1990\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia illustris \u003c/em\u003e(Denkmann)\u003c/p\u003e\n\u003cp\u003eOther ammonoids:\u003cem\u003e \u003c/em\u003e\u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eC\u003c/em\u003e. cf. \u003cem\u003eraquinianum\u003c/em\u003e, \u003cem\u003eO\u003c/em\u003e. \u003cem\u003ebicarinatum\u003c/em\u003e, \u003cem\u003eH.\u003c/em\u003e aff. \u003cem\u003eillustris\u003c/em\u003e, \u003cem\u003eB. primaria, P\u003c/em\u003e. \u003cem\u003esubregale \u003c/em\u003e(Fig. 9f), \u003cem\u003eP. aratum \u003c/em\u003e(Fig. 9g)\u003cem\u003e, G. costatum\u003c/em\u003e;\u003cem\u003e \u003c/em\u003e\u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eO. bicarinatum\u003c/em\u003e, \u003cem\u003eOsperlioceras \u003c/em\u003espp.\u003cem\u003e,\u003c/em\u003e \u003cem\u003eHaugia\u003c/em\u003e sp. (Fig. 7e), \u003cem\u003eP. subregale,\u003c/em\u003e \u003cem\u003eP. aratum,\u003c/em\u003e \u003cem\u003eP. discoides,\u003c/em\u003e \u003cem\u003eG.\u003c/em\u003e cf\u003cem\u003e. costatum.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003ePhillipsi Horizon Gabilly, 1990\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugia phillipsi \u003c/em\u003e(Simpson) (Fig. 9d)\u003c/p\u003e\n\u003cp\u003eOther ammonoids: \u003cstrong\u003eAB\u003c/strong\u003e: \u003cem\u003eB. primaria\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. cf. \u003cem\u003ephillipsi\u003c/em\u003e, \u003cem\u003eH. \u003c/em\u003ecf. \u003cem\u003emetallaria\u003c/em\u003e, \u003cem\u003eHaugia\u003c/em\u003e sp., \u003cem\u003eD. tumefacta\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. cf. \u003cem\u003estruckmanni\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. aff. \u003cem\u003ebingmanni\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. \u003cem\u003ebodei\u003c/em\u003e, \u003cem\u003eG\u003c/em\u003e. cf. \u003cem\u003ecostatum\u003c/em\u003e; \u003cstrong\u003eBCB:\u003c/strong\u003e \u003cem\u003eOsterlioceras\u003c/em\u003e sp., \u003cem\u003eP. discoides\u003c/em\u003e, \u003cem\u003eH.\u003c/em\u003e cf. \u003cem\u003ephillipsi\u003c/em\u003e, \u003cem\u003eG\u003c/em\u003e. cf. \u003cem\u003ecostatum.\u003c/em\u003e\u003c/p\u003e\n\n\u003cp\u003eVitiosa Subzone Gabilly et al., 1971 \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugiella vitiosa\u003c/em\u003e (Buckman)\u003c/p\u003e\n\u003cp\u003eIn this subzone, apart from the index species, there are several species of \u003cem\u003ePseudogrammoceras\u003c/em\u003e (\u003cem\u003eP. muelleri\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. aff. \u003cem\u003ebingmanni\u003c/em\u003e) and \u003cem\u003eG\u0026egrave;czyceras\u003c/em\u003e (\u003cem\u003eG. costatum,\u003c/em\u003e \u003cem\u003eG. clausum\u003c/em\u003e). In adjacent basins, Faur\u0026eacute; (2002) describes two new species of \u003cem\u003eHaugiella\u003c/em\u003e in the Pyrenean Range and Goy \u0026amp; Mart\u0026iacute;nez (1990) cite, apart from \u003cem\u003eG\u0026egrave;czyceras\u003c/em\u003e, \u003cem\u003eP. discoides, Haugia \u003c/em\u003esp. and \u003cem\u003eD. tumefacta.\u003c/em\u003e\u003c/p\u003e\n\n\u003cp\u003eVitiosa Horizon Gabilly, 1976\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003eHaugiella vitiosa\u003c/em\u003e (Buckman)\u003cem\u003e \u003c/em\u003e(Fig. 7h)\u003c/p\u003e\n\u003cp\u003eOther ammonoids:\u003cem\u003e \u003c/em\u003e\u003cstrong\u003eAB\u003c/strong\u003e:\u003cem\u003eP\u003c/em\u003e. \u003cem\u003emuelleri\u003c/em\u003e,\u003cem\u003e P\u003c/em\u003e. aff. \u003cem\u003ebingmanni, G. clausum\u003c/em\u003e, \u003cem\u003eG. \u003c/em\u003eaff. c\u003cem\u003eostatum\u003c/em\u003e; \u003cstrong\u003eBCB\u003c/strong\u003e: \u003cem\u003eG. costatum\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003e4.1.4 Upper Toarcian\u003c/p\u003e\n\n\u003cp\u003eThe lower boundary of the upper Toarcian is marked by the presence of \u003cem\u003eP. bingmanni\u003c/em\u003e in the base of the Thouarsense Zone.\u003c/p\u003e\n\n\u003cp\u003eThouarsenseZone Brasil, 1896\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e:\u003cem\u003e Grammoceras thouarsense\u003c/em\u003e (d\u0026rsquo;Orbigny)\u003c/p\u003e\n\u003cp\u003eAlthough this zone is traditionally considered to commence with the first record of \u003cem\u003eP. bingmanni \u003c/em\u003e(Denckmann), this species poses several problems with regard to its use as an indicator of the start of the upper Toarcian. On one hand, it presents great variability and is associated with forms displaying a morphology that is very close to the standard type of \u003cem\u003eP. bingmanni\u003c/em\u003e (Gabilly, 1976; Roulleau, 1989); on the other hand, in Causses it was found from the start of the Vitiosa Subzone (Guex, 1975) and on the platforms of the IB there is evidence that it also coexisted with \u003cem\u003eHaugiella\u003c/em\u003e in the upper part of the Variabilis Zone (Comas-Rengifo et al., 1996).\u003c/p\u003e\n\n\u003cp\u003eBingmanni Subzone Gabilly, 1976\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIndex species\u003c/em\u003e: \u003cem\u003ePseudogrammoceras bingmanni\u003c/em\u003e (Denckmann)\u003cem\u003e \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eIt is conserved as the first subzone of the upper Toarcian in order to maintain the nomenclatural stability; however, perhaps it would be preferable to commence the substage with the first record of the genus \u003cem\u003eGrammoceras\u003c/em\u003e Hyatt, 1867, including \u0026ldquo;\u003cem\u003ePseugogrammoceras.\u003c/em\u003e \u003cem\u003edoerntense\u003c/em\u003e Denckmann, 1887\u0026rdquo;, a species that some authors consider to be a \u003cem\u003eGrammoceras\u003c/em\u003e (G\u0026egrave;czy, 1967a; Guex, 1975; Schlegelmilch, 1976).\u003c/p\u003e\n\u003cp\u003eIn the standard scale of the NW European Province, in the Thouarsense Subzone, two horizons have been defined, the Doertense Horizon and the Thouarsense Horizon\u003cstrong\u003e.\u003c/strong\u003e In the AB, this subzone is very thin and is consequently difficult to distinguish from the Bingmanni Subzone. Currently, taxonomic records have been recognised for \u003cem\u003eP\u003c/em\u003e. \u003cem\u003ebingmanni\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e. cf. \u003cem\u003edoerntense\u003c/em\u003e and \u003cem\u003eP\u003c/em\u003e. cf. \u003cem\u003ethouarsense\u003c/em\u003e, below the first \u003cem\u003eEsericeras\u003c/em\u003e. In the BCB the Thouarsense Subzone is affected by a discontinuity which reaches the Fascigerum Subzone.\u003c/p\u003e"},{"header":"5 Discussion and Correlations","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Sequential stratigraphy and Palaeobiogeography\u003c/h2\u003e \u003cp\u003eThe Interval studied comprises the terminal part of the T4-R4 cycle and the T5-R5 cycle (p.p.) described by Quesada et al. (\u003cspan citationid=\"CR151\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) in the BCB, which is equivalent to the LJ-3 cycle of de G\u0026oacute;mez \u0026amp; Goy (\u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) in the Iberian Range. Specifically, it ranges from the regressive part of the LJ3-1 subcycle (Spinatum Zone, Hawskerense Subzone) to the terminal part of the LJ3-3 subcycle (Variabilis Zone, Vitiosa Subzone).\u003c/p\u003e \u003cp\u003eIn the Spinatum Zone, following a cold episode, which occurred in the Apyrenum Subzone, where the water temperature is 10.5\u0026ndash;11\u0026ordm; on average (Rosales et al., \u003cspan citationid=\"CR174\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; G\u0026oacute;mez et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), the tendency changes and the temperature rises, reaching approximately 17.5\u0026ordm; towards the end of the regressive part of the LJ3-1cycle, a fact that coincides with the extinction of the Amaltheidae Family. From this time onwards (sub-cycle LJ3-2), oceanic palaeotemperatures display remarkable fluctuations, with an increasing tendency to rise, which significantly affected the ammonoids and other groups of benthic and planktonic organisms, giving rise to extinction events in the Tenuicostatum Zone (boundary between the Mirabile and Semicelatum subzones) and the boundary between the Semicelatum y Elegantulum subzones of the Serpentinum Zone. (Jenkyns Event). During the LJ3-3 subcycle, the average temperature continued to rise up to the upper part the Bifrons Zone, surpassing the average temperature (27\u0026ordm;) in the east of the Iberian Peninsula (G\u0026oacute;mez et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis transgressive general episode appears to have caused significant provincialism in the in the W of Europe and in the N of Africa, with three palaeobiogeographic provinces: Subboreal, Submediterranean and Mediterranean, defined by Page \u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), which include the epicontinental seas in the NW of Europe, the basins of France, Germany and the N of Iberia and the truly Tethysic basins of the Betic Range, Apennines, Hungary and the N of Africa, among others. During the Variabilis Zone, which corresponds to the regressive part of the LJ-3 cycle, it is difficult to differentiate the Submediterranean Province; consequently, it is usually decided to differentiate a NW European Province and a Mediterranean Province (Elmi et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1997\u003c/span\u003e, Page, \u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAfter the Variabilis Zone, the first two subzones of the Thouarsense Zone are quite thin throughout the Cantabrian Range where, as a whole, the thickness is less than 1 m (Goy et al., \u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; G\u0026oacute;mez et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Figures\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e9\u003c/span\u003e refer to both subzones since, at least in the AB there is a taxonomic record of the index species (Goy et al., \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). However, in the boundary between the Variabilis-Thouarsense zones, there is evidence of small discontinuities in the AB and in the Santa Mera section, and of noteworthy discontinuities in the BCB, which can be seen in the Salinas de Pisuerga, San Andres, Camino and Castillo Pedroso sections (Comas-Rengifo et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Bernad, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1993\u003c/span\u003e, Goy et al.; \u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e1994\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn basins close to those studied, such as the northern part of the Iberian Range, in the Ricla section, where the first two subzones are also thin (1.5 m), the Bingmanni and Thouarsense subzones have been characterised; they are separated by a small discontinuity (Goy \u0026amp; Mart\u0026iacute;nez, \u003cspan citationid=\"CR97\" class=\"CitationRef\"\u003e1990\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Correlation with the standard scale and with other Iberian basins\u003c/h2\u003e \u003cp\u003eFor the reasons given in subchapter 5.1, in order to correlate the basins of the Cantabrian Range (AB and BCB) with others on the Iberian Peninsula, on one hand we considered the horizons recognised between the Hawskerense Subzone and the Bifrons Subzone (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e), where three different palaeobiogeographic provinces have been differentiated; on the other hand, the horizons recognised in the Variabilis Zone (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e9\u003c/span\u003e) were taken into account; therein, only two provinces were differentiated, NW Europea and Mediterranea.\u003c/p\u003e \u003cp\u003eFor the correlation with the standard scales for the provinces cited, as well as for the IB, LB and BB (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e), we used as reference studies (Howarth, \u003cspan citationid=\"CR112\" class=\"CitationRef\"\u003e1955\u003c/span\u003e, \u003cspan citationid=\"CR114\" class=\"CitationRef\"\u003e1973\u003c/span\u003e, \u003cspan citationid=\"CR115\" class=\"CitationRef\"\u003e1978\u003c/span\u003e, 1992; Dean et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1961\u003c/span\u003e; Mouterde, \u003cspan citationid=\"CR139\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Guex, \u003cspan citationid=\"CR102\" class=\"CitationRef\"\u003e1972\u003c/span\u003e, \u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e1975\u003c/span\u003e; Gabilly, 1976; Comas-Rengifo, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Goy et al. \u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e1988\u003c/span\u003e, 1990, \u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e1994\u003c/span\u003e, \u003cspan citationid=\"CR101\" class=\"CitationRef\"\u003e2006b\u003c/span\u003e, \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Elmi et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1994\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1997\u003c/span\u003e, 2007; Comas-Rengifo et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1996\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2010a\u003c/span\u003e; Faur\u0026eacute;, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Page, \u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e, \u003cspan citationid=\"CR149\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; B\u0026eacute;caud, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; G\u0026oacute;mez et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; G\u0026oacute;mez \u0026amp; Goy, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Rocha et al., \u003cspan citationid=\"CR169\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Duarte et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003eb\u003c/span\u003e; Salazar-Ram\u0026iacute;rez et al., \u003cspan citationid=\"CR178\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, in the Mediterranean Tethysic areas and in the Atlantic sector of Morocco, we considered as reference studies (G\u0026egrave;czy, 1967a, b; Rivas, \u003cspan citationid=\"CR166\" class=\"CitationRef\"\u003e1972\u003c/span\u003e; Guex, \u003cspan citationid=\"CR103\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Elmi et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1974\u003c/span\u003e; Jim\u0026eacute;nez \u0026amp; Rivas, \u003cspan citationid=\"CR120\" class=\"CitationRef\"\u003e1981\u003c/span\u003e, 1991, 1992; Braga, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Braga et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Jim\u0026eacute;nez, \u003cspan citationid=\"CR119\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Goy et al., \u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Benshili, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Mouterde \u0026amp; Elmi (\u003cspan citationid=\"CR140\" class=\"CitationRef\"\u003e1991\u003c/span\u003e), Cresta et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Macchioni, \u003cspan citationid=\"CR129\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Rakus \u0026amp; Guex, \u003cspan citationid=\"CR152\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Faur\u0026eacute; et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Lachkar et al., \u003cspan citationid=\"CR125\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Bilotta et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Ettaki et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, Kov\u0026aacute;ks, 2011; Reolid et al., \u003cspan citationid=\"CR161\" class=\"CitationRef\"\u003e2012a\u003c/span\u003e, \u003cspan citationid=\"CR162\" class=\"CitationRef\"\u003eb\u003c/span\u003e, \u003cspan citationid=\"CR160\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, \u003cspan citationid=\"CR163\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the terminal Pliensbachian (Spinatum Zone, Hawskerense Subzone) and the Toarcian (Tenuicostatum to Bifrons zones), the succession of horizons characterised in the AB and the BCB is very similar to that displayed by the standard scale of the Submediterranean Province and, in most cases, the horizons are the same as those of the aforementioned scale. Only the occasional difference is observed in the Interval corresponding to the Hawskerense and Paltum subzones, as a result of the greater abundance of Mediterranean species recorded in the Cantabrian Range. Correlation with the standard scale of the Subboreal Province initially appears to be more difficult, because we employed different methodologies to define the zones; different indices are frequently used to denominate the chronostratigraphic units established. Additionally, different classification systems have been used, one based upon the succession of biohorizons and another one based on the succession of chronohorizons. Nonetheless, in most cases, the ammonoids used as a reference in the subboreal areas were also recorded in the Submediterranean areas, such as the AB and the BCB. Moreover, Page (\u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e) established a correlation between both standard scales which facilitates comparison with other basins. The succession of the IB is practically identical to the zones and subzones characterised; only the horizons exhibit some differences, and there are also some elements of correlation which minimise the inaccuracies. In the LB, above all in the BB, the differences existing are more noteworthy both in the subzones and in the horizons. The difficulties involved in correlating the Toarcian in the IB and in the BB were previously described by Goy et al. (\u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e1988\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the middle Toarcian (Variabilis Zone), the sedimentary changes that occurred as from the base of this zone modified the conditions of the epicontinental basins of W Europe in such a way that, in the Cantabrian Range, with slight changes, the succession obtained is very similar to that of the standard scale (Gabilly, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e1990\u003c/span\u003e; Elmi et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e) and the same can be said for the PB (Faur\u0026eacute;, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). As for the IB, the succession presents quite a few analogies and some differences with respect to the basins of the Cantabrian Range. Interestingly, \u003cem\u003eP. aratum\u003c/em\u003e, a frequent species in the IB, constitutes a good element of correlation with our study area, and with the LB and the BB; moreover, the Alticarinatus/Bodei Horizon in the IB occupies a position similar to that of the Phillipsi Horizon of the AB-BCB.\u003c/p\u003e \u003cp\u003eWith regard to the LB, until the end of the Bifrons Zone, the succession established is similar to that of the basins of the Submediterranean Province, showing few differences in relation to the basins of the Cantabrian Range. Nonetheless, as from the base of the Variabilis Zone (in the NW European Province) or Gradata Zone (in the Mediterranean Province), the succession of ammonoids presents a clear difference, to the extent that there is only one good element of correlation, \u003cem\u003eP. aratum\u003c/em\u003e, throughout the Variabilis/Gradata Zone. Other taxa have been recorded in the aforementioned basins, among which the following ones can be highlighted: \u003cem\u003eP. sternale\u003c/em\u003e and \u003cem\u003eCollina\u003c/em\u003e, which can be found sporadically in the lower part of the Gemma Subzone, \u003cem\u003eP. subregale\u003c/em\u003e, which are located in the upper part of the same subzone and below the Alticarinatus Subzone, and \u003cem\u003eG. costatum\u003c/em\u003e, to be found in the upper part of the Gradata Zone. The index species of the Alticarinatus Subzone is relatively frequent in the LB, rare in the IB, and has not been cited in the Cantabrian Range.\u003c/p\u003e \u003c/div\u003e"},{"header":"6 Conclusions","content":"\u003cp\u003eThe sections studied are generally quite well expanded, with no significant discontinuities, with the exception of the boundary between the Variabilis Zone and the Thouarsense Zone in the Basque-Cantabrian Basin. The lower Toarcian presents a thickness of 12 m and the middle Toarcian is approximately 23 m thick. As a whole, between the Tenuicostatum and Variabilis zones, in the Asturian Basin, over 120 successive levels containing ammonoids have been identified. In the same Interval of the Basque-Cantabrian Basin, 110 successive levels have been identified.\u003c/p\u003e \u003cp\u003eThe associations recorded have enabled the characterisation of six zones (Spinatum, Tenuicostatum, Serpentinum, Bifrons, Variabilis, Thouarsense \u003cem\u003ep.p\u003c/em\u003e.), eleven subzones (Hawskerense, Paltum/Mirabile, Semicelatum, Elegantulum, Falciferum, Bifrons, Semipolitum, Variabilis, Illustris, Vitiosa, Bingmanni) and twenty-six horizons (or zonules); all these are described in detail in Chap.\u0026nbsp;4.1.1 and are compared with the standard scales (Dean et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1961\u003c/span\u003e, Dommergues et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1997\u003c/span\u003e, Elmi et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1997\u003c/span\u003e, Page, \u003cspan citationid=\"CR148\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). The lower boundary of the Toarcian is situated in levels WR27 and LA50s (Asturias) and in level SM33 (Cantabria). The start of the Toarcian is marked by the first appearance of \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eEodactylites\u003c/em\u003e) Schmidt-Effing, \u003cspan citationid=\"CR180\" class=\"CitationRef\"\u003e1972\u003c/span\u003e, above levels containing \u003cem\u003eEmaciaticeras\u003c/em\u003e Fucini, 1931 and \u003cem\u003eTauromeniceras\u003c/em\u003e, Mouterde, \u003cspan citationid=\"CR139\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; these succeeded the last levels with \u003cem\u003ePleuroceras\u003c/em\u003e Hyatt, 1867, in the Spinatum Zone of the Pliensbachian, in a similar manner to what occurs in the Peniche (Portugal) and Almonacid de la Cuba sections (E of Spain), where the GSSP and the ASP of the Toarcian Stage are situated (Comas-Rengifo et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2010a\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003eb\u003c/span\u003e; Rocha et al. \u003cspan citationid=\"CR169\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn relation to the ammonoids, three significant extinction events have been detected. The first of these is situated in the terminal part of the Hawskerense Subzone and affects practically the whole Amaltheidae Family at regional or global scale. The second took place in the boundary between the Mirabile/Paltum Subzone and the lower part of the Semicelatum Subzone; it is a staggered event that affects genera and species of the subfamilies Dactylioceratinae, Arieticeratidae, Harpoceratinae and Hildoceratinae. The third extinction event occurred in the boundary between the Semicelatum and Elegantulum subzones; it is likely at global scale and significantly affects the subfamilies Dactylioceratinae, Arieticeratinae and Harpoceratinae, as well as some species of Bouleiceratinae.\u003c/p\u003e \u003cp\u003eThe ammonoids obtained are typical of the Submediterranean Province up to the end of the Bifrons Zone and of the NW European Province in the Variabilis Zone. The associations recorded are similar to those found in the Iberian Range; they present a noteworthy similarity to the successions of the NE of England, France and, to a lesser extent, the Lusitanian Basin and the Betic Range. On the contrary, the elements typical of the Mediterranean Province are limited to the intervals coinciding with transgressive episodes, such as the interval between the terminal part of Hawskerense Subzone and the Paltum/Mirabile Subzone and in the Bifrons Zone.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupplementary information\u003c/strong\u003e The online version contains supplementary material available \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u0026nbsp;\u003c/strong\u003eOur sincere thanks to those responsible for the Jurassic Museum of Asturias (MUJA) who for twenty years have given us their support and facilitated research on ammonoids and other Jurassic fossil groups in the Cantabrian Mountains and, in particular, in Asturias. To colleagues from the University of Granada, Profs. J.C. Braga and P. Rivas, as well as Prof. A. Jim\u0026eacute;nez, with whom numerous field campaigns were carried out between 1981 and 1988, which, besides being enjoyable, provided us with important stratigraphic and palaeontological data related to this article. To Profs. J.J. G\u0026oacute;mez, C. Herrero, G. Mart\u0026iacute;nez, L.C. Su\u0026aacute;rez Vega and S. Ureta, who participated in the papers that constitute the main background of the present work, in 1994 and 2010, we are very grateful for their valuable contributions. To other members of the research teams of the aforementioned projects, specialists in groups other than ammonoids: C. Arias, E. Barr\u0026oacute;n, M. Canales, L.V. Duarte, A. Fraguas, F. Garc\u0026iacute;a Joral, N. Perilli, and A. Rodrigo, we thank them for their contributions and comments for a better understanding of the extinction events studied here.\u003c/p\u003e\n\u003cp\u003eData for this article was collected with the projects CGL2008-03112/BTE, CGL2011-25894, CGL2015-66604-R of the Spanish Ministry of Economy and Competitiveness, developed in the Department of Geodynamics, Stratigraphy and Palaeontology (Complutense University of Madrid). This work is a contribution to Research Group 910431 \u0026ldquo;Mesozoic Biotic Processes\u0026rdquo; of the Complutense University of Madrid. We are grateful to Gema Mart\u0026iacute;n (Palaeontology Area of the Geological Science Faculty) for their excellent photographic works, to Cormac de Brun for reviewing the English version.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Financial support for L. Pi\u0026ntilde;uela and J.C. Garc\u0026iacute;a-Ramos was provided by Sociedad P\u0026uacute;blica de Gesti\u0026oacute;n y Promoci\u0026oacute;n Tur\u0026iacute;stica y Cultural del Principado de Asturias (Board of Tourism and Culture Management and Promotion of the Principality of Asturias).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatements and declarations\u003c/strong\u003e We declare that this manuscript is original, has not been published before and is not currently being considered for publication elsewhere.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest\u0026nbsp;\u003c/strong\u003eWe know of no conflicts of interest associated with this publication, and there has been no significant financial support for this work that could have influenced its outcome. As Corresponding Author, I confirm that the manuscript has been read and approved for submission by all the named authors.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOpen Access\u0026nbsp;\u003c/strong\u003eThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article\u0026apos;s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article\u0026apos;s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit\u0026nbsp;http:// creat iveco mmons. org/ licen ses/ by/4. 0/.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAberhan, M. \u0026amp; F\u0026uuml;rsich, F. (2000). Mass origination versus mass extinction: the biological contribution to the Pliensbachian-Toarcian extinction event. \u003cem\u003eJournal of the Geological Society of London,\u003c/em\u003e \u003cem\u003e157\u003c/em\u003e, 55\u0026ndash;60. https://doi.org/10.1144/jgs.157.1.55\u003c/li\u003e\n\u003cli\u003eArias, C. (2013). 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Mancinelli (ed.) : \u003cem\u003eBiostratigrafia dell\u0026rsquo;Italia Centrale\u003c/em\u003e. \u003cem\u003eStudi Geologici Camerti\u003c/em\u003e, vol. spec., 247\u0026ndash;297. \u003c/li\u003e\n\u003cli\u003eFaur\u0026eacute;, P. (2002). Le Lias des Pyr\u0026eacute;n\u0026eacute;es. \u003cem\u003eStrata,\u003c/em\u003e s\u0026eacute;r. 2, \u003cem\u003e39\u003c/em\u003e, 1\u0026ndash;761.\u003c/li\u003e\n\u003cli\u003eFaur\u0026eacute;, P. (2013). Le Toarcien Moyen (Zones \u0026agrave; Bifrons et \u0026agrave; Variabilis, Jurassique Inf\u0026eacute;rieur) des Corbi\u0026egrave;res (Aude, France) Biostratigraphie et \u0026eacute;volution s\u0026eacute;dimentaire. \u003cem\u003eBulletin de la Soci\u0026eacute;t\u0026eacute; d\u0026rsquo;\u0026Eacute;tudes Scientifiques de l\u0026rsquo;Aude\u003c/em\u003e, \u003cem\u003e103\u003c/em\u003e, 13\u0026ndash;34. \u003c/li\u003e\n\u003cli\u003eFaur\u0026eacute;, P., Alm\u0026eacute;ras, Y., Sekatni, S. \u0026amp; Zargouni, F. (2007). 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Base of the Toarcian Stage of the Lower Jurassic defined by the Global Boundary Stratotype Section and Point (GSSP) at the Peniche section (Portugal). \u003cem\u003eEpisodes\u003c/em\u003e, 39(3), 460\u0026ndash;481. https://doi.org/10.18814/epiiugs/2016/v39i3/99741\u003c/li\u003e\n\u003cli\u003eRodrigues, B., Silva, R. L., Mendo\u0026ccedil;a Filho, J. G., Comas-Rengifo, M. J., Goy, A. \u0026amp; Duarte, L. V. (2020). Kerogen assemblages and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC of kerogen the uppermost Pliensbachian-lower Toarcian succession of the Asturias Basin (northern Spain). \u003cem\u003eInternational Journal of Coal Geology\u003c/em\u003e, 229, 103573. https://doi.org/10.1016/j.coal.2020.103573\u003c/li\u003e\n\u003cli\u003eRodrigues, B., Silva, R. L., Mendo\u0026ccedil;a Filho, J. G., Reolid, M., Sadki, D., Comas-Rengifo, M. J., Goy, A. \u0026amp; Duarte, L. V. (2021). The Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian. In: M. Reolid, L. V. Duarte, E. Mattioli, \u0026amp; W. Ruesbsam, (Eds). Carbon Cycle and Ecosystem Response to the Jenkyns Event in the Early Toarcian (Jurassic). \u003cem\u003eGeological Society, London\u003c/em\u003e, \u003cem\u003e514\u003c/em\u003e, 291\u0026ndash;307. https://doi.org/10.1144/SP514-2020-271\u003c/li\u003e\n\u003cli\u003eRodr\u0026iacute;guez-Tovar, F. J. (2021). Ichnology of the Toarcian Oceanic Anoxic Event: an underestimated tool to nassesspalaeoenvironmental interpretation. \u003cem\u003eEarth Sci. Rev.\u003c/em\u003e, \u003cem\u003e216 \u003c/em\u003e(7-9), 103579. https://doi.org/10.1016/j.earscirev.2021.103579\u003c/li\u003e\n\u003cli\u003eRosales, I., Barnolas, A., Goy, A., Sevillano, A., Armend\u0026aacute;riz, M. \u0026amp; L\u0026oacute;pez-Garc\u0026iacute;a, J. M. (2018). Isotope records (C-O-Sr) of late Pliensbachian-early Toarcian environmental perturbations in the westernmost Tethys (Majorca Island, Spain). \u003cem\u003ePalaeogeography, Palaeoclimatology, Palaeoecology\u003c/em\u003e, \u003cem\u003e497\u003c/em\u003e, 168\u0026ndash;185. https://doi.org/10.1016/j.palaeo.2018.02.016\u003c/li\u003e\n\u003cli\u003eRosales, I., Quesada, S. \u0026amp; Robles, S. (2004). Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, Northen Spain. \u003cem\u003ePalaeogeography, Palaeoclimatology, Palaeoecology\u003c/em\u003e, \u003cem\u003e203\u003c/em\u003e, 253\u0026ndash;275. https://doi.org/10.1016/S0031-0182(03)00686-2\u003c/li\u003e\n\u003cli\u003eRulleau, L. (1989). Les Grammoceratinae du Toarcien sup\u0026eacute;rieur de la regi\u0026oacute;n lyonnaise. \u003cem\u003eSection g\u0026eacute;ologie et pal\u0026eacute;ontologie du Comit\u0026eacute; d\u0026rsquo;\u0026Eacute;tablissiements des ciments Lafarge, Lozanne\u003c/em\u003e, France, 1\u0026ndash;11.\u003c/li\u003e\n\u003cli\u003eRulleau, L. (1993). Les ammonites du Toarcien inf\u0026eacute;rieur et moyen de la r\u0026eacute;gion lyonnaise. \u003cem\u003eSection g\u0026eacute;ologie et pal\u0026eacute;ontologie du Comit\u0026eacute; d\u0026rsquo;\u0026Eacute;tablissiements des ciments Lafarge, Lozanne\u003c/em\u003e, France, 1\u0026ndash;15.\u003c/li\u003e\n\u003cli\u003eRulleau, L., B\u0026eacute;caud, M. \u0026amp; Neige, P. (2003). Les ammonites traditionnellement regroup\u0026eacute;es dans la sous-famille des Bouleiceratinae (Hildoceratidae, Toarcien): aspects phylog\u0026eacute;n\u0026eacute;tiques, biog\u0026eacute;ographiques et syst\u0026eacute;matiques. \u003cem\u003eGeobios\u003c/em\u003e, \u003cem\u003e36\u003c/em\u003e, 317\u0026ndash;348. DOI: 10.1016/S0016-6995(03)00034-2\u003c/li\u003e\n\u003cli\u003eSalazar-Ram\u0026iacute;rez, R. W., Herrero, C. \u0026amp; Goy, A. (2020). Lower Toarcian ammonites and foramin\u0026iacute;fera assemblages in the San Miguel de Aguayo Section (Basque-Cantabrian Basin, Spain). \u003cem\u003eJournal of Iberian Geology\u003c/em\u003e, \u003cem\u003e46\u003c/em\u003e, 39\u0026ndash;60. https://doi.org/10.1007/s41513-019-00118-8\u003c/li\u003e\n\u003cli\u003eSandoval, J, Bill., M., Aguado, R., O\u0026apos;Dogherty, L., Rivas, P., Morard, A. \u0026amp; Guex, J. (2012). The Toarcian in the Subbetic basin (southern Spain): Bio-events (ammonite and calcareous nannofossils) and carbon-isotope stratigraphy. \u003cem\u003ePalaeogeography, Palaeoclimatology, Palaeoecology\u003c/em\u003e, \u003cem\u003e342\u0026ndash;343\u003c/em\u003e, 40\u0026ndash;63. https://doi.org/10.1016/j.palaeo.2012.04.028\u003c/li\u003e\n\u003cli\u003eSchmidt-Effing, R. (1972). Die Dactylioceratidae, eine Ammoniten-Familie des unteren Jura \u003cem\u003e(Systematik, Stratrigraphie, Zoogeographie, Phiylogenie mit besonderer Ber\u0026uuml;cksichtigung\u003c/em\u003e spanischen Materials). Zur Pal\u0026auml;onlogie jurassischer Invertebraten. \u003cem\u003eM\u0026uuml;nstersche Forschungenzur Geologie Pal\u0026auml;ontologie,\u003c/em\u003e \u003cem\u003e25/26\u003c/em\u003e, 1\u0026ndash;255.\u003c/li\u003e\n\u003cli\u003eSilva, R. L., Ruhl. M., Barry, C., Reolid, M., Ruebsam, W. (2021). Pacing of late Pliensbachian and early Toarcian carbon cycle perturbations and environmental change in the westernmost \u003cem\u003eTethys (La Cerradura Section, Subbetic zone of the Betic Cordillera, Spain). Geological Society, London, Special Publications\u003c/em\u003e, \u003cem\u003e514\u003c/em\u003e, 387\u0026ndash;408. https//doi.org/10.1144/SP514-2021-27\u003c/li\u003e\n\u003cli\u003eSu\u0026aacute;rez Vega, L. C. (1974). Estratigraf\u0026iacute;a del Jur\u0026aacute;sico en Asturias. \u003cem\u003eCuadernos de Geolog\u0026iacute;a Ib\u0026eacute;rica, 3,\u003c/em\u003e 1\u0026ndash;369.\u003c/li\u003e\n\u003cli\u003eValenzuela Fern\u0026aacute;ndez, M. (1988). \u003cem\u003eEstratigraf\u0026iacute;a, sedimentolog\u0026iacute;a y paleogeograf\u0026iacute;a del Jur\u0026aacute;sico de Asturias\u003c/em\u003e. Tesis Doctoral, Facultad de Geolog\u0026iacute;a, Universidad de Oviedo (in\u0026eacute;dita).\u003c/li\u003e\n\u003cli\u003eValenzuela, M., Garc\u0026iacute;a-Ramos, J. C., Su\u0026aacute;rez de Centi, C. (1986). The Jurassic sedimentation in Asturias (N Spain). \u003cem\u003eTrabajos de Geolog\u0026iacute;a,\u003c/em\u003e \u003cem\u003e16\u003c/em\u003e, 121\u0026ndash;132.\u003c/li\u003e\n\u003cli\u003eVenturi, F. \u0026amp; Ferri, R. (2001). \u003cem\u003eAmmoniti Liassici dell\u0026rsquo;Appennino Centrale\u003c/em\u003e, Tibergraph, Citt\u0026agrave; di Castello (Perugia), 271 p. \u003c/li\u003e\n\u003cli\u003eWignall, P. B, Newton, R. J. \u0026amp;Little, T. S. (2005). The timing of paleoenvironmental change and cause-and-effect relationships during the Early Jurassic mass extinction in Europe. \u003cem\u003eAmerican Journal of Science\u003c/em\u003e\u003cem\u003e, 305(\u003c/em\u003e10).1014\u0026ndash;1032. https://doi.org/10.2475/ajs.305.10.1014\u003c/li\u003e\n\u003cli\u003eWiedenmayer, F. (1980). Die Ammoniten der mediterranen Provinz im Pliensbachian und unteren Toarcian aufgrund neuer Untersuchungen im Generoso-Becken (Lombardische Alpen). \u003cem\u003eM\u0026eacute;moires de la Soci\u0026eacute;t\u0026eacute; helv\u0026eacute;tique des Sciences naturelles\u003c/em\u003e, \u003cem\u003e93,\u003c/em\u003e 1\u0026ndash;197.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-iberian-geology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jibg","sideBox":"Learn more about [Journal of Iberian Geology](http://link.springer.com/journal/41513)","snPcode":"41513","submissionUrl":"https://www.editorialmanager.com/jibg/default2.aspx","title":"Journal of Iberian Geology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Lower Jurassic, Pliensbachian-Toarcian boundary, ammonite zonal chronostratigraphy, extinction, ammonoid provincialism","lastPublishedDoi":"10.21203/rs.3.rs-4224858/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4224858/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe present paper studies the ammonite associations from the terminal Pliensbachian (Spinatum Zone, Hawskerense Subzone) and from the lower-middle Toarcian (Tenuicostatum to Variabilis Zones) in two areas of the Cantabrian Range, situated in the Asturian Basin (AB) and in the Basco-Cantabrian Basin (BCB). The outcrops examined in the AB were situated on the coast, between Villaviciosa and Ribadesella and those of the BCB were located inland, in the provinces of Cantabria and Palencia.\u003c/p\u003e \u003cp\u003eThe lower boundary of the Toarcian was accurately established with the first record of the genus \u003cem\u003eDactylioceras\u003c/em\u003e in both basins. In the Cantabrian Range, we characterised all the standard zones and subzones of the Toarcian Stage. In order to establish the chronostratigraphic horizons, we considered the evolution of the Dactylioceratidae (Dactylioceratinae) in the Tenuicostatum Zone, of the Hildoceratidae (Harpoceratinae) in the Serpentinum Zone, of the Hildoceratidae (Hildoceratinae) from the last horizon of the Falciferum Subzone to the end of the Bifrons Zone, and of the Phymatoceratidae (Phymatoceratinae) in the Variabilis Zone.\u003c/p\u003e \u003cp\u003eWe identified the following main regional or global biotic events: 1) the mass extinction of the Amaltheidae Family in the upper part of the Hawskerense Subzone; 2) the expansion of the Dactylioceratinae Subfamily as from the base of the Tenuicostatum Zone; 3) the extinction of practically all the late Arieticeratinae (\u003cem\u003eEmaciaticeras\u003c/em\u003e, \u003cem\u003eCanavaria\u003c/em\u003e, \u003cem\u003eTauromeniceras\u003c/em\u003e), of the \u003cem\u003eLioceratoides\u003c/em\u003e and of the \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eEodactylites\u003c/em\u003e) in the boundary between the Paltum/Mirabile and Semicelatum subzones; 4) the final extinction of the aforementioned groups, and of the \u003cem\u003eNeolioceratoides\u003c/em\u003e, \u003cem\u003eProtogrammoceras\u003c/em\u003e (\u003cem\u003ePaltarpites\u003c/em\u003e) and almost all the \u003cem\u003eDactylioceras\u003c/em\u003e (\u003cem\u003eOrthodactylites\u003c/em\u003e) in the boundary between the Tenuicostatum and Serpentinum zones, coinciding with the final stage of the Jenkyns Event. When the factors that caused this event came to an end, at regional or global scale there occurred a recovery of the Dactylioceratinae, Harpoceratinae and Hildoceratinae within a short time interval, with significant radiations of these subfamilies. The Phymatoceratinae subsequently radiated from the Bifrons Zone.\u003c/p\u003e","manuscriptTitle":"Ammonites from the lower and middle Toarcian (Jurassic) in the Cantabrian Range (Asturias and Basco-Cantabrian Basin, Northern Spain). Chronostratigraphy, biotic events and correlations with other Iberian basins","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-19 12:45:07","doi":"10.21203/rs.3.rs-4224858/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-04-16T14:28:04+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-16T11:18:50+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Iberian Geology","date":"2024-04-09T07:12:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-09T06:26:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Iberian Geology","date":"2024-04-09T01:58:39+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-iberian-geology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jibg","sideBox":"Learn more about [Journal of Iberian Geology](http://link.springer.com/journal/41513)","snPcode":"41513","submissionUrl":"https://www.editorialmanager.com/jibg/default2.aspx","title":"Journal of Iberian Geology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6101f4c3-1332-4c9e-8a2b-97be35ff491e","owner":[],"postedDate":"April 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-10-14T16:02:43+00:00","versionOfRecord":{"articleIdentity":"rs-4224858","link":"https://doi.org/10.1007/s41513-024-00252-y","journal":{"identity":"journal-of-iberian-geology","isVorOnly":false,"title":"Journal of Iberian Geology"},"publishedOn":"2024-10-09 15:57:46","publishedOnDateReadable":"October 9th, 2024"},"versionCreatedAt":"2024-04-19 12:45:07","video":"","vorDoi":"10.1007/s41513-024-00252-y","vorDoiUrl":"https://doi.org/10.1007/s41513-024-00252-y","workflowStages":[]},"version":"v1","identity":"rs-4224858","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4224858","identity":"rs-4224858","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}