Environmental Conditions in the Pre-jenkyns Event Times (Late Pliensbachian – Early Toarcian) in the Southiberian Palaeomargin (Betic External Zones, Southern Spain)

Environmental Conditions in the Pre-jenkyns Event Times (Late Pliensbachian – Early Toarcian) in the Southiberian Palaeomargin (Betic External Zones, Southern Spain) | 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 Environmental Conditions in the Pre-jenkyns Event Times (Late Pliensbachian – Early Toarcian) in the Southiberian Palaeomargin (Betic External Zones, Southern Spain) Luis M. Nieto, Chaima Ayadi, Agela Fraguas, José Miguel Molina, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4182071/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Oct, 2024 Read the published version in Journal of Iberian Geology → Version 1 posted 5 You are reading this latest preprint version Abstract Three stratigraphic sections of the Betic External Zones have been studied, two from the Median Subbetic (PEL and PR) and one from the External Subbetic (CE). The upper Pliensbachian materials and the transition to the lower Toarcian have been dated with calcareous nannofossils in PEL and PR in this paper, while in the CE section, previous ammonite and nannofossil biostratigraphies have been considered. The dominant facies are alternance of marly limestone - marl, although in the CE section, the Toarcian is represented by marls, where the Jenkyns Event has been recorded. In terms of ichnofossils, in the PEL section Macaronichnus predominates. In the PR and CE sections, the ichnoassemblages are dominated by Planolites , Thalassinoides and Chondrites . Therefore, the facies and ichnofacies observed were generated in pelagic or hemipelagic marine environments. Analysis of the correlation between δ 13 C and δ 18 O and of each of them with Sr and Fe/Ca and Sr/Ca, as well as the Z-factor, indicate that the geochemical signal has not been modified by diagenesis. In the PEL and PR sections, the δ 13 C and δ 18 O ratios do not allow to clearly identify isotopic events, except in CE where the Jenkyns Event was recorded. The proxies used to study detritism (Zr/Rb, Sr/Cu, CIA and C-value) show trends opposite to those detected in other Tethys sections and even between them. These peculiarities in the geochemical data are interpreted as the result of the opening of the Hispanic Corridor, the mixing of Panthalassa and Tethys seawaters and extensional tectonics, which favoured the development of half grabens with significant differential subsidence, especially during the NJT5b Subzone (latest Pliensbachian). These half grabens could be affected by contourite currents according to the Macaronichnus assemblage in some of these sections. Early Jurassic Southern Iberian palaeomargin ichnofossils calcareous nannofossil biostratigraphy geochemical proxies of detritism Hispanic Corridor contourite currents Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. INTRODUCTION The Pliensbachian was a very dynamic Jurassic stage, in which very important changes took place: 1) palaeogeographic (opening of the Hispanic Corridor; Dera et al., 2009a , b ; Krencker et al., 2019 ; and references herein), 2) palaeoclimatic (waxing and waning of ice caps as a consequence of declines and rises in seawater temperature; Gómez et al., 2016 ; Price et al., 2016 ; Bougeault et al., 2017 ; Krencker et al, 2019 ; and references herein) and 3) palaeoceanographic (modification of the marine current system in the Tethys, Boreal and Central Atlantic; Dera et al., 2009a ; Bodin et al., 2016 , 2023 , for example). All these events induced shifts of different orders in global seawater chemistry (Price et al., 2016 ). While long-lived events have been associated with variations in CO 2 concentration, short-lived changes are difficult to explain (e.g., Price et al., 2016 ). Based on isotopic data, the early Pliensbachian has been interpreted as a warming interval (ranging from 16 to 18ºC in the Asturian Basin of North Iberia according to Gómez et al., 2016 ). This climatic trend covered the Ibex and Davoei zones and the earliest part of the Lavinianum Zone. A subsequent cooling occurred during the late Pliensbachian that may have promoted the formation of high-latitudinal glaciation at their most extensive in the latest Pliensbachian to earliest Toarcian (Dera et al., 2011 ; Korte and Hesselbo, 2011 ; Gómez et al., 2016 ; Ruebsam et al., 2019 ; Ruebsam and Schwark, 2021 ). Latest Pliensbachian to early Toarcian equatorial sea surface temperatures fluctuated between 22 and 32°C, attesting to highly variable and contrasting climate conditions (Ruebsam et al., 2020a ). During the early Toarcian, related to the Jenkyns Event carbon cycle perturbation, sea water temperature in the tropical to subtropical latitudes raised by about 10°C (Ruebsam et al., 2020a ). Sea-level changes were related to these climatic changes. Therefore, the end Pliensbachian is characterized by a sea-level fall with subsequent flooding and a negative Carbon Isotope Excursion (CIE) related to the Pliensbachian-Toarcian boundary event (Bodin et al., 2016 ; Fantasia et al., 2019 ; Rodrigues et al., 2019 ; Fleischmann et al., 2022 ). Bougeault et al. ( 2017 ), based on the study of the kaolinite/illite ratio, recognized a decrease in the runoff occurred at the end of Pliensbachian stage, considering that a cold stage, possibly associated with cold ice cap growth, has also been recorded in this time interval (Gómez et al., 2016 ; Bougeault et al., 2017 ; Krencker et al., 2019 ; Bodin et al., 2023 ; among others). However, Bougeault et al. ( 2017 ) also recognised minor oscillations in kaolinite/illite ratio values during the late Pliensbachian interpreted as oscillations in runoff. A factor to consider in the development of the climate changes during the Pliensbachian is the modification of the oceanic current system due to palaeogeographic changes (tectonically driven) and sea level variations (Dera et al., 2009a , b ; Price et al., 2016 ). Prior to the opening of the Hispanic Corridor (Davoei-Lavinianum zones; early-late Pliensbachian transition), isotopic data support the idea of a flow from the Boreal domains into the Tethys Ocean via the Viking Corridor (Dera et al., 2009a ). The opening of the Hispanic Corridor led to a change in the oceanic circulation system, such that a current develops through this palaeogeographic feature connecting Panthalassa with the Tethys. On the other hand, the formation of this corridor also favoured the establishment of a current from the Tethys and Panthalassa Oceans towards the Boreal Domain. The opening of the Hispanic Corridor was associated with the rifting process and the beginning of the formation of the Central Atlantic. This developed a major system of tilted blocks and small, generally, shallow sub-basins. In addition, in connection with the rifting, an increase in volcanic activity related to the Central Atlantic Magmatic Province and the Karoo-Ferrar Large Igneous Province (LIP) took place (Franceschi et al., 2014 ; Schöllhorn et al., 2020a , b ; Krencker et al., 2022 ; among others). During the Pliensbachian, the South Iberian Palaeomargin, was affected by these tectonic, palaeoclimatic and palaeoceanographic processes according to its palaeogeographic position (Vera, 2004 ; Ruiz-Ortiz et al., 2019 ; Nieto et al., 2023 ; among others). As a consequence of rifting and the opening of the Hispanic Corridor, the shallow carbonate platform developed during the Hettangian and Sinemurian (represented by the Gavilán Formation) collapsed. Numerous tilted blocks were formed, with very different bathymetries in which the sedimentary record was very changeable both in sedimentation rate and facies, with blocks in which wide hiatuses developed and others with more continuous sedimentary record (Nieto et al., 2023 ). The sediments deposited were marly limestones and marls with a clear hemipelagic and pelagic nature (represented by the Zegrí Formation). During the late Pliensbachian, alternating marly limestones and marl predominate, whereas, coinciding with the beginning of the Toarcian, mainly marly sedimentation taken place. In addition, the chemistry of its waters must have undergone changes due to modifications in the oceanic circulation system. The progressive opening of the Hispanic Corridor (early-late Pliensbachian transition), favoured the developing of a current pattern affecting the South Iberian Palaeomargin from Panthalassa and from Tethys towards Boreal domains (e.g., Dera et al., 2009a ; Price et al., 2016 ; Nieto et al., 2023 ). The chemistry of the seawaters would also be influenced by the contributions of continental waters, which would reflect the weathering processes that affected the Iberian massif. The record of the oxygen depleted conditions (Toarcian Oceanic Anoxic Event or T-OAE) related to the Jenkyns Event is very irregular in the South Iberian Palaeomargin, being confined to small, more subsiding pelagic basins where locally suboxic facies developed (e.g. Reolid et al., 2014 , 2021 ). As in other areas of the Tethys where the T-OAE is recorded, this event and the environmental conditions that prevailed during its development are well known in the South Iberian Palaeomargin (e.g. Rodríguez-Tovar and Uchman, 2010 ; Rodríguez-Tovar and Reolid, 2013 ; Reolid et al., 2014 , 2015 ; Rodrigues et al., 2019 ; Ruebsam et al., 2020b ; Kovacs et al., 2024). However, the environmental changes that preceded the development of this event need to be further investigated. This also happens for the South Iberian Palaeomargin. The aim of this paper is to analyse the environmental conditions at this palaeomargin in the time just before the Jenkyns Event (late Pliensbachian-earliest Toarcian). The influence of water runoff on sedimentation occurring in the South Iberian Palaeomargin, mainly during the late Pliensbachian and the Pliensbachian-Toarcian transition, will be discussed. This will bring us some light about the prevailing climatic conditions that conditioned continental weathering. For this purpose, a multi-proxy analysis of different detrital ratios, such as Zr/Rb, Sr/Cu, CIA and C-value, will be carried out on samples taken from three stratigraphic sections with Pliensbachian and lower Toarcian records, according to calcareous nannofossil biostratigraphy, from Subbetic (Betic Cordillera). 2. GEOLOGICAL SETTING The studied sections belong to the Lower Jurassic of the Subbetic, in the External Zones of the Betic Cordillera (SE Spain), which is the westernmost Alpine Mediterranean Chain, being 600 km long and 200 km wide (García-Hernández et al., 1980 ). The Betic Cordillera is subdivided into the Internal Zones and the External Zones. The External Zones represent the South Iberian Palaeomargin that developed during the Mesozoic in the westernmost Tethys, approximately at 20º N during the Early Jurassic (Bassoullet et al., 1993 ) and can be further divided into Prebetic (more proximal areas) and Subbetic (more distal areas) domains (Fig. 1 ). The Subbetic is subdivided from north to south in Intermediate Domain, External, Median, and Internal. The studied sections are located in the External and Median Subbetic (Fig. 1 ). The Lower Jurassic of the Subbetic is composed by the Gavilán and Zegrí formations. The Gavilán Formation (Hettangian-lower Pliensbachian) is made by platform carbonates (crinoidal limestones, oolitic and oncolitic limestones, cherty limestones and dolostones) and the Zegrí Formation (upper Pliensbachian-lower Bajocian) is composed by pelagic and hemipelagic deposits (marly limestones and marls and marly Ammonitico Rosso). Both formations are limited at the base by the intra-Pliensbachian discontinuity. The thickness of the Zegrí Formation ranges from just a few metres to 500 m in the External and Median Subbetic (Nieto et al., 2004 ). The lower part of the Zegrí Formation (Pliensbachian-lower Toarcian) is made up of marly limestone-marl rhythmites and marls. The middle-upper Toarcian is commonly represented by cherty limestones and red nodular marly limestones (marly Ammonitico Rosso facies) (Molina, 1987 ; Reolid et al., 2015 ). Three stratigraphic sections have been considered, Sierra Pelada (PEL), Puente Romano (PR) and La Cerradura (CE) (Figs. 1 , 2 ). The PEL and PR sections are located in the Median Subbetic and were previously studied by González-Donoso et al. ( 1971 ) and Jiménez ( 1986 ) in terms of ammonite biostratigraphy. The CE section, attributed to the External Subbetic, whose ammonites were initially studied by Braga ( 1983 ) and Jiménez ( 1986 ), and later investigated in detail by Reolid et al. ( 2014 ) and Silva et al. ( 2021 ) among others, from an ichnological and geochemical point of view. The Sierra Pelada (PEL) section is located to the north of Sierra Pelada ravine, 200 m NE of the Cortijo del Madroñal, province of Granada (section bottom coordinates: 37º 20’ 24.3” N; 3º 53’ 44.6” W). The Puente Romano (PR) section is located near the Roman bridge on the Colomera river, 500 m to the NE of the Colomera village, province of Granada (section bottom coordinates: 37º 22’ 36.6” N; 3º 42’ 31.4” W). La Cerradura (CE) section is in the E trench of motorway A-44, km 56.8, 15 km S of Jaén city (section bottom coordinates: 37º 41’ 51.9” N; 3º 38’ 0.1” W). In the PEL and PR sections there is a good record of the upper part of the Gavilán Formation, dated as lower Pliensbachian (Nieto et al., 2023 and references in this paper) and its contact with the Zegrí Formation, where the upper Pliensbachian and lower Toarcian are recorded. In the CE section there is a good upper Pliensbachian – lower Toarcian record, including the materials in which the T-OAE was detected (Reolid et al., 2014 ; Ruebsam et al., 2020a , b ). 3. MATERIALS AND METHODOLOGY 3.1. Fieldwork and facies analysis The fieldwork in the studied sections was focused on the analyses of sedimentary structures, trace fossils, recovery of fossil macroinvertebrates and sampling for subsequent analyses of microfacies, geochemistry and calcareous nannoplankton. We have used for the CE section the same 34 samples of the original work of Reolid et al. ( 2014 ). Both the PEL and PR sections were sampled on a bed by bed; 72 samples from PEL section and 49 samples from PR section. Samples from indurated marly limestones and limestones were selected for preparation of thin sections and polished slabs. Samples consisting of soft marls were selected for analyses of stable isotopes (C and O) and elemental inorganic geochemistry. For the microfacies studies, a Leica M205C binocular microscope was used to study a total of 121 thin sections. Analysis of trace fossils in the field was completed with the preparation of 22 polished slabs. The reference ammonite biostratigraphy used to date the materials of the studied sections is that of Braga ( 1983 ) and Jiménez ( 1986 ) for the South Iberian Palaeomargin, while for calcareous nannoplankton is that of Ferreira et al. ( 2019 ) (Fig. 3 ). The study of calcareous nannoplankton was carried out in PEL and PR sections. The biostratigraphic framework of the CE section is based on ammonite record (Braga, 1983 ; Jiménez, 1986 ; Reolid et al., 2014 ), and on the calcareous nannoplankton (Reolid et al., 2014 ), whose used the biostratigraphy of calcareous nannoplankton from Mattioli and Erba ( 1999 ). 3.2. Calcareous nannofossils A total of 23 and 21 smear slides were prepared from the original samples collected from the PEL and the PR sections, respectively. In both cases, the standard preparation technique of Bown and Young ( 1998 ) were used, and semi-quantitative analyses were carried out with a Leica DMLP light microscope and a Leica DFC 420 digital camera at 1250x magnification. For the PEL samples, four transverses were analyzed per sample, resulting in more than 500 fields of view, to identify rare or very rare species. Total abundance and degree of preservation of calcareous nannofossil assemblages, and the relative abundances of each species identified were obtained for each sample (see Table 1 for further details), following the approach of Perilli et al. ( 2010 ) and Fraguas et al. ( 2015 , 2018 ). Mitrolithus spp. and Crepidolithus spp. include all the specimens belonging to both genera recognized in lateral view or those that cannot be identified taxonomically at species level, since they are lacking their diagnostic characters. The appendix A includes all the calcareous nannofossil species mentioned within the text in alphabetical order. From the 21 smear slides prepared from the samples taken in PR section, a total of 2000 fields of view were analyzed per sample for semiquantitative analysis, in order to identify those species very rare. The results obtained were included in Nieto et al. ( 2023 ). 3.3. Elemental and C-O isotope geochemistry The elemental analysis of the samples of the three sections considered in this paper were obtained in the Centro de Instrumentación Científica (CIC) of the Universidad de Granada. Whole-rock analyses of major elements were made using X-ray Fluorescence (XRF) in a Philips PW1040/10 spectrometer. Trace elements were analysed using an inductively coupled plasma-mass spectrometer (ICP-MS), the Perkin Elmer Sciex-Elan 5000. The C and O isotopes were analyzed from bulk samples from CE section by Reolid et al. ( 2014 ), PR section by Nieto et al. ( 2023 ) and PEL section in this paper. The 72 samples of the last section were analyzed at the Laboratory of the Scientific and Technological Centre (CCiT) of the University of Barcelona with a Finningan MAT 253 isotope ratio mass spectrometer with a Kiel IV carbonate analysis device (ThermoFisher Scientific). The isotope ratios obtained were referred to the VPDB standard notation in ‰. Analytical precision was kept between 0.01 and 0.05 for δ 13 C and δ 18 O. The Chemical Index Alteration (CIA) corrected for carbonate contents, was calculated according to the expression (1) from Nesbitt and Young ( 1982 ; 1989 ): $$CIA=100 \times \frac{{Al}_{2}{O}_{3}}{{Al}_{2}{O}_{3}+ CaO+ {Na}_{2}O+ {K}_{2}O} \left(1\right)$$ To analyze the influence of diagenesis in the primary geochemistry signal, the Z factor was used, calculated for each studied section according to the expression (2), given by Keith and Weber ( 1964 ) and Babalola et al. ( 2023 ). \(Z=2.048(\) δ 13 C + 50) + 0.498(δ 18 O + 50) (2) The C-value plot, proposed by Zhao et al. ( 2007 ), was used to discriminate general climatic conditions throughout the deposition of the studied sediments. This parameter is calculated according to the next expression (3): $$C-value = \frac{\sum \left(Fe+Mn+Cr+Ni+V+Co\right)}{\sum \left(Ca+Mg+Sr+Ba+K+Na\right)} \left(3\right)$$ If C-value is comprised between 0 and 0.2, the climate is arid. If C-value is between 0.2 to 0.4, the climate is semiarid. When this parameter is in a range 0.4 to 0.6, the climate is semiarid to semimoist. The values in the range between 0.6 to 0.8, shown a semimoist climate. Finally, if the C-value is higher than 0.8, recorded a moist climate. 4. RESULTS 4.1. Biostratigraphy and chronostratigraphy The biostratigraphy and chronostratigraphy related to the boundary between the Gavilán and Zegrí Formations have just been studied in detail by Nieto et al. ( 2023 ). These authors identified up to five discontinuities of hiatus with variable amplitude between them and between different stratigraphic sections. At the bottom of the PEL section, cherty limestones have been recognized, alternating with marls (Figs. 2 and 3 ) attributed to the upper part of the Gavilán Formation. No features have been observed at the top of these limestones that would indicate the existence of a stratigraphic discontinuity. In the PR section, some limestones with cherts have been identified, which have been attributed to the upper part of the Gavilán Formation (Figs. 2 , 3 ). In this case, based on regional data, the hiatus associated with the discontinuity between the two formations has been considered to span the Ibex-Lavinianum zones (Nieto et al., 2023 ). In the studied interval of the CE section there is no record of the Gavilán Formation. Consequently, Nieto et al. ( 2023 ) state that the top of the Gavilán Formation and the bottom of the Zegrí Formation are heterochronous. With respect to the calcareous nannofossil biostratigraphy of the studied area, there are data from the CE and PR sections already published. At CE section (Reolid et al., 2014 ), the base of the NJT5b Subzone is marked by the first occurrence of Lotharingius sigillatus around the Solare/Elisa ammonite Subzone boundary of the Emaciatum ammonite Zone, and the boundary between the NJT5/NJT6 zones is based upon the first occurrence of Carinolithus superbus around the Polymorphum/Serpentinum ammonite Zone boundary, considering the nannofossil biostratigraphic scheme proposed by Mattioli and Erba ( 1999 ) for the Tethyan Domain. In the PR section (Nieto et al., 2023 ), based upon the more recent biostratigraphic scheme of Ferreira et al. ( 2019 ) for the Western Tethys, the NJT5b Subzone has been identified based upon the FO of L. crucicentralis within the upper Pliensbachian and NJT5c Subzone (lower part of the Polymorphum Zone) considering the FO of Zeugrhabdothus erectus , which enabled the approximation of the upper Pliensbachian/lower Toarcian boundary. A total of 26 species belonging to 14 genera were identified in the 23 smear samples from PEL section (check Table 1 for further details). Most of the samples belonging to the Gavilán Formation are barren or show a poor preservation, including only extremely rare specimens of Schizosphaerella punctulata and Calcivascularis jansae . This last is also the case for the lowermost samples of the Zegrí Formation until sample PEL-46m. Excluding three samples (PEL-42, 27 and 13; Table 1 ), a considerable increase in both abundance and diversity, as well as a much better preservation, can be noted from sample PEL-45 up-section. They yield up to 16 different species (samples PEL-17 and 15) and are dominated by relatively well-preserved specimens of Schizosphaerella puntulata, Calcivascularis jansae, Mitrolithus lenticularis and Lotharingius hauffii . Considering the biostratigraphic scheme proposed by Ferreira et al. ( 2019 ), a nannobiohorizon has been identified in the PEL section (Figs. 2 , 3 ): the first occurrence of Zeugrhabdothus erectus in sample PEL-20 (Table 1 ). This bioevent marks the boundary between the NJT5b/NJT5c subzones and helps to approach the Pliensbachian/Toarcian boundary. 4.2. Facies analysis and ichnofacies 4.2.1. Facies and microfacies analysis The Sierra Pelada (PEL) section begins in the cherty limestones of the top of the Gavilán Formation (first 5 m; Figs. 2 , 4 A). The microfacies are wackestone of radiolaria and sponge spicule (Fig. 5 A) with Thalassinoides densely bioturbated by Phycosiphon . There are also very small (less than 0.15 mm in size) crinoidal fragments and other unidentifiable small bioclasts. The siliceous radiolarian tests have been replaced by microcrystalline calcite, obscuring their textural details. The siliceous megasclere spicules, mainly monaxon, have also been dissolved, and their moulds are filled with granular calcite cement. The rest of the section (NJT5 Zone), spans around 50 m and is made up by marls and marly limestones of the Zegrí Formation (Figs. 2 , 4 B). The lower part of the Zegrí Formation, densely bioturbated (Fig. 4 C) is dominated by limestone beds (first 13 m above the cherty limestones), followed by a thick interval of marls with carbonate upwards increasing sequences (around 25 m thick). The uppermost part of the studied section (within NJT5c Subzone, Polymorphum Zone, lower Toarcian) is composed by 12 m of marls and marly limestones alternation with progressive increase in carbonate content (Fig. 2 ). In PEL section, the microfacies differentiated for the Zegrí Formation (Fig. 5 B) is a packstone of peloids, spicules and radiolaria with ostracods, calcispheres, benthic foraminifera (mainly Lenticulina ) and some bioclasts. Small burrows are also observed in thin section, any times with iron oxides or hydroxides. Locally, a mudstone with scarce radiolaria and bioclasts could be detected. In these microfacies are also observed small burrows. The phytodetritus are locally abundant in darker stratigraphic intervals. The studied interval in the Puente Romano (PR) section (Fig. 2 ) corresponds to the Zegrí Formation and begins on the cherty limestones of the Gavilán Formation (Fig. 4 D) (Nieto et al., 2023 ). The microfacies of the Gavilán Formation in this section are peloidal and bioclastic wackestone-packstone (Fig. 5 C, D). The peloids have an average size of 0.1 mm. The bioclasts are mainly crinoids, and secondarily sponge spicules, radiolarians, and thin-shelled bivalves (“filaments”). Less abundant there are also benthic foraminifera ( Lenticulina ), ostracods and calcispheres. The lower 7 m of the section (NJT5a Subzone) are made up by a limestones/marl alternation and above by an alternation of dark marls/marly limestones of the upper Pliensbachian-lowermost Toarcian (Fig. 4 E). La Cerradura (CE) section is formed by a lower part constituted by marl and marly limestone alternation (Fig. 4 F) (Emaciatum Zone, NJT5a and NJT5b subzones) and an upper part represented by a dark marls interval of the Serpentinum Zone (NJT6 Zone) (Fig. 2 ). The microfacies are mudstone-wackestone with trace fossils (Fig. 5 E), in which abundant coal grains are concentrated (Fig. 5 F). 4.2.2. Ichnofacies In the PEL section (Fig. 6 C, D), the ichnoassemblage recorded in the top of the Gavilan Formation is characterized by abundant horizontal to oblique sinuous burrows corresponding to Macaronichnus and secondarily Thalassinoides , Planolites , Chondrites , and Zoophycos . Other scarce trace fossil is Lamellaeichnus . In the Zegrí Formation, the ichnoassemblage is similar with dominant Macaronichnus densely packed. Phycosiphon is very common burrowing within Thalassinoides sediment infilling. Secondary trace fossils are Thalassinoides , Planolites , Zoophycos and Chondrites , and less commonly Lamellaeichnus and Palaeophycos . Macaronichnus and Phycosiphon are infilled with clear sediment. In the case of Macaronichnus the mantle is comparatively darker than the surrounding sediment whereas the sediment infilling is clearer. The bioturbation index keeps very high in both formations in the PEL section ranging 3 to 5. The diversity is variable from 4 to 7 ichnogenera corresponding to the Cruziana ichnofacies. This diverse assemblage presents a good tiering with Macaronichnus and Thalassinoides dominating the upper tier, and Zoophycos and Chondrites dominating the lower tier. The ichnoassemblage of the PR section (Fig. 6 A, B) is similar to that described in the Zegrí Formation of CE section by Reolid et al. ( 2014 ) and Simo and Reolid ( 2021 ). Commonly the trace fossils present a sediment infilling darker than the surrounding sediment. Some trace fossils present iron-rich sediment. Dominant trace fossils are Planolites , Thalassinoides and Chondrites (both large and small ones). Secondary trace fossils, but locally abundant, are Lamellaeichnus , Teichichnus and Zoophycos , and scarce Palaeophycus and Taenidium . The bioturbation index is commonly ranging from 2 to 3 and only decrease to 1 in the Pliensbachian/Toarcian boundary, where only scarce small Chondrites and Planolites are recorded. The number of ichnogenera in each level varies from 1 to 7 with lowest values located in the lower part of the NJT5a Subzone (upper Pliensbachian) and the top of the NJT5c Subzone (Polymorphum Zone, lower Toarcian). The lower part of the NJT5c Subzone records higher content of ferruginous trace fossils, principally Chondrites and Planolites . The trace fossils recorded in the PR section correspond to the Cruziana ichnofacies. The ichnoassemblage is relatively diverse and present a good tiering with Planolites and Thalassinoides dominating the upper tier, Lamellaeichnus and Teichichnus as main representants of a middle tier, and, finally, Chondrites and Zoophycos dominating the lower tier. Finally, the ichnoassemblage of CE section (Fig. 6 E) was studied by Reolid et al. ( 2014 ), Reolid and Reolid ( 2020 ) and Simo and Reolid ( 2021 ). This is mainly composed by Planolites , Thalassinoides and Chondrites (both small and large) and secondarily by Lamellaeichnus , Taeinidum , Teichichnus and Trichichnus . Other trace fossils such as Zoophycos and Palaeophycus , recorded in the PR section (Fig. 6 A, B), or Macaronichnus and Physosiphon recorded in PEL section (Fig. 6 C, D), are not present in CE section. In general, the bioturbation index and the diversity are similar to those of PR and lower than in PEL section, but decreasing in the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian). The assemblage corresponds to the Cruziana ichnofacies. The ichnoassemblage is relatively diverse in the marl and marly limestone rhythmite, with Planolites and Thalassinoides dominating the upper tier, Lamellaeichnus and Teichichnus as main representants of a middle tier and, finally, small Chondrites dominating the lower tier. The bioturbation index is commonly ranging from 2 to 3, and decrease in the uppermost Pliensbachian and lower Toarcian where ranges from 1 to 2. The diversity is reduced in the beginning of the Toarcian, top of the marly limestone rhythmite (Polymorphum Zone, lower Toarcian) where Chondrites dominates. Only in the top of the Polymorphum Zone, large Chondrites turns very abundant and rich in organic matter (Reolid and Reolid, 2020 ). The first meter of the dark marls of the Serpentinum Zone (coincident with the negative CIE of the Jenkyns Event) are barren of benthic macroinvertebrates and trace fossils (Baeza-Carratalá et al., 2017 ). The assemblage rapidly recovers initially with the record of Chondrite s, and subsequently with Planolites and Trichichnus (Simo and Reolid, 2021 ). 4.3. Geochemistry 4.3.1. δ 13 C and δ 18 O isotopes The values of δ 13 C (‰ VPDB) in PEL section fluctuate between − 0.41‰ and 1.22‰, (average 0.50‰, σ = 0.39). From the base of the stratigraphic section to meter 15, coinciding with the lowest rocks of the upper Pliensbachian in this section, the isotope ratio remains slightly above the average value (Fig. 2 ), although it shows some fluctuations in the first five meters of the sequence and between meters 12.5 and 15 (Fig. 2 ). Between meters 15 and 27, coinciding with the lower part of the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian), the marls are more abundant, in which there are many fluctuations, but always around the average. In the central part of the same subzone (between meters 27 and 30) a decrease of the isotope ratio values is observed, which varies between 0.50 and − 0.41. From meter 30 onwards, there is an increase in the value of the isotopic ratio (from − 0.41 to 0.53, obtained in meter 31). From this level to the top of the stratigraphic section, the δ 13 C again shows several oscillations in its values, with a decreasing deviation respect to the average in the NJT5c Subzone (lower part of the Polymorphum Zone) (Fig. 2 ). The δ 18 O in the PEL section ranges between − 4.43 and − 2.25‰ (average − 3.52‰, σ = 0.59). As happened with the C isotope ratio, the δ 18 O shows, in general, values slightly above the average between the base of the section and meter 15 (Fig. 2 ), coinciding with the levels dated as lower part of the upper Pliensbachian. Coinciding with the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian), the values of this isotopic ratio are below the average, reaching the lowest values between meters 27 and 30, around the mid part of the NJT5b Subzone (Fig. 2 ). In the NJT5c Subzone, the δ 18 O starts to increase its value until it is slightly above the average value. In the PR section, the δ 13 C values in the bulk sample change between 0.47 and 1.45‰ (Fig. 2 ) (average 1.11‰, σ = 0.17). In general, the values of this isotopic ratio show very little variations around the average value throughout the stratigraphic section, with no trend to be highlighted. Regards δ 18 O, the values range from − 2.76‰ to − 0.67‰ (average − 2.17‰, σ = 0.33). Although the complete stratigraphic sequence shows numerous small-range fluctuations, all they are around the average, with no clear trends (Fig. 2 ). In the CE section the values of δ 13 C in bulk sample range between 0.41 and 1.93‰, (average 1.35, σ = 0.32). In the marl-marly limestone rhythmite (upper Pliensbachian to Polymorphum Zone; Fig. 2 ), they are arranged around 1.20‰. Above the top of the rhythmite (Fig. 2 ), a negative CIE is observed, changing the values of this isotope ratio from 1.20‰ to 0.41‰ (Fig. 2 ) corresponding to the lower part of the Serpentinum Zone (lower Toarcian). From meter 30, in the lower part of the Serpentinum Zone or lower part of the NJT6 Zone (Fig. 2 ), towards the top of the stratigraphic sequence, there is an increase in the value, increasing from 0.41‰ to 2.47‰. The δ 18 O shows a minimum value of − 2.50‰ and the maximum value is − 1.34‰ (average − 1.96‰, σ = 0.29). This ratio decreases sharply in the Polymorphum Zone (lower Toarcian), where it reaches the minimum value, coinciding with the contact between the marl-marly limestone rhythmite and the dark marl interval. Here, an isotope excursion of − 0.55‰ is recorded. In the base of the dark marls (top of the Polymorphum Zone; Fig. 2 ), a positive excursion (difference in isotope ratio of 1.00‰) is recorded, reaching a value of − 1.50‰. After the first 2 m of the dark marls, the δ 18 O ratio reaches values similar to those of the upper Pliensbachian. 4.3.2. Detrital and palaeoclimatic proxies The Zr/Rb ratio in PEL section (Fig. 7 ) shows high values at the base of the section that includes the top of the Gavilán Formation and the lower part of the Zegrí Formation (average 1.24, σ = 0.13; Fig. 7 ). The values decrease in the marl-dominated interval (NJT5b Subzone, Emaciatum Zone, upper Pliensbachian) and the upper part of the studied section (NJT5c Subzone, lower part of the Polymorphum Zone, lower Toarcian) (average 0.88, σ = 0.08). The Sr/Cu ratio shows a stratigraphic distribution with similar trends to Zr/Rb but the fluctuations are stronger (Fig. 7 ). Sr/Cu is higher in the lower part of the section (average 281.4, σ = 122) than in the upper part (average 118.6, σ = 83). Respect to the CIA and C-value present the lowest values in the lower part of the section (CIA average 0.04, C-value average 2.27) before the NJT5b Subzone of the marl-dominated interval of the Zegrí Formation (CIA average 0.13, C-value average 9.74; Fig. 7 ). The values of these parameters increase and present stronger fluctuations in the rest of the section and describe an opposite stratigraphic distribution respect to the Sr/Cu ratio. In the PR section (Fig. 8 ), two stratigraphic intervals are differentiated, a lower interval that includes the first 7 m corresponding to NJT5a Subzone (Algovianum Zone, upper Pliensbachian), and the upper part formed by 18 m including the NJT5b (Emaciatum Zone, upper Pliensbachian) and NJT5c Subzones (lower part of Polymorphum Zone, lower Toarcian). The Zr/Rb ratio (Fig. 8 ) presents relatively low values in the lower stratigraphic interval (from 0 m to 8 m, NJT5a Subzone; Fig. 8 ) with small fluctuations (average 1.44, σ = 0.05), and then is followed by a relative increase of Zr/Rb in the upper stratigraphic interval (average 1.52, σ = 0.08). The Zr/Rb values progressively decrease in the lower Toarcian (NJT5c Subzone; Fig. 7 ). The Sr/Cu ratio shows high values in the lower part of the studied section with low fluctuations (average 41.4, σ = 7.7), whereas the upper part of the section is characterized by relatively low values (average 27.4) with high fluctuations (σ = 13.1). CIA exhibits low values (average 10.1) and minor fluctuation (σ = 2.4) in the lower part of the section (Fig. 8 ), then a slightly increasing trend is recorded with high values in the upper stratigraphic interval (average 14.2) and important fluctuations (σ = 5.1). Finally, C-value presents a stratigraphic distribution similar to CIA in the PR section (Fig. 8 ). The lower stratigraphic interval present low values (average 0.18, σ = 0.02), whereas the upper stratigraphic interval records high values with abrupt fluctuations (average 0.23, σ = 0.05). The Zr/Rb ratio of the CE section (Fig. 9 ) shows low values (mostly < 0.75) in the rhythmite of the lower part of the section (from 0 m to 26 m, Emaciatum Zone, upper Pliensbachian; Fig. 9 ) with a Zr/Rb average value of 0.74 (σ = 0.03). The Zr/Rb values increase from the beginning of the dark marl (average 0.80, σ = 0.07) with important fluctuations and reaches the maximum during the negative CIE. Respect to the Sr/Cu ratio. it shows relatively high values in the marl and marly limestone rhythmite (average 45.6, σ = 17.9) with the highest values in the lower part of the NJT5a Subzone, Emaciatum Zone (upper Pliensbachian; Fig. 9 ). The top of the rhythmite, in the Polymorphum Zone (lower Toarcian) presents a prominent increase of Sr/Cu; however, the overlying dark marls (NJT6 Zone, Serpentinum Zone) are characterized by a significant depletion (average 18.3, σ = 8.4). Finally, CIA also shows two different parts with relatively low values in the rhythmite (average 13.8, σ = 6.1) and higher values in the dark marls (average 29.3, σ = 8.1; Fig. 9 ). C–value shows a stratigraphic pattern similar to CIA (Fig. 9 ), with the lowest values corresponding to the rhythmite (average 0.13, σ = 0.04) and higher values in the dark marls (average 0.27, σ = 0.07). The highest values correspond to the beginning of the Serpentinum Zone, during the negative Carbon Isotope Event (CIE) followed by a light decrease. 4.4. Diagenetic signature Correlation diagrams between the two isotope ratios, δ 13 C and δ 18 O, have been plotted for each of the stratigraphic sections considered (Fig. 10 ). For PEL and PR sections, the correlation is positive, with a low coefficient of determination (R 2 = 0.43) in the first section, and a value of R 2 = 0.54 in PR section. However, in the CE section, both ratios show a negative correlation with a value of coefficient of determination of R 2 = 0.16 (Fig. 10 ). The Fig. 11 shows the correlation diagrams between δ 13 C and Sr (ppm) and between δ 18 O and the Fe/Ca and Sr/Ca ratios for each of the sections considered, according to the proposal of Babalola et al. ( 2023 ). These authors use the degree of correlation (shown by the value of the coefficient of determination between both values, R 2 ) as an indicator of the primary origin of the geochemical values. In the PEL section, the correlation between δ 13 C and Sr (ppm) is clearly positive but low (R 2 = 0.25; Fig. 11 A). The correlation between δ 18 O and the Fe/Ca ratio (R 2 = 0.33, Fig. 11 B), is negative and low, while between δ 18 O and Sr/Ca there is no correlation (R 2 = 0.04, Fig. 11 C). In the PR section, δ 13 C and Sr (ppm) show a low positive correlation (R 2 = 0.26, Fig. 11 D). The correlation of δ 18 O with Fe/Ca and Sr/Ca is low and negative (R 2 = 0.36 and 0.51 respectively, Figs. 11 E, F). Finally, in CE section, the correlation between δ 13 C and Sr (ppm) is slightly negative, with very low correlation (R 2 = 0.002, Fig. 11 G). In the case of the correlations of δ 18 O and the Fe/Ca (R 2 = 0.53) and Sr/Ca (R 2 = 0.16) ratios in CE section (Fig. 11 H, I), are clearly negative. The value of the Z factor has also been calculated for each of the sections considered, according to the definition of this factor given by Keith and Weber ( 1964 ) and Babalola et al. ( 2023 ) and shown in the methodological section of the current paper. If Z > 120, the limestones could be classified as marine; if Z < 120, they are materials generated in or affected by meteoric waters. Finally, if Z has values close to 120, the limestones should be classified as of undetermined origin. In the studied sections the Z values is always > 120 (PEL section ranges between 124.31 and 128.67; PR section ranges between 127.00 and 129.94; CE section ranges between 127.48 and 130.33). Therefore, Z values confirm marine origin for the isotopic signal, and they have not undergone processes of meteoric diagenesis that have distorted their primary geochemical signature. 5. DISCUSSION 5.1. Interpretation of facies and facies association In the PEL and PR sections, materials attributed to the Gavilán Formation are recorded in the lower part. According to their microfacies and regional palaeogeographical context described before, the sediments were deposited in a distal carbonate platform. The presence of packstone with abundant peloids and crinoids supports the interpretation of a shallower depth and more energetic conditions for the deposits in the PR section, but the record of radiolarians confirms the hemipelagic influence. In the studied sections there are not sedimentary structures pointing to high energy conditions related to waves or tempestites. In this sense, the environment is interpreted as representing a bottom below the storm wave base. The beginning of the deposition of the rhythmite of the Zegrí Formation coincides with the start of the main phase of intracontinental breaking (rifting), developed from the early-late Pliensbachian (e.g. Reolid et al., 2018 ; Nieto et al., 2023 ). The bottom topography of the basin would be irregular with different semigrabens and changeful local subsidence and sedimentation rates (Vera, 2001 ; Nieto et al., 2004 ; Reolid et al., 2015 ; Nieto et al., 2023 ), as is observed in other Tethyan Alpine domains (e.g. de Graciansky et al., 1998 ; Marok and Reolid, 2012 ; Jenkyns, 2020 ). Respect to the Gavilán Formation, the Zegrí Formation represent a decrease in carbonate content mainly related to topographic changes at the sea bottom, with the development of troughs and swells (Vera, 2001 ; Reolid et al., 2015 , 2018 ; Nieto et al., 2023 ), in addition to the transgressive regional and global context (e.g. Hallam, 1987 , 1997 ; Jenkyns, 1988 ; de Graciansky et al., 1998 ; Wignall et al., 2005 ; Korte and Hesselbo, 2011 ; Haq, 2018 ; Storm et al., 2020 ). The alternation of grey marls and marly limestones of the Zegrí Formation represents a pelagic to hemipelagic environment, according to the record of ammonites, radiolarians, and siliceous sponge spicules. However, there is continental input evidenced by the terrigenous content of clay minerals, as reported for other areas of the Subbetic (Palomo, 1987 ; Rodríguez-Tovar and Reolid, 2013 ) and the described record of millimetric coal (wood) fragments and large coal fragments in the case of CE section (Reolid et al., 2019 ; Reolid and Reolid, 2020 ). There are not sedimentary structures pointing to high energy conditions. The abundance of trace fossils in the studied sections confirms favourable conditions for infaunal organisms (oxygen and nutrient availability) as evidenced by previous papers in the Zegrí Formation for the upper Pliensbachian and Toarcian (Rodríguez-Tovar and Uchman, 2010 ; Rodríguez-Tovar and Reolid, 2013 ; Reolid et al., 2015 ; Simo and Reolid, 2021 ). Only in the dark marls of the Serpentinum Zone (NJT6 Zone) of the CE section, there is a sensible decrease of bioturbation that is locally absent during the negative CIE (Reolid et al., 2014 ). The ichnoassemblages indicate a relatively soft ground with a good infaunal tiering. The genetic interpretation of this rhythmic marl and marly limestone alternation is complex according to our recent data and needs to be studied to identify the Milanković cycles and to distinguish primary signatures of astronomically forced carbonate cycles (dilution, productivity or dissolution cycles) from the secondary effects of early diagenesis. Only in the case of CE section there is a cyclostratigraphic study that indicate orbital frequencies corresponding to long and short eccentricity mainly (Silva et al., 2021 ). 5.2. Diagenetic control in the primary geochemical proxies A first approximation to the influence of diagenesis on the values of the different geochemical proxies considered can be made by comparing the δ 13 C and δ 18 O variation intervals of each of the sections considered with the ranges of variability of these same isotope ratios in other sections of the Western Tethyan Domain where materials of similar age are recorded (Fig. 12 ). From this comparison, shown in Fig. 12 , it is observed that the ranges of variation of both isotope ratios in the considered sections are shorter than those of other stratigraphic sections from different basins such as the Lusitanian Basin in Portugal (Duarte et al., 2014 ), the Iberian Basin in east Spain (Rosales et al., 2001 ), or the Atlasic Basin in Moroccan Atlas (Mercuzot et al., 2020 ). The Subbetic ranges are comprised within those of other basins. This is interpreted as meaning that diagenesis did not substantially modify the geochemical values and, therefore, they could be considered as primary. Several authors have considered that the value of the correlation coefficient between δ 13 C and δ 18 O values in bulk sample can be a good signal of the intensity of diagenesis in carbonates (Jenkyns and Clayton, 1986 ; Duchamp-Alphonse et al., 2007 ; Mercuzot et al., 2020 ; Babalola et al., 2023 ). A low value of the coefficient of determination (R 2 ) could be interpreted as the record of a low-intensity diagenesis and, therefore, a primary origin could be attributed to the isotope values. In the sections studied in the Subbetic, R 2 is low (0.43 for PEL section, 0.54 for PR section, and 0.16 for CE section) (Fig. 10 ). However, Swart and Oehlert ( 2018 ) indicate that a low value of the coefficient of determination or a lack of correlation between both isotope ratios should not necessarily indicate that the studied materials record the original isotope signal. Babalola et al. ( 2023 ) make a detailed analysis of the influence of diagenesis in Middle Jurassic samples and propose that, in addition to the comparison of the fluctuation intervals of the isotope values, and the study of the coefficient of determination (R 2 ), the values of this coefficient obtained from the correlation of the isotope ratios with different elements (Fe, Ca, Mn, Sr) and some of their ratios (Fe/Ca, Sr/Ca, for example) could be considered. Figure 11 shows correlation diagrams of each of the isotope ratios with Sr, Fe/Ca and Sr/Ca for the studied sections. The coefficient of determination in all cases is very low for Sr and δ 13 C (R 2 < 0.26), for Fe/Ca and δ 18 O (R 2 < 0.53), and also for Sr/Ca and δ 18 O (R 2 < 0.51). Considering the data as a whole, the values of the R 2 show values below 0.5, except in the CE section (Fe/Ca vs. δ 18 O) and in PR section (Sr/Ca vs. δ 18 O), with values slightly above 0.5. These values would indicate a weak diagenetic influence that would not substantially modify the primary geochemical signal. On the other hand, the values of the Z factor > 120 indicate that the materials studied are of marine origin and, therefore, with little or no influence of meteoric waters that have altered the primary diagenetic signal (Babalola et al., 2023 ). The scarce diagenetic effect on these sections is also confirmed by the microfacies where cements and radiolarians, sponge spicules and calcareous nannoplankton is generally preserved. 5.3. Carbon isotope stratigraphy The δ 13 C curves of the studied sections (Fig. 13 ) do not clearly show the excursions described for the Pliensbachian by authors as Mercuzot et al. ( 2020 ). In the PEL section, between metres 42 and 46 (upper part of the NJT5b Subzone and lower part of the NJT5c Subzone) a negative excursion, correlatable with the Pliensbachian-Toarcian Boundary Event (PTBE) of Korte and Hesselbo ( 2011 ), Bodin et al. ( 2016 ), Fantasia et al. ( 2019 ), could be considered (Fig. 13 ). In the PR section, in a stratigraphic position equivalent to the one mentioned in the PEL section, the same event could also be identified. Finally, in the CE section, the PTBE is not observed, there is a clear negative CIE in the lower part of the Serpentinum Zone (NJT6 Zone, lower Toarcian) correlative with the Jenkyns Event as reported by Reolid et al. ( 2014 ) from δ 13 C of bulk rock, and Ruebsam et al. ( 2020a , b ) and Kovács et al. ( 2024 ) from δ 13 C of organic matter. 5.4. Palaeoclimatic changes Important environmental changes can be identified according to the distribution of values of geochemical detrital proxies in PEL section. The lower part of the section, including the top of the Gavilán Formation and the lower part of the Zegrí Formation, records high values of Zr/Rb and Sr/Cu ratios that are interpreted as related to warm conditions. Sr/Cu is a weathering proxy that increases under warmer conditions (Bai et al., 2015 ; Cao et al., 2015 ; Moradi et al., 2016 ; Reolid et al., 2023 ). The Zr/Rb ratio is used as a proxy of the silt/clay ratio (Kylander et al., 2011 ) with Zr content related to eolian input (Pye, 1987 ; Hamroush and Stanley, 1990) and Rb related to fluvial transport to the basin (Chester et al., 1977 ; Reolid et al., 2012 ). That is, environmental conditions represented by the beginning of the Zegrí Formation in the Sierra Pelada section were arid and relatively warm. CIA and C-value present the lowest values in this part of the section that confirm arid conditions. In the marl dominated interval mainly corresponding to the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian) and in the upper part of the studied section corresponding to the NJT5c Subzone (lower part of the Polymorphum Zone, lower Toarcian), the Zr/Rb ratio shows low values that indicate relatively humid conditions and enhanced fluvial input to the Median Subbetic. The Sr/Cu ratio shows a similar trend with stronger fluctuations that allow to interpret some warm episodes. The CIA and C-value present higher values in the NJT5b and NJT5c subzones than in the lower part of the section confirms an enhanced weathering and more humid conditions but probably abrupt fluctuations mainly in the early Toarcian as evidenced in the upper part of the section (NJT5c Subzone). In the PR section two stratigraphic intervals have been differentiated according to the geochemical detrital proxies. The lower interval of the Zegrí Formation corresponding to the NJT5a Subzone (Algovianum Zone, upper Pliensbachian) is characterized by relatively low Zr/Rb, CIA and C-values, as well as relatively high values of Sr/Cu. Relatively warm and arid conditions are evidenced from these data, however, relatively low values of Zr/Rb point to higher influence of fluvial input than eolian input for this part of the Median Subbetic. From the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian) there is an environmental change recorded by the increase of CIA and C-value that indicate enhanced weathering and moist conditions compared to the lower part of the section. A Zr/Rb increase occurs around the Pliensbachian/Toarcian boundary and lower part of the NJT5c Subzone (lower part of Polymorphum Zone, lower Toarcian) and indicate more arid conditions (more eolian input) which is opposite to the CIA and C-value interpretation. The Zr/Rb values progressively decrease across the lower Toarcian (NJT5c Subzone) pointing to higher incidence of fluvial inputs in the upper part of the section. The Sr/Cu show strong fluctuations but a general decreasing trend in the lower Toarcian interpreted as relatively cold conditions (Cao et al., 2015 ; Moradi et al., 2016 ). In CE section, the lower stratigraphic interval (marly limestone rhythmite of the upper Pliensbachian), is characterized by low Zr/Rb, CIA and C-value, that indicate dominance of fluvial detrital inputs and relatively low weathering. The Sr/Cu in this lower stratigraphic interval shows progressively decreasing values in the NJT5a Zone (Solare Subzone, Emaciatum Zone) that points to a cooling trend. The top of the marly limestone rhythmite, corresponding to the Polymorphum Zone (lowermost Toarcian) evidences a perturbation herald of the Jenkyns Event with initial abrupt decrease of Sr/Cu in the Pliensbachian/Toarcian boundary correlated with a cooling episode, and a subsequent abrupt increase related to a warming. The beginning of the dark marls of the Serpentinum Zone (NJT6 Zone, lower Toarcian), also characterized by a negative CIE (Reolid et al., 2014 ; Ruebsam et al., 2020b ; Kovács et al., 2024 ), presents increasing values of Zr/Rb that indicate a stratigraphic shift in grain size for detritic input (Kylander et al., 2011 ) related to eolian sources congruent with more arid conditions interpreted for this palaeomargin by Rodrigues et al. ( 2019 ) from palynofacies. The Sr/Cu decrease points to a relative cooling climate that is contrary to the global warming interpreted after the study of δ 18 O from belemnites (e.g. Rosales et al., 2004 ; Danise et al., 2019 ; Fernández et al., 2020 ) and brachiopods (e.g. Suan et al., 2010 ; Ferreira et al., 2019 ; Hesselbo et al., 2020b ). The increasing CIA and C-value at the onset of the Jenkyns Event indicate enhanced continental weathering and sediment maturity under moist conditions. The highest values correspond to the beginning of the Serpentinum Zone, during the negative CIE followed by a light decrease. 5.5. Palaeogeographic considerations In the previous section it has been shown that the geochemical signal of the detrital proxies analysed in each of the sections considered in this paper gives palaeoclimatic information that may be contradictory. For example, in the Algovianum Zone, the proxies indicating aeolian (Zr/Rb) or fluvial (Sr/Cu) influences show opposite trends in the PEL and PR sections. These disparities in geochemical signal indications could be interpreted considering the palaeogeographical position of the South Iberian Palaeomargin in a zone of mixing of marine waters from the eastern Tethys and Panthalassa. During the Davoei-Lavinianum Zones, the opening of the Hispanic Corridor (e.g. Price et al., 2016 ) occurred as a consequence of Central Atlantic rifting, which was also an important stage of volcanic activity of the Central Atlantic Magmatic Province and Karoo-Ferrar LIP (e.g., Krencker et al., 2022 ). The opening of this Corridor led to the establishment of a connection between Tethys and Panthalassa waters, the latter with a geochemistry that recorded the significant volcanic activity. In other words, a mixture of waters with a different geochemical imprint was produced (Dera et al., 2009a ). In addition, the pattern of currents was modified, as the Viking Current, coming from Boreal domains to the South, disappeared and a current of waters, resulting from the mixing of the Panthalassa and Tethys waters, was established towards the North. On the other hand, important changes occurred in the top of the Zegrí Formation in the sections considered. It is interesting to analyse the change in the materials attributed to the NJT5b Subzone of Ferreira et al. ( 2019 ), equivalent to the Emaciatum Zone (upper Pliensbachian) (Fig. 3 ), with a duration close to 720 ka, according to these authors (Fig. 3 ). These changes could be explained by (1) the development of sedimentary sub-basins (half grabens) in a rifting palaeotectonic context, with very different sedimentary input rates, (2) probable sediment by-pass situations due to the establishment of a new marine current system and/or (3) differential subsidence controlled by rifting. Molina et al. ( 1999 ), Ruiz-Ortiz et al. ( 2004 ), Reolid et al. ( 2015 ) or Nieto et al. ( 2023 ), among others, indicate that, once the shallow carbonate platform of the lower Pliensbachian had disintegrated, a system of half-graben controlled by listric faults developed that could favoring differences on subsidence, sedimentation rate, facies, and connection within different sub-basins in the South Iberian Palaeomargin. The rate of sedimentation would be conditioned by sediment by-pass related to the action of currents and by a differential subsidence that would generate areas working as favorable depocenters. In the CE section of the External Subbetic, the materials attributed to the Elisa Subzone (that are close equivalent to the NJT5b Subzone of Ferreira et al., 2019 ) have a thickness of 11.2 m (Fig. 2 ). Considering this value and the duration of the subzone, a sedimentation rate of 0.018 mm/ka is estimated. In the PR section of the Median Subbetic, the strength of the materials corresponding to this subzone is 4.24 m, which gives a sedimentation rate of 0.006 mm/ka. Finally, in the PEL section, also attributed to the Median Subbetic but located to the south, the rocks representing the NJT5b Subzone are 28.6 m thick, which gives a sedimentation rate of 0.040 mm/ka. From a palaeogeographical point of view, the External Subbetic is closer to the Iberian Continent than the Median Subbetic, in positions that clearly belong to pelagic environments and where it must have been more difficult for continental inflows to reach. In the case of the PEL section, where the sedimentation rate was higher (0.04 mm/ka), it was located in the most distal position and probably affected by Hispanic Corridor currents. The higher sedimentation rate and input of sediment from currents are the factors that explain this enhanced sedimentation rate. Moreover, the trace fossil assemblage dominated by Macaronichnus , not recorded in the southern studied sections, have been related to contourite depositional setting (Miguez-Salas et al., 2020 ). According to Rebesco et al. ( 2014 ) and Eberli and Betzler ( 2018 ), most of the described large contourite deposits are located in the western side of the largest oceanic basins, as well as around circumpolar basins. In the case of the South Iberian Palaeomargin, it was located in the westernmost part of the Tethys Ocean, connecting with the Hispanic Corridor. This is congruent with the interpretation of the deposits of the Zegrí Formation in the PEL section as related to contour currents. Macaronichnus was related to sandy siliciclastic contourites (Miguez-Salas et al., 2022 ). This would be calcareous muddy contourites according to Rebesco et al. ( 2014 ) composing a carbonate drift as described by Reolid and Betzler ( 2018 ). The homogeneous and fine grain size as well as the dense bioturbation are not favorable for the identification of potential sedimentary structures related to currents such as lamination. Moreover, the dense accumulation of Macaronichnus indicates the abundance of nutrients in the environment (Miguez-Salas et al., 2020 ) and this trace fossil has been related to highly productive waters in connection with upwelling (Quiroz et al., 2019 ). 6. CONCLUSIONS Three stratigraphic sections of the Betic External Zones have been studied, two from the Median Subbetic, Sierra Pelada (PEL) and Puente Romano (PR) and another one from the External Subbetic, La Cerradura (CE), where the Jenkyns Event was recorded by previous authors. In these sections, the upper Pliensbachian materials and the transition to the lower Toarcian have been sampled level by level. In the PEL and PR sections these rocks have been dated using calcareous nannoplankton, considering the biostratigraphic scheme of Ferrerira et al. (2019); in the PEL section the NJT5b and NJT5c Subzones have been recognized, whose boundary is marked by the FO of Z. erectus . In the PR section, the NJT5a, NJT5b, and NJT5c Subzones were recognised, whose boundaries coincide with FO of L. crucicentralis and FO of Z. erectus , respectively. In the CE section, both ammonite and calcareous nannoplankton biostratigraphies previously established by Reolid et al. ( 2014 ) have been considered. The dominant upper Pliensbachian facies in the three sections consist of a marly limestone - marl alternation. In both PEL and PR sections these same facies have been dated as lower Toarcian, but in the CE section, this interval is represented by marls, in which Reolid et al. ( 2014 ) identified the Jenkyns Event. In the PEL section, Macaronichnus ichnofossils predominate. In the PR and CE sections, the ichnoassemblages are dominated by Planolites , Thalassinoides and Chondrites . It can help to interpret that the facies and ichnofacies observed were generated in hemipelagic marine environments influenced by continental sediments, as reflected in the clay contents studied by previous authors. The analysis of the correlation between δ 13 C and δ 18 O in each of the sections considered and of these isotopic ratios with Sr and with Fe/Ca and Sr/Ca, respectively, show low or very low correlations, with values of the coefficient of determination (R 2 ) lower than 0.5; moreover, the Z factor presents values higher than 120 in the three sections, indicating a clear marine origin of the rocks studied. These parameters indicate that the geochemical signal has not been modified by diagenesis and can be considered to be of primary origin. In the PEL and PR sections, the δ 13 C and δ 18 O ratios do not allow to clearly identify isotopic events during the late Pliensbachian, except for the transition to the early Toarcian, where the Pliensbachian - Toarcian Boundary Event (PTBE) could be recognized. In the CE section, where the Jenkyns Event was recorded, the PTBE is not clear the recognition of this event. The proxies used to study detritism (Zr/Rb, Sr/Cu, CIA and C-value) and to establish palaeoclimatic changes in the time interval studied show trends contrary to those detected in other sections from the Tethyan Domain and even among the sections studied here. The geochemical signals, facies, microfacies and inchnofossil data have been interpreted as the result of the opening of the Hispanic Corridor, associated with the Central Atlantic rifting stage, which favored the mixing of Panthalassa and Tethys seawaters, also establishing a system of currents towards Boreal domains. Extensional tectonics, which affected the South Iberian Palaeomargin, favored the development of half grabens with important differential subsidence, especially during the NJT5b nannofossil Subzone (Emaciatum Zone, latest Pliensbachian). In addition, a possible by-pass effect of the established marine circulation system could transport sediments deposited in these half-grabens to other marine domains. This effect is clear in the PEL section (Median Subbetic), where the trace fossil assemblage, dominated by Macaronichnus and not recorded in the other two studied sections, have been related to contourite depositional setting. Considering the palaeogeographic position of the South Iberian Palaeomargin, in the westernmost part of the Tethys Ocean, and connected to the Hispanic Corridor, the existence of these contourite currents could have really occurred. 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Global and Planetary Change , 185 , 1030096. Schöllhorn, I., Adatte, T., Charbonier, G., Mattioli, E., Spangenberg, J. E., & Föllmi, K. B. (2020b). Pliensbachian environmental perturbations and their potential link with volcanic activity: Swiss and British geochemical records. Sedimentary Geology , 406 , 105665. Silva, R. L., Rühl, M., Barry, C., Reolid, M., & Ruebsam, W. (2021). Pacing of late Pliensbachian and early Toarcian carbon cycle perturbation 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. Simo, V., & Reolid, M. (2021). Palaeogeographical homogeneity of trace-fossil assemblages in Lower Jurassic spotted marls and limestones: comparison of the Western Carpathians and the Betic Cordillera. Geological Society London Special Publications , 514 , 185–211. Storm, M. S., Hesselbo, S. P., Jenkyns, H. C., & Gorbanenko, O. (2020). Orbital pacing and secular evolution of the Early Jurassic carbon cycle. Pnas , 117 (8), 3974–3982. https://doi.org/10.1073/pnas.1912094117 . Suan, G., Mattioli, E., Pittet, B., Lécuyer, C., Suchéras-Marx, B., Duarte, L. V., Philippe, M., Reggiani, L., & Martineau, F. (2010). Secular environmental precursors to Early Toarcian (Jurassic) extreme climate changes. Earth and Planetary Science Letters , 290 , 448–458. Swart, P. K., & Oehlert, A. M. (2018). Revised interpretations of stable C and O patterns in carbonate rocks resulting from meteoric diagenesis. Sedimentary Geology , 364 , 14–23. Vera, J. A. (2001). Evolution of the southern Iberian continental margin. In P. A. Ziegler, W. Cavazza, A. H. F. Robertson, & S. Crasquin-Soleau (Eds.), Peri-Tethys Memoir 6: Peri-Tethyan Rift/Wrench Basins and Passive Margins (Vol. 186, pp. 109–143). Memoires du Museum National d’Histoire Naturelle Paris. Vera, J. A. (Ed.). (2004). Geología de España . SGE-IGME. Wignall, P. B., Newton, R. J., & Little, C. T. S. (2005). The timing of paleoenvironmental change and cause-and-effect relationships during the Early Jurassic mass extinction in Europe. American Journal of Sciences , 305 , 1014–1032. Zhao, Z., Zhao, J., Wang, H., Liao, J., & Liu, C. (2007). Distribution characteristics and applications of trace elements in Junggar Basin. Natural Gas Exploration and Development , 30 , 30–33. Tables Table 1 is available in the Supplementary Files section. Supplementary Files Table1.docx Table 1. Distribution chart of the calcareous nannofossils identified at Sierra Pelada (PEL) section, with the results obtained from the semiquantitative analyses. Calcareous nannofossil zones and subzones identified in this work are indicated. Main events are written in bold. Assemblage abundance classes: A = abundant (10-15 specimens in each field of view), C = common (1-10 specimens in each field of view), F = few (1 specimen in 1-10 field/s of view), R = rare (1 specimen in 11-100 fields of view), VR = very rare (1 specimen in more than 101 fields of view). Species abundance classes: A = abundant (1-5 specimens in each field of view), C = common (1 specimen in 2-10 fields of view), F = few (1 specimen in 10-30 fields of view), R = rare (1 specimen in 31-100 fields of view), VR = very rare (1 specimen in more than 101 fields of view). Preservation classes: G = good (the majority of the specimens show their diagnostic characteristics and only some of them are slightly etched and/or overgrown), M = moderate (the majority of the specimens are recognizable, even if some of them are etched and/or overgrown and/or fragmented), B = poor (the majority of the specimens are heavily etched or/and overgrown and/or fragmented and the identification of the species is sometimes difficult), VB = very poor (only a few specimens are recognizable). Cite Share Download PDF Status: Published Journal Publication published 18 Oct, 2024 Read the published version in Journal of Iberian Geology → Version 1 posted Reviewers agreed at journal 08 Apr, 2024 Reviewers invited by journal 03 Apr, 2024 Editor invited by journal 31 Mar, 2024 Editor assigned by journal 29 Mar, 2024 First submitted to journal 29 Mar, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4182071","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":287047598,"identity":"6d7ce4e7-a148-40b8-a1b4-383f1638c9ed","order_by":0,"name":"Luis M. Nieto","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAw0lEQVRIiWNgGAWjYBACPiA+AMRyEIoYwAbWksBgTJoWBqCWxAaiHcYmdvbggY8/bNI3HDz88HEBg409YS3SeQkHZySk5W44cMzYeAZDGmHr2KRzDA7zJBwGajlgJs3DcDiBCFuAWv4kHE43OHD8+28ehv/EOAyohSHhcILBgTNmzDwMBxiJctjBnrQ0w5kHzhRL8xgkE/YLv3SO8YcfNjbyfDeOb/zMU2FH2GEIIHEASBiQoAFoH0EXjYJRMApGwUgFAKHwPVF9gVW6AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-9907-2455","institution":"University of Jaén: Universidad de Jaen","correspondingAuthor":true,"prefix":"","firstName":"Luis","middleName":"M.","lastName":"Nieto","suffix":""},{"id":287047599,"identity":"8c1cb03d-b37d-463c-b5a0-ef82da2ee5b5","order_by":1,"name":"Chaima Ayadi","email":"","orcid":"","institution":"University of Jaén: Universidad de Jaen","correspondingAuthor":false,"prefix":"","firstName":"Chaima","middleName":"","lastName":"Ayadi","suffix":""},{"id":287047600,"identity":"4a79d579-9e48-4263-ac4c-4b5279eda6cb","order_by":2,"name":"Agela Fraguas","email":"","orcid":"","institution":"Rey Juan Carlos University: Universidad Rey Juan Carlos","correspondingAuthor":false,"prefix":"","firstName":"Agela","middleName":"","lastName":"Fraguas","suffix":""},{"id":287047601,"identity":"1d55e0d7-d90f-4a8a-b530-e6021f94af44","order_by":3,"name":"José Miguel Molina","email":"","orcid":"","institution":"University of Jaén: Universidad de Jaen","correspondingAuthor":false,"prefix":"","firstName":"José","middleName":"Miguel","lastName":"Molina","suffix":""},{"id":287047602,"identity":"47f7547a-6b87-45f9-a012-4133e8d45b94","order_by":4,"name":"Matías Reolid","email":"","orcid":"","institution":"University of Jaén: Universidad de Jaen","correspondingAuthor":false,"prefix":"","firstName":"Matías","middleName":"","lastName":"Reolid","suffix":""}],"badges":[],"createdAt":"2024-03-28 11:58:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4182071/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4182071/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s41513-024-00254-w","type":"published","date":"2024-10-18T15:57:46+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54278268,"identity":"1c544ef1-4987-4664-8095-f595caa560a7","added_by":"auto","created_at":"2024-04-08 08:22:51","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3029053,"visible":true,"origin":"","legend":"\u003cp\u003eGeographical and geological setting. A. Location of the Betic Cordillera in the South of Spain. B. Geological sketch of the Betic Cordillera with location of the stratigraphic sections studied (CE: La Cerradura; PR: Puente Romano; PEL: Sierra Pelada). C. Palaeogeographic sketch of the Pliensbachian with the location of the South Iberian Palaeomargin and the Hispanic Corridor (modified from Nieto et al., 2023).\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/d8dcf40e585e9c18f2709148.jpg"},{"id":54278264,"identity":"d6d84351-e885-48b9-ba82-00cdf3a1d0d6","added_by":"auto","created_at":"2024-04-08 08:22:51","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2661996,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of the stratigraphic sections considered in this paper. For each section the d\u003csup\u003e13\u003c/sup\u003eC (V-PDB in ‰) and d\u003csup\u003e18\u003c/sup\u003eO (V-PDB in ‰) curves with indication of average value are represented.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/255061241bfeadf4f941a905.jpg"},{"id":54278266,"identity":"0c2ca670-ff1f-42f5-a79f-2902b8ea6269","added_by":"auto","created_at":"2024-04-08 08:22:51","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2562223,"visible":true,"origin":"","legend":"\u003cp\u003eBio- and chrono- stratigraphic diagram for the Lower Jurassic (Pliensbachian-lower Toarcian) form the data obtained in the stratigraphic sections considered in this paper. The numerical ages and the Tethyan Ammonites zones are from Hesselbo et al. (2020a). The Tethyan calcareous nannofossils are from Ferreira et al. (2019) and Mattioli and Erba (1999). The unconformities R1 to R5 are from Nieto et al. (2023).\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/fd220f008d0b8d95e759749a.jpg"},{"id":54278759,"identity":"7285c57b-9c51-46e5-93b5-7b0bafb4104f","added_by":"auto","created_at":"2024-04-08 08:30:51","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":4623613,"visible":true,"origin":"","legend":"\u003cp\u003eField view of the studied sections. A. Top of the Gavilán Formation in the Sierra Pelada (PEL) section (Median Subbetic). B. Lower part of the Zegrí Formation in the PEL section (Median Subbetic). C. Detail of the stratigraphic surface of a bed located in the lowermost Zegrí Formation (upper Pliensbachian, PEL section) with abundant\u003cem\u003e Macaronichnus\u003c/em\u003e (Mac) and \u003cem\u003eThalassinoides\u003c/em\u003e, the last one densely bioturbated by \u003cem\u003ePhycosiphon \u003c/em\u003e(Phy). D. Thick bedding in the top of the Gavilán Formation at the Puente Romano (PR) section (Median Subbetic), arrows point to black chert nodules. E. Marly-and marly limestone alternation in the lower part of the Zegrí Formation at the PR section (Median Subbetic). F. Marl and marly limestone rhythmite and overlying dark marls from the La Cerradura (CE) section (External Subbetic) with indications of the boundaries between Pliensbachian/Toarcian (Pli/Toa) and Polymorphum/Serpentinum zones (Pol/Ser) of the lower Pliensbachian.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/7336424c2267724a07570938.jpg"},{"id":54278758,"identity":"cbfeac5f-ad38-43d2-aa77-e317af759c4f","added_by":"auto","created_at":"2024-04-08 08:30:51","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":4757141,"visible":true,"origin":"","legend":"\u003cp\u003eMicrofacies of the studied upper Pliensbachian-lower Toarcian sedimentary rocks of the Subbetic. A. Microfacies of the top of Gavilán Formation with \u003cem\u003eThalassinoides\u003c/em\u003e densely bioturbated by \u003cem\u003ePhycosiphon\u003c/em\u003e (Phy), PEL section. B. Detail of microfacies packstone of peloids, radiolarians (Rd) and sponge spicules (Sp) of the Zegrí Formation, PEL section. C. Packstone of radiolarians from the Zegrí Formation in the PR section. D. Specimen of ammonite (Amm) of the packstone of radiolarians from the Zegrí Formation at PR section. E. Mudstone to wackestone with trace fossils of \u003cem\u003eChondrites\u003c/em\u003e (Ch) from the Zegrí Formation at CE section. F. Mudstone to wackestone with abundant coal grains (dark grains), specially concentrated in the dark areas corresponding to trace fossils, Zegrí Formation, CE section.\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/e6406b49176edc9f8cdab6ac.jpg"},{"id":54278270,"identity":"1c0b67ce-9ffa-4a0c-aac1-ad7ec3affefc","added_by":"auto","created_at":"2024-04-08 08:22:51","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2419418,"visible":true,"origin":"","legend":"\u003cp\u003eExamples of ichnofossils in samples from the PR section (A, B), PEL section (C, D), and CE section (E).\u003c/p\u003e","description":"","filename":"Figure6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/24138aaae2b0caeb5410c3d1.jpg"},{"id":54278271,"identity":"117708e9-2820-410a-b371-64e20e3db53b","added_by":"auto","created_at":"2024-04-08 08:22:51","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2350165,"visible":true,"origin":"","legend":"\u003cp\u003eGeochemical proxies of detritism from Sierra Pelada (PEL) section.\u003c/p\u003e","description":"","filename":"Figure7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/c764e4f2dad8a6d5cc01f236.jpg"},{"id":54278760,"identity":"a38c4b89-0ac1-4223-9a40-95e81e180eaa","added_by":"auto","created_at":"2024-04-08 08:30:52","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":2200913,"visible":true,"origin":"","legend":"\u003cp\u003eGeochemical proxies of detritism from Puente Romano (PR) section.\u003c/p\u003e","description":"","filename":"Figure8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/12c397c53c19d1354ab675c6.jpg"},{"id":54278272,"identity":"4ce92605-2dad-4115-9bba-b72eb98dccc9","added_by":"auto","created_at":"2024-04-08 08:22:51","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":2278165,"visible":true,"origin":"","legend":"\u003cp\u003eGeochemical proxies of detritism from La Cerradura (CE) section.\u003c/p\u003e","description":"","filename":"Figure9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/3e60fd9b6ff867f949744c6d.jpg"},{"id":54278273,"identity":"209d6196-bc04-417b-96be-62aad75d9257","added_by":"auto","created_at":"2024-04-08 08:22:52","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":2074715,"visible":true,"origin":"","legend":"\u003cp\u003eCross-plots of d\u003csup\u003e18\u003c/sup\u003eO versus d\u003csup\u003e13\u003c/sup\u003eC (V-PDB in ‰) for each stratigraphic sections studied with expression of correlation equation and the values of the coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e). In each plot, N means the number of samples analyzed.\u003c/p\u003e","description":"","filename":"Figure10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/5888b8bbdaeb308c4bb73e31.jpg"},{"id":54278275,"identity":"fd4fefd1-cba3-488d-8194-e9bfa829eb43","added_by":"auto","created_at":"2024-04-08 08:22:52","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":1115092,"visible":true,"origin":"","legend":"\u003cp\u003eCross-plots of diagenetic elements, including Sr (in ppm) versus d\u003csup\u003e13\u003c/sup\u003eC and the Fe/Ca and Sr/Ca ratios versus d\u003csup\u003e18\u003c/sup\u003eO for each one of the stratigraphic sections studied. For each diagram the correlation equation and the coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e) is shown. The number of samples in each section is shown in the figure 10, PEL: N = 72; PR: N = 49; CE: N = 34.\u003c/p\u003e","description":"","filename":"Figure11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/442aa4745f6d1c903c014a41.jpg"},{"id":54278274,"identity":"9bedb7ee-fd10-41d1-855f-f5dcbc6c0dcc","added_by":"auto","created_at":"2024-04-08 08:22:52","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":794125,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the range of variation of d\u003csup\u003e13\u003c/sup\u003eC (V-PDB in ‰) and d\u003csup\u003e18\u003c/sup\u003eO (V-PDB in ‰) in the three sections considered in this paper (CE: La Cerradura section; PR: Puente Romano section; and PEL: Sierra Pelada section) with the ranges of variation of these same isotope ratios in other Tethyan sections where materials of the same age as those studied in this research are recorded.\u003c/p\u003e","description":"","filename":"Figure12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/980d1d1809233e1167fc0a0e.jpg"},{"id":54278277,"identity":"7b0dd714-3eb1-4932-a3fb-9f0942da3498","added_by":"auto","created_at":"2024-04-08 08:22:52","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":2372837,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of d\u003csup\u003e13\u003c/sup\u003eC curves of the sections considered in this paper with the curve of the Peniche section (Fantasia et al., 2019) and the Amellago section (Bodin et al., 2016). The possible location of the Pliensbachian-Toarcian Boundary Event (PTBE) in the sections studied in this paper is indicated from their position on the reference d\u003csup\u003e13\u003c/sup\u003eC curves.\u003c/p\u003e","description":"","filename":"Figure13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/478099265442dd6365966e88.jpg"},{"id":67149657,"identity":"53b52b2e-c2d6-4108-8e19-61242bf693b6","added_by":"auto","created_at":"2024-10-21 16:13:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":35121480,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/c0abff9a-a44f-4424-ad5b-19db03e3ba20.pdf"},{"id":54278265,"identity":"ceb5a654-f5e9-482f-a39c-ea3b70a52d74","added_by":"auto","created_at":"2024-04-08 08:22:51","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":33808,"visible":true,"origin":"","legend":"\u003cp\u003eTable 1. Distribution chart of the calcareous nannofossils identified at Sierra Pelada\u003cstrong\u003e \u003c/strong\u003e(PEL) section, with the results obtained from the semiquantitative analyses. Calcareous nannofossil zones and subzones identified in this work are indicated. Main events are written in bold.\u003c/p\u003e\n\u003cp\u003eAssemblage abundance classes: A = abundant (10-15 specimens in each field of view), C = common (1-10 specimens in each field of view), F = few (1 specimen in 1-10 field/s of view), R = rare (1 specimen in 11-100 fields of view), VR = very rare (1 specimen in more than 101 fields of view).\u003c/p\u003e\n\u003cp\u003eSpecies abundance classes: A = abundant (1-5 specimens in each field of view), C = common (1 specimen in 2-10 fields of view), F = few (1 specimen in 10-30 fields of view), R = rare (1 specimen in 31-100 fields of view), VR = very rare (1 specimen in more than 101 fields of view).\u003c/p\u003e\n\u003cp\u003ePreservation classes: G = good (the majority of the specimens show their diagnostic characteristics and only some of them are slightly etched and/or overgrown), M = moderate (the majority of the specimens are recognizable, even if some of them are etched and/or overgrown and/or fragmented), B = poor (the majority of the specimens are heavily etched or/and overgrown and/or fragmented and the identification of the species is sometimes difficult), VB = very poor (only a few specimens are recognizable).\u003c/p\u003e","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-4182071/v1/991039ae3e277dad89b392b5.docx"}],"financialInterests":"","formattedTitle":"\u003cp\u003eEnvironmental Conditions in the Pre-jenkyns Event Times (Late Pliensbachian – Early Toarcian) in the Southiberian Palaeomargin (Betic External Zones, Southern Spain)\u003c/p\u003e","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eThe Pliensbachian was a very dynamic Jurassic stage, in which very important changes took place: 1) palaeogeographic (opening of the Hispanic Corridor; Dera et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009a\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003eb\u003c/span\u003e; Krencker et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; and references herein), 2) palaeoclimatic (waxing and waning of ice caps as a consequence of declines and rises in seawater temperature; G\u0026oacute;mez et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Price et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Bougeault et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Krencker et al, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; and references herein) and 3) palaeoceanographic (modification of the marine current system in the Tethys, Boreal and Central Atlantic; Dera et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009a\u003c/span\u003e; Bodin et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, for example). All these events induced shifts of different orders in global seawater chemistry (Price et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). While long-lived events have been associated with variations in CO\u003csub\u003e2\u003c/sub\u003e concentration, short-lived changes are difficult to explain (e.g., Price et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBased on isotopic data, the early Pliensbachian has been interpreted as a warming interval (ranging from 16 to 18\u0026ordm;C in the Asturian Basin of North Iberia according to G\u0026oacute;mez et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). This climatic trend covered the Ibex and Davoei zones and the earliest part of the Lavinianum Zone. A subsequent cooling occurred during the late Pliensbachian that may have promoted the formation of high-latitudinal glaciation at their most extensive in the latest Pliensbachian to earliest Toarcian (Dera et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Korte and Hesselbo, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; G\u0026oacute;mez et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Ruebsam et al., \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ruebsam and Schwark, \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Latest Pliensbachian to early Toarcian equatorial sea surface temperatures fluctuated between 22 and 32\u0026deg;C, attesting to highly variable and contrasting climate conditions (Ruebsam et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e). During the early Toarcian, related to the Jenkyns Event carbon cycle perturbation, sea water temperature in the tropical to subtropical latitudes raised by about 10\u0026deg;C (Ruebsam et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e). Sea-level changes were related to these climatic changes. Therefore, the end Pliensbachian is characterized by a sea-level fall with subsequent flooding and a negative Carbon Isotope Excursion (CIE) related to the Pliensbachian-Toarcian boundary event (Bodin et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Fantasia et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Rodrigues et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Fleischmann et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBougeault et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), based on the study of the kaolinite/illite ratio, recognized a decrease in the runoff occurred at the end of Pliensbachian stage, considering that a cold stage, possibly associated with cold ice cap growth, has also been recorded in this time interval (G\u0026oacute;mez et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Bougeault et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Krencker et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Bodin et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; among others). However, Bougeault et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) also recognised minor oscillations in kaolinite/illite ratio values during the late Pliensbachian interpreted as oscillations in runoff.\u003c/p\u003e \u003cp\u003eA factor to consider in the development of the climate changes during the Pliensbachian is the modification of the oceanic current system due to palaeogeographic changes (tectonically driven) and sea level variations (Dera et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009a\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003eb\u003c/span\u003e; Price et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Prior to the opening of the Hispanic Corridor (Davoei-Lavinianum zones; early-late Pliensbachian transition), isotopic data support the idea of a flow from the Boreal domains into the Tethys Ocean via the Viking Corridor (Dera et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009a\u003c/span\u003e). The opening of the Hispanic Corridor led to a change in the oceanic circulation system, such that a current develops through this palaeogeographic feature connecting Panthalassa with the Tethys. On the other hand, the formation of this corridor also favoured the establishment of a current from the Tethys and Panthalassa Oceans towards the Boreal Domain.\u003c/p\u003e \u003cp\u003eThe opening of the Hispanic Corridor was associated with the rifting process and the beginning of the formation of the Central Atlantic. This developed a major system of tilted blocks and small, generally, shallow sub-basins. In addition, in connection with the rifting, an increase in volcanic activity related to the Central Atlantic Magmatic Province and the Karoo-Ferrar Large Igneous Province (LIP) took place (Franceschi et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Sch\u0026ouml;llhorn et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003eb\u003c/span\u003e; Krencker et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; among others).\u003c/p\u003e \u003cp\u003eDuring the Pliensbachian, the South Iberian Palaeomargin, was affected by these tectonic, palaeoclimatic and palaeoceanographic processes according to its palaeogeographic position (Vera, \u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Ruiz-Ortiz et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; among others). As a consequence of rifting and the opening of the Hispanic Corridor, the shallow carbonate platform developed during the Hettangian and Sinemurian (represented by the Gavil\u0026aacute;n Formation) collapsed. Numerous tilted blocks were formed, with very different bathymetries in which the sedimentary record was very changeable both in sedimentation rate and facies, with blocks in which wide hiatuses developed and others with more continuous sedimentary record (Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The sediments deposited were marly limestones and marls with a clear hemipelagic and pelagic nature (represented by the Zegr\u0026iacute; Formation). During the late Pliensbachian, alternating marly limestones and marl predominate, whereas, coinciding with the beginning of the Toarcian, mainly marly sedimentation taken place. In addition, the chemistry of its waters must have undergone changes due to modifications in the oceanic circulation system. The progressive opening of the Hispanic Corridor (early-late Pliensbachian transition), favoured the developing of a current pattern affecting the South Iberian Palaeomargin from Panthalassa and from Tethys towards Boreal domains (e.g., Dera et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009a\u003c/span\u003e; Price et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The chemistry of the seawaters would also be influenced by the contributions of continental waters, which would reflect the weathering processes that affected the Iberian massif.\u003c/p\u003e \u003cp\u003eThe record of the oxygen depleted conditions (Toarcian Oceanic Anoxic Event or T-OAE) related to the Jenkyns Event is very irregular in the South Iberian Palaeomargin, being confined to small, more subsiding pelagic basins where locally suboxic facies developed (e.g. Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As in other areas of the Tethys where the T-OAE is recorded, this event and the environmental conditions that prevailed during its development are well known in the South Iberian Palaeomargin (e.g. Rodr\u0026iacute;guez-Tovar and Uchman, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Rodr\u0026iacute;guez-Tovar and Reolid, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Rodrigues et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ruebsam et al., \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e; Kovacs et al., 2024). However, the environmental changes that preceded the development of this event need to be further investigated. This also happens for the South Iberian Palaeomargin. The aim of this paper is to analyse the environmental conditions at this palaeomargin in the time just before the Jenkyns Event (late Pliensbachian-earliest Toarcian). The influence of water runoff on sedimentation occurring in the South Iberian Palaeomargin, mainly during the late Pliensbachian and the Pliensbachian-Toarcian transition, will be discussed. This will bring us some light about the prevailing climatic conditions that conditioned continental weathering. For this purpose, a multi-proxy analysis of different detrital ratios, such as Zr/Rb, Sr/Cu, CIA and C-value, will be carried out on samples taken from three stratigraphic sections with Pliensbachian and lower Toarcian records, according to calcareous nannofossil biostratigraphy, from Subbetic (Betic Cordillera).\u003c/p\u003e"},{"header":"2. GEOLOGICAL SETTING","content":"\u003cp\u003eThe studied sections belong to the Lower Jurassic of the Subbetic, in the External Zones of the Betic Cordillera (SE Spain), which is the westernmost Alpine Mediterranean Chain, being 600 km long and 200 km wide (Garc\u0026iacute;a-Hern\u0026aacute;ndez et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1980\u003c/span\u003e). The Betic Cordillera is subdivided into the Internal Zones and the External Zones. The External Zones represent the South Iberian Palaeomargin that developed during the Mesozoic in the westernmost Tethys, approximately at 20\u0026ordm; N during the Early Jurassic (Bassoullet et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1993\u003c/span\u003e) and can be further divided into Prebetic (more proximal areas) and Subbetic (more distal areas) domains (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The Subbetic is subdivided from north to south in Intermediate Domain, External, Median, and Internal. The studied sections are located in the External and Median Subbetic (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The Lower Jurassic of the Subbetic is composed by the Gavil\u0026aacute;n and Zegr\u0026iacute; formations. The Gavil\u0026aacute;n Formation (Hettangian-lower Pliensbachian) is made by platform carbonates (crinoidal limestones, oolitic and oncolitic limestones, cherty limestones and dolostones) and the Zegr\u0026iacute; Formation (upper Pliensbachian-lower Bajocian) is composed by pelagic and hemipelagic deposits (marly limestones and marls and marly Ammonitico Rosso). Both formations are limited at the base by the intra-Pliensbachian discontinuity. The thickness of the Zegr\u0026iacute; Formation ranges from just a few metres to 500 m in the External and Median Subbetic (Nieto et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). The lower part of the Zegr\u0026iacute; Formation (Pliensbachian-lower Toarcian) is made up of marly limestone-marl rhythmites and marls. The middle-upper Toarcian is commonly represented by cherty limestones and red nodular marly limestones (marly Ammonitico Rosso facies) (Molina, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThree stratigraphic sections have been considered, Sierra Pelada (PEL), Puente Romano (PR) and La Cerradura (CE) (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The PEL and PR sections are located in the Median Subbetic and were previously studied by Gonz\u0026aacute;lez-Donoso et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1971\u003c/span\u003e) and Jim\u0026eacute;nez (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1986\u003c/span\u003e) in terms of ammonite biostratigraphy. The CE section, attributed to the External Subbetic, whose ammonites were initially studied by Braga (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1983\u003c/span\u003e) and Jim\u0026eacute;nez (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1986\u003c/span\u003e), and later investigated in detail by Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and Silva et al. (\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) among others, from an ichnological and geochemical point of view.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Sierra Pelada (PEL) section is located to the north of Sierra Pelada ravine, 200 m NE of the Cortijo del Madro\u0026ntilde;al, province of Granada (section bottom coordinates: 37\u0026ordm; 20\u0026rsquo; 24.3\u0026rdquo; N; 3\u0026ordm; 53\u0026rsquo; 44.6\u0026rdquo; W). The Puente Romano (PR) section is located near the Roman bridge on the Colomera river, 500 m to the NE of the Colomera village, province of Granada (section bottom coordinates: 37\u0026ordm; 22\u0026rsquo; 36.6\u0026rdquo; N; 3\u0026ordm; 42\u0026rsquo; 31.4\u0026rdquo; W). La Cerradura (CE) section is in the E trench of motorway A-44, km 56.8, 15 km S of Ja\u0026eacute;n city (section bottom coordinates: 37\u0026ordm; 41\u0026rsquo; 51.9\u0026rdquo; N; 3\u0026ordm; 38\u0026rsquo; 0.1\u0026rdquo; W).\u003c/p\u003e \u003cp\u003eIn the PEL and PR sections there is a good record of the upper part of the Gavil\u0026aacute;n Formation, dated as lower Pliensbachian (Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e and references in this paper) and its contact with the Zegr\u0026iacute; Formation, where the upper Pliensbachian and lower Toarcian are recorded. In the CE section there is a good upper Pliensbachian \u0026ndash; lower Toarcian record, including the materials in which the T-OAE was detected (Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Ruebsam et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003eb\u003c/span\u003e).\u003c/p\u003e"},{"header":"3. MATERIALS AND METHODOLOGY","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Fieldwork and facies analysis\u003c/h2\u003e \u003cp\u003eThe fieldwork in the studied sections was focused on the analyses of sedimentary structures, trace fossils, recovery of fossil macroinvertebrates and sampling for subsequent analyses of microfacies, geochemistry and calcareous nannoplankton.\u003c/p\u003e \u003cp\u003eWe have used for the CE section the same 34 samples of the original work of Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Both the PEL and PR sections were sampled on a bed by bed; 72 samples from PEL section and 49 samples from PR section. Samples from indurated marly limestones and limestones were selected for preparation of thin sections and polished slabs. Samples consisting of soft marls were selected for analyses of stable isotopes (C and O) and elemental inorganic geochemistry. For the microfacies studies, a Leica M205C binocular microscope was used to study a total of 121 thin sections. Analysis of trace fossils in the field was completed with the preparation of 22 polished slabs.\u003c/p\u003e \u003cp\u003eThe reference ammonite biostratigraphy used to date the materials of the studied sections is that of Braga (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1983\u003c/span\u003e) and Jim\u0026eacute;nez (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1986\u003c/span\u003e) for the South Iberian Palaeomargin, while for calcareous nannoplankton is that of Ferreira et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The study of calcareous nannoplankton was carried out in PEL and PR sections. The biostratigraphic framework of the CE section is based on ammonite record (Braga, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Jim\u0026eacute;nez, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), and on the calcareous nannoplankton (Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), whose used the biostratigraphy of calcareous nannoplankton from Mattioli and Erba (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e1999\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Calcareous nannofossils\u003c/h2\u003e \u003cp\u003eA total of 23 and 21 smear slides were prepared from the original samples collected from the PEL and the PR sections, respectively. In both cases, the standard preparation technique of Bown and Young (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1998\u003c/span\u003e) were used, and semi-quantitative analyses were carried out with a Leica DMLP light microscope and a Leica DFC 420 digital camera at 1250x magnification. For the PEL samples, four transverses were analyzed per sample, resulting in more than 500 fields of view, to identify rare or very rare species. Total abundance and degree of preservation of calcareous nannofossil assemblages, and the relative abundances of each species identified were obtained for each sample (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for further details), following the approach of Perilli et al. (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) and Fraguas et al. (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). \u003cem\u003eMitrolithus\u003c/em\u003e spp. and \u003cem\u003eCrepidolithus\u003c/em\u003e spp. include all the specimens belonging to both genera recognized in lateral view or those that cannot be identified taxonomically at species level, since they are lacking their diagnostic characters. The appendix A includes all the calcareous nannofossil species mentioned within the text in alphabetical order.\u003c/p\u003e \u003cp\u003eFrom the 21 smear slides prepared from the samples taken in PR section, a total of 2000 fields of view were analyzed per sample for semiquantitative analysis, in order to identify those species very rare. The results obtained were included in Nieto et al. (\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Elemental and C-O isotope geochemistry\u003c/h2\u003e \u003cp\u003eThe elemental analysis of the samples of the three sections considered in this paper were obtained in the Centro de Instrumentaci\u0026oacute;n Cient\u0026iacute;fica (CIC) of the Universidad de Granada. Whole-rock analyses of major elements were made using X-ray Fluorescence (XRF) in a Philips PW1040/10 spectrometer. Trace elements were analysed using an inductively coupled plasma-mass spectrometer (ICP-MS), the Perkin Elmer Sciex-Elan 5000.\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe C and O isotopes were analyzed from bulk samples from CE section by Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), PR section by Nieto et al. (\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) and PEL section in this paper. The 72 samples of the last section were analyzed at the Laboratory of the Scientific and Technological Centre (CCiT) of the University of Barcelona with a Finningan MAT 253 isotope ratio mass spectrometer with a Kiel IV carbonate analysis device (ThermoFisher Scientific). The isotope ratios obtained were referred to the VPDB standard notation in \u0026permil;. Analytical precision was kept between 0.01 and 0.05 for δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe Chemical Index Alteration (CIA) corrected for carbonate contents, was calculated according to the expression (1) from Nesbitt and Young (\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1989\u003c/span\u003e):\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$CIA=100 \\times \\frac{{Al}_{2}{O}_{3}}{{Al}_{2}{O}_{3}+ CaO+ {Na}_{2}O+ {K}_{2}O} \\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eTo analyze the influence of diagenesis in the primary geochemistry signal, the Z factor was used, calculated for each studied section according to the expression (2), given by Keith and Weber (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1964\u003c/span\u003e) and Babalola et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(Z=2.048(\\)\u003c/span\u003e \u003c/span\u003eδ\u003csup\u003e13\u003c/sup\u003eC + 50) + 0.498(δ\u003csup\u003e18\u003c/sup\u003eO + 50) (2)\u003c/p\u003e \u003cp\u003eThe C-value plot, proposed by Zhao et al. (\u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), was used to discriminate general climatic conditions throughout the deposition of the studied sediments. This parameter is calculated according to the next expression (3):\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$C-value = \\frac{\\sum \\left(Fe+Mn+Cr+Ni+V+Co\\right)}{\\sum \\left(Ca+Mg+Sr+Ba+K+Na\\right)} \\left(3\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIf C-value is comprised between 0 and 0.2, the climate is arid. If C-value is between 0.2 to 0.4, the climate is semiarid. When this parameter is in a range 0.4 to 0.6, the climate is semiarid to semimoist. The values in the range between 0.6 to 0.8, shown a semimoist climate. Finally, if the C-value is higher than 0.8, recorded a moist climate.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. RESULTS","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e4.1. Biostratigraphy and chronostratigraphy\u003c/h2\u003e \u003cp\u003eThe biostratigraphy and chronostratigraphy related to the boundary between the Gavil\u0026aacute;n and Zegr\u0026iacute; Formations have just been studied in detail by Nieto et al. (\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). These authors identified up to five discontinuities of hiatus with variable amplitude between them and between different stratigraphic sections.\u003c/p\u003e \u003cp\u003eAt the bottom of the PEL section, cherty limestones have been recognized, alternating with marls (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) attributed to the upper part of the Gavil\u0026aacute;n Formation. No features have been observed at the top of these limestones that would indicate the existence of a stratigraphic discontinuity. In the PR section, some limestones with cherts have been identified, which have been attributed to the upper part of the Gavil\u0026aacute;n Formation (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In this case, based on regional data, the hiatus associated with the discontinuity between the two formations has been considered to span the Ibex-Lavinianum zones (Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In the studied interval of the CE section there is no record of the Gavil\u0026aacute;n Formation. Consequently, Nieto et al. (\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) state that the top of the Gavil\u0026aacute;n Formation and the bottom of the Zegr\u0026iacute; Formation are heterochronous.\u003c/p\u003e \u003cp\u003eWith respect to the calcareous nannofossil biostratigraphy of the studied area, there are data from the CE and PR sections already published. At CE section (Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), the base of the NJT5b Subzone is marked by the first occurrence of \u003cem\u003eLotharingius sigillatus\u003c/em\u003e around the Solare/Elisa ammonite Subzone boundary of the Emaciatum ammonite Zone, and the boundary between the NJT5/NJT6 zones is based upon the first occurrence of \u003cem\u003eCarinolithus superbus\u003c/em\u003e around the Polymorphum/Serpentinum ammonite Zone boundary, considering the nannofossil biostratigraphic scheme proposed by Mattioli and Erba (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e1999\u003c/span\u003e) for the Tethyan Domain.\u003c/p\u003e \u003cp\u003eIn the PR section (Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), based upon the more recent biostratigraphic scheme of Ferreira et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) for the Western Tethys, the NJT5b Subzone has been identified based upon the FO of \u003cem\u003eL. crucicentralis\u003c/em\u003e within the upper Pliensbachian and NJT5c Subzone (lower part of the Polymorphum Zone) considering the FO of \u003cem\u003eZeugrhabdothus erectus\u003c/em\u003e, which enabled the approximation of the upper Pliensbachian/lower Toarcian boundary.\u003c/p\u003e \u003cp\u003eA total of 26 species belonging to 14 genera were identified in the 23 smear samples from PEL section (check Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for further details). Most of the samples belonging to the Gavil\u0026aacute;n Formation are barren or show a poor preservation, including only extremely rare specimens of \u003cem\u003eSchizosphaerella punctulata\u003c/em\u003e and \u003cem\u003eCalcivascularis jansae\u003c/em\u003e. This last is also the case for the lowermost samples of the Zegr\u0026iacute; Formation until sample PEL-46m. Excluding three samples (PEL-42, 27 and 13; Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), a considerable increase in both abundance and diversity, as well as a much better preservation, can be noted from sample PEL-45 up-section. They yield up to 16 different species (samples PEL-17 and 15) and are dominated by relatively well-preserved specimens of \u003cem\u003eSchizosphaerella puntulata, Calcivascularis jansae, Mitrolithus lenticularis\u003c/em\u003e and \u003cem\u003eLotharingius hauffii\u003c/em\u003e. Considering the biostratigraphic scheme proposed by Ferreira et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), a nannobiohorizon has been identified in the PEL section (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e): the first occurrence of \u003cem\u003eZeugrhabdothus erectus\u003c/em\u003e in sample PEL-20 (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This bioevent marks the boundary between the NJT5b/NJT5c subzones and helps to approach the Pliensbachian/Toarcian boundary.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e4.2. Facies analysis and ichnofacies\u003c/h2\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e4.2.1. Facies and microfacies analysis\u003c/h2\u003e \u003cp\u003eThe Sierra Pelada (PEL) section begins in the cherty limestones of the top of the Gavil\u0026aacute;n Formation (first 5 m; Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). The microfacies are wackestone of radiolaria and sponge spicule (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA) with \u003cem\u003eThalassinoides\u003c/em\u003e densely bioturbated by \u003cem\u003ePhycosiphon\u003c/em\u003e. There are also very small (less than 0.15 mm in size) crinoidal fragments and other unidentifiable small bioclasts. The siliceous radiolarian tests have been replaced by microcrystalline calcite, obscuring their textural details. The siliceous megasclere spicules, mainly monaxon, have also been dissolved, and their moulds are filled with granular calcite cement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe rest of the section (NJT5 Zone), spans around 50 m and is made up by marls and marly limestones of the Zegr\u0026iacute; Formation (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). The lower part of the Zegr\u0026iacute; Formation, densely bioturbated (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC) is dominated by limestone beds (first 13 m above the cherty limestones), followed by a thick interval of marls with carbonate upwards increasing sequences (around 25 m thick). The uppermost part of the studied section (within NJT5c Subzone, Polymorphum Zone, lower Toarcian) is composed by 12 m of marls and marly limestones alternation with progressive increase in carbonate content (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In PEL section, the microfacies differentiated for the Zegr\u0026iacute; Formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB) is a packstone of peloids, spicules and radiolaria with ostracods, calcispheres, benthic foraminifera (mainly \u003cem\u003eLenticulina\u003c/em\u003e) and some bioclasts. Small burrows are also observed in thin section, any times with iron oxides or hydroxides. Locally, a mudstone with scarce radiolaria and bioclasts could be detected. In these microfacies are also observed small burrows. The phytodetritus are locally abundant in darker stratigraphic intervals.\u003c/p\u003e \u003cp\u003eThe studied interval in the Puente Romano (PR) section (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) corresponds to the Zegr\u0026iacute; Formation and begins on the cherty limestones of the Gavil\u0026aacute;n Formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD) (Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The microfacies of the Gavil\u0026aacute;n Formation in this section are peloidal and bioclastic wackestone-packstone (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC, D). The peloids have an average size of 0.1 mm. The bioclasts are mainly crinoids, and secondarily sponge spicules, radiolarians, and thin-shelled bivalves (\u0026ldquo;filaments\u0026rdquo;). Less abundant there are also benthic foraminifera (\u003cem\u003eLenticulina\u003c/em\u003e), ostracods and calcispheres. The lower 7 m of the section (NJT5a Subzone) are made up by a limestones/marl alternation and above by an alternation of dark marls/marly limestones of the upper Pliensbachian-lowermost Toarcian (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE).\u003c/p\u003e \u003cp\u003eLa Cerradura (CE) section is formed by a lower part constituted by marl and marly limestone alternation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eF) (Emaciatum Zone, NJT5a and NJT5b subzones) and an upper part represented by a dark marls interval of the Serpentinum Zone (NJT6 Zone) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The microfacies are mudstone-wackestone with trace fossils (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eE), in which abundant coal grains are concentrated (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e4.2.2. Ichnofacies\u003c/h2\u003e \u003cp\u003eIn the PEL section (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC, D), the ichnoassemblage recorded in the top of the Gavilan Formation is characterized by abundant horizontal to oblique sinuous burrows corresponding to \u003cem\u003eMacaronichnus\u003c/em\u003e and secondarily \u003cem\u003eThalassinoides\u003c/em\u003e, \u003cem\u003ePlanolites\u003c/em\u003e, \u003cem\u003eChondrites\u003c/em\u003e, and \u003cem\u003eZoophycos\u003c/em\u003e. Other scarce trace fossil is \u003cem\u003eLamellaeichnus\u003c/em\u003e. In the Zegr\u0026iacute; Formation, the ichnoassemblage is similar with dominant \u003cem\u003eMacaronichnus\u003c/em\u003e densely packed. \u003cem\u003ePhycosiphon\u003c/em\u003e is very common burrowing within \u003cem\u003eThalassinoides\u003c/em\u003e sediment infilling. Secondary trace fossils are \u003cem\u003eThalassinoides\u003c/em\u003e, \u003cem\u003ePlanolites\u003c/em\u003e, \u003cem\u003eZoophycos\u003c/em\u003e and \u003cem\u003eChondrites\u003c/em\u003e, and less commonly \u003cem\u003eLamellaeichnus\u003c/em\u003e and \u003cem\u003ePalaeophycos\u003c/em\u003e. \u003cem\u003eMacaronichnus\u003c/em\u003e and \u003cem\u003ePhycosiphon\u003c/em\u003e are infilled with clear sediment. In the case of \u003cem\u003eMacaronichnus\u003c/em\u003e the mantle is comparatively darker than the surrounding sediment whereas the sediment infilling is clearer. The bioturbation index keeps very high in both formations in the PEL section ranging 3 to 5. The diversity is variable from 4 to 7 ichnogenera corresponding to the Cruziana ichnofacies. This diverse assemblage presents a good tiering with \u003cem\u003eMacaronichnus\u003c/em\u003e and \u003cem\u003eThalassinoides\u003c/em\u003e dominating the upper tier, and \u003cem\u003eZoophycos\u003c/em\u003e and \u003cem\u003eChondrites\u003c/em\u003e dominating the lower tier.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe ichnoassemblage of the PR section (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA, B) is similar to that described in the Zegr\u0026iacute; Formation of CE section by Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and Simo and Reolid (\u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Commonly the trace fossils present a sediment infilling darker than the surrounding sediment. Some trace fossils present iron-rich sediment. Dominant trace fossils are \u003cem\u003ePlanolites\u003c/em\u003e, \u003cem\u003eThalassinoides\u003c/em\u003e and \u003cem\u003eChondrites\u003c/em\u003e (both large and small ones). Secondary trace fossils, but locally abundant, are \u003cem\u003eLamellaeichnus\u003c/em\u003e, \u003cem\u003eTeichichnus\u003c/em\u003e and \u003cem\u003eZoophycos\u003c/em\u003e, and scarce \u003cem\u003ePalaeophycus\u003c/em\u003e and \u003cem\u003eTaenidium\u003c/em\u003e. The bioturbation index is commonly ranging from 2 to 3 and only decrease to 1 in the Pliensbachian/Toarcian boundary, where only scarce small \u003cem\u003eChondrites\u003c/em\u003e and \u003cem\u003ePlanolites\u003c/em\u003e are recorded. The number of ichnogenera in each level varies from 1 to 7 with lowest values located in the lower part of the NJT5a Subzone (upper Pliensbachian) and the top of the NJT5c Subzone (Polymorphum Zone, lower Toarcian). The lower part of the NJT5c Subzone records higher content of ferruginous trace fossils, principally \u003cem\u003eChondrites\u003c/em\u003e and \u003cem\u003ePlanolites\u003c/em\u003e. The trace fossils recorded in the PR section correspond to the Cruziana ichnofacies. The ichnoassemblage is relatively diverse and present a good tiering with \u003cem\u003ePlanolites\u003c/em\u003e and \u003cem\u003eThalassinoides\u003c/em\u003e dominating the upper tier, \u003cem\u003eLamellaeichnus\u003c/em\u003e and \u003cem\u003eTeichichnus\u003c/em\u003e as main representants of a middle tier, and, finally, \u003cem\u003eChondrites\u003c/em\u003e and \u003cem\u003eZoophycos\u003c/em\u003e dominating the lower tier.\u003c/p\u003e \u003cp\u003eFinally, the ichnoassemblage of CE section (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eE) was studied by Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), Reolid and Reolid (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and Simo and Reolid (\u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This is mainly composed by \u003cem\u003ePlanolites\u003c/em\u003e, \u003cem\u003eThalassinoides\u003c/em\u003e and \u003cem\u003eChondrites\u003c/em\u003e (both small and large) and secondarily by \u003cem\u003eLamellaeichnus\u003c/em\u003e, \u003cem\u003eTaeinidum\u003c/em\u003e, \u003cem\u003eTeichichnus\u003c/em\u003e and \u003cem\u003eTrichichnus\u003c/em\u003e. Other trace fossils such as \u003cem\u003eZoophycos\u003c/em\u003e and \u003cem\u003ePalaeophycus\u003c/em\u003e, recorded in the PR section (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA, B), or \u003cem\u003eMacaronichnus\u003c/em\u003e and \u003cem\u003ePhysosiphon\u003c/em\u003e recorded in PEL section (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC, D), are not present in CE section. In general, the bioturbation index and the diversity are similar to those of PR and lower than in PEL section, but decreasing in the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian). The assemblage corresponds to the Cruziana ichnofacies. The ichnoassemblage is relatively diverse in the marl and marly limestone rhythmite, with \u003cem\u003ePlanolites\u003c/em\u003e and \u003cem\u003eThalassinoides\u003c/em\u003e dominating the upper tier, \u003cem\u003eLamellaeichnus\u003c/em\u003e and \u003cem\u003eTeichichnus\u003c/em\u003e as main representants of a middle tier and, finally, small \u003cem\u003eChondrites\u003c/em\u003e dominating the lower tier. The bioturbation index is commonly ranging from 2 to 3, and decrease in the uppermost Pliensbachian and lower Toarcian where ranges from 1 to 2. The diversity is reduced in the beginning of the Toarcian, top of the marly limestone rhythmite (Polymorphum Zone, lower Toarcian) where \u003cem\u003eChondrites\u003c/em\u003e dominates. Only in the top of the Polymorphum Zone, large \u003cem\u003eChondrites\u003c/em\u003e turns very abundant and rich in organic matter (Reolid and Reolid, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The first meter of the dark marls of the Serpentinum Zone (coincident with the negative CIE of the Jenkyns Event) are barren of benthic macroinvertebrates and trace fossils (Baeza-Carratal\u0026aacute; et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The assemblage rapidly recovers initially with the record of \u003cem\u003eChondrite\u003c/em\u003es, and subsequently with \u003cem\u003ePlanolites\u003c/em\u003e and \u003cem\u003eTrichichnus\u003c/em\u003e (Simo and Reolid, \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.3. Geochemistry\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e4.3.1. δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO isotopes\u003c/h2\u003e \u003cp\u003eThe values of δ\u003csup\u003e13\u003c/sup\u003eC (\u0026permil; VPDB) in PEL section fluctuate between \u0026minus;\u0026thinsp;0.41\u0026permil; and 1.22\u0026permil;, (average 0.50\u0026permil;, σ\u0026thinsp;=\u0026thinsp;0.39). From the base of the stratigraphic section to meter 15, coinciding with the lowest rocks of the upper Pliensbachian in this section, the isotope ratio remains slightly above the average value (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), although it shows some fluctuations in the first five meters of the sequence and between meters 12.5 and 15 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Between meters 15 and 27, coinciding with the lower part of the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian), the marls are more abundant, in which there are many fluctuations, but always around the average. In the central part of the same subzone (between meters 27 and 30) a decrease of the isotope ratio values is observed, which varies between 0.50 and \u0026minus;\u0026thinsp;0.41. From meter 30 onwards, there is an increase in the value of the isotopic ratio (from \u0026minus;\u0026thinsp;0.41 to 0.53, obtained in meter 31). From this level to the top of the stratigraphic section, the δ\u003csup\u003e13\u003c/sup\u003eC again shows several oscillations in its values, with a decreasing deviation respect to the average in the NJT5c Subzone (lower part of the Polymorphum Zone) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe δ\u003csup\u003e18\u003c/sup\u003eO in the PEL section ranges between \u0026minus;\u0026thinsp;4.43 and \u0026minus;\u0026thinsp;2.25\u0026permil; (average \u0026minus;\u0026thinsp;3.52\u0026permil;, σ\u0026thinsp;=\u0026thinsp;0.59). As happened with the C isotope ratio, the δ\u003csup\u003e18\u003c/sup\u003eO shows, in general, values slightly above the average between the base of the section and meter 15 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), coinciding with the levels dated as lower part of the upper Pliensbachian. Coinciding with the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian), the values of this isotopic ratio are below the average, reaching the lowest values between meters 27 and 30, around the mid part of the NJT5b Subzone (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In the NJT5c Subzone, the δ\u003csup\u003e18\u003c/sup\u003eO starts to increase its value until it is slightly above the average value.\u003c/p\u003e \u003cp\u003eIn the PR section, the δ\u003csup\u003e13\u003c/sup\u003eC values in the bulk sample change between 0.47 and 1.45\u0026permil; (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) (average 1.11\u0026permil;, σ\u0026thinsp;=\u0026thinsp;0.17). In general, the values of this isotopic ratio show very little variations around the average value throughout the stratigraphic section, with no trend to be highlighted. Regards δ\u003csup\u003e18\u003c/sup\u003eO, the values range from \u0026minus;\u0026thinsp;2.76\u0026permil; to \u0026minus;\u0026thinsp;0.67\u0026permil; (average \u0026minus;\u0026thinsp;2.17\u0026permil;, σ\u0026thinsp;=\u0026thinsp;0.33). Although the complete stratigraphic sequence shows numerous small-range fluctuations, all they are around the average, with no clear trends (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the CE section the values of δ\u003csup\u003e13\u003c/sup\u003eC in bulk sample range between 0.41 and 1.93\u0026permil;, (average 1.35, σ\u0026thinsp;=\u0026thinsp;0.32). In the marl-marly limestone rhythmite (upper Pliensbachian to Polymorphum Zone; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), they are arranged around 1.20\u0026permil;. Above the top of the rhythmite (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), a negative CIE is observed, changing the values of this isotope ratio from 1.20\u0026permil; to 0.41\u0026permil; (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) corresponding to the lower part of the Serpentinum Zone (lower Toarcian). From meter 30, in the lower part of the Serpentinum Zone or lower part of the NJT6 Zone (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), towards the top of the stratigraphic sequence, there is an increase in the value, increasing from 0.41\u0026permil; to 2.47\u0026permil;. The δ\u003csup\u003e18\u003c/sup\u003eO shows a minimum value of \u0026minus;\u0026thinsp;2.50\u0026permil; and the maximum value is \u0026minus;\u0026thinsp;1.34\u0026permil; (average \u0026minus;\u0026thinsp;1.96\u0026permil;, σ\u0026thinsp;=\u0026thinsp;0.29). This ratio decreases sharply in the Polymorphum Zone (lower Toarcian), where it reaches the minimum value, coinciding with the contact between the marl-marly limestone rhythmite and the dark marl interval. Here, an isotope excursion of \u0026minus;\u0026thinsp;0.55\u0026permil; is recorded. In the base of the dark marls (top of the Polymorphum Zone; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), a positive excursion (difference in isotope ratio of 1.00\u0026permil;) is recorded, reaching a value of \u0026minus;\u0026thinsp;1.50\u0026permil;. After the first 2 m of the dark marls, the δ\u003csup\u003e18\u003c/sup\u003eO ratio reaches values similar to those of the upper Pliensbachian.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e4.3.2. Detrital and palaeoclimatic proxies\u003c/h2\u003e \u003cp\u003eThe Zr/Rb ratio in PEL section (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) shows high values at the base of the section that includes the top of the Gavil\u0026aacute;n Formation and the lower part of the Zegr\u0026iacute; Formation (average 1.24, σ\u0026thinsp;=\u0026thinsp;0.13; Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The values decrease in the marl-dominated interval (NJT5b Subzone, Emaciatum Zone, upper Pliensbachian) and the upper part of the studied section (NJT5c Subzone, lower part of the Polymorphum Zone, lower Toarcian) (average 0.88, σ\u0026thinsp;=\u0026thinsp;0.08). The Sr/Cu ratio shows a stratigraphic distribution with similar trends to Zr/Rb but the fluctuations are stronger (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Sr/Cu is higher in the lower part of the section (average 281.4, σ\u0026thinsp;=\u0026thinsp;122) than in the upper part (average 118.6, σ\u0026thinsp;=\u0026thinsp;83). Respect to the CIA and C-value present the lowest values in the lower part of the section (CIA average 0.04, C-value average 2.27) before the NJT5b Subzone of the marl-dominated interval of the Zegr\u0026iacute; Formation (CIA average 0.13, C-value average 9.74; Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The values of these parameters increase and present stronger fluctuations in the rest of the section and describe an opposite stratigraphic distribution respect to the Sr/Cu ratio.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the PR section (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e), two stratigraphic intervals are differentiated, a lower interval that includes the first 7 m corresponding to NJT5a Subzone (Algovianum Zone, upper Pliensbachian), and the upper part formed by 18 m including the NJT5b (Emaciatum Zone, upper Pliensbachian) and NJT5c Subzones (lower part of Polymorphum Zone, lower Toarcian). The Zr/Rb ratio (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) presents relatively low values in the lower stratigraphic interval (from 0 m to 8 m, NJT5a Subzone; Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) with small fluctuations (average 1.44, σ\u0026thinsp;=\u0026thinsp;0.05), and then is followed by a relative increase of Zr/Rb in the upper stratigraphic interval (average 1.52, σ\u0026thinsp;=\u0026thinsp;0.08). The Zr/Rb values progressively decrease in the lower Toarcian (NJT5c Subzone; Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The Sr/Cu ratio shows high values in the lower part of the studied section with low fluctuations (average 41.4, σ\u0026thinsp;=\u0026thinsp;7.7), whereas the upper part of the section is characterized by relatively low values (average 27.4) with high fluctuations (σ\u0026thinsp;=\u0026thinsp;13.1). CIA exhibits low values (average 10.1) and minor fluctuation (σ\u0026thinsp;=\u0026thinsp;2.4) in the lower part of the section (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e), then a slightly increasing trend is recorded with high values in the upper stratigraphic interval (average 14.2) and important fluctuations (σ\u0026thinsp;=\u0026thinsp;5.1). Finally, C-value presents a stratigraphic distribution similar to CIA in the PR section (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). The lower stratigraphic interval present low values (average 0.18, σ\u0026thinsp;=\u0026thinsp;0.02), whereas the upper stratigraphic interval records high values with abrupt fluctuations (average 0.23, σ\u0026thinsp;=\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Zr/Rb ratio of the CE section (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e) shows low values (mostly\u0026thinsp;\u0026lt;\u0026thinsp;0.75) in the rhythmite of the lower part of the section (from 0 m to 26 m, Emaciatum Zone, upper Pliensbachian; Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e) with a Zr/Rb average value of 0.74 (σ\u0026thinsp;=\u0026thinsp;0.03). The Zr/Rb values increase from the beginning of the dark marl (average 0.80, σ\u0026thinsp;=\u0026thinsp;0.07) with important fluctuations and reaches the maximum during the negative CIE. Respect to the Sr/Cu ratio. it shows relatively high values in the marl and marly limestone rhythmite (average 45.6, σ\u0026thinsp;=\u0026thinsp;17.9) with the highest values in the lower part of the NJT5a Subzone, Emaciatum Zone (upper Pliensbachian; Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The top of the rhythmite, in the Polymorphum Zone (lower Toarcian) presents a prominent increase of Sr/Cu; however, the overlying dark marls (NJT6 Zone, Serpentinum Zone) are characterized by a significant depletion (average 18.3, σ\u0026thinsp;=\u0026thinsp;8.4). Finally, CIA also shows two different parts with relatively low values in the rhythmite (average 13.8, σ\u0026thinsp;=\u0026thinsp;6.1) and higher values in the dark marls (average 29.3, σ\u0026thinsp;=\u0026thinsp;8.1; Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). C\u0026ndash;value shows a stratigraphic pattern similar to CIA (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e), with the lowest values corresponding to the rhythmite (average 0.13, σ\u0026thinsp;=\u0026thinsp;0.04) and higher values in the dark marls (average 0.27, σ\u0026thinsp;=\u0026thinsp;0.07). The highest values correspond to the beginning of the Serpentinum Zone, during the negative Carbon Isotope Event (CIE) followed by a light decrease.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.4. Diagenetic signature\u003c/h2\u003e \u003cp\u003eCorrelation diagrams between the two isotope ratios, δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO, have been plotted for each of the stratigraphic sections considered (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). For PEL and PR sections, the correlation is positive, with a low coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.43) in the first section, and a value of R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.54 in PR section. However, in the CE section, both ratios show a negative correlation with a value of coefficient of determination of R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.16 (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows the correlation diagrams between δ\u003csup\u003e13\u003c/sup\u003eC and Sr (ppm) and between δ\u003csup\u003e18\u003c/sup\u003eO and the Fe/Ca and Sr/Ca ratios for each of the sections considered, according to the proposal of Babalola et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). These authors use the degree of correlation (shown by the value of the coefficient of determination between both values, R\u003csup\u003e2\u003c/sup\u003e) as an indicator of the primary origin of the geochemical values.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the PEL section, the correlation between δ\u003csup\u003e13\u003c/sup\u003eC and Sr (ppm) is clearly positive but low (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.25; Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eA). The correlation between δ\u003csup\u003e18\u003c/sup\u003eO and the Fe/Ca ratio (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.33, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eB), is negative and low, while between δ\u003csup\u003e18\u003c/sup\u003eO and Sr/Ca there is no correlation (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.04, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eC). In the PR section, δ\u003csup\u003e13\u003c/sup\u003eC and Sr (ppm) show a low positive correlation (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.26, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eD). The correlation of δ\u003csup\u003e18\u003c/sup\u003eO with Fe/Ca and Sr/Ca is low and negative (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.36 and 0.51 respectively, Figs.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eE, F). Finally, in CE section, the correlation between δ\u003csup\u003e13\u003c/sup\u003eC and Sr (ppm) is slightly negative, with very low correlation (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.002, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eG). In the case of the correlations of δ\u003csup\u003e18\u003c/sup\u003eO and the Fe/Ca (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.53) and Sr/Ca (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.16) ratios in CE section (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eH, I), are clearly negative.\u003c/p\u003e \u003cp\u003eThe value of the Z factor has also been calculated for each of the sections considered, according to the definition of this factor given by Keith and Weber (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1964\u003c/span\u003e) and Babalola et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) and shown in the methodological section of the current paper. If Z\u0026thinsp;\u0026gt;\u0026thinsp;120, the limestones could be classified as marine; if Z\u0026thinsp;\u0026lt;\u0026thinsp;120, they are materials generated in or affected by meteoric waters. Finally, if Z has values close to 120, the limestones should be classified as of undetermined origin. In the studied sections the Z values is always\u0026thinsp;\u0026gt;\u0026thinsp;120 (PEL section ranges between 124.31 and 128.67; PR section ranges between 127.00 and 129.94; CE section ranges between 127.48 and 130.33). Therefore, Z values confirm marine origin for the isotopic signal, and they have not undergone processes of meteoric diagenesis that have distorted their primary geochemical signature.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. DISCUSSION","content":"\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e5.1. Interpretation of facies and facies association\u003c/h2\u003e \u003cp\u003eIn the PEL and PR sections, materials attributed to the Gavil\u0026aacute;n Formation are recorded in the lower part. According to their microfacies and regional palaeogeographical context described before, the sediments were deposited in a distal carbonate platform. The presence of packstone with abundant peloids and crinoids supports the interpretation of a shallower depth and more energetic conditions for the deposits in the PR section, but the record of radiolarians confirms the hemipelagic influence. In the studied sections there are not sedimentary structures pointing to high energy conditions related to waves or tempestites. In this sense, the environment is interpreted as representing a bottom below the storm wave base.\u003c/p\u003e \u003cp\u003eThe beginning of the deposition of the rhythmite of the Zegr\u0026iacute; Formation coincides with the start of the main phase of intracontinental breaking (rifting), developed from the early-late Pliensbachian (e.g. Reolid et al., \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The bottom topography of the basin would be irregular with different semigrabens and changeful local subsidence and sedimentation rates (Vera, \u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Nieto et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), as is observed in other Tethyan Alpine domains (e.g. de Graciansky et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Marok and Reolid, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Jenkyns, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRespect to the Gavil\u0026aacute;n Formation, the Zegr\u0026iacute; Formation represent a decrease in carbonate content mainly related to topographic changes at the sea bottom, with the development of troughs and swells (Vera, \u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Nieto et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), in addition to the transgressive regional and global context (e.g. Hallam, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1987\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Jenkyns, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; de Graciansky et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Wignall et al., \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Korte and Hesselbo, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Haq, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Storm et al., \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The alternation of grey marls and marly limestones of the Zegr\u0026iacute; Formation represents a pelagic to hemipelagic environment, according to the record of ammonites, radiolarians, and siliceous sponge spicules. However, there is continental input evidenced by the terrigenous content of clay minerals, as reported for other areas of the Subbetic (Palomo, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Rodr\u0026iacute;guez-Tovar and Reolid, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and the described record of millimetric coal (wood) fragments and large coal fragments in the case of CE section (Reolid et al., \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Reolid and Reolid, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). There are not sedimentary structures pointing to high energy conditions.\u003c/p\u003e \u003cp\u003eThe abundance of trace fossils in the studied sections confirms favourable conditions for infaunal organisms (oxygen and nutrient availability) as evidenced by previous papers in the Zegr\u0026iacute; Formation for the upper Pliensbachian and Toarcian (Rodr\u0026iacute;guez-Tovar and Uchman, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Rodr\u0026iacute;guez-Tovar and Reolid, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Simo and Reolid, \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Only in the dark marls of the Serpentinum Zone (NJT6 Zone) of the CE section, there is a sensible decrease of bioturbation that is locally absent during the negative CIE (Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The ichnoassemblages indicate a relatively soft ground with a good infaunal tiering.\u003c/p\u003e \u003cp\u003eThe genetic interpretation of this rhythmic marl and marly limestone alternation is complex according to our recent data and needs to be studied to identify the Milanković cycles and to distinguish primary signatures of astronomically forced carbonate cycles (dilution, productivity or dissolution cycles) from the secondary effects of early diagenesis. Only in the case of CE section there is a cyclostratigraphic study that indicate orbital frequencies corresponding to long and short eccentricity mainly (Silva et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e5.2. Diagenetic control in the primary geochemical proxies\u003c/h2\u003e \u003cp\u003eA first approximation to the influence of diagenesis on the values of the different geochemical proxies considered can be made by comparing the δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO variation intervals of each of the sections considered with the ranges of variability of these same isotope ratios in other sections of the Western Tethyan Domain where materials of similar age are recorded (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e). From this comparison, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e, it is observed that the ranges of variation of both isotope ratios in the considered sections are shorter than those of other stratigraphic sections from different basins such as the Lusitanian Basin in Portugal (Duarte et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), the Iberian Basin in east Spain (Rosales et al., \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), or the Atlasic Basin in Moroccan Atlas (Mercuzot et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The Subbetic ranges are comprised within those of other basins. This is interpreted as meaning that diagenesis did not substantially modify the geochemical values and, therefore, they could be considered as primary.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSeveral authors have considered that the value of the correlation coefficient between δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO values in bulk sample can be a good signal of the intensity of diagenesis in carbonates (Jenkyns and Clayton, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Duchamp-Alphonse et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Mercuzot et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Babalola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). A low value of the coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e) could be interpreted as the record of a low-intensity diagenesis and, therefore, a primary origin could be attributed to the isotope values. In the sections studied in the Subbetic, R\u003csup\u003e2\u003c/sup\u003e is low (0.43 for PEL section, 0.54 for PR section, and 0.16 for CE section) (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). However, Swart and Oehlert (\u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) indicate that a low value of the coefficient of determination or a lack of correlation between both isotope ratios should not necessarily indicate that the studied materials record the original isotope signal.\u003c/p\u003e \u003cp\u003eBabalola et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) make a detailed analysis of the influence of diagenesis in Middle Jurassic samples and propose that, in addition to the comparison of the fluctuation intervals of the isotope values, and the study of the coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e), the values of this coefficient obtained from the correlation of the isotope ratios with different elements (Fe, Ca, Mn, Sr) and some of their ratios (Fe/Ca, Sr/Ca, for example) could be considered. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows correlation diagrams of each of the isotope ratios with Sr, Fe/Ca and Sr/Ca for the studied sections. The coefficient of determination in all cases is very low for Sr and δ\u003csup\u003e13\u003c/sup\u003eC (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.26), for Fe/Ca and δ\u003csup\u003e18\u003c/sup\u003eO (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.53), and also for Sr/Ca and δ\u003csup\u003e18\u003c/sup\u003eO (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.51). Considering the data as a whole, the values of the R\u003csup\u003e2\u003c/sup\u003e show values below 0.5, except in the CE section (Fe/Ca vs. δ\u003csup\u003e18\u003c/sup\u003eO) and in PR section (Sr/Ca vs. δ\u003csup\u003e18\u003c/sup\u003eO), with values slightly above 0.5. These values would indicate a weak diagenetic influence that would not substantially modify the primary geochemical signal. On the other hand, the values of the Z factor\u0026thinsp;\u0026gt;\u0026thinsp;120 indicate that the materials studied are of marine origin and, therefore, with little or no influence of meteoric waters that have altered the primary diagenetic signal (Babalola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The scarce diagenetic effect on these sections is also confirmed by the microfacies where cements and radiolarians, sponge spicules and calcareous nannoplankton is generally preserved.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e5.3. Carbon isotope stratigraphy\u003c/h2\u003e \u003cp\u003eThe δ\u003csup\u003e13\u003c/sup\u003eC curves of the studied sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e) do not clearly show the excursions described for the Pliensbachian by authors as Mercuzot et al. (\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In the PEL section, between metres 42 and 46 (upper part of the NJT5b Subzone and lower part of the NJT5c Subzone) a negative excursion, correlatable with the Pliensbachian-Toarcian Boundary Event (PTBE) of Korte and Hesselbo (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), Bodin et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), Fantasia et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), could be considered (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e). In the PR section, in a stratigraphic position equivalent to the one mentioned in the PEL section, the same event could also be identified. Finally, in the CE section, the PTBE is not observed, there is a clear negative CIE in the lower part of the Serpentinum Zone (NJT6 Zone, lower Toarcian) correlative with the Jenkyns Event as reported by Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) from δ\u003csup\u003e13\u003c/sup\u003eC of bulk rock, and Ruebsam et al. (\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003eb\u003c/span\u003e) and Kov\u0026aacute;cs et al. (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) from δ\u003csup\u003e13\u003c/sup\u003eC of organic matter.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e5.4. Palaeoclimatic changes\u003c/h2\u003e \u003cp\u003eImportant environmental changes can be identified according to the distribution of values of geochemical detrital proxies in PEL section. The lower part of the section, including the top of the Gavil\u0026aacute;n Formation and the lower part of the Zegr\u0026iacute; Formation, records high values of Zr/Rb and Sr/Cu ratios that are interpreted as related to warm conditions. Sr/Cu is a weathering proxy that increases under warmer conditions (Bai et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Cao et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Moradi et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The Zr/Rb ratio is used as a proxy of the silt/clay ratio (Kylander et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) with Zr content related to eolian input (Pye, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Hamroush and Stanley, 1990) and Rb related to fluvial transport to the basin (Chester et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1977\u003c/span\u003e; Reolid et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). That is, environmental conditions represented by the beginning of the Zegr\u0026iacute; Formation in the Sierra Pelada section were arid and relatively warm. CIA and C-value present the lowest values in this part of the section that confirm arid conditions.\u003c/p\u003e \u003cp\u003eIn the marl dominated interval mainly corresponding to the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian) and in the upper part of the studied section corresponding to the NJT5c Subzone (lower part of the Polymorphum Zone, lower Toarcian), the Zr/Rb ratio shows low values that indicate relatively humid conditions and enhanced fluvial input to the Median Subbetic. The Sr/Cu ratio shows a similar trend with stronger fluctuations that allow to interpret some warm episodes. The CIA and C-value present higher values in the NJT5b and NJT5c subzones than in the lower part of the section confirms an enhanced weathering and more humid conditions but probably abrupt fluctuations mainly in the early Toarcian as evidenced in the upper part of the section (NJT5c Subzone).\u003c/p\u003e \u003cp\u003eIn the PR section two stratigraphic intervals have been differentiated according to the geochemical detrital proxies. The lower interval of the Zegr\u0026iacute; Formation corresponding to the NJT5a Subzone (Algovianum Zone, upper Pliensbachian) is characterized by relatively low Zr/Rb, CIA and C-values, as well as relatively high values of Sr/Cu. Relatively warm and arid conditions are evidenced from these data, however, relatively low values of Zr/Rb point to higher influence of fluvial input than eolian input for this part of the Median Subbetic.\u003c/p\u003e \u003cp\u003eFrom the NJT5b Subzone (Emaciatum Zone, upper Pliensbachian) there is an environmental change recorded by the increase of CIA and C-value that indicate enhanced weathering and moist conditions compared to the lower part of the section. A Zr/Rb increase occurs around the Pliensbachian/Toarcian boundary and lower part of the NJT5c Subzone (lower part of Polymorphum Zone, lower Toarcian) and indicate more arid conditions (more eolian input) which is opposite to the CIA and C-value interpretation. The Zr/Rb values progressively decrease across the lower Toarcian (NJT5c Subzone) pointing to higher incidence of fluvial inputs in the upper part of the section. The Sr/Cu show strong fluctuations but a general decreasing trend in the lower Toarcian interpreted as relatively cold conditions (Cao et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Moradi et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn CE section, the lower stratigraphic interval (marly limestone rhythmite of the upper Pliensbachian), is characterized by low Zr/Rb, CIA and C-value, that indicate dominance of fluvial detrital inputs and relatively low weathering. The Sr/Cu in this lower stratigraphic interval shows progressively decreasing values in the NJT5a Zone (Solare Subzone, Emaciatum Zone) that points to a cooling trend.\u003c/p\u003e \u003cp\u003eThe top of the marly limestone rhythmite, corresponding to the Polymorphum Zone (lowermost Toarcian) evidences a perturbation herald of the Jenkyns Event with initial abrupt decrease of Sr/Cu in the Pliensbachian/Toarcian boundary correlated with a cooling episode, and a subsequent abrupt increase related to a warming.\u003c/p\u003e \u003cp\u003eThe beginning of the dark marls of the Serpentinum Zone (NJT6 Zone, lower Toarcian), also characterized by a negative CIE (Reolid et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Ruebsam et al., \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e; Kov\u0026aacute;cs et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), presents increasing values of Zr/Rb that indicate a stratigraphic shift in grain size for detritic input (Kylander et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) related to eolian sources congruent with more arid conditions interpreted for this palaeomargin by Rodrigues et al. (\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) from palynofacies. The Sr/Cu decrease points to a relative cooling climate that is contrary to the global warming interpreted after the study of δ\u003csup\u003e18\u003c/sup\u003eO from belemnites (e.g. Rosales et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Danise et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Fern\u0026aacute;ndez et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and brachiopods (e.g. Suan et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Ferreira et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Hesselbo et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e). The increasing CIA and C-value at the onset of the Jenkyns Event indicate enhanced continental weathering and sediment maturity under moist conditions. The highest values correspond to the beginning of the Serpentinum Zone, during the negative CIE followed by a light decrease.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e5.5. Palaeogeographic considerations\u003c/h2\u003e \u003cp\u003eIn the previous section it has been shown that the geochemical signal of the detrital proxies analysed in each of the sections considered in this paper gives palaeoclimatic information that may be contradictory. For example, in the Algovianum Zone, the proxies indicating aeolian (Zr/Rb) or fluvial (Sr/Cu) influences show opposite trends in the PEL and PR sections. These disparities in geochemical signal indications could be interpreted considering the palaeogeographical position of the South Iberian Palaeomargin in a zone of mixing of marine waters from the eastern Tethys and Panthalassa.\u003c/p\u003e \u003cp\u003eDuring the Davoei-Lavinianum Zones, the opening of the Hispanic Corridor (e.g. Price et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) occurred as a consequence of Central Atlantic rifting, which was also an important stage of volcanic activity of the Central Atlantic Magmatic Province and Karoo-Ferrar LIP (e.g., Krencker et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The opening of this Corridor led to the establishment of a connection between Tethys and Panthalassa waters, the latter with a geochemistry that recorded the significant volcanic activity. In other words, a mixture of waters with a different geochemical imprint was produced (Dera et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009a\u003c/span\u003e). In addition, the pattern of currents was modified, as the Viking Current, coming from Boreal domains to the South, disappeared and a current of waters, resulting from the mixing of the Panthalassa and Tethys waters, was established towards the North.\u003c/p\u003e \u003cp\u003eOn the other hand, important changes occurred in the top of the Zegr\u0026iacute; Formation in the sections considered. It is interesting to analyse the change in the materials attributed to the NJT5b Subzone of Ferreira et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), equivalent to the Emaciatum Zone (upper Pliensbachian) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), with a duration close to 720 ka, according to these authors (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). These changes could be explained by (1) the development of sedimentary sub-basins (half grabens) in a rifting palaeotectonic context, with very different sedimentary input rates, (2) probable sediment by-pass situations due to the establishment of a new marine current system and/or (3) differential subsidence controlled by rifting. Molina et al. (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1999\u003c/span\u003e), Ruiz-Ortiz et al. (\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2004\u003c/span\u003e), Reolid et al. (\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) or Nieto et al. (\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), among others, indicate that, once the shallow carbonate platform of the lower Pliensbachian had disintegrated, a system of half-graben controlled by listric faults developed that could favoring differences on subsidence, sedimentation rate, facies, and connection within different sub-basins in the South Iberian Palaeomargin. The rate of sedimentation would be conditioned by sediment by-pass related to the action of currents and by a differential subsidence that would generate areas working as favorable depocenters.\u003c/p\u003e \u003cp\u003eIn the CE section of the External Subbetic, the materials attributed to the Elisa Subzone (that are close equivalent to the NJT5b Subzone of Ferreira et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) have a thickness of 11.2 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Considering this value and the duration of the subzone, a sedimentation rate of 0.018 mm/ka is estimated. In the PR section of the Median Subbetic, the strength of the materials corresponding to this subzone is 4.24 m, which gives a sedimentation rate of 0.006 mm/ka. Finally, in the PEL section, also attributed to the Median Subbetic but located to the south, the rocks representing the NJT5b Subzone are 28.6 m thick, which gives a sedimentation rate of 0.040 mm/ka. From a palaeogeographical point of view, the External Subbetic is closer to the Iberian Continent than the Median Subbetic, in positions that clearly belong to pelagic environments and where it must have been more difficult for continental inflows to reach.\u003c/p\u003e \u003cp\u003eIn the case of the PEL section, where the sedimentation rate was higher (0.04 mm/ka), it was located in the most distal position and probably affected by Hispanic Corridor currents. The higher sedimentation rate and input of sediment from currents are the factors that explain this enhanced sedimentation rate. Moreover, the trace fossil assemblage dominated by \u003cem\u003eMacaronichnus\u003c/em\u003e, not recorded in the southern studied sections, have been related to contourite depositional setting (Miguez-Salas et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). According to Rebesco et al. (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and Eberli and Betzler (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), most of the described large contourite deposits are located in the western side of the largest oceanic basins, as well as around circumpolar basins. In the case of the South Iberian Palaeomargin, it was located in the westernmost part of the Tethys Ocean, connecting with the Hispanic Corridor. This is congruent with the interpretation of the deposits of the Zegr\u0026iacute; Formation in the PEL section as related to contour currents. \u003cem\u003eMacaronichnus\u003c/em\u003e was related to sandy siliciclastic contourites (Miguez-Salas et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This would be calcareous muddy contourites according to Rebesco et al. (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) composing a carbonate drift as described by Reolid and Betzler (\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The homogeneous and fine grain size as well as the dense bioturbation are not favorable for the identification of potential sedimentary structures related to currents such as lamination. Moreover, the dense accumulation of \u003cem\u003eMacaronichnus\u003c/em\u003e indicates the abundance of nutrients in the environment (Miguez-Salas et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and this trace fossil has been related to highly productive waters in connection with upwelling (Quiroz et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"6. CONCLUSIONS","content":"\u003cp\u003eThree stratigraphic sections of the Betic External Zones have been studied, two from the Median Subbetic, Sierra Pelada (PEL) and Puente Romano (PR) and another one from the External Subbetic, La Cerradura (CE), where the Jenkyns Event was recorded by previous authors. In these sections, the upper Pliensbachian materials and the transition to the lower Toarcian have been sampled level by level.\u003c/p\u003e \u003cp\u003eIn the PEL and PR sections these rocks have been dated using calcareous nannoplankton, considering the biostratigraphic scheme of Ferrerira et al. (2019); in the PEL section the NJT5b and NJT5c Subzones have been recognized, whose boundary is marked by the FO of \u003cem\u003eZ. erectus\u003c/em\u003e. In the PR section, the NJT5a, NJT5b, and NJT5c Subzones were recognised, whose boundaries coincide with FO of \u003cem\u003eL. crucicentralis\u003c/em\u003e and FO of \u003cem\u003eZ. erectus\u003c/em\u003e, respectively. In the CE section, both ammonite and calcareous nannoplankton biostratigraphies previously established by Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) have been considered.\u003c/p\u003e \u003cp\u003eThe dominant upper Pliensbachian facies in the three sections consist of a marly limestone - marl alternation. In both PEL and PR sections these same facies have been dated as lower Toarcian, but in the CE section, this interval is represented by marls, in which Reolid et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) identified the Jenkyns Event. In the PEL section, \u003cem\u003eMacaronichnus\u003c/em\u003e ichnofossils predominate. In the PR and CE sections, the ichnoassemblages are dominated by \u003cem\u003ePlanolites\u003c/em\u003e, \u003cem\u003eThalassinoides\u003c/em\u003e and \u003cem\u003eChondrites\u003c/em\u003e. It can help to interpret that the facies and ichnofacies observed were generated in hemipelagic marine environments influenced by continental sediments, as reflected in the clay contents studied by previous authors.\u003c/p\u003e \u003cp\u003eThe analysis of the correlation between δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO in each of the sections considered and of these isotopic ratios with Sr and with Fe/Ca and Sr/Ca, respectively, show low or very low correlations, with values of the coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e) lower than 0.5; moreover, the Z factor presents values higher than 120 in the three sections, indicating a clear marine origin of the rocks studied. These parameters indicate that the geochemical signal has not been modified by diagenesis and can be considered to be of primary origin.\u003c/p\u003e \u003cp\u003eIn the PEL and PR sections, the δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO ratios do not allow to clearly identify isotopic events during the late Pliensbachian, except for the transition to the early Toarcian, where the Pliensbachian - Toarcian Boundary Event (PTBE) could be recognized. In the CE section, where the Jenkyns Event was recorded, the PTBE is not clear the recognition of this event.\u003c/p\u003e \u003cp\u003eThe proxies used to study detritism (Zr/Rb, Sr/Cu, CIA and C-value) and to establish palaeoclimatic changes in the time interval studied show trends contrary to those detected in other sections from the Tethyan Domain and even among the sections studied here.\u003c/p\u003e \u003cp\u003eThe geochemical signals, facies, microfacies and inchnofossil data have been interpreted as the result of the opening of the Hispanic Corridor, associated with the Central Atlantic rifting stage, which favored the mixing of Panthalassa and Tethys seawaters, also establishing a system of currents towards Boreal domains. Extensional tectonics, which affected the South Iberian Palaeomargin, favored the development of half grabens with important differential subsidence, especially during the NJT5b nannofossil Subzone (Emaciatum Zone, latest Pliensbachian). In addition, a possible by-pass effect of the established marine circulation system could transport sediments deposited in these half-grabens to other marine domains. This effect is clear in the PEL section (Median Subbetic), where the trace fossil assemblage, dominated by \u003cem\u003eMacaronichnus\u003c/em\u003e and not recorded in the other two studied sections, have been related to contourite depositional setting. Considering the palaeogeographic position of the South Iberian Palaeomargin, in the westernmost part of the Tethys Ocean, and connected to the Hispanic Corridor, the existence of these contourite currents could have really occurred.\u003c/p\u003e \u003cp\u003eThis paper highlights that the local oceanographic variables may play an important role at controlling the facies distribution and detrital input in highly complex and fragmented palaeomargins as this developed in South Iberia during the studied time interval.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors wish to acknowledge Antonio Piedra-Mart\u0026iacute;nez and M\u0026ordf; Jos\u0026eacute; Campos, Technicians of the Laboratory of Geology (University of Ja\u0026eacute;n). LMN, JMM, CA and MR thank to RNM-200 Research Group of Junta de Andaluc\u0026iacute;a. AF thanks to the Spanish research group UCM-900431.\u003c/p\u003e\u003cp\u003eThe authors declare that there is NO conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBabalola, L. O., Alqubalee, A. M., Kaminski, M. A., \u0026amp; Abdullatif, O. M. (2023). Stable carbon and oxygen isotope records in a Middle Jurassic carbonate sequence: implications for paleoenvironmental, and sea-level fluctuation, central Saudi Arabia. \u003cem\u003eInternational Journal of Earth Sciences\u003c/em\u003e, \u003cem\u003e112\u003c/em\u003e, 585\u0026ndash;613. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00531-022-02261-7\u003c/span\u003e\u003cspan address=\"10.1007/s00531-022-02261-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBaeza-Carratal\u0026aacute;, J. 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Distribution characteristics and applications of trace elements in Junggar Basin. \u003cem\u003eNatural Gas Exploration and Development\u003c/em\u003e, \u003cem\u003e30\u003c/em\u003e, 30\u0026ndash;33.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\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":"Early Jurassic, Southern Iberian palaeomargin, ichnofossils, calcareous nannofossil biostratigraphy, geochemical proxies of detritism, Hispanic Corridor, contourite currents","lastPublishedDoi":"10.21203/rs.3.rs-4182071/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4182071/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThree stratigraphic sections of the Betic External Zones have been studied, two from the Median Subbetic (PEL and PR) and one from the External Subbetic (CE). The upper Pliensbachian materials and the transition to the lower Toarcian have been dated with calcareous nannofossils in PEL and PR in this paper, while in the CE section, previous ammonite and nannofossil biostratigraphies have been considered. The dominant facies are alternance of marly limestone - marl, although in the CE section, the Toarcian is represented by marls, where the Jenkyns Event has been recorded. In terms of ichnofossils, in the PEL section \u003cem\u003eMacaronichnus\u003c/em\u003e predominates. In the PR and CE sections, the ichnoassemblages are dominated by \u003cem\u003ePlanolites\u003c/em\u003e, \u003cem\u003eThalassinoides\u003c/em\u003e and \u003cem\u003eChondrites\u003c/em\u003e. Therefore, the facies and ichnofacies observed were generated in pelagic or hemipelagic marine environments. Analysis of the correlation between δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO and of each of them with Sr and Fe/Ca and Sr/Ca, as well as the Z-factor, indicate that the geochemical signal has not been modified by diagenesis. In the PEL and PR sections, the δ\u003csup\u003e13\u003c/sup\u003eC and δ\u003csup\u003e18\u003c/sup\u003eO ratios do not allow to clearly identify isotopic events, except in CE where the Jenkyns Event was recorded. The proxies used to study detritism (Zr/Rb, Sr/Cu, CIA and C-value) show trends opposite to those detected in other Tethys sections and even between them. These peculiarities in the geochemical data are interpreted as the result of the opening of the Hispanic Corridor, the mixing of Panthalassa and Tethys seawaters and extensional tectonics, which favoured the development of half grabens with significant differential subsidence, especially during the NJT5b Subzone (latest Pliensbachian). These half grabens could be affected by contourite currents according to the \u003cem\u003eMacaronichnus\u003c/em\u003e assemblage in some of these sections.\u003c/p\u003e","manuscriptTitle":"Environmental Conditions in the Pre-jenkyns Event Times (Late Pliensbachian – Early Toarcian) in the Southiberian Palaeomargin (Betic External Zones, Southern Spain)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-08 08:22:46","doi":"10.21203/rs.3.rs-4182071/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-04-08T16:51:22+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-03T10:21:46+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Iberian Geology","date":"2024-03-31T17:40:54+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-30T03:48:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Iberian Geology","date":"2024-03-29T04:20:52+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":"31e4a5c8-44ee-4df7-9909-2193b99cc2cf","owner":[],"postedDate":"April 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-10-21T16:08:22+00:00","versionOfRecord":{"articleIdentity":"rs-4182071","link":"https://doi.org/10.1007/s41513-024-00254-w","journal":{"identity":"journal-of-iberian-geology","isVorOnly":false,"title":"Journal of Iberian Geology"},"publishedOn":"2024-10-18 15:57:46","publishedOnDateReadable":"October 18th, 2024"},"versionCreatedAt":"2024-04-08 08:22:46","video":"","vorDoi":"10.1007/s41513-024-00254-w","vorDoiUrl":"https://doi.org/10.1007/s41513-024-00254-w","workflowStages":[]},"version":"v1","identity":"rs-4182071","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4182071","identity":"rs-4182071","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}