Seismostratigraphy of Buried Pleistocene Deltas on the Mangyshlak Threshold, Caspian Sea

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A. Putans, O. V. Levchenko This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5366595/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 Feb, 2026 Read the published version in Pure and Applied Geophysics → Version 1 posted 9 You are reading this latest preprint version Abstract The change in sedimentation conditions from shelf to deep-water, including deltas and underwater cones of outflow, can be traced on the regional profiles of the Mangyshlak Threshold. It is possible to confidently identify several continuous seismic horizons. Upper part of sedimentary cover consists of two types of sediments with essentially different acoustical image, i.e. seismic sequences. The first type of sediments appears to be accumulated under enough quiet hydrodynamic conditions of high seas far from coastline, i.e. they are marine sediments. On the contrary, the second acoustical pattern evidences active lithodynamics inhering in shallow-water and subaerial environment, which are affected essentially by fluvial processes. The characteristic lenslike architecture of the sediments allows us to interpret them as deltaic and avandeltaic sequences, which were accumulated during lowstand stage of the Caspian Sea. According to geographical location of the buried valleys and deltaic sequences, one can assume that the discussed accumulative units relate rather to the paleo-Ural River. Caspian Sea deltaic complexes seismoacustics seismostratigraphy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction The Caspian Sea is divided into three individual morphological parts: northern, middle and southern. Structural border between the Northern Caspian Sea and Middle Caspian Sea is the Mangyshlak Threshold. Buried incised paleochannels of rivers, deltaic and avandeltaic sequences, erosional surfaces and other similar evidences of multiple Pleistocene regressions in the Caspian Sea would be located over its shallow-water northern part and adjacent southern flank of the Mangyshlak Threshold. Therefore, detailed studies of sediments structure over the transition zone between the Northern Caspian Sea and Middle Caspian Sea are important to reconstruct evolution of the whole Caspian region during the Quarter time. These evidences of sea lowstand occurring within the uppermost stratigraphic section can be reviled by high resolution seismic reflection profiling. Instead, low resolution multichannel seismic reflection surveys were carried out mainly for oil and gas exploration within deep sedimentary layers. High resolution seismic reflection survey over the Mangyshlak Threshold area is very poor, so the questions about amplitudes of sea level lowering as well as age and borders of regressive basins are still open for discussion. Among few publications about structure of the Quarter sedimentary sequence in the region, paper by Lokhin and Mayev ( 1990 ) could be mentioned as one of most reliable. The authors have reviled two deltaic sequences lying one beneath another which were formed during the Atelian (70 − 30 kyr) and Enotanian (12–13 kyr) time relatively. Other one is paper by Bezrodnykh et al. (2002), who have determined absolute age (C 14 ) of the Pleistocene sediments in the Northern Caspian Sea: the Novocapian 0–7 kya, the Mangyshlak 7–9 kya, the Upper Khvalynian 9–16 kya and the Lower Khvalynian from 17 to > 30 kya. The P.P.Shirshov Institute of Oceanology, Russian Academy of Sciences had carried out geological and geophysical studies in the conjugation zone of the Northern Caspian Sea and Middle Caspian Sea in cruises of RV Rift in 2006, 2007 and 2012 (Fig. 1 ). The cruises were focused on studies of buried deltaic sequences, first of all the Volga and Ural Rivers paleodeltas. The cruise in 2006 and afterward research were performed by Belgium-Russian project ”Reconstructing Holocene water-level fluctuations and paleoenvironments in the Caspian Sea based on geophysical and core investigation of the lowstand Volga paleodelta, where the P.P.Shirshov Institute of Oceanology was collaborating with the Geographical Faculty of the Moscow State University and Ghent University. Our results appear to complete and specify available data; especially we suppose to prove new age identification of the deltaic sequences. In general, the paleodeltas studies allow to understand the impact of recent sea-level changes on lowstand delta architecture and on paleoenvironmental conditions during lowstands as well as to obtain a more detailed chronology of lowstands and to appreciate scale of the Caspian Sea regressions during the Pleistocene and Holocene. 2. Geological setting The Mangyshlak Threshold is a large accumulative sedimentary feature in the conjugation zone of the Northern and Middle Caspian Sea. From the north, the Mangyshlak Threshold is bounded by small scarp sloping northward, water depths are mainly near 10 m. In the south, the depth extends up to 50 m isobath. The Mangyshlak Threshold consists of small individual submarine rises, swells and banks and the whole extended chain elongates from the Tub-Karagan Peninsula in the east to the Agrakhansky Peninsula in the west. In general, shape of the Threshold resembles an arc bending slightly northward (Fig. 1 ). The seafloor has gentle slope southward. General gradient is 1-1.2 m/km, i.e. about 0.001, so a general slope angle is less than five minutes. Two large distinct meandering depressions are expressed in the seafloor topography of the Mangyshlak Threshold area. They are thought to be paleochannels of the Volga and Ural Rivers. These depressions divide the Threshold on approximately equal areas: off Dagestan, middle and off Mangyshlak. In the whole area seafloor consists mostly of coarse-grained, compact sediments: shells and shelly detritus, gravel, grus, sand, and a lesser degree – siltstone and silt (Kuprin et al., 1992). The isobaths outline a gentle arc curved northward whereas the isohypses trend toward NW-SE. N-S striking depression could be visible in relief of the Upper Khvalynian-Novocaspian deposits base in the west of the region (Kuprin, Roslakov, 1992). Eastern side of the depression has gentle slope, while western one is conversely steep (of 50 m amplitude). Broad erosional depression in the middle part of the Mangyshlak Threshold cuts the whole region from the north to the south. The depression stands very close with channel of the paleo-Volga River which was reviled by multichannel seismic reflection profiles within deeper older deposits (Bezrodnykh et al., 2002). So, the N-S depression appears to be an inherited feature. The vast gentle swell by “watershed” with flat top is located near to the Volga paleo-valley. The vast swell is sloping generally southward; no local features are reviled here. One more N-S striking erosional depression in the basal surface is located in the eastern part of the Mangyshlag Threshold, ~ 70 km to the west from the Tub-Karagan Peninsula. That is typical buried river’s valley with pronounced channel, valley and deltaic sequence. Its maximum depth is 50 m, wide of the paleo-valley is 10–12 km. According to its geographical location, origin of the depression relates to the paleo-Ural River. A swell similar to the above mentioned “watershed” is between the paleo-Volga and paleo-Ureal Rivers (Kuprin et al., 1992). Accumulation of the sand and clay deposits occurred here at that time when adjacent sea areas sank toward the Derbent Basin with rise of eastern maritime land. That is evidenced by available seismic reflection profiles, in which erosional surfaces within the Quarter deposits as well as alternation of stratified and transparent sediments are observed. In general, the deltaic sequence developed and grew from the south to the north. The Mangyshlak Threshold represents huge accumulative body formed during the Pleistocene as result of discharge of large rivers, first of all the paleo-Volga and paleo-Ural, which transported great volume suspended terrigenous sediments. The accumulating of the sediments just near the Mangyshlak Threshold could be explained by strong recent tectonic movements, which affected the seafloor topography. According to the work (Putans, 2010), the change in sedimentation conditions from shelf to deep-water, including deltas and underwater cones of outflow, can be traced on the regional profiles of the Mangyshlak Threshold. It is possible to confidently identify several continuous seismic horizons. The two brightest and most sustained divide the section into three seismic complexes: the lower one is chaotically bumpy, the middle one is parallel-layered, and the upper one with many angular inconsistencies (Table 1 ). By direct correlation with the well sections, the geological age of the seismostratigraphic horizons was determined on a local stratigraphic scale: the lower complex was assigned to the pre–Baku time (QIap), the middle one to the Baku and Khazar (QIIb + haz), and the upper one to the Khvalyn and Novocaspian (QIIIhv + QIVnc). This stratigraphy of the Mangyshlak threshold is generally consistent with studies of previous years (Kuprin idr., 1991), (Kuprin, Roslyakov, 1991). Moreover, these horizons are regional stratigraphic discrepancies and correspond to the reflecting horizons OG-3 and OG-5 highlighted in the mentioned works. Table 1 Regional seismostratigraphic complexes of the Middle Caspian Sea Complex Age, kyr Seismic Pattern Upper Khvalynian-newcaspian 30 − 0 kyr) Complex wave pattern; many angular inconsistencies; alternation of parallel-layered, oblique-layered and acoustically transparent recordings Horizon OG-5 Middle AfterBakin-Khazar (500 − 30 kyr) Parallel layered stratum with several bright horizons, sometimes weakly pronounced angular inconsistencies and buried lenses of chaotically bumpy reflections Horizon OG-3 Lower Bakin and pre-Bakin (before 500–600 kyr) Chaotic bumpy reflections up to acoustic transparency The regressive stages caused essential changes of sedimentological processes as well as processes forming the seafloor topography over the Caspian Sea shelf. Great sea-level drop during the Atelian (70 − 30 kyr) and Enotanian (12–13 kyr) regressions (dating from Kurbanov et.al., 2024 ) caused migration of the coastline and river mouths to outer shelf areas, where the large accumulative clinoformes of ancient deltas were formed. They were covered later by marine sediments during following transgressions. The development of paledeltas caused progradation of the shelf and its advancement in to deep-water basin as well as increase angle of northern slope of the Derbent Basin (Kuprin and Roslyakov, 1991). 3. Methods The geophysical and geological coring data were collected by P.P.Shirshov Institute of Oceanology RV Rift : displacement 1380 t, length 54 m, width 11 m, draught 4.5 m. The paleodeltaic sequence was studied on the detailed research area – Polygon 1 by 60 x 65 km in size near the Mangyshlak Threshold (Fig. 1 ). Four geological sites were proposed for sediments coring in 2006 and tree sites in 2007. Total length of collected seismic reflection profiles is about 570 km. The survey was carried out at a speed of 4 knots. Satellite navigation system GPS provides the equipment positioning and coordinates’ accuracy < 30 m. 3.1. Sparker data High-resolution seismic reflection data were collected using the single-channel profiling system “Geont-shelf” by 600 J power developed in the Moscow State University. The sparker source with a frequency ranging from about 100 to 1000 Hz (central frequency is ~ 400 Hz) provides range of penetration up to 300–400 m bsf and resolution up to 2 m. The collected data were processed using special software RadExpro and KingdomSuite. 3.2. Geological coring Gravitational geological corer by 4 m long and grabber produced by P.P.Shirshov Institute of Oceanology were used to collect sediment cores. Site “Delta 1” (130 m water depth) is located in south-eastern part of the Polygon 1 (Fig. 1 ). Total length of cored sediments is 225 cm. Site “Delta 2” (86 m water depth) is located in central part of the Polygon 1. Geological coring was unsuccessful. Site “Delta 3” (74 m water depth) is located in central part of the Polygon 1 to north from the site “Delta 2”. Several large and perfect conserved shells were collected as result of some attempts. Site “Delta 4” (60 m water depth) is located in northern part of the Polygon 1. Geological coring was unsuccessful. So, coring at the sites “Delta 1” and “Delta 3” provides some information about the seafloor sediments. The numerous large shells at site “Delta 3” seem to evidence, that seafloor in the area is reinforcing by these compact shells. Same was for 2007 coring (01/07, 02/07, 03/07). More weighted gravitational geological corer must be used here for successful geological coring. 4. Results 4.1 High-resolution seismic reflection (sparker) data 4.1.1 Regional unconformities Seismic sections represent distinct strong reflectors which appear to be stratigraphic unconformities marking change of sedimentation regime. It is necessary to note some signs of erosion. The bottom of the marine complex corresponds to the regional horizon of OG-5, and in some areas the horizon of OG-3 is visible, although it is mostly hidden under multiple waves. On the Fig. 2 there are sections along the profiles of the polygon: No.5–9 at the intersection of the slope, No. 4 along the slope (see the polygon diagram in Fig. 1 ). Scale 1:100. The reference horizons of OG-3 and OG-5 are shown, the horizons are the boundaries of the stratigraphic "floors", and the structure of the delta complex (internal boundaries and zones of chaotic bumpy reflections) is schematically outlined. 4.1.2. Seismic sequences Upper part of sedimentary cover consists of two area of sediments with essentially different acoustical image, i.e. seismic sequences (Fig. 3 , Fig. 4 ). The first type is characterized by continuous near parallel and near horizontal reflectors. The reflectors are basically weak except for few local areas with amplitudes similar to “bright spot”. The second type of seismic sequence is characterized by much lesser regularity. The reflectors are sloping steeper and they are ranging from very strong to very weak. Both lateral and vertical variations of visible acoustical pattern are quite great: from extended and smooth reflectors to oblique, hummocky and chaotic ones. In general, the sequence look like lens seismic facies unit. These sediments form lenslike bodies of tens meters thick and several tens kilometers in size. Numerous buried incised depressions and local unconformities are there. Upper sequence D-1 The upper deltaic sequence D-1 lies just beneath seafloor and it is covered by thin sedimentary layer in some places. Thickness of the layer is comparable with the resolution of seismic records, i.e. it is less than 2–3 m. As it can be seen from the isopach map (Fig. 5 ), the sequence represents spatial feature similar to a large convex lenslike mass of 80 m maximum thick. It is necessary note that the maximum thicknesses mass near edge of shelf. This peculiarity is shown distinctly by N-S seismic profiles (Fig. 4 ). Large acoustically transparent zones dominate near the area of maximum thicknesses. Nevertheless, zones of hummocky and parallel seismic reflection configuration occur often too. Contrariwise, interrupted hummocky reflectors predominate on limbs of the convex lenslike mass. They create an oblique seismic reflection pattern where incline of reflectors conform to the general trend of seafloor. However, acoustically transparent zones and sigmoid reflections occur as well. It is interesting that the sigmoid pattern is observed both on N-S and on E-W seismic reflection profiles (Figs. 3 and 4 ). Intermediate sequence S The sequence is represented by acoustically layered seismic facies unit. There are extended/parallel and slightly undulating internal reflectors. It represents stratum, which is draping topography of underlying sedimentary layer. Thickness of the stratum increases from 10 m in the north to 45 m in the south (Fig. 5 ). It increases most distinctly beneath the water-depth of 100 m, i.e. behind edge of shelf. The evident pattern of the seismic onlap, which is seen in some places especially in northern part of the area, represents structural unconformity between the two subsequences S-1 and S-2. Instead, the boundary between them in deeper southern part shows no structural features. Lower deltaic sequence D-2 Top of the sequence is going down gradually from 22 m bsf in the north to 110 m bsf in the south. Its internal structure is more similar to the same of the upper deltaic sequence D-1 than to the intermediate sequence S. Approximate thickness of the lower sequence D-2 could be estimated due to strong multiples, it is less 40–50 m, i.e. lesser than thickness of the upper sequence D-1. It is necessary to note especially a possible existence of gas-charged sediments here. Numerous local “bright spots”, which are accompanied by acoustical shadows below in some places, may be caused by the gassy sediments. 4.2. Lithology Section collected with geological corer at the site Delta 1 represents structure and contain of the deltaic sediments (Table 2 ). Density and strength of the sediments were measured as well. The density for the sedimentary section varies from 1.60 to 1.65 g/cm 3 . The shear strength increases essentially downward from 2 g/cm 2 at the depth of 60 cm to 20 g/cm 2 at the depth of 115 cm and to 60 g/cm 2 at the depth of 220 cm. Core Delta-1 is clearly correlated with seismic section (Fig. 6 ). Table 2 Lithology of sediments at the site Delta 1 № п/п Depth bsf, cm Lithology 1 0–37 Small shells and detritus of grey color with a touch of clayey siltstone of grey-brown color Thin layer of siltstone is at a depth of 25 cm. Amount of shells and detritus decreases gradually in base of the interval. 2 37–65 Clayey-siltstone silt of grey-brown color with thin layer and lens of siltstone 3 62–98 Clayey-siltstone sediments of grey-olive-colored with numerous lenses and thin layers of siltstone and sand. The lenses and thin layers are unequal. Probably, the substance flowed down as silty fluid therefore, there is no sorting of siltstone and sand pars. Lower boundary of the interval is very clear due to changing of sediments’ color from grey-olive-colored grey-brown to brown. 4 98–225 Mostly clayey-siltstone sediments with numerous interrupted or extensive thin layers of hydrotroilite which imitate appearance of horizontal stratification. The sediments are grey-brown in range of 98–110 cm, olive-colored in range of 110–138 cm, brown in range of 1380165 cm and olive-colored in range of 165-200cm, deeper they are clayey-siltstone. Quite thin layer of sand sorted poorly is at a depth of 138 cm, and small sandy lens is at a depth of 175 cm. 5. Discussion As a result of the carried out survey, two sequences D-1 and D-2 are distinguished clearly in the research area. The upper sequence D-1 and lower one D-2 are divided by quite thin package S. Comparing the isopach maps (Fig. 5 ) of the sequences, one can see some discrepancy in their distribution over the research area. Large acoustically transparent zones dominate near the area of maximum D-1 thicknesses (Fig. 5 ). They might be interpreted as massive sand- siltstone formations representing consolidated fluvial mouth bars. Nevertheless, zones of hummocky and parallel seismic reflection configuration occur often too. To the south on slope, internal structure of the deposits is to be regulated and it represents a progradational reflection configuration. Near pinch of the upper sedimentary wedge, the internal reflectors are becoming parallel and extended typical for prodeltas. This acoustically pattern is an evidence of enough quiet hydrodynamic conditions of high seas far from coastline. On the other hand, the marine sequence seems to be sheet drape seismic facies unit. The transgressive marine sequence seems to be divided by a strong internal reflector R2a in two subsequences M-1 and M-2 of approximately equal thickness 5.1. Age and stratigraphy Previously mentioned horizons OG-3 and OG-5 are regional uncomformities, so they could be clearly traced up to deep site PRV-1 and correlated with dated site. (Fig. 7 ). The reflector marking top of the lower deltaic sequence represents an erosional surface and was formed simultaneously with accumulation of the deltaic sediments. The sequence can be traced uninterruptedly to the borehole PRV-1 in the west from the polygon (location on Fig. 1 ), where its top is at the depth of 40 m bsf and its thickness is 12–15 m. That allows to doubt about the Atelian age (70 − 30 kyr) of the lower deltaic sequence supposed by Lokhin and Mayev ( 1990 ) because base of the Khvalinian deposits corresponding to the Atelian regression (70-30kyr) was drilled in the borehole much deeper at the depth 84 m bsf. Moreover, the Novocaspian (0–7 m bsf) and Khvalinian (7–42 m bsf) deposits determined by fauna were drilled here at the two shallow boreholes PR-1 (depth of 27 m) and PR-2 (depth of 42 m). So, one may declare that the lower deltaic sequence was formed during the Khvalinian regression, probably the Enotaivan one between the Early and Late Khvalinian time. The other strong reflector marking the Atelian regression near the borehole PRV-1 (84 m bsf) is sinking near the polygon 1 up to greater depths. It is impossible to determine age of the upper deltaic sequence in the borehole PRV-1 because the sequence is pinching out at 15 km to the east, where its base outcrops in the seafloor. Hence, its age appears to be regarded as more young, i.e. the upper deltaic sequence could be formed during the Mangyshlak regression but not during the Enotaivan one as proposed by Lokhin and Mayev ( 1990 ). 5.2 Seismic facies Two seismic facies appear to be recognized within the upper deltaic sequence D-1. First unit is the river channel facies which is characterized by subparallel seismic reflection configuration and slight roughness of inner reflectors. Second unit is the progradation facies which is characterized by progradational reflection configuration or parallel oblique seismic reflection configuration. It is distributed on both sides of the main channel as obliquely layered clinoforms. The main channel, where accumulated the first facies, and sedimentary flows from the main channel forming the second facies. The area near intersection of profile 7 (Fig. 4 ) with profile 2 (Fig. 5 ) is very difficult for interpretation. That seems to be due to bend of the main channel and, perhaps, due to existence of heteradirectional confluents here. Figure 8 5.3. Geographical position of the deltaic sequences One of the most important questions is – to which paleo-river or paleo-rivers is related formation of the studied deltaic sequences? A supposition, that the paleo-Volga was responsible for such process, is not as evident as it could be considered. The erosional valley of the Volga River formed before the Late Pliocene was revealed by multichannel seismic reflection profiles and confirmed by drilling (the borehole PRV-1) (Gadjiev, Popkov, 1988 ). The valley is located far in the east from the polygon 1. Channel of the Volga River does not manifest itself within more recent sediments over the Northern Caspian Sea so clearly (Sorokin et al., 2018 ). On the assumption of general geological situation, one can suppose logically its migrating still further to the west due to continued sinking of axial zone in the Tersky-Caspian flexure. Two erosional valleys are seen clearly in the isopach map of base of the Khvalinian-Novocaspian deposits near the Mangyshlak Threshold (Fig. 1 ), the western valley is related to the paleo-Volga River while the eastern one - to the paleo-Ural River (Kuprin and Roslyakov, 1991). According to geographical location of the polygon 1, formation of the studied deltaic sequences was related rather to the eastern valley but not to the western one, i.e. presumably to the paleo-Ural River. To answer finally the question mapping of the buried Upper Pleistocene valleys must be continued over the shallow Northern Caspian Sea. 6. Conclusions The development of paleodeltas is clearly visible on seismic sections. Three seismic complexes are confidently distinguished: two with complex chaotically bumpy reflections - delta complexes (power in the depocenter on the edge is about 50 m), and a layered marine complex separating them in parallel (power from 10 m on the shelf to 30 m at the foot). It should also be noted the zones of seismic attenuation the signal at the bend of the shelf (isobate 100 m) up to acoustic transparency. The bottom of the marine complex corresponds to the regional horizon of OG-5, and in some areas the horizon of OG-3 is visible, although it is mostly hidden under multiple waves. The same seismostratigraphic division of this area was made earlier, and the system itself was assigned by position to the combined Volga-Ural river system, and in later works to the Ural River. The age estimate in these studies was based on the average sedimentation rate, and the upper delta complex was assigned to the Enotaevskaya, and the lower one to the Athelskaya regression. Since there is currently a correlation with the PRV-1 and Central wells, it is possible to revise the age of the complexes towards rejuvenation in the northeast of the Mangyshlak threshold in the area of the Paleoral outflow cone, undulating folds formed as a result of the "flow" of decompressed clay rocks are observed. This flow is accompanied by compression and stretching deformations, which gives rise to a characteristic wave structure with flat peaks and narrow valleys between them. According to geographical location of the buried valleys and deltaic sequences, one can assume that the discussed accumulative units relate rather to the paleo-Ural River. Declarations Funding The work was carried out within the framework of the state task no. FMWE-2024-0019. Author Contribution Both authors wrote the main manuscript text. Both authors reviewed the manuscript. Acknowledgement Special acknowledgement to Dr.Alexander Roslyakov for highly professional consultations on geology and stratigraphy. Data Availability Seismic data are available after official contact with Institute of Oceanology administration References Bezrodnikh Y.P., Romanov B.D., Reny S.V. (2002) Biostratigraphy and structure of the Upper Quarter deposits and some feature of paleogeography of the Northern Caspian Sea. Stratigraphy and geological correlation - №1 - p.20-35 Gadjiev A.N., Popkov V.I. (1988) New geological data in Middle Caspian. Academy of Science presentations - Vol.299 #3 pp 682-685 Kuprin P.N., Roslaykov A.G. (1991) Geological structure of the Mangyshlak Threshold. Geotectonics - №2 - p.28-40 Kuprin P.N., Rybakova N.O., Semenov E.O. (1991) Stratigraphy of Pliocene-Quaternary deposits on the mangyshlak Threshold. Oceanology - Vol.31, iss.5, p.1022-1031 Kuprin P.N., Luksha V.L., Semenov E.O. (2015) Structure of section and lithology of the Pliocene-Quarter deposits on the Mangyshlak Threshold in the Caspian Sea . Lithology and mineral resources. №5 - p.35-50 Kurbanov R., Murray A., Yanina T., Buylaert J.P. (2024) Dating the Middle and Late Quaternary Caspian Sea-level fluctuations: first luminescence data from the coast of Turkmenistan. Quaternary Geochronology , Volume 83 https://doi.org/10.1016/j.quageo.2024.101599 Lokhin M.Y. and Mayev E.G. (1990) Late Pleistocene deltas on the northern self of the Caspian Sea. Vestnik of the Moscow Universit y. Ser.5. Geography - №3 - 34-39 Sorokin V.M., Yanina T.A., Romanuyk B.F. (2018) On age of upper quaternary deposits in North Caspian. Vestnik of the Moscow University - Vol 4 –pp.75-85 DOI: 10.55959/MSU0579-9406-4-2023-63-4-75-85 Yanina, T. A, Sorokin V.M., Bezrodnykh Yu, Romanyuk B.F. (2017) Late Pleistocene climatic events reflected in the Caspian Sea geological history (based on drilling data). Quaternary International DOI: http://dx.doi.org/10.1016/j.quaint.2017.08.003 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 25 Feb, 2026 Read the published version in Pure and Applied Geophysics → Version 1 posted Editorial decision: Revision requested 26 Jan, 2025 Reviews received at journal 09 Dec, 2024 Reviews received at journal 29 Nov, 2024 Reviewers agreed at journal 27 Nov, 2024 Reviewers agreed at journal 08 Nov, 2024 Reviewers invited by journal 02 Nov, 2024 Editor assigned by journal 02 Nov, 2024 Submission checks completed at journal 02 Nov, 2024 First submitted to journal 31 Oct, 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-5366595","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":375868050,"identity":"d6cb4bc0-97b5-4e72-8fd8-6bedb7334b6c","order_by":0,"name":"V. A. Putans","email":"","orcid":"","institution":"Institute of Oceanology. PP Shirshov Russian Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"V.","middleName":"A.","lastName":"Putans","suffix":""},{"id":375868051,"identity":"8c2faabf-b32c-436b-9438-bbe44903e503","order_by":1,"name":"O. V. Levchenko","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAr0lEQVRIiWNgGAWjYDACdgglx8DA2HiAOC3MEMoYqKWBNC2JDUCCOC38zMzHJH9U1KWvbT/ccIBxz2HCWiSb2dKkec4czt12JhHosGdEaDE4zGNszNh2IHfbAZCWA0Rp4f9s+PNfXbrZ+YdEa+FhfMDbwJxgdoNYW4B+MXzMc+yw4bYbQFsSDqQT1sLP3vzg4I+aOnmz8+kPH3w4YE1YCypIIFXDKBgFo2AUjALsAAB0lD9PNC3GVgAAAABJRU5ErkJggg==","orcid":"","institution":"Institute of Oceanology. PP Shirshov Russian Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"O.","middleName":"V.","lastName":"Levchenko","suffix":""}],"badges":[],"createdAt":"2024-10-31 09:53:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5366595/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5366595/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00024-026-03942-z","type":"published","date":"2026-02-25T15:57:47+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":70286221,"identity":"9ab1e2fe-bac7-4cd5-b83e-4976aac6a643","added_by":"auto","created_at":"2024-12-01 16:30:44","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":13089412,"visible":true,"origin":"","legend":"\u003cp\u003eLocation map of cruise #20 of \u003cem\u003eRV Rift\u003c/em\u003e in the Middle Caspian Sea. Seismic profiles and sites of geological coring on the Polygon 1 near the Mangyshlak Threshold are shown (zoom at the foot). Legend: 1 – isobaths, m; 2 – seismoacoustic profiles; 3 – main rivers; 4 – site of geological coring; 5 – site of parametric borehole; 6 – paleoVolga (by (Kuprin, Roslakov, 1992))\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/eca86e8134d201f21683f43b.png"},{"id":70286226,"identity":"f932df5e-1330-4214-80ef-5041d7b5d850","added_by":"auto","created_at":"2024-12-01 16:30:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5938296,"visible":true,"origin":"","legend":"\u003cp\u003eTraced seismic sections with regional and local unconformities\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/118c0df66795ade7d317efbc.png"},{"id":70286228,"identity":"0ef318ab-bfb5-45e0-8f98-b3f22c7e07de","added_by":"auto","created_at":"2024-12-01 16:30:45","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":10151204,"visible":true,"origin":"","legend":"\u003cp\u003eSeismic reflection profile №2 (location see in fig. 1). Seismic stratigraphic sequences: D-1 and D-2 - upper and lower deltaic sequence, respectively; S - marine sequence, separating in two subsequences S-1 and S-2.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/2ba531faac0aaa573da46b98.png"},{"id":70286724,"identity":"8079439f-cb02-4d01-b076-93520dc35425","added_by":"auto","created_at":"2024-12-01 16:38:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":10667357,"visible":true,"origin":"","legend":"\u003cp\u003eSeismic reflection profile №7 (location see in fig. 1). Seismic stratigraphic sequences: D-1 and D-2 - upper and lower deltaic sequence, respectively; S - marine sequence, separating in two subsequences S-1 and S-2\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/d9655af352fba966d3824f81.png"},{"id":70286225,"identity":"311afe36-e563-4e27-b956-31a249dadc9c","added_by":"auto","created_at":"2024-12-01 16:30:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2680212,"visible":true,"origin":"","legend":"\u003cp\u003eIsopach map of the upper deltaic sequence D-1 (left) and marine sequence S (right), spacing 10 m\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/f0e83e49fa4ad0b9a976df89.png"},{"id":70286223,"identity":"524d61a7-1f43-44a0-85bc-6649f3a27ad2","added_by":"auto","created_at":"2024-12-01 16:30:44","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":5672301,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation with geological core Delta-1 (on Polygon). Legend: 1 – clay, 2 – sand, 3 – silt, 4 - detritus\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/a65bbb98e26fc160303315cf.png"},{"id":70286227,"identity":"ff15788d-b858-45ea-aa1d-c65c2f777d77","added_by":"auto","created_at":"2024-12-01 16:30:44","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":5066586,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation with Site PRV-1. Regional time: on 7 m – Mangyshlak regression (D1 erosion), 42 m – Enotanian regression (reflector between S1 and D2); 84 m – Atelian regression (dipping reflector). Legend: 1 – clay, 2 – sand, 3 – detritus, 4 - limnestone\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/293f0a49e9b6b2b34bde1d43.png"},{"id":70286229,"identity":"dc306154-9dd6-413b-949f-612a40910e64","added_by":"auto","created_at":"2024-12-01 16:30:45","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1739943,"visible":true,"origin":"","legend":"\u003cp\u003eDeltaic complexes scheme. Legend: 1 – isobaths, m; 2 – seismic profiles; 3- border of upper deltaic complex (D1); 4 – D1 isopachits; 5 – paleochannels in D1; 6 – border of lower delta complex (D2)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/8c9db40913992817d60264ac.png"},{"id":103765935,"identity":"1703e915-8a9f-469b-b600-8efa20cb7f3f","added_by":"auto","created_at":"2026-03-02 16:11:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":70726893,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5366595/v1/6d142832-9da8-4f58-ae71-c3d0b65d6026.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eSeismostratigraphy of Buried Pleistocene Deltas on the Mangyshlak Threshold, Caspian Sea\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe Caspian Sea is divided into three individual morphological parts: northern, middle and southern. Structural border between the Northern Caspian Sea and Middle Caspian Sea is the Mangyshlak Threshold. Buried incised paleochannels of rivers, deltaic and avandeltaic sequences, erosional surfaces and other similar evidences of multiple Pleistocene regressions in the Caspian Sea would be located over its shallow-water northern part and adjacent southern flank of the Mangyshlak Threshold. Therefore, detailed studies of sediments structure over the transition zone between the Northern Caspian Sea and Middle Caspian Sea are important to reconstruct evolution of the whole Caspian region during the Quarter time. These evidences of sea lowstand occurring within the uppermost stratigraphic section can be reviled by high resolution seismic reflection profiling. Instead, low resolution multichannel seismic reflection surveys were carried out mainly for oil and gas exploration within deep sedimentary layers. High resolution seismic reflection survey over the Mangyshlak Threshold area is very poor, so the questions about amplitudes of sea level lowering as well as age and borders of regressive basins are still open for discussion. Among few publications about structure of the Quarter sedimentary sequence in the region, paper by Lokhin and Mayev (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) could be mentioned as one of most reliable. The authors have reviled two deltaic sequences lying one beneath another which were formed during the Atelian (70\u0026thinsp;\u0026minus;\u0026thinsp;30 kyr) and Enotanian (12\u0026ndash;13 kyr) time relatively. Other one is paper by Bezrodnykh et al. (2002), who have determined absolute age (C\u003csup\u003e14\u003c/sup\u003e) of the Pleistocene sediments in the Northern Caspian Sea: the Novocapian 0\u0026ndash;7 kya, the Mangyshlak 7\u0026ndash;9 kya, the Upper Khvalynian 9\u0026ndash;16 kya and the Lower Khvalynian from 17 to \u0026gt;\u0026thinsp;30 kya.\u003c/p\u003e \u003cp\u003eThe P.P.Shirshov Institute of Oceanology, Russian Academy of Sciences had carried out geological and geophysical studies in the conjugation zone of the Northern Caspian Sea and Middle Caspian Sea in cruises of \u003cem\u003eRV Rift\u003c/em\u003e in 2006, 2007 and 2012 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The cruises were focused on studies of buried deltaic sequences, first of all the Volga and Ural Rivers paleodeltas. The cruise in 2006 and afterward research were performed by Belgium-Russian project \u0026rdquo;Reconstructing Holocene water-level fluctuations and paleoenvironments in the Caspian Sea based on geophysical and core investigation of the lowstand Volga paleodelta, where the P.P.Shirshov Institute of Oceanology was collaborating with the Geographical Faculty of the Moscow State University and Ghent University. Our results appear to complete and specify available data; especially we suppose to prove new age identification of the deltaic sequences. In general, the paleodeltas studies allow to understand the impact of recent sea-level changes on lowstand delta architecture and on paleoenvironmental conditions during lowstands as well as to obtain a more detailed chronology of lowstands and to appreciate scale of the Caspian Sea regressions during the Pleistocene and Holocene.\u003c/p\u003e"},{"header":"2. Geological setting","content":"\u003cp\u003eThe Mangyshlak Threshold is a large accumulative sedimentary feature in the conjugation zone of the Northern and Middle Caspian Sea. From the north, the Mangyshlak Threshold is bounded by small scarp sloping northward, water depths are mainly near 10 m. In the south, the depth extends up to 50 m isobath. The Mangyshlak Threshold consists of small individual submarine rises, swells and banks and the whole extended chain elongates from the Tub-Karagan Peninsula in the east to the Agrakhansky Peninsula in the west. In general, shape of the Threshold resembles an arc bending slightly northward (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The seafloor has gentle slope southward. General gradient is 1-1.2 m/km, i.e. about 0.001, so a general slope angle is less than five minutes. Two large distinct meandering depressions are expressed in the seafloor topography of the Mangyshlak Threshold area. They are thought to be paleochannels of the\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eVolga and Ural Rivers. These depressions divide the Threshold on approximately equal areas: off Dagestan, middle and off Mangyshlak.\u003c/p\u003e \u003cp\u003eIn the whole area seafloor consists mostly of coarse-grained, compact sediments: shells and shelly detritus, gravel, grus, sand, and a lesser degree \u0026ndash; siltstone and silt (Kuprin et al., 1992). The isobaths outline a gentle arc curved northward whereas the isohypses trend toward NW-SE. N-S striking depression could be visible in relief of the Upper Khvalynian-Novocaspian deposits base in the west of the region (Kuprin, Roslakov, 1992). Eastern side of the depression has gentle slope, while western one is conversely steep (of 50 m amplitude). Broad erosional depression in the middle part of the Mangyshlak Threshold cuts the whole region from the north to the south. The depression stands very close with channel of the paleo-Volga River which was reviled by multichannel seismic reflection profiles within deeper older deposits (Bezrodnykh et al., 2002). So, the N-S depression appears to be an inherited feature. The vast gentle swell by \u0026ldquo;watershed\u0026rdquo; with flat top is located near to the Volga paleo-valley. The vast swell is sloping generally southward; no local features are reviled here.\u003c/p\u003e \u003cp\u003eOne more N-S striking erosional depression in the basal surface is located in the eastern part of the Mangyshlag Threshold, ~ 70 km to the west from the Tub-Karagan Peninsula. That is typical buried river\u0026rsquo;s valley with pronounced channel, valley and deltaic sequence. Its maximum depth is 50 m, wide of the paleo-valley is 10\u0026ndash;12 km. According to its geographical location, origin of the depression relates to the paleo-Ural River. A swell similar to the above mentioned \u0026ldquo;watershed\u0026rdquo; is between the paleo-Volga and paleo-Ureal Rivers (Kuprin et al., 1992).\u003c/p\u003e \u003cp\u003eAccumulation of the sand and clay deposits occurred here at that time when adjacent sea areas sank toward the Derbent Basin with rise of eastern maritime land. That is evidenced by available seismic reflection profiles, in which erosional surfaces within the Quarter deposits as well as alternation of stratified and transparent sediments are observed.\u003c/p\u003e \u003cp\u003eIn general, the deltaic sequence developed and grew from the south to the north. The Mangyshlak Threshold represents huge accumulative body formed during the Pleistocene as result of discharge of large rivers, first of all the paleo-Volga and paleo-Ural, which transported great volume suspended terrigenous sediments. The accumulating of the sediments just near the Mangyshlak Threshold could be explained by strong recent tectonic movements, which affected the seafloor topography.\u003c/p\u003e \u003cp\u003eAccording to the work (Putans, 2010), the change in sedimentation conditions from shelf to deep-water, including deltas and underwater cones of outflow, can be traced on the regional profiles of the Mangyshlak Threshold. It is possible to confidently identify several continuous seismic horizons. The two brightest and most sustained divide the section into three seismic complexes: the lower one is chaotically bumpy, the middle one is parallel-layered, and the upper one with many angular inconsistencies (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). By direct correlation with the well sections, the geological age of the seismostratigraphic horizons was determined on a local stratigraphic scale: the lower complex was assigned to the pre\u0026ndash;Baku time (QIap), the middle one to the Baku and Khazar (QIIb\u0026thinsp;+\u0026thinsp;haz), and the upper one to the Khvalyn and Novocaspian (QIIIhv\u0026thinsp;+\u0026thinsp;QIVnc). This stratigraphy of the Mangyshlak threshold is generally consistent with studies of previous years (Kuprin idr., 1991), (Kuprin, Roslyakov, 1991). Moreover, these horizons are regional stratigraphic discrepancies and correspond to the reflecting horizons OG-3 and OG-5 highlighted in the mentioned works.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRegional seismostratigraphic complexes of the Middle Caspian Sea\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComplex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAge, kyr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSeismic Pattern\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUpper\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKhvalynian-newcaspian\u003c/p\u003e \u003cp\u003e30\u0026thinsp;\u0026minus;\u0026thinsp;0 kyr)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eComplex wave pattern; many angular inconsistencies; alternation of parallel-layered, oblique-layered and acoustically transparent recordings\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003eHorizon OG-5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMiddle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAfterBakin-Khazar\u003c/p\u003e \u003cp\u003e(500\u0026thinsp;\u0026minus;\u0026thinsp;30 kyr)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eParallel layered stratum with several bright horizons, sometimes weakly pronounced angular inconsistencies and buried lenses of chaotically bumpy reflections\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003eHorizon OG-3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLower\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBakin and pre-Bakin\u003c/p\u003e \u003cp\u003e(before 500\u0026ndash;600 kyr)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChaotic bumpy reflections up to acoustic transparency\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe regressive stages caused essential changes of sedimentological processes as well as processes forming the seafloor topography over the Caspian Sea shelf. Great sea-level drop during the Atelian (70\u0026thinsp;\u0026minus;\u0026thinsp;30 kyr) and Enotanian (12\u0026ndash;13 kyr) regressions (dating from Kurbanov et.al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) caused migration of the coastline and river mouths to outer shelf areas, where the large accumulative clinoformes of ancient deltas were formed. They were covered later by marine sediments during following transgressions. The development of paledeltas caused progradation of the shelf and its advancement in to deep-water basin as well as increase angle of northern slope of the Derbent Basin (Kuprin and Roslyakov, 1991).\u003c/p\u003e"},{"header":"3. Methods","content":"\u003cp\u003eThe geophysical and geological coring data were collected by P.P.Shirshov Institute of Oceanology \u003cem\u003eRV Rift\u003c/em\u003e: displacement 1380 t, length 54 m, width 11 m, draught 4.5 m. The paleodeltaic sequence was studied on the detailed research area \u0026ndash; Polygon 1 by 60 x 65 km in size near the Mangyshlak Threshold (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Four geological sites were proposed for sediments coring in 2006 and tree sites in 2007. Total length of collected seismic reflection profiles is about 570 km. The survey was carried out at a speed of 4 knots. Satellite navigation system GPS provides the equipment positioning and coordinates\u0026rsquo; accuracy\u0026thinsp;\u0026lt;\u0026thinsp;30 m.\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Sparker data\u003c/h2\u003e \u003cp\u003eHigh-resolution seismic reflection data were collected using the single-channel profiling system \u0026ldquo;Geont-shelf\u0026rdquo; by 600 J power developed in the Moscow State University. The sparker source with a frequency ranging from about 100 to 1000 Hz (central frequency is ~\u0026thinsp;400 Hz) provides range of penetration up to 300\u0026ndash;400 m bsf and resolution up to 2 m.\u003c/p\u003e \u003cp\u003eThe collected data were processed using special software RadExpro and KingdomSuite.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Geological coring\u003c/h2\u003e \u003cp\u003eGravitational geological corer by 4 m long and grabber produced by P.P.Shirshov Institute of Oceanology were used to collect sediment cores. Site \u0026ldquo;Delta 1\u0026rdquo; (130 m water depth) is located in south-eastern part of the Polygon 1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Total length of cored sediments is 225 cm. Site \u0026ldquo;Delta 2\u0026rdquo; (86 m water depth) is located in central part of the Polygon 1. Geological coring was unsuccessful. Site \u0026ldquo;Delta 3\u0026rdquo; (74 m water depth) is located in central part of the Polygon 1 to north from the site \u0026ldquo;Delta 2\u0026rdquo;. Several large and perfect conserved shells were collected as result of some attempts. Site \u0026ldquo;Delta 4\u0026rdquo; (60 m water depth) is located in northern part of the Polygon 1. Geological coring was unsuccessful. So, coring at the sites \u0026ldquo;Delta 1\u0026rdquo; and \u0026ldquo;Delta 3\u0026rdquo; provides some information about the seafloor sediments. The numerous large shells at site \u0026ldquo;Delta 3\u0026rdquo; seem to evidence, that seafloor in the area is reinforcing by these compact shells. Same was for 2007 coring (01/07, 02/07, 03/07). More weighted gravitational geological corer must be used here for successful geological coring.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e4.1 High-resolution seismic reflection (sparker) data\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e4.1.1 Regional unconformities\u003c/h2\u003e \u003cp\u003eSeismic sections represent distinct strong reflectors which appear to be stratigraphic unconformities marking change of sedimentation regime. It is necessary to note some signs of erosion. The bottom of the marine complex corresponds to the regional horizon of OG-5, and in some areas the horizon of OG-3 is visible, although it is mostly hidden under multiple waves. On the Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e there are sections along the profiles of the polygon: No.5\u0026ndash;9 at the intersection of the slope, No. 4 along the slope (see the polygon diagram in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Scale 1:100. The reference horizons of OG-3 and OG-5 are shown, the horizons are the boundaries of the stratigraphic \"floors\", and the structure of the delta complex (internal boundaries and zones of chaotic bumpy reflections) is schematically outlined.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e4.1.2. Seismic sequences\u003c/h2\u003e \u003cp\u003eUpper part of sedimentary cover consists of two area of sediments with essentially different acoustical image, i.e. seismic sequences (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The first type is characterized by continuous near parallel and near horizontal reflectors. The reflectors are basically weak except for few local areas with amplitudes similar to \u0026ldquo;bright spot\u0026rdquo;. The second type of seismic sequence is characterized by much lesser regularity. The reflectors are sloping steeper and they are ranging from very strong to very weak. Both lateral and vertical variations of visible acoustical pattern\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eare quite great: from extended and smooth reflectors to oblique, hummocky and chaotic ones. In general, the sequence look like lens seismic facies unit. These sediments form lenslike bodies of tens meters thick and several tens kilometers in size. Numerous buried incised depressions and local unconformities are there.\u003c/p\u003e \u003cp\u003e \u003cem\u003eUpper sequence D-1\u003c/em\u003e \u003c/p\u003e \u003cp\u003eThe upper deltaic sequence D-1 lies just beneath seafloor and it is covered by thin sedimentary layer in some places. Thickness of the layer is comparable with the resolution of seismic records, i.e. it is less than 2\u0026ndash;3 m. As it can be seen from the isopach map (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), the sequence represents spatial feature similar to a large convex lenslike mass of 80 m maximum thick. It is necessary note that the maximum thicknesses mass near edge of shelf. This peculiarity is shown distinctly by N-S seismic profiles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Large acoustically transparent zones dominate near the area of maximum thicknesses. Nevertheless, zones of hummocky and parallel seismic reflection configuration occur often too.\u003c/p\u003e \u003cp\u003eContrariwise, interrupted hummocky reflectors predominate on limbs of the convex lenslike mass. They create an oblique seismic reflection pattern where incline of reflectors conform to the general trend of seafloor. However, acoustically transparent zones and sigmoid reflections occur as well. It is interesting that the sigmoid pattern is observed both on N-S and on E-W seismic reflection profiles (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cem\u003eIntermediate sequence S\u003c/em\u003e \u003c/p\u003e \u003cp\u003eThe sequence is represented by acoustically layered seismic facies unit. There are extended/parallel and slightly undulating internal reflectors. It represents stratum, which is draping topography of underlying sedimentary layer. Thickness of the stratum increases from 10 m in the north to 45 m in the south (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). It increases most distinctly beneath the water-depth of 100 m, i.e. behind edge of shelf. The evident pattern of the seismic onlap, which is seen in some places especially in northern part of the area, represents structural unconformity between the two subsequences S-1 and S-2. Instead, the boundary between them in deeper southern part shows no structural features.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eLower deltaic sequence D-2\u003c/em\u003e \u003c/p\u003e \u003cp\u003eTop of the sequence is going down gradually from 22 m bsf in the north to 110 m bsf in the south. Its internal structure is more similar to the same of the upper deltaic sequence D-1 than to the intermediate sequence S. Approximate thickness of the lower sequence D-2 could be estimated due to strong multiples, it is less 40\u0026ndash;50 m, i.e. lesser than thickness of the upper sequence D-1. It is necessary to note especially a possible existence of gas-charged sediments here. Numerous local \u0026ldquo;bright spots\u0026rdquo;, which are accompanied by acoustical shadows below in some places, may be caused by the gassy sediments.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.2. Lithology\u003c/h2\u003e \u003cp\u003eSection collected with geological corer at the site Delta 1 represents structure and contain of the deltaic sediments (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Density and strength of the sediments were measured as well. The density for the sedimentary section varies from 1.60 to 1.65 g/cm\u003csup\u003e3\u003c/sup\u003e. The shear strength increases essentially downward from 2 g/cm\u003csup\u003e2\u003c/sup\u003e at the depth of 60 cm to 20 g/cm\u003csup\u003e2\u003c/sup\u003e at the depth of 115 cm and to 60 g/cm\u003csup\u003e2\u003c/sup\u003e at the depth of 220 cm. Core Delta-1 is clearly correlated with seismic section (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLithology of sediments at the site Delta 1\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e№ п/п\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDepth bsf, cm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLithology\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u0026ndash;37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSmall shells and detritus of grey color with a touch of clayey siltstone of grey-brown color Thin layer of siltstone is at a depth of 25 cm. Amount of shells and detritus decreases gradually in base of the interval.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37\u0026ndash;65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eClayey-siltstone silt of grey-brown color with thin layer and lens of siltstone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62\u0026ndash;98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eClayey-siltstone sediments of grey-olive-colored with numerous lenses and thin layers of siltstone and sand. The lenses and thin layers are unequal. Probably, the substance flowed down as silty fluid therefore, there is no sorting of siltstone and sand pars. Lower boundary of the interval is very clear due to changing of sediments\u0026rsquo; color from grey-olive-colored grey-brown to brown.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e98\u0026ndash;225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMostly clayey-siltstone sediments with numerous interrupted or extensive thin layers of hydrotroilite which imitate appearance of horizontal stratification. The sediments are grey-brown in range of 98\u0026ndash;110 cm, olive-colored in range of 110\u0026ndash;138 cm, brown in range of 1380165 cm and olive-colored in range of 165-200cm, deeper they are clayey-siltstone. Quite thin layer of sand sorted poorly is at a depth of 138 cm, and small sandy lens is at a depth of 175 cm.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5. Discussion","content":"\u003cp\u003eAs a result of the carried out survey, two sequences D-1 and D-2 are distinguished clearly in the research area. The upper sequence D-1 and lower one D-2 are divided by quite thin package S. Comparing the isopach maps (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) of the sequences, one can see some discrepancy in their distribution over the research area. Large acoustically transparent zones dominate near the area of maximum D-1 thicknesses (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). They might be interpreted as massive sand- siltstone formations representing consolidated fluvial mouth bars. Nevertheless, zones of hummocky and parallel seismic reflection configuration occur often too.\u003c/p\u003e \u003cp\u003eTo the south on slope, internal structure of the deposits is to be regulated and it represents a progradational reflection configuration. Near pinch of the upper sedimentary wedge, the internal reflectors are becoming parallel and extended typical for prodeltas. This acoustically pattern is an evidence of enough quiet hydrodynamic conditions of high seas far from coastline. On the other hand, the marine sequence seems to be sheet drape seismic facies unit. The transgressive marine sequence seems to be divided by a strong internal reflector R2a in two subsequences M-1 and M-2 of approximately equal thickness\u003c/p\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e5.1. Age and stratigraphy\u003c/h2\u003e \u003cp\u003ePreviously mentioned horizons OG-3 and OG-5 are regional uncomformities, so they could be clearly traced up to deep site PRV-1 and correlated with dated site. (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The reflector marking top of the lower deltaic sequence represents an erosional surface and was formed simultaneously with accumulation of the deltaic sediments. The sequence can be traced uninterruptedly to the borehole PRV-1 in the west from the polygon (location on Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), where its top is at the depth of 40 m bsf and its thickness is 12\u0026ndash;15 m. That allows to doubt about the Atelian age (70\u0026thinsp;\u0026minus;\u0026thinsp;30 kyr) of the lower deltaic sequence supposed by Lokhin and Mayev (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) because base of the Khvalinian deposits corresponding to the Atelian regression (70-30kyr) was drilled in the borehole much deeper at the depth 84 m bsf. Moreover, the Novocaspian (0\u0026ndash;7 m bsf) and Khvalinian (7\u0026ndash;42 m bsf) deposits determined by fauna were drilled here at the two shallow boreholes PR-1 (depth of 27 m) and PR-2 (depth of 42 m). So, one may declare that the lower deltaic sequence was formed during the Khvalinian regression, probably the Enotaivan one between the Early and Late Khvalinian time. The other strong reflector marking the Atelian regression near the borehole PRV-1 (84 m bsf) is sinking near the polygon 1 up to greater depths. It is impossible to determine age of the upper deltaic sequence in the borehole PRV-1 because the sequence is pinching out at 15 km to the east, where its base outcrops in the seafloor. Hence, its age appears to be regarded as more young, i.e. the upper deltaic sequence could be formed during the Mangyshlak regression but not during the Enotaivan one as proposed by Lokhin and Mayev (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Seismic facies\u003c/h2\u003e \u003cp\u003eTwo seismic facies appear to be recognized within the upper deltaic sequence D-1. First unit is the river channel facies which is characterized by subparallel seismic reflection configuration and slight roughness of inner reflectors. Second unit is the progradation facies which is characterized by progradational reflection configuration or parallel oblique seismic reflection configuration. It is distributed on both sides of the main channel as obliquely layered clinoforms. The main channel, where accumulated the first facies, and sedimentary flows from the main channel forming the second facies. The area near intersection of profile 7 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) with profile 2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) is very difficult for interpretation. That seems to be due to bend of the main channel and, perhaps, due to existence of heteradirectional confluents here. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e5.3. Geographical position of the deltaic sequences\u003c/h2\u003e \u003cp\u003eOne of the most important questions is \u0026ndash; to which paleo-river or paleo-rivers is related formation of the studied deltaic sequences? A supposition, that the paleo-Volga was responsible for such process, is not as evident as it could be considered. The erosional valley of the Volga River formed before the Late Pliocene was revealed by multichannel seismic reflection profiles and confirmed by drilling (the borehole PRV-1) (Gadjiev, Popkov, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). The valley is located far in the east from the polygon 1. Channel of the Volga River does not manifest itself within\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003emore recent sediments over the Northern Caspian Sea so clearly (Sorokin et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). On the assumption of general geological situation, one can suppose logically its migrating still further to the west due to continued sinking of axial zone in the Tersky-Caspian flexure. Two erosional valleys are seen clearly in the isopach map of base of the Khvalinian-Novocaspian deposits near the Mangyshlak Threshold (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the western valley is related to the paleo-Volga River while the eastern one - to the paleo-Ural River (Kuprin and Roslyakov, 1991). According to geographical location of the polygon 1, formation of the studied deltaic sequences was related rather to the eastern valley but not to the western one, i.e. presumably to the paleo-Ural River. To answer finally the question mapping of the buried Upper Pleistocene valleys must be continued over the shallow Northern Caspian Sea.\u003c/p\u003e \u003c/div\u003e"},{"header":"6. Conclusions","content":"\u003cp\u003eThe development of paleodeltas is clearly visible on seismic sections. Three seismic complexes are confidently distinguished: two with complex chaotically bumpy reflections - delta complexes (power in the depocenter on the edge is about 50 m), and a layered marine complex separating them in parallel (power from 10 m on the shelf to 30 m at the foot). It should also be noted the zones of seismic attenuation the signal at the bend of the shelf (isobate 100 m) up to acoustic transparency. The bottom of the marine complex corresponds to the regional horizon of OG-5, and in some areas the horizon of OG-3 is visible, although it is mostly hidden under multiple waves. The same seismostratigraphic division of this area was made earlier, and the system itself was assigned by position to the combined Volga-Ural river system, and in later works to the Ural River. The age estimate in these studies was based on the average sedimentation rate, and the upper delta complex was assigned to the Enotaevskaya, and the lower one to the Athelskaya regression. Since there is currently a correlation with the PRV-1 and Central wells, it is possible to revise the age of the complexes towards rejuvenation in the northeast of the Mangyshlak threshold in the area of the Paleoral outflow cone, undulating folds formed as a result of the \"flow\" of decompressed clay rocks are observed. This flow is accompanied by compression and stretching deformations, which gives rise to a characteristic wave structure with flat peaks and narrow valleys between them. According to geographical location of the buried valleys and deltaic sequences, one can assume that the discussed accumulative units relate rather to the paleo-Ural River.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe work was carried out within the framework of the state task no. FMWE-2024-0019.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eBoth authors wrote the main manuscript text. Both authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eSpecial acknowledgement to Dr.Alexander Roslyakov for highly professional consultations on geology and stratigraphy.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eSeismic data are available after official contact with Institute of Oceanology administration\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBezrodnikh Y.P., Romanov B.D., Reny S.V. (2002) Biostratigraphy and structure of the Upper Quarter deposits and some feature of paleogeography of the Northern Caspian Sea. \u003cem\u003eStratigraphy and geological correlation\u003c/em\u003e - №1 - p.20-35\u003c/li\u003e\n \u003cli\u003eGadjiev A.N., Popkov V.I. (1988) New geological data in Middle Caspian. \u003cem\u003eAcademy of Science presentations\u003c/em\u003e - Vol.299 #3 pp 682-685\u003c/li\u003e\n \u003cli\u003eKuprin P.N., Roslaykov A.G. (1991) Geological structure of the Mangyshlak Threshold. \u003cem\u003eGeotectonics -\u003c/em\u003e №2 - p.28-40\u003c/li\u003e\n \u003cli\u003eKuprin P.N., Rybakova N.O., Semenov E.O. (1991) Stratigraphy of Pliocene-Quaternary deposits on the mangyshlak Threshold. \u003cem\u003eOceanology -\u003c/em\u003eVol.31, iss.5, p.1022-1031\u003c/li\u003e\n \u003cli\u003eKuprin P.N., Luksha V.L., Semenov E.O. (2015) Structure of section and lithology of the Pliocene-Quarter deposits on the Mangyshlak Threshold in the Caspian Sea\u003cem\u003e. Lithology and mineral resources.\u003c/em\u003e №5 - p.35-50\u003c/li\u003e\n \u003cli\u003eKurbanov R., Murray A., Yanina T., Buylaert J.P. (2024) Dating the Middle and Late Quaternary Caspian Sea-level fluctuations: first luminescence data from the coast of Turkmenistan. \u003cem\u003eQuaternary Geochronology\u003c/em\u003e, Volume 83 https://doi.org/10.1016/j.quageo.2024.101599\u003c/li\u003e\n \u003cli\u003eLokhin M.Y. and Mayev E.G. (1990) Late Pleistocene deltas on the northern self of the Caspian Sea. \u003cem\u003eVestnik of the Moscow Universit\u003c/em\u003ey. Ser.5. Geography\u0026nbsp;- №3 - 34-39\u003c/li\u003e\n \u003cli\u003eSorokin V.M., Yanina T.A., Romanuyk B.F. (2018) On age of upper quaternary deposits in North Caspian. \u003cem\u003eVestnik of the Moscow University\u003c/em\u003e - Vol 4 \u0026ndash;pp.75-85 DOI: 10.55959/MSU0579-9406-4-2023-63-4-75-85\u003c/li\u003e\n \u003cli\u003eYanina, T. A, Sorokin V.M., Bezrodnykh Yu, Romanyuk B.F. (2017) Late Pleistocene climatic events reflected in the Caspian Sea geological history (based on drilling data). \u003cem\u003eQuaternary International\u003c/em\u003e\u0026nbsp; DOI: http://dx.doi.org/10.1016/j.quaint.2017.08.003\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"pure-and-applied-geophysics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"paag","sideBox":"Learn more about [Pure and Applied Geophysics](https://www.springer.com/journal/24)","snPcode":"24","submissionUrl":"https://submission.nature.com/new-submission/24/3","title":"Pure and Applied Geophysics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Caspian Sea, deltaic complexes, seismoacustics, seismostratigraphy","lastPublishedDoi":"10.21203/rs.3.rs-5366595/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5366595/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe change in sedimentation conditions from shelf to deep-water, including deltas and underwater cones of outflow, can be traced on the regional profiles of the Mangyshlak Threshold. It is possible to confidently identify several continuous seismic horizons. Upper part of sedimentary cover consists of two types of sediments with essentially different acoustical image, i.e. seismic sequences. The first type of sediments appears to be accumulated under enough quiet hydrodynamic conditions of high seas far from coastline, i.e. they are marine sediments. On the contrary, the second acoustical pattern evidences active lithodynamics inhering in shallow-water and subaerial environment, which are affected essentially by fluvial processes. The characteristic lenslike architecture of the sediments allows us to interpret them as deltaic and avandeltaic sequences, which were accumulated during lowstand stage of the Caspian Sea. According to geographical location of the buried valleys and deltaic sequences, one can assume that the discussed accumulative units relate rather to the paleo-Ural River.\u003c/p\u003e","manuscriptTitle":"Seismostratigraphy of Buried Pleistocene Deltas on the Mangyshlak Threshold, Caspian Sea","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-01 16:30:39","doi":"10.21203/rs.3.rs-5366595/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-01-26T21:12:32+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-12-09T14:27:55+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-29T06:39:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"207391179489080780149934375595704720736","date":"2024-11-27T09:21:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"162984941427861434391216924120488155641","date":"2024-11-08T16:55:29+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-02T18:10:31+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-11-02T15:01:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-11-02T14:47:40+00:00","index":"","fulltext":""},{"type":"submitted","content":"Pure and Applied Geophysics","date":"2024-10-31T09:43:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"pure-and-applied-geophysics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"paag","sideBox":"Learn more about [Pure and Applied Geophysics](https://www.springer.com/journal/24)","snPcode":"24","submissionUrl":"https://submission.nature.com/new-submission/24/3","title":"Pure and Applied Geophysics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e46b556d-1393-48c3-b5c4-1caea5ed4a3d","owner":[],"postedDate":"December 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-02T16:07:43+00:00","versionOfRecord":{"articleIdentity":"rs-5366595","link":"https://doi.org/10.1007/s00024-026-03942-z","journal":{"identity":"pure-and-applied-geophysics","isVorOnly":false,"title":"Pure and Applied Geophysics"},"publishedOn":"2026-02-25 15:57:47","publishedOnDateReadable":"February 25th, 2026"},"versionCreatedAt":"2024-12-01 16:30:39","video":"","vorDoi":"10.1007/s00024-026-03942-z","vorDoiUrl":"https://doi.org/10.1007/s00024-026-03942-z","workflowStages":[]},"version":"v1","identity":"rs-5366595","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5366595","identity":"rs-5366595","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}