Hauterivian Interval Research Articles

Biostratigraphy of Liminic Ostracoda (Crustacea) from the Quiricó Formation, Lower Cretaceous of the São Francisco Basin, Minas Gerais State, Brazil: An approach on paleozoogeographic evolution of Gondwana

The present study is the first biostratigraphic framework based on limnic ostracods for the Quiricó Formation, São Francisco Basin, Brazil. Three sections located at Minas Gerais State were approached: 1. Stratotype section of the Quiricó Formation, Presidente Olegário County; 2. Hypostratotype section of the Tereza Farm, João Pinheiro County; and 3. São Bento Farm section, Carmo do Paranaíba County. After ostracod taxonomic analysis and integration with previous studies, six biostratigraphic units are described, one superzone and five zones. From the lower to the upper part of the Quiricó Formation, zones are: Zone Brasacypris ovum, OSF-0; Zone Timiriasevia sanfranciscanensis, OSF-1.1; Zone Cypridea hystrix, OSF-1.2; Zone Alicenula longiformis, OSF-1.3; and Zone Harbinia spp., OSF-1.4. Superzone Penthesilenula pintoi, OSF-1, comprises zones Timiriasevia sanfranciscanensis, Cypridea hystrix, Alicenula longiformis and Harbinia spp, and is attributed to the Berriasian–Albian? interval. The Brasacypris ovum Zone is attributed to the Berriasian; the Timiriasevia sanfranciscanensis Zone is attributed to the Berriasian; the Cypridea hystrix Zone is attributed to the Valanginian–Hauterivian interval; the Alicenula longiformis Zone is attributed to the Barremian; and the Harbinia spp. Zone is attributed to the Aptian. A paleozoogeographic analysis showed faunal similarities with several sedimentary basins in Brazil, Argentina, Gabon, Gamba, Congo and Cabinda during the late assemblage of Gondwana previous to the complete breakup of the supercontinent.

Morphogenesis of Balkhania balkhanica Mamontova, 1966 (benthic foraminifera) from Lower Cretaceous successions along the northern Tethyan margin (NE and Central Iran): Time and environmental control

Among large benthic foraminifera, Balkhania genus is one of the most valuable taxon that has been used to better constrain the biostratigraphy of the Lower Cretaceous successions along the Tethyan carbonate platforms. The species Balkhania balkhanica is considered as biostratigraphical index for the Barremian-Aptian interval. This study is focused on the B. balkhanica-bearing intervals of the Tirgan and Taft formations from two sections, deposited on the carbonate platform of the Iranian Tethyan margin (Kopet-Dagh Basin, NE Iran and Yazd Block, Central Iran). The age of the studied sections has already been determined in previous works. In present research, morphology and stratigraphical and ecological distribution of the recorded specimens are interpreted. According to the morphological changes, two morphotypes of B. Balkhanica have been introduced. Small-size morphotype is recorded in the Upper Valanginian to Upper Hauterivian interval of the Tirgan Formation. The Upper Barremian to Lower Aptian successions are mostly associated with larger sized specimens having a coarse quartz agglutinated wall, and named arenaceous morphotype. Their wall is in contrast to the Turkmenistan type specimens having a calcite microgranular-agglutinated wall. Inherent evolutionary factor suggests an evolutionary trend of this species from smaller to larger sized specimens during the Late Valanginian to Early Aptian. A preliminary study of the depositional environment also indicates an environmental control for this type of morphological variation. It suggests that the small-size morphotype mostly occurred in an under-stress shallow-water environment, while the larger size morphotype was associated with deeper and more stable outer-shelf environments.

Late Valanginian extinction and turnover of Tethyan brachiopods: A signal of the Weissert Event (Bakony Mountains, Hungary)

Brachiopods, together with ammonoids, were collected bed-by-bed from several Lower Cretaceous pelagic sections and localities in the Bakony Mountains (Transdanubian Range, Hungary), dated by detailed ammonoid and nannofossil biostratigraphy. These yielded abundant and diverse brachiopod material (1015 specimens, 25 species), and a possibility to determine the stratigraphic ranges of the brachiopod species. Two sections, including the Berriasian to Hauterivian interval, were studied in detail. In the Hárskút HK-12 section the early late Valanginian Weissert Event was documented previously by stable isotope investigations and it was biostratigraphically correlated with the Édesvíz Key section. The Lower Cretaceous brachiopod record in the Bakony was separated into four assemblages. The abundant early Berriasian brachiopod Assemblage 1 diminished and with a stepwise extinction and partial turnover passed to an impoverished Assemblage 2 in the early Valanginian. These species ultimately disappeared at the early/late Valanginian boundary. This extinction is interpreted as the effect of the global Weissert Event. The extinction horizon is marked by an almost monospecific, dwarf brachiopod fauna (Assemblage 3). In the late Valanginian an abundant and diverse brachiopod fauna appeared, with a complete turnover of species (Assemblage 4). The development of this assemblage in the late Valanginian and Hauterivian was probably controlled by environmental changes, (1) by a switch in palaeoclimate, i.e. by the late Valanginian cooling episode and (2) by the change in the sedimentary environment.

High-resolution stratigraphy of buchiid bivalves and ammonites from the Jurassic–Cretaceous boundary beds in the Paskenta area (California)

A bed-by-bed biostratigraphical study of two key Californian outcrop sections of the Jurassic–Cretaceous transition interval is presented. The studied succession is characterized by the occurrence of abundant buchiid bivalves and a discontinuous ammonite record. Several Lower Cretaceous ammonite zones were introduced in the literature, but the precise stratigraphic position of key ammonite records remains unclear. Consequently, the buchiid zonation established in the 1970s is still considered the prime biostratigraphic tool, and ammonites have supplementary value. The buchiid zonation is revised herein, and the nomenclature and boundaries are updated. The Buchia sublaevis zone (upper Valanginian (?) to lower Hauterivian) is for the first time recognised in California. Two further biostratigraphic units, i.e. ‘Buchia inflata beds’ (between B. uncitoides and B. pacifica zones) at McCarty Creek and ‘Buchia aff. volgensis-B. unschensis beds’ (between B. piochii and B. okensis zones) at Grindstone Creek, are proposed. The positions of zonal boundaries are determined more precisely than previously, and are based on the first or mass occurrence of index species. As a result, the Panboreal correlation of Tithonian to Hauterivian buchiid zones is improved. Ammonite biohorizons are used as an additional correlative tool, and the following succession is proposed for the Upper Tithonian to earliest Hauterivian interval of the study area: Fierrites dilleri, Paradontoceras storssi, Proniceras maupinense, Neocosmoceras euchrense, Paskentites paskentaensis, Kilianella crassiplicata, Neotollia mutabilis, Sarasinella hyatti, Thurmanniceras stippi, T. jenkinsi and Jeannoticeras jeannoti. A new genus, Howarthiceras n. gen. is established for “Groebericeras” baylei Imlay and Jones.

Two new bairdiid ostracod species from the early Barremian–Hauterivian of the northern and central North Sea to the Atlantic margin off Norway

Abstract. Two new species of bairdiid Ostracoda are described from the lower Barremian – Hauterivian interval of the Valhall and Åsgard formations in the northern and central North Sea and Atlantic margin off Norway. The new species are Pontocyprella valhalla (lsid:zoobank.org:act:CA6B273F-CFF6-4C38-B9F4-18188225A711, 18 January 2018) and Bairdia asgarda (lsid:zoobank.org:act:4A4DC817-A028-45FB-9287-ABF3794F2FCB, 18 January 2018). These species dominate the ostracod assemblage that occurs abundantly in early Barremian–Hauterivian deep marine sediments of the northern and central North Sea and Haltenbanken area off Norway. Pontocyprella valhalla is restricted to this interval and because of its large size and distinct shape is a useful stratigraphic marker species, its last appearance being within the early Barremian.

Carbon cycle history through the Jurassic–Cretaceous boundary: A new global δ13C stack

We present new carbon and oxygen isotope curves from sections in the Bakony Mts. (Hungary), constrained by biostratigraphy and magnetostratigraphy in order to evaluate whether carbon isotopes can provide a tool to help establish and correlate the last system boundary remaining undefined in the Phanerozoic as well provide data to better understand the carbon cycle history and environmental drivers during the Jurassic–Cretaceous interval. We observe a gentle decrease in carbon isotope values through the Late Jurassic. A pronounced shift to more positive carbon isotope values does not occur until the Valanginian, corresponding to the Weissert event. In order to place the newly obtained stable isotope data into a global context, we compiled 31 published and stratigraphically constrained carbon isotope records from the Pacific, Tethyan, Atlantic, and Boreal realms, to produce a new global δ13C stack for the Late Oxfordian through Early Hauterivian interval. Our new data from Hungary is consistent with the global δ13C stack. The stack reveals a steady but slow decrease in carbon isotope values until the Early Valanginian. In comparison, the Late Jurassic–Early Cretaceous δ13C curve in GTS 2012 shows no slope and little variation. Aside from the well-defined Valanginian positive excursion, chemostratigraphic correlation durSchning the Jurassic–Cretaceous boundary interval is difficult, due to relatively stable δ13C values, compounded by a slope which is too slight. There is no clear isotopic marker event for the system boundary. The long-term gradual change towards more negative carbon isotope values through the Jurassic–Cretaceous transition has previously been explained by increasingly oligotrophic condition and lessened primary production. However, this contradicts the reported increase in 87Sr/86Sr ratios suggesting intensification of weathering (and a decreasing contribution of non-radiogenic hydrothermal Sr) and presumably a concomitant rise in nutrient input into the oceans. The concomitant rise of modern phytoplankton groups (dinoflagellates and coccolithophores) would have also led to increased primary productivity, making the negative carbon isotope trend even more notable. We suggest that gradual oceanographic changes, more effective connections and mixing between the Tethys, Atlantic and Pacific Oceans, would have promoted a shift towards enhanced burial of isotopically heavy carbonate carbon and effective recycling of isotopically light organic matter. These processes account for the observed long-term trend, interrupted only by the Weissert event in the Valanginian.

Astrochronology of the Valanginian Stage from reference sections (Vocontian Basin, France) and palaeoenvironmental implications for the Weissert Event

High-resolution gamma-ray measurements performed on five biostratigraphically well-dated reference sections from the Vocontian Basin (south-eastern France) are used to develop a new astrochronology of the Valanginian Stage and its subdivisions (i.e. ammonite and calcareous nannofossil zones and subzones). Spectral analyses show a pervasive dominance of 405-kyr eccentricity cycles with the expression of 100-kyr eccentricity, obliquity and precession. Previous rough estimates of Valanginian Stage duration ranged from 3.9 to 6.5myr but were generally based on less reliable or indirect methods. This study provides a precise duration of 5.08myr, tuning the series to the 405-kyr eccentricity cycle, thus further enhancing the accuracy of the Geologic Time Scale. New durations of magnetochrons are proposed based on intercalibration between ammonite and calcareous nannofossil biozones, cyclostratigraphy and carbon-isotope stratigraphy. After integrating orbitally calibrated durations and available radio-isotopic ages for the Berriasian–Hauterivian interval, a link between the Weissert Event and the emplacement of the Paraná–Etendeka Traps now appears unlikely.Strontium, carbon and oxygen isotope stratigraphy, sedimentological and palaeontological features, clay mineralogy, and the orbital record during the Upper Valanginian all suggest that a transient cool, arid climate occurred after the carbon isotope event, possibly associated with limited polar ice.

MESOZOIC MAGMATISM IN THE FALKLAND ISLANDS (SOUTH ATLANTIC) AND THEIR OFFSHORE SEDIMENTARY BASINS

Recent mineral and hydrocarbons exploration in and around the Falkland Islands has provided data that allows correlation of the onshore and offshore histories of magmatism. New Ar‐Ar age dating of onshore dykes in East Falkland has extended their Cretaceous age range back to ca. 135 Ma (Valanginian – Hauterivian) from the previously reported age of ca. 121 Ma (Aptian). Widespread onshore, ca.188–178 Ma, Jurassic dykes are generally considered a part of the regional Karoo‐Ferrar magmatism linked to the initial break‐up of Gondwana, but we relate the Early Cretaceous dykes, with their characteristic north‐south orientation, to extension of the Falklands Plateau during initiation of spreading in the South Atlantic Ocean. The onshore dykes demonstrate east‐west Early Cretaceous extension, whilst to the north of the archipelago the offshore North Falklands Basin extended between north‐south boundary fault systems from the Late Jurassic onwards. Intrusion of Valanginian – Hauterivian dykes onshore was penecontemporaneous with the intrusion of sills and the extrusion of lavas in the Falkland Plateau Basin. This magmatism, more extensive than previously supposed, may be linked to regional uplift associated with initial opening of the South Atlantic Ocean. The uplift can be demonstrated from seismic data and DSDP boreholes to have occurred during the Berriasian – Hauterivian interval. The thermally‐driven uplift of the platform region played a crucial role in elevating potential sediment source areas and providing the large volumes of sand that were shed intermittently into the surrounding basins from the Valanginian to the Aptian or Albian.

A Late Jurassic fossil assemblage in Gondwana: Biostratigraphy and correlations of the Tacuarembó Formation, Parana Basin, Uruguay

The Tacuarembó Formation has yielded a fossil assemblage that includes the best known body fossils, consisting of isolated scales, teeth, spines, and molds of bones, recovered from thin and patchy bonebeds, from the Botucatu Desert, Parana Basin, South America. The remains are preserved in the sandstones widespread around the city of Tacuarembó. We propose a new formalized nomenclature for the Tacuarembó Formation, naming its “Lower” and “Upper” members as the Batoví (new name) and Rivera (new rank) members, respectively. An assemblage zone is defined for the Batoví Member (fluviolacustrine and aeolian deposits). In this unit, the freshwater hybodontid shark Priohybodus arambourgi D’Erasmo is well represented. This species was previously recorded in Late Jurassic–Early Cretaceous units of the Sahara and the southern Arabian Peninsula. Globally considered, the fossil assemblage of this member ( P. arambourgi, dipnoan fishes, Ceratosaurus-like theropods, and conchostracans) is indicative of a Kimmeridgian–Tithonian age, which in combination with the stratigraphic relationships of the Tacuarembó Formation with the overlying basalts of the Arapey Formation (132 My average absolute age) implies that the latter was deposited during the Kimmeridgian–Hauterivian interval.

Early Cretaceous (Valanginian – Hauterivian) belemnites from western Morocco: stratigraphy and palaeoecology

Recent field work in Lower Cretaceous successions of the Agadir-Essaouira region, western High Atlas, Morocco, have resulted in 489 belemnite guards collected bed-by-bed from the lower Valanginian – upper Hauterivian interval. These findings are described and discussed in their biostratigraphic, taxonomic, palaeoecologic and palaeobiogeographic context. The most common belemnite genera, Hibolithes, Vaunagites?, and Duvalia, are of Meditteranean affinities and closely related to Spanish, French, and Bulgarian faunas. Less common taxa include Pseudoduvalia and Berriasibelus. The genus Pseudobelus, however, common in southeastern France and southern Spain, is rare in the Moroccan sections. The palaeoecological interpretation of these observations result in the recognition of three belemnite assemblages, characterizing different marine settings: 1) A Hibolithes - Duvalia assemblage which is typical for inner to middle shelf settings. These are relatively shallow marine environments with a high input of siliciclastics. 2) A Duvalia - Hibolithes assemblage of the outer shelf setting. Duvalia spp. is the most common genus, Hibolithes spp. is less common, while Berriasibelus spp. and Pseudobelus spp. are rare. 3) A Duvalia - Pseudobelus assemblage of hemi-pelagic preference. Duvalia is most common, next is Pseudobelus.

Palaeotemperatures, polar ice-volume, and isotope stratigraphy (Mg/Ca, δ18O, δ13C, 87Sr/ 86Sr): The Early Cretaceous (Berriasian, Valanginian, Hauterivian)

Temporal trends through Early Cretaceous time of δ 13C, δ 18O, Mg/Ca, and 87Sr/ 86Sr in calcite, and δ 18O in seawater, are discussed using belemnites from SE France and SE Spain. Both positive and negative excursions in δ 13C c are seen in the Berriasian–Hauterivian interval, but none appear to be connected to Paraná–Etendeka volcanism and none can be tied convincingly to changes in sea level. Negative excursions to − 2‰ in δ 13C c occur in the Upper Berriasian and in the Lower Valanginian. Small positive excursions in δ 13C c occur in the uppermost Valanginian (upper C. furcillata Zone) and uppermost Hauterivian ( B. balearis/ P. ohmi Zones). A major positive excursion in δ 13C c in the Valanginian rises to + 1.5‰ through the upper K. biassalense Subzone (upper B. campylotoxus ammonite Zone of the Lower Valanginian), which correlates to Chron M11An.1n., and continues through the S. verrucosum Zone (Upper Valanginian). Extrapolation from carbon-isotope correlations of the onset of this excursion shows that the base of the Hauterivian (F.A. of Acanthodiscus ammonite genus) coincides with the base of Chron M10n and has a numerical age of 133.9 Ma. In Berriasian, Lower Valanginian and Upper Hauterivian belemnites, δ 18O c is mostly negative (around − 0.3‰, three-point mean) but becomes positive (up to + 0.4‰, three-point mean) in the Upper Valanginian and Lower Hauterivian before returning to negative values in the Upper Hauterivian. The transition from negative to positive values, through the S. verrucosum Zone, is accompanied by a 30% decrease in Mg/Ca in belemnite calcite, confirming that the trend in δ 18O c represents mostly cooling. The trend of δ 18O sw, computed from Mg/Ca and δ 18O c, lags trends in Ca/Mg and δ 18O c and becomes around 0.8‰ more positive through the Upper Valanginian and Lower Hauterivian in response, we postulate, to the formation of substantial amounts of polar ice after a period of global cooling. By Late Hauterivian times, temperature proxies ( δ 18O c and Mg/Ca) show substantial warming had occurred and δ 18O sw had returned to less positive values, presumably as a result of waning ice-volume. Sea level lowstands of up to 90 m, reported to occur in the Late Berriasian and Early Valanginian, are not recorded in our δ 18O c or Mg/Ca data, so they were either not real or were tectonic in origin. Values of 87Sr/ 86Sr in seawater rose monotonically by 0.000294 through Berriasian, Valanginian and Hauterivian time, except in Late Valanginian time, when a plateau in 87Sr/ 86Sr occurred. Through extrapolation, the value of 87Sr/ 86Sr is estimated to be 0.707180 ± 0.000010 at the base of the Berriasian and 0.707474 ± 0.000010 at the base of the Barremian; it is fixed by regression analysis to be 0.707294 ± 0.000005 at the base of the Valanginian and 0.707383 ± 0.000005 at the base of the Hauterivian.

Early Cretaceous (Valanginian ‐ Hauterivian) calcareous nannofossils and isotopes of the northern hemisphere: proxies for the understanding of Cretaceous climate

From three boreholes (DSDP Site 535; ODP Site 638; BGS borehole 81/43) of the Central Atlantic and the North Sea Basin 379 samples of early Cretaceous age (Valanginian-Hauterivian) were examined. The localities cover a S-N transect of approximately 3000 km stretching from 17°N to 40°N palaeolatitude. The distribution of calcareous nannofossils and fluctuations of the stable isotopes (δ13C, δ18O) have been recorded and were compared with results of recent studies. We differentiate between high nutrient indicators and oligotrophic taxa and propose a four step scheme to characterize the trophic level of the surface water. (1) High abundances of the fertility group (Biscutum constans/Zeugrhabdotus spp.) combined with a high dominance of B. constans and low abundances of Watznaueria barnesae/W. fossacincta represent a high nutrient environment (eutrophic setting). (2) High abundances of the fertility group combined with a high dominance of Zeugrhabdotus spp. and low abundances of W. barnesae/W. fossacincta reflect enhanced nutrient contents of the surface water (mesotrophic setting). (3) Enhanced abundances of the fertility group combined with high abundances of W. barnesae/W. fossacincta indicate slightly increased nutrient contents of the surface water (meso- to oligotrophic setting). (4) Low abundances of the fertility group and high abundances of W. barnesae/W. fossacincta are of low nutrient affinities (oligotrophic setting). Our estimations of seawater palaeotemperatures in combination with literature data show a distinctive trend for the Valanginian to Hauterivian interval. A general decrease of water temperature from the Valanginian to the early Hauterivian is obvious. This decrease of temperature coincides with the southward migration of the high latitudinal cold water species Crucibiscutum salebrosum to lower latitudes. Our findings shed new light on the evolution of the earliest Cretaceous climate, which may be characterized as a warm greenhouse world with interludes of short cooling.

A Late Hauterivian short-lived anoxic event in the Mediterranean Tethys: the ‘Faraoni Event’

A Late Hauterivian interval (∼127. 5M a ), called the ‘Faraoni Event’, which is characterised by the deposition of deep-marine black shales in the Mediterranean Tethys, is demonstrably of sufficient geological brevity to be qualified as an anoxic event. This event lies within the Pseudothurmannia catulloiammonite subzone, coincides with the extinction of the calcareous nannofossil species Lithraphidites bollii, and records an increase in a globular planktonic foraminifer. High quantities of marine organic matter were preserved in pelagic successions from northern and central Italy, Switzerland, southeastern France, southern Spain and probably elsewhere in the Mediterranean Tethys and Atlantic Ocean. Carbon-isotope stratigraphy from Tethyan and Atlantic sections shows a minor positive excursion in the uppermost part of the Hauterivian and Lowermost Barremian, suggesting accelerated extraction of organic carbon from the ocean reservoir just after the ‘Faraoni Event’. The duration of this short event is less than 100 ka according to cyclostratigraphy and coincides with a third-order sea-level rise. It is likely that similar forcing mechanisms responsible for global OAEs operated during this short time interval. To cite this article: F. Baudin, C. R. Geoscience 337 (2005).

The Jurassic of East Greenland: a sedimentary record of thermal subsidence, onset and culmination of rifting

The Late Palaeozoic – Mesozoic extensional basin complex of East Greenland contains a record of deposition during a period of Rhaetian – Early Bajocian thermal subsidence, the onset of rifting in the Late Bajocian, its growth during the Bathonian–Kimmeridgian, culmination of rifting in the Volgian – Early Ryazanian, and waning in the Late Ryazanian – Hauterivian. The area was centred over a palaeolatitude of about 45°N in the Rhaetian and drifted northwards to about 50°N in the Hauterivian. A major climate change from arid to humid subtropical conditions took place at the Norian–Rhaetian transition. Deposition was in addition governed by a long-term sea-level rise with highstands in the Toarcian–Aalenian, latest Callovian and Kimmeridgian, and lowstands in the latest Bajocian – earliest Bathonian, Middle Oxfordian and Volgian. The Rhaetian – Lower Bajocian succession is considered the upper part of a megasequence, termed J1, with its base in the upper Lower Triassic, whereas the Upper Bajocian – Hauterivian succession forms a complete, syn-rift megasequence, termed J2. The southern part of the basin complex in Jameson Land contains a relatively complete Rhaetian–Ryazanian succession and underwent only minor tilting during Middle Jurassic – earliest Cretaceous rifting. Rhaetian – Lower Jurassic deposits are absent north of Jameson Land and this region was fragmented into strongly tilted fault blocks during the protracted rift event. The syn-rift successions of the two areas accordingly show different long-term trends in sedimentary facies. In the southern area, the J2 syn-rift megasequence forms a symmetrical regressive–transgressive–regressive cycle, whereas the J2 megasequence in the northern area shows an asymmetrical, stepwise deepening trend. A total of eight tectonostratigraphic sequences are recognised in the Rhaetian–Hauterivian interval. They reflect major changes in basin configuration, drainage systems, sediment transport and distribution patterns, and in facies and depositional environments. The sequences are bounded by regional unconformities or flooding surfaces and have average durations in the order of 10 Ma. They are subdivided into conventional unconformity-bounded depositional sequences with durations ranging from tens of thousands of years, in the Milankovitch frequency band, up to several million years. Deposition was alluvial and lacustrine in the Rhaetian–Sinemurian, but almost exclusively marine during the Pliensbachian–Hauterivian time interval when a marine strait, up to 500 km wide and more than 2000 km long, developed between Greenland and Norway, connecting the Arctic Sea and the North Sea. Coal-bearing fluvial and paralic deposits occur, however, at the base of the onlapping Middle Jurassic succession in the central and northern part of the basin complex. The sedimentary development is similar to that in the Northern North Sea and on the Norwegian shelf, and East Greenland offers important onshore analogues for virtually all of the types of deeply buried Jurassic depositional systems of these areas and especially their hydrocarbon reservoirs.

Sequence Stratigraphy, Facies, and Sea Level Change of the Hauterivian Productive Complex, Priobskoe Oil Field (West Siberia)

The productive complex of the Priobskoe field formed during the Hauterivian in the central part of the West Siberian basin as part of the Neocomian (Early Cretaceous) progradational complex. Its depositional setting was a shelf-break margin with well-developed clinoform units and a 1-2° slope gradient. Two depositional sequences have been identified and consist of distinct systems tracts. The lowstand systems tract of the lower sequence (AC12.2-4) formed as a result of rapid high-amplitude relative sea level fall, and is clearly differentiated into lowstand fan and lowstand prograding wedge deposits. Sea level fall of lower amplitude (and rate) led to deposition of a lowstand systems tract in the upper sequence (AC10.1-2) in which no lowstand fan unit was deposited. A thin transgressive systems tract of the lower sequence (AC11.0) formed during a short-term sea level rise. In contrast, prolonged high-amplitude sea level rise led to deposition of a thick transgressive deposit in the upper sequence (AC10.0-AC8). Deposition of the sandiest units is related to shelf (shoal-water) deltas and shelf-edge deltas on the shelf, and to submarine fans in basinal portions. Deposition of shelf-edge deltas was accompanied by abundant gravity-driven processes and formation of shingled turbidites, during which the basin margin significantly prograded and infilled accommodation space. In many cases, sediment supply into the deep-marine systems of Priobskoe was provided from multiple feeder entry points that led to coalescence of individual submarine fans into thick submarine ramps. Because it is based on copious drilling and seismic data, the sequence stratigraphic framework developed for the Priobskoe field may serve as a useful analog model for exploration and prospect generation in Hauterivian clinoforms, as well as in the entire West Siberian Neocomian. There is good correspondence between the relative sea level change interpreted for Priobskoe to the quantified eustatic curve (QEC) generated from Russian platform stratigraphy. This implies that eustasy played an important role in controlling sedimentation in the Priobskoe field. In addition, it supports the validity for the Hauterivian interval of the QEC.