Late Barremian Research Articles

First results of stratigraphic drilling in the North-Eastern Laptev Sea

The Stratigraphic Drilling Project of the Russian Arctic Shelf conducted by the PJSC Rosneft is aimed at discover the stratigraphic age and rock composition of sedimentary succession of its subsurface. In 2021, six shallow wells for the first time have been drilled with core sampling in the east of the Laptev Sea. Drilling revealed folded sedimentary succession dated back to the Late Barremian – Early Aptian. The synrift complex overlying unconformably dates to the Paleocene. The upper strata dates from Eocene to Pleistocene and contains significant hiatuses. The data discovered together with the results of seismic interpretation clarified the regional geological model and dated the stages of its tectonic evolution.

STRATIGRAPHY AND DIAGENESIS OF THE THAMAMA‐B RESERVOIR ZONE AND ITS SURROUNDING DENSE ZONES IN ABU DHABI OILFIELDS AND EQUIVALENT OMAN OUTCROPS

We review published studies characterizing the Thamama‐B reservoir zone in the upper Kharaib Formation (late Barremian) in Abu Dhabi oilfields and at outcrops in Oman. Available data for oxygen and carbon isotope compositions, fluid inclusion measurements, cement abundance and formation water composition are interpreted in terms of a paragenetic model for the Thamama‐B in field F in Abu Dhabi where the interval is deeply buried. The present synthesis provides a useful basis for understanding and predicting reservoir quality in static models and undrilled prospects, as well as for planning promising directions for further research. The goals of this study were to summarize the geologic setting and petrology of the Thamama‐B reservoir and its surrounding dense zones, and to examine how sedimentology, stratigraphy and diagenesis have interacted to control porosity and permeability. Results that may have useful applications for similar microporous limestone reservoirs in general include: the depositional environments and stratigraphy of the subject strata; a model for how porosity variations result mainly from calcite cementation sourced from stylolites, with little dependence on lithofacies other than the localization of chemical compaction by depositional clay linked to sequence stratigraphy; the use of solidity (rock thickness with porosity removed) as a check on porosity creation by burial dissolution; observations linking high‐permeability streaks with storm lag beds and fractures; the concept of strata being gradually buried through a relatively static salinity‐stratified water column; integration of conventional and clumped stable‐isotope data with petrologic observations to constrain the timing of porosity evolution.

Systematic of a Massively Constructed Specimen of Iguanodon galvensis (Ornithopoda, Iguanodontidae) from the Early Barremian (Early Cretaceous) of Eastern Spain

Styracosternan ornithopods are plenty abundant in the Lower Cretaceous fossil record of Europe. In particular, Iguanodon, the second genus of dinosaurs described worldwide, has been found in UK, Belgium, France, Germany, and Spain, evidencing a wide geographical distribution. Currently, the genus Iguanodon comprises two species, the type species I. bernissartensis from the late Barremian–Aptian of Europe and I. galvensis from the early Barremian of Teruel, Spain. The latter species is well known mainly from perinate and juvenile specimens. Here, axial and appendicular fossils of an adult, large and massively constructed ornithopod from the lower Barremian (Lower Cretaceous) Camarillas Formation of Galve (province of Teruel, Spain) are described. Fossil dimensions and some osteological evidence reveal that the specimen was a large (roughly 10 m long) ornithopod. An autapomorphic feature in the ischium and other characters allow us to ascribe this specimen to I. galvensis. In addition, postcranial co-ossification and fusion of the neurocentral suture indicate that the specimen was skeletally mature. Part of the material studied here was unknown in adults of I. galvensis, providing a better knowledge of the axial and appendicular region of this species.

Morphology and ultrastructure of cicatricose spores found in an isolated sporangium-bearing structure of a schizaealean fern from the Lower Cretaceous rocks at Casal do Borracho, Torres Vedras, western Portugal

Fossil spores provide important insights into the evolutionary history of ferns, including their morphological changes and adaptations over time. The morphology and ultrastructure of trilete spores with cicatricose sculpture composed of sets of parallel or near-parallel ribs (muri) have been studied. Observations on the spores were performed using light microscopy, scanning electron microscopy, and transmission electron microscopy. The cicatricose spores were extracted from a single sporangium-bearing structure collected from Casal do Borracho mesofossil flora near Torres Vedras (Lusitanian Basin, western Portugal) from sediments belonging to the Almargem Formation, considered to be of late Barremian or early Aptian age (and possible younger than that). The sporangium-bearing structure of a schizaealean fern and in situ cicatricose spores are compared with the family Anemiaceae. On the basis of spore size and shape, laesura length, with about 20 proximal narrow ribs, oriented perpendicular to the spore sides, and three sets of distal ribs forming V-shaped patterns, the cicatricose spores in the present study are clearly assigned to the fossil-taxon Cicatricosisporites venustus. The spore ultrastructure includes a homogeneous exospore of a blechnoid type with a slight difference in the thickness in the proximal, distal, and equatorial regions. The morphology and ultrastructure of the studied spores are corresponded to Anemia type.

Ammonite families Phylloceratidae, Gaudryceratidae, Oppeliidae and Desmoceratidae from Kopet Dagh Basin NE of Iran; Palaeobiogeographical and palaeoecological application

The Kopet Dagh sedimentary basin is situated in the northeast of Iran and the south of Turkmenistan. The present work focuses on the systematic representative's species of the Family Phylloceratidae Zittel, 1884, of the Family Gaudryceratidae Spath 1927, of the Family Oppeliidae H. Douvillé, 1890, and of the Family Desmoceratidae Zittel, 1895, all of which are for the first time in the basin. Based on previous studies and assemblage fauna in this study, a late Barremian-early Aptian age is suggested for the measured sequences. The palaeobiogeographical distribution of the ammonites indicates that during the late Barremian to the late Aptian the basin formed part of the Tethyan realm, Mediterranean-Himalayan Province. The studied fauna and other reported ammonites in previous publication might suggest nearshore to offshore an epipelagic to pelagic environment. There is also a relation between the lithology and the morphotype of ammonites.

Integrated multi-proxy source-to-sink analysis of Late Barremian (Lower Cretaceous) clastic systems in the Essaouira-Agadir Basin

This study investigates the provenance of the continental and marine Late Barremian clastics of the Bouzergoun Formation, exposed in the Essaouira-Agadir Basin (EAB). Thin section petrography, Scanning Electron Micrography, heavy minerals analysis, and detrital zircon dating were conducted and integrated with a large dataset of published Low-Temperature Thermochronology (LTT) studies to reconstruct the associated source-to-sink system(s). The results constrain the source and size of the system, and composition of deposited clastics, and investigate the mechanism for delivery of coarse clastics into the offshore domain, a key target for hydrocarbon exploration.The homogeneity of rock composition fingerprints throughout the basin indicates a common provenance for both the northern and southern studied transects. Hinterland analysis based on LTT data identifies the Western Meseta and Massif Ancien de Marrakech (MAM) regions as the only possible source candidates exhuming during the Late Barremian, confirmed by detrital zircon geochronology. Heavy mineral populations reveal partly recycled sediment including a probable igneous source. Rock fragment populations comprise limestones, sandstones, and volcanic composition, which correlate with lithologies of the MAM.The integration of all data suggests a best-fit model for the Late Barremian of a source-to-sink system of moderate size (200–300 km long), dominantly sourced from the MAM (western High Atlas). This provided a sand-rich mix of sediment resulting from the erosion of exhuming Triassic continental basins, with associated clays from the weathering of basalts and Triassic/Jurassic mudstones.Late Barremian eustatic sea level fall, together with regional uplift in the hinterland, is interpreted to have resulted in a forced regression that allowed the system to prograde towards the slope margin, offering enhanced potential for sand delivery into the deep offshore domain. Seismic imaging offshore provides tentative interpretation of synchronous high reflectivity deepwater channels located in structural lows controlled by diapiric salt movement.The Mesetian domain was likely undergoing denudation at the same time and shedding clastic-rich sediments to the northern part of the EAB, beyond the studied region. Sediment supply from the MAM may be mixed with the Mesetian sands to the northern part of the EAB and tentatively in the offshore Essaouira.

New theropod remains from the late Barremian (Early Cretaceous) of Eastern Iberian Peninsula

ABSTRACT In the last decade, the Iberian Peninsula has become a hot spot in the understanding of the early evolutionary history of large-bodied theropods from the Early Cretaceous, especially for the Spinosauridae and Carcharodontosauridae families. To date, at least five species of spinosaurids and one species of carcharodontosaurid inhabited the Iberian region during the Barremian. However, the discovery of new fossil remains suggests that such a diversity of medium- to large-sized theropods could be even higher. Here, we describe an unpublished large theropod tooth and two caudal vertebrae collected in the late 70s in the upper Barremian strata of the Arcillas de Morella Formation (Morella, eastern Spain). The tooth element displays a series of features that allow its identification as cf. Protathlitis, while the vertebral elements are tentatively attributed to an indeterminate carcharodontosaurid. Interestingly, these last remains are different from those of Concavenator, allowing speculation about the occurrence of another species of carcharodontosaurid allosauroids in the Iberian Peninsula during the Early Cretaceous apart from the famed humpbacked dinosaurs and with some reminiscence to Acrocanthosaurus. Therefore, the new findings clearly illustrate the significance of any new theropod remains in depicting the theropod diversity before the final break-up of Pangea in the Iberian Peninsula.

Rise and demise of the Urgonian platform in Switzerland

Abstract Defined in the Provence region of France, the rudist-bearing Urgonian Limestone is typical of northern Tethyan shallow-marine carbonate series, and is dated based on benthic fauna and flora, calcareous nannofossils and ammonites. This contribution reports on recent findings that refine the stratigraphy of the Urgonian Limestone in the western Swiss Jura and the Helvetic Alps of Switzerland. In the former location, the high-resolution facies and isotope analysis of samples permits the identification of major periods of subaerial exposure, while a diverse assemblage of calcareous nannofossils indicates a Barremian age for the Urgonian deposits. In the latter location, biostratigraphical data indicate a Late Barremian–Early Aptian age for Urgonian deposits, while the repartition of facies along a proximal-to-distal transect highlights the Late Barremian progradation of the platform. The detailed understanding of the stratigraphy of Urgonian deposits in these regions inscribes them into a broader context that acknowledges palaeoclimatic and palaeoenvironmental conditions. A warmer and more humid climate prone to continental weathering and transport of nutrients to an epicontinental sea characterized the Early Barremian; this was detrimental to the health of carbonate-producing benthic ecosystems. In the Late Barremian, a reduced nutrient supply allowed Urgonian communities to thrive.

TAXONOMIC AND BIOSTRATIGRAPHIC REMARKS ON TORINOSUELLA MAYNC, 1959 AND BALKHANIA MAMONTOVA, 1966, LARGER BENTHIC FORAMINIFERA FROM THE LOWER CRETACEOUS OF IRAN (SANGESTAN, TIRGAN FORMATIONS)

The monospecific genera Torinosuella Maync [type-species T. peneropliformis (Yabe & Hanzawa)] and Balkhania Mamontova (type-species B. balkhanica Mamontova) have been reported from the Lower Cretaceous of Iran, respectively the ‘Carbonate Member’ of the Sangestan Formation (Central Iran) and the Tirgan Formation (NE Iran). The literature review reveals a range of late? Tithonian–early Barremian for Torinosuella and late Barremian–early Aptian for Balkhania. In a recent publication dealing with the ‘Taft’ Formation (Central Iran) and the Tirgan Formation (northeastern Iran), both taxa have been lumped together and described as two morphotypes of B. balkhanica based essentially on size differences. This mixing was associated with incorrect phylogenetic, taxonomic, biostratigraphic (e.g., First Appearance Datum) and palaeoecological conclusions that are herein addressed and corrected. Without clarification about the spatial and temporal distribution of individual taxa, the usefulness of larger benthic foraminifera for biostratigraphy, palaeoecology and palaeobiogeography would be distinctly reduced.

Clay mineral assemblages as a tool in source-to-sink studies: an example from the Lower Cretaceous of the North Sea Basin

The alternating marlstone and chalk of the Lower Cretaceous succession in the Danish Central Graben (DCG) are important for the understanding of the evolution of the larger North Sea Basin. This study focusses on the clay mineral assemblages of the upper Hauterivian – lower Aptian in the DCG and Danish Basin (DB) and their implications. Clay mineral assemblages are predominantly used to assess palaeoclimate. In this study, however, they were additionally used in a source-to-sink context. Kaolinite was found to form a dominant component of the clay mineral assemblage in the sampled wells of the DCG and in the DB, suggesting that a feldspar- or kaolinite-rich source was present and actively eroded in the region during the Early Cretaceous. Moreover, a decreasing gradient west to east of average kaolinite content is observed in the three studied wells for the early Hauterivian to late Barremian (BC9-BC17), with the highest content observed in the North Jens-1 well (av. 74%), followed by the Boje-2C well (av. 49%) and lastly in the Vinding-1 well (av. 39%). Due to the relatively rapid settling of kaolinite in marine environments compared to other clay minerals, this gradient suggests that the main clay mineral source was located in the south-western part of the DCG. Isochore maps, a new palaeogeographic map of the DCG and the western part of the German sector of the North Sea illustrates where Lower Cretaceous rocks are absent in this region, due to either erosion or non-deposition. Potential subaerially exposed highs included the distant Baltic Shield to the north, the Ringkøbing–Fyn High to the east and the Heno Plateau within the DCG, with the latter being located closest to the North Jens-1 well and containing feldspar-rich sandstones of the Heno Formation (upper Kimmeridgian – lowermost Volgian/Tithonian). During the Early Cretaceous, part of the Heno Formation was potentially subaerially exposed or subject to wave reworking/erosion in parts of the Danish and German sectors. The sandstones could weather into kaolinite and this structural high is therefore suggested to have been the main source area for this part of the DCG, with minor sediment influxes from the Ringkøbing–Fyn High and Baltic Shield. In addition, the overall decrease in kaolinite in the DCG from the late Hauterivian to the late Barremian indicates a climatic change towards drier conditions, with some minor, slightly more humid periods.

Pachytraga gracilis sp. nov. (Hippuritida, Caprinidae) from the Barremian of the Sub-Alpine region (SE France). Evolutionary and biogeographic implications for the genus Pachytraga Paquier

A new species of Pachytraga (family Caprinidae) is described from the Forêt de Coulmes (Northern Vercors, Subalpine region of SE France) and dated from the Taveraidiscus hugii- Nicklesia nicklesi ammonite Zones (lowermost Barremian). Pachytraga gracilis sp. nov. has an undivided posterior myocardinal cavity on the left valve and an anterior myophore supported by a single row of rectangular canals. The right valve bears a row of anterior canals, a partitioned posterior perimyophoral cavity and a network of minute pallial canals on the dorsal side. The new species represents an evolutionary link in between the Hauterivian Pachytraga tubiconcha and the Late Barremian–early Aptian Pachytraga paradoxa, so shortening the West European Barremian Lazarus phase of the genus Pachytraga. The possibility of a Barremian p.p. ecological rather than geographical refuge is proposed. We consider the new species as a potential biostratigraphic marker of the West European lowermost Barremian. It is the oldest member of canaliculated Caprinidae. Number of traits of Pachytraga gracilis sp. nov. (shape, mode of canaliculation), are absent in its assumed descendant P. paradoxa, but present in other advanced taxa, Praecaprina, Caprina, hence the new taxon was a precursor in more ways than one.

Burial history and hydrocarbon generation model of the Lower–Middle Jurassic sediments in the Tarnovo depression

This study deals with the geodynamic evolution in the Tarnovo depression, contributes to a better understanding of the burial and thermal history, and gives a model of the generation of hydrocarbons from the Lower–Middle Jurassic rocks. The implications of the complex heat flow scenario for the timing of hydrocarbon generation from the Stefanets Member of the Etropole Formation in selected sections were also analyzed. The Tarnovo depression is defined as a small tectonic unit in the central part of the South Moesian Platform margin developed mainly during the Early–Middle Jurassic. Therefore, the sediment subsidence during the Early–Middle Jurassic is largely a consequence of the tectonic processes in an extensional basin with tilted, fault-bounded, and eventually rotated blocks. There is a trend of increasing tectonic and basin subsidence in southern direction, observed in modeled well sections. The Lower–Middle Jurassic rocks enter the “oil window” in the late Barremian, Hauterivian, or even the late Valanginian towards the south, starting active generation in the middle Aptian. The model shows that gas generation is possible only in the southern and marginal zones of the Tarnovo depression. Among the sequence, the Stefanets Member of the Etropole Formation (Aalenian–early Bajocian in age), composed of shales and siltstones, possesses source rock qualities and good hydrocarbon generation potential. The research model argues for peak of the oil generation from the Stefanets Member at the end of the Barremian up to the Albian to the north and gas generation starting in the Barremian and continuing during the Cenozoic only in the southern part.

New Insights into the Platform-to-basin Anatomy of the Urgonian Bas-Vivarais Domain (Lower Cretaceous; SE France)

This paper offers a new contribution to our ongoing harmonization efforts concerning the chronostratigraphic model of the southern France Urgonian-type carbonate platforms, which surrounded the Vocontian Basin during the Early Cretaceous. A multi-stratigraphic approach on the classical sections of the Ardèche River gorges and the Saint-Remèze Plateau have been used for reconstructing the evolution of the Bas-Vivarais Urgonian domain along an inner-to-outer platform profile; the latter being nearly perpendicular to the eastern Vocontian platform margin. In our transect, the installation and first developments of the Urgonian platform domain occured during the early Barremian Taveraidiscus hugii and Kotetishvilia nicklesi ammonite zones. This first platform stage was interrupted at a brief emersion episode that lasted through the Nicklesia pulchella ammonite zone, and resulted in the deposition of a sedimentary wedge with limited gradual downward, basinward shift in inner platform facies. This was followed by the regional deposition of shallow-water communities dominated by corals, echinoids, and orbitolinids, which passes basinward into open-marine, ammonite-bearing marly deposits in the Saint-Remèze Plateau outcrops. This change in facies was previously referred to as the Serre de Tourre Beds (STB), and dated to the Kotetishvilia compressissima and Moutoniceras moutonianum ammonite zones. The STB are further identified to as the local sedimentary expression of the Mid-Barremian Event recording a brief warming climate pulse testified by the presence of Offneria simplex, a caprinid rudist of Caribbean origin. Above, there is a regional recovery of inner platform Urgonian facies during the early late Barremian showing a striking progradational basinward trend. The latter, and its subsequent developments are in need of investigations. Taken together, the general evolution of the Urgonian Bas-Vivarais domain shows strong similarities with the sedimentary context of the nearby Subalpine Urgonian platform during the early Barremian. The finding of common sedimentary signals is more difficult with the Provence platform domain at that time.

A new pterosaur specimen from the Lower Cretaceous Yixian Formation of Liaoning Province, China: The oldest fossil record of Nurhachius

ABSTRACT The Istiodactylidae is one of three ornithocheiroid pterosaur lineages, characterised by a large nasoantorbital fenestrae and labiolingually compressed teeth. Their remains have been reported from Early Cretaceous rocks of northeastern China and Western Europe. A new istiodactylid pterosaur from the upper part of the Yixian Formation (Jingangshan Member) of the Jehol Group, distributed in western Liaoning Province and neighbouring areas, is described on the basis of an incomplete specimen including the partial skull, forelimb and hindlimb bones, and pelvis. This individual, here designated as a referred specimen of Nurhachius (Nurhachius sp.) is a skeletally almost mature pterosaur with an estimated wingspan of 1.6 m. This specimen is not only the geologically oldest known occurrence of Nurhachius, but also a new component of the pterosaur assemblage of the Jingangshan Member, and provides new information on the pelvis and hindlimb of istiodactylids and the palaeobiology of this clade. Considering previous reports of the istiodactylid remains and the geological ages of the strata that yielded them, it is suggested that different istiodactylids existed in Europe and China during the late Barremian.

The helochelydrid turtle Helochelydra nopcsai from the Early Cretaceous (late Barremian – early Aptian) fissure fills of Balve, North Rhine-Westphalia, Germany, including a large sample of granicones

Early Cretaceous (late Barremian – early Aptian) fissure fill deposits near Balve, North Rhine Westphalia, Germany, have yielded a rich continental vertebrate fauna over the course of the last two decades. More than 250 fragmentary specimens, including more than 150 osteoderms (i.e., granicones), represent the late Early Cretaceous helochelydrid Helochelydra nopcsai, which had previously been reported from the UK, France, and Spain. The new material mostly differs from that from the type section by exhibiting a reduced to absent entoplastral scute and by displaying distinct cranial scute sulci, both of which are interpreted as intraspecific variation. Although morphological insights are limited, the new material reveals that the visceral cavity extends anteriorly and posteriorly to the bridge, a relatively novel feature previously reported for an eclectic mix of compsemydids, pleurosternids, and other helochelydrids. The available sample of granicones reveals great shape diversity, but a morphometric analysis concludes that no distinct morphotypes exist.

Nomenclatural status of Orbitolina pileus Fossa-Mancini 1928 (Foraminifera) (junior synonym Palorbitolinoides orbiculatus Zhang 1986) from the Lower Cretaceous of the Himalaya (Ladakh, Tibet)

ABSTRACT The published literature concerning Lower to mid-Cretaceous (late Barremian–Albian, early Cenomanian) Tibetan Orbitolinidae suggests an apparent extreme high diversity with almost exclusive reference to taxa displaying a complex embryo (subfamily Orbitolininae). The majority of them, among Orbitolina pileus Fossa Mancini described in the late twenties from the border areas of Ladakh (India) and Tibet (China), however need taxonomic reconsideration. The original images of O. pileus are herein interpreted as a mixture of a high-conical mesorbitolinid (of unclear species identity) and a section of Palorbitolinoides orbiculatus Zhang described in the early 80ies from Tibet. The concluding new nomenclatural act considers P. orbiculatus a junior synonym of O. pileus validated herein as Palorbitolinoides pileus (Fossa-Mancini) comb. nov. with the designation of a lectotype. The present study refers to data from the literature and own material from the Albian Langshan Fm. of the northern Lhasa Block of Tibet.

A new spinosaurid dinosaur species from the Early Cretaceous of Cinctorres (Spain)

A new spinosaurid genus and species is described based on the right maxilla and five caudal vertebrae of a single specimen from the Arcillas de Morella Formation (Early Cretaceous) at the locality of Cinctorres (Castellón, Spain). Protathlitis cinctorrensis gen. et sp. nov. is diagnosed by one autapomorphic feature as well as by a unique combination of characters. The autapomorphy includes a subcircular depression in the anterior corner of the antorbital fossa in the maxilla. The new Iberian species is recovered as a basal baryonychine. The recognition of Protathlitis cinctorrensis gen. et sp. nov. as the first baryonychine dinosaur species identified from the Arcillas de Morella Formation (late Barremian) from the same time as Vallibonavenatrix cani, the first spinosaurine dinosaur from the same formation in the Morella subbasin (Maestrat Basin, eastern Spain), indicates that the Iberian Peninsula was home to a highly diverse assemblage of medium-to-large bodied spinosaurid dinosaurs. It seems that spinosaurids appeared during the Early Cretaceous in Laurasia, with the two subfamilies occupying the western part of Europe during this period. Later, during the Barremian–Aptian, they migrated to Africa and Asia, where they would diversify. In Europe, baryonychines were dominant, while in Africa, spinosaurines were most abundant.

Biome responses to a hydroclimatic crisis in an Early Cretaceous (Barremian–Aptian) subtropical inland lake ecosystem, Northwest China

The Early Cretaceous palaeoclimate was characterized by arid–humid alternation and accompanied by a series of short-term extreme environmental events, resulting in significant disturbances to the terrestrial ecosystem. However, the discontinuity of terrestrial geological records leads to a lack of detailed research on the coevolution mechanism of organisms and the environment. This study aims to investigate the response of the late Barremian–early Aptian subtropical lake biome structure to the hydroclimate crisis in the Yin'e Basin based on palynology, macropalaeontology, and geochemistry (i.e., major and trace elements, organic carbon isotopes, and biomarkers). The warm and semihumid climate promoted an increase in the abundance and degree of divergence in the vegetation, and the brackish–oxic conditions of the water column were conducive to the prosperity of aquatic organisms. The early aridification of the climate led to a decline in the lake level and a salinity crisis. The saline–suboxic conditions of the water column triggered the first aquatic crisis, while bacterial populations increased gradually. Cooling and continuous aridification led to a significant reduction in the types and amount of vegetation. The insufficient supply of nutrients and the continuous shrinking of the lake caused a second aquatic crisis, and several macroscopic organisms disappeared. The multivariate correlation analysis based on geochemical parameters showed that the palaeoclimate was the key driving factor for the evolution of palaeolakes and their conditions in the water column, and there was a close relationship among the ecological environmental indicators. The petrological and geochemical parameters suggest the existence of lacustrine hydrothermal activity, which could also have a direct impact on the ecological environment of the lake. This study of the Bayingebi Formation palaeolake in the Yin'e Basin provides a strong example of the close coupling changes in the palaeoclimate and lake ecosystem to understand the continental sedimentary response to Early Cretaceous palaeoclimate warming events.

Early Cretaceous (late Barremian−Early Albian) expanding aeolian activity in East Asia: Evidence from the stratigraphic evolution of aeolian deposition in the Baiyin-Jingyuan Basin, northern China

Cretaceous aeolian deposition is important for understanding variations of the tropical−subtropical atmospheric circulation under the greenhouse background. Nevertheless, detailed records revealing the response of aeolian deposition to rising atmospheric CO2 are still lacking. To shed light on their linkage, we examined the Early Cretaceous stratigraphic evolution of the Hekou Group in the Baiyin-Jingyuan Basin, northern China, using multiple methods. The results indicate that the lower Hekou Group is characterized by a transition from submerged alluvial to shallow lacustrine deposition. Overlying these facies is loess-like deposition without bedding, distinguished by grain-size distribution, surface microtextures, and geochemical analysis, which is followed by palustrine deposition. In the palustrine deposition, aeolian sand-dune and sand-sheet deposition can be identified, which gradually developed upward in the Hekou Group, with intercalated wet interdunes, damp interdunes, and pebble-sand sheetflood beds. Finally, aeolian sand dunes and sand sheets dominated the upper Hekou Group. Overall, the upward-changing facies indicated the development of aeolian deposition from an aqueous environment, revealing a long-term paleoclimatic shift from semi-humid, semi-arid to extremely arid, which reflects the expanded aeolian activity in East Asia during the Early Cretaceous. Furthermore, various records were combined to investigate the expanding aeolian activity in East Asia, which indicates a west−east-trending arid belt that was wider than the modern counterpart during the late Barremian−Early Aptian and late Aptian−Early Albian, respectively. These stepwise expansions of aeolian activity were mainly driven by rising atmospheric CO2, which strengthened the subsiding branches of Hadley circulation and the subtropical high, eventually leading to intensified aridification.

Late Barremian–Aptian paleoenvironmental variations and OAE1a environmental effect in the eastern Crimea

The early Aptian Oceanic Anoxic Event 1a (OAE1a, or Selli Event) is widely known from many oceanic and inland sections as an interval of enhanced accumulation of sediments rich in total organic carbon (TOC), associated with the turnover in the global carbon budget and dramatic biotic variations. Our multidisciplinary study of the upper Barremian to lower upper Aptian deposits from the eastern part of Crimean Peninsula allowed us to confirm the presence of a layer that correlates to OAE1a and revealed significant reorganization in the planktonic and benthic foraminifera, nannofossils, ostracod and terrestrial plant communities at this level. The low-calcareous OAE1a deposits from the eastern Crimea lack in TOC that is not typical sedimentological response to this critical event. The OAE1a onset was associated with a nannoconid crisis, occurrence of low-abundance Hedbergella planktonic foraminifera, increased abundance of benthic foraminifera and ostracods and the bloom of Classopolis on the adjacent land. The calcareous microplankton biota was highly oppressed during OAE1a up to total elimination in the core of the event. Benthic assemblages indicate the occurrence of dysoxic conditions at the sea-floor. The absence of organic matter in the deposits of the OAE1a interval points to the low basinal biotic productivity and low input of terrestrial organic matter. We suggest that oligotrophication of the basin was related to the transgressive pulse, which led to small-scale landward moving of the coastal line barriered by coastal highland. The hot arid climatic conditions indicated by terrestrial plants, prevented the supply of nutrients and terrestrial organic matter into the basin that caused low algal and bacterial productivity and prevented accumulation of TOC-rich sediments. The termination of OAE1a coincides with the occurrence of warm humid climate and erosion of ephemeral coastal highland, more likely, built up by soft clayey sediments. The transit restoration of the normal marine biota in the early late Aptian was interrupted in the middle late Aptian by new long-lived regression led to enhanced terrestrial runoff and, possibly, fresh water input killed marine biota and caused the accumulation of low-calcareous clay.