Early Bathonian Research Articles

Geochemical and palynological records of the Early‐Middle Jurassic in the Turpan‐Hami Basin, NW China: Implications for paleoenvironment and paleoclimate change

The Early‐Middle Jurassic is one of the crucial coal‐forming geologic periods in the world and an important target for hydrocarbon exploration in the Turpan‐Hami Basin, China. The paleoenvironment and vegetation reconstruction of the Early‐Middle Jurassic have been investigated using elemental geochemistry and palynological analysis to reveal paleoclimate evolution. A total of 48 genera of pteridophyte spore and 35 genera of gymnosperm pollen were identified, and 5 palynological assemblages were longitudinally divided, which showed significant differences in geochemical behaviours. The paleoenvironment was a transition from suboxidation to anoxia and then to an oxidation environment under freshwater conditions. The paleowater in the northern Taibei Sag was deeper than that in the southern part during the Middle Jurassic, which coincided with the sedimentary background of the sublacustrine fan in the north and the shallow braided river delta in the south. The paleovegetation evolved from mixed lowland–upland forest in the Hettangian‐Toarcian, to lowland fern forest in the Aalenian‐Bajocian, to upland conifers forest in the early Bathonian, to upland Cheirolepidiaceae forest in the late Bathonian‐Callovian. The Toarcian and Bathonian‐Callovian arid climate and the Hettangian‐Pliensbachian and Aalenian‐Bajocian warm‐humid climate were responses to the continued global warming events and the intensification of the East Asian monsoon circulation, respectively. The influence of the Bathonian‐Callovian aridification event on the sedimentary response in the southern Taibei Sag will be delayed due to the gradual southward migration of the depositional centre.

THE FIRST RECORD OF A REPRESENTATIVE OF THE TOARCIAN-EARLY AALENIAN BELEMNITES IN KIMBERLITES OF THE OBNAZHENNAYA PIPE (NORTHEASTERN SIBERIAN PLATFORM)

Berlites of the Obnazhennaya pipe of the Kuoika kimberlite field (northeastern Siberian Platform, Olenyok uplift), a rostrum fragment of a representative of Toarcian–Early Aalenian (latest Early Jurassic–earliest Middle Jurassic) belemnites was found for the first time, namely Arcobelus cf. krimholzi (Sachs, 1970). It is shown that belemnite records previously known from here and dated to the Late Jurassic or Early Cretaceous, may be of Bajocian–Bathonian (Middle Jurassic) age. The stage of kimberlite magmatism of 177 ± 1.5 Ma, recently established in the northeastern part of the Siberian craton according to U–Pb geochronological data, falls on the time of the existence of belemnites of the genus Arcobelus. The estimated Late Bajocian–Early Bathonian age of the representative of the genus Pachyteuthis previously found in kimberlites of the Obnazhennaya pipe is consistent with the 40Ar/39Ar age (167 Ma) as well as with the age based on some paleomagnetic data (168 ± 11 Ma) reported for the pipe. In the paleogeographic schemes of the northeastern part of the Siberian Platform during the Toarcian–Early Bathonian interval, the inner part of the shelf should be extended to the territory of the Kuoika kimberlite field, taking into account the new data on belemnites.

The First Record of a Representative of the Toarcian–Early Aalenian Belemnites in Kimberlites of the Obnazhennaya Pipe (Northeastern Siberian Platform)

A rostrum fragment of a representative of the Toarcian–Early Aalenian (the latest Early Jurassic–the earliest Middle Jurassic) belemnites Arcobelus cf. krimholzi (Sachs, 1970) was found for the first time in kimberlites of the Obnazhennaya pipe of the Kuoika kimberlite field (northeastern Siberian Platform, Olenek Uplift). It was shown that the belemnite records previously known here and dated to the Late Jurassic or Early Cretaceous may be of Bajocian–Bathonian (Middle Jurassic) age. The stage of kimberlite magmatism of 177 ± 1.5 Ma, recently established in the northeastern part of the Siberian craton according to U–Pb geochronological data, falls on the time of the existence of belemnites of the genus Arcobelus. The estimated Late Bajocian–Early Bathonian age of the representative of the genus Pachyteuthis, previously found in kimberlites of the Obnazhennaya pipe, is consistent with the 40Ar/39Ar age (167 Ma), as well as with the age based on some paleomagnetic data (168 ± 11 Ma) reported for the pipe. Taking into consideration the new data on belemnites, the internal part of the shelf should be extended to the territory of the Kuoika kimberlite field in the paleogeographic schemes of the northeastern part of the Siberian Platform during the Toarcian–Early Bathonian.

Ammonite biozonation and chronostratigraphy of the Upper Bajocian–Upper Oxfordian of the Dalichai Formation at the Kuh-e-Varvari section (North of Damghan, Alborz and North Iran)

ABSTRACT The Middle–Upper Jurassic strata in the eastern part of the Alborz, North of Iran (Dalichai Formation) were studied based on ammonite fauna to correlate with zonation of other West Tethyan areas (Sub-Mediterranean province). In this section, like other studied sections in North and northeast of Iran, the ammonite assemblages such as Parkinsoniidae, Morphoceratidae, Sphaeroceratidae, Macrocephalitidae and Reineckeiidae mainly show the characteristics of etyan groups. Abundant ammonite fauna in some levels has enabled an accurate chronostratigraphy. The presence of this ammonite fauna that is seen in the epicontinental seas, bordering the northern margins of the western Thetys, led to the identification of some zones in accordance with the standard of Sub-Mediterranean province zonation. The Garantiana and Parkinsoni Zones of the Late Bajocian, the Zigzag and Aurigerus Zones of the Early Bathonian, the Retrocostatum and Discus Zones of the Late Bathonian, the Bullatus and Gracilis Zones of the Early Callovian, the Anceps and Coronatum Zones of the Middle Callovian and the Athleta and Lamberti Zones of the Late Callovian have been recognised and characterised. These assemblages show a relation between these regions with the Sub-Mediterranean province during the Jurassic. Low percentage of Phylloceratidae in this section is an indicative of Sub-Mediterranean affinity. Based on the ammonite fauna, the Dalichai Formation is Late Bajocian-Late Oxfordian in age.

New Middle to ?Late Jurassic dinosaur tracksites in the Central High Atlas Mountains, Morocco.

Besides bones, fossil tracks and trackways are important sources of knowledge about dinosaur palaeobiology. Here, we report three new tracksites from two different synclines in the Imilchil area, Central High Atlas, Morocco. The tracks and trackways are preserved in fluvial deposits in different levels of the Isli Formation (Early Bathonian-?Upper Jurassic), and contain impressions made by sauropods, theropods and ornithopods, as well as tracks that might represent bird-like non-avian theropod dinosaurs. In addition to traditional field measurements, three-dimensional digital models of the track sites were created using photogrammetry. These new tracksites add to the rich faunal ichnoassemblage already recorded from the High Atlas Mountains and North Africa, which is considerably richer than the contemporaneous body fossil record, and also provide new data on dinosaurs-substrate interactions.

Palynostratigraphy and paleoenvironmental inferences of the Jurassic successions, Darag Basin, Gulf of Suez, Egypt

The present study shows the advantage of the palynostratigraphy and paleoenvironmental inferences concepts in subdividing and interpreting the depositional environment of the Jurassic rocks, depending on two sections in two boreholes drilled in the Darag Basin, Egypt. Six Jurassic rock units representing the mixed siliciclastic and carbonate sediments were recognized from top to base; the Tauriat, Arousiah, Kehailia, Safa, Shusha and Rajabiah formations. The palynomorph assemblage associated with moderately diversified dinoflagellate cysts and fewer sporomorphs, show poor to fair preservation. About 20 dinoflagellate cysts, 8 pollen, and 3 pteridophytic spore species have been recorded. The Jurassic rocks are originated from the late Jurassic (early Oxfordian) and early (Toarcian - Aaleneian) based on the recovered marker taxa. The studied sections are differentiated into six biozones, Systematophora sp. (Callovian-Oxfordian), Gonyaulacysta jurassica (Callovian), Dichadogonyaulax sellwoodii (Late Bathonian), Sentusidinium sp. (Early Bathonian), Pareodinia ceratophora (Bajocian) and Psilate spores, Classopollis and Sphaeripollenites Acme Zone (Toarcian-Aalenian).According to the Particulate Organic Matter (POM) composition in the studied wells, the palynofacies assemblages led to identifying three depositional settings, the palynofacies −1 (PFA-1), which is characterized by opaque phytoclasts and high volume of spores and pollen grains was deposited in a marginal shallow-marine environment during a relative sea-level fall. The PFA-2 is composed of brown phytoclasts, moderate Amorphous Organic Matter (AOM) with pollen grains and dominated dinocysts. It was deposited during a slight sea level rise in a proximal inner neritic environment. Simultaneously, the PFA-3, which was dominated by AOM and dinoflagellate cysts with moderate brown phytoclast content, was deposited as a distal inner neritic environment during a relatively high relative sea level.

Bajocian–Bathonian dinoflagellate cyst assemblages from the Middle Atlas, Morocco: Palynostratigraphic and paleoenvironmental implications

The Bajocian–Bathonian transition has been identified for the first time in the Skoura syncline of the folded Middle Atlas of Morocco based on dinoflagellate cyst and palynofacies analysis of the Ich Timellaline/Bou Akrabene Formation carbonates. This palynological study involved 109 samples of marls and limestones whose organic content yielded diverse and well-preserved dinoflagellate cyst assemblages comprising 68 taxa including stratigraphic marker taxa. Two association biozones have been defined for the late Bajocian–early Bathonian interval. The Cribroperidinium crispum-Ctenidodinium cornigerum (CC/CC) biozone is defined between the base of the Recifa Formation (Upper Bajocian) and the Ich-Timellaline / Bou Akrabene Formation (Upper Bajocian–Lower Bathonian). The second association biozone of Ctenidodinium combazii and Dichadogonyaulax sellwoodii (CC/DS) corresponds to the upper interval of the FD section (top of the Ich-Timellaline / Bou Akrabene Formation and the base of the El Mers I Formation). These two biozones were correlated with the late Bajocian–early Bathonian biozones defined in the Sub-Boreal (northwest Europe), Tethyan, and Australian domains. Close similarity between the Moroccan Middle Atlas, the Tethyan, and the Sub-Boreal domain associations has been noted. Quantitative analysis of organic matter constituents has allowed the paleoenvironmental reconstruction of the late Bajocian–early Bathonian. The organic residues of the studied samples recorded an increased land-derived phytoclasts dominance compared to amorphous organic matter and palynomorphs, indicating a proximal oxic shelf depositional environment with high terrestrial and freshwater influx during the late Bajocian–early Bathonian. During the Late Bajocian, the depositional environment corresponds to a proximal continental shelf with fluctuations from a distal to a marginal/stagnant environment.Below the Upper Bajocian–Lower Bathonian boundary, a significant marine incursion, or rather a transgression, is recorded in the studied sediments attested by an important marine fraction and dinoflagellate cysts abundance, which probably corresponds to the last Bajocian Maximum flooding surface (MFS).During the early Bathonian, the depositional environment evolved towards a distal continental shelf with an increasing marine fraction including dinoflagellate cysts and high species diversity. This may be related to the rising sea level which corresponds to the first Bathonian eustatic elevation. The proximal /marginal conditions are restored at the uppermost part of the section.

A ‘long-forgotten’ plesiosaur provides evidence of large-bodied rhomaleosaurids in the Middle Jurassic of Germany

ABSTRACT Described in 1858, Trematospondylus macrocephalus is one of the earliest established plesiosaur taxa. However, despite being historically significant, the taxon disappeared from the literature shortly after its initial description and has not been mentioned for over a century. Thus, it has never been properly assessed. The holotype comprises seven vertebrae, including a supposed sacral vertebra and caudal vertebrae. The specimens were collected from the Lochen mountain massif near Balingen in southwestern Germany and derive from the Dentalienton Formation. As such, they are most likely early Bathonian (Middle Jurassic) in age. Here, we provide a thorough redescription of the material, illustrate it, and assess its phylogenetic affinities through a parsimony analysis. Our results show that T. macrocephalus shares characters with members of the Rhomaleosauridae, including, for example, the length-height ratio of the caudal centra as well as the placement of caudal ribs and hemapophyseal facets. Rhomaleosaurid affinities of the material are likewise supported by our phylogenetic analysis. Comparisons further indicate that the taxon belonged to large-bodied members of the clade, with a body length similar to that of Rhomaleosaurus. Even though the material does not enable Trematospondylus to be properly diagnosed, thus making it a nomen dubium, it still adds to the rare Middle Jurassic record of rhomaleosaurid plesiosaurs. At the same time, it enhances our knowledge of the plesiosaur taxic diversity during the pre-Callovian Middle Jurassic, which has been very limited.

Jurassic bivalves from the Spiti area of the Himalayas, northern India

The present study describes and illustrates six bivalve taxa from the Early Bathonian to Early Callovian Ferruginous Oolite Formation and 24 taxa from the Callovian to basal-most Cretaceous Spiti Shale Formation of the Spiti and Zanskar areas in the Indian Himalayas. The Spiti Shale Formation contains a low-diversity bivalve fauna that is concentrated in few horizons, particularly in the lower member of the formation. With few exceptions, the bivalves are poorly preserved. Bivalve taxa recorded by earlier studies are revised wherever possible. Several of the taxa, most of which are from mid- to outer shelf environments, are characteristic of the south-eastern margin of the Neotethys, but some are also closely related to forms occurring in Kachchh, a rift basin situated at the western margin of the Indian Craton.

Plasticity in the morphology of the fused frontals of Albanerpetontidae (Lissamphibia; Allocaudata)

ABSTRACT Albanerpetontidae form an enigmatic extinct group of lissamphibians, ranging from the early Bathonian to the early Pleistocene. The Upper Jurassic outcrops of Portugal yield a large collection of material, suitable for addressing the intraspecific variation in and diagnostic potential of the characteristic fused frontals. We revise 58 specimens from the Guimarota beds of the Kimmeridgian Alcobaça Formation and describe 62 new frontal bones from the Kimmeridgian – Tithonian Lourinhã Formation. Smaller specimens exhibit a vermicular dorsal ornamentation, while it is polygonal in larger specimens and other albanerpetontids. Compared to small specimens, larger specimens display: (1) larger ventrolateral crests extending posteriorly after the parietal margin; (2) a relatively shorter internasal process; (3) a frontal width across posterior edges relatively smaller; and (4) a ventromedian crest less pronounced. Morphometric analyses suggest a single species with different ontogenetic stages. Specimens are attributed to aff. Celtedens sp., based on a bell-shaped outline with a curved orbital margin (although variable in Portuguese specimens), and a flabellate, bulbous-shaped internasal process. The species is more similar to C. megacephalus than C. ibericus, but its phylogenetic position comprises an unresolved trichotomy. Our results show that intraspecific variation and homoplasy render the fused frontal non-diagnostic below the generic level.

Petrographic and geochemical characterization of the Middle\u2012Upper Jurassic Fe\u2013Mn crusts and mineralizations from Monte Inici (north-western Sicily): genetic implications

Fe–Mn concretions and mineralizations, associated with condensed horizons and hardground, are significant archives in ancient carbonate rocks. Their petro-chemical study allows an assessment of the palaeoenvironmental context in which they were formed also connected to their biotic or abiotic origin. At the western side of the Monte Inici (Fornazzo section, north-western Sicily) a well exposed outcrop of condensed pelagic limestones (Rosso Ammonitico facies: Middle‒Upper Jurassic) is well-known and thoroughly studied. In this section, the base of the Rosso Ammonitico facies consists of a very condensed level rich in fossils with a variable thickness deposited from the early Bathonian to the early/middle Callovian. It is characterized, at the top, by the noticeable presence of Fe–Mn concretions, typical of the Tethyan Jurassic and related to very low sedimentation rates. For this study, Fe–Mn crusts and mineralizations from the Fornazzo section were investigated using X-ray diffraction, scanning electron microscopy, X-ray fluorescence, ICP and stable-isotope mass spectrometry. The collected samples, deposited in submarine conditions (as testified by stable oxygen and carbon isotopes), have been subdivided in two typologies with different macroscopic and mineralogical features. The Fe–Mn crusts consist of hematite, todorokite and birnessite and are characterized by a relatively low Mn/Fe ratio. Their content in trace elements, rare earths and yttrium (REY) is compatible with a hydrogenetic origin involving the oxy-hydroxides colloids precipitation directly from seawater. Microbially mediated processes are here testified by the recognition of filamentous and coccoid-shaped microstructures referable to coexistence of chemosynthetic fungi and photosynthetic cyanobacteria and accounting for a deposition in the deep euphotic zone. An average growth rate of ~ 8.5 mm/Myr for the Fe–Mn crusts, estimated by cobalt concentrations, suggests a time elapsed for deposition of ~ 3.5 ± 1 Myr. This value is compatible with the stratigraphic gap embracing the time span from the early/middle Callovian to the middle Oxfordian. In the neighbouring pelagic limestones, Fe–Mn deposits are present in the form of micro-dendrites mainly consisting of pyrolusite, sometimes associated with carbonato-fluorapatite. The geochemical composition gives evidence of a prevalent early diagenetic origin with precipitation, at the sediment/water interface or in the first centimeters of sediments, of metals diffused from the crusts as consequence of fluctuating redox conditions. Although the well-preserved Frutexites texture is commonly related to a microbial activity, other bacterial microstructures have not been recognized, having probably been obliterated during the growth of the dendrites. Nevertheless, it is possible to suppose a deepening in the bathymetry consistent with the involvement of chemosynthetic microorganisms in the formation of Frutexites structures.

Chapter 2 Structural development of the Arabian Intrashelf Basin region

Abstract This chapter summarizes the tectonic events that have affected the region of the Arabian Intrashelf Basin and the development of the intrashelf basin. Precambrian–Infracambrian fault systems provided a structural framework, which was later reactivated during the Late Paleozoic. Further development along the structural trends continued in the Triassic and Early Jurassic with the development of an Early Jurassic tectonically controlled intrashelf basin. The accommodation space was filled with Dhruma Formation carbonates by the early Bathonian, resulting in a broad and fairly flat platform. A crucial factor is how suppressed tectonism was during the Mid- and Late Jurassic. The intrashelf basin developed on the broad, tectonically stable Tethyan passive margin continental shelf 200--300 km distant from the Tethyan outer shelf edge. During the Mid- and Late Jurassic, this tectonic stability provided the foundation for a broad, stable Tethyan continental shelf region at least 1000 × 1200 km in area, far removed from siliciclastic sources, within which the huge Arabian Intrashelf Basin formed and the sequences of carbonate rocks and evaporites that created the Jurassic hydrocarbon system were deposited. Tectonism during the Mid- to Late Jurassic evolution of the Arabian Intrashelf Basin initially included only moderate subsidence. There was subtle uplift along some of the structural trends in the Late Jurassic and uplift and westwards structural tilt along the Tethys oceanic margin. Relatively stable tectonism continued after the Jurassic and was a major factor in the accumulation of the vast reserves of Jurassic sourced oil. Tectonic stability prevented major faulting and structural compartmentalization of the basin features, which provided large areas for hydrocarbon migration as the large and broad anticlines developed into the huge structural traps. The lack of major faulting limited the movement of burial fluids, preserving the early formed porosity and the regionally extensive seals. The present day structures primarily developed from the Late Cretaceous to Miocene as the Tethys Ocean closed.

The age of the Pre-Callovian Jurassic sequence at the southwest of Tatarstan (central Russia, Tarkhanovskaya Pristan’–Dolinovka reference section) and the status of the Upper Bajocian “Garantiana-beds”, previously described from here

In the present paper we describe and discuss belemnite finds from the basal part of the middle Jurassic sequence at the southwest of the Republic of Tatarstan (Tetyushi district). The belemnites were collected from the outcrops located along a shoreline of the Kuybyshevskoye reservoir (Volga river) between the place Tarkhanovskaya pristan and the former village Dolinovka. These belemnites indicate that the basal part of the Jurassic sequence is Early Bathonian (Ishmae Zone) or, less probable, Middle Bathonian in age. Such dating triggers a critical review for the age of the middle Jurassic sequence in the region. In particular, poorly preserved ammonites previously collected from the same outcrops higher in the succession and interpreted as members of the Late Bajocian subfamily Garantianinae, are in fact Late Bathonian Gowericeratinae. Consequently, Beds with Garantiana nominally the most ancient ammonite-based biostratigraphic unit within the whole Jurassic of European Russia, based on this assemblage, is invalid.

Microfacies, biofacies, and depositional environments of the Bajocian–Bathonian Middle Dhruma carbonates, central Saudi Arabia

Three cliff-forming outcrops of the Dhruma Formation representing the carbonate platform in the Hafirat Nisha district west of Riyadh, Saudi Arabia, were investigated to identify and understand the microfacies variability in a carbonate ramp setting. An integrated approach including detailed field investigations, petrographic, biofacies, and micropaleontological analyses was used to construct a model of the depositional environments of the investigated outcrop sections. The depositional model indicates that the identified lithofacies were predominantly deposited in outer ramp, middle ramp, inner ramp, and lagoonal settings. The presence of the benthic foraminifera Redmondoides lugeoni and Nautiloculina oolithica and the trace fossil Thalassinoides indicates deposition in shallow-water environments and the prevalence of warm climatic conditions during the Middle Jurassic. The occurrences of calcareous and agglutinated benthic foraminiferal species Pseudomarssonella maxima, Siphovalvulina variabilis, Timidonella sarda, N. oolithica, R. lugeoni, Praekurnubia crusei, Paleopfenderina salernitana, Haurania deserta, Siphovalvulina spp., Lenticulina sp., Textulariopsis sp., and Amijella amiji imply that our studied sections are situated within the Dm-2 to Dm-5 biozones (Bajocian to early Bathonian). This is also supported by the calcareous nannofossil assemblages that show a Bajocian to early Bathonian age. The depositional sequences indicate a shift in the depositional environment from low-energy lagoonal with intermittent shoal complexes in the D2 and D3 Units to predominantly shoal complex and open-marine settings in the D4 Unit, suggesting a seaward shift towards the top of the D4 Unit. The interpreted depositional settings are similar to those previously documented in the subsurface equivalent, Faridah reservoir. This indicates that the investigated D2–D4 Units outcrops are excellent analogues of the subsurface reservoir.

Revisiting the Age of Jurassic Coral Bioherms in the Pieniny Klippen Belt (Western Carpathians) on the Basis of Benthic Foraminifers

Abstract Coral bioherms of the Vršatec Limestone that formed massive, several tens of meters thick complexes during the Jurassic were important sources of carbonate production, with carbonate sediment exported to deeper parts of the Pieniny Klippen Basin (Western Carpathians). However, the age of these carbonate factories remains controversial. New analyses of benthic foraminiferal assemblages occurring in coral bioherms and peri-biohermal deposits of the Vršatec Limestone at five sites in the western Pieniny Klippen Belt (Vršatec-Castle, Vršatec-Javorníky, Malé Hradište, Malé Hradište-Kalvária, and Drieňová Hora) show that these sediments were deposited during the Bajocian and were lateral equivalents of crinoidal limestones and breccias, in contrast to previous studies suggesting that they were deposited during the Oxfordian. First, all sites are characterized by similar composition of foraminiferal assemblages on the basis of presence–absence data, although foraminiferal assemblages in biosparitic facies at Vršatec are dominated by miliolids whereas biomicritic facies at Malé Hradište are dominated by the spirillinid Paalzowella. The composition of foraminiferal assemblages does not differ between the lower and upper parts of the Vršatec Limestone. Second, foraminifer species that were assumed to appear for the first time in the Oxfordian already occur in the Middle Jurassic sediments of the northern Tethyan shelf. Third, the first and last appearances of foraminifers documented in other Tethyan regions are in accordance with stratigraphic analyses and ammonoid occurrences, demonstrating that bioherm-forming coral communities developed on the Czorzstyn Ridge during the Bajocian. Several species of foraminifers of the Vršatec Limestone appeared for the first time during the middle or late Aalenian (Labalina occulta, Paalzowella feifeli) and during the Bajocian (Hungarillina lokutiense, Radiospirillina umbonata, Ophthalmidium caucasicum, O. terquemi, O. obscurum, Paalzowella turbinella, Cornuspira tubicomprimata, Nubecularia reicheli) or appeared for the last time in the Bajocian (Tethysiella pilleri) or Early Bathonian (Ophthalmidium caucasicum, O. obscurum). The composition and diversity of communities with benthic foraminifers of the Vršatec Limestone is similar to the composition of foraminiferal communities on carbonate platform environments with corals of the French Jura and Burgundy during the Bajocian.

Ammonites and infrazonal stratigraphy of the lower bathonian besnosovi zone of the Russian plate

Ammonites and deposits of the Lower Bathonian Besnosovi Zone of the central and southern regions of the Russian Plate are studied. The paper discusses the infrazonal stratigraphy and correlation of two reference sections: the Pletnyovka Quarry in the north of the Penza oblast and the Sokur Quarry near the city of Saratov. The successive biohorizons Oraniceras issae, O. calvum, and O. besnosovi are recognized on the basis of ammonites of the genus Oraniceras (family Parkinsoniidae) in the Besnosovi Zone. Provisional O. mojarowskii and O. scythicum biohorizons are proposed below the above-mentioned biohorizons, whereas the O. cf./aff. besnosovi Biohorizon is proposed above them. The Besnosovi Zone corresponds to the middle part of the Western European Zigzag Zone. The Michalskii Zone underlining the Besnosovi Zone apparently corresponds to the Bajocian–Bathonian boundary interval. It is suggested that only one A. excentricum migrational biohorizon, corresponding to the upper part of the O. besnosovi Biohorizon and correlating with the lowermost part of the Ishmae Zone of the Boreal scale, can be established on the basis of Boreal ammonites of the genus Arcticoceras in the Sokur Section. Central Russian representatives of the genera Oraniceras [M] and Sokurella [m] are assigned here to the subfamily Pseudocosmoceratinae that is eudemic to the Central Russian late Bajocian–early Bathonian sea. It is suggested that the above-mentioned genera evolved from Pseudocosmoceras [M and m] that is cryptogenic neoendemic of the East European Peritethyan marine basin. New species are described: Oraniceras issae sp. nov. [M], O. calvum sp. nov. [M], Sokurella pletniovkae sp. nov. [m], and S. elshankae sp. nov. [m].

First Bathonian (Middle Jurassic) nautiloid Paracenoceras Spath from Ethiopia

The earliest find of a Bathonian nautiloid Paracenoceras aff. prohexagonum Spath from the Lower Limestone Member (former Gohatsion Formation) exposed at Mugher (Blue Nile Basin, Ethiopia) is reported. Due to lack of index forms for the entire pre–Late Jurassic duration in Ethiopia, the age estimate of the nautiloid is done on the basis of palaeobiogeography where the oldest P. prohexagonum Spath record comes from definite Saudi Arabian Early Bathonian strata and the youngest from the Middle–Late Bathonian of the Kachchh basin (Western India). Ethiopia being an intermediate region, hence, a Late Bathonian age is safe to assume. However, the key for a more well–constrained age for the Ethiopian strata may actually lie in the re–assessment of the ammonite records from the neighboring Somalia, another intermediate region and a step closer to the otherwise well–constrained records from the Kachchh basin (India). Additionally, this contribution also provides a brief stratigraphic update of the Lower Limestone Member (of the Antalo Limestone Supersequence) exposed at Gohatsion and the corresponding nautiloid–bearing section at Mugher (∼20 km southwest of Gohatsion) within the Blue Nile basin. Based on field and sedimentological observations, sequence stratigraphy, and previously published data on faunal content, the prevailing paleoenvironment and relative sea level curve for the Lower Limestone Member is also inferred. Palaeobiogeography is briefly outlined to explain the age and occurrence of the reported nautiloid.

Lower Bathonian Belemnites and Biostratigraphy of the Central and Southern Parts of the East European Platform: Part 2. Cylindroteuthididae and Belemnotheutididae

Belemnites from the lower Bathonian deposits of the Russian Plate are revised and discussed on the basis of study of the two reference sections—Pletnyovka and Sokur quarries. This is the second part of the investigation dealing with representatives of the family Cylindroteuthididae, and “rostrum-less” belemnites of the family Belemnotheutididae, while members of the family Megateuthididae were discussed in detail in the first part (Ippolitov, 2018). The cylindroteuthidids are found only in the Sokur Quarry and comprise four species all assigned to the genus Pachyteuthis, including a new species, Pachyteuthis mittai sp. nov. For Belemnotheutididae, the presence of a single species Acanthoteuthis foliorostris sp. nov. is recorded, which is the first confirmed record of the genus Acanthoteuthis in the pre-Callovian strata. The study of morphological changes within Cylindroteuthididae across the succession allowed two biohorizons to be recognized and the existing belemnite-based scheme for the lower Bathonian of the Volga Region and its correlation with sections in the Pechora River basin to be updated. As the result of the revision, a complex zonal and infrazonal belemnite-based stratigraphic scheme of the lower Bathonian of the Volga Region is introduced. The presence of an endemic genus deriving from Arctic-Boreal immigrants in the lower Bathonian of the Middle Russian Sea allows the belemnite fauna of this age to be interpreted as the first isolated episode of differentiation of the Boreal-Atlantic Province in belemnites. The study of the development of the cephalopod fauna in the early Bathonian of the Russian Plate indicates a biphase formation of the meridional strait connecting the Middle Russian Sea with the Arctic basins and also supports the hypothesis of a short-term opening of a sublatitudinal Pripyat Strait during the maximum highstand.

Jurassic–earliest Cretaceous tectonostratigraphic evolution of the Erlian Basin, Northeast China: Records of polyphase intracontinental deformation in Northeast Asia

Abstract The Erlian Basin is an important part of the late Mesozoic extensional basin system in Northeast Asia. The basin contains thick Jurassic–Lower Cretaceous rocks and provides excellent opportunities to understand intracontinental deformation in Northeast Asia during the late Mesozoic. However, the Jurassic–Early Cretaceous evolution of the basin and associated driving mechanisms remain disputed. Based on 13 new zircon U-Pb ages for the Jurassic–lowest Cretaceous strata in the Erlian Basin, the correlation of Jurassic–lowest Cretaceous strata between the Erlian Basin and the Yan Shan is reestablished and a high-precision chronostratigraphic framework is presented. The Aqitu–Qiha formations are ascribed to the Aalenian–early Bathonian (ca. 174–167 Ma), the Xing'anling Group to the Oxfordian–early Kimmeridgian (ca. 163–153 Ma), the Hugejiletu Formation to the Tithonian–early Valanginian (ca. 151–139 Ma), and the Aershan Formation to the Valanginian–? (≤ca. 138 Ma). Combined with seismic reflection profiles, the Jurassic–earliest Cretaceous tectonostratigraphic evolution of the Erlian Basin is reconstructed and five major phases of deformation are revealed. These deformation phases include Aalenian–early Bathonian initial extension, late Bathonian–Callovian compression, Oxfordian–early Kimmeridgian extension, late Kimmeridgian–earliest Valanginian compression, and Valanginian extension. Integrated with geological evidences from peripheral regions of the Erlian Basin, potential driving mechanisms related to far-field tectonic events along Asian margins are suggested for each of these deformation phases.

Lower Bathonian Belemnites and Biostratigraphy of the Central and Southern Parts of the East European Platform: Part 1. Megateuthididae

Belemnites from the lower Bathonian of the Russian Plate are revised on the basis of the study of two reference sections—Pletnyovka and Sokur quarries. The first part of the study deals with the members of the family Megateuthididae. They include eight species of the genus Barskovisella gen. nov., neoendemic to the territory of the Russian Plate and originating from high Boreal taxa—species of the genus Paramegateuthis Gustomesov, 1960, which immigrated to the Middle Russian Sea in the early Bathonian via a short-lived meridional strait. The new genus includes six new species described in the present paper—Barskovisella pseudoishmensis sp. nov., B. issae sp. nov., B. variabilis sp. nov., B. barskovi sp. nov., B. gracilis sp. nov., and B. renegata sp. nov. The beds with Barskovisella, a new belemnite-based unit, corresponding to the Oraniceras besnosovi ammonite zone and including four successive phylogenetic biohorizons well comparable in resolution with ammonite-based infrazonal subdivisions, are introduced.