Oksana S. Dzyuba

Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia)

The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite δ18O data show an irregular decrease from values reaching up to +1.6‰ in the Middle Oxfordian and from +0.8 to −1.7‰ in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon δ13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem.

Belemnites and biostratigraphy of the Jurassic-Cretaceous boundary deposits of northern East Siberia: New data on the Nordvik Peninsula

The study of new collections from the Urdyuk-Khaya Cape (Nordvik Peninsula) made it possible to specify the taxonomic composition of belemnites from the Volgian and basal Ryazanian in northern East Siberia. Cylindroteuthis knoxvillensis Anderson, 1945, C. cf. newvillensis Anderson, 1945, and Arctoteuthis tehamaensis (Stanton, 1895) known from northern California, as well as the new species C. venusta sp. nov. and A. britanna sp. nov. are first described from the Arctic region. Belemnite stratigraphy of Jurassic-Cretaceous boundary layers is fundamentally revised, allowing a new refined version of their scale to be proposed as a Boreal standard. Two independent successions of biostratigraphic units are defined in the section interval spanning the uppermost Middle Volgian Substage to the basal Ryazanian Stage: (1) Liobelus russiensis Zone, Lagonibelus gustomesovi and Arctoteuthis porrectiformis beds; (2) Lagonibelus napaensis, Arctoteuthis tehamaensis, and Cylindroteuthis knoxvillensis zones.

Biostratigraphy and sedimentary settings of the Upper Bajocian-Lower Bathonian in the vicinity of Saratov (Central Russia)

This paper presents the results of a detailed study of the Bajocian-Bathonian sections in the “Sokur” Quarry near the city of Saratov and of a borehole drilled in the same quarry. The study of these Bajocian-Bathonian boundary beds, unique for the Boreal-Tethyan ecotone, offers a solution to the much-debated problem of the Middle Jurassic Boreal-Tethyan correlation. The BajocianBathonian boundary beds of this section contain both Peri-Tethyan and Boreal ammonite species, allowing recognition of the Boreal ammonite zones and associated “Boreal” Bathonian zones based on belemnites, bivalves, and foraminifers. This integrated biostratigraphy allows correlation of the Late Bajocian-Early Bathonian boundary interval of the Boreal Jurassic scale with the Submediterranean standard scale.

Belemnites in the Jurassic-Cretaceous boundary interval of the Mauryn’ya and Yatriya River sections, Western Siberia: Biostratigraphic significance and dynamics of taxonomic diversity

The stratigraphic distribution and taxonomic diversity of belemnites from the Volgian and Ryazanian deposits exposed in the eastern foothills of the North and Subpolar Urals, are studied and analysed. Studies of new collections from the Mauryn’ya and Yatriya rivers have revealed within the Laugeites groenlandicus-basal Surites analogus ammonite zones, the East Siberian Lagonibelus napaensis, Cylindroteuthis knoxvillensis, and Liobelus russiensis belemnite zones (the latter in the beds’ rank), the Lagonibelus gustomesovi and Arctoteuthis porrectiformis Beds, and local beds with Boreioteuthis explorata and Simobelus compactus. Since in the boundary beds of the Volgian and Ryazanian stages a great number of belemnite species known from the Tordenskjoldberget Member, Kong Karls Land, Svalbard, were found, it is inferred that the accumulation of the member started not in the Valanginian as many researchers believe but immediately at the beginning of the Cretaceous. The dynamics of belemnite species diversity in the northwestern margin of the West Siberian marine basin correlates well with climatic events. An increase of species number in the terminal Volgian-beginning of the Ryazanian corresponds to a temperature elevation in the Siberian paleoseas, and the subsequent reduction of species diversity in the second half of the Ryazanian is correlated with a gradual cooling. The peak of belemnite taxonomic diversity falls at the beginning of the Cretaceous when up to 15 species belonging to eight Cylindroteuthididae genera occurred concurrently. The new species Cylindroteuthis ornata sp. nov., Acroteuthis pseudoconoides sp. nov., Pachyteuthis eximia sp. nov., and Simobelus compactus sp. nov. are described.

Biofacies of Upper Jurassic and Lower Cretaceous Sediments of Central West Siberia

Paleontological study of Upper Jurassic and Lower Cretaceous sediments recovered by boreholes in the Agan-Vakh and Nadym-Vengapur interfluves clarified environments of their deposition. As is shown, influx of siliciclastic material to central areas of the West Siberian sea basin varied through time. Taxonomic composition and ecological structure of nektonic and benthic fossil assemblages are analyzed and considered in terms of environmental factors such as hydrodynamics, aeration, temperature, and salinity of seawater.

New belemnites (Megateuthididae, Cylindroteuthididae) from the Bajocian and Bathonian of the Yuryung-Tumus Peninsula, northern Siberia, Russia and their palaeobiogeographic implications

New species of Paramegateuthis (Megateuthididae) and Cylindroteuthis (Cylindroteuthididae) are described from the Bajocian–Bathonian boundary interval of the Yuryung-Tumus Peninsula, northern Siberia, Russia. Additionally, Paramegateuthis subishmensis Stoyanova-Vergilova, 1983, first documented from the Sub-Mediterranean region, is described herein from the Arctic. We propose the presence of a temporary passage between the Boreal and Tethyan seas in the European part of Russia during the Early Bajocian Humphriesianum Chronozone as an explanation of the migration of P. subishmensis. New belemnite records from the Yuryung-Tumus section contribute to the palaeontological characteristics of the Arctic domain.KurzfassungNeue Arten von Paramegateuthis (Megateuthididae) und Cylindroteuthis (Cylindroteuthididae) aus dem Bajocium–Bathonium-Grenzintervall der Yuryung-Tumus-Halbinsel in Nordsibirien (Russland) werden beschrieben. Desweiteren wird Paramegateuthis subishmensis Stoyanova-Vergilova, 1983, zuvorderst submediterran nachgewiesen, aus der Arktis nachgewiesen. Deshalb schlagen wir, zur Erklärung für die Migration von P. subishmensis, die Anwesenheit einer temporären Passage (im europäischen Teil von Russland) zwischen dem Boreal- und dem Tethys-Meer im frühen Bajocium (Humphriesianum Chronozone) vor. Die neuen Belemnitenbelege aus dem Yuryung-Tumus-Profil erbringen einen wesentlichen Beitrag zur Paläontologie der Arktis.

Sr isotope composition in belemnites from the Jurassic–Cretaceous boundary section (Maurynya River, Western Siberia)

The belemnite Sr isotope characteristics obtained over an interval from the Upper Volgian Regional Substage to the lower part of the Ryazanian Regional Stage in the section on the Maurynya River (Western Siberia) fills a gap in the 87Sr/86Sr ocean water variation curve over the Jurassic–Cretaceous boundary. The increase in the 87Sr/86Sr values from 0.707172 to 0.707242 revealed in the section coincides with a general rise in this ratio in the Late Jurassic–Early Cretaceous ocean.

Early Bajocian belemnites of Southcentral Alaska: new data and new perspectives on mid-Middle Jurassic Megateuthididae and Belemnopseidae biogeography

In this study, Lower Bajocian belemnites from Southcentral Alaska are formally investigated and described for the first time. Representatives of the families Megateuthididae (Belemnitina) and Belemnopseidae (Belemnopseina) occur in the Parabigotites crassicostatus to Sphaeroceras oblatum ammonite zones (Propinquans to Humphriesianum chronozones) within the Tuxedni Group of the Cook Inlet region and the Talkeetna Mountains. Among Megateuthididae, we introduce the first records of Brevibelus from Alaska, and the first records of Brevibelus gingensis and Eocylindroteuthis from outside Europe. The new taxa Pseudosimobelus tuxedniensis Dzyuba & C. D. Schraer gen. et sp. nov., Eocylindroteuthis gracilenta Dzyuba & C. D. Schraer sp. nov. and Eocylindroteuthis riegrafi Dzyuba & C. D. Schraer sp. nov. are also described. We conclude from our morphological analysis that Pseudosimobelus gen. nov. represents a transitional form between Megateuthididae and Cylindroteuthididae or may even have been ancestral to the latter. The single rostrum of Belemnopseidae identified herein as Hibolithes? sp. juv. is the earliest record of the family from Alaska. Biogeographically, the belemnites represent pan-Tethyan (Brevibelus and Hibolithes?), typically west Tethyan (Brevibelus gingensis, Brevibelus cf. breviformis and Eocylindroteuthis) and endemic north-east Pacific (Pseudosimobelus gen. nov. and Eocylindroteuthis spp. nov.) elements. These palaeontological data suggest a location of the Peninsular terrane in the Early Bajocian south of the present location. We postulate that the appearance of Brevibelus, Eocylindroteuthis and possibly Hibolithes near the north-western shores of North America in the late Early Bajocian was due to their westward migration via the Hispanic Corridor, the migratory seaway between the western Tethys and the eastern Pacific. http://zoobank.org/urn:lsid:zoobank.org:pub:BCF66B22-795B-46EC-9C86-2595433E22EF

New data on Callovian (Middle Jurassic) belemnites and palynomorphs from the Northern Caucasus, southwest Russia

Abstract Palaeontological data on the Caucasus are highly important for large-scale stratigraphical and palaeobiogeographical assessment of the northern Tethyan margin, but this information is often scarce and not available in English. Field studies in the Northern Caucasus have now permitted to amass some new data. Two belemnite species are described from the stratotype section of the Kamennomostskaja Formation (Callovian, Middle Jurassic) near the town of Kamennomostskij in Adygeja (Northern Caucasus). These are Belemnopsis subhastata (von Zieten, 1831) and Rhopaloteuthis ominosa Gustomesov, 1968. The latter is a rare species, and the present find allows new insights into its taxonomy. A palyno-logical analysis of the belemnite-bearing sample was carried out, and a diverse assemblage of dinocysts, acritarchs and prasinophytes, plus pollen and spores recognised. The most abundant palynomorphs are Micrhystridium and Classopollis. Data on belemnites coupled with those on palynomorphs indicate the early Callovian age of the sample level. This interpretation differs slightly from previous conclusions based on ammonites and dinocysts. If this age is correct, the degree of condensation of Callovian deposits in the section studied was lesser than previously assumed.

Buchia faunas and biostratigraphy of the Jurassic-Cretaceous boundary deposits in the Komsomolsk section (Russian Far East)

Abundant Buchiidae (Bivalvia) from the Upper Volgian-Lower Valanginian sediments of the Northern Sikhote-Alin (Russian Far East) were studied in the key section at right bank of the Amur River opposite to Komsomolsk-on Amur. The analysis of the Buchiidae stratigraphic distribution in the section allowed us to reveal the sequence of Buchia-bearing beds: this is well correlated with the Buchia zonal scales of many Arctic regions. Here, from the base upward, there have been recognized the following: beds with Buchia terebratuloides, beds with B. unschensis and B. terebratuloides, beds with B. volgensis, and beds with B. inflata and B. keyserlingi. The beds with B. unschensis and B. terebratuloides also yielded the Berriasian ammonite Pseudosubplanites? sp. of Tethyan affinity. The obtained paleontological data confirm the occurrence of a large syncline in the studied section. The data also permit one to refine the age spans of the local stratigraphic units.