G. N. Aleksandrova

Paleocene–Eocene warming and biotic response in the epicontinental West Siberian Sea

We present a Paleocene–Eocene (ca. 60–52 Ma) sea-surface temperature record from sediments deposited in the epicontinental West Siberian Sea. TEX86 paleothermometry indicates long-term late Paleocene (∼17 °C ca. 59 Ma) to early Eocene (26 °C at 52 Ma) sea-surface warming, consistent with trends previously observed for the Southern Ocean and deep oceans. Photic zone and seafloor anoxia developed as temperatures rose by 7 °C to ∼27 °C during the Paleocene–Eocene Thermal Maximum (PETM). Based on paired palynological and TEX86 data, we suggest that the minimum temperature for the proliferation of Paleocene and early Eocene members of the dinoflagellate family Wetzelielloideae, which includes the PETM marker taxon Apectodinium , was ∼20 °C.

Palynological and paleobotanical investigations of Paleogene sections in the Maoming basin, South China

The complex paleobotanical investigations carried out in the Maoming sedimentary basin (Guangdong Province, South China) yielded first data on the taxonomic composition and ecological properties of two large paleofloras from the Youganwo and Huangniuling formations. The palynomorph assemblages from these formations indicate their middle-late Eocene age (Lutetian-Bartonian and Priabonian for the former and latter, respectively). It is shown that sediments of the Youganwo Formation were deposited in an intermittently swamped lacustrine-fluvial plain, which gave way to a freshwater lake. Vegetation of this period was represented by wet subtropical forests with evergreen Fagaceae, Lauraceae, and Palmae. The Huangniuling flora reflects the biome of seasonal tropical forests developed in a broad fluvial plain and its margins. The Eocene floras of the Maoming Basin are marked by the appearance of several recent plant genera, which is also evident from finds of remains of their reproductive structures. The Eocene flora from low latitudes of South China exhibits a notable share of floral elements from middle and high latitudes of East Asia.

Platimeliphyllum reznikoviorum N. Maslova, sp. nov. (Angiospermae) and associated infructescence from the Paleogene of central Kazakhstan

A new species Platimeliphyllum reznikoviorum N. Maslova is described from the Paleogene of Nizhnii Ashut locality (central Kazakhstan) based on the leaf macromorphological and epidermal characteristics. A capitate infructescence sharing characters of Platanaceae and some Hamamelidaceae was found together with the leaves. Small reticulate tricolpate pollen grains were found adhered to the carpel surface. The fossil leaves and reproductive structure are supposed to belong to the same plant. Fossil leaves attributed to Platimeliphyllum are associated with reproductive structures of various genera belonging to different families. Therefore we use the morphological classification for dispersed angiosperm leaves proposed by Krassilov (1979) to define the taxonomic position of this genus.

Mid-Cretaceous Tuor-Yuryakh Section of Kotelnyi Island, New Siberian Islands: How Does the Probable Basement of Sedimentary Cover of the Laptev Sea Look on Land?

The model of geological structure of sedimentary cover of the Laptev Sea accepted by most geologists suggests that the lower seismic complex of the cover begins by the Aptian–Albian sedimentary rocks. They can be studied in natural outcrops of Kotelnyi Island. The section of the Tuor-Yuryakh Trough, which exposes the lower part of the Cretaceous complex, is described in the paper. It is composed of continental coaliferous rocks ~100 m thick. The marking beds divide it into five members, which are traced along the western wall of the trough at the distance up to 3 km. The spore–pollen complexes and plant megafossils indicate that almost the entire visible section of the mid-Cretaceous is Albian. Only its lower part no more than 14 m thick can probably belong to the Aptian. Marine facies with Albian foraminifers were found 15 m above the bottom of the Cretaceous complex. The section of the Cretaceous rocks is underlain by the Lower Jurassic marine clays and siltstones. The foraminifer assemblages of this part of the section are typical of the upper Sinemurian–Pliensbachian and fossil bivalves indicate late Sinemurian age of the host rocks. The hiatus ~70 Ma duration has no expression in the section and this boundary can de facto be substantiated only by microfossils. This vague contact between the Lower Jurassic and mid-Cretaceous rocks does not correspond to geophysical characteristics of the bottom of the lower seismic complex of the cover of the eastern part of the Laptev Sea. The latter is described as the most evident seismic horizon of the section of the cover, suggesting unconformable occurrence of the lower seismic complex on a peneplenized surface of lithified and dislocated rocks. This is mostly similar to the bottom of the Eocene sediments, which were observed on Belkovsky and Kotelnyi islands. The paper discusses possible application of our land results for interpretation of the shelf seismic sections of the Laptev Sea. It is concluded that local reasons are responsible for a vague boundary between the Lower Jurassic and mid-Cretaceous sequences in the section studied. Our observations support ideas on possible Aptian–Albian age of the rocks of the basement of the lower seismic complex; however, it is proposed to use also the previously popular idea on the Eocene age of the lower seismic complex of sedimentary cover of the eastern part of the Laptev Sea as one of the possible working scenarios.

Paleocene–Lower Eocene paleontological record of the Ulyanovsk-Syzran facial district, Volga-Peri-Caspian region

The stratigraphic subdivisions of the Paleogene included in the updated regional stratigraphic scheme of the Ulyanovsk-Syzran facial district with a wide development of biosiliceous deposits, are described and paleontologically characterized. The biostratigraphic subdivision of the reference sections using diatoms and dinocysts is discussed. The recently recognized stratigraphic units, Smyshlyaevka and Karanino within the Kamyshin (Upper Paleocene) and Proleyka (Lower Eocene) regional stages are described.

Age and genesis of the Upper Cenozoic deposits of the Tyumen oblast (Western Siberia) enriched in biogenic silica

An integrated micropaleontological study of deposits enriched in biogenic silica was conducted on material drilled in the Zyryanka and Uspenka fields of the southwestern Tyumen oblast (Western Siberia). The data obtained on palynology and diatoms allowed the assignment of the Zyryanka Field to the Turtas Formation (lower part of the Chattian Stage of the Oligocene) and the deposits of the Uspenka Field to be dated as Pleistocene. The absence in the Zyryanka Field diatom assemblage of in situ marine taxa and the mass occurrence of freshwater species, gemmuloscleres of freshwater sponges, and zygospores of Zygnematales algae suggest that a nonmarine basin existed in the early Turtas time. A considerable proportion of redeposited diatoms and dinocysts in the Quaternary deposits of the Uspenka Field suggest strong erosional processes during the time of deposition.

New data on the lithology of coastal facies of the Turtas formation (Upper Oligocene, Southwestern Siberia)

Peculiarities of the material composition and microstructure of coastal facies of Turtas Lake–Sea were studied in its marginal southwestern part for the first time. Interpretation of the lithological data showed that the deposits considered were formed under the conditions of a slightly saline basin and nearby full-flow river network. Based on the lithological, geochemical, and micropaleontological studies of clay–siliceous rocks of the Lower Turtas Formation (the boundary zone between the Tyumen and Sverdlovsk regions), additional support for the freshwater lake regime of the Late Oligocene Turtas basin is given.

Lower Cretaceous palynological assemblages of the Levashi Formation in the Aimaki section of Central Dagestan

We present the results of the study of higher plant spores and pollen in a section of the Levashi Formation near the village of Aimaki. The Hauterivian and Barremian palynological associations were defined on the basis of changes in the taxonomic content of terrestrial plant spores and pollen. The associations are comparable with Hauterivian and Barremian assemblages of various regions of the Caucasus with respect to the composition of major groups and individual taxa. A transition in the vegetation was noted, from the coniferous palynological association of the Hauterivian to a fern association in the Barremian. The predominance of hygrophilous ferns and the presence of lycophytes and representatives of Taxodiaceae and Sphagnopsida in the Barremian (which were nearly absent in the Hauterivian), accompanied by a significant decrease in thermophilic Cheirolepidiaceae and other conifers, indicate a change in climate characterized by an increase in humidity and a decrease in temperature.