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Vol 31, No 4 (2023)
Early Jurassic (Sinemurian) Ammonoids from the Boulders of the Greek Quarry, Central Crimea
Abstract
The Sinemurian ammonoids from the boulders in the Greek quarry (Salgir River basin, south-east of Simferopol city) are described. The assemblages are represented by Phylloceratidae (Phylloceras, Zetoceras and Partschiceras), Juraphyllitidae (Juraphyllites and Paradasyceras), Schlotheimiidae (Phricodoceras), Arietitidae (Coroniceras, Metophioceras, Arnioceras and Asteroceras), Oxynoticeratidae (Gleviceras), Echioceratidae (Plesechioceras, Orthechioceras, Echioceras and Paltechioceras), Eoderoceratidae (Eoderoceras), Epideroceratidae (Epideroceras) and, questionably, Coeloceratidae (?Tetraspidoceras). A new species Asteroceras dommerguesi sp. nov. is described. A sequence of biostratigraphic units was reconstructed and correlated with known biostratigraphic units (zones, subzones and biohorizons) of the Mediterranean area. The ammonite assemblages were found to be close to those of the northern Tethyan margin (Pontic and Austroalpine subprovinces).
3-60
The Ammonite Catacadoceras Barnstoni Beds and the Problem of Separation of the Middle and Upper Substages of the Bathonian Stage in Northern Siberia
Abstract
The paper presents the results of studying the taxonomic composition of ammonites of the family Cardioceratidae in the Bathonian of northern Siberia in the range of distribution of the last representatives of the genus Arcticoceras and the first representatives of the genus Catacadoceras to solve the problem of distinguishing between the Middle and Upper Bathonian. The incorrectness of all previous identifications of the Middle Bathonian species Arcticoceras cranocephaloide Callomon et Birkelund, 1985 based on the northern Siberian material has been established. These determinations were mainly based on Late Bathonian ammonites belonging to the species Catacadoceras barnstoni (Meek, 1859) or the form characterized by a narrow umbilicus and described herein as Cat. aff. barnstoni. An updated zonal scale of the Middle–Upper Bathonian of Siberia based on ammonites is proposed, which is recommended for use both in the regional stratigraphic schemes of the Jurassic deposits of Eastern (Middle) Siberia and in the Boreal (Siberian) zonal standard of the Bathonian Stage. The extreme importance of preserving an auxiliary biostratigraphic subdivision in this scale, the Cat. barnstoni Beds, is noted, which is due to the wide distribution and abundance of the index species in Siberian sections, as well as its significance for the correlation of the lower part of the Upper Bathonian of northern Canada, northern Siberia, Franz Josef Land and East Greenland. In addition, two intervals, namely interval with Cat. aff. barnstoni and interval with Cat. perrarum, are fixed as benchmarks, which are useful for the rapid age estimation and correlation of the Upper Bathonian deposits in Arctic sections within the upper part of the Cat. barnstoni Beds.
61-86
Phytostratigraphic Scale of the Non-Marine Cretaceous of North-Eastern Russia: An Attempt to Create and Results
Abstract
In the early 1970s, palaeobotanist V.A. Samylina published her concept of stratofloras – a stratigraphic scale of the Cretaceous non-marine deposits of North-Eastern Asia based on plant megafossils. It was based on data on the evolution of the systematic composition of plant communities during the transition from the Mesophyte to Cenophyte. Since the detail of this scale was not inferior to that of marine deposits, it almost immediately began to be used to determine the age and correlation of continental deposits in the region. The paper considers changes in ideas on the development of the regional flora in the process of receiving new data. It is shown that it is impossible to create a single regional scale, since the palaeolandscape environments in this territory were different. The precision of the scales for parts of the region with the same palaeolandscape setting appeares to be lower than the stages of the General Stratigraphic Scale.
87-102
Cenomanian Radiolarians and Stratigraphy of the Sel’-Bukhra Section, Republic of Crimea
Abstract
New radiolarian data from the type section of the middle Cenomanian Pseudoaulophacus lenticulatus Zone located on the northern and southern slopes of the Sel’-Bukhra Mountain section (southwestern Crimea) are reported. The Pseudoaulophacus lenticulatus Zone radiolarians have been studied and analyzed in this section for the first time. Five species previously unknown in this region have been found here. Lithology of the lower part of the upper Cenomanian Triactoma parva Zone from the southern slope of the Sel’-Bukhra Mountain section is reported. Both Pseudoaulophacus lenticulatus and Triactoma parva Zones have more than 60% species distributed in the Tethyan Superrealm.
103-117
Foraminifera and Paleogene Stratigraphy of the Submarine Lomonosov Ridge, Arctic Ocean
Abstract
Materials on the Paleogene biostratigraphy of the Lomonosov Ridge in the Arctic Ocean are presented, including new data on foraminifers from the M0004A borehole section (interval 390–391 m) in its polar part. The studied benthic foraminifers are united into the complex with Reticulophragmium coksuvorovae of the upper Zelandian–the lower Thanetian stages, which includes some characteristic species of the North Atlantic and West Siberian basins. It also contains information about the connection of these Arctic seas in the Paleocene time.
118-129
Paleogeography and Natural Environment of the Karelian Coast of the White Sea in the Holocene According to the Study of Lake Sediments Near the Mouth of the Keret River
Abstract
The article presents the results of a comprehensive (diatom and spore-pollen analysis and 14C-dating) study of the Holocene bottom sediments of a lake located on the coast of the Kandalaksha Bay of the White Sea near the mouth of the Keret River. Three stages in the development of the lake basin have been identified: marine, transitional, and lacustrine. Diatom assemblages characteristic of each facies are given. The indicator value of pollen, spores and non-pollen palynomorphs for identifying marine, transitional and freshwater sedimentation conditions is noted. A decrease in sea level was established at the turn of 7200 calendar years ago. The change of the marine environment of sedimentation to the lacustrine was recorded approximately at the turn of 6700 calendar years ago. For a given time, the position of the coastline of the sea is shown within the studied coast. The data of spore-pollen analysis were used for relative dating of post-glacial deposits. Vegetation was reconstructed from the end of the early Holocene to the present.
130-146