A. S. Biakov

Late Permian to Middle Triassic palaeogeographic differentiation of key ammonoid groups: evidence from the former USSR

Palaeontological characteristics of the Upper Permian and upper Olenekian to lowermost Anisian sequences in the Tethys and the Boreal realm are reviewed in the context of global correlation. Data from key Wuchiapingian and Changhsingian sections in Transcaucasia, Lower and Middle Triassic sections in the Verkhoyansk area, Arctic Siberia, the southern Far East (South Primorye and Kitakami) and Mangyshlak (Kazakhstan) are examined. Dominant groups of ammonoids are shown for these different regions. Through correlation, it is suggested that significant thermal maxima (recognized using geochemical, palaeozoogeographical and palaeoecological data) existed during the late Kungurian, early Wuchiapingian, latest Changhsingian, middle Olenekian and earliest Anisian periods. Successive expansions and reductions of the warm– temperate climatic zones into middle and high latitudes during the Late Permian and the Early and Middle Triassic are a result of strong climatic fluctuations.

Permian to earliest Cretaceous climatic oscillations in the eastern Asian continental margin (Sikhote-Alin area), as indicated by fossils and isotope data

Palaeozoological, palaeobotanical and geochemical analyses of Lower Permian to the lowermost Cretaceous sediments exposed in the southern Russian Far East (Bureya–Jiamusi–Khanka superterrane and the Sergeevka terrane), and higher latitude areas (northern Russian Far East and Spitsbergen) suggest a direct relationship with global climatic events defined by the data from oxygen-isotopic palaeotemperatures. Several positive carbon-isotopic anomalies discovered within the uppermost Cisuralian, Guadalupian, early Lopingian and Aalenian–Bajocian intervals are possibly connected to strong hydrological intermixing of oceanic waters under the influence of considerable thermal gradients.

The first detailed δ 13 С оrg record in Permo-Triassic boundary deposits in the Kolyma–Omolon region (Northeast Asia)

We have obtained the first detailed δ13Сorg record in Permian-Triassic boundary sediments in deepwater facies in Northeast Asia (Kolyma–Omolon region, Balygychan Basin). Our data show good convergence both with the Setorym River section (South Verkoyansk region), where the Permian-Triassic boundary has been determined approximately, and with a number of other sections of Permian-Triassic boundary sediments in the Boreal and Tethyan Superrealms, in particular, in the Buchanan Lake section in Arctic Canada, the Festningen section on Spitsbergen, the Wadi Shahha section on the Arabian Peninsula, and published sections in the Dolomites.

Permian ammonoids of the Okhotsk Region, Northeast Asia

Beds with ammonoids are recognized as a result of the study of goniatitids and prolecanitids from the Nyut, Khuren, and Ayan-Yuryakh in the Okhotsk Region. Beds with Neopronorites tenkensis, assigned to the Upper Artinskian Substage, correspond to the upper part of the Echian Horizon of the Verkhoyansk Region. Beds with Paragastrioceras–Baraioceras characterize the middle part of the Kungurian Stage and correlate with the upper sunhorizon of the Tumarian Horizon of the Verkhoyansk Region. Beds with Sverdrupites harkeri correspond to a biostratigraphic subdivision with the same name widely distributed in the Vekhoyansk-Kolyma Region and assigned to the Roadian Stage. The new species Neopronorites tenkensis is described.

Importance of carbon isotopic data of the Permian-Triassic boundary layers in the Verkhoyansk region for the global correlation of the basal Triassic layer

This paper is dedicated to a global correlation of marine Permian-Triassic boundary layers on the basis of partially published and original data on the δ13Corg and δ13Ccarb values of the Suol section (Setorym River, South Verkhoyansk region). The section consists of six carbon isotopic intervals, which are easily distinguishable in the carbon isotopic curves for a series of Permian-Triassic reference sections of Eurasia and Northern America, including paleontologically described sections of Central Iran, Kashmir, and Southern China. This suggests that the Permian-Triassic boundary in the Suol section is close to the carbon isotopic minimum of interval IV. In light of new data, we suggest considering the upper part of the Late Permian Changhsingian Stage and the lower substage of the Early Triassic Induan Stage of Siberia in the volumes of the rank Otoceras concavum zone and the Tompophiceras pascoei and Wordieoceras decipiens zones, respectively. The O. concavum zone of the Verkhoyansk region probably corresponds to the Late Changhsingian Hypophiceras triviale zone of Greenland. The carbon isotopic intervals II, III, IV, and V in the Permian-Triassic boundary layers of the Verkhoyansk region traced in a series of the reference sections of Eurasia correspond, most likely, to intensification of volcanic activity at the end of the Late Changhsingian and to the first massive eruptions of Siberian traps at the end of the Changhsingian and the beginning of the Induan Stages. New data indicate the possible survival of ammonoids of the Otoceratoidea superfamily at the species level after mass extinction of organisms at the end of the Permian.

New records of the Late Carboniferous ammonoid genus Eoshumardites in the Kolyma–Omolon Region, and notes on the evolution of Eoshumarditidae

A new species, Eoshumardites popowi Kutygin sp. nov., is described from the Upper Carboniferous of the upper reaches of the Paren’ River in the Gizhiga Province of the Kolyma–Omolon Region. The ontogeny of the sutural and shell morphology of the new species is described. In the level of sutural organization, E. popowi occupies an intermediate position between E. lenensis (Popow) and E. sublenensis Klets. It has been suggested that Eoshumardites evolved from the genus Syngastrioceras rather than Aktubites and, on this basis, a new monotypic endemic family, Eoshumarditidae, has been proposed. This family existed in the Kasimovian synchronously with members of the family Parashumarditidae.

Biogeography of the Permian marine Boreal basins based on bivalves

The biogeography of Permian marine bivalves of the Boreal Superrealm is considered. Two biochores, the Western Boreal and Eastern Boreal realms, divided into a number of provinces are distinctly recognized. The Western Boreal Realm, which comprises the East European, West European, Greenland–Canadian, and Spitsbergen provinces, is distinguished by the widespread occurrence of pteriacians, myalinids, mitilids, Pseudomonotis, Cyrtorostra, and Netschajewia. The Eastern Boreal Realm comprises the Pechora, Novaya Zemlya, Taimyr, Verkhoyansk–Okhotsk, Kolyma–Omolon, Mongol–Transbaikalian, and Yukon provinces and is characterized by the widespread occurrence of Inoceramus-like bivalves of the family Kolymiidae and a high proportion of genera with bipolar distribution.

New Species of Inoceramus-like Bivalves of the Subfamily Kolymiinae from the Middle Permian of Northeastern Asia

Middle Permian Inoceramus-like bivalves of the genera Kolymia Licharew and Cyrtokolymia Astafieva endemic to the East Boreal Biogeographic Realm are considered. Cyrtokolymia, previously regarded by the author as endemics of the Verkhoyansk–Okhotsk Province and including only the type species, are also recorded in the Kolyma–Omolon Province, where they are represented by the endemic species C. bobini sp. nov. An emended diagnosis of the genus Cyrtokolymia is provided. The genus Kolymia comprises about 30 species. The greatest diversity of Kolymia (24 species, 13 of which are endemic) is known from the Verkhoyansk–Okhotsk Province, which is the center of diversification of this genus. The Kolyma–Omolon Province is characterized by 12 species, only three of which are endemic. In other provinces of the East Boreal Realm, only individual members of Kolymia are known. From the Middle Permian of the Omolon Massif, northern Verkhoyansk Region, and Penzhinsky Ridge, the following new species are described: Kolymia posneri Muromzeva, Kusnezov et Biakov, sp. nov., K. pontoneica Biakov, sp. nov., K. simkiniformis Biakov, sp. nov., and Cyrtokolymia bobini Biakov, sp. nov.

Discovery of the Late Changhsingian Bivalve Complex and Two Fauna Extinction Episodes in Northeastern Asia at the End of the Permian

A late Changhsingian bivalve complex including species from the genera Palaeonucula, Dacryomya, Malletia ?, Sarepta ?, Myalina, Pteria, Maitaia, and Unionites is discovered in northeastern Asia for the first time. The transition from the Permian to the Triassic in high-boreal basins has been shown to include two extinction episodes similar to those observed in the low-boreal basins and apparently evoked by trap volcanism activation in Siberia. Changes in benthic foraminifera diversity and vertical distribution of ammonoidea of the genus Otoceras in transitional Permian–Triassic deposits also are considered. Images of bivalves from the most typical taxa are presented.

New results of U–Pb SHRIMP dating of zircons from upper Wuchiapingian (Upper Permian) deposits in northeastern Russia

The first results are presented for U-Pb SHRIMP-II dating of zircons from the upper part of the Khivachian regional horizon (stage) of the Regional Stratigraphic Scale (RSS) of the Permian in northeastern Russia. The obtained isotope age of 255 ± 2 Ma is close to that of the present boundary between the Wuchiapingian and Changhsingian stages of the Permian system in the International Stratigraphic Scale (254.1 Ma). Based on the distribution of bivalves—Intomodesma spp. and Claraioides aff. primitivus (Yin)—in the sections considered, their relations to the stratigraphic positions of the samples considered and dated formerly, and in view of the interregional correlation of recent δ13Сorg data for clayey rocks, one may assume with certainty that most of the regional zone of Intomodesma costatum corresponds to the upper part of the Wuchiapingian stage. Here, the Changhsingian stage in northeastern Asia complies only with the uppermost part of this zone within the I. postevenicum subzone and, partially, of Otoceras layers within the Otoceras concavum zone.