The ammonoid recovery after the end-Permian mass extinction: Evidence from the Iran-Transcaucasia area, Siberia, Primorye, and Kazakhstan

Investigations of the Upper Permian strata in the Iran−Transcaucasia resulted in identification of 32 ammonoid genera. The majority of ammonoids in this collection belong to the order Ceratitida (75%). Among Dzhulfian ceratitid ammonoids representatives of the family Araxoceratidae (Otoceratoidea) are most abundant. The assemblage structure changed radically during latest Permian (Dorashamian) time, bringing a domination of the family Dzhulfitidae. The Induan (Lower Triassic) succession in the Verkhoyansk area provided a few groups of ammonoids which are Palaeozoic in type: families Episageceratidae (Episageceras), Xenodiscidae (Aldanoceras and Metophiceras), and Dzhulfitidae (Tompophiceras) and superfamily Otoceratoidea (Otoceras and Vavilovites). It demonstrates the survival of ammonoids belonging to these groups the Permian–Triassic (P–T) boundary extinction event and their quick migration to the vast ar− eas of higher latitudes (together with some representatives of the Mesozoic−type families). Induan–Olenekian ammonoid successions in South Primorye, Mangyshlak, and Arctic Siberia illustrate the high rate of Early Triassic ammonoid recov− ery in both the Tethys and the Boreal realm. New ammonoid taxa are described: Proptychitina subordo nov., Ussuritina subordo nov., Subbalhaeceras shigetai gen. and sp. nov. (Flemingitidae), Mesohedenstroemia olgae sp. nov. (Heden− strormiidae), and Inyoites sedini sp. nov. (Inyoitidae)

Variations in Nitrogen Isotope Composition in Clay Deposits of the Permian–Triassic Boundary Beds in the Verkhoyansk Region (Northeast Asia) and Their Implication for Reconstruction of Marine Environments

Abstract: The first sediment N-isotope data on the Permian–Triassic boundary transition of the Verkhoyansk region are obtained. Together with the other published materials on other regions of eastern Russia allow us to distinguish a number of N-isotope intervals of various ranks in the Permian–Triassic of eastern Russia. In addition to the well-known method of reconstructing the redox conditions of the marine environment from N‑isotope data (in combination with data on elevated concentrations of redox-sensitive trace metals), the possibility of using N-isotope data also to determine the direction of temperature changes in the marine environment is substantiated. It is assumed that N-isotope signals are primarily a reflection of events associated with denitrification and N2 fixation, the main processes of the global nitrogen biogeochemical cycle (NBC). Deviations in the direction of increasing δ15N values in the considered sections are associated with an increase in upwelling activity and the supply of cool deep waters enriched in the heavy N isotope to the shelf zone; the opposite deviations are associated with a slowdown or cessation of inflow of cool deep waters. The N-isotope data obtained, in combination with the published materials on O-isotope thermometry in the Tethyan Superrealm during the Permian and Triassic, indicate a very likely coincidence of the direction of temperature changes caused by both regional (upwelling) and global (climatic) events of that time. In this regard, the reconstructions of the marine environment that we conduct by the example of the Permian–Triassic sections of Northeast Asia (Verkhoyansk, Kolyma–Omolon, and South Primorye) seem to be appropriate, although they require additional confirmation on the material from other sections of the world. The problems associated with differences in the average δ15N values in the Permian–Triassic sections of different provinces of the Boreal Superrealm, as well as other superrealms, are considered

The Position of the Wuchiapingian–Changhsingian Boundary in Northeast Russia on the Basis of Radioisotopic and Chemostratigraphic Data

Abstract: The approximate position of the Wuchiapingian–Changhsingian boundary of the Upper Permian in Northeast Russia was determined for the first time on the basis of the comparison of δ13С trends established in the sections of South China and Iran, the Tethyan Superrealm, and the Pautovaya River section (Kolyma–Omolon region, Boreal Superrealm). This boundary runs in the middle part of the Intomodesma costatum bivalve zone of the Khivachian regional horizon. This conclusion is also confirmed by the previous dating of zircons from a tuff layer below the Wuchiapingian–Changhsingian boundary in the same section and by 87Sr/86Sr values from well-preserved brachiopod-spiriferid shells from the stratotypical section of the upper part of the Khivachian regional horizon on the Omolon massif