Features of Dispersal of Late Anisian Ammonoids of the Boreal Realm

Abstract

Abstract —Identifying patterns of geographic differentiation of individual groups of marine invertebrate fauna in the geological past is important for understanding their evolutionary history, solving issues and problems of biostratigraphic division, and correlation of deposits. Paleobiogeographic data is also necessary to identify the development stages of biota and the geological history of marine paleobasins and verify paleogeodynamic reconstructions. In this work, considering the latest data on paleontology and biostratigraphy of the Boreal Triassic, the taxonomic composition and distribution of Upper Anisian ammonoids in various regions of the Boreal realm are revised. A correlation of Upper Anisian deposits of Northeast Asia, British Columbia, Canadian Arctic Archipelago, Svalbard, Franz Josef Land, and Khabarovsk Krai was carried out at the zonal level and a basis was obtained for a comparative analysis of coeval ammonoid faunas. As a result of a qualitative and quantitative comparative analysis of ammonoid assemblages for various phases of the Late Anisian age, it was established that in the Late Anisian age, British Columbia was constantly part of the Canadian province of the Boreal realm, and Northeast Asia was part of the Siberian province. At the end of the Late Anisian age (most of the late part of the Frechites nevadanus or Frechites chischa phases), provincial differences were smoothed out and for the first time, all Boreal regions were included in the Siberian province, except the territory of British Columbia. Analysis of the geographical distribution of some groups of ammonoids in the Late Anisian age and changes in the areas of taxa over time made it possible to identify probable migration routes of Longobarditidae (genus Longobardites) and to introduce significant changes in the ideas about the centers of origin and migration of some Beyrichitidae.