NEW DATA ON THE JURASSIC PHYTOSTRATIGRAPHY IN KAZAKHSTAN

Abstract

Based on new original paleofloral and stratigraphic data, collected recently from Jurassic sections in southern Kazakhstan, and on a critical revision of available collections and published data on Jurassic continental sequences, a new stratigraphic scheme is suggested for Jurassic coal-bearing deposits of Kazakhstan. Five phytostratigraphic (correlative) assemblages were defined, and provided grounds to correlate sections in different basins and to prove their ages. Comparative analysis of the taphoflora taxonomic composition permitted paleophytogeographic environments in Kazakhstan and their changes with time to be considerably specified. It was established that in the Early to early Middle Jurassic, the majority of Kazakhstan's territory, except its western areas, was occupied by flora of the Siberian type. During the second half of the Middle Jurassic and Late Jurassic, the Siberian flora was replaced by the Euro-Sinian assemblages throughout the region, except in northern Kazakhstan. This was caused by paleogeographic reorganizations that mainly resulted from transgression of the Tethys. The defined patterns in temporal flora distribution provided a reliable criterion for the correlation of coal-bearing deposits and their age determination, as well as for the refinement of phytochoria boundaries.