Lithogeochemistry of Vendian fine-grained clastic rocks in the Nepa-Zhuya region of the Siberian Platform

摘要

The possibility of reconstructing lithogenetic settings, composition of rocks in provenances, and geodynamic regimes characteristic of the formation of Vendian rocks in the Patom and Nepa-Botuoba sedimentary basins during the late Dal'nyaya Taiga-early Zhuya time and defining interrelations between organic-walled fossils and depositional environments is considered on the basis of the lithogeochemical data. For reconstructing paleogeodynamic depositional settings of sedimentary sequences, several well-known discriminant diagrams, such as K2O/Na2O-SiO2/Al2O3, SiO2-K2O/Na2O, and Th-La-Sc, were used. It is shown that some of them may be used with a variable degree of reliability for reconstructing depositional environments for platformal sedimentary successions composed of both sandstones and fine-grained clastic rocks. The most taxonomically diverse and abundant microfossil assemblages from the Ura and Parsha formations of the Zhuya-Lena area and Nepa-Botuoba anticlinorium, respectively, are confined to structurally and mineralogically immature silty-clayey shelf sediments buried rapidly under new portions of sediments in disoxic environments.