Geochemical Indicators of “Camouflaged” Pyroclastic Material in the Upper Jurassic–Lower Cretaceous Deposits of the Eastern Russian Platform

Abstract

Based on the results of studying the lithological–geochemical features of the Upper Jurassic–Lower Cretaceous mudrocks and black shales in the Eastern Russian Platform, the continuous distribution of pyroclastic material in the whole section is established. Possible sources of acid pyroclastics were active volcanoes of the Transcaucasian ensialic island arc. The explosions of the Sanandaj–Senjan ensimatic island arc (in the Late Jurassic) and the Arctic Large Igneous Province (in the Aptian) could have been the source of basaltic pyroclastics in the black shale horizons. The highest activity of the Transcaucasian and Elburs island arcs in northwest Tethys was apparently recorded during the Albian, which determined the maximum content of felsitic material in the Middle Albian bentonite-like mud rocks.