New Data on Carboniferous Deposits in the Southern Part of the East-Timan Megaswell

Abstract

Research subject. Lower Pennsylvanian deposits exposed by mine excavations in the watershed part of South Timan.Materials and methods. The research material included data obtained by a field description of sections and an optical microscopy analysis of rock samples (26 specimens). For micropaleontological analysis, oriented thin-sections (97 specimens) were additionally prepared. Trace fossil taxa were determined based on both field photographs and collected specimens. Four oriented rock samples were used to determine the phase composition of the clay fractions from diffraction patterns.Results. The rocks of the Askynbashian (2.7 m), Tashastian (1.4 m), and Akavasian (2.5 m) Regional Stages of the Bashkirian Stage are exposed in the Ikhnitovyi quarry, and the Upper Vereiskian deposits of the Moscovian Stage (1.9 m) are exposed in the Vyemka section. The Ikhnitovyi quarry section exhibits a distinctly cyclic pattern. The cycle bases are distinguished by the appearance of coral and algae limestones, above which thin bedded fine-grained bioclastic and peloidal limestones occur. Greenish illite and chlorite clays indicate shallow sedimentation environments. The carbonate sediments experienced two cementation stages separated by the phase of compaction. The trace fossil assemblage recognized in the Ikhnitovyi quarry characterizes Cruziana ichnofacies. The Vyemka section is of particular interest due to the find of Eofusulina and the presence of typical carbonate tempestites.Conclusions. The Bashkirian deposits were accumulated under quiet shallow-water conditions (coral and algae limestones), on low-gradient tidal flats (fine-grained grainstones), and under a low hydrodynamic activity (probably low-amplitude tides). The illite and chlorite clays identify the accumulation of aeolian material (clay paticles) in ponds.