Lithological features, reconstruction of redox setting, and composition of the provenances of the Upper Triassic Kular–Nera shale belt

Abstract

Comprehensive lithogeochemical analysis is carried out for Norian sediments from the central part of the Kular–Nera shale belt. The sediments are represented by alternation of sandstones and siltstones. Petrochemical typification shows that the sandstones are subdivided into graywacke, arkose, and subarenite, while the siltstones belong to shale. The Norian sediments were mainly deposited in an oxidizing environment of a well-aerated basin in the distal parts of the Verkhoyansk passive continental margin. They are characterized by a high sorting of sedimentary material. The correlation between the rock-forming elements and the wide range of (La/Yb)_n ratios indicate that the sedimentation basin contained the disintegration products of both acid [(La/Yb)_n = 10.52–27.26] and mafic [(La/Yb]_n = 6.22–8.96)] rocks. The high values of the La/Sc and Th/Co ratios are typical of acid rocks. The low K₂O/Al₂O₃ values (0.16 ± 0.02) and high Zr/Sc ratio (10.1 ± 2.74) are typical of redeposited material. It is established that several provenances were involved in the formation of the Norian sediments in the central part of the Kular–Nera shale belt. Multicomponent clastics and well-sorted recycled material were supplied into the sedimentation basin.