Lithofacial characteristic and cyclic analysis of the Middle Triassic of the Pronchishchev Range (north of Middle Siberia)

Abstract

The object of study is clastic Middle Triassic of the central part of the Pronchishchev Range. The territory of researches is located on the border of Ust’-Anabar and Lena-Olenek facies districts and has poor geological knowledge. During field study of outcrops and test pits new data for Triassic of the right bank of the Peschanaya River were obtained. Lithofacial analysis and analysis of cyclical structure of the Anisian and Ladinian were carried out. The stratigraphic subdivision of the strata was made according to the results of a comprehensive bio- and lithostratigraphic analysis. The succession includes the Karangatinskaya and the Tuora-Khainskaya (Anisian), the Ust’-Olenekskaya and Olimpiiskaya (Ladinian) formations. The lithofacial analysis showed that the sedimentation occurred in mainly sea-shallow conditions with constant exposure of normal waves. Upward the succession a part of coastal sediments increase. Stages of fast sea level rising took place. The analysis of cyclical structures showed that the studied deposits represent the series of regressive sedimentological cycles of decameter scale with а transgressive orientation. They form the large regressive sedimentary cycle with a pronounced binomial structure. It has been found that the Anisian part of the studied section has very similar features of a structure with Leno-Olenek type sections. The structure of the Ladinian part is also similar to the sections of the Lena-Olenek type and is characterized by a slightly reduced thickness of the Olympic formation. It is typical for the western part of the Lena-Olenek facies district. Structural features of the selected cycles allow you to use them in lithostratigraphic correlations of geological sections within the considered sedimentation basin. This is especially true for sites with rare and relatively uniform fossil fauna.