Petrography and Lithogeochemistry of the Uppermost Middle Jurassic–Lowermost Lower Cretaceous Strata in the Lower Reaches of the Anabar River (East Siberia, Arctic)

Abstract

Abstract —Based on the analysis of the petrographic and lithogeochemical features of the Middle Jurassic–Lower Cretaceous strata in the lower reaches of the Anabar River, we have studied the regularities of changes in the composition of the upper parts of the Yuryung-Tumus and Sodiemykha formations and the lower part of the Buolkalakh Formation. It has been established that the silt–sandy rocks of the first and basal beds of the second formation are graywacke arkoses and essentially feldspathic varieties, and most of the Sodiemykha Formation is composed of quartz–feldspathic and scarcer feldspar–quartz graywackes. A chemical classification of the rocks was made; most of them were assigned to normosiallites. The rocks of the marker beds, namely, the Fe-containing deposits of the Sodiemykha Formation, the basal glauconite bed of the Buolkalakh Formation, and the overlying clay bed, were classified as hypohydrolysates. All the studied deposits are of low sedimentary maturity, with essentially petrogenic clastic material. These are predominantly igneous rocks of intermediate and, less, felsic composition. The provenances were characterized by moderate chemical weathering. In the periods of the formation of the marker beds, chemical weathering intensified, and the amount of mafic and, partly, ultramafic rocks increased. The established changes in the composition of the parental strata are observed in the Middle Jurassic–Lower Cretaceous deposits of the entire considered petromineralogical province, which permits them to be used for correlation.