Reference sections OF Cisuralian Series (Permian System): geochemical features

Abstract

Object.Geochemical features of rocks from the Dal’ny Tulkas and Mechetlino sections located in the southern part of the West Urals foredeep are considered and are offered as International Standards for the global correlation (GSSP) of the lower boundaries of the Artinskian and Kungurian stages.Materials and methods.The content of rock-forming oxides and other components were studied for 15 and 20 samples of carbonate, clay and sandy rocks respectively in the sections of Dalnii Tyulkas and Mechetlino. The determination of the chemical composition of rocks was performed using a wave-dispersive X-ray fluorescence spectrometer S8 Tiger (Bruker, Germany). Results. The lithological characteristics of the sections, the content of oxides in mudstones and limestones of the boundary Sakmarian-Artinskian and of the boundary ArtinskianKungurian are taken. Mudstones of different stage are almost identical in average contents of the main components, whereas limestones have some differences. Correlative connections of oxides are analyzed and conclusions about mineral composition of rocks are made. Using the petrochemical modules and diagrams, it was established that the clay rocks in considered sections have mainly a hydromica composition. Based on the analysis of the indices of chemical weathering CIA, it is shown that the climate in the Cisuralian Epoch was predominantly arid. The tectonic environment of forming demolition sources, presumably corresponded to the active and passive margins of the continents.Conclusions.The main lithochemical characteristics of the rocks of the two sections under consideration are somewhat different, however, the boundaries of the stratigraphic subdivisions of each of them are virtually indistinguishable by lithochemical parameters, which may indicate the benefit of the continuity of sedimentation at the borders of centuries of the Cisuralian Epoch in this region. The conditions of sedimentation and the nature of eroded rocks in the area of demolition remained relatively constant. This is a positive point when looking the sections as International Standards for the global correlation (GSSP) reference objects – “golden nails”.