Clastic Rocks of the Basement-Overlying Proterozoic Sedimentary Sequences: Communication 2. Sandstones and Main Features of Lithogeochemistry

Abstract

Based on the analysis of the bulk chemical composition of sandstones that make up the Proterozoic sedimentary sequences, which unconformably overlie the basement (Ai and Prikamsk formations; Mukun and Valdai groups; Kerur Formation; Gwalior, Athabasca, Libby Creek, Wufoshan, and Birim groups, and others), it has been shown that the content of the major oxides and trace elements in them in the overwhelming majority of cases differs significantly from the chemical composition of the average Proterozoic cratonic sandstone. Their composition corresponds mainly to litharenites, sublitharenites, arkoses, and subarkoses according to the classifications proposed by F.J. Pettijohn with co-authors and M. Herron. Most of the sandstones from the analyzed set belong to rocks containing a significant or predominant part of the lithogenic component. The detrital material composing the sandstones was sourced from fairly mature substrates, with insignificant role of the basic igneous and metamorphic (?) rocks. The bulk chemical composition of sandstones and the paleogeodynamic nature of rocks suggest that the substrates were produced by various orogenic/collisional and rifting events. As with the fine-grained clastic rocks in the studied Proterozoic sedimentary sequences, obviously, not all of the discriminant diagrams used in this study yield consistent results.