Authigenic Sanidine as a Mineral Indicator of Gravitation-Brine Catagenesis in Carboniferous Rocks in the Southern Limb of the Moscow Syneclise

Abstract

The article presents data on numerous findings of authigenic K-feldspars in the Lower–Upper Carboniferous carbonate and terrigenous rocks in the southern limb of the Moscow syneclise, including the Oka–Tsna bar. In terms of the composition and crystalline structure, all feldspar morphotypes (idiomorphic monocrystalline fringes on the surface of sandy clastic grains, fine-crystalline aggregates, pseudomorphously replacing organogenic carbonate detritus, and pseudoskeletal crystals) are composed of K-sanidine with the overwhelming predominance of K over Na and extremely low concentrations of Ca, Ba, and Sr. As can be seen from 40Ar/39Ar dating, the authigenic sanidine mineralization took place during the Permian, i.e., 20–55 Ma later than the accumulation of host Carboniferous rocks. Mineralogical observations, as well as paleofacies and paleogeographic reconstructions, suggest that the formation of authigenic K-feldspars is associated with the gravitation-brine catagenesis in the southern limb of the Moscow syneclise as a result of the seepage of high-mineralization brines from Permian evaporate marine basins into the underlying older rocks.