Dolocretes in the uppermost Famennian to Mississippian siliciclastic deposits (Šķervelis Formation, Latvia)

Siliciclastic deposits and dolostones of the Šķervelis Formation in southwestern Latvia were studied in outcrops, polished slabs, thin sections, and by geochemical methods, including stable isotope analyses. Siliciclastic fluvial deposits alternate with soils and carbonates. As the soil processes became dominant, up to 6 m thick dolocretes formed, but they still preserve remnant sedimentary structures and textures. The strong role of soil processes is indicated by the presence of ooids and pisoids together with fine laminar layers, chert and phosphatic inclusions, rhizoids, and stable isotope values. Peculiar vertical clay-dolomite structures, up to 1.7 m long, are root structures or their combination with Vertisol-like soil development. The extensive development of soil processes and formation of the vertical structures was stimulated by seasonally wet monsoon climate. The scarcity of fossils in the studied deposits does not allow their age to be determined precisely, but probably the thick dolocrete unit in the upper part of the studied succession formed during the end-Devonian glaciation and the period of related sea regression.