Middle Moscovian climate of eastern equatorial Pangea recorded in paleosols and fluvial architecture
Opluštil et al
Fluvial architecture in conjunction with the morphology, petrographical, mineralogical and geochemical composition of intercalated paleosols of the Middle Moscovian upper Radnice Member of the continental Kladno-Rakovník Basin, Czech Republic, were studied in order to decipher climatic signals in the eastern Pangea region during the Late Paleozoic Ice Age. Analysis of architectural elements reveals vertical changes from strongly amalgamated channel fills of bedload-dominated braided streams, to isolated ribbon-like meandering channel fills in mud-dominated floodplain strata. The resulting large scale fining upward cycles separated by laterally widespread bounding surfaces are interpreted as having been formed in response to allocyclic processes driven by variable intensities of precipitation which affected the density of vegetation cover across the landscape and, in turn, the amount and character of sediment supply. Bedload-dominated parts of the cycles were deposited during periods of low water tables and sparse vegetation, whereas periods of maximum precipitation resulted in higher water tables and a greater density of vegetation cover, which, in turn stabilized the floodplains and fixed streams to narrow meandering/anastomosing channels in mud-dominated floodplain strata. Associated paleosols resemble modern Vertisols, which form under seasonal precipitation in modern settings. However, coeval formation of inertinite-rich peat represented by histosols and gleyed low chroma Vertisols in the stratigraphically lowest paleosol succession occurred under overlapping marginal conditions for the climatically different types of soils (i.e., under a seasonal climate where precipitation exceeds evapotranspiration for 6 to 8 months out of the year). Mean annual precipitation calculated from the geochemistry of B horizons of Vertisols (CALMAG proxy) varies between 1815 and 1730 mm/yr.