Paleopedology and fluvial sedimentology of the Upper Devonian Catskill Formation, Central Pennsylvania: A test of the distributive fluvial system

Abstract

The Upper Devonian Catskill Formation represents marginal marine and alluvial sediments which prograded into the Appalachian Basin during the Acadian Orogeny. Distributive fluvial systems (DFS) are prevalent in modern actively aggrading basins in all tectonic and climatic regimes and may be common in the rock record. In this study, I reinterpret the Catskill Formation as a prograding distributive fluvial system (DFS) on the basis of up-section variability in paleosols, channel sandstone textural trends, and alluvial architecture. At least three distinct pedotypes representative of prevailing soil forming conditions are identified during deposition of the Irish Valley, Sherman Creek, and Duncannon Members of the Catskill Formation. Increased paleosol drainage is inferred from an up-section transition from hydromorphic aqualfs within the Irish Valley Member to non-calcareous, uderts within the Duncannon Member. Qualitative field observations of channel sandstone morphology show an increase in channel size up-section. Channels occur as small isolated bodies at the base of the section, transitioning to relatively larger, amalgamated channels, and finally, large isolated channel bodies up-section. Sandstones are litharenites and coarsen-upward throughout the Catskill Formation overall. This coarsening upward trend results from increasing paleo-flow competency in larger channels up-section. These results are consistent with deposition of the Catskill Formation by DFS processes and demonstrate the utility of paleopedological analysis in interpreting alluvial depositional processes. Identifying DFS in the rock record has implications for paleosol-based paleoclimatic studies, as paleosols forming on prograding DFS have increased paleosol drainage up-section, which could potentially be misinterpreted as a shift from prevailing humid to arid paleoclimatic conditions. Recognition of DFS in the rock record also has implications for basin analysis and exploration of fluvial aquifers and hydrocarbon reservoirs, as the stratigraphic architecture of DFS are fundamentally different from tributary systems at the basin scale.