PALEOCLIMATE DURING DEPOSITION OF THE LATE DEVONIAN GREATER TWILIGHT PARK CONGLOMERATE, SOUTHEASTERN NEW YORK

The Acadian Foreland Basin formed as a result of the collision of various terranes with the continent of Laurentia primarily during the Devonian Period. This created the southward propagating Acadian Orogeny. Formation of the basin and the cratonward-prograding Catskill clastic wedge caused deposition of the Devonian siliciclastic rocks seen today in the Catskill Mountain region of southeastern New York. The first major progradation of synorogenic gravels appear in the Oneonta Formation of this region. The Oneonta Formation is generally interpreted to be early Late Devonian in age and contains sandstone, shale, and conglomerate layers known as the Greater Twilight Park Conglomerate (GTPC). Paleosols found in between layers of the GTPC are important archives of past climate. Floodplain deposits exhibiting pedogenesis from four locations were selected due to proximity to layers of the GTPC. Field observations of paleosols show vertic features and clay translocation, indicating seasonal wetting and drying and sufficient precipitation. Petrographic analyses reveal oriented clay fabrics as well as iron-oxide and clay translocation, reinforcing macromorphological interpretations of seasonality. Chemical Index of Alteration minus Potash (CIA-K) on bulk geochemistry from B horizons most proximal to GTPC layers show an average mean annual precipitation (MAP) of ~ 1211 mm yr-1 suggesting these soils formed in a humid environment. CIA-K values of paleosols from the upper Middle Devonian give an average MAP of ~ 1109 mm yr^-1. Estimates of paleotemperature from the Paleosol Weathering Index (PWI) show a Mean Annual Temperature (MAT) of 11.65° C. Values from the upper Middle Devonian Paleosols give a MAT estimate of 11.5° C. Due to the absence of a drastic increase in precipitation during the GFT, a significant global or regional regressive-transgressive sea level change and orogenic activity are possible drivers, likely associated with the onset of a new tectophase of the Acadian Orogeny.