Stable Isotope Geochemistry and Paleohydrology of the Poison Strip Sandstone, Early Cretaceous, Eastern Utah

Abstract

The Poison Strip Sandstone Member is a unique unit in the early Cretaceous Cedar Mountain Formation of eastern Utah. A previous chemostratigraphic study of the Poison Strip Sandstone at the Ruby Ranch Road (RRR) section east of Green River, Utah produced a noteworthy dataset with interesting δ18O results (Ludvigson et al., 2015). The Poison Strip at the type section of the Ruby Ranch Member contains poikilotopic calcite cements that yield δ18O values that range between -16 and -13.5‰ VPDB (Ludvigson et al, 2015). These isotopic values represent a major departure from the typical δ18O values of about -8‰ VPDB documented during earlier studies of the Cedar Mountain formation and have either major paleoclimatic or later diagenetic implications for the unit. Through detailed petrographic, diagenetic, and stable isotopic analysis, we were able to determine that that the atypical δ18O values produced from the poikilotopic calcite cements of the Poison Strip Sandstone are the result of deep burial diagenesis. The precipitation of poikilotopic calcite cements were likely influenced by petroleum migration through the basin and may have also been impacted by hydrothermal fluids. Preliminary temperature and depth estimates of 2 – 3km and 73 to 90° C were calculated from the intergranular volumes and isotopic data.