Connections between Interglacial Variation and Lithological Variability within Midland Basin Permian Shale Rocks in Martin County, Texas

The Upper Pennsylvanian (323.2–289.9 Ma) and Lower Permian (289.9-251 Ma), (Wolfcamp and Spraberry formations) interval of the Midland Basin, West Texas, contains a mixed succession of shale, carbonate, and siltstone/sandstone lithofacies that accumulated in a deep-water marine environment under variable hydrographic restrictions. The heterogenous stratigraphy found in the Wolfcamp and Spraberry formation was formed in response to variations in sea level and a transition from a glacial to an interglacial climate during the Early Permian. These fluctuations left behind alternating beds of mudstone and carbonate, interwoven with thin sandstone beds. Because the Wolfcamp and Spraberry formations are highly heterolithic, it is critical to understand how the stratigraphic and lateral variability in lithology changes if they are to be exploited as hydrocarbon reservoirs. A highly-resolved (5-cm vertical) X-Ray fluorescence (XRF)-based chemostratigraphic study was undertaken on eleven wells from Martin Co., Texas. The study incorporates data from cuttings and cores from intervals of the Wolfcamp and Spraberry formations. Major and trace elements compositions were measured on cuttings and slabbed cores using XRF methods. Correlation of the geochemical data across the wells was undertaken in order to correlate known changes in climate with changes in lithology. After correlation of chemofacies across the eleven wells was completed, a sequence stratigraphy analysis was conducted in order to assign general basin conditions to each major sea level change