DO CARBON ISOTOPIC VALUES VARY ALONG A DEPTH GRADIENT IN THE LATE PERMIAN DELAWARE BASIN?

Carbon isotopes are important tools in paleoclimatic and chemostratigraphic studies. Tracing patterns in carbon isotopic trends can be useful for correlation and determining the relationship between different stratigraphic units. Significant fluctuations in carbon isotopic values can be used to infer changes in the global carbon cycle. These applications require that carbon isotopic trends roughly approximate global process and are not overwhelmed by regional/local signals. However, studies of ancient and modern carbonate platforms have demonstrated that carbon isotopic values are different in nearshore versus deep water environments. Nearshore environments tend to have lower carbon isotopic values and the magnitude of excursions are maximized while deep water environments have higher carbon isotopic values and the magnitude of excursions are minimized. This suggests that regional/local factors were contributing to recorded trends. This study explores the issue of depth gradients in carbon isotopes in the Late Permian Delaware Basin. We chose this study location because it is an ancient analog for the Great Bahama Banks (GBB), one of the modern carbonate settings where gradients in carbon isotopic values have been observed. We focused on the Yates Formation, Tansil Formation, and Lamar Limestone Member of the Bell Canyon Formation exposed at the Guadalupe Mountains National Park and Carlsbad Caverns National Park. We measured and described three sections along a depth gradient and placed these rocks into the existing sedimentological and sequence stratigraphic framework. Hand samples for carbon isotopes were collected and drilled to generate trends in the crest, toe of slope, and basin settings. Based on these results, we explore the relationship between carbon isotopic trends and position relative to shore.