GUADALUPIAN/LOPINGIAN CHEMOSTRATIGRAPHY OF THE DELAWARE BASIN: UNRAVELLING REGIONAL VERSUS GLOBAL FACTORS

Carbon isotope excursions in marine carbonates often record changes in the global carbon cycle through geologic time. However, apparent δ¹³C excursions may also reflect the influence of regional oceanographic effects, especially in restricted or epieric settings. Proper interpretation of the carbon isotope record relies on an accurate assessment as to the regional or global nature of these disturbances. If excursions are the result of global carbon cycle changes, then they can often be used as global chronostratigraphic markers related to periods of rapid environmental change (e.g. mass extinction). If instead these excursions are the result of regional processes, they may provide useful record of changes in local basin water chemistry. The potential effect of these regional changes in oceanographic conditions must be critically evaluated before an excursion is deemed suitable for global correlation.

The Guadalupian/Lopingian (Permain) boundary and its associated mass extinction have received considerable attention in the recent literature. Unlike the larger end-Permian extinction, the δ¹³C excursion associated with the end-Guadalupian extinction is not present globally. This study examines variations in trace element and stable isotope geochemistry from the Delaware Basin of West Texas and New Mexico. Interpretation of geochemical data within a pre-existing shelf-to-basin stratigraphic framework suggests a link between basin water chemistry and sea level changes during the entirety of the Guadalupian. In light of this potential control, severe restriction of the basin near the Guadalupian/Lopingian boundary should be considered a possible influence on the local carbon isotope record. Unraveling these regional signals is an important step towards gaining a clearer understanding of how chemostratigraphy and sedimentology can be used to interpret oceanographic effects in the carbonate record.