Depositional architecture and geochemical evolution in Permian Capitan platforms of the Delaware Basin, Texas and New Mexico
Geochemical data from carbonate sediments are used to constrain chemical changes in ancient oceans. Marine carbonates can be representative of the global ocean, but many ancient carbonates precipitated in isolated water masses such as restricted basins and interior seaways. As a result, geochemical and paleontological records from isolated basins may reflect both global environmental forcing and local water mass evolution. Understanding the interaction between global and local palaeoceanographic change is a key step in unravelling enigmatic marine biotic crises such as the Mid-Capitanian extinction. This study examines factors controlling salinity, stratification, and oxygenation in the Capitanian (Middle Permian) Delaware Basin, USA. Elemental and carbon isotope measurements from time-equivalent strata reveal differences between shallow- and deep- water masses, pointing to local controls such as stratification and de-oxygenated bottom water. Basinal dolomites and evaporites mark periods of elevated salinity commonly tied to sea-level lowstands, which correlate with turnover in fusulinid and brachiopod communities. Faunal turnover in the Delaware Basin demonstrates a fundamental attribute of restricted basin settings: water chemistry is often tightly coupled to physical process such as sea level change. We suggest that the relationships among sea level change, chemical changes, and biotic turnover may explain why the Capitanian mass extinction was more severe in isolated basins than the open ocean.