AN EVALUATION OF THE CENOMANIAN-TURONIAN OCEANIC ANOXIC EVENT IN THE GULF OF MEXICO THROUGH A CORE RECOVERED FROM THE TUSCALOOSA MARINE SHALE, SOUTHEAST LOUISIANA

A core recovered from Eads Poitevent #1 in the Lacombe Bayou Field of St. Tammany Parish, Louisiana, contains a nearly complete section of the Tuscaloosa Marine Shale (TMS). The TMS is an organic-rich shale interbedded with sandstones and siltstones, deposited on the shelf of the Gulf of Mexico during the Upper Cretaceous. During this time, the Gulf of Mexico experienced periods of anoxia, including the Oceanic Anoxic Event #2 (OAE 2), occurring at the Cenomanian-Turonian transition (93 Ma).

To determine the presence of OAE 2 recorded in the TMS, the following parameters were evaluated to determine the oxidizing conditions during the deposition using the Eads Poitevent #1 core: (1) Amount of Total Organic Carbon; (2) Elemental composition focusing on redox-sensitive elements and their enrichment factors; (3) Bulk Carbon Isotope Analysis to identify a positive carbon isotope excursion signature; (4) Petrographic analysis using sedimentology and stratigraphy; and (5) Biostratigraphy using Foraminifera counts.

Preliminary geochemical analysis and biostratigraphy concluded that the OAE 2 is recorded in the Louisiana trend of the Tuscaloosa Marine Shale at the base of the core. In this interval, XRF analysis showed an increase in redox-sensitive elements, along with IRMS showing a positive Carbon Isotope Excursion occurring in this interval. Preliminary petrographic analysis of the core concluded that the TMS was deposited under rising sea level conditions during the Cenomanian and Turonian, below storm wave base in open marine conditions of the offshore distal continental marine shelf.