Upper Cretaceous sequence stratigraphy, sea-level fluctuations and Oceanic Anoxic Events 2 and 3, Northeastern Gulf of Mexico

Abstract

The relationship between Oceanic Anoxic Events (OAEs) and sea-level fluctuations can be determined by placing OAE sediments into an integrated sequence stratigraphic framework based on biostratigraphic age control, and regional seismic and well-log data. Two Upper Cretaceous black shale units in the northeastern Gulf of Mexico area, the Marine Tuscaloosa shale and the downdip Eutaw shale, are interpreted to be deposited in association with Late Cretaceous OAE 2 (Cenomanian–Turonian boundary event) and OAE3 (late Coniacian – early Santonian). TheMarine Tuscaloosa shale accumulated during the maximum flooding event of the UKI sequence (middle Cenomanian to upper Turonian); and the downdip Eutaw shale accumulated as the early transgressive systems tract of theUKII sequence (upperConiacian to upperCampanian). These OAEs can be classified into two categories according to their sequence stratigraphic positions. Type I OAE (e.g., OAE 2) occurred during a maximum flooding event, and the black shale associated with this type of event was deposited in an open shelf environment. Type II OAE (e.g., OAE 3) occurred during the early phase of a marine transgression that resulted in the inundation of large coastal areas and the formation of lagoons and estuaries, which acted to trap large quantities of terrestrial organic carbon.