Micropalaeontological and geochemical evidence of mid-Cretaceous dysoxic-anoxic palaeoenvironments in the Sergipe Basin, northeastern Brazil

Abstract

Abstract Combined micropalaeontological, geochemical and sedimentological studies of the mid-Cretaceous (upper Aptian to Turonian) succession of the Sergipe Basin, northeastern Brazil, indicate that intermittent dysoxic-anoxic events occurred in the basin, most likely associated with the interplay of processes such as restricted physiography in the deep basin, salinity-stratified water masses, increased epipelagic primary productivity and high sea levels. Three maxima in oxygen depletion are recorded in the succession from middle neritic to upper bathyal environments: the late Aptian-earliest Albian, the early Cenomanian, and the latest Cenomanian-earliest Turonian. Improving oxidizing conditions (dysoxic to oxic) are apparent during middle-late Albian and early-middle Turonian times. The existence of a rich and diverse planktonic biota throughout the mid-Cretaceous succession suggests widespread oxygenated epipelagic layers of variable thickness in space and time in the basin.