Paleoecology of Cretaceous Foraminifera: Examples from the Atlantic Ocean and Gulf of Mexico Region
Foraminifera (single-celled protists) have a long geological record. They are both numerous and taxonomically diverse in assemblages throughout the Mesozoic and Cenozoic and have been used extensively in the oil industry since Józef Gryzbowski studied the stratigraphy of the Potok Oilfield (southern Poland) in the late 19th century. Both planktic and benthic foraminifera are used for biostratigraphy in various locations throughout the world, based on both processed residues and—where appropriate—thin-sections. In the Cretaceous successions of the Gulf of Mexico and the passive margins of the Atlantic Ocean, foraminifera provide vital evidence of changing paleoecology, paleoceanography, and major extinction events. This is particularly significant in the interpretation of oceanic anoxic events in the mid-Upper Cretaceous and the extinction events associated with the Cenomanian/Turonian and Cretaceous/Paleogene boundaries. By using planktic:benthic ratios and various forms of morphotype analysis—coupled with an understanding of modern ecology—the distribution of foraminifera are often important indicators of sea-level changes, ocean acidification events, and the low-oxygen environments, which often create hydrocarbon source rocks. Shelf successions below modern-day oxygen-minimum zones, while supporting different species from those from fully oxygenated environments, do not normally generate anoxic sediments and restricted assemblages: there must be other factors, such as basin isolation, involved. Models developed for the offshore basins of Brazil have been applied in many areas of the world, with the neritic areas of the Gulf Coast and North Atlantic margins providing many examples of how such models can be applied elsewhere.
AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015