Effects of Water-Mass Changes on Quaternary Biostratigraphy, Gulf of Mexico

DENNE, RICHARD A., Exxon Company, U.S.A., Houston, TX, and BARUN K. SEN GUPTA, Louisiana State University, Baton Rouge, LA

The quantitative record of benthic foraminifera in 61 cores from the northwestern Gulf of Mexico slope (283-1341 m; 90-95 degrees W) indicates a strong relationship between the distribution of benthic foraminifera and that of water masses during the last 15,000 years, producing potentially useful biostratigraphic datums. In the extreme case, the effect of water-mass changes may be reflected in the local stratigraphic limits of a species. More commonly, such changes may significantly affect abundance variations of species in the stratigraphic column. During the last deglaciation (13-11 Ka), several common species of the Subantarctic Intermediate Water (e.g., Bulimina alazanesis, Osangularia culter ) reappeared in the gulf with the reentry of this water mass, whereas Valvulineria "A" di appeared because of a drastic reduction in the production of the Glacial North Atlantic Intermediate Water. Thus, within the depth range of these species, coeval oceanographic events produced a biostratigraphic datum that is isochronous throughout the gulf. At the same time, at a water depth of about 800 m, the relative abundances of Bolivina albatrossi, Bolivina ordinaria, and Epistominella exigua increased, while those of Gavelinopsis translucens, Neocrosbyia minuta, and "Valvulineria opima" decreased. Our data also show that numerous species, including some recognized depth indicators, underwent changes in their depth adaptations during the deglaciation because of shifts of particular water-mass boundaries; these changes have to be taken into account in paleobathymetric interpretation of species occurrences or abundances.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)