High-Resolution Stable Isotope and Microfossil Record from the Gulf of Mexico

Abstract

ODP Site 625B was hydraulically piston cored in the northeastern Gulf of Mexico providing an apparently complete sedimentary record for the last 5.35 my. A high-resolution chronology was derived by tuning the oxygen isotope record to variations in orbital obliquity. Ages for calcareous nannofossil and planktonic foraminiferal datums were determined. Eight of the 11 nannofossil last appearances occur during glacials or during the onset of glacial periods. Of the eight foraminiferal last appearances, half occur during glacials. Results from open-ocean records also show a preponderance of last appearances within glacial intervals for the last 2.5 my. The higher frequency of last appearances during glacial intervals may result from greater environmental stress. Late Pliocene (2.30-1.66 Ma) and early Pleistocene (1.66-0.73 Ma) oxygen isotope anomalies with magnitudes of {minus}1.4 to {minus}2.0{per thousand} indicate glacial meltwater discharge from the Mississippi River implying that an ice sheet has been present at midlatitudes in North America periodically since 2.3 Ma.