Late neogene biostratigraphy and stable isotope stratigraphy of a drilled core from the Gulf of Mexico

Late Neogene stable isotope stratigraphy and planktonic foraminiferal biostratigraphy have been examined in a high sedimentation rate core (E67-135, Shell Oil Co.) drilled at 725 m water depth in the De Soto Canyon, Gulf of Mexico. The 305 m core contains sections that are Late Miocene, Early Pliocene, Late Pliocene, and Quaternary in age, and is rich in well-preserved assemblages of planktonic foraminifera. A biostratigraphy has been established based on the ranges of 34 selected species of foraminifera. The core 3orrelates with sections from the Gulf of Mexico, the Caribbean Sea, and the subtropical North and South Atlantic Oceans using, as datums, the evolutionary appearances of Globorotalia miocenica Palmer and Globorotalia margaritae evoluta Cita, the extinction of Globorotalia miocenica and the first appearance of Globorotalia truncatulinoides (d'Orbigny). Oxygen and carbon isotope stratigraphy is based on analysis of the benthonic foraminifer, Uvigerina d'Orbigny. Isotopic trends are similar to those observed in the Pacific and Atlantic Oceans. From Early Pliocene to Late Pleistocene time, average δ 18O values increase (2.42‰ to 3.36‰) and exhibit a wider range of values (0.71‰ in Early Pliocene compared to 1.65‰ in Late Pleistocene sediments), probably reflecting Late Neogene climatic deterioration. The ratio 13 C 12 C decreases significantly by −0.21‰ from the Late Miocene to the Early Pliocene. A decrease in δ 13C is observed in other cores and is probably related to changing oceanic circulation patterns in Late Miocene time.