ABSTRACT

Study of planktonic foraminifers from deep-water sediment cores in the northern Gulf of Mexico indicates the presence of alternating cold-- and warm--water faunas which are interpreted to represent glacial and interglacial stages of the Pleistocene. Globorotalia menardii (warm) and Globorotalia inflata (cold) are the most sensitive indicators for delineating severe changes in Pleistocene temperature in the Gulf of Mexico.

On the basis of planktonic datums the cold-warm cycles are correlated with water-depth changes in the shallower shelf environment which are interpreted to represent eustatic sea-level changes. The cold intervals represent times of lowered sea level and are correlated with the glacial stages of North America. Age relationships between the glacially related events recognized in the marine Pleistocene section and the continental glacial stages are well documented to about 35,000 years ago on the basis of carbon 14 dates. Age relationships between the older part of the marine Pleistocene and the continental glacial stages are not so well documented but can be inferred from correlation between the glacial-interglacial cycles and paleomagnetic reversal events, which are well dated by potassium-argon.

Onset of severe climatic deterioration and beginning of the Quaternary (Nebraskan Stage) in the Gulf of Mexico correspond with the extinction horizon of Globoquadrina altispira. Correlation of this horizon with the paleomagnetic reversal events gives an age of about 2.8 m.y. ago for the Pliocene-Pleistocene boundary.

Placement of the Pliocene-Pleistocene boundary at 2.8 m.y. ago allows recognition of five major glacially related events in the marine Pleistocene based on climatic and eustatic criteria. Faunal data indicate that the Nebraskan, Illinoian, and Wisconsinan were severely cold periods, whereas the Aftonian, Kansan, Yarmouthian and Sangamonian were warmer, with the Aftonian the warmest. Carbon 13/12 isotope data support these conclusions.

Foraminifers and discoasters from the marine Calabrian Stage of southern Italy at Santa Maria di Catanzaro indicate a correlation with the marine Nebraskan Stage, as here defined, in the Gulf of Mexico. Paleontological evidence indicates that the Pliocene-Pleistocene boundary of Glass et al. (1967), Berggren et al. (1967), and Ericson and Wollin (1968) falls near the base of the Kansan. The cold and warm intervals shown below the Pliocene-Pleistocene boundary of Glass et al. (1967) are interpreted to represent the Nebraskan and Aftonian Stages. Paleomagnetic evidence suggests that the Olduvai magnetic event of these authors probably represents the Gilsa event at about 1.6 to 1.8 m.y. ago.

Advances in paleomagnetic stratigraphy indicate that the magnetic reversals facilitate dating and correlating marine stages at latitudes where differing paleontologic criteria must be used to delineate the glacial and interglacial episodes. Seemingly, the major paleomagnetic epochs are reliable for stratigraphic correlation; however, the minor events of relatively short duration appear to be less reliable as unique stratigraphic markers.

Globorotalia pertenuis, n. sp., a right-coiling member of the Globorotalia menardii group, is described.