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ABSTRACT: Plio-Pleistocene Bio-Chronostratigraphy of DSDP Site 502B, Caribbean Sea: Implications for Gulf of Mexico Exploration Stratigraphy

Richard H. Fillon

The stratigraphic importance of the successive appearances and disappearances of the Globorotalia menardii/tumida lineages in the Atlantic during the Pleistocene has been recognized since the pioneering work of Ericson. The lineages, which developed in the Indian/western Pacific Ocean in the Miocene, have intermittently spread westward into the tropical Atlantic but have not been able to maintain a permanent foothold there. Their presence in the Atlantic is modulated by the opening and closing of a narrow window of environmental conditions and surface currents at the southern tip of Africa. When climatic variability during the last 5 m.y. shut the window, the population in the tropical Atlantic has undergone spurts of endemism (e.g., G. miocenica, G. exilis) or has failed totally. When the window opened, the population increased dramatically and endemism has disappeared.

At Site 502B, the waxing and waning of Atlantic menardii/tumida populations is recorded in excellent detail back to about 3.5 Ma. The longest interval over which menardii/tumida are observed to be continuously present is approximately 0.4 m.y., whereas the longest period of exclusion is approximately 0.2 m.y. In its external forcing and stratigraphic potential, the inclusion/exclusion record of menardii/tumida in the Atlantic resembles reversals of the earth's magnetic field. Thus, the principles used in magnetic reversal chronology provide a guide for developing a menardii/tumid-based biochronostratigraphy for important exploration areas in the Gulf of Mexico and elsewhere in the tropical and subtropical Atlantic. The golden rule of both geomagnetic chronology and menardii/tumida chr nology is not to use it with supportive faunal and floral range data. When combined with reliable planktonic foraminiferal and calcareous nannofossil range data, delineation of menardii/tumida inclusion/exclusion zones provides an immediate two-fold enhancement in stratigraphic resolution.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990