--> ABSTRACT: The Gulf of Mexico Transect: Neogene Biostratigraphy, Biofacies and Bathymetry, by M.-P. Aubry, W. A. Berggren, M. Katz, K. G. Miller; #91020 (1995).

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The Gulf of Mexico Transect: Neogene Biostratigraphy, Biofacies and Bathymetry

M.-P. Aubry, W. A. Berggren, M. Katz, K. G. Miller

We have conducted an integrated study on calcareous plankton (forams and nannofossils) and benthic forams (calcareous and agglutinated) from the Neogene part of the stratigraphic record in a six-well transect extending from Main Pass (NE) to Green Canyon (SW) in the Gulf of Mexico. The Eureka coreholes and ODP Hole 62513 (~110 km to the E) and sidewall cores from Chevron Main Pass 254 provide biostratigraphic control for the study which is otherwise based primarily on ditch cuttings.

The Neogene stratigraphic record exhibits similarities with the Eureka boreholes with notable variation in thickness of various chronostratigraphic units and marked discontinuities. One or more late Pliocene-Pleistocene hiatuses are recorded in four wells; a late Miocene to early Pliocene hiatus is recorded in two, and probably, a third well; the shallowest well, Main Pass (92 m present water depth) is riddled with hiatuses and only ~1/3 of the past 30 m.y. is represented by sediments.

Biofacies analysis indicates a range of neritic (Amphistegina -miliolid) to middle to upper bathyal environments. Low oxygen conditions began in the late early Miocene at Viosca Knoll 736 and in the middle Miocene at Main Pass 254. Intensified low oxygen environments became evident at all locations by the late Miocene with the appearance of the Agua Salada "flysch-type" fauna in at least two (Viosca Knoll 736 and Mississipi Canyon 455, ~8.5 Ma) and probably a third (Viosca Knoll 817, ~12 Ma) well; a contemporary Uvigerina biofacies developed in two wells (Ewing Bank 788 and Main Pass 254). The disappearance of the Agua Salada fauna in the latest Miocene (~6 Ma) is considerably younger than in Venezuela, North Africa and elsewhere. Better oxygenated conditions are recorded in calcareous faunas at Viosca Knoll 817 by the latest Miocene and in the late early Pliocene in Green Canyon, whereas lower oxygen conditions persisted at Main Pass 254 and Mississippi Canyon 455. Development of lower oxygen conditions as a result of an expansion of the oxygen minimum zone in the middle to late Miocene is consistent with the expansion of the Uvigerina biofacies in the Eureka cores.

This project has been supported by BP, Chevron, Marathon, Texaco and Unocal.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995