AAPG Bulletin, V. 82 (1998), No. 5B (May 1998 Part B), P. 961-985.

Biostratigraphic Techniques for Analyzing Benthic Biofacies, Stratigraphic Condensation, and Key Surface Identification, Pliocene and Pleistocene Sediments, Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf of Mexico¹

Tomas Villamil,² Claudia Arango,³ Paul Weimer,⁴ Art Waterman,⁵ Mark G. Rowan,⁴ Peter Varnai,⁶ Andrew J. Pulham,⁴ and Jennifer R. Crews⁴

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received January 6, 1997; revised manuscript received November 10, 1997; final acceptance November 19, 1997.
²Energy and Minerals Applied Research Center, Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309-0250. Present address: Advance Exploration Organization, Conoco, Inc., P.O. Box 2197, Houston, Texas 77252-2197.
³Energy and Minerals Applied Research Center, Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309-0250. Present address: Marathon Oil Company, P.O. Box 3128, Houston, Texas 77252-3128.
⁴Energy and Minerals Applied Research Center, Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309-0250.
⁵Paleo-Data, Inc., 6619 Fleur de Lis Dr., New Orleans, Louisiana 70124.
⁶Energy and Minerals Applied Research Center, Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309-0250. Present address: Exxon Exploration Company, P.O. Box 4480, Houston, Texas 77210.

We thank the following companies and their many representatives for their support and input: Agip, Anadarko, Amoco, BHP, BP Exploration, Burlington Resources, Chevron USA, CNG, Conoco, CXY Energy, Enterprise, Exxon, Marathon, Mobil, Occidental, Pan Canadian, Pennzoil, Petrobras, Phillips, Shell, Texaco, Total, Union Pacific, Unocal, and the donors of the Petroleum Research fund, administered by the American Chemical Society. Their support has been crucial for the success of this research. We extend special thanks to Halliburton Geophysical (now Western Geophysical), specifically to Bob Graebner, John Anderson, and Gary White, for the seismic data used in this project. We are indebted to Paleo-Data, Inc. for use of their biostratigraphic data. Digital logs were kindly provided by Marathon (Tricia Santogrossi). Software donations from GeoQuest, CogniSeis Development (Pat Poe, Roy Kligfield, Robert Ratliff), Landmark Graphics (Thom Fisher), and Zeh Graphics (Jerry Martin) were also essential to the success of our study. Thanks to Ryan Crow for his help with drafting some of the figures. We thank Conoco for defraying costs of color figures. We thank Laurie Lamar, M. S. Wacker, and AAPG reviewers Scott W. Starratt, Finn Surlyk, Kevin Biddle, and an anonymous reviewer for their valuable comments that improved the quality of this paper. 

ABSTRACT

The northern deep Gulf of Mexico is a geologically complex province consisting of Neogene intraslope minibasins created by sediment loading onto and evacuation of allochthonous salt. Sedimentary fill in the minibasins consists of bathyal turbidite systems with highly variable facies distribution. In this paper, we present three biostratigraphic techniques developed to increase our understanding of the geologic evolution of the northern Green Canyon and Ewing Bank lease areas.

The first two techniques address the nature of stratigraphic condensation in minibasins and the relative areal extent of the condensed sections. The third technique uses benthic foraminifers to improve the stratigraphic knowledge of the area. (1) The first technique is concerned with sediment accumulation plots from wells helping to identify possible areas of condensation based on variations in the rate of accumulation. By displaying several wells together, the areal extent of the condensed section can be identified, and the causes for the condensation can be evaluated. (2) The second technique addresses condensation within one minibasin during a 2.5-m.y. interval. Relative abundance values are plotted from a series of wells at selected time surfaces and tied to seismic horizons that are correlated throughout the basin. This allows plotting a series of maps that show how stratigraphic condensation changes throughout a basin. (3) The third technique develops benthic biofacies maps that more accurately reflect the highly irregular paleobathymetry of the slope at the time of deposition. These maps were created by plotting the benthic biofacies of the sediments recovered from a well at the stratigraphic extinction of 29 selected planktonic foraminifer and calcareous nannoplankton species. The maps are integrated with lithostratigraphic and structural palinspastic reconstructions. The resulting maps are interpreted to more accurately reflect benthic biofacies of the continental slope at specific geological times during the Pliocene and Pleistocene.