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-MEXICO

The northern deep Gulf of Mexico is a geologically complex province co nsisting of Neogene intraslope minibasins created by sediment loading onto and evacuation of allochthonous salt. Sedimentary fill in the min ibasins consists of bathyal turbidite systems with highly variable fac ies distribution. In this paper, we present three biostratigraphic tec hniques developed to increase our understanding of the geologic evolut ion of the northern Green Canyon and Ewing Bank lease areas. The first two techniques address the nature of stratigraphic condensation in mi nibasins 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 sedi ment accumulation plots from wells helping to identify possible areas of condensation based on variations in the rate of accumulation. By di splaying several wells together, the areal extent of the condensed sec tion can be identified, and the causes for the condensation can be eva luated. (2) The second technique addresses condensation within one min ibasin during a 2.5-m.y. interval. Relative abundance values are plott ed from a series of wells at selected time surfaces and tied to seismi c horizons that are correlated throughout the basin. This allows plott ing 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 paleobathymetr y of the slope at the time of deposition. These maps were created by p lotting the benthic biofacies of the sediments recovered from a well a t the stratigraphic extinction of 29 selected planktonic foraminifer a nd calcareous nannoplankton species; The maps are integrated with lith ostratigraphic and structural palinspastic reconstructions. The result ing maps are interpreted to more accurately reflect benthic biofacies of the continental slope at specific geological times during the Plioc ene and Pleistocene.