Three-Dimensional Mapping of Benthic Biofacies and Planktic Assemblage Variations: A New Method to Interpret Areal Changes in Sedimentation Rate for Sequence Stratigraphy

Tomas Villamil, Paul Weimer, Arthur S. Waterman, Peter Varnai, Mark Rowan, Zurilma Acosta, Fadjar Budhijanto, Barry Mcbride, Rafael Martinez, Alonso Navarro

Benthic foraminifera biofacies integrated with variations in diversity and abundance of planktic foraminifers and nannofossils were contoured in three-dimensional maps representing time slices for two complete sequences of the Plio-Pleistocene of the Gulf of Mexico (3.8-3.0 Ma and 1.1-0.8 Ma; Ewing Bank, Green Canyon, and South Timbalier South areas). The data base used for the construction of maps comprises more than 100 wells combined with chronostratigraphic horizons derived from seismic lines.

Assuming relatively constant conditions within the photic zone over the area, and during the time-slice for each individual map, contours of biofacies and planktic assemblages are interpreted in terms of paleo water depth and relative sedimentation rate. Faunal assemblage maps show general trends in paleotopography of the sea bottom. Paleotopography is interpreted in terms of highs and lows that represent small-scale basins controlled by the location of salt withdrawal sites (lows), salt domes and salt flow sites (highs), differential compaction sites (lows and highs), and location of growth faults (lows and highs). Faunal assemblage contour maps, particularly of planktic foraminifer and nannofossil abundance and diversity, also show general sedimentation rate trends in space and time These sedimentation rate trends are interpreted in terms of auto- and allocyclic oscillations in sediment supply and sequence development which are controlled by eustatic changes in sea level. This method of analyzing faunal characteristics can be used iteratively with seismic facies maps and structural restorations to understand the development of sequences and the fill of a basin in a more comprehensive manner.

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