Preliminary Correlations of Lithology and Seismic Reflectors in Prograding Neogene Carbonate of Great Bahama Bank

EBERLI, GREGOR P., Geological Institute, Zurich, Switzerland, and ROBERT N. GINSBURG, PETER K. SWART, DONALD F. MCNEILL, and JEROEN A. M. KENTER, University of Miami, Miami, FL

Excellent overall recovery of 80% in two continuous core borings provides the data on lithology necessary to calibrate prograding late Cenozoic sequences and their seismic signatures. Hole UNDA, 10 km inside the modern platform edge of Great Bahama Bank (GBB), penetrated onlapping and topset reflectors and a buried platform rim. The 500 m core revealed two platform sequences alternating with fine grainstone units with internal hardground surfaces. At hole CLINO, 5.5 km farther basinward, 657 m of core document the progradation of GBB with 150 m of shallow platform deposits and reefal sequences over mostly fine-grained, foraminifera-rich periplatform slope sediments with intercalations of coarser beds, some of which contain platform lithoclasts. Within these slope deposits, there is si nificant variation in the degree of cementation; friable, porous limestones alternate with well cemented beds. Preliminary correlations between lithofacies and seismic signatures suggest a strong influence of both the sedimentologic and diagenetic facies on the seismic signal. Major lithologic changes, such as from mudstone to coral-bearing packstone or from skeletal sand to reefal limestone, produce strong reflectors. These latter transitions also coincide with seismic sequence boundaries. Within the more homogeneous slope sections, where seismic reflection horizons are not characterized by a facies change, differential cementation seems to be responsible for the seismic signal. Nevertheless, three reflectors identified as sequence boundaries are overlain by units containing coarse-grai ed beds with platform lithoclasts and blackened grains, indicating that these deposits were shed during low sea level and represent parts of the lowstand systems tract.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)