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ABSTRACT: Contribution of Sea Level-Induced Erosional Events in Platform/Periplatform Deposits to Lowstand Sedimentation in the Bahamas

Donald F. McNeill

New accumulation curves for Bahamian platform and periplatform carbonates are used to elucidate, with good time control, a regional-scale erosional event believed to be triggered by sea level regression. Magnetostratigraphic dating of cores from Little Bahama Bank and San Salvador in conjunction with nearby biostratigraphically and magnetostratigraphically dated periplatform cores collected by the Ocean Drilling Program (ODP) leg 101 (Sites 633, 630) allow comparison of periods of accumulation and erosion. These two periplatform cores (and four additional ODP cores) show an erosional gap from about 2.2 to over 3.0 Ma, whereas the platform flooding record measured from the core areas and Great Bahama Bank shows the onset of subaerial exposure at about 2.4 Ma, continuing in ermittently to about 0.8 Ma. Overlap of these two profiles suggests that a regional-scale erosional event, likely slope failure as avalanching gravity flows, occurred just after initial exposure of the platform 2.4-2.2 Ma. Net accumulation curves suggest that this event occurred after a prolonged highstand capable of producing and storing large quantities of uncemented sediment. This large sediment reservoir may have loaded the platform margin and upper slope as sea level and the wave base regressed through several high-frequency events. These data suggest that initial lowering of sea level triggered this regional erosion event on the platform flanks, thus moving periplatform sediment basinward, although other triggering mechanisms (i.e., tectonic) are possible. This sequence of events m y contribute significantly to lowstand deposits seen in seismic profiles from pure carbonate environments.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990