A 5 MY CHRONOLOGY OF CARBONATE PLATFORM MARGIN AGGRADATION SOUTHWESTERN LITTLE BAHAMA BANK, BAHAMAS

Results of integrated age dating are reported from two core borings (6 0 m and 61 m) on the southwestern margin of Little Bahama Bank (LBB). On the outer margin (core GB-1), seven chronostratigraphic units, some unconformity bounded, are correlated with of the inner margin (core G B-2), about 11 km away to the north. The southern margin of LBB shows a general shallowing-upward succession that records three distinct int ervals of differing sediment accumulation. This outer margin core prog resses from a relatively deep water (similar to 30 m) margin (at simil ar to 5-6 Ma) to shallower reef-associated sands (about similar to 5 M a) and reefal conditions (similar to 5-3? Ma), followed by peloidal sa nds (similar to 3-2? Ma) and subaerial exposure (around similar to 2-1 Ma), and finally intermittent, Quaternary nonskeletal sedimentation ( similar to 1 Ma to Holocene), The facies indicate a change from a wind ward, open-type margin (> 30 m water depth) to a windward, protected-t ype margin (reef/island), This change in the platform margin may have been in response to reef accretion along the margin, The long-lived re efal or near-reef facies in the outer margin core suggests that this m argin has been predominantly aggradational since at least the earliest Pliocene in contrast to the rapidly prograding margins on other Baham ian platforms during the same time period. However, the general facies succession, from transgressive/highstand (early Pliocene) to lowstand (mid-Pliocene/early Pleistocene) to intermittent highstand (mid/late Pleistocene), is consistent with dated successions from other platform s. The three sediment accumulation intervals and their respective faci es, Likely representing third-order scale sea-level fluctuations, are also consistent with changes in both the proposed eustatic curve and t he oxygen-isotope curve.