Abstract

Results of integrated age dating are reported from two core borings (60 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 GB-2), about 11 km away to the north. The southern margin of LBB shows a general shallowing-upward succession that records three distinct intervals of differing sediment accumulation. This outer-margin core progresses from a relatively deep-water ( approximately 30 m) margin (at approximately 5-6 Ma) to shallower reef-associated sands (about approximately 5 Ma) and reefal conditions ( approximately 5-3? Ma), followed by peloidal sands ( approximately 3-2? Ma) and subaerial exposure (around approximately 2-1 Ma), and finally intermittent, Quaternary nonskeletal sedimentation ( approximately 1 Ma to Holocene). The facies indicate a change from a windward, open-type margin (> 30 m water depth) to a windward, protected-type margin (reef/island). This change in the platform margin may have been in response to reef accretion along the margin. The long-lived reefal or near-reef facies in the outer-margin core suggests that this margin has been predominantly aggradational since at least the earliest Pliocene in contrast to the rapidly prograding margins on other Bahamian 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 platforms. The three sediment accumulation intervals and their respective facies, likely representing third-order-scale sea-level fluctuations, are also consistent with changes in both the proposed eustatic curve and the oxygen-isotope curve.

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