Lidar-guided stratigraphic model of Pleistocene strata, San Salvador Island, Bahamas: Implications for Sea-level reconstructions, sedimentologic models, and carbonate platform development
Abstract
Pleistocene carbonates of San Salvador Island, Bahamas, have served as a guidepost as well as a lightning rod for studies of past sea-level and icehouse carbonate depositional patterns over the last 400 ka. A recent effort to understand both the rock-based geologic framework as well as the karst hydrologic/fluid flow characteristics of the island has inspired a new phase of core sampling, petrography, mapping, and hydrologic monitoring across the island. An airborne lidar-generated topo-bathy bare-earth image illuminates detailed geomorphic elements of the Holocene and Pleistocene, notably through the heavily vegetated interior as well as the spectacular coastal exposures.
Mid-Pleistocene units (two minimum) of MIS 9 and/or 11 include heavily karst-modified ooid grainstones and widespread weakly lithified bioclastic facies. For the first time shallow marine facies are recognized in this Owls Hole Fm., constraining subsidence scenarios for the island. The lower MIS 5e reef-bearing Cockburn Town member (now shown to be contemporaneous with French Bay and Fernandez Bay mbrs.) shows a strong preferred south to north longshore drift and SL elevation of +2-4 m. The upper MIS 5e is characterized by eastward and northward accreting aeolian dune-ridge complexes with foreshore elevations from +6 to -0.5 m that show a distinct forced regressive pattern observed elsewhere across the Bahamas. MIS 5a bioclastics of the Almgreen Cay Fm. are imaged on land (aeolian only) and in the shallow marine shelf of the island (marine? and aeolian), forming preferentially on the east and north highest-energy margins. Airborne lidar topo-bathy models of the Pleistocene of the Bahamian archipelago creates a unique opportunity to apply 3D process sedimentologic/geomorphic analysis to the ancient rock record, and greatly improves our understanding of this critical sea-level and climate archive. Quantification of sediment volumes deposited over the well-constrained interglacial episodes reveals a range of responses of the carbonate factory to climate extremes not previously appreciated.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP41C1567K
- Keywords:
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- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 1051 Sedimentary geochemistry;
- GEOCHEMISTRY;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL;
- 4912 Biogeochemical cycles;
- processes;
- and modeling;
- PALEOCEANOGRAPHY