10-11 A Comparative Analysis of Diagenetic Processes and Allochem Composition in the Holocene Hanna Bay and North Point Limestones, San Salvador and Little Exuma, The Bahamas: Implications for Sea-level Rise’s Impact on Island Geomorphic History

Session: Undergraduate and Graduate Geoscience Student Showcase (Posters)

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The Bahamian Islands are key locations for studying carbonate systems that respond to eustatic sea-level changes. Aeolian limestones can develop during both regression (lower sea level) and transgression (higher sea level). This study compares the Hanna Bay (transgressive) and North Point (regressive) Members of the Rice Bay Formation on San Salvador and Little Exuma islands to examine how carbonate materials respond to changing rates of sea-level rise (SLR). The North Point Member is of middle Holocene age, deposited when sea level was lower and larger areas of the Bahama Banks were subaerially exposed. Hanna Bay Member sediments are late Holocene; were deposited when sea level was positioned close to modern levels, when the rate of SLR was slow, permitting the regressive progradation of Bahamian islands, and the banks were subtidally flooded. The purpose of this study was to investigate the allochem compositions and diagenetic characteristics of aeolianites from both Members to determine if diagnostic differences could be discerned.  Fieldwork, stratigraphic context, petrographic analyses, and a review of published research were utilized. Eight thin sections from aeolian facies were evaluated, including five from Hanna Bay and three from North Point, collected at Moriah Harbor Cay and Salt Beacon Cliffs (Little Exuma) and the North Point locality (San Salvador). Allochems and diagenetic features were point counted (300 points per section), noting allochem type, cement type (vadose/phreatic; marine/freshwater), and degree of micritization. Porosity was defined as any void space located at a counting point and quantified using point counting. Hanna Bay contains blocky isopachous cement with little to no contact meniscus, higher porosity (~68% vs ~48%), a higher incidence of ooids (2.4% vs. 1.6%), grains with micritic envelopes (~41% vs. ~21%), and more peloids (~84% vs ~77%) than North Point. North Point contains blocky to isopachous cements with contact meniscus. The higher occurrence of ooids, peloids, and micritic envelopes in Hanna Bay is consistent with the existence of a larger subtidal platform area where the allochems are generated and with a longer residence time for micritization during the late Holocene highstand. The results were consistent across outcrops on two islands and paint a clearer picture of how sea-level fluctuations influenced the composition and alteration of carbonate materials at each site.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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