--> ABSTRACT: Cross-Bedded Limestone Facies on San Salvador Island, Bahamas: New Perspective on Eolian Calcarenites, by Mario V. Caputo; #91023 (1989)

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Cross-Bedded Limestone Facies on San Salvador Island, Bahamas: New Perspective on Eolian Calcarenites

Mario V. Caputo

Limestones of eolian origin have been known from worldwide tropical regions since the early 1900s. On San Salvador Island, most of the exposed bed rock is Holocene and Pleistocene eolian calcarenite made of skeletal, peloidal, and oolitic fine to medium sand. The Pleistocene Grotto Beach Formation is composed of 50-90% ooids. An eolian interpretation for this interval is supported by paleosols, subaerial crusts, vadose cement, terrestrial fossils, karst features, associated reef and beach deposits, grainfall, sandflow, and climbing ripple strata, and shore-parallel sand bodies. Whole dune-forms are locally preserved; they were stabilized or "frozen" in place by early cementation and/or vegetation.

Eolian strata in the Grotto Beach Formation display consistent weathering patterns in outcrop. The patterns reflect the degree of cementation controlled by grain textures imparted by eolian grain fall, sand flow, and ripple migration. Fine sand is concentrated in grain fall and basal wind ripple and sand-flow strata. These strata usually exhibit moderately tight packing and small pores. Such a packing-pore relationship has favored high fluid capillarity and surface tension and therefore the complete retention of interstitial fluid. Consequently, the laminations are tightly cemented and show aspects of phreatic cementation all within a vadose diagenetic environment. They crop out as positive-relief micro-ledges in weathered exposures. The upper parts of wind-ripple and sand-flow strata are characterized by loosely packed medium sand and large pores. Decreased surface tension and capillarity related to the pore-packing characteristics have favored the growth of meniscus and pendant cements typical of vadose diagenesis. Consequently, the poorly cemented strata crop out as negative-relief microrecesses. The correlation between weathered strata, cementation patterns, grain textures, and eolian processes may (1) aid in the recognition of other eolian limestones, (2) provide a foundation for comparing similar patterns among subaqueous cross-bedded limestone facies, and (3) foster an understanding of sedimentologic variations within calcareous reservoir facies of eolian origin.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.