Freshwater cementation of Holocene sands in the Bahamas provides a modern analog to enhance our understanding of some cements in Jurassic grainstones of southern Arkansas. The Joulters Cays, three late Holocene islands on Great Bahama Bank, formed when ooid sands were subaerially exposed and lithified by freshwater cements. Cement fabric above the standing water table (vadose zone) and below (phreatic zone) is strikingly different. Vadose cements, characterized by

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patchily distributed spar most common at grain-contacts, change abruptly across the water table to phreatic cements, displaying a uniform rim of rhombohedrons surrounding each grain. Vadose cements preserve primary porosity and increase variation in permeability more than phreatic cements.

The updip Smackover grainstone reservoirs in southern Arkansas are characterized by (1) early cements that predate hydrocarbon emplacement and that resemble the Joulter Cays freshwater cements, (2) preserved primary intergranular porosity, and (3) leached moldic porosity. Vadose imprint is characterized by poorly developed cement rims around grains, a grain-contact meniscus fabric producing rounded pores, and a patchy distribution of block spar with crystals that increase in size away from the grains. The meniscus fabric is only partly preserved where grain interpenetration has occurred during burial. Phreatic cements occur as moderately to well-developed non-isopachous rims around most or all of the grain margins. They line pores forming jagged boundaries, and are patchy to extensive y developed showing an increase in crystal size away from the grain. The cement rims are commonly broken and separated from the grains during compaction. Compaction features and late cements are not distributed uniformly in the grainstones, owing perhaps to heterogeneous porosity and permeability patterns established by early cements.

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