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The slowly subsiding, low-dip, South Florida basin centered on Florida Bay was an area of carbonate and evaporite deposition. Several structural features mapped in the basin during the study include the Charlotte high (Charlotte County), the Martin high on the northeast, the Largo high in the southeast, and the Pine Key arch in the south. The Broward trough and the center of the basin are the only persistent negative features. Neither the Lee-Collier swell, a very low and ephemeral feature extending offshore from the southwest part of the peninsula, nor the Forty Mile Bend high in the lower part of the peninsula, are persistent.
The common types of limestone, dolomite, and anhydrite textures occur in a series of cycles within the so-far nonproductive Dollar Bay Formation. A cycle typically culminates in porous calcarenite between anhydrite end members. Environments from shallow shelf to euxinic are present. Light carbonates usually occur over highs and dark carbonates in the structurally low areas.
The Dollar Bay Formation is 450 ft thick and consists of 4 units. All contacts above, below, and within the formation are conformable. The formation contains many zones of porosity; numerous oil shows have been reported.
Unit D at the base of the Dollar Bay consists of a single cycle about 55 ft thick. The favorable facies usually is a dark-brown, finely crystalline dolomite with intercrystalline porosity. Five poor shows of oil have been recorded in this unit.
The overlying unit C is a single sedimentary cycle averaging 325 ft thick, consisting characteristically of chalky dolomite and limestone. Interspersed are beds of fine-grained calcarenite with effective porosity. Fifteen oil shows have been reported from this unit, one of which consisted of a recovery of 15 ft of oil on a drill-stem test. In Hendry County, unit C thins and becomes a dark, petroliferous micrite, undoubtedly the source for the oil shows within this unit.
Units B and A consist of multiple thin cycles. They have few favorable characteristics and shows of oil are scarce. The Dollar Bay Formation, particularly unit C, has the best potential for oil production of any nonproductive section in the South Florida basin. Although structure will control local oil accumulation, stratigraphy will determine the favorable areas in which to search. Unfortunately, the Dollar Bay favorable areas do not coincide with the Sunniland Limestone favorable trend.
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