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Reconnaissance geochemical analyses--total organic carbon (TOC) and Rock-Eval pyrolysis--were conducted on drill cuttings of pre-Punta Gorda rocks in seven widely scattered boreholes in south Florida to assess the petroleum source-rock potential. The rocks judged to have the best source-rock characteristics, by virtue of their relatively high TOC contents (0.4 to 3.2 wt. %) and relatively high pyrolytic hydrocarbon yields (0.4 to 16 mg/g rock), occur chiefly in the upper half of the Pumpkin Bay carbonates (upper Coahuilan) and to a lesser extent in the Alva, the topmost unit of the overlying Lehigh Acres carbonates (Trinity 'F' of Exxon). Geographically, the richest of these rocks are located in the vicinity of the Lehigh Park field and in the lower part of the Florida Ke s.
The rocks in the lower part of the Pumpkin Bay and in the underlying Bone Island (lower Coahuilan) and Wood River sequences (Jurassic?) have low TOC contents (< 0.3%) and low pyrolytic hydrocarbon yields (< 0.3 mg/g rock). These data suggest that the potential for oil is poor for rocks below the middle Pumpkin Bay. Potential for natural gas, however, cannot be ruled out even though the levels of organic matter seem insufficient. Gas shows have been reported in at least one well at 15,700 ft (4,785 m) in the Phillips-Mobil 1-C Seminole; hence, the pre-Punta Gorda rocks of south Florida may have some potential for gas, depending on factors such as porosity, permeability, and the distribution of traps.
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