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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 50 (2000), Pages 743-750

Evidence of Volcanic Activity During the Cretaceous in the Sunniland Formation of Southwestern Florida: A New Oil Exploration Play

Hugh J. Mitchell-Tapping


During an examination of cores from oil wells drilled in southwestern Florida, two layers of black glass, interpreted as obsidian, were observed in a core from a dry-hole well near the LeHigh Park Field. These glassy layers were observed in the core at 3,492.7 m (11,459 ft), driller depth, within the Lower Cretaceous Sunniland Formation. The upper black glassy layer cuts across the core with a slope of about 1.5 degrees and is about 7 cm thick at one side of the core thinning to about 4 cm at the other. The lower layer is much thinner. Between the two glassy black layers lies a light-gray carbonate mudstone containing many microfossils and two Caprinid shell fragments. There is an irregular contact boundary between the limestone and the obsidian. The obsidian has conchoidal fractures and varies from dark dense black to smokey-black in color: some flaws can be seen in the thicker smokey-black section. No prior reports of volcanic deposits in the subsurface sedimentary strata of the Florida Peninsula have been recorded in the literature, although igneous and metamorphic basement rocks have been reported in many wells. The Cretaceous "serpentine" igneous volcanic plugs of Texas are considered a profitable exploration target, having tested as much as 1,100 BOPD. Perhaps the same type of play could be applied to southern Florida in the future.

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