MITCHELL-TAPPING, HUGH J. , Estero Bay Marine Laboratory Inc. P.O. Box 08275, Fort Myers, FL 33908

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. In between the 2 glassy black layers lies a light-gray carbonate mudstone containing many microfossils and 2 Caprinid shell fragments. There is an irregular contact boundary between the limestone and the obsidian. The obsidian has conchoidal fractures and the glass varies from dark dense black to smokey-black in color, and some flaws can be seen in the thicker smokey-black section.

No prior reports of volcanic deposits in the subsurface strata of the Florida Peninsular have been recorded in the literature, although igneous and metamorphic basement rocks have been reported in many wells.

The Cretaceous serpentine palagonite 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.

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas