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Abstract: Unique Hydrocarbon Seep Deposits from Caves on the Cumberland Plateau Escarpment, Tennessee and Alabama

University of Akron, Akron, OH
Texaco Central Exploration Department, Bellaire, TX
Cave Research Foundation, Atlanta, GA

Tumbling Rock Cave, Alabama, and Zarathustra's Cave, Tennessee contain unique natural asphalt seeps and associated deposits. Both caves are on the Cumberland Plateau Escarpment, and are formed in the Mississippian aged Monteagle Limestone. Natural asphalt seeps in caves are extremely rare, with only 6 caves in the world having documented this occurrence. Zarathustra's Cave contains stained wallrock and minor floor accumulations. Similar deposits are found in Tumbling Rock Cave, along with a stalagmite composed of asphalt, the only one of its kind in the world.

In an effort to better understand these deposits, we collected small samples of broken material. We conducted elemental and HPLC analysis, 15C+ saturate hydrocarbon gas chromatography, mass spectroscopic analysis of saturated biomarkers, and carbon isotopic composition analysis. Marked differences were found. In Tumbling Rock the extractable bitumen composition was 62% hydrocarbons, vs. 12% for Zarathustra. Both samples exhibited biodegradation, with loss of alkanes. Biomarkers in the Tumbling Rock sample indicated severe biodegradation, but there is also evidence of active seepage. Degradation may be occurring both in the cave and in the carrier bed.

AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio