FLYNN CREEK CRATER: THE BIRTHPLACE OF IMPACT SPELEOLOGY

Subsurface environments have been postulated as a potential environmental niche for extant life on Mars, a planet with surface conditions hostile to known biologic activity. Carbonate has been detected in approximately ~3% of the martian surface and carbon-cycle models predict substantially higher amounts. Vast, dust-covered regions of Mars, immune from spectral analysis by orbiting thermal infrared spectrometers, may contain significant amounts of buried carbonates. If so, caves may have formed by dissolution along preferred zones of weakness, such as bedding planes, fractures, and faults within these units, such as they do on Earth.

We have discovered that impact cratering, one of the dominant surface-modifying forces on Mars and elsewhere in the solar system, can also exert control over cave passage development and the location of subsurface microclimates. Such is the case at the Flynn Creek crater, a 3.8 km diameter complex crater that formed in Ordovician-aged rocks of what is now Jackson County, Tennessee. Flynn Creek target rocks (to within 1500' of the crater rim) contain 5.5x the concentration (1 cave/2.38 km²) of known solutional caves found elsewhere in the county (1 cave/13.14km²). Nine of the caves are concentrated along the crater rim, while one formed in the central uplift.

With lowering of regional base level, cave development first occurred at Flynn Creek at the highest elevations of limestone/dolostone exposure in target rocks, namely along the crater rim. Similar to other non-impact related caves, many at Flynn Creek developed preferentially according to the strike and dip of the crater rim. However, others formed along extensional fractures in the fold axes of anticlines and along major faults where compression of the crater rim and wall collapse, respectively, occurred.

The control of cave development by impact-related geomorphology and structural geology features have resulted in subterranean environmental niches along the crater rim and central uplift. The caves here are home to diverse fauna and somewhat buffered ecosystems common to caves elsewhere in the region. Thus, the constraining of karstification in impact craters may serve as a predictive tool for locating subterranean environments on Mars.