Gray Fossil Site
Origin of the site
As mentioned in the introduction, the origin is problematic. One of the difficulties is how (or whether) the site could have been both a death trap and a habitat for aquatic animals, particularly large ones. The clays are layered, and not bioturbated as would be the case if animals were mired in a sticky material. Many bones are articulated and none have been gnawed or scattered by scavengers.
The diagrams below were prepared as part of a poster presentation at the 2005 Tennessee CritterFest at the Nashville Bicentenial Mall. The original version showed a partially empty Stage 2, with a substantial free-fall into the water. A large empty space, a cavern above a lower water level would explain the presence of cave onyx, blocks of which were found in the clays. However, in that case a visible pool of water might not have been present, a likely attractant to animals during dry seasons. It is also possible the water level would rise and fall with the seasons. Not shown is the source of sediment and debris-laden surface waters. These may have cascaded directly into the hole, or entered via a sink some distance away.
A high-resolution gravity study conducted by George Whitlaw (see Links) indicates the structure may be more complex than shown here, and suggests several partly merged bodies of sediment are present.
|Stage 1. Openings form underground, perhaps a joint-controlled cavity in the phreatic zone. It fills with a slow influx of sediment, derived from a nearby sinking creek.||Stage 2. After surface erosion, roof collapse activates the trap. Slanted layers of dots indicate in-place residuum, the typical reddish clays of the region derived from weathering of cherty bedrock.|
|Stage 3. After further erosion and infilling, with buff-colored transported gravels, the buried trap is preserved. Stage 2.5 (not shown) is the downward-warping of clay layers as they compact under their own weight before deposition of the top layers of gravel.||Stage 4. Prior to its discovery, the deposit forms the core of a small knoll.|
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