Independent Sedimentological Studies on Fluvial and Lacustrine Sediments from the Gray Fossil Site Sinkhole, Northeastern TN

The Gray Fossil Site (northeastern TN) is a sinkhole formed within Cambro-Ordovician Knox Group carbonates. The sinkhole is filled with Mio-Pliocene fauna and flora as well as interlayers of coarse- (fluvial) and fine-grained (lacustrine) sediments. An independent study was conducted on each size fraction from a 39-m split spoon auger taken from the site in 2004.

Nine sand layers are concentrated at the base of the core, and were analyzed by standard grain size and textural techniques. Results indicate that the sands are quartz dominated and exhibit a clay coating of kaolinite and illite. The quartz grains are frosted, well rounded, and well sorted. The surfaces of chert grains (>0.5 mm fraction) exhibit rhombic voids, indicative of the dolomolds found in the upper Conococheague Formation (Cambrian) and throughout the lower Chepultepec Formation (Ordovician). Additionally, well-rounded, frosted grains are also found in these Formations, and indicate a local source <2 km to the southeast. The rounding and sorting of these grains occurred during Cambro-Ordovician deposition and therefore cannot be used as a proxy for transport distance to the Gray Fossil Site in the Tertiary.

Microlaminations are the predominant feature of the fine-scale fraction (0.5 mm to ~5 mm). To better understand their origin, compositional maps of several small, oriented sediment blocks were produced. Using EDAX Genesis software, several elements were mapped (e.g., Fe, Si, Ca) but the only observable pattern was an enrichment of iron and a coincident depletion in silicon. Despite the visible presence of laminations, no other compositional differences can yet explain their existence. We expect that a map of carbon distribution within these sediments will yield a correlation, and if present, would suggest that the laminations record a change in lake chemistry (e.g., oxidizing and/or reducing conditions that affect carbon preservation).