Paper No. 12
Presentation Time: 5:10 PM
PRELIMINARY ASSESSMENT OF ECHINODERM-TRILOBITE SHELL BEDS IN THE NOLICHUCKY FORMATION (CAMBRIAN) OF EASTERN TENNESSEE
Recent drought conditions in the southeast has exposed a near vertical interbedded sequence of thinly laminated to thinly bedded shale containing laterally continuous thin packstone beds belonging to the Nolichucky Formation (Upper Cambrian; Saltville thrust sheet) that now crop out along extreme low-water shores of Cherokee Lake in Grainger County, Tennessee. Regionally, the Nolichucky is interpreted as a series of cyclic shallow shelf shale to peritidal carbonate environments of a sloping carbonate ramp system and with intrashelf basin lithofacies developed distally. The Cherokee Lake sequence consists of over 20m of predominantly sparsely fossiliferous shale and thin (1-3cm thick) packstone interbeds and stringers. Some layers are better characterized as intrapackstones as they contain 1-5cm, irregular to regular shaped, rounded intraclasts of unfossiliferous micrite intraclasts. Packstone beds are dominated by highly fragmented angular to slightly slightly rounded echinoderm plates and plate fragments, along with less abundant large (up to 2cm) trilobite cephala, genal spines, and thorax fragments. The echinoderm and trilobites fragments often as occur dense enough accumulations, without interparticulate sediment, to form a coquina-like lense that grades vertically to typical packstones within the same 1-3cm layer. The highly fragmented nature of the echinoderms has thus far precluded taxonomic identification. Echinoderm plate fragments occur in nested clusters showing imbrications and evidence of swirling pattern that orient fragments into nested clusters. The degree of fragmentation of echinoderm plates, highly sorted nature of the echinoderm plates, imbrications, and rounded nature of intraclasts suggests accumulation due to high energy regimes, most likely sporadic storms, within an otherwise below fair-weather wave base protected setting, as indicated by the intervening shales. Tentatively we interpret this exposure to be part of an intrashelf basin region shedding storm generated echinoderm and trilobite debris into deeper shale rich waters of the ramp system.