Paleoenvironmental Analysis and Test of Stratigraphic Cyclicity in the Nolichucky Shale and Maynardville Limestone (Upper Cambrian) in Central East Tennessee

The Upper Cambrian Nolichucky Shale and Maynardville Limestone (upper Conasauga Group) crop out along a succession of southeastward dipping imbricate thrust sheets, which trend northeast-southwest in the Valley and Ridge of eastern Tennessee. In the vicinity of Oak Ridge and Knoxville, Nolichucky and Maynardville outcrop and drill core have been examined at six localities. The Nolichucky contains an abundance of thick shale and thinly bedded shale and limestone, whereas the Maynardville is composed of very thick-bedded carbonate, predominantly limestone. In central east Tennessee fourteen major lithofacies are identified in the upper Conasauga Group. The Nolichucky/Maynardville sequence is subdivided into three parts representing: (1) a slightly "deeper" intracratonic basin (30-50 m water depth; lower Nolichucky, (2) a shallow intracratonic basin (5-30 m deep; upper Nolichucky), and (3) a peritidal platform (0-5 m deep; Maynardville).

The Nolichucky Shale was deposited in a storm-dominated paleo­environmental setting, whereas the Maynardville Limestone is similar to other ancient tidally-influenced deposits. In the Nolichucky, the majority of carbonate production occurred in and around shoals and within cyanobacterial mats. Storms were effective in moving carbonate sediment off the shoals and mats into adjacent shale-dominated subtidal areas. The Maynardville represents small tidal flats that accreted vertically and migrated laterally. Sediment was produced in open-water subtidal areas, which were adjacent to tidal flats, and tides, storms, and fairweather waves transported sediment to nearby low-relief intertidal banks and supratidal islands. The distribution of facies along the Nolichucky/Maynardville bathymetric profile was much more irregular (mosaic-like) than predicted by the depositional model of earlier workers.

An integrated approach of overlying substitutability analysis, embedded Markov chain analysis, and modified autoassociation analysis to verify statistically the occurrence of cycles in stratigraphic sequences is applied to the upper Conasauga Group of central east Tennessee. Stratigraphic sections within the Nolichucky Shale and in the Maynardville Limestone show weakly developed cyclicity, which is probably a result of the storm- and tide-dominated paleoenvironmental setting. Local processes were more important in controlling lithologic repetition than were larger-scale processes (e.g., geoidal, tectonic, or glacioeustatic). Large-scale processes have been documented in modern and other ancient settings, but their record may be masked in many sequences by local events.