Abstract

The Chilhowee Group is a thick clastic sequence of Early Cambrian (and possibly older) age exposed along the western border of the Blue Ridge province in the southern Appalachians. In central-eastern and southeastern Tennessee, the group is divided into the Cochran Formation, Nichols Shale, Nebo Sandstone, Murray Shale, Hesse Sandstone and Helenmode Formation from bottom to top. The Cochran is the thickest formation and is composed primarily of coarse, moderately sorted subarkose. It is overlain by silty and sandy shale (Nichols and Murray) and medium to fine-grained, well sorted sandstone containing little or no feldspar (Nebo and Hesse). The Helenmode is a thin calcareous unit of shale, siltstone and sandstone. Integration of petrologic and stratigraphic data suggests that the lower Chilhowee detritus accumulated in a basin subsiding rapidly and unevenly along strike. During this time, shallow water nearshore to transitional muddy and sandy environments of low physical energy predominated. In later Chilhowee time, tectonism moderated and the region became more stable. The basin then sank slowly and at an almost equal rate parallel to the shoreline. Shallow marine, higher energy environments in which beach, offshore bar and island, and intertidal sand bodies accumulated characterized this phase of sedimentation. The deposition of argillaceous and calcareous sediments at the end of Chilhowee time completed the cycle of tectonic transition from rapidly subsiding marginal basin to slowly sinking shelf. The primary source area for most of the Chilhowee elastics was an extensive granitic basement complex situated west of the basin. This crystalline landmass was originally of moderate relief and supplied coarse, feldspathic detritus. Intense weathering and low relief in the provenance area subsequently produced fine-grained, primarily quartzose sediments. Patches of metamorphic rocks lying on and folded into the basement complex shed minor amounts of detritus during early Chilhowee deposition. These were apparently stripped off as weathering and erosion lowered source area relief. Pre-existing sediments located also to the west within the craton composed the second major Chilhowee source terrane. The older sediments were the predominant clastic contributors during deposition of the Nebo and Hesse orthoquartzites.

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