The depositional environments represented by the uppermost part of the Crab Orchard Group and the facies relations of the enclosed ichnofauna have been based on study of the rock type and physical and biogenic sedimentary structures at five exposures in Fentress County, Tennessee. The sequence includes sandstone, shales, and coals deposited in deltaic and nearshore environments. Rocks of the (?)tidal facies consist of thin-bedded, fine-grained sandstones separated by very thin shale interbeds; individual beds are traceable over 100 m. Some sandstone beds are graded, and low amplitude interference ripples are present but not abundant. Trace fossils include Astericites, Planolites, ?Biformites, a small form of Skolithos, and abundant trails of the Palaeobullia type. Thinly edded laminated and cross-laminated sandstones deposited under higher energy conditions lack shale interbeds and have abundant oscillation and interference ripples. They have more silica cement and less fine-grained matrix. The ichnofauna consists of Skolithos, Palaeobullia, Gordia, ?Lennea and ?Kouphichnium as well as clearly defined horseshoe crab resting traces. Physical sedimentary structures originally present in lagoonal or interdistributary bay sands were destroyed by intense bioturbation; recognizable trace fossils are Conostichus, Planolites, Olivellites, and two types of Asterosoma.

The ichnofaunal distribution in these rocks is significant for two reasons. (1) It shows that the distribution of trace producers was controlled by factors readily interpretable from the rock record. (2) The occurrence of horseshoe crab impressions, Astericites, and other marine traces gives further evidence that this part of the Tennessee Pennsylvanian section was deposited under predominantly marine conditions.

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