Sedimentation and Stratigraphy of the Rome Formation in East Tennessee

The late Early Cambrian Rome Formation is the oldest formation that is exposed widely across the Valley and Ridge Province. It is brought to the surface by major thrust faults, and in many cases is topographically the highest exposed formation; consequently, the bottom and the top of the Rome are usually missing. Nowhere is a complete section of the Rome formation exposed except in northeast Tennessee.

The Rome is a heterogeneous formation of red, maroon, brown and green colored sandstone, siltstone and shale and local beds of gray limestone and dolomite, all of which vary greatly in proportion and distribution throughout the formation. Sandstone and siltstone predominate in the northwestern belts of the Appalachian Valley with lesser amounts of shale and carbonates, while to the southeast shales predominate and carbonates make up approximately half of the formation, thus indicating a western source for the Rome sediments. This is confirmed by elastic ratios, and paleocurrent measurements of cross-bedding and ripple marks in the study area.

A striking feature of the Rome Formation is the abundance of primary sedimentary and organic structures. Sedimentary structures which point to a tidal flat type of environment are: mud cracks, halite crystal casts, ripple marks, rain prints, tidal balls, current lamination, ripple lamination, flaser and lenticular bedding. Biogenic sedimentary structures are found throughout the formation of which the most important environmental indicators are Scoyenia (supratidal), Skolithos (beach) and Cruziana (Supratidal to subtidal). Cruziana in the Rome Formation does not fit Seilacher's ichnofacies model in which Cruziana is confined to the subtidal zone.

Evidence from the Rome sediments indicates that they were deposited in the following environments: supratidal, mud flat, mixed flat, sand flat, tidal flat gullies, lagoon and oolite shoals. The general coarsening upward in the Rome indicates a general transgressive sequence. The transgressive and regressive phases within the Rome sections can be correlated across strike.

Previous studies of the Rome have indicated that the formation is difficult to correlate due to the scarcity of fossils and absence of marker beds. The present study indicates that there are marker beds at the top of the formation and that the Rome can be correlated easily for a distance of 40 km along Pine Ridge and for lesser distances along other ridges. Across strike the formation can be correlated with difficulty over a palinspastic distance of 105 km by utilizing the oolite and Skolithos zones as markers.

The Pumpkin Valley Shale which is Middle Cambrian in age is a facies equivalent of the upper Rome, while the top of the Shady Dolomite is a facies equivalent of the lower part of the Rome. Thus the Rome is of late Early Cambrian age in the Appalachian Valley and probably Middle Cambrian in the subsurface in central Tennessee where it lies non-conformably over the Precambrian basement. The sea advanced over the craton in the present position of the Appalachian Valley during Rome time. The craton had been previously peneplained and deeply weathered in a tropical to subtropical climate. The weathered products were transported and deposited in the Rome sea and tidal flats.

(The dissertation is a large file: 38 MB. Plates 1-6 are uploaded as an Additional File.)