F.L. Sachnik, R.D. More, 1983. "Southern Appalachian Folding and Faulting", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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In the southeastern United States, the Appalachian mountain structural system has been peneplaned and subsequently buried by Mesozoic and Cenozoic Coastal Plain sediments of the Gulf of Mexico marginal basin. A seismic line from the updip Gulf Coastal Plain shows the position and structural style of the frontal edge of the buried Appalachian orogeny on its southwestern extension from the surface exposure in central Alabama.
The seismic line is near the Mississippi-Alabama state line approximately 100 mi (161 km) southwest of Birmingham, Alabama, and 40 mi (64 km) north of Meridian, Mississippi (Figure 1). In this area gently dipping Lower Cretaceous sandstones rest unconformably on the truncated structured Paleozoic sediments in this area, and no test has penetrated the entire stratigraphic sequence. However, regional studies and seismic projections give a reasonably close estimate of the Paleozoic rock sequence for the area.
The major-units of the Paleozoics are the continuation of those exposed in mountain outcrops to the northeast. The youngest of these is the Lower Pennsylvanian Pottsville sandstones and shales, which subcrop the unconformity in synclinal or offstructure positions. The Lower Pennsylvanian is underlain by approximately 1,500 to 2,000 ft (457 to 610 m) of Mississippian sediments. These grade from marine shales in the upper part to shales, thin sands, and limestones in the basal units.
The Mississippian is underlain by approximately 1,000 ft (305 m) of Devonian cherts and cherty limestones. These in turn overlie a Silurian section that, like the Devonian, consists of approximately 300 ft (91 m) of cherts and/or cherty limestones. The Silurian overlies the upper Ordovician, which is a limestone averaging about 800 ft (244 m) in thickness.
The Cambro-Ordovician Knox group unconformity underlies the Upper Ordovician and consists of approximately 5,000 ft (1,524 m) of dolomites. These overlie the Middle Cambrian Conasauga formation which is approximately 2,000 ft (609 m) thick. The Conasauga is composed of limestones in the upper part and grades into shales at its base.
The Conasauga overlies a Lower Cambrian section consisting of quartzites and shales of varying thicknesses and in turn rests on Pre-Cambrian basement.