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.
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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
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.