J. M. Reed, 1983. "Lower Cretaceous Shelf Edge, Offshore Louisiana, Main Pass Area, Line “B”", 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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Line B was recorded offshore Mississippi/Louisiana to define the position of the Lower Cretaceous shelf edge. The shelf edge arcs across the southern part of the North American plate from offshore West Florida, through the southern states and into Mexico. At its eastern position the shelf edge is coincident with the West Florida escarpment where two cores from the exposed carbonate bank complex were recovered by the Oceanographic Department of Texas A & M University and indicated to be Lower Cretaceous (Albian) in age.
Although increasingly buried by the younger section of the Gulf Coast geosyncline, the seismic signature of the Lower Cretaceous shelf edge is well defined from offshore Florida to the offshore Louisiana Main Pass area. This definition deteriorates to the west becoming nonexistent or of reduced dimensions in some parts of western Louisiana.
Exploratory tests in the vicinity of this seismic section have drilled into the shelf edge feature, revealing it to be the same age (Lower Cretaceous-Albian) as indicated by the offshore Florida cores. This extensive shelf edge or shelf bank complex remains an elusive petroleum target.
The trend effectively defines the separation between Interior and Gulf Coast salt basins and provides the focal position for extensive seaward thickening of the younger section. Classical fault patterns with expanded downthrown section are displayed. The "rollover" anomaly displayed on the fault just forward of the shelf edge is not productive here, but is typical of many producing structures in both younger and older sections. in South Louisiana and to the west of this line of section, the now-famous Tuscaloosa gas-trend of lower Upper Cretaceous age is positioned just seaward of this carbonate bank. Production is derived from an expanded sand section and rollover fault structures.
This section provides a view of a major structural and stratigraphic element of Gulf Coast geology along which significant petroleum reserves remain to be found.
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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.