R.T. Buffler, 1983. "Structure and Stratigraphy of the Sigsbee Salt Dome Area, Deep South-Central Gulf of Mexico", 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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The seismic line presented here ((WG-3E) is part of a long regional line (WG-3) that extends across the entire western Gulf of Mexico from the Mexican shelf on the west to the Campeche Escarpment on the east (Figure 1). The line was collected and processed in 1974-75 by the University of Texas Institute for Geophysics (UTIG). See Appendix I for further line information.
Line WG-3 has been used and discussed in several earlier publications. Part of the line was first presented by Ladd et al (1976), who used it in developing a preliminary seismic stratigraphic framework for the thick sedimentary section lying beneath the deep central Gulf of Mexico basin. The entire line was later published as American Association of Petroleum Geologists (AAPG) Seismic Section No. 1 (Watkins et al, 1976). Parts of the line were also included in several later publications (Watkins et al, 1978; Worzel and Burk, 1979).
The western part of the line is presented again here because it (1) shows many interesting and significant structural and stratigraphic features, (2) shows the thick sedimentary section that fills the deep central Gulf basin, (3) shows the six deep-Gulf seismic stratigraphic units defined by UTIG in their "type" area (Shaub et al, in press), and (4) summarizes the geologic history of the deep south-central Gulf of Mexico basin. Discussion of this geologic history can be conveniently subdivided into two major periods, the pre-middle Cretaceous and the post-middle Cretaceous. Rocks representing these two periods are separated by a prominent unconformity and/or reflector that can be followed and mapped throughout the deep Gulf basin and adjacent margins. It has been dated tentatively as middle Cretaceous in age (Buffler et al, 1980, 1981; Addy and Buffler, in press; Shaub et al, in press). Recent DSDP drilling (Leg 77) in the southeastern Gulf indicates that the unconformity in this region is a condensed section that spans the entire Late Cretaceous (Schlager et al, in press). This unconformity and/or reflector is informally designated "MCU" for middle Cretaceous unconformity.
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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.