R.T. Buffler, 1983. "Structure of the Sigsbee Scarp, 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
Download citation file:
The lower Texas-Louisiana continental slope between Alaminos Canyon and De Soto Canyon is a unique geomorphic and geologic province (Figure 1). Between 1975 and 1977 the University of Texas collected regional multifold seismic data across the region (Figure 1). Examples of these data are included here to show some of the geomorphic and geologic features of the area (Figures 2 through 5). The figures are duplicates of most of the figures from an earlier paper presented at the 1978 Offshore Technology Conference (Buffler et al, 1978). The reader is referred to this paper for a more detailed discussion of (1) previous studies in the area, (2) the seismic data, and (3) preliminary conclusions. The lines are repeated here because this is such a unique province containing some very interesting structural and stratigraphic features.
The lower continental slope can be divided into two major provinces, the Sigsbee Bulge area and the Central Slope/Mississippi Fan area (Figure 1). The Sigsbee Bulge area is where the lower slope bulges seaward into the deep central Gulf. It forms a broad terrace-like feature about 50 to 75 km (164 to 246 ft) wide (Figure 2). Its southern boundary is marked by a prominent change in slope and geology known as the Sigsbee Scarp (Figures 1, 2). The Bulge area is characterized by a shallow, irregular high-amplitude reflector overlain by a relatively thin sedimentary section (Figure 2). The reflector is generally interpreted to be the top of mobilized salt. The geometry and extent of the mobilized mass beneath the lower slope is not clear on these seismic data (Figure 2). The leading edge of the mobilized zone forms the Sigsbee Scarp, which is characterized by material thrust up to 10 to 15 km (6.2 to 9.3 mi) seaward over flat-lying rise sediments (tongues, Figure 3).
Figures & Tables
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.