Cocorp Deep Seismic Profiles Across the Wind River Mountains, Wyoming
R.W. Allmendinger, L.D. Brown, J.E. Oliver, S. Kaufman, 1983. "Cocorp Deep Seismic Profiles Across the Wind River Mountains, Wyoming", 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 origin of basement uplifts in the Laramide province has long been a major controversy in the tectonics of the western United States. Surface geology on a regional scale (Figure 1) has emphasized the diversity of fault trends and orientations of uplifts, resulting in interpretations favoring dominantly vertical uplift (Prucha et al, 1965; Stearns, 1971). Others working with the same data base have concluded that horizontal compression was more important (Berg, 1962; Blackstone, 1963; Sales, 1968). Because the Laramide deformation occurred 1,000 to 1,500 km (621 to 932 mi) from the coeval plate margin along the western margin of North America, resolution of this controversy has important implications for the dynamics of plate interactions and the deformation of continental crust.
The Wind River Mountains are the largest Laramide uplift in Wyoming. The structure is a northwest trending, asymmetric feature, approximately 220 km (137 mi) long and 70 km (43 mi) wide. On the northeast side, Paleozoic shelf sediments, resting unconformably on Archean crystalline basement, dip gently to the northeast into the Wind River basin. The southwest side of the uplift is a northeast-dipping reverse fault, as shown by surface mapping, industry and government boreholes, and industry seismic reflection data (Berg, 1962; Royse et al, 1975). The minimum vertical structural relief between the Precambrian in the high peaks of the Wind River Mountains and the bottom of the Green River basin to the southwest is about 13 km (8 mi).
The Archean rocks consist of migmatites from deeper crustal levels now exposed in the core of the uplift north of the COCORP profiles, and at the south end in the vicinity of the seismic lines, granitic intrusions into gneisses and schists that represent shallower levels of the crust. These supracrustal rocks, which include iron formation, metaandesite, and metagraywacke, are steeply dipping and strongly folded. Condie (1972) suggested that an Archean greenstone belt and suture zone is located in the region beneath the COCORP profiles.
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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.