Frontal Thrust Structure, South-Central Colorado
Published:January 01, 1983
R.G. Ouillette, D.A. Boucher, 1983. "Frontal Thrust Structure, South-Central Colorado", 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 Frontal Thrust Structure seismic line is a northeast to southwest traverse located in the south-central part of Colorado on the eastern flank of the Sangre de Cristo Mountains. The upthrusting of the basement fault block which formed the Sangre de Cristo Mountains displaced the overlying sediments toward the east into the Raton basin syncline. The combination of the block faulting and gravity sliding resulted in a series of east-northeast trending thrusts which affected the Tertiary through Pennsylvanian rocks. Based on the relative thickness of the intervals between the identifiable seismic events on the section, the major detachment zone for these thrusts appears to be between the Pennsylvanian red beds and the Paleozoic carbonate (?) complex. No wells have penetrated beyond the red beds to verify the lithology of the seismic event or the actual detachment zone. Thrusting is evident, however, in several wells drilled in the area. Expanded or repeated beds occur in association with numerous thrusts and are encountered anywhere in the section from Upper Cretaceous to Permo-Pennsylvanian sediments. Overturned strata are occasionally encountered in the thrusted block. In addition, normal faulting is evident behind the main thrust fault zone due to tensional forces exerted on the trailing portion of the thrust block. This resulted in the ramping of the overthrusted plate and the rollover of the overlying materials of the long north to south trending folds.
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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.