A Cocorp Seismic Reflection Profile in Northeastern Kansas
T. Setzer, L. Brown, L. Serpa, H. Farmer, J. Oliver, S. Kaufman, 1983. "A Cocorp Seismic Reflection Profile in Northeastern Kansas", 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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Seismic reflection profiling in northeastern Kansas by COCORP was initiated to investigate several prominent features of the midcontinent, including the Midcontinent Geophysical Anomaly (MGA), which has been associated with a buried extension of the Keweenawan rift, and the Nemaha Uplift, part of a crystalline basement block uplifted in Pennsylvanian time (Figure 1). The MGA is characterized by gravity and aeromagnetic highs extending from the Lake Superior region to near the Kansas-Oklahoma border (Figure 1, 2, 3; see Yarger, 1981). Surface exposures in the north, as well as samples drilled along the trend of the anomalies, indicate that mafic volcanic rock and associated clastic sediments were deposited in a narrow trough formed by continental rifting of Keweenawan age (1.1 b.y. ago; see also King and Zietz, 1971; Chase and Gilmer, 1973).
The Nemaha Uplift is a north-south trending feature extending from Omaha, Nebraska to northern Oklahoma (Figure 1). in northeastern Kansas the Nemaha separates the Forest City basin from the Salina basin to the west (Steeples, in press). The origin of the Nemaha Uplift and associated Humboldt border fault (Figure 4) is enigmatic, but their lateral proximity and subparallelism to the MGA suggests that they may represent reactivated rift structures (Yarger, 1981).
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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.