J.G. Wiston, 1983. "Kodiak Shelf, Gulf of Alaska", 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 Kodiak Shelf basin is part of an extensive forearc region formed by the convergence of the Pacific and North American plates. This convergence and subsequent subduction of the Pacific plate began in earliest Mesozoic time with the development of a volcanic arc (Aleutian Peninsula) and associated nearshore trench along the entire extent of today's Aleutian Peninsula. During the Mesozoic and earliest Tertiary the trench received thousands of feet of melange, turbidites, and hemipelagic sediments. Uplift of the first forearc basin shelf-edge high (non-volcanic arc) probably occurred during late Eocene or earliest Oligocene forming today's Kenai Peninsula together with Kodiak and the surrounding islands.
After this regional uplift, the present-day Kodiak forearc basin began to form. Subsidence and subsequent deposition of a transgressing shallow-marine sequence of Oligocene-Miocene clastics probably occurred over much of the shelf. Deposition was interrupted by a second regional uplift at the end of the Miocene which removed much of the Oligo-Miocene sequence. This uplift also formed a shelf-edge high about 48 to 56 km (30 to 35 mi) seaward of Kodiak Island, especially in the southern part of the shelf where, in all likelihood, a small northeast to southwest trending island chain was formed. Deposition resumed in the Pliocene and, except for a few localized unconformities, has continued uninterrupted since than.The relation of the Kodiak Shelf basin to the tectonic setting of the Aleutian margin is illustrated in the generalized cross section. The seismic line, shot from northwest to southeast, is situated offshore southeast of Kodiak Island (see index map). The seismic line is displayed in three separate and overlapping segments, labeled (from northwest to southeast) KS 1, KS 2, and KS 3, respectively. The Kodiak Shelf basin shown here is elongate in a northeast to southwest direction and extends for over 483 km (300 mi) from just off Chirikof Island (southwest of Kodiak) to near Montague Island off the Kenai Peninsula.
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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.