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Book Chapter

Recognition of the Shelf-Slope Break Along Ancient, Tectonically Active Continental Margins

By
Raymond V. Ingersoll
Raymond V. Ingersoll
1
Present address: Department of Earth and Space Sciences, University of California, Los Angeles, California 90024.
Department of Geology, University of New Mexico
Albuquerque, New Mexico 87131
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Stephan A. Graham
Stephan A. Graham
School of Earth Sciences, Stanford University
Stanford, California 94305
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Published:
January 01, 1983

ABSTRACT

Tectonically active continental margins include transform, protoceanic and convergent settings. In transform settings, numerous small basins develop on oceanic, transitional and continental crust. Protoceanic gulfs may be formed by orthogonal or oblique rifting; both types are characterized by segmented crust with consequent juxtaposition of deep basins and active uplifts. Convergent margins include the following types of basins: intramassif basins, major forearc basins and accretionary basins (trench-slope basins). Extensional backarc margins have structural styles and histories similar to protoceanic gulfs.

Shelf-slope breaks in these settings tend to be transient in time and space because of rapid vertical movements; abrupt facies changes are the result. Two types of shelf-slope breaks are common: elastic-starved and progradational. The former type is characterized by unconformities or biostratigraphically compressed intervals separating shallow-marine/nonmarine from slope/basinal deposits. Commonly, glauconitic and phosphatic lithologies mark the clastic-starved shelf-slope break. Progradational shelf-slope breaks are characterized by deltaic outbuilding, which results in coarse shallow-marine, shoreline and fluvial deposits prograding over slope mudrocks. Clastic-starved shelf-slope breaks tend to predominate in transformal and protoceanic settings due to the segmented nature of crust and the structural control on shelfedges. Most detritus bypasses outer-shelf and upper-slope environments. Deltaic progradation is the dominant process in forearc basins, with abundant detritus supplied by neighboring magmatic arcs. During the latest stages of filling of forearc basins, shelf-slope breaks may correspond with the structural boundary between forearc basins and subduction complexes. Shelf-slope break deposits involved in continental collision in general are destined to be destroyed during continental suturing.

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SEPM Special Publication

The Shelfbreak: Critical Interface on Continental Margins

Daniel Jean Stanley
Daniel Jean Stanley
Division of Sedimentology Smithsonian Institution
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George T. Moore
George T. Moore
Chevron Oil Field Research Company La Habra California
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SEPM Society for Sedimentary Geology
Volume
33
ISBN electronic:
9781565761636
Publication date:
January 01, 1983

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