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Seismic Facies of Shelfedge Deposits, U.S. Pacific Continental Margin

By
Michael E. Field
Michael E. Field
U.S. Geological Survey
Menlo Park, California 94025
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Paul R. Carlson
Paul R. Carlson
U.S. Geological Survey
Menlo Park, California 94025
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Robert K. Hall
Robert K. Hall
U.S. Geological Survey
Menlo Park, California 94025
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Published:
January 01, 1983

ABSTRACT

Pacific-style continental margins, such as that of western North America, are marked by large contrasts in the type of shelfedge sedimentary deposits and the processes that form them. The Pacific shelves of the United States are generally much narrower than the Atlantic shelves, and the source areas exhibit more relief. The greater relief of Pacific coast source terranes results in a relatively high rate of sedimentation in humid areas and fluctuating (areally and seasonally) sedimentation patterns and rates in semiarid areas. Sediment shed from the adjacent landmass is discharged, generally seasonally, onto the Pacific Continental Shelf at point sources. Many of the sediment sources of the northwestern United States and southern Alaska feed directly onto swell- and storm-dominated shelves. On such narrow unprotected shelves, sediment has a short residence time in submarine deltaic deposits before being remobilized and dispersed to outer-shelf and upper-slope environments.

Through study of high-resolution seismic-reflection profiles, we have identified four principal types of shelfedge deposits: (1) starved, (2) draped, (3) prograded, and (4) upbuilt and outbuilt. Each type of shelfedge deposit results from a characteristic balance between sedimentation rate and distributive energy (waves and currents) and is, therefore, characterized by distinctive seismic facies and bedding patterns. A special type, the cut-and-fill shelfedge, and a composite type consisting of two or more of the main depositional styles supplement the four principal types of shelfedge. Incorporated within each of these facies, especially on the upper slope, are chaotic deposits formed by slumps or slides, which are common along technically active margins.

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Contents

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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