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Book Chapter

Sequence-Bounding Unconformities

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Published:
January 01, 1987

Abstract:

The stratigraphic record of Quaternary transgressions due to glacio-eustatic rise varies as a function of sediment supply from rivers to the paralic realm. Extremes from low to high sediment supply are represented by the Atlantic and Gulf coasts of the United States, respectively.

The vertical sequence produced by these transgressions at the low sediment supply end of the spectrum consists of paralic and fluvial lithosomes erosionally truncated by shoreface retreat and overlain by shelf marine lithosomes. The lithosomes produced in the landward portion of the paralic realm are commonly preserved, whereas the lithosomes from the more shoreward part are less likely to be preserved. Thus, beach facies are rarely incorporated into the transgressive stratigraphic record, except as a peak sea-level deposit preserved by abandonment. Erosional truncation of the paralic section produces a unique stratigraphic surface, the ravinement surface, which exhibits many of the physical characteristics of a major break in deposition. The surface is then overlain by nearshore to offshore shelf facies in a deepening-upward succession.

When encountered in the stratigraphic record, the ravinement surface is likely to be interpreted as a depositional sequence boundary. When this occurs, a continuous cycle of deposition during transgression is not recognized. When a ravinement and its associated facies are properly interpreted, a complete cycle of transgression and regression in response to changing sea level can be recognized.

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SEPM Special Publication

Sea-Level Fluctuation and Coastal Evolution

Dag Nummedal
Dag Nummedal
Department of Geology and Geophysics Louisiana State University, Baton Rouge, Louisiana
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Orrin H. Pilkey
Orrin H. Pilkey
Department of Geology Duke University, Durham, North Carolina
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James D. Howard
James D. Howard
Skidaway Institute of Oceanography Savannah, Georgia
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SEPM Society for Sedimentary Geology
Volume
41
ISBN electronic:
9781565760950
Publication date:
January 01, 1987

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