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The Transgressive Barrier-Lagoon Coast of Delaware: Morphostratigraphy, Sedimentary Sequences and Responses to Relative Rise in Sea Level

By
John C. Kraft
John C. Kraft
Department of Geology, University of Delaware, Newark, Delaware 19716
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Michael J. Chrzastowski
Michael J. Chrzastowski
Department of Geology, University of Delaware, Newark, Delaware 19716
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Daniel F. Belknap
Daniel F. Belknap
Department of Geological Sciences, University of Maine at Orono, Orono, Maine 04469
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Marguerite A. Toscano
Marguerite A. Toscano
Department of Geology, University of Delaware, Newark, Delaware 19716
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Charles H. Fletcher, III
Charles H. Fletcher, III
Department of Geology, University of Delaware, Newark, Delaware 19716
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Published:
January 01, 1987

Abstract:

Transgressive barriers of the embayed Atlantic and Gulf coast are generally similar in overall form, processes, and landward migration in response to relative sea-level rise, but they vary greatly in potential sources and volume of sand supply. Delaware's transgressive barriers vary in thickness from 25 m to less than 5 m; dunes may rise to 20 m above sea level, whereas barrier-spit and inlet sand reach depths of 10–18 m below sea level. Widths vary between 0 m at eroding headlands and 4–6 km near tidal delta and spit complexes.

A complete Holocene paralic sequence for Delaware includes a basal sand and/or gravel overlain by marsh, lagoon, and barrier lithosomes. Shoreface erosion, as the barrier lithosome moves landward, occurs to an average depth of 10 m, with about 50% of eroded sediment derived from Holocene and Pleistocene lagoonal mud outcrops. Since the suspended material is carried out of the shoreface, its removal requires a re-evaluation of the volumetric model commonly inferred from the Bruun mechanism. Also, the third dimension of longshore transport of coarse material needs to be considered.

As transgression continues, the ravinement surface exposes lagoonal sediments, marsh mud, irregularly shaped basal remnants of the Holocene barrier lithosome, or varied Pleistocene strata. These are then blanketed by varying thicknesses of inner-shelf sand. Ultimately, the transgressive barrier and associated paralic environments migrate landward to peak interglacial positions where the entire transgressive record may be preserved. A relatively complete vertical sequence of transgressive coastal lithosomes might also be preserved at the outer edge of the continental shelf at glacial sea-level minima. Thus, the optimal chance for total preservation of a transgressive coastal lithosome sequence lies at the extremes, landward at the peak interglacial when eustatic sea-level rise stops and the coastal lithosome sequences become stranded, and possibly on the outer edge of the shelf as deglaciation begins and there is rapid rate of sea-level rise.

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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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