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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 39 (1989), Pages 571-576

Distribution and Textural Character of Surficial Sediments, Isles Dernieres to Ship Shoal Region, Louisiana

S. Jeffress Williams (1), Shea Penland (2), Ronald C. Circe (1)

ABSTRACT

Since 1986, the U. S. Geological Survey and the Louisiana Geological Survey have undertaken field studies of the physical processes responsible for the widespread and extremely rapid coastal erosion of Louisiana's barriers along the Mississippi River delta plain coast. The study area encompasses the coastal and inner shelf region from Raccoon Point to Sandy Point and includes a data base of 40 ft (12 m) long vibracores, surface grab samples, sidescan sonar, high-resolution seismic reflection profiles, and precision hydrographic profiles.

This paper presents results from detailed grab sample surveys in the coastal-shelf sector that includes the Isles Dernieres barrier island chain seaward almost 19 mi (30 km), to include Ship Shoal. The surface and near surface sediments of the region reflect fluvial, deltaic and nearshore marine origins with evidence of winnowing and reworking by waves and currents associated with frequent tropical storms and winter cold fronts.

Beach sediments on the four islands are remarkably uniform in grain size (fine quartz sand), except for often abundant beach rock and carbonate shell debris, and are generally moderately to very well-sorted. The shoreface and inner shelf are mantled with muddy sands and sandy muds, whereas Ship Shoal is almost wholly fine quartz sand, similar in many sedimentologic respects to the Isles Dernieres. These findings are consistent with the model of coastal evolution presented by Penland et al (1988) in which Ship Shoal was described as the prototypical example of a drowned coastal barrier undergoing submarine reworking and migrating landward in pace with the rapid rates of eustatic sea-level rise and basin subsidence.


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