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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Shelf Sands and Sandstones — Memoir 11, 1986
Pages 337-337
Symposium Abstracts: Sediment Source, Supply and Dispersal

Sedimentology of Sand Shoals on the Louisiana Continental Shelf: Abstract

J. R. Suter1, T. F. Moslow2, S. Penland3

Abstract

More than 1000 km of high-resolution seismic profiles correlated with seventeen 10 to 12 m vibracores provide the data base for analyzing the sedimento-logical characteristics of transgressive sand shoals on the Louisiana continental shelf. The development of these shoals is initiated by abandonment of older Holocene complexes of the Mississippi delta, followed by a subsidence-induced rise in sea level. Ship and Trinity Shoals are the largest of these shelf sand bodies and provide a possible modern analogue for some Cretaceous shelf sandstones of the Western Interior.

The Ship Shoal sand lies disconformably on the deltaic muds of the Maringouin complex, abandoned some 6150 years B.P. The shoal is asymmetric landward, 32 km long, and 2 to 4 km wide. Relief ranges from 2 to 6 m from east to west, with a corresponding decrease in water depth over the shoal crest from -6 to -3 m. Maximum sand body thickness is 7 m in the western region, pinching out seaward on the erosional inner shelf and terminated landward by a depositional surface. Internally, the shoal is characterized by very low-angle, landward-dipping clinoforms, while the underlying deltaic sequence contains low-angle, seaward dipping clinoforms. Numerous small channels occur below the shoal in the western area, although no large channels were seen on seismic profiles. Cores show a 3 to 7 m thick, coarsening upward sequence of fine grained sand and shell, overlying a dark, organic rich, silty clay with numerous wavy and lenticular interbeds of silt; burrowing is very rare.

Trinity Shoal is associated with the Teche complex, abandoned some 3500 years B.P. The shoal is a lunate, shore-parallel feature some 36 km long and 5 to 10 km wide. Relief ranges east-west from 2 to 3 m, with a corresponding decrease east-west in water depth over the shoal crest from -5 to -2 m. The Trinity Shoal sand body is 5 to 7 m thick, and is composed internally of a set of low-angle, westward dipping clinoform reflectors. Three levels of channeling that related to sea level changes in the Early Wisconsinan, Late Wisconsinan, and Holocene (Maringouin delta) underlie and occur seaward of Trinity Shoal. Continued sedimentation of the modern Atchafalaya Delta will soon encase Trinity Shoal in mud.


 

Acknowledgments and Associated Footnotes

1 Louisiana Geological Survey, Coastal Geology Program, University Station, Box G, Baton Rouge, Louisiana 70893, U.S.A.

2 Louisiana Geological Survey, Coastal Geology Program, University Station, Box G, Baton Rouge, Louisiana 70893, U.S.A.

3 Louisiana Geological Survey, Coastal Geology Program, University Station, Box G, Baton Rouge, Louisiana 70893, U.S.A.

Copyright © 2008 by the Canadian Society of Petroleum Geologists