Skip to Main Content
Book Chapter

Development of a Modern Subaqueous Mud Delta on the Atchafalaya Shelf, Louisiana

By
Mead A. Allison
Mead A. Allison
1
Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118.
Search for other works by this author on:
Ciara F. Neill
Ciara F. Neill
1
Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118.
Search for other works by this author on:
Published:
January 01, 2003

Abstract

Sediment cores and high-resolution CHIRP seismic data were collected on the inner shelf adjacent to Atchafalaya Bay, Louisiana to examine the evolution of the newly forming mud delta associated with the Atchafalaya River lobe of the Mississippi deltaic plain. 210Pb accumulation rates from sediment cores show maximum sedimentation rates (10-20 cm/yr) are concentrated on the innermost shelf (<6 m water depth) immediately seaward of the Pt. Au Fer shell reef at the bay mouth. Rates decrease rapidly offshore to 8-10 m water depth, where seismic profiles show modern deposits pinch out adjacent to shoals formed by erosional remnants of older Holocene deltaic deposits. Alongshore, rates remain relatively high to the west (along the chenier coast of West Louisiana) following the trend of coastal currents. The wedge-shaped prodelta reaches 2.5 m in thickness and is gas-charged adjacent to the Atchafalaya dredge channel on the shelf. In areas where accumulation rates exceed ~1 cm/yr, the prodelta muds take the form of cm-scale interlaminations of silty sands (proximal) or silts (distal) and clayey silt layers. At accumulation rates of ~0.5-1 cm/yr, primary fabric is partially destroyed by macrofaunal burrows. In seaward areas, 10-25 m water depth, where modern sediments are accumulating but rates are low, clayey silt and silty clay deposits are completely homogenized by burrowing activity. Sediment dispersal paths can be traced seaward of the bay mouth and westward, along the direction of prevailing coastal currents, using coarse silt content of the mud delta. This indicates that coarse silts behave as individual particles and are preferentially sorted, while fine-medium silts are contained within flocs with clay-size mineral grains, and show no preferential sorting downdrift from the source.

You do not currently have access to this article.

Figures & Tables

Contents

SEPM Miscellaneous Publication

Siltstones, Mudstones and Shales: Depositional Processes and Characteristics

Erik D. Scott
Erik D. Scott
Shell International Exploration & Production, 200 North Dairy Ashford, Houston, Texas 77079
Search for other works by this author on:
Arnold H. Bouma
Arnold H. Bouma
Dept. of Geology & Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803
Search for other works by this author on:
William R. Bryant
William R. Bryant
Dept. of Oceanography, Texas A&M University, College Station, Texas 77843
Search for other works by this author on:
SEPM Society for Sedimentary Geology
Volume
1
ISBN electronic:
9781565760943
Publication date:
January 01, 2003

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal