About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 52 (2002), Pages 1031-1040

Accumulation Rates and Stratigraphic Character of the Modern Atchafalaya River Prodelta, Louisiana

Allison, Mead A., Neill, Ciara F.

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 prodelta 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 Point 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. Seismic data and older bathymetric surveys suggest the locus of maximum accumulation on the prodelta is shifting seaward (sediment bypassing). In areas where accumulation rates exceed sim.gif (57 bytes)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 sim.gif (57 bytes)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. Relict deposits of variable sand-silt-clay granulometry are present on the Teche-Maringouin deltaic shoal complex (5-12 m water depth) and seaward of 15 m water depth.


Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24