The western Louisiana inner shelf along the Chenier Plain coast has experienced fluid mud deposition in response to increased fine sediment supplied by the Atchafalaya River since ~1950s. The goal of this project is to assess the characteristics comprising the sedimentary strata and stratigraphic architecture that result from mud deposition on the inner shelf. Recent time-series cores collected from the inner shelf along the Chenier plain coast show the region is subject to transient fluid mud deposition, leading to high long-term accumulation rates. Sediment cores were collected in May 2001, March and May 2002 from the inner shelf landward of the 10 m isobath, 100 km west of Atchafalaya Bay. Porosity, granulometry, X-radiography, and 7Be, 210Pb and 137Cs geochronology indicate the presence of high-porosity event layers 2-25 cm thick composed of clay with basal silt laminations. These event layers appear to concentrate around a depocenter located 95-110 km west of the Atchafalaya River, landward of the 7 m isobath, but can be ephemeral features on a seasonal time scale.
The combination of high-energy benthic hydrodynamics and sufficient fine sediment can result in cross-shelf gravity-driven flows (on very low slopes) that can blanket hundreds of square kilometers to thicknesses exceeding 10 cm. The sedimentary fabric that results from gravity-driven flows consists of a stacked pattern of predominantly fine-grained, fining upward packages. The resulting morphology of the shelf may be a clinoform, with maximum deposition occurring on the foreset (convex upward) region. The observations from the western Louisiana inner shelf (mud/silt couplets that comprise the fine-scale stratigraphy of the region, ephemeral 7Be deposits, and clinoform morphology exhibiting erosional features in sidescan and chirp data) are consistent with the wave-enhanced gravity-driven flow model. These results indicate that wave-enhanced gravity driven flows may be an important component in the dispersal of Atchafalaya River sediment.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-06222004-145908 |
| Date | 23 June 2004 |
| Creators | Rotondo, Kristina Anne |
| Contributors | Jaye Cable, Harry H. Roberts, Sam Bentley |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-06222004-145908/ |
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