HR: 0800h
AN: H51D-0403    [Abstracts]
TI: How Does the Morphology of Shelf-Margin Deltas Relate to Sea-Level Elevation? Clues From the Modern Mississippi River Delta
AU: * Ghoshal, S
EM: sghosh2@lsu.edu
AF: Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA 70803 United States
AU: Bart, P J
EM: pbart@geol.lsu.edu
AF: Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA 70803 United States
AB: Scientists have attempted to precisely determine eustatic changes using various techniques. One of these is the sequence stratigraphic technique which relies on vertical changes in the position of coastal onlap (Vail et al, 1977). In subsequent years, several authors have recognized many limitations in this approach (Christie-Blick et al., 1990). Our ongoing study focuses on the possibility of using the morphology of modern and ancient shelf-margin deltas as sea-level indicators to determine past sea-level elevations. The Mississippi River Delta provides an excellent opportunity to study the precise relationship between shelf-edge delta morphology and sea-level elevation. A morphological analysis of the modern Mississippi River Delta suggests that there may be a direct relationship between the sea-level and the offlap break features of the delta. The offlap break is defined at the intersection of topset and foreset at the location of a marked increase in slope. At this point, the bathymetric curvature (i.e. second derivative of sea-floor) is highest. This is analogous to O'Grady and Syvitski (2002) definition of shelf break offshore Greenland. More than a hundred bathymetric cross sections were made across the modern Balize lobe of the Mississippi River Delta using Rivertools software. The geomorphic analysis showed that there were two distinct morphologic types of the delta. In one type, there is a sharp transition from the topset to the foreset, whereas in a second type, the topset-foreset transition is gradual. It was observed that sharp offlap breaks characterize the eastern part of the delta at water depths of 1 ± 0.3 m. The southern and southwestern parts of the delta are characterized by gradual offlap breaks at water depths of 4 ± 2 m.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1819 Geographic Information Systems (GIS)
DE: 1824 Geomorphology: general (1625)
DE: 1825 Geomorphology: fluvial (1625)
SC: Hydrology [H]
MN: Fall Meeting 2005