HR: 15:25h
AN: H33F-08    [Abstracts]
TI: Does Sea-Level Lowstand Always Lead to Cross-Shelf Valley Formation and Source-to-Sink Sediment Flux?
AU: * Tornqvist, T E
EM: tor@tulane.edu
AF: Department of Earth and Environmental Sciences, Tulane University, 6823 St. Charles Avenue, New Orleans, LA 70118-5698 United States
AU: Wortman, S R
EM: swortm1@uic.edu
AF: Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7059 United States
AU: Mateo, Z R
EM: zmateo1@uic.edu
AF: Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7059 United States
AU: Milne, G A
EM: g.a.milne@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Science Labs, Durham, DH1 3LE United Kingdom
AU: Swenson, J B
EM: jswenso2@d.umn.edu
AF: Department of Geological Sciences, University of Minnesota Duluth, 1114 Kirby Drive, Duluth, MN 55812 United States
AB: It is commonly believed that the efficiency of sediment flux from continents to oceans is maximized during relative sea-level (RSL) lowstands, by means of cross-shelf valleys that are directly connected to the continental slope and deep-marine environment. While such conditions have been documented for the last RSL lowstand along several passive margins, there is increasing evidence that radically different conditions persisted during the Last Glacial Maximum (LGM) elsewhere, with lowstand shorelines that remained on the continental shelf. Here, we analyze the relationship between the LGM (21 ka) shoreline and the shelf edge for the Gulf of Mexico off the United States and the Bay of Biscay off France. A geophysical model is used to compute shoreline positions corrected for isostatic movements, and the shelf-edge position is quantified by means of curvature. The conditions in the two study areas differed markedly: throughout the northern Gulf of Mexico LGM sea level dropped to a point commonly ~40 m below the shelf edge, consistent with conventional sequence-stratigraphic models, while in the Bay of Biscay the LGM shoreline remained well landward of the shelf edge, in places separated by hundreds of kilometers. Such contrasting responses of continental margins to transient forcing hint at potentially major implications for (1) the source-to-sink sediment flux from continents to oceans and its variation in time and space; (2) sequence-stratigraphic models that predict deep-marine sedimentation as being particularly prominent during RSL lowstands; and (3) the occurrence of paleovalleys and related features on the continental shelf.
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1861 Sedimentation (4863)
DE: 3022 Marine sediments: processes and transport
DE: 4556 Sea level: variations and mean (1222, 1225, 1641)
SC: Hydrology [H]
MN: Fall Meeting 2005