HR: 1330h
AN: OS23B-02    [Abstracts]
TI: Distribution and Morphology of Sorted Bedforms on the U.S. Atlantic Inner Continental Shelf: Implications for Regional Geology, Sediment Supply, and Sediment Transport
AU: * Thieler, E R
EM: rthieler@usgs.gov
AF: U.S. Geological Survey, 384 Woods Hole Rd, Woods Hole, MA 02543
AU: Schwab, W C
EM: bschwab@usgs.gov
AF: U.S. Geological Survey, 384 Woods Hole Rd, Woods Hole, MA 02543
AB: Regional seafloor mapping surveys show that sorted bedforms (grain-size-sorted features with wavelengths of 10s-1000s m and heights generally <1 m, oriented usually at a high angle to the local shoreline) are abundant, nearly ubiquitous morphologic features of the U.S. Atlantic inner shelf. Their occurrence appears to be controlled by several geologic factors, including: 1) regional geology, 2) shelf bathymetry, and 3) relative sediment abundance. Although sorted bedforms may develop as the result of emergent behaviors, sorted bedforms often occur where the underlying geologic framework contributes different sediment size classes to the shelf sediment cover in a spatially heterogeneous manner (e.g., braided glacial outwash deposits; complex fluvio-estuarine valley-fill deposits). These abrupt changes in grain size may initiate and enhance morphodynamic feedbacks. Sorted bedforms tend not to occur in areas with well-developed bathymetric features (e.g., ridge and swale topography with meters of relief over <1 km spatial scales) that trend at a high angle to their oft-observed shore-perpendicular orientation. Sorted bedforms also tend to be absent in locations where there are well-developed shoreface-attached sand bodies that reflect local- to regional-scale sediment abundance on this otherwise generally sediment-starved shelf. Where observed at storm-event to decadal time-scales, sorted bedforms are shown to be temporally persistent in their size, orientation, and location, and may reflect a preferred morphologic state of the seabed that is adjusted to regional physical and environmental variables. Examples from the Mid-Atlantic and South Atlantic Bights illustrate aspects of sorted bedform occurrence described here.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments--processes and transport
DE: 4219 Continental shelf processes
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly