HR: 0800h
AN: OS21B-1228    [Abstracts]
TI: Sedimentary Processes and Morphodynamic Controls on Facies Distribution in a Seismically Active Fjord: Simpson Bay, Prince William Sound, Alaska.
AU: Dellapenna, T M
EM: dellapet@tamug.edu
AF: Texas A&M University at Galveston, 1001 Texas Clipper Rd Suite 710, Galveston, TX 77554 United States
AB: Simpson Bay is a macrotidal, turbid outwash fjord situated in a temperate rainforest with high precipitation rates (250 centimeters per year). An easily eroded drainage basin and constant uplift contribute to some of the highest sediment loads in the world. Modern sedimentary processes were investigated using a multifaceted approach. Side scan sonar images, magnetometer data, bathymetry data, and sediment grab samples were collected to describe the distribution of surface sediment textures as well as to map seafloor morphology. This data provides evidence of fine grain sediments constrained to deeper parts of the bay, while coarse grain sediments are found in shallow high energy environments and deep water terminal moraines. Spatial sediment distribution is controlled by seafloor morphology and deposition resulting from the remobilization of sediment due to seismic processes. Shallow seismic data and the stratigraphy and geochemistry of short (1-2 meter) gravity cores were analyzed to piece together the depositional history of the fjord on a decadal scale. The seismic data shows a glacial surface (bedrock and till) overlain by sedimentary units with complexly ponded stratigraphy. Radioisotope profiles of 210Pb activities were used as an investigative tool to determine sedimentary processes. Seismic events leave specific radioisotope signatures in activity profiles. The 1964 Good Friday earthquake, centered just 110 kilometers away, mobilized unstable near surface sediments that are traceable throughout the basin. Sedimentation rates derived from sediment activities were calculated to investigate and describe depositional environments. Radioisotope profiles were used to determine physical and biological mixing dynamics in surface sediments.
DE: 4235 Estuarine processes
DE: 3022 Marine sediments--processes and transport
DE: 3094 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting