HR: 17:30h
AN: OS44A-07    [Abstracts]
TI: Quaternary Turbidite Sedimentation in the Moresby Trough, Preliminary Observations from the Papua New Guinea S2S Study Area
AU: * Bentley, S J
EM: sjb@lsu.edu
AF: Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803 United States
AU: Muhammad, Z
EM: zmuham1@paws.lsu.edu
AF: Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803 United States
AU: Dickens, J
EM: jerry@rice.edu
AF: Department of Earth Science, Rice University, Houston, TX 77251 United States
AU: Droxler, A
EM: andre@rice.edu
AF: Department of Earth Science, Rice University, Houston, TX 77251 United States
AU: Peterson, L
EM: peterson@rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149 United States
AU: Opdyke, B
EM: bno@ems.anu.edu.au
AF: Dept. of Earth and Marine Science, Australia National University, Canberra, ACT 0200 Australia
AB: Multicores and jumbo piston cores were collected from the Moresby Trough from the R/V Melville in March-April 204 to study patterns of off-shelf sediment flux from the Gulf of Papua to the deep sea over Pleistocene-Holocene timescales. The Moresby Trough represents the primary deep-sea sediment conduit linking the Source to Sink Gulf of Papua study area to the north with the Coral Sea Basin to the south. Core locations were navigated from the surface using dynamic positioning and multibeam bathymetric mosaics collected during the cruise. Selected cores have been analyzed using a multi-sensor core logger, X-radiography, granulometry, and Pb-210 geochronology. Most piston cores collected from the Moresby Trough contain abundant mafic sandy turbidites overlain by fine-grained hemipelagic deposits 1-2 m thick. X-radiographs of multicores reveal mostly bioturbated hemipelagics. However, one core, MV25-0403-24MC, was collected from the axis of a primary channel, and contains at least two fine-grained turbidites within the upper 0.5 m of sediment. The uppermost turbidite contains low but uniform activities of excess Pb-210, and may have been 15-20 cm thick at the time of deposition (i.e., before subsequent disruption by bioturbation), based on fabric and radiochemical evidence. Application of a simple box-model for physical mixing (i.e., during the flow) and subsequent decay suggests that the uppermost turbidite was deposited 70-120 years before present. Bioturbation has since reworked about 60% of the bed, suggesting that such beds will only escape destruction by bioturbation if they are $>$ 10 cm thick, and are deposited more frequently than once per century. Based on these observations, we suggest that gravity flows are presently active in the Moresby trough, and may account for a significant fraction of the hemipelagic drape present in channel systems. However, fabric evidence for these thin, fine-grained beds may be obscured by subsequent bioturbation. Also, at some point in the past, possibly at the onset of the Holocene Transgression, the character of sediment flux to the Moresby Trough shifted from sandy mafic-rich sandy turbidity currents to much finer sediments, delivered downslope by both benthic flows and vertical flux through the water column.
DE: 4211 Benthic boundary layers
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
DE: 1815 Erosion and sedimentation
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting