HR: 17:15h
AN: OS44A-06    [Abstracts]
TI: Development of the Holocene Clinoform in the Gulf of Papua
AU: * Slingerland, R
EM: sling@geosc.psu.edu
AF: Penn State University, Department of Geosciences 513A Deike Bldg, University Park, PA 16802 United States
AU: Milliman, J D
EM: milliman@vims.edu
AF: College of William and Mary Virginia Institute of Marine Science, PO Box 1346, Gloucester Point, VA 230621346 United States
AU: Driscoll, N W
EM: ndriscoll@ucsd.edu
AF: Scripps Institutions of Oceanography, Geosciences Research Division University of California, San Diego, CA 92093-0244 United States
AU: Walsh, J P
EM: walshj@mail.ecu.edu
AF: East Carolina University, Department of Geology Room 101, Graham Building, Greenville, NC 27858 United States
AU: Keen, T R
EM: Keen@nrlssc.navy.mil
AF: Naval Research Laboratory, NRL Code 7322, Stennis Space Center, MS 39529 United States
AB: The Gulf of Papua (GoP) off the southeastern coast of Papua New Guinea, is a modern example of a marine foreland basin in mid-life. Loading of the Australian plate by New Guinea is creating accommodation space that is being filled by clastic sediment delivered by rivers draining the central mountains. Collectively, the Fly, Turama, Kikori, and Purari rivers discharge $>200 x 10^{6}$ t/yr into the basin. Filling is both longitudinal (Fly and Turama Rivers) and transverse, creating a crescentic shelf, similar to ancient shelves such as the Miocene shelf of the Alpine foreland. To develop a model for GoP-type shallow-marine shelf processes and products we have collected 21 piston cores, 24 gravity cores, 4000 nmi of CHIRP and 1000 nmi of multi-electrode sparker profiles in the GoP, and conducted numerical experiments with NCOM, the US Navy Coastal Ocean Model. Morphologically the GoP shelf is characterized by three treads and two risers, which define two clinoforms; here we focus on the upper Holocene clinoform whose face extends from ~20 to ~80 m water depth, where it downlaps onto an erosional surface etched into topsets of an older clinoform. The face of the Holocene clinoform undulates along strike in a series of subtle promontories and reentrants. Geometrical relationships of stratal packages suggest that the undulations are caused by progradation of sand/mud lobes across the roll-over and oblique transport down the clinoform. Intercalated on- and off-lapping wedges suggest a multi-stage clinoform growth, with upslope sand-rich build-outs alternating with mud-rich toe of slope build-outs. The latest sediments consist of a subjacent heterolithic facies, deposited during a phase of oblique clinoform growth, overlain everywhere by an acoustically transparent facies that forms an on- and down-lapping toe of the wedge. We assume that this transparent facies represent sediment winnowed from topset strata, suggesting that the rate of clinoform growth has slowed. The causes of these variations in clinoform growth and stratal geometry are presently uncertain but may reflect temporal variations in climate, coastal circulation, or longer-term Holocene changes in sea level. Computed annual circulation of the GoP in response to trade wind and monsoon conditions shows that the flow fields are significantly different. During trade winds sediment particle paths on the clinoform top are obliquely offshore to the east. A zone of convergence lies near the 25-m isobath along the clinoform face, where offshore-directed waters on the shelf meet onshore-directed bottom waters climbing the clinoform face, possibly localizing sediment deposition there. During monsoon conditions average bottom flow is landward on the modern clinoform top and minimal over much of the slipface, suggesting that variations in sediment type at the bed level may be circulation related and seasonal.
DE: 4850 Organic marine chemistry
DE: 4851 Oxidation/reduction reactions
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