HR: 17:45h
AN: OS44A-08    [Abstracts]
TI: Neogene Evolution of the Mixed Carbonate/Siliciclastic Margin of the Gulf of Papua: Preliminary Results of Spring 2004 PANASH Cruise on the R/V {\it Melville}
AU: * Droxler, A W
EM: andre@rice.edu
AF: Earth Science Department, MS-126, Rice University, P.O. Box 1892, Houston, TX 77251 United States
AU: Dickens, G R
EM: jerry@rice.edu
AF: Earth Science Department, MS-126, Rice University, P.O. Box 1892, Houston, TX 77251 United States
AU: Bentley, S J
EM: sjb@lsu.edu
AF: Coastal Studies Institute, Department of Oceanography and Coastal Sciences, LSU, 302 Howe-Russell Geosciences Complex , Baton Rouge, LA 70803 United States
AU: Peterson, L C
EM: lpeterson@rsmas.miami.edu
AF: RSMAS, MGG, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AU: Opdyke, B N
EM: bno@ems.anu.edu.au
AF: Department of Earth and Marine Sciences, The Australian National University, Linneaus Way, Canberra, ACT 0200 Australia
AB: A series of NNE trending ridges and troughs, probably Eocene in age, influenced the establishment and development of carbonate platforms during the Oligocene and Miocene on parts of the topographic positive relief in the northeastern part of the Australian plate. This overall physiography of NNE trending troughs, separated by isolated carbonate platforms, can still be observed today east of the modern Gulf of Papua (GOP) shelf edge and as imaged in seismic lines and gravity maps in the sub seafloor of the GOP shelfal areas. Earlier drilling for oil and gas exploration showed that most of these platforms burried under the GOP shelf flourished until the early Miocene and had already drowned by the late early Miocene or the middle Miocene. Those drowned platforms perhaps after being exposed for sometime, subsided through time but remained topographic positive features without being buried by hemipelagic sediments for most of the late Miocene and early Pliocene. Preliminary results of spring 2004 PANASH cruise on the R/V {\it Melville} in the Ashmore, Pandora, and Moresby troughs show that some of the carbonate platforms in the offshore areas had also drowned probably by the late part of the early Miocene, upper (uTe) zone based upon the occurrence of {\it Lepidocyclina (Nephrolepidina)} and {\it Spirockypena margaritatus}, and remained unburied for more than 15 My. Others, however, have remained active, back stepped, and aggraded until today (i.e. Ashmore, Boot, Portlock, Eastern Field Reefs). Its only since the late Pliocene that the majority of siliciclastic sediments, products of erosion of the newly formed PNG mountains, began to quickly infill the different troughs from west to east and at the same time to bury the drowned platforms by more than 1.5 -2.0 km of sediments. The thick late Pliocene and Quaternary sedimentary section, observed under the GOP shelf, represents a vertical succession of sedimentary deposits including at their base deep basin fans which probably underlie some slope depositional environments. These are in turn capped by shelf edge lowstand deltas and aggrading shelf deposits. In the Moresby Trough, the eastern most and deepest basin, the basin floor deposits represent a poorly developed fan, whereas in the northern part of Pandora Trough adjacent to the GOP shelf edge, thick muddy slope deposits were encountered and are currently partially covering an isolated carbonate platform. In the northern part of the Ashmore Trough, the westernmost and shallowest basin, what was likely a lowstand coastal system and shelf edge delta deposited during the Last Glacial Maximum is observed. In conclusion, a lateral east-west distribution in the modern troughs, of basin, slope, and shelf edge environments was encountered that corresponds to the vertical stack of similar successions imaged and drilled in the sub-seafloor of the GOP shelf itself.
DE: 4556 Sea level variations
DE: 3025 Marine seismics (0935)
DE: 3045 Seafloor morphology and bottom photography
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting