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AAPG Bulletin, V.
Progradation along a deeply submerged OligoceneMiocene heterozoan carbonate shelf: How sensitive are clinoforms to sea level variations?
1Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, 4412 Spicewood Springs Rd., Bldg. 600, Austin, Texas; Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, C1100, Austin, Texas; Present address: Geoscience Australia, GPO Box 378, Canberra, Australian Capital Territory, 2601, Australia; email: [email protected]
2Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, 4412 Spicewood Springs Rd., Bldg. 600, Austin, Texas
3Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, 4412 Spicewood Springs Rd., Bldg. 600, Austin, Texas; present address: 48A Olympus Way, Lyons, Australian Capital Territory, 2606
Donna Cathro graduated with a B.Sc. (Hons.) degree in geology and geophysics from the University of Adelaide in 1989. She worked as a sedimentary petrologist prior to joining Geoscience Australia in 1992. In 2002, she was awarded a Ph.D. from the University of Texas at Austin and returned to Geoscience Australia. Donna is a member of AAPG, the American Geophysical Union, and the Petroleum Exploration Society of Australia.
James Austin (Ph.D. 1979, Woods Hole Oceanographic Institution, Massachusetts Institute of Technology Joint Program in Oceanography and Applied Ocean Sciences and Engineering) has worked at the University of Texas Institute for Geophysics since 1979. His primary research interest has always been the structural and stratigraphic evolution of passive continental margins, using primarily seismic reflection techniques supported by drilling and coring.
Graham Moss (Ph.D. 1995, University of Adelaide) worked at Geoscience Australia with the National Biostratigraphic Database from 1995 to 1997. In 1998, he joined the Gulf of Mexico Intraslope Basins Project at the Institute for Geophysics, University of Texas at Austin. His interests include ecostratigraphy and marine paleoecology, including the interpretation of environmental change and paleoceanography using foraminiferal successions.
This work forms part of the lead author's Ph.D. dissertation research at the University of Texas at Austin. The research was primarily supported by Geoscience Australia (formerly Australian Geological Survey Organisation). Funding has also been supplied by the donors of the Petroleum Research Fund, administered by the American Chemical Society, ACS-PRF #35451-AC8, and the American Association of University Women. The 3-D data were contributed by Woodside Australian Energy. The authors are also indebted to M. Bradshaw, R. Buffler, W. Fisher, C. Fulthorpe, W. Galloway, G. Karner, J. Kennard, D. Lockhart, R. Loucks, B. McGowran, H. Olson, J. Pacht, K. Romine, and W. Schlager for critical reviews that greatly improved the manuscript. The senior author publishes with the permission of the Chief Executive Officer, Geoscience Australia. University of Texas, Institute for Geophysics Contribution No. 1637.
We combine two- and three-dimensional seismic stratigraphic interpretation with paleobathymetric analysis from benthic foraminifera to understand the genetic significance of prominent seismic discontinuity surfaces typically mapped as sequence boundaries and flooding surfaces in the late Paleogene–early Neogene northern Carnarvon Basin.
The progradational succession, dominated by heterozoan carbonate sediments, is divided into 5 northwest-prograding clinoformal sequences and 19 subsequences. Clinoform fronts progress from smooth to highly dissected, with intense gullying apparent only after the middle Miocene optimum. Once initiated, gullies become the focus for sediment distribution across the front. Bottomsets remain relatively sediment starved without the development of aprons on the lower slope and basin. Small-scale variability suggests heterogeneous sediment dispersal through the slope conduits. Along-strike sediment transport superimposed on progradation changes from southwest directed in the late Oligocene to northeast directed in the late middle Miocene, suggesting a major reorganization of circulation in the southeastern Indian Ocean.
Prominent seismic discontinuity surfaces represent both intervals of shallow paleowater depth and flooding of the shelf. Partial exposure of the shelf indicated by karst morphology is coeval, with middle to outer neritic paleowater depths on the outer shelf. Instead of building to sea level, progradation occurs with shelf paleowater depths at the clinoform rollover greater than 100 m. Therefore, in the northern Carnarvon Basin, onlap onto the clinoform front is not coastal, and the sensitivity of the clinoforms to sea level changes is muted.
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