HR: 0830h
AB: Stratal architecture records the effects of depositional and erosional processes that operate on various spatial scales in three dimensions. We present interpretations within a 1500 km2 3D seismic volume that document stratal pattern variations within a late Paleogene-early Neogene succession, NCB. Our immediate goal is to understand the controls on clinoform geometry, specifically how these clinoforms, which represent carbonate clastic progradation, relate to changes in relative sea level. Ultimately, we will attempt to define the role of eustasy in shaping this stratal architecture, first by determining tectonic history using kinematic and flexural modeling, then by defining the synchroneity and paleobathymetry of events recognized in well data. Carbonate clastic and minor intercalated siliciclastics form stacked clinoforms that prograde at various rates to the northwest (basinward), superimposed on a tectonic history that includes multiple extensional phases since the Permian. Thermal subsidence produced by Tithonian-Valanginian rifting and breakup created accommodation now filled by Cretaceous and Tertiary sediments. Late Cenomanian-Turonian inversion, and latest Oligocene-Present collision along the northern Australia plate boundary, may also influence stratal development. We analyze laterally extensive (70 km, NE-SW along strike), high-density (spacing, 12.5-25 m), moderate resolution (frequencies, 35-50 Hz) 3D MCS provided by Woodside Energy, Ltd. (Australia), directly tied to 16 exploration wells. This data volume is supplemented by regional (600 km, NE-SW), widely spaced (10-100 km), lower resolution (frequency, ~30 Hz) 2D MCS data acquired by the Australian Geological Survey Organisation. Successive 2D traverses suggest five internally variable stratal packages, designated A to E (bottom-to-top). These are separated by prominent downlap surfaces, which may record rapid production of carbonate clastics. Shingled clinoforms of A, with dip-oriented headless gullies ~20 m deep at their toes, are overlain by sigmoid reflections of B, suggesting increasing accommodation. A backstep of ~6 km occurs at the base of high-amplitude reflectors of C. Within C, stratal architecture changes landward and seaward of the breakpoint of B. Landward, shingled clinoforms prograde across older topsets. Accommodation is limited. Seaward, where accommodation increases, sigmoid clinforms dominate. Incisions ~40 m deep are common on the mid-lower clinoform front. Low-amplitude reflectors dominate in D and E; sigmoid to shingled clinoforms, indicating progressive decrease in accommodation, are disrupted by post-early Neogene incisions ~120 m deep. Within the 3D volume, mapped seismic terminations of the lowermost mid-Oligocene surface (base A) reveal spatial variability superimposed on the overall 2D stratal signature. Downlapping reflectors form both arcuate and linear trends and isolated mounds. Orientations deduced from downlap patterns indicate multiple sediment sources and transport directions. Progradation is to the NW in the SE, but co-exists with W-directed bypass in the basin. Subtle NW-SE - oriented truncation between the clinoform toe and an along-strike topographic high implies current deposition and erosion. This is supported by isolated lobes and mounds seaward of the front, which suggest transport directions from the N, NW and SW. Mass sediment flows occur along NE-SW fronts up to 30 km wide.
AN: OS21C-23
TI: Development of Late Paleogene-Early Neogene Carbonate Clastic Stratal Architecture From 3D Seismic Data, Northern Carnarvon Basin (NCB), Northwest Australia.
AU: * Cathro, D L
EM: dcathro@mail.utexas.edu
AF: Inst. for Geophysics, University of Texas, 4412 Spicewood Spgs Rd, Bldg 600, Austin, TX 78759 United States
AU: * Cathro, D L
EM: dcathro@mail.utexas.edu
AF: Dept. of Geological Sciences, University of Texas, Austin, TX 78701 United States
AU: * Cathro, D L
EM: dcathro@mail.utexas.edu
AF: Aust. Geological Survey Organisation, Canberra, ACT, 2601 Australia
AU: Austin, J A
AF: Inst. for Geophysics, University of Texas, 4412 Spicewood Spgs Rd, Bldg 600, Austin, TX 78759 United States
AU: Karner, G D
AF: Lamont-Doherty Earth Observatory, Palisades, NY, 10964 United States
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: OS
MN: Fall Meeting 2000