Seismic Geomorphology and Stratigraphic Evolution of a Tertiary-Aged Isolated Carbonate Platform System, Browse Basin, North West Shelf of Australia—Part II
Steven L. Bachtel, Henry W. Posamentier, Thomas P. Gerber, 2010. "Seismic Geomorphology and Stratigraphic Evolution of a Tertiary-Aged Isolated Carbonate Platform System, Browse Basin, North West Shelf of Australia—Part II", Seismic Imaging of Depositional and Geomorphic Systems, Lesli J. Wood, Toni T. Simo, Norman C. Rosen
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Three-dimensional seismic data from the Torosa Field (Torosa 3D Survey) in the Browse basin of the North West Shelf, Australia display a series of well imaged isolated carbonate platforms that evolve from platform initiation to terminal drowning. The application of seismic geomorphology allows recognition of various carbonate geomorphic elements (depositional and diagenetic) including prograding margins, slope fan and gullied slope deposits, platform interior patch reefs, and karst fabrics. Mapping these features in successive horizon-slices and comparing the spatial changes with changes in seismic geometries (cross-sectional view) allow a more detailed understanding of platform response to relative changes in sea level and the relative complexity of the systems through time.
Platform growth initiates as a series of kilometerscale buildups characterized by a circular to elliptical morphology (in plan view). These small-scale buildups quickly coalesce into a series of build-up complexes (2-6 km) with progradational margins. These complexes display either elliptical or rhombohedral shapes. Individual patch reefs can be observed in the platform interiors of the build-up complexes. A second phase of coalescence occurs and the build-up complexes combine into a larger platform (25 × 10 km). This large platform then backsteps and is characterized by a strongly elongate and elliptical shape. The backstepped platform progrades up to 3 km prior to final drowning and burial.
The growth of elliptical and rhombohedral buildup shapes appear to be influenced by focused currents between the platforms. A distinct windward-leeward asymmetry has not been recognized in the platforms. The rhombic platform complexes are characterized by a unique “pointed promontory” morphology that develops (perpendicular to the long dimension) as the elliptical complexes evolve into more rhombic shapes through time. Sand waves are also observed in the bottom of the interplatform seaways. The backstepped platforms display prograding seismic reflectors that terminate laterally and are confined to areas of the platform margin protected from influence of currents. Coalescence of the platforms followed the growth of small buildups in the mouths of the interplatform seaways, effectively blocking the seaways and allowing sediment to accumulate in the previously current swept passage. This dataset provides an alternative growth model for platforms strongly influenced by currents, rather than the more common model of progradation with sediment flux dominated by windward-leeward sediment transport.