Donna L. Cathro1,
James A. Austin2
(1) University of Texas at Austin, Department of Geological Sciences, Austin, TX
(2) University of Texas, Austin, TX
Abstract: True three-dimensional images of stacked, prograding late Paleogene-early Neogene clinoforms, Northern Carnarvon Basin (NCB), North West Shelf (NWS), Australia
Paleogene to Neogene mixed carbonate clastic-siliciclastic sediments beneath the NWS are characterized by stacked prograding clinoforms; the complex development of this stratal configuration can only be studied properly using nested 2D and 3D multichannel seismic (MCS) data tied to exploration wells. Stratigraphic complexity is enhanced by the varied long-term structural evolution of the NWS since the Paleozoic. Present-day convergence at the distant northern Australia plate boundary, and continued thermal subsidence since the Valanginian, influence Tertiary stratal configurations in the NCB.
Laterally extensive (70km along strike), high-density (line spacing 12.5-25m), moderate resolution (dominant frequencies 35-50Hz) 3D MCS data, directly tied to exploration wells, are embedded within a regional (600km NE-SW), widely spaced (10-100km), lower resolution (dominant frequency ~30Hz) 2D seismic grid. Initial interpretation has revealed previously unmapped, along strike and down-dip drainage networks associated with clinoform (inclined) surfaces. Near an upper Oligocene clinoform toe, bifurcated and singular, down-dip oriented, 5-15m deep channels spaced at 300-1100m intervals occur. In contrast, on a mid-Miocene surface, 6km up-dip from and parallel to the breakpoint a single, predominantly straight along-strike channel is u-shaped in cross-section, up to 30m deep, and at least 3.5km long. Little meandering occurs.
Sequence biostratigraphic analysis on well samples available across the clinoform succession, will translate our geometric seismic interpretation into real geologic history. Both sets of analyses will be combined with a regional 2D interpretation to determine the relationship between the observed clinoform wedge and the complex and evolving tectonic framework.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana