THE DEVELOPMENT AND REGIONAL SIGNIFICANCE OF RIFT-RELATED DEPOSITIONAL SYSTEMS IN THE DAMPIER SUB-BASIN

Abstract

The influence of tectonic control is more apparent than eustatic control on the rift-related stratigraphy of the Dampier Sub-basin. The correlation of observed depositional events to causative processes and global events is problematic due to the use of alternative geological time scales, causing ambiguity and uncertainty. The Harland (1989) time scale with a revised palynological allocation, combined with genetic sequence stratigraphy, and Prosser's concept of the tectonic systems tract, has proved useful during evaluation of the stratigraphy of the Dampier Sub-basin.Palaeo-topography was a major factor in sediment distribution and facies architecture of rift-related strata in the Dampier Sub-basin. This must be considered when assessing the stratigraphic trapping potential for hydrocarbons. There is a close association between the styles of depositional systems observed in the Dampier Sub-basin and stage of rifting and basin development. Five tectonic systems tracts, each with unique depositional systems have been identified and described; pre-rift, rift initiation, rift climax, immediate post-rift and late post-rift tectonic systems tracts.The use of a single time scale has enhanced the relationship between tectonic systems tracts (super-cycles) and the timing of depositional events recorded during previous genetic stratigraphic studies in the North West Shelf. The tectonic nature of super-cycle scale events should be temporally and spatially assessed in detail before the effects of eustatic change are evaluated for rift-related successions of the North West Shelf. The problem can be further exacerbated when the absolute error of chronological dating exceed the temporal frequency of eustacy, causing tenuous correlations of depositional events to a global eustatic curve.