Seismic Stratigraphy And Palaeogeography Of The Early Paleocene To Mid Eocene Of The Dampier Sub-Basin, North West Shelf.
Honours Degree, 2000
University of Adelaide
High-resolution palaeogeographic reconstruction of the Early Tertiary mixed carbonate-terrigenous succession of the Dampier Sub-basin, North West Shelf, is valuable in explaining the distribution of depositional systems. A chronostratigraphic framework of the depositional systems has assisted with reservoir prediction and development of play concepts.
Using a combination of seismic interpretation, wireline logs, micropaleontology, sidewall cores and cuttings from 85 wells in the Dampier Sub-basin it has been shown that there was significant terrigenous and carbonate sediment supply after the base Tertiary erosional event (65Ma). Reservoir sandstones are predominately terrigenous clastics, that occur in two distinct seismic packages within the same depositional sequence; Lowstand deposits occur in the T1-T3 foraminifera time zone (Early Paleocene), and a highstand deposit occurs in the T5-T6 foraminifera time zones (Late Paleocene).
Deposition during the Early Paleocene was controlled by the emergent Rankin Trend that forced sedimentation along the Kendrew and Lewis Troughs. The Early Paleocene package has thick terrigenous sandstone deposits (200m at Dampier-1) in the Lewis Trough that rapidly thin to the north on the shelf edge. During this period there was significant sediment supply capable of depositing further terrigenous clastics down depositional dip in deeper paleo-water depths.
The Early Paleocene lowstand terrigenous clastic deposits were followed in the Late Paleocene by mixed carbonate-terrigenous transgression and a highstand systems tract. The highstand systems tract had increased sediment supply rates that sourced a thick deposit along Kendrew Trough. This deposit represents two possible depositional environments. The deposit could be from point-sourced mud/sand-rich turbidites deposited during canyon retreat (highstand shedding), or alternatively be a set of prograding shoreface systems. Due to the increased sediment supply, further deposition of submarine/slope fans elsewhere in the basin could serve as possible reservoirs.