Sequence Stratigraphic Evolution Of The Albian To Recent Section Of The Dampier Sub-Basin, North West Shelf, Australia.
Hull, Jonathan N.F.
Doctor of Philosophy, 1999
University of Adelaide
An integrated biostratigraphic, wireline, seismic, lithological and 3D-Chronostrat sequence stratigraphic study has been conducted to investigate the evolution of the Albian to Recent section of the Dampier Sub-basin on Australia?s North West Shelf. The study used 4100km of regional seismic data and 38 wells with a variable suite of wireline logs, biostratigraphic reports and lithology data.
During the study, a model for the sequence stratigraphic interpretation of the carbonate wireline log motifs was developed from biostratigraphic constraints, wireline log patterns and theoretical considerations. This model has enabled the subdivision of the section into 29 genetically-related sequences which have been further subdivided into 98 time-bounded units of strata termed ?chronosomes?. While the timing of these units has been estimated, the boundaries of the 29 sequences has been tightly constrained by reference to published foraminiferal zonations. A combination of sequence and chronosome architecture with biostratigrapbic, lithostratigraphic and wireline log data have been used to generate a suite of depth, isochron, and paleogeographic maps.
The Oligocene to Recent section of the Dampier Sub-basin is characterised by a series of prograding carbonate-dominated clinoforms within which periods of predominant progradation and aggradation have been identified. Quantitative analysis of sedimentation rates, clinoform angles and clinoform heights of this section has been conducted using stacking velocities and chronosome volumes output from 3D-Chronstrat. Calculated sedimentation rates for the aggradational sequences have shown them to be 1.5 times the sedimentation rate of the progradational sequences. The morphology of the clinoforms is a function of these progradational and aggradational periods. Progradational sequences have increasing clinoform slope angles with only a minor associated increase in clinoform height whilst aggradational sequences are characterised by decreasing clinoform angles and a marked increase in clinoform height. The aggradational sequences correspond to periods when the high-frequency (1-3Ma) and low-frequency (10Ma) eustatic curves of Haq et al. (1987) are coincident and progradational periods correspond to periods when the curves are separated. When both the high and low frequency eustatic curves combine to produce a relative sea level high significant shelf-top accommodation space is created and the margin responded by aggrading. When the rate of accommodation space creation on the shelf top is low, the sequences deposited are predominantly progradational in nature and characterised by lower sedimentation rates, progressivley increasing clinoform slope angles and relatively constant clinoform height.