Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Application of Critical-Taper Wedge Mechanics to Structural Style in Fossilized and Active Late Cretaceous-Tertiary Delta—Deepwater Fold-Thrust Belts
(1) Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
(2) School of Geosciences, University of Aberdeen, Aberdeen, United Kingdom.
(3) School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA, Australia.
(4) Deep Exploration Technologies Cooperative Research Centre, Adelaide, SA, Australia.
The Hammerhead Delta—Deepwater Fold-Thrust Belt (DDWFTB) is a fossilized short-lived gravity-gliding system that developed during the Campanian-Maastrichtian on Australia’s passive southern margin. Rapid progradation of deltaic sediments over Turonian-Santonian water-prone mud initiated overpressure development and deformation under gravitational forces. This resulted in a broad segregation of the delta into extensional and compressional provinces, whereby margin-parallel gravitationally-driven extensional stresses on the delta top drove down-dip, margin-normal, compressional stresses in the deepwater fold-thrust belt.
Newly acquired 2D seismic data has been used to further investigate the structural style of the Hammerhead DDWFTB. The regional structural and basal detachment(s) geometry reveal an increase in structural complexity from west to east. This is demonstrated by progressive faulting in the delta top and delta toe and the development of a detachment fold province that corresponds to an increased thickness of both the deltaic wedge and the overpressured pro-delta mud upon which it prograded. Structural variations have been investigated with 2D kinematic restorations which indicate a near-balanced system that achieved critical-taper while it was active but failed to develop into an extensive passive margin DDWFTB due to a cut-off in sediment supply.
We analyze the present-day Hammerhead DDWFTB geometry to determine if critical-taper wedge mechanics can be applied to the observable structures. By plotting the covariation of the surface slope angle (α) and the basal detachment angle (β) with the change in thickness of the wedge (Δt) for a series of points along adjacent 2D seismic profiles a negative inverse relationship is clearly demonstrated. This indicates that systems with seaward dipping detachments (-β values) can be used to demonstrate that critical-taper is achieved.
In addition, we apply critical-taper wedge mechanics to quantify variations of basal pore fluid pressure (λb) in 3 dimensions for both fossilized Late Cretaceous and active Tertiary DDWFTB systems. Initial results suggest that sub-regional variations in λb correspond to changes in structural style throughout DDWFTBs.