3D seismic analysis of normal fault growth and interaction within a gravitational detachment delta system in the Ceduna Sub-Basin, Great Australian Bight.

Abstract

We use three-dimensional (3D) seismic reflection data to determine the structural evolution of thin-skinned listric fault growth, at the extensional top of a gravitationally driven delta system, in the central Ceduna Sub-Basin. We present analysis of a strike and dip-linked extensional fault system, which is decoupled at the base of a marine mud interval of late Albian age. The fault system is oriented NW-SE with strike-linkage of fault segments and dip-linkage through the Santonian interval which connects a Cenomanian-Santonian period of kilometre scale fault growth and post-Santonian normal faulting. Understanding the growth of listric faulting requires quantifying heave and throw, which involves simplistic depth conversion of fault plane time measurements to establish a fault plane model to translate throw into fault plane displacement. Our analysis constrains fault growth into six evolutionary stages: [1] early Cenomanian nucleation and isolated radial propagation of fault segments; [2] substantial segment linkage established by the latest Cenomanian; [3] late Santonian cessation of a majority of fault growth; [4] heavy erosion at continental breakup of Australia and Antarctica (c. 83 Ma); [5] early Campanian independent nucleation of the post-Santonian fault system; and [6] fault assemblages fully linked by the Cenozoic, with continued accumulation of displacement. The structural evolution of this fault system is compatible with the 'isolated fault model'. In particular, we emphasise the importance of dip-linkage in this fault system, which controls the present day geometry of the fault array.