Gartrell, Anthony¹, Chris Hudson², Brian Evans³
(1) CSIRO Petroleum, Perth, Australia
(2) ChevronTexaco Australia, Perth, Australia
(3) Curtin University of Technology, Perth, Australia

ABSTRACT: Oblique Inversion of the Makassar Straits Rift System and the Role of Basement Faults : Insights from Analog Models

Analog modeling techniques were used to investigate the influence of cross-trending basement faults during extension and subsequent oblique inversion in an attempt to understand the likely geometry and evolution of similar structures located in the Makassar Straits rift system. Multilayer models composed of sand, silicone putties and a silicone/plasticine mixture were constructed so that laterally offset rift basins would form on either side of a pre-existing basement fault. During extension, transfer zones comprised of a series of en echelon normal faults, that connect downwards with the basement fault, formed to link the laterally offset rift basins. Subsequent oblique inversion of the models resulted in a general progression starting with broad folding, followed by the development of small-scale inversion anticlines associated with reactivated rift faults, to thrust faulting, and finally to the formation of cross-trending wrench faults. Rift fault reactivation and wrench fault development was prominent in the transfer zones due to the orientation of the constituent faults (oblique to the shortening direction) and their connection with the underlying basement fault. The addition of an intra-sedimentary detachment layer, which represents a thick overpressured shale present in the vicinity of the economically important Mahakam Delta , allowed gravitational collapse and extensional faulting to occur on structural highs. The cross-trending basement fault was again the locus for inversion structures, both above and below the detachment layer in the latter case. The results of the experiments may help to identify poorly imaged exploration targets beneath the overpressured shale layer in this area.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.