Evolution of Oblique Extensional System in Flexed Regime, North-Western Bonaparte Basin, Australia

Abstract

The Bonaparte Basin is a long-lived sedimentary basin having complex Phanerozoic history. The recent tectonic evolution of the basin is marked by flexure-induced extension formed in the context of Neogene collision between the Australian plate and the Banda Arc. Extensional faults were superimposed obliquely over Mesozoic rift-related structures. The interplay of these two tectonic events is key to understand the controls on hydrocarbon trap integrity in an area which is well-known for breach and leak. The area also offers a good opportunity to investigate the dynamics and architecture of oblique extension system. Here we analyse the relationships between pre-existing rift structures and younger (Neogene-Recent) structural style and intensity using a 3D seismic megasurvey (referred to as the Vulcan MegaSurvey), covering an area of 18,000 km² calibrated by publicly-available biostratigraphic and wireline data from 20 petroleum exploration wells. The results indicate that main controls on the Neogene-Recent fault style, density and segmentation/linkage include: (1) the orientation of inherited structures; (2) the obliqueness of younger extension and; (3) the proximity to the Timor Trough. The pre-existing Mesozoic rift architecture strongly controls the distribution of younger deformation, both at regional and local scale. Segmentation of younger faults increases with degree of obliqueness between Neogene extension and older faults. Hard linkages are likely to develop where both fault systems trend parallel increasing risk for trap integrity. The flexural extension produced a new set of NE-trending purely extensional faults generally forming en echelon geometries, at places accompanied by the reactivation of the Mesozoic faults. In addition, episodes of stratigraphic growth provide critical evidence regarding the timing of fault activity. Results demonstrate that episodes of stratigraphic growth (mainly occurring during the latest Miocene to upper Pleistocene) correspond to the tectonic loading on the Timor Island and development of lithospheric flexure. It suggests that extensional deformation, on the descending Australian margin, accompanied the early stages of foreland basin formation.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015