Continental margin compression: a comparison between compression in the Otway Basin of the southern Australian margin and the Rockall-Faroe area in the northeast Atlantic margin

Abstract

There is growing recognition that many passive margins have undergone compressional deformation subsequent to continental breakup, including the southern Australian margin. This deformation commonly results in formation of domal anticlines with four-way dip closures that are attractive targets for hydrocarbon exploration, and many such structures host major hydrocarbon accumulations in the Otway and Gippsland basins; however, the driving mechanisms behind formation of these structures are not completely understood. We compare the history of post-breakup compression in the Otway Basin of the southern Australian margin, with that of the Rockall-Faroe area of the northeast Atlantic margin, which has been far more extensively studied with the aim of establishing a better understanding of the genesis and prospectivity of such structures. Both margins have experienced protracted Mesozoic rifting histories culminating in final continental separation in the Eocene, followed by distinct phases of compressional deformation and trap formation. Whilst the structural style of the anticlines in both margins is similar (mainly fault-propagation folds formed during tectonic inversion), the number, amplitude, and length of the structures in the northeast Atlantic margin are much higher than the southern Australian margin. We propose that compressional structures at both margins formed due to far-field stresses related to plate boundaries, but the magnitude of these stresses in the northeast Atlantic margin is likely to have been higher, and the strength of the lithosphere lower. In the northeast Atlantic margin, the presence of Early Cenozoic basalt lava flows may have also contributed to an increase in pore-fluid pressure in the underlying sediment making pre-existing faults more prone to reactivation.