Ron Hackney

Structural analysis of extended Australian continental crust: Capel and Faust basins, Lord Howe Rise

Abstract The Capel and Faust basins (northern Lord Howe Rise) are located in the SW Pacific between Australia, New Zealand and New Caledonia. New seismic, gravity, magnetic and bathymetry data and rock samples have enabled the construction of a three-dimensional geological model providing insights into the crustal architecture and basin stratigraphy. Multiple large depocentres up to 150 km long and 40 km wide, containing over 6 km of sediment, have been identified. These basins probably evolved through two major Early Cretaceous rifting episodes leading to the final break-up of the eastern Gondwanan margin. Pre-break-up plate restorations and potential field data suggest that pre-rift basement is a collage of several discrete terranes, including a Palaeozoic orogen, pre-rift sedimentary basins and rift-precursor igneous rocks. It is likely that a pre-existing NW-trending basement fabric, inherited from the New England Orogen (onshore eastern Australia), had a strong influence on the evolution of basin architecture. This basement fabric was subjected to oblique rifting along an east–west vector in the ?Early Cretaceous to Cenomanian and NE–SW-oriented orthogonal rifting in the ?Cenomanian to Campanian. This has resulted in three structural provinces in the study area: Eastern Flank, Central Belt and Western Flank.

Interpretation and modelling of new Browse Basin airborne magnetic data for igneous rocks and basement

The Browse Basin on Australia’s North West Shelf is a NE-trending Paleozoic to Cenozoic depocentre that contains more than 15 km of sediments. These sediments host significant hydrocarbon reserves, some of which are currently under development. The basin also has the potential to store large volumes of carbon dioxide. Recently-acquired aeromagnetic data over the Browse Basin provide new impetus for studies of the nature of basement, the role of structural inheritance and controls on the distribution of volcanic rocks. Initial interpretation of the new magnetic data has utilised magnetic source polygons and depth estimates derived from the tilt-angle filter. Exploration wells that intersect mainly volcanic flows or tuffaceous rocks tend to lie on or adjacent to source polygons.Computed tilt depths show that these sources tend to coincide with the depth to the top of volcanics in wells and that tilt depths extend deep into the basin (up to ~10 km). The magnetic susceptibility distribution inferred from minimally-constrained, regional-scale inversion models also indicates that magnetic anomalies arise from features deep in the basin and within basement. These results highlight the importance of understanding the role of volcanic rocks in basin evolution and their influence on reservoirs that may host hydrocarbons or that may be suitable for CO2 storage.

Geophysical studies of Australia's remote eastern deep-water frontier: results from the Capel and Faust Basins

Introduction The Capel and Faust basins are located in a frontier part of offshore eastern Australia, about 800 km east of Brisbane in 1000–3000 m of water (Fig. 1). These basins are being evaluated for their petroleum potential as part of the Australian Government’s Offshore Energy Security Program. This article outlines the current status of integrated interpretation of 2D seismic reflection, sonobuoy refraction and potential-field data acquired during Geoscience Australia marine survey GA-302 conducted between late 2006 and early 2007. This survey collected 5920 km of high-quality 106-fold seismic reflection data using an 8 km streamer to 12 s two-way time at 37.5 m shot interval and a line spacing of 20–50 km. A subsequent swath-bathymetry and geological sampling survey (GA-2436), completed in late 2007, also collected potential-field data in the north-west of the study area with a 3–4 km line spacing (Fig. 1). These data have been integrated in 3D to help constrain the geometry and thickness of sediment depocentres in the region.