Offshore Northern Perth Basin 2D and 3D Models of Depth to Magnetic Basement

During 2009-11 Geoscience Australia completed a petroleum prospectivity study of the offshore northern Perth Basin as part of the Australian Government's Offshore Energy Security Program. A significant component of the program was the acquisition of a regional 2D reflection seismic and potential field survey GA-310 in 2008/09, which has aided in furthering the understanding of basement within the northern Perth Basin. Geologic basement in the northern Perth Basin, defined here to be Precambrian and older, is deep and generally not resolved in the reflection seismic data. However the GA-310 magnetic anomaly data combined with Geoscience Australia's magnetic ship-track database and magnetic anomaly grid allowed an assessment of depth to magnetic sources, and estimation of sediment thickness, providing new insight into basement depth and trends. New magnetic susceptibility measurements taken from core of offshore wells of the northern Perth Basin, seismic interpretation and depth to magnetic source estimates using the magnetic spectral method have been used to constrain 2.5D magnetic forward models.
These magnetic models indicate that intrusion of the deepest sediments by high-susceptibility bodies is probable. The reflection seismic evidence for these bodies is not clear, though in some cases they may be associated with faults and structural highs. Where the modelled bodies penetrate the sediments they are mostly below or within the Permian strata. A moderate positive magnetic anomaly along the Turtle Dove Ridge is modelled in 2D by massive bodies whose tops are 5-15 km below sea floor. A depth to magnetic basement map highlights sub-basins and structural highs within the northern Perth Basin, and is shown to be a good first order approximation of sediment thickness and basin geometry. For instance maximum sediment thicknesses of the Abrolhos, Zeewyck and Houtman sub-basins are shown to be 10, 13.5 and 12 km respectively.

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