The Capel and Faust Basins in Australia's remote eastern offshore frontier, 800 km east of Brisbane in 1000-3000 m of water, are being studied as part of the Australian Government's Energy Security Initiative. A variety of geophysical data has been obtained and efforts are currently focussed on integrated interpretation of 2D seismic reflection data, sonobuoy refraction data and marine potential-field data.
Negative residual gravity anomalies generally correlate with basins evident in the seismic reflection data. The anomalies highlight elongate, roughly N-S-trending or arcuate depocentres, with limited strike extent, that are best developed in the north and northwest of the survey area where increased crustal extension appears to have occurred. The 20-50 km separation between 2D seismic lines and the isolated nature of the basin depocentres complicates the process of linking structures between lines, but 3D mapping of faults and horizons is facilitated by the potential-field data. Instead of correlating with depocentres and basement highs, reduced-to-pole positive magnetic anomalies may reflect the distribution of volcanics and intrusives, variably evident as high-amplitude or low-frequency reflectors, and volcanic features at or near the seafloor.
Interpretation of the seismic reflection data suggests the presence of four main syn-rift megasequence packages (?Early Cretaceous-?Santonian) and several post-rift sag packages (?Early Campanian-Recent). Maximum unequivocal depocentre thickness is ~4s TWT. Forward and inverse modelling of the gravity and magnetic data in 3D is providing a means to characterise different basement terranes and to construct surfaces that represent the sequence boundaries within the depocentres.
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