Sedimentary basins reconnaissance using the magnetic Tilt-Depth method

We compute the depth to the top of magnetic basement using the Tilt-Depth method from the best available magnetic anomaly grids covering the continental USA and Australia. For the USA, the Tilt-Depth estimates were compared with sediment thicknesses basedondrilling data and showa correlation of 0.86between the datasets. If randomdatawere used then the correlation value goes to virtually zero. There is little to no lateral offset of the depth of basinal features although there is a tendency for theTilt-Depth results to be slightly shallower than the drill depths.We also applied theTilt-Depthmethod to a local-scale, relatively high-resolution aeromagnetic survey over the Olympic Peninsula ofWashington State. The Tilt-Depth method successfully identified a variety of important tectonic elements known from geological mapping. Of particular interest, the Tilt-Depth method illuminated deep (3 km) contacts within the non-magnetic sedimentary core of the Olympic Mountains, where magnetic anomalies are subdued and low in amplitude. For Australia, the Tilt-Depth estimates also give a good correlation with known areas of shallow basement and sedimentary basins. Our estimates of basement depth are not restricted to regional analysis but work equally well at the micro scale (basin scale) with depth estimates agreeing well with drill hole and seismic data.We focus on the eastern Officer Basin as an example of basin scale studies and find a good level of agreement between previously-derived basin models. However, our study potentially reveals depocentres not previously mappeddue to the sparsedistributionofwell data.This example thus shows thepotential additional advantageof themethod in geological interpretation. The success of this study suggests that the Tilt-Depth method is useful in estimating the depth to