Abstract

An interpretation of geologic structure at King Sound in the Canning Basin was completed using airborne gravity gradient, magnetic, and seismic data. During the Late Devonian and Mississippian periods, the elevated part of the basement in the north was rimmed by carbonate reefs and redeposited carbonate debris, whereas in the south, siliciclastic submarine fans and turbidites were deposited along the margin of the basement in a deep-marine environment.

Three principal lithologic units were identified from the vertical gravity gradient (GDD) in the basin: (1) the Fairfield Group carbonates of high density are interpreted to be the source of prominent positive gravity anomalies; (2) forereef debris and carbonate clastics reworked from carbonates higher up the slope or from the carbonate platform are interpreted to be the source of medium-density responses; and (3) turbidites, debris flows, and associated clastic basinal sequences of low density are interpreted to be the source of prominent negative gravity anomalies. Depth slices of GDD indicate the channelized nature of turbidite flows. In the lower section of the basin, intrasedimentary intrusives were identified from magnetic, GDD, seismic, and well data. Depth to magnetic basement calculation indicates that the surface of the Archean to Paleoproterozoic basement ranges from 3200 to 130 m (10,499–427 ft) below sea level. The northwest- and northeast-oriented south-dipping faults cut the basement and propagate upward into the sediments.

A three-dimensional geologic model constructed for King Sound satisfies all known geologic constraints and is consistent with the gravity, magnetic, seismic, and well data.

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