| Abstrakt: |
The Jurassic-Cretaceous Eromanga Basin in eastern Australia is a relatively undisturbed sedimentary sequence covering the Devonian Quilpie Trough and the Early Palaeozoic Canaway Ridge and Cheepie Shelf. Seismic refraction recording across these three features, with additional reflection, gravity, and well information, has been used to determine the velocity structure to a depth of 10 km. The thickness of the Eromanga Basin sequence along the traverse varies between 1.1 and 1.4 km, with P-wave velocities ranging from 2.0 to 3.8 km/s. The maximum thickness of the underlying Quilpie Trough is about 3.8 km, but the base of the trough is hard to define; the velocities in this Devonian sequence range from 4.0 to 5.0–5.5 km/s. Two small bodies with a velocity of 4.0–4.5 km/s occur immediately below the Eromanga Basin sediments on the Canaway Ridge and the Cheepie Shelf; they may be remnants of Devonian sediments on an erosion surface. The velocities within the ?Ordovician basement are less below the Canaway Ridge than under the Cheepie Shelf and Quilpie Trough. They reach 6.0 km/s at 7 km depth below the ridge, at 4 km depth under the shelf, and at an intermediate depth under the trough. From gravity modelling, the density of the basement to the Quilpie Trough increases at a depth of about 7 km; this may be related to volcanics found in the basement further north. The Canaway Ridge has a lower density than the Cheepie Shelf or the basement of the Quilpie Trough; relative vertical movement between these three features may, in part, be related to these density differences. |
