Subsurface Sequence Stratigraphy of Devonian Carbonates, Canning Basin, Western Australia

SOUTHGATE, PETER N., JIM JACKSON, JOHN M. KENNARD, PHIL E. O'BRIEN, VIRGINIA L. PASSMORE, and JOHN F. LINDSAY, Bureau of Mineral Resources, Canberra, Australia, and ANN E. HOLMES and NICHOLAS CHRISTIE-BLICK, Lamont-Doherty Geological Observatory, Palisades, NY

The Canning basin of Western Australia is best known for its Devonian reef complexes. In 1990 the Australian Bureau of Mineral Resources (BMR) began a sequence stratigraphic study of key parts of the basin. This work integrates industry seismic and well data with two deep-crustal, regional seismic lines acquired by BMR in 1988. Initial work on the Lennard Shelf and adjacent Fitzroy trough has established a new sequence stratigraphy.

At the margin of the Fitzroy trough, the most prominent features on seismic sections are alternating wedge-shaped and tabular bodies up to 150 m and 50 m thick, respectively. Internal reflections in the wedge-shaped bodies show downlap toward the basin and onlap toward the platform margin. On strike lines these wedges exhibit complex lensoidal geometries. Drillcore indicates that the wedges comprise basement-derived conglomerates with a sandy calcareous matrix. These geometries and lithologies imply deposition during relative sea-level lowstands and preferential accumulation of clastic sediments in the trough. The intervening tabular intervals lack distinctive internal reflections and are interpreted as transgressive and highstand carbonate deposits. The lowstand wedges pinch out at o below the platform margin. The tabular units pass laterally into obliquely prograding units on the Lennard Shelf comprising reef and platform carbonates interpreted as highstand deposits.

Seismic and well data suggest five Late Devonian sequences. The wedges and oblique prograding units are thickest and most easily recognized in the upper three sequences (Late Frasnian-Famennian?). The underlying thinner sequences probably correlate with the classic back-stepping Frasnian reefs identified in outcrop by Playford. Recognition of lowstand deposits in the Devonian reef complexes represent a new hydrocarbon exploration play.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)