ABSTRACT: New Perspectives on Ordovician Sequences in the Canning Basin, Western Australia

HOLMES, A. E., and Nicholas CHRISTIE-BLICK, Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY

Sequence stratigraphy has not yet been widely applied in Paleozoic successions. As part of an ongoing effort in the stratigraphic analysis of seismic reflection profiles, borehole data and core from the Canning basin, Western Australia, we report new results from strata of Early and Middle Ordovician age, the oldest preserved Paleozoic rocks in the basin. The Ordovician succession consists of as much as 1000 m of mixed predominantly fine terrigenous and carbonate rocks, deposited in shallow marine to marginal marine environments. The best record of this geology is preserved in the subsurface in the Willara subbasin and along the Broome platform, a horst that developed for the most part during late Paleozoic time. We have also examined briefly limited outcrop along the northern margin f the basin. Sequence boundaries are tentatively identified within this succession at two horizons in the Nambeet Formation (Tremadoc to Arenig), in the Willara Formation (Arenig), in the Goldwyer Formation (Llanvirn), in the uppermost Goldwyer or Nita formations (upper Llanvirn to Llandeilo), and at the contact with evaporite-bearing rocks of the overlying Carribuddy Formation (Late Silurian?). Evidence supporting these interpretations consists of the documentation of onlap and erosional truncation in seismic reflection profiles and the analysis of parasequence stacking patterns in well logs. Current research is aimed at testing the sequence stratigraphic interpretation with reference to available core. An important application of the work is in the elucidation of the early evolution of the Canning basin, prior to two main phases of lithospheric extension during Late Silurian(?) to Middle Devonian and Late Carboniferous to Early Permian time.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)