Publication Name: Eastern Australian Basins Symposium 2001
Authors: A.S. Leach and M.W. Wallace
Date Published: November 2001
Number of Pages: 32
Reference Type: Magazine Article
Abstract:Well preserved submarine canyon systems are present in the Oligocene-Miocene cool water carbonates of the Heytesbury Group and the Pliocene-Recent Whalers Bluff Formation of the offshore Otway Basin. From seismic profiles, two morphologically distinct submarine canyon types are present in the cool water carbonates:
I. Miocene canyon systems; and
2. Pliocene to Recent canyon systems.
Miocene canyon systems consist of long-lived laterally migrating canyons. These systems are found on the eastern side of the offshore Otway Basin, with two major canyons systems being present. The Miocene canyons migrate laterally towards the west, with each progressively younger canyon within the system being located slightly to the west of the underlying canyon. The fill within each canyon similarly pro grades towards the west.
Pliocene to Recent canyons have been seismically mapped offshore in the vicinity of Portland. The fill within Pliocene to Recent canyons is generally symmetric or slightly eastward-oriented. The oldest Pliocene canyons are visible on magnetic images of the shelf, indicating a magnetic (probably clastic) component in the canyon-fill. Modern canyons are also found in the vicinity of Portland around the slope. The larger modern canyons occupy positions immediately seaward of their Pliocene counterparts. There is no evidence that these canyons overly
transfer faults, as previously suggested.
The change in canyon migration direction, from westerly during the Miocene to easterly during the Pliocene, is probably the result of a major oceanographic change, occurring around the Mio-Pliocene boundary. A strong westerly-directed current appears to have dominated the region in the Miocene, while a weak easterly-directed current appears to have existed during the Pliocene to Recent. It is likely that Late Miocene-Early Pliocene tectonics also affected the development of the canyons, with distinctly different canyon regimes being formed before and after uplift.