Print this pageDepositional Environments on the East Coast of Australia: More Bumps along the Sequence Stratigraphic Road
LECKIE, DALE A., LEE F. KRYSTINIK, and RON BOYD
The wave-dominated east coast of Australia provides a superb laboratory to test the largely conceptual and interpretive models of sequence stratigraphy. We will show examples to demonstrate this. For example, into which systems tract should estuarine valley fill occur. The model indicates that fill should occur in the late lowstand to transgressive systems tract. But, globally, sea-level is now in a highstand situation and the Australian east coast contains numerous incised valleys currently being infilled with estuarine deposits. This is a sediment supply issue; valleys which were filled during the transgression have a larger catchment area.
The lower reaches of many of these estuaries are filled with the deposits of long-shore sourced, reservoir-quality flood-tidal sands extending inland for 5 to 10 km. Here a continuing transgression will fill the valley with marine sand.
Elsewhere, research carried out by coastal geomorphologists has demonstrated the complexity inherent in the progradation of wave-dominated coastlines. At Forster-Tuncurry, NSW, sea-level fluctions over the past 260,000 years have juxtaposed shoreface and shelf sand bodies, into a complex mosaic which forms a nearly continuous sand body ranging from +4 to -50 m, yet is full of subtle but significant unconformities and flooding surfaces. The sea level history would be extremely difficult, if not impossible to unravel and predict in most comparable hydrocarbon-bearing ancient analogs.