Control of Sedimentary and Biofacies by Ocean Currents: The Mixed Siliclastic-Carbonate Northern New South Wales Continental Shelf, Australia

Claudia J. Schroder-Adams¹, Ron Boyd², and Jason Roberts^3
1 Carleton University, Ottawa, ON
² University of Newcastle, Callaghan, Australia
³ University of Newcastle, Newcastle, NSW, Australia

The narrow Eastern Australian continental shelf of northern New South Wales provides an important example of a wave and current-dominated shelf with mixed clastic and carbonate sediments in a low accommodation setting. Sediment distribution and biofacies are determined by: a) sea level oscillations, b) the strong, warm East Australia Current, and c) year-round, high-energy waves. These processes prevent fine-grained sediments from depositing in less than 35 m water depth on the shelf, but coastal headlands and a relatively large sediment input from the Clarence River allows for some fine sediments to settle near Yamba.

Five facies associations were identified including inner shelf siliclastic sands, mid shelf clastic sands, outer shelf and upper slope temperate carbonate sands and gravels, and estuarine sediments. Quaternary temperate carbonate outer shelf sediments are rich in calcareous foraminiferal abundance and species diversity supported by warm Coral Sea water and reduced storm energy. Paleoestuaries that developed on the inner to mid shelf during the last interglacial period and that were subsequently filled during early transgression contain assemblages that responded to complex ecological conditions as seen in modern estuaries in the same region. Inner to mid shelf sediments seaward of the Clarence River contain a higher mud content and distinct biofacies compared to the cleanly swept inner to mid shelf sands elsewhere. Results show that paleocurrent circulation patterns have to be taken into account when interpreting ancient facies and benthic biofacies.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005