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Unravelling the Source of the Cretaceous Ceduna Delta Systems using Detrital Zircon and Apatite Fission Track Analysis

MacDonald, Justin *1; Green, Paul F.2; Holford, Simon P.1; Duddy, Ian R.2; King, Rosalind C.3; Backe, Guillaume 1; Hillis, Richard 4
(1) Australian School of Petroleum, Adelaide, SA, Australia.
(2) Geotrack International Pty Ltd, Melbourne, VIC, Australia.
(3) School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA, Australia.
(4) Deep Exploration Technologies Cooperative Research Centre, Adelaide, SA, Australia.

The Ceduna Sub-basin is part of the Late Jurassic-Cenozoic Bight Basin located on the Southern Margin of Australia. The basin contains two fossilized deltas of Cenomanian and Campanian-Maastrichtian age. The source of the sediment for these extensive delta systems, comparable in size to the Niger Delta, has never been convincingly demonstrated.

To investigate the potential sediment sources of the Ceduna delta system we sampled 22 onshore and offshore wells and collected surface samples from the Eyre Peninsula for apatite fission track and detrital zircon analysis. The detrital zircon results demonstrate for the first time that a continent scale river system with a potential catchment area > 2,000,000 km2 was active throughout the Late Cretaceous, draining a significant portion of the central and eastern Australian continent into the Ceduna Sub-basin. In addition, initial apatite fission track results from the onshore Eyre Peninsula indicate a regionally extensive Late Cretaceous cooling and exhumation event across the region, with samples currently at surface levels having cooled from temperatures of > 50-80° C beginning between 100 and 60 Myr ago. Assuming an average geothermal gradient of 25° C/km, these data imply ~ 1-2 km of exhumation immediately adjacent to the delta systems. We demonstrate for the first time that Australia’s largest Late Cretaceous river system was shut off by proximal exhumation of the Gawler Craton and adjacent Flinders Ranges in the intra-Maastrichtian.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California