Tuesday, March 27, 1:00pm

Mr. Hamish C. Young

PhD Candidate, NCPGG, The University of Adelaide

The Middle Cretaceous to Recent sequence stratigraphic evolution of the Exmouth-Barrow Margin, Western Australia


Five supersequences have been revealed by a regional sequence stratigraphic study conducted in the Albian (109 Ma) to Recent section of the Exmouth-Barrow passive margin. The interpretation utilises a new sequence stratigraphic model developed for mixed siliciclastic-carbonate lithofacies. A high degree of resolution is brought to the study by identification of thirty-seven regional sequence boundaries controlled by biostratigraphic, wireline and seismic data. Ditch cutting analysis, integrated into the new chronostratigraphic framework, provided detailed lithofacies maps.

The five supersequences, named the Gallic, Senonian, Palaeogene, Middle Neogene and Pliocene, are based upon regional lowstand, transgressive and highstand phases. The Gallic Supersequence (Late Tithonian-latest Cenomanian) represents a marine incursion of siliciclastic sediments coincident with the rifting and accelerated movement of India away from Australia. A Senonian Supersequence (latest Cenomanian-middle Maastrichtian) truncates the previous supersequence with incised canyons developed on the outer shelf. The evolution of the Senonian section corresponds to the Australian separation from Antarctica and the first appearance of carbonates.

The Palaeogene Supersequence (middle Maastrichtian-late Early Miocene) dominates much of the Tertiary and is identified by a basinward shift of facies following a Maastrichtian-Paleocene sea level fall. Enhanced subsidence on the outer shelf during the Eocene created a forced transgression with carbonate mudstone-siltstone deposition. A highstand during the Oligocene-Early Miocene formed the distinctive prograding carbonate shelf recognised throughout the North West Shelf. A Middle Neogene Supersequence (late Early Miocene-Early Pliocene) is identified by an erosive base and the development of a thin lowstand fan on the outer shelf. The supersequence is largely characterised by backstepping reefs following a Middle Miocene transgression. A Late Miocene eustatic stillstand restricted reef development to the inner shelf, generating coarse-grained carbonate progrades from highstand-shedding. The final Pliocene Supersequence (Pliocene-Recent) was initiated by a eustatic fall during the Early Pliocene and was followed by the development of a transgressive, aggrading shelf.

Biography of the Speaker

Hamish Young graduated with a BSc from the University of Adelaide in 1994. He completed his Honours degree in petroleum geology at the National Centre for Geology and Geophysics (NCPGG) in 1995. Hamish is currently in the final year of a PhD at the NCPGG, University of South Australia. His research topic is the Middle Cretaceous to Recent sequence stratigraphic evolution of the Exmouth-Barrow Margin. He is a member of PESA and AAPG.