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Life and Death of WA’s Barriers Reefs during the Past 20 Myrs

The Western Australia’s North West Shelf (NWS) is a world-class gas province where up to 3 kilometres of Cenozoic “overburden” sedimentary rocks have accumulated above the hydrocarbon reservoirs. Geophysical and geological analysis of this overburden has revealed the presence of ancient “barriers reefs” that formed along the NWS margins several million years ago. Three distinct episodes of reef growth (and demise) have been recognized along a ~ 2000 km transect stretching from Exmouth to Darwin. Our research attempts to extend mapping of these old barrier reefs and investigate the paleo-oceanographic and paleo-tectonic controls at the origin of the repeated “growth” and “death” events.

This research is based on integrating regional petroleum exploration well data (petrophysical and geological) with extensive geophysical (seismic) datasets. Most datasets were acquired by the oil and gas industry and made available either by Geoscience Australia or through individual company donations.  Using state-of-the-art interpretation 3D seismic techniques (including innovative software and high-end computer workstation) has allowed the development of cost-effective workflows that enable very high-resolution 3D imaging of the ancient reefs along extensive areas. 3D reef architecture and its evolution through time and space allow a determination of their periods of growth, expansion and demise. These data are then integrated with ground-truth lithological, petrophysical and stratigraphic data, including biostratigraphy and isotope geochemistry.

Three distinct episodes of reef growth (and demise) have been recognized in the region: the middle Miocene (~ 15 to 11 Million years ago), the late Pliocene (~ 3 Million years ago), and the late Quaternary (~ last 1 Million year). The data collected suggest that the youngest episode of reef growth is at the origin of the modern Ningaloo fringing reef as well as the offshore reefs observed off the coast of the Pilbara (Rowley Shoals) the Kimberley (Scott Reef) and the Timor Sea (Ashmore and Sahul Shoals).

Carbonate reef systems are very sensitive to changes in oceanography (e.g., water temperature, salinity, and chemistry), climate and relative sea level changes (including tectonically induced changes). Therefore, these results have some important implications for reconstructing the paleo-environmental and paleo-tectonic history of Western Australia.

Moreover, the Cenozoic overburden strata overlie the petroleum-producing rocks and play an important role in the process of hydrocarbon maturation and expulsion. Additionally these ancient reef systems represent potential hazards for drilling activities in the region and are causing major problems for seismically imaging the hydrocarbon-bearing formations lying beneath them. This research is contributing to a multi-industry funded project within the Centre of Energy Geoscience at UWA.

Collaborator/s

  • IFREMER, the University of Tokyo, Aachen University
  • Brest, France
  • Tokyo, Japan
  • Aachen, Germany