Gemma Roberts, BSc (Hons)

PhD Candidate

Madsen Building (F09), Room 412
Phone: + 61 2 9036 6545
Fax: + 61 2 9351 2442
Email:

Supervisor
Associate Professor Patrice Rey

Research

PhD: Hyperspectral mapping of opal-bearing mineralogical assemblages in the Great Artesian Basin and comparison to Mars

The Great Artesian Basin (GAB), located in central Australia, is one of the largest intra-continental basins on Earth and host of precious sedimentary opal deposits. These deposits are found almost nowhere else on Earth and their formation has yet to be explained.

The Earthbyte Research Group at Sydney University is currently investigating a new model that proposes the formation of opal via acidic oxidative weathering during the regression of the epicontinental sea that flooded central Australia between 125 and 95 million years ago. Uplift, deep weathering and erosion of strongly reduced Lower Cretaceous shallow marine to fluviatile rocks was continuous between 95 and 65 million years ago, and the opal that formed at the surface within that time was progressively eroded away until uplift ceased 65 million years ago. The near-surface opal-bearing redox front was then preserved when Cainozoic sediments were deposited. Acidic oxidative weathering is the process that is also suggested to explain the formation of opal-bearing assemblages on Mars, thereby suggesting that the GAB could be one of the best terrestrial analogues for the Martian surface processes.

Hyperspectral satellite images, in particular Advanced Spaceborne Thermal Emission and Reflection Radiometric (ASTER) images, are widely available on the internet. Spectral emissions across the GAB will be analysed to map:

  • the distribution of deep weathering and its various mineralogical assemblages to constrain changes in pH and oxidation-reduction conditions
  • the unconformity between Tertiary sedimentary rocks and the Lower-Cretaceous formations
  • the preserved opalised redox front beneath this unconformity

Maps showing the distribution of opal-bearing mineralogical assemblages in the GAB will be compared to that of Mars.
Because we can provide the opal mining industry with maps showing where precious opal can still be found and where it has been eroded away, this project has the potential to revive opal mining in Central Australia. This project will also establish the Great Artesian Basin as one of the best terrestrial analogues for Martian surface processes, and a possible natural laboratory for the search of extra-terrestrial life in our solar system.