Postgraduate Profiles

Vanessa Markwitz

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Thesis: Detrital fingerprinting of sedimentary source to sink relationships: case studies from Palaeozoic and modern deposits in Western Australia

Determining the source of sediments can be fundamental for palaeogeography, basin evolution, hydrocarbon reservoir characterisation and mineral exploration. Whereas a common approach to study provenance is through detrital zircon age spectra, the multi-cycle nature of zircon can present ambiguities in detrital studies, and age distribution patterns in sedimentary rocks can contain inherited components. An underlying question often posed is: does the zircon heavy mineral cargo reflect material eroded directly from exposed metamorphic rocks and carried into the basin or is it derived from a pre-existing sedimentary rock that was itself formed in a previous cycle of erosion and deposition? Consequently, zircon age data alone may not be sufficient to uncover provenance where similar-aged host rocks are widespread.

The initial study will focus on the Palaeozoic Tumblagooda Sandstone and recent stream sediments of the Murchison River channel in Western Australia. It will refine the methodology of provenance studies by also including feldspar, rutile, titanite and garnet, which are more likely to be first cycle indicator minerals and may thus provide an important link to likely sources source. To facilitate a more ‘unique source’ identification, other isotopic and chemical tracers will also be used, including oxygen isotope ratios in monazite and the determination of trace element abundances in garnets and rutile by laser ablation ICPMS and SHRIMP. In addition, U-Th/He-dating of apatites and zircon will be used to constrain cooling and exhumation history of the basement and provide insight into sediment dispersal timing.

The contemporary stream network will be analysed to determine likely past source regions, changes in grain shapes/sizes of heavy minerals, sedimentary composition, and age distribution along present transport pathways. These findings will be used as a possible partial analogue for past events. The methodology developed will lead to an improved characterisation of sedimentary provenance, transport pathways and residence times of detrital sediments and provide greater insight on the occurrence and nature of likely controls on sediment yield processes required to account for sedimentary deposition.

Why my research is important

Refining provenance studies is of fundamental importance in basin studies and the objective of determining source-sink relationships and their significance has implications for interpreting the detrital record. This study will extend the knowledge of multi-signature dating on heavy minerals to help determining unique sources of basin fill. This perspective broadens the analytical techniques and refines the methodology of provenance studies. Various heavy minerals will be studied to determine isotopic ages, trace element compositions analysed, exhumation ages for basement collected, and changes in detrital records documented to fingerprint mineral assemblages to their sources. Foremost is addressing the immediate question: does the detrital record preserve information on source changes through time or is it just an artefact of preservation?

Funding

Feb 2014

Feb 2017

Supervisors