Project Title: 

Novel isotope techniques to explore Centralian Superbasin:

Coupled K-Ca and Rb-Sr dating and Ca isotope stratigraphy

Project Description and Research Aims: 

Recent advances in analytical instrumentation for geoscience applications, such as the advent of collision cell mass spectrometry coupled with laser ablation systems, have provided new research opportunities but also raised new challenges in basin exploration and earth system evolution studies. For example, in-situ Rb-Sr dating of sediments and sedimentary rocks (by targeting authigenic phases such as illite, glauconite, feldspar, etc) can provide large and rapidly generated geochronological datasets and ‘ages’. However, the geological significance and fidelity of these is often uncertain. Do these ‘ages’ reflect specific geological events or processes (e.g., early marine authigenesis associated with sediment deposition) or rather some later burial and post-depositional phenomena (linked to fluid flow or thermal resetting) thus generating spurious ‘ages’ or mixing trends between primary and secondary phases rather than true isochrons?

To resolve these issues and challenges this project will explore a coupled K-Ca and Rb-Sr dating approach which will be applied to sedimentary archives of the Centralian Super basin (Officer, Amadeus/Warburton and Georgina Basins) in Australia, primarily targeting illite-rich shales and glauconite-rich sandstones and carbonates, as well as celadonite phases hosted in synsedimentary volcanics. It is anticipated that such coupled K-Ca and Rb-Sr dating will provide a robust way to assess and validate the preservation of geologically valid and meaningful ages and thus significant events occurring in the Centralian Superbasin (i.e., yielding ‘concordant’ K-Ca and Rb-Sr ages, similar to well-established U-Pb approach). Such concordant ages would then reflect either the timing of (i) primary sediment deposition or alternatively (ii) secondary but complete diagenetic resetting of the above geochronometers due to some later stage geological event. In contrast, ‘discordant’ ages will point to more complex and protracted burial or diagenetic histories of studied samples linked to their different fluid alteration/mobilisation of radiogenic products (i.e., ⁴⁰Ca and ⁸⁷Rb isotopes) or closure temperatures of these geochemically similar negative beta decay geochronometers.

Importantly, this project will take advantage of new analytical developments allowing high-precision isotope measurements of radiogenic ⁴⁰Ca anomalies in small sample sizes (e.g., few glauconite grains, illite separates, etc) via a TIMS Phoenix Instrument equipped with ATONA signal amplification system (developed by IsotopX), coupled with a direct measurement of ⁴⁰K/⁴⁴Ca ratios via single collector ICP-MS/MS with collision cell (Agilent 8900) at the University of Adelaide. These approaches will be complemented by further testing of both solution- and laser-based K-Ca and Rb-Sr dating via multi-collector collision cell (CC)-ICP-MS instruments available at collaborative institutions. Finally, the above analytical platforms (TIMS-ATONA, and MC-CC-ICP-MS) will be tested and employed for novel Ca isotope chemostratigraphy of Neoproterozoic and Cambrian carbonates (calcite/dolomite) and evaporites (anhydrite) deposited in the Centralian Superbasin for paleo-environmental reconstructions and basin-correlation purposes. The generated datasets will be incorporated into the sedimentological and sequence stratigraphy framework to gain a more robust understanding of the studied depositional system and the Earth system evolution.

Applicant requirements

• Must have a BSc Hons (first class) or Masters (by research) in geoscience (ideally related to geochemistry, geochronology, sedimentary geology) by the time of appointment.
• The candidate requires the ability to work both independently and with a broad range of people from diverse backgrounds, as well as evidence of strong oral and written scientific English language competencies.
• The candidate requires a demonstrated commitment to publish results in scientific journals. Evidence of research experience, academic awards/publications/presentations at conferences is desirable.