Our research develops our understanding of the evolution of Earth’s surface environments and sedimentary systems. To do this we integrate sedimentology, stratigraphy and geochemistry in both field and lab work. We are strong advocates for having a thorough understanding of paleoenvironmental conditions and diagenesis prior to any geochemical analysis. Our group uses sedimentology and component-specific geochemistry (trace metals, metal isotopes) of both marine and diagenetic carbonates and other chemical sediments to determine the chemical composition of ancient oceans. Additionally, we work on a range of other projects including paleo-climate history, reef evolution, changes in carbonate mineralogy, marine oxygenation, sediment-hosted ore deposits and the process of dolomitisation in Precambrian and Phanerozoic sequences.
If you are interested in Honours, Masters or PhD research in this area, please email us with your CV and your research interests at mww <at> unimelb.edu.au or hood.a <at> unimelb.edu.au
Precambrian-Phanerozoic sediments and oxygenation
Carbonate and other chemical sediments play a key role in unlocking the secrets of the early Earth. Precambrian carbonates of North America, Australia and Africa contain newly discovered, primary marine carbonate precipitates that can reveal the redox chemistry of seawater over time. The development of these marine cements as a reliable proxy for ocean oxygenation forms part of our research at the University of Melbourne. We hope to better constrain the redox state and associated chemical depth gradients of Precambrian and Phanerozoic seawater by geochemical and sedimentological examination of well-preserved marine cements. Geochemical analysis includes Laser Ablation- ICPMS of these components, and the application of several different isotope systems (U, Cr, Fe, Sr, C, O). Using the Ce anomaly redox proxy in well-preserved marine cements, we showed that the Earth’s oceans only approached appreciable oxygen concentrations during the Devonian, associated with the rise of land plants. In another project we are using petrographic analysis to show basic variations in primary carbonate mineralogy through the Precambrian, suggesting overall high marine Mg/Ca during the Precambrian “dolomite-aragonite seas”. Work by Max Lechte on Sturtian ironstones has demonstrated that Cryogenian ironstones form due to the mixing of oxygenated glacial fluids with ferruginous seawater, providing an important record of marine conditions during one of the most severe ice ages in Earth’s history. Ashleigh Hood has also worked on silicification in Ediacaran sandstones. All of these sediments are beginning to reveal just how unusual the oceans were during the Precambrian, and highlight the complexity of the evolution of the ocean-atmosphere through Earth’s history.
Reefs and reef ecosystems
Malcolm Wallace has worked on reef systems since his PhD on the Devonian reefs of the Canning Basin, Western Australia. Recently Malcolm and his students have been documenting the sedimentology, stratigraphy and paleo-environmental conditions of Neoproterozoic reef systems. The interglacial Cryogenian reefs of the Flinders Ranges are a topic of ongoing research for the Sedimentology Group. These reefs host unusual deep-water frameworks with ecosystems dominated by low-light, low-oxygen conditions and reef organisms of an unknown affinity. The chambered biota which make up these frameworks have now been documented in Neoproterozoic stratigraphy of Namibia, China and Canada. Ashleigh Hood and Malcolm Wallace are also working on characterising these Neoproterozoic reefs of Namibia, and collaborative work with Galen Halverson at McGill is being undertaken to look at Cryogenian reefs of the Yukon.
Diagenesis and dolomite
Ashleigh Hood’s favourite mineral is dolomite. Her and Malcolm Wallace have been working together to look at different aspects of the process of dolomite cementation and dolomitisation during marine, early and late diagenesis. Malcolm has been studying dolomite and dolomitisation since his PhD, and has recently been working on the formation of zebra dolomite and diagenetic conditions promoting dolomitisation. Ashleigh’s PhD work documented primary marine dolomite cements from the Neoproterozoic. Over the last few years, the group has been looking at the effects of different types of diagenesis on geochemical paleo-redox proxies to the creation of promote robust paleo-environmental records.
Terrestrial and marine sediments preserve important records of past climate change on Earth. The Sedimentology Group studies Earth’s climate history from Neoproterozoic ice ages to the Cenozoic floral history of south eastern Australia. We are currently working on Cryogenian glacial sediments from the Flinders Ranges which preserve a record of Earth’s most extreme glaciations. Carbonates which bracket, and occur within these glacial sediments, can be used to help understand how the Earth escaped global glaciation. There is ongoing work on the Cenozoic climate history of Australia. Sandra McLaren and Malcolm Wallace documented the onset of aridity in Australia as step-wise and significantly earlier than previously suggested using stratigraphic and sedimentological techniques on palaeo megalake Bungunnia. Vera Korasidis’ PhD research on the palynology and sedimentology of Victoria’s brown coals has revealed a comprehensive record of paleo-climate conditions from the Eocene to Miocene.
Sediment-hosted ore deposits
Through geological history Earth’s sedimentary systems have hosted many different economically-valuable metal deposits. We are interested in exploring the link between diagenesis, mineralisation and Earth surface conditions through the Precambrian and Phanerozoic. Malcolm Wallace has worked on carbonate and shale hosted Pb-Zn mineralisation throughout his career in Australia and Ireland. We have also looked at sediment-hosted copper deposits in Asia and Africa. Our current research look at the distribution of sedimentary ore deposits through time and the links to Earth’s surface oxygenation.
What can the co-evolution of life and environmental conditions on Earth tell us about the possibility for life on other planets? Earth’s early ocean-atmosphere conditions may inform us as to the the limits of habitability on our planet, but can also be used to understand surface conditions on other planets that might be signs of life. With Noah Planavsky at Yale, we have been working on methods to refine the use of paleo-redox and paleo-environmental proxies in order to develop an ecosystem-specific perspective within Earth’s broader evolution. Ashleigh has also been working with Sean McMahon at Edinburgh on the ‘deep biosphere’ or life in the sub-surface, with implications for the search for life on Mars. Additionally, Ashleigh is excited to collaborate with Ann Ollila on new research calibrating a laser luminescence tool on a Mars rover that is to be sent off in the next few years (fingers crossed the NASA grant comes through!)
The Sedimentology Group works on basin-scale projects with implications for basin evolution, environmental change and ore deposit formation. Currently Malcolm and Liz Mahon are working on a seismic and sedimentological study of the Gippsland Basin, from small-scale environmental conditions to basin-wide subsidence and uplift. Jackson McCaffrey is working with Malcolm and Stephen Gallagher on Miocene reefs of the North West Shelf which were as extensive as the current Great Barrier Reef during one of the Cenozoic’s peak climatic warm periods.