Postgraduate Profiles

Karl Bischoff

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Thesis: Sedimentology of microbialite-bearing coastal lake systems: example from Rottnest Island

Coastal lakes are a common feature of coastlines globally and may contain records of Holocene environmental change. Southwest WA hosts several such lake systems, including at Yalgorup National Park (e.g. Lake Clifton), Lake Walyungup and Lake Thetis. These lakes host microbial ecosystems that form domal carbonate structures called microbialites, including stromatolites (layered internal structure) and thrombolities (clotted internal structure). These are modern analogues of ancient examples which provide the first fossil evidence for life, from about 3.5 billion years ago. Studies of coastal lake systems typically focus on the depositional history of the lakes, often as it relates to the microbialites. Few studies exist on the modern sedimentology of coastal lake systems.

Rottnest Island contains six permanent and two ephemeral lakes on the western side of the island. While microbialites have been recognised on the island since the work of Playford (1977, 1988) no detailed work has been done on them. Similarly, the sedimentology of the lakes, both modern and recent, has received little attention.

Part (1) of this study will characterise the modern sedimentology of the lakes on Rottnest Island, with surface sediment samples and grainsize / component / and mineralogical (X-ray diffraction) analysis.

Part (2) of this study will establish the Holocene history of the lakes, through integration of stable isotope geochemistry and radiometric (14C, 210Pb) dating of microbial and associated facies.

Part (3) will characterise the microbialites forming in the and around the lakes, primarily through petrographic (light and scanning electron microscopy) and mineralogical (Energy dispersive spectroscopy, X-ray diffraction) analysis.

Why my research is important

This work will provide a baseline on the modern sedimentology of the Rottnest Island lakes, which can be used to reference future environmental change against.

New data on Holocene environmental change, including climate and sea level change will be produced.

Finally this study will provide the first detailed study of the microbialites forming around the lakes, including new data on their tolerance to environmental change.


Mar 2015

Nov 2018