What do fungi, fossils, opals and slime moulds all have in common?
Join us and find out at our first webinar of the new series!
Biogenic processes in opal formation
Tuesday 7th December 11am AEDT
John is a recently retired geologist with the Geological Survey of NSW, and his career involved fascinating work on fossil microbes in opals at Lightning Ridge, which may have played an important role in the opal formation process. Full abstract and bio below.
Webinars are free for Fungimap members (become a member here), or a donation is requested from non-members. Register here for the event, all registrations will be sent the recording afterwards. The event is held via Zoom, and Zoom links will be sent out on the day.
Biogenic Processes in opal formation at Lightning Ridge
Lightning Ridge produces about $50 million dollars worth of the world’s best quality black opal each year. The opal occurs in geode-like nobbies up to many centimetres in diameter and in seam-like structures in an Early Cretaceous volcaniclastic host rock. The host rock at Lightning Ridge is a finely laminated silty claystone that commonly has a high content of organic detritus. Evidence of bioturbation is common, as are opalised macrofossils. Recent work on seam and nobby-type opal has shown that microbe communities exist within both the host rock and opal. Layers of bacteria within nobbies and seam opal and evidence of fungi lining the cavity wall and within the nobby have been identified. All microbes are autochtonous and of the same age as the opal. The presence of microbes provides important constraints on the environment of formation of opal and they may also have played an important role in the opal formation process.The fossil evidence (microbes and macrofossils) reinforces the importance of Cretaceous palaeochannels (particularly palaeo-billabongs, swamps etc.) as sites for the production of silica-hydrosol for the formation of opal.
John joined the Geological Survey of NSW in 1981. In 1985 he completed an assessment of the opal resources at Lightning Ridge which resulted in the publication “Future prospects for Opal Mining in the Lightning Ridge Region.” This publication emphasised the importance of weathering and structural controls on opal deposits. Throughout much of his career in the Survey, John was involved in regional-scale mapping projects in the Lachlan Fold Belt in central New South Wales and bioregion assessment projects throughout the State. He also managed the successful Exploration NSW initiative and maintained an ongoing interest in opal genesis. In 2011 he published the results of work with Professor Hans Behr (Gottingen University) on fossil microbes in opal from Lightning Ridge. John recently retired from the position of Assistant Director Regional Mapping and Exploration Geoscience in the Geological Survey. John has a Master of Economic Geology degree, a Bachelor of Science (Geology), and a Graduate Diploma in Management.