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Geological Society of Australia WA Division talk presented by John Bunting, J A Bunting & Associates
Synopsis
Preparing a field guide to the SW Capes region of WA to help teachers of the senior-school Earth and Environmental Science course provided a wonderful opportunity to explore, understand(!) and describe the geology of this incredible area. The Field Guide, which was published in May this year by Earth Science Western Australia (ESWA), describes in detail seven localities between Cape Naturaliste and Cape Leeuwin, with brief descriptions of several others. Unravelling and understanding the geology of the area has proved challenging. Equally challenging has been to describe very complicated rocks in terms that teachers, many of whom are not geologists, and the general public will understand, but will still be of interest to geologists.
The rocks are certainly complex. The high-temperature metamorphic rocks, derived from various intrusive phases ranging in age from Mesoproterozoic (1100 Ma) to early Cambrian (520 Ma), contain evidence for multiple deformation, partial melting and retrogression. The Quaternary limestone units are equally complex, with evidence for multiple changes in sea level related to global variations caused by glacial/interglacial cycles. Of particular interest are the warm-water corals at Foul Bay, up to 3 metres above present sea level. North of Cape Leeuwin recent tufa deposits, derived from microbial activity in freshwater springs, contain stromatolitic layering, and are still forming as flowstones or rimstone pools.
Add into the mix great examples of dykes, basement faults, folds, unconformities, cross bedding, rhizoliths, caves/dolines, stalactites, megafauna, ilmenite-garnet sand, various coastal processes, and more, all accompanied by superb coastal scenery that is constantly changing. This is great for teaching purposes, but also of huge interest to the general public and geologists.
The field work also brought up several geological conundrums that will be addressed (not necessarily answered) in the talk, such as the relationship of the Leeuwin Inlier to the rest of Australia, the relationship of the limestones of the region to the Quaternary sequence on the Swan Coastal Plain, and just what is the Tamala Limestone?
About the speaker
After a 40+ year career in geology and mineral exploration (mainly in WA) John is now semi-retired. His work history includes periods with the Geological Survey of Western Australia, several large and small mining/exploration companies, and his own consulting company. He has published research on meteorite impact structures (including the discovery of the Yarrabubba structure) and recently helped to organize and run a field excursion to various meteorite impact sites around WA for the Meteoritical Society. In a largely voluntary role with Earth Science WA he has written field guides to the geology of the Perth region (2011) and the Capes region of southwest WA (2014) for teachers of the upper-school Earth and Environmental Science course.
