Snowball Earth - glaciation at Bimbowrie
Thursday August 5th 2021
Mawson Lecture Theatre
Department of Earth Sciences
North Terrace Campus
University of Adelaide
Adjunct A/Prof. Colin Conor
University of South Australia
Glacial conditions were such during Sturtian geological times that they gave rise to the concept of 'Snowball Earth', a period of successive worldwide freezing. The moving ice of ice sheets and glaciers is an aggressive eroder, gouging the land's surface and depositing the debris in massive chaotic accumulations. Such deposits are known on nearly all the current continents, though at the time these were grouped as the supercontinent of Rodinia. A peculiarity of glaciers is that they transport rock debris great distances from the source of erosion, in places leaving large fragments of rock on totally different rock substrate, for example granite boulders on fossiliferous limestone, these anomalous rocks are known as 'erratics'. Apart from being a beautiful bit of South Australia, the Bimbowrie Conservation Reserve preserves an ancient rift valley of Sturtian age, which is filled with glacially derived debris. Included are great blocks of granite that a were first recorded in the 1958 SA Geological Olary map. The geological name for these blocks is megaclasts, and there are at least ten exposed greater in size than 100m. The largest is 1.25 km in length, and in a recent AJES publication, Wolfgang Preiss and I have suggested that it is the largest of its type known on Earth.
Colin became interested in the ancient glacial deposits of the Neoproterozoic while involved in a student mapping project in the Scottish Highlands. Then he had no idea of living near the similar rocks of South Australia where he started work in 1969. Colin's first degree in geology was from Leicester University, and this was followed many years later by an MSc from Adelaide University on the geology of the Eastern Musgrave Ranges of Central Australia. Colin had two spells with the SA Geological Survey obtaining experience in geological mapping, metal exploration, industrial minerals and engineering geology. Additionally Colin has 15 years of mine geology and mineral exploration which included the early years of underground development of Olympic Dam. Since retiring in 2010 Colin has worked with Barry Cooper and the GSA Field Guide Subcommittee, with Cynthia Pyle completing a guide on the ancient glacials of Sturt Gorge. Recently also, Colin and Wolfgang Preiss have published a description of the glacial megaclasts of Bimbowrie Conservation Reserve.
If you wish to attend it is essential to arrive early to sign in due to COVID. Be prepared to wear a face mask if regulations require it.