Price, Colin1, Bradshaw, Marita2, Smith, Mike2
1Daramalan College P.O.Box 84 Dickson ACT 2602, Australia; 2National Rock Garden, Suite 8, Level 2,141 Peats Ferry Road, Hornsby, NSW 2077, Australia
Daramalan College provides Earth and Environmental Science (EES) students with direct exposure to the challenges of geological analysis by conducting practical field excursions. One excursion takes Year 11 students to a field northwest of Yass where there is a prominent exposure of a volcanic ash flow, an ignimbrite, which is overlain by a sequence of various sedimentary rocks. All of the units dip at about 20 degrees to the west, enabling students to walk across the rocks and so recognise and describe the layered sequence of sandstone, siltstone and limestone. The exposures are in creek beds and on gently undulating sheep pasture.
The students describe what they can see and then interpret the depositional environment for each rock unit, noting the progressive changes in that environment from the older rocks to the younger rocks. The sequence records a marine transgression, from volcanics on land to shallow water with coral patches, and then deep water as the shales were deposited by settling of fine particles. The students experience the reality of fieldwork, contrasting the poor to non-existent outcrop of the fine-grained units to the thrill of finding fossils in the limestones. The most common fossils are tabulate and rugose corals, crinoid ossicles and stromatoporoids that help bring alive a picture of what life was like in an ancient shallow tropical sea.
The rocks are part of the Silurian (Wenlock) section of the Yass Syncline in the Lachlan Foldbelt, from the Laidlaw Volcanics up into the Bowspring Limestone Member, Silverdale Formation, Hattons Corner Group. Radiometric dating of the volcanics and a biostratigraphic age from a conodont in the limestone indicates that the sequence the students investigate represents about 3 million years of earth history.
By examining the remains of a volcanic chain and an ancient seabed now found as rocks outcropping in the paddocks near Yass, the students have a rich educational experience and get a sense of the environmental changes that can occur over an interval of geological time. Science staff at Daramalan College are also enthusiastic about the capacity of the National Rock Garden to help teachers to engage with young people studying the rock cycle in Year 8, plate tectonics in Year 9 and those undertaking the Year 11/12 EES course. In one place they can view a great variety of lithologies from all over Australia, displayed in large and interesting rock specimens with polished areas that provide a window to view in detail igneous and metamorphic textures, sedimentary structures, and fossils.
Colin Price was an exploration geologist for 20 years before becoming an Earth and Environmental Science (EES) teacher at Daramalan College in Canberra. Colin received a Highly Commended award in the 2019 Prime Minister’s Prizes for Science, for promoting open-ended learning and for his work in EES education.