Unfortunately we are unable to offer face to face field trips but are developing a range of virtual field trips. The virtual field trips will focus on Tasmania’s unique geology and landforms as listed below.
Eastern Tasmania is usually considered to have a basement terrane with a quite separate origin to western Tasmania. It is often correlated with the Melbourne zone of the Lachlan Fold Belt in Victoria, although this is still arguable. The basement comprises turbidite-hosted siliceous sediments of the Mathinna Supergroup, of Ordovician to early Devonian age. These are intruded by numerous Late Devonian – Early Carboniferous granitic batholiths and related igneous rocks. These intrusions are locally accompanied by Sn-W mineralisation of varying styles. There are also numerous small to medium sized gold deposits of mesothermal/turbidite-hosted vein style, similar to the Victorian goldfields. These rocks are locally covered by the Parmeener supergroup sediments of Late Carboniferous – Triassic age, thick Jurassic dolerite intrusions, and Cenozoic basalts and sediments; the Cenozoic sediments locally have rich alluvial tin and/or gold deposits. To the west this eastern Tasmania terrane is juxtaposed with the Western Tasmania terrane (Proterozoic to Late Devonian), in a structure known as the Tamar fracture zone, probably active from the Cambrian to the Cenozoic. Some of this structure can be seen in the Beaconsfield area, where there is a melange of Cambrian ultramafics, with diverse slivers of Precambrian to possibly Siluro-Devonian sediments. This site also includes the famous Beaconsfield gold mine. The trip will see most of the above-mentioned formations and mineralisation types in some very spectacular coastal and mountain settings.
Tasman Peninsula – Land & Sea
South-eastern Tasmania is largely underlain by horizontal to gently dipping beds of sandstone, siltstone, limestome and coal. These rocks, dating from the Permian and Triassic were later intruded by bodies of Jurassic dolerite (183 million years ago) which formed sheets between layers of sedimentary rocks. This was a widespread phenomena covering over one third of Tasmania, and possibly more in the past. This intrusion also affected Antarctica, Argentina and South Africa. This has been called the Karoo-Ferrar large igneous province. Three to five million cubic kilometres of magma were intruded overall. The magma cooled to form columnar dolerite, which have been eroded to form sea stacks all around the coastline of Tasman Peninsula.
As sea levels fell during the glacial stages od the Pleistocene (125,000 – 20,000 years ago) rivers cut valleys to levels below the current sea level. The melting of ice sheets, about 10,000 years ago, resulted in a rise in sea level, forming the current drowned coastline features evident over much of southeast Tasmania.
Cygnet Alkaline Complex
Numerous small bodies of enigmatic suite of Cretaceous syenitic rocks intrude a Permo-Carboniferous shelf sequence and Jurassic dolerite in one of Tasmania’s most picturesque coastal areas. They range from silica-saturated to moderately under-saturated compositions, with a diverse mineralogy, some spectacular textures and are associated with sub-economic gold mineralisation.
Kunanyi / Mt Wellington – Geological features, periglacial features and natural hazards
Kunanyi’s impressive columnar dolerite rock formations, an isolated basaltic centre, mass wasting features, history of landslides and periglacial features will form the focus of this field trip.
The field trip also includes an overview of Triassic sandstones and Jurassic dolerite along the Hobart Rivulet Track.
Blinking Billy Point
Eastern Tasmania is usually considered to have a basement terrane with one of the earliest geological investigations in Australia. The site includes some Cenozoic basalt flows, dykes and pyroclastic deposits, with some hydrothermal veins. There are also some Tertiary boulder beds, fossiliferous Permian sequences and some unusually laminated Jurassic dolerite intrusion. There are also some geotechnical/geohazard interest as much of the cliffline, especially the boulder beds, rich in variably weathered dolerite, is rapidly eroding and many houses on the clifftop look precarious.
NW Tasmania – exploring Tasmania’s Proterozoic rocks
Tasmania’s oldest rocks include the Rocky Cape Group. The remarkably well-preserved packages of rocks in NW Tasmania is considered to have once been attached to similar rocks in western North America between 1.45 billion and 1.33 billion years ago. Well preserved sedimentary features can be observed at Sisters Beach, Rocky Cape and far western Tasmania along the Tarkine Coast. Above the Rocky Cape Group, an uncomfortable boundary is marked by the Forest Conglomerate and the Donaldson Formation (West Head and Goat Island). The field trip will focus on notable outcrops of Rocky Cape Group, Forest Conglomerate and Oonah Fmn including dykes and syn-sedimentary intrusions.