Geology of Tasmania - Geological History

Geological History

Tasmanian Geological Timeline -1400 — – -1200 — – -1000 — – -800 — – -600 — – -400 — – -200 — – 0 — Stenian Tonian Cryogenian Ediacaran Cambrian Ordovician Silurian Devonian Carboniferous Triassic Permian Jurassic Cretaceous Tertiary Quaternary Ectasian ← Separation from Antarctica ← Glaciation ends ← Tyennan Orogeny ← Granite in west ← Granite in east ← Oldest Tasmanian rock
on King Island ← Strathgordon phyllite ← Lyell Highway metamorphosed siltstone ← arc continent collision ← Orogeny ← Massive dolerite intrusion ← Permian glaciation ← Marinoan Glaciation ← Sturtian glaciation An approximate time-scale of events
in the Geological history of Tasmania.
Axis scale is in millions of years ago.

The earliest geological history is recorded in rocks from over 1,270 million years ago. These older rocks from western Tasmania and King Island were strongly folded and metamorphosed into rocks such as quartzite. After this there are many signs of glaciation from the Cryogenian, as well as the global warming that occurred at the start of the Ediacaran period. An orogeny folded the older Precambrian rocks. In the Cambrian time the Tyennan block forming the south west and central Tasmania, was pushed up and slightly over the land of north west Tasmania, the Tyennan Orogeny. Then there were volcanic action and sediments from the Cambrian and Ordovician. The large ore deposits were formed on the West Coast. The north east of Tasmania began to form as part of the Lachlan Orogen with turbidity flows of mud and sand on to the ocean floor. In the Devonian the Taberabban Orogeny caused more folding, and intrusion of granite on the west and east coasts, and probably joined the east of Tasmania to the west.

In the Permian period, conditions were again glacial and the Tasmania basin formed, with low sea levels in the Triassic. A giant intrusion of magma happened in the Jurassic forming diabase, or dolerite which gives many of the Tasmanian mountains their characteristic appearance. Continental breakup happened in the Cretaceous and Tertiary Periods, splitting off undersea plateaus, forming Bass Strait and ultimately breaking Tasmania away from Antarctica. In the Tertiary, a couple of basins extended inland from Macquarie Harbour and the northern Midlands. The higher mountains were glaciated during the Pleistocene.