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Geological Timeline - Tasmania

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Geological Timeline - Tasmania GEODIVERSITY Geological Timeline - Tasmania Tasmania’s spectacular geodiversity has contributed Chains of volcanoes form across Tasmania, including Mt directly to the islands’ biodiversity. The State’s Read Volcanic Belt, a highly significant mineralised belt. geodiversity is a result of continental drift, ice ages, humid, hot conditions and earthquakes occurring over 443 - 408 Million Years Ago more than a billion years. Extensive erosion and subsequent deposition form the sandstones and conglomerates of West Coast Range and A very brief and summarised account of Tasmania’s Denison Range. geological history is outlined below. Although Tasmania is referred to frequently, it was not until about 45 Tasmania partly covered by a warm tropical sea and part million years ago that Tasmania began to look anything of a much larger land mass of Gondwana situated near like it does today. the equator. Gordon Limestone formed from the debris of marine life. Today this limestone outcrops in parts of 4600 - 635 Million Years Ago the Franklin and Gordon River valleys and around Mole The Earth formed about 4600 million years ago. Creek, where subsequent disolving by water has formed many karst and cave systems. Little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth’s history. This is 408 - 360 Million Years Ago because traces of the geological heritage of Precambrian Warm shallow continental seas provide a hospitable times have been erased by relentless subsequent erosion. environment for marine life of all kinds. Coral reefs made First evidence of simple life forms, cyanobacteria, the their first appearance during this time, and first bony fish building blocks for stromatolites, are among the oldest appear. Brachiopods, bryozoa, molluscs, and trilobites form of life on Earth, dating back 3.5 billion years. abundant and diverse. Their ability to extract hydrogen from water through In eastern Tasmania the water was deeper and fossils are the process of photosynthesis led to oxygen being sparse. released which, over long ages, led to an increase in the atmospheric concentration of oxygen, and paved the The first fossil records of vascular plants appear. way for explosion of aerobic life which was ultimately to 360 - 325 Million Years Ago follow. Marine faunas continue to be dominated by bryozoa, Sequences of rock known as dolomite (aged at around diverse and abundant brachiopods and corals. In the late 800 million years) contain Tasmania’s oldest stromalolite Devonian the lobe-finned fish appear, giving rise to the fossils. first tetrapods (four-legged creatures). The oldest rocks in Tasmania are found in the west. By the end of the Devonian, the first seed-forming plants These were laid down as sediments in a shallow sea and appear. Primitive arthropods co-evolve with diversified subsequently folded and transformed into quartzites and terrestrial vegetation structure. Vertebrates and schists. Examples of these ancient metamorphic rocks arthropods solidly established on the land. can be seen in the Arthur and Frankland Ranges and Great Dividing Range in eastern Australia forms by Frenchmans Cap. collision of two tectonic plates. This major mountain 635 - 542 Million Years Ago building event generated a tremendous amount of First complex multicelled life forms appear roughly 600 heat resulting in widespread melting in the crust deep mya. Life confined to the oceans. below the surface. The heat produced magma (molten rock), which gradually rose bouyantly then cooled at What is now Tasmania was largely covered by shallow considerable depth below the surface. It is this cooled seas magma that formed the spectacular granites extending 490 - 443 Million Years Ago from the Tasman Peninsula to Wilsons Promontory in Victoria, and including the Freycinet Peninsula. Global explosion of life in the seas. Tasmania has some fossils from this time, including trilobites. Department of Environment, Parks, Heritage and the Arts 328 - 286 Million Years Ago 144 - 65 Million Years Ago Amphibians diverse and common (more so than they High sea levels cause widespread flooding by sea - Great are today). Evolution of first reptiles and conifers Artesian Basin forms. (gymnosperms). Between 100 and 80 mya the climate was mostly Significant accumulations of coal begin to occur in warm again. The Terminal Cretaceous Event 65 mya northern hemisphere. is accompanied by sudden cooling, many extinctions (including extinction of dinosaurs), volcanic activity, 286 - 250 Million Years Ago possibly caused by asteroid/comet impact. Towards end of Permian, first archosaurs appear. Some archosaurs would evolve into more advanced types, Gondwana continues to fragment. 125 mya Africa eventually into dinosaurs. separates from Antarctica. India separates from Antarctica and Australia and moves north at 20cm a year; 100 Dense fossil shell deposits form at Fossil Cliffs on Maria mya Africa separates from South America; 80 mya New Island. The site contains large drop stones in layers near Zealand separates from Australia as Tasman Sea forms. the fossils, indicating that icebergs melted and dropped Australia stays attached to Antarctica. the eroded material. 100 mya flowering plants evolve; 90 mya flowering plants The Tasmanian and eastern Australian landmass slowly migrate to all continents and begin to compete with uplifts. As the sea retreats and the climate warms up, the conifers; 80 mya southern conifers dominant in Australia Tasmania Basin is drained by broad meandering river - Huon Pine, Phyllocladus, Callitris. First Proteaceae in systems. Dinosaurs roam the Earth, though interestingly Australia. Nothofagus arrives via Antarctica and South dinosaur fossils have not been found in Tasmania. Tree America, but does not reach Africa. ferns similar to those found today are abundant. 65 - 58 Million Years Ago 250 - 208 Million Years Ago Mainly warm and wet. 50 mya India collides with Asia and The Earth’s major extinction event marks the Permian- forms Himalayas. Seafloor spreading in Great Australian Triassic boundary. 90% or more of all marine species Bight causes Australia to separate from Antarctica 45 became extinct. Appearing at the end of the Permian mya. Tasmania hangs on to Antarctica. South Tasman Rise were the first cynodonts, which would go on to evolve continued to provide migration route to Antarctica until into mammals during the Triassic. 45 mya. Towards the end of the Triassic the supercontinent First occurrence of Casuarinas, Banksia, Myrtaceae, Pangaea began to break into Laurasia to the north and Restioneaceae, Winteraceae and Epacridaceae Gondwana to the south. 58 - 40 Million Years Ago Australia’s oldest deposits of black coal, found in NSW Grass pollen appears. and Queensland, were laid down between 225 and 180 mya. Australia severes its final link with Gondwana about 45 mya, carrying with it its cargo of Gondwanan plants which 208 - 144 Million Years Ago evolve in isolation for 30 million years. Rich sub-tropical Ancient flora, such as conifers, ferns, cycads, gingkos, rainforest covers much of Australia (now confined to N.E. lycopods, horsetails - some survive today. Fossils of ferns, Queensland, New Guinea and New Caledonia.) conifers and cycads occur. Globally climate warm and wet. 40 - 24 Million Years Ago Circum-polar current forms. Climate becomes cooler Between 170 and 180mya Gondwana begins a long and drier. First glaciers on Antarctica. Drake Passage period of break up, molten rock (magma) is forced up opens, severing connection between South America and though the Earth’s crust and intruded sideways. The Antarctica. Tasmania carried north on Australian plate cooled and solidified magma becomes the dolerite which from about 65º S. forms many of the spectacular columnar mountain tops and sea cliffs so typical of eastern Tasmania, such as at Temperate rainforest widespread with much Nothofagus. Ben Lomond, Mt Wellington and Tasman Peninsula. (Also in Antarctica and South America). 25 mya Acacia and Eucalyptus pollen first recognised in Australia. Basalt eruption buries Jurassic forest at Lune River in Tasmania’s far south. 24 - 5.3 Million Years Ago Warm and wet for a short period initially. Coals mined in Tasmania are typically between 140 and 180 million years old. 20 mya isolation and cooling of Antarctica; 17 mya Antarctic flora succumbs to cold. Geodiversity – Tasmania 15 mya Australian plate (of which New Guinea is at northern leading edge) collides with southern Asia forming the New Guinea Highlands. 15 mya change from closed forest to wet sclerophyll forest, dry forest to open woodland and grasses. Eucalypts, acacias, casuarinas, grasses become dominant; 10 mya Australia drifts north at 6-7cm/yr, becoming dryer and arriving in sub-tropics. Fire becomes important factor in Australian ecosystem. Cold, dry, arid period. 5.3 - 1.6 Million Years Ago Antarctica freezes over. Brief warm period, then colder again. Northern ice cap forms. Australian plate collides with Timor region. Migration of plants and animals from south-east Asia into Australia. Tasmania arrives at latitude 42ºS. Cool, temperate and moist. 5 mya sub-tropical forest species migrate to refuges in Queensland and New Guinea. Invasion by Asian plants from north. Myrtaceae dominate. 2 mya dry sclerophyll, woodlands and deserts expand. 1.6 - 0.01 Million Years Ago Several glacial stages shape the current character of Tasmanian highlands. Sea levels rise and fall many times. Climate drying. Humans arrive in Australia about 60,000 years. Intermittent
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