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history:evolution_australia

How Australia evolved in geological terms and evolution

In the beginning

  • The Australian landmass has been part of all major supercontinents, but its association with Gondwana is especially notable as important correlations have been made geologically with the African continental mass and Antarctica.

Archaean

  • There are three main cratonic shields of recognised Archaean age within the Australian landmass: The Yilgarn, the Pilbara and the Gawler cratons.
  • Wave Rock in WA is thought to have been created 2700mya with its current form due to erosion since then
  • The cratons appear to have been assembled to form the greater Australian landmass (2,400-1,600mya)

Rodinia

  • the Rodinia supercontinent was assembled c1300-1230mya
  • tectonic activity between 1300-1100 Mya led to the assembly of Proterozoic Australia from collision of the 3 main cratons as an early component of the supercontinent of Rodinia.
  • Australia was well north of the equator and adjacent Eastern Antarctica, India, South China and Laurentia
  • c 850-800mya a rift developed between the continental masses of present-day Australia, East Antarctica, India and the Congo and Kalahari cratons on one side and later Laurentia, Baltica, Amazonia and the West African and Rio de la Plata cratons on the other.
  • Adelaide Rift Complex of sedimentary deposits begin to form 870mya through to 500 mya (hence the Ediacaran fossils in this region) with the southern parts ending with the Delamerian Orogeny 514-500mya (the northern parts such as Cooper and Perdirka Basins still continue to have deposition
  • 830mya - rifting to the east formed the “Adelaide Geosyncline”
  • 830-750mya - the Centralian Superbasin developed over the junction of the North, South, and West Australian cratons
  • 620-540mya - King Leopold, Paterson, Petermann Ranges, and Pinjarra orogenies
  • Rodinia broke up in four stages between 825–550
  • Rodinia existed before complex life colonized dry land

rodinia_reconstruction.jpg

Gondwana

  • several cratons joined to form a supercontinent the size of 2/3rds of current continental area on earth called Gondwana
    • this commenced between 800-650mya with the East African Orogeny – the collision of India and Madagascar with East Africa
      • Note that southern parts of the Australia craton lay just north of the magnetic equator c750mya
      • the break up of Rodinia resulted in the Terra Australis Orogen (TAO) which became the oceanic southern margin of Gondwana which stretched from South America to Eastern Australia and encompassed South Africa, West Antarctica, New Zealand and Victoria Land in East Antarctica
      • Snowball Earth of the Cryogenian Period with extreme cooling of global climate 717–635 mya
      • Ediacaran soft bodied fauna lived in shallow seas in Australia c670 mya
      • the Cambrian animal life explosion commenced around 600 mya but these were all living in water (1st air breathing animal and first vascular plant did not evolve until c400mya)
    • it completed b 600-530mya with the collision of South America with Africa and the addition of Australia and Antarctica
    • the final stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia (which would later become north America) and western Gondwana. During this interval, the Cambrian explosion occurred.
    • 620-540mya - King Leopold, Paterson, Petermann Ranges, and Pinjarra orogenies
    • 550mya, erosion of the Petermann Ranges starts to form the sandstone deposit that will eventually form Uluru
    • volcanic activity c550mya laid down rock in southern Gippsland in Victoria (eg. around Cape Liptrap)
    • Delamerian Orogeny 514-500mya ends the sedimentary deposits on the Adelaide Rift Complex
    • shortly after this the 1st Ice Age occurred c500mya

upload.wikimedia.org_wikipedia_commons_2_22_positions_of_ancient_continents_2c_550_million_years_ago.jpg

the splitting of Gondwana and the separation of Australia

  • Ordovician period (485-444 mya)
    • deepwater sedimentation of the St Arnaud and Castlemaine Group turbidites, which are now emplaced in the Stawell and Bendigo Zones followed by deposition of the Sunbury Group in the Melbourne Zone, Bendoc Group and formation of the Molong Arc
    • Lachlan Orogeny in eastern Australia
  • Silurian period (444-420mya)
    • a giant water scorpion, the first animal found to walk on the Australian continent in NW of WA
    • volcanic arcs in eastern Australia
    • Granite intrusions formed in New South Wales and Victoria
    • Deep water sediments formed in the Cowra, Tumut and Hillend Troughs
  • Devonian period (420-360mya)
    • conditions were warm in Australia
    • 439-400mya, the hard sandstone deposit from erosion of the Petermann Ranges folded and tilted 85deg in the Alice Springs Orogeny to form Uluru 1)
  • Carboniferous period (360-mya)
    • Pangaea supercontinent formed
    • a major ice age left over half of Australia glaciated
    • the great Coal Forests in Australia and the beginning of the evolution of ferns, seed ferns, horsetails and gymnosperms
    • presumably the Gondwanide orogeny created the orogenic Great Dividing Range on Australia's east coast region which formed 300mya and they are believed to have been as high as any mountains on the planet today, but they have been almost completely eroded since

Pangaea supercontinent, much of Pangaea was in the southern hemisphere and surrounded by a superocean, Panthalassa.

Fossil evidence to support Pangaea concept

Permo-Triassic period (289-201mya)

  • formation of a rift basin on the West Australian coast creating de-oxygenated rift valley lakes in the Swan Coastal Plain and Pilbara resulting in petroleum
  • Antarctica has been near or at the South Pole since the formation of Pangaea about 280 Ma
  • a major Permian ice age which left over half of the continent glaciated and this eroded then extensive central Australian mountain ranges such as the Petermann Ranges
  • 280-160mya: ice sheets covered most of south and southeastern Australia (eg. Werribee Gorge)
  • Permian Extinction event 252mya greatly impacted insects and resulted in the loss of over 90% of marine and 70% of terrestrial species
  • the Triassic (252-201mya) was getting hotter and dryer in Australia but a large part of Australia was under the influence of a monsoonal regime.
  • the South Pole was over eastern Australia but there were no ice caps and carbon dioxide levels were about three times higher than today and coal swamps had virtually disappeared. Most of Australia was land but some large sedimentary basins persisted.

Jurassic period (200-145mya)

  • western Australia had a tropical savannah to jungle environment
  • 182mya initial rifting of East-Gondwana starts in a SE orientation 2)
  • Pangaea supercontinent begins breaking up 175 mya
  • Australia was mainly at 45-60deg South and began rifting away from Antarctica in the Jurassic, this caused subsidence which formed the Gippsland, Bass and Otway Basins in Victoria and the offshore shelf basins of South Australia and Western Australia, all of which host significant oil and gas deposits
    • a 600km wide Rift Valley formed and the crust at the inner 350km thinned from 40km to 10km thick allowing the hot lithosphere to rise closer to the surface resulting in magma being forced upwards
    • the rifting commenced at the West Australian end c160mya and would result in the North-West oil and gas deposits
  • c150mya, an extensive sea forms between Africa and Antarctica
  • c150 Mya a strip of terrain separated the present coast of eastern Australia from the proto-Pacific Ocean. This terrain is now marked by the Lord Howe Rise, Queensland Plateau and New Caledonia.
  • Most of Australia was land with large sedimentary basins developing in both eastern and western Australia, but there is not much evidence for dinosaurs in Australia during this period, unlike the rest of the world
  • There were no polar ice caps and the world climate was warm and increasingly humid with little differentiation into climatic belts. Carbon dioxide levels were about seven times higher than today.

Cretaceous period (145-66mya)

  • 160-132mya, 1st phase of rifting, the West Australian end of the rift had opened up as far as the Great Australian Bight.3)
  • 140mya Africa separates from Sth America
  • by 132mya the position of the South Pole had shifted, bringing Australia's most southerly point at the time, somewhere near the Queensland-New South Wales border to about 80deg South. By 120mya the South Pole was close to Tasmania.
  • 132-96 mya, the remainder of Australia separated. During this phase, India started rotating northwestward from Australia. As a result of this the Perth Basin subsided allowing the sea to flow in. Australia was joined to Antarctica along the eastern edge of that continent. What is now Australia's east coast was then it's southern coast.
    • 2nd phase, rifting shifted direction. Australia rotated to the northwest, so that the southern (now eastern) end of the rift opened forming the Otway Basin and Torquay Basin. About 15 million years later rifting of an arm of the Tasman Sea formed the Gippsland Basin. This rotation squeezed the West Australian section, forcing thinner basin crust, with overlying sediments, against the solid Yilgarn Block. This resulted in the heaving up of the Stirling Ranges.
  • 110mya, Australia's 1st mammals evolved such as the 1st monotremes (ancestors of the platypus) which appeared before the 1st marsupials (evolved 100mya in Nth America) migrated from South America and which arrived in Australia c55 mya (Tasmania was still connected to Antarctica until 30mya)
  • Atlantica, today's South America and Africa, finally separated from eastern Gondwana (Antarctica, India and Australia)
  • India moved northwards from Pangaea then 40mya later, Australia starts moving northwards with continued rifting from Antarctica resulting subsidence and the formation of a rift valley and vast flood plain where Bass Strait is
    • Victoria's southern coast (especially around Inverloch) has areas of early Cretaceous period layers of siltstone and sandstone as well as conglomerate exposed which contains dinosaur fossils as well as early amphibians and mammals from 105-120mya when Victoria was located at latitude 70-75deg South and the climate was cool temperate similar to current day Tasmania uplands. Vulcanism dated to 99.9mya extruded igneous rock over some areas. The swampy backwaters were to form the coal seams as well as the oil and gas deposits in the region.
  • Whitsunday Islands formed from volcanism
  • Madagascar separates from India (100-90mya)
  • New Zealand, New Caledonia and the rest of Zealandia begin to separate from Australia
  • sea level rise and water entering the Carpentaria Basin resulted in flooding of central Australia, peaking in 115-110mya, forming the muddy, stagnant Eromanga Sea (the size of 1/3rd of the continent but poorly connected to the oceans) which broke the continent into four distinct islands which resulted in local diversification of flora - South Western Australia, Adelaide Region and South-Eastern Australia
    • the marine deposits of sandstone and limestone between these islands meant that:
      • the deep underground freshwater sediments became covered with an impermeable layer and thus formed the Great Artesian Basin which continued to be fed with fresh water from the east as at the eastern edge of the basin the layers of sandstone are warped up sufficiently to allow water to seep into it from the rain falling on the western slope of the Great Divide, but this water takes 2 million years to reach Lake Eyre!
      • once the flood was over, the flora could not migrate to other islands due to the pH of the limestone soils and the high salinity of the sandy soils between them, and this forced plants to evolve to tolerate these soils
      • the acidic oxidative weathering resulted in this region having the highest prevalence of opals in the world
  • Australia had a cool, wet climate
  • much of Australia was covered with conifer forests, cycads and ferns while dinosaurs still dominated
  • 96mya, Great Dividing Range formed
  • 85-65 Ma, Tasmania was still connected to Antarctica by the stretched crust of the South Tasman Rise. Climate was hot and humid. Australia was separated from Antarctica by 100km. Bass Strait was then the Bassian Plain - a rift valley of river flood plains, swamps and lakes.
  • Australia appears to have been spared in the global mass extinction event of 65mya.
  • 65mya the southern tip of Sth America was still connected to Antarctica, as was Australia, but Africa, Madagascar and India were well separated, having broken away 200-250mya.

Tertiary period (65-2.6mya)

  • In the Tertiary period (65 mya) the climate was moist and mild. The entire Australian continent was probably covered by a subtropical rainforest-type vegetation.
  • 63mya, the islands of Indonesia start to form from volcanic activity resulting from the Indian and Australian plates colliding and slipping under the Sunda Plate.
  • 60mya, south-eastern South Australia started to sink and rivers began to deposit sediment into the newly forming Lake Eyre Basin
  • 55mya, small marsupials migrate to Australia from Sth America via Antarctic
  • 50mya, the Transantarctic Mountains were thrust up.
  • 40mya, whales evolved from ancestors of the hippopotamus
  • 38-36mya, Australia's climate changed becoming much drier and duricrusts formed over much of the continent, as the large-scale ice sheets became established in East Antarctica
  • 27mya, the circum-polar Southern Ocean formed with the last connections of Sth America and of Tasmania to Antarctica gone which then allowed the Antarctic to freeze, being isolated from the warmer ocean currents.
  • From 30-35mya, there was a period of global drying and cooling (perhaps due to the formation of the Himalayas which increased Earth's total rainfall and thus washed out carbon dioxide levels and the uplift of the Tibetan Plateau above the snow line which increased albedo effect), causing Antarctic to freeze over, and from 15 mya the Antarctic ice sheet formed
  • 25mya Australian continent colonised with Elapid snakes - presumably an early sea krait
  • 20mya, Australia had drifted far enough north for its northernmost parts to move into the zone of influence of the tropical monsoon climate
  • 15mya goannas migrated to Australia from the Nth Hemisphere
  • 10mya increasing aridity and prolonged droughts was being caused in Australia, especially in the interior, by the greatly expanding ice sheets in Antarctica. This led to reduced erosion and deposition.
  • c8mya Pythonidae migrate to Australia from Asia although some had migrated to NW Australia 14mya? 4)
  • 4-20mya Australian Elapid snakes evolve into the modern genera of Elapids
  • 6-7mya 1st humans evolve in Africa
  • Sand deserts and large inland salt lakes formed in Australia within the last 5 million years
  • the Australian megafauna evolved
  • 80% of Australian native flora species are found only in Australia
  • Australian and Indian rainforests share 47 genera thanks to the close proximity in Gondwana
  • 2.8mya - the connection of North and South America at the Isthmus of Panama cut off the warm ocean currents from the Pacific Ocean entering the Atlantic Ocean leaving only the newly created Gulf Stream to transfer heat to the Arctic Ocean, driving warm, wet weather over northern Europe which allowed increased rainfall and thus ice production over the Arctic Cap, laying part of the foundation for the Quaternary Ice Age Event

Quaternary Period (2.58mya-present)

Pleistocene

  • 2.58mya, the Quaternary Glaciation / Quaternary Ice Age event resulted in:
    • formation of the Arctic ice cap
    • a rapid desertification of the Lake Eyre Basin
    • cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacial periods
    • sea levels falling by 110m
  • 1.5-1.6mya H. erectus man lived in Indonesia but no evidence he made it to Australia
  • placental mammals such as bats and rodents made their reappearance in Australia in the Pleistocene (20,000-50,000 yrs ago), as Australia continued to move closer to Indonesia
  • Australian flora was largely unaffected by the 4 main Ice Ages, as unlike the very thick widespread ice glaciation up to 3km thick in northern continents, these were mainly only 10m thick and only reached 30m thick in the higher altitudes of Tasmania and the Snowy Mountains
  • Aboriginal indigenous peoples migrated to northern Australia c45,000yrs ago from Sri Lanka region
  • Australian megafauna die out
  • the glaciation maximum which occurred 18,000 yrs ago resulted in the central basin of Bass Strait being enclosed by raised sills forming a large shallow lake

Holocene

  • 11,650 yrs ago marked the end of the last glaciation event and the start of an interglacial period
  • sea levels rose resulting in:
    • the sills of the Bassian Basin were breached resulting in the formation of Bass Strait 8000 yrs ago which now has an average depth of 60m
    • Sundaland (greater Indonesia) was submerged under shallow sea, creating Malacca Strait, South China Sea, Karimata Strait and Java Sea and forming Malay peninsula, Sumatra, Java, Borneo and other islands.
    • New Guinea and Aru Islands became separated from the Australia mainland
  • 5000 yrs ago - most of Australia suffered a drought for several centuries with only small wetter pockets being unaffected - The Grampians, Mount Buffalo, Flinder's Ranges. This drier period with nutrient poor soils and frequent fires allowed Eucalypts and Acacias to evolve from the northern rainforests and dominate the dry sclerophyll regions.
  • 4850 years ago the latest of the volcanic activity occurred in the Mt Gambier region in South Australia, and about 4500 years ago at Tower Hill in Victoria.
history/evolution_australia.txt · Last modified: 2019/02/14 04:33 by gary1