Table of Contents
How Australia evolved in geological terms and evolution
- my blog posts:
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.
- 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)
- 2.229 billion years ago, the 70km wide Yarrabubba impact crater in WA the result of an asteroid impact (the oldest known impact crater although controversially, the “oldest-known impact structure” should go to the Maniisoq formation in southwest Greenland, which is around 3 billion years old although this may have been tectonic rather than impact) which is thought to have helped end the “snowball earth” period
Columbia / Nuna super-continent
- the super-continent of Columbia or Nuna containing almost all of Earth's continental blocks is thought to have assembled following global scale collisional events in 2.1-1.8 billion years ago.
- The eastern coast of India was attached to western North America, with southern Australia in the northern hemisphere against western Canada.
- Most of South America was rotated such that the western edge of modern-day Brazil lined up with eastern North America, forming a continental margin that extended into the southern edge of Scandinavia.
- Tasmania was separated from Australia and sandwiched between Arizona and Antarctica and after a sea had formed between Tasmania and Arizona around 1.5bya, Tasmania gradually drifted towards southern Australia by around 500mya
- 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
- 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
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 as well as gold-bearing quartz reefs formed from hot salty fluids 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)
- sea levels had dramatically fallen from around 150m higher than current to around current levels by 300mya and then continued to rise for the next 200 million years until they peaked at around 100mya
- 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
- evolution of Wollemi pines (100-200mya) which once grew across most of Australia but now only some 200 wild specimen remain, hidden in a secret part of Wollemi NP in NSW 3)
- 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.4)
- 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.
- it is probable during this period that the two remaining Eidothea sp. which include Nightcap Oak found only in northern NSW and another species found near Cairns, both belong to Proteaceae subfamily Proteoideae suggesting an origin in Africa - earliest known fossils are 15-20mya from Ballarat, the fruit of which are little changed from today5)
- 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.
- 125mya, small dinosaurs on the present south Victorian coastline (formerly, the Australian-Antarctic rift valley) such as Galleonosaurus dorisae, Qantassaurus intrepidus and 12 million years later, Diluvicursor pickeringi - these ornithopods are closely related to those from Patagonia in Argentina 6)
- 110mya elaphrosaur found at Eric the Red West area of the Eumeralla Formation in the Otways in 2015
- 107mya a new large megaraptorid Theropod dinosaur bones with 20cm long hand claw found in the Eric the Red West area of the Eumeralla Formation in the Otways in 2011-2017
- 95mya Australovenator megaraptorid Theropod dinosaur, ornithopods and large long necked sauropods (Diamantinasaurus and Savannasaurus) lived in Queensland
- pre-109mya, Eucalypts evolve somewhere in the Weddellian Biogeographic Province (which includes southern South America, western Antarctica and south-eastern Australia), in an area with high natural fire frequency
- 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)
- 112-65mya, the first Varanidae family of monitor lizards evolved in Asia, migrated to Africa 49-33mya (possibly via Iran), and to Indonesian archipelago 39-26mya, thence to Australia
- 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)
- 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
- 85mya: New Zealand, New Caledonia and the rest of the now submerged continent of Zealandia begin to separate from Australia forming the Tasman Sea 7)
- 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 largely spared in the global mass extinction event of 65-66mya when 75% of animal species died out including all the dinosaurs - this is now confirmed to be due to an asteroid hitting Mexico's Yucatan Peninsula where it created a 200km crater. There had been a preceding increased volcanic activity in the Deccan which was in fact responsible for a brief warming phase 200,000 years before the mass extinction, but this had no long-term effect on life and the climate.
- 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.
125mya there was a 4000km long volcanic region along Australia's east coast.8)
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
- perhaps the ancestors of the Hickmaniidae spider migrated from Andes to Tasmania at this time
- at 50mya, earth had tropical conditions as far as latitude 40deg, there was no continental glaciation and even at the south pole, the climate was cool temperate, thanks largely to CO2 levels being 6x higher than pre-industrial levels at 1700ppm and thus sea levels were 150-200m higher than present, but then started a prolonged global cooling phase which we are still in and has resulted in glaciation events which have intensified over the last 1 million years
- 50mya, the Transantarctic Mountains were thrust up.
- 50mya: Pacific Ring of Fire formed as Zealandia continued to sink in a “subduction rupture event” 9)
- 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
- 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, increased rock weathering which washed out carbon dioxide levels, while the uplift of the Tibetan Plateau above the snow line increased the albedo effect, which combined with less greenhouse gases made the earth more sensitive to small changes in orbital variations - solar flux at 60deg latitude can vary 25% due to orbital variations)
- 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.
- 25mya Australian continent colonised with Elapid snakes - presumably an early sea krait
- a period of thawing of Antarctica ice
- the rise of the Eucalypts which were a minority of plant life in Australia 30-50mya but eventually flourished from 21mya (the oldest known fossil in Australia) onwards, initially in the drier interior but as these areas became too dry, in the Miocene, they migrated to the margins and overtook the previously dominant coastal non-Eucalypt forests thanks to their evolutionary advantages with fires which their design promotes, and their tough sclerophyll leaves which tolerate drought and heat, their opercula which cover the flowers preventing it from drying out or being attacked by insects. However, frequent fires will wipe out even Eucalypts locally as they are unable to re-seed or regenerate from lignotubers or budding and presumably this then leads to desertification.
- 22mya, “modern” penguins evolve in Australia and NZ then migrate to Antarctica and 12mya when the Drake Passage between Sth America and Antarctica opened, they migrated to the other continents10) Penguins had split from the sister group of Procellariiformes 60mya.
- 20mya, Australia had drifted far enough north for its northernmost parts to move into the zone of influence of the tropical monsoon climate
- 17-19mya - Riversleigh, Boodjamulla National Park, N-W Queensland World Heritage Site of limestone fossils (“D-site”) and New Riversleigh
- cells are so well preserved even the nuclei are fossilized
- desert sloth - “marsupials the size of sheep, which graze in treetops and hang upside down like sloths”
- sabre-toothed bandicoot
- 15mya the Antarctic ice sheet re-formed
- 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? 11)
- 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)
- 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 which occurred at 350,000yrs ago, 250,000yrs ago, 140,000 yrs ago and the most recent one peaked 18,000yrs ago and ended 10,000yrs ago, over this time there have been several “warm periods” when temperatures rapidly rose similar to present day but they only last 3000-4000yrs before steadily cooling into another glaciation period 12)
- 129,000-116,000 years ago in the last inter-glacial era when the West Antarctic ice sheet melted due to <2degC ocean warming, sea levels possibly rose 6-9m13)
- sea levels falling by 110m
- 1.5-1.6mya H. erectus man lived in Indonesia but no evidence he made it to Australia
- 1.5mya megalania - a giant monitor lizard (became extinct c50,000yrs ago)
- 900,000 yrs ago - weathering of mountains result in quartz sediment from northern NSW rivers such as the Hawkesbury travel northwards due to South-east trade currents and form the sandy beaches along the coast, culminating in the development of Fraser Island, the world's largest sand island, and what is though to have allowed the development of the Great Barrier Reef as further sand gets pushed north-eastwards into deep waters off the continental shelf allowing the coast northwards to become dominated by corals.
- 70,000yrs ago: modern course of the Murray River was carved when a series of earthquakes and aftershocks that went for years lifted the ground along the 80km Cadell fault line which stretches from Deniliquin through Echuca, to Rochester in northern Victoria. A series of six very large earthquakes events occurring every 5000-10000yrs formed the fault scar, which is up to 10 to 15 metres high at Mathoura resulting in the river being diverted from Mathoura to Echuca. This fault line is regarded as being dormant as no quakes have occurred in the past 20,000yrs, although it could be overdue for its 1 in 10,000yr magnitude quake.
- 20,000-50,000 yrs ago, placental mammals such as bats and rodents made their reappearance in Australia 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
- c45,000yrs ago Aboriginal indigenous peoples migrated to northern Australia from Sri Lanka region
- Australian megafauna die out
- Varanus priscus, a giant goanna formally known as Megalania prisca, became extinct c50,000yrs ago
- c40,000yrs ago, 13 species of super-sized megafauna species, including five reptilian megapredators, a marsupial “lion” and the world’s largest wombats and kangaroos became extinct near Mackay, Qld and the cause seems to be successive loss of water flow, intensified drying, increased burning and vegetation change although the arrival of Aborigines several thousand years earlier may also have contributed 14)
- 37,000yrs ago - Tower Hill volcanic eruption in SW Victoria covers indigenous axes and presumably forms the oldest known oral history still being told by Aboriginal Gunditjmara people of the area 15)
- 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
Migration of Australian indigenous tribes based on Hep B virus strains to Sahul (the connected landmass of New Guinea, Australia and Tasmania 50,000yrs ago) 16)
- 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
- 8000 yrs ago - peak of natural interglacial warming period but the expected fall in CO2 levels and temperatures due to orbital effects have not been realised initially due to agricultural clearing of land, then 5,000yrs ago rice terracing cultivation and beef cattle domestication which caused a rise in methane levels, and now industrialisation usage of fossil fuels which add 9 gigatons of CO2 into the air each year (volcanoes add 0.2 gigatons per year) has further contributed to rapidly rising greenhouse gases which has averted another glaciation period
- 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.