The Adelaide Superbasin (previously known as the Adelaide Geosyncline and Adelaide Rift Complex) is a major

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...

to middle

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

geological province in central and south-east

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest o ...

, western

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

, and western

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

. The Adelaide Superbasin consists of a thick pile of

sedimentary rocks Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particle ...

and minor

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...

s that were deposited on the eastern margin of Australia during the time of breakup of the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

Rodinia Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago and broke up 750–633 million years ago. were prob ...

. A number of authors have noted the similarity in these sedimentary rocks with rocks found in western North America and have suggested that they were formerly adjacent to each other in Rodinia. This is one major correlation in the

SWEAT Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...

(south-west USA against East Antarctica)

reconstruction Reconstruction may refer to: Politics, history, and sociology * Reconstruction (law), the transfer of a company's (or several companies') business to a new company *''Perestroika'' (Russian for "reconstruction"), a late 20th century Soviet Unio ...

of Rodinia. Particularly notable events that are preserved in the rock record of the Adelaide Superbasin are the two Neoproterozoic

Snowball Earth The Snowball Earth hypothesis proposes that, during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen. It is believed that this occurred sometime before 650 M.Y.A. (million years ago) du ...

events (the Sturtian and Marinoan Glaciations), the Neoproterozoic Oxygenation Event, the Ediacaran Acraman bollide ejecta layer and the rise of Ediacaran Fauna.

Geography

North–south it stretches over from the Peake and Denison Ranges in the central-north of South Australia down through the

Flinders Ranges The Flinders Ranges are the largest mountain range in South Australia, which starts about north of Adelaide. The ranges stretch for over from Port Pirie to Lake Callabonna. The Adnyamathanha people are the Aboriginal group who have inhabit ...

and Mount Lofty Ranges, narrowing at the

Fleurieu Peninsula The Fleurieu Peninsula () is a peninsula in the Australian state of South Australia located south of the state capital of Adelaide. History Before British colonisation of South Australia, the western side of the peninsula was occupied by the ...

and extending onto

Kangaroo Island Kangaroo Island, also known as Karta Pintingga (literally 'Island of the Dead' in the language of the Kaurna people), is Australia's third-largest island, after Tasmania and Melville Island. It lies in the state of South Australia, southwest ...

. West–east it stretches about from the eastern margin of Lake Gairdner across to the

Barrier Ranges The Barrier Ranges or sometimes the Barrier Range and historically the Stanley's Barrier Range, is a mountain range that comprises a series of hills and higher grounds in the far western region of New South Wales, Australia, surrounding the city o ...

of New South Wales. The true northern and eastern extent of the Adelaide Superbasin is not well known due to much of the basin being buried beneath younger basins, including the

Murray Basin The Murray Basin is a Cenozoic sedimentary basin in south eastern Australia. The basin is only shallow, but extends into New South Wales, Victoria and South Australia. It takes its name from the Murray River which traverses the Basin from ...

, and is the subject of current research. It is thought that the

Moyston Moyston is a town in the Western District region of Victoria, Australia, near the Grampians mountain range. The town is located in the Rural City of Ararat local government area, north west of the state capital, Melbourne. At the 2021 cen ...

Fault in Victoria marks the eastern boundary and the northern extension may continue underneath and potentially include the Warburton Basin; however, this remains speculative.Counts, John W. (2017). The Adelaide Rift Complex in the Flinders Ranges: geologic history, past investigations and relevant analogues. ''Report Book'', no. 2017/00016. Geological Survey of South Australia. Department of Premier and Cabinet. Adelaide, South Australia.https://sarigbasis.pir.sa.gov.au/WebtopEw/ws/samref/sarig1/wcir/Record?r=0&m=1&w=catno=2039731 Most of the outcropping rock today is within the two major mountain ranges of South Australia: the

and the Mount Lofty Ranges. Much like the partly coeval Centralian Superbasin it contains several named basins and sub-basins. The oldest and largest of these is the Adelaide Rift Complex, with the adjoining and relatively undeformed Stuart Shelf, Torrens Hinge Zone and Coombalarnie Platform making up the remaining Neoproterozoic provinces. The Stansbury Basin (including its sub-province the Kanmantoo Province/Trough) and Arrowie Basin (including its sub-province the Yalkalpo Sub-basin) are the two known Cambrian provinces within the Adelaide Superbasin.

Geologic history

Deposition in the Adelaide Superbasin began just prior to 830 Ma as

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

(and possibly an intervening continent, see

for alternative reconstructions) began to rift away from Australia during the breakup of the supercontinent Rodinia. Deposition continued through to the Delamerian Orogeny c. 514–490 Ma at which time deposition in the Adelaide Superbasin stopped and the rocks were folded and deformed. Initially, deposition occurred from gradual subsidence of

peneplain 390px, Sketch of a hypothetical peneplain formation after an orogeny. In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage ...

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years ...

before developing into a rift basin. After about 725 Ma, deposition continued in a mostly

passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting cre ...

setting along the western edge of the Palaeo-Pacific Ocean, with renewed rifting during the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...

to the east (present day) of the main depocentres until being terminated by the Delamerian Orogeny. The most abundant rock types indicate a transition from evaporitic depositional environments through to proximal marine, glacial and marine

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

s. The thickest parts of the stratigraphy reach a total cumulative thickness of about 24,000 m.

Basin subdivision

The Adelaide Superbasin composed of several named basins and sub-basins. In total there are currently eight defined basins/sub-basins within the Adelaide Superbasin. Basin_subdivision_of_the_Adelaide_Superbasin

Adelaide Rift Complex

The Adelaide Rift Complex is the oldest and most central part of the Adelaide Superbasin. It is a series of rift troughs and passive margins

basins Basin may refer to: Geography and geology * Depression (geology) ** Back-arc basin, a submarine feature associated with island arcs and subduction zones ** Debris basin, designed to prevent damage from debris flow ** Drainage basin (hydrology), a ...

with protracted development from c. 840 Ma to c. 550 Ma with the top of the sedimentary sequence marked by a major basin-wide

disconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

separating it from the Cambrian Arrowie and Stansbury Basins.

Torrens Hinge Zone

The Torrens Hinge Zone is a transitional area between the relatively undeformed platform deposits of the Stuart Shelf and the deformed rocks of the central Adelaide Rift Complex. It runs along the western margin of the primary rift basin.

Stuart Shelf

The Stuart Shelf is a region of platform deposits on the western rift shoulder that overlies the

Gawler Craton The Gawler Craton covers approximately 440,000 square kilometres of central South Australia. Its Precambrian crystalline basement crustal block was cratonised ca. 1550–1450 Ma. Prior to 1550 Ma the craton comprised a number of active Proter ...

. It experienced deposition in the late Neoproterozoic after the Sturtian Glaciation during a period of

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

and remains relatively undeformed to this day.

Coombalarnie Platform

The Coombalarnie Platform, like the Stuart Shelf, is a region of platform deposits; however, it overlies the Curnamona Province to the north-east of the main depocentre. Deposition occurred only after a major marine transgression event during the late Neoproterozoic after the Sturtian Glaciation.

Stansbury Basin

The Stansbury Basin is one of the two known Cambrian basins of the Adelaide Superbasin. It is exposed in the south of the superbasin, extending from Kangaroo Island and the Mount Lofty Ranges toward Victoria underneath the Murray Basin. The true eastward extent of this basin is not well understood and is a focus of current geological research in South Australia. It is likely that deposition was continuous with the Arrowie Basin to the north.

Kanmantoo Province

The Kanmantoo Province (also Kanmantoo Trough) is a deeply subsident rift formed in early Cambrian. It forms the eastern and southern portion of the Stansbury Basin, extending to the Glenelg River region of Victoria. Most rocks were highly deformed and experienced moderate to high grade

metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...

during the Delamerian Orogeny.

Arrowie Basin

The Arrowie Basin is second of the two known Cambrian basins of the Adelaide Superbasin. It extends from the Stuart Shelf in the west across the Flinders Ranges to western New South Wales where it forms part of the Neoproterozoic–Cambrian cover on the Curnamona Province.

Yalkalpo Sub-basin

The Yalkalpo Sub-basin is the easternmost part of the Arrowie Basin. Its western boundary is the

basement high In geology, a basement high is a portion of the basement in a sedimentary basin that is higher than its surroundings. Commonly, structures referred to as basement highs are hidden by the sedimentary fill of the basin. Usually basement highs are e ...

Benagerie Ridge of the Curnamona Province.

Lithostratigraphy

The

lithostratigraphy Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

of the Adelaide Superbasin is divided into three supergroups with further division into numerous

groups A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

and

subgroups In group theory, a branch of mathematics, given a group ''G'' under a binary operation ∗, a subset ''H'' of ''G'' is called a subgroup of ''G'' if ''H'' also forms a group under the operation ∗. More precisely, ''H'' is a subgrou ...

and over 140 formations.

Delamerian orogeny

Sedimentation in the Adelaide Superbasin ended in the middle Cambrian, when

tectonic inversion In structural geology inversion or basin inversion relates to the relative uplift of a sedimentary basin or similar structure as a result of crustal shortening. This normally excludes uplift developed in the footwalls of later extensional fau ...

occurred along the eastern margin of Neoproterozoic and Cambrian cratonic Australia and the margin became a subduction zone of the Palaeo-Pacific. After this time the region experienced an

orogeny Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An '' orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted ...

(mountain-building period) extending into the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

. Foden et al. (2006) suggest that this orogeny lasted from ~514 Ma to 490 Ma. This event is called the Delamerian Orogeny, named after Delamere, a small town on the Fleurieu Peninsula where evidence was found for the event. The orogeny caused substantial folding, buckling, and faulting of the strata, and resulted in the creation of a major mountain range, the eroded stumps of which can today be seen as the Mount Lofty and Flinders Ranges. Not all of the basin experienced tectonic activity; the deposits on the Stuart Shelf and Coombalarnie Platform to the north-west and north-east remained undisturbed (and still do today). Accompanying this folding and faulting were several

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s: the granites at Victor Harbor were intruded at this time, as were those at Palmer in the eastern South Mount Lofty Ranges.

Fossil content

Fossils of the earliest

Animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

ia are found in the Adelaide Superbasin. The first of these might be the probable sponges found in the Trezona Formation, although the first confirmed Animalia are the world-renowned Ediacaran fauna, named for the

Ediacara Hills Ediacara Hills are a range of low hills in the northern part of the Flinders Ranges of South Australia, around north of the state capital of Adelaide. The hills are known for being the location of significant fossils, and have given their nam ...

where they were first discovered in South Australia in 1946. They occur at the end of the

, and in 2004 the location gave its name to the last geological period of the era, the

Recent geological history

The ranges formed during the Delamerian orogeny continue to erode, and intra-plate subsidence is occurring. In the South Mount Lofty Ranges this has resulted in rifting and the formation of

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic conte ...

structures, creating the long parallel faults which shape the

Adelaide Plains The Adelaide Plains (Kaurna name Tarndanya) is a plain in South Australia lying between the coast (Gulf St Vincent) on the west and the Mount Lofty Ranges on the east. The southernmost tip of the plain is in the southern seaside suburbs of Ade ...

References

External links

Atlas of South Australia

Geoscience Australia

Geological Survey of South Australia
Sedimentary basins of Australia Aulacogens Rift basins Neoproterozoic rifts and grabens Precambrian Australia Geology of South Australia