Australia: The Land Where Time Began
The Neoproterozoic has been subdivided into the:
By 1300-1000 Ma, Archaean and Palaeoproterozoic-Mesoproterozoic blocks had assembled, being amalgamated along the Albany-Fraser Orogeny, Musgrave Orogeny and Rudall Orogeny (Myers et al., 1996). Load metamorphism and granite emplacement were among the activities that occurred subsequently along the sutures. The Victoria River Basin overlies the North Australian Craton in the north, which has swarms of dolerite dykes in the south. Prior to the Neoproterozoic, Gondwana appears to have possibly been composed only of Antarctica and Australia, the other continents joining Gondwana in the Neoproterozoic (Rogers et al., 1995).
Early Neoproterozoic lacuna 1000-840 Ma
Dolerite intrusion in the Mt Webb region, 23o S, 128o E, dated to 972 +/- 8 Ma and 976 +/- 3 Ma, is the only event in the lacuna that has been reliably dated (Veevers, 2000).
Centralian Superbasin and Adelaide Rift Complex 840-544 Ma
Throughout the Neoproterozoic, these were areas where contiguous deposition occurred. Towards the end of the Neoproterozoic and the late Palaeozoic, this deposition was disrupted. Structural basins now represent the Centralian Superbasin (CS), and the Adelaide Fold Belt represents the Adelaide Rift Complex (ARC). Continuity within the Centralian Superbasin is indicated by facies. With the exception of the Musgrave Block, which arose following the deposition of the Bitter Springs Formation on it, indicated by clasts in the Winnall beds, the periphery of the superbasin is the location of shoreline deposits.
The main areas of outcrop are the Amadeus Basin and the Adelaide Rift Complex. In the Late Cambrian, 500 Ma, the Adelaide Rift Complex was inverted to become the Adelaide Fold Belt. About 700 Ma, the rising of the Musgrave Block disrupted the Centralian Superbasin for the first time, then again from 580-530 Ma, in the Neoproterozoic-Cambrian, and in the Middle Carboniferous, the last time, disrupting it into structural basins about 320 Ma, in the Alice Springs Orogeny.
Four supersequences and 6 volcanic intervals have been recognised in the Neoproterozoic of Australia.
The Adelaide Rift Complex (ARC) has the most complete stratigraphic record, that is unique in Australia, with successions from 805-790 Ma, 780-745 Ma, excepting the Officer Basin, in the middle of the lacuna of the Centralian Superbasin, (?824-700 Ma). In the Polda Basin are evaporites that are 1.7 km thick, that are believed to be from the SS1 period. The record in the Adelaide Rift Complex between 700 and 544 Ma is virtually complete. In this period, there is a lacuna in the Centralian Superbasin between 635 and 600 Ma. In the Adelaide Rift Complex, there is a record of 220 of the 296 million years from 840-544 Ma. The record in the Centralian Superbasin covers a period of 135 million years. Evaporites and mafic volcanics, 840-750 Ma, glacials at 700 and 600 Ma, and mafic volcanics between 595 and 580 Ma, and at about 560 Ma, characterise the period covered.
Supersequence I - beginning
The deposition of Supersequence I began about 840 Ma in the Centralian Superbasin and the Adelaide Rift Complex. At the base of Supersequence I is a sand sheet, deposited in environments that ranged from fluvial to shallow marine, stretching from the Wolfe Basin (Grey & Blake, 1999) south, and west of the Tasman Line to the Savory Basin, and included conglomerates at the base of the Adelaide Rift Complex
The direction of palaeocurrents and isopachs in the Heavitree Quartz of the Amadeus Basin indicate the material originated to the northeast and north-northeast of the deposit. In the Georgina Basin, the correlative Yackah beds where northward thinning and wedging out against granite basement, supporting the conclusion of an origin for the material in the northeast-north-northeast. The main facies are fluvial, with some intertidal and very shallow marine facies (Clarke, 1976). Large amounts of sediment deposited in high-energy, open-shelf environments on a ramp of low gradient that was subsiding, leading to the geometry of the sheet (Lindsay, 1999). In the Ngalia Basin, the Vaughn Springs Quartzite is believed to be an alluvial fan deposit, which has been overlain by fluvial, tidal-flat and marine sandstone and conglomerate, and in the Officer Basin, the Townsend Quartzite as a sandstone of shallow marine to deltaic origin. There was a central depocentre in the Savory Basin that received sand and gravel from inflowing rivers. Some believe the basal sands of the Savory Basin are lateral equivalents of those of the Officer Basin (Bagas et al., 1999), making it the northwestern part of the Officer Basin. "Savory Basin" is retained by Walter & Veevers (2000), regarding it as the structural remnant of the Superbasin, as applies to the names of all the other basins. The basal sand can be traced to the north through the Birrindudu Basin, northward to the Mount Kinahan Sandstone in the Wolfe Basin (Grey & Blake, 1999).
Deposition was probably in proximal alluvial fans in the Adelaide Rift Complex, the sediments grading towards the basin to braided streams and possibly meandering streams (Preiss, 1987, p. 332). Fine sand, silt and mud were subsequently deposited offshore during marine transgression.
Carbonate-evaporite succession and dyke swarms
This stage, beginning at about 830 Ma, is characterised by interbedded deposits of stromatolitic carbonate and evaporite, with both halite and anhydrite, as well as basalt magma. The evidence for lithostratigraphic correlations within the Centralian Superbasin is regarded as convincing, comprising isotopic correlations (Hill & Walter, 2000; Walter et al., 2000), distinctive lithologies, continuity in outcrop or in seismic records, columnar stromatolites assemblages that are distinctive.
Thick halite and anhydrite, also dolostone and fine siliciclastics ,were deposited in a restricted marine environment (Hill et al., 2000b) in the lower (Gillan) member of the Bitter Springs Formation (BSF), in the Amadeus Basin. Overlying the Bitter Springs Formation is the Loves Creek Member that was deposited under conditions that ranged from lakes on shallow flood plains to arid supra-tidal flats, that have been compared to the subkhas of the Persian Gulf, and nearby was a complex of lagoon and offshore shoals. During subsequent deformation the salt beds became a decollment surface. Throughout the succession are thin basaltic flows.
Siltstone and shale, with stromatolitic cherty dolostone inderbeds, are found in the Albinia Formation, Ngalia Basin, and Yakah beds, of the Georgina Basin. The Eliot Range Dolomite and the Illjarra Sandstone represent the succession in the Wolfe Basin. The Browne Formation and the Madley Formation of the Officer Basin are made up of stromatolitic dolostone, anhydrite, and halite interbedded with sandstone, siltstone and shale. Beginning in the Neoproterozoic, diapirism, in which the mobile core of salt or gypsum, of an anticlinal fold, has broken through the overlying rock that is more brittle, was caused by the salt beds, persisted until the Cretaceous at the earliest, as happened at Woolnough Hills. In the Youalga sub-basin, a thickness of at least 4000 m is indicated by seismic interpretation. A set of palaeoenvironments similar to those of the Bitter Springs Formation are suggested by columnar stromatolites, Acaciella australica, chert microfossils, sedimentary facies and stable isotopes.
In the northeast of the Savory Basin, the Skates Hill Formation is comprised of stromatolitic dolostone, sandstone, siltstone, shale, local thick conglomerate, minor chert, evaporation is suggested by cauliflower chert and crystal voids after gypsum. Facies and stromatolites are similar to those from the Bitter Springs Formation. A facies change towards the west, from carbonate to sand, is indicated in the Mundadjini Formation by mostly siliciclastic with abundant evaporite pseudomorphs. Stromatolitic carbonates, red beds and evaporites mark the northern edge of the Savory Basin (Bagas et al., 1996).
Some of the same marine stromatolites that are found in the Loves Creek Member are also found in the Coominaree Dolomite in the Adelaide Rift Complex. Reddish brown laminated siltstone and mudstone, with minor sandstone and anhydrite aggregates, layers and veins, interlayered with amygdaloidal basalts, in the nearby Polda Basin, dated by K-Ar to 768+/- 9 Ma and 764 +/- 42 Ma (Flint et al., 1988). Fluvial and playa-like environments on an intracratonic volcanic graben is indicated by this association. To the west, massive halite, with minor interbeds of siltstone, have been penetrated to a depth of 1707 m (Preiss et al., 1993, p. 202-203), that is similar to the thick salt deposits of the Bitter Springs Formation.
According to Walter & Veevers, (2000), possible correlations may be made with a number of sites
Volcanic Interval I is comprised of the Bitter Springs Formation, mafic lavas, western Musgrave Inlier (WMI) 824 Ma dolerite, Callanna Group, flood basalts, the Amata dyke swarm and the Gairdner dyke swarm (Zhao et al., 1994; Wingate et al., 1998; Barovich & Foden, 2000). In the Adelaide Rift Complex, the Curdimurka Subgroup, a siliciclastic-carbonate-evapotite deposit, that was 6 km thick, was laid down after a 20 million year lacuna, in what is believed to have been environments of fluvial and evaporite (alkaline) lacustrine and restricted marginal marine environment in a northwest trending graben (Preiss et al., 1993, p. 175). The only record of the Volcanic interval II is the Rook Tuff, an 802 Ma dark grey siltstone that has a porphyritic dacite lens.
755 Ma. In the west there are dyke swarms, and in the east, restricted deposition of carbonates, and at 777 Ma, rhyolite and basalt. In Volcanic Interval III, rhyolite has been dated to 777 +/- 7 Ma (Preiss, 2000), and in the Rhynie Sandstone, associated amygdaloidal basalt. In Volcanic Interval IV, at Mundine, Muggamurra, and Northampton, dyke swarms have been dated to 755 +/- 3 Ma (Wingate & Giddings, 2000). It is thought the Kilroo Formation basalt may also be included. By 760 Ma, granite intrusions occurred at a location in King Island, Tasmania.
Deposition expanded to the central Officer Basin and the Adelaide Rift Complex (Walter & Veevers, 2000). In the central Officer Basin, the Kanpa Formation and the Hussar Formation are comprised of dolomite, shale, siltstone, and sandstone. The stromatolite Baicalia burra is found in these formations and the Skillogalee Dolomite (Walter & Veevers, 2000).
In the Adelaide Rift Complex, the Emeroo Sub-Group is comprised of fluvial to marginal marine sandstone with halite casts, siltstone and dolomite forming offshore. In the shallower areas, the Skillogalee carbonate was deposited, and in the southeast, black mud. Deposition in marginal marine environments is indicated by Oolitic, stromatolitic and intraclastic facies. In lagoons, magnesite deposition occurred. Siliciclastic deposition dominated at the end of this stage, as sand deltas spread from the margin, and offshore, in fairly deep environments below wave-base, muds rich in organic matter were deposited. After the Auburn dolomite, that formed during a marine transgression, the final deposition occurred when the regressive Belair Sandstone was laid down.
700 Ma. The Sturt Glaciation (see Australian Glaciation) and the beginning of Supersequence 2. With the exception of the Savory Basin, glacial sediments have been found at the base of Supersequence 2 in all parts of the Centralian Superbasin. Silty dolomite (cap dolomite) caps the glacial sediments, and locally they are capped with ironstone, the ARC containing the thickest deposits. Syndeposition faulting has led, at least in part, to rapid thickness changes and patchy distribution.
In the Areyonga Formation, in the Amadeus Basin, in small steep sided valleys cut into the Bitter Springs Formation, are randomly orientated blocks. Boulders in the Areyonga Formation indicate that the Heavitree Quartzite, the Bitter Springs Formation, and the Arunta Complex were all exposed in the landmasses in the north that were glaciated (Wells et al., 1970, p.31), and areas in the south of the Amadeus Basin were uplifted in the Areyonga Movement, providing a source of sediment. The thinning of the Inindia Beds, of equivalent and younger age, from 2000 m along the southwest margin of the Amadeus Basin to 100 m of the Areyongs Formation in the northeast (Wells et al., 1970, p.27), is an indication of a newly uplifted source in the Musgrave Block. Grey silty dolomite caps diamictite, conglonerate and sandstone, with occasional dropstones and minor shale elsewhere. Clasts originate both within and outside the basin. The lower part of the succession is believed to probably be marine, changing to a fluvial succession in higher levels. Sub-glacial and ice margin deposits are probably represented by the thinner overlying diamictites. The final stage of deposition was shallow marine with nearby ice, the deposit being poorly bedded diamictites and sandstone bodies with much soft-sediment deformation.
In the Georgina Basin, the Yardida Tillite consists of green-grey diamictite and laminated siltstone with occasional fine- to coarse-grained sandstone and arkose, with a capping of grey silty dolomite. The Mount Cornish Formation, that is equivalent, consists of blue-green diamictites, with clasts up to 12 m in diameter, with gneiss, pegmatite, granite, dolerite, sandstone and dolostone with interbedded green varved siltstone.
The Chambers Bluff Tillite, in the Officer Basin, consists of basal graded sandy siltstone (?glacial varves), above which are pebbly, silty and calcareous (?marine-glacial) diamictite with many polymictic clasts. There is also a thin sandstone unit and minor limestone. It has been suggested the succession probably transgressed westward above basement (Walter & Veevers, 2000). Deposits in the east are comprised of deeper marine, ferruginous sediment.
A dolomite cap, associated with patches of magnetite ironstone, caps the correlative Sturt glacials of the Adelaide Rift Complex (Preiss, 1987). The glacials are on a regional unconformity that cuts progressively deeper to the north in the Burra Group. The Gawler Craton to the west appears to have been a source of the glaciogenic sediment, and in the northeast, the Curnamona Cratonic Nucleus and the Muloorina Ridge, are believed to have also contributed sediment. Ice was shed into valley glaciers from highlands in these areas, the glaciers coalescing in the lowlands to form a continuous ice sheet over the shelf. The cap dolomite of the Walsh Tillite could be a Sturt equivalent, as indicated by limited palaeomagnetic information (Li, 2000).
650 Ma. Mud and silt were deposited widely in a shallow empeiric sea to form a thick deposit, reflecting a glacio-eustatic sea level rise (Walter et al., 2000). In the Adelaide Rift Complex, the succession shallows up to a peritidal carbonate, and in the Amadeus Basin, to sand. In the Aralka Formation, in the Amadeus Basin, the deposit is comprised of a basal dark grey siltstone and shale with dolostone concretions (cap dolomite), above which are green siltstone and shale, that is evenly bedded, with subordinate sandstone. Laminated siltstone and shale that show ripple marks are believed to have been deposited in fairly deep water above the storm wave base. In the Inindia Beds, siltstone and sandstone succession replaces the siltstone in the southwest. The Ringwood Member, in the northeast part of the basin, comprised of littoral stromatolitic dolostone, oolitic and intraclastic limestone, indicate a return to shallow deposition.
In the Adelaide Rift Complex the Tapley Hill Formation, that is coeval, is 2400 m thick, is believed to be marine, some parts of it probably being deposited below wave base. Pyrite in the deposit is extremely depleted in 32S, that is believed to probably indicate depletion in the ocean globally (Gorjan et al., 2000). The Tapley Hill Formation was the first unit to transgress to the west to the Stuart Shelf of the Gawler Craton across the Torrens Hinge Zone.
610 Ma. In the Umberatana Group in the central Flinders Ranges, Adelaide Rift Complex, the upper part, on the west side, is comprised of a carbonate platform between 2 redbeds, on the north and south it is comprised of shale. The cross-bedded oolitic limestone, with stromatolite bioherms, of the Etina Formation, was deposited during the rise of the Enorama Diapir. The transgressive Enorama Shale, that overlies the Etina Formation, that has bioherms on the flanks of the diapir (Lemon, 2000), shallows up to the intraclastic, oolitic and stromatolitic limestone, with calcareous siltstone, of the Terezona Formation (Preiss et al., 1993). There are no other known deposits of this age in Australia.
600 Ma. Beginning of Supersequence 3, Marinoan Glaciation. At the base of Supersequence 3 the glaciogenic rocks indicate they were probably deposited in conditions similar to those of Supersequence 2. The distribution of diamictites is patchy, being completely unknown from the Georgina Basin. Glacial outwash is believed to be the origin of the widespread deposits of arkose and conglomerate as well as arkosic sand.
A distinctively reddish diamictite, that includes clasts that are striated and faceted, and dropstones, all indicating it was tillite, have been found in the Olympic Formation, in the Amadeus Basin. Red and green mudstone and siltstone, with intercalated sandstone, conglomerate and dolostone, comprise the remainder of the formation. In siltstone beds overlying mass-flow conglomerates, lonestones are rarely found. Most of the clasts are composed of carbonate, other compositions being quartz, quartzose sandstone, granite, and gneiss. The composition of the clasts has been interpreted as indicating the environment under which they formed was periglacial, and not a continental ice sheet (Field, 1991). Field regarded the environment of their formation being possibly a trough between 2 glaciated areas, with parts that were nonmarine lacustrine and marine, with some deposits being of shoreface and foreshore origin, on the margin of the ice sheet of fringing glaciers. Glacial outwash from the tillite of the Olympic Formation is believed to be the origin of the Pioneer Sandstone.
Deposits 1000 m thick of arkose, pebbly arkose, conglomerate, siltstone and shale were laid down in half-grabens in the Black Swamp and Ooldea Arkoses in the Georgina Basin.
Subrounded, faceted and striated clasts, up to 4 m diameter, including igneous and metamorphic rocks, sandstone and dolostone, occur in poorly sorted boulder, cobble and pebble conglomerates, diamictite and arkose, in the Mt Davenport Member the lower part of the Mt Doreen Formation in the Ngalia Basin.
In the Wolfe Basin, the Fargoo Tillite and equivalents (Grey & Corkeron, 1998) overlie glaciated pavements, and are capped by cap dolomites, similar to those found above the Marinoan glacials in the Adelaide Rift Complex. In the northeast, in the Litchfield area of the Northern Territory, there are also glaciogenic sediments above striated pavements.
Diamictite, rhythmite, glauconic sandstone, pebbly sandstone and conglomerate are found in the lower part of the Boondawari Formation in the Savory Basin Grey et al., 1999). A wide variety of sedimentary rocks, as well as metamorphic and igneous rocks, are found as pebbles, cobbles and boulders, all angular, subrounded or wedge-shaped, polished, striated and faceted. A cap dolomite grades upward to shale. Sandstone is the main rock in the middle of the Boondawari Formation. The diamictites were interpreted as glaciogenic, indicating that they formed in a shallow marine environment under glacial conditions, but distant from the source of ice, the middle of the formation being deposited on a shelf (Williams, 1992a).
Patterned ground and dunefields were produced on the Stuart Shelf by periglacial conditions. The Marinoan Glaciation in the Adelaide Rift Complex, represented by the Elatina Formation, is composed of paralic sandstone, that tongues out laterally to the east and northeast into tillite. It has been suggested that tidal cycles are recorded in the rhythmite of the Elatina Formation, (Williams, 1989), and that the opening to a fully marine basin is indicated in the southeast by siltstone (Preiss, 1987). Deposition of the Elatina Formation in near equatorial conditions is indicated by palaeomagnetic studies. The Moonlight Valley Tillite, and equivalents, of the Wolfe Basin, are the only known location of glaciated pavements indicating grounded ice at low altitudes [?latitudes] (Coats & Preiss, 1980), currently 15o N of the Elatina Formation. In the Yerelina Subgroup, in the northern Flinders Ranges, a deposit of laminated siltstone that is 1000 m thick, containing occasional dropstones, and lenses of cobble, lies beneath a deposit of marine tillite 90 m thick, that grades up to glacial-outwash feldspathic sandstone. The basal deposits of the Wilpena Group were laid down above glaciogenic deposits during a time of glacio-eustatic sea level rise, micritic dolomite and shale of the Nuccaleena Formation and the overlying red-brown and olive-green marine siltstone and fine sandstone of the Brachina Formation (Preiss et al., 1993).
On King Island, distinctive glacial diamictite/pink cap dolomite indicate that by this time Tasmania had probably reached its present position in relation to the mainland of Australia (Calver & Walter, 2000). Supporting evidence is seen in the succeeding rift volcanoes that correlate with the rift volcanoes about the Tasman Line, 600-580 Ma, in New South Wales and Victoria.
580 Ma. Uplift of the Musgrave Block and rifting in the east, and post-glacial shale and sand sheet. The palaeogeography has been generalised to include the shaly lower and middle Wilpena Group of the Adelaide Rift Complex, and shale in the Savory Basin, Amadeus Basin and Georgina Basin, as well as the Acraman meteorite impact crater. This impact that occurred on the Gawler Craton spread a blanket of ejecta debris into the Dey Dey Formation in the northern part of the Officer Basin, and the Bunyeroo Formation of the Adelaide Rift Complex. Also at this time, about 580 Ma, the eastern half of the Centralian Superbasin, comprised of Grant Bluff, Cyclops Unit, Murnaroo Unit, and ABC Unit, was covered by a sand sheet sandwiched within shale.
In the upper part of the Duerdin Group, in the Wolfe Basin, a succession of shale, siltstone, greywacke, and sandstone overlie glacial deposits and the succeeding cap dolomites.
In the Amadeus Basin, the Pertatataka Formation, of laminated, micaceous siltstone and shale, of grey-green and purple-brown colour, within which are thin sandstone interbeds and occasional limestone. Glauconitic and clay pellets are present in some places, distal turbiditic sandstone in others. Where palaeocurrents are indicated, they are to the northeast. Deposition within storm wave-base is indicated by wave-rippled tops. The formation is distinguished in seismic sections by parallel reflectors that are weak and discontinuous, with north N-propagating clinoforms. The Pertatataka Formation appears to be predominantly marine, as indicated by the diverse assemblage of acritarchs that are presumed to be marine plankton (Zang & Walter, 1992), it is believed to be part of a single sequence that is upward-shallowing, that includes the carbonate of the Julie Formation that overlies it. Deposition of the Pertatataka Formation began during the rapid deepening of the basin, the initial depth being at maximum. The deposition from northward travelling turbidity currents of pelagic muds and turbidites in an outer submarine fan to a basin plain rising to a strandline in the northeast. This is represented by the sheet of the Cyclops Sandstone Member. The Winnall beds, in the southwest, are shallow marine, glauconitic and phosphatic, siltstone, sandstone, pebbly sandstone, dolostone and limestone. Conglomerates within these indicate that initial uplift occurred in the south with erosion of the Bitter Springs Formation, as well as metamorphic and igneous rocks. The initial disruption of the Superbasin by the uplift of the Musgrave Block about 590 Ma is indicated by the facies variation. The older Superbasin shed sediment and basement northeast through conglomerate to shale, distal turbidite in a central depression, shoaling to a strandline.
In the eastern part of the Officer Basin, on the far side of the Musgrave Block, the Meramangye Formation, comprised of 590 Ma siltstone and shale, are overlain by the Murnaroo Sandstone and the Rodd beds, the basal Dey Dey Formation of which contains ejecta from the Acraman impact (Walter et al., 2000). In the eastern Officer Basin, the widespread Murnaroo Formation is composed of fine-grained to coarse-grained, occasionally conglomeratic glauconitic sandstone. In the Rodda beds are grey-green calcareous and dolomitic siltstone with limestone and dolostone beds, feldspathic and calcareous sandstone. Significantly, there are also beds of pebble-cobble conglomerate, the Dey Dey Formation, Tanana Formation, Munyari Formation, and Narana Formation, as well as the Karlaya Limestone. The Rodda beds were deposited by mass flow, turbidity currents and hemipelagic processes in a subtidal through shelf ramp to deep-water slope-and-basin environment. They contain wedges that are basinward prograding.
At 590 Ma, definitive uplift of the Musgrave Block, with disruption of the Centralian Superbasin, during post-glacial sea level rise, was reflected by the onset of subsidence of the Meramangye Formation on the south and the Pertatataka Formation on the north. Rapid uplift and stripping of the Musgrave Block is indicated by the sand sheet of 580 Ma, and possibly a rift shoulder in the southeast, as indicated by the coeval ABC Quartzite of the Adelaide Rift Complex. Rapid stripping is also indicated by cooling of the Musgrave Block between 560 and 530 Ma (Maboko et al., 1991, 1992), presumably accompanied by the deposition of the piedmont (undated) Uluru Arkose at Uluru (Ayeres Rock) and the Mt Currie Conglomerate at Kata Tjuta (the Olgas) (Sweet & Crick, 1994), as well as the distal Arumbera Sandstone (dated). At 530 Ma, the final cooling coincided with the change from the Arumbera Sandstone to the Todd River Dolomite. At 565 Ma, canyons were cut in the eastern Officer Basin, and at 560 Ma and 555 Ma in the Adelaide Rift Complex. This is considered consistent with block uplift (Walter & Veevers in Veevers, 2000).
To the west, through the Officer Basin, deposition of shale, sandstone, anhydrite, gypsum and conglomerate took place. The Elyuah Formation and the Grant Bluff Formation, as well as parts of the Elkera Formation and Central Mount Stuart Formation, in the Georgina Basin were all deposited. In the Elyuah Formation, the rocks are mainly grey, green or red shale. In the Grant Bluff Formation, the rocks are mainly fine-grained quartz arenite, that are undulose laminated to thin-bedded. The deposit is mainly comprised of interbedded siltstone, shale and sandstone, with anhydrite nodules in the lower Elkera Formation. A shallow marine environment is suggested by trace fossils, stromatolites, ripple marks and sulphate evaporites. These units grade into the Central Mount Stuart Formation further to the west, where there is a higher proportion of sandstone.
The Brachina Formation, in the Adelaide Rift Complex, underlies the ABC Quartzite, that is of deltaic origin, which is overlain by the Bunyeroo Formation, a deposit of transgressive mud and silt, and includes the Acraman impact ejecta layer, which was deposited in what has been interpreted as a moderately deep marine environment in which islands were formed by diapirs (Preiss, 1987). The ABC Quartzite prograded from the west and the Faraway Hills Quartzite, the equivalent, prograded from the east (Preiss, 1987, p. 398). It is believed this could have been from the rising shoulder of the volcanic rift system that was the precursor of breakup.
Volcanoes were emplaced in Tasmania, that had by then amalgamated with Australia, along the same incipient margin.
560 Ma. This was the time of the breakup, the formation of the Petermann Ranges Orogeny, and flood basalt. The post-glacial siliciclastics successions shallow upwards to carbonate, and locally, with evaporites, ooid grainstones, and stromatolites. The Julie Formation, in the Amadeus Basin, the upper part of an upward-shallowing sequence beginning with the Pertatataka Formation, a succession of shallow marine dolostone, limestone and siltstone, with sandstone lenses. The dolostone is often oolite, locally containing stromatolites. In the Boord Formation in the western part of the Amadeus Basin, the equivalent upper part is composed of oolitic, stromatolitic calcilutite and calcarenite, with interbedded bands of siltstone and shale.
Interbedded siltstone, stromatolitic dolostone, sandstone and shale comprise the Elkera Formation in the Georgina Basin. Anhydrite and the shale halite pseudomorphs, are contained locally in the sandstone. A shallow marine environment is suggested by the presence of stromatolites, ripple marks and sulphate evaporites. To the west, the formation grades into sandstone of Central Mount Stuart Formation, that is of deltaic origin. Flood basalt of the Helen Springs Volcanics, an equivalent of the Antrim Plateau Volcanics (HSV), overlaps the basement at the northern edge of the basin, in which the Middle Cambrian limestone marks the upper age limit.
Diamictites of the Egan Formation, in the Wolfe Basin, that is coeval with the deformation that occurred in the King Leopold Orogen, have been suggested to possibly represent a third glaciation that has not been identified in other Australian basins (Grey & Corkeron, 1998). There are some possible equivalents in the Adelaide Rift Complex, but they are not proven at the time of writing (Walter & Veevers, in Veevers, 2000). Correlation with the Julie Formation is suggested by Tungussia julia, a stromatolite. Walter & Veevers (in Veevers, 2000) have 570 Ma as the age of the Egan formation. The diamictites have been attributed to glaciation of a local mountain. The dolomitic sandstone of the Albert Edward Group overlies them, which is in turn overlain by the flood basalt of the Antrim Plateau Volcanics. The age of these volcanics is limited by the age of the youngest rocks they cover, the Egan Formation at 570 Ma, and the rocks of the Middle Cambrian limestone, which is above the volcanics, of 520 Ma age. Stromatolites in interbedded cherts provide the only internal evidence of age, suggesting the latest Neoproterozoic (Walter, 1979, p. 49). Walter and Veevers have placed it tentatively at 560-555 Ma [Precise radiometric dating was expected at the time of writing]. The Antrim Plateau Volcanics covered an area of 425,000 km2 in northern Australia. The deposits, 1500 m thick, are comprised of massive amyddaloidal [amygdaloidal] and vesicular tholeiitic basalt flows and agglomerate containing interbeds of nonmarine conglomerate sandstone, chert and limestone.
The basalt Table Hill Volcanics in the central Officer Basin covers 90,000 km2 to the southwest of the Musgrave Block (GSWA, 1990, p. 377). They have been tenuously dated (Rb/Sr) to 563 +/- 40 Ma (recalculated from Compston, 1974), or latest Neoproterozoic. It has been suggested they may be of a similar age to the Antrim Plateau Volcanics. A sample from a Yowalga 2 core, at 2760 feet, had a K-Ar date of 500 +/- 7 Ma, that has been interpreted by McDougall (1995) as a minimum date. In the southwestern Yilgarn Block, the Boyagin dyke swarm, that is suggested to possibly be part of this vast basalt province, has been dated to 578-548 Ma by Rb/Sr (GSWA, 1990, p.273).
An argillaceous-carbonate association of shale and siltstone that is upward-coarsening to fine-grained to coarse-grained sandstone, with halite clasts and oolitic, pisolitic and stromatolitic dolostone is present in the Savory Basin.
The middle Rodda Beds, in the eastern part of the Officer Basin, are comprised of rocks such as limestone and dolostone, siltstone and shale, as well as feldspathic and calcareous sandstone. It is believed the Rodda beds were deposited by mass flow, turbidity currents and hemipelagic processes in an environment of a deep-water slope and basin. A canyon-forming event has been described, cutting down from the top of the Munyarai Formation, about 565 Ma, that cut 600 m into the underlying Murnaroo Sandstone (Lindsay & Leven. 1996; Calver & Lindsay, 1998). The cutting of the canyons took place during the growth of the basement ridges and anticlines that were induced by compression, being amplified by movement of salt from the underlying Alinya Formation, an equivalent of the Bitter Springs Formation. From a southern platform, the canyons were oriented to the north, downslope, and not from the Musgrave Block that was overthrusting. It has been suggested that it was coeval, as well as possibly cogeneric, with the uplift of the Musgrave Block, during a period when structural change was taking place, including rifting along the incipient eastern margin (Walter & Veevers in Veevers, source 1).
Lime mud and fine calcareous sand and silt that characterises the Wonka Formation, in the Adelaide Rift Complex, were deposited in an environment of a deep shelf to slope. A locally stratified ocean in a restricted basinal environment is indicated by divergent carbon-isotopic composition of kerogen and carbonate (Calver, 2000).
Valleys or canyons were deeply cut, up to 1 km deep, from levels near the middle of the Wonka Formation (Christie-Black, 1995), calibrated by Walter & Veevers to 560 Ma, and at 555 Ma near the top. The high-order valleys have been interpreted as having been eroded in a subaerial environment, resulting from episodic lowering of the depositional base level. Rapid tractional sedimentation in a fluvial or fluvial dominated shallow drowned valley environment is believed to have led to the formation of conglomerate. From a shallow zone in the central Flinders Ranges, the basin deepened to the north and the south for the first time (Preiss, 1987). The incision in the eastern part of the Officer Basin occurred at about 565 Ma. At about 560 Ma, the uplift occurred that led to the 1 km incision, at the age of breakup at the Tasman Surface. Modern morphological analogues occur in the wadis that have been cut into the Arabian margin of the Red Sea.
550 Ma. Supersequence 4, piedmont gravel and sand. The Pteermann Ranges Nappe and the Woodruff Fault Complex in the Musgrave Block, continued producing coarse sediment that was deposited in the Amadeus basin, bypassing the emergent Officer Basin, the only exception being the Punkerri Sandstone in Birksgate-1, in the northwest corner of South Australia. The Arumbera Sandstone was the main deposit in the Amadeus Basin, consisting of red-brown and white sandstone and minor siltstone, shale, conglomerate and carbonate. Metazoan body fossils of the Ediacaran Fauna of the latest Neoproterozoic, among which is Charniodiscus, are found in Units 1 &2, the lower Arumbera Sandstone. Sand from the southwest was carried by braided streams and deposited in coastal deltas on plains facing a shallow sea. In the south, the Mt Currie Conglomerate and the Uluru Arkose (Sweet & Crick, 1994) are believed to be proximal correlates of the Arumbera Sandstone, though it is not known whether they correlate with the lower, latest Neoproterozoic or the upper Neoproterozoic part, the upper Early Cambrian. In the western part of the basin, the same uncertainty applies to the Sir Frederick Conglomerate, and the correlative Ellis Sandstone.
Soft-bodied metazoan and trace fossils from the Ediacaran Fauna are found in the sandstone and siltstone of the Upper Mount Stuart Formation of the Georgina Basin.
In the Savory Sub-basin, the McFadden Formation, that is believed to be possibly of this age, consists of sandstone, minor pebble and granule conglomerate, and siltstone. Grain-size increases to the north to the margin of the basin. From the Peterson Orogeny, palaeocurrents indicate the presence of a west-southwesterly palaeoslope from the Peterson Orogen. There are no known sediments from the King Leopold Orogen in the north.
The Pound Subgroup represents Supersequence 4 in the Adelaide Rift Complex, of which the constituent Bonney Sandstone was deposited "as a prograding coastal sandflat or tidal delta" (Walters & Veevers, 2000). The overlying Rawnsley Quartzite was deposited as a "prograding shoreface, barrier and tidal channel facies complex" (Preiss, 1987). Soft-bodied metazoans of the Ediacaran Fauna are preserved in the muddy sands of the Rawnsley Quartzite, possibly the deposits of pro-delta channels (Geyling, 2000). To the southeast and northeast there are deeper basinal sands and muds. The Rawnsley Quartzite is composed of the most resistant rock in the Flinders Ranges, and is the main reason for the scenic attractions of Wilpena Pound, as well as other scenic parts of the Ranges.
The Nemakit-Daldynian lacuna, of early Early Cambrian age, that is found throughout Australia, with the exception of Units 3 & 4 of the Arumbera Sandstone, has been attributed to a eustatic sealevel fall. In the Tommotian, of later Early Cambrian age, deposition in fluvial and shallow marine environments resumed.
Proterozoic analogues of the Adelaide Rift Complex and the Neoproterozoic Superbasin
The Adelaide Rift Complex of the Neoproterozoic & the Perth Rift Complex of the Palaeozoic-Mesozoic
In the west, the internal Gawler Craton and in the east, the external Curnamona Craton-Willyama Block, confine the part of the Adelaide Rift Complex that is north of 32o S in the Flinders Ranges. This Flinders Zone has been compared with the Bass Basin of the Mesozoic-Cenozoic, a failed arm in southeastern Australia, that is confined by the internal mainland craton and external Tasmanian Craton (Preiss, 1990). The Fleurieu-Nackara Arc of Delamerian age, on the southeast is matched by the passive margin, that are the successful arms, offshore of western Victoria and western Tasmania. This general model is followed by Walters & Veevers (2000) in their interpretation, and in particular, the model of the Flinders Zone by von der Borch (1980), regarding it as an intracratonic rift between the Gawler Craton and the Curnamona Craton, of Neoproterozoic age, about 840-560 Ma, that was transformed to a failed arm by continental breakup along the southeastern part about 560 Ma.
The Adelaide Rift Complex mimics the salient features of the Perth Rift Complex in cross section (Walter & Veevers, in Veevers, 2000).
The Adelaide Rift Complex corresponds with the Perth Rift Complex, by about +400 Ma, as represented by the complete Carnarvon Basin - inception age being similar, 840 Ma vs 500 Ma, evaporites, 830 Ma vs 420 Ma, glacials, 300 Ma vs 700 Ma.
Centralian Superbasin of the Neoproterozoic vs Canning and Amadeus Basins of the Palaeozoic
The Centralian Superbasin, at 2000 km long, is almost the same size, 1900 km, as the Canning and Amadeus Basins of the Palaeozoic.
Australia's connection with Antarctica, as part of East Gondwana, can be traced back to the breakup in the Middle Cretaceous through the Australian-Antarctic Depression, throughout the Mesozoic and Palaeozoic to the late Neoproterozoic and earlier by structural continuity, such as the foreland basin along the Panthalassan margin in the Permian-Triassic (Du Toit, 1937), and the Prydz-Leeuwin Belt of about 600 Ma, as well as the provenance linkage by 600-500 Ma zircons (Veevers, 2000, Ch.17).
Australia was linked to Laurentia in and out of Pangaea B.
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|