2.a.1. Yudnamutana Subgroup

The glaciogenic nature of rocks within the Yudnamutana Subgroup was first recognized by Howchin (Reference Howchin1901), with those sequences being traced throughout the Mount Lofty, Flinders and Olary Ranges during the early 20th century (Preiss et al. Reference Preiss, Gostin, McKirdy, Ashley, Williams, Schmidt, Arnaud, Halverson and Shields-Zhou2011). Of particular note are the Yudnamutana Subgroup ‘tillites’ that rose to international prominence at the start of the 1900s (David, Reference David1906; Howchin, Reference Howchin1908; Cooper, Reference Cooper2010 and references therein). As a result, a significant amount of research on the nature of the Yudnamutana Subgroup has been published over the past century (e.g. Howchin, Reference Howchin1901; Howchin, Reference Howchin1904; David, Reference David1906; Howchin, Reference Howchin1906; Howchin, Reference Howchin1908; Howchin, Reference Howchin1920; Segnit, Reference Segnit1939; Mawson & Sprigg, Reference Mawson and Sprigg1950; Sprigg, Reference Sprigg, Glaessner and Sprigg1952; Thomson et al. Reference Thomson, Coats, Mirams, Forbes, Dalgarno and Johnson1964; Forbes & Cooper, Reference Forbes and Cooper1976; Coats & Forbes, Reference Coats and Forbes1977; Preiss et al. Reference Preiss, Walter, Coats and Wells1978; Link & Gostin, Reference Link and Gostin1981; Preiss, Reference Preiss1987; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998; Preiss, Reference Preiss2000; Fanning & Link, Reference Fanning and Link2008; Le Heron et al. Reference Le Heron, Cox, Trundley and Collins2011; Preiss et al. Reference Preiss, Gostin, McKirdy, Ashley, Williams, Schmidt, Arnaud, Halverson and Shields-Zhou2011; Cox et al. Reference Cox, Halverson, Minarik, Le Heron, Macdonald, Bellefroid and Strauss2013; Le Heron et al. Reference Le Heron, Busfield and Collins2014; Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b; Conor & Preiss, Reference Conor and Preiss2019; Virgo et al. Reference Virgo, Collins, Amos, Farkaš, Blades and Subarkah2021).

The Fitton Formation (Figs. 3, 4) is the oldest known unit of the Yudnamutana Subgroup and is present only in the Yudnamutana Trough of the northern Flinders Ranges (Fig. 1). The Fitton Formation consists of a basal conglomeratic facies, known as the Hamilton Creek Member, while the remainder of the formation is predominantly finely laminated mudstone and hornfels. The Hamilton Creek Member comprises laminated silty mudstone interbedded with gravel to boulder conglomerates and minor sandstone. The conglomerates range from a few centimetres to 20 m in thickness and are mostly massive although some have crude stratification. Sandy orthoconglomerates predominate, some are graded, with diamictite present in the lower parts of the unit. Mudstones are commonly interbedded with thin sandstone layers and gravel-to-pebble conglomerate. Some rare ripple-cross laminations are present in the unit, and dropstones are noted in the upper part of the member (Young & Gostin, Reference Young and Gostin1989b). The majority of the Fitton Formation primarily comprises laminated silty mudstones containing abundant metamorphic scapolite, with diamictite beds throughout. Minor conglomerates, sandstones and actinolitic marbles are also present. Sandstones are more abundant in the lower half of the formation, while diamictite is more abundant in the upper half, as are dropstones (Preiss, Reference Preiss1987; Young & Gostin, Reference Young and Gostin1989b). The formation has been interpreted as recording a sequence of glacial advance, retreat and then a second advance (Young & Gostin, Reference Young and Gostin1989b). The Fitton Formation is conformably overlain by the Bolla Bollana Tillite (Young & Gostin, Reference Young and Gostin1989b; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998).

Figure 4.

Generalized composite stratigraphic log of the Fitton Formation, Sturt Formation and Lyndhurst Formation at their type sections near MacDonald Creek, Arkaroola area. Based on data from Young and Gostin (Reference Young and Gostin1989b).

The Bolla Bollana Tillite is one of six formally named diamictite-abundant formations of the Yudnamutana Subgroup, which are lithostratigraphic correlatives (Figs. 3, 5). The six correlative formations are the Appila Tillite (Thomson et al. Reference Thomson, Coats, Mirams, Forbes, Dalgarno and Johnson1964) (based on the section of Segnit, Reference Segnit1939), the Bolla Bollana Tillite (Thomson et al. Reference Thomson, Coats, Mirams, Forbes, Dalgarno and Johnson1964; Coats & Forbes, Reference Coats and Forbes1977), the Calthorinna Tillite (Ambrose et al. Reference Ambrose, Flint and Webb1981), the Merinjina Tillite (Coats & Preiss, Reference Coats, Preiss and Preiss1987), the Pualco Tillite (Forbes & Cooper, Reference Forbes and Cooper1976) and the Sturt Tillite (Howchin, Reference Howchin1920; Mawson & Sprigg, Reference Mawson and Sprigg1950). These six correlative formations are here combined and referred to as the Sturt Formation (Figs. 3, 5) with a formal redefinition presented in section 5.e.1 below.

Figure 5.

Generalized stratigraphic logs of the Sturt Formation at its type section and additional reference sections. For coordinates of locations see the accompanying stratigraphic unit definition (Appendix 2). Copley, Yankaninna, Willouran Ranges and Vulkathuhna-Gammon Ranges sections are from logging done by authors in this study. Type section is based on data from Belperio (Reference Belperio1973) and Young and Gostin (Reference Young and Gostin1989b). Other sections are compiled from Segnit (Reference Segnit1939), Forbes and Cooper (Reference Forbes and Cooper1976), Coats and Preiss (Reference Coats, Preiss and Preiss1987) and Link (Reference Link1977).

At the type locality, the Sturt Formation comprises (boulder) diamictite showing evidence for glaciogenic origin and numerous subsidiary lithologies including poorly sorted sandstones and conglomerates through to finely laminated shales containing a wide variety of lonestones and dropstones (Fig. 4). Four generalized lithofacies are defined at the type location (Belperio, Reference Belperio1973; Young & Gostin, Reference Young and Gostin1989b). The lowermost unit comprises very poorly sorted conglomerates with sandy matrix to diamictites with muddy, silty and even very fine sandy matrix. Clasts range up to boulder size (largest observed is ∼1 m) and there are minor interbeds of laminated siltstone. A higher concentration of larger clasts is present in the lower sections. The next lithofacies comprises interbedded, well-laminated shales and sandy micaceous siltstones. There are minor pebbly lenses and silty arenites with cross-bedding present and are often ripple marked. The third lithofacies comprises crudely stratified diamictite (lithic wacke, muddy to silty matrix) with clasts ranging up to boulder size (max. observed: 90 cm). There are minor interbeds of calcareous shale and thick interbeds of massive diamictite. The uppermost lithofacies is similar to the third; however, it has a higher mud content in the matrix and is mostly massive diamictite. There are also a greater number of clasts with greater size diversity ranging up to 1.25 m (observed) in this uppermost lithofacies.

In general, the lithologic sequence common throughout the basin for the Sturt Formation (Fig. 5) for complete or near-complete sections consists of three units. The lowermost is a poorly sorted, gravel-to-boulder conglomerate (diamictite in some areas) with a generally sandy matrix. Scoured bases are common in areas where the Fitton Formation is not present. The middle unit comprises interbedded fine laminated siltstones and shales to cross-bedded sandstones with few lonestones/dropstones. The uppermost unit is either a massive or stratified boulder diamictite. Regional variation does occur, notably arkosic, poorly sorted immature sandstones and cross-bedded sandstones are predominant in some areas. Carbonate matrixes and interbeds are abundant in some regions (Hood et al. Reference Hood, Penman, Lechte, Wallace, Giddings and Planavsky2021). Clast size and type in diamictite vary greatly across the basin, with sizes up to boulder megaclasts of ∼1.25 km (Conor & Preiss, Reference Conor and Preiss2019). Iron-rich sections are present within the Sturt Formation underlying the Benda Siltstone and Holowilena Ironstone (Preiss, Reference Preiss1987; Preiss et al. Reference Preiss, Gostin, McKirdy, Ashley, Williams, Schmidt, Arnaud, Halverson and Shields-Zhou2011; Lechte & Wallace, Reference Lechte and Wallace2015).

The Benda Siltstone, Old Boolcoomata Conglomerate Member and Holowilena Ironstone either overlie or form the Sturt Formation (Fig. 3) but are only found in the Baratta Trough (Fig. 1) (Preiss, Reference Preiss2006; Lechte & Wallace, Reference Lechte and Wallace2015; Conor & Preiss, Reference Conor and Preiss2019). The accurate stratigraphic correlation of these units is still uncertain; however, they are likely partial equivalents of both underlying (Sturt Formation) and overlying (Wilyerpa and Lyndhurst formations) stratigraphy. The Benda Siltstone and Holowilena Ironstone have complex interfingering stratigraphic relationships with the Sturt Formation and Wilyerpa Formation.

The Benda Siltstone comprises dark-weathering, calcareous, dark and medium grey laminated siltstone and minor silty limestone. Iron-rich siltstone occurs in the lower part of the Benda Siltstone. Regional variation includes interbedded sandstones and dolostones (Preiss, Reference Preiss1987). The Old Boolcoomata Conglomerate Member of the Benda Siltstone comprises mainly clast-supported oligomictic conglomerate and minor arkosic grit. Clasts in the Old Boolcoomata Conglomerate Member are predominantly well-rounded to subrounded and mainly consist of two-mica S-type granites from the early Mesoproterozoic Bimbowrie Suite, with subsidiary clasts of migmatite, psammite, psammopelite, pelitic schist, albistized metasediment and calcalbitite (Preiss, Reference Preiss2006).

The Holowilena Ironstone is defined as a haematite siltstone with lenses of dolomite and wacke with glacial erratics and is considered to be an unmetamorphosed equivalent of the Benda Siltstone (Thomson et al. Reference Thomson, Coats, Mirams, Forbes, Dalgarno and Johnson1964; Preiss, Reference Preiss1987, Reference Preiss, Drexel, Preiss and Parker1993). The Holowilena Ironstone comprises hematitic siltstone, siltstone with minor lenses of dolostone, quartzite and pebbly to boulder, often massive ironstone (Thomson et al. Reference Thomson, Coats, Mirams, Forbes, Dalgarno and Johnson1964; Preiss, Reference Preiss1987; Lechte & Wallace, Reference Lechte and Wallace2015). The silty units are thinly and evenly bedded, occasionally with small cross-bedding. Regionally, some jasper is present.

The Wilyerpa Formation (Thomson et al. Reference Thomson, Coats, Mirams, Forbes, Dalgarno and Johnson1964; Dalgarno & Johnson, Reference Dalgarno and Johnson1966; Forbes, Reference Forbes1971) and correlative Lyndhurst Formation (Figs. 3, 4) (Thomson et al. Reference Thomson, Coats, Mirams, Forbes, Dalgarno and Johnson1964; Young & Gostin, Reference Young and Gostin1989b) are the youngest units of the Yudanamutana Subgroup (Fig. 2) and have been interpreted to represent the waning of the Sturtian Glaciation (Preiss, Reference Preiss1987; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998; Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b).

The Wilyerpa Formation is a variably thick unit (up to 4,400 m) comprising grey to green siltstones and shales with interbedded arenites and subsidiary diamictites and dolostones. Arkosic and quartzitic sandstones are common and predominate in some areas (Preiss, Reference Preiss1987). Two members, the Warcowie Dolomite Member and Bibliando Tillite Member, are defined within the Wilyerpa Formation. While originally thought to be restricted to the Baratta Trough (Fig. 1), subsequent research indicates that the Wilyerpa Formation may be more widespread (Fanning & Link, Reference Fanning and Link2006; Fanning & Link, Reference Fanning and Link2008; Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b). Relationships with the underlying stratigraphy (Sturt Formation, Benda Siltstone, Holowilena Ironstone) are variable with some areas being gradational and others disconformable, the latter likely due to active tectonics (Preiss, Reference Preiss1987; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998; Preiss, Reference Preiss2000).

The Lyndhurst Formation is a sequence of predominantly laminated and ripple cross-laminated, blue pyritic and silty shale with minor green silty shale and interbedded quartzite, grits and sparse pebbly diamictites (Fig. 4). The unit conformably overlies the Sturt Formation and is considered to be restricted to the Yudnamutana Trough (Fig. 1) (Preiss, Reference Preiss1987; Young & Gostin, Reference Young and Gostin1989b; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998).

2.a.2. Yancowinna Subgroup

The Yancowinna Subgroup, Torrowangee Group, of western New South Wales was defined by Cooper and Tuckwell (Reference Cooper and Tuckwell1971) and described in more detail by Cooper et al. (Reference Cooper, Tuckwell, Gilligan and Meares1974). It consists of a sequence of coarse poorly sorted siliciclastics that include arkose, quartzite, sandstone, siltstone, conglomerate and diamictite (Cooper et al. Reference Cooper, Tuckwell, Gilligan and Meares1974; Preiss, Reference Preiss1987; Fitzherbert & Downes, Reference Fitzherbert and Downes2015). Tillite has only been confidently recognized in one area (Cooper, Reference Cooper1973), but many of the facies closely resemble probable correlatives (Fig. 2) in South Australia (Preiss, Reference Preiss1987).

The Yancowinna Subgroup is overlain by the Euriowie Subgroup (postglacial) that is in turn overlain by the Teamsters Creek Subgroup (Fig. 2), which has been interpreted as recording the younger Cryogenian Marinoan (Elatina) Glaciation (Preiss, Reference Preiss1987; Fitzherbert & Downes, Reference Fitzherbert and Downes2015). The stratigraphic position of the Yancowinna Subgroup supports correlation with the Yudnamutana Subgroup of South Australia. Aside from detailed mapping and the original sedimentological work, there is extraordinarily little research on the Torrowangee Group (Fig. 2) sequences, and no geochronology has been published to date. As such the correlations are likely but uncertain and not yet confirmed by geochronology.

2.a.3. Nepouie Subgroup

The postglacial Nepouie Subgroup (Fig. 2) is believed to begin with the Serle Conglomerate, a sequence of stratified to crudely stratified conglomerates, with interbedded sandstones and shales (Young & Gostin, Reference Young and Gostin1989a; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998). The conglomerates of the Serle Conglomerate trend from primarily sandy siliciclastic matrix to carbonate-rich matrix up-sequence and are interpreted to have been deposited as part of a submarine fan complex (Young & Gostin, Reference Young and Gostin1989a). The stratigraphic position of the Serle Conglomerate is still somewhat uncertain; however, it appears to conformably underlie the Tapley Hill Formation and unconformably overlie the Lyndhurst Formation (Fig. 3) with an erosional contact (Young & Gostin, Reference Young and Gostin1989a; Dyson, Reference Dyson1996; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998; Dyson, Reference Dyson2004).

The Tapley Hill Formation primarily comprises well-sorted, commonly carbonaceous, calcareous or dolomitic siltstone, with pyritic shale and dolostone at its base (i.e. the Tindelpina Shale Member). Grain size and carbonate content tend to increase up-sequence, and fine laminations are abundant throughout the Tapley Hill Formation. While extensive in both distribution (basin-wide) and lithological uniformity, there are several minor lithofacies variations within the Tapley Hill Formation, including arkose, wacke, siltstone, dolostone and lenticular conglomerate beds (Preiss, Reference Preiss1987; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998; Virgo et al. Reference Virgo, Collins, Amos, Farkaš, Blades and Subarkah2021). The latter is attributed to debris flows reworking the underlying glaciogenic sequences (Preiss, Reference Preiss1987). Where the Serle Conglomerate is not present, the base of the Tapley Hill Formation is often disconformable with the underlying Yudnamutana Subgroup, although it may be gradational over a few centimetres in some areas (Preiss, Reference Preiss1987).

The youngest units of the Nepouie Subgroup are the Brighton Limestone and Balcanoona Formation, which conformably overlay and often interfinger with the Tapley Hill Formation. Both formations are predominately limestones with oolitic and stromatolitic features (Preiss, Reference Preiss1987, Reference Preiss2000). The Balcanoona Formation is coeval with the upper Tapley Hill Formation, forming large palaeo-reef systems above it and passing laterally into it (Wallace et al. Reference Wallace, Hood, Woon, Giddings and Fromhold2015), while the Brighton Limestone has been interpreted as the culmination of shallowing at the top of the Nepouie Subgroup (Preiss, Reference Preiss2000).

5.b.1. Maximum depositional ages

The older limit of expected depositional age for samples in this study is constrained by two DZ MDAs from the underlying Belair Subgroup, namely the Gilbert Range Quartzite (731 ± 34 Ma, Keeman et al. Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020; Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020) and Mitcham Quartzite (720 ± 21 Ma, van der Wolff, Reference van der Wolff2020). The younger age limit for deposition of the Yudnamutana Subgroup is constrained by a 663.03 ± 0.76 Ma tuff in the Wilyerpa Formation (Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018). The Serle Conglomerate is older than the c. 642 Ma minimum depositional age of the Tapley Hill Shale (Re–Os shale, Kendall et al. Reference Kendall, Creaser and Selby2006) that it is interpreted to underlie.

An MDA of 1134 ± 24 Ma was obtained for the combined Fitton Formation samples. This is significantly older than the expected depositional age c. 730–663 Ma.

The MDAs for the Sturt Formation, both existing and newly obtained, are presented in Table 1 according to the groupings outlined in section 4.a.2 above. There is significant scatter in MDAs across samples from the Sturt Formation; however, DZ age spectra are similar (Figs. 7, 9) throughout all samples (spanning more than 500 km north–south, Fig. 1). Three independent samples covering a distance of ∼250 km north–south have MDAs within uncertainty of each other. While DZ population spectra variations occur locally, as is expected across a large basin, and with significant recycling of underlying stratigraphy in glacially derived sediment, the remarkable similarity of most samples’ spectra (Figs. 7, 9) is consistent with lithostratigraphic mapping, which indicates that these units are correlative. In addition, many researchers have noted that the Sturt Formation often consists of two diamictite-abundant units separated by an argillaceous or arenaceous sequence (Lechte & Wallace, Reference Lechte and Wallace2015; Virgo et al. Reference Virgo, Collins, Amos, Farkaš, Blades and Subarkah2021). Different regions of the basin likely preserve deposits from different parts of the Sturtian glacial event where the two diamictite-abundant units may represent discrete periods of glacial advance or various phases of the glaciation (Lechte & Wallace, Reference Lechte and Wallace2015; Lechte et al. Reference Lechte, Wallace, Hood and Planavsky2018). Chronological constraints for the Sturt Formation had been almost non-existent up until recently but are now robust enough to bracket deposition of the Sturt Formation and Fitton Formation to between 720 ± 21 Ma and 663.03 ± 0.76 Ma (Fanning & Link, Reference Fanning and Link2008; Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b; Keeman et al. Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020; van der Wolff, Reference van der Wolff2020). Given the younger limit imposed by the Wilyerpa Formation tuff, the MDA of c. 663 ± 11 Ma is likely close to the true depositional age for at least the terminal deposits (upper portion) of the Sturt Formation.

Table 1.

Sturt Formation MDAs

* Keeman et al. (Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020); Lloyd et al. (Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020).

Figure 9.

Non-metric multidimensional scaling plot of samples analysed (n > 30) in this study (purple circles) with data from potential correlative formations of the Centralian Superbasin (purple squares), potential source regions (black and grey circles and triangles), older stratigraphy within the basin (blue and orange circles) and synthetic distributions (black stars) generated from the primary and secondary peaks of a KDE that combines all new data in this study. This plot shows relative similarity of all data to each other and is intended as a visual guide. Points that plot closer together suggest greater similarity and points that plot further away from each other indicate greater dissimilarity. Axes are omitted as the algorithm used produces normalized values with no physical meaning and can be safely removed. Produced using IsoplotR with the Kolmogorov-Smirnov metric (Vermeesch, Reference Vermeesch2018).

GSNSWKB002 was a reconnaissance sample collected from undifferentiated Yancowinna Subgroup in the Barrier Ranges of New South Wales to test the general correlation with the Yudnamutana Subgroup of South Australia. This area is the easternmost known extension of the Adelaide Superbasin during the Neoproterozoic (Cooper & Tuckwell, Reference Cooper and Tuckwell1971; Cooper, Reference Cooper1973; Preiss, Reference Preiss1987; Fitzherbert & Downes, Reference Fitzherbert and Downes2015; Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020). The sample is from a highly weathered diamictite with clasts ranging up to pebble size and a silty to fine sand matrix. An MDA of 1065 ± 18 Ma was obtained from the sample, with a DZ population spectrum similar to that of the probable correlatives in South Australia (Figs. 7, 9]. This provides limited but supporting evidence of a shared detrital source and that these two subgroups are correlative as is indicated by the existing lithostratigraphic framework (Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020).

An MDA of 1477 ± 33 Ma was obtained from the Wilyerpa Formation (FR1_005_02) sampled in the Clare Valley. This is significantly older than the expected depositional age (i.e. c. 663 Ma) and may be a factor of low zircon yield and/or no zircon close to depositional age being present in the sample.

An MDA of 1246 ± 24 Ma was obtained from the Serle Conglomerate sample (FR3_004). Again, this is significantly older than true depositional age, which is expected to be between c. 663 Ma and c. 642 Ma. The DZ population spectrum somewhat differs (Figs. 7, 9) from the nearby Sturt Formation sample (FR3_006), although this may partially be an artefact of the much lower zircon yield from the Serle Conglomerate sample.

5.b.2. Provenance

Two DZ populations, c. 1840–1790 Ma and c. 1640–1580 Ma, form major peaks in virtually all samples. The exact age positions and magnitude of the population peaks vary slightly by sample, with broad north–south and east–west variations, generally trending to older Palaeoproterozoic age populations in the west and south. It is likely that there is significant recycling of the unconformably underlying stratigraphy due to sub-glacial erosion (Young & Gostin, Reference Young and Gostin1989b). The similarity of the DZ spectra within the samples of this study to each other, and to earlier rocks of the Adelaide Superbasin (Fig. 9), suggests homogenization of detrital material over a large area, potentially with extra-basin material, as well as intra-basin recycling of earlier stratigraphy, presumably by glacial erosion.

Zircons with ages greater than c. 1400 Ma are likely sourced locally from the Gawler Craton, Barossa Complex and Curnamona Province that collectively record numerous zircon generation events and sedimentary sequences known to contain DZ of these ages (Swain et al. Reference Swain, Woodhouse, Hand, Barovich, Schwarz and Fanning2005; Fanning et al. Reference Fanning, Reid and Teale2007; Barovich & Hand, Reference Barovich and Hand2008; Conor & Preiss, Reference Conor and Preiss2008; Reid et al. Reference Reid, Hand, Jagodzinski, Kelsey and Pearson2008; Stevens et al, Reference Stevens, Page and Crooks2008; Belousova et al. Reference Belousova, Reid, Griffin and O’Reilly2009; Fraser & Neumann, Reference Fraser and Neumann2010; Fraser et al. Reference Fraser, McAvaney, Neumann, Szpunar and Reid2010; Jagodzinski & Fricke, Reference Jagodzinski and Fricke2010; Wade, Reference Wade2011; McAvaney, Reference McAvaney2012; Meaney, Reference Meaney2012; Reid & Hand, Reference Reid and Hand2012; Kromkhun et al. Reference Kromkhun, Foden, Hore and Baines2013; Morrissey et al. Reference Morrissey, Hand, Wade and Szpunar2013; Reid et al. Reference Reid, Jagodzinski, Armit, Dutch, Kirkland, Betts and Schaefer2014a; Reid et al. Reference Reid, Jagodzinski, Fraser and Pawley2014b; Jagodzinski & McAvaney, Reference Jagodzinski and McAvaney2017; Meaney, Reference Meaney2017; Reid & Payne, Reference Reid and Payne2017; Reid et al. Reference Reid, Jagodzinski, Wade, Payne and Jourdan2017; Morrissey et al. Reference Morrissey, Barovich, Hand, Howard, Payne and Reid2018; Morrissey et al. Reference Morrissey, Barovich, Hand, Howard and Payne2019; Reid, Halpin & Dutch, Reference Reid, Halpin and Dutch2019; Jagodzinski et al. Reference Jagodzinski, Werner, Curtis, Fabris, Pawley and Krapf2020; Reid et al. Reference Reid, Tiddy, Jagodzinski, Crowley, Conor, Brotodewo and Wade2021). The southernmost samples from Sturt Gorge are dominated by c. 1840 Ma zircons, and northward progression through the basin system generally sees a shift in dominance of the c. 1840 Ma population to the younger c. 1590 Ma population of zircon. This observation is likely a result of the variation in local basement geology of the Gawler Craton and Curnamona Province near the sample sites.

The generally minor Stenian population of zircon at c. 1160 Ma suggests provenance from the Musgrave Province (Smithies et al. Reference Smithies, Howard, Evins, Kirkland, Bodorkos and Wingate2008; Wade et al. Reference Wade, Kelsey, Hand and Barovich2008; Smithies et al. Reference Smithies, Howard, Evins, Kirkland, Kelsey, Hand, Wingate, Collins and Belousova2011; Smits et al. Reference Smits, Collins, Hand, Dutch and Payne2014), but as noted in Lloyd et al. (Reference Lloyd, Collins, Blades, Gilbert and Amos2022), they may be sourced from an as yet undiscovered but inferred late Mesoproterozoic (c. 1300–1000 Ma) source to the east (Wysoczanski & Allibone, Reference Wysoczanski and Allibone2004; Fergusson et al. Reference Fergusson, Henderson, Fanning and Withnall2007; Mackay, Reference Mackay2011; Korsch et al. Reference Korsch, Huston, Henderson, Blewett, Withnall, Fergusson, Collins, Saygin, Kositcin, Meixner, Chopping, Henson, Champion, Hutton, Wormald, Holzschuh and Costelloe2012). This Stenian zircon population is generally more abundant in samples closer to the eastern and western margins of the basin (Figs. 7, 1). Alternative sources of this late Mesoproterozoic zircon could be the South Tasman Rise (Fioretti et al. Reference Fioretti, Black, Foden and Visonà2005), Coompana Province (Pawley et al. Reference Pawley, Dutch and Wise2020) or far-field transport across Antarctica from the Tonian Oceanic Arc Super Terrane (Jacobs et al. Reference Jacobs, Elburg, Läufer, Kleinhanns, Henjes-Kunst, Estrada, Ruppel, Damaske, Montero and Bea2015). Again, recycling of underlying stratigraphy is a likely source of some of these zircons.

Neoproterozoic zircons with ages between c. 900 Ma and c. 780 Ma can be attributed to igneous events early in the Adelaide Superbasin. The known igneous events of the Adelaide Superbasin for this time period are the Willouran Large Igneous Province c. 830 Ma (Wingate et al. Reference Wingate, Campbell, Compston and Gibson1998; Preiss, Reference Preiss2000; Wade et al. Reference Wade, McAvaney and Gordan2014; Lloyd et al. Reference Lloyd, Collins, Blades, Gilbert and Amos2022), Oodla Wirra Volcanics c. 798 Ma (Fabris et al. Reference Fabris, Constable, Conor, Woodhouse, Hore and Fanning2005), Boucaut Volcanics c. 788 Ma (Armistead et al. Reference Armistead, Collins, Buckman and Atkins2020) and magmatism associated with the Kooringa Member of the Skillogalee Dolomite c. 7 0 Ma (Preiss et al. Reference Preiss, Drexel and Reid2009).

Zircon younger than 780 Ma is much more difficult to reconcile. It is apparent that some zircon-bearing igneous events were occurring c. 700 Ma to c. 660 Ma, and that these zircons were in the sediment supply of the Sturt Formation. The igneous events may have been distal to the basin and may have occurred as short-lived pulses. While a 663.03 ± 0.76 Ma tuff has been dated (Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b) from within the Wilyerpa Formation immediately post-dating deposition of the Sturt Formation, the site of the volcanic centre for the ashfall is unknown. Additionally, zircon of c. 700–660 Ma within the Sturt Formation has so far only been found on the far western margin of the Adelaide Rift Complex within the Adelaide Superbasin (Fig. 10), indicating this magmatic source may have been to the west of or on the western margin of the basin.

Figure 10.

Schematic map with pie charts at sample locations to highlight the changes in zircon population spectra relative to geographic location. Arrows are generalized schematic indicators of palaeo-sediment transport direction. Includes data from this study, Preiss (Reference Preiss2014), Keeman et al. (Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020) and Lloyd et al. (Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020).

Within the Centralian Superbasin, the syn-glacial Yardida Tillite and Areyonga Formation, and the post-glacial Aralka Formation are suggested as correlatives of the Sturt Formation and Tapley Hill Formation, respectively (Preiss et al. Reference Preiss, Walter, Coats and Wells1978; Edgoose, Reference Edgoose, Ahmad and Munson2013; Kruse et al. Reference Kruse, Dunster, Munson, Ahmad and Munson2013; Normington & Donnellan, Reference Normington and Donnellan2020). Interestingly, the DZ age spectrum of the Yardida Tillite (Georgina Basin, Northern Territory/Queensland) is very similar (Fig. 9) to that of the local basement of South Australia (e.g. Gawler Craton). This is explained by its proximity to the Mount Isa and Aileron provinces, suggested to be the primary zircon source for the Yardida Tillite (Verdel et al. Reference Verdel, Campbell and Allen2021). These provinces host abundant c. 1850–1640 Ma zircon that is also found in the Gawler Craton and Curnamona Province. In addition, palaeomagnetic and geological reconstructions for the time suggest that the South Australian Craton may have been rotated closer to the Georgina Basin at that time (Li & Evans, Reference Li and Evans2010; Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020). The DZ age spectra of the Areyonga Formation and Aralka Formation (Amadeus Basin, Northern Territory/Western Australia) are similar to the Burra Group and Sturt Formation samples (Fig. 9) from the western margin of the Adelaide Rift Complex. All these units may have received zircons from the Musgrave Province where Stenian-aged zircons are abundant, and both basins have abundant nearby sources of pre-Stenian zircon. Notably, no zircon younger than c. 800 Ma has been found in the Areyonga and Aralka formations to date.

5.b.3. Comparison to palaeocurrent data

Observations drawn in this study from DZ generally support existing palaeocurrent data. Palaeocurrent data from the Yudnamutana Subgroup suggest a westerly transport direction in the Mount Painter area and along the Paralana fault system, northerly transport on the northern side of the Gammon syncline and Yankaninna anticline and north-easterly transport along the western edge of the Adelaide Rift Complex (Copley area, south-eastern Willouran Ranges) (Link & Gostin, Reference Link and Gostin1981; Young & Gostin, Reference Young and Gostin1989b; Young & Gostin, Reference Young, Gostin, Anderson and Ashley1991). It is likely that underlying strata were recycled by sub-glacial erosion, making the use of DZ spectra for determining palaeo-transport paths difficult. However, the only area where detrital data from this study potentially differ in transport direction from the existing palaeocurrent data is the Vulkathuhna-Gammon Ranges. The DZ populations in our data (Fig. 7: FR3_073, Fitton Formation samples) are most similar (Fig. 9) to older stratigraphy of the basin and to nearby basement sources located to the northeast (Fig. 1). This suggests a south or south-westerly sediment transport (Fig. 10) direction from these neighbouring basement sources into the depocentre.

5.e.1. South Australian formal stratigraphy

The correlation of diamictite-abundant units of the Yudnamutana Subgroup was subject to much debate during the 1970s and 1980s, with arguments both for and against these rocks representing two discrete glacial events separated by an unconformity (Coats & Forbes, Reference Coats and Forbes1977; Murrell et al. Reference Murrell, Link and Gostin1977; Coats & Preiss, Reference Coats, Preiss and Preiss1987). Subsequent research showed that the rocks named ‘Tillites’ of the Yudnamutana Subgroup were consistent with only one glacial event (Preiss, Reference Preiss, Drexel, Preiss and Parker1993; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998; Preiss, Reference Preiss2000) but representing ice sheet advance-retreat cycles (Le Heron, Reference Le Heron2012). The conjecture regarding correlation of the diamictite-abundant units using a specific clast type, and mapping by numerous individuals over a long period of time, has led to six formal names for a unit that is now known to be correlative across the entire Adelaide Superbasin. The six different names for what are the same unit have led to unnecessary artefacts on geologic maps (e.g. a unit changing name across a map sheet boundary) and can be confusing to those who are unfamiliar with local formal stratigraphic nomenclature.

No significant lithological differentiation distinguishes the diamictite-abundant units (Fig. 5) within the Yudnamutana Subgroup from each other, and both stratigraphic position and geochronology support their broad equivalence (Young & Gostin, Reference Young and Gostin1989b; Preiss et al. Reference Preiss, Dyson, Reid and Cowley1998, Reference Preiss, Gostin, McKirdy, Ashley, Williams, Schmidt, Arnaud, Halverson and Shields-Zhou2011; Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b; Keeman et al. Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020; Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020; this study). Considering this evidence, we propose a refined stratigraphic nomenclature for the diamictite-abundant formations of the Yudnamutana Subgroup (e.g. Appila Tillite, Bolla Bollana Tillite, Sturt Tillite) as the Sturt Formation (Fig. 3). The name ‘Sturt’ is retained as the first glacial diamictite formally named the Sturtian tillite (Howchin, Reference Howchin1920; Mawson & Sprigg, Reference Mawson and Sprigg1950); therefore, it takes precedence over all other correlative formation names. Furthermore, it has become eponymous with the global Sturtian Glaciation. ‘Tillite’ has been dropped in favour of ‘Formation’ as, while glacial diamictite is the most distinctive lithology, it was not exclusively deposited by the direct action of glacial ice (much of it is glaciomarine) and is not the most volumetrically abundant rock type within the Sturt Formation across the entire Adelaide Superbasin (Preiss et al. Reference Preiss, Gostin, McKirdy, Ashley, Williams, Schmidt, Arnaud, Halverson and Shields-Zhou2011). Instead, the Sturt Formation comprises numerous lithologies that were deposited under general glacial conditions (Link, Reference Link1977; Link & Gostin, Reference Link and Gostin1981; Preiss, Reference Preiss1987; Preiss, Reference Preiss2000; Preiss et al. Reference Preiss, Gostin, McKirdy, Ashley, Williams, Schmidt, Arnaud, Halverson and Shields-Zhou2011; Virgo et al. Reference Virgo, Collins, Amos, Farkaš, Blades and Subarkah2021). The use of ‘Formation’ instead of ‘Tillite’ was proposed previously by Murrell et al. (Reference Murrell, Link and Gostin1977) and follows the international stratigraphic guide. A formal definition card accompanies this paper as Appendix 2, with the generalized stratigraphic logs of the type and reference sections presented in Figures 4 and 5. An additional stratigraphic log from drillhole SR13/2 on the Stuart Shelf is provided in Supplementary Figure S4.

5.e.2. Sturtian Glaciation (Cryochron)/Laurentian Neoproterozoic Glacial Interval

Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) proposed that the name ‘Laurentian Neoproterozoic Glacial Interval’ be used in favour of the name ‘Sturtian Glaciation’ for the first of two, major pan-glacial events recognized in Cryogenian rocks. Further, they suggest that the term ‘Sturtian Glaciation’ should be exclusively used for Australian strata, and that the global geochronologic data permit only a short 2.4 Ma long global glacial event or diachronous shifting of ice-centres across Rodinia. While Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) highlight the issue of interpreting results in a model-led approach, a notion we agree on, we disagree with their suggestion that use of the name Sturtian Glaciation for the first major Cryogenian pan-glacial event is no longer justifiable. This suggestion was primarily based on their interpretation that most rocks representing the Sturtian Glaciation in Australia chronometrically lie outside of the Sturtian glacial interval, c. 717–661 Ma (Rooney et al. Reference Rooney, Strauss, Brandon and Macdonald2015; Rooney et al. Reference Rooney, Yang, Condon, Zhu and Macdonald2020). Only the tuff from near the base of the Wilyerpa Formation (663.03 ± 0.76 Ma, Cox et al. Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b) was considered to be within the time interval defined for the Sturtian glacial event; this argument was reiterated by Kennedy et al. (Reference Kennedy, Eyles and McArthur2020).

However, the interpretation by Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) appears to hinge on the previous lack of data from early Cryogenian glacial (Yudnamutana Subgroup) and late Tonian pre-glacial (Burra Group) sequences in South Australia. Even with the challenges associated with constraining deposition by DZ studies, two studies (Keeman et al. Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020; Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020) have provided MDA constraints from the Sturt Formation (Table 1). This study presents a further ten DZ samples with two samples yielding MDAs within the 717–661 Ma period (Table 1), and a new in-situ Rb–Sr age from the Sturt Formation of 684 ± 37 Ma (Fig. 8). Importantly, DZ MDA constraints from the underlying Belair Subgroup (Fig. 2), namely the Gilbert Range Quartzite (731 ± 34 Ma, Keeman et al. Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020; Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020) and Mitcham Quartzite (720 ± 21 Ma, van der Wolff, Reference van der Wolff2020), provide maximum age estimations for when final deposition of the upper Burra Group began.

Additionally, Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) consider the Cox et al. (Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b) tuff age (Wilyerpa Formation, AUS) to be an MDA; however, both Fanning and Link (Reference Fanning and Link2006) and Cox et al. (Reference Cox, Isakson, Hoffman, Gernon, Schmitz, Shahin, Collins, Preiss, Blades, Mitchell and Nordsvan2018b) demonstrate that the tuff is syn-depositional, with their dating indicating volcanism was coeval with deglaciation. The tuff age provides neither a maximum nor minimum age for the Wilyerpa Formation as it occurs ∼80 m below the base of the Tapley Hill Formation; however, it provides a robust minimum age constraint for the underlying Sturt Formation.

Thus, the MDAs from the underlying Burra Group and the syn-depositional tuff in the Wilyerpa Formation require that rocks representing the early Cryogenian Sturtian Glaciation in South Australia (Sturt Formation, Fitton Formation) were deposited ≤730 Ma and ≥663 ± 0.76 Ma, thereby independently constraining the age of the Sturt Formation to the globally defined interval for the Sturtian Glaciation (Rooney et al. Reference Rooney, Strauss, Brandon and Macdonald2015; Rooney et al. Reference Rooney, Yang, Condon, Zhu and Macdonald2020). Initiation of final deglaciation for the Sturtian Glaciation can also be constrained, albeit loosely, by data in this study to c. 674–663 Ma, as sample FR3_139 from the upper Sturt Formation (MDA: 663 ± 11 Ma) came from the same stratigraphic interval as the Wilyerpa Formation tuff.

Furthermore, data from our study refute the Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) suggestion of a short, 2.4 million year, Sturtian Glaciation, 659.6 ± 10.2 Ma to 657.2 ± 5.4 Ma, based on Re–Os ages from the Aralka Formation (Kendall et al, Reference Kendall, Creaser and Selby2006), and Ballachulish Slate (Rooney et al. Reference Rooney, Chew and Selby2011) as the Australian Sturtian Glaciation deposits are definitively older than this proposed interval, there is an erosional unconformity between the Yudnamutana Subgroup rocks and the overlying post-glacial transgressive sequences, and the Aralka Formation is demonstrably post-glacial.

In contrast to the Wilyerpa Formation tuff, Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) interpret the age of an epiclastic tuff in the Pocatello Formation, USA (Fanning & Link, Reference Fanning and Link2004), as a minimum age estimate for the formation. This epiclastic tuff from the upper diamictite of the Pocatello Formation has been re-evaluated as an MDA and may actually be from a late Cryogenian Marinoan glacial sequence, unconformably overlying a non-glacial sequence, which in turn unconformably overlies a lower Sturtian glacial sequence (Isakson, Reference Isakson2017). Additionally, Isakson (Reference Isakson2017) had earlier revised several of the igneous ages presented in the Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) compilation, notably a syn-Sturtian age of the Hogback Rhyolite from 684 ± 4 Ma (Lund et al. Reference Lund, Aleinikoff, Evans and Fanning2003; Lund et al. Reference Lund, Aleinikoff, Evans, duBray, Dewitt and Unruh2010) to 693.03 ± 0.73 Ma. Isakson (Reference Isakson2017) presented two additional ages, 697.05 ± 0.28 Ma and 697.78 ± 0.18 Ma, from volcanics in the lower Scout Mountain Member of the Pocatello Formation, previously interpreted to be 686 ± 4 Ma (Fanning & Link, Reference Fanning and Link2008). The data of Keeley et al. (Reference Keeley, Link, Fanning and Schmitz2013) from the lower Scout Mountain member (685 ± 0.4 Ma) are presented as a depositional age by Le Heron et al. (Reference Le Heron, Eyles and Busfield2020), rather than as an MDA as the original authors and Isakson (Reference Isakson2017) present.

Available geochronology suggests that deposition of early Cryogenian glaciogenic rocks in at least Australia (Keeman et al. Reference Keeman, Turner, Haines, Belousova, Ireland, Brouwer, Foden and Wörner2020; Lloyd et al. Reference Lloyd, Blades, Counts, Collins, Amos, Wade, Hall, Hore, Ball, Shahin and Drabsch2020; this study), Arabia/Nubia (MacLennan et al. Reference MacLennan, Park, Swanson-Hysell, Maloof, Schoene, Gebreslassie, Antilla, Tesema, Alene and Haileab2018; Park et al. Reference Park, Swanson-Hysell, MacLennan, Maloof, Gebreslassie, Tremblay, Schoene, Alene, Anttila, Tesema and Haileab2019), Baltica (Środoń et al. Reference Środoń, Gerdes, Kramers and Bojanowski2022), Laurentia (Rooney et al. Reference Rooney, Macdonald, Strauss, Dudas, Hallmann and Selby2014; Isakson, Reference Isakson2017; Macdonald et al. Reference Macdonald, Schmitz, Strauss, Halverson, Gibson, Eyster, Cox, Mamrol and Crowley2018), South China (Song et al. Reference Song, Wang, Shi and Jiang2017; Wang et al. Reference Wang, Zhu, Zhao, Yan, Li, Shi and Zhang2019; Lan et al. Reference Lan, Huyskens, Lu, Li, Zhang, Lu and Yin2020; Rooney et al. Reference Rooney, Yang, Condon, Zhu and Macdonald2020) and Siberia (Rud‘ko et al. Reference Rud‘ko, Kuznetsov, Shatsillo, Rud‘ko, Malyshev, Dubenskiy, Sheshukov, Kanygina and Romanyuk2020) occurred globally within the c. 717–661 Ma interval. These ages cannot eliminate some diachroneity in the timing of onset of glaciation or the possibility of glacial advance and retreat cycles. Globally, final deglaciation appears to be relatively synchronous at c. 663–661 Ma (Fig. 6).

While Figure 6 and the equivalent diagram in Le Heron et al. (Reference Le Heron, Eyles and Busfield2020) provide brevity for visualization and assessment of the expanding global Cryogenian geochronologic datasets, they lack detailed stratigraphic context and methodology: unavoidable limitations for this style of diagram, with size, legibility and accessibility considerations all contributing factors (e.g. Crameri et al. Reference Crameri, Shephard and Heron2020). The ideal, more accurate representation of global Cryogenian chronostratigraphic datasets would include detailed stratigraphic logs, accompanying regional correlations, and detailed geochronometric methodology and results. In some regions, these datasets are currently unavailable, unreliable or limited.

The apparent diachroneity of glacial onset present in Laurentia (Fig. 6) is likely a result of complexity in zircon age determinations and chronostratigraphic misinterpretations (e.g. syn-depositional instead of MDA). Eyster et al. (Reference Eyster, Ferri, Schmitz and Macdonald2018) also highlight how this style of misinterpretation was used to argue for diachroneity of onset (Baldwin et al. Reference Baldwin, Turner and Kamber2016). Careful scrutiny of geochronologic data, its methodological limitations and its chronostratigraphic interpretation is essential to prevent spurious conclusions.