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Alluvial-channel and overlying eolian deposits exposed in coastal cliffs in the Port Campbell australite (Australian tektite) strewn field, SW Victoria, were studied stratigraphically and dated by optically stimulated luminescence (OSL) for quartz sand grains to illuminate the occurrence of australites in this area. The channel deposits, termed the Dog Trap Bay Sand, yielded OSL ages from 420 ± 40 to 230 ± 15 ka for four sites, and the two eolian units OSL ages of 203 ± 16 and 93 ± 11 ka. The ages support field evidence that, contrary to the conclusions of a previous study by others, the channel deposits are stratigraphically distinct from and much younger than the Pliocene Hanson Plain Sand, which forms a regionally extensive system of marine strandlines to the north and NE of Port Campbell. The OSL ages show some preference for times of negative temperature anomalies marking the last four glacial periods of the Middle and Late Pleistocene as indicated by ice-core data from Antarctica. Eolian and at leas...

Sedimentary features characteristic of ice-rafting are present in the Bunyeroo Formation (Wilpena Group) of the Adelaide Geosyncline and in the coeval Dey Dey Mudstone (Ungoolya Group) of the eastern Officer Basin (Figs 66.1 & 66.2), providing evidence of a mid-Ediacaran glacial climate in South Australia. The Acraman asteroid impact, a negative shift in marine δ 13 C, and a major acritarch turnover coincided with this frigid epoch.

The record of two Neoproterozoic glaciations in South Australia has been known for about a century. The earlier glaciation, of Sturtian age, is represented by the Yudnamutana Subgroup and is characterized by widespread diamictites with both intrabasinal and extrabasinal clasts, some locally faceted and striated. Associated facies include shallow-water sandstone, bedded and laminated siltstone with lonestones and dropstones, and sedimentary ironstones (mainly ferruginous siltstone and diamictite). Proximal settings adjacent to the Curnamona Province display massive basement-derived conglomerate and gigantic basement megaclasts (up to hundreds of metres across). Sturtian glaciogenic sediments of the Yudnamutana Subgroup unconformably overlie a variety of older rock units, including crystalline basement near basin margins and uppermost Burra Group sediments in the depocentre, and were deposited both in shallow marine shelf environments and in tectonically active rift basins encircling the Curnamona Province, with corresponding increases in total thickness from 100–300 m to more than 5 km. Recent U–Pb zircon SHRIMP dating of a thin volcaniclastic layer indicates that the waning stages of the Sturtian glaciation occurred at c. 660 Ma. Unlike the deposits of the younger Elatina glaciation, the Yudnamutana Subgroup has so far not yielded reliable palaeomagnetic data.

Isolated quartzose pebbles, clusters of quartz granules, orthogonal aggregates of poorly sorted quartzose coarse sand, and ovoid pellets (≤2 mm long) of quartz silt occur in hemipelagic marine mudstone of the mid-Ediacaran Bunyeroo Formation exposed in the Adelaide Geosyncline (Adelaide Rift Complex), and ovoid pellets of quartz silt in cores of the correlative marine Dey Dey Mudstone from deep drillholes in the Officer Basin, South Australia. This detritus is interpreted respectively as dropstones, dumps, and frozen aggregates dispersed by sea ice possibly of seasonal origin, and till pellets transported by glacial ice. The ice-rafted material in the Bunyeroo Formation only has been found 500 km northwest of ...

David Haberlah, Peter Glasby, Martin A. J. Williams, Steven M. Hill, Frances Williams, Edward J. Rhodes, Victor Gostin, Anthony O'Flaherty and Geraldine E. Jacobsen

The late Cryogenian Elatina glaciation in South Australia, of Marinoan age, is named after the Elatina Formation of the glaciogenic Yerelina Subgroup, which covers ∼200,000 km2 in the Adelaide Geosyncline and on the cratonic Stuart Shelf and is up to ∼1500 m thick. The Elatina glaciation is marked by numerous facies that are like those of Phanerozoic glaciations: • Basal diamictite displaying glacitectonites with penetrative deformation of preglacial beds, indicating grounded ice or scouring by icebergs. • Glaciomarine diamictites containing numerous faceted and striated clasts up to several metres across of intrabasinal and extrabasinal origin. • Laminated siltstone and mudstone containing scattered, ice-rafted dropstones in outer marine-shelf environments. • Sandstones deposited in fluvial, deltaic and inner marine-shelf settings. • Tidalites deposited in estuaries and on tidal deltas during interstadial rise of sea level, with cyclic tidal rhythmites recording the annual oscillation of sea level and displaying wave-generated ripple marks, which together indicate long-lived and extensive open seas. • Siltstone containing acicular crystal pseudomorphs implying the formation of evaporite minerals in littoral deposits. • Permafrost regolith of frost-shattered quartzite breccia ≤20 m deep, displaying large-scale periglacial structures including primary sand wedges 3 m deep that indicate a frigid, strongly seasonal climate near sea level. • Periglacial–aeolian sandstone covering 25,000 km2 and containing primary sand wedges near its base. These deposits record a spectrum of settings ranging from permafrost regolith and periglacial sand sheet on the Stuart Shelf in the west, through fluvial, deltaic and inner marine-shelf in the western and central parts of the Adelaide Geosyncline, to outer marine-shelf in the north and southeast. The widespread and persistent rainout of fine-grained sediment and ice-rafted debris indicates that the sea was not frozen over during the Elatina glaciation. No direct age determination is available for the Elatina glaciation, and only maximum and minimum age limits of ∼640 and ∼580 Ma, respectively, can at present be applied. High-quality palaeomagnetic data for red beds from the Elatina Formation, supported by positive fold tests on soft-sediment slump folds that demonstrate the early acquisition of magnetic remanence, indicate deposition within 10° of the palaeoequator. The Yerelina Subgroup in the Adelaide Geosyncline and on the Stuart Shelf is disconformably to unconformably overlain by the Nuccaleena Formation “cap carbonate” that marks the early Ediacaran post-glacial marine transgression. The presence in near-equatorial palaeolatitudes of glaciomarine deposition, grounded ice and permafrost near sea level, a strongly seasonal periglacial climate, and widespread open seas implies a paradoxical palaeoclimate and palaeogeographic setting for the Elatina glaciation. The strong evidence for a non-actualistic late Cryogenian glacial climate in South Australia has been a stimulus to worldwide multidisciplinary research on Cryogenian glaciogenic successions.

Within the Neoproterozoic sequence of the Adelaide Fold-Thrust Belt, South Australia, two of the most severe ice ages in Earth history (Sturtian and Marinoan) are recorded in the glacigenic rocks which mark the base and top of the 4.5 km-thick Umberatana Group, the focus of the present chemostratigraphic study. Rock units from three drillholes and ten measured outcrop sections, located in the southern and central Flinders Ranges and on the Stuart Shelf, were sampled for isotopic analysis of their co-existing calcite (δ13Ccal), dolomite (δ13Cdol) and kerogen (δ13Corg). Strontium and sulphur isotopic analyses were also run on selected samples. The sample sites are in tectonic domains where regional metamorphism has been insufficient to significantly alter the isotopic composition of the kerogen. The resulting data, when integrated with the lithostratigraphy of the Umberatana Group, yield one of the most complete records of secular variation in the C-isotope signature of the late Cryogenian ocean between ∼750 and 680 Ma. Its composite δ13Ccarb curve begins with a sharp positive excursion (−3 to +1.5‰ in the dolomitic Tindelpina Shale which caps Sturtian glacial diamictites (Wilyerpa Formation). Then follows a steady climb through the shoaling upward Tapley Hill Formation reaching +4‰ in the Brighton Limestone and culminating in a plateau of 13C enrichment within the platformal carbonates of the Etina Formation (+8 to +10‰). The upper part of the temporal trend shows a decline to +6 to +7‰ in the stromatolite reef facies of the Enorama Shale; and a dramatic drop to −8 to −9.5‰, followed by a recovery to –3‰, in the youngest carbonate unit (Trezona Formation) beneath the Marinoan glacigenic Elatina Formation. The latter is capped by a thin dolostone, the Nuccaleena Formation, which records a consistent up-section decrease in δ13C (−1 to −3‰). Superimposed on this overall pattern of C-isotopic variation are second and third-order fluctuations attributable to eustatic sea-level change. Pyritic sulphur in the lower Tapley Hill Formation (δ34S=+9 to +40‰) is distinctly heavier than that in the underlying Wilyerpa Formation (+4 to +20‰). Minimum 87Sr/86Sr values obtained from the Brighton Limestone (0.7071) and Etina Formation (0.7076) are consistent with their late Cryogenian age. This Sturtian to Marinoan interglacial succession is more complete than equivalent sequences elsewhere, and thus provides a useful reference for global chemostratigraphic correlation. Notable features of its C-isotope curve are the strong post-Wilyerpa positive excursion, also seen in key sections from Svalbard and western Mongolia; the ‘Etina plateau’ of 13C enrichment which is remarkably similar to maxima in the terminal Proterozoic C-isotope records of western Mongolia, north-western Canada and Brazil; and the spectacular depletion of 13C in the lower Trezona relative to similar carbonate facies in the underlying Etina Formation and Enorama Shale. A preglacial offset in δ13Ccarb values of such proportions (∼14‰) is almost unprecedented, except perhaps for that recently documented in the upper Ombaatjie Formation beneath tillites of the Ghaub Formation, Otavi Group, Namibia. It represents a key piece of evidence in the case presented by the proponents of a Neoproterozoic ‘snowball’ Earth.

The seafloor morphology and lithology of northern Spencer Gulf, South Australia, is related to successive transgressions and regressions accompanying glacial and non-glacial periods. Vibrocoring has revealed a veneer of Holocene bioclastics and a sequence of Pleistocene marine strata which display varying degrees of pedogenesis, oxidation, decalcification and clay illuviation. The contact between the Holocene and Pleistocene sediments is marked by either a thin alluvial or aeolian horizon or by a soil horizon of variable development. The Pleistocene marine strata have been assigned to four Formations (older Pleistocene marine beds, Mambray Fm., False Bay Fm., and Lowly Point Fm.) based on superposition of lithofacies and intervening pedogenic horizons. A sequence of slightly altered, laminated lagoonal clays (Lowly Point Formation) and bryozoan rich limestones (False Bay Formation) has been encountered in deeper parts of the Gulf. Stratigraphically below these is a widespread, weathered marine unit (Mambray Formation) which contains abundant remains of the bivalve Anadara trapezia and the foraminifer Marginopora vertebralis, species absent from the present biota. This unit, in turn, is underlain by a sedimentary sequence strongly altered by pedogenesis and clay illuviation (older Pleistocene marine beds); its original marine character has been largely obliterated. A dearth of fluvial gravels and sand from the vibrocores, as well as evidence from palaeosols, indicate that a predominantly semi-arid to arid climate has persisted in the northern Gulf region since ca. 125,000 yrs ago, and that there has been little subsequent terrigenous material transported to the Gulf.

The late Proterozoic Sturtian succession in the northern part of the Adelaide ‘Geosyncline’ is disposed in a southward-closing arcuate outcrop belt that is largely fault-bounded on its southern margin. On the west side the glacigenic portion of the Sturtian succession is between 100 and 800 m thick. A thin discontinuous basal breccia is present on the older rocks of the Burra Group. This is followed by a locally developed diamictite with associated lenticular sandstones, interpreted as a tillite and glacial outwash deposits, respectively. The succeeding Sturtian units are much more widespread. Unit 2 is a mudstone-dominated heterogeneous succession of siliciclastic rocks formed by traction currents, gravity flows and rain-out from floating ice. A second diamictite (Unit 3) is massive in the southeasterly part of the study area near the town of Copley, but is stratified and heterogeneous in an area to the northwest. This diamictite is probably a marine deposit formed in the south by rapid rain-out from floating ice and in the north by a variety of processes that largely reworked the glacigenic sediment. The topmost unit (4) is also heterogeneous and resulted from the interplay of gravity flows, traction currents and ice rain-out. Palaeocurrents indicate a dominantly southeasterly transport but some herringbone cross bedding suggests tidal activity. Dolostones are present in Unit 4 and stromatolitic bioherms were noted in the basal diamictite. In this region the Sturtian succession is considered to be the product of glaciation centred to the west and north, feeding into an elongate basin here termed the ‘North Flinders Basin’. Palaeocurrent data and thickness changes suggest that the basin may have opened to the east. In late Proterozoic time this basin may have been separated from the main part of the Adelaide ‘Geosyncline’ to the southeast by the shallow-to-emergent Central Flinders zone.

The Serle Conglomerate is a lenticular unit (8 km × 160 m) at the top of the Late Proterozoic (Sturtian) glacigenic Yudnamutana Subgroup in the northeastern part of the Adelaide “Geosyncline”. In its type area at the west end of the Fitton Trough it can be subdivided into five stratigraphic units interpreted as the products of deposition in the mid-to-upper portions of a submarine fan complex. Progradation of submarine fans under conditions of eustatic sea-level rise was probably due to concomitant fault activity and isostatic readjustments(?) along the basin margins. In an area about 10 km west of the type area, similar conglomerates overlie glacigenic rocks of the Yudnamutana Subgroup with an erosional contact and therefore are younger than them. There is no definitive evidence of glacial influence during deposition of the Serle Conglomerate, so that previous correlations with glacigenic diamictites elsewhere in the Adelaide “Geosyncline” are unlikely. There is no justification, in this area, for inferring two separate early Sturtian glaciations.

The Yudnamutana Subgroup is a thick succession of upper Proterozoic (Sturtian) glacigenic rocks preserved in the Yudnamutana trough in the northeastern part of the Adelaide "geosyncline." In ascending order, the subgroup comprises the Fitton, Bolla Bollana, and Lyndhurst Formations. The name "Hamilton Creek Member" is proposed for a locally developed conglomeratic facies at the base of the Fitton Formation. These rocks are interpreted as the products of two glacial advances. The first is evidenced by the Hamilton Creek Member, which includes sediment gravity flows derived from subaqueous glacial outwash. The Fitton Formation is composed mainly of basinal siltstones and mudstones with associated coarser-grained rocks that are largely sediment gravity flows. Diamictites in the upper part of the formation signify the onset of a second glacial advance. Thick diamictites of the Bolla Bollana Formation are interpreted as rainout deposits from floating ice derived from ice streams debouching from a steep and high hinterland into a fault-controlled basin. The Lyndhurst Formation is mainly fine-grained rocks. Dropstones and sparse diamictites attest to the presence of some floating ice, but some of the diamictites are probably mass-flow deposits. Paleocurrent data from the Yudnamutana Subgroup indicate transport to the west-northwest. The Sturtian glacigenic rocks are overlain by a transgressive shale. Stratigraphic similarities exist between the Yudnamutana Subgroup and thinner successions to the west. These stratigraphic similarities probably reflect paleoclimatic changes. The twice-repeated sequence of diamictite followed by mudstone is attributed to two glacial advance-retreat cycles. Local variations in thickness and stratigraphic succession are probably related to contemporaneous faulting.

Analyses of major oxides and some trace elements (Ga, Rb, Sr, and B) were carried out on 25 samples of tillite matrix materials of the major Late Precambrian glacial episode in South Australia. The results indicate the dominantly granitic nature of the source rocks and suggest deposition under marine glacial conditions.

An assumed glacial pavement at the base of a Late Proterozoic glacigene sequence in the Wooltana district is explained as a tectonic feature. Similar surfaces, not associated with glacigene sedimen...