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Paul F. Hoffman Series 256 PAUL F. HOFFMAN SERIES eDepartment of Earth Science provenance data from the Elatina Fm. University of California suggest that glacial sediment may have Santa Barbara, CA, USA 93106 been partially sourced from the cratons of Western Australia and that the SUMMARY Whyalla Sandstone, even if stratigraph- The Elatina Fm. records the younger ically correlative, was not a sediment Cryogenian ice age in the Adelaide Rift source. The remainder of the Elatina Complex (ARC) of South Australia, Fm. stratigraphy mostly records the which has long-held the position as the deglaciation and can be divided into type region for this low-latitude glacia- three facies: a slumped sandstone, tion. Building upon a legacy of work, dropstone diamictite, and current- we document the pre- and syn-glacial reworked diamictite. The relative sea The End-Cryogenian sedimentary rocks to characterize the level fall within the upper Elatina Fm. Glaciation of South dynamics of the glaciation across the requires that regional deglaciation ARC. The Elatina Fm. records an array occurred on the timescale of ice sheet Australia of well-preserved glacial facies at many – ocean gravitational interactions a,b different water depths across the basin, (instant) and/or isostatic rebound Catherine V. Rose , Adam C. 4 a a including ice contact tillites, flu- (~10 years). Structures previously Maloof , Blair Schoene , Ryan C. vioglacial sandstones, dropstone inter- interpreted as soft-sediment folds with- Ewingc, Ulf Linnemannd, Mandy d e vals, tidal rhythmites with combined- in the rhythmite facies that were used Hofmann , and John M. Cottle flow ripples, and turbidites. The under- to constrain the low-latitude position of South Australia at the time of the a lying Yaltipena Fm. records the pro- Department of Geosciences glacial influx of sediment from Elatina glaciation are re-interpreted as Princeton University encroaching land-based ice sheets. The stoss-depositional transverse ripples Guyot Hall, Washington Road onset of the glaciation is heralded by with superimposed oscillatory wave Princeton, NJ, USA 08544 the major element ratios (Chemical ripples. These combined-flow ripples Index of Alteration) of the pre-glacial across the ARC attest to open seas b Department of Earth and Planetary facies across the platform that show a with significant fetch during the initial Sciences reduction in chemical weathering and a retreat of local glaciers. In addition, Washington University in St. Louis deterioration in climate towards the this interpretation no longer requires 1 Brookings Drive, St. Louis, MO, USA base of the Elatina Fm. The advancing that the magnetization be syn-deposi- 63130 ice sheets caused soft-sediment defor- tional, although we have no reason to E-mail: [email protected] mation of the beds below the glacial believe that the low-latitude direction is diamictite, including sub-glacial push a result of remagnetization, and posi- cDepartment of Geology and Geophysics structures, as well as sub-glacial erosion tive reversal tests and tectonic fold Texas A&M University, MS 3115, of the carbonate unit beneath. Meas- tests are at least consistent with syn- College Station, Texas, TX, USA 77843 ured stratigraphic sections across the depositional magnetization. Together, basin show glacial erosion up to 130 m these paired sedimentological and dSenckenberg Naturhistorische Sammlungen into the carbonate platform. However, chemostratigraphic observations reveal Dresden δ13C measurements of carbonate clasts the onset of the glaciation and advance Museum für Mineralogie und Geologie within the glacial diamictite units were of the ice sheet from land to create a Königsbrücker Landstrasse 159, D-01109 used to assess provenance and relative heavily glaciated terrain that was Dresden, Germany timing of δ13C acquisition, and suggest incised down to at least the base of the that at least 500 m of erosion occurred pre-glacial Trezona Fm. somewhere in the basin. Detrital zircon Geoscience Canada, v. 40, http://dx.doi.org/10.12789/geocanj.2013.40.019 © 2013 GAC/AGC® GEOSCIENCE CANADA Volume 40 2013 257 SOMMAIRE Formation d’Elatina représente princi- colloquially referred to as the older La Formation d’Elatina représente la palement la déglaciation, laquelle peut ‘Sturtian’ and younger ‘Marinoan’ low- phase précoce de l’âge glaciaire du être divisée en trois faciès : un grès latitude glaciations (Hoffman and Cryogénien de l’Adelaide Rift Complex plissé, une diamictite à galets de Schrag 2002; Hoffman 2005, 2011). (ARC) dans le sud de l’Australie, région délestage, et une diamictite remaniée Banded iron formation within the thick qui a longtemps été la région type de par des courants. La baisse du niveau Sturtian diamictite units, and sedimen- cette glaciation de basse latitude. À relatif de la mer dans la partie tologically and geochemically distinc- partir d’un legs de travaux, nous nous supérieure de la Formation d’Elatina tive ‘cap’ carbonate sequences that sommes appuyés sur l’étude des roches suppose une déglaciation régionale sur consistently drape both glacial deposits sédimentaires préglaciaires et syn- une échelle de temps de l’ordre de celle (Williams 1979; Kennedy 1996; glaciaires pour caractériser la de la nappe de glace – interactions Kennedy et al. 1998; Hoffman et al. dynamique de la glaciation à travers gravitationnelles de l’océan (instanta- 2007; Rose and Maloof 2010), may l’ARC. La Formation d’Elatina ren- nées) et/ou rebond isostatique (~ 104 indicate long-term isolation of the ferme une gamme de faciès glaciaires ans). Des structures décrites ocean from the atmosphere. Together, bien préservés correspondant à dif- précédemment comme des plis de sédi- these observations led to the contro- férentes profondeurs d’eau à travers le ments mous dans des faciès de rhyth- versial ‘snowball Earth’ hypothesis, bassin, dont des tillites de contact mites qui impliquait une position de wherein an ice-albedo runaway feed- glaciaire, des grès fluvioglaciaires, des basse latitude pour l'Australie du Sud à back caused ice to advance rapidly to intervalles à galets de délestage, des l'époque de la glaciation Elatina, sont the equator and seal the entire ocean in rythmites tidales avec des combi- réinterprétées comme des rides sédi- ice for millions of years (Kirschvink naisons de rides d’écoulement, et des mentaires transverses asymétriques 1992; Hoffman et al. 1998, 2002). turbidites. La Formation sous-jacente avec des rides de vagues oscillatoires Early work on these enigmatic de Yaltipena est constituée de sédi- superposées. Ces combinaisons de low-latitude glaciations focused on ments proglaciaires provenant de rides d’écoulement à travers l’ARC identifying and describing the glacial lentilles de glace en progression. Le confirment l’existence d’un milieu deposits around the world (Spencer début de la glaciation est reflété dans marin ouvert d’une ampleur certaine au 1971; Deynoux and Trompette 1976; les ratios des éléments majeurs (indice moment de la retraite initiale des gla- Hambrey and Harland 1981; Deynoux d’altération chimique) des faciès ciers locaux. En outre, cette interpré- 1985; Lemon and Gostin 1990). How- préglaciaires de la plateforme qui mon- tation ne nécessite plus que la magnéti- ever, this focus on the glacial deposits tre une réduction de l’altération chim- sation soit synsédimentaire, bien que led to different interpretations and ique et une détérioration du climat à nous n'ayons aucune raison de penser some workers proposed a debris flow l’approche de la base de la Formation que l’orientation magnétique de basse origin for the conglomeratic beds d’Elatina. La progression des nappes latitude soit le résultat d’une ré-aiman- (Schermerhorn 1974; Eyles 1993; de glace a entraîné une déformation tation, et que les tests de réversibilité Arnaud and Eyles 2006). Eyles and des lits de sédiments meubles sous la positifs et les tests de plissement tec- Januszczak (2004) argued that both the diamictite glaciaire, montrant entre tonique sont au minimum conformes à glacigenic deposits and associated car- autres des structures de poussée sous- une magnétisation synsédimentaire. bonate rocks could be explained by glaciaires ainsi que de l’érosion sous- Ensemble, ces observations sédimen- continental rifting, with carbonate glaciaire de l’unité de carbonate sous- tologiques et chimiostratigraphiques deposited in restricted basins starved jacente. Les mesures de coupes strati- mettent en lumière le début de la of clastic input. Although not wide- graphiques à travers le bassin montrent glaciation et l'avancée du couvert de spread, high-latitude carbonate and que l’érosion glaciaire a enlevé jusqu’à glace continental menant à une région evaporite rocks coexist with glacigenic 130 m du carbonate de la plateforme. fortement englacée qui a été incisée sediments today (Walter and Bauld Toutefois, les signatures isotopiques jusqu'à à la base de la Formation 1983). A close examination of the pre- δ13C de fragments de carbonate dans préglaciaire de Trezona. and post-glacial Neoproterozoic rocks les unités de diamictites glaciaires util- in the North Atlantic region, however, isées pour établir la provenance et la INTRODUCTION determined that these carbonate units chronologie d’acquisition relative de la At least two Neoproterozoic glacigenic, were probably deposited in warm signature δ13C des fragments, permet poorly sorted conglomeratic units are water and thus climatic fluctuations de penser qu’il y a eu au moins 500 m present on all continents except between ‘balmy’
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