Stable-isotope geochronology of the Australian regolith

https://doi.org/10.1016/0016-7037(89)90104-XGet rights and content

Abstract

Australian regolith profiles can be assigned to one of three post-Palaeozoic age groups on the basis of the oxygen-isotope composition of authigenic clay minerals developed in the profile. Systematic variations in the isotopic composition of meteoric waters, and therefore of the authigenic regolith minerals that formed in equilibrium with them, are a result of the continent's drift from high to low latitudes and changes in global climate.

Residual clays (collected in situ from regolith profiles) of post-mid Tertiary age have δ18O values between +17.5 and +21.3%., with the exception of samples from northern Australia (north of approximately 20°S), which have anomalously low values because meteoric waters in northern Australia are largely derived from monsoonal rain. The high δ18O, values of post-mid Tertiary residual clays are consistent with Australia's northward drift to low (warm) latitudes during this time, compared with the much higher latitudes it occupied for most of its post-Palaeozoic history. Late Tertiary residual clays have δ18O values that are indistinguishable from all other post-mid Tertiary clays, indicating that further subdivision of the sample groups is not feasible on a continent-wide scale. Comparison with hypothetical “modern” clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in Australia since the mid-Tertiary.

Pre-mid Tertiary clays have lower δ18O values, between +10.0 and +17.5%., which are consistently lower than post-mid-Tertiary clays. δ18O values of less than +14 to +15%. are thought to reflect weathering events during much earlier geologic periods, perhaps early or mid Mesozoic, when Australia was at high latitude and the Australian climate was humid and cool to cold. Several workers have documented the existence of very old regolith profiles and land surfaces in Australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre-late Mesozoic age which have δ18O values between +10.2 and +12.3%..

Regolith profiles composed of low-18O clays (< +15%.) are widespread in Australia, and it is possible that a much greater part of the modern landscape than previously recognized developed in the early- or mid-Mesozoic. The δ18O values of transported (i.e., sedimentary) kaolinites reveals that the major source for many Tertiary kaolinitic sediments was this postulated pre-late Mesozoic low-18O regolith. The stableisotope evidence that much of the Australian regolith formed in comparatively cold conditions suggests that, contrary to some traditional interpretations, lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub-tropical climates.

The hydrogen-isotope composition of the clays range from −115 to −50%.; however, it is inferred that the majority of clays have undergone some post-formational hydrogen-isotope exchange which renders their δD composition unsuitable for dating purposes.

References (126)

  • L.S Land et al.

    Cementation of a Pennsylvanian deltaic sandstone: isotopic data

    J. Sediment. Petrol.

    (1978)
  • J.R Lawrence et al.

    Hydrogen and oxygen isotope systematics in weathering profiles

    Geochim. Cosmochim. Acta

    (1972)
  • E Linacre et al.

    The Australian Climatic Environment

    (1977)
  • O.P Mehra et al.

    Iron oxide removal from soils and clays by a dithionite-citrate system buffered by sodium bicarbonate

    Clays Clay Mineral.

    (1960)
  • H.B Owen

    Bauxite in Australia

    Australian Bur. Mineral Resources Bull.

    (1954)
  • S.M Savin et al.

    Oxygen and hydrogen isotope geochemistry of ocean sediments and shales

    Geochim. Cosmochim. Acta

    (1970)
  • P.W Schmidt et al.

    Sub-basaltic weathering, damsites, palaeomagnetism and the age of lateritization

    J. Geol. Soc. Australia

    (1976)
  • B.R Senior et al.

    A proposed method of defining deeply weathered rock units in regional geological mapping in southwest Queensland

    J. Geol. Soc. Australia

    (1979)
  • P Aharon

    Analysis of the anomalous 18O16O and D/H isotope ratios in tropical rainfall over the western Pacific Ocean

    Eos

    (1983)
  • P Aharon et al.

    Isotope studies of insular phosphates explain atoll phosphatization

    Nature

    (1984)
  • M Ahmad et al.

    Groundwater regimes and isotopic studies, Ranger mine area, Northern Territory

    Australian J. Earth Sci.

    (1986)
  • P.L Airey et al.

    Aspects of the isotope geochemistry of the Great Artesian Basin, Australia

  • P.L Airey et al.

    Aspects of the isotope hydrology of two sandstone aquifers in arid Australia

  • G.B Allison et al.

    Effect of climate and vegetation on oxygen-18 and deuterium profiles in soils

  • G.J Ambrose et al.

    Billa Kalina 1:250,000 Geological Sheet: Explanatory notes (SH/53-7)

    (1981)
  • Anon

    Commodity review—Clay

    N.S.W. Mining Explor. Quart.

    (1984)
  • C.J Baker et al.

    Kaolin in New South Wales

    Geol. Surv. N.S. W. Min. Res.

    (1982)
  • G Bell

    Notes on the bauxite deposits of the Mirboo North district of South Gippsland

    Mining Geol. J.

    (1959)
  • M.I Bird

    An isotopic study of the Australian regolith

  • M.I Bird et al.

    Oxygen-isotope dating of the Australian regolith

    Nature

    (1988)
    M.I Bird et al.

    Oxygen-isotope dating of the Australian regolith

    Nature

    (1988)
  • M.I Bird et al.

    Stable-isotope evidence for low-temperature weathering and post-formational hydrogen-isotope exchange in Permian kaolinites

    Chem. Geol.

    (1988)
  • M.I Bird et al.

    An isotopic study of surficial alunite in Australia.2: Potassium-argon geochronology

    Chem. Geol.

    (1989)
  • R.P Bourman

    Geomorphic evolution of the Fleurieu Peninsula, South Australia

  • R.P Bourman et al.

    Investigations of ferricretes and related surficial ferruginous materials in parts of southern and eastern Australia

    Z. Geomorph.

    (1987)
  • G.E Calf

    The isotope hydrology of the Mereenie Sandstone aquifer, Alice Springs, Northern Territory

    J. Hydrol.

    (1978)
  • D.C Christophel et al.

    Tertiary megafossil flora of Maslin Bay, South Australia: A preliminary report

    Alcheringa

    (1978)
  • G.J Churchman et al.

    Intercalation method using formamide for differentiating halloysite from kaolinite

    Clays Clay Mineral.

    (1984)
  • R.N Clayton et al.

    The use of bromine pentafluoride in the extraction of oxygen in silicates for isotopic analysis

    Geochim. Cosmochim. Acta

    (1963)
  • M.D Connolly

    Petrography, distribution, origin and age of ferricrete and silcrete in the Armidale area, N.S.W

  • R.J Coventry et al.

    Chronology of landscape evolution and soil development in the upper Flinders River area, Queensland, based on isotopic dating of Cainozoic basalts

    Australian J. Earth Sci.

    (1985)
  • C.D Curtis et al.

    Diagenetic development of kaolinite

    Clays Clay Mineral.

    (1971)
  • B Daily et al.

    The age of the lateritized summit surface on Kangaroo Island and adjacent areas of South Australia

    J. Geol. Soc. Australia

    (1974)
  • W Dansgaard

    Stable isotopes in precipitation

    Tellus

    (1964)
  • T Dincer

    Use of environmental isotopes in arid-zone hydrology

  • G.H Dury

    Duricrusted residuals on the Barrier and Cobar pediplains of NSW

    J. Geol. Soc. Australia

    (1966)
  • G.H Dury et al.

    A minimum age for the duricrust

    Australian J. Sci.

    (1969)
  • P.K Dutta

    In search of the origin of cement in siliciclastic sandstones: an isotopic approach

    Chem. Geol.

    (1985)
  • S.P Dutton et al.

    Meteoric burial diagenesis of Pennsylvanian arkosic sandstones, southwestern Anadarko Basin, Texas

    Amer. Assoc. Petrol. Geol. Bull.

    (1985)
  • N.F Exon et al.

    The age and geomorphic correlations of deep-weathering profiles, silcrete and basalt in the Roma-Amby region

    J. Geol. Soc. Australia

    (1970)
  • L.A Frakes

    Climates throughout Geologic Time

  • Cited by (94)

    • Stable isotope proxy records in tropical terrestrial environments

      2020, Palaeogeography, Palaeoclimatology, Palaeoecology
    • Antiquity of the giant inselberg Burringurrah (Mount Augustus), Western Australia, inferred from oxygen isotope dating of kaolinitic weathering

      2019, Geomorphology
      Citation Excerpt :

      With decreasing age, these minerals are progressively enriched in 18Ο, and by correlating sample δ18Ο values with independent age constraints, it has been possible to establish a timescale, which allows application of the dating method to profiles of unknown ages. Accordingly, samples from known-age weathering profiles in eastern and central Australia, provide a chronology wherein Permian kaolinites have δ18Ο values of +6 to +10‰, Jurassic-early Cretaceous +10 to +15‰, late Cretaceous-Paleogene +15 to +17.5‰ and Neogene +17.5 to +21.3‰ (Bird and Chivas, 1988a, 1989, 1993). That such a range of δ18Ο values (15‰ variation) is still faithfully preserved at Earth's surface is testament to the lack of later oxygen isotopic exchange, as all profiles have been subject to rain- and groundwaters with progressively changing (increasing) δ18Ο values.

    • Landscape evolution and geochemical dispersion of the DeGrussa Cu-Au deposit, Western Australia

      2019, Ore Geology Reviews
      Citation Excerpt :

      This led to a decrease in erosion rates and allowed deep weathering to occur under a humid sub-tropical to tropical climate (e.g., De Broekert, 2002 and references therein). This long surficial exposure time resulted in a complex history of weathering that dates back to at least the Late Mesozoic (Bird and Chivas, 1989). Residual weathering profiles resulted from the overprinting of several climatic changes, including water table fluctuations, together with variations in salinity and groundwater residence times.

    • Rare-earth element and stable isotope signatures of kaolin from a Pliocene lateritic weathering profile at mid-latitude region (Andalusia, Spain): Implications for paleoweathering and paleoclimatic reconstructions

      2018, Catena
      Citation Excerpt :

      In fact, kaolinite is an abundant clay mineral in paleosol profiles that formed in paleotropical sites (e.g. Sheldon and Tabor, 2009). However, the stable isotope composition of kaolinite reveals that much of the kaolinitic regoliths formed under relatively cold conditions, suggesting that, contrary to classical interpretations, laterization and deep weathering phenomena are not solely the result of weathering in tropical or subtropical climates (Bird and Chivas, 1989). It has been also suggested that development of kaolinitic profiles at extra-tropical latitudes may be the result of a greenhouse warming induced by increased atmospheric CO2 levels (e.g. Dowsett et al., 1992; Barron et al., 1993; Thiry, 2000; Krause et al., 2010).

    View all citing articles on Scopus

    Present address: Department of Geology, University of Western Ontario, London, Ontario, N6A 5B7, Canada.

    View full text