Biogeographic, ecological and stratigraphic relationships of the Miocene brown coal floras, Latrobe Valley, Victoria, Australia

I. R.K. Sluiter, A. P. Kershaw, G. R. Holdgate, D. Bulman

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    Abstract

    Palaeobotanical studies of the brown coal deposits of the Latrobe Valley have contributed significantly towards an understanding of the age of the deposits, existing climatic conditions and detailed depositional environments. This paper re-assesses some past reconstructions for the Early to Mid Miocene coals using recent information on plant distributions and their bioclimatic significance and on a marine incursion model for coal lithotype formation. The brown coal flora is composed overwhelmingly of rainforest taxa that presently cover a range of different environments within the Australasian region. The application of a bioclimatic prediction model to these taxa allows the construction of consistent and quantitative estimates of climates during coal-forming phases. It is considered that rainfall in the area was more than twice the 850 mm received today, with significant seasonal variation. The mean annual temperature estimate of about 19°C, indicating a mesothermal or subtropical environment, is some 2-5C higher than present and higher than previous estimates. It does, however, correspond with sea-surface temperature estimates for the Southern Ocean at this time. The original model of lithotype formation, which suggests that lithotypes conform to a successional sequence from open water in the lightest coloured lithotypes to raised bog in the darkest lithotypes, is considered to be inconsistent with the evidence for lightening upwards sequences within the coals, a central feature of the proposed marine incursion model of coal formation. The two models are reconciled to some degree by a reinterpretation of the palaeobotanical data and by the postulation of climatic rather than autogenic successional control over lithotype formation.

    Original languageEnglish
    Pages (from-to)277-302
    Number of pages26
    JournalInternational Journal of Coal Geology
    Volume28
    Issue number2-4
    DOIs
    Publication statusPublished - 1 Jan 1995

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