The applicability of modern tidal analogues to pre-vegetation paralic depositional models

Ginny-Marie Bradley, Jonathan Redfern, David Hodgetts, A.D. George, G.D. Wach

    Research output: Contribution to journalArticlepeer-review

    Abstract

    n modern siliciclastic environments terrestrial and aquatic vegetation binds substrate, controls weathering and erosion rates, influences run-off, sediment supply and subsequent depositional architecture. This study assesses the applicability of modern depositional models that are impacted by vascular vegetation, as analogues for ancient pre-land plant systems. A review of pre-Devonian published literature demonstrates a paucity of described tidal successions; this is possibly due to the application of modern analogues for interpreting the record when there is a lack of tidal indicators. This paucity suggests a need for revised models of tidal deposition that consider the different environmental conditions prior to land plant evolution. This study examines the Ordovician–Silurian Tumblagooda Sandstone, which is exposed in the gorge of the Murchison River and coastal cliffs near Kalbarri, Western Australia. The Tumblagooda Sandstone comprises stacked sand-rich facies, with well-preserved bedforms and trace fossils. Previous interpretations of the depositional setting have proposed a mixed sheet-braided fluvial and intertidal flats; to a continental setting dominated by fluvial and aeolian processes. An enigmatic element is the rarity of mud-rich facies preserved in the succession. Outcrop logging, facies and petrographic analysis record dominantly shallow water conditions with episodes of emergence. Abundant ichnotaxa indicate that marine conditions and bi-directional flow structures are evidence for an intertidal and subtidal depositional environment. A macrotidal estuary setting is proposed, with evidence for tidal channels and repeated fluvial incursions. Physical and biogenic sedimentary structures are indicative of tidal conditions. The lack of clay and silt resulted in the absence of flaser or lenticular-bedding. Instead cyclic deposition of thin beds and foreset bioturbation replacing mud drape deposits. Higher energy conditions prevailed in the absence of the binding activity of plants in the terrestrial and marine realm. This is suggestive of different weathering processes and a reduction in the preservation of some sedimentary features.
    Original languageEnglish
    JournalSedimentology
    Early online date31 Jan 2018
    DOIs
    Publication statusPublished - 2018

    Keywords

    • intertidal
    • Lower Palaeozoic
    • paralic
    • pre-vegetation
    • subtidal
    • Tumblagooda Sandstone

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