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Submarine cementation in tide-generated bioclastic sand dunes: epicontinental seaway, Torres Strait, north-east Australia
Keene, J.B.; Harris, P.T. (1995). Submarine cementation in tide-generated bioclastic sand dunes: epicontinental seaway, Torres Strait, north-east Australia, in: Flemming, B.W. et al. (Ed.) Tidal Signatures in Modern and Ancient Sediments. Special Publication of the International Association of Sedimentologists, 24: pp. 225-236
In: Flemming, B.W.; Bartholomä, A. (Ed.) (1995). Tidal Signatures in Modern and Ancient Sediments. Special Publication of the International Association of Sedimentologists, 24. Blackwell Science: Oxford. ISBN 0-86542-978-2. 358 pp., more
In: Special Publication of the International Association of Sedimentologists. Blackwell: Oxford; London; Edinburgh; Melbourne. ISSN 0141-3600, more

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Keyword
    Marine

Authors  Top 
  • Keene, J.B.
  • Harris, P.T.

Abstract
    Torres Strait forms a shallow ( <20 m deep) 150 km wide seaway between Cape York, Australia, and Papua New Guinea. This shallow marine environment is part of a larger active foreland basin forming by subsidence of continental crust as the Indo-Australian plate converges with island terranes to the north. Large subtidal bioclastic dunes (sandwaves) form a sand belt across the shallow sill in this setting. Side-scan sonar and seismic reflection profiles show dunes with an average height of 5.4 m and crests oriented north-south in the study area in central Torres Strait. Current meter data confirm that high tidal energy defines the dominant sediment transport control mechanism. During the north-west Monsoon the tidal flow is asymmetrical, the dominant ebb current flowing eastwards (maximum of 1.15 m s· 1) and the subordinate flood current westwards, the latter below the transport threshold of the dune sediments (0.59 m s-1 ). Reversal of dune asymmetries occurs during winter under the influence of the south-east Trade Winds. Two vibrocores recovered from dune fields penetrated cross-bedded carbonate sand containing weakly cemented layers at depths > 1.6 m below the sea-floor. One vibrocore penetrated 2.6 7 m of dune deposited cross-bedded sets overlying Pleistocene limestone. The lower metre of this bioclastic sediment was found to be variably lithified forming a skeletal grainstone. Aragonite needles form an isopachous cement in this highly permeable gravelly sand. Peloids are present within the cement and appear to have formed by precipitation. A 14C age of 530± 180 yr BP from shell at the base of the sediment indicates the transitory nature of unconsolidated sand deposits in this high-energy environment. The proposed mechanism for cementation is tidal pumping of sea water through the sand body which overlies an impermeable limestone. The cementation is contemporary and not formed at the sediment-water interface. Such internal (subsurface) cementation in carbonate dunes and sand bodies may be more common than previously recognized and enhances the preservation potential of the basal section of dunes by providing resistance to reworking. Hardgrounds elsewhere may have formed in this manner rather than by exposure at or near the sea-floor during periods of quiescence.

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