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Sedimentation in the mesotidal Rias Bajas of Galicia (north-western Spain): Ensenada de San Simon, Inner Ria de Vigo
Nombela, M.A.; Vilas, F.; Evans, G. (1995). Sedimentation in the mesotidal Rias Bajas of Galicia (north-western Spain): Ensenada de San Simon, Inner Ria de Vigo, in: Flemming, B.W. et al. (Ed.) Tidal Signatures in Modern and Ancient Sediments. Special Publication of the International Association of Sedimentologists, 24: pp. 133-149
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 
  • Nombela, M.A.
  • Vilas, F.
  • Evans, G.

Abstract
    The mesotidal (2-4 m) Rias Bajas of Galicia are fault-bounded depressions drowned by the sea during the Flandrian transgression to form elongate coastal embayments, which are being infilled by land-derived siliciclastic detritus and locally produced biogenic carbonate. Small fluvio-tidal bay-head deltas have developed at the landward extremities where the rivers debouch into the rias. Muds and sands accumulate in narrow marshes, on Zostera nana covered mud-flats and on sand-flats, which are crossed by estuarine channels floored with sands fashioned into a wide variety of bedforms. Seawards of the sand-flats associated with the fluvio-tidal deltas, the inner subtidal parts of the rias are covered with a dense carpet of Zostera marina which traps and prevents the seaward dispersal of sands. These are stratified and rich in Cerastoderma edule (Facies III), floor the inner rias, and pass seawards into diffusely stratified muds which are poor in skeletal debris and rich in organic matter (5-6%) (Facies II). Structures produced by organically generated gas are common in these sediments. The surficial sediments are underlain ( <2 m) by better stratified muds with higher amounts of skeletal debris (Facies 1), indicating recent changes in depositional conditions in the inner rias. Generally, if the subtidal sediments were preserved in the geologic record, the tidal character of the deposits would not be recognized unless the adjacent intertidal deposits were also preserved. Man has influenced the environment by dumping sand to produce beds for Cerastoderma edule, thereby artificially extending the areas of natural sand deposition seawards of the fluvio-tidal deltas. In addition, the deposition of fine-grained sediment has been increased by the introduction of mussel rafts for Mytilus galloprovincialis.

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