A New Evaluation of Fining Upward Sequences in a Mud-Rock Dominated Succession of the Lower Old Red Sandstone of South Wales, UK

  1. Michael D. Blum4,
  2. Susan B. Marriott5 and
  3. Suzanne F. Leclair6
  1. Susan B. Marriott5,
  2. V. Paul Wright1,2 and
  3. Brian P. J. Williams3

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304350.ch27

Fluvial Sedimentology VII

Fluvial Sedimentology VII

How to Cite

Marriott, S. B., Wright, V. P. and Williams, B. P. J. (2009) A New Evaluation of Fining Upward Sequences in a Mud-Rock Dominated Succession of the Lower Old Red Sandstone of South Wales, UK, in Fluvial Sedimentology VII (eds M. D. Blum, S. B. Marriott and S. F. Leclair), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304350.ch27

Editor Information

  1. 4

    Baton Rouge, Louisiana, USA

  2. 5

    School of Geography and Environmental Management, University of the West of England, Bristol BS16 1QY, UK

  3. 6

    Department of Earth and Environmental Sciences, Tulane University, Dimwiddie Hall, New Orleans, LA 70118, USA

Author Information

  1. 1

    Department of Earth Sciences, Cardiff University, Cardiff, CF10 3YE, UK

  2. 2

    BG Group, 100 Thames Valley Park Drive, Reading RG6 1PT, UK

  3. 3

    Department of Geology and Petroleum Geology, University of Aberdeen, King's College, Aberdeen AB24 3UE, UK

  4. 5

    School of Geography and Environmental Management, University of the West of England, Bristol BS16 1QY, UK

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 15 FEB 2005

Book Series:

  1. Special Publication Number 35 of the International Association of Sedimentologists

Book Series Editors:

  1. Ian Jarvis

Series Editor Information

  1. School of Earth Sciences and Geography, Centre for Earth and Environmental Science Research, Kingston University, Penrhyn Road, Kingston-upon-Thames KT1 2EE, UK

ISBN Information

Print ISBN: 9781405126519

Online ISBN: 9781444304350

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Keywords:

  • Lower Old Red Sandstone of South Wales;
  • alluvial sediments of late Silurian to early Devonian age in South Wales;
  • facies 1conglomerate/sandstone;
  • cyclicity of facies;
  • interpretation and facies associations;
  • facies model for Rat Island mudstone;
  • Rat Island Mudstone - relating to ephemeral channel flow

Summary

As much as 80% of the 4.5-km-thick succession of alluvial sediments of late Silurian to early Devonian age in South Wales is composed of mudstone, generally regarded as overbank suspension deposits. Studies of selected formations reveal a variety of lithofacies associations in these mud-dominated intervals, which suggest diverse mechanisms for mud emplacement. For example, there are distinct fining upward units, 2.5–5 m thick, that represent ephemeral channel-zone deposits in which extensive reworking of palaeo-Vertisols took place as clay pellet bedload material. The overall depositional system has many similarities with that described from the Channel Country of central Australia, where anastomosing fluvial systems are associated with distal mud sheetflood deposits. The exact channel planforms for the Old Red Sandstone systems, however, cannot be readily determined, although where larger channel sandbodies exist they have a sheet-like occurrence with a high width/depth ratio, and possibly may be the result of large-scale, low-frequency sheet-flood events. The development of palaeosols with vertic features, calcretes, alternations of desiccation and burrowing in the channel deposits suggests marked seasonality with a flashy regime. The Channel Country represents a fairly stable low-relief cratonic interior, whereas the Old Red Sandstone in South Wales was deposited on a coastal-plain in a subsiding basin setting. There are, however, similarities in terms of depositional products despite the disparity in morpho-tectonic setting, which may reflect extremely low gradients and climatic influences such as frequency and magnitude of flood events.