Gravel Bars in Low-Sinuosity Streams (Permian and Triassic, Central Spain)

  1. J. D. Collinson and
  2. J. Lewin
  1. Amparo Ramos1 and
  2. Alfonso Sopeña2

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch24

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Ramos, A. and Sopeña, A. (1983) Gravel Bars in Low-Sinuosity Streams (Permian and Triassic, Central Spain), in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch24

Author Information

  1. 1

    Departamento de Estratigrafía, Facultad de Ciencias Geológicas, Universidad Complutense, Madrid 3, Spain

  2. 2

    Instituto de Geología Económica C.S.I.C., Madrid 3, Spain

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 7 FEB 1983

ISBN Information

Print ISBN: 9780632009978

Online ISBN: 9781444303773

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Keywords:

  • gravel bars in low-sinuosity streams – Permian and Triassic, central Spain;
  • fluvial sequence;
  • sediment accumulation;
  • Buntsandstein deposition;
  • upstream imbrication

Summary

The Buntsandstein sequence of the central area of Spain ranges from a variety of fluvial facies, low in the succession, to tidal mudstones and carbonates in the youngest and most eastern areas. This paper is restricted to the conglomerates in the lowest part of the fluvial sequence. These were deposited in bar and channel systems dominated by gravelly, low-sinuosity braided streams. Their distribution reflects both the pre-existing topography and synsedimentary tectonic movements.

Six main facies have been distinguished (in order of decreasing abundance): sheets of massive conglomerates, channel-fill conglomerates, coarse–medium sandstones, lateral accretion conglomerates. tabular cross-stratified conglomerates, fine-grained sediments.

Sheets of gravels, formed as longitudinal bars, were by far the major feature of sediment accumulation. Units of lateral accretion, if not very frequent, are quite important as they probably represent modifications of bars during waning stage.

Two big cycles may be seen in these conglomerates. They correspond to different physiographic models. The lower cycle was mainly formed by smaller channels and bars than was the upper cycle. The lower cycle is mainly formed by channel deposits, whilst in contrast, the upper cycle is mainly made up of longitudinal bars.

The change in sedimentation may be due to tectonic movements that occurred in the basin during Buntsandstein deposition.