Coarse-Grained Meander Lobe Deposits in the Jarama River, Madrid, Spain

  1. J. D. Collinson and
  2. J. Lewin
  1. Alfredo Arche

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch25

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Arche, A. (1983) Coarse-Grained Meander Lobe Deposits in the Jarama River, Madrid, Spain, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch25

Author Information

  1. Instituto de Geología Económica, C.S.I.C., Facultad de Ciencias Geológicas, 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:

  • coarse-grained meander lobe deposits – Jarama River, Madrid, Spain;
  • conglomeratic units;
  • meander lobe lateral migration;
  • gravel imbrication;
  • megacross-stratification

Summary

The sediments of the 18–20 m terrace of the Jarama River have been studied in an area between Velilla de San Antonio and Arganda, near Madrid, and compared with the deposits of the active channel.

Two main vertical sequences are found in the channel sequences of the terraces: one consists mainly of conglomerates with few variations in pebble size and the other is composed of a lower conglomeratic member and an upper sandy member with a sharp or erosive contact. The conglomeratic units can be traced laterally for several hundred metres and have planar bases, convex tops and many internal accretionary surfaces. Lateral migration of meander lobes was the process responsible for the formation of the conglomeratic units. There is a ridge-and-swale topography on top surfaces; varying discharge is the main factor controlling this topography.

Some swales and chute channels receive water from the main channel during moderate floods, plugging them with sand. The sand units have a lenticular geometry, with concave bases and planar tops; they accumulated as transverse and chute bars which accreted longitudinally because of lateral topographic restriction. Overbank deposits overlie these channel sequences and were deposited as crevasse splays, natural levées, suspension deposits and abandoned channel fills. The high proportion of gravel in these deposits can be explained by the presence of thick, erodible conglomerates of Pliocene age at the headwaters of the Jarama River.