Sandy Fluvial Point-Bar Sediments from the Middle Eocene of Dorset, England

  1. J. D. Collinson and
  2. J. Lewin
  1. A. G. Plint

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch29

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Plint, A. G. (1983) Sandy Fluvial Point-Bar Sediments from the Middle Eocene of Dorset, England, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch29

Author Information

  1. Department of Geology and Mineralogy, Parks Road, Oxford OX1 3PR, UK

  1. Department of Geology, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick E3B 5A3, Canada

Publication History

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

ISBN Information

Print ISBN: 9780632009978

Online ISBN: 9781444303773

SEARCH

Keywords:

  • sandy fluvial point-bar sediments – middle Eocene of Dorset, England;
  • middle Eocene alluvial sediments;
  • conglomerates;
  • convolute bedding;
  • channel plugs

Summary

Middle Eocene alluvial sediments occupy the western portion of the Hampshire Basin and are laterally equivalent to estuarine, lagoonal and shallow marine sediments to the east. The alluvial sediments are up to 250 m thick and comprise point-bar sands and laminated interchannel muds. Point-bar sands form erosive-based and upward-fining sequences, 3–15 m thick, which are laterally traceable for hundreds of metres. Basal erosion surfaces are usually overlain by intraformational mudclast conglomerates. Metre-scale cross-bedding of transverse bars sometimes occurs low in the sequence. The bulk of the point-bar is composed of decimetre-scale trough and tabular cross-bedded coarse to fine sand. This may be interbedded with low-angle or horizontally laminated sand, or with convolute bedding. Rarely, the upper part of the point-bar is preserved. This consists mainly of fine, rippled or plane-laminated sand passing up into thinly interbedded fine sand and mud of the levée. Usually the sequence is truncated and locally capped by muds deposited in abandoned chute channels. The point-bar sands enclose large, mud-filled abandoned channels which average 130 m in width and 11 m in depth. Within a single point-bar unit palaeocurrents are fairly consistent, but between units there is a wide divergence. The sedimentary characteristics as a whole suggest deposition on the point-bars of relatively sinuous rivers with a mixed load and variable discharge.