Proximal to Distal Sedimentological Variation in a Linear Turbidite Trough: Implications for the Fan Model

  1. Dorrik A. V. Stow
  1. David I. M. Macdonald

Published Online: 29 APR 2009

DOI: 10.1002/9781444304473.ch42

Deep-Water Turbidite Systems

Deep-Water Turbidite Systems

How to Cite

Macdonald, D. I. M. (2009) Proximal to Distal Sedimentological Variation in a Linear Turbidite Trough: Implications for the Fan Model, in Deep-Water Turbidite Systems (ed D. A. V. Stow), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304473.ch42

Editor Information

  1. Department of Geology, University of Southampton, UK

Author Information

  1. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 11 NOV 1991

ISBN Information

Print ISBN: 9780632032624

Online ISBN: 9781444304473

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Keywords:

  • Lower Cretaceous Cumberland Bay Formation;
  • concept of proximality;
  • South Georgia, comprising elements of a volcanic arc–back-arc basin system;
  • Marnoso-Arenacea;
  • Jurassic Brae field, providing fault-controlled fan system

Summary

Determination of geographically dependent sedimentological variation (‘proximality’) in ancient flysch deposits formed an important part of early turbidite studies. Attempts to quantify this variation highlighted anomalies which were neatly resolved by application of vertical sequence analysis and the use of fan models. However, there are many turbidite formations, such as the Lower Cretaceous Cumberland Bay Formation (CBF) of South Georgia, which cannot be described in terms of existing fan models but show strong proximal to distal sedimentological changes. The CBF is a thick sequence of volcaniclastic sandstone turbidites deposited in a linear back-arc basin, principally by currents flowing WNW, parallel to the basin margin. Four lithofacies associations are recognized on the basis of sandstone/shale ratio. The two finer-grained associations are constant in character across the CBF outcrop. In the coarse-grained associations there is a change in character WNW, down the palaeocurrent direction. This is brought out by decreasing sandstone bed thickness and percentage amalgamation, but these changes are not always marked or consistent. In contrast, the internal character of the sandstone beds changes strongly, with a marked proportional increase in Tb and Tc divisions within the bed downcurrent. The evidence suggests that the system was aggradational rather than progradational: tectonic control of the basin margins prevented major migration of the depositional system, and most areas remained in the same position relative to source through time. Comparison of the CBF with other turbidite formations suggests two end-member states which will produce radically different vertical sequences. Progradational systems will produce strong vertical facies changes, where beds deposited in distal environments are overlain by beds deposited in environments progressively nearer source, however there will be no lateral change in the character of any particular facies type. In contrast in aggradational systems the major sedimentological variation will be lateral rather than vertical.