The Late Ordovician Glacial Sedimentary System of the North Gondwana Platform

  1. Michael J. Hambrey4,
  2. Poul Christoffersen4,5,
  3. Neil F. Glasser4 and
  4. Bryn Hubbard4
  1. Jean-Francois Ghienne1,
  2. Daniel Paul Le Heron1,2,
  3. Julien Moreau1,
  4. Michael Denis3 and
  5. Max Deynoux1

Published Online: 24 MAR 2009

DOI: 10.1002/9781444304435.ch17

Glacial Sedimentary Processes and Products

Glacial Sedimentary Processes and Products

How to Cite

Ghienne, J.-F., Le Heron, D. P., Moreau, J., Denis, M. and Deynoux, M. (2007) The Late Ordovician Glacial Sedimentary System of the North Gondwana Platform, in Glacial Sedimentary Processes and Products (eds M. J. Hambrey, P. Christoffersen, N. F. Glasser and B. Hubbard), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304435.ch17

Editor Information

  1. 4

    Centre for Glaciology, Institute of Geography & Earth Sciences, Aberystwyth University, Wales, Ceredigion SY23 3DB, UK

  2. 5

    Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge, CB2 1ER, UK

Author Information

  1. 1

    Ecole et Observatoire des Sciences de la Terre, Centre de Géochimie de la surface, CNRS-UMR 7517, 1 rue Blessig, 67084 Strasbourg, France

  2. 2

    Institut für Geologie, Leibniz Universität Hannover, Callinstrasse 30, D-30167, Germany

  3. 3

    UMR 5561, Biogéosciences, Université de Bourgogne, 6 Bd Gabriel, 21 000 Dijon, France

Publication History

  1. Published Online: 24 MAR 2009
  2. Published Print: 14 DEC 2007

Book Series:

  1. Special Publication Number 39 of the International Association of Sedimentologists

Book Series Editors:

  1. Isabel Montanez

Series Editor Information

  1. University of California, Davis, USA

ISBN Information

Print ISBN: 9781405183000

Online ISBN: 9781444304435

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Keywords:

  • Late Ordovician glacial sedimentary system of North Gondwana platform;
  • pre-glacial setting;
  • recognition of glacial erosion surfaces;
  • Ice sheet margins;
  • ice-marginal areas - effects of glacial erosion less pronounced;
  • Hirnantian glacial event - multiphase glaciation;
  • North Gondwana platform during the Hirnantian;
  • ice-proximal, coarse-grained glaciomarine successions

Summary

The Late Ordovician (Hirnantian) glaciation is examined through the North Gondwana record. This domain extended from southern high palaeo-latitudes (southeastern Mauritania, Niger) to northern lower palaeo-latitudes (Morocco, Turkey) and covered a more than 4000 km-wide section perpendicular to ice-flow lines. A major mid-Hirnantian deglaciation event subdividing the Hirnantian glaciation in two first-order cycles is recognised. As best illustrated by the glacial record in western Libya, each cycle comprises 2–3 glacial phases separated by ice-front retreats several hundreds kilometres to the south. From ice-proximal to ice-distal regions, the number of glacial surfaces differentiates (i) a continental interior with post-glacial reworking of the glacial surfaces), (ii) a glaciated continental shelf that is subdivided into inner (1–2 surfaces), middle (2–5 surfaces) and outer (a single surface related to the glacial maximum) glaciated shelves, and (iii) the non-glaciated shelf. Ice-stream-generated glacial troughs, 50–200 km in width, cross-cut these domains. These troughs are zones of preferential glacial erosion and subsequent sediment accumulation. A glacial depositional sequence, bounded by two glacial erosion surfaces, records one glacial phase. The position either within or outside a glacial trough controls the stratigraphic architecture of a glacial sequence. Glaciomarine outwash diamictites are developed at or near the maximum position of the ice-front. During ice-sheet recession, and in an ice-stream-generated trough, a relatively thin sediment cover blankets the foredeepened erosion surface. An initial rapid ice-sheet withdrawal is inferred. Marine-terminating ice fronts then evolve later into more slowly retreating, land-terminating ice fronts. In adjacent inter-stream areas where a more gradual ice-sheet recession occurred, fluvioglacial deposits prevailed. The progradation of a delta-shelf system, coeval with fluvial aggradation, that may be locally interrupted by a period of isostatic rebound, characterises the late glacial retreat to interglacial conditions. This model should facilitate the sequence stratigraphic interpretation of Late Ordovician glacial deposits and other ancient glacial successions.