Metal Precipitation Related to Lower Ordovician Oceanic Changes: Geochemical Evidence from Deep-Water Sedimentary Sequences in Western Newfoundland

  1. John Parnell,
  2. Ye Lianjun and
  3. Chen Changming
  1. J. W. Botsford1,† and
  2. D. F. Sangster2,‡

Published Online: 3 APR 2009

DOI: 10.1002/9781444303872.ch10

Sediment-Hosted Mineral Deposits: Proceedings of a Symposium Held in Beijing, People's Republic of China, 30 July-4 August 1988

Sediment-Hosted Mineral Deposits: Proceedings of a Symposium Held in Beijing, People's Republic of China, 30 July-4 August 1988

How to Cite

Botsford, J. W. and Sangster, D. F. (1990) Metal Precipitation Related to Lower Ordovician Oceanic Changes: Geochemical Evidence from Deep-Water Sedimentary Sequences in Western Newfoundland, in Sediment-Hosted Mineral Deposits: Proceedings of a Symposium Held in Beijing, People's Republic of China, 30 July-4 August 1988 (eds J. Parnell, Y. Lianjun and C. Changming), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303872.ch10

Editor Information

  1. Department of Geology, The Queen's University of Belfast, Belfast BT7 INN, UK

Author Information

  1. 1

    Centre for Earth Resources Research, Memorial University of Newfoundland, St. John's, Newfoundland Canada, A1B 3X5

  2. 2

    Geological Survey of Canada, 601 Booth St., Ottawa, Canada K1A 0E8

  1. Newfoundland and Labrador Science and Technology Advisory Council, 114 Empire Ave., St John's, Newfoundland, A1C 3G2

  2. Derry Laboratory for Sedimentary Geochemistry and Mineral Deposits, Ottawa-Carleton Geosciencc Centre, Ottawa, Canada

Publication History

  1. Published Online: 3 APR 2009
  2. Published Print: 27 SEP 1990

ISBN Information

Print ISBN: 9780632028818

Online ISBN: 9781444303872

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Keywords:

  • Humber Arm and Hare Bay Allochthons;
  • Cow Head and Northern Head Groups;
  • Early Cambrian Labrador Group;
  • Middle Arm Point shales;
  • Early Ordovician transition;
  • Irish town - Cooks Brook Formation;
  • in situ mobilization of metals

Summary

Lower Palaeozoic deep-water sedimentary sequences are preserved within the Humber Arm Allochthon in western Newfoundland, where they have been thrust westward and now structurally overlie coeval shallow-water sequences. Of particular interest are the laterally equivalent Cow Head and Northern Head Groups, base-of-slope shale-rich sediment apron deposits which span the latest Middle Cambrian to late Early Ordovician.

A pronounced Early Ordovician change in oceanic conditions is particularly evident in the Northern Head Group, based upon: (1) a marked increase in bioturbation; (2) anomalously high manganese and barium content; and (3) changes in carbon: sulphur ratios. All suggest a transition to a new depositional regime characterized by ventilated depositional and early diagenetic conditions. This is much more subtly reflected in the Cow Head Group; the contrast is ascribed to along-strike differences in original margin morphology which the two groups embody. The contrast extends to sulphides within shales through the section. In the Northern Head Group, anomalous metal (zinc, copper and lead) concentrations (up to 300 ppm) occur within Lower Ordovician (Lower Arenigian) shales. Disseminated sulphides within this horizon appear remobilized and replacive. On the other hand, localized metal concentrations within the Cow Head Group are scattered throughout the entire stratigraphic interval and are generally associated with organic carbon.

The sulphur isotopic profiles of early precipitated pyrite through the stratigraphic interval in both groups are also suggestive of a marked Lower Ordovician change from stratified to ventilated conditions based upon a decrease in δ34S values in the Late Tremadocian. Immediately following this, δ34S values display a positive deflection suggestive of a temporary return to stratified conditions in the Arenigian. These apparent circulation changes may have controlled redox conditions, and in turn have governed metal mobilization and precipitation.