Silurian Microbial Buildups of the Canadian Arctic

  1. C. L. V. Monty,
  2. D. W. J. Bosence,
  3. P. H. Bridges and
  4. B. R. Pratt
  1. T. A. de Freitas and
  2. O. A. Dixon

Published Online: 14 APR 2009

DOI: 10.1002/9781444304114.ch5

Carbonate Mud-Mounds: Their Origin and Evolution

Carbonate Mud-Mounds: Their Origin and Evolution

How to Cite

de Freitas, T. A. and Dixon, O. A. (1995) Silurian Microbial Buildups of the Canadian Arctic, in Carbonate Mud-Mounds: Their Origin and Evolution (eds C. L. V. Monty, D. W. J. Bosence, P. H. Bridges and B. R. Pratt), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304114.ch5

Author Information

  1. Ottawa-Carleton Geoscience Centre and Department of Geology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada

  1. Institute of Sedimentary and Petroleum Geology, 3303, 33rd Street, NW, Calgary, Alberta, Canada T2L 2A7

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 17 JUL 1995

ISBN Information

Print ISBN: 9780865429338

Online ISBN: 9781444304114

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Keywords:

  • Silurian microbial buildups;
  • ‘northern’ and ‘southern’ mudmounds;
  • facies succession and palaeogeo-graphic setting;
  • Late Silurian-Early Devonian mud-mound complex;
  • mud-mound facies overlain by ‘grey pelletoidal and algal boundstone’;
  • Sponge mud-mounds of Douro Formation and large microbial buildups

Summary

Four Silurian microbial buildups occur on Ellesmere Island in three main depositional settings: (i) on the edge of a drowned Ordovician platform margin; (ii) on the slope of a progradational platform; and (iii) on, and slightly basinward from, the slope of a backstepped Silurian platform. Buildups in the first setting are up to 1140 m thick, 15 km wide, and more than 25 km in length. Some show a four-part facies succession, indicating upward shallowing through the first three parts, and then deepening in the last. These facies are, from base to top: (i) a sparsely fossiliferous, bioturbated lime mudstone; (ii) a microbial boundstone and microbialite lime mudstone; (iii) a stromatoporoid-rich floatstone and boundstone; and (iv) a microbial boundstone and microbialite-rich lime mudstone.

Packstone, grainstone and microbialite constitute two 5–8 m thick Wenlock age mud-mounds on central Ellesmere Island that were deposited on a slope of progradational platform. Metre-scale wackestone and grainstone beds, locally stromatactoid-rich, are interbedded with red-stained, cephalopod-, crinoid-, and ostracode-rich lime mudstone and wackestone. Stromatoporoids form a small proportion of boundstone in the upper parts of the mound. Microbial structures surrounding grains and some cavities, and abundant, variably distributed, syndepositional, coarse marine cements, are evidence for early lithification. The mud-mounds were also influenced by bottom currents that are likely to have winnowed some fine, uncemented material and caused cross-stratified grainstone to be deposited locally.

A Llandovery–Ludlow age mud-mound and several coeval microbial lime mudstone-cored pinnacle reefs occur on the slope, and basinward, of a backstepped Silurian platform. While the pinnacle reefs show a complete, shallowing-upward sequence capped by coral-microbial boundstone and oolite deposited in the surf zone, the isochronous mud-mound contains predominantly deeper-water facies, suggesting that local variation in subsidence or palaeoenvironment significantly influenced the growth of these buildups.

Stromatactis and stromatactoid structures occur in some Silurian microbial buildups of the Arctic. Lithistid sponges also occur sporadically, and their presence in some microbial buildups may be attributed to lower light intensities in conditions of greater turbidity and/or depth.