Origin of White Sucrosic Dolomite within Shallow-Water Limestones, ODP Hole 866A, Resolution Guyot, Mid-Pacific Mountains: Strontium Isotopic Evidence for the Role of Sea Water in Dolomitization

  1. G. F. Camoin2 and
  2. P. J. Davies3
  1. P. G. Flood

Published Online: 27 MAY 2009

DOI: 10.1002/9781444304879.ch7

Reefs and Carbonate Platforms in the Pacific and Indian Oceans

Reefs and Carbonate Platforms in the Pacific and Indian Oceans

How to Cite

Flood, P. G. (1998) Origin of White Sucrosic Dolomite within Shallow-Water Limestones, ODP Hole 866A, Resolution Guyot, Mid-Pacific Mountains: Strontium Isotopic Evidence for the Role of Sea Water in Dolomitization, in Reefs and Carbonate Platforms in the Pacific and Indian Oceans (eds G. F. Camoin and P. J. Davies), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304879.ch7

Editor Information

  1. 2

    CEREGE, Aix-en-Provence, France

  2. 3

    University of Sydney, Australia

Author Information

  1. University of New England, Division of Earth Sciences, Armidale, NSW 2351, Australia

Publication History

  1. Published Online: 27 MAY 2009
  2. Published Print: 23 MAR 1998

ISBN Information

Print ISBN: 9780632047789

Online ISBN: 9781444304879

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Keywords:

  • borehole temperature;
  • interior pore-waters active exchange within the ‘drowned’;
  • dolomite - ubiquitous in Barremian sediments;
  • dolomite textures in cores display - coarsely crystalline grains;
  • oxygen and carbon isotopes

Summary

Strontium isotopic (87Sr/86Sr) measurements obtained from a 30-m-thick unit of massive white sucrosic dolomite at a depth of 1250–1280 mbsf (metres below sea-floor) within the 1620-m-thick shallow-water limestone sequence recovered by the Ocean Drilling Program in Hole 866A at Resolution Guyot indicate that the dolomite was precipitated from slightly modified sea water at 24 Ma, some 100 Myr after deposition of the enclosing limestones. The temperature of formation of the dolomite is consistent with the temperature of the pore-waters recorded by the downhole temperature probe.

Oxygen and carbon stable isotopes also indicate a marine source for the Mg-rich dolomitizing solutions. Solution of the precursor limestone below 1000 mbsl (metres below sea-level) is responsible for the development of solution cavities and mouldic porosity which is infilled by the dolomite-precipitating fluids. In addition to the formation of new crystals of dolomite within the cavities, occasionally the original grains are mimically replaced and then the original texture is preserved.

Conditions of dolomitization include the following: (i) a permeable substrate; (ii) contiguous deep ocean water supplying an abundant source of Mg2+ ions and capable of dissolving aragonite and calcite and replacing them with dolomite; (iii) a sufficiently thick limestone pile to impose a thermal gradient allowing a geothermal convective process to operate. Such a process has been called geothermal endo-upwelling.

Although some researchers have indicated that sea-water can be responsible for the transformation of a carbonate precursor by secondary replacement dolomite, the strontium isotopic data obtained from ODP Hole 866A, Resolution Guyot, provide confirmatory evidence of the marine water dolomitization model.