Dolomite in an upper Ordovician sequence composed of the Irene Bay and Thumb Mountain Formations on Devon Island in the Canadian Arctic Archipelago is confined to burrows. Micron-sized dolomite crystals may have formed in burrows contemporaneous with deposition because of seasonal salinity changes in the Irene Bay-Thumb Mountain shelf lagoon. These penecontemporaneous dolomite crystals formed nuclei for the selective precipitation of late diagenetic dolomite from dilute subsurface solutions. Post-lithification crystal growth during late diagenesis caused idiotopic dolomite fabrics with intercrystalline micrite to become more coarsely crystalline xenotopic fabrics with no intercrystalline micrite. Dolomite crystal growth was accompanied by a progressive decrease in strontium and sodium contents and by a lowering of the amount of excess calcium. A possible rule regarding dolomite compositional variations is that high Mg/Ca solution ratios favor precipitation of more stoichiometric dolomite whereas low Mg/Ca solution ratios favour precipitation of calcium-rich dolomite with the exception that solutions of very low salinities will precipitate stoichiometric dolomite regardless of their Mg/Ca solution ratios.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.