Origin of dolomites and associated porosities in lower ordovician boat harbour formation carbonates, western Newfoundland, Canada

• Main Author: Olanipekun, Babatunde John
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2016
• Subjects: Canada; Main Brook; Boat Harbour; Newfoundland
• Online Access: https://research.library.mun.ca/11874/; https://research.library.mun.ca/11874/1/thesis.pdf

The Boat Harbour Formation constitutes the upper part of the Lower Ordovician St. George Group on the Northern Peninsula, western Newfoundland. It varies in thickness from 140 m at Main Brook to 96 m at Daniel’s Harbour (about 200km). Dolomitization of the carbonate sequence is more pervasive in the lower 30–40 m at Main Brook, whereas at Daniel’s Harbour the section is entirely dolomitized. Petrography suggests that the formation has been affected by three phases of dolomitization: earliest (near-surface/syn-sedimentary) phase is D1 dolomicrite, mid–burial phase D2 dolomite, and late stage D3 dolomite. The earliest (near-surface/syn-sedimentary) phase is D1 dolomicrite. The geochemical composition suggests that D1 was developed from fluids of a mixture of meteoric and marine waters at near-surface conditions. The mid–burial phase D2 dolomite consists of coarse planar sub–euhedral crystals that precipitated from hot fluids that circulated through crustal rocks with progressive burial. The late stage D3 dolomite has large and coarse non–planar crystals that exhibit sweeping extinction. In addition to its micro-thermometric data these factors suggest that it likely precipitated during deeper burial in pulses and from hot fluids. For porosity the data suggest that it is mainly associated with the mid–burial D2 dolomite. Intercrystalline porosity is the dominant type and it varies in the formation from <1 to 8 % at Main Brook and from 7 to 12 % at Daniel’s Harbour. Recrystallization to more stoichiometric dolomite is usually accompanied by characteristic textural and geochemical signatures. These signatures are primarily studied using multiple populations of crystals, comparison of modern and ancient dolomites, or from results of high temperature dolomite formation experiments. This approach is inadequate. Therefore study was done using multi proxy high resolution approaches to carry out imaging and ion microprobe elemental analyses of individual dolomite (burial) crystals viz: Scanning Electron Microscopy (SEM), ...