Abstract

Several types of quartz cement and replacive quartz fabrics occur in the Silurian platform carbonates of northern New Brunswick. Petrographic relationships with calcite, pyrite, dolomite, and intraformational erosional clast surfaces indicate that this quartz formed during early burial at depths ranging from the upper few meters to perhaps tens of meters. The quartz cement microtextures suggest that it is a primary precipitate. A close spatial association of fossils and authigenic quartz suggests some kind of organic control on silica precipitation and that the quartz authigenesis was controlled more by molecular diffusion than fluid flow. Several lines of evidence point to bacterial sulfate reduction coupled with oxidation of organic matter as a key process leading to quartz authigenesis, including: 1) documented dominance of this kind of reaction in shallow buried marine sediments, 2) close spatial association of authigenic quartz and pyrite, 3) quartz replacement of gypsum, and 4) experimental evidence that sulfate-reducing bacteria mediate silica precipitation (Birnbaum 1984).

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