Monday, December 16, 2013

Highlights—Dolomitization sans Evaporites

Many dolomitized platform carbonate successions are associated with evaporites, and many studies link dolomite to reflux associated with hypersaline brines. In this paper, Rott and Qing describe petrographic observations and geochemical data to explore the genesis of pervasive matrix-replacive dolomite in a succession not associated with evaporites, the Mississippian Alida Beds in the Williston Basin of Canada. Petrographic observations and δ13C compositions suggest an initial dolomitizing event driven by slightly evaporated seawater (but not enough for gypsum saturation), although depleted δ18O values, elevated 87Sr/86Sr ratios, and correlation of dolomite crystal sizes and δ18O values are interpreted to represent variable recrystallization of this early dolomite.  This proposed conceptual model may explain the occurrence of pervasive, matrix-replacive dolomite in the absence of depositional evaporites, and may be appropriate for other regions and hydrocarbon pools.

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