Abstract

Dolomitization in the uppermost pisolitic limestone of the Wyman Formation has produced individual dolomitized pisoliths, dolomite pods that are tens of meters across, and tabular bodies (dikes), usually 1 to 12 cm in width, that generally lie at high angles to the stratification and have transitional or sharp contacts. A replacement origin for the dolomite in the pods and dikes is evidenced by transitional margins and relic pisoliths in some of these bodies. The dikes are believed to result from dolomitization along fractures that are now healed. The slightly ferroan composition and undulatory extinction of the dolomite crystals suggest that replacement was late diagenetic, following neomorphism of the pisoliths. Low delta O 18 values for the dolomite (-12.8 per mil) suggest that exchange occurred between the original carbonate material and hydrothermal waters. Coarse texture, presence of tremolite, and strained dolomite crystals indicate that metamorphism followed dolomitization.

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