Dolomitization and Neomorphism of Irish Lower Carboniferous (Early Mississippian) Limestones: Evidence from Petrographic and Isotopic Data
Wayne R. Wright, Ian D. Somerville, Jay M. Gregg, Aaron W. Johnson, Kevin L. Shelton, 2003. "Dolomitization and Neomorphism of Irish Lower Carboniferous (Early Mississippian) Limestones: Evidence from Petrographic and Isotopic Data", Permo-Carboniferous Carbonate Platforms and Reefs, Wayne M. Ahr, Paul M. (Mitch) Harris, William A. Morgan, Ian D. Somerville
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The bulk of the replacive dolomite in the Lower Carboniferous (Dinantian) of Ireland is characterized by planar texture and (C, O) isotope signatures that are consistent with a modified Dinantian seawater origin at near-surface temperatures. Only a volumetrically minor (~ 5%) part of the dolomite is characterized by nonplanar texture. Petrographic evidence for fabric-preserving neomorphism of mimetic replacement planar dolomite is the preservation of concentric ooid textures and planar dolomite zonation (in plane-polarized light) retained within mosaics of mainly planar/nonplanar and nonplanar crystals. Neomorphosed dolomite commonly forms an interlocking mosaic of planar/nonplanar crystals and appears to have slightly increased crystal size relative to fine crystalline planar dolomite. In cathodoluminescence, neomorphosed dolomite tends to possess a uniform medium-intensity red color that lacks zonation. The oxygen isotope data from the planar and neomorphosed dolomites (planar and planar/nonplanar morphologies) further supports the petrographically defined division of the two dolomite types.