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Dolomitization and Neomorphism of Irish Lower Carboniferous (Early Mississippian) Limestones: Evidence from Petrographic and Isotopic Data

By
Wayne R. Wright
Wayne R. Wright
Robertson Research International Ltd., Llandudno, North Wales, LL30 ISA, North Wales, United Kingdom e-mail: wrw@robresint. co. uk
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Ian D. Somerville
Ian D. Somerville
Department of Geology, University College Dublin, Dublin 4, Ireland e-mail: ian. somerville@ucd. ie
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Jay M. Gregg
Jay M. Gregg
Department of Geology and Geophysics, University of Missouri-Rolla, Rolla, Missouri 65409, U. S. A. e-mail: greggjay@umr. edu
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Aaron W. Johnson
Aaron W. Johnson
Department of Geological Sciences, University of Missouri-Columbia, Columbia, Missouri 65211, U. S. A. e-mail: aw914@mizzou. edu; sheltonKl@missouri.
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Kevin L. Shelton
Kevin L. Shelton
Department of Geological Sciences, University of Missouri-Columbia, Columbia, Missouri 65211, U. S. A. e-mail: aw914@mizzou. edu; sheltonKl@missouri.
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Published:
January 01, 2003

Abstract

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.

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SEPM Special Publication

Permo-Carboniferous Carbonate Platforms and Reefs

Wayne M. Ahr
Wayne M. Ahr
Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77843-3115, U.S.A.
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Paul M. (Mitch) Harris
Paul M. (Mitch) Harris
ChevronTexaco E&P Technology Company, 6001 Bollinger Canyon Road, San Ramon, California 94583-0746, U.S.A.
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William A. Morgan
William A. Morgan
ConocoPhillips, Inc., P.O. Box 2197, Houston, Texas 77252-2197, U.S.A.
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Ian D. Somerville
Ian D. Somerville
Department of Geology, University College - Dublin, Belfield, Dublin 4, Ireland
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SEPM Society for Sedimentary Geology
Volume
78
ISBN electronic:
9781565763340
Publication date:
January 01, 2003

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