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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Dolomite occurs in the matrix of the Onondaga Limestone (Middle Devonian) in New York as scattered grains ranging in size from 4 to 150 ยต. Detrital quartz is associated with the dolomite. Study of etched and stained thin sections shows a correlation between grain size of the dolomite and quartz. Limited data show a correlation between grain size of dolomite, quartz, and detrital calcite (silt to fine sand) matrix. In addition there is a correlation between abundance of dolomite and quartz, where high dolomite values occur with high quartz values.
These data suggest that dolomite in the Onondaga is detrital. Source of the dolomite is uncertain, but reworked, penecontemporaneous supratidal sediments and older (for example Silurian) dolomites are possibilities. Wind is a likely mechanism for transport of the detritus.
Deposition of detrital dolomite, followed by later diagenetic overgrowths on the detrital nuclei is suggested as a mechanism for "dolomitization." This process is compatible with the following phenomena observed in dolomitic rocks: (1) association of insoluble detritus with dolomite, (2) occurrence of dolomite in fine-grained limestone, and (3) dolomite interpreted as "primary" (being fine grained) and dolomite interpreted as "replacement" (being coarse grained). Two models for the origin of dolomitic rocks are proposed.
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