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Dolomitization and dolomite neomorphism; Trenton and Black River limestones (Middle Ordovician) northern Indiana, U.S.A.

Chan Min Yoo, Jay M. Gregg and Kevin L. Shelton
Dolomitization and dolomite neomorphism; Trenton and Black River limestones (Middle Ordovician) northern Indiana, U.S.A.
Journal of Sedimentary Research (January 2000) 70 (1): 265-274

Abstract

The Trenton and Black River Limestones are dolomitized extensively along the axis of the Kankakee Arch in Indiana, with the proportion of dolomite decreasing to the south and southeast of the arch. Planar and nonplanar dolomite replacement textures and rhombic (type 1) and saddle (type 2) void-filling dolomite cements are present. Three stages of dolomitization, involving different fluids, are inferred on the basis of petrographic and geochemical characteristics of the dolomites. Nonferroan planar dolomite has relatively high delta (super 18) O values (-1.8 to -6.1 per mil PDB) and has (super 87) Sr/ (super 86) Sr ratios (0.70833 to 0.70856) that overlap those of Middle Ordovician seawater. Petrography, geochemistry, and the geometry of the dolomitized body suggest that the planar dolomite was formed in Middle and Late Ordovician seawater during the deposition of the overlying Maquoketa Shale. Ferroan planar and nonplanar dolomite occurs in the upper few meters of the Trenton Limestone, confined to areas underlain by planar dolomite. This dolomite contains patches of nonferroan dolomite with cathodoluminescence (CL) characteristics similar to underlying planar dolomite. Ferroan dolomite has relatively low delta (super 18) O values (-5.1 to -7.3 per mil PDB) and has slightly radiogenic (super 87) Sr/ (super 86) Sr ratios (0.70915 to 0.70969) similar to those obtained for the overlying Maquoketa Shale. These data indicate that ferroan dolomite formed by neomorphism of nonferroan planar dolomite as fluids were expelled from the overlying Maquoketa Shale during burial. The absence of ferroan dolomite at the Trenton-Maquoketa contact, in areas where the earlier-formed nonferroan planar dolomite also is absent, indicates that the fluid expelled from the overlying shale did not contain enough Mg (super 2+) to dolomitize limestone. Type 1 dolomite cement has isotopic compositions similar to those of the ferroan dolomite, suggesting that it also formed from shale-derived burial fluids. CL growth zoning patterns in these cements suggest that diagenetic fluids moved stratigraphically downward and toward the southeast along the axis of the Kankakee Arch. Type 2 saddle dolomite cements precipitated late; their low delta (super 18) O values (-6.0 to -7.0 per mil PDB) are similar to those of the type 1 dolomite cement. However, fluid-inclusion data indicate that the saddle dolomite was precipitated from more saline, basinal fluids and at higher temperatures (94 degrees to 143 degrees C) than the type 1 cements (80 degrees to 104 degrees C). A trend of decreasing fluid-inclusion homogenization temperatures and salinities from the Michigan Basin to the axis of Kankakee Arch suggests that these fluids emerged from the Michigan Basin after precipitation of type 1 cement.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 70
Serial Issue: 1
Title: Dolomitization and dolomite neomorphism; Trenton and Black River limestones (Middle Ordovician) northern Indiana, U.S.A.
Affiliation: University of Missouri-Rolla, Department of Geology and Geophysics,, Rolla, MO, United States
Pages: 265-274
Published: 200001
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 37
Accession Number: 2000-029821
Categories: Isotope geochemistrySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch maps
N37°45'00" - N41°45'00", W88°10'00" - W84°45'00"
Secondary Affiliation: University of Missouri-Columbia, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 200010
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