Geochemistry of regionally extensive dolomites, Burlington and Keokuk Formations (Mississippian), Iowa and Illinois

Conference · Fri Feb 01 04:00:00 EST 1985 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:5961532

Banner, J; Hanson, G; Meyers, W; Prosky, J

The Burlington and Keokuk Formations (Mississippian) contain 2 major generations of dolomite throughout the several ten-thousand square kilometers of study area. Dolomite I (oldest) is luminescently zoned, Ca-rich, Fe- and Mn-poor, and has Mississippian /sup 87/Sr//sup 86/Sr; dolomite II is unzoned, nearly stoichiometric, Fe- and Mn-rich, and has radiogenic /sup 87/Sr//sup 86/Sr; dolomite III, a minor zone, is nonluminescent and very Fe-rich. Dolomites I and II formed before nonmarine calcite cements, and all dolomites formed before Late Mississippian under shallow burial conditions. Stable isotopes of dolomite I average +2.3 per thousand delta/sup 13/C and -0.3 per thousand delta/sup 18/O PDB. Dolomite I is slightly depleted in /sup 13/C and /sup 18/O with respect to estimated Mississippian marine dolomite. Thus, dolomite I may have formed in waters only slightly depleted in /sup 18/O and /sup 13/C compared with seawater at low temperatures (approx. 25/sup 0/C). Dolomite II averages -4.1 per thousand delta/sup 18/O PDB, +2.8 per thousand delta/sup 13/C PDB, and has a wide range of delta/sup 18/O (-0.5 to -6.6 per thousand PDB) and a narrower range of delta/sup 13/C (+1 to +4 per thousand). These data suggest that temperatures of precipitation were less than the 80/sup 0/C-110/sup 0/C ranges implied by the contained 2-phase fluid inclusions, unless the waters were isotopically heavy (approx. +3 to 11 per thousand delta/sup 18/O SMOW). Dolomite II shows a regional geographic trend of decreasing delta/sup 18/O and increasing delta/sup 13/ from north to south. This trend can be accounted for by either a northward decrease in temperature or in /sup 18/O content of diagenetic waters.

• Research Organization: State Univ. of New York, Stony Brook
• OSTI ID: 5961532
• Report Number(s): CONF-850322-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 69:2
• Country of Publication: United States
• Language: English

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