Geochemistry of regionally extensive dolomites, Burlington and Keokuk Formations (Mississippian), Iowa and Illinois
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-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 69:2; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
Similar Records
Petrologic and geochemical constraints on the origin of regionally extensive dolomites of the Mississippian Burlington and Keokuk fms. , Iowa, Illinois and Missouri
Calcite veins of the Stripa granite (Sweden) as records of the origin of the ground waters and their interactions with the granitic body
Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
DIAGENESIS
DOLOMITE
FEDERAL REGION V
FEDERAL REGION VII
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
ILLINOIS
IOWA
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
MISSISSIPPIAN PERIOD
NORTH AMERICA
OXYGEN COMPOUNDS
PALEOZOIC ERA
RESERVOIR ROCK
USA