Petrologic and geochemical constraints on the origin of regionally extensive dolomites of the Mississippian Burlington and Keokuk fms. , Iowa, Illinois and Missouri
The marine carbonates of the Mississippian Burlington and Keokuk Formations of Iowa, Illinois and Missouri have been subject to several episodes of pervasive and regionally extensive (100,000 km{sup 2}) dolomitization. Cathodoluminescent petrography defines two major and at least three minor generations of dolomite which can be correlated over a regional extent. Sr and O isotopic compositions and Sr concentrations show significant differences between the early dolomite generation, dolomite I, and the later replacement dolomites II and II{prime}. Compared to dolomite I, dolomites II and II{prime} have significantly higher Sr-isotopic compositions of 0.70885 to 0.70942, lower Sr concentrations of 50 to 63 ppm and depleted d{sup 18}O values of {minus}1.0 to {minus}6.6. The geochemistry of the replacement dolomites and quantitative modeling of water-rock interaction suggest that extraformational brines recrystallized the less stoichiometric dolomite I at fluid/rock ratios on the order of 10{sup 2} or greater. The consistency of REE patterns and the presence of anomalously lower abundances of cerium in most diagenetic phases suggest that seawater-derived REE dominate the system, and that subsequent, non-marine diagenetic fluids did not significantly alter the REE patterns, except in late, vug-filling carbonates associated with minor mineralization. The regional extent of pervasive fluid-rock interaction required for the petrogenesis of second generation replacement dolomite in the Burlington and Keokuk Fms. is an order of magnitude greater than has been previously proposed for carbonate-hosted Pb-Zn ore deposits in the midcontinent region.
- Research Organization:
- State Univ. of New York, Stony Brook, NY (USA)
- OSTI ID:
- 5097352
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
CALCULATION METHODS
CATHODOLUMINESCENCE
DATA
DATA ANALYSIS
EXPERIMENTAL DATA
GEOLOGIC FORMATIONS
INFORMATION
ISOTOPES
LUMINESCENCE
MEASURING INSTRUMENTS
MEASURING METHODS
MISSISSIPPI RIVER BASIN
NUMERICAL DATA
OXYGEN ISOTOPES
PETROGRAPHY
STRONTIUM ISOTOPES
WATERSHEDS