Dolomitization of the Devonian Jefferson Formation, south-central Montana
- Washington State Univ., Pullman (USA)
- Texas A M Univ., College Station (USA)
Dolomitization of the Devonian Jefferson Formation in south-central Montana probably occurred as a result of multiple dolomitizing events. Petrographic and geochemical studies show the presence of five distinct dolomite types: cathodoluminescently nonzoned euhedral dolomite, nonzoned subhedral/anhedral dolomite mosaics, zoned euhedral dolomite, irregularly luminescent dolomite, and zoned dolomite cement. Data from Jefferson Formation dolomite indicate a progression from early, nonstoichiometric, euhedral replacive dolomites, to nearly stoichiometric, subhedral/anhedral dolomite mosaics. {delta}{sup 18}O and {delta}{sup 13}C ratios decrease with increasing degree of dolomitization. Euhedral replacive dolomites in lower dolomitic limestone layers probably formed by early, refluxing hypersaline brines in evaporitic settings. These dolomites are the least stoichiometric and have the heaviest {delta}{sup 18}O signatures of all dolomites which were analyzed. Massive dolomitization of the upper two-thirds of the Jefferson Formation probably occurred when dolomitizing brines migrated downward through the upper Jefferson Formation during deposition of thick evaporite sequences in the overlying Three Forks Formation. Mass balance calculations indicate that this mechanism was more than adequate to cause the massive dolomitization in the upper Jefferson Formation. Massive dolomitization during Logan Gulch deposition may have been the final phase of dolomitization, or dolomite may have recrystallized to more stoichiometric, {sup 18}O- and {sup 13}C-depleted subhedral/anhedral mosaics during later burial.
- OSTI ID:
- 6904336
- Journal Information:
- Mountain Geologist; (USA), Journal Name: Mountain Geologist; (USA) Vol. 26:3; ISSN MOGEA; ISSN 0027-254X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ALKALINE EARTH METAL COMPOUNDS
BRINES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON 13
CARBON COMPOUNDS
CARBON ISOTOPES
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
CHEMISTRY
CRYSTALLIZATION
DEPOSITION
DEVONIAN PERIOD
DOLOMITE
EVAPORITES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION VIII
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
LIMESTONE
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MASS BALANCE
MINERALIZATION
MINERALS
MONTANA
NORTH AMERICA
NUCLEI
ORIGIN
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PALEOZOIC ERA
PETROGRAPHY
PHASE TRANSFORMATIONS
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
STOICHIOMETRY
USA