Significance of anoxic dolomite in the Laney Shale member of the Green River Formation

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6194871

Kelts, K; McKenzie, J

The mode of origin of dolomite laminae in the Green River Formation has previously been attributed to evaporitic environments and implied that shallow, hypersaline conditions are necessary for the origin of oil shales. The authors are now able to show from stable isotopic and sedimentological evidence that most of the dolomite laminae in the central basin of the Laney Shale Member derive from early diagenetic processes in conjunction with methanogenesis. The authors study is based mainly on samples from a continuous, Department Energy core Nr.9A taken near Green River, Wyoming. The sediments are laminated, kerogen-rich, carbonate mudstones which have pure dolomite to aragonitic to calcitic compositions. Scattered ostracods occur. Dolomite is calcian-rich and bulk samples have carbon isotope ratios of delta /sup 13/C= + 3.6%o to +13.45%o PDB. Purest dolomites have delta /sup 13/C > +6.7%o. The delta /sup 13/C values for aragonite and calcite range from +2.9%o to +5.7%o which are not unusual for highly productive intermontane basin lakes. Oxygen isotope ratios for all samples are negative, ranging from -8%o to -5%o for calcite or aragonite mixtures and -5% to -0.25%o for dolomites. These indicate that pore waters were not derived from highly evaporated solutions. They conclude that dolomite is an early diagenetic product. High delta /sup 13/C signals for dolomites suggest strong methanogenesis to overcome a precursor carbonate reservoir effect, and thus indicates a sulfate-depleted environment which would be conducive to preservation of organic matter.

• Research Organization: EAWAG-Geology, Dubendorf (Switzerland)
• OSTI ID: 6194871
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMICAL COMPOSITION
CHEMISTRY
DIAGENESIS
DOLOMITE
EVAPORITES
FEDERAL REGION VIII
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
GREEN RIVER FORMATION
ISOTOPE RATIO
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
NORTH AMERICA
ORIGIN
OXYGEN COMPOUNDS
PETROLOGY
ROCKS
SEDIMENTARY ROCKS
USA
WYOMING