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Mineralogy of the Mahogany marker tuff of the Green River Formation, Piceance Creek Basin, Colorado

Conference · · Oil Shale Symp. Proc.; (United States)
OSTI ID:5167184
The Mahogany marker tuff is a chronostratigraphic marker which was deposited in Eocene Lake Uinta approximately 45-46 million years ago when the lake was at its maximum size. The Mahogany marker lies 3 to 6 meters above the Mahogany oil shale bed in the upper part of the Parachute Creek Member of the Green River Formation. The mineralogy of the marker was studied in drill cores by X-ray diffraction and hand specimen examination. The Mahogany marker consists of authigenic sodium feldspar, analcime, quartz, ankerite, dolomite, potassium, feldspar, calcite with lesser amounts of siderite, hematite, pyrite, undifferentiated clays, pyrrhotite, biotite, marcasite, and locally dawsonite. Analcime is not present in all samples and in samples which are analcime-free, K-feldspar shows a greater abundance. Dawsonite is locally present only in analcime-free samples. The presence or absence of analcime and K-feldspar is attributed to the geochemical conditions that existed in the lake at the time of deposition of the Mahogany marker. The evidence supports a stratified lake model of oil shale deposition, with extremely alkaline pH values existing in deeper central portions of Lake Uinta.
OSTI ID:
5167184
Report Number(s):
CONF-830434-
Conference Information:
Journal Name: Oil Shale Symp. Proc.; (United States)
Country of Publication:
United States
Language:
English