GENERAL32961

• Permit No: M1999002
• IBM Index Class Name: General Documents
• Doc Date: 8/18/1998
• Doc Name: COMMERCIAL MINE PLAN SUBMITTED TO BLM SECTION 7
• Media Type: D
• Archive: No

• The lower contact of the Uinta Formation with the Green River Formation is
marked by an abrupt transition from gray siltstone to dark brown, moderately rich
oil shale. Below this contact, siltstone and other detrital rocks are rare.
Green River Formation
The Green River Formation in the Piceance Creek Basin is divided into four
members: the Parachute Creek (upper member), Garden Gulch (intermediate
member), Douglas Creek (lowest member), and Anvil Points (lateral correlative of
the Douglas Creek and Garden Gulch Members, as well as being part of the lower
Parachute Creek Member). At the top of the Parachute Creek Member, tongues of
the Green River Formation are interfingered with the lower part of the Uinta
Formation. The Green River Formation rests conformably on top of the Wasatch
Formation.
Tongues of the Green River Formation Five major tongues of the Green River
Formation composed of marlstone, silty marlstone, and lean oil shale are
interstratified with the sandstones and siltstones of the Uinta Formation. These
tongues, which are associated with lacustrine deposition, include in descending
order the Coughs Creek, Black Sulfur (Black Sulphur), Thirteenmile Creek, Dry
Fork, and Yellow Creek Tongues (Duncan et al. 1974, O'Sullivan 1975).
These marlstone and silty marlstone horizons are usually tan to brown in color and
are usually well stratified. Contortion and folding of these sediments near the base
of sandstones is due to soft sediment deformation where compaction and
dewatering of the original sediment mass occurred.
Parachute Creek Member The Parachute Creek Member is the uppermost unit of
the Green River Formation. The Parachute Creek Member contains virtually all of
the oil shale, nahcolite, and dawsonite resources in the Piceance Creek Basin. The
Parachute Creek Member exceeds 2,000 feet in thickness in the depositional center of
the basin. At the Piceance Site, the Parachute Creek Member is about 1,500 feet thick.
The upper part of the Parachute Creek Member is transitional with the Uinta
Formation.
The Parachute Creek Member is composed of marlstone and lean to rich oil shale,
some of which contains nahcolite, halite, and nahcolitic halite. These sedimentary
rocks were predominantly chemically precipitated, which resulted in indistinct
boundaries between the different rock types.
The mineral composition of the Parachute Creek oil shale and marlstones is similar,
except that oil shale has a higher kerogen content. The general composition of these
two rock types includes quartz, calcite, dolomite, analcime, potassium feldspar,
albite, and minor concentrations of illite. Dawsonite may be disseminated
• throughout certain stratigraphic horizons. Nahcolite and halite are generally absent
or in minor concentrations, except when nahcolite and halite become secondary
American Soda, L.L.P. '7_5
Commercial Mine Plan
Augusf 18, 1998