Geologic map of the Rulison quadrangle, Garfield County, Colorado

Paleontological overview of oil shale and tar sands areas in Colorado, Utah, and Wyoming.

“…It is perhaps best exposed to the west of Rifle, where it outcrops as picturesque badlands at the base of the steep slopes of the Colorado River Valley to roughly onethird of the way up the Roan Cliffs (~5,500 to 7,000 ft in elevation north of Sharrard Park). In the Roan Cliffs area, the DeBeque Formation sequence is mapped as the Shire Member of the Wasatch Formation (Yeend et al 1988), which is described as variegated purple, lavender, red, gray, and brown claystone; there is some locally lenticular fine-to coarse-grained sandstone. It also contains minor conglomerate, limestone, coal, and carbonaceous shale (O 'Sullivan 1986).…”

“…Oil shale deposits within the formation, deposited in deep water lacustrine conditions, give the Green River Formation great economic importance. The Green River Formation has been assigned three members in ascending stratigraphic order: the Anvil Points Member, the Garden Gulch Member, and the Parachute Creek Member Yeend et al 1988). The Parachute Creek Member is conformably overlain by, and intertongues with, the Uinta Formation ).…”

“…It grades westward into the Garden Gulch Member with a decrease in number and thickness of sandstone beds. Lithologically, the Anvil Points Member consists of brown and buff, massive, fine-to coarse-grained sandstone that forms conspicuous ledges, minor amounts of light-gray siltstone, marlstone, and several beds of low-grade oil shale (Yeend et al 1988). The Garden Gulch Member is composed of light-gray marlstone, dark-brown to black locally fissile shale with some oil shale, light-gray oolitic limestone and sandstone, light-gray algal limestone, and some massive brown fine-to medium-grained sandstone.…”

“…The Parachute Creek Member consists of black, brown, and gray marlstone, which weathers gray (and includes cliff-forming oil shale); it also includes minor amounts of light-gray siltstone, light-gray and brown medium-grained sandstone, and numerous very thin beds of analcite and tuff. The base of the richest oil shale bed, the 2-to 4-ft-thick Mahogany bed (early Bridgerian NALMA), occurs approximately 40 to 80 ft above the base of the Parachute Creek Member (Donnell 1964;O'Sullivan 1986;Yeend et al 1988). The Mahogany bed is the lowest bed in the approximately 74-ft-thick "Mahogany Zone" (Yeend et al 1988).…”

“…The base of the richest oil shale bed, the 2-to 4-ft-thick Mahogany bed (early Bridgerian NALMA), occurs approximately 40 to 80 ft above the base of the Parachute Creek Member (Donnell 1964;O'Sullivan 1986;Yeend et al 1988). The Mahogany bed is the lowest bed in the approximately 74-ft-thick "Mahogany Zone" (Yeend et al 1988). named four stratigraphically higher Green River Formation tongues, which interfinger with the Uinta Formation in the northern part of the Piceance Creek Basin.…”