Stratigraphic divisions and geologic history of the Laney Member of the Green River Formation in the Washakie Basin in southwestern Wyoming

Abstract

The Laney Member, formerly the Laney Shale Member, of the Eocene Green River Formation in the Washakie Basin in southwestern Wyoming is herein divided into three new rock-stratigraphic units: a basal oil-shale section named the LaClede Bed; a middle wedge of tuffaceous sandstone and siltstone named the Sand Butte Bed; and an upper sequence mainly of mudstone alternating with sandstone, limestone, and shale named the Hartt Cabin Bed. The fossil and strati graphic records indicate that the LaClede Bed was deposited in Lake Gosiute in the early middle Eocene during a stage when the lake had great areal extent, that the introduction of air-laid volcanic ash later in the early middle Eocene initiated a southeastward retreat and shallowing of the lake during the deposition of the Sand Butte Bed, and that the lake dried up and disappeared near the end of the middle Eocene during the deposition of the Hartt Cabin Bed. The thickness, areal distribution, stratigraphic relations, age, and geologic histories of the beds are discussed and illustrated in a cross section and by maps, and the lithologies are described in type sections.