THE PARACHUTE CREEK ATLAS PROJECT: AN OVERVIEW OF THE MEGAFLORA OF THE GREEN RIVER FORMATION FROM COLORADO AND UTAH

The Middle Eocene Parachute Member of the Green River Formation is widely exposed in the Piceance Creek and Uinta Basins of Colorado and Utah. This unit has been a major focus of oil shale exploration and represents a maximum high stand of Lake Uinta. A widespread organic-rich marker bed, the Mahogany Bench (and Mahogany Marker) allows for regional stratigraphic control. Most of the published paleobotanical reports from the formation discuss fossils from the vicinity of the Mahogany Bench. The flora and fauna from this unit enjoy huge popular interest and the collecting sites near Bonanza, Utah and Douglas Pass, Colorado are internationally known. Despite this interest, no single collection or monograph adequately represents the diversity of this assemblage and there remain a number of interesting questions about the age and nature of the vegetation and its paleoclimatic and paleoenvironmental significance. To document the relative abundance of common species, we excavated a quarry near Bonanza in 1996. The resulting collection of 989 identifiable specimens represents 48 species. The most common genera were Parvileguminophyllum (27%), Cedrelospermum (25%), Macginitiea (8%), Rhus (7%), Allophylus (6%), Caesalpina (4%), and Cardiospermum (4%). We have surveyed public and private collections and have recorded approximately 200 species from the Parachute Creek Member. This flora represents material that has been transported as much as 40 km from the source vegetation. The distribution of plant parts so far from the shoreline remains an interesting taphonomic problem that greatly complicates reconstruction of the ancient lake margin vegetation. Conversely, this high degree of transportation allows for the preservation of an extremely diverse paleoflora.