Field trip no. 23 from “Geologic Excursions to the Rocky Mountains and Beyond,” field trip guidebook of the 1996 Annual Meeting of the Geological Society of America. (SP-44 has the complete set.) 67 pages. Digital PDF download. OF-96-04-23D
From the Abstract:
The Codell and Juana Lopez Members of the Carlile Shale (Upper Cretaceous- Middle to Late Turonian) occur at the surface and in the subsurface of the Denver, Canon City, and northern Raton Basins, Colorado. Comprising a widespread inner neritic to supratidal marine sequence, these strata represent the waning regressive phase of the Greenhorn Regressive Hemicyclothem, which furnishes a model for eustatically generated cyclic sedimentation in Cretaceous epicontinental seas. Outcrop and core studies indicate the thicker, underlying Codell Member consists mainly of fine-grained sandstones and silty shales; whereas, the thinner, overlying Juana Lopez Member contains phosphoritic calcarenites with abundant vertebrate fragments, as well as lenticular biosparites.
Type one, two, and three Codell deposits are then discussed relative to hydrocarbon production. Next the Juana Lopez rocks are discussed relative to the lack of commercial hydrocarbons, although where fracture production occurs at the top of the Codell, the Juana Lopez and the overlying Fort Hays Limestone form a commingled reservoir.