Permian Hennessey Group red beds. Geochemical analyses reveal characteristics of both coal and petroleum. Carbon isotopic analyses favor a petroleum-related origin. Suggested model: crude oil, migrating from depth, is initially altered near the surface to a more viscous material; concurrently migrating uranium-bearing ground water is then stripped of its uranium by the degraded petroleum. Presence of such nodules in the shallow subsurface may suggest buried petroleum deposits.--Modified journal abstract.