PALEONTOLOGY OF THE BASSAM PARK FOSSIL BEDS (PENNSYLVANIAN), SAN ISABEL NATIONAL FOREST, COLORADO

The presence of Pennsylvanian marine fossils in Bassam Park has been known for years, but a systematic study of this resource was lacking. Thus, a cooperative research project was undertaken by the Forest Service and the University of Colorado at Denver, with assistance from the Western Interior Paleontological Society. Though still underway, the project has already produced significant results.

Mapping and section measuring show that the most abundant fossils occur at two laterally continuous horizons in the upper Kerber and lower Belden formations. These horizons were useful in accurately locating the Kerber/Belden contact, and facilitated the resolution of some mapping problems in this structurally complex area.

Throughout the field area, the Kerber horizon contains a distinctive sequence of black, coaly shale; mollusk-dominated calcareous shale; and brachiopod-dominated calcareous shale. The sequence is inferred to be the result of a marine transgression. Systematic data collection and analysis has revealed at least 43 genera of marine invertebrates, including a new species of the ammonoid Gastrioceras.

Vertebrate fossils from the Kerber horizon include a Petalodus (shark) tooth and Sagenodus (lungfish) skull and tooth plates. Conodonts indicate a late Morrowan to early Atokan age, and ammonoids an early Atokan age, for the Kerber horizon. To our knowledge, this is the first Pennsylvanian lungfish locality reported from Colorado, and the only report of Atokan Sagenodus in the United States.

The lower Belden horizon contains abundant spiral fish coprolites, along with sparse marine mollusks. The silicified coprolites contain fish scales and bivalves. The horizon extends continuously for about four miles around the axis of a plunging syncline, and is possibly the largest fish coprolite locality in North America.

This project has been beneficial for the Forest Service, the University, and WIPS. The Forest Service has a better understanding of the occurrence and significance of these fossil resources. Several university students and WIPS members had the opportunity to participate in a sponsored research project. These new discoveries from Bassam Park have also added to scientific understanding of Pennsylvanian life and geography in the western United States.