Late Pliocene and Pleistocene History of the Donnelly Ranch Vertebrate Site, Southeastern Colorado

Résumé du livre

Two superposed faunas were discovered in southeastern Colorado at the Donnelly Ranch vertebrate site. Sediments containing a late Blancan assemblage are unconformably overlain by sediments containing a Rancho La Brean assemblage. The pre-Nebraskan Donnelly Ranch fauna is slightly older than the Sand Draw, Broadwater, and Blanco faunas. It is younger than the Curtis Ranch fauna. Faunal and paleomagnetic correlation indicate it is about 2.5 m.y. old. Tapirus, Geoche/one, and Sigmodon indicate the climate was mild and precipitation was much more effective than at present. Savanna, plains, and marsh communities are represented by the fauna. The Sangamon Mesa De Maya fauna correlates best with the early Sangamon Cragin Quarry fauna. Mammals, molluscs, and pollen indicate that temperatures were more equable than present and precipitation may have been slightly more effective during cooler summers. The fauna consists primarily of grassland inhabitants but a marsh comÂ-- munity is represented in artesian spring sediments.