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The
Florissant Formation: A Virtual Tour
Upper Pumice Conglomerate |
 Close-up of Upper Pumice Conglomerate |
The Upper Pumice Conglomerate The upper pumice conglomerate unit consists of pumice-rich white sandstones and conglomerates. Fossil finger clams found in the lower part of this unit indicate the pumice conglomerate was deposited into Lake Florissant. The upper cross-bedded conglomerate beds represent deposition by streams within the valley, recording an end to the Florissant lake. The upper pumice conglomerate is exposed north of Boulder Creek (Evanoff, McIntosh & Murphey, 2001, p. 11). The youngest unconformity rests between the upper pumice conglomerate and Quaternary deposits. This unconformity represents 32 million years of missing time from the Oligocene, Miocene, and Pliocene Epochs (KellerLynn, 2006, p. 21). Pleistocene deposits at Florissant are composed of weathered and eroded Pikes Peak Granite, Wall Mountain Tuff, and fragments of shale, mudstone, sandstone, and fossil wood from the Florissant Formation. Parts of the Florissant Formation that have survived weathering and erosion are exposed around the perimeter of the old lake (KellerLynn, 2006, p. 26). |
Bibliography |
| Evanoff,
E., McIntosh, W.C. and Murphey, P.C. (2001). Stratigraphic
Summary and 40Ar/39Ar Geocrhonology of the Florissant Formation,
Colorado. In Evanoff, E., Gregory-Wodzicki K.M. and Johnson,
K.R. [Eds.] Fossil Flora and Stratigraphy of the Florissant
Formation, Colorado. (pp. 1-16). Proceedings of the
Denver Museum of Nature and Science, series 4, number 1. KellerLynn, K. (2006). Florissant Fossil Beds National Monument Geologic Resource Evaluation Report. Natural Resource Report NPS/NRPC/GRD/NRR—2006/009. National Parks Service, Denver, Colorado |