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The
Florissant Formation: A Virtual Tour
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Upper Pumice Conglomerate
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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).
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Bibliography
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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 |
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