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The Florissant Formation: A Virtual Tour
Introduction & Pikes Peak Granite

Introduction

The Florissant Formation represents an Eocene-aged accumulation of rock units including tuffs, mudstones, shales, sandstones and conglomerates. These different rock types were formed by pyroclastic flows, lahars, lake and river environments. Fossils embedded within the lahar mudstones and lake shales give scientists a window into the latest Eocene ecosystems of Florissant.

Our virtual tour will explore the six informal units of the Florissant Formation as described by Evanoff et. al. (2001). It is helpful to study older rock units to provide a geological context for understanding the events that led to the deposition of the Florissant Formation. We will briefly describe two older stratigraphic units, the Pikes Peak Granite and the Wall Mountain Tuff.


Mary Klass Resting Comfortably Atop Pikes Peak Granite


Pikes Peak Granite


Pikes Peak, at an elevation of 14,110 ft, is just 12 miles South East of Florissant. Pikes Peak granite has a radiometric age of 1,080 Ma (Evanoff, McIntosh & Murphy, 2001, p. 3). The billion year old pink Pikes Peak granite formed as an intrusive batholith during the Precambrian and covers 1,150 square miles (Foos & Hannibal, 1999, p. 1). The mountain building episode known as the Larimide Orogeny, which started in the Late Cretaceous 65 to 70 Ma ago, created the current Rocky Mountains and resulted in the uplift and exposure of the Pikes Peak Granite (Meyer, 2003, p. 23). During the Late Eocene, rivers eroded the granite to form a valley. Late Eocene sediments from volcanic activity, lakes, and rivers, filled the valley depositing the rock units in the Florissant Formation.


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.

Foos, A. & Hannibal, J. (1999). Geology of Florissant Fossil Beds National Monument.
http://www.nature.nps.gov/geology/education/foos/flfo.pdf

Meyer, H.W. (2003). The Fossils of Florissant. Washington: Smithsonian Books.

 
 

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