The
Lower Mudstone Unit
The lower mudstone unit consists of mudstones, conglomerates,
and sandstones. Ribbons of sandstones and conglomerates within
this unit trace the course of stream channels. The lower mudstone
unit represents a river system within the Florissant Valley.
A 5 meter layer of sandy mudstone at the top of this unit records
a lahar deposit that buried parts of a forest growing by the
stream in the ancient Florissant valley. The mudflow represents
a single event that encased trees in situ (Gregory-Wodzicki,
2001, p.164).
Over time, trees buried in place were permineralized
with silica released from the volcanic rocks to form a petrified
forest. The lower mudstone unit is exposed behind the Big Stump
with the middle shale unit and caprock conglomerate above. |
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.
Gregory-Wodzicki,
K. M. (2001). Paleoclimatic Implications of Tree-Ring Growth
Characteristics of 34.1 Ma Sequoioxylon pearsallii from
Florissant, Colorado. In Evanoff, E., Gregory-Wodzicki
K.M. and Johnson, K.R. [Eds.] Fossil Flora and Stratigraphy
of the Florissant Formation, Colorado. (pp. 163-186).
Proceedings of the Denver Museum of Nature and Science,
series 4, number 1. |