The Parachute
Creek Atlas Project:
A plan
to document the megaflora of the Green River Formation
from Colorado
and Utah and to publish this atlas as a
Proceedings
of the Denver Museum of Nature & Science.
Project team
members:
Kirk Johnson,
William Bateman, Michael Graham, Rich Barclay, Nicole Boyle
Denver Museum
of Nature & Science
Steven Manchester
Florida Museum
of Natural History
Bruce Handley
Pleasant Hill,
California
August, 2002
The Middle
Eocene Parachute Member of the Green River Formation is widely exposed
in the Piceance Creek and Uinta Basins of Colorado and Utah. This unit
has been a major focus of oil shale exploration and represents a maximum
high stand of Lake Uinta. A widespread organic-rich marker bed, the Mahogany
Bench (and Mahogany Marker) allows for regional stratigraphic control.
Most of the published paleobotanical reports from the formation discuss
fossils from the vicinity of the Mahogany Bench. These fossils are much
younger and considerably different from the fossils from the fish-bearing
Green River Formation from Fossil Lake near Kemmerer, Wyoming. Parachute
Creek sites primarily produce fossil plants and insects but fish, birds,
lizards, and other vertebrates are occasionally recovered. The flora and
fauna from this unit enjoy huge popular interest and the collecting sites
near Bonanza, Utah and Douglas Pass, Colorado are internationally known.
Despite this
interest, no single collection or monograph adequately represents the diversity
of the Parachute Creek assemblage, which has not been studied since MacGinitie
(1974). There are a number of interesting questions about the age and nature
of the vegetation and its paleoclimatic and paleoenvironmental significance.
To document the relative abundance of common species, we excavated a quarry
near Bonanza in 1996. The resulting collection of 989 identifiable specimens
represents 48 species. The most common genera are Parvileguminophyllum
(27%), Cedrelospermum (25%), Macginitiea (8%), Rhus (7%), Allophylus (6%),
Caesalpina (4%), and Cardiospermum (4%) (Wilf et al., 2001; Johnson et
al., 2002) . This flora represents material that has been transported as
far as 40 km from the source vegetation, as calculated by the position
of the fossil quarry relative to the lake margin. The distribution of plant
parts so far from the shoreline remains an interesting taphonomic problem
that greatly complicates reconstruction of the ancient lake margin vegetation.
Conversely, this high degree of transportation allows for the preservation
of an extremely diverse paleoflora.
Due to the
popularity of the Bonanza and Douglas Pass sites, we perceive a need and
a demand for a comprehensive atlas of the flora. Such an atlas would be
useful for amateur collectors because it would allow them to identify their
fossils. It would be useful for land managers because it would help them
to define the scientifically significant and rare fossils. Fossils that
are significant include not only the rare species but also common species
preserved in botanical attachment. For example, Macgintiea leaves and fruits
are both common but they have never been found attached. Scientists would
benefit by having a more educated collecting public who could then recognize
rare specimens and donate them to research museums. A book on the Green
River fish (Grande, 1984) has been very successful and has been reprinted
many times by the Wyoming Geological Survey.
Recent developments
in the study of leaf architecture (LAWG, 1999) provide a terminology for
this atlas and the Denver Museum of Nature & Science has been collecting
and borrowing specimens with this project in mind. To date, we have surveyed
a number of public and private collections and have recorded approximately
200 species from the Parachute Creek Member. The Denver Museum of
Nature & Science Proceeding Series is the proposed publication venue.
DMNS Proceedings have recently been published on the flora of the Hell
Creek (Johnson, 1996) and Florissant Formations (Evanoff et al., 2001),
establishing this series as one known for paleobotanical topics.
Format:
At present,
the volume is projected to contain photographs of all common and rare plant
species and such diagnostic information as to allow the reader to identify
their fossils.
Schedule:
Preparation
of the manuscript should be complete by May, 2003, allowing for publication
by September, 2003.
References:
Evanoff, E.,
Gregory-Wodzicki, K. M., and Johnson K. R., 2001, Fossil flora and stratigraphy
of the Florissant Formation, Colorado, Proceedings of the Denver Museum
of Nature & Science, series 4, no. 1, 218 p.
Grande, L.,
1984, Paleontology of the Green River Formation, with a review of the fish
fauna: Geol. Surv. Wyo. Bull., v. 52, p. 333.
Johnson, K.
R., 1996, Description of seven common plant megafossils from the Hell Creek
Formation (Late Cretaceous: late Maastrichtian), North Dakota, South Dakota,
and Montana). Proceedings of the Denver Museum of Natural History,
series 3, no. 12, 48 p.
Johnson, K.
R. 2002, in press, The Parachute Creek Atlas Project: An Overview of the
Megaflora of the Green River Formation from Colorado and Utah. Geological
Society of America Abstracts with Program v. 34, no. 6, p. 480.
Johnson. K.
R. and Plumb, C., 1995, Common plant fossils from the Green River Formation
at Douglas Pass, Colorado, and Bonanza, Utah in W. R. Averett (editor),
The Green River Formation in the Piceance Creek and Eastern Uinta Basins,
Grand Junction Geological Society Guidebook, p. 121-130.
Leaf Architecture
Working Group, 1999, Manual of Leaf Architecture - morphological description
and categorization of dicotyledonous and net-veined monocotyledonous angiosperms.
65 p., Washington, D. C., ISBN 0-9677554-0-9.
MacGinitie,
H. D., 1969, The Eocene Green River flora of northwestern Colorado and
northeastern Utah: Univ. Cal. Pub. Geol. Sci., v. 83, p. 140.
Wilf, P.,
Labandeira, C.C., Johnson, K.R., Coley, P. D., and Cutter, A. D., 2001,
Insect herbivory, plant defense, and early Cenozoic climate change. Proceedings
of the National Academy of Sciences USA, v. 98, p. 6221-6226.
