Plants, fish, turtles, and insects from the Morrison Formation: A Late Jurassic ecosystem near Cañon City, Colorado
Published:January 01, 2008
Mark A. Gorman, II, Ian M. Miller, Jason D. Pardo, Bryan J. Small, 2008. "Plants, fish, turtles, and insects from the Morrison Formation: A Late Jurassic ecosystem near Cañon City, Colorado", Roaming the Rocky Mountains and Environs: Geological Field Trips, Robert G. Raynolds
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The Morrison Formation is a laterally extensive terrestrial deposit representingan ecologically diverse assemblage of paleoenvironments from the Late Jurassic ofwestern North America. Although the Morrison Formation has recently been interpretedas a semiarid lowland savannah on the basis of geological and paleobiologicalindicators, many microenvironments within this system are more consistent with newinterpretations of the Morrison as a ground-water dominated “wetland” deposit. Herewe report new fossils from a little-studied exposure of the Morrison Formation in andaround Temple Canyon Park near Cañon City, Colorado. The Temple Canyon sectionshows a relatively thin sequence of conglomerate, sandstone, siltstone, mudstone, andlimestone beds representing alluvial to fluvial and possibly lacustrine deposition. Thesection rests on Precambrian basement and is unconformably overlain by the LowerCretaceous Lytle Formation. The mudstone and limestone beds preserve an abundantfossil flora and fauna distinct from those previously described from the MorrisonFormation. The floral assemblage includes species of algae, bryophytes, ferns, ginkgophytes,horsetails, cycads, bennettites, and conifers; together these plants indicatea warm climate with abundant local water supply. The faunal assemblage containsostracodes, conchostracans, traces of aquatic insect larvae, a terrestrial insect bodyfossil, prosobranch and pulmonate gastropods, many species of fish, a possible frog,and rare turtle remains. The presence of prosobranch gastropods, fish, and aquaticinsect larvae suggests a perennial water body with high oxygen content, while thepresence of conchostracans and pulmonate gastropods may indicate some fluctuationin water quality.
Keywords: Morrison Formation, Jurassic, Cañon City, Colorado, paleoecology.
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Roaming the Rocky Mountains and Environs: Geological Field Trips
Prepared following the 2007 GSA Annual Meeting in Denver, Colorado, these 15 guides illustrate the latest geological and archeological thinking on a variety of current research themes. Regional-scale topics include landscape responses to dynamic processes of volcanism and uplift in Yellowstone and western Colorado, geomorphic evolution along the Front Range of Colorado and on the High Plains of South Dakota, and geoarchaeological research in central Colorado and western Nebraska. A series of papers illustrates tectonic and stratigraphic processes through time and space, with discussions of Precambrian structures in western Colorado, Jurassic deposition in south-central Colorado, and near-shore stratigraphic patterns in the Cretaceous strata of the Book Cliffs. One paper reviews potential seismic signatures in Cretaceous and Early Tertiary strata in northern Wyoming and Montana, and another discusses patterns of extension in southern Nevada and adjacent portions of California. Other topics in this well-rounded volume include the history of volcanism and gold mineralization at Cripple Creek, development of coalbed methane resources in the Powder River Basin, and a long-lived subsurface coal fire in western Colorado. Follow in the footsteps of these field trips, and see for yourself the patterns and evidence discussed.