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Abstract Detail

Paleobotanical Section

Baghai-Riding, Nina Lucille [1], Hotton, Carol [2], Gorman, Mark [3], Davidson, Taylor [4].

A Unique Wetland Ecosystem in the Late Jurassic Morrison Formation, U.S.A.

The Upper Jurassic Morrison Formation, deposited in the western interior U.S., is justly famous for its abundant and diverse dinosaurs and other vertebrate fossils. Other components of the biota, especially plants, are much more poorly known. Here we present preliminary data on the megaflora and palynology of a recently discovered locality near the base of the Morrison Formation in Temple Canyon Park, near Canon City, Colorado. This locality, comprising several exposures within an area of about 5 km, is unique in the Morrison Formation in preserving a diversity of plant and animal fossils, the latter including fresh-water fish, rare amniotes, insects, gastropods, conchstracans, ostracodes and caddisfly cases. The fossiliferous units occur 9-10 m above the base of the section and consist of a laterally extensive, laminated limestone overlain by laminated, thinly bedded mudstones and intercalated sandstone lenses. The deposit likely represents a permanent and relatively deep lake and lake margin environment punctuated by periodic storm events. Plant (as well as animal) fossils occur in all rock types but each contains a distinct assemblage. Ginkgoalean and conifer (Araucariaceae and Cupressaceae) megafossils occur predominantly in the limestones, whereas ferns and cycads occur primarily in sandstone lenses. Of the plant megafossils, ferns are the most common, with nine morphotypes, including Gleicheniaceae, followed by cycads (Nilssoniocladus). The palynomorph assemblage shows only partial overlap with the megaflora. Fern spores are abundant and diverse, especially in the mudstones and include Osmundaceae and possibly Schizaeaceae. Lycopsid spores are also diverse and abundant although not in the megafossil record. Araucarian pollen is dominant or co-dominant with bisaccate pollen, which is particularly abundant in the limestone units probably due to taphonomic filters. Taxodiaceous pollen (represented in the megaflora) and the extinct conifer family Cheirolepidaceae (absent from the megafossil record) are subdominant or rare. Although monosulcate producting plants (cycads, Ginkgoales, Czekanowskiales, Bennettitales) are present in the megaflora, monosulcate pollen is rare to absent. Perhaps the most puzzling discrepancy is the lack of any recognizable megafossils that produce bisaccate pollen; could these elements of the palynofloral record represent long-distance transport? The presence of an extensive lake system in the base of the Morrison suggests a climate wet enough to sustain it, although probably still seasonally dry. Further study of the biota of this unique assemblage will provide additional clues to the climate and paleoecology of the dinosaur dominated landscaope of the Morrison.

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1 - Delta State University, Division of Biological and Physical Sciences, PO Box 3262, Cleveland, MS, 38733, USA
2 - NIH/NLM/NCBI - BLDG 45, 45 CENTER DR MSC 6510, Building 45, Rm 6an.18, BETHESDA, MD, 20892-6510, USA
3 - University of Chicago, Geophysical Sciences, 5734 S. Ellis Ave., Chicago, IL, 60637, USA
4 - Delta State University, Division of Biological and Physical Sciences, , Cleveland, MS, 38733, USA

Morrison Formation
Late Jurassic

Presentation Type: Poster:Posters for Sections
Session: P
Location: Grand Salon A - D/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 5:30 PM
Number: PPB009
Abstract ID:859
Candidate for Awards:None

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