Baghai-Riding, Nina L. , Hotton, Carol .
Disparate Climate Signals from Plant Megafloras and Palynofloras in the Late Jurassic Morrison Formation, U.S.A.
The Late Jurassic Morrison Formation of the Western Interior, U.S.A., has long been studied for its abundant and spectacular dinosaur and other vertebrate fossils. Despite this, there is still considerable uncertainty over its climate and vegetation. Sedimentology and climate models suggest a seasonally dry to sub-arid climate at lower latitudes with a northward and upsection trend towards wetter conditions, but the sparse plant megafloral record has been interpreted to indicate mesic climate and lush forest vegetation. Here we compare the published megafloral record with our recent palynological analysis of sites from the upper part of the Morrison in Arizona, New Mexico, Colorado, Utah and Wyoming, which is largely congruent with the sedimentological evidence. The palynofloral and megafloral (adpression and permineralization) records only partially overlap taxonomically. Conifers (Cheirolepidiaceae, Podocarpaceae, Araucariaceae, Taxodiaceae) are well represented in both palynofloral and megafloral records, and likely dominated throughout. Relict fern families, such as Osmundaceae, also occur in both preservation modes. However, cycads, Bennettitales, and gingkophytes, prominent in megafloras, are rare to absent in palynofloras. Palynofloras display much higher per/site diversity compared to megafloras, and include taxa not recognized in the existing megafloral record, such as Equisetosporites (?= Gnetales), as well as filicalean ferns and gymnosperms of unknown affinities. Taxonomic disparity between megafloral and palynofloral composition is influenced by both life history and taphonomic factors. Megafloras, especially adpression fossils, typically reflect temporally and geographically constrained events in waterlogged environments; consequently, fossil megafloras may signal a wetter climate than actually existed. Palynofloras, although subject to their own biases, include extrabasinal as well as local elements and are usually time-averaged; thus they may be somewhat more reliable indicators of regional vegetation, and by inference, climate. Ideally, however, megafloras and palynofloras should be combined within a detailed sedimentological framework to extract maximum paleoenvironmental information.
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1 - Delta State University, Division of Biological and Physical Sciences, Cleveland, MS, 38733, USA
2 - National Institute of Health (NIH), National Library of Medicine (NLM), National Center for Biotechnology Information (NCBI), GenBank, Room 6an.18, Building 45, 45 Center Drive, MSC 6510, Bethesda, MD, 20892, USA
Presentation Type: Poster:Posters for BSA Sections
Location: Event Tent/Cliff Lodge
Date: Tuesday, July 28th, 2009
Time: 5:30 PM