Tomescu, Alexandru MF , Pratt, Lisa M , Rothwell, Gar W. .
Early Paleozoic terrestrial biotas of the Appalachians: insights from geochemical and isotopic studies.
THE Appalachian basin in eastern North America contains an extensive megascopic record of Early Paleozoic life in terrestrial environments, with excellent potential to open new perspectives on early phases of the colonization of land by higher plants. Fossil assemblages, most of which have not been studied to date, span the Late Ordovician to Late Silurian interval and occur in rocks characterized sedimentologically as littoral to deltaic and fluvial. Among these are the Oswego Sandstone (Late Ordovician, studied at Conococheague Mountain, Pennsylvania), the Massanutten Sandstone (Early Silurian, Passage Creek, Virginia), and the Bloomsburg Formation (Late Silurian, Port Clinton, Pennsylvania). Assemblages of carbonaceous compressions in these units consist principally of thalloid macrofossils. Chemical analyses of fossils and their sedimentary matrix are conducted in parallel with morpho-anatomical characterization of fossils, in an effort to resolve systematic affinities and to characterize depositional settings. C/S ratios of the fossiliferous matrix at the three localities are characteristic of freshwater deposits and corroborate sedimentological data supporting a non-marine origin for the fossils. Organic matter at the three localities is enriched significantly (by 8-10 permil) in 13C compared to age-equivalent marine phytoplankton. These values combined with the morphology and sedimentary settings of fossils indicate terrestrial photosynthetic organisms. Extractable organic matter (bitumens) in samples at the three localities reveal conspicuous differences in relative abundances of individual n-alkanes and complex mixtures of branched and cyclic compounds in the biomarker region (n-C29 to n-C33), showing excellent potential for detailed molecular characterization and compound specific isotopic study. Carbon isotopes and bitumen compositions are good indicators of systematic affinities, especially when combined with morpho-anatomical data and compared with equivalent data from living morphological analogues of the fossils. Chemistry can contribute crucial data to our understanding of organisms comprising early terrestrial biotas and of evolutionary pathways leading to complex life on continents.
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1 - Humboldt State University, Department of Biological Sciences, Arcata, California, 95521, USA
2 - Indiana University, Department of Geological Sciences, Bloomington, Indiana, 47405, USA
3 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 8:30 AM