Tomescu, Alexandru MF , Pratt, Lisa M , Rothwell, Gar W. .
Terrestrial stable carbon isotope signatures in Ordovician-Silurian (455-420 Ma) compression biotas of the Appalachians.
Late Ordovician – Silurian sedimentary sequences of the Appalachians host a suite of fossil biotas that represent the earliest communities of complex organisms on land, providing potentially crucial information about the origin of land plants. These biotas present two main challenges: the taxonomic affinities of fossils are largely unresolved, and continental depositional environments are difficult to establish with certainty. As part of sustained efforts to better understand these biotas, stable carbon isotope analyses have been performed at seven fossil localities in the Martinsburg Formation (early-mid Katian, ca. 452 Ma); Oswego Sandstone (late Katian, ca. 447 Ma); Massanutten Sandstone and Tuscarora Formation (Rhuddanian, ca. 441 Ma); Rose Hill Formation (Telychian, ca. 432 Ma); Bloomsburg Formation (Gorstian, ca. 422 Ma). Î´13C of fossils and sedimentary organic matter (OM) varies -27.5 to -28.8‰ PDB (mean -28.3) in the Martinsburg; -27.1 to -28.5‰ (mean -27.7) in the Oswego; -24.9 to -28.2‰ (mean -26.4) in the Massanutten-Tuscarora; -26.2 to -26.8‰ (mean -26.5) in the Rose Hill; -26.6 to -28.8‰ (mean -27.3) in the Bloomsburg. A worldwide database compiled by us for marine fossils and OM shows Î´13C means of -28.3‰ PDB for the early-mid Katian; -30.1‰ for the late Katian; -30.6‰ for the Rhuddanian; -29.1‰ for the Telychian; -31.0‰ for the Gorstian. Significant differences between Î´13C values at our fossil localities (heavier, 13C-enriched) and coeval marine values (lighter, 12C-enriched) indicate continental depositional environments in all the rock units studied except the Martinsburg. Our Î´13C data correlate well with the published terrestrial organic carbon isotope record for the Paleozoic, extending it deeper in time. Although Î´13C signatures do little to resolve the taxonomic affinities of the fossils, they provides the first benchmark evidence of continental depositional environments for several thalloid biotas that predate the origin of vascular plants with bioturbating root systems.
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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
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 1:30 PM