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Tournaisian forested wetlands in the Horton Group of Atlantic Canada

By
Michael C. Rygel
Michael C. Rygel
Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 3J5
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John H. Calder
John H. Calder
Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia, Canada, B3J 2T9
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Martin R. Gibling
Martin R. Gibling
Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 3J5
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Murray K. Gingras
Murray K. Gingras
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3
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Camilla S.A. Melrose
Camilla S.A. Melrose
Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 3J5
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Published:
January 01, 2006

The Horton Group (late Famennian to Tournaisian) of Atlantic Canada provides an unusually complete record of Early Mississippian wetland biota. Best known for tetrapod fossils from “Romer's Gap,” this unit also contains numerous horizons with standing vegetation. The taphonomy and taxonomy of Horton Group fossil forests have remained enigmatic because of poor preservation, curious stump cast morphology, and failure to recognize the unusual sedimentary structures formed around standing plants.

Four forested horizons within the Horton Group are preserved as cryptic casts and vegetation-induced sedimentary structures formed by the interaction of detrital sediment with in situ plants. Protostigmaria, the lobed base of the arborescent lycopsid Lepidodendropsis, occur as sandstone-filled casts attached to dense root masses. Mudstone-filled hollows formed when a partially entombed plant decayed, leaving a void that was later infilled by muddy sediment. A scratch semi-circle formed where a current bent a small plant, causing it to inscribe concentric grooves into the adjacent muddy substrate. Obstacle marks developed where flood waters excavated erosional scours into sandy sediment surrounding juvenile Lepidodendropsis. These cryptic lycopsid forests had considerably higher densities than their Pennsylvanian counterparts.

Vegetation-induced sedimentary structures are abundant in Horton Group strata and could easily be misidentified as purely hydrodynamic or soft-sediment deformation structures without careful analysis. Recognition of these structures in early Paleozoic strata has great potential to expand our knowledge about the distribution of early land plants.

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Contents

GSA Special Papers

Wetlands through Time

Stephen F. Greb
Stephen F. Greb
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William A. DiMichele
William A. DiMichele
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Geological Society of America
Volume
399
ISBN print:
9780813723990
Publication date:
January 01, 2006

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