Dillhoff, Richard , Dillhoff, Thomas , Devore, Melanie , Greenwood, David , Pigg, Kathleen .
The Eocene Thomas Ranch flora, Allenby Formation, Princeton, British Columbia, Canada.
The first descriptions of Eocene fossil plants from the Allenby Formation, south-central British Columbia, Canada were published over a century ago. Both compression and permineralized floras are known from this formation. Since 1973, the Princeton Chert flora alone has generated over 45 publications. Compression floras at Thomas Ranch and One Mile Creek have yielded several new species including Pseudolarix arnoldi (Pinaceae); Tetracentron hopkinsii (Trochodendraceae); Betula leopoldae, and Palaeocarpinus stonebergae (Betulaceae); Stonebergia columbiana and Neviusia dunthornei (Rosaceae) and several species of Acer (Sapindaceae). However, these individual localities have not been assessed for their floral diversity and paleoenvironmental reconstruction. We have surveyed the Thomas Ranch locality using plant mega- and microfossils. The fossils record a diverse mixed floral assemblage of gymnosperms and angiosperms. Collections to date have yielded a total of 71 megafossil morphotypes representing at least 61 nominal species when multiple organs and leaf morphologies of the same species are eliminated. Thirty-three morphotypes are identified to at least generic level, including: Ginkgo, Abies, Pinus, Pseudolarix, Acer, Alnus, Betula, Fagus, Sassafras, Platanaceae, Prunus, and Ulmus. Over 70 pollen and spore types are recognized, 37 of which are assignable to family or genus. The pollen samples are heavily dominated by conifers (85-97%), with Betulaceae accounting for most of the angiosperm pollen. Azolla-dominated beds and gypsum deposits suggest periodic fluctuations in water level. Leaf physiognomic (CLAMP, LMA and other approaches) and taxon-based analog methods have been used to provide climate estimates for the Thomas Ranch site. Differences between the mean annual temperature (MAT) estimates provided by these two approaches reflect inherent uncertainties in the methods, but both estimates are at the low end of the MAT range that has been published for other Okanagan Highland localities, indicating a temperate climate consistent with the floristic character of a mixed conifer-deciduous forest.
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Presentation Type: Oral Paper:Papers for Sections
Location: Forsyth Room/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 11:00 AM