A flora from Thomas Ranch near Princeton, British Columbia, Canada, is assessed for biodiversity and paleoclimate. This latest Early to early Middle Eocene flora occurs in the Allenby Formation. Seventy-six megafossil morphotypes have been recognized, representing at least 62 species, with 29 identified to genus or species. Common taxa include Ginkgo L., Metasequoia Miki, Sequoia Endl., Abies Mill., Pinus L., Pseudolarix Gordon, Acer L., Alnus Mill., Betula L., Fagus L., Sassafras J Presl, Macginitiea Wolfe & Wehr, Prunus L., and Ulmus L. More than 70 pollen and spore types are recognized, 32 of which are assignable to family or genus. The microflora is dominated by conifers (85%–97% abundance), with Betulaceae accounting for most of the angiosperms. The Climate Leaf Analysis Multivariate Program (CLAMP) calculates a mean annual temperature (MAT) of 9.0 ± 1.7 °C and bioclimatic analysis (BA) calculates a MAT of 12.8 ± 2.5 °C. Coldest month mean temperature (CMMT) was >0 °C. Mean annual precipitation (MAP) was >70 cm/year but is estimated with high uncertainty. Both the CLAMP and BA estimates are at the low end of the MAT range previously published for other Okanagan Highland localities, indicating a temperate climate consistent with a mixed conifer–deciduous forest.

No abstract

The John Day Basin of central Oregon contains a remarkably detailed and welldated Early Eocene-Late Miocene sedimentary sequence, known for its superb fossils. This fi eld trip examines plant fossil assemblages from throughout the sequence in the context of their geological and taphonomic setting and regional and global signifi cance. The Early to Late Eocene (>54-39.7 Ma) Clarno Formation contains fossil plants and animals that occupied an active volcanic landscape near sea level, interspersed with meandering rivers and lakes. Clarno assemblages, including the ca. 44 Ma Nut Beds fl ora, record near-tropical "Boreotropical" rainforest, which was replaced during late Clarno time by more open and seasonal subtropical forest. The overlying John Day Formation (39.7-18.2 Ma) was deposited in a backarc landscape of low hills dotted with lakes and showered by ashfalls from the Western Cascades. Fossils and paleosols record the advent of the "Icehouse" Earth during the earliest Oligocene, with decreasing winter temperature and more seasonal rainfall that supported open deciduous and coniferous forest, much like that of the southern Chinese highlands today. Sixteen and a half million years ago the Picture Gorge fl ood basalt covered the region. Animals and plants fossilized in the overlying (ca. 16 to >12 Ma) Mascall Formation occupied a relatively fl at landscape during a warm and moist period known as the Middle Miocene Climatic Optimum. In total this sequence preserves a detailed series of time slices illustrating regional biotic and landscape evolution during the Cenozoic that is highly relevant for deciphering regional and global biotic, climatic, and geological trends.

Abstract:The Bruneau Woodpile site has long been popular among fossil collectors; however, the deposit has received scant attention from scientists. Our research reveals that the fossilized wood was deposited ca. 6.85 Ma, within the Chalk Hills Formation, and was mineralized with carbonate-fluorapatite. The diverse assemblage of conifers and hardwoods is representative of the warm temperate forests that flourished in southwest Idaho, USA during the late Miocene. Limb and trunk fragments preserved in a single thin sandstone bed appear to represent woody debris that was transported by streams. One possible explanation is that wood, pumice, and sandy volcaniclastic sediment arrived separately as a result of ordinary stream action, and later were combined into a single assemblage during a subsequent high-energy sedimentation event. We favor an alternate hypothesis: a catastrophic event (e.g., a windstorm) damaged trees on slopes bordering the ancient lake. Branches and small trunk fragments were carried by wind and rain into local streams and ponds where they became waterlogged. After a delay that allowed pumice and wood to become saturated, storm water transported these materials, along with finer volcaniclastic sediment, into a lake. The resulting density current produced a fining-upward sedimentary cycle where wood was preserved in the lowest, coarsest stratum.

Silicified wood occurs abundantly in Middle Miocene flows and sedimentary interbeds of the Columbia River Basalt Group (CRBG) in central Washington State, USA. These fossil localities are well-dated based on radiometric ages determined for the host lava. Paleoenvironments include wood transported by lahars (Ginkgo Petrified Forest State Park), fluvial and palludal environments (Saddle Mountain and Yakima Canyon fossil localities), and standing forests engulfed by advancing lava (Yakima Ridge fossil forest). At all of these localities, the mineralogy of fossil wood is diverse, with silica minerals that include opal-A, opal-CT, chalcedony, and macrocrystalline quartz. Some specimens are composed of only a single form of silica; more commonly, specimens contain multiple phases. Opal-A and Opal-CT often coexist. Some woods are mineralized only with chalcedony;however, chalcedony and macrocrystalline quartz are common as minor constituents in opal wood. In these specimens, crystalline silica filling fractures, rot pockets, and cell lumen may occur. These occurrences are evidence that silicification occurred as a sequential process, where changes in the geochemical environment or anatomical structures affected the precipitation of silica. Fossilization typically began with precipitation of amorphous silica within cell walls, leaving cell lumen and conductive vessels open. Diagenetic transformation of opal-A to opal-CT in fossil wood has long been a widely accepted hypothesis; however, in opaline CRBG specimens, the two silica polymorphs usually appear to have formed independently, e.g., woods in which cell walls are mineralized with opal-A but in which lumen contain opal-CT. Similarly, opal-CT has been inferred to sometimes transform to chalcedony; however, in CRBG, these mixed assemblages commonly resulted from multiple mineralization episodes.