The Eocene Thomas Ranch flora, Allenby Formation, Princeton, British Columbia, Canada

Abstract

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.

A review of paleobotanical studies of the Early Eocene Okanagan (Okanogan) Highlands floras of British Columbia, Canada, and Washington, USA

“…The dating of these sites as "Middle Eocene" has been widely cited in the literature on the Okanagan Highlands floras and faunas (e.g., Wilson 1977c). However, current concepts about Cenozoic geochronology place the EarlyMiddle (Ypresian-Lutetian) Eocene boundary younger than 50 Ma, at 47.8 Ma (Cohen et al 2013), so that even when applying the older K-Ar dates (Hills and Baadsgaard 1967;Read 2000), the majority of the interior British Columbia Okanagan Highlands fossil sites should be considered Early Eocene Moss et al 2005;Radtke et al 2005;Archibald et al 2011;Dillhoff et al 2013;Eberle et al 2014) (Fig. 3).…”

“…There is considerable literature of megafossil and microfossil systematics of these sites, some of which include summaries of particular floras or complement faunal studies of fish and insects (e.g., Wolfe and Wehr 1991;Stockey 2002;Stockey and Wehr 1996;Pigg and Stockey 1996;Smith 2011;Smith et al 2012;Dillhoff et al 2005Dillhoff et al , 2013Archibald et al 2011). More recently, a greater emphasis on the paleoenvironments of the Okanagan Highland floras has appeared both in locality studies (Dillhoff et al , 2013Smith et al 2009Smith et al , 2010Gushulak et al 2016;Mathewes et al 2016) and in studies dedicated to broader issues of paleoenvironment (Greenwood and Wing 1995;Wolfe et al 1998Wolfe et al , 2000Greenwood et al 2005;Moss et al 2005;Smith et al 2012;Feng and Poulsen 2016).…”

“…More recently, a greater emphasis on the paleoenvironments of the Okanagan Highland floras has appeared both in locality studies (Dillhoff et al , 2013Smith et al 2009Smith et al , 2010Gushulak et al 2016;Mathewes et al 2016) and in studies dedicated to broader issues of paleoenvironment (Greenwood and Wing 1995;Wolfe et al 1998Wolfe et al , 2000Greenwood et al 2005;Moss et al 2005;Smith et al 2012;Feng and Poulsen 2016). Archibald et al (2011) provided a preliminary synthesis of the Okanagan Highlands sites, focusing on their potential as Lagerstätten to answer questions in paleoecology incorporating both insects and plants.…”

Fossil palm beetles refine upland winter temperatures in the Early Eocene Climatic Optimum

“…Palm pollen (as Sabal granopollenites) has been reported in the Allenby Formation and other Okanagan Highlands sites at Driftwood Canyon, Falkland, Hat Creek, and McAbee (18,19), although not at others of this series, e.g., Quilchena or Republic. Searches of Quilchena slides prepared by R.W.M.…”

“…Floral proxies indicate a considerably warmer climate in coeval nearby coastal lowland formations, with a substantial elevational MAT gradient upslope to the cooler Okanagan Highlands (16,17,19,(36)(37)(38)(39). It is highly unlikely that all localities bearing Pachymerina were situated at the precise elevation of the coldest limits of palm tolerance.…”