Regional and local vegetation community dynamics of the Eocene Okanagan Highlands (British Columbia – Washington State) from palynology

Abstract

Palynofloras from the middle Early to early Middle Eocene Okanagan Highlands (northern Washington State and southern British Columbia) are used to reconstruct vegetation across a broad upland Eocene landscape. In this preliminary report, forest floristic composition is reconstructed using palynological analysis of sediments from Republic, Washington; localities of the Allenby Formation in the Princeton region (Hospital Hill, One Mile Creek and Summers Creek Road), Hat Creek, McAbee, Falkland, Horsefly, and Driftwood Canyon, British Columbia. Wind-dispersed taxa were dominant in all samples, consistent with floras preserved in lacustrine and paludal depositional environments. Pseudolarix was dominant in five of the floras, but Abies (Falkland) or Ulmus (Republic Corner Lot site) were dominant in individual samples for some floras. Betulaceae were dominant for McAbee (Alnus) and Allenby Formation (Betula), matching megafloral data for these sites. Some taxa common to most sites suggest cool conditions (e.g., Abies, other Pinaceae; Alnus, other Betulaceae). However, all floras contained a substantive broad-leaved deciduous element (e.g., Fagaceae, Juglandaceae) and conifers (e.g., Metasequoia) indicative of mesothermal conditions. Palms were only abundant in the Hat Creek coal flora, with very low counts recorded for the Falkland, McAbee, and Allenby Formation sites, suggesting that they were rare in much of the landscape and likely restricted to specialized habitats. Thermophilic (principally mesothermal) taxa, including palms (five sites) and "taxodiaceous" conifers, may have occurred at their climatic limits. The limiting factor controlling the regional distribution of thermophilic flora, which include primarily wetlands taxa, may be either climatic or edaphic.