HIGH RESOLUTION PALYNOLOGY FROM THE EARLY EOCENE HORSEFLY AND FALKLAND SITES, BRITISH COLUMBIA

Early Eocene floras from British Columbia are a rich resource for reconstructing western North American early Paleogene vegetation. A series of lake-shale deposits coined the Okanagan Highlands, span 1000km in a N-S transect from Republic in northern Washington to Driftwood Canyon in north-central British Columbia. Radiometric dating of associated volcanic ash in these deposits show that most fall within the Early Eocene Climatic Optimum (EECO), the longest duration of the early Paleogene hyperthermals. Several of these EECO lake shales show fine laminations previously interpreted as annual varves typical of seasonal ice-cover. In this report we focus on high resolution sampling of short sequences of these putative varves for the Falkland and Horsefly sites to determine if they record decadal to millennial scale vegetation change during the EECO. The Horsefly and Falkland shales consist of alternating dark- and light-coloured laminae representing diatomaceous varves, thought to reflect winter/summer deposition, along with interleaved tephras from volcanic eruptions. At both sites it is apparent that deposition occurred over several millennia, providing insight into environmental alterations at centennial to decadal scales. Pollen samples from Horsefly and Falkland were processed using the heavy liquid (Na-polytungstate) method. Pollen grains were counted under light microscopy using a standard transect method, with clustering analysis determining whether the data show any long term trends in plant representation and abundance. At both sites our data show that regional vegetation was impacted by centennial to decadal scale climatic variability, as well as the effects of volcanic eruptions. At Horsefly, there appears to be alterations in vegetation assemblages (Birch-Golden Larch association to Fir-Spruce) that reflect longer term (decadal to centennial) climatic transitions (i.e. warm/wet to cool/dry). The Falkland site shows similar changes, with several alterations in the two plant assemblages in response to climate change, but a volcanic eruption has a marked impact on vegetation representation, with a dramatic increase in Fir and Pine pollen at the expense of Alder and Birch, which do eventually recover. These results suggest mid-latitude EECO climatic variability comparable to today.