A window into mid-latitudinal Early Eocene environmental variability: a high-resolution palynological analysis of the Falkland site, Okanagan Highlands, British Columbia, Canada

Abstract

A series of Eocene lake shale deposits from British Columbia, coined the Okanagan Highlands, are dated from associated volcanic ash as mostly from the Early Eocene Climatic Optimum (EECO), the longest persisting of the early Paleogene hyperthermals. In this report we focus on high-resolution palynological sampling of short sequences for the Falkland site to determine if they record centennial- or millennial-scale vegetation change during the EECO. The Falkland shales consist of alternating dark- and light-coloured irregular laminae, along with interleaved tephras from volcanic eruptions. At this site it is apparent that deposition occurred over several millennia. 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. Our data show that regional vegetation was impacted by millennial- to centennial-scale climatic variability, as well as the effects of volcanic eruptions. At Falkland there appears to be alterations in vegetation assemblages (birch – golden larch association to fir–spruce) that reflect longer-term (centennial to millennial) climatic transitions (warm/wet to cool/dry). Within this sequence, a period of environmental disturbance (reflected in the presence of multiple volcanic ash layers, wave ripple marks, and a fish-kill layer) has a marked impact on vegetation representation, with a dramatic increase in Abies and Picea pollen at the expense of Alnus and Betula, which do eventually recover. These results suggest mid-latitude millennial-scale climate oscillations in the waning period of the EECO of a similar magnitude to Holocene variability.