CLIMATE ANALYSIS OF THE EOCENE THOMAS RANCH FLORA, BRITISH COLUMBIA

Studies of fossil plants allow us to infer ancient climates. Leaf Margin Analysis and the Climate Leaf Assemblage Multivariate Program (CLAMP) use the relationship between modern leaf morphology and the climate in which the leaves grow to derive quantitative estimates of climate variables from fossil leaf floras. LMA and CLAMP have been used extensively to study climates of the Cretaceous and Eocene, when the Earth was significantly warmer than it is today. This study focuses on climate analysis of the late Early to early Middle Eocene Thomas Ranch flora of the Okanogan Highlands in lower British Columbia. The fossils were preserved in volcanic ash deposited in a lacustrine environment allowing for excellent preservation of their morphological details. The flora was found to consist of 26 morphotypes with the most common morphotype probably related to the family Betulaceae. Mean Annual Temperature (MAT) for the flora, as estimated from LMA, is 11.04°C ±2.59°C. Using CLAMP, the MAT is estimated at 11.44°C ±1.18°C. These MATs are in the same range as those from previous analyses of fossil floras of similar age and location and contrasts with the modern MAT for the Pacific Northwest of 6.5°C.