FLORISTIC EVIDENCE FOR CONTRASTING PALEO-ENVIRONMENTS IN THE EARLY EOCENE OF WASHINGTON STATE

Abundant palms and tree ferns found in the Chuckanut Formation document warm temperate to subtropical conditions along the lowland rivers of Early Eocene Washington. A temperate, mixed conifer/hardwood forest with diverse and abundant Pinaceae is recorded in lake beds of similar age found near Republic, Washington. Climate-Leaf Analysis Mulitivarite Program (CLAMP) has previously been used to estimate a mean annual temperature of 15° C for the Bellingham Bay member and 12º C for Republic. Paleoelevation was proposed by Wolfe and Wehr to explain the climactic difference apparent between the Republic and Eocene Puget Group floras. Taxonomy, taphonomy and age correlation present challenges to making a direct comparison. Morphotype analysis is used to overcome the higher degree of taxonomic resolution possible for the Republic flora. A study of the fluvial Puget Group concluded a variety of depositional environments must be sampled to properly reflect the heterogeneity of a floodplain deposit so more localities were included in the Chuckanut morphotype set than at Republic. The Republic flora was most recently dated as 49.4 Ma. The Chuckanut Formation consists of over 3,000 meters of sediments deposited over an uncertain time period but a radiometric date of 49.9 Ma was obtained from a tuff near the top of the Bellingham Bay member. Only sites from that member were morphotyped for this study. The Bellingham Bay member flora includes abundant palms, a diverse assemblage of tree ferns and a depauperate conifer flora. Entire margined leaves predominate and a broad leaf lamina size range includes very large partial leaves that would have exceeded 50 cm if complete. Republic plants have a temperate aspect with an abundant, diverse conifer component and only rare herbaceous ferns. Republic angiosperm morphotypes are dominated by small to mid size leaves with toothed lamina accounting for three quarters of the total. There is almost no overlap between the floras at the species level. This study represents the first attempt to morphotype a portion of the Chuckanut flora and specifically compare it to the flora found at Republic.