GSA Connects 2021 in Portland, Oregon

Paper No. 75-11
Presentation Time: 11:05 AM


LOVE, Renee, Department of Geology and Geography, University of Idaho, 875 Perimeter Drive,, Moscow, ID 83844

A compilation of paleoclimate estimates using physiognomic characteristics from dicotyledon fossil leaves in the Paleocene-Eocene of the Pacific Northwest are compared here. These fossil flora span over 20 million years of lowland fluvial deposition in southern British Columbia, Washington, and Oregon and record paleoclimatic changes during the hyperthermal events of the mid-Paleocene to mid-Eocene. Mean annual temperatures (MAT) and precipitation (MAP) estimates were derived using Leaf Margin Analysis (LMA), Climate Leaf Analysis Multivariate Program (CLAMP), and techniques from Wilf et al. (1998) and Peppe et al. (2011). The lowermost Huntingdon Formation in British Columbia yielded MAT estimates of 11.2 ° to 14.6 °C from LMA and 14.8 °C from CLAMP using 41 morphotypes. MAP was estimated at ∼140 cm/yr. Floras from Washington yielded higher MAT and MAP overall. Using 125 morphotypes from the Chuckanut Formation, MAT values derived from LMA ranged from 17.0° to 28.8 °C for the lowermost and 13.0° to 19.5 °C for the uppermost Chuckanut Formation. MAP estimates were also high at ~120 to 200 cm/yr. The Manastash Formation had MATs ranging from 17.1 °C to 29.1 °C using 22 and 45 morphotypes for the two members. With CLAMP, MAT ranged from 15.3° to 19.4 °C for the lowermost and 12.3° to 15.6 °C for the uppermost Chuckanut Formation and 15.8 ° to 21.3 °C for the Manastash Formation.

Preliminary estimates from the Swauk Formation yielded MAT between 24.2 ° to 30.6 °C using LMA and 19.8 °C using CLAMP from 28 morphotypes. MAP was estimated at ~120 to 150 cm/yr. The Herren Formation of Oregon yielded MAT estimates between 21.8 ° to 26.9 °C using LMA and 19.2 °C with CLAMP from only 20 morphotypes with MAP at ~180 cm/yr. At least 30 morphotypes are needed to determine more accurate estimates and data collection is ongoing. The mid-Paleocene Pacific Northwest contained a mixed conifer–broadleaf forest in the microthermal to lower mesothermal range with mild winters. Late Paleocene to early Eocene also had mild winters but contained mesothermal to megathermal broadleaf evergreen forests synchronous with the early Eocene warming. The mid-Eocene had similar forests to the mid-Paleocene, recording the general decline in temperatures. Future work includes analysis of the Roslyn and Naches formations and more localities in the Swauk Formation.