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Date of Award

Fall 2023

Document Type

Masters Thesis

Department or Program Affiliation


Degree Name

Master of Science (MS)



First Advisor

Ponton, Camilo

Second Advisor

Lemkau, Karin

Third Advisor

Foreman, Brady


Wildfires are expected to increase in frequency and severity as climate changes in the Pacific Northwest of North America. To better understand the effect of warming climate on wildfire regimes, I present the first reconstruction of past wildfire frequency and severity during the Paleocene-Eocene transition in northwest Washington state, U.S.A. The Chuckanut Formation is a late Paleocene to Eocene sedimentary unit with a robust paleobotanical record showing the existence of subtropical forests in northwest Washington during the Paleocene, transitioning to a relatively cooler Eocene, dominated by temperate mixed forests. Geochemical records of environmental change coinciding with Paleocene-Eocene climatic change in this region are understudied.

Polycyclic aromatic hydrocarbons (PAHs) are molecules produced during incomplete combustion of biomass that readily preserve in the sedimentary record and are used to reconstruct past wildfire frequency and severity. Analyses of PAH concentrations on Paleocene-age and Eocene-age members of the Chuckanut Formation indicate that wildfires were infrequent in the Paleocene, outside of two distinct stratigraphic intervals of increased fire activity, compared to more frequent wildfires in the Eocene. The aromatic structure of PAHs preserved in both members does not indicate a marked change in wildfire severity between the Paleocene and Eocene. I propose that a wetter hydroclimate during the Paleocene may explain the lower occurrence of wildfires compared to the Eocene, despite higher temperatures. Wildfire regime reconstructions combined with regional paleohydrology studies can provide insight into the environmental changes the Pacific Northwest may experience as a consequence of future climate change.




Chuckanut Formation, PAH, Wildfire Regime, Paleoclimate


Western Washington University

OCLC Number


Subject – LCSH

Fire ecology--Washington (State)--Chuckanut Mountains; Wildfires--Washington (State)--Chuckanut Mountains; Paleoclimatology--Washington (State)--Chuckanut Mountains; Paleoclimatology--Paleocene; Paleoclimatology--Eocene; Biochemical markers; Polycyclic aromatic hydrocarbons; Chuckanut Mountains (Wash.)

Geographic Coverage

Chuckanut Mountains (Wash.)




masters theses




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