Abstract
We characterize the topographic evolution of the Pacific Northwest, United States, during the Cenozoic. New paleosol carbonate stable isotope (δ18O) results from central Oregon are presented, along with published proxy data, including fossil teeth, smectites, and carbonate concretions. We interpret a polygenetic history of Cascade Mountain topographic uplift along-strike, characterized by: 1) Steady uplift of the Washington Cascades through the Cenozoic due long-term arc rotation and shortening against a Canadian buttress, and 2) Uplift of the Oregon Cascades to similar-to-modern elevations by the late Oligocene, followed by topographic stagnation as extension developed into the Neogene. Since the Miocene, meteoric water δ18O values have decreased in Oregon, possibly due to emergence of the Coast Range and westward migration of the coastline. Spatial variability in isotopic change throughout the Pacific Northwest suggests that secular global climate change is not the primary forcing mechanism behind isotopic trends, though Milankovitch cycles may be partly responsible for relatively short-term variation.
Highlights
Stable isotope ratios of water illuminate temporal changes in a region’s climate and topography (e.g. Savin, 1982; Garzione et al, 2000; Rowley and Garzione, 2007)
We combine our results with published data throughout the region, including 172 paleosol carbonates from Washington and Oregon (Takeuchi et al, 2010), 367 paleosol carbonates from Oregon (Retallack et al, 2004), 22 smectites from Washington (Takeuchi and Larson, 2005), 243 fossil teeth from Oregon (Kohn and Fremd, 2007), 31 modern carbonates from Washington (Lechler et al, 2018), and 119 carbonate concretions from Washington (Methner et al, 2016) (Figures 1B2 and Supplementary Table S1)
Sample δ18O values from individual studies are averaged within 2.5 million-year bins to emphasize trends in climate and topography across geologic time (Figure 2)
Summary
Stable isotope ratios of water illuminate temporal changes in a region’s climate and topography (e.g. Savin, 1982; Garzione et al, 2000; Rowley and Garzione, 2007). Stable isotope ratios of water illuminate temporal changes in a region’s climate and topography We present new soil carbonate δ18O data and synthesize existing paleowater proxy data to provide a more comprehensive interpretation of spatial (Pacific Northwest) and temporal (Cenozoic) patterns. By comparing temporal patterns of stable oxygen isotopes in the Pacific Northwest to the record of global Cenozoic δ18O change and Milankovitch-scale variation Orographic precipitation is significant in mountains across the region, including the Cascade Volcanic Arc (Cascades), the Olympic Mountains in Washington, and the Oregon Coast Range. The Clarno Formation of central Oregon (Bestland et al, 1999), Siletz River, and Crescent Formations of Washington contain significant amounts of subaerial volcanic rock that erupted as early as 51 Ma (Wells et al, 2014), suggesting some terrestrial settings by that time.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
