Volcanic glass as a proxy for Cenozoic elevation and climate in the Cascade Mountains, Oregon, USA

Bershaw, John; Cassel, Elizabeth J.; Carlson, Tessa B.; Streig, Ashley R.; Streck, Martin J.

doi:10.1016/j.jvolgeores.2019.05.021

Cited by 11 publications

(17 citation statements)

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“…Kohn and Fremd (2007) present data that may reflect near modern elevations in the Cascades by the late Oligocene, with an additional ∼800 m of uplift in the last ∼6 Ma. This interpretation is consistent with an interpretation of volcanic glass data (Bershaw et al, 2019). Retallack (2004a) shows that late Oligocene paleosols track Milankovitch cycles, but also suggests that Cascade uplift and rainshadow development play roles in longer-term trends (Retallack, 2004b).…”

Section: Introductionsupporting

confidence: 88%

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Molecules to Mountains: A Multi-Proxy Investigation Into Ancient Climate and Topography of the Pacific Northwest, USA

Mclean

Bershaw

2021

Front. Earth Sci.

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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.

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Section: Introductionsupporting

confidence: 88%

“…While studies have looked at Cascade Mountain uplift using single proxies for analysis (e.g. Kohn et al, 2002;Kohn and Law, 2006;Bershaw et al, 2019), few comprehensive studies have taken a multi-proxy approach.…”

Section: Introductionmentioning

confidence: 99%

Molecules to Mountains: A Multi-Proxy Investigation Into Ancient Climate and Topography of the Pacific Northwest, USA

Mclean

Bershaw

2021

Front. Earth Sci.

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“…If rock uplift along the entire Cascade Range was a response to climate‐driven erosion, the north‐south timing would be expected to be broadly synchronous, vary in magnitude from west to east, and systematically lag behind the timing of rain shadow formation. Timing estimates for rain shadow formation vary along the Cascade Range, from circa 27 Ma (Bershaw et al, 2019; Kohn et al, 2002) to circa 16 Ma (Takeuchi & Larson, 2005) (Figure 10). Thermochronologic data reveal circa 17–10 Ma exhumation on the eastern flank of the Washington Cascades initiated earlier than on the western flank (Reiners et al, 2002, 2003) but was likely driven by crustal shortening (Enkelmann et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

“…Geomorphologic analyses from the Washington Cascades reveal that smoothly decreasing mean and maximum altitudes obscure a polygenetic topographic history, implying multiple modes of topography formation have been active throughout the Cascade Range (Mitchell & Montgomery, 2006). Paleoclimate studies suggest that the Oregon Cascade Range has diminished in elevation since its peak elevation in the mid‐Miocene, while the Washington Cascade segment likely continued to gain elevation (Bershaw et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

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Exhumation Timing in the Oregon Cascade Range Decoupled From Deformation, Magmatic, and Climate Patterns

et al. 2020

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The Cascade Range in the Pacific Northwest, USA, developed as an Eocene to recent volcanic arc along the Pacific/North American ocean-continent subduction zone. The volcanic arc is characterized by temporally and spatially variable magmatism. Crustal deformation that accompanied development of the arc transitions from N-S transpression in the Yakima Fold Belt and Puget lowland (western Washington, northern Oregon) to generally E-W transtension in the south (central and southern Oregon). Orography focuses precipitation along the western flank of the Cascade Range, whereas the eastern flank is relatively arid. We use the unique spatial variation in deformation, magmatic history, and orographic precipitation to investigate the contributions from tectonic and surface processes to rock uplift. We reconstruct the exhumation pathway of plutonic rocks throughout the Cascade Range by exploiting the unique juxtaposition of basalt-capped ridges above valleys exposing exhumed Cenozoic plutons. Multiple bedrock geochronometers and thermochronometers constrain the thermal history in six catchments along the Cascade arc from southern Oregon to southern Washington. U-Pb geochronology defines circa 10-24 Ma pluton crystallization ages. Apatite and zircon (U-Th)/He thermochronology ages range from circa 8-23 Ma. 40 Ar/ 39 Ar geochronology defines circa 5-8 Ma basalt emplacement. Our results reveal spatially and temporally variable shallow exhumation in the southern Washington and Oregon Cascades and that the timing of exhumation is earlier than circa 6-12 Ma exhumation previously reported in the Washington Cascades. Spatially and temporally variable exhumation highlights that crustal deformation plays a significant role in rock uplift in addition to erosional mass removal in concert with orographic precipitation. Plain Language Summary Geoscientists have long wondered whether slow, incremental plate tectonics that shapes our planet have direct impacts on Earth surface processes (like precipitation or erosion). More provocatively, could surface processes actually impact tectonics? Existing studies have provided a range of interpretations but often focus on places where intense precipitation (like the Indian monsoon) and deformation (the Himalaya) change spatially together. This makes it challenging to determine whether tectonics or climate is the main driver. We wanted to investigate this problem along the Cascade Range in Oregon and Washington, where precipitation and deformation patterns do not vary together, allowing us to disentangle the influence of surface and tectonic processes. We use geochronology and thermochronology to determine when rocks were exhumed from deep to shallow levels in the earth. This gave us clues on the timing of rock uplift. We hypothesized that if climate was the main driver, which is similar in the Cascades from north to south, the timing would be synchronized north to south. However, we found that the timing is variable along the Cascades. We conclude that the combination and interaction between tecto...

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Drier winters drove Cenozoic open habitat expansion in North America

Kukla¹,

Rugenstein²,

Ibarra³

et al. 2021

Preprint

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The shift from denser forests to open, grass-dominated vegetation in west-central North America between 26 and 15 million years ago is a major ecological transition with no clear driving force. This open habitat transition (OHT) is considered by some to be evidence for drier summers, more seasonal precipitation, or a cooler climate, but others have proposed that wetter conditions and/or warming initiated the OHT. Here, we use published (n=2065) and new (n=173) oxygen isotope measurements (δ18O) in authigenic clays and soil carbonates to test the hypothesis that the OHT is linked to increasing wintertime aridity.Oxygen isotope ratios in meteoric water (δ18Op) vary seasonally, and clays and carbonates often form at different times of the year. Therefore, a change in precipitation seasonality can be recorded differently in each mineral. We find that oxygen isotope ratios of clay minerals increase across the OHT while carbonate oxygen isotope ratios show no change or decrease. This result cannot be explained solely by changes in global temperature or a shift to drier summers. Instead, it is consistent with a decrease in winter precipitation that increases annual mean δ18Op (and clay δ18O) but has a smaller or negligible effect on soil carbonates that primarily form in warmer months. We suggest that forest communities in west-central North America were adapted to a wet-winter precipitation regime for most of the Cenozoic, and they subsequently struggled to meet water demands when winters became drier, resulting in the observed open habitat expansion.

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Volcanic glass as a proxy for Cenozoic elevation and climate in the Cascade Mountains, Oregon, USA

Cited by 11 publications

References 88 publications

Molecules to Mountains: A Multi-Proxy Investigation Into Ancient Climate and Topography of the Pacific Northwest, USA

Molecules to Mountains: A Multi-Proxy Investigation Into Ancient Climate and Topography of the Pacific Northwest, USA

Exhumation Timing in the Oregon Cascade Range Decoupled From Deformation, Magmatic, and Climate Patterns

Drier winters drove Cenozoic open habitat expansion in North America

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