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The US Pacific Northwest (PNW), including Washington, Oregon, and Idaho, hosts an extensive suite of Oligocene–Miocene fossil plant sites that have the potential to showcase terrestrial vegetation and climate response to several pronounced environmental perturbations. These include the Mid-Miocene Climatic Optimum (MMCO; ca. 17-14 Ma), the Middle Miocene Climatic Transition (MMCT; ca. 14-13 Ma), and the eruption of the Columbia River Basalts (~95% of its volume 16.7 to 15.9 Ma). This collaborative study focuses on 18 PNW fossil plant sites spanning ca. 32 to 10 Ma, many of which have extensive pre-existing macrofossil collections. First, we radiometrically date interbedded tuffs at these sites to establish a high-resolution temporal framework, using U-Pb/CA-ID-TIMS. We present new dates for the Clarkia/Emerald Creek, Alvord Creek, Juliaetta, Pickett Creek, Whitebird, and Trout Creek fossil sites. Within this temporal framework, we are: 1) documenting regional climate change in the PNW during the MMCO and MMCT using paleobotany-based paleoclimate proxies, and 2) providing an integrated perspective on the response of plant communities to these mid-Miocene environmental changes by combining macrofossil, palynomorph, and phytolith evidence. Taken together, these data will provide a regionally-comprehensive perspective on the sensitivity of terrestrial vegetation and climate to global climatic events known more extensively from marine records.
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This content will become publicly available on November 8, 2025
Mechanisms of rapid plant community change from the Miocene Succor Creek flora, Oregon and Idaho (USA)
The fossil record of the U.S. Pacific Northwest preserves many Middle Miocene floras with potential for revealing long-term climate-vegetation dynamics during the Miocene Climatic Optimum. However, the possibility of strong, eccentricity-paced climate oscillations and concurrent, intense volcanism may obscure the signature of prevailing, long-term Miocene climate change. To test the hypothesis that volcanic disturbance drove Middle Miocene vegetation dynamics, high-resolution, stratigraphic pollen records and other paleobotanical data from nine localities of the Sucker Creek Formation were combined with sedimentological and geochemical evidence of disturbance within an updated chronostratigraphic framework based on new U-Pb zircon ages from tuffs. The new ages establish a refined, minimum temporal extent of the Sucker Creek Formation, ~15.8 to ~14.8 Ma, and greatly revise the local and regional chronostratigraphic correlations of its dispersed outcrop belt. Our paleoecological analysis at one ~15.52 Ma locality reveals two abrupt shifts in pollen spectra coinciding with the deposition of thick ash-flow tuffs, wherein vegetation dominated by Cupressaceae/Taxaceae, probably representing aGlyptostrobus oregonensisswamp, and upland conifers was supplanted by early-successional forests with abundantAlnusandBetula. Another ephemeral shift from Cupressaceae/Taxaceae swamp taxa in favor of upland conifersPinusandTsugacorrelates with a shift from low-Ti shale to high-Ti claystone, suggesting a link between altered surface hydrology and vegetation. In total, three rapid vegetation shifts coincide with ash-flow tuffs and are attributed to volcanic disturbance. Longer-term variability between localities, spanning ~1 Myr of the Miocene Climatic Optimum, is chiefly attributed to eccentricity-paced climate change. Overall, Succor Creek plant associations changed frequently over ≤105years timespans, reminiscent of Quaternary vegetation records. Succor Creek stratigraphic palynology suggests that numerous and extensive collection of stratigraphically controlled samples is necessary to understand broader vegetation trends through time.
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- PAR ID:
- 10557360
- Editor(s):
- Huang, Huasheng
- Publisher / Repository:
- PLOS
- Date Published:
- Journal Name:
- PLOS ONE
- Volume:
- 19
- Issue:
- 11
- ISSN:
- 1932-6203
- Page Range / eLocation ID:
- e0312104
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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