9-11 TERRESTRIAL PALEOCLIMATE AND PROVENANCE ACROSS THE EOCENE–OLIGOCENE TRANSITION IN THE WENATCHEE FORMATION, CENTRAL WASHINGTON

Session: Sedimentary Systems and Provenance in the Western Cordillera (Posters)

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Abstract:

Between 40 and 32 million years ago (Ma), Central Washington experienced significant environmental changes. Sedimentary rocks from this time period offer an opportunity to evaluate the roles of climate and tectonics in shaping Earth’s surface. Specifically, the Eocene Chumstick and Oligocene Wenatchee formations capture the transition from a warm, “greenhouse” world to a colder “icehouse” climate during the Eocene-Oligocene Transition (EOT). These formations record the interaction of climate, tectonic activity, and depositional processes over millions of years. Despite their importance for understanding climate–tectonic interactions in the Pacific Northwest, the depositional history, sediment provenance, and paleoenvironmental evolution of these rocks remain poorly constrained.

This study integrates stratigraphy and sedimentology, floristic data, Climate Leaf Analysis Multivariate Program (CLAMP), and detrital zircon (DZ) analysis to address two key questions: (1) How do the Chumstick and Wenatchee formations differ, and what drives those differences? (2) What do variations in sediment provenance within the Wenatchee Formation tell us about the role of tectonics and climate in central Washington during the Oligocene? We measure stratigraphic sections and describe lithofacies to reconstruct depositional environments and basin evolution. Additionally, we analyze fossil leaf assemblages and apply CLAMP to estimate terrestrial temperature and precipitation. We further compare floristic composition across stratigraphic intervals to identify shifts in vegetation structure associated with long-term climate change. Finally, we incorporate DZ geochronology to evaluate sediment provenance and test for changes in sediment routing pathways through time.

Preliminary findings from fossil leaf assemblages indicate a shift toward cooler, drier conditions during the Oligocene. Changes in leaf structure suggest a transition from the warm, humid Eocene to more temperate Oligocene ecosystems. These findings will help clarify how terrestrial basins in Central Washington recorded interconnected climate and tectonic changes during a significant Cenozoic climate transition and will enhance understanding of how sedimentary systems respond to long-term environmental forces.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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