Stratigraphy, age, and provenance of the Eocene Chumstick basin, Washington Cascades; implications for paleogeography, regional tectonics, and development of strike-slip basins: Comment

In the Pacific Northwest (North America) are a series of Paleogene basins infilled by non-marine sedimentary and volcanic rocks. Starting in the 1980s, significant efforts have been made to determine the relationships between the various basins; the underlying causes for basin formation, deposition, and basin inversion; and the histories of regional fault systems. One research group has recently produced two papers in GSA Bulletin, proposing that these sedimentary basins reflect the accretion history of the Siletzia terrane between 51.3 and 49.9 Ma, concurrent with the onset of regional dextral strike-slip faulting between 50 and 46 Ma (Eddy et al., 2016). The paper by Donaghy et al. (2021) uses this geochronology data to conduct a detailed depositional systems analysis of one of these basins, the Chumstick basin (filled by the Chumstick Formation), to clarify the sedimentary response to dextral strike-slip faulting and to validate the Eddy et al. (2016) terrane accretion model. To quote the abstract: “These data allow us to reconstruct regional Eocene paleo-drainage systems of Washington and Oregon and suggest that drainage within the Chumstick basin fed a regional river system that flowed into a forearc or marginal basin on the newly accreted Siletzia terrane.