Stratigraphic relationship between Rimrock Lake and Hay Lake playa sediments, Harney Basin, eastern Oregon, USA

Abstract

Seven sediment cores from Rimrock Lake (n\u2009=\u20094) and Hay Lake (n\u2009=\u20093) playas (Harney Basin, northwest Great Basin, Oregon, USA) were used to characterize their stratigraphic relationships through time. End-member mixing analysis, conducted on grain-size distributions, identified five end-members (EM), which explain 97.23% of total variance across all samples and represent two major environments of deposition, lacustro-eolian and fluvio-lacustrine. Normalized differences between finest and coarsest EMs were calculated to serve as a visual proxy for comparison of changes in energy within the playas. Playa and watershed morphometric analysis, using GIS, indicates both playas are relatively large (~\u200954 ha) compared to other wetlands within Harney Basin. Both playas were established as marshy environments during the late Pleistocene, ca. 19,500–18,500 cal yr BP, and experienced increased fluvial activity during the early Holocene, between ca. 9000 and 8000 cal yr BP. Rimrock Lake playa continued to experience a lacustrine environment with alternating lake levels well into the middle Holocene, even during times of increased regional aridity, whereas Hay Lake playa did not seem to have experienced an expanded lacustrine environment into the middle Holocene. Digital elevation models, aerial imagery, and documented late Quaternary tectonic activity, suggest that tectonics may have played a role in diverting ephemeral channels toward Rimrock Lake and away from Hay Lake.