Eolian evidence for climatic fluctuations during the Late Pleistocene and Holocene in Wyoming

Evaluation of eolian features, particularly sand dunes, in the Ferris-Lost Solider area of south-central Wyoming demonstrates the dynamic character of late Pleistocene and Holocene climatic fluctuations in a high altitude, intermontane basin. Directly- and indirectly-dated stratigraphic, sedimentary, and geomorphic evidence documents recurrent late Quaternary eolian activity as well as the timing and severity of episodic aridity during the Altithermal. Eolian activity in the Ferris-Lost Solider area began under cool and arid conditions by the late Pleistocene. Radiocarbon-dated dune and interdune strata reveal that Holocene sand dune building at Ferris-Lost Solider peaked between ca. 7660 and 4540 years b.p. The first phase of dune building was the most extensive and lasted until ca. 6460 years b.p. Warm, persistently arid conditions during this time favored active dunes with slipfaces, even in historically well-vegetated locales subject to high water tables. Increased effective moisture from ca. 6460 to 5940 years b.p. promoted dune stabilizing vegetation; but renewed dune building, lasting until ca. 4540 years b.p., followed this climatic moderation. Subsequent dune and interdune deposits reveal a return to climatic conditions where only sporadic and localized dune reactivations have interrupted overall dune stability. The most significant recent reactivation, probably associated with a regional decrease inmore » effective moisture, occurred ca. 290 years b.p.« less