MICROMORPHOLOGY OF A PLEISTO-HOLOCENE LOESS-PALEOSOL SEQUENCE IN CENTRAL ALASKA, USA

Loess is the most areally-extensive surficial deposit in Alaska, and its depositional history may extend as far back as three million years. Its significance as a paleoclimate proxy has begun to receive well-deserved attention. Previous studies have found that numerous paleosols are present in the loess sections of central Alaska. The presence of buried soils indicates that intervals and rates of loess deposition did not impede pedogenesis. In fact, the two appear to be competing processes. This poster presents the results of a micromorphological investigation of a terminal Pleistocene/early Holocene loess-paleosol sequence at the Chena Hot Springs Road site, a highway road cut exposure near Fairbanks, Alaska, USA. The procedure identified and described soil microstructure, basic mineral components and their related distributions, organic inclusions, and pedogenic features. Micromorphology reconfirmed the presence of a number of thin, discontinuous, weakly-expressed soils that evince disturbance by diagenetic, graviturbative, and cryoturbative processes. Well-preserved organic remains within the sediments indicate the presence of a boreal forest that would have acted as a highly effective sediment trap. The presence of detrital iron-oxide grains points to deposition by strong paleowinds, whereas non-pedogenic clay accumulations within the profile imply weaker paleowind strength. The alternating wind conditions may explain the interglacial loess/soil formation cycles. Loess deposition would inhibit pedogenesis during periods of greater wind strength, while pedogenesis would operate most effectively during periods of reduced wind strength and competence across a more stable landscape surface.