Investigations of Interior Alaska Loess Sources: Reconstructing Quaternary Glacial/Interglacial Storms

Wind-blown dust (i.e., loess) is an important record of terrestrial paleoclimate and paleoenvironmental conditions. The origins of loess can be used to reconstruct the strength and direction of winds during glacial/interglacial cycles, which is factored into models of atmospheric circulation. In interior Alaska, the Gold Hill loess deposit is a climate data reservoir stretching from 130,000 to as far back as three million years ago (e.g., Westgate et al., 1990; Muhs et al., 2003; Péwé et al., 2009). This deposit preserves anthropologically significant Hominid remains (Begét, 1996) as well as the Dawson Cut Forest Bed, whose remains push the limit of northern boreal forest in northwestern North America back to 2 Ma (e.g., Péwé et al., 2009). While the stratigraphy and ages of Gold Hill Loess deposits are well studied, the only information on provenance comes from qualitative geochemical analyses. These suggest the loess is derived from local sources: the Alaska Range to the south and Yukon-Tanana Uplands to the north, both~100 km away. In contrast, ash layers in the loess have eastern Aleutian arc and Wrangell volcanic field geochemical signatures, suggesting wind transport from >1200 km away. We seek to pinpoint where the Fairbanks loess came from using two common geochronological tracers: zircon U/Pb and muscovite 40Ar/39Ar analyses. We will date 100 grains from each of eight samples from the Gold Hill loess to correlate age populations with well-known U/Pb zircon and muscovite 40Ar/39Ar ages of Alaska bedrock. We will partner with NASA paleobotanist Dorothy Peteet to document the plant and animal fossil transitions preserved in the loess and soil deposits. The study described here, which will resolve the direction and distance of wind-borne particle transport during glacial/interglacial cycles, addresses one of the key questions of NASA’s Science Mission Directorate: How and why are Earth’s climate and the environment changing?