ELEMENTAL DISTRIBUTION IN THE ALASKAN LANDSCAPE

Natural variation in the elemental composition of soils and sediments reflects the geochemical characteristics of bedrock and surficial deposits, and also areas of mineralization or alteration. Element distribution in soils and sediments is influenced by geochemical cycling and anthropogenic factors. Single element maps are a useful tool to identify anomalous elemental concentrations, whereas multivariate analysis facilitates interpretation of geochemical patterns and their links to local and regional geology. We use soil data from a regional geochemical soil transect and statewide legacy sediment data to evaluate geochemical patterns across Alaska. The resultant maps highlight anomalous element concentrations that correlate with geology. Some elements reflect the primary bedrock, whereas other elements reflect secondary surficial geology and soil development. For example, geochemical signatures of soils and sediments reflect the presence of ultramafic rocks and enrichments of U, Th, and REE associated with alkaline igneous rocks. Comparison of the elemental content between soil horizons helps distinguish geogenic enrichment in surface soil from enrichment due to elemental cycling or anthropogenic factors. Comparison of magnetic and nonmagnetic heavy mineral concentrates helps determine what minerals occur with different types of mineralization, and also helps to constrain the relative mobility of different elements in the surface environment. Futhermore, watershed-based analyses of sediment samples identify hydrologic subbasins where sediment samples on average have high, moderate, or low mean element concentrations. Watershed-based maps, when combined with alteration mapping derived from Landsat 8 Operational Land Imager data, show areas where rocks may be altered and weathered, possibly less competent, prone to enhanced weathering, and possible source areas for downslope soils and sediments. The suite of techniques applied here helps evaluate the geologic sources of geochemical anomalies across the state.