NOAA/WDS Paleoclimatology - Stoneman Lake Arizona, USA, Magnetic Susceptibility and XRF Count Data Over the Past 1.3 Ma

Predicting responses of semi-arid to montane landscapes in southwestern North America to ongoing anthropogenic changes requires understanding of past interplay among geomorphic, ecologic, and climatic factors. This study utilizes modern weathering and sediment transport processes to inform the interpretation of a 250-kyr lacustrine sediment record of paleoecology, hydrology, and erosion from a small, closed basin, basaltic catchment on the southwestern edge of the Colorado Plateau. Geochemical and mineralogical analyses of bedrock, colluvium, and lake sediments indicate clastic sediments in the basin are a mixture of local physical weathering products (albite and ilmenite) and eolian dust (quartz, illite, and zircon). Dust fractions increase during glacial periods coincident with lower overall sedimentation rates suggesting this pattern results from decreased local erosion rates, not increased dust deposition. Titanium counts from XRF core scanning records past local erosion rates by tracing ilmenite content. The highest erosion rates, inferred from the highest Ti counts, follow climatic transitions towards interglacial conditions (MIS 5e, 3a, and the Holocene), periods characterized by vegetation changeover (observed in the core’s pollen record), higher temperatures (piñon-juniper-oak pollen abundance), lower effective precipitation (shallow lake facies), and increased wildfire activity (microscopic charcoal particle counts and sizes). While brief inferred episodes of erosion occur following abrupt transitions to cooler and wetter conditions indicated by abundance of subalpine tree (spruce and fir) pollen and deeper lake facies, landscapes appear more stable during glacial periods. This long-term perspective suggests that increased aridity and its consequences of vegetation succession and increased forest fires will increase erosion rates here and in similar settings regionwide.