Paper No. 17-7
Presentation Time: 10:15 AM
STONEMAN LAKE, ARIZONA: ARCHIVING SURFACE PROCESSES AT LOCAL TO REGIONAL SCALE SINCE THE EARLY PLEISTOCENE
Core STL14 from Stoneman Lake on the southwestern edge of the Colorado Plateau in central Arizona contains a multi-indicator archive of past climate and associated surface conditions since before 1 Ma. While the lake’s drainage is underlain by basalt, XRD analyses show lake sediments are dominated by grain sizes characteristic of far-traveled (>100 km) atmospheric dust and mostly composed of allochthonous quartz and illite. High dust content is ubiquitous throughout multiple glacial cycles. Furthermore, modern catchment soils exhibiting a range of development all contain significant amounts of dust. XRF geochemistry of modern soils and bedrock supports the ratio of zirconium to titanium (Zr/Ti) as an indicator of eolian versus local sedimentation. In XRF core scans, Zr/Ti is elevated during glacial periods and following major climate transitions. During interglacials, Zr/Ti is lower and accompanied by drier conditions (lake facies), increased fire frequency (charcoal counting), up-elevation displacement of forests (pollen analysis), and Glomus, an arbuscular mycorrhiza indicative of local soil erosion. Siliciclastic mass accumulation rate (SMAR) indicates the highest dust fluxes occur following major climate transitions. These periods, including the Early Holocene, MIS 4, and MIS 5e, are characterized by greater activity on major dust emitting features like alluvial fans, flood plains, and pluvial lake margins. SMAR is lower during the Last Glacial and glacial MIS 6, 10, and 12, but dust accumulation is still high relative to local inputs. Viewing dust accumulation as an integrated signal of upwind regional conditions, dust fluxes in southwestern North America appear to be broadly controlled by sediment availability, greatly enhanced during periods of geomorphic instability. High SMAR and Zr/Ti throughout MIS 15 suggest considerable sediment availability, related perhaps to major geomorphic reorganization following MIS 16, one of the first major glaciations in North America following the mid-Pleistocene Transition. Outside being a long record of critical zone behavior in its local montane ecosystem, core STL14 from Stoneman Lake chronicles broad trends in surface processes occurring across the desert southwest, archiving change beyond that which is evident in preserved surfaces.