New Mexico Geological Society Annual Spring Meeting & Ft. Stanton Cave Conference — Abstracts

Stoneman Lake (Mogollon Rim, central Arizona) is found within a circular, 40 m-deep, 1.2 km-diameter depression on the southwestern edge of the Colorado Plateau. Stratigraphically beneath the lake’s 3.5 km² basaltic watershed is the Kaibab Limestone, raising the possibility that this depression is one of the largest karstic sinkholes in the region. Taken from the lake’s northern depocenter, core STL14 is an ~ 80 m-long, continuous, multi-indicator archive of past climate and associated surface processes since the Early Pleistocene (~ 1.3 Ma). Tephrostratigraphy, radiocarbon dating, sedimentary facies analysis, and palynology indicate consistent sensitivity of the local ecosystem to glacial-interglacial hydroclimatic changes with diverse responses to each of the over 10 glacial cycles contained in the archive. The mid-Pleistocene transition manifests as a glacial intensification after ~ 900 ka.

Quantitative mineralogy (qXRD) and geochemical (XRF) analyses indicate dust exerts significant influence on the composition of catchment soils and lake sediments. In lake stratigraphy containing the last two glacial cycles (Marine Isotope Stages 1 - 7), mineralogy is dominated by quartz and illite indicating consistent dust accumulation in this ecosystem. A time series of catchment erosion rate (ER) is calculated using dry bulk density measurements, our age model, and qXRD of locally derived minerals (albite and ilmenite). Similar terms along with qXRD of allochthonous minerals are used to estimate dust mass accumulation rate (DMAR). Both ER and DMAR exhibit ranges comparable to results from other studies and their timeseries resemble the sawtoothed character of mid-to-late Pleistocene global climate trends. Both measures are roughly an order of magnitude higher during interglacials (MIS 1 and 5 ER: ~1 – 5 mm/kyr; DMAR: 0.5 – 4 g/cm²/kyr) than during glacials (MIS 2,3,4, and 6 ER: ~0.1 – 2 mm/kyr; DMAR: 0.1 – 1 g/cm²/kyr).

Particle size distributions (PSD) of lake sediments generated by laser granulometry are statistically unmixed into endmember (EM) PSDs representing various sediment sources for the lake. Three EM PSDs account for most of the clastic sediment volume in Stoneman Lake. EM 1 represents local catchment-derived clastics and corresponds to ER, other erosion indicators (Ti_XRF and Glomus, an arbuscular mycorrhiza indicative of soil erosion), thermophilus tree species, fire frequency (charcoal), and overall drier conditions (lake facies). EM 2 represents fine-grained, far traveled (>100 km) regional atmospheric dust and corresponds to periods of alluvial fan activity in the Mojave and Sonoran Deserts. EM 3 represents coarser-grained short-traveled (10’s of km) dusts and more closely follows patterns of regional fluvial aggradation, occurring during wetter glacial periods. 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 transitional climatic periods characterized by geomorphic instability. Core STL14 is an archive of Quaternary processes from catchment to regional scale and is uniquely situated to probe surficial behaviors of the desert southwest beyond that which are preserved in geomorphic surfaces.