DIFFERENTIATING HYDROCLIMATES USING ALLUVIAL FAN GEOCHRONOLOGY IN THE VIZCAINO DESERT, CENTRAL BAJA CALIFORNIA, MEXICO

Alluvial fans in the deserts of southwestern North America can record climatic change in their sedimentation patterns. Studies conducted in the Mojave and Sonoran Deserts have suggested that alluvial fan sedimentation is mostly caused by vegetation changes on glacial-interglacial timescales, while studies from the southern Baja California Peninsula have indicated that deposition on alluvial fans is caused by changes in storm activity on precessional (~21 ka) timescales. This study aims to understand the climatic processes that have produced large-scale alluvial fans in the Vizcaino Desert in the central Baja California Peninsula by constructing a more detailed alluvial fan stratigraphy and chronology. Field observations have indicated that there are four main Quaternary units, Q1 (oldest), Q2, Q3, and Q4 (youngest). Initial AMS radiocarbon and optically stimulated luminescence (OSL) dates suggest that the youngest unit, Q4 is composed of three Holocene events (1.2 ± 0.1 ka, 2.5 ± 0.1 ka, and 4.8 ± 0.5 ka). OSL ages for the two intermediate units, Q3 and Q2, are 15 ± 1 ka and 71 ± 14 ka, respectively. These ages are similar to alluvial fan ages from the southern Baja Peninsula which suggests that alluvial fan sedimentation in the Vizcaino Desert may be controlled by storm activity on precessional timescales.