SOIL-LANDSCAPE EVOLUTION ACROSS AN ALLUVIAL FAN-PLAYA-DUNE SYSTEM IN THE LOWER SONORAN DESERT, SOUTHWESTERN ARIZONA

Knowledge of late Quaternary landscape evolution in the low elevation Sonoran Desert of southwestern Arizona is hampered by lack of numerical age constraints coupled with an incomplete understanding of the climatic conditions responsible for inciting geomorphic change.

Shifts in the density and composition of post-LGM (last glacial maximum) hillslope vegetation and/or discrete periods of enhanced precipitation have traditionally been implicated as the primary driving mechanisms of soil-landscape changes. Owing to a lack of high-resolution terrestrial records, however, these ideas remain largely untested in this region of the desert southwest. As part of my dissertation research, numerical dates (OSL and ¹⁴C AMS) on soil-stratigraphic successions in the Mohawk Dune Field and laterally adjacent dry playa and alluvial fan settings are providing higher-resolution terrestrial records that can be directly correlated to local and regional climate proxy data. Although some results are still forthcoming, five discrete eolian depositional units in the Mohawk Dune Field have been tentatively correlated to eolian sources along the lower Gila River and local tributaries. Numerical dates from a 4+ meter soil-stratigraphic playa succession are also beginning to provide temporal constraints on regional wet-dry cycles that potentially date back to the latest Pleistocene. Future work will focus on the Mohawk Mountain alluvial fan soil chronosequence and will include soil micromorphological analysis of desert pavements and subjacent horizons along with 10Be depth profiles.

The inspiration for this research began when I was first introduced to Peter Birkeland’s book (Soils and Geomorphology 3^rd edition) as an undergraduate student in geosciences. As the grateful recipient of the 2020 GSA Peter Birkeland Award I am honored to continue Pete’s legacy by studying soil geomorphology and geoarchaeology in the hot deserts of the American southwest.