GEOPHYSICAL RECONNAISSANCE SURVEYS FOR SITING OF CRITICAL ZONE INVESTIGATIONS IN RED LAKE PLAYA, JORNADA DEL MUERTO, NEW MEXICO

Funding to study dryland critical zones (in both natural and agricultural settings) has motivated the use of geophysical surveys as aids for locating two natural sites within the Jornada Experimental Range northeast of Las Cruces, New Mexico. The first site, focused on monitoring unsaturated zone fluxes in a caliche-dominated piedmont environment, required reconnaissance studies to avoid fault zones and rapid facies transitions, thus providing the best approximations for 1-D hydrologic models. We used LiDAR, DEM and regional potential fields data to design the initial magnetic field and EM conductivity surveys. We then collected magnetic field, magnetic susceptibility and EM conductivity measurements to aid in site selection and to design ongoing local seismic and gravity surveys. The second site, the Red Lake playa, was selected to investigate the most likely location of regional groundwater recharge with significant episodic water accumulation. Within the playa, Rio Grande rift related subsidence stacks surficial playa deposits on top of fluvial deposits of the ancestral Rio Grande on top of Oligocene-Miocene volcaniclastics of the Doña Ana, Organ and Emory Calderas. Lacustrine clay with deep shrinkage cracks precludes use of many geophysical techniques (e.g. seismic, radar, DC resistivity). Magnetic field, magnetic susceptibility, DEM and EM conductivity identified potential Rio Grande channel locations relative to basin faulting. We underestimated depositional and structural complexity at the playa site, requiring resurveying with a 5 m magnetic gradiometer spacing, to provide a usefully unaliased dataset.