USING A GIS SITE SUITABILITY ANALYSIS TO INFORM GEOBIOLOGY

Springs sourced in the mantle units of ophiolites serve as windows to the deep biosphere, and thus hold promise in elucidating survival strategies of extremophiles, and may also inform discourse on the origin of life on Earth. Spring locations associated with serpentinites have traditionally been located using a variety of field techniques. The chemical properties of these springs are unique; they reflect a reducing subsurface environment reacting at low temperatures producing high pH, Ca²⁺-rich formation fluids with high dissolved hydrogen and methane. This study applies GIS site suitability analysis to locate high pH springs in Coast Range Ophiolite serpentinites in Northern California. We used available geospatial data (e.g., geologic maps, elevation data, fault locations, known spring locations, etc.) and ArcGIS software to predict new spring localities. Important variables in the suitability model were: (a) bedrock geology (i.e., serpentinite/peridotite), (b) fault locations, (c) regional data for the location of groundwater and (d) slope. The GIS model derived from these data sets predicts the most likely regions for novel and known high pH springs sourced in serpentinite outcrops in California as 250-m-diameter fields, thus focusing field work. Preliminary model confirmation in the field was not successful, and two refinements to the model are presented here: the revision includes (i) integration of gabbro-serpentinite unit boundaries via neighborhood analysis, and (ii) overlay of the areal extent of serpentine endemic plant communities. This presentation highlights a powerful GIS-based technique for accelerating field exploration in this area of ongoing research.