CHARACTERIZATION OF SILICA-BASED LIVING STROMATOLITES WITHIN A GEOTHERMAL LAKE

Borax Lake is located within the Alvord Basin, Oregon, USA, and is a relatively small lake that is fed by a subsurface geothermal spring. The lake is roughly 300 m in diameter and most of the lake is 1-2m deep. The average water temperature is 25-30°C although a maximum temperature of 118°C has been recorded deep within the vent. The vent feeding the lake is approximately 30m deep and 35m across and is located in the southwestern part of the lake. Along the northern edge of Borax Lake, ~150-200m from the vent, are located numerous mounds suggestive of living stromatolites. The formations are domal to columnar in shape and are of similar size. A cross section cut through a piece of one of the formations showed a thin layer of green mucoid material approximately 2mm below the outermost surface of the mound. Above and below the green layer is a white porous substrate rich in Si and O, and the outermost part of the mound is covered by a thin dark brown rind rich in S, Ca, and Mn. Powder X-ray diffraction showed the substrate to be amorphous suggesting the formation is primarily opal-A. We present a detailed characterization of the geology and biology of these unusual siliceous stromatolites.