TUFA MOUNDS, SEARLES LAKE, CALIFORNIA

Over 500 tufa pinnacle mounds occur in 4 areas spread out over the dry bed of Searles Lake, southeastern California. These Pleistocene mounds range from minor features to over 40m in height, most are between 5 and 12m high. The tufa is essentially all calcite and highly porous on a micro to cavernous scale. Faunal remains are rare to non-existent, deposition of most of the deposits appear to be microbially related.

The pinnacles in the middle group display a complex architecture that consists of cylindrical columns, which grew upward from spring vents in the lake bottom, and inter-columnar deposits. The columns generally are composed of 3 distinctly different concentric zones, (1) a very porous interior composed of an highly irregular mass of anastomosing threads and thin, commonly sub-vertically oriented, curved sheets of calcite (calcitized cyanobacteria and biofilm?), (2) a denser region of radially arranged layers of arborescent calcite crystals, and (3) an exterior composed of a finely laminated crust. In general, the highly porous interiors are 10 to 25cm in diameter whereas the total width of the columns commonly ranges from 0.25 to 1m. Areas between the columns are composed of an irregular tangle of calcite encrusted organic structures, much of which displays a vague vertical orientation. A minor amount of thin sub-horizontal crusts also occur in this region between the cylindrical columns. These crusts have planar tops and undersides with extensive downward projecting crystal growth, i.e., the crusts formed at the water-air interface. These crusts are similar to crusts forming today on pool surfaces at active sites of travertine and speleothem accumulation. Thus, the planar crusts are an indication of partial subaerial exposure of the pinnacles during periods of lower lake levels.