Microprobe Line Profiles of Varnish Chemistry, Mojave Desert, Western USA

Figure Caption    Optical (left) and chemical (right) microstratigraphies in rock varnish from late Quaternary lava flows in the Mojave Desert, California. The black layers in the varnish are enriched in Mn and Ba (but depleted in Si), and the yellow layers are depleted in Mn and Ba (but enriched in Si). The orange layers contain intermediate amounts of Mn and Ba. Note that the absolute concentrations of Mn and Ba in the outermost yellow layers change from sample to sample, but their relative concentrations are generally lower than those in the underlying black and orange layers. Also note that some orange layers in the varnish contain anomalously high content of Fe, as marked by the dark arrows in A and C, leading to extremely low content of Mn and Ba in these layers.