Lake Bonneville Tufa
What
is the hard white material on the Bonneville shorelines?
Figure 2:
capping tufa (pink) coating bedrock (grey) has <10% clastic material
Figure 3:
Beachrock : tufa coated clasts consists of
>90% clastic material
Why does Tufa form on the
Shorelines?
Calcium carbonate
precipitates out of waters in the shorezone of the ancient lake. Tufa has a biological component that can be
identified by looking at thin sections under a microscope. Algal filaments make up a large part of the
tufa fabric. Along with biologic contributions,
tufa also needs a firm substrate in which to form. Areas that were exposed to
high wave energy in the lake, like headlands, have large deposits of tufa. We suggest that wave action agitates the
lake water, degassing it of CO2, subsequently raising the local pH
of the water. This rise in pH leads to
precipitation of Calcium Carbonate deposits.
The interplay of biologic factors, substrate, lake water chemistry, and
wave energy contribute to the formation of tufa deposits on the Bonneville
shorelines.
Figure 4: Tufa infilling cracks
in a Cherty limestone, Utah west desert
Figure 5:
Tufa capping a rhyolite boulder, northeast of Wendover, Ut.
Comments or Questions?? mailto:afelton@mines.utah.edu
