Evaporites are common in the Green River Formation.
Evaporites occur in several of the Green River Formation basins. In the
Green River Basin of Wyoming numerous units of halite, trona, and oil
shale occur interbedded. The trona is mined commerically. Some of the
trona contains up to 1% brine shrimp eggs, suggesting an autochthonous
paleoenvironment. The process of preconcentration of brines via spring
origin could have increased the rate of brine evolution, but certainly
not putting it into the framework of the short spans of time being
discussed here. At Lake Natron (African Rift) trona is erupted directly
from a volcano, covering it's slopes with a white snow of "evaporite".
Springs rich in disolved salts also contribute to the lake brines.
There is abundant evidence of springs in Lake Gosiute (Green River
Formation in Wyoming), some with dolomitized crusts indicating evulsion
of highly concentrated spring water. Again, however, when you consider
the abundant beds of evaporites, stromatolites, and other in-situ
ecologic factors, it is clear that the Green River deposits represent a
significant time span.