Castile Formation Evaporites - The layers in this rock represent annual varves. The
dark organic-rich calcite layers represent peroidic (annual?)
freshening of the water and development of plankton blooms. The
white anhydrite layers represent restricted, more evaporitic conditions.
There are over 260,000 calcite-evaporite cycles in this formation.
These cycles provide one of the longest continuous Phanerozoic
paleoclimate records available. I found this sample near the Guadalupe
Mountains in western Texas. Notice the normal fault running through
the sample.
