Facies

Facies is a term in geology. It means the look of a rock. If one looks up at a cliff of rock, the appearances changes from one layer to another. This because the ecological conditions changed as the rock was laid down. So, the facies reflect the process of sedimentation. 
Regular changes in the facies usually means regular changes in the ancient climate. As the climate chaged, so the sea level rose and fell. What was deep water became shallow water, and so on. In the Milankovich cycle, the climate changes regularly. As it does so, deeper water carbonates may alternate with shallow-water shales and silts. These "facies" are seen in the column of rocks.
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