In [[:file:applied-paleontology_fig17-17.png|Figure 1]], biofacies associations reflect different and distinctive populations living in different paleoenvironments. Biofacies are arranged from left to right in order of inferred increasing oxygen concentration. The stratigraphic distribution strongly suggests systematic shifts in oxygen concentration. | In [[:file:applied-paleontology_fig17-17.png|Figure 1]], biofacies associations reflect different and distinctive populations living in different paleoenvironments. Biofacies are arranged from left to right in order of inferred increasing oxygen concentration. The stratigraphic distribution strongly suggests systematic shifts in oxygen concentration. |