Although the Ediacaran period does contain soft-bodied fossils ( the Ediacaran biota ) , its start is defined at the base of a carbonate layer , referred to as a `` cap carbonate '' . This caps glacial deposits and shows a sudden climatic change at the end of the Marinoan ice age . Rather , the beginning is defined at the base of a chemically distinctive carbonate layer ( this bed is characterized by an unusual depletion of 13C ) , referred to as a `` cap carbonate '' , because it caps glacial deposits and indicates a sudden climatic change at the end of the Marinoan ice age .