sentences:  By adding carbonates as a third component complicated successions can be created, because silica is not only incompatible with clays but also with carbonates.During diagenesis the silica within the carbonate-rich layers starts pinching and coagulates into ribbons, nodules and other irregular concretions.Resulting are complex layering relationships that depend on the initial clay/silica/carbonate ratio and the temporal variations of the single components during sedimentation.