Types of sedimentary overlap
Introduction The sedimentary formations of the earth’s crust fall readily into two great stratigraphic groups, the marine and the non-marine, which in their essential characteristics are strongly contrasted and which in the analysis of sedimentary series must be carefully differentiated. In spite of the practice to the contrary, stratigraphers will admit that only marine deposits are suited to furnish the record for a complete time scale, and that consequently the standard column of any region should be based on marine deposits only. Where, as is often the case, the column selected as a standard contains non-marine members, the column is imperfect as long as these are retained. Thus the standard Cretacic column of North America is impaired by the retention in it of the non-marine Dakota and Laramie formations, and until recently the standard Triassic section of Germany was practically useless, as it contained only one marine member. The substitution . . .