Grain size representation by CM patterns as a geologic tool

ABSTRACT The characteristics of a depositional agent are reflected in the texture of the sediment. This relationship is particularly evident if the texture is represented by two parameters of the grain size distribution: C the one percentile and M the median diameter. CM patterns formed by sample points of a deposit are characteristic of the agent of deposition. Since the first discussion of CM patterns (Passega 1957) more than ten thousand analyses of sediments ranging in age from Paleozoic to Recent, sampled in basins of all types and sizes, including the Rhine graben, mobile basins of the Apennines and southeast Iran, and Cratonic Sahara basins, confirmed the conclusions of the earlier paper. They also disclosed new relationships between CM patterns and sedimentation, valid under greatly different conditions. The most notable progress of recent research was the construction of paleobathymetric maps and logs showing the depth of ancient seas and the variations of this depth in a stratigraphic section. Paleobathymetry is geologically important as it seems related to such characteristics of the sediments as facies, permeability and possibly also petroleum productivity. CM patterns are a means for analyzing transportation mechanisms and determining the mechanisms that form peculiar deposits, such as stratigraphic traps. Turbidites and certain tractive current deposits have several common characteristics. Their texture shows that they may have a common origin as wave suspensions. The many applications of grain size analyses indicate that they are a versatile means of investigation that discloses the orderly arrangement of a number of geological factors. This order is a fertile field for geological research.