ABSTRACT

Mechanical analyses of deposits of various sedimentary environments have been made by means of a new type of sedimentation balance for grain sizes from 500 to 5 µ. The results have been plotted on arithmetic probability paper. Well-sorted sands give on this paper straight lines proving that they have a symmetrical size frequency distribution when an arithmetic grade scale is used. The size frequency distribution of the sand and silt grades of argillaceous sediments commonly is a part of a symmetrical one.

The arithmetic probability paper enables us to study the phenomena caused by the differentiation of the transported detritus. Three main types of frequency distribution called R-, S- and T-types occur in sedimentary deposits due to the sorting of the transporting medium. The characteristic features of a sedimentary size frequency distribution are found in the extremes and not in the central half of the distribution. Statistical values based on quartiles, therefore, do not give satisfactory results.

The characteristic shape of the extremes of the distributions caused by the differentiating action are frequently blurred by later mixing of material due to variations in the capacity of the transporting medium. Composite frequency distributions, however, are commonly recognized if the results are plotted on the probability paper.

As far as analyses by means of the sedimentation balance have been made sedimentary environments can be recognized by the predominance or alternation of certain frequency distributions.