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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 34 (1964)No. 1. (March), Pages 156-164

Modification of Sediment Size Distributions

William F. Tanner

ABSTRACT

Sediment size distributions commonly plot, on probability paper, as zig-zag lines. Nevertheless, the hypothesis that the basic distribution is normal (i.e., Gaussian) and will therefore plot as a straight line, is specifically retained. Possible modifications of the straight line plot include the following: simple mixing (adding of two or more basic components), censoring of a single component, truncation of a single component, filtering of a single component, or a combination of these. Simple mixing is the simplest, and therefore the one most likely to be successful in explaining zig-zag curves. Filtering is, in some ways, a negative version of mixing. An additional factor in the wide-spread appearance of zig-zag curves is the seemingly universal deficiency of certain sediment sizes minima which separate gravel bed load, sand bed load, and wash load).

A variety of methods are available to the analyst who wishes to determine the "original" basic components in a given sample. These include a graphical method, and the method of finite differences. However, experience and intuition are more important than methodology in effecting a successful separation.

Bimodal distributions having a sharp inflection point near 2^phgr are conceivably the result of mixing sands from two different sources (such as a river, and wave erosion of standstone exposed on the near-shore shelf), or of transporting sands in the same area by two different agencies (water currents; wave motion). A possible sand dune history of sands such as this is examined and rejected. If the dual-transportation suggestion is correct, the 2^phgr "break" may be useful in interpreting environments of deposition of sands of the past.

The abundance of zig-zag curves, in sediment size distribution studies, makes clear the necessity for examining the detailed plot. rather than two or three statistical parameters (such as the mean and the standard deviation) which do not represent the zig-zag curve very well.


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