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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)


Journal of Sedimentary Petrology
Vol. 44 (1974)No. 4. (December), Pages 1174-1185

Paleocurrent Analysis of Alluvial Sediments: A Discussion of Directional Variance and Vector Magnitude

Andrew D. Miall


A tabulation of recent work on current indicators in modern rivers shows that directional variance increases with decreasing structure scale, in fairly close agreement with the structure hierarchy concept of Allen (1966).

Fluvial currents are vectors, definable by direction and magnitude, but most paleocurrent studies ignore magnitude. It is proposed that azimuth readings be weighted according to the cube of current structure thickness, this being a volume measure corresponding to the distance in all three dimensions over which a local flow vector might reasonably be assumed to maintain the same direction. It is also a measure of the quantity of sediment moved by the flow vector.

Examples are presented in which the proposed weighting factor is applied to data from the fluvial Isachsen Formation (Cretaceous) and deltaic Eureka Sound Formation (Cretaceous-Tertiary) of Banks Island, Arctic Canada. It is shown that the use of the weighting factor can differentiate flow patterns on the basis of sedimentary structure size, leading to interpretations of channel size, sinuosity, and other parameters of sedimentological importance. The weighting factor also provides an important check on calculations of vector mean.

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