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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)


Journal of Sedimentary Petrology
Vol. 38 (1968)No. 4. (December), Pages 1013-1023

Wheeler Gorge Turbidite-Conglomerate Series, California; Inverse Grading

Richard V. Fisher, James M. Mattinson


A coarse-grained sequence of turbidite-conglomerates at Wheeler Gorge, California, was deposited by a series of high density, highly fluid underwater flows into deep water. Inverse grading is developed at the base of each conglomerate trait within the sequence, and one unit forcibly intruded shales to form graded sills. One sill is over 100 feet long.

The development of reverse grading may in part be explained by Bernoulli's principle, whereby pressures near the boundary of deposition tend to drive the large particles upward. Bernoulli's principle relates the velocity in a fluid system to the pressure in the fluid. The resultant of the pressures is a net upward or inward pressure away from the boundary which operates most effectively on the largest particles.

The "Bernoulli boundary Previous HitlayerNext Hit Previous HiteffectTop" may explain reverse grading in coarse-grained turbidite deposits, in mudflows, possibly in ignimbrite layers, and in igneous intrusions of the "Muskox type" which have boundaries that are finer-grained than their interior parts.

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