Assessment of dispersive pressure as a beach placer mechanism |
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| Authors: | MATT R TOMKINS PETER NIELSEN TOM E BALDOCK |
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| Institution: | Division of Civil Engineering, The University of Queensland, Brisbane, Qld 4072, Australia (E‐mail: mattt@westerapartners.com.au) |
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| Abstract: | The concept of sediment sorting extending from the Bagnold constitutive relationship for sediment under shear is examined in the context of beach placer formation. The traditional interpretation of shear sorting is found to be inconsistent with data from new granular flow experiments. A binary mixture satisfying the shear equivalence relationship displayed pronounced segregation during shear. This observation is contrary to shear sorting as applied in the literature where no such segregation for this pairing of mineral species is expected. Further experiments minimizing the potential of grain percolation of smaller grains or kinetic sieving also demonstrated sorting patterns inconsistent with the existing shear sorting interpretation. Consequently, the shear sorting process, as currently formulated, may not be an appropriate means to describe beach placer formation. Kinetic sieving appears to be a more likely mechanism in this context, enhanced by the shearing and dilation of the granular‐fluid flow. |
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| Keywords: | Dispersive pressure granular flow heavy minerals shear sorting swash |
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