Can the changes in sediment concentration be recorded by the three-dimensional grain fabric in plane-bed deposits? :

Analyses using the X-ray microtomography

Abstract

The effects of sedimentation rate on the three dimensional grain fabric were examined using X-ray microtomography. Samples are cut out from plane bed sediments which were aggradated under the four different supply rates with the small recirculating flume. Samples were imaged at SR X-ray microtomogaphic system BL20B2 of SPring-8, Japan. The grain identification program was used to get the information about their axes' direction and length. We analyzed 12 samples by two methods. One is projection of long axes onto equal-area Schmidt net. The other is newly developed method of five dimensional cluster analysis. Grains which long axes are horizontal and parallel to the flow are dominant. Concentration of axes' direction is less in the largest amount of sediment supply on the Schmidt net. Sediment supply affects dominant combination of orientation and shapes of grains.