Abstract
In this study, rice grains were used as the bed material in flume experiments conducted to analyze three-dimensional grain fabrics in microdelta deposits, developed under three sets of hydraulic conditions. Rice grains are nearly uniform ellipsoids, making it possible to interpret not only patterns of imbrication, but also the orientations of individual grains based on the apparent lengths of their long axes projected onto a vertical section parallel to the current direction. Two predominant fabrics were observed at the center of experimental microdelta deposits: (1) grains oriented parallel to the current direction with an imbrication angle close to the foreset dip angle, and (2) grains with random orientations and horizontal imbrication. The first type of fabric appears in grains that have first settled on the uppermost lee slope and have subsequently been relocated and reoriented by discontinuous grain flows (avalanches). The second type of fabric appears in grains that have dropped over the full length of the lee slope and have not been relocated or reoriented by later grain-flow events. The results of this study suggest that the characteristics of three-dimensional grain fabrics may contribute toward an understanding of the depositional conditions of deposits formed by slip-face progression.
