STUDIES IN FLUVIATILE SEDIMENTATION - ELEMENTARY GEOMETRICAL MODEL FOR THE CONNECTEDNESS OF AVULSION-RELATED CHANNEL SAND BODIES

Real alluvial sand-body packings are probably neither perfectly random nor perfectly regular and at present are little known in terms of direct field observations. The properties, especially the connectedness, of regular packings of uniform sand bodies are readily calculated, however, and a geometrical model is attractive as a guide where economic operations are mounted on the basis of limited data in the form of one-dimensional stratigraphic samples (drilling records, sedimentological logs). The model shows that there is little chance that alluvial sand bodies are connected if such bodies comprise less than approximately one-half of the succession. But as the sand-body content rises above this value, there is a rapid increase in connectedness as measured by body spacing, extent of contact with neighbouring bodies (average fractional contact), and numbers of contacts with neighbours (coordination). Although defining a limiting case (perfectly ordered packing), the regular packing-model gives numerical results in substantial agreement with a previously described but more complex process-related model that includes realistic stochastic elements. The process-related model in turn yields packings apparently closely similar to real ones. © 1979.