ABSTRACT

Cross-stratification azimuths in an Upper Carboniferous fluvial formation, the Rhondda Beds of South Wales, Great Britain, provide a complex aggregate distribution. Mean or modal vectors furnish only a crude representation of the orientation of the currents responsible for deposition of this formation, and statistical tests are required to resolve the complexity of the vector data into three component flow-systems directed toward northwest, west, and south-southwest, respectively. Overlapping of these flow-systems, both laterally and vertically, accounts for the common bimodality of vector-distributions and explains the insensitivity of mean or modal values derived from the aggregated data.

Multilevel analyses of the variance of cross-stratification azimuths in different parts of the basin reveal differences which are interpreted in terms of the relative contribution of each of a hierarchially ordered series of environmental parameters.

Study of one type of Planar cross-stratification demonstrates a broad increase in both unit thickness and maximum foreset dip in a downstream direction, towards the central and western parts of the basin. Such changes are linked with a general diminution in hydraulic energy in this direction.