ABSTRACT

Measurement of thousands of quartz particle shapes from a variety of modern and ancient settings has led to the following conclusions concerning the origin and nature of shape frequency distributions: 1) Quartz shape frequency distributions are polydimensional and polymodal; six or more independent variables are necessary to account for more than 90 percent of shape variation, with each variable generating a polymodal frequency distribution; 2) Each source rock yields quartz particles which are represented by shape frequency distributions with 3 modes or more; mixed sediment samples are so complexly polymodal that they can be considered to be unique "fingerprints"; and 3) This provenance-produced polymodality tends to be reduced with increasing abrasion in the variables which describe the finer details of the particle shape (higher harmonics). However, even in the most mature sands of the Saint Peter Sandstone, shape variables which describe large scale shape components (lower harmonics) persist, Thus, in the same sample, both provenance and process history (degree of abrasion) can be evaluated.

A relationship between size and shape exists and must be considered in any shape analysis. The relationship is not continuous but is manifest by discrete shifts in shape frequency distributions at around 125 microns. We feel that this shift is related to provenance associated with the different rates of transport of grain sizes above and below 125 microns.