A stepwise multiple discriminant-function analysis was used to evaluate the effectiveness in differentiating between heavy-mineral assemblages of the foreshore, berm, and dune subenvironments along the Outer Banks barrier island system of North Carolina. Samples from each of the three subenvironments were collected from 23 regularly spaced localities along the barrier island system. Ten heavy-mineral variables were determined for each sample. The discriminant method using heavy-mineral analyses resulted in extremely limited differentiation between these three subenvironments.
The discriminant analyses were performed in two designs. The first analysis, using a total of 69 samples from all three subenvironments, yielded a correct assignment of 43% of the samples, based on their tourmaline content. A second analysis consisted of three separate discriminant analyses of the heavy-mineral assemblages, differentiating the following pairs of subenvironments: (1) foreshore and dune, (2) foreshore and berm, and (3) berm and dune. A total of 74% of the samples were correctly assigned in the analysis of foreshore and dune subenvironments, based on amphibole and tourmaline as significant discriminators; 63% of the samples were correctly assigned in the foreshore and berm subenvironments, based on tourmaline as the most significant discriminator; and 0% of the samples were assigned in the berm and dune subenvironments where none of the heavy-mineral variables was determined as a significant discriminator.
Thus, the discriminant-function analysis recorded a general lack of success in differentiating between the heavy minerals of the three subenvironments. More specifically, our study suggests that equidimensional heavy minerals, and to some degree elongate heavy minerals, are not useful for discriminating between subenvironments in the nearshore area.