A comparison of methods for the quantification of assemblage zones

Abstract

Several methods of quantitative biostratigraphy that are based on assemblage zones are examined utilizing three sets of faunal distribution data. Two of the data sets are structured simply and one is complex. Various types of cluster analysis and multidimensional scaling are applied to weighted and unweighted binary (presence/absence) data. For weighted data, the presences are multiplied by the relative biostratigraphic values (RBV) of the taxa. There are two options for calculating the RBV's. One method (RBV2) emphasizes timestratigraphic correlation, whereas the other is a compromise between time-stratigraphic correlation and biofacies correlation (RBV1). Results from lateral tracing also are examined. The case studies allow the formulation of a general strategy. Weighting is not appropriate if paleoecological groupings are sought. If biostratigraphic zonation is required, weighted data may produce clusters that are stratigraphically more homogeneous than those based on unweighted data. Also the RBV's can point out species that can be deleted from the analysis without losing significant biostratigraphic information. Range through data should be employed in most situations. Similarity matrices between samples can be calculated from various coefficients based on presences. Biostratigraphic zones are extracted from the similarity matrix by cluster analysis, multidimensional scaling and lateral tracing to produce an overall view of the data structure. Lines of correlation and fence diagrams can be constructed between the samples in adjacent stratigraphic sections using the same techniques.