Main articleSubsequent to the publication of the above paper (in which a number of errata appeared) certain points of discussion have been raised regarding the interpretation of the single axis spatial ordinations. In particular delineation of the numerical assemblage zones based upon the spacings between the clustered groups has been in question. In order to
understand fully the significance of these groupings the following points should be borne in mind.Non

Falcon, R. M. S.

Main articleThe aim of this paper is to explore the possibility of using numerical methods in the sub-division of the palynological assemblages encountered upwards in the stratigraphic sequence in one borehole core situated in a central position in the Mid-Zambezi Basin, Rhodesia. Due to its apparently conformable thick succession and the variable micro-floras already encountered within it, this borehole has been proposed as a palynological type section for the Zambezi Basin, Rhodesia. The numerical methods used to delineate zones of similar assemblages were basically very simple, using only presence-absence data of a set range of species. The formulae employed were those of Jaccard, Simpson and Sokal (the only linear method), and the methods of classification were simplified
forms of divisive or shaded half matrices, agglomerative using single linkage clustering, and spatial ordination techniques.
The results support the concept of distinct changes of microfloras up the stratigraphic sequence. Groups of assemblages bearing similar microfloras appear stratigraphically adjacent to one another, barring certain minor instances of transition floras in the younger sequences. Measurable delineations or boundaries between these assemblage zones are illustrated. These numerically defined zones coincide very closely with the assemblage zones already proposed on a visual (quantitative and qualitative) basis.Non

Falcon, Rosemary M. S.

Wits Institutional Repository on DSPACE

Numerical methods in the definition of palynological assemblage zones in the Lower Karroo (Gondwana) of Rhodesia

153 Palaeont. atr., 20, 153 (1977) DISCUSSION ON: NUMERICAL METHODS IN THE DEFINITION OF PALYNOLOGICAL ASSEMBLAGE ZONES IN THE LOWER KARROO (GONDWANA) OF RHODESIA (Paiaeant. afr., 19, 1-20, 1976) by R. M. S. Falcon Subsequent to the publication of the above paper (in which a number of errata appeared) certain points of discussion have been raised regarding the interpretation of the single axis spatial ordinations. In particular delineation of the numerical assem-blage zones based upon the spacings between the clustered groups has been in question. In order to understand fully the significance of these groupings the following points should be borne in mind. The degree of resolution (or spacing) between, and the detailed associations within, these groupings have been seen to vary depending on the reference samples chosen. However, the overall pattern of major grouping of stratigraphically adjacent sam-ples into the major microfloral biozones appears to occur repeatedly, irrespective of stratigraphic bias or distance, in high Djk valued reference pairs. Theoretically, these results may be explained as follows: the projections of the data onto different reference axes will provide different arrangements of the sample points. If, in fact, the data points are clustered into a number of broad groups in n-di-mensional space, this clustering will be evident when the data is projected onto a number of different axes, although some projections will tend to high-light the clusters while others will tend to obscure them. If the same basic picture emerges from each axial projection (remembering that some of the clusters could overlap on some projections) then the observed clusters are likely to represent true cluster-ings of the data. This is the case in the present exer-cise, where in fact the reference pairs chosen herein do emphasize the clusterings of adjacent or associ-ated samples with a maximum of resolution between them thereby highlighting the constant overall pat-tern seen in other reference projections. The concepts may therefore be summarised as fol-lows: the repeated clustering together of stratigra-phically adjacent samples is regarded in this context as constituting a numerical biozone or unit. How-ever, the delineation of such a group by means of spatial definition, although distinct in pairs with high Djk values, must be regarded as a variable fac-tor due to a certain degree of overlap on certain other projections. The same philosophy and approach applies to the double axis ordination technique, with the excep-tion that an added dimension may enhance the clus-terings so far shown. 

Discussion on: numerical methods in the definition of palynological assemblage zones in the Lower Karroo (Gondwana) of Rhodesia

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