PALINOLOGIA DEL PALEOCENO DE CHUBUT. III. Análisis numérico. 1 Introducción y matrices de similitud

Sergio Archangelsky


Nurnerical analysis is applied with a stratigraphic purpose using the System of Multivariate Computer Programs (NT-SYS) of Rohlf, Kíshpaug and Kirk. The Operatíonal Taxonomic Units (OTU) are the samples (sediments ) of different surface and subsurface sections, wich have already been used in the previous contribution. Four techniques have been used for storing the data: 1) Specíes presence (with microplankton, MP, and geographic location, SG); 2) Frequency of groups (with MP and SG); 3) Presence of all species with their frequency (with MP and SG); 4) Presence of most abundant species with their frequency (with MP and SG). Each technique has internal variations. It is to be noted that at species level only 54 angiosperms have been considered. Thirteen basic matríxes of data were analyzed by 4 dífferent methods, using either the Jaccard or the Rogers and Tanimoto similarity coeffícíent, both with UPGMA or WPGMA (unweighted 01' weighted pair-group method using arithmetic averages). The present study deals only with the analysís of the similarty coefficients between pairs of OTU's. It is inferred that those samples having the heighest coefficients are comparable (in each matrix) and may be correlated. A number of "key" samples have been recognízed and the correlatíon scheme is based upon them. The results are discussed in relation to the individual schemes obtained from each matrix. The introduction of the MP and SG characters is not satísfactory for stratigraphíc purposes being rather of ecological significance (though distortions in the present case are seldom significant ). The best stratigraphic results were obtained wíth the simple presence- absence of species, and with group Frequency. The palynological assemblages are rather similar in most of the samples and only at the base of some wel] sections and at the Visser surface section, significant changes do occur, which are considered stratigraphically important.

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