Wydzielanie mikrolitofacji w piaskowcach kambru przy użyciu jednej z metod taksonomii numerycznej

Magdalena Sikorska

Abstract


 Przedstawiono próbę zastosowania jednej z metod taksonomii numerycznej do wydzielania mikrolitofacji w monotonnym kompleksie piaskowców kambryjskich na przykładzie osadów z otworu wiertniczego Terebiń IG 5. Za podstawę do obliczeń posłużyły wyniki mikroskopowych badań składu mineralnego, cech strukturalnych i teksturalnych. W pracy niezbędne było zastosowanie elektronicznej techniki obliczeniowej. Otrzymane tą drogą wyniki pozwoliły na wydzielenie ośmiu mikrolitofacji.

 

IDENTIFICATION OF MICROUTHOFACIES IN CAMBRIAN SANDSTONES WITH THE USE OF Q-MODE CLUSTER ANALYSIS

 

The paper presents an attempt to use mathematic method of classification of sands tones with reference to Cambrian sandstones on the basis of core material from the borehole Terebin IG 5. The rocks are mainly represented by quartz arenites (often of the orthoquartzite type) or, sometimes, quartz wackes. The rocks are very similar to one another and characterized by mineralogical and textural maturity which makes it necessary to analyse and compare simultaneously about a dozen petrographic characters and, therefore, the use of computer. The studies were carried out with the use of Q-mode cluster analysis of semi-quantitative and qualitative data. In general, the method involves selection of samples with the maximum mutual similarity, determined with the use of the Jaccard's coefficient of association (Sj).

The most similar samples are joined in pairs and, thereafter, in clusters of samples displaying similar mineralogical, structural and textural characters. This makes it possible to treat each of the clusters as a separate microlithofacies.

For the purposes of the analysis, petrographic data were coded as follows (Table I): “I” means the lack of a given character in a given sample and “2” – its presence. When a given character is highly varying, it is coded in a few steps, each of them representing an appropriate combination of 1's and 2's.

The results of calculations made with the use of the POP 11/45 computer were obtained in the form of dendrogram (Fig. 1). The dendrogram shows samples' most close to one another and their pairs grouped in clusters. For the studied Cambrian sandstones there were obtained 8 clusters representing different microlithofacies.


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