Tufity ze zlepieńców myślachowickich okolic Olkusza

Abstract

TUFFITES FROM MYŚLACHOWICE CONGLOMERATES IN THE VICINITY OF OLKUSZ

Summary

In the vicinity Olkusz the Lower Permian deposits are represented by the Myślachowice conglomerates described in detail by A. Siedlecka (1964). Drilligs made within the area between Olkusz and Wolbrom encountered a new patch of these conglomerates, situated at Pazurek, nesr Chrząstowice (Fig. 1-D). These conglomerates include a thick intercalation of tuffites. The sequence from bottom to top in this drilling is as follows; limestones and marly shales of Upper Devonian age, the Lower Permian Myślachowice conglomerates, then sands, clays, limestones and dolomites Triassic in age, and Jurassic sandstones, ferruginous oolites, marls and limestones, overlain with the Quaternary tills and sands (Fig. 1-A). The Myślachowice conglomerates are of considerable thickness (180 m). They consist of pebbles and fragments of Palaeozoic limestones and dolomites, with an admixture of quartz and effusive rocks (porphyries). The profile reveals a triple alternation of coarse-grained and medium-grained conglomerates here (Fig. 1-B). About 50 metres above the bottom of the conglomerates there occurs an intercalation of psammitic and clayey tuffites, red and grey-green in colour. They have been subdivided into 7 banks (Fig. 1-C). Microscope examinations demonstrate that clay minerals with relicts of primary minerals, i.e. potassium feldspars lacking any twinnings, are predominant components of the tuffites. Quartz occurs here in different morphological forms (wedge-shaped, comma-shaped, etc.), and shows features of a pyrogenous mineral. Biotite flakes, mostly chloritized are scarcely represented. They are accompanied also by small zircon grains. Locally tuffites reveal fragments of magmatic rocks of microfelsitic texture (quartz porphyries). Curves of thermal-differential analyses show thermal effects that are characteristic of montmorillonite dehydratization. Particularly abundant is this mineral in banks 2 and 4. Some tuffite samples disclose the presence of a considerable admixture of calcite, which can be also be seen in the diagrams attached to the text (Fig. 2). X-ray examinations have been made on samples taken from the banks 2 and 4. The results obtained prove that montmorillonite is here the main components of the rocks, quartz being a subordinate one (Table 1). Chemical analysis has been made on a sample from upper part of the bank 2 (Table 2). Significant is here a relatively high percentage of Al₂O₃ and water, i.e. constituents that make the composition of montmorillonite. A taxonomic analysis, based on four selected parameters (Table 3) calculated from chemical analyses cited in the geological literature (Catalogue ... 1959, 1961), has been made in order to compare the tuffites from the vicinity of Olkusz with other tuffites and tuffs of Permian age from Kraków Upland area. After calculations made using method of absolute mean differences, “taxonomic distances” D have been obtained for every pair of tufogenic rocks, as measures of their resemblance. This has been a basis to draft a dendrite by the method of Wrocław taxonomy (W. Młynarczyk, 1970). It results from the dendrite that three types of pyroclastic rocks of Permian age can be distinguished in the region of Kraków (Fig. 3). These are: I type – Alweria tuffite, II type – Tworzeń tuffite, and III type – Filipowice tuff. The calculation of the mean taxonomic distances (D) demonstrates that the differentiation within the types mentioned above is considerably lower than the difference between the individual types (Table 4), emphasizing thus their individuality.
The petrographical examinations are a basis to draw conclusions that the described pyroclastic rock found to occur in the Myślachowice conglomerates in the vicinity of Olkusz is a strongly altered (montmorillonitized) porphyry tuffite.