GENEZA OSADÓW ILASTYCH FORMACJI CIECHOCIŃSKIEJ (JURA DOLNA, TOARK) W POŁUDNIOWEJ POLSCE A ICH ZNACZENIE GOSPODARCZE

Abstract

ORIGIN OF THE CIECHOCINEK FORMATION CLAYS (LOWER JURASSIC, TOARCIAN) FROM SOUTHERN POLAND AND THEIR ECONOMIC SIGNIFICANCEAbstract. This paper summarizes the results of research performed on the Ciechocinek Formation clays (Lower Jurassic, Toarcian) and presents the results of a new mineralogical and geochemical study of the Brody–Lubienia BL-1 and Suliszowice BN-38 boreholes. In the lower part of the studied sections (tenuicostatum zone), clay minerals assemblages comprise predominantly detrital illite with subordinate kaolinite and chlorite. Illite-dominated sedimentation was interrupted by an increased input of kaolinite at the VIIIb/VIIIc parasequence boundary. In the upper part (falciferum zone) the kaolinite content is significantly higher than in the lower part. Smectite was not observed in the whole section. The clay minerals composition was mostly controlled by climatic conditions and weathering regime. During the tenuicostatum zone, the influence of Late Pliensbachian cooling was still noticeable. It coincides with the higher illite and chlorite content in the lower interval due to prevention from extended hydrolysis. Levels of the high kaolinite/illite ratio at the VIIIb/VIIIc parasequence boundary interval suggest strong continental weathering in the humid-subtropical to tropical climate related to the onset of the main phase of global warming that was recorded in many sections of Europe at the top of the tenuicostatum zone. In the upper interval of the Ciechocinek Formation, kaolinite is still the dominant clay mineral suggesting mostly warm and humid climate conditions. The palaeoclimate record was slightly modified by mineralogic composition of material supplied from source areas and by palaeoenvironmental conditions. Diagenetic pro-cesses were not sufficient to transform the initial kaolinite, but it may have altered smectite and mixed-layers into illite and/or chlorite. Only the clay deposits from the lower part of the Ciechocinek Formation locally reveal a real economic significance because of lithologic development and lower siderite content. They contain economic resources and reserves of raw materials very good for building ceramics and some type of stoneware clays. In contrast to Hettangian deposits the refractory and other ceramic clays are absent because of kaolinite depletion.