engleski

MINERALOGY AND GEOCHEMISTRY OF MIOCENE PELITIC SEDIMENTS FROM THE SOUTH-WESTERN PART OF THE PANNONIAN BASIN, CROATIA

The aim of the study was mineralogical and geochemical characterisation of the Miocene (Ottnangian-Pontian) pelitic sediments from the SW part of the Pannonian Basin. Fifty-two samples of pelitic sediments taken from outcrops on Medvednivca Mt., Moslavačka Mt, Psunj Mt. and from wells in Sava depression and Požega sub-deperession were investigated. These sediments have been deposited in different marine, brackish and freshwater environments depending on Pannonian Basin development. Carbonate minerals, clay minerals and quartz are main constituents of pelitic sediments in all investigated sediments, except samples from Moslavačka Mt. which do not contain calcite. Feldspars, pyrite, opal-CT, and hematite are present as minor constituents in some rocks. Depending on environment and diagenetic changes, high-Mg calcite, aragonite, dolomite and ankerite/Ca-dolomite are present besides calcite. Smectite or illite-smectite (>85% smectite) are main clay minerals in outcrop sample. Minor constituent were ubiquitous detrital illite and kaolinite which were present in almost all samples. In some samples minor chlorite was also present. Concentrations of illite, chlorite and quartz gradually increased with increasing sampling depth in wells, while at the same time concentrations of smectite, calcite and kaolinite decreased. As a results, dominant components of <2&#956; m fraction of pelitic sediments taken from greater depths were illite and chlorite. Higher concentrations of illite, quartz and chlorite are consequence of smectite illitization process. Results of investigation revealed that qualitative and quantitative mineral composition of investigated pelitic sediments was dependant on deposition environment, clastic material provenance, and on degree of diagenetic processes. Major elements and rare earth elements patterns used in provenance analysis show that all analysed samples have a composition similar to the composition of the continental crust and average Post-Archaic Australian Shale (PAAS). Concentration of major and trace elements as well as SiO2/Al2O3, K2O/Al2O3, Na2O/K2O, Eu/Eu*, La/Sc, Th/Sc, La/Co Th/Co, Th/Cr, Ce/Ce* and LREE/HREE ratios, diagrams of K2O-Fe2O3-Al2O3 La-Th-Sc, Hf-Th-Co, Th/Co-La/Sc and Th/Sc-Cr/Th show that the analysed pelitic rocks were formed by weathering of different types of rocks, mostly acidic (silicic) i.e. felsitic rocks. The term &#8220; acid&#8221; rocks stands for silicic magmatic, older sedimentary and metamorphic rocks.

pelitic sediments; Miocene; Pannonian Basin

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