engleski

Altered tephra layers in the Upper Jurassic Lemeš deposits near Maovice (Dalmatia, Croatia): Clay mineralogy and basic soil mechanic properties

Two bentonite layers in the vicinity of Maovice village in the Dalmatian hinterland intercalate within typical Lemeš deposits. These layers were subjected to mineralogical and geochemical research in order to reveal its mineralogical properties and possible origin of clay material. Standards soil mechanics tests were performed as well. Preliminary results from two localities (Bunarić and Gornji Ždanj) are displayed in Abstract (PDF file, attached) and herein briefly reported. The XRD analysis of global samples reveals montmorillonite as the principal mineral in both samples accompanied by calcite, cristobalite, plagioclase (albite ?), quartz and biotite in the Bunarić sample and calcite, quartz, clinoptilolite and cristobalite in Gornji Ždanj sample. In the grain size fraction 63-125 μ m, the sample from Bunarić locality contains comparatively high amount of volcanic crystalloclasts (biotite, sanidine, quartz, augite etc.). Volcanoclastic mineral composition and mineral chemistry of analyzed tephra layers strongly suggest a high-K calc-alkaline (rhyolitic?) volcanic arc as the source of tephra. Grain size composition and content of calcite classify Bunarić sample as clayey silt and Gornji Ždanj sample as calcareous silty clay (KONTA, 1969 classification scheme). Performed soil mechanic tests data clearly imply high compressibility, high swell aptitude and wide range of plastic state of analyzed bentonites.

clay mineralogy; soil mechanics properties; crystalloclasts; origin; Maovice (Dalmatia; Croatia)

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