Triassic Radiolarites from Mts. Kalnik and Medvednica (Northwestern Croatia)

Abstract

Bedded radiolarites of Mt. Kalnik are of Carnian-Norian age, while similar rocks of Mt. Medvednica are of Late Ladinian - Carnian age, as determined on the basis of radiolarian assemblages. Radiolarites from Mt. Kalnik concordantly rest upon the pillow-lavas, or are interbedded with them. Their footwall at Mt. Medvednica is not known, due to tectonic reduction. The sedimentary rocks described were deposited from low-density turbidity currents, therefore representing fine-grained turbidites. They were deposited closely below, and partially above the CCD. Results of petrological, sedimentological and geochemical investigations indicate sedimentation under terrigenous influence with contemporaneous hydrothermal activity. The studied sections are correlated with the nearest outcrops of Triassic radiolarites associated with basic effusive rocks, i.e. with the Vardar Zone and the Meliata Unit.