| Abstract (english) | The NW part of Croatia represents a tectonically complex area at the junction of the Dinarides and the Southern Alps. In Očura Quarry on Ivanščica Mt. there is 34 m thick section composed of volcanic, volcaniclastic and carbonate rocks that can be divided into three parts. The lower interval (7 m) is composed of dominantly basaltic rocks (SiO2 = 43–51 wt%). In the basal part glomeroporpyric basalt is followed by basaltic autoclastic breccia. The second interval (7–19 m) is composed of cm–dm irregularly and wavy bedded calcarenites, occasionally coarsening upward, with lithoclasts varying in size from fine sand up to fine breccia. Carbonate lithoclasts are mostly micritic limestones – biomicrite, pelmicrite, pelsparite, intrasparite, also bioclasts of bivalves, crinoids, ammonoids, brachiopods, and gastropods. Two types of basaltic lithoclasts are present in the dominantly calcarenite interval, one with the porphyric to glomeroporphyric texture, similar to the basalts of the lower part; and the other type completely hyaline. Lithoclasts are cemented by sparry calcite. In the coarser varieties lithoclasts are the same, with the only difference in the matrix found between the clasts, that is composed of fine calcarenites with basaltic lithoclasts. Calcarenites are interlayered by thin layers of biomicrites with filaments and radiolarians, and thin layers of fine to coarse ash vitriclastic tuffs. In the middle of this interval around 1.5 m thick matrix supported breccia occurs with limestone and basaltic lithoclasts. Third interval of the section (19–34 m) is composed of extremely unsorted breccia with slump texture. Clasts of limestones, calcarenites, and subordinary basalts are supported by fine grained matrix of carbonate and basaltic particles. Abundant framestone clasts are present in the breccia, containing complex reef community, dominating of sponge Celyphia zoldana, with other microorganisms of uncertain taxonomy Plexoramea cerebriformis and Olangocoelia otti, and others. Generally in this interval carbonate material is predominant over basaltic lithoclasts. The investigated section represents sedimentation in the deeper marine environment near the steep edge of the carbonate platform and reef. Basalts found at the base of the section present effusions in the marine areas, and their fragmentation and reworking. A thick interval of calcarenites with basaltic lithoclasts is formed by shedding of the carbonate material from the nearby platform to the pelagic/basinal areas, indicated by the pelagic limestone interlayers. Chaotic breccia with meter sized fragments of reefal limestones indicates a more proximal position to the shallow marine area from which these clasts were derived. Slump texture emphasizes gravitational processes. The general trend of coarsening upward, as well as the predominance of the framestone clasts in the breccias imply the progradation of the platform over the basinal areas. Therefore, indicating a relatively rapid closure of the basinal/pelagic areas and cessation of the extensional tectonics related to the Neotethyan rifting. One sample (OD-15A) bears conodonts Gladigondolella tethydis (Huckriede), Paragondolella trammeri (Kozur), that indicate Illyrian to Lower Longobardian age of this section. That age is in the accordance with the regional cessation of the volcanic activity in the Ladinian, and progradation of the platforms over the basinal areas that were filled with various clastic, volcaniclastic, silicious and pelagic sediments. |
