engleski

Late Albian Silicification Event(s) in Istria, Croatia

In the NW part of the Adriatic Carbonate Platform (AdCP), in Istria region, during Late Albian diagenetic silicification occured. Silicification took place within the peritidal carbonate sequences comprising intertidal carbonate breccias and laminated cyanobacterial limestones, as well as subtidal mudstones peloidal wackstones/packstones. Three silicified layers can be traced, more or less continuously, along the 30km traverse. According to their position in the sedimentary column and to their geometry, they are interpreted as three possible events of aeolian input of silica (volcanic ash) to carbonate platform environment. Sedimentological, mineralogical and geochemical analysis were performed on the samples from the silicified layers (ranging from 15cm to 2m in thickness), as well as from the related limestones and marls/clayey limestones. Silicification changed primary carbonate sediments in places almost completely and formed so-called "quartz diagenetic sediments" (up to 98% of SiO2), which contain several types of quartz (idiomorphic authigenic quartz, microcrystaline quartz aggregates, chert-like clusters). Distributions of microelements and REE indicate differences of the silicified layers from surrounding limestones. Insoluble residues of clayey limestones predominantly contain illite-smectite minerals, together with quartz, some feldspars and amorphous material. These results support assumption about the input of the source material for silicification to carbonate platform. Current investigations (SEM) should give additional informations about the source and mechanisms of silicification.

Late Albian; silicification; Istria; Croatia

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