Age of the Jurassic hemipelagic sediments from the Ljubiš area (Zlatibor Mt., SW Serbia)

The type section of the Ljubiš Formation, (Djokov Potok, Zlatibor area, western Serbia) is characterized by abundant poorly-to-moderately preserved radiolarians. The lower part of the type section is characterized by Middle Jurassic (? Bajocian to Bathonian) radiolarian assemblages with Japonocapsa fusiformis (YAO), Takemuraella weghae (GRILL & KOZUR), Eoxitus hungaricus KOZUR, E. baloghi KOZUR, Helvetocapsa matsuokai (SASHIDA), Quarkus japonicus (YAO), Hexasaturnalis suboblongus (YAO), H. tetraspinus (YAO). Taking into account previous data from the upper part of the Ljubiš Formation, the age of the formation can be estimated to be in the interval from the ? Bajocian to Bathonian-Oxfordian. The new biostratigraphic data clearly show the onset of tectonic motion in the Middle Jurassic, documented by the presence of mass transport deposits intercalated in the radiolarite successions. This suggests a Middle Jurassic onset of ophiolite obduction which triggered the rapid deepening of the Adria margin, documented by the abrupt change from carbonate to radiolarite deposition. needs careful analysis of all sedimentary deposits, including their biostratigraphy, facies, history of deposition, and tectonic events. In recent work GAWLICK et al. (2017), SUDAR & GAW­ LICK (2018) and GAWLICK & MISSONI (2019) propose a new stratigraphic scheme for the Triassic and Jurassic of the Inner Di­ narides. Numerous stratigraphic series (formations) were ana­ lyzed: some of them were revised, others were established for the first time. Radiolarite formations in this scheme are most com­ mon in the Middle and Upper Jurassic deposits. Biostratigraphic data of these numerous formations are variable. In some instances they are very comprehensive, while in the other cases they are scarce or rare. Some formations still have only limited biostrati­ graphic control and their stratigraphic positions were determined by indirect methods. GAWLICK et al. (2017) recently proposed a late Middle Jurassic to Late Jurassic age for the Ljubiš Forma­ tion, but the dating was not precise due to poor preservation of the radiolarians. During the 2015 field season, we studied the reference sec­ tion of the Ljubiš Formation (sensu GAWLICK et al., 2017) in Djokov Potok, and present here the first biostratigraphic data from these sedimentary rocks based on radiolarians. 2. GEOLOGICAL OVERVIEW The research area is situated in SW Serbia, in Ljubiš Village on the eastern flanks of Mt. Zlatibor. The wider area is characterized by a rather complicated structure. According to SCHMID et al. (2008), it comprises the Adria-derived Drina-Ivanjica (DIU) and East Bosnian-Durmitor Units (EBDU), with the West Vardar ophiolites superimposed on top, i.e. presently located between the DIU to the northeast and the EDBU to the southwest (Fig.1). Both Adria-derived units (Drina-Ivanjica and East Bosnian-Dur­ mitor) being thrust by the ophiolitic mélange during the Late Ju­ rassic (SCHMID et al., 2008). The present-day position of the Drina-Ivanjica above the East Bosnian-Durmitor unit is a result of out-of-sequence thrusting during the Cretaceous (SCHMID et Article history: Manuscript received January 24, 2020 Revised manuscript accepted July 29, 2020 Available online October 22, 2020