Borna Lužar-Oberiter

Variable sources of beach sands of north Adriatic islands: examples from Rab and Susak

The composition of beach sands from the Islands of Rab and Susak (northern Adriatic) has been studied in order to determine how individual beaches are supplied with detritus. The beaches on both islands are composed of quartz dominated siliciclastic sand, with subordinate carbonate content. Three end-member heavy mineral assemblages have been identified among the studied beach sands, each one associated with a specific source rock: (1) a garnet dominated assemblage and (2) a zircon, rutile and tourmaline dominated assemblage on Rab Island, as well as (3) an assemblage dominated by unstable minerals on Susak Island. Sands from individual beaches contain one of these specific assemblages or display a mixing of two varieties. The end-member assemblages are very comparable with those of Eocene and Pleistocene sediments which crop out on the two islands, identifying them as the principal sources of detritus. Cretaceous and Eocene carbonate rocks, although present to a considerable extent in the study area, has shown to be a negligible source of sandy material. Thus, the supply of detritus to the beaches is primarily controlled by erosion of siliciclastic rocks in the immediate or nearby hinterland.

Provenance of Paleozoic very low- to low-grade metasedimentary rocks of South Tisia (Slavonian Mountains, Radlovac Complex, Croatia)

Abstract Monazite age dating, detrital heavy mineral content and whole-rock geochemistry provided insight into the provenance, depositional history and paleogeological setting of the Radlovac Complex very low- to low-grade metasedimentary rocks (South Tisia, Slavonian Mountains, Croatia). Electron microprobe based Th-U-Pb dating of detrital monazite indicates a Variscan age of the protolith (330 ± 10 Ma). The detrital heavy mineral assemblages of representative metasedimentary rocks are dominated by apatite, zircon, tourmaline and rutile accompanied by minor quantity of epidote/zoisite, monazite and titanite. Judging from the heavy mineral assemblage, felsic igneous rocks served as the source material. This is consistent with the major and trace element spectrum of studied metasedimentary rocks characterized by high concentration of Th, high L + MREEs and high ratios of La/Sc, Th/Sc, La/Co, Th/Co and Th/Cr. The occurrence of magmatic monazite, zircon and xenotime and the absence of metamorphic heavy minerals suggest that granitoids, migmatites and migmatitic gneisses served as one major source for the metapsammites. Such rock types are commonly exposed in the Papuk Complex of the older surrounding complexes, while the Psunj Complex also contains metamorphic rocks. This is in good correlation with the monazite ages presented here which fits better with ages of Papuk Complex representative rocks than with those of the Psunj Complex known from the literature. Overall, data show that the Radlovac Complex represents the detritus of the local Variscan crust characterized by granitoid bodies, migmatites and migmatitic gneisses typical for the Papuk Complex.

Characteristics of Pleistocene aeolian – alluvial sediments of the northern coastal cliff of Vrgada island (Adriatic sea, Croatia)

Aeolian-alluvial deposits on the northern part of Vrgada Island were investigated in order to interpret deposition mechanisms and environmental conditions. Preliminary results of basic sedimentological analyses of 49 samples allowed distinguishing 3 facies along the cliff.

DIGITAL MODELLING OF THE LATE ALBIAN SOLARIS DINOSAUR TRACKSITE (ISTRIA, CROATIA)

Abstract: The late Albian Solaris dinosaur tracksite in Istria (Croatia), which is characterized by an abundance of theropod and sauropod footprints, was surveyed using a combination of GNSS georeferencing, terrestrial laser scanning, and photogrammetry. The entire outcrop was digitally captured with millimeter-scale resolution and high spatial accuracy, allowing both outcrop-scale observations and analysis of fine morphological features at the scale of individual footprints. Quantitative ichnological data acquired from the digital model is equivalent to published results based on traditional methods. Inspection of the digital outcrop model has revealed a number of new tridactyl footprints previously undocumented at the Solaris tracksite. All of the newly identified prints are exceptionally shallow and bear characteristics typical of medium-sized bipedal theropod dinosaurs. The study testifies to how approaches involving digital modelling are able to supplement and improve upon traditional methods of field observation and help revise previous ichnological studies. They can be a particularly effective solution for studying complex, heavily trampled tracksites with highly variable print depths and preservation.

Climatic cycles recorded in the Middle Eocene hemipelagites from a Dinaric foreland basin of Istria (Croatia)

Climatic cycles recorded in the Middle Eocene hemipelagites from a Dinaric foreland basin of Istria (Croatia) Middle Eocene hemipelagic marls from the Pazin-Trieste Basin, a foreland basin of the Croatian Dinarides, display repetitive alternations of two types of marls with different resistance to weathering. This study focuses on the chemical composition, stable isotopes, and palynomorph content of these marls in order to better understand the nature of their cyclic deposition and to identify possible paleoenvironmental drivers responsible for their formation. The less resistant marls (LRM) have consistently lower carbonate content, lower δ18O and δ13C values, and more abundant dinoflagellate cysts than the more resistant marls (MRM). We interpret these differences between the two marl types to be a result of climatic variations, likely related to Milankovitch oscillations. Periods with wetter climate, associated with increased continental runoff, detrital and nutrient influx produced the LRM. Higher nutrient supply sparked higher dinoflagellate productivity during these times, while reduced salinity and stratification of the water column may have hampered the productivity of calcareous nannoplankton and/or planktonic foraminifera. In contrast, the MRM formed during dryer periods which favoured higher carbonate accumulation rates. This study provides new information about the sedimentary record of short-scale climate variations reflected in wet-dry cycles during an overall warm, greenhouse Earth.