Evaporite minerals suggesting multiple submergence of a stalagmite from Kvarner region (Croatia)

We present the preliminary results of mineralogical analyses of submerged speleothem collected within the project SEALeveL (HRZZ-IP- 2019-04-9445) funded by Croatian Science Foundation. The ML-12 stalagmite was collected 12 m below the water table in a submerged coastal cave on Lošinj Island. Several orange layers are visible on the longitudinal cross section of the stalagmite. A thin section was prepared for investigation by petrographic and scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) system. Prior to SEM analysis, the freshly-cut surface was also analysed by X-ray fluorescence (XRF) analysis. Oil was used for thin section preparation to avoid dissolution of highly soluble minerals. Optical inspection showed reduction in crystal size and relatively high porosity within the orange-coloured layers indicating a change in depositional environment.. XRF analysis show the presence of chlorine, sulphur and silicon bearing minerals in these orange layers but not in the clean calcitic parts. SEM inspection of these layers show presence of several minerals in the pores within this orange layer. Chemical composition obtained by EDS analysis suggests that these minerals are quartz, halite, gypsum, muscovite, hematite, and an unidentified phosphate. Especially halite, but also gypsum are highly soluble minerals that are abundant in solute form in the sea. This indicates that the sea might have played a key role in the speleothem formation environment and deposition of the minerals found in the orange layers. The formation of the orange layers might have been as well controlled by sea- level oscillations. Further analysis is necessary to confirm such hypothesis.