| Popis: |
Phreatic overgrowths on speleothems (POS), a secondary depositional structure (carbonate phreatic encrustation) which precipitates at the water table around pre-existing vadose speleothems if favourable geochemical conditions are acquired. Since the POS precipitate at the very top of the water column, i.e. at the water-air interface, their occurrence is limited to a very narrow band of the tide-induced groundwater level fluctuation. POS can be precisely dated with U-Th as well as with radiocarbon method, and their occurrence in caves guarantees protection from weathering. The combination of their narrow occurrence, datability, and preservation makes POS excellent sea-level indicators. So far, it has been used in sea-level research in only several locations in the world while most of the investigated sites are located in Mallorca. Recently, within the project SEALeveL (HRZZ-IP- 2019-04-9445) funded by Croatian Science Foundation, phreatic overgrowths on speleothems (POS) have been discovered in Croatian coastal caves. Since the POS investigation is the first of that kind in the Adriatic, information on their morphology, conditions and time of deposition, will contribute to a better understanding of the POS as sea-level indicator and will allow comparison with results from other parts of the Mediterranean basin. We present the preliminary results of U-Th dating and XRD, XRF analyses of POS samples from Šipun Cave (Cavtat, southern Dalmatia) and Medvjeđa špilja Cave (Lošinj island, Kvarner region) which resulted in first relative sea-level index point 3000 years, indicating a relative sea-level stability for a few hundred years 1 m below modern sea level. |
