Speleothems are formed under conditions where water becomes oversaturated with calcite. This can occur above the water table, where vadose speleothems form, and below the water table leading to formation of phreatic speleothems. Speleothems serve as a useful archive material for a variety of processes and enable high-resolution reconstruction of paleoenvironmental conditions. In the current study, we compared speleothems formed during overlapping periods (6-9 Ma) in two caves in the Ma'ale Meyshar region of the Israeli Negev Desert. The upper cave where the vadose speleothems were found is located 630 m asl, approximately 150 meters higher than the lower cave where phreatic speleothems (mamillaries) formed the same time, showing that during the Late Miocene the water table was located between the two caves.

Eight samples were used for clumped isotopes analysis. The measurements from four mammillary layers in the lower cave indicate that the temperatures in the groundwater varied between 39˚C±2˚C to 52±2˚C. Four measurements of the flowstone layers in the upper cave show temperatures ranging from 24˚C±3˚C to 36±4˚C. The paleotemperatures below the groundwater level cannot be explained by deep burial of the cave applying the geothermal gradient, therefore indicating that hydrothermal activity took place there. It seems that this hydrothermal contribution is consistent in the phreatic aquifer of the studied region during the Late Miocene. That may be linked to increased water circulation along Arif-Batur fault zone.