Dating an ancient spring tunnel using archaeological artefacts functioning as nuclei of cave pearls

Cave pearls are spherical concentric speleothems growing radially around nuclei in shallow pools saturated with calcite. They are very rare in the Southern Levant. We present a unique assemblage of 50 cave pearls found in the Iron Age Joweizeh artificial spring tunnel in the Jerusalem Hills of Israel. Some of these deposits represent the first global evidence of formation on archaeological artefacts: pottery sherds and ancient plaster. Multi-analyses were conducted to date and characterize the different nuclei and pearls. Charcoal samples extracted from the plaster nuclei of two pearls were ¹⁴C dated to the Hellenistic period. Two pearls were formed on sherds of Hellenistic lamps. XPS found Co colour remains, suggesting both had been imported. The Hellenistic date is also supported by archaeomagnetic dates of seven other pottery nuclei. Most Hellenistic remains are probably the outcome of a renovation campaign in the tunnel. Four pearls were sampled for stable isotopes (δ¹³C and δ¹⁸O). The range of δ¹⁸O values from the Joweizeh pearls is compatible with the Holocene Soreq and Jerusalem caves’ records. The δ¹³C differences between Joweizeh and Soreq indicate local changes in the overlying vegetation throughout history. The various lines of evidence enabled us to characterize the pearls’ formation process, reconstruct the Joweizeh spring tunnel's hydraulic environment and detect changes that occurred in its water flow regime throughout history.