Luminescent microbanding in speleothems: High-resolution chronology and paleoclimate

When illuminated by ultraviolet light, many calcite speleothems (stalagmites, stalactites, flowstones) display luminescence caused by the presence of organic (humic) substances occluded in the calcite. The amplitude of luminescence varies in a banded pattern parallel to growth layering. Through ¹⁴C and thermal ionization mass spectrometry uranium-series dating, we show that cyclical oscillations in the luminescence have periodicities ranging from a few days to ≥10⁵ yr. A well-defined annual cycle is present in many vadose-zone speleothems and can be used to define the chronology of short-term events. This cycle is probably a response to hydrological events in the recharge to the cave. Longer term oscillations are inferred to be controlled by climate, through its effect on organic activity in the overlying soil.