U-Th and radiocarbon dating of calcite speleothems from gypsum caves (Emilia Romagna, North Italy)

Andrea Columbu, Russell Drysdale, John Hellstrom, Jon Woodhead, Hai Cheng, Quan Hua, Jian xin Zhao, Paolo Montagna, Edwige Pons-Branchu, R. Lawrence Edwards

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Abstract

High-resolution U-Th and 14C dating of two calcite flowstones (RTf: Last Interglacial; RTy: Late Holocene) from the Re Tiberio – Monte Tondo karst system (North Italy) is presented to investigate the palaeoclimate potential of speleothems from gypsum caves. To date, there is a lack of information regarding the dating potential of calcite speleothems that have grown in such gypsum karst environment (e.g. no pseudokarst). High-resolution U-Th dating, aimed at establishing if these speleothems can provide robust radiometric age sequences, is first presented. Although both samples show promise for reliable radiometric dating, about 20% of the ages in the RTf dataset were excluded from the age-model as outliers. These outliers are best explained by post-depositional diagenetic processes affecting the U-Th system rather than anything specific to gypsum karst environment conditions. In contrast, outliers were not detected in the RTy sample, but U-Th analysis was not able to constrain its relatively young age (∼600 years before present, B.P.). Consequently, radiocarbon measurements were undertaken, and combined with the U-Th ages to build an age-model. The latter allowed the estimation of “dead carbon fraction” (DCF), which yields a constant value through time, and a magnitude comparable to other sites where climate is similar to Monte Tondo. Soils were considered the main source of carbon, because bedrock dissolution acted predominantly under open-system conditions, and soil organic matter (SOM) turnover rate appears above average compared to sites studied elsewhere.

Original languageEnglish (US)
Pages (from-to)51-62
Number of pages12
JournalQuaternary Geochronology
Volume52
DOIs
StatePublished - Jun 2019

Keywords

  • Evaporite karst: Gypsum caves
  • Palaeoclimate
  • Radiocarbon
  • Speleothems
  • U-Th dating

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    Columbu, A., Drysdale, R., Hellstrom, J., Woodhead, J., Cheng, H., Hua, Q., Zhao, J. X., Montagna, P., Pons-Branchu, E., & Edwards, R. L. (2019). U-Th and radiocarbon dating of calcite speleothems from gypsum caves (Emilia Romagna, North Italy). Quaternary Geochronology, 52, 51-62. https://doi.org/10.1016/j.quageo.2019.04.002