| Popis: |
The U-series dating of young and dirty speleothems is challenging due to difficulties in assessing the isotopic composition of contaminating detrital fractions and the low- abundance of the in situ-generated 230Th. Here we propose a new dating approach based on the comparison of magnetic directions recorded by speleothems with reference curves from global paleomagnetic reconstructions. The studied stalagmite was collected in the Soprador do Carvalho cave, in the Central Region of Portugal. The radiometric age model, built using four U-series ages and three 14C, suggests relatively steady carbonate precipitation from ~ 5760 BCE until ~ 1920 CE. Forty-five, 6 mm-thick, subsamples were submitted to alternating field and thermal demagnetization, providing well-defined, primary magnetic directions. An archaeomagnetic age model of the stalagmite was obtained by fitting its paleomagnetic record with the reference paleosecular variation curves obtained by previous paleo-reconstruction models, applying statistical bootstrapping analysis to define their best fit. The resulting archaeomagnetic age models fit closely with the radiometric age model but provide a significantly higher time resolution. We reach the same conclusion when applying this approach to another stalagmite from the Algarve region of Portugal. Archaeomagnetic age models thus appear a promising alternative to date dirty speleothems. |
