A multi-radionuclide approach for in situ produced terrestrial cosmogenic nuclides: ~(10)Be, ~(26)Al, ~(36)Cl and ~(41)Ca from carbonate rocks

摘要

In contrary to siliceous environments, there is a severe lack of cosmogenic nuclides, that can be used for in situ dating of calcareous environments. Thus, we have investigated other nuclides than ~(36)Cl as possible dating tools by cross-calibration. Cosmogenic ~(10)Be is highly contaminated with atmospheric ~(10)Be and cannot be removed quantitatively, even by a very sophisticated chemical cleaning procedure. Only working on clay-free calcite provides correct ~(10)Be data, giving a 2.7 times higher production rate of ~(10)Be from CaCO_3 than from SiO_2. Though, the production rate of ~(26)A1 is only ～4.6% (CaCO_3 relative to SiO_2), ~(26)A1 can be easily determined in calcite, as the low intrinsic ~(27)Al concentration yields to nearly as high ~(27)Al/~(27)A1 as within corresponding quartz. The measurement of ~(41)Ca, mainly produced via thermal-neutron-capture, is hindered by very low ~(41)Ca/Ca:<5 × 10~(-15).