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Trace element variations in coeval Holocene speleothems from GB Cave, southwest England

Roberts, Mark S., Smart, Peter L., Hawkesworth, Chris J., Perkins, William T., Pearce, Nicholas J.G.
TheHolocene 1999 v.9 no.6 pp. 707-713
atomic absorption spectrometry, barium, calcite, dolomite, hydrology, magnesium, mixing, models, paleoecology, rocks, strontium, temperature, England
We report trace element (Mg, Sr and Ba) records based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) from three coeval Holocene speleothems from Great Chamber in GB Cave, southwest England. The trace element records are placed on a common timescale on the basis of a suite of TIMS ²³⁰Th-²³⁴U ages. This permits assessment of the reproducibility of the trace element record in coeval speleothems. The trace element records are not coherent, raising dobuts over the reliability of individual trace element records as potential archives of palaeoenvironmental information. Mg/Sr in speleothem calcite has been proposed as a potential palaeothermometer as Mg partitioning into calcite from water is temperaturedependent, while Sr partitioning into calcite is temperature-independent. However, we present the results of calculations which demonstrate that the observed Mg/Sr values in the three stalagmites cannot have been produced by Holocene temperature changes alone and that other processes must play a dominant role. We present a model which suggests that the observed trace element variations in the three speleothems reflect hydrological mixing of waters in the epikarstic zone above the cave which have interacted with two geochemi cally distinct source rocks (calcite and dolomite).