Speleothem Palaeosecular Variation Records from China: Their Contribution to the Coverage of Holocene Palaeosecular Variation Data in East Asia

抄録

Five stalagmitic speleothems from two caves in Sichuan province China, have yielded data on the palaeosecular variation (PSV) of the past 8.9 ka. The uranium-thorium disequilibrium method has been utilised in order to estimate the age of each record. Due to the high detrital load contributing some allogenic thorium, age corrections had to be applied to most sub-samples. The directional agreement between coeval central and lateral sub-samples where growth layers are horizontal and steeply dipping respectively suggests that inclination errors are absent in these speleothems. Correlation between features of declination and inclination in the individual records, even after time-averaging, are reasonable indicating a local consistency in recorded PSV and adding to the reliability of the palaeomagnetic and age data. Comparisons between our speleothem directions and the directions of the modern field drifted westward past our site at 0.13° yr^-1 suggests westward drifting of non-dipole sources during the past 2.8 ka. Using directional data from two speleothems with the longest growth periods a composite curve covering the past 8.9 ka has been constructed. The resulting VGP path again indicates predominantly westward drift. The declination and inclination features of these speleothems also compare reasonably with features of PSV in contemporaneous records from China and Japan.