9.4.2. Accuracy of the individual records of PS V.
The NRM intensities of both Spanish and Chinese speleothems were low. These low NRM intensities are common in speleothems and have been reported by several workers (Latham et al, 1986, 1989; Perkins and Maher, 1993; Lean et al, 1995 amongst others). The NRM intensity will be a function of the type(s) of magnetic mineral and of their concentrations. These increased errors (derived from magnetometer noise and incompletely nulled field during measurement and demagnetisation) coupled with the measurement of the low NRM intensities have decreased the precision of the directions obtained from some sub-samples. In this study precision was indicated by the MAD
(095
in the case of SC01). It was noted that an increase in directional scatter occurred during demagnetisation of the weakest sub-samples and during the later stages of demagnetisation in the stronger sub-samples. Despite this directional scatter the majority of directions trended towards the origin of the Zijderveld plots after the removal of any VRM. This was interpreted to be the primary remanence in each case.
Unfortunately, none of the Chinese speleothems were of sufficient width to allow double sub-sampling i.e. two parallel vertical slices. This method of sample preparation would allow at least two adjacent coeval sub-samples to be taken from the drip-cap of one central vertical slice (Figure 5.4). A second set of coeval sub-samples could be taken from the drip-cap of the second slice (a method used by Latham et al, 1989 for example). Thus, four directions may be obtained per horizon. Records produced from sampling in this fashion would have allowed a) inter-central slice comparisons b) intra-horizon directional consistency checks and c) a potential reduction in the measurement errors by allowing directions to be combined using Fisher statistics (Fisher, 1953). Limited double sub-sampling of this nature was possible with TR02. The second set of sub-samples were taken from the single vertical slice where the drip-cap was of sufficient width. Unfortunately, because of the weak magnetic signal no reliable directions were obtained.
Tests for the presence of inclination errors within the Chinese and Spanish speleothems were not exhaustive, primarily due to a lack of sufficient lateral material after sub-sampling. However, the tests performed (Chapters 6 and 7) indicated that there
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