Geology Reference
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Fig. 7. Trends in S and P in the last few years of growth of sample Obi84. The horizontal scale is distance rather than
time since infiltration laminae were not clearly visible in this section, but the P peaks match the lamina widths in a
laterally adjacent profile (but note poor P peak in 1996 and double peak in 2000). S displays low intervals partly
overlapping and partly following P peaks, and also displays a distinct downward inter-annual trend; likewise dripwater
sulphate declined by 25% between 1999 - 2003 in S¨ulenhalle (Sp¨ tl et al. 2005).
Mapping of elemental distribution across event
laminae was carried out within a zone in the
sample that was also subsequently used for the
EBSD analysis of Figure 2. Figure 10a illustrates a
map of several annual layers with Pb enrichments,
and the boxed area was analyzed at ultra-high resol-
ution (Fig. 10b). The results obtained require some
knowledge of the physics of X-ray fluorescence
generation for their interpretation. The spectrum
(Fig. 10c) reflects the excitation of various elements
by radiation with energy of 2.9 keV. The sensitivity
of excitation decreases rapidly at lower energies and
is not high enough to excite Ca, so the consistent
total ion flux is used to justify an assumption that
the element records are concentrations. Normally,
only K-shell excitation is expected, but if the con-
centration of an element is high, L- and even
M-shell excitation can occur. Since the Pb is abun-
dant in the sample and the M-shell signal lies
fairly close to the excitation energy, this technique
proved especially sensitive for Pb. Zn L-shell exci-
tation also proved much stronger than Na K-shell
excitation (Fig. 10c), but was much less responsive
than the Pb peak. P and Mg Ka radiation could
also be detected. A key point is that the use of soft
X-rays causes excitation very close to the sample
surface and so generates a sharply defined truly
2-dimensional map, so the sample offers excep-
tional clarity of the distribution of Pb.
Figure 10b illustrates two features. Running
horizontally across the maps is the position of the
infiltration lamina. Within a broad zone in the
centre of the map enrichment in Pb, Zn and P can
be seen. It is hard to discern a similar enrichment
in Mg, but this peak is weaker and Mg in any case
does not normally show the annual pattern quite as
distinctly as P (Fig. 8a). This broad zone is 15 -
20 mm high compared with the 80 - 150 mm thick-
ness of the entire annual layers in Figure 10a and
therefore only forms during a subordinate part of
the year (perhaps 1 - 3 months). Within the enriched
zone, two continuous peaks in Pb (and less distinctly
in Zn and P) are visible 1 - 2 pixels (i.e. 1 - 2 mm)
across. Based on the annual growth rate, the narrow
metal peaks must represent individual events of at
most a few days duration when Pb and other ele-
ments were flushed onto the stalagmite. Also visible
in Figure 10b are structural features running NE -
SW across the maps. These have the same dimen-
sions as the crystallites of Figure 2c and Figure 3b
and so demonstrate a different chemical compo-
sition associated with the flat crystal faces of
Figure 3b compared with the rough surfaces that
surround them (corresponding also to the zigs and
the zags of laminae in Figs 3a & 4a).
Obi84 was also studied using hard X-ray
synchrotron excitation, with energy of 23 keV, on
a portion of the sample just below the very top
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