Geology Reference
In-Depth Information
division was 5 mm, making frequent use of photo-
mosaics, and varying the optical conditions to opti-
mize lamina visibility. In Obi84, the thickness of
the last 140 laminae was measured in at least three
traverses and the mean value determined.
A representative piece of the top cm of sample
Obi84 was ground into a powder in a pestle and
mortar and analysed using a Siemens D5000 X-ray
diffractometer in transmission geometry. Data
were collected in 0.028 steps with a counting time
of 11 s/step over the range 2u 108 to 808 using Cu
Ka radiation. Rietveld refinement was carried out
in the software GSAS (Larson & Von Dreele 2000).
The electron backscatter diffraction (EBSD)
analyses were acquired using the HKL Channel 5
analysis system on the Philips XL30CP scanning
electron microscope (SEM) in the School of Geo-
Sciences, University of Edinburgh. The SEM was
operated at an accelerating voltage of 20 kV and a
c. 2 nA beam at a working distance of 20 mm and
a tilt angle of c. 708. The sample was given a final
colloidal silica polish to remove surface crystal
damage after mechanical polishing and the sample
was used uncoated with the SEM operating at a con-
trolled pressure of 0.1 mbar to minimise any char-
ging effects. For each point the diffraction pattern
was collected and solved by the software for the
calcite crystal structure to within ,18. Maps for
the orientation of the crystal structure of the
sample were generated from point analyses col-
lected every 1 mm over a 2 2 grid of maps each
c. 500 mm wide and which were subsequently tiled
together to form the final map. The whole map
was then processed to highlight any variation in
orientation
(Fairchild & Treble 2009). We also required
samples from different seasons. There are signifi-
cant logistical difficulties in accessing the cave
chambers regularly and this had only been possible
(monthly) during a previous intense period of moni-
toring (Sp¨tl et al. 2005). We checked the collection
of (unacidified) waters which had been collected up
to three years previously and, where the samples
were intact, acidified them to release all trace
metals into solution. An Agilent single-collector
instrument was used for dissolved powders and
waters, supplemented by a high mass-resolution
Axiom instrument for S and P analysis of dissolved
speleothem powders, as reported in Frisia et al.
(2005). Both solutions from speleothem powders
(50 mg in 100 mls solution) and acidified waters
were analyzed in a matrix of 2% Aristar-grade
HNO 3 . Standardization procedures are as reported
in Borsato et al. (2007) and all reported results are
well above calculated detection limits with analyti-
cal precision of 5%.
Ion microprobe analysis at the Edinburgh Ion
Microprobe Facility (EIMF) was carried out under
a variety of experimental conditions using polished
gold-coated samples. One sub-set of analytical work
was summarized by Smith et al. (2009), with more
examples being given here. This employed similar
methods to those of Fairchild et al. (2001) and
Borsato et al. (2007), using a Cameca ims-4f instru-
ment, with a primary 20 nA beam of diameter
c. 30 mm. Each of the three stalagmite samples
was bombarded with a primary O 2 beam leading
to sputtering of secondary ions of 1 H þ , 23 Na þ ,
26 Mg þ , 31 P þ , 44 Ca þ , 88 Sr þ and 138 Ba þ which were
measured. The step scan mode was used to
analyse the sample at approximate 5 mm intervals,
with ions being drawn from an area with an approxi-
mate diameter of 8 mm. Measurements were taken
along linear traverses at 5 or 10 mm intervals.
Precision of results for most elements is typically
1 - 5% (but worse for H and Na whose analyses
are regarded as semi-quantitative because of vari-
able surface effects); Mg, Sr and Ba were referred
to a carbonate standard (Oka) and other elements
to an apatite standard (Durango) with agreement
within 10% of mean bulk analyses as determined
by Borsato et al. (2007).
Sample Obi84 was also analysed on the Cameca
ims-1270 instrument at the EIMF under three differ-
ent experimental conditions using a primary Cs þ
beam to generate negative secondary ions. Precise
analysis of 13 C/ 12 C ratios was carried out in two ses-
sions in February and May 2005. The primary beam
current was 30 nA (February) or 40 - 45 nA (May),
and a 50 - 60 mm image field, to yield an elliptical
analytical spot. The area of gold removed is typi-
cally 35 30 mm, but SEM analysis of February
pits showed a pit 13 - 20 20 mm with a narrow
of
the
crystal
structure
within
the
sample.
Samples for stable oxygen and carbon isotope
analysis were micromilled at 100 mm intervals for
all three stalagmites (using methods as in Sp¨tl &
Mattey 2006). Measurements were performed
using an on-line, automated carbonate preparation
system linked to a triple collector gas source isotope
ratio mass spectrometer at Innsbruck University.
Values are reported relative to VPDB standard.
Long-term precision of the d 13 C and d 18 O values,
estimated as the 1s-standard deviation, is 0.06 and
0.08‰, respectively (Sp¨tl & Vennemann 2003).
Methods for water analyses are given in Sp¨tl
et al. (2005).
Elemental analysis by inductively coupled
plasma mass spectrometry (ICP-MS) analysis was
conducted at the NERC ICP-MS facility at Kingston
University UK, on drilled sub-samples from stalag-
mites and on selected water samples. We needed to
use water samples that had been collected within
a 24 hour period because colloidally transported
trace elements tend to bind to the surfaces of
tubing and collection vessels over longer periods
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