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development of a large air inclusion (Fig. 3a). Some
years show a more complex structure in which two
or three such laminae are found close together,
although the optical imaging of these is complicated
by internal reflections (Fig. 4a). The zig-zag shapes
have dimensions consistent with those of the crys-
tallites in Figures 2c and 3b. Laterally, some
laminae may become diffuse and apparently are
composed of a zone of fluid inclusions, locally
inclusions forming vertical trains at crystallite
margins. These areas are interpreted as representing
places where crystallites coalesced just below the
growth surface (as in Kendall & Broughton 1978).
In Obi84, which was collected in December
2002, the latest visible lamina lies very close to
the top surface (Fig. 3a), implying that it formed
in the autumn. In the review of Fairchild et al.
(2007), we presented a similar figure to Figure 3a
and identified these features as infiltration
laminae, implying a formation by infiltration of
water excess (Fairchild et al. 2006a), but we now
regard this interpretation as not proven, and here
use the term 'event laminae' instead. By event
lamina we mean a layer deposited in relation to a
specific time-limited set of processes.
Re-nucleation horizons are present in each of the
three samples and are sufficiently prominent as to
suggest they each represent a hiatus in growth.
However, it is notable that the hiatuses do not
contain enrichments in insoluble residues or signs
of corrosion, and so are distinct from those that
represent significant time gaps in speleothems
(Tan et al. 2006). Indeed, close study of the promi-
nent event shown in Figure 4c reveals that, locally,
growth continues through the event, and that it is no
more than two or three years in duration (Fig. 4d).
The prominent hiatus in Obi84 occurs at the level
of the 1834 - 1835 A.D. laminae around 23 mm
below the top, whereas in Obi55 there is one just
9 mm from the top and in Obi12 at 12 mm from
the top. Since the statistical analyses of Smith
et al. (2009) show that the growth rate of each
stalagmite is similar, the hiatuses are clearly of
different ages in each sample.
Fig. 4. Stalagmite petrology. (a) Sample Obi 84, transmitted light, illustrating two annual infiltration laminae. The lower
one illustrates three (arrowed) sub-laminae plus internal reflections, whereas the upper one is a single lamina. The fibrous
sub-vertical structure of crystallites is seen to correspond to the zig-zag lamina structure. (b) Sample Obi84. Arrow
illustrates hiatus between infiltration laminae for the years 1889 and 1890. To the left of the arrow the hiatus disappears. To
the right (the stalagmite flank) various laminae converge to give more prominent hiatus (i.e. renucleation) surface. (c, d)
Sample Obi12. (c) Prominent hiatus surface with box (0.9 mm long) showing location of photo d. (d) enlargement of
hiatus, illustrating local area where growth continued throughout (arrows indicate individual annual infiltration laminae).
The hiatus itself, although very prominent in photo c, is only of three or four years duration.
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