Geology Reference
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elements ...', failed to specify its size, and did not
provide an illustration. Thus, the morphology of
cave microbes, at least from a microbiological
perspective, is now deemed of secondary impor-
tance in their description, characterization, and
classification.
Boring
Boring microbes commonly infest and destroy
calcite crystals that line near-surface cavities in
the karst terrains of the Cayman Islands (Jones
1987). In contrast, Jones (1995) did not find any evi-
dence of endolithic microbes in substrates collected
from the twilight zones of various caves on the
Cayman Islands. New samples collected from the
twilight zone of the Old Man Village cave,
however, did reveal the presence of boring microbes
(Fig. 2f-l). That borings were found in these
samples but not in previous samples probably
reflects issues of sampling for features that are so
variable even on a microscale.
Borings in the calcitic substrates from the twi-
light zone of the Old Man Village cave, which are
up to 10 mm in diameter, start beneath the biofilm
(Fig. 2f ) and penetrate to depths of 1 mm
(Fig. 2g- j). Some borings contain calcified masses
that may be preserved remnants of the formative
microbe (Fig. 2j). Boring appears to have been
mediated by etching as the walls of the borings are
characterized by highly irregular microtopographies
that display features indicative of dissolution
(Fig. 2k, l). The lack of morphological features pre-
cludes definitive identification of the microbes that
formed the borings.
Migration and colonization
As the microbial biotas of caves become better
known and characterized it is also becoming appar-
ent that similar taxa are present in caves that are geo-
graphically distant and isolated from each other. In
other words, as asked by Jones (1965), 'How did
the algae get into the speleo-environment ...'. As
yet, the mechanism by which the same or related
microbes colonize different, geographically dispa-
rate caves has not been resolved. Microbes are, by
definition, very small (commonly ,1 mm long)
and hence easy to transport. Thus, any assessment
of the role that microbes may play in the formation
of speleothems must first ascertain if the microbes
are residents that thrive in the cave or simply 'detri-
tus' that were transported into the cave. Claus
(1955), for example, suggested that microbes may
be carried into caves by streams, air current,
animals (e.g. bats), and/or water that gradually
seeps into the cave. Similarly, caution must also
be exerted against contamination of samples
during sampling and/or microbes that migrated
into a sample, via cracks; long after the substrate
was originally precipitated (Barton et al. 2001).
Opening caves for public viewing of the prehistoric
art work, for example, has commonly led to signifi-
cant problems because this has disturbed atmos-
pheric equilibrium in the caves as humidity, CO
2
content of the air, and air temperature were modified
and bacteria, fungi and algae were introduced (e.g.
Lefevre & Laporte 1969). In many cases, microbes
have been implicated in the deterioration of histori-
cally significant cave paintings (e.g. Giacobini et al.
1987; Monte & Ferrari 1993; Groth et al. 2001).
Dissolution
Dissolution of calcitic substrates, mediated by
microbial biofilms, commonly produces, spiky
calcite (Fig. 3a-c), irregular etching (Fig. 3d),
blocky calcite (Fig. 3e, f ), and/or residual calcite
(Fig. 3h, i). Such features are evident in natural
samples (Jones 1987, 1989, 1995; Ca˜averas et al.
2001) and have also been produced experimentally
by allowing fungi to grow on crystals of Iceland
Spar (Jones & Pemberton 1987a, b). Dissolution
of this type, which commonly follows the crystallo-
graphic precepts of the substrate, is typically slow
and probably reflects surface-reaction-controlled
kinetics (cf. Berner 1978). Such etching is mediated
by the biofilm and does not involve vast quantities
of water.
Residual calcite (¼ sparmicrite of Kahle 1977) is
a common byproduct of substrate breakdown caused
by boring and dissolution (Fig. 3h, i). Irregular
etching of a substrate, for example, produces monti-
culi (small islands still connected to substrate by
narrow neck) that will eventually break away from
the substrate and form individual grains (Jones &
Pemberton 1987b; Jones & Kahle 1995). Water
Microbial destruction of substrates
Cave walls are commonly covered with biofilms
(Fig. 2) that mediate substrate destruction through
boring and dissolution (Ca˜averas et al. 2001;
Jones 2001). Such processes release Ca and CO
3
back into the system, cause breakdown of the host
substrate, and may generate residue micrite that
can be transported to other parts of the cave (Jones
& Kahle 1995).
Fig. 2. (Continued) and calcite crystal (arrow). Note borings (below arrow) penetrating calcite crystal. (h, i) Borings in
calcite crystal just below surface biofilm. ( j) Enlarged view of borings in calcite crystal. (k) Borings extending from
outer surface (upper part of image) into calcite crystals. Note etched surfaces on the borings. (l) Etched surface of boring.
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