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have their long axes at 908 to the filament surface
(Fig. 5b, c, e, h, i). Some filaments appear to be
encased by a double layer of calcite crystals
(Fig. 5b, c). Elsewhere, the same filaments are
host to small crystal rosettes (Fig. 5j). Mucus associ-
ated with these filaments also seems to mediate the
growth of calcite crystals (Fig. 5k, l). This style of
calcification preserves the general form of the
microbe but does not preserve many of the morpho-
logical features that might allow identification in
terms of extant taxa.
The factors that control the morphology of the
calcite crystals involved in the calcification of
microbes is open to debate. The idea that calcifica-
tion style and crystal morphology may be taxon-
specific (Desikachary 1959; Bourrelly 1970;
Riding 1977; Krumbein 1979; Jones & Kahle
1986; Jones 1988; Merz 1992) arises because
some microbes seem to be more susceptible to cal-
cification than others, and different microbes com-
monly display different styles of calcification with
crystals of different morphologies. Nevertheless,
there is also the possibility that the style of calcifica-
tion and/or morphology of the calcite crystals are
controlled solely by environmental conditions such
as saturation levels (Golubic 1973). The former
implies that the microbes, through their metabolic
activities, play a direct role in calcification,
whereas the latter holds that the microbes played
no role in calcite precipitation. This is difficult to
assess as there is so little information that relates
specific microbes to specific styles of calcification
under specific environmental conditions.
filamentous microbes (Fig. 6d, e); (2) the presence
of textures that are consistent with the notion that
growth was achieved by the trapping and binding
of sediment grains to the substrates; and (3) micro-
bes forming a substantial part of the structures
(Jones 2001). Nevertheless, it is virtually impossible
to prove that the microbes played an active role
in the growth and development of the laminated
columns.
Alternating light and dark lamina, calcite micro-
rods, organic inclusions, microbialite-like structures
found in stalactites from various caves in northern
India have been attributed to the trapping and
binding activity of microbes (Baskar et al. 2007;
Baskar et al. 2009). The presence of mineralized
filamentous microbes in some of the stromatolite-
like structures from these stalactites added further
support to this suggestion (Baskar et al. 2007).
Stalactites form Old Man Village cave com-
monly contain small, irregular-shaped micritic col-
umns that radiate from growth surfaces (Fig. 6f, g).
The fact that enveloping calcite layers are deflected
around such structures shows that they were growth
structures that developed as projections from the
exteriors of the stalactites (Fig. 6f ). Although most
of these structures are formed of dense accumu-
lations of micrite, some stalactites have columns
that are formed of diffuse micrite (Fig. 6g).
Despite the lack of lamina in these 'stromatolitic'
columns (Fig. 6a-c), it is still tempting to attribute
their formation to biogenic processes. The fact that
microbes have not yet been located in such struc-
tures, however, makes the case for biogenicity ques-
tionable. Thus, their origin and mode of growth
must remain open to question.
Trapping and binding
Mediation of CaCO
3
precipitation
Microbes, through their metabolic activities, can
encourage CaCO
3
precipitation by modifying the
saturation index (SI) of the solution or by neutraliz-
ing kinetic factors that may inhibit precipitation
(Bosak & Newman 2003, 2005; Barton & Northup
2007). The potential importance of biologically
induced precipitation (Lowenstam 1981; Barton &
Northup 2007) has been well illustrated by the fol-
lowing studies that used laboratory experiments to
show that microbes can induce CaCO
3
precipitation.
† In laboratory experiments, Castanier et al.
(1999) showed that the development of Bacillus
cereus involved a phase of latency that was fol-
lowed by a phase of exponential growth increase
that eventually gave way to steady state bacterial
Filamentous microbes have the capacity to trap and
bind detrital grains to a cave substrate (Cox et al.
1989a, b; James et al. 1994; Contos et al. 2001;
Jones 2001). Ca˜avas et al. (2001), for example,
noted filamentous microbes that were actively trap-
ping and binding micrite grains, animal fragments,
and spores to cave substrates.
The formation of laminated bulbous stromato-
lites is commonly attributed to the filamentous
microbes that trap and bind sediment grains to a sub-
strate. Thus, it is tempting to suggest that the
outward expanding laminated columns found in
some speleothems (Fig. 6a-c) originated through
microbial activity as suggested by Jones &
Motyka (1987). That microbes played an active
role in the growth and development of the laminated
columns can be inferred from: (1) the presence of
Fig. 5. (Continued) forming around filament. ( j) Clusters of calcite crystals associated with filaments. (k) Surface of
calcite crystal covered with mucus, filaments and small clusters of precipitated calcite. (l) Small calcite platelets on
surface of calcite crystal - note consistent orientation of platelets.
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