Geology Reference
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considered them to be subaqueous pool structures
because they: (1) hang down from shelfstone that
formed around the edge of cave pools; (2) are the
same colour as the shelfstone; and (3) are absent at
levels above the shelfstone. Pool fingers from
Hidden Cave, New Mexico, USA, which have a
rough outer surface with knobs 10-20 mm wide
that extend outward for 1-10 mm, are internally
laminated with layers of dark micrite alternating
with layers formed of clear dogtooth calcite crystals
(Melim et al. 2001). Individual micrite laminae are
variable in thickness, largely because local protru-
sions extend outward for 50-150 mm (Melim et al.
2001, figs 6A-C). Needle fibre and dendrite calcite
crystals commonly form between the micrite
patches. Two types of calcified filaments were
found in the micrite layers, but not in the layers
formed of dogtooth spar calcite. These filaments
c. 1 mm in diameter and 5-50 mm long, include
forms that have a smooth exterior (Melim et al.
2001, figs 7A-B) and forms that display a crosshatch
surface texture (Melim et al. 2001, figs 7C-D). The
identity of these microbes and especially the one
with the crosshatch surface texture remains open to
debate (Melim et al. 2008).
On the basis of: (1) internal fabrics that are
similar to microbialites; (2) the presence of minera-
lized microbes; and (3) the consistent depletion of
d 13 C in the micrite layers relative to the spar
layers, Melim et al. (2001) argued that bacteria
exerted a strong influence over the growth of the
pool fingers and largely controlled their internal
and external morphology.
debate. In many cases the possibility that microbes
played a role in their formation was automatically
excluded because it was assumed that algae could
not grow in the absence of light (Donahue 1965,
1969; Gradzinski & Radomski 1967). In other situ-
ations, failure to detect microbes has been used as
evidence for an abiogenic origin of the pisoliths
(e.g. Nader 2007).
Cave pisoliths from Old Man Village (Jones &
MacDonald 1989), up to 8 cm long, have laminated
cortices that are commonly characterized by lami-
nated, outward expanding columns (Fig. 7). The
presence of mineralized spores (Fig. 7a-h), mucus
(Fig. 7h, i), and calcified filamentous microbes
(Fig. 7i-l) in the cortices of these pisoliths raises
the possibility that microbes influenced growth of
the pisoliths by being direct contributors, trapping
and binding of detrital grains brought into the
spring pools, and possibly by indirectly mediating
calcite precipitation. Gradzinski (2001, 2003), for
example, suggested that cave pisoliths grow as
calcite is precipitated due to the metabolic activity
of bacteria that reside in the mucilaginous biofilm
that coat the surfaces of the pisoliths.
Moonmilk
Moonmilk, found in caves throughout the world, is a
whitish, porous, plastic deposit formed of crystals
and water (White 1976; Hill & Forti 1997). The
crystals may be formed of many different minerals,
including calcite, aragonite, monohydrocalcite,
vaterite, huntite or gypsum (Onac & Ghergari
1993; Ca˜averas et al. 1999; Borsato et al. 2000;
Ca˜averas et al. 2006; Mart´nez-Arkarazo et al.
2007). Calcitic moonmilk is typically formed of
long, fiber crystals (Borsato et al. 2000; Ca˜averas
et al. 2006), including crystals known as lublinite
(Krischtafowitsch 1906; Morozewicz 1907, 1911;
Muegge 1914; Ulrich 1938; Kowalinski et al.
1972; Stoops 1976). Bernasconi (1981) and Jones
& Kahle (1993), however, recommended abandon-
ment of the term lublinite.
Calcitic moonmilk has been attributed to both
biogenic and abiogenic origins. The debate over
the role of microbes in the formation of moonmilk
has arisen because filamentous microbes and/or
bacteria are commonly associated with these depos-
its (Mason-Williams 1959; Bertouille 1972; James
et al. 1982; Dziadzio et al. 1993; Ca˜averas et al.
1999; Mulec et al. 2002; Ca˜averas et al. 2006).
Some studies have suggested that the long fibre
crystals form through the calcification of bacterial
cells (Gradzinski et al. 1997), as coatings on fila-
ments (Moore & Bukry 1968), or by dissolving the
bedrock and thereby generating the CaCO 3 needed
for calcite precipitation (G`ze et al. 1956; G`ze &
Pob´guin 1956).
Cave pisoliths
These coated grains (also known as 'cave pearls',
'oolites'), which are typically formed of a nucleus
that is encased by concentrically laminated cortical
lamina, have been reported from caves in Australia
(Baker & Frostick 1947, 1951), Austria (Kirch-
mayer 1969, 1987), Belgium (Li´geois 1956), the
Cayman Islands (Jones & MacDonald 1989), Cuba
(Gradzinski & Radomski 1967), Norway (Erdman
1902), Ireland (Coleman 1949), North America
(Hess 1930; Stone 1932; Keller 1937; Pond 1945;
Black 1952; Thrailkill 1963), Lebanon (Abdul-Nour
1991; Choppy 1991; Karkabi 1991; Nader 2007),
and Poland (Barcyzk 1956; Gradzinski 1999).
These coated grains have been divided into:
(1) spherical to subspherical forms with a polished
exterior and distinct, compact cortical lamina that
typically grow in highly agitated splash pools; and
(2) irregular shaped forms with a rough, unpolished
surface and indistinct, porous lamina that form in
pools where there is little agitation.
The role that microbes may play in the growth
and development of cave pisoliths is open to
In the absence of microbes,
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