Petrographic and geochemical study on cave pearls from Kanaan Cave (Lebanon)

Abstract

The Kanaan cave is situated at the coastal zone, north of Beirut City (capital of Lebanon). The cave is located within the upper part of the Jurassic Kesrouane Formation (Liassic to Oxfordian) which consists mainly of micritic limestone. Twenty seven cave pearls were subjected to petrographic (conventional and scanning electron microscopy) and geochemical analyses (major/trace elements and stable isotopes). The cave pearls were found in an agitated splash-pool with low mud content. They are believed to have formed through chemical precipitation of calcite in water over-saturated with calcium. The nucleus and micritic laminae show δ18OV-PDB values of about -5.0‰ and δ13C V-PDB values of -11.8‰, while the surrounding calcite spar laminae resulted in δ18OV-PDB ranging between -5.3 and -5.2‰, and δ13C V-PDB between -12.3 and -12.1‰. A genesis/diagenesis model for these speleothems is proposed involving recrystallization which has selectively affected the inner layers of the cave pearls. This is chiefly invoked by sparry calcite crystals ‘invading’ the inner micrite cortical laminae and the nuclei (cross-cutting the pre-existing mud-envelopes), and the slight depletion in δ18O values from inner to outer cortical layers. The calculated δ18OV-SMOW of the water (-4.2‰) matches with data on meteoric water signature for the central eastern Mediterranean region.

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International Journal of Speleology 36 (1) 39-50 Bologna (Italy) January 2007
Petrographic and geochemical study on cave pearls from Kanaan Cave
(Lebanon)
Fadi H. Nader1
INTRODUCTION
A considerable amount of papers have documented
concentrically laminated grains – termed as cave-
pisoids, or pearls – found in low energy rimstone
pools and high energy splash pools in caves (e.g.
Baker & Frostick, 1947; Gradzinski & Radomski,
1967; Donahue, 1969; Jones & Kahle, 1986;
Jones & MacDonald, 1989; Hill & Forti, 1997 and
references herein; Gradzinski, 2001). Only a very
few contributions, strictly descriptive, have reported
similar cave speleothems from the Middle-East (e.g.
Abdul-Nour, 1991; Choppy, 1991; Karkabi, 1991). This
contribution presents results of the rst petrographic
and geochemical studies on cave pearls found in
Lebanon – collected from the Kanaan cave (central
Lebanon). New data about the formation of this type
of speleothems in a typical Mediterranean setting is
provided. Also, the various controlling factors on the
genesis and growth of cave pearls with a special focus
on the inherent role of diagenesis are discussed.
Nader F.H. 2007. Petrographic and geochemical study on cave pearls from Kanaan Cave (Lebanon).
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). ISSN 0392-6672.
The Kanaan cave is situated at the coastal zone, north of Beirut City (capital of Lebanon). The cave is located within the upper part
of the Jurassic Kesrouane Formation (Liassic to Oxfordian) which consists mainly of micritic limestone. Twenty seven cave pearls
were subjected to petrographic (conventional and scanning electron microscopy) and geochemical analyses (major/trace elements
and stable isotopes). The cave pearls were found in an agitated splash-pool with low mud content. They are believed to have formed
through chemical precipitation of calcite in water over-saturated with calcium. The nucleus and micritic laminae show δ18OV-PDB values
of about -5.0‰ and δ13C V-PDB values of -11.8‰, while the surrounding calcite spar laminae resulted in δ18OV-PDB ranging between
-5.3 and -5.2‰, and δ13C V-PDB between -12.3 and -12.1‰. A genesis/diagenesis model for these speleothems is proposed involving
recrystallization which has selectively affected the inner layers of the cave pearls. This is chiey invoked by sparry calcite crystals
‘invading’ the inner micrite cortical laminae and the nuclei (cross-cutting the pre-existing mud-envelopes), and the slight depletion in
δ18O values from inner to outer cortical layers. The calculated δ18OV-SMOW of the water (-4.2‰) matches with data on meteoric water
signature for the central eastern Mediterranean region.
Keywords: Speleothems, diagenesis, aggradational crystal growth, δ18O, Lebanon.
Abstract:
Received 5 May 2006; Revised 14 October 2006; Accepted 14 November 2006
GEOLOGICAL BACKGROUND
Lebanon covers 10452 km2 of surface area and
stretches along the central eastern coast of the
Mediterranean Sea (Fig. 1A). Geomorphologically, it
consists of two mountain chains (Mount-Lebanon
and Anti-Lebanon) separated by a high inland plain
(the Bekaa; Fig. 1A). The western chain (Mount-
Lebanon) borders the Mediterranean Sea, displaying
relatively gentle slopes on its western anks and
steeper ones on its eastern anks. The highest point
in Lebanon is located in the northern part of this
mountain chain; i.e. the Qornet es Saouda, 3083 m
above sea level (asl). Precipitation (rain and snow)
falls in abundance on the Lebanese mountain chains,
especially on Mount-Lebanon. The precipitation
rate varies between 700 and 1200 mm/year with
increasing elevations (i.e. higher altitudes) across
Mount-Lebanon, and about 80% of the yearly
precipitation falls from November through February
(Edgell, 1997).
Carbonate rocks (limestone and dolostone)
dominate the known Lebanese rock succession.
The oldest exposed rocks are of Liassic age (part of
the Early-Middle Jurassic Kesrouane Formation;
Dubertret, 1975). The Jurassic strata constitute
Available online at www.ijs.speleo.it
International Journal of Speleology
Ofcial Journal of Union Internationale de Spéléologie
1 Department of Geology, American University of Beirut, PO
Box: 11-0236/26 Beirut, Lebanon
Spéléo-Club du Liban, PO Box: 70-923 Antelias, Lebanon.
E-mail: fadi.nader@aub.edu.lb
Paper presented during the 14th International Congress of Speleology, Kalamos (Greece) 21-28 August 2005.
21-28 AUGUST
2005
Anniversary
40th

40
the cores of the Mount-Lebanon and Anti-Lebanon.
The Cretaceous strata – especially the Cenomanian-
Turonian Sannine and Maameltain Formations
– form the anks of the mountain chains, covering
most of the country surface-area. The stratigraphy
of Lebanon has been investigated by a number of
authors; e.g. Dubertret (1955), Saint-Marc (1974
and 1980), Walley (1997), Beydoun (1988), and
Nader (2000).
The Late Jurassic is characterized by a period
of regional uplift, emergence and erosion. Upon
emergence, the Jurassic rock-mass was deeply
fractured and karstied before volcanism took place.
Subsequently, volcanic deposits and continental
debris lled-up the pre-existing fractures and
depressions accentuating the palaeotopography
(Renouard, 1955; Nader et al., 2003). During the
Cretaceous times, the Early Jurassic strata were
buried to a depth reaching 3 km (Nader et al.,
2004). The nal uplift of Mount-Lebanon mainly
occurred during the Oligocene (Dubertret, 1975;
Nader & Swennen, 2004). Since the Miocene, the
morphology of Mount-Lebanon was not very different
than that of today (Dubertret, 1975; Walley, 2001).
Subsequently, karstication, part of the meteoric
diagenesis processes, is expected to have affected
the exposed Mount Lebanon at least since that time
(i.e. Miocene).
KANAAN CAVE SETTINGS
The Kanaan cave is located in the Kassarat area
to the east of the coastal town of Antelias, a few
kilometers north of Beirut City (capital of Lebanon;
Fig. 1B). The cave is located within the deeply
and intensively karstied rocks of the Kesrouane
Formation (Fig. 1B). The deepest known sinkholes
(Houet Fouar ed Dara, -622 m and Houet Qattine
Azar, -450 m) as well as the longest cave in Lebanon
(Magharet Jeita, 9 km) are found within this rock
unit. The Kanaan cave was discovered in 1997, when
its entrance became exposed during rock-quarrying.
The entrance is situated at around 100 m above sea-
level, almost at the foot of a steep limestone cliff with
a height exceeding 150 m (Fig. 2A). The monotonous
blue-grey (fossiliferous) micritic limestone lithology
characterizing the Kesrouane Formation (Dubertret,
1975; Walley, 1997) is, nevertheless, disrupted with
minor clayey/marly horizons – in some places evidence
supporting paleosols and subaerial exposure were
also suggested (see Nader & Swennen, 2004). A marly
horizon, rich in brachiopods, including relatively thin
seams of coal, was observed underlying the Kanaan
cave entrance and its underground network. This
horizon provides a local, impermeable substratum for
karstication, playing an important hydrogeological
role with respect to the cave speleogenesis.
The Kanaan cave, which amounts to some 120 m
Fig. 1. Simplied topographic map of Lebanon (A) – inset map showing the position of Lebanon in the Levant Region. (B) Geological map showing
the location of the Kanaan cave – modied from Dubertret (1955) and Walley (1997).
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Fadi H. Nader

41
of underground passages and chambers, is divided
into three parts (Fig. 2B): (i) the Entrance, (ii) the Mud
Gallery, and (iii) the Calcite Gallery. The cave entrance
overlies a rock-collapse slope (quarrying debris) and
forms an articial direct access (due to quarrying) to
a room with a high chimney, hosting a community
of bats. A low passage trending northward leads to
another room with another chimney (ca. the Northern
Chamber, Fig. 2B). The Mud Gallery is named after
the considerable amount of mud existing in this part
of the cave forming small hills of slippery mud. Here,
relatively thick rock slabs (with thickness exceeding
1 m) collapsed from the cave-ceiling. These massive
limestone rocks lay randomly on the cave-oor that
is covered with mud. The southernmost part of the
Kanaan cave, the Calcite Gallery, is loaded with a
wide variety of speleothems. It consists of a big hall
with a high ceiling (more than 20 m) and a lateral
development with reverse “7” shape (see Fig. 2B). The
oor is calcitic and overlies brown mud that is similar
to the mud found in the Mud Gallery). A wide diversity
of speleothems is observed (stalagmites, stalactites,
helictites, ‘curtains’, owstones, rimstone pools,
among others). The investigated cave pearls were
collected from the middle part of this hall (Fig. 2B;
Fig. 3A, B). Here, the calcitic oor is wet and includes
small depressions hosting cave pearls (Fig. 3C, D). To
the opposite side, a relatively large, but shallow, water
pool exists (Fig. 2B).
MATERIAL AND METHODS
Twenty-seven cave pearls were collected from the
Kanaan cave. Petrographic observations included
conventional microscopy and scanning electron
microscopy. Ca, Mg, Na, Sr, Fe, Mn, Zn, and K
concentrations in powdered samples, micro-drilled
from the various concentric growth layers within cave
pearls, were analyzed by ame atomic absorption
spectrometry (AAS). Powdered samples (1g of each)
were leached in 40 ml (1 molar) HCl and left on
hot plates until evaporation – the strength of the
acid was chosen to be as low as possible in order
to leach the minimum possible quantity of the non-
carbonate fraction. The residues were dissolved for a
second time in 20 ml (1 molar) HCl, then ltrated and
diluted before AAS analysis. Analytical precision was
generally better than 10 % at the 95% condence level,
Fig. 2. The Kanaan cave, Antelias – central Lebanon: (A) Photograph showing the cave entrance, photo facing east – photo by Hughes Badaoui;
(B) cave survey showing the three distinct sections and the location of the cave pearls (from Nader, 1998).
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Petrographic and geochemical study on cave pearls from Kanaan Cave (Lebanon)

42
and the detection limit was 1 ppm. Water, sampled
from the cave pools, was also subjected to chemical
analyses (including Ca, Mg, Na, Sr, Fe, Mn, Zn, and K
concentrations). Various diagenetic phases were micro-
sampled for measurement of their carbon and oxygen
stable isotopic composition. Stable isotope analyses
were done at the University of Erlangen - Germany
(Institute of Geology and Mineralogy). The carbonate
powders were subjected to reaction with phosphoric
acid (density >1.9; Wachter & Hayes, 1985) at 75°C
in an online carbonate preparation line (Carbo-Kiel
- single sample acid bath) connected to a Finnigan
Mat 252 mass-spectrometer. All values are reported
in per mil (‰) relative to Vienna Pee Dee Belemnite
(V-PDB). Reproducibility based on replicate analysis
of laboratory standards is better than ±0.02‰ for δ13C
and ±0.03‰ for δ18O.
KANAAN CAVE PEARLS
The approach followed by Jones & MacDonald
(1989) to characterize cave pearls according to their
size and shape, external appearance, nucleus, and
cortical laminae is applied here as well. The observed
and collected Kanaan pearls range in size from about
1 to 3 cm (with rare exceptions exceeding 5 cm; Figs.
3 & 4). The shape of these cave pearls varies between
spherical, subspherical (with one side almost at),
and ellipsoidal forms. Some of them are attached to
the calcitic oor (Fig. 3C, D). The great majority of the
observed cave pisoids show an external smooth, well-
polished, lustrous morphology (Fig. 3C) – advocating
their classication as ‘cave pearls’ (Baker & Frostick,
1947; Donahue, 1969; Hill & Forti, 1997). Less
commonly, some cave pearls show rough, irregular
crenulated surfaces made up of tiny trigonal calcite
crystals (Fig. 4).
The majority of the cut and polished cave pearls
show distinct, relatively spherical nuclei (Fig. 5). Only
a few samples revealed elongated ellipsoidal nuclei
irrespectively of the external shape of the cave pearls.
The nuclei are relatively small with respect to the cave
pearls (less than 10 mm; Fig. 5). Yet, a relatively thick,
yellowish aureole usually surrounds the nucleus. The
investigated cave pearls revealed several concentric
growth layers around the nuclei. These cortical
laminae consist of a repetition of grayish translucent
and massive milky white laminae (Fig. 5). The number
of these growth zones (and their thickness) is not
related to the size of the cave pearls (Fig. 5).
PETROGRAPHY
Five thin-sections were prepared out of the twenty-
seven sampled cave pearls. The thin-sections were
stained with alizarin red S, conrming that the cave
pearls consist only of calcite. They were examined
with conventional microscopic techniques.
The thin-sections show two types of cave pearl
nuclei. In the rst group, the nucleus is elliptical
in shape. It consists of terra-rossa with some pyrite
(opaque minerals shining under induced light)
and probable organic matter as well as oxides/
hydroxides (yellowish-brown stained material; Fig.
6A). In the second group, the nucleus is made up of
clear micritic, anhedral calcite crystallites including
clear calcite spars (Fig. 6B, C). Relatively thin, dark
cortical laminae envelop the nucleus displaying
micritic calcite and a considerable amount of terra-
rossa. In both cases, the nucleus is surrounded by
an aureole of darkish (impurity-rich) micritic calcite.
It is worth mentioning that the second group of cave
pearls clearly shows under polarized view a divergent
outward, pseudo-uniaxial cross extinction (Fig. 6D),
resulting from the convergent fabric of elongated
columnar or “palisade” length-fast calcite crystals
(cf. Kendall & Tucker, 1973; Folk & Assereto, 1976).
The cortical laminae which are close to the nucleus
(inner laminae) consist of micritic calcite crystals
(often trigonal in shape; Fig. 7A, B). Here the
intercrystalline porosity is occluded with impurities
(probably terra-rossa, clay and/or organic matter).
The outer cortical laminae consist of elongated,
radial, sparry calcite crystals (size exceeding 1
mm; Fig. 7C, D) similar to length-fast (palisade)
calcite crystals (cf. Folk & Assereto, 1976), with the
original intercrystalline porosity occluded by other
generations of calcite spars. Similar crystal fabrics
were called ‘feather-like calcite crystals’ by Gradzinski
& Radomski (1967) and ‘dendrite calcite crystals’ by
Jones & MacDonald (1989). Alternatively, the growth
competition may have resulted in similar textures
where some crystals did not grow fast as the others,
and remained of smaller sizes due to lack of space
(Fig. 7C, D). Fig. 8A shows the transition from inner
micritic calcite cortical laminae to outer sparry calcite
laminae. A faint syntaxial growth is revealed, as the
same extinction is displayed. The impurity-rich thin
layer (mud-cover) separating these cortical laminae
show a discontinuous pattern, where extensions
of the sparry calcite crystals prevail (Fig. 8B). This
pattern – i.e. the local removal of impurity-rich thin
laminae – suggests that recrystallization during
and/or after the sparry calcite formation must have
occurred.
The external morphology of the cave pearls was
mainly investigated through scanning-electron
microscopy (Fig. 9A, B). The calcite crystals of the
outermost growth layer display a general trigonal
morphology (crystal size: 150 to 500 µm). Further
investigation show that the apexes of these crystals are
rhombohedra faces that are combined to the trigonal
prism faces (Fig. 9A, B). This crystalline framework
results in a considerable amount of intercrystalline
porosity (Fig. 9A). Further investigations of the
calcite crystals revealed that they consist of several
generations of smaller, embedded trigonal crystals
welded together (Fig. 9B). This could be viewed as
an aggradational crystal growth, keeping the same
crystalline morphology and leading to larger crystals.
Note that the sharp extremities of the trigonal crystals
are often broken, probably due to corrosion induced
by movement of the pearl.
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Fadi H. Nader

43
Fig. 3. Photographs showing the spot where the cave pearls where found (A, B) (Photos by Sami Karkabi). Macrophotographs showing the cave
pearls at a closer zoom (C, D). Note that some pearls are well polished (C) others are more or less crenulated (D).
Fig. 4. The twenty-seven cave pearls collected from the Kanaan cave. The sizes of the cave pearls range between 1 and 3 cm.
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Petrographic and geochemical study on cave pearls from Kanaan Cave (Lebanon)

44
Fig. 5. Scanned polished cut-faces of some cave pearls from the Kanaan cave. Note that [QA1] and [QA2] are not from the Kanaan cave – these
are added for reference.
Fig. 6. Photomicrographs illustrating the main petrographic characteristics of the cave pearls’ nuclei: (A) plane- transmitted light photomicrograph
showing a nucleus made-up of brownish terra-rossa, surrounded by clear micritic calcite cortical laminae; (B) plane- transmitted light
photomicrograph showing a nucleus made-up of clear micritic calcite and a spar, surrounded with brownish impurities-rich laminae; (C) crossed-
polarized photomicrograph showing (B) at a slightly higher magnication – note the uniaxial extinction continuum from the spar through the micritic
calcite crystallites and the inner cortical laminae; (D) crossed-polarized photomicrograph showing crystal continuum from the nucleus through the
inner micrite laminae to the outer spar laminae.
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Fadi H. Nader

45
Fig. 7. Photomicrographs illustrating the main petrographic characteristics of the cave pearls’ cortical laminae: (A, B) plane- transmitted light
photomicrographs showing the ne micritic trigonal calcite crystals – note the dark spots are impurities (Fe-oxides/hydroxides) within intercrystalline
porosity; (C, D) crossed-polarized photomicrographs showing the calcite spar laminae with elongated dendritic crystals – note that some crystals
are of smaller sizes and seem embedded within the calcite spars.are added for reference.
Fig. 8. Photomicrographs showing the transition from inner micrite laminae
to outer spar laminae: (A) Crystalline continuum from nucleus to outer
layer – note that the mud-envelope is not continuous and faint under
crossed-polarized view; (B) transmitted light photomicrograph showing the
“purication” of the mud-envelope by the calcite spars, see text for details.
Fig. 9. SEM Photomicrographs showing crystal microfabrics of the
external (outermost) layers of the cave pearls: (A) trigonal calcite
crystals with rhombohedral apexes and a considerable amount
of intercrystalline porosity; (B) aggradational growth of trigonal
crystallites within larger trigonal crystals – see text for details.
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Petrographic and geochemical study on cave pearls from Kanaan Cave (Lebanon)

46
GEOCHEMISTRY
Table 1 shows the major and trace element
composition of the only water sample (A) collected
from the rimstone pool located opposite to the
location of the pearls (cf. Fig. 2), the inner and outer
parts of the cave pearls and a typical spelean calcite
from a nearby coastal cave (B). Table 2 shows the
δ18O and δ13C results (in ‰ V-PDB) of the cortical
laminae from four different cave pearls. The stable
isotopic values of a recent spelean calcite (less
than 30 years old; precipitated in a tunnel dug in
1971) are also added as a reference for the actual
isotopic signature of speleothems in central coastal
Lebanon.
Temperature measurements inside the cave were
conducted during several visits. The air temperature
in the Calcite Gallery (cf. Fig. 2B) is constantly about
20°C, while the water temperature – measured in the
rimstone pool opposite to the location of the pearls,
cf. Fig. 2B – is about 18°C with a pH of 7.65. The cave
water has a calcium concentration ranging between
54.6 and 57.1 wt.%, hence it is over-saturated with
Ca. The same water possesses about 10 ppm of Na,
about 1 ppm of Sr. The measured Fe, Mn, Zn and K
concentrations in the pool-water were all below the
detection limit.
The inner and outer layers of the cave pearls
display almost the same Ca concentrations (ca.
about 36.4 wt.%). The inner layers show a relatively
high Na content (54 ppm) with respect to that of the
outer layers (37 ppm). The Sr, Fe, Mn, Zn, and K
contents are almost the same for inner and outer
layers, and they are higher than those of the cave
water (see Table 1A, B). The insoluble residue (IR%,
after dissolution in 1 molar HCl) is slightly higher for
the outer layers (1.2 wt.%) with respect to that of the
inner layers (1.7 wt.%). When compared to similar
trigonal spelean calcite from a nearby coastal cave,
Ca and Fe contents in the cave pearls are found
higher, while Na and Sr concentrations are much
lower, respectively. The higher Na and Sr values
could be related to sea-water incursions into that
coastal cave.
Figure 10 is a crossplot featuring the δ18O versus
δ13C values for the cortical lamina from different cave
pearls collected from the Kanaan cave (Table 2). The
data show clearly a decreasing trend for both δ18O and
δ13C from inner to outer cortical layers. The average
oxygen isotopic values of the inner layers are in the
order of -5.0‰ V-PDB, and the corresponding δ13C
Fig. 10. Oxygen versus carbon isotopic compositions of the nucleus and various cortical laminae from four different cave pearls (Kanaan cave; data
from Table 2).
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Fadi H. Nader

47
values are around -11.8‰ V-PDB. The outer layers
exhibit δ18O values ranging between -5.3 and -5.2‰
V-PDB, and δ13C between -12.3 and -12.1‰ V-PDB.
Recent spelean calcite (wall owstone), collected
from the tunnel dug in 1971 in Jurassic limestones
in order to reach the underground network of a
nearby Jerita cave, reveals an average δ18O value in
the order of -6.1‰ V-PDB and δ13C value around -
9.1‰ V-PDB. While this oxygen isotope signature
is lighter than those recorded in the Kanaan cave
pearls, the carbon isotopic value is less depleted.
DISCUSSION
According to Baker & Frostick (1947) and Donahue
(1969) the Kanaan spherical to subspherical
concretions, which have smooth (polished) and
lustruous shining surface, may be termed “cave pearls”
and are believed to have formed in agitated water.
Donahue (1969) related the genesis of ooid and pisoid
grains to the prevailing energy (agitated versus non-
agitated conditions). The ‘agitated grains’ were, thus,
characterized by distinct concentric laminations, a
pseudo-uniaxial cross (under polarized view), nucleus,
smooth polished surfaces, low insoluble residue. All of
these characteristics match well with the investigated
cave-pearls.
Some of the Kanaan cave pearls contain nuclei
surrounded with yellow-brownish aureoles (Fig.
5). These are impurity-rich micritic calcite cortical
laminae directly enveloping the nucleus. Such pearls
usually include a nucleus with preserved terra-rossa.
They do not display uni-axial cross under polarized
light. The impurity-rich nucleus and lamina in some
pearls could suggest the presence of organic matter
as well as clay and oxides/hydroxides. However, their
occurrence is relatively limited when compared to the
overall volumes of the investigated pearls. Jones &
MacDonald (1989) have discussed some similar micrite
laminae in spearls from a cave in the British West
Indies. These authors suggested seven alternatives
for the origin of the micritic calcite; out of which
several scenarios could also work for the Kanaan cave
pearls – e.g. inorganic precipitation from cave water,
formation of destructive coatings, and/or formation
of constructive envelopes. The role of bacteria in the
genesis of the Kanaan cave is refuted based on: (1) the
cave pearls were found in splash-pools where water
Fig. 11. Graphical display of the oxygen isotopic equilibrium relationship between water, temperature of precipitation and calcite minerals (Woronick
& Land, 1985). Estimation of the δ18O composition of the water from which the cave pearls precipitated for temperatures between 18 and 20°C. The
bar on the horizontal axis represents the estimated range for δ18OV-SMOW composition of the calcitizing uid (ca. -4.2‰ V-SMOW).
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Petrographic and geochemical study on cave pearls from Kanaan Cave (Lebanon)

48
motion is considerable and agitation prevails, and (2)
no fungal laments or algal mats have been observed
(Jones & MacDonald, 1989; Gradzinski, 2001). Yet,
advanced calcication (and recrystallization) may have
effectively destroyed pre-existing bacterial patterns.
The clear micritic calcite crystallites, devoid of
impurities, and the presence of sparry calcite crystals
with extinction pattern similar/uniaxial to the length-
fast crystals in the surrounding cortical laminae (see
Figs. 6 and 7) advocate for recrystallization phases
that are believed to have occurred after the formation
of the nucleus. This also suggests that the uni-
axial cross pattern could be associated with some
degrees of recrystallization of the pearls, especially
when length-fast calcite crystals are observed in the
nucleus and the different cortical lamina (Fig. 7A,
B). The spar calcite laminae consist of elongate fast-
length calcite spar crystals including some other ner
crystals (Fig. 7C, D). This fabric may be explained
by growth competition, whereby some crystals grew
faster than the others in a radial, outward direction
(e.g. Fig. 6D). Alternatively, the spars were formed
and then the inter-/ intracrystalline porosity was
occluded by another phase of calcite cement. The
“feather-like arrangement” (Gradzinski & Radomski,
1967) has been observed where the nucleus is
made up of calcite micrite and spars rather than
terra-rossa. Here, the spars seem to invade the
inner cortical laminae and the nucleus (Fig. 6). In
addition, the mud envelopes (impurity-rich thin
layers thought to have covered the pearl during its
growth) are incorporated within the length-fast sparry
calcite crystals (Fig. 8). Such envelopes appear like
‘ghost’ inclusions within the calcite and may invoke
recrystallization. The sparry calcite represents rapid
growth from supersaturated solutions, in response
to certain temperature conditions (Jones & Kahle,
1986; Jones & MacDonald, 1989). The water in the
Kanaan cave’s rimstone is highly saturated with Ca
(about 56 wt.%) and its temperature is about 18°C
and the pH around 7.65.
The outermost l
ayers of the investigated cave
pearls consist of crystals having rhombohedra
apexes combined to trigonal prism faces, where a
considerable amount of intercrystalline porosity
remains preserved. Similar crystalline fabrics to the
ones discussed by Jones & MacDonald (1989) are
observed in the Kanaan cave pearls. The prismatic
trigonal crystals reveal through SEM investigation
that they consist of crystallites displaying similar
trigonal morphology (Fig. 9B). This aggradational
crystal growth, with ner crystals welded together
to form coarser crystals, invokes the role of
recrystallization as well. Trigonal crystals are believed
Fig. 12. Simplied schematic illustration describing the major genetic and diagenetic characteristics of the Kanaan cave pearls (inset photo shows
two polished cut faces of cave pearls – note the darkish yellow, impurity-rich nuclei aureoles).
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Fadi H. Nader

49
to form exclusively in meteoric vadose environments
where the uids are low in Ca/Mg ratios, have low
salinity and through CO2 degassing (Binkley et al.,
1980; Given & Wilkinson, 1985). The actual water
in the Kanaan cave has a relatively high Ca/Mg
ratio, suggesting that its low salinity and especially
CO2 degassing are the controlling factors for the
precipitation of the trigonal crystals. The Jurassic
Kesrouane limestones are characterized by Na
concentrations ranging between 103 and 214 ppm
(Nader et al., 2004), higher than the Na contents
measured in the cave pearls. These rocks have Sr
contents between 110 and 193 ppm (Nader et al.,
2004). Na and Sr concentrations measured in the
investigated cave pearls could have originate from
the dissolution of the host-rock (i.e. the Kesrouane
limestones) and/or clays and impurities. Iron and
manganese contents are believed to be related to
the vadose and near-surface environments (cf.
Lohmann, 1988).
The oxygen and carbon isotope values from the
various layers from four cave pearls showed that
a decrease in both δ18O and δ13C generally prevails
from inner to outer layers. The δ18O depletion could
be related to precipitation from water that has lower
δ18O values, higher temperature or recrystallization
(Lohmann, 1988). Degassing of CO2 may also result
in a depletion in δ13C values (Given & Wilkinson,
1985), this is further supported by the trigonal
crystalline pattern observed at the outer part of the
pearls (see above). The approach of Woronick & Land
(1985) was used in order to estimate the δ18OSMOW of
the uid from which the cave pearls precipitated (Fig.
11). The temperature was set between 18 and 20°C
and the δ18OPDB of the calcite was measured between
-5.33 and -4.94‰. This resulted in δ18OSMOW around
-4.2‰. Note that the δ18O of the meteoric water in
the eastern Mediterranean region ranges between
-6 and -4‰ V-SMOW (Emery & Robinson, 1993).
Cave pearls Genesis/Diagenesis Model
In general, the nuclei of the investigated pearls show
a yellowish aureole with either terra-rossa (preserved
at the center) or micrite. The original terra-rossa fabric
within the nucleus and the cortical laminae seems
to have been destroyed by calcite crystal formation
and recrystallization. The micrite calcite cortical
laminae which envelope the nuclei, possess relatively
higher δ18O and δ13C values reecting possible
genesis during spelean evaporative conditions, i.e.
CO2 degassing (Gradzinski & Radomski, 1967). The
overlying spar calcite laminae resulted from fast
precipitation in water highly saturated with Ca and
during further degassing of CO2. This is justied by
the relative depletion in δ18O and δ13C with respect to
the inner part of the pearl. Petrographic investigation
suggests the predominance of recrystallization in
some pearls (especially where the nucleus is devoid
of terra-rossa). This is somehow supported by the
corresponding lower δ18O values. Figure 12 shows
two cut-faces of two distinct cave pearls and a sketch
presenting a tentative model explaining the formation
of the cave pearls and their related recrystallization.
After the precipitation of the nucleus and impurity-
rich, inner micrite cortical laminae, the surrounding
spar laminae (length-fast calcite) were formed in
water highly saturated with Ca with enhanced
CO2 degassing. Subsequently, trigonal prismatic
calcite crystals were precipitated on the outermost-
layers. Such process has also triggered selective
recrystallization of the inner layers. With each new
concentric layer added some inner layers would
have severed some degrees of (re)crystallization; e.g.
destruction of mud envelopes, occlusion of porosity
and crystal aggradations
.
CONCLUSIONS
Based on petrographic and geochemical data of some
cave pearls from the Kanaan cave (Jurassic, central
Lebanon), the following points can be concluded:
1. The environment of cave pearl formation consists
of an agitated splash-pool, with low mud content.
2. The formation of the cave pearls is believed to
be due to chemical precipitation of calcite in a uid
over-saturated with calcium – here biogenic related
precipitation is dismissed. The internal nucleus and
micritic laminae (δ18OV-PDB: -5.0‰; δ13 CV-PDB:-11.8‰)
include impurity-rich calcite crystal framework; while
the surrounding length-fast calcite spar laminae
(δ18OV-PDB: -5.3 to -5.2‰; δ13CV-PDB: -12.3 to -12.1‰)
have precipitated from water with low salinity,
highly saturated with Ca and during enhanced CO2
degassing.
3. A model for the formation of the Kanaan cave
pearls is proposed involving recrystallization which
has selectively affected the inner layers of the cave
pearls during the growth of the successive outermost
layers.
4. The calculated δ18OV-SMOW of the water (-4.2‰)
matches with data on meteoric water signature for the
central eastern Mediterranean region.
ACKNOWLEDGEMENTS
The author is grateful to Joanna Doummar (Dept. of
Geology, American University of Beirut, AUB – Lebanon)
for assistance in the eldwork and in the petrographic
analyses. Dr. Rudy Swennen (Katholieke Universiteit
Leuven, KUL – Belgium) is thanked for his support,
without which this contribution would have never
been succeeded. Dr. Michael Joachimski (University
of Erlangen – Germany) is thanked for performing the
isotopic analyses. H. Nijs (KUL – Belgium) and M. Ijreiss
(Dept. of Geology, AUB – Lebanon) are also acknowledged
for the technical assistance. This work is partially
sponsored by the Katholieke Universiteit Leuven (Afd.
Fysico-chemische geologie). The Spéléo-Club du Liban is
acknowledged for providing data related to the Kanaan
cave (central Lebanon). Critical reviews and valuable
comments made by Dr. Calaforra, an anonymous
reviewer and the editor (Dr. De Waele) have improved the
presentation and content of this contribution, and are
greatly appreciated.
International Journal of Speleology, 36 (1), 39-50. Bologna (Italy). January 2007
Petrographic and geochemical study on some pearls from Kanaan Cave (Lebanon)

50
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