Sciences, Technologie & Développement
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Trace elements geochemistry of clay deposits of Missole II from the Douala
sub-basin in Cameroon (Central Africa) : a provenance study
Vol. 13, n°1, 20 – 35
NGON NGON G. F.*, BAYIGA E., NTAMAK-NIDA M. J., ETAME J., NOA TANG S.
Department of Earth Sciences, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon
*E-mail : [email protected]
R. YONGUE-FOUATEU
Laboratory of Applied Geology-Metallogeny, Department of Earth Sciences, Faculty of Science, University of
Yaounde I, P.O. Box 812 Yaoundé, Cameroon
Abstract
Trace and rare earth element (REE) concentrations of the clay deposits of Missole II from the Paleocene-Eocene
N’Kapa Formation in the Douala sub-basin of Cameroon have been investigated to determine their provenance.
To carry out this study, X-ray diffraction and inductively coupled plasma mass spectrometry (ICP/MS) were
performed to determine respectively the mineralogical and chemical data of Missole II clayey materials. Clay
sediments are essentially made up by kaolinite, quartz, illite, goethite, anatase, minor amounts of K-feldspar and
occasionally hematite. The average value of Eu/Eu* (0.5), La/Sc (8.0), Th/Sc (0.99), La/Co (26.9), Th/Co (4.1),
and Cr/Th (8.3) ratios support essentially a felsic rocks source for these clay sediments. Total REE concentrations
of these clay sediments reflect the variations in their grain-size fractions. Chondrite-normalized REE patterns with
LREE enrichment, flat HREE, and negative Eu anomaly are attributed to felsic rocks source main characteristic of
Missole II clay sediments.
Key words: Clay deposits; Cameroon; Douala sub-basin; Missole II; Provenance; Trace elements.
Résumé
Les concentrations d’éléments trace et terres rares des dépôts d’argiles de Missole II de la Formation PaléocèneEocène de N’Kapa dans le sous-bassin de Douala au Cameroun ont été étudiées en vue de déterminer leur source
d’apport. Pour effectuer cette étude, la diffraction des rayons X et la spectrométrie par induction couple plasmamass (ICP/MS) ont été réalisées respectivement pour les analyses minéralogique et chimique des matériaux
argileux de Missole II. Les argiles sont essentiellement constituées de kaolinite, quartz, illite, goethite, anatase,
d’une petite quantité de feldspath potassique et occasionnellement de l’hématite. La valeur moyenne de ratios de
Eu/Eu* (0.5), La/Sc (8.0), Th/Sc (0.99), La/Co (26.9), Th/Co (4.1) et Cr/Th (8.3) soutient essentiellement une
source de roches felsiques. Les concentrations totales en REE de ces sédiments d’argiles reflètent les variations
de leurs fractions granulométriques. Les diagrammes de REE normalisés aux chondrites présentant un
enrichissement en LREE, de faible HREE et d’une anomalie négative en Eu sont attribués à une source de roches
felsiques, caractéristique principale des sédiments d’argiles de Missole II.
Mots clefs: Dépôt argileux, Cameroun, Sous bassin de Douala, Missole II, Source d’apport, Eléments en trace.
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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III.
INTRODUCTION
al., 2004). Among clastic sediments, clay-bearing
In humid tropical region the trace elements
rocks have a much higher concentration of total
more resistant to
trace elements. It is for this reason that the trace
supergene phenomena notably to redistribution due
elements and notably the REE content of the clay-
to
rich sediments are used in order to establish the
are particularly considered
alteration,
weathering
or
the
sediment
transportation and deposition processes (Mclennan
sedimentary
& Taylor, 1983; Condie et al., 1992; Singh &
provenance. Based on this idea we have conducted
Rajamani, 2001a, b). Due to their properties, trace
this study on clay deposits of the Missole II area.
elements and notably REE have already been
Previous studies in this area were focused mainly on
extensively used as tracers of various geochemical
stratigraphy (Njike Ngaha, 1984; Mooh, 2009;
processes (Mclennan et al., 1990; Dupre et al.,
Fowe, 2010) and on the prospection of the useful
1996; Fralick, 1997; Laveuf et al., 2008; Khawar &
clay deposits (Samba, 2010). Studies about the
Noor, 2009). For their high field strength (ionic
geochemistry of clay-rich sediments in the Gulf of
charge/ionic radius) these elements are useful for
Guinea
provenance analysis as they are insoluble and
Cameroonian basins.
usually
immobile
under
surface
basins
This
conditions
processes
are
study
and
rare,
to
identify
particularly
presents
the
in
the
the
geochemical
(Bertolino et al., 2007). Because of their typical
signature of clay deposits of the Missole II area,
behavior
which
during
fractionation,
mineral
weathering
and
and
geochemical
recycling,
they
aims
at
determining
the
sedimentary
processes in order to discern their provenance.
preserve characteristics of the source rocks in the
sedimentary record (Taylor & McLennan, 1985;
IV.
Mclennan et al., 1993, 2003).
GEOLOGICAL SETTING
Immobile elements like Al, Fe, Ti, Th, Sc,
Co, Cr, REEs, and particularly their ratios are useful
tracers of provenance as they are least affected by
processes such as weathering, transport and sorting
(Taylor & McLennan, 1985; Singh, 2009). Th/Sc,
La/Sc, La/Th, Th/Co ratios are especially sensitive
to the nature of source. They are useful to
distinguishing mafic and felsic sources. In fact, Sc
and Co as compatible elements are good tracers of
basic
or
less
fractionated
GEOGRAPHIC AND
source
component
particularly when compared with Th, which is
incompatible and thus enriched in felsic rocks
(Taylor & McLennan, 1985; McLennan et al.,
1990).
Missole II is located on the eastern part of
the Douala sub-basin (Cameroon, Central Africa)
between latitude 3°59’-3°54’ N and longitude 9°54’9°58’ E (Fig. 1). It is located within a humid
equatorial climatic zone. Annual rainfall ranges
between 3000 and 5000 mm, and the annual average
temperature is 26 °C (Olivry, 1986). The vegetation
is a dense rainforest transformed by the human
activities (Letouzey, 1985). The geomorphology of
the study area is a domain of the Cameroon coastal
plain; it has low altitudes (120-40m). This domain
shows hills with flat and sharp summits and is
deeply dissected by V and U shape valleys of
MBongo, Bongougou, Missolo and Bongo the main
Clastic rocks may preserve detritus from
long-eroded source rocks and may provide the only
available clues to the composition and timing of
exposure of such source rocks (Armstrong-Altrin et
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
rivers of the area. According to the geological map
of SNH/UD report (2005), the relative age of the
Missole
II
sediments
is
Paleocene-Eocene
corresponding to the N’Kapa Formation.
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Fig. 1 - Geological sketch map of Cameroonian coastal basins (SNH/UD, 2005)
The study area is linked to the opening of
Nguene et al. (1992), Benkhelil et al. (2002),
the South Atlantic Ocean. Several studies have been
Lawrence et al. (2002) and SNH/UD (2005) report,
done on the opening of the South Atlantic Ocean
three major episodes of the geodynamic and
(Fairhead & Okereke, 1987; Fairhead, 1988;
sedimentary evolution can be differentiated: (i) the
Guiraud & Maurin, 1991, 1992; Maurin & Guiraud,
extensional rift phase in the Early Cretaceous; (ii)
1990, 1993; Pletsch et al., 2001). The theories
the passage from rift to drift phase marked by the
developed suggest that the West African margin
accentuation of the transformed directions resulting
opened like a “zipper” from south to north and did
from a series of cross faults; (iii) the passive margin
not reach Cameroon before the Barremian - Aptian
wedge during the Late Cretaceous and Tertiary.
(Nguene et al., 1992; Meyers et al., 1996; Manga,
The lithostratigraphy of Douala sub-basin
2008). By mid Aptian, the Cameroon margin
consists of seven major Formations related to the
underwent major structural reconfiguration with the
geodynamic and sedimentary evolution (Regnoult,
onset of oceanic transform faulting and their margin
1986; Nguene et al., 1992, SNH/UD, 2005). The
extensions resulting in a segmentation of the rift
syn-rift
structures of the margin (Benkhelil et al., 2002).
Formation (Aptian-Cenomanian) is discordant to the
period
represented
by
the
Mundeck
the
Precambrian basement and consists of continental
northern part of the Cameroon’s Douala/Kribi-
and fluvio-deltaic deposits (coarse sandstones,
Campo Basin, which is located in the Gulf of Guinea
conglomerates). The post-rift sequence includes: the
between the Cameroon Volcanic Line and the Rio
Logbadjeck Formation (Cenomanian-Campanian),
Muni Basin (Equatorial Guinea). According to
discordant to the Mundeck Formation and composed
The
Douala
sub-basin
represents
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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of
sand,
sandstone,
and
Mineralogical examinations were carried
Formation
out on bulk samples using a Brünker diffractometer
(Maestrichien), mainly composed of sandstone, sand
D8 ADVANCE with a copper source (λ = 1.5489 Å)
and fossiliferous clay; the N'kapa Formation
working under 40 kV and 40 mA. The exposure time
(Paleocene-Eocene) is rich in marl, clay with lenses
for qualitative analysis was 2 h. Samples were
of sand, fine to coarse crumbly sandstone; the
pulverized with an agate mortar; the resulting
Souellaba
lying
powder was picked up on a piece of tape before
unconformably on N'kapa deposits and characterized
being irradiated with CuKα radiation in the
by marl deposits with intercalations of lenses and
diffractometer. The resulting diffraction spectra
channels
were compared with a computerized data base of
microconglomerates;
limestone,
the
Formation
of
sand;
the
Logbaba
clay
(Oligocene)
Matanda
Formation
(Miocene), dominated by deltaic facies interbedding
common
minerals,
whose
with layers of volcanic deposits and unconformably
matching
function
was
overlie all earlier deposits, and the Wouri Formation
identification of phases consistent with the known
(Plio-Pleistocene) which consists of coarse beds,
compositions of the materials. Phase proportions
gravels and sand with a clayey matrix.
were estimated by the peak matching program
automatic
assisted
by
mineraloperator
without calibration to synthetic mixtures of known
V.
MATERIAL AND METHODS
Systematic sampling of sediments from
various geomorphic surfaces was done from two
road embankments along the Douala-Edéa road for a
distance of about 1.5 km and one well drilling on the
lower slope of the valley. A geological survey has
permitted the description of the four clayey profiles
in terms of texture, structure, distribution and color.
The color was obtained using a Munsell soil color
chart, and the terminology adopted for the
description was that of Miall (1996) and Postma
phase proportions. Semi quantitative analysis was
performed according to Charkravorty & Ghosh
(1991).
Trace
and
rare
earth
elements
were
determined on bulk material by inductively coupled
plasma mass spectrometry (ICP/MS). Powders were
previously
rusted
then
mixed
with
lithium
tetraborate before analyzing it with an ICP-MS
instrument, type Perkin - Elmer Elan 9000, for
lanthanide analyses. The IM-101 ICP-MS is a
lithogeochemical package that focuses on REE,
LILE, and HSFE in which the trace elements are
(1990).
Thirteen lithofacies were observed in the
three profiles of the road embankments and the
traditional well studied (Fig. 2, Table 1). The eight
clayey samples collected come from the most clayey
material layers (lithofacies F1, F2, F3) of the
profiles, with F3 the most laminated clayey layer.
Different analyses were performed on the
samples collected for mineralogical data at the
chemical laboratory of the University of Limoges
(France), and chemical data at the Geoscience
calibrated against solutions made up from single or
multi-elemental solution standards. The instrumental
precision of almost all lanthanides was above 5%
(2σ) for either all or 5 of the 6 compiled solutions
where the elements were above the limit of
quantification (LLoQ). Where the concentrations
approached the LLoQ (e.g., La and Pr in the traceelement poor basalt standard BIR-1, or Eu in the
rhyolite standard RGM), the error increased is
between 5 and 8.5% (Burhnam & Schweyer, 2004).
Laboratories (Geo Labs) of the Ontario Geological
Survey in Sudbury Ontario (Canada).
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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Fig. 2 - Profiles of the road embankments and the valley. - (a) Profile of the lower slope (interfluves with altitude 60m); - (b)
Profile of the upper slope (interfluves with altitude 60 m); - (c) Profile of the middle slope (interfluves with altitude 80 m); (d) Profile of the valley. Samples were collected in the clayey material layers of F1 (M2A2b, M2P3b, M2P4a, M2P4b), F2
(M2A2a and M2P3a), and F3 (M2A3a and M2A3b) of the profiles.
Table 1. Facies descriptions of the Missole II representative profiles
Facies code
Descriptions
Colour
S0
Humiferous layer
5YR2/1
S1
Yellowish sandy-clay (2 - 6 m thickness)
5Y7/6
S2
Reddish sandstones and micro conglomerates bed
5R4/2
S3
Rusty and fine- to medium-grained sandstones (0.5 – 1 m thickness)
5R2/2
S4
Orangey yellow sandy-clay (1 – 2 m thickness)
5Y7/6
S5
Reddish micro conglomerates bed with gravels of quartz and ferruginous (1 – 2 m
thickness)
5R2/2
S6
Yellowish grey medium to coarse sandstones
5Y8/1
S7
Fine yellowish grey sandstones
5Y7/6
S8
Yellow sandy-clay with gravels of quartz and some reddish fragments of
ferruginous duricrust (2 – 3 m thickness)
5Y6/4
S9
Reddish ferruginous duricrust bed (1 m of thickness)
5Y2/2
F3
Purplish grey laminated clay with muscovite and some yellowish and reddish
spots (2 – 4 m thickness)
5R4/2
F2
Grey silty-clay with yellowish, reddish and purplish spots
5Y6/1
F1
Mottled silty-clay with reddish, yellowish and greyish spots (3 - 4 m of
thickness)
5Y6/1
Note that F1 and F2 appear at the base of the profiles of the road embankments in the interfluves with altitude 60 m, while F3 only appears
in the profile of the valley with altitude 40 m.
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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VI.
RESULTS AND DISCUSSION
mineralogy of regional soils where kaolinite is the
major component (Segalen, 1995).
4.1 Mineralogy
The bulk mineralogy of sediment samples
from the Missole II clay deposits has essentially
kaolinite > quartz > illite > goethite > anatase minor
amounts of K-feldspar and occasionally hematite
(Fig. 3). The clay mineralogy is similar in all
samples but differ in proportions. It is characterised
by poorly crystallised kaolinite (50 – 72%) and illite
(5 – 15%).
ISSN 1029 - 2225
This mineral suite reflects the
Nicolas (1957) and Roberts (1958) showed
that kaolinite as abundant mineral of these sediments
comes from slow decomposition of feldspars and
others rocks in sharp milieu during geological times.
Generally, kaolinite is found in nature within clayey
material in relation with iron hydroxides, quartz and
micas. The presence of illite and goethite in these
sediments characterises humid conditions.
Fig. 3 - XRD patterns of bulk clay samples from Missolle II area. A: Anatase; G: Goethite; He: Hematite; Il: Illite;
K: Kaolinite; Q: Quartz; F: K-feldspar.
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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1985), the clay sediments are depleted in many
4.2 Trace elements geochemistry
Trace element concentrations of Missole II
elements notably Cs, Rb, Sr, Cu, Co, Ba and Ni, and
clay sediments are reported in Table 2. In
enriched in Ta, Zr, Hf, Nb, Pb. In general, similar
comparison with average PAAS set (Post-Archaean
values to PAAS are found for Cr, Ga, Th, U and V
Australian average shale after Taylor & McLennan,
(Fig. 4a).
Table 2. Trace element concentrations (in ppm) of the Missole II clay sediments
Profiles
a
M2A2a
Depth (m)
Profiles of the road embankments
b
c
M2A2b
M2P3a
M2P3b
M2P4a
M2P4b
Profiles of the valley
c
M2A3a
M2A3b
PAAS
6.5
7.5
7
8
7.5
8
0.5
1
Ba
158.5
164.2
183.7
116.5
121.5
120.8
167.5
187.4
650
Co
3.17
3.02
5.18
4.77
6.73
5.94
2.57
2.54
23
Cr
108
141
153
123
183
154
110
89
110
Cs
0.376
0.389
0.584
0.552
0.57
0.548
0.36
0.417
15
Cu
8.6
9.2
6.9
13
15.1
15.9
4.5
4.5
50
Ga
23.61
24.4
28.64
23
30.09
27.64
22.15
20.71
20
Hf
12.41
12.97
16.44
16.83
14.69
13.86
12.31
13.36
5
Nb
31.204
31.281
50.464
44.653
42.37
41.171
29.325
28.517
19
Ni
12.2
11.7
20.5
19.2
27.2
24.8
7.2
7
55
Pb
33.4
34.7
144.6
46
27.5
24.3
29.4
26
20
Sc
14.9
15.6
14.7
18.5
20.4
21.1
13.5
13.3
16
Rb
11.88
12.22
11.83
9.69
10.75
10.82
11.03
11.8
160
Sr
31.2
30.6
110.1
36.9
31.7
27.5
18.8
17.1
200
Ta
1.9
1.925
3.067
2.809
2.64 9
2.556
1.881
1.834
0.026
Th
12.874
13.542
22.266
17.924
20.536
19.049
10.054
14.425
14.6
U
1.874
1.99
2.659
2.588
2.753
2.608
1.789
2.054
3.1
V
184
235.2
136.5
163.2
255.9
215.2
142.4
107.7
Y
8.62
8.68
17.28
19.47
10.21
8.94
39.92
20.65
Zr
482
498
642
637
561
534
469
503
For comparison average values are shown for sedimentary rocks of PAAS after Taylor and McLennan (1985).
150
27
210
Sample/PAAS
100
M2A2a
M2A2b
10
M2A3a
M2A3b
1
M2P3a
M2P3b
M2P4a
0,1
M2P4b
0,01
Ba Co Cr Cs Cu Ga Hf Nb Ni Pb Rb Sr Ta Th U V Zr Sc Y
Fig. 4 - (a) PAAS normalized traces patterns
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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The results of REE analysis are given in
depletion in Missole II clay sediments characterize
Table 3 and are shown as chondrite-normalized
some weathered materials of South Cameroon
patterns and PAAS-normalized patterns in figures
basement (Bayiga et al., 2011).
4(b) and 4(c) respectively. ∑REE concentrations
vary widely in Missole II clay sediments (215.28-
4.3 Provenance
REE, Th, and Sc are most useful for
1498.67 ppm). All analyzed samples have ∑REE
abundances higher than the average PAAS (185.3,
inferring
Taylor & McLennan, 1985). The LREE are enriched
distribution
relatively to PAAS, whereas the HREE are
diagenesis and metamorphism and is less affected by
impoverished.
REE
heavy-mineral fractionation than that for elements
concentrations in clay sediments are partly due to
such as Zr, Hf, and Sn (Cullers et al., 1979; Bhatia
the presence of the REE-bearing minerals (as illite).
& Crook, 1986; Wronkiewicz & Condie, 1987; Cox
However, clay sediments of the profiles of the
et al., 1995; Mclennan, 2001; Armstrong-Altrin et
interfluves are generally richer in REE than those of
al., 2004). REE and Th abundances are higher in
the valley (respectively 259.46-1498.67 ppm against
felsic than in mafic igneous source rocks and in their
215.28-299.52 ppm). In clay layers, REE content of
weathered products, whereas Co, Sc, and Cr are
the profiles of the interfluves increase from the base
more concentrated in mafic than in felsic igneous
to the top while they increase inversely from the top
rocks and in their weathered products (Armstrong-
to the base in the profile of the valley (Table 3). This
Altrin et al., 2004). Furthermore, ratios such as
observation shows the influence of the water
Eu/Eu*, La/Sc, Th/Sc, La/Co, Th/Co, and Cr/Th are
movement in clay sediments of the valley, which
significantly different in mafic and felsic rocks
transported trace elements towards the base of the
source and can therefore provide information about
profile. Most clay sediments show similar chondrite-
the provenance of sedimentary rocks (Cullers et al.,
normalized patterns with high LREE concentrations
1988; Wronkiewicz & Condie, 1989; Condie &
and (La/Yb)N ratios ranging between 13.2 and 34.0.
Wronkiewicz, 1990; Cullers, 1994). In this study,
The sample M2P3a exhibit a more distinct pattern
those ratios of the Missole II clay sediments are
due to much higher enrichment in LREE and higher
similar to the values of sediments derived essentially
fractionation between light and heavy REEs, with a
from felsic rocks source (Table 4), suggesting that
(La/Yb)N ratio of 114. Also, samples show negative
these clay sediments probably were derived from
Eu anomalies (Fig. 4b) with (Eu/Eu*)N ratios
felsic rocks source.
The
abundances
of
crustal
is
compositions,
not
significantly
because
their
affected
by
ranging between 0.58 and 0.65, and no Ce anomaly,
with the exception of one sample (M2A3a) with
However, for fractionated crust, Th/Sc,
slight negative Ce anomaly (0.81). Middleburg et al.
Th/Co, La/Sc ratios are high and for mafic rocks
(1988) suggested that significant REE fractionation
they are low. Typically, for post Archaean UCC the
occurs during the advanced stages of weathering. In
ratio of Th/Sc is ~ 1, for granitic rocks it is higher
fact, high fractionation observed in Missole II clay
and for Archaean and mafic it is less than 1 (Singh,
sediments is due to the weathering materials. Also,
2009).
Braun et al. (1993) showed that LREE enrichment
in clay sediments should be resulted from weathered
materials. This LREE enrichment and HREE
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
27
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Table 3. Rare earth element concentrations (in ppm) of the Missole II clay sediments
Profiles of the road embankments
Profile
a
b
Profile of the valley
c
d
M2A2a
M2A2b
M2P3a
M2P3b
M2P4a
M2P4b
M2A3a
M2A3b
6.5
7.5
7
8
7.5
8
0.5
1
La
80.94
79.27
354.29
105.27
79.93
64.43
60.99
68.15
38
Ce
159.79
155.29
808.66
228.99
163.5
130.57
95.54
137.81
80
Pr
14.658
14.004
73.868
22.186
15.54
12.549
8.373
14.159
8.9
Nd
40.23
37.11
219.56
71.17
47.89
39.26
27.29
49.78
34
Sm
3.806
3.693
20.967
8.286
4.733
4.181
4.587
9.523
5.6
Eu
0.725
0.708
3.31
1.535
0.792
0.708
0.909
1.851
1.1
Gd
2.026
1.968
7.858
4.542
2.202
2.038
3.983
6.29
4.7
Tb
0.314
0.308
0.817
0.625
0.329
0.292
0.642
0.884
0.8
Dy
1.992
1.946
3.946
3.801
2.066
1.856
4.51
4.933
4.7
Ho
0.39
0.388
0.679
0.778
0.437
0.377
1.063
0.866
1
Er
1.226
1.251
1.977
2.378
1.384
1.228
3.303
2.387
2.9
Tm
0.212
0.216
0.3
0.364
0.225
0.2
0.475
0.341
0.4
Yb
1.609
1.664
2.096
2.538
1.695
1.521
3.124
2.218
2.8
Lu
0.256
0.269
0.341
0.401
0.275
0.246
0.489
0.325
0.43
∑REE
308.17
298.08
1498.67
452.86
320.99
259.46
215.28
299.52
185.33
LREE
299.42
289.37
1477.35
435.90
311.59
250.93
196.78
279.42
172.3
HREE
8.75
16.73
21.31
16.96
9.40
8.46
18.49
20.09
13.03
LREE/HREE
34.22
17.30
69.31
25.69
33.13
29.64
10.64
13.91
13.22
(Ce/Ce*) N
1.00
1.01
1.13
1.07
1.02
1.01
0.81
0.98
1.02
(Eu/Eu*) N
0.65
0.65
0.58
0.64
0.59
0.59
0.62
0.65
0.66
(La/Yb)N
33.99
32.19
114.22
28.03
31.87
28.62
13.19
20.76
9.2
Depth (m)
PAAS
Abbreviation normalization of REE to chondrites after Taylor and McLennan (1985)
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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1000
Sample/Chondrite
M2A2a
M2A2b
100
M2A3a
M2A3b
M2P3a
10
M2P3b
M2P4a
M2P4b
1
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig. 4 - (b) Chondrite normalized REE patterns
M2A2a
M2A2b
M2A3a
M2A3b
M2P3a
M2P3b
M2P4a
M2P4b
Sample/PAAS
10
1
0,1
La
Ce
Pr
Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig. 4 - (c) PAAS normalized REE patterns of the Missole II clay deposits
(after Taylor and McLennan, 1985).
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Table 4. Element ratios
Profile
a
Profile of the valley
Profiles of the road embankments
b
d
c
M2A2a
6.5
M2A2b
7.5
M2P3a
7
M2P3b
8
M2P4a
7.5
M2P4b
8
M2A3a
0.5
M2A3b
1
PAAS
Th/U
6.87
6.81
8.37
6.93
7.46
7.30
5.62
3.56
4.70
Th/Co
4.06
4.48
4.30
3.76
3.05
3.21
3.91
5.68
0.63
Cr/Th
8.39
10.41
6.71
6.86
8.91
8.08
10.95
6.17
7.53
Zr/Sc
32.35
31.92
43.67
34.43
27.5
25.31
34.74
37.82
13.13
Th/Sc
0.86
0.87
1.51
0.97
1.01
0.90
0.74
1.08
0.91
La/Co
25.54
26.25
68.40
22.07
11.88
10.85
23.73
26.83
1.65
La/Sc
9.39
9.13
20.50
5.41
7.83
7.21
1.53
3.30
2.40
La/Th
6.29
5.85
15.91
5.87
3.89
3.38
6.07
4.72
2.60
Depth (m)
Th/Sc values for the studied samples vary
Moreover, the relative REE patterns,
between 0.74 and 1.08, with the exception of one
(La/Yb)N and the size of the Eu anomaly also have
sample (M2P3a) with Th/Sc=1.51 that suggest
been used to infer sources of sedimentary rocks
influence of a granitic source. All the other samples
(Taylor & McLennan, 1985; Wronkiewicz &
have Th/Sc values similar to that of the UCC (0.75,
Condie, 1987). They are useful to differentiate the
Taylor & Mclennan, 1985) and Paas (0.91).
mafic and felsic source. Felsic rocks generally show
Incompatible trace element abundance of shale
fractionated chondrite normalized REE patterns
reflect that of the average upper-continental crust,
with higher (La/Yb)N ratios and prominent Eu
but lower in absolute abundances due to the
anomalies, in contrast the mafic rocks have less
presence of sediments with lower Th, REE and
fractionated chondrite normalized REE pattern with
other trace element abundances such as sandstones,
low (La/Yb)N ratios and little or no Eu anomalies
carbonates,
(Taylor & Mclennan, 1985). Clay sediments in this
and
evaporates.
Therefore,
the
variability found in Missole II clays may be related
study
with granulometry and the abundance of quartz that
normalized REE patterns with higher (La/Yb)N
act as a dilute of some trace element abundances.
ratios with averages 16.78 and 44.82 (Table 3) for
However, Th/Sc vs Zr/Sc can be used to observe
clay sediments of the profile in the valley and the
igneous differentiation but also to see sediment
profiles of the
recycling. Fig. 5 showed that Missole II clayey
prominent Eu anomalies (0.62 in average), suggest
materials are plotted to the UCC source and also
felsic rock source as those from Tertiary and
shows sediment recycling (McLennan et al., 2003).
Precambrian crystalline environment of the South
show
strongly
fractionated
chondrite
interfluves respectively,
and
Cameroon coastal plain basement;
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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1,6
sediment recycling
upper continental crust
1,4
1,2
Th/Sc
1
0,8
0,6
0,4
0,2
Clay sediment
mantle
0
0
10
20
30
40
50
Zr/Sc
Fig. 5 - Th/Sc vs Zr/Sc diagram to reveal the main source composition
(after McLennan et al., 1990).
Table 3. Rare earth element concentrations (in ppm) of the Missole II clay deposits
Profile
a
Profiles of the road embankments
b
Profile of the valley
d
c
M2A2a
M2A2b
M2P3a
M2P3b
M2P4a
M2P4b
6.5
7.5
7
8
7.5
8
0.5
1
La
80.94
79.27
354.29
105.27
79.93
64.43
60.99
68.15
38
Ce
159.79
155.29
808.66
228.99
163.5
130.57
95.54
137.81
80
Pr
14.658
14.004
73.868
22.186
15.54
12.549
8.373
14.159
8.9
Nd
40.23
37.11
219.56
71.17
47.89
39.26
27.29
49.78
34
Sm
3.806
3.693
20.967
8.286
4.733
4.181
4.587
9.523
5.6
Eu
0.725
0.708
3.31
1.535
0.792
0.708
0.909
1.851
1.1
Gd
2.026
1.968
7.858
4.542
2.202
2.038
3.983
6.29
4.7
Tb
0.314
0.308
0.817
0.625
0.329
0.292
0.642
0.884
0.8
Dy
1.992
1.946
3.946
3.801
2.066
1.856
4.51
4.933
4.7
Ho
0.39
0.388
0.679
0.778
0.437
0.377
1.063
0.866
1
Er
1.226
1.251
1.977
2.378
1.384
1.228
3.303
2.387
2.9
Tm
0.212
0.216
0.3
0.364
0.225
0.2
0.475
0.341
0.4
Yb
1.609
1.664
2.096
2.538
1.695
1.521
3.124
2.218
2.8
Lu
0.256
0.269
0.341
0.401
0.275
0.246
0.489
0.325
0.43
∑REE
308.17
298.08
1498.67
452.86
320.99
259.46
215.28
299.52 185.33
LREE
299.42
289.37
1477.35
435.90
311.59
250.93
196.78
279.42
172.3
HREE
8.75
16.73
21.31
16.96
9.40
8.46
18.49
20.09
13.03
LREE/HREE
34.22
17.30
69.31
25.69
33.13
29.64
10.64
13.91
13.22
(Ce/Ce*) N
1.00
1.01
1.13
1.07
1.02
1.01
0.81
0.98
1.02
(Eu/Eu*) N
0.65
0.65
0.58
0.64
0.59
0.59
0.62
0.65
0.66
(La/Yb)N
33.99
32.19
114.22
28.03
31.87
28.62
13.19
20.76
9.2
Depth (m)
M2A3a M2A3b PAAS
Abbreviation normalization of REE to chondrites after Taylor and McLennan (1985)
Ngon Ngon et al. Vol. 13, (2012), n°1, 20 – 35
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Contributions to Mineralogy and Petrology 92,
V. CONCLUSION
The mineralogy of clay deposits of Missole
II from lower slope in valley and interfluves are
181 – 193.
[3] Bayiga C.E., Bitom D., Ndigui D.P., Bilong P.
made up by kaolinite, quartz, illite, goethite, anatase,
(2011).
Mineralogical
minor amounts of K-feldspar and occasionally
characterization
hematite. Many trace elements, such as Cs, Rb, Sr,
amphibolites at SW Eséka (Northern border of the
Ba, Co, Cu and Ni are depleted in the clay sediments
Nyong unit, SW Cameroon). Journal of Geology
relatively to PAAS, whereas others, mainly Ta, Hf,
and Mining Research, Vol.3 (10), pp. 281 – 293.
of
and
weathering
geochemical
products
of
Zr and Nb, are enriched. REE present similar trends
[4] Benkhelil J., Giresse P., Poumot C., Nguetchoua
with high LREE and low HREE, and are
G. (2002). Lithostratigraphic, geophysical and
systematically enriched in clay deposits. Chondrite-
morpho-tectonic studies of the South Cameroon
normalized
shelf. In: Marine and Petroleum Geology 19, 499-
REE
patterns
show
negative
Eu
anomalies and high fractionation between LREE and
517.
HREE. The LREE are enriched in relation to PAAS,
[5] Bertolino A.R.R., Zimmermann U., Sattler F.J.
but the HREE present lower concentrations. Th/Sc,
(2007). Mineralogy and geochemistry of bottom
La/Sc, La/Th, Th/Co and Cr/Th ratios showed clay
sediments from water reservoirs in the vicinity of
sediments essentially derived from felsic rocks
Cordoba, Argentina: Environmental and health
source when fractionated chondrite normalized REE
constraints. Applied Clay Science 36, 206 - 220.
[6] Braun J.J., Pagel M., Herbillon A., Rosin C.
patterns also indicate felsic rocks source.
(1993). Mobilization and redistribution of REEs
and thorium in a syenitic lateritic profile a mass-
ACKNOWLEDGEMENTS
The authors are grateful to the staff of the chemical
laboratory of the University of Limoges, France and
chemical data at the Geoscience Laboratories (Geo
Labs) of the Ontario Geological Survey in Sudbury
balance study, Geochimica et Cosmochimica
Acta, 57: 4419 – 4434.
[7] Burhnam M.O., Schweyer J. (2004). Trace
element analysis of geological samples by
inductively coupled plasma-mass spectrometry at
Ontario (Canada).
the geosciences laboratories: revised capacities
due to improvements to instrumentation. Ontario
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Geo-chimica
Cosmochimica Acta, v. 53, p. 1537–1549.
35
et