The cover formation consists of ochre sands that overlie a large part of the ancient geological formations in the Republic of Congo. It spans a significant portion of the west-Central Africa region, referred to as the Atlantic (including Gabon, the Democratic Republic of Congo, Cameroon, the Central African Republic, and the Republic of Congo) (
Segalen, 1969)
and
Linol (2012)
. This formation has been the subject of several studies. In the Batéké Plateaux, the works of (
Cosson, 1955
;
Le Maréchal, 1966
;
Dadet, 1969
;
Desthieux et al., 1993
) suggest that this formation corresponds to the lithological level Ba2, the ultimate stage of the Batéké Plateaus series. The aspects concerning the paleoenvironmental interpretation of the cover formation are controversial in the Central Atlantic African sub-region. In Gabon, the work of (
Thiéblemont, 2013
) attributes a wind origin to this training and determined a Holocene age, from 3000 to 2000 years B.P., and determined a Holocene age, from 3000 to 2000 years B.P., 14carbon dating of coals. This age is contemporary with the arid climate phase experienced by the Congo basin. In Congo,
(Cosson, 1955
;
Le Maréchal, 1966
;
Dadet, 1969
;
Desthieux et al., 1993
;
Bauer et al., 2015
;
Callec et al., 2015
;
Miyouna et al., 2016
;
Miyouna et al., 2019)
support the aeolian origin of these formations, whereas
Ngakosso Ngolo et al. (2021)
concluded a fluvial origin in the Chaillu Massif sector. In the Democratic Republic of Congo, the works of
Cahen et al. (1946)
;
Cahen and Lepersonne (1952)
;
and Cahen (1954)
equate the cover formation with the Kalahari of Southern Africa. In the Batéké Plateaus, only
Le Maréchal (1966)
suggested a dual shaping, first aeolian and then aqueous, for the cover formation sands based on morphoscopic study. Additionally,
De Ploey et al. (1968)
in the Democratic Republic of Congo assert that the deposits of ochre sands can be linked to both aeolian and alluvial processes, and
Lepersonne (1978)
favors a fluvial environment for the deposition of ochre sands. According to
Guillocheau et al. (2015)
, the questions of the age and paleoenvironmental context of the ochre sands remain unresolved, and the age and origin found in Gabon by
Thiéblemont (2013)
should be considered for this region due to multiple observations that challenge the generalization of these conclusions. This study contributes to the understanding of the depositional paleoenvironments of the cover formation in the Batéké Plateaus. This study aims to determine the paleoenvironments to deposit the coverage formation in the Batéké plateaus by lithological descriptions, granulometric analyzes (sieving and sedimentometry) allowing the determination of the granulometric parameters from which the transport dynamics are determined, and by the microscopic observations.
2. Material and Methods2.1. Study Area
The Batéké Plateaus are a geomorphological unit located between the 2nd and 4th degrees of South latitude, north of Brazzaville, and occupy the central part of the country (Congo).
The unit consists of four plateaus: the Koukouya Plateau, the Djambala Plateau, the Ngo-Nsa Plateau, and the Mbé Plateau (
Figure 1
). The various plateaus are separated by very deep incisions occupied by rivers flowing NE-SW. The Batéké Plateaus cover approximately 13,000 km2, with the Mbé Plateau being the largest at 7500 km2. The whole structure exhibits a slight NW-SE dip (
Cosson, 1955
;
Le Maréchal, 1966
;
Dadet, 1969
). The cover formation (formerly called Ba2), formed of ochre sands, is the ultimate term of Batéké plateaus. Thus, these sands are the material for our present study.
Figure 1. Map of the study area and location of sampling sites (<xref ref-type="bibr" rid="scirp.137044-3">
Bauer et al., 2015
</xref>; <xref ref-type="bibr" rid="scirp.137044-9">
Callec et al., 2015
</xref>).
2.2. Methodology
To this end, six (06) lithological logs were created, and forty-two (42) samples were collected for laboratory analysis. Granulometric analysis was conducted through sieving and sedimentometry. This analysis determines the different granulometric classes contained in the collected samples. The procedure involved weighing 200 g of the sample, washing it with running water using a 0.63 µm sieve, and then drying it in an oven. The fine fraction, less than 0.63 µm, was used for sedimentometric study using the hydrometer method. For the coarse fraction, 100 g of sand was poured onto the top of a column of 6 sieves, following the Udden-Wentworth (US Standard) progression, where each main class corresponds to a diameter that is double or half of the neighboring class, with the base class being 2 mm. The column is placed on a sieve that will vibrate it at a known frequency, for a time of 10 minutes at 50 vibrations (
Fournier et al., 2012
). The reject of each sieve is then poured into a capsule to be weighed. The percentage of each particle size class and the cumulative numbers are determined using Excel. The particle size distribution parameters are determined by the software “Gradistat V.8” (
Blott & Pye, 2001
), using the method of moments recommended nowadays by
Mercier (2013)
and the method of
Folk and Ward (1957)
.
The results of the sedimentometry allowed for the plotting of textural ternary diagram SSA (Sand - Silt - Clay) according to the model of
Assale and Aka (2019)
, and those of the coarse granulometric allowed for the plotting of the cumulative curves, with the main facies determined using Tricart method (
Tricart, 1965
). The mode of transport is determined by the CM diagram of
Passega (1957)
and the deposition environments by the dispersion diagrams of
Friedman (1967)
and
Moiola and Weiser (1968)
.
The morphoscopic study was conducted with the 250 µm fraction using a binocular loupe, according to Pettijohn method (Pettijohn, 1975) in
Chamley and Deconinck (2011)
, based on grain shape, and Cailleux method (
Cailleux, 1947
), and based on the aspect or texture of quartz grains.
3. Results3.1. Logs Description
The macroscopic description of the lithofacies was supplemented by sedimentometric results and some granulometric parameters.
The macroscopic description of the lithological log at the Mandiélé site shows fine silty sands 1 cm thick, fine silty-clayey sands about 8 cm thick, topped by a level of fine clayey-silty sands 1.5 cm thick (
Figure 2
).
The log of the Inoni quarry shows fine clayey-silty sands about 4.5 cm thick resting on a layer of fine bedded sands, separated by a discontinuous and sinuous stone line (
Figure 3
).
Figure 2. Lithological log of the Mandiélé site.
The macroscopic description of the section of the Léfini quarry reveals fine sands, a stone line intercalated between these sandy layers, and a layer of ochre yellow fine sands over a layer of clayey-silty sands (
Figure 4
).
The outcrop at the Ontsouankié quarry shows an alternation of fine sands, silty-clayey, and clayey-silty sands, with a stone line about 2 m thick separating the sandy facies, which rests on weathered sandstones (
Figure 5
).
The description of the log from the Lampama site shows medium-sized, ochre to brown, homogeneous sands (
Figure 6
).
The macroscopic description of the outcrop at the Mpouya II site shows silty-clayey sands separating two layers of clayey-silty sands. The entire unit rests on a stone line (
Figure 7
).
Figure 3. Lithological log of the Inoni site.
3.2. Textural Analysis
After sieving and sedimentometry, the results obtained made it possible to represent the ternary diagram of the different particle size fractions using the Sigmaplot 12.0 software, according to the models of
Assale and Aka (2019)
.
The different particle size classes present in the samples sands, silts and clays. Sand is the major component with approximately 75.73% and 24.27% for the matrix, (with 12.90% of silts and 11.37% of clays). The analysis of the different particle size fractions on the 42 samples gives 30.95% of sands sensu stricto, 2.38% of silty sands, 33.33% of silty-clayey sands and 33.33% of clayey-silty sands. Their representation indicates 66.67% of sands and 33.33% for silts and clays, in the SSA diagram, “Sand”, “Silt” and “Clay” (
Figure 8
).
Figure 4. Lithological log of the Léfini site.
3.3. Granulometric Parameters
The granulometric parameters of the coverage of the coverage by study site are summarized by histograms (
Figure 9
) and in detail, see the table in the appendix.
The sands of the Batéké Plateaus exhibit two size types: fine sands with mean values ranging from 2 Φ < Mz < 3 Φ, and medium sands with mean values between 1 Φ < Mz < 2 Φ. Fine sands are predominant (35 samples), while medium sands (05 samples) are rare and only found in Lampama (Plateau Koukouya).
Figure 5. Lithological log of the Ontsouankié site.
Three grading types are defined for the sands of the cover formation in the Batéké Plateaus: well graded (0.35 < σф < 0.50), fairly well-graded (0.50 < σф < 0.70), and moderately graded (0.70 < σф < 1.00). Fairly well-graded (18 samples) and moderately graded sands (17 samples) are predominant than well graded sands (07 samples).
The sands of the cover formation in the Batéké Plateaus exhibit three types of asymmetries:
- symmetrical (−0.43 < Skф < +0.43): the curve is normal, with fine and coarse particles symmetrically graded on either side of the mean.
Figure 6. Lithological log of the Lampama site.
- asymmetrical towards coarse particles (−0.43 < Skф < −1.30): the coarse fraction is predominant and better graded.
- highly asymmetrical towards coarse particles (Skф < −1.30): the coarse fraction is highly predominant and better graded.
These sands are largely symmetrical (28 samples), and asymmetrical towards coarse particles (13 samples) and very rarely very asymmetrical towards the coarse particles, and they are unimodale with two values, 2.5 ф (36 samples) and 1.5 ф (06 samples).
The frequency curves of the sands (
Figure 10
) of the cover formation have four types of flattening according to the kurtosis values, they are platykurtic (extended curves), mesokurtic (normal curves), leptokurtic (pointed curves) and very leptokurtic (very pointed curves). The frequency curves in order of importance are mesokurtic (21 samples), leptokurtic (17 samples), very leptokurtic (03 samples) and platikurtic (01 sample).
Figure 7. Lithological log of the Mpouya II site.
3.4. Granulometric Facies
The sands of the cover formation in the Batéké Plateaus have two types of granulometric facies: The hyperbolic facies or sigmoid facies (S shaped with a regular slope) present in five out of six sites, and the parabolic facies for the Mpouya II sands (
Figure 11
).
Figure 8. Ternary textural diagram SSA (Sand-Silt-Clay) of the sands of the Plateaus.
3.5. Mode of Transport of the Sands
The Passega diagram shows that almost all sands in the Batéké Plateaus occupy the RQ and QP segments (
Figure 12
). Thus, these sands are transported by saltation (RQ) and saltation and rolling (QP) (
Passega, 1957
).
3.6. Depositional Environment
The depositional environment of the sands of the cover formation is determined by the dispersion of points using the
Friedman (1967)
Sk-So diagram (
Figure 13
) and the
Moiola and Weisser (1968)
Sk-Md diagram (
Figure 14
).
The dispersion of points on the
Friedman (1967)
Sk-So diagrams (
Figure 13
) and the discrimination on the
Moiola and Weisser (1968)
Sk-Md diagram (
Figure 14
) allowed the determination of two types of depositional environments for the cover formation sands in the Batéké Plateaus: a dune environment (aeolian dune) and a fluvial environment.
Figure 9. Granulometric parameters of the sands of the cover formation by study site.
3.7. Morphoscopy
The morphoscopic study of quartz grains reveals that most grains are rounded with high sphericity. Regarding the surface aspect of quartz grains, results show that most grains are round, matt, and clean. These grains exhibit several impact marks. The presence of many broken quartz grains is noted. Of the 1050 grains analyzed, 46.10% are round, matt, and clean (RM); 28.60% are round, matt, and dirty (RS); 12.87% are shiny blunted (EL); and 12.47% are shiny, round (RL). Dirty, round, matt grains have a ferruginous cement on their surface. Round, matt grains (both clean and dirty) show several impact marks on their surface and are larger than the shiny blunted ones, which are sub-rounded (
Figure 15
).
Figure 10. Different frequency curves of cover formation sands: (a): Mandiélé; (b): Inoni; (c): Léfini; (d): Ontsouankié; (e): Lampama; (f): Mpouya II.
Figure 11. (a)-(d) Cumulative curves of the cover formation sands: (a): Mandiélé; (b): Inoni; (c): Léfini; (d): Ontsouankié. (e)-(f) Cumulative curves of the cover formation sands: (e): Lampama; (f): Mpouya II.--Figure 11. (a)-(d) Cumulative curves of the cover formation sands: (a): Mandiélé; (b): Inoni; (c): Léfini; (d): Ontsouankié. (e)-(f) Cumulative curves of the cover formation sands: (e): Lampama; (f): Mpouya II.
Figure 11. (a)-(d) Cumulative curves of the cover formation sands: (a): Mandiélé; (b): Inoni; (c): Léfini; (d): Ontsouankié. (e)-(f) Cumulative curves of the cover formation sands: (e): Lampama; (f): Mpouya II.--Figure 11. (a)-(d) Cumulative curves of the cover formation sands: (a): Mandiélé; (b): Inoni; (c): Léfini; (d): Ontsouankié. (e)-(f) Cumulative curves of the cover formation sands: (e): Lampama; (f): Mpouya II.
Figure 12. C/M diagram of <xref ref-type="bibr" rid="scirp.137044-32">
Passega (1957)
</xref>for the cover formation sands in the Batéké Plateaus.
Figure 13. Dispersion of the sands of the cover formation in the Batéké Plateaus on the <xref ref-type="bibr" rid="scirp.137044-18">
Friedman (1967)
</xref> Sk-So diagram.
Figure 14. Discrimination of sands on the Sk-Md diagram by <xref ref-type="bibr" rid="scirp.137044-29">
Moiola and Weisser (1968)
</xref>.
Figure 15. Different shapes and textures of quartz grains in sands. (a) Clean, matt rounded grains (RM); (b) Shiny blunt grains (EL); (c) Shiny rounded grains (RL); (d) Dirty matt rounded grains (RS).
4. Discussion
The lithological analysis of the sands from the cover formation in the Batéké Plateaus shows a succession of elementary sequences consisting of fine sands, rarely medium-sized (Lampama), sometimes silty in certain areas (Mandiélé, Ontsouankié, Mpouya II), or fine sands that are occasionally clayey, intercalated with a polygenic stone line. Such a succession indicates, according to
Cojan and Maurice (2013)
and
Chamley and Deconinck (2011)
, a fluvial-type sedimentation. Gravelly layers correspond to flood events, while fine silty and occasionally clayey layers, and represent sedimentation by settling during low flow periods. The highly variable thickness of the elementary sequences suggests that the floods had varying durations and intensities.
The results of the grain size (sieving and sedimentometry) give approximately 75.73% and 24.27% for the mud, 12.90% silts and 11.37%. They are comparable to those
Le Maréchal (1966)
for which the fine fraction (silts and clays) is less than 20%, white it is around 24.27%. This slight difference can be explained by increase in the content of clays following the polyphasic alteration affecting these materials (
Bauer et al., 2015
;
Callec et al., 2015
).
The particle size parameters vary depending on the study site, within the same log and from one plateau to another. The sands of the cover formation in the Batéké Plateaus are predominantly fine and sometimes medium (Lampama site). This evolution of the size is from the Lampama site located on the highest Koukouya Plateau, because all the plateaus are inclined slightly NW-SE, is consistent with the assertions of
Chamley and Deconinck (2011)
on the evolution of the granulometric parameters for the samples of a series or of the same sedimentary level which says that “the elements transported by a watercourse, the size decreases and the better the gradind”. These sands are fairly well classified, moderately classified and poorly classified. The grading of these sands does not obey the assertions of Chamley and Deconinck. This variable behavior of the average suggests a sedimentation in several phases. These sands are mostly symmetrical and asymmetrical towards the coarse particles. These sands are unimodal.
These granulometric parameters vary from one site to another in a regular manner. Such an evolution of the granulometric parameters favors, according to
Chamley and Deconinck (2011)
and
Cojan and Renard (2013)
, a mixture of allochthonous sediments with the autochthonous sediments which would be deposited in a calm environment.
With kurtosis values (Kф < 3), the flattening indicates the presence of distribution tails, that’s to say the excess of fines or coarses. Such a distribution was interpreted by
Mercier (2013)
as characteristic of a deposit that took place in several phases. This characteristic is observable on all the study sites of these sands.
The cumulative curves of the sands from the sites studied have a sigmoidal (hyperbolic) shape, which defines a homogeneous sedimentary stock (
Tricart, 1965
). This shape also indicates sedimentation resulting from a variation in the competence of the transport current, indicating a progressive reduction in the energy of the transport agent (
Tricart, 1965
;
Rivière, 1977
;
Saaidi, 1991
). The predominance of fine silty sands and sometimes clayey sands also justifies the hyperbolic shape of the cumulative curves. Indeed, this shape characterizes facies justifying sedimentation by settling (
Fournier et al., 2012
). The parabolic shape of certain cumulative curves at the Mpouya II site characterizes sediments where the proportion increases exponentially with size, corresponding to deposition conditions in a relatively fast current. Coarse particles are excessively suspended and deposit in greater abundance (
Fournier et al., 2012
); this is confirmed by the predominance of the coarse fraction in these deposits. According to
Atoui and Brahim (2009)
, the parabolic facies indicates a heterogeneity of the sandy stock corresponding to sedimentation by excess load.
These results are comparable to those of
Le Maréchal (1966)
and
Miyouna et al. (2019)
, but there are some differences.
Le Maréchal (1966)
only found fine and well-sorted sands, while we obtained fine sands with coarse sand layers that appear rudimentary; the latter are fairly to moderately sorted. The cumulative curves are mostly sigmoid, dominating over those of the parabolic facies. However,
Le Maréchal (1966)
did not find the hyperbolic facies. This may be explained by the very small number of samples analyzed by this author. As for
Miyouna et al. (2019)
, the cumulative curves of the sands from the southern part of Brazzaville show the same shape. Furthermore, the shape of the cumulative curves is comparable to those obtained by
Ngakosso Ngolo et al. (2021)
for the superficial formations in Chaillu (Mossendjo sector).
The primary mode of transport is saltation (segment QR), while rolling (segment QP) concerns only a small amount of sediments (
Figure 12
). According to
Hajek et al. (2010)
, rolling transport pertains to sediments with a high mode and positive skewness. This is the case for the sands of Lampama and some sandy fractions of Léfini, which exhibit these characteristics.
The dispersion of points on the Sk-So diagrams of
Friedman (1967)
(
Figure 13
) and Sk-Md of
Moiola and Weiser (1968)
(
Figure 14
) shows that these sands have two types of paleoenvironmental deposition: aeolian and fluvial.
The morphoscopic study reveals four types of grains: clean matte rounds (RM), dirty matte rounds (RS), shiny blunt (EL) and shiny rounds (RL). The matte round grains show several marks of shock, which characterize an aeolian transport
(Richot & Cailleux, 1971)
. The shiny blunt grains mark an aqueous transport. These results are comparable with those of
Le Maréchal (1966)
. The dirty matt round grains (RS) wear ferruginous cement on their surface, sometimes coated on certain shiny blunt grains. This suggests that these sands have been redesigned (
Guilcher, 1945
;
Ritchot & Cailleux, 1971
;
Girolimetto, 1982
). The shiny blunt grains characterize a wet phase of the evolution of sediment. These results show that these sands have undergone transport in two phases, the first wind phase and the second aqueous. This result is close to those obtained by
Ngakosso Ngolo (2022)
on the superficial formations of the Congolese bowl in the Republic of Congo. Thus, these sands are deposited in two paleoenvironments, aeolian environment and fluvial environment.
5. Conclusion
The study of the sedimentary dynamics of the sands of the cover formation in the Batéké Plateaus, based on a descriptive study of lithofacies in the field and granulometric analyses in the laboratory, shows that this formation is structured by a succession of elementary sequences of fine sands, rarely medium, sometimes silty in certain areas, or by fine sands with occasional clay intercalated by a polygenic stone-line. These sands are fairly well sorted to moderately sorted and poorly sorted. They are symmetrical and this asymmetry tends towards coarse grain. The cumulative curves are sigmoidal or S-shaped, and there are few parabolic curves. The primary mode of transport for these sands is saltation, while few sediments are transported by rolling. The dispersion of a number of parameters using Sk-So and Sk-Md diagrams enabled us to determine two depositional palaeoenvironments, aeolian and fluvial. The Morphoscopy of the quartz grains in these sands reveals rounded matt grains (both clean and dirty) transported by the wind, shiny grains (blunt and rounded) typical of aqueous transport, and many broken grains, indicating a complex transport process by the wind and then by water. This study shows that the sands of the cover formation in the Batéké Plateaus are not exclusively of eolian origin, as suggested by previous studies.
Although this study shows that the deposit was done in two paleoenvironments, it would be even better if we managed to date this training to better understand and timed the sediment deposit phases, wind and fluviatile, in evolution paleoclimatic of the Congo basin. The Holocene age, 3.000 - 2.500 B.P., determined in Gabon, corresponding to the arid climate period would be marked at least with a wet episode well circumscribed in time.
Appendix
Table A1. Granulometric parameters of cover formation sand in the Batéké plateaus.
Sample number
Granumometric indices
METHOD OF MOMENTS
Description
Arithmetic (mm)
Logarithmic (ф)
Mand 1
Mean
230.6
2.910
Fine sand
Sorting
91.68
0.484
Well graded
Skewness
1.958
−0.838
Symmetrical
Kurtosis
8.66
3.972
Leptokurtic
Mand 2
Mean
214.4
2.398
Fine sand
Sorting
85.42
0.497
Well graded
Skewness
2.100
−0.460
Asymmetrical towards the coarse
Kurtosis
10.08
4.562
Leptokurtic
Mand 3
Mean
215.2
2.386
Fine sand
Sorting
83.55
0.474
Well graded
Skewness
2.238
−0.626
Asymmetrical towards the coarse
Kurtosis
10.82
4.935
Leptokurtic
Mand 4
Mean
213.4
2.405
Fine sand
Sorting
85.45
0.501
Fairly well graded
Skewness
2.103
−0.427
Asymmetrical towards the coarse
Kurtosis
10.17
4.536
Leptokurtic
Mand 5
Mean
208.0
2.455
Fine sand
Sorting
87.43
0.540
Fairly well graded
Skewness
1.988
−0.233
Symmetrical
Kurtosis
9.769
4.020
Leptokurtic
Mand 6
Mean
214.4
2.394
Fine sand
Sorting
84.18
0.484
Well graded
Skewness
2.190
−0.541
Asymmetrical towards the coarse
Kurtosis
10.61
4.795
Leptokurtic
Mand 7
Mean
207.5
2.450
Fine sand
Sorting
84.79
0.517
Fairly well graded
Skewness
2.157
−0.297
Symmetrical
Kurtosis
10.90
4.438
Leptokurtic
Mand 8
Mean
213.6
2.413
Fine sand
Sorting
89.04
0.526
Fairly well graded
Skewness
2.070
−0.354
Symmetrical
Kurtosis
10.04
4.253
Leptokurtic
Mand 9
Mean
207.2
2.459
Fine sand
Sorting
86.61
0.535
Fairly well graded
Skewness
2.042
−0.241
Symmetrical
Kurtosis
10.16
4.117
Leptokurtic
Mand 10
Mean
207.4
2.463
Fine sand
Sorting
88.35
0.551
Fairly well graded
Skewness
1.940
−0.208
Symmetrical
Kurtosis
9.485
3.868
Leptokurtic
Mand 11
Mean
202.6
2.515
Fine sand
Sorting
93.05
0.597
Fairly well graded
Skewness
1.918
−0.186
Symmetrical
Kurtosis
9.417
3.381
Mesokurtic
Inoni 1
Mean
216.9
2.350
Fine sand
Sorting
71.05
0.396
Well graded
Skewness
1.675
−1.220
Asymmetrical towards the coarse
Kurtosis
4.188
4.552
Leptokurtic
Inoni 2
Mean
236.1
2.257
Fine sand
Sorting
87.11
0.497
Well graded
Skewness
0.857
−0.395
Symmetrical
Kurtosis
2.072
2.737
Mesokurtic
Inoni 3
Mean
216.6
2.377
Fine sand
Sorting
89.81
0.464
Well graded
Skewness
2.963
−1.085
Asymmetrical towards the coarse
Kurtosis
15.28
6.250
Leptokurtic
Inoni 4
Mean
266.3
2.161
Fine sand
Sorting
176.1
0.743
Moderately graded
Skewness
3.410
−0.652
Asymmetrical towards the coarse
Kurtosis
21.46
3.982
Leptokurtic
Inoni 5
Mean
262.7
2.189
Fine sand
Sorting
136.6
0.712
Moderately graded
Skewness
1.459
−0.042
Symmetrical
Kurtosis
6.030
2.692
Mesokurtic
Inoni 5
Mean
262.7
2.189
Fine sand
Sorting
136.6
0.712
Moderately graded
Skewness
1.459
−0.042
Symmetrical
Kurtosis
6.030
2.692
Mesokurtic
Inoni 6
Mean
255.8
2.232
Fine sand
Sorting
133.7
0.722
Moderately graded
Skewness
1.423
−0.018
Symmetrical
Kurtosis
6.026
2.596
Mesokurtic
Inoni 7
Mean
269.4
2.162
Fine sand
Sorting
145.2
0.728
Moderately graded
Skewness
1.504
−0.094
Symmetrical
Kurtosis
5.830
2.719
Mesokurtic
Léfini 1
Mean
269.5
2.163
Fine sand
Sorting
133.3
0.760
Moderately graded
Skewness
0.900
0.318
Symmetrical
Kurtosis
4.737
2.274
Platykurtic
Léfini 2
Mean
233.8
2.311
Fine sand
Sorting
106.5
0.602
Fairly well graded
Skewness
1.598
−0.201
Symmetrical
Kurtosis
7.193
3.174
Mesokurtic
Léfini 3
Mean
233.6
2.303
Fine sand
Sorting
110.2
0.649
Fairly well graded
Skewness
1.397
−0.272
Symmetrical
Kurtosis
6.482
3.377
Mesokurtic
Léfini 4
Mean
241.9
2.309
Fine sand
Sorting
124.1
0.719
Moderately graded
Skewness
1.318
0.003
Symmetrical
Kurtosis
5.877
2.456
Platykurtic
Léfini 5
Mean
246.7
2.264
Fine sand
Sorting
122.3
0.677
Fairly well graded
Skewness
1.462
−0.064
Symmetrical
Kurtosis
6.436
2.752
Mesokurtic
Léfini 6
Mean
248.3
2.266
Fine sand
Sorting
126.3
0.704
Moderately graded
Skewness
1.404
−0.021
Symmetrical
Kurtosis
6.151
2.611
Mesokurtic
Lampama 1
Mean
336.5
1.863
Medium sand
Sorting (σф):
179.9
0.794
Moderately graded
Skewness
1.026
0.262
Symmetrical
Kurtosis
3.656
2.663
Mesokurtic
Lampama 2
Mean
336.8
1.856
Medium sand
Sorting
177.7
0.784
Moderately graded
Skewness
1.032
0.276
Symmetrical
Kurtosis
3.727
2.707
Mesokurtic
Lampama 3
Mean
364.9
1.729
Medium sand
Sorting
185.1
0.765
Moderately graded
Skewness
0.911
0.355
Symmetrical
Kurtosis
3.235
2.895
Mesokurtic
Lampama 4
Mean
365.8
1.723
Medium sand
Sorting
185.2
0.757
Moderately graded
Skewness
0.921
0.317
Symmetrical
Kurtosis
3.220
2.871
Mesokurtic
Lampama 5
Mean
342.4
1.837
Medium sand
Sorting
181.7
0.796
Moderately graded
Skewness
0.988
0.303
Symmetrical
Kurtosis
3.541
2.699
Mesokurtic
Ontsoua 1
Mean
224.5
2.328
Fine sand
Sorting
113.0
0.665
Fairly well graded
Skewness
1.831
−0.704
Asymmetrical towards the coarse
Kurtosis
8.590
4.439
Leptokurtic
Ontsoua 2
Mean
232.1
2.366
Fine sand
Sorting
125.9
0.694
Fairly well graded
Skewness
1.870
−0.272
Symmetrical
Kurtosis
7.844
3.016
Mesokurtic
Ontsoua 3
Mean
235.5
2.346
Fine sand
Sorting
126.8
0.699
Moderately graded
Skewness
1.774
−0.225
Symmetrical
Kurtosis
7.433
2.906
Mesokurtic
Ontsoua 4
Mean
238.9
2.355
Fine sand
Sorting
139.3
0.755
Moderately graded
Skewness
1.747
−0.250
Symmetrical
Kurtosis
6.857
2.700
Mesokurtic
Ontsoua 5
Mean
245.1
2.294
Fine sand
Sorting
134.6
0.710
Moderately graded
Skewness
1.758
−0.241
Symmetrical
Kurtosis
7.039
2.917
Mesokurtic
Ontsoua 6
Mean
245.2
2.292
Fine sand
Sorting
134.8
0.706
Moderately graded
Skewness
1.794
−0.267
Symmetrical
Kurtosis
7.142
2.980
Mesokurtic
Ontsua 7
Mean
241.9
2.348
Fine sand
Sorting
142.0
0.782
Moderately graded
Skewness
1.595
−0.176
Symmetrical
Kurtosis
6.271
2.459
Platykurtic
Mpouya II 1
Mean
196.0
2.510
Fine sand
Sorting
173.4
0.773
Fairly well graded
Skewness
5.818
−1.674
Asymmetrical towards the coarse
Kurtosis
42.78
7.464
Très leptokurtic
Mpouya II 2
Mean
169.2
2.703
Fine sand
Sorting
85.39
0.683
Fairly well graded
Skewness
2.671
−1.129
Asymmetrical towards the coarse
Kurtosis
17.45
6.091
Leptokurtic
Mpouya II 3
Mean
160.8
2.870
Fine sand
Sorting
85.37
0.625
Fairly well graded
Skewness
2.779
−0.638
Asymmetrical towards the coarse
Kurtosis
16.43
3.188
Mesokurtic
Mpouya II 4
Mean
169.7
2.847
Fine sand
Sorting
132.1
0.688
Fairly well graded
Skewness
6.029
−1.125
Asymmetrical towards the coarse
Kurtosis
55.10
5.387
Leptokurtic
Mpouya II 5
Mean
174.4
2.753
Fine sand
Sorting
92.31
0.631
Fairly well graded
Skewness
2.778
−0.493
Asymmetrical towards the coarse
Kurtosis
15.71
3.386
Mesokurtic
Mpouya II 6
Mean
184.5
2.696
Fine sand
Sorting
129.5
0.646
Fairly well graded
Skewness
6.159
−0.874
Asymmetrical towards the coarse
Kurtosis
57.30
5.794
Leptokurtic
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