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Thierry Desjardins

Bruno Turcq

Jean-Pierre Nguetnkam

Gaston Achoundong

Magloire Mandeng-Yogo

Fethyé Cetin

Anne-Marie Lézine

δ13C variation of soil organic matter as an indicator of vegetation change during the Holocene in central Cameroon

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Makhlouf Ounissi

Noureddine Bouchareb

Michel Petit

Nutrient distribution and fluxes from three Mediterranean coastal rivers (NE Algeria) under large damming

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Ankita Singh

Nachiketa Acharya

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Performance of Multi Model Canonical Correlation Analysis (MMCCA) for prediction of Indian summer monsoon rainfall using GCMs output

Frédéric Moynier

Toshiyuki Fujii

Gregory A. Brennecka

Sune G. Nielsen

Nuclear field shift in natural environments

Denis Thiéblemont

Christine Flehoc

Michel Ebang-Obiang

Christophe Rigollet

Jean-Pierre Prian

François Prognon

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C. R. Geoscience 346 (2014) 206–208
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omment on: ‘‘Geochronological arguments for a close
lationship between surficial formation profiles and
nvironmental crisis (c. 3000–2000 BP) in Gabon (Central
frica)’’ – D. Thiéblemont et al., 2013, C.R. Geoscience, 345,
72–283
ominique Schwartz
R 7362, Laboratoire Image, Ville, Environnement, Université de Strasbourg – CNRS, Faculté de géographie et d’aménagement, 3, rue de
rgonne, 67083 Strasbourg cedex, France
Thiéblemont et al. (C.R. Geoscience 345, 2013) consider
at the soils from Central Africa and Gabon were restored
 aeolian deposits after an environmental crisis, c. 2000
. The authors are convinced that the surficial formation
ing on the stone-lines are sediments rather than soil
rizons (discussion, pp. 277–278). The main argument
staining this conviction lies in the fact that the upper
ers are relatively homogenous on a particle-size point of
ew, which would be incompatible with biological activity
. 278, l. 15 and following).
It is not possible to consider that all soil scientists who
ork – or did work – in the area mistake (or mistook) the
ological surficial formation with the thick soils, known
 sols ferrallitiques, oxisols, ferralsols, which characterize
ntral Africa. The formation of these soils and their
orphological features have been discussed in numerous
pers. Soils from Gabon, Congo, and Cameroun with
ne-line profiles alone have been the subject of hundreds
 articles, which have notably shown the high genetic
lationships between the rocks from the substratum and
the loose levels that cover the stone-lines (see, for
example: Schwartz, 1996; Vogt and Vincent, 1966a,b).
Furthermore, the argumentation raised by the authors
contradicts the numerous studies highlighting the role of
bioturbation as a major process of soil dynamics.
Reworking of ground by termites or worms leads to the
homogenization of particle-size fractions, although a slow
increase with depth in the clay fraction is often observed in
the case of sandy soils. As a consequence, bioturbation also
leads to the scattering of coarse elements originally laying
on the topsoil within the soil.
This process is frequent for charcoal (Carcaillet and
Talon, 1996), but also for archeological artifacts. In a recent
paper, Schwartz and Gebhardt (2011) have described a real
case study: scattering and sinking of Bronze Age shards at
50 to 75 cm depth into a sandy soil due to bioturbation by
worms, the soil becoming strictly homogenous on a
particle-size point of view. These articles refer to
temperate areas, but the conclusions reached should also
apply in the case of intertropical regions given the very fast
biological activity. Termites especially are very abundant,
and can bring ground from several meters depth up to the
surface. Moreover, the description of a profile given by
Thiéblemont et al. (Fig. 6 of the commented paper) argues
in favor of the presence of biological activity. On a 1 m
depth profile, several charcoal layers having approxi-
mately the same age (about 2000 years) occur. Such a
feature most likely results from scattering of charcoal by
bioturbation after a single forest fire event, rather than
being due to several distinct fire events, each of them being
followed by quick and fast aeolian deposits.
R T I C L E I N F O
icle history:
ceived 9 April 2014
cepted after revision 10 April 2014
ailable online 18 June 2014
Email address: dominique.schwartz@live-cnrs.unistra.fr.
Contents lists available at ScienceDirect
Comptes Rendus Geoscience
w ww.s c ien ced i rec t . c o m
p://dx.doi.org/10.1016/j.crte.2014.04.00931-0713/ 2014 Published by Elsevier Masson SAS on behalf of Académie des sciences.
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Comment / C. R. Geoscience 346 (2014) 206–208 207The theory of a recent (2000 years) aeolian origin of the
oil horizons overlaying the stone-lines, both in Gabon or
ll Central Africa, and the generalized formation of the
tone-lines predating this event, is supported neither by
eld observations nor by analytical measurements.
Typical aeolian landforms are completely lacking in
entral Africa, except coastal linear dunes edging the
oastal plains. In other areas, aeolian landforms are often
ell preserved. For example, in Amazonia, fields of linear
unes have been formed between 32000 and 8000 BP
Carneiro Filho et al., 2002). Since that, they are stabilized.
owever, they can still be easily recognized (see, for
xample, Carneiro Filho and Zinck, 1994, or Google Earth:
8 320 18,78‘‘N; 638 180 43,15’’ O). How would it be
ossible that strong/intense aeolian episodes, not older
han 2000 years, did not leave recognizable features in
entral Africa?
Aeolian transport leaves typical impacts on sand
articles (Le Ribault, 1977). However, in Central Africa,
uch impacts cannot be observed by scanning microscopy.
or example, on the Bateke sands, aeolian marks are
ontemporary with Tertiary deposits, these marks being all
olished by more recent fluviatile reworking (Schwartz,
985).
Aeolian transport should also result in the formation of
custrine silt deposits. Many lakes have been investigated
 Cameroon, Gabon and Congo during the last twenty
ears (see in Maley’s comment). Up to now, the only
eolian deposit that has been recognized consists of
aharan diatoms (Nguetsop et al., 2004).
Particle-size composition of soil horizons overlaying
e stone-lines is very variable in Central Africa, and
eflects the composition of the parent material. The
roportion of the loam fraction is low (< 15%), which is
e general rule in ferralsols. The part of clays and sands is
ery variable, and the soils are generally poorly sorted,
hereas aeolian processes should result in very well-
orted sediments.
Aeolian sediments can be transported over long
istances. This is totally in contradiction with the general
ase noticed in Central Africa, i.e. the high genetic
elationship between the mineralogical and petrographical
atures of the soil horizons overlaying the stone-lines and
e parent rocks in place (Schwartz, 1996; Lanfranchi and
chwartz, 1991; Vogt and Vincent, 1966a,b).
Many archeological prospections in Gabon, south-
ameroon, North and South-Congo have shown the large
ccurrence of Sangoan type (70000–40000 BP) artefacts on
e top of the stone-lines (Lanfranchi and Clist, 1991;
anfranchi and Schwartz, 1990) in all these areas. It was
ometimes possible to recognize structures such as
napping sites, which demonstrate that the artefacts are
trictly in position and that the soil profiles were not
isturbed since burial (at least, 40000 BP). On the contrary,
e more recent lithic industries are rarely directly on
ontact with the stone-lines, except in some savannah
reas that were submitted to high erosion processes during
e Upper Holocene (Nyanga and Lopé in Gabon, Niari in
ongo). In the latter case, lithic industries are mixed on the
p of the stone-lines, whereas in the general case
and Iron Age industries occur within the soil horizons
overlaying the stone-lines. As a consequence, these
horizons were predominantly formed before the presumed
‘‘aeolian’’ crisis reported by Thiéblemont et al. The oldest
metallurgic site of the Congo (about 2100 BP), for example,
was discovered at 50 cm depth, well above (i.e., 1 m) the
stone-line (Schwartz et al., 1990).
The d13C composition of the organic matter (SOM) of
savannah soils from Congo (Schwartz, 1991) and Gabon
(Delègue et al., 2001) also brings good proxies. As a very
general feature, the d13C fingerprint of SOM in the upper
horizons (0–30/50 cm) is typical of savannah, whereas this
d13C signature is typical of forest in the deep soil horizons.
In the medium horizons, one can notice a very progressive
change from savannah to forest signature, as a conse-
quence of the mixing between young savannah SOM and
ancient forest SOM. This mixing is the result of millennia of
bioturbation activity, at least 7000 years according to the
mean residence time of SOM in deep horizons. As a
consequence of this bioturbation, the distribution of the
SOM follows a bi-modal model, as shown by Schwartz et al.
(1992). If the surficial formations overlaying the stone-
lines were consisting of sediments deposited during
several distinct episodes, the d13C changes of the SOM
should not be progressive, but should show (very) abrupt
changes.
According to me, there are no solid elements to argue in
favor of strong aeolian processes in Central Africa during
the Upper Holocene, except in coastal plains. The general
formation of stone-lines at about 3000 BP and its burying c.
2000 BP are not demonstrated. On the contrary, this
hypothesis is not suitable given the numerous field and
analytical observations.
References
Carcaillet, C., Talon, B., 1996. Aspects taphonomiques de la stratigraphie
et de la datation de charbons de bois dans les sols: exemple de
quelques sols des Alpes. Geogr. Phys. Quatern. 50, 233–244.
Carneiro Filho, A., Zinck, J.A., 1994. Mapping paleo-aeolian sand cover
formations in the northern Amazon basin from TM images. ITC J.
1994–3, 270–282.
Carneiro Filho, A., Schwartz, D., Tatumi, S.H., Rosique, T., 2002. Amazonian
paleodunes provide evidence for drier climate phases during the Late
Pleistocene–Holocene. Quaternary Res. 58, 205–209.
Delègue, M.A., Fuhr, M., Schwartz, D., Mariotti, A., Nasi, R., 2001. Recent
origin of a large part of the forest cover in the Gabon coastal area
based on stable carbon isotope data. Oecologia 129, 106–113.
Lanfranchi, R., Schwartz, D. (Eds.), 1990. Paysages quaternaires de
l’Afrique centrale atlantique. Coll. Didactiques, ORSTOM, Paris
(535 p.).
Lanfranchi, R., Clist, B. (Eds.), 1991. Aux origines de l’Afrique Centrale.
CCF/CICIBA, Libreville, Gabon (270 p.).
Lanfranchi, R., Schwartz, D., 1991. Les remaniements de sol pendant le
Quaternaire supérieur au Congo. Evolution des paysages dans la
région de la Sangha. Cah. ORSTOM. Ser. Pedol. 26, 11–24.
Le Ribault, L., 1977. L’exoscopie des quartz. Elsevier Masson, Paris (150 p.).
Nguetsop, F., Servant-Vildary, S., Servant, M., 2004. Late Holocene climatic
changes in West Africa, a high resolution diatom record from equa-
torial Cameroon. Quatern. Sci. Rev. 23, 591–609.
Schwartz, D., 1985. Histoire d’un paysage: le lousseke. Paléoenvironne-
ments quaternaires et podzolisation sur sables Bateke (Quarante
derniers millénaires, région de Brazzaville, R. P. du Congo). (thèse
d’État). Université Nancy-1 (published 1988, ORSTOM, Paris, 285 p.).
Schwartz, D., 1991. Intérêt de la mesure du d13C des sols en milieu naturel
équatorial pour la connaissance des aspects pédologiques et écolo-
giques des relations savane-forêt. Exemples du Congo. Cah. ORSTOM.
Ser. Pedol. 26, 327–341.shitolian (10000–6000 BP), Neolithic (6000–c. 2400 BP)
Sch
Sch
Sch
Comment / C. R. Geoscience 346 (2014) 206–208208wartz, D., 1996. Archéologie préhistorique et processus de formation
des stone-lines en Afrique centrale (Congo-Brazzaville et zones pér-
iphériques). Geo. Eco. Trop 20, 15–38.
wartz, D., Gebhardt, A., 2011. L’enfouissement de vestiges archéolo-
giques par la bioturbation: la colline du Hexenberg (Leutenheim, 67)–
un cas d’école. Étud. Gest. Sols 18, 287–300.
wartz, D., de Foresta, H., de Dechamps, R., Lanfranchi, R., 1990.
Découverte d’un premier site de l’Âge du fer ancien (2110 B.P.) dans
le Mayombe congolais. Implications paléobotaniques et pédologi-
ques. C. R. Acad. Sci. Paris. Ser. II 310, 1293–1298.
Schwartz, D., Mariotti, A., Trouvé, C., Van Den Borg, K., Guillet, B., 1992. Étude
des profils isotopiques 13C et 14C d’un sol ferrallitique sableux du littoral
congolais. Implications sur la dynamique de la matière organique et
l’histoire de la végétation. C.R. Acad. Sci. Paris, Ser. II 315, 1411–1417.
Vogt, J., Vincent, P.L., 1966a. Terrains d’altération et de recouvrement en
zone intertropicale. A–Le complexe de la stone-line. Mise au point (by
J. Vogt). Bull. BRGM 4, 2–51.
Vogt, J., Vincent, P.L., 1966b. Terrains d’altération et de recouvrement en
zone intertropicale. B- Les formations meubles superficielles au Sud
du Congo et du Gabon (by P.L. Vincent). Bull. BRGM 4, 53–111.

Geochronological arguments for a close relationship between surficial formation profiles and environmental crisis (c. 3000–2000 BP) in Gabon (Central Africa)

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Seismic random noise attenuation by time-frequency peak filtering based on joint time-frequency distribution

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<i>δ</i><sup>13</sup>C variation of soil organic matter as an indicator of vegetation change during the Holocene in central Cameroon

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A new editorial policy for <i>Comptes rendus Geoscience</i>

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Nutrient distribution and fluxes from three Mediterranean coastal rivers (NE Algeria) under large damming

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Performance of Multi Model Canonical Correlation Analysis (MMCCA) for prediction of Indian summer monsoon rainfall using GCMs output

Nuclear field shift in natural environments

Geochronological arguments for a close relationship between surficial formation profiles and environmental crisis (c. 3000–2000 BP) in Gabon (Central Africa)

Seismic random noise attenuation by time-frequency peak filtering based on joint time-frequency distribution

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