Pleistocene fluvial systems of the Creuse river (Middle - INFO-SED

Jackie Despriée
Robert Gageonnet
Pierre Voinchet
Jean Jacques Bahain
Christophe Falguères
Jean Duvialard
François Varache
Pleistocene fluvial systems of the Creuse river (Middle Loire
Basin - Centre Region, France) [ Les systèmes fluviatiles
pléistocènes de la Creuse (Bassin moyen de la Loire, Région
Centre, France).]
In: Quaternaire - Volume 15 - Numéro 1-2 - 2004. pp. 77-86.
Citer ce document / Cite this document :
Despriée Jackie, Gageonnet Robert, Voinchet Pierre, Bahain Jean Jacques, Falguères Christophe, Duvialard Jean, Varache
François. Pleistocene fluvial systems of the Creuse river (Middle Loire Basin - Centre Region, France) [ Les systèmes fluviatiles
pléistocènes de la Creuse (Bassin moyen de la Loire, Région Centre, France).]. In: Quaternaire - Volume 15 - Numéro 1-2 2004. pp. 77-86.
doi : 10.3406/quate.2004.1756
http://www.persee.fr/web/revues/home/prescript/article/quate_1142-2904_2004_num_15_1_1756
Abstract
The Creuse River is a tributary of the Vienne River which joins the Loire Valley on its left bank
downstream Tours (Centre Region, France). Recent field works has significantly increased the number
of fossil fluvial formations identified in the Middle Creuse River Valley, has confirmed their penglacial
character and shown the impact of recent tectonics and the magnitude of uplift which affect the
geometry of the deposits on the northern edge of the Massif Central and the southern and western parts
of the Pans Basin.
Three sectors have been distinguished :
- a "Massif Central" sector, with an endogenous bed-rock, where some five stepped higher alluvial
formations are studied.
- an "Intermediate" sector characterized by the opening of the valley when the river joins the Pans
Basin. Eleven sandy formations, which constituted advancing fans in this actively tectonic zone, have
been identified.
- a "Pans Basin" sector in which the Creuse flows westwards along a major fault. Eight stepped terraces
have been recognized here.
Several geochronological data were obtained by electronic spin resonance (ESR) method applied to
bleached alluvial quartz. The results show a good reproducibihty and generally a good coherence with
the altimetry. They indicate, in close correlation with sedimentological and tectonic studies, that the
response of the river is variable and depends of local geology and tectonic characteristics.
From the results obtained on each sector, a first synthetic but schematic history of the fluvial system can
be proposed for the Middle Creuse River valley between 1,7 Ma BP and today Some major tectonic
movements are dated between 1,7 and 1,2 Ma, around 600 ka and between 450 and the present. On
the other hand, the "Pont-de-Lavaud" Early Palaeolithic site with archaic pebble quartz industry was
dated to the end of the Lower Pleistocene, around 1,1 Ma BP.
Résumé
La Creuse est un affluent de la Vienne qui rejoint la Loire sur sa rive gauche en aval de Tours (Région
Centre, France). Dans sa moyenne vallée, les recherches récentes ont permis d'augmenter
significativement le nombre de formations alluviales, de confirmer leur caractère pénglaciaire, et de
montrer l'impact de la tectonique récente et l'ampleur du soulèvement de la bordure nord du Massif
Central et du sud-ouest du Bassin de Paris. Trois secteurs ont été distingués :
- un secteur " Massif Central " au substrat endogène, où sont actuellement reconnues cinq formations
alluviales ;
- un secteur "intermédiaire ", caractérisé par l'élargissement de la vallée à son entrée dans le Bassin
Pansien. Onze nappes sableuses formant des cônes d'épandage progradants ont été individualisées
dans cette zone tectonique active ;
- un secteur "Bassin parisien" dans lequel la rivière suit une grande faille orientée E-0. Un système de
huit nappes étagees y a été reconnu.
Plusieurs points de repères géochronologiques ont été obtenus par la méthode de Résonance
Paramagnétique Electronique (RPE) appliquée aux quartz fluviatiles blanchis. D'une excellente
reproductibilité et d'une bonne cohérence, elles permettent, en liaison avec la sédimentologie, de
souligner l'importance de la géologie locale et de ses caractéristiques tectoniques. A partir des résultats
obtenus pour chaque secteur, une première synthèse chronologique schématique de la vallée moyenne
de la Creuse couvrant les derniers 1,7 Ma est proposée. Plusieurs périodes de mouvements
tectoniques sont ainsi datés du Quaternaire notamment entre 1,7 et 1,2 Ma, autour de 600 ka, et entre
450 et l'actuel. Le site préhistorique de " Pont-de-Lavaud ", avec son industrie archaïque sur quartz et
son sol aménagé, a pour sa part été daté du Pléistocène inférieur, vers 1 , 1 Ma BP.
Quaternaire, 15, (1-2), 2004, p 77-86
PLEISTOCENE FLUVIAL SYSTEMS
OF THE CREUSE RIVER
(Middle Loire Basin - Centre Region, France)
Jean- Jacques
Jackie
DESPRIÉE*,
BAHAIN*,
Robert
Christophe
GAGEONNET*,
FALGUÈRES*,
Pierre VOINCHET*,
Jean DUVIALARD**
and François VARACHE***
ABSTRACT
The Creuse River is a tributary of the Vienne River which joins the Loire Valley on its left bank downstream Tours (Centre Region, France).
Recent field works has significantly increased the number of fossil fluvial formations identified in the Middle Creuse River Valley, has confirmed their
penglacial character and shown the impact of recent tectonics and the magnitude of uplift which affect the geometry of the deposits on the northern
edge of the Massif Central and the southern and western parts of the Pans Basin.
Three sectors have been distinguished :
- a "Massif Central" sector, with an endogenous bed-rock, where some five stepped higher alluvial formations are studied
- an "Intermediate" sector characterized by the opening of the valley when the river joins the Pans Basin Eleven sandy formations, which
constituted advancing fans in this actively tectonic zone, have been identified
- a "Pans Basin" sector in which the Creuse flows westwards along a major fault Eight stepped terraces have been recognized here.
Several geochronological data were obtained by electronic spin resonance (ESR) method applied to bleached alluvial quartz. The results show a
good reproducibihty and generally a good coherence with the altimetry They indicate, in close correlation with sedimentological and tectonic studies,
that the response of the river is variable and depends of local geology and tectonic characteristics.
From the results obtained on each sector, a first synthetic but schematic history of the fluvial system can be proposed for the Middle Creuse
River valley between 1,7 Ma BP and today Some major tectonic movements are dated between 1,7 and 1,2 Ma, around 600 ka and between 450 and
the present On the other hand, the "Pont-de-Lavaud" Early Palaeolithic site with archaic pebble quartz industry was dated to the end of the Lower
Pleistocene, around 1,1 Ma BP
Key-words: Creuse River, pleistocene fluvial systems, ESR dating, Early Palaeolithic, tectonics.
RÉSUMÉ
•
LES SYSTÈMES FLUVIATILES PLEISTOCENES DE LA CREUSE (Bassin moyen de la Loire, Région Centre, France)
La Creuse est un affluent de la Vienne qui rejoint la Loire sur sa rive gauche en aval de Tours (Région Centre, France) Dans sa moyenne vallée,
les recherches récentes ont permis d'augmenter significativement le nombre de formations alluviales, de confirmer leur caractère pénglaciaire, et de
montrer l'impact de la tectonique récente et l'ampleur du soulèvement de la bordure nord du Massif Central et du sud-ouest du Bassin de Pans
Trois secteurs ont été distingués
- un secteur " Massif Central " au substrat endogène, où sont actuellement reconnues cinq formations alluviales ;
un secteur "intermédiaire ", caracténsé par l'élargissement de la vallée à son entrée dans le Bassin Pansien Onze nappes sableuses formant
des cônes d'épandage progradants ont été individualisées dans cette zone tectonique active ;
un secteur "Bassin pansien" dans lequel la nvière suit une grande faille onentée E-0 Un système de huit nappes étagees y a été reconnu.
Plusieurs points de repères géochronologiques ont été obtenus par la méthode de Résonance Paramagnétique Electronique (RPE) appliquée aux
quartz fluviatiles blanchis D'une excellente reproductibihté et d'une bonne cohérence, elles permettent, en liaison avec la sédimentologie, de souligner
l'importance de la géologie locale et de ses caracténstiques tectoniques. A partir des résultats obtenus pour chaque secteur, une première synthèse
chronologique schématique de la vallée moyenne de la Creuse couvrant les derniers 1,7 Ma est proposée Plusieurs pénodes de mouvements tectoniques
sont ainsi datés du Quaternaire notamment entre 1,7 et 1,2 Ma, autour de 600 ka, et entre 450 et l'actuel Le site préhistonque de " Pont-de-Lavaud ",
avec son industne archaïque sur quartz et son sol aménagé, a pour sa part été daté du Pleistocene inféneur, vers 1 , 1 Ma BP.
Mots-clés : Vallée de la Creuse, systèmes fluviatiles pleistocenes, datations par RPE, neotectonique, industnes prehistonques archaïques du Paléolithi
que
ancien.
* Département de Préhistoire du Muséum National d'Histoire Naturelle, Institut de Paléontologie Humaine, 1 rue René Panhard, F-75013 PARIS FRE
2677 du CNRS (jache despnee@free fr)
** Comité Départemental du Patrimoine et de l 'Archéologie en Loir-et-Cher, les Jacobins, rue Anne-de-Bretagne, F-41000 BLOIS
*** Centre Régional de Recherches Archéologiques, 18, rue Charles-Lindbergh, F-41000 BLOIS
Manuscrit reçu le 04/12/2002, accepté le 03/01/2004
78
INTRODUCTION
The Creuse River is a tributary of the Loire catchment
system which drains the south-western part of the Paris
Basin (France) (fig. 1). The studied area corresponds of
the middle part of the valley between Eguzon and Le
Blanc, in the Indre department (Centre Region), before
the river arrives in the Touraine area and joins the Vienne
River, a left-bank tributary of the Loire River.
At the end of the XIXth century, several alluvial terra
ceswere identified, and the presence of Pleistocene fauna
and biface industries was recorded (Hubert, 1905). More
recently, additional alluvial levels, especially higher for
mations,
have been studied (Velasquez, 1974; Flageolet,
1977; Macaire, 1981; Rolin, 1981; Gageonnet, 1986,
1987, 1988; Lorenz et al, 1990; Rasplus et al, 1989;
Cohen- Jullien et al, 1989, 1998). Over the past more
than twenty years, thematic surveys researching of the
most ancient human industries in Europe were underta
ken
in this valley (Despriée and Alilaire, 1991; Despriée
and Gageonnet, 1999). Important engineering works,
some are very large, have allowed researchers to observe
the different fluvial sequences of the Creuse River more
thoroughly. Finally, significant improvements in the Elec
tron Spin Resonance (ESR) dating method applied to
bleached sedimentary quartz have enabled us to begin
fitting these fluvial systems into Quaternary chronology
(Voinchet, 1997; Falguères et al, 2002; Voinchet, 2002).
Not all of the Creuse alluvial formations have been
thoroughly studied as yet. Identification, surveying and
dating are still in progress. Here, therefore, we present
the current state of our research.
GEOGRAPHICAL AND GEOLOGICAL
CONTEXT
The Creuse river has its source in the Limousin Mount
ains, on the Millevaches Plateau (877 m), near Ussel
(Corrèze). It is a torrent who flows northward to Aubusson, then turns towards the north-west along a major
fault between the Marche Mounts and the Combrailles
Region. Its narrow basin is constrained between the Cher
and the Vienne Basins.
The Creuse then crosses the Marche Fault and flows
northward through the crystalline rocks of the Aigurande
Plateau (Eguzon-Chantôme area) (fig. 1) (Rolin, 1981)
and, upstream of Argenton, through the sedimentary fo
rmations
of the Paris Basin (Freytet et al, 1986; Lorenz
and Lorenz, 1984 and 1985; Lorenz et al, 1990; CohenJullien et al, 1989 and 1998). The river then heads
westward, along the major "Saint-Gaultier Fault" into the
Jurassic limestones, towards the Touraine Region.
EXPERIMENTAL APPROACH
This study is primarily based on the field works of
Jackie Despriée and Robert Gageonnet since twenty years
in the Middle Creuse River Valley. Since 1999, intense
survey and systematic sedimentological and electron spin
resonance (ESR) dating analyses have been undertaken
in the context of a research program financially supported
by the french Ministry of Culture and the Centre Region
Council.
Recent improvement of the ESR method and its appli
cation to the dating of bleached quartz extracted from
sediments currently allows to provide chronological dates
on Pleistocene fluvial deposits and associated archaeol
ogicalsites (Yokoyama et al, 1985; Laurent et al, 1998;
Voinchet et al, 2004, this issue).
An ESR age is obtained from the ratio of the total
dose received by the sample during its history (palaeodose) to the annual radiation dose rate. The application
on sedimentary quartz is well described by Voinchet et al
(2004). For this material, the palaeodose is not related to
the time elapsed since the mineral formation, but to the
time elapsed since its deposition and burial in an alluvial
terrace. In fact, the dating is based on the hypothesis of
a zeroing of the ESR traps by sunlight during the trans
portphase in the river. However, the ESR center used for
the age determination, here the Al-center (Yokoyama et
al, 1985), is not completely bleached during the sunli
ghtexposure; its intensity decreases in terms of the expo
sure time and reaches a plateau value which represents a
«residual» dose. The palaeodose received by the sample
since the burial is obtained then by subtraction of this
residual dose to the total dose. This residual value is
determined by studying the response of the quartz sam
ples to an ultra-violet light exposure. The maximal blea
ching value is generally obtained after a equivalent six
months exposure (Voinchet et al, 2003).
THE MIDDLE CREUSE VALLEY ALLUVIAL
DEPOSITS
The bedrocks geological and tectonic characteristics
provide a three part division of the Middle Creuse Valley,
respectively called "Massif Central", "Intermediate" and
"Paris Basin" sectors (fig. 1).
THE "MASSIF CENTRAL" SECTOR
The Massif Central sector is located between Crozant
and Ceaulmont (fig. 1 & 2). Here the valley is cut into
igneous and metamorphic rocks of the Aigurande Plateau
more than 140 m deep along a path largely dependent on
the innumerable fractures and faults in the old basement.
Five alluvial formations, indexed from A (the lowest)
to E (the higher), have been identified in this part of
the valley. The present-day topographic position of the
known outcrops of the two higher formations leads us to
believe that the valley must have been about 1 km wide
during the aggradation phases. ESR data obtained for this
sector are showed in table 1 .
- Sheet E (+115 / +130 m) - "le Pin" alluvial format
ion.
Only one outlier of the very high formation has been
identified near the hamlet of "le Pin ". The major part of
the alluvial deposits is sandy and the upper part contains
many well-rounded quartz pebbles.
This outcrop was previously included into the Sheet D
(+90 / +110 m) (Gageonnet, 1986, 1987, 1988; Aârab,
79
CHANNEL
Dogger-Tertiary
I
I.
I
I
I
\,
1,
,
'I
i,I
i,I'
',II'
I'I
1i,I
i,I
III II l\M 1,3.
I.*S IT-T
i,I1'
I'I
Ii,I
Ii,I'
FT
1',
I,
I
I'
I
'Argenton-sur-Creuse Sj
Z
Lias-Trias
+ -h Metamorphic and magmatic rocks
±1^
// Faults
/
~k
^: Sector's limits
ESR Samples
Fig. 1: Location map of the Middle Creuse River Valley between Crozant (Creuse) and Le Blanc (Indre), from the northwestern part of the
Aigurande Plateau (Massif Central) to the entrance in the Touraine Region (after Freytet et ai, 1986; Cohen-Jullien et ai, 1989; Freytet et ai,
1989; Rasplus et ai, 1989; Lorenz et al., 1990; Cohen-Jullien et ai, 1998).
Fig 1 Carte de situation de la vallée de la Creuse moyenne entre Crozant (Creuse) et Le Blanc (Indre), de la bordure nord-ouest du plateau d' Aigu
rande (Massif Central) a l'entrée en Touraine (d'après Freytet et al , 1986, Cohen-Jullien et al , 1989, Freytet et al , 1989, Rasplus et al , 1989, Lorenz
étal, 1990, Cohen-Jullien et al , 1998)
1994) because the present altimetry of the remnant is
+100 / +1 16 m). However, the ESR results (tab. 1) assign
an age around 1.7 ± 0,2 Ma to this formation which is
much older than the D sheet age. In fact, a major fault, the
"Gargilesse fault" (F2) separates the "/e ftn" outlier from
the closest remnant of the Sheet D at "le Cerisier" (fig.
2). The small altitudinal difference between these two
formations is probably due to a postdepositional reacti
vation of this fault (Freytet et al, 1986, 1989; Cohen-Jull
ien,
1989, 1998). Therefore, on account of the remaining
thickness of the Sheet E (15 m) and of the relative alt
itude of the plateau at the top of the slope (140 m), the
"le Pin " alluvial remnant should be initially located at an
approximate altitude of around +115/+130m. The fault
down-throw would thus be around 15 to 20 m.
- Sheet D (+ 90 / + 110 m) - "le Cerisier / Pont-deLavaud" alluvial formation.
This alluvial formation is the best preserved in this
sector of the valley, especially downstream from the
Eguzon dam, over a distance of more than 15 km on both
sides of the river valley (fig. 2).
The base of the sheet, at a constant altitude of + 90 m,
has been observed only upstream the Eguzon dam. Fur
ther south, significant erosion, probably due to the uplift
of a post-depositional anticline (Freytet et al., 1986),
has reduced the thickness of the rare outcrops that still
exist over small surface areas in hollows in the substra
tum
than 2 m (Crozant, "la Chaudronnière"; EguzonChantôme, "Fressignes", "la Croix-de-Chambon" and
"Pont-de-Lavaud". This basal unit corresponds to slope
80
I/Intermediate
sector
Ceaulmon
Gargilesse - Dampierre
"la Garenhe
Bourny
le Censm,
Massif Central
sector
1
I
Fressignes
uzon iwm Pont-de Lavaud
Plateau deposits
Sheet E +115/+130m
SheetD+90/+110m
SheetC+60/+75m
Sheet B +45 /+S0 ra
Sheet A altitude)
(relative
+15/+25m
Plateau deposits
Sheet E +U5/+l30m
SheetD+90/+110m
"Pont de-Lavaud" site
SheetC+60/+75m
Sheet A +15/+25mOttten
Fig. 2: Middle Creuse River Valley, "Massif Central" Sector: map
of outcrops of the alluvial formations on the Aigurande Plateau and
in the Creuse River Valley; synthetic transverse profile of the step
ped sheets that have not been flooded by the dam (after Despriée et
Gageonnet, 2003, modified).
Fig 2 Vallée moyenne de la Creuse, secteur " Massif Central " carte
des affleurements des formations alluviales du plateau et de la vallée de
la Creuse et profil transversal synthétique des nappes etagées non mas
quées par les barrages (d'après Despnée et Gageonnet, 2003, modif
iée)
deposits that include authigenic weathered rocks (micaschist, gneiss, amphibolite), blocks of vein quartz and
well-rounded quartz pebbles probably derived from an
overlying alluvial formation, with interbedded lenses of
sand. At "Pont-de-Lavaud", cryoturbation phenomena,
preferentially developed in the fracture zones in relation
with the weathered and decayed rocks, have deformed
and penetrated the basal unit, creating various types of
structures (polygons, circles, diapirs, injections of alterite...) (Despriée and Gageonnet, 2003).
The fluvial deposits, 10 to 15 m thick, are made up, for
the most part, of inclined beds of coarse-grained sand cut
by discontinuous beds of quartz pebbles, more abundant
in the top.
One prehistoric site has been found in the basal deposits
of the sheet D, at Eguzon-Chantôme "Pont-de-Lavaud"
(Indre). This site has been excavated between 1984 and
0/+5m
+5/+ 10m
+10/+15m
+15/+30m
+30/+4Sm
+45/+50m
+50/+55m
+55/+60IÎ!
+60/+70m
+78Z+85 m
+85/+ 105 m
Fig. 3: Middle Creuse River Valley, " Intermediate " Sector: loca
tion map of the alluvial formations showing the highest layers about
+ 78/+ 105 m in Ceaulmont, the insetted alluvial fans in the Le
Pêchereau "buttonhole" and the extensives layers in the half graben
below Saint-Marcel to Le Pont-Chrétien. The numbers indicate the
sampled and dated sites (from J. Despriée and J. Duvialard fieldtrips).
Fig 3 Vallée moyenne de la Creuse, secteur "Intermédiaire " carte
des nappes alluviales des hauts niveaux de +78/+105 m à Ceaulmont,
des dépôts progradants du secteur du Pêchereau et des nappes étalées
dans le demi-fosse de Saint-Marcel - Le Pont-Chretien (Indre) Les étoi
lesindiquent les sites prélevés et dates
1994. The prehistoric industry was found in the basal
deposits and also on anthropic pavements builded with
quartz blocks in the upper part of these deposits (Des
priée and Gageonnet, 1999 and 2003). About 5 000 arte
facts have been recording, included pebble-tools, core
and flakes, as well as pebbles and vein quartz, broken
with hammer-stone on quartz anvil, and their fragments.
No weathering of this very archaic prehistoric industry is
observable.
Ten ESR dates have been obtained for this formation
and place it at the end of the Early Pleistocene, between
0.9 and 1.2 Ma (tab. 1). In fact, the dates derived from
the sediments sampled in the best preserved sections (up
to 15 m thick - Baraize, "Montcocu"; Dampierre-Gargilesse, "le Cerisier") are grouped between 1.1 and 1.2
Ma, whereas samples from the thinnest outcrops (less
than 2 m thick preserved - Eguzon-Fressignes «le Jardinle-Nué» ; Eguzon, "Pont-de-Lavaud") have been dated at
about 0.9-1 Ma. These slightly younger ages would result
from pedogenesis (Aârab, 1994; Laurent, 1993).
81
Relative
altitudes (m)
E
+115/+130
D
+90/+110
C
B
+60/+75
+52
Samples
Gargilesse-Dampierre "le Pin" 1
Gargilesse-Dampierre "le Pin" 2
Gargilesse-Dampierre "le Pin" 3
Gargilesse-Dampierre "le Cerisier" 1
Gargilesse-Dampierre "le Cerisier" 2
Gargilesse-Dampierre "le Cerisier" 3
Gargilesse-Dampierre "le Cerisier" 4
Baraize "Montcocu" 1
Baraize "Montcocu" 2
Eguzon, Fressignes "Jardin le Nué"
Eguzon " Pont-de-Lavaud" 1
Eguzon "Pont-de-Lavaud" 2
Eguzon "Pont-de-Lavaud" 3
Gargilesse "Bourny"
Gargilesse "la Garenne"
Fressignes "Chantecreuse"
'
Sheets
Bleaching Archaeological doses Water (%) Annual
doses
(%)
(Gy)
(u Gy/year)
257 ± 24
22
25
151± 14
273 ± 26
24
20
162 ±15
269 ±27
19
20
153 ±15
25
198 ±20
18
167 ±16
202 ± 20
30
17
183 ±18
27
195 ±20
17
168 ±17
211 ±21
34
18
189 ±19
219±22
28
20
198 ±20
229 ± 22
34
20
204 ± 20
227 ± 22
21
12
217±22
212 ±20
211 ±21
25
17
22
225 ± 22
17
230 ±22
226 ± 22
249 ± 25
24
17
210±20
350 ±32
26
18
31
172 ±18
23
287 ±28
26
155 ±16
20
355 ±32
Ages (ka)
1702 ±200
1686 ±200
1756 ±200
1187 ±200
1103 ±200
1161 ±200
1116 ± 150
1106 ±150
1122 ±150
1045 ± 160
1001 ± 150
977 ±100
905 ± 100
602 ± 65
600 ± 65
437 ± 50
Tab. 1: ESR results obtained on samples carried out from the "Massif Central" Sector, showing analytical data (archaeological and annual
doses, water content in sediment, maximal bleaching percentages) and ages.
Tab 1 Tableau de résultats des analyses RPE du secteur " Massif Central ", présentant les données analytiques (Dose archéologique et dose annuelle,
teneur en eau des sediments, taux de blanchiment maximum) et les âges obtenus
- Sheet C (+ 60 / +75 m) - "Gargilesse" alluvial for
mation.
Only one remnant of the Sheet C was observed south
of Gargilesse ( "la Garenne " and "Bourny "). The strat
igraphy, about 10 m thick, is essentially sandy with irr
egular beds of quartz pebbles embedded in rubified and
reddish-brown sandy clay. ESR measurements gave cons
istent results, around 600 ka (tab. 1).
The river valley narrowed, probably due to relatively
more rapid general uplift, which reactivate old faults nearer
to each other (Despriée and Gageonnet, 2003, fig. 5).
- Sheet B (+ 45 / + 50 m) - "Fressignes D. 45" alluvial
formation
Downstream the Eguzon dam (+60 m), is a very small
remnant of the Sheet B shown a gravely sand ; the thick
nessand the area of which are unknown. One ESR age of
437 ± 50 ka was obtained for this sheet (tab. 1).
- Sheet A (+ 15 / + 25 m) and eventual lower alluvial
formations
In the Massif Central sector, the lower part of the valley
is hidden by recent sediments or by several barrier lakes.
Sheet A was recognized at Baraize, "le Pré-Marteau ".
The sediment is rich in pebbles and blocks, including
very large metamorphic and magmatic rocks, especially
amphibolite and granite examples.
THE "INTERMEDIATE" SECTOR
The transition of the river from the crystalline Massif
Central into the sedimentary Paris Basin can be seen
clearly in the morphology of the valley and in the deve
lopment of its alluvial formations. This can be attributed
both to the lithological differences and to a very active
recent tectonics. This "Intermediate" sector of the river,
from Ceaulmont to Pont-Chrétien (about 15 km long)
was divided in three subsectors : the first one from Ceaul
mont to Le Menoux, the second from Le Menoux to
Argenton-sur-Creuse and the third from Argenton-surCreuse to Le Pont-Chrétien (fig. 3).
Eleven sheets, indexed from I to XI, have been distin
guished, in the intermediate sector. The complete stepped
terraces system has never been observed however (fig. 3).
Not all the recognized terraces have been studied. Table
2 summarizes ESR data for this sector.
- Subsector 1 (ssl - fig. 3)
From Ceaulmont to Le Menoux, the Creuse river cuts
successively northward the migmatites then Liassic fo
rmations
(clay and clayey limestones). Intense faulting
(lowered substratum blocks) coupled with the less resis
tantsubstrat has led to the widening of the valley. In this
context, the alluvial sheets was spreading in large dejec
tioncones, which can be observed over an area nearly
4 km wide on either side of the river from Badecon-LePin to "les Granges ".
The main alluvial outcrops observed in this area are the
higher sheets near Ceaulmont. Sheet XI (+ 85 / +105 m)
and Sheet X, (+ 78 / + 85 m) were respectively recogni
zed
at "les Granges " and at "les Pessols ", but these fo
rmations
have not be studied at this time.
Below these deposits, the valley narrows and its straight
SE-NW section follows the Ceaulmont fault (F3). In this
part of the valley, only small remnants of the middle
sheets survive. Sheet VIII (+ 55 / + 60 m - "Villarnoux"
formation) corresponds to a thick bed of coarse basal
deposits, including blocks and pebbles of endogeneous
rocks (quartz, granite, micaschiste, etc.), covered by 3 m
of coarse clayey rubified sand. The stratigraphy of Sheet
VI (+ 45 / + 50 m - "la Châtaigne" formation) shows
four metres of fine to coarse grained sands, with little
pebbles and horizontal or oblique stratifications, capped
by a layer of 5 to 50 cm long pebbles of endogeneous
rocks. Only this last alluvial sheet was dated by ESR.
Three samples gave ages ranging between 300 and 350
ka (tab. 2).
- Subsector 2 (ss2 - fig. 3)
In this area, the river erodes the poorly resistant format
ionsof the Lias and the basal Dogger limestone.
82
Sheets
Relative
altitudes (m)
VII
+50/+55
VI
+45/+50
V
+30/+45
IV
+15/+30
III
II
I
+10/+15
+5/+ 10
0/+5
Samples
Saint-Marcel "les Coutures" 1
Saint-Marcel "les Coutures" 2
Ceaulmont "la Châtaigne" 1
Ceaulmont "la Châtaigne" 2
Ceaulmont "la Châtaigne" 3
Saint Marcel "Les Pommeurs" 1
Saint Marcel "Les Pommeurs" 2
Saint Marcel "Les Mersans" 1
Saint Marcel "Les Mersans" 2
Ceaulmont "le Petit-Multon"
Le Pêchereau "Maison-Rouge"
Le Pêchereau "Courbas"
Saint Marcel "la Sous station"
Saint Marcel "le Motocross"
Le Pont Chrétien "Les Champs-de-laChaume"
Saint Marcel " les-Champs-du-Chereau"
Le Pont Chrétien "la Sablière Deville"
Saint Marcel "les Chambons"
Bleaching Archaeological doses
(%)
(Gy)
28
142 ±15
26
164 ±16
23
162 ±18
25
142 ±15
140 ± 16
19
20
129 ±12
29
155 ±15
27
153 ±15
35
159 ±16
19
201 ±20
18
69 ±7
25
82 ±8
28
90 ±9
22
92 ±9
29
69 ±7
22
67 ±7
30
70 ±7
23
51 ±5
Water
(%)
12
13
19
20
19
22
23
15
15
18
19
18
18
16
9
18
15
14
Annual
doses
(u Gy/year)
277 ± 27
329 ±31
462 ± 44
469 ± 46
456 ± 45
374 ± 37
309 ±31
418 ±42
350 ±34
439 ±44
293 ± 30
429 ±43
419 ±42
406 ±40
309 ±31
325 ± 32
310 ±31
392 ± 40
Ages (ka)
510 ±59
498 ± 58
351 ± 40
303 ± 45
307 ± 45
344 ± 45
501 ± 62
366 ± 45
453 ± 55
458 ± 60
236 ± 28
190 ± 22
215 ± 25
227 ± 25
221 ± 27
206 ± 28
226 ± 27
131 ± 20
Tab. 2: ESR results obtained on samples carried out from the "Intermediate" Sector, showing analytical data (archaeological and annual doses,
water content in sediment, maximal bleaching percentages) and ages.
Tab 2 Tableau de résultats des analyses RPE du secteur " Intermédiaire ", présentant les données analytiques (Dose archéologique et dose annuelle,
teneur en eau des sédiments, taux de blanchiment maximum) et les âges obtenus
The rare outcrops of the highest alluvial formations
have not been studied. Below 50 m of relative altitude,
the valley is shaped like a buttonhole. Its width varies
from 0,250 km at Le Menoux to 2,7 km at Le Pêchereau
then the valley narrows down to 0,4 km near Argenton-sur-Creuse. Fluvial sediments are deposited in large
prograding fans in this sector, forming a basin in the con
tinuation
of the Ceaulmont-Le Menoux fault (F3). The
eight lowest sheets are present in this subsector, but only
Sheet IV (+ 15 / + 30 m) has been studied by ESR
on three different localities with various sedimentological characteristics. At "le Petit-Multon" the stratigr
aphy
(10 m thick observed) shows an alternance of sandy
cross-bedded strata and coarse levels with quartz pebbles
and endogeneous rocks. An age of 458 ± 60 ka was obtai
ned; At "la Maison-Rouge" and at "le Courbas", the
deposits are exclusively sandy but the sedimentological
data vary considerably between these two localities. A
prehistoric biface industry was identified at the end of
the XlXth century near the " la Maison-Rouge" locality
(Hubert, 1905). The ESR results are respectively of 236
± 28 ka and 190 ± 22 ka for these two sites (tab. 2).
- Subsector 3 (ss3 - fig. 3)
From Argenton-sur-Creuse, the bottom of the valley
narrows rapidly where the river flows through the Dogger
limestone. On its left bank, the valley is then limited by a
60-meters-high cliff. Below Saint-Marcel, in a large halfgraben more than 3 km wide (Argenton Fault, F4) (Freytet et al., 1986; Cohen- Jullien et al, 1998) eight sandy
alluvial formations were observed on the right bank, des
cending
from East to West from an relative altitude of +
60 m down to the present river bed. In this wider valley,
these layers up to 12 to 15 m thick are very extensive
(fig. 3). Locally, the alluvial deposits partly fill karstic
cavities. The different sheets of this subsector show prac
tically the same sedimentological features. ESR analyses
were performed on sediments sampled from sheets I to
V and VII (tab. 2). Sheet I (0 / + 5 m), studied at SaintMarcel «les Chambons», gave an age of 13 1 ± 20 ka. The
ESR results obtained for the samples from sheets II (+5
/ + 10 m), III (+10 / + 15 m) and IV (+15 / + 30 m) are
quite similar, respectively 226 ± 27, 206 ± 28 and 222 ±
30 ka (3 samples). Two groups of dates were determined
for the sediments of sheet V (+30 / + 45 m), sampled
at Saint-Marcel «les Mersans» and «les Pommeurs». At
these two localities, the lower part was dated at 450-500
ka when the ages of the upper part range around 350 ka.
Finally, two samples of sheet VII (+50 / + 55 m) provide
an mean age around 500 ka.
The "Paris Basin" sector
Between Le Pont-Chrétien and Le Blanc, the river
flows westward along the major Saint-Gaultier Fault (F5)
(Freytet et al., 1986) and the valley is asymmetrical
(fig. 4). The plateau deposits (around 75 m at Oulches)
are only observed on the top of the south slope. It corres
ponds to residual veneer of water worned blocks quartz,
sands and gravels (Rasplus et al, 1989). On this left
bank, the north- facing slope is rather steep and the allu
vial formations are clearly truncated by erosion.
The right bank has a gentler slope, which might corre
spond to the tilting of northern blocks. Its lower altitude
at the summit (+ 55 m) might also have been caused by
subsidence of the La Brenne tectonic Basin (Lorenz and
Lorenz, 1984). All of the studied formations (sheets 8, 7,
6, 3) are situated on the right bank.
The eight alluvial formations, their relative position,
and the limestone bedrock have been recently observed
over a 3 -km- wide strip all along a gas pipeline (fig. 4).
- Sheet 8 (base at + 55 m) - the "les Brandes-deMontflamme" formation
The sheet 8 is constituted by a gravel layer with sandy
lenses, nearly 3 m thick, visible at the top on the edge of
the Brenne Basin (Ciron, Indre). This outcrop represents
83
.
la PiecelesBrandes- du-Cormier
Le Champ- . \ Scou
le-Mont/lamme^ de-Chaume /
Altitude
(mNGF)
90 -I
05
15
25
3km
Fig. 4: Middle Creuse River Valley. Situation of the samples in the " Paris basin " Sector; and north-south section crossing Thenay and Chasseneuil showing the dissymetry of the valley which follows the major Saint-Gaultier Fault.
Fig 4 Vallée de la Creuse moyenne Situation des prélèvements dans le secteur " Bassin parisien " et coupe n-s (Thenay-Chasseneuil) montrant la
dissymetne de la vallée qui suit la faille majeure de Saint-Gaultier
the base of the alluvial formation. An ESR age of 794 ±
1 10 ka was obtained on a sandy sediment (tab. 3).
- Sheet 7 (base at + 45 m) - the "les Grands-Champs"
formation
A fluvial terrace (sheet 7) is well developed at Scoury
(Ciron, Indre). The alluvial sequence contains clayed
coarse sands with rare small quartz pebbles and was
dated at 450 ± 55 ka (tab. 3).
- Sheet 6 (+30 / +45 m) - the "Chitray-gare" format
ion
The sheet 6 is a thick (> 5 m) sandy cross-bedded layers
formation, overlayed by a gravel deposit (granite and
metamorphic rocks). ESR results range around 320-350
ka (tab. 3).
- Sheet 3 (+ 10 / + 20 m) - the "les Champs-deChaume" and "la Pièce-des-Cormiers" formation
This terrace (about 10 m thick) is visible along all the
"Paris Basin" sector. Its is exclusively sandy (horizontal
and cross-bedded layers) with heterogeneous gravel over
lays. Prehistoric industries, with pebble-tools, handaxes
and cores are founded on the Jurassic bedrock. ESR data
assign to this level an age of 200-280 ka (tab. 3).
SYNTHESIS AND DISCUSSION
Different conclusions can be drawn from this study,
still incomplete, of the Middle Creuse Valley.
- The sedimentology of the Middle Creuse River fo
rmations
show very similar deposits, although the river
flowed successively through the Aigurande crystalline
Relative
altitudes
+50/+55
+45/+47
+30/+45
'
Bleaching Archaeological doses Water (%) Annual
Samples
doses
Ages (ka)
(%)
(Gy)
(u Gy/year)
Ciron " Brandes-de-Montflamme"
8
28
152,95 ±15
18
192,53 ± 19 794 ± 110
7
24
153,8 ±15
17
341,2 ±34 450 ±55
Ciron, Scoury, "les-Grands-Champs"
Chitray "la Gare" 1
35
126,54 ±12
19
365,74 ± 36 345 ± 40
6
Chitray "la Gare" 2
30
119,3 ±12
18
365,59 ±36 326 ± 42
Ciron "Pièce des Cormiers" 1
24
56,37 ± 5
20
239,02 ± 24 235 ± 28
3
+10/+20m
Ciron "Piece des Cormiers"!
28
50,12 ±4
19
240,17 ±24 208 ± 25
Ciron carrière "les-Champs-de-Chaumes"
335,97 ± 32 278 ± 32
20
93,65 ±9
27
Tab. 3: ESR results obtained on samples carried out from the "Paris Basin" Sector, showing analytical data (archaeological and annual doses,
water content in sediment, maximal bleaching percentages) and ages.
Tab 3 Tableau de résultats des analyses RPE du secteur " Bassin de Paris ", présentant les données analytiques (Dose archéologique et dose annuelle,
teneur en eau des sédiments, taux de blanchiment maximum) et les âges obtenus
Sheets
84
Plateau then the sedimentary aureoles of the Paris Basin.
The classical alluvial sequence presents slope gravels, not
always visible, containing authigenic weathered rocks
and well rounded quartz pebbles, then sandy-clayed
deposits with endogenous rocks pebbles, finally format
ionsincluding large blocks and pebbles in argilloferruginous matrix. These upper deposits correspond to the last
river response to the cold climatic variations.
- The total incision from the plateau to the present river
bed decreases downstream. It peaks at about + 140 m
in the Aigurande plateau (Crozant-Eguzon), + 125 m at
the opening of the "Paris Basin" (Ceaulmont), + 80 m at
Saint-Marcel, + 75 m at Oulches to about + 60 m near Le
Blanc.
- ESR geochronological results permit the construction
of a logical chronostratigraphical framework for each
studied sector, but the influence of local tectonics is also
clearly perceptible.
In the «Massif Central» sector, the ages of the studied
sheets range from 450 ka (sheet B) to 1.7 Ma (sheet
E), with for each alluvial formation a good reproducibility and a overall coherence. These results suggest a
fault reactivation in the Gargilesse area, which had signi
ficantly modified the relative altitude of the «le Pin» ter
race. Tectonics had also effected on the geometry of the
"Pont-de-Lavaud" block (Sheet D), which has recently
tilted probably during the Lower Pleistocene (Despriée
and Gageonnet, 2003). Finally, ESR data permit to place
the archaeological «Pont-de-Lavaud» site in the Lower
Pleistocene and to connect it with mediterranean Early
Palaeolithic sites as Monte Poggiolo (Italy) or Atapuerca
Gran Dolina (Spain).
In the «Intermediate sector», some ESR results seem to
be aberrant but might also be explained by the influence
of tectonics. Hence, the ages obtained on «la Châtaigne»
and «le Petit-Multon» localities seem to be reversed in
comparison to their relative altitude. This could be rela
ted to movements along the major fault of Ceaulmont
which has caused tilting of scattered bedrock blocks.
Sedimentological differences between «le Petit Multon»
and the others localities of Sheet IV seem to corroborate
such an explanation. Another apparent discrepancy cor
responds
to the results obtained on the sites of «les Mersans» and «les Pommeurs» at Saint-Marcel. On these
both localities, the two groups of ESR ages seems in
l
Plateau
Massif Central
depoMb
sector
_^Sheet E(+115/+130m)-17Ma
SheetD(^90/+ll0m)-llMa
"Pont-de-Lavaud" .site
\ SheetC(+6O/+75m) 600 ka
Sheet B (+45/+50 m) - 450 ka
Sheet A (+15 +25 m)
fact related to the superposition of two distinct alluvial
formations, which is confirm both by stratigraphical and
sedimentological studies (Aârab, 1994). Finally, in this
sector, the ages obtained for sheets II to IV are undistinguishable and seem indicate the deposits of several
alluvial formations during isotopic stage (IS) 7, around
180-220 ka.
Only a few ESR data are available for the «Paris Basin»
sector and new analyses are necessary, but the great diffe
rence observed between the ages of sheets 7 and 8 seems
to be in contradiction with their altimetric gap.
- The comparison of the obtained synthetic stepped
systems (fig. 5) permits to observe several analogies.
Sheets B, VI and 7 (+ 45 / + 50 m) can be attributed to
the IS 12, around 450 ka. In the same way, sheets V and
6 (+30 / + 45 m) are dated around 350 ka and could cor
respond
to IS 10. These results permit the suggestion that
during a part of the Middle Pleistocene, the three sectors
have known the same evolution.
For the higher formations, only the «Massif Central»
sector outcrops have been consistently dated, but, in this
sector where the survey is particularly difficult, the age
gap between the various alluvial formations could indi
cate the existence of unidentified intercalated terraces. In
the intermediate and Paris Basin sectors, ESR analyses of
sheets VIII to XI and 8 are in progress, in order to confirm
the supposed Early Pleistocene age of these formations.
Four and five alluvial formations are observed, respec
tivelyin the intermediate and Paris Basin sectors, between
the present river valley and the 350 ka terrace. It could
indicate either the act of recent tectonics or local land
slides, or the formation of several stepped terraces during
a same isotopic stage, in particular IS 7. Such a model
has been proposed for the Somme system where two allu
vial sheets were attributed to IS 7 (Antoine et al, 2000).
However, the poor ESR sensitivity of the Al-center do not
permit a precise estimation of the ages of these youngest
levels. New studies using the titanium-ESR center, which
is more sensitive, are still in progress.
CONCLUSION
Systematic surveys and analyses undertaken on the
alluvial remnants of the Middle Creuse River Valley
between Crozant and Le Blanc have permitted the recoPans Bassin
sector
Plateau
Sheet VIII (+55/+60 m)
deposits Sheet 8 (+S2/+S5 m) 800 ka
Sheet VII (+5O/+55m) 500 ka
Sheet 7 Q 45/ 47m)- 450 ka
SheetVU^45+50m}
450
ka
' Sheet V (+30/+45 m) 350 ka
Sheet 6 Sheet
(+30 +45
m) 330mjka
5 [+25/+3O
Sheet IV [+15 +30 m) 220 ka
Sheet
4 H20/->25 m)
Sheet Ul (+10M5 m) 200 ka
/
Sheet 3jt +1O/+20 mj( -J50
ka
f Sheet Sheet
U(+5/+10m)
I (0-5m) 130 fc
Sheet 1 MOjn)
(0/+5. n
Fig. 5: Schematic chronological synthesis of the Creuse River fluviatil system, according to the ESR dating results obtained in the three sectors.
Fig 5 Synthèse chronologique schématique des trois secteurs de la vallée moyenne de la Creuse d'après les résultats obtenus par la méthode RPE
85
gnition of a complex fluvial system which covers all the
Pleistocene. Numerous ESR analyses allow a prelimi
nary
chronological framework to be proposed.
At least eleven alluvial formations are identified. The
more ancient alluvial formation, at "Le Pin", is dated at
1.7 Ma and indicate the antiquity of the beginning of the
incision; this date is quite similar to data obtained in the
Somme (Antoine et al, 2000 and 2003) and Thames sys
tems (Maddy et al, 2001; Westaway et al, 2002). Anot
her sheet is attributed to the Early Pleistocene, around
1.1 Ma. In this terrace, archaeological remains attest of
a local ancient human settlement, as observed in others
sites of the Mediterranean area.
As noted in others north european fluvial systems, the
Middle Pleistocene is characterized by an increase of
the uplift rate. However, the interpretation of the Creuse
system is complicated by intense local tectonics and the
exact number of alluvial sheets need to be precisate.
Only the IS 12 and 10 are clearly recognized in the dif
ferent studied sectors. Finally, the response of the fluvial
system to IS 7 could be complex, with at least two allu
vial sheets.
Not all the alluvial formations are not yet been thor
oughly studied, but their relative positions were recently
recognized over a three kilometers wide strip along the
gas pipeline that was being laid in 2000. New ESR ana
lyses but also the use of other geochronological methods
(such as OSL and palaeomagnetism) will help reconst
ructa more precise chronostratigraphical history for the
setting of this fluvial system.
ACKNOWLEDGEMENTS
The authors thank :
- The french Ministry of Culture (Sous-Direction de l'Archéologie,
Service régional de l'Archéologie en région Centre), the Centre Région
Council, the Indre department, the Community of Argenton-sur-Creuse
Country Communes, the towns of Argenton-sur-Creuse, Baraize, SaintMarcel and Le Pêchereau, the " Association de sauvegarde du Site
Archéologique d'Argentomagus " (ASSAAM) and the archaeological
museum of Saint-Marcel for financial and technical supports ;
- The Ile-de-France Région Council for financial support related to
the ESR spectrometer acquisition ;
- Mr Jean-Michel Dolo (LNHB-CEA) for the irradiation facilities,
Miss Cécile Pansseaux (Ecole des Mines, Pans) and Mr Bernard Monn
(SIARE, university of Pans VI) for their helps dunng ESR measure
ments;
- Ms Anna Kay-Bourg and Miss Hannelore Janssens for the english
translation;
- Mr Martin R Bates, David Bndgland and Rob Westaway for their
comments and suggestions to ameliorate this paper.
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