Quaternary International 302 (2013) 184e198
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Clay minerals of late Pleistocene sites (Jonzac and Les Cottés, SW France): Applications of X-ray diffraction analyses to local paleoclimatic and paleoenvironmental reconstructions Marine Frouin a, *, Florian Ploquin b, Marie Soressi c, d, e, William Rendu f, Roberto Macchiarelli g, h, Abderrazak El Albani b, Alain Meunier b a
IRAMAT-CRP2A, UMR 5060 CNRS, Université Bordeaux 3, Esplanade des Antilles, 33607 Pessac, France IC2MP-HYDRASA, UMR 7285 CNRS, Université de Poitiers, Bât. B 8, rue Albert Turpain, 86022 Poitiers cedex, France INRAP (Institut national de recherches archéologiques préventives), 525 Avenue de la Pomme-de-Pin, F-45075 Saint Cyr-en-Val, France d Max Planck Institute for Evolutionary Anthropology, Department of Human Evolution, Leipzig, Germany e UMR 7041 Antet, F-92023 Nanterre, France f TRACES, UMR 5608 CNRS, Université Toulouse e Le Mirail, Maison de la Recherche, 5 allée A. Machado, 31058 Toulouse cedex 9, France g UMR 7194, Département de Préhistoire, Muséum National d’Histoire Naturelle, 1 rue René Panhard, 75013 Paris, France h Département Géosciences, Université de Poitiers, 40 avenue du Recteur Pineau, 86022 Poitiers Cedex, France b c
a r t i c l e i n f o
a b s t r a c t
Article history: Available online 17 December 2012
The crystal-chemical properties of clay minerals are closely dependent on the physicochemical conditions prevailing at the time when they formed in soils and weathered zones. The degree of alteration of primary minerals and the composition of the secondary products are clearly linked to climate and plant cover. In particular, changes are rapid under temperate conditions which favor the development of thick soils, but slow in cold contexts favoring thin and fragile soils. In this paper, the mineral composition of two Pleistocene clay-rich deposits is investigated in order to contribute to reconstructing paleoenvironmental changes. Jonzac (Charentes, SW France) and Les Cottés (Vienne, SW France) are two rockshelters with long archaeological sequences which include faunal remains and were recently radiometrically dated. The decomposition of XRD patterns at each site allows identification of the principal mineral phases and semi-quantitative estimation of their relative proportions. The variation of these proportions is analyzed through indexes based on the relative intensities of the decomposed bands. The clay fraction of both sites mostly results from the transformation of the minerals forming the sediments in the surrounding area of the rock-shelter terrace, including contributions from the hillside. Mineralogical clay data are compared with the faunal spectrum identified at both sites in order to discuss paleoenvironmental implications. At Jonzac, during the Quina Mousterian period dated to MIS4, the environment was cold and dry. The dominant mineralogical phases are inherited from the rocks (weak pedogenesis). This is consistent with the faunal analysis data typical of the MIS4. During the Mousterian of Acheulean Tradition period, dated to MIS3, the mineralogical composition of the clay deposits changed significantly, suggesting a less wet environment. The Aurignacian deposits dated to the end of MIS3/early MIS2 are rich in mixed layer minerals (MLMs) which are produced by the hydrolysis processes in soils. The climatic conditions probably became milder. However, because no faunal remains were found, this evolution is uncertain. The Les Cottés deposits, dated between MIS3 and early MIS2, are mineralogically typical of a cold environment where soil reactions are not very active. However, some weak variations of the indexes suggest temporary temperate conditions during the Les Cottés interstadial and in the Aurignacian. The parallelism between mineral signature and paleontological evidence in recording relatively rapid variations between contrasted climates suggests that clay mineral assemblages from rock-shelter deposits can be used to assess paleoclimatic and paleoenvironmental dynamics at a local scale. Ó 2012 Elsevier Ltd and INQUA. All rights reserved.
* Corresponding author. E-mail address:
[email protected] (M. Frouin). 1040-6182/$ e see front matter Ó 2012 Elsevier Ltd and INQUA. All rights reserved. http://dx.doi.org/10.1016/j.quaint.2012.12.011
M. Frouin et al. / Quaternary International 302 (2013) 184e198
1. Introduction Caves and rock shelters usually constitute relatively stable environments which favour the preservation of anthropogenic and paleobiological remains (Rouzaud, 1997). In particular, these domains act as excellent local sedimentary traps, likely to record environmental and climatic fluctuations through mineralogical changes occurring in sediment composition (Campy, 1985, 1990; Quinif and Bastin, 1993, 2006; Quinif et al., 1994; Verheyden et al., 1999; Salomon, 2000; Texier, 2000, 2001; Le Fillâtre, 2001; Häuselmann et al., 2002; Lenoble and Bertran, 2004; Pirson et al., 2006; Bertran et al., 2008). The crystal-chemical properties of clay minerals are closely related to the physicochemical conditions prevailing when they form in soils and weathered zones, and the degree of alteration of primary minerals and the composition of the secondary mineral products reflect local climate and plant cover (Banfield et al., 1999; Sheldon and Tabor, 2009; Graz et al., 2010). Accordingly, the clay signature can be used as a proxy to characterize the evolution of the local environmental conditions in response to global climatic changes. They may contribute to the study of time-related changes affecting the ecosystems (Deocampo et al., 2010; El Albani et al., 2011). Nonetheless, in spite of their potential informative value and the fact that clay minerals are usually abundant, they have not been identified with high precision in such contexts (Robert et al., 1991; Elsass and Robert, 1992; Delagnes et al., 1999; Foos et al., 2000; Polyak and Güven, 2000). This is now possible thanks to recent developments in the
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interpretation of x-ray diffraction patterns (XRD). Clays have become an increasingly useful tool suitable for climatic and environmental reconstructions in archaeological contexts (e.g. El Albani et al., 2011). The Charente and Vienne basins, in SW France (Poitou-Charentes region), have been known for over a century for the wealth of their Middle and Upper Paleolithic sites, which have delivered a significant number of Neanderthal and Anatomically Modern Human (AMH) fossil remains. This quite favourable area for prehistoric and paleoanthropological research relates to the widespread presence in the region of rock shelters and caves hosted in Jurassic and Cretaceous limestone formations which have been locally excavated and shaped by rivers and then partly filled by Quaternary alluvial and colluvial deposits (e.g. El Albani et al., 2011). Within this framework, the purpose of the present study is to make a comparative assessment of the climaticenvironmentally-related variations using the clay mineralogical composition of the sedimentary deposits in two Late Pleistocene rock-shelters located in southwest France: Jonzac and Les Cottés. They are both anthropic sites which were occupied from the Middle Paleolithic to the beginning of the Upper Paleolithic. Recent radiometric dates have shown that deposits are as old as MIS (marine isotope stage) 4 at Jonzac, as old as MIS 3 at Les Cottés, and up to the end of MIS 3 and early MIS2 at both sites (Talamo et al., 2012; Richter et al., 2013). This key-period in Western Europe saw the decline and disappearance of Neanderthals and the firm establishment of anatomically modern humans.
Fig. 1. Localisation of Jonzac and Les Cottés caves sites, SW France, in geological map of the area (Barrier et al., 2006 modified).
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M. Frouin et al. / Quaternary International 302 (2013) 184e198
2. Geological and stratigraphic setting The site of Jonzac (also named Chez Pinaud) is a rock-shelter located against a small Turonian (Upper Cretaceous) limestone cliff along the Seugne River in the department of CharenteMaritime (Fig. 1). Following the original field work conducted by J. Airvaux (Archeological Service of Poitou-Charente; Airvaux, 2004; Airvaux and Soressi, 2005), a multidisciplinary research project was conducted at the site by the Max Planck Institute (MPI) of Leipzig and University Bordeaux 1 from 2004 to 2007 (Jaubert et al., 2008). The deposit, which has a 6 m-thick sedimentary sequence from the Middle to the first part of the Upper Paleolithic (Fig. 2B), consists (from bottom to top) of the following 25 levels (US) of archeological interest: US-25 to US-09, associated with a Neanderthal occupation as indicated by a Quina Mousterian technology; US-08 to US-06, documenting the late Middle Paleolithic Neanderthals (Levallois Mousterian with denticulates, and Mousterian of Acheulian tradition); and US-05 to US-01 (Aurignacian and Gravettian) corresponding to sparse AMH occupations (Jaubert et al., 2008). Thermoluminescence dating of heated flint artefacts places the Quina type Mousterian into MIS 4. The overlying assemblage of Levallois Mousterian with denticulates, which is followed by two layers with Mousterian of Acheulean Tradition, are all assigned to MIS 3 (Richter et al., 2013). The Aurignacian is about 35 3 ka BP (Richards et al., 2008). The faunal assemblages
of the Quina Mousterian and Levallois/Mousterian of Acheulian Tradition levels are respectively dominated by reindeer and horse, and bovids (Beauval, 2004; Bourdillat, 2004; Jaubert et al., 2008; Niven et al., 2012). For the present study, 12 sediment samples were collected for mineralogical analysis along the entire archaeological sequence from Quina Mousterian to Aurignacian. The site of Les Cottés is located near the village of Saint-Pierrede-Maillé, in the department of Vienne (Fig. 1). The cave lies on a Jurassic limestone plateau, 12 m above the Gartempe River (e.g. Barrier et al., 2006; Soressi et al., 2009). Since 2006, a new excavation and study program directed by M.S. and supported by the Max Planck Institute (MPI) of Leipzig has been undertaken. Archeological field work originally run by L. Pradel during the 1950s mostly concerned the deposits on the terrace directly in front of the cave, where an undisturbed stratigraphic sequence documenting a Mousterian (Middle Paleolithic), a Perigordian II (or evolved Chatelperronian), and a Aurignacian I (Upper Paleolithic) occupation phases have been reported, together with scattered elements of “primitive Perigordian, of Gravettian or Perigordian IV” identified towards the top of the sequence (Pradel, 1959, 1961, 1963, 1967). As a whole, the lithic assemblage at Les Cottés shows a typotechnological evolution from a classical Mousterian (Charentian type), through the Chatelperronian (locally characterized by the socalled “Les Cottés points”), to an early Aurignacian (with split-base bone points) (Soressi et al., 2010). The 4 m-thick deposit, which is
Fig. 2. Stratigraphic profile from the main section of Jonzac and origin of the sediments samples (from Airvaux and Soressi, 2005).
M. Frouin et al. / Quaternary International 302 (2013) 184e198
surmounted by a few cm-thick humic horizon (US-00), consists of the following five stratigraphic units (from bottom to top): U1, represented by the US-09 and US-08 levels corresponding to a Neanderthal occupation associated to a Mousterian lithic
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then submitted to acid attack (using 1/10 N hydrochloric acid and 1 N acetic acid). The insoluble residue was used to prepare oriented slides (Moore and Reynolds, 1989) in air-dried (AD) and ethylene glycol solvated (EG) for analyzes by X-ray diffraction.
Table 1 List of the samples from Jonzac, Les Cottés and from their surrounding area, used for clay mineral analysis. Location
Sample reference
Type
Sample origin
X, Y, Z (local landmark)
Archeological context
Jonzac
D12-78 E13-1926 E13-1925
Sediment Sediment Sediment
US-02 US-05 US-06
1004.668,1088.436,2.752 1005.58,1087.567,4.207 1005.61,1087.505,4.433
E12-1212
Sediment
US-08
1005.649,1088.5,4.476
F12-881 F9-606 F9-603 F9-602 F9-599 G9-3468 G9-3465 G9-3463 JZC- 01 JZC-02 JZC-03 JZC-04 JZC-05 JZC-06 A3-181 A3-183 A3-184 A3-185 A3-186 A3-188 A3-190 A3-191 A3-192 A3-193 Z2-52 Z2-53 Z2-56 CTS-01 CTS-02 CTS-03
Sediment Sediment Sediment Sediment Sediment Sediment Sediment Sediment Limestone Limestone Limestone Limestone Limestone Limestone Sediment Sediment Sediment Sediment Sediment Sediment Sediment Sediment Sediment Sediment Sediment Sediment Sediment Limestone Limestone Limestone
US-09 US-10 US-13 Limit US-14/US-15/US-16 US-19e20 US-22 upper US-22 bottom US-23 Eocene Campanian Santonian Coniacian Turonian Cenomanian US-01 Limit US-01/US-02 US-03 upper US-03 bottom US-04 upper US-04 bottom Limit US-04/US-05 US-05 US-06 Limit US-06/US-07 Limit US-06/US-07 US-07 US-08 Lower Oxfordian Upper Oxfordian Cenomanian
1006.163,1088.696,4.686 1006.577,1091.794,4.249 1006.581,1091.788,4.583 1006.615,1091.792,4.711 1006.707,1091.831,5.1 1007.329,1091.181,5.857 1007.241,1091.238,6.213 1007.315,1091.292,6.525
Aurignacian Aurignacian Mousterian of Acheulean Tradition (MTA) Levallois with denticulates Mouterian Quina Mousterian Quina Mousterian Quina Mousterian Quina Mousterian Quina Mousterian Quina Mousterian Quina Mousterian Quina Mousterian
Les Cottés
assemblage; U2 (US-07), corresponding to the Middle to Upper Paleolithic techno-cultural boundary (the so-called “Les Cottés interstade”); U3 (US-06), relative to a Chatelperronian phase; the U4 Aurignacian occupation (US-05 to US-02 levels); and U5 (US-01 level), delivering scarse upper paleolithic remains. The levels above US-06 are unequivocally associated with the presence of AMH. Recently available AMS 14C dates constrain the Middle to Upper Palaeolithic sequence between 44 1 (final Mousterian) to 36.7 0.3 ka (Early Aurignacian) (Talamo et al., 2012). The fauna spectrum represented so far mostly consists of reindeer, bison, and horse. The sediment of the US-08 to US-03 is clayey gravelly, red brown to grey brown. The sediment of the upper level is clearly finer, dark brown edified by mudslide (Soressi et al., 2010). For the purposes of the present study, thirteen sediment samples were collected for mineralogical analysis along the entire sequence (Fig. 3). 3. Analytical methods 3.1. X-ray diffraction preparations The limestone samples from the surrounding cliff of each site (Table 1) were crushed to prepare randomly-oriented powders and
Cavity formation 1001.426,1003.828,1.233 1001.385,1003.754,1.676 1001.247,1003.258,1.869 1001.272,1003.245,2.071 1001.184,1003.299,2.319 1001.154,1003.262,2.476 1001.121,1003.238,2.594 1001.096,1003.21,2.687 1001.126,1003.174,2.78 1001.05,1003.156,2.893 1000.804,1002.153,2.689 1000.756,1002.173,2.829 1000.719,1002.168,2.963
Undefined Upper Paleolithic
Early Aurignacian Proto-Aurignacian
Chatelperronian
Interstadial “Les Cottés” Mousterian Cavity formation
The total sedimentary samples from each site (Table 1) and the >2 mm fraction was ground to obtain randomly-oriented powders. Samples were separated into three particle size fractions from the bulk soil by wet-sieving and after ultrasonic treatment and centrifugation to obtain a
