Climatic and environmental patterns in southwestern France

The evidence for climatic and environmental conditions in the Perigord and adjacent regions of southwestern France derives almost entirely from one rather specialized geological source, namely, from the various stratigraphic sequences preserved within the cave and rock-shelter sites of the region. These sequences can be studied from several different perspectives by studies of the detailed sedimentology; geochemistry and micro-morphology of the deposits, by analyses of the preserved pollen content, and by studies of the associated faunal assemblages, including both macro-faunal and micro-fau-nal remains. All these approaches have been applied extensively within southwestern France over the past 30 years, providing an impressive battery of detailed information from many different sites. In particular, the studies of Laville and others on the sedimentology of the cave and rock-shelter and sequences, Paquereau, Leroi-Gourhan and Leyroyer on the palynology of the deposits, and Prat, Delpech, Guadelli, Laquay and others on the faunal assemblages, have been crucially important. We have far more information on these aspects of the cave and rock shelter sequences within southwestern France than we do for any other region of Europe at the present time.

In practice, there are a number of problems in studying and interpreting climatic and palaeoenvironmental data from cave and rock shelter sequences which have been widely debated in the recent literature. The use of sedimentological data in particular has come under close scrutiny, mainly owing to the sparsity of controlled studies of the precise effects of varying climatic regimes on different types of bedrock formations and the difficulty of assessing the impact of local or even humanly induced factors on the specific climatic and environmental conditions of the individual sites (e.g. Farrand 1975,1988; Tex-ier 1990). The interpretation of pollen samples from cave and rock-shelter deposits is also problematical, partly owing to the possibility of downwashing of pollen grains in relatively coarsely textured sediments and partly to the danger of selective destruction of particular pollen taxa in the highly calcareous, alkaline environments encountered in most sites (Turner 1985; Turner & Hannon 1988; Sánchez Goñi 1991, 1993). Even the study of faunal assemblages is not without problems: the challenge here is to differentiate between the effects of purely climatic and ecological changes on the composition of local faunal communities and the role of human selection in the economic exploitation of different species (see Chapter 7 below). In addition one must correlate and synchronize individual stratigraphic sequences recorded in the different sites and recognize significant depositional or erosional hiatuses within the deposits (Laville 1988; Laville et al 1986; Farrand 1975,1988).

Whether or not these problems are as serious in practice as in theory is debatable. Most of the cave and rock-shelter sequences which have been systematically studied within southwestern France present a generally coherent and internally consistent record of climatic and environmental events during the later stages of the Pleistocene in which the majority of the parallel and complementary lines of evidence lead to similar conclusions. The aim of this section is to focus on the most complete and fully documented of these sequences and see how far they can be used to construct a general climatic and environmental framework for the associated records of Middle Palaeolithic occupation in the region.

The Combe Grenal sequence

By far the most detailed and complete record of climatic and environmental conditions throughout the Middle Palaeolithic period in southwestern France is provided by the long sequence excavated by François Bordes at the site of Combe Grenal between 1953 and 1965. The site at present consists of a small cave behind a rock overhang, which lies on the flanks of a small dry valley one kilometre to the south of the Dordogne river (Bordes 1955, 1972; Laville et al 1980). Over the course of its geological history the position of the rock shelter receded gradually towards the north (as a result of progressive weathering and erosion of the bedrock limestone deposits) leaving the major phases of the geological infilling standing on a series of separate rock platforms, which are progressively younger with increasing height above the adjacent valley (Fig. 2.20). The depth of the filling is almost 13 metres. All this sequence has now been studied in detail from the perspectives of sedimentology, pollen analysis and the composition of the associated faunal assemblages (Bordes et al 1966; Laville 1975; Laville et al 1980; Bordes & Prat 1965; Delpech et al 1983; Laquay 1981; Guadelli 1987; Guadelli & Laville 1990) (Figs 2.21, 2.22). As a record of changing climatic and ecological conditions throughout the greater part of the Middle Palaeolithic time range, this sequence is unique within southwestern France.

H 4 ¡ I 4 I J 4 | K 4 i K5 I K6 I K7 I K8 I K9 iKlOlK 111 K 121 K 13IK 14 IK 14 I L 14 lMl4lNl4lO 141 P 141

H 4 ¡ I 4 I J 4 | K 4 i K5 I K6 I K7 I K8 I K9 iKlOlK 111 K 121 K 13IK 14 IK 14 I L 14 lMl4lNl4lO 141 P 141

Figure 2.20 Stratigraphy of the rock-shelter deposits at Combe Grenal (Dordogne, southwestern France), showing the upper (above) and lower (below) parts of the sequence. (Note that the section shown here is folded, and therefore includes both lateral and transverse components of the stratigraphy, as indicated in the central diagram.) Note how the deposits lie on a series of erosional platforms in the underlying limestone, which become progressively younger in age as the rock shelter recedes towards the north. The deposits span a total of over 13 metres, and cover the period from the end of the penultimate ('Riss') glaciation (layers 56-65) to around the middle of the last glaciation (see Fig. 2.23). After Bordes 1972.

Figure 2.20 Stratigraphy of the rock-shelter deposits at Combe Grenal (Dordogne, southwestern France), showing the upper (above) and lower (below) parts of the sequence. (Note that the section shown here is folded, and therefore includes both lateral and transverse components of the stratigraphy, as indicated in the central diagram.) Note how the deposits lie on a series of erosional platforms in the underlying limestone, which become progressively younger in age as the rock shelter recedes towards the north. The deposits span a total of over 13 metres, and cover the period from the end of the penultimate ('Riss') glaciation (layers 56-65) to around the middle of the last glaciation (see Fig. 2.23). After Bordes 1972.

Briefly, the main features of the sequence can be summarized as follows:

1. The basal part of the filling (layers 65-56) consists of a series of stony 'eboulis' deposits which extend over a depth of ca 2.5 metres and lie on the lowermost erosional step in the bedrock formation (Fig. 2.20). All available evidence indicates that these levels were formed under extremely severe climatic conditions - possibly the coldest conditions in the whole of the Combe Grenal sequence. The percentages of arboreal pollen recorded in these levels (Fig. 2.21) remain consistently below 15 percent and in the majority of levels pine is the only tree species represented (Bordes et al 1966). The same pattern is reflected in the character of the associated sediments, which also point to a period of extremely cold, dry climate with intensive frost action and little evidence for any contemporaneous chemical weathering of the deposits (Bordes et al. 1966; Laville 1975; Laville et al. 1980). The composition of the associated faunal assemblages provides further support for this conclusion (Fig. 2.22); throughout all levels remains of reindeer account for between 92 and 97 percent of total ungulate remains with only sporadic traces of other species such as red deer and horse (Bordes & Prat 1965).

All the available evidence therefore points to exceptionally rigorous conditions during the formation of the lower levels, which are assumed to correlate with the period of extremely cold, full glacial conditions represented by the later stages of oxygen-isotope stage 6 (Fig. 2.23) (Laville et al 1983, 1986; Guadelli & Laville 1990; Mellars 1986a, 1988). Archaeologically, these levels produced a series of late Acheulian industries characterized by rather crudely made hand axes and low frequencies of Levallois technique (Bordes 1971a).

2. The second major climatic episode in the Combe Grenal sequence is represented by a period of heavy weathering and associated soil formation which affected virtually all deposits formed during the preceding 'Ris-sian' period to a depth of at least 1.0 metres. According to Laville (1975; Laville et al 1980), it is unlikely that any entirely new deposits were laid down during this interval and it would seem that the upper levels of the associated soil horizon were truncated and eroded by the effects of heavy humidity during the later stages of this period. As a result there are no direct records of either pollen, faunal remains or associated archaeological assemblages for this interval. Nevertheless, it is clear that this period represents a prolonged episode of very warm, humid climate which must have persisted for several thousand years. All authors are now agreed that this can be correlated with the peak of the last interglacial period (i.e. isotope stage 5e of the deep-sea core sequence) and accordingly dated to around 120-125,000 BP (Fig. 2.23) (Laville et al 1983,1986).

3. The third major phase in the Combe Grenal sequence is represented by the block of deposits between levels 55 and 38 spanning approximately 2.5 metres in depth and lying, once again, on a separate erosional step in the bedrock formation. The combination of the sedimentological and pollen evidence shows that these deposits formed during a succession of four major climatic oscillations comprising two major cold episodes and two prolonged episodes of much warmer climate. The cold episodes, represented in layers 55-53 and 49-44, were characterized by severe climatic conditions leading to intensive frost action in the formation of the associated sediments and reducing tree-pollen frequencies in the local habitat to around 12-15 percent (Fig. 2.21). Nevertheless, it is significant that arboreal pollen frequencies in these levels are consistently higher than those recorded in the majority of underlying Tate Rissian' levels and show a continuous record of species such as juniper alder and hazel in addition to the hardier species of

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