As a result of large-scale archaeological surveys in the Sierra de Atapuerca Mountains, materials from the first half of the late Pleistocene (marine oxygen-isotope stage 4) were discovered at open-type sites. The Middle Paleolithic complexes of the Hundidero site, discovered in 2004, date back to 70-56 thousand years ago. Typological and technological features of this monument are paralleled in the collections of 30 synchronous open-type sites in the Atapuerca Mountains. Perhaps all these sites were periodically visited by groups of Neanderthals-carriers of the same cultural tradition, which is characterized by poorly modified stone tools, various methods of secondary processing, the use of mainly dorsal retouching, a tendency to microlitization and reuse of tools.

Keywords: Middle Paleolithic, rock technology, oxygen-isotope stage 4, open-type sites, human settlements, Sierra de Atapuerca (Spain).

Introduction

The Hundidero site, as well as 30 other open-type sites in the Sierra de Atapuerca Mountains, became known due to intensive large-scale archaeological surveys in 2000-2003 (Navazo and Diez, 2001, p. 7; Navazo, 2002, p. 77). Documentation of all open-type monuments, which was carried out directly in the Sierra de Atapuerca and around them, revealed 181 Stone Age sites, including 31 Middle Paleolithic settlements. Before that, there were Middle Paleolithic pa-

mints in the karst cave landscape common to Atapuerca were not known. Geological and archaeological materials were identified and typologized in order to determine the sources of raw stone for Middle Paleolithic sites (Navazo et al., 2008, p. 1962), the primary outcrops and secondary locations of which were discovered during exploration. The raw materials are represented by two types of flint (Cretaceous and Neogene) and quartzite. In 2003, during the second stage of research, several pits were laid at the Hundidero site to study the stratigraphic sequence and distribution of cultural deposits and determine the prospects for excavation of this monument. As a result, several levels of habitat belonging to the Late Pleistocene (marine oxygen-isotope (hereinafter referred to as MIS) stage 4) were traced in the stratigraphy of the site. Since 2004, the third stage of the study has begun, its goal is to identify sites where archaeological materials and stratigraphic sequences have been preserved in an undisturbed state.

This article presents the results of studying the 8 ^m2 Hundidero site excavated in 2004-2006.

Geological and geomorphological contexts

The study site is located on the right side of the middle part of the Arlanson River Valley, in the northeastern sector of the Cenozoic Duero River basin (north-central Iberian Peninsula). In the east, the Duero basin is connected to the Ebro River basin by the Burebo corridor (Fig. In this part of the Duero basin, continental tertiary deposits surround outcrops of Mesozoic rocks extending along the Sierra de Atapuerca mountain range from north-northeast to south-southwest (Figure 1B). The latter are mainly represented by Upper Cretaceous dolomites, limestones, and to a lesser extent marl, sandstone, and conglomerates; the Jurassic period is also present. limestone, Triassic clay, and evaporites (Pineda, 1997, p. 8). Upper Cretaceous carbonate rocks are subject to karst formation (Benito, 2004, p. 62; Ortega et al., 2005, p. 165), an example of which is the karst system in which the cave archaeological sites of the Sierra de Atapuerca are located (Fig.

In the Neogene, Mesozoic rocks were denudated and leveled by four erosional surfaces with simultaneous filling of the Duero Valley (Benito-Calvo and Pérez-González, 2007, p. 226) with synorogenic conglomerates and clays, which were overlain by post-horogenic Miocene alluvial and Lacustrine sedimentary deposits (Santisteban et al., 1996, p. 183; Armenteros et al. al., 2002, p. 309]. A limestone layer containing flint is also found in this sequence (Pineda, 1997; Navazo et al., 2008, p. 1961).

In the Quaternary, the sediments in the northeastern part of the Duero Basin were dissected by a system of watercourses that formed the valleys of the Arlanson River and its tributaries (Fig. 1 (B)) (Benito, 2004, p. 159; Benito-Calvo et al., 2008, p. 196). They have a sequence of 14 levels of fluvial terraces.

The results of thermoluminescent dating suggest that terrace 14 (+2 - 3 m) belongs to the Holocene (4,827 ± 338 bp), and terrace 11 (+12 - 13 m), 115,052 ± 11,934 BP, belongs to the boundary between the Middle and Late Pleistocene [Benito-Calvo et al., 2008, p. 198]. Magnetostratigraphic data show a normal polarity for terrace 4 (+ 60-67 m), which suggests the Early Pleistocene age of this and earlier terraces. During the formation of the Early Pleistocene terraces, the endocarst system of the Sierra de Atapuerca was open, which determined the possibility of penetration of allochthonous deposits into the karst cavities and human habitation in caves (Carbonell et al., 2008, p. 465).

Deposits of the Hundidero site are located in the southern part of terrace 4, at the level of +66 m. Here, on the flat, flat surface of the terrace, a semi-drainless area is marked, where in the late Pleistocene, temporary watercourses formed deposits of the water-erosion cycle - quartz sands, well-rounded quartzite gravel, and illuvial clays. This system of temporary channels originates in the south, in the sediments of a small valley that drained the semi-drained area in the direction of the Arlanson River (Fig. There was a small seasonal pond in the inner area of the terrace, and its traces are still recorded today (Fig. Further to the north, slope deposits moved from the surface of terraces 3 (+75 m) and 2 (+84 m) are noted. The rock base of the terrace consists of Middle Miocene marls and clays, underlain by limestone, which contains flint nodules up to 1 m in size. This siliceous layer is exposed in a number of places on the terrace cliffs (Figs. 1, C, D).

Stratigraphy

Deposits of the Hundidero site are detrital sediments that were deposited as a result of erosion of Terrace 4 (+66 m), originally created by alluvial processes (Fig. They consist of gravel and stratified sediments, for which

1. Geological and geomorphological contexts of the Hundidero site. A - main geological divisions on the Iberian Peninsula: 1-Cenozoic; 2-Mesozoic; 3-Paleozoic-Precambrian; B - topography of the middle part of the Arlanson Valley and the Sierra de Atapuerca Mountains; C-geomorphological map of the site's surroundings: 1-Miocene clays and marls; 2-Miocene limestones; 3-Early Pleistocene river terraces 4-Middle Pleistocene river terraces; 5-detritus deposits; 6 - outflow cones; 7-colluvium; 8-river terrace cliffs; 9-rock cliffs; 10-runoff system; 11-flow directions; D-geomorphological synthetic model of formation of parking lot deposits.

it is characterized by an increase in grain size up the section from fine-grained to fine-grained. The sediments were affected by illuvial and hydromorphic processes of pedogenesis, which caused the formation of illuvial clays, gley horizons, and manganese oxides.

In these deposits, four stratigraphic levels were identified that are inconsistent (Figure 2). The lower, respectively oldest, level 4 (thickness 50-60 cm) is inconsistent with the Middle Miocene rocks. It is represented by well-rounded quartz grains, pebbles and boulders (max.-

2. Chronostratigraphic sequence of deposits of the Hundidero site. 1 - sands and silts; 2, 3-clays; 4-quartzite gravel; 5-continental clays and marls; 6 - "fresh" artifacts; 7 - "fresh" artifacts with weathered edges; 8-rounded artifacts.

individual sizes up to 20 cm) associated with temporary watercourses. The filling rock of red-brown and yellow color is created by illuvial processes; its mechanical composition varies from sandy loam to clay. Some level 4 fragments are found in the underlying continental rock: they got there as a result of gravitational processes. Level 3 with a thickness of 20 cm lies above level 4. Its base is composed of well-rounded quartzite gravel and pebbles (the maximum size of individuals is 14 cm), the upper part-sediments consisting mainly of clays (more than 60%) and to a lesser extent of sand and silt. The presence of pebbly material at the base of the level is associated with the activity of the same temporary watercourses, while the accumulation of clay in the upper part of the sediments is associated with slow deposition in a stationary water environment. Level 2 (thickness 15 - 40 cm) is characterized by a predominance of clay (up to 80%); it also contains some rounded fragments and manganese oxides. A high proportion of clays and a gentle slope angle suggest relatively stable sedimentation conditions, presumably associated with seasonal reservoirs, fine sediment deposition, and sporadic currents. The upper layer 1 (thickness 20 - 50 cm) is intensively processed as a result of plowing, has a sandy structure; gravel is found in it - another evidence of periodically flowing water here.

Luminescent dating of quartz grains performed at the Laboratory of Dating and Radiochemistry of the Independent University of Madrid yielded the following dates: for the top of level 4 - 70,556 ± 11,011 bp (TL), for level 3 - 56,157 ± 4389 BP (OSL). A significant chronological gap was established between the base of Level 2 - (58,788 ± 4,907 BP (TL)) and its top (30,221 ± 3,636 BP (OSL)) (Figure 2). The nature of the tool assemblage found at this stratigraphic level and the consistent distribution of other chronological definitions confirm these definitions.

Archaeological materials

For the manufacture of stone tools, Neogene flint was mainly used. The outcrops of tertiary marls around Hundidero contained limestone with blocks of Neogene flint up to 1 m in size included in them (Fig. 3, A). Analysis of sections of this material revealed very high porosity, especially in the area adjacent to the crust; color change due to a high content of iron oxide (FeO); the presence of some gypsum in the surface of the crust. 3, B) (Navazo et al., 2008, p. 1966).

The structure of silicon was studied by inductive coupled plasma mass spectrometry (ICP-MS). Compared to the traditional methods, this geochemical method has several advantages: the ability to determine most elements of the periodic table (except for the lightest elements), even if they are represented in negligibly low concentrations; the minimum degree of sample destruction during analysis [Kennett et al., 2001] - only 12-17 mg of rock is required; very short (approximately 4 min) the time required to conduct the study (Navazo et al., 2008, p. 1964). The ICP-MS method was used to study samples from level 2 (both untreated flint and those with traces of processing), which were almost identical in composition.

Complexes of archaeological levels of the Hundidero site are relatively few (pl. 1), but they have a fairly high information potential. In accordance with the analytical logical system of stone inventory description (Carbonell and Mora, 1986), a technological description and classification of stone tools were compiled.

Level 1, which is closest to the daytime surface, is represented by sediments processed in the course of modern human activity, and is located in the soil horizon A with the remains of grass roots.

3. Natural flint nodule (A); sections with traces of accumulation of spherical dark opaque (left) and ribbon inclusions of gypsum (right) (B).

Table 1. Stone inventory of the Hundidero parking lot levels under study, units.

vegetation. Until 1971, this site was plowed. The complex is located in the original stratigraphic position, but the spatial position of the artefacts was disturbed as a result of agricultural activities (Navazo and Diez, 2008, p. 323).

The collection of this archaeological level contains 109 items: 103 items made of flint and 6 items made of quartzite. A fragmented (dimensions 96x70x33 mm) pebble implement with a negative of deliberate chipping on the surface was found. Three disc-shaped nuclei were also found on flint flakes. For two products, the residual impact area of the blank served as a splitting plane or a spin platform (Fig. 4, B). 4, A). The flakes are made of flint (92%) and quartzite (8%). Most of them have smooth impact pads, while the smaller part has linear and dotted ones; individual flakes retain dihedral and faceted pads. The dorsal surface of almost all artefacts lacks a natural crust. Several products are derived from a disc-shaped nucleus (Pseudolevallois flakes); Levallois flakes and edge chips are presented. There are products with traces of recycling on the longitudinal edges. Environments-

Figure 4. Level 1 industry.

The largest size of flakes is 28 × 24×8 mm; these are micro-flakes (Bagolini, 1968). Five retouched flakes are slightly larger in average size (31×25×11 mm) than non-retouched ones. They are represented by toothed, notched, and beak-shaped tools, a scraper, and a scraper (Fig. The latter is made of quartzite, it has a smooth impact pad and a dorsal surface without traces of natural crust, the rest of the products are made of flint.

Level 2 is saturated with fine detritus, characterized by a high concentration of illuvial clays. These deposits contain artifacts that we have divided into two groups. The first one includes 99 items with a "fresh", non-modified surface, the second one-10 items with eroded planes and" fresh " longitudinal edges. These artefacts were probably eroded without being moved from their original location. The collection consists of 105 items: 98 units-made of flint, 6 units. - made of quartzite and 1 unit. - quartz.

Two tools were found on quartzite nodules with traces of longitudinal unidirectional cuts that form the working edge. A depleted core (dimensions 106×91×85 mm) of quartzite was found, having an impact pad formed by a single removal, and negatives of deep longitudinal unidirectional chips. Two nuclei on the flakes demonstrate a disc-shaped design technique. They are similar in size: one (48x38x27 mm) is made on biface, the second (42x43x17 mm) is made on a fragmented edge chip. The latter has cleavage marks on the ventral plane; in terms of the degree of patination, the negatives of the images differ from the blank of the nucleus.

Only 75 flakes were found. Analysis of the negative images taken on the dorsal surfaces showed that 11% of flakes were obtained as a result of using centripetal splitting technology, and some products represent the use of the kombev technique. There are many edge chips in the collection. Flakes are mostly small and medium (average size 26 × 24×9 mm). Some of them bear traces of use. Almost all of them, except for one tip, have non-faceted and smooth drum pads. More than 85% of the impact sites are the result of a single cleavage; they are followed in representativeness by sites decorated with two shots; only a few objects have preserved natural impact sites. The dorsal surfaces of almost all artifacts are free of traces of natural crust. Many flakes have crusted edges (Fig. 5, A-B).

25 retouched flakes were found, 10 of them. 5, D). Almost all products are made of flint, with the exception of a toothed tool made of quartzite; the impact pads are usually smooth. Dorsal surfaces do not bear traces of natural crust. The most widely presented cool retouching. 5, F) and notched tools predominate, there are also scrapers (one with elements of scaly retouching), scrapers and a point. Several flakes were obtained using a disk-shaped cleavage system. In one toothed tool, the retouched surface differs in the degree of patination from the rest of the surface (Fig. 5, D). This artifact (dimensions 41x38x14 mm) is slightly larger than non-retouched items. In one of the end scrapers, the thicker proximal end shows signs of deliberate design - on one longitudinal edge, the back, characteristic of knives, is sharply retouched (Fig. 5, E).

Tools with "fresh" edges and slightly rounded planes (like other products) have smooth impact pads (with the exception of one pad formed by two removals) and dorsal surfaces without traces of crust. Typologically, these include toothed tools, end scrapers, and scrapers. Some flakes belong to the category

Figure 5. Level 2 industry.

they are of medium size - 39×35×14 mm. We believe that during the formation of level 2 (less than 56 KA BP), there were several episodes of settlement of the site; this is evidenced by different patinization on the nucleus and toothed tool.

Level 3 with a thickness of 15 cm is quite close to level 2 in terms of sediment characteristics.It is composed of bluish clay, which is inherent in poorly drained soils, in which manganese oxides are present and gley processes occur. A complex of 39 artifacts was found here: more than half are flakes, followed by retouched flakes, atypical cores and chippers. Almost all objects are made of flint, only five artifacts are made of quartzite and two are made of quartz. A few highly eroded objects were not analyzed; they entered the layer, most likely from the surface of Terrace 4 (+ 66 m), which was eroded in the Middle Pleistocene. Two quartzite breakers were found. One (dimensions 63×48×31 mm) has traces of clogging, the other bears two negative chips produced after fragmentation of the product. Two nodules were found that were used to remove flakes: one from quartz (Fig. 6, B), the other from flint (Fig. 6, A). The first one showed traces of clogging at the base and negatives of very deep flat unilateral removals at the distal end. The second object is a disc-shaped single-sided nucleus.

One of the two nuclei on the flakes is distinguished by its small size. It has three splitting fronts and several shock pads. This artifact most likely represents the testing stage. Another nucleus made on a Kombev flake retained a faceted impact pad (Fig. 6, D).

The small category (dimensions 21×17×8 mm) includes 12 flakes with smooth impact pads. Their dorsal planes are without traces of crust. It can be assumed that some flakes were chipped using a centripetal splitting system.

Two of the seven retouched objects are toothed tools (Figure 6, F); there are also two notched tools, two scrapers, a short end scraper (Figure 6, E) and a toothed point. One toothed tool is made on a rounded chip. The collection includes scrapers with elements of steep retouching at the transverse distal end (Fig. 6, C) and with traces of ventral retouching on the right longitudinal edge, as well as with signs of use on the left edge (Fig. 6, E). The new working blade on the longitudinal edge of the last artifact could have been designed after the first one was removed. the transverse edge became unusable, and it is also possible that the tool was used during two different episodes of settlement of the parking lot. The average size of the guns (41 × 37×14 mm) is slightly larger than that of non-retouched flakes. In terms of morphological characteristics, the tools are close to non-retouched chips - they have smooth impact pads and dorsal planes without traces of natural crust. The small proportion of tools and the presence of signs of their reuse suggest that during the accumulation of Level 3 sediments, the Hundidero site was repeatedly visited by Neanderthals.

Level 4 is characterized by sediments composed of quartzite gravel that was displaced from river terrace 4 (+66 m). During excavations at this level, two quartzite chocks were found with traces of clogged dimensions of 72 × 62×53 and 52×47×40 mm (Fig. 7, A). A nucleus with dimensions of 165× 90 ×58 mm was also found. This object on one plane of the transverse distal end bears traces of splitting, at the proximal end there are traces of clogging. It can be assumed that the product was used as a pest for processing organic raw materials.

Figure 6. Level 3 industry.

Figure 7. Level 4 industry.

The disk-shaped cleavage system is represented by both ordinary nuclei and nuclei on flakes. One of the five usual nuclei is fragmented, the second is multi - site, the third is two-sided longitudinal, multi-site, the fourth is orthogonal bilateral, the fifth is a fragment with negatives of several flakes taken in the longitudinal direction. There is a flint block with traces of two test shots. Three of the five nuclei on the flakes belong to the discoid category (Fig. 7 (B)); the fourth is a fragment of a large flake, on which two longitudinal unidirectional negative images are traced; the fifth is made on a large edge chip, from which two flakes were removed in the unipolar longitudinal direction (Fig. 7 (C)).

Most of the flakes are made of flint, only two are made of quartzite. The impact pads are mostly smooth. The vast majority of artefacts ' dorsal surfaces are uncrusted. In terms of average size, these flakes (37x29x14 mm) are slightly larger than the same chips from other levels of Hundidero (usually no more than 30x30 mm). Many of these flakes have an obushka; some belong to the category of "diving" chips; one item can be defined as a knife with a natural back. Several flakes were removed from the disc-shaped nuclei. The shape of individual chips was determined by previous preparation; some of them have traces of recycling.

There are 37 retouched flakes, which is 29% of the total number of artifacts in the analyzed complex. All of them, except for two items made of quartzite, are made of flint. The average size of the guns is 39 × 32×14 mm. Morphotechnical characteristics of retouched flakes are similar to non-retouched chips: the impact pads are smooth and the dorsal planes are not crusted. Many tools are made on edge and" diving " chips, as well as on fragments of flakes. 7, F) and notched (51%) tools, scrapers (17%), scrapers (11%, Fig. 7, E), truncated products (11%), points (5%) and beak-shaped tools (5%) are typologically distinguished. At least three toothed tools (Fig. 7, E), two notched tools, and two tronked products show the presence of two different types of patination on their surfaces. It is possible that there was a certain period of time between the processes of chipping from the nucleus and re-registration into tools. As for the excavated tools, one of them was formed on a disk-shaped nucleus, the other-on a fragment of a chip. The ventral plane of one toothed implement bears traces of flaking removal. They may have appeared in the course of deliberate refinement of an object or the use of an artifact in two qualities - as a retouched chip and as a nucleus. The use of core thinning is reflected in materials from the sites of Axlor (Ríos, 2005, p. 333) and Prado Vargas (Navazo et al., 2005, p. 163; Navazo and Díez, 2009, p. 130). One longitudinal scraper is made on a rounded chip, and one tronked product is made on a flake with traces of deliberate fragmentation (Fig. 7, E). A knife with a back is made on the corner of the scraper, in its distal part, in the same manner as the end scraper from level 2 (see Fig. 5, E). One scraper belongs to products with two working edges, and one working edge has undergone a secondary re-registration, the other is decorated on a fragment of flake, two types of patina are marked on it. The two remaining end scrapers have elements of vertical, almost perpendicular retouching. Many objects show signs of vertical retouching; they reflect attempts to shape the point with two-sided retouching along one of the edges, which was intended for a more reliable grip of the tool by hand.

Discussion

The four archaeological levels of the Hundidero monument were formed over a period of about 15 thousand years between 70-56 thousand years AGO, which corresponds to MIS 4. Hundidero is an open-type site located on the edge of a semi-drainless area, where in ancient times there might have been a shallow seasonal reservoir (see Fig. 2).

The most important technological features of the facility's industry are the dominance of the flake production system based on the disc-shaped technique, which is reflected in materials of all levels, as well as the subordinate position of the Combev and Levallois techniques. The nuclei did not split to the full degree of depletion, only a few removals were made from them, and these forms were left at the stage of single-site nuclei with longitudinal or multipolar removals. In the sediments of all levels, only small flakes were found, in the upper three levels - no more than 30 mm, in the oldest - slightly larger (Table 2).

In the complexes of all four levels of parking, flakes predominate, followed by tools (approx. 30%), including toothed and notched ones, scrapers, followed by scrapers, points and beak-shaped tools. The dating results confirm the assumption that Hundidero was settled in the first half of the Late Pleistocene (70-50 Ka BP).

On the impact sites of chips and tools, there is practically no natural crust, which is due to the peculiarities of stone raw materials. The raw material for the Neanderthals who visited Hundidero was flint, whose outlets are located in the parking lot (see Figure 1). For the manufacture of tools, large blocks of raw materials, some up to 1 m in size, were used (see Figure 3, A). If these blocks were split due to natural causes and fragments were collected nearby, then there was no primary crust on their surface. Thus, unlike in most other industries, the abundance of smooth impact pads in the Hundidero assemblages may indicate that the main labor costs during the initial splitting occurred during the initial splitting cycle. The inhabitants of the parking lot spent very wasteful stone raw materials, very little attention was paid to the initial preparation before the production of chips-blanks.

Another feature of the Hundidero industries, which is also characteristic of other open-type sites in the Sierra de Atapuerca Mountains that belong to the same chronological stage , is the tendency to microlitize inventory, and the tools were smaller than untreated chips (Table 2). Complexes containing microinventaries are known in Europe and the Levant; they have previously become the subject of various types of equipment. discussions [Burdukiewicz and Ronen, 2003, p. 223]. Aspiration

Table 2. Dimensions of flakes and tools from the Hundidero parking lot industries, mm

The tendency to microlitization is explained by the influence of climate, the peculiarity of stone raw materials, the functional characteristics of sites and the duration of their settlement, as well as cultural specifics. As in many Middle Paleolithic sites on the Iberian Peninsula, France (Delagnes and Meignen, 2006, p. 85; Dibble and Mc Perron, 2006, p. 777), and Central Europe (Moncel, 2003, p. 117), Hundidero contains flakes that were used without additional secondary processing. Climate-based interpretations of this phenomenon suggest that these microindustries existed in Central Europe during the interglacial period (Valoch, 2003, p. 189). However, the Hundidero site was inhabited both during the glacial phase and during the previous warm period corresponding to MIS 5. In addition, the MIS 4 period was followed by another cold phase, MIS 3, during which microlytic assemblages appeared, indicating intensive splitting of flint blocks, re-formation and reuse of tools (Navazo and Diez, 2009, p. 137). The most ancient microindustries in Western Europe date back to ca. 500 thousand years ago [Otte, 2003, p. 223]. The available data confirm that the plateaus of Northern Spain were settled during cold periods, but do not reveal the reasons for the trend towards "microliticity" of industries. The assumption that the small size of tools is determined by the small size of raw material blocks is unacceptable for Hundidero materials (see Fig. 3, A). It is possible that small flakes were effective in processing elephant and rhino carcasses [Moncel, 2003, p. 120], but not all sites with microlytic industries were used for skinning and cutting up these animals.

Hypotheses that explain the features of stone industries by the length of residence in a particular place are based on the fact that the bearers of the traditions of the Middle Paleolithic microindustries used parking lots periodically, for a very short time. These mobile groups passed on knowledge about such places from generation to generation [Moncel, 2003, p. 140; Navazo and Diez, 2009, p. 138]. There is evidence that Hundidero and other sites in Atapuerca were occupied repeatedly and for a short time. However, the assumption of periodic settlement of the site does not explain the peculiarity of the tool kit and the small size of artifacts, although the importance of this issue is obvious: its understanding will allow us to assess how Neanderthals could have planned, formulated their strategies based on past experience, and followed them within a social group (Soressi, 2005, p. 389).

The inhabitants of Hundidero used small objects obtained using various splitting systems. The main morphotechnical characteristics (impact pads, unidirectional centripetal or multipolar dorsal faceting) support the assumption that chipping was mainly performed by the disc-shaped method (Boëda, 1993). Sometimes the nuclei were used repeatedly, already as tools. It is impossible to explain this by the lack of raw materials. The re-use of artefacts, some of which were made during previous settlement episodes, may have been consistent with a strategy that involved adapting items left behind by previous groups. In this case, the task of making tools was made easier if a suitable artifact created by groups that had previously lived here could be found in the inhabited area. However, in our opinion, the microlitic nature of the industry is a specific cultural tradition. This is known from more ancient sites on the Iberian Peninsula, such as Bolomor (Fernández, 2007); this phenomenon is interpreted as a "local trend" at sites in the Levantine zone of the peninsula (Baena and Carrión, 2006, p. 60]. Most likely, the Hundidero industries can be correlated with the North Iberian tradition of producing simple flake forms and making crenellated and notched tools.

In open-air sites located on river terraces and pre-quaternary landforms in the Atapuerca Mountains, the most widely represented types of tools are crenellated and notched. Beak-like tools, scrapers and scrapers are less common (they are found on terraces, incisors and points are found at higher levels of terrain). Some researchers, such as Jones [Jones, 1980], associate the dominance of non-dried chipping, pebble and toothed tools in the industries with butchering and removing meat from bones. Other experts believe that plates with elements of jagged retouching were used when working with plant raw materials and wood [Martínez-Moreno, 2005], elongated and/or edge chips were used for cutting [Lemorini, 2000], and small chips were used for woodworking [Niewoehner, 2001, p. 2979]. The presence of flakes, choppers, pestles, etc.suggests that Hundidero was used for the primary cutting of prey, as well as the processing of plants. Hundidero, together with 30 other Late Pleistocene sites in the Atapuerca Mountains, formed a network of settlements that was probably characterized by functional diversification of the space organized along the tributaries of second-order rivers and their valleys. This suggests that the Neanderthals of this region had a complex settlement organization as early as at least 60 thousand years ago.

The repeated use of artefacts noted in Hundidero indicates that the site was visited repeatedly. Most likely, we have an example of stone processing with minimal labor costs. For the inhabitants of the parking lot, the edge of the artifact, suitable for use, was important. Most often, the basis for making artifacts was flint nodules, sometimes flakes (some of which were used during previous settlements) or naturally rounded nuclei. Wallace and Shea (2006) define the practice of minimal labor-intensive cleavage in the production of chips as a "fast-cooking technology"; it is associated with disc-shaped and amorphous cleavage systems, as well as with pebble nuclei. This technology was used by social groups with a low degree of mobility.

Conclusions

The Hundidero site is evidence of the presence of Neanderthals in the Sierra de Atapuerca Mountains during the late Pleistocene epoch. It is located near flint outcrops, as are 29 other Middle Paleolithic sites discovered during archaeological exploration in this mountainous area (Navazo et al., 2008, p. 1961).

Morphological and technical characteristics of the stone inventory complexes and dates for stratigraphic levels in which the artifacts were found serve as indisputable evidence for the presence of Neanderthals in the Sierra de Atapuerca Mountains during the late Pleistocene. According to the results of dating using the OSL method, the site was inhabited at the time corresponding to MIS 4, for no more than 20 thousand years. This is too small a chronological segment to allow us to identify differences between industries at different stratigraphic levels. Undoubtedly, the living area at the Hundidero parking lot was organized around the reservoir, its placement depended on the change in the area of the latter. We have a very small set of artifacts at our disposal. Undoubtedly, more significant conclusions about Neanderthal populations can be made only after a comprehensive study of assemblages of the site under consideration, using data on other synchronous open-type sites in the Sierra de Atapuerca. This will allow us to identify common features and reconstruct patterns of human settlement and behavior in the Middle Paleolithic in this region.

The lack of crust on the Hundidero artefacts does not mean that the finds represent an advanced stage of stone splitting; rather, Neanderthals used material stripped of its crust by natural causes. In the sediments of levels 2 and 4, tools with a back were found, for example, a scraper in level 2 (see Fig. 5, E) and a scraper in level 4 (see Fig. 7, D). The complexes also feature guns with a natural edge (see Fig. 5, A), which may have provided a more confident grip of the gun during its use. The presence of micro-splinters at all levels is interpreted as the result of purposeful production of small items.

All these features suggest that the parking lot was visited by people who followed the same model of settlement and use of the territory for several generations. The same applies to the method of using stone raw materials, in which only minimal preparation for splitting was made.

Hundidero was part of the socio-economic parking system in the Sierra de Atapuerca. Here, groups of Neanderthals, as shown by studies on the predictability of resources and their availability [Benito et al., 2005, p. 102; Bermúdez de Castro et al., 1995, p. 9], may have lived for a long time, periodically leaving the sites and returning to them. This behavior is not like a random movement, it can be considered as a tradition, a manifestation of collective memory. The stability of the shape, size, and procedure for obtaining stone cleavage micro-products can probably also be explained by social memory.

So, the appearance of the Hundidero industries is determined by the following features: local stone raw materials were used; the nuclei were not subjected to primary preparation before splitting, there is no natural crust on them, which is explained by the specifics of local raw materials; the nuclei were re-formed into tools; artifacts left during previous visits to the parking lot were used (determined by the different degree of patination on some tools); the edges small flakes and micro-flakes were used in the work without additional adjustment; preference was given to tools with convex edges (especially for toothed tools); there are tools with an obushka, sometimes specially prepared.

It is more difficult to characterize the character of settlement of the site, since each stratigraphic level of Hundidero contains material accumulated during several episodes of life activity, over an indefinite period. The presence of patina of varying degrees on the tools indicates that the Hundidero stone complexes were part of several episodes of settlement and Neanderthals periodically visited this territory (this is also typical for other settlements close in chronology

in the Atapuerca Mountains). Finally, Hundidero is an element of the Middle Paleolithic Neanderthal settlement system in the Sierra de Atapuerca Mountains. These settlements are characterized by a tendency to produce microlithic artifacts, reuse of certain places and tools. The Hundidero site was periodically visited by hunter-gatherer groups during the late Pleistocene. The results of analysis of their technology (production of micro-chips, double-sided retouching on tools with a shell) and methods of using stone raw materials (by the degree of patination, the absence of large artifacts, the dominance of flint extracted in one place) support our assumption that these groups have a cultural tradition of returning to this site. The re-use of the territory was embedded in the group's collective memory.

Acknowledgements

The study was supported by the Spanish Ministry of Education and Science (project CGL2006-13532-C03-03: "Pleistocene and Holocene of the Sierra de Atapuerca: Paleobiology and Paleoeconomics of Human Populations"). M. Navazo and R. Alonso received fellowships from the Atapuerca Foundation and the Dukes of Soria Foundation. The authors are grateful to A. Colin for his help with ICP-MS, S. Dominguez for his help with thin films, and the Atapuerca Research Team, especially the participants of the Hundidero and X excavations. Vallverdu, for valuable assistance in the field, and A. Olle, for assistance in creating databases.

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