The caves and their infilling
The Cueva del Arco complex includes distinct karstic cavities clustered around the natural bridge (named “Arco I”) and in its surroundings, in particular along the walls of the collapsed karstic valley to the East of the bridge (“Arco II”, see Fig. 2).
Three main cavities (Fig. 4) are accessible from the large karstic hollow (Cave C) behind (upstream) the natural bridge, which shows sub-circular shape and a diameter of c. 10 m: to its Southeast, Cave B, a c. 5-m-wide, tafoni-like rock shelter, without sedimentary infilling, which continues to the Southeast in form of a karstic gallery (approximately towards Arco II); to the Northeast, Cave E, a narrow cavity developed along a subvertical fissure, with rock art painted along its walls (Fig. 5); to the North, Cave D, one of the cavities that has been explored archaeologically.
Cave A is located below the natural bridge and forms a relatively large rock shelter, situated along the left slope of Barranco de la Tabaquera, a talus scree scattered with fallen limestone boulders. Cave A deposit features both Upper and Middle Palaeolithic cultural assemblages.
Cueva del Arco: Cave A
The succession of Cave A is the most complete and the richest among the deposits filling the distinct cavities of Cueva del Arco. This is the reason why field campaigns have mostly been directed at the excavation of Cave A.
Stratigraphy of Cave A
Four distinct excavation units compose the succession of Cave A (excavation units I, II and III, and the bottom part of the succession, which is unnamed archaeologically, see Fig. 6). The deposit is characterized by the presence of common to abundant limestone fragments with sub-angular and angular shape.
The excavation unit I is the Holocene series (GFUs A1 and A2). It is thin, and its lower boundary is well recognised, even if irregular due to ancient biological activity. This unit consists of dark sediment, rich in organic matter and combustion by-products (for the complete description and the correspondence between GFUs and archaeological units see Table 2).
The archaeological units II and III (GFUs A3 to A7) are the Pleistocene series. They are made up of sediments with a dominant clastic coarse fraction (limestone fragments, mostly with angular shape) and fine material, the colour of which ranges from yellowish to brownish hues. The coarse inputs are limestone fragments from the cave wall. Among them, frost slabs are detected; they may indicate frost action (among other processes of wall disintegration) and cold, moist climate context. The provenance of fine material is not clear; it may derive from wall disintegration, or even from aeolian inputs. The whole set of layers is almost horizontal in inner squares (ex. D19) and dips very slightly outwards (very few degrees) in sq. C19. GFUs A3, A4 and A5 form an almost homogeneous sedimentary set featuring a slightly coarser intercalation (GFU A4). GFU A6 is a few-cm-thick lenticular layer thinning eastwards, mostly composed of combustion by-products (ash and microcharcoal fragments), in particular in its upper part. The lower boundary to GFU A7 shows a 1-cm-thick reddened (5YR4/4) belt due to thermal impact.
Below the excavation unit III, more layers were distinguished (GFUs A10, A11 and A12). They are slightly different from the overlying upper Pleistocene deposit described above. GFU A10 is made up of gravel infilling a sort of canal, the geometry and extension of which are unknown. The outer limit of the canal corresponds to the boundary between GFUs A11 and A12, being GFU A11 a slope-like sediment resting on the erosive boundary, while GFU 12 seems an alluvial-like deposit, probably related to hydric activity of waters flowing in the Barranco de la Tabaquera. No archaeological remains have ever been found from GFUs A10, A11 and A12, and the explanation of their origin and nature is made difficult by the limited extension of the sounding in which they were detected.
No relevant post-depositional dynamics were detected within the Pleistocene succession, with the exception of slight secondary carbonate accumulation, with local weak cementation of some layers (see Table 2).
The succession of Cave A is rather thin, which indicates low sedimentation rate through its accumulation. This can be related to the position within the cave (that is, sedimentary inputs in this position of the cave were scarce and mostly coming from cave walls). It should also be noticed that the boundary between GFUs A2 and A3 (that is, between the excavation units I and II) is erosive, which means that part of the Pleistocene series has probably been removed by natural or human-related dynamics.
Short information on the dating and the cultural and faunal assemblages of Cave A
Excavation unit I includes evidence relating to the latest documented occupations corresponding to a time at the end of the early Neolithic period, from which various pottery fragments have been recovered, some of them decorated by incisions and impressions. We have also found some geometric projectiles from this stage. This is a layer that has been significantly affected by superficial erosive processes and by the burrows of small mammals, which has prevented us from documenting these occupations in greater detail.
Below these occupations, in the lower part of excavation unit I, and also highly affected by erosion and burrowing, there is an Evolved-Solutrean II occupation, which in the regional sequence is placed at c. 23,000-20,500 cal BP (19,000-17,000 BP, see Table 3). This occupation is very interesting as it corresponds to the style of the existing rock art samples in Cave E. Although the erosion processes mean this stratum is not continuously preserved, two Mediterranean shouldered points in particular, confirm the occupation of the cavity towards the end of the Solutrean (Fig. 7).
The next documented occupation is assigned to the Gravettian and refers to excavation unit II. Unlike the previous ones, it is well preserved, as proved by the occurrence of several hearths in primary position. The main hearth (H1) is 60 cm long by 40 cm wide and is built on a slight basin that has some small/medium- sized clasts inside. There does not seem to be a boundary marked by stones, although about 30 cm from the structure some degree of emptying of the hearth has been documented.
Among the materials associated with these structures, various Gravette and Microgravette points, as well as backed items clearly linked to the Gravette period, are the outstanding features. This is confirmed by the three radiocarbon dates obtained from both hearth H1 and the archaeological level, all between 30,870-30,070 cal BP. The faunal remains from these levels are being studied by Dr C. Real (Universitat de València) and it seems that, apart from the great predominance of rabbits (a common occurrence in the Iberian Mediterranean), the Capra pyrenaica (Iberian ibex) is the dominant animal in the group, together with other ungulates and some carnivores (ongoing study).
Below these occupations, a thin level of gravel has been documented at some points of the cave, but we cannot rule out as corresponding to a previous Upper Palaeolithic occupation. It marks the contact between archaeological units II and III. In fact, just below hearth H1, a small bladelet with very fine retouches was recovered which we hesitate to classify as a Dufour type. Together with the existence of a radiocarbon date of 33,580-31,620 cal BP, this suggests that there may have been some occupation in the Aurignacian which until now could not have been properly documented.
Below these Upper Palaeolithic occupations, there is an important sedimentary package assigned to the Middle Palaeolithic, excavated as a whole as archaeological unit III. Its differentiation from the upper stratum leaves no room for doubt. Together with the change in stone tools, this allows us to clearly assign it to the Mousterian period. In relation to the materials recovered, the large quantity of retouched tools appearing as a proportion of the lithic industry as a whole is striking. Scrapers (lateral, transversal and convergent) are extremely abundant at the percentage level, together with various Mousterian points and some notched and denticulated pieces (Fig. 7). The extraordinary quality of the manufacture and retouching of many of these pieces is also worth highlighting. More detailed studies of this lithic assemblage, together with the recovered bone and plant remains, are ongoing, but these industrial characteristics are nonetheless surprising. This layer has been dated by 14C, revealing a greater age than what we initially expected, between c. 45,000-55,000 BP.
Cueva del Arco: Cave D
Cave D is filled with a thick sedimentary succession that, unfortunately, yielded almost no archaeological record dating from the Palaeolithic.
Stratigraphy of Cave D
The succession of Cave D consists of two distinct series, easily distinguished thanks to their sedimentary characteristics and to the sharp boundary that separate one from the other (see Table 4 for complete description and Fig. 8): unit D1 is the Holocene succession and units D2 and D3 constitute the Pleistocene deposit.
Unit D1 contains common stones, is enriched in organic matter and shows evidence related to Holocene soil formation (mainly structure development), especially at the cave mouth. Unit D1 was further divided into two GFU, D1a and D1b, which respectively correspond to the horizons A and BC of the soil that has developed on part of the succession and that has also affected underlying units.
Units D2 and D3 form the Pleistocene succession. Under the microscope, they broadly show a prevalence of angular silt-sized siliciclastic components (quartz and feldspar, mainly) in the lower part of the deposit, while clastic carbonate components (fragments of limestone, including frost-slabs, and carbonate minerals; see Fig. 9-a and 9-b) increase upwards (i.e., in unit D2). Among biogenic and anthropogenic components, rare charcoal fragments, few bones and shell fragments were detected (see Fig. 9-c). The fine material is brown, made up of micrite and with crystallitic b-fabric. The pedofeatures are scarce and related to biological activity and accumulation of secondary calcium carbonate. Specifically, they include infillings of biopores and passage features, few silt coatings around limestone fragments (see Fig. 9-d) as well as micrite coatings and hypocoatings on void surfaces (the last one only in unit D2a, see below).
Unit D2 (further subdivided in GFUs D2a, D2b and D2c) is mainly composed of coarse angular fragments and shows evidence of soil formation. Unit D2a is a 2B horizon developed at the cave entrance. Soil structure is clearly visible in thin section in form of granular aggregation, in association with common biopores. The most relevant pedofeature in unit D2a is connected to the accumulation of secondary carbonate calcium in form of micrite coatings and hypocoatings (see Fig. 9-e). Unit D2b is a 2Bw soil horizon. Under the microscope it shows evidence of soil formation, mainly recognizable in its microstructure. Unit D2c is the transitional layer to the underlying unit D3.
The bottom unit, GFU D3, is composed of silt with few stones, quite homogeneous through its thickness, even if secondary carbonate accumulation, weak lamination (see Fig. 9-f) and discontinuous stone-lines locally occur. Slight evidence of sin-depositional biological activity is also present.
Short information on the dating and the cultural and faunal assemblages of Cave D
In Cave D, the decision was made to carry out an initial excavation because of all the features it had pointing to Palaeolithic occupations. The thickness of the deposit, its location at the bottom of the Cueva del Arco complex, right next to Cave E (with Palaeolithic rock art), and the possibility that it was a larger cavity that had filled up, led us to first carry out a small test pit, later an excavation of the upper part of the stratification (Neolithic), and finally an excavation in extension towards the bottom of the cavity to try to confirm its original depth.
These excavations have allowed us to confirm the existence of a surface occupation level from the end of the early Neolithic period, possibly the same one as is documented in Cave A.
Below this layer, the change in sedimentation is very pronounced (see above) and, despite having recovered several scattered Palaeolithic materials (lithic industry, ornaments and fauna), it has not been possible to determine the presence of any preserved level of occupation. Everything seems to be the product of reworking from outside the cavity. The features of the materials point tentatively towards an attribution to the Solutrean or the Gravettian periods, although there is no clear evidence allowing us to confirm this.
Cueva del Arco: Cave E
A 1-m² test pit was excavated at Cave E in 2019, at the position where the hind is depicted on the wall, in order to verify the possible presence of archaeological sediment.
Two units were detected in the sounding (Fig. 10). GFU E1 is a set of horizontally laminated layers enriched with organic matter (0-7 cm). They consist of very-dark-grey silty loam, with fine sand, a few cm-sized limestone fragments and common organic matter; the lower boundary is sharp, linear and horizontal. The lower layer (GFU E2, explored on a total thickness of 1 m) is massive brown silt with low porosity, occasional roots, and scarce angular limestone fragments (max. size 12 cm), scattered on its whole thickness. No apparent organization was observed unless for thin post-depositional intercalations of gypsum (Fig. 11-a).
No evidence of human occupation has been detected in the deposit. Nonetheless, preliminary observation of thin sections from the GFU E1 has shown the presence of combustion by-products (microcharcoal fragments and ash) and of biogenic inputs (spherulites, Fig. 11-b). The absence of evidence does not permit to understand if the Cave E was only used for symbolic practices – in particular the production of the rock art detected there (see above) – or if later human activities removed previously-existing archaeological sediments. The latter could be suggested by the boundary between the upper and the lower units, which is an erosive interface. Its regularity indicates an artificial, human-made origin as a surface for levelling the cave’s ground floor (Fig. 11-c), perhaps by shepherds who used the caves as a shelter for flocks of ovicaprines.