Dating of Archaeological sites from Northern Spain . Mollusc shells
Many caves in the northern part of the Iberian Peninsula have provided evidence of human activity during the Paleolithic, Mesolithic and Neolithic, reflecting an intensive exploitation of mollusks mixed with animal bones and stone tools, constituting Shell middens which occur in a variety of forms . Although some species can be absent, the limpet Patella is present in all localities.
The presence of the large-sized limpet Patella vulgata var. sautuolae , which in some cases reaches diameters of 50-52 mm (Madariaga de la Campa, 1994), together with the winkle Littorina littorea , are interpreted as Upper Paleolithic (specially Magdalenian) indicators. These were substituted in Mesolithic deposits by an association of Patella intermedia and Osilinus lineatus (typical of warmer waters) (Vega del Sella, 1930; Clark, 1976; González-Morales, 1982; Arias, 1991; González-Morales, 1996; Gutiérrez Zugasti, 2005, 2006).
Several dating methods can be used to determine the age of such middens but, until recently, the radiocarbon technique has been almost the only one used for archaeological purposes. However, in most cases, only a single sample is dated with the 14 C method. Moreover, there are some controversies about the age of the Magdalenian/Azilian, Azilian/Asturian, and Mesolithic/Neolithic transitions in the north of Spain (cf. Straus, 1979, 1981, 1985a,b, 1986; Fernández Tresguerres, 1980, 1983; González-Morales, 1982, 1992, 1995, 1996; Blas Cortina and Fernández-Tresguerres, 1989; Clark, 1989; Arias, 1991, 1995, 1996; González Sáinz, 1994; Strauss et al. , 2002; Peña-Chocarro et al. , 2002, 2005), mainly because some radiocarbon ages reflect a certain time-overlap.
Among other available dating methods, amino acid racemization has provided coherent results for determining the ages of archaeological samples in the Iberian Peninsula (Fortea et al ., 1995, 2003; Torres et al ., 1997, 2002, 2007).
Within this Project, we provided the first report on the ages of 54 archaeological levels in 38 caves in northern Spain (Fig.1 ) by means of the aspartic acid D/L ratios measurements in Patella shells with good results (Fig.2). For this purpose, we developed an age calculation algorithm which allows the numerical dating of deposits from other archaeological localities in the area and nearby regions. We conclude that the sample size, that is to say, the number of shells analysed within a single level reinforce the importance of analyzing numerous specimens per horizon and the understanding of time-averaging concept. T he ultraestructure of different species of Patella shells was also studied showing c alcite in their apex and aragonite at their margins.
Figure 1. Geographical location of the caves studied in this paper. 1-El Juyo, 2-Altamira, 3 -Barra, 4-Tina 6, 5-La Cabrera, 6-Las Madalenas, 7-Santa Marina, 8-Entecueva, 9-Juan de Covera, 10-Cordoveganes, 11- Cueto Molino, 12- Andrín, 13-Águila, 14-Sonrasa, 15-Horadada, 16-Peña, 17-Ciernes, 18-Toral, 19-Collamosa, 20-Colmenera, 21-Covajorno, 22-El Quintanal, 23-Fonfría, 24-Los Menores, 25- Mary, 26- Quintana, 27-La Riera, 28-Bricia, 29-Coberizas, 30-Cámara, 31-Llamorey, 32-Penicial, 33- Cuetu La Hoz, 34- Ceñil, 35- Lloseta, 36-Les Pedroses, 37-Molino, 38-Carmona.
Figure 2. Mean and standard deviation of ages obtained through aspartic acid racemization and den sity plots calculated using the mean and standard deviation of radiocarbon ages published elsewere for each period. The sites dated by amino acid racemization are plotted at the right to the correspondent attributed period .
