BASIC VOLCANIC ROCKS (BVR) Mafic composition, porphyritic texture with phenocrysts. They can be found as rounded pebbles, of dark gray or black color, with a range of diameter of 5 to 15 cm. They are considered of poor to medium quality for knapping, because of the large number of vesicles (Figure 2). INTRODUCTION Archaeological studies in the northeast of Santa Cruz (Argentine Patagonia) have been scarce and unsystematic, with the exception of the coastal strip. This was motivated in part by the lack of stratigraphic contexts -like rock shelters- and also because of the intensive development of oil extraction activity, which has affected the landscape in a notorious way. Most of the archaeological information was generated in the last years from environmental impact studies and environmental baselines made by the oil companies. In general this information is not published (with some interesting exception, like Ratto 2009, Ratto y Carniglia 2013, Matera y López 2015), and is not easily accessible for archaeological research. In the last years we have begun to systematize and organize the existing information of this type of sources, which allowed us to generate a spatial database of the superficial archaeological record. In this sense, we have verified that two types of raw material, basic volcanic rocks (BVR) and translucent white chalcedony (TWC), represent together approximately 85% of the lithic artifacts of the northeast of Santa Cruz. In this poster, through distributional analysis and GIS tools, we explore ways to advance in the characterization of the type of sources of these specific raw materials and their strategies of use, circulation and discard. THE NORTHEAST OF SANTA CRUZ The study area encompass a strip of land that extends between 46°S and 47°S from north to south, and between 66°50'O 2 and 70°10'O from east to west. This represents an area of 110 x 260 km, and approximately 28.000 km (Figure 1). It includes different environments: the Atlantic coast; vast inland plateaus; and the Deseado and Senguerr valleys. Recent studies (Zubimendi et al., 2016) shows that the coastal strip has higher densities of lithic artifacts and occupations of hunter-gatherer populations at least since 3500 BP years. On the other hand, the interior territory has lower densities of artifacts, although relatively higher in the northwest of the area, in the valley of Senguerr. These studies continue to investigate the nature of human use of the different spaces in the study area, north-east and north-central of the Río Deseado Valley Most of the area corresponds to a huge sedimentary basin which began to form possibly in the middle Jurassic, although it's filling occurs in the Cretaceous and culminates at the end of the Tertiary. These sediments are covered by extensive mantles of gravels of fluvioglacial origin (Tertiary-Quaternary). On these mantles are deposited modern sediments of varied origin, both continental and marine (Feruglio 1950, López et al. 2011). The sector has a steppe ecosystem, associated with arid or semi-arid conditions. Average temperature varies between 17°C in summer and 6°C in winter. Rainfall is just over 200 mm annually, decreasing inland. The highest rainfall occurs during the winter, decreasing considerably during the summer. The prevailing wind is of the west, which usually runs with great force (greater than 100 km/h), especially in the summer months, which generates a high evapotranspiration and extreme dryness. ARCHAEOLOGICAL BACKGROUNDS AND METHODOLOGY In a previous presentation, we present an archaeological database and a Geographical Information System (GIS) using 2169 points with archaeological information which was originated from environmental impact studies and environmental baselines for the oil companies (Zubimendi et al. 2016). This information were transformed and analysed in relation to the spatial and environmental location, using the geoforms as the minimal spatial unit. Considering the great differences in data collection and information available, we decided to systematize some simple variables and characteristics that were present in all studies and could easily be compared. In this sense, we registered: number and percentage of different raw materials, type of archaeological context (regarding quantity and density of materials), and artifacts classes (debitage debris, cores and instruments). This way, we verified that only two types of raw material, basic volcanic rocks (BVR) and translucent white chalcedony (TWC) (see box), represents together more of 85% of the lithic artifacts registered in the northeast of Santa Cruz. Other raw materials (ORM) were registered in lower percentages, among these, flint (10.9%), other of poor to medium quality for knapping, like riolits (2.1%), and black obsidian (0,8%). Because of the lack of systematic research of this vast area, we pretend to explore ways to advance in the identification of the type of the main lithic sources by making a model of the availability using the distributional information and GIS tools. We sum all the archaeological information inside each geoforms and create one point per geoforms, which has data of the following variables: a) archaeological density; b) relative frequency of BVR; c) relative frequency of TWC; d) relative frequency of ORM. In order to make a lithic landscape analysis (sensu Barrientos et al. 2015, Catella et al. 2017), we create a continuous surface by Inverse Distance Weighted (IDW) with a power value of 2. This way, we create several surfaces by interpolation, and by a virtual transect we consider fall-off curves. To compare and analyse we also create surfaces and curves of archaeological density and a topographic profile. Miguel Ángel Zubimendi. CONICET. División Arqueología. Museo de Ciencias Naturales de La Plata. UNLP. Paseo del Bosque s/n. La Plata, Argentina. C. P. 1900. Universidad Nacional de la Patagonia Austral, Argentina. mikelzubimendi@gmail.com Pablo Ambrústolo. CONICET. División Arqueología. Museo de Ciencias Naturales de La Plata. UNLP. Paseo del Bosque s/n. La Plata, Argentina. C. P. 1900. pambrustolo@hotmail.com Sebastían Matera. Instituto de Arqueología. FFyL-UBA. 25 de Mayo 217/221 3er piso, 1002. Ciudad Autónoma de Buenos Aires. Email: sjmatera@gmail.com. Lisandro Guillermo López. Centro de Arqueología Urbana (FADU-UBA). Ciudad Autónoma de Buenos Aires. lisandroglopez@gmail.com EXPLORING THE DISTRIBUTION OF LITHIC RAW MATERIALS IN NORTHEAST OF SANTA CRUZ, ARGENTINE PATAGONIA TRANSLUCENT WHITE CHALCEDONY (TWC) Silica mineral, microcrystalline, related to quartz. It is presented as amorphous or nodular masses of light white or light gray, medium to large in size (in some cases, more than 20 cm). They have a quality for knapping that varies from good to very good (Figure 3). 900 600 300 0 0 30 60 90 120 150 180 0,005 0 0 30 60 90 120 150 180 1 0 Meters above sea level % of lithic raw materials Distance Distance Density of lithic artifacts RESULTS As we can see in Figure 4 and 5, there is almost a perfect correlation in the spatial distribution between %BVR and %TWG; with a lower percentage of other raw materials in all the area under analysis. The major relative frequency of %BVR (ca. 85%) is clearly correlated with inland and higher territories, such as Castillo, Verdún and Inland %ORM %ORM %ORM %TWC %TWC %TWC %BVR %BVR %BVR FINAL CONSIDERATIONS The analysis of the distribution of the main lytic raw materials in the archaeological record of the northeast of Santa Cruz (BVR and TWC) allowed us to generate a first hypothetical model of the potential availability of these rocks. The importance of this model is based on the use of data from the systematization of information derived from impact studies, mostly unpublished, and that come from an area that does not have previous research's. The clearly unequal distribution of lithic basalt artifacts in high plateau lands and translucent white chalcedonies on the plateau flank and coast correlates directly with the potential availability of these raw materials in the study area. The distributions of the raw materials in the landscape allow us to state that BCR would present a high availability in the plateaus, probably forming part of the so-called "rodados tehuelches"; their dispersion would be diffuse and ubiquitous in such geoforms. The exploitation of this rock, as reflected by the trends observed in the virtual transect, would be of less intensity in the remaining territory at the east of the analysed area. On the other hand, the image that emerges about TWC would suggest that this raw material would be available in a localized way in potential secondary sources distributed in the coast and plateau flank, especially in Gran Bajo. These deposits would probably correspond to tertiary continental outcrops surrounded by colluvial and quaternary alluvial sediments. Then, BCR and TWC would reflect the intensive use of locally available rocks by ancient hunter gatherers of the area, and, to a lesser extent, the exploitation of non-local raw materials of better quality for knapping. Finally, we want to highlight the interpretative value of predictive models in the generation of information on the potential availability of lytic raw materials in wide spaces, as a mean to generate working hypotheses that can be contrasted in field works. Figure 2. Figure 3. Figure 5. Figure 4. Senguerr Valley Senguerr Valley Senguerr Valley Inland plateaus Inland plateaus Inland plateaus Deseado Valley Deseado Valley Deseado Valley Verdún plateau Verdún plateau Verdún plateau Virtual transect Virtual transect Virtual transect Bajo Oriental Bajo Oriental Bajo Oriental Figure 1. REFERENCES Barrientos, G.; L. Catella y F. Oliva. 2015. The spatial structure of lithic landscapes: the late Holocene record of east-central Argentina as a case study. Journal of Archaeological Method and Theory 22(4): 1151–1192. Catella, L.; G. Barrientos y F. Oliva. 2017. La identificación del uso de fuentes secundarias de materiales líticos asistida por SIG: el Arroyo Chasicó (Argentina) como caso de estudio. Estudios Geológicos 73(1): 1-20. Feruglio, E. 1950. Descripción geológica de la Patagonia, Tomo 3. Dirección General de Yacimientos Petrolíferos Fiscales, Buenos Aires. López, C., P. Rial, N. Elissalde, E.Llanos y S. Behr. 2011. Grandes unidades del paisaje de la Patagonia argentina. En: Actas Jornadas Regionales de Información Geográfica y Ordenamiento Territorial, B. Días y P. Calviño (eds), Tomo 2, pp. 217-229. Matera, S. y L. López. 2015. Estudios de impacto arqueológico en el Norte de Santa Cruz. Los alcances del registro arqueológico en zonas con diferentes niveles de modificación antrópica. En Estudios de impacto ambiental y la protección del patrimonio arqueológico, editado por S. Matera, M. Kergaravat y G. Spengler, pp. 77-104. Imprenta Digital, Buenos Aires. Ratto, N. 2009 Aportes de la arqueología de contrato al campo de la investigación: estudios de casos en Patagonia y Noroeste de la Argentina. Revista de Arqueología Americana 27:49-70. Ratto, N., y D. Carniglia. 2013. Propiedades del Registro y Tafonomía de conjuntos líticos: el caso del norte de la provincia de Santa Cruz. En A. Zangrando, R. Barberena, A. Gil, G. Neme, M. Giardina, L. Luna, S. Paulides, L. Salgán (Eds.), Tendencias teórico-metodológicas y casos de estudio en la arqueología de la Patagonia, pp. 485-494. Malargüe, Museo de Historia Natural de San Rafael. Zubimendi, M. A., L. López y S. Matera. 2016. Caracterización del paisaje arqueológico del norte de Santa Cruz mediante la integración de distintas fuentes de información (EIA, rescates y estudios sistemáticos). En: Actas del XIX Congreso Nacional de Arqueología Argentina, Serie Monográfica y Didáctica, 54: 1267-1270. plateaus, which consist of extensive Pleistocene alluvial sediments that rest over tertiary continental and marine sediments covered by patagonian pebbles. Here %TWA is very low (ca. 10%). This geoforms correspond to the higher part of the analysed area, with 300 to 600 meters above sea level; and in archaeological terms, an area of low density. On the other hand, the territory between the coast and the plateaus is and irregular inclined land which is dissected by deep and wide canyons (called Cañadones). They area covered by colluvial and quaternary alluvial sediments, appearing in some sectors tertiary continental and marine sediments. In this part (Gran Oriental, plateau flanks and the coast of San Jorge gulf), %BVR varies between 20% and 50%, with a decreasing tendency towards the coast, where are higher densities. The relative frequency of TWA is higher in this part, with an important emphasis in Bajo Oriental. ACKNOWLEDGMENT We would like to thanks to Sonia Quenardelle for her help in the microscope identification of lithic raw materials, and also to Diego Gobbo with GIS tools. This poster is part of two research projects: Estudios regionales en el eje Deseado (cuencas media e inferior) para definir los rangos de acción de grupos cazadores recolectores costeros en el marco de la ocupación humana del Holoceno de Patagonia (UNLP N739); and Historia y Patrimonio Cultural: rutas turísticas e itinerarios culturales en el noreste de Santa Cruz (UNPA 29/B201-1). Density Density Density BVR BVR BVR TWC TWC TWC ORM ORM ORM 11 th INTERNATIONAL SYMPOSIUM ON KNAPPABLE MATERIALS 11 th INTERNATIONAL SYMPOSIUM ON KNAPPABLE MATERIALS Buenos Aires & Necochea (Argentina), November 7-12 th , 2017 Buenos Aires & Necochea (Argentina), November 7-12 th , 2017 11 th INTERNATIONAL SYMPOSIUM ON KNAPPABLE MATERIALS Buenos Aires & Necochea (Argentina), November 7-12 th , 2017 IA Topographic profile