Prehistoric quarrying and surface collecting strategies in the Southern Pampas of Argentina

Abstract

The aim of this paper is to present the results of an ongoing research aimed at understanding the processes that structured - at different scales - the spatial distribution of lithic materials from diverse sources in the southern Pampas of Argentina. This region, inhabited by hunter-gatherer societies throughout the Holocene, is characterized by a heterogeneous distribution of lithic resources. The main orographic feature is the Ventania system, a group of ancient (Paleozoic), eroded but well-defined mountain ranges, 180 km long and 60 km wide, which are composed of sedimentary rocks (quartzites, sandstones and siltstones) with various degree of metamorphism. Also found on the southwestern slope of the hills and on the surrounding plain are isolated outcrops of quartzite, granite and rhyolite. The sources of lithic materials appear both, in the form of primary outcrops and of secondary deposits of cobbles and pebbles. The latter are mainly distributed along the many streams that have their headwaters in the hills and in some exposures, south of Ventania, of the Patagonian Shingle Formation (Tehuelche Beds or Rodados Patagónicos), composed of gravel deposits of extra-regional provenance. For the purpose of our study, we have classified the lithic sources as either point or diffuse. A point source is a localized and a more or less isolated primary (e.g. a bedrock exposure or outcrop) or secondary (e.g. a stream, beach, or talus slope deposit) rock extraction place. A diffuse source is a very extensive and a difficult-to-delimit rock extraction place, consisting of either a primary (e.g. a large-scale geologic formation) or a secondary (e.g. a geographically extended gravel mantle rock extraction place. As long as each kind of source has very specific conditions in terms of relevant variables like visibility, accessibility or exploitability (which is conditioned by lithic raw material abundance, quality and yield), it is expected the implementation of different and recognizable extractive strategies through time, involving a various combination of quarrying and surface collection practices. In order to identify such strategies, the methodological approach adopted in this study is based on the use of: a) qualiquantitative evidence collected in the sources themselves and in other archaeological locations around them, and b) GIS-based spatial modeling. In the presentation we will illustrate the approach using a selected set of rocks (quartzites, rhyolites, opaque siliceous stones) and sources.