Cobble selection in the Quaternary terraces of the Segre river: the case of black quartzites and n12 archaeological unit of Roca dels Bous (Eastern Pre-pyrenees, Iberia)

Abstract

Studies about the procurement of lithic raw materials are usually based on the study of primary geological outcrops, leaving apart the so called “secondary deposits”, formed by the dismantling of preexisting ones. Secondary deposits present varying features not comparable with those of the primary outcrops. For this reason, their study can be very interesting depending on the geographical context. Recurrent exploitation of this kind of deposits is evident in Roca dels Bous (Eastern Pre-pyrenees). Cobble fragments abound among lithic remains in late Middle Paleolithic archaeological levels. These cobbles were collected in fluvial deposits of Segre river, that drains a vast watershed from the metamorphic Pyrenean axial zone southwards carrying lithologies of different types and ages (Ordovician – Oligocene). We developed a geoarchaeologic study in wich quaternary terraces near Roca dels Bous were systematically sampled. The purpose was to know in detail the availability of raw materials in these deposits. At a later stage, the study of N12 archaeological level of Roca dels Bous (composed by more than 25.000 lithic remains) has shown a strong dominance of a particular lithology: the so called black quartzite, relatively scarce in quaternary terraces according to the results of our surveys. An interesting and unexpected scenario outlines for a very specific period of the late Middle Paleolithic in which there was an intensive exploitation of terrace quaternary deposits. Such exploitation was clearly selective and was aimed at obtaining a very particular type of rock: the black quartzite.