L'evoluzione pleistocenica medio-superiore di un settore astigiano (Piemonte): Dati geologici e archeologici

Abstract

A small sector of the Piedmont hills region displayng a series of fluvial morphological units (terraces) has been studied in great detail. Previous studies showed the presence of modest reliefs in the substratum, and of relics of an extensive plain, gently sloping southwards and formed of fluvial silt deposits. These units (now referred to as Unit 1 and Unit 2) are cut by a series of valleys, each of which being about 40 m deep. The conclusion of the present study is that these valleys include relics of two southwards dipping N-S stretching terrace surfaces (Units 3 and 4), which are at 20 and 10 m above the present valley floor, respectively. These relic surfaces consist of fluvial gravel-sand deposits, which generally are less than 1 m thick. On the contrary of Unit 2 surface, which is linked to one of the main W to E draining collectors of the southern Piedmont basin, Units 3 and 4 are related to the local present hydrographic net. This new drainage system has progressively gouged the Tertiary substratum, depositional stages being of short duration. On the basis of degree of pedogenic evolution, Unit 2 and 3 deposits may roughly be dated back to the transition between Middle and Upper Pleistocene, and those of Unit 4 to Upper Pleistocene. This conclusion is confirmed by the age of Moncucco Torinese correlated fossiliferous deposits, which are also linked to the same drainage pattern. Prehistoric flint and quartzite artifacts are widespread on both the terrace surfaces made up of Units 3 and 4 gravel-sand fluvial deposits. On the basis of their different shape and lithotechnique, the artifacts can be divided into two sets. Artifacts of the first set (now including more than 600 findings) are the most weathered and rolled, and reflect an earlier "expedient" type stone industry. Because the artifacts of this set show evident traces of river transport, they may be as old as the time of gravel and sand deposition. In particular, at least the beginning of human flaking activities seems to be coeval to Unit 3. This group of artifacts may be attributed to the European late cultural traditions dating to Lower Paleolithic times in the transitional period from Middle to Upper Pleistocene. The second set of artifacts consists - by-now - of very few findings. Artifacts are much less weathered and rolled than those of the other set, and display an evident lithotechnical discontinuity. Since there are no traces of river transport and because of the type of lithotecnique used, these artifacts may be assigned to a time subsequent to both Units 3 and 4. Although the specimens so far found are a few, this second set of artifacts seems to belong to one of the most recent Mid-Paleolithic "Mousterian" traditions, which most probably dates to Upper Pleistocene times. It can thus be said that archaeological data are in fairly good agreement with the chronological attributions given on the basis of geological grounds.