Silicite („flint”) from Opole-Groszowice: Contribution to recognition of the raw materials used during prehistory in the Odra River valley

Until recently it was thought that all the erratic flints found at the Stone Age sites in the upper part of the Odra Valley were considered as silicites from the Baltic Sea. Their age of Baltic flints is associated with the Cretaceous, more precisely with the Maastrichtian or Palaeogene. However, it turns out that among these rocks, there are also silicites that are of different age and origin. They were first found in outcrops of sands and gravels around Opole-Groszowice, SW Poland. So far, these flints have not been distinguished in archaeological assemblages.
Petrographic analysis presented in this article proves that these silicites of brown colour are of Jurassic age. They entered the glacial sediments via the lobes of the Drenthe glaciation. They were used in the same way as raw materials of Baltic origin. In this paper we show some examples of Palaeolithic and younger sites, where artifacts made of brown silicite occurred. In the past, these kind of flints from this region were often regarded as imports from the Kraków-Częstochowa Plateau.