Weathering pits in slates from La Serena (Badajoz)

Abstract

A rare case of weathering pits or gnammas developed in Precambrian shale outcrops are described in La Serena region (Badajoz, SW of Spain). They appear in the scarce outcrops of slates, of vertical foliation, which form horizontal surfaces. These pits are mainly elliptical in plant, developed transversely to the bedrock foliation pattern, and of small size (average length, width and depth of 66x38x18 cm). Its genesis, considering the type of rock and bedrock outcrop characteristics, their size and number, as well as potential origin linked to weathering processes due to seasonal water storage is discussed.