Morphology and micro-fabrics of weathering features on gyprock exposures in a semiarid environment (Ebro Tertiary Basin, NE Spain)

Gyprock is a common rock in evaporitic formations, which have a wide distribution across all continents. However, outcrops of gyprock are rather limited, occurring mainly in low rainfall areas (i.e. southwest of USA, Italy, Spain). Gyprock is one of the most common lithology in the Ebro Tertiary Basin. Here, semiarid conditions propitiate the development of specific weathering processes and landforms with significant implications for understanding the genesis of soils and the geomorphological evolution of these areas. Gypsum crystallization within the pores and fissures of gyprock close to the surface leads to volume increase and pressures, with the consequent weathering of this rock. As a result, considerable porosity develops producing peculiar morphologies on gyprock outcrops (domes and decimetre-scale blisters), specific microscopic features (voids with plain walls, horse-shoe pores and serrated pores), as well as microscopic fabrics (grating fabric, skeletal fabric, fan fabric and botryoidal fabric). This paper presents a morphological characterization of the material forming the various types of weathering features, from microscopic to mesoscopic scale. The macromorphology and micromorphology of those features were used to interpret their genesis.