Peculiar landforms in the gypsum karst of Sorbas (southeastern Spain)

Abstract

The gypsum karst of Sorbas is developed in selenitic Messinnian gypsum, the sequence being about 120 meters in depth. Within an outcrop of only 12 km2 there is a great variety of karstic forms, among which the high density of dolines and cavities (over 1000 identified to date) is a notable feature. There also exist many and varied karren landforms, interstratification forms, and tumuli. The karren landforms are strongly developed and are of diverse types. There are also examples of microkarren and nanokarren, such as exfoliation karren or dissolved vacuoles determined by the texture and gypsum crystalline orientation. Some of these forms are unique to gypsum materials and have been described for the first time in this area. The interstratal erosion karst is very well developed due to the marly intercalations existing in the gypsum deposits. This circumstance determined the speleogenesis of the area, with the formation of galleries following the stratification planes. With this structure, the gypsum strata are little altered, and erosion of the marly strata occurs. In some zones, there is an erosive interstratification karst. The tumuli are hollow subcircular domes of the most superficial layer of the gypsum, with sizes varying from a few centimeters to several meters in diameter. Their origin is determined by processes of intercrystalline solution and precipitation, together with the capillary movement of the interstitial water in the gypsum stratum. Their development is related to the abrupt changes in temperature and humidity that are characteristic of semidesert zones such as Sorbas.