In the Olvera area (Cádiz Province, Andalusia, Spain) different karstic lithologies (preferentially carbonates and gypsum) are recognizable, relating to rainfall values of the zone and producing a karst complex of a certain interest. The major karst landforms developed in gypsum terrains of Subbetic Triassic Unit (Keuper German-Andalusian facies type) as it occurs in other areas of the External Zones of the Betic Ranges. The Triassic extensive gypsum outcrops are characterized by the presence of a significant number of karst depressions, not yet studied and about which this work gives a general preliminary description. The gypsum Keuper facies terrains, along with high gradients of water granted by the nearby Guadamanil and Guadalporcún rivers, promote the development of impressive collapse dolines (and associated minor karst conduits), grouped into two large fields located NE of Sierra de Líjar. Some of these depressions have great steepness, with collapsed sides that are 15-20 meters deep, occasionally coalescent (with widespread edges and sizes up to 1000 meters long and 100-150 meters wide), intercepting deep fluvial drainage system of some complexity, affecting an area of significant size, estimable (through photointerpretation and spatial analysis) in at least 715,000 m². The Triassic gypsum terrains collect and convey infiltrating waters, acting as permeable and transmissive elements of negligible capacity, guaranteed by surrounding lithologies (helping to regulate the drainage of the karst system). A clear structural component in the doline origin is evident in the apparent alignment of the dolines with the regional structural lines. In the Triassic Keuper facies, along with major exokarstic forms, centimetric to metric microforms are also recognizable. They mainly consist in rillenkarren, whose average length is 10-60 cm, 1-3 cm in width and depth less than a centimeter. The origin and evolution of the doline fields seems to be related to the initial episodes of valley deepening of the surrounding Guadamanil and Guadalporcún rivers, which form gorges excavated upon an erosion surface of a presumably Pleistocene age.
GYPSUM KARST IN THE OLVERA AREA (CADIZ PROVINCE, ANDALUSIA, SPAIN)
SUMA, Andrea;DE COSMO, Pietro Domenico
2009
Abstract
In the Olvera area (Cádiz Province, Andalusia, Spain) different karstic lithologies (preferentially carbonates and gypsum) are recognizable, relating to rainfall values of the zone and producing a karst complex of a certain interest. The major karst landforms developed in gypsum terrains of Subbetic Triassic Unit (Keuper German-Andalusian facies type) as it occurs in other areas of the External Zones of the Betic Ranges. The Triassic extensive gypsum outcrops are characterized by the presence of a significant number of karst depressions, not yet studied and about which this work gives a general preliminary description. The gypsum Keuper facies terrains, along with high gradients of water granted by the nearby Guadamanil and Guadalporcún rivers, promote the development of impressive collapse dolines (and associated minor karst conduits), grouped into two large fields located NE of Sierra de Líjar. Some of these depressions have great steepness, with collapsed sides that are 15-20 meters deep, occasionally coalescent (with widespread edges and sizes up to 1000 meters long and 100-150 meters wide), intercepting deep fluvial drainage system of some complexity, affecting an area of significant size, estimable (through photointerpretation and spatial analysis) in at least 715,000 m². The Triassic gypsum terrains collect and convey infiltrating waters, acting as permeable and transmissive elements of negligible capacity, guaranteed by surrounding lithologies (helping to regulate the drainage of the karst system). A clear structural component in the doline origin is evident in the apparent alignment of the dolines with the regional structural lines. In the Triassic Keuper facies, along with major exokarstic forms, centimetric to metric microforms are also recognizable. They mainly consist in rillenkarren, whose average length is 10-60 cm, 1-3 cm in width and depth less than a centimeter. The origin and evolution of the doline fields seems to be related to the initial episodes of valley deepening of the surrounding Guadamanil and Guadalporcún rivers, which form gorges excavated upon an erosion surface of a presumably Pleistocene age.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
