3 one-day excursions (19 July) are being arranged: Bentonite deposits at Cabo de Gata (Almeria), Guadix-Baza basin, and Alpujarra. 50 registrants allowed.
Bentonites from Cabo de Gata (Almería): volcanism and alterations (EUR 70.00)
The Neogene volcanic region of Cabo de Gata, Almería, SE Spain, is dotted with many outcrops of bentonite, some of them of significant economic interest. The bentonites have their origin in the hydrothermal alteration of pyroclastic rocks (15-7 Ma). The deposits are usually associated with fractures. The major mineral is a dioctahedral Fe- and Mg-smectite (89-75%) and this is accompanied by minor amounts of feldspars, quartz, amphiboles, pyroxenes, biotite, zeolites, disordered tridymite, calcite, etc.
The Cabo de Gata volcanic outcrops are part of a more extensive volcanic area mainly submerged beneath the Alboran Sea. The origin of these volcanic rocks is associated with the geotectonic dynamics of the Western Mediterranean Sea during the Neogene. The Cabo de Gata rocks have been exposed to marine and meteoric conditions throughout the geological history of the region. The late volcanic activity also created hydrothermal systems with flow of marine and/or meteoric waters. Therefore, fluids with different chemical composition and different temperatures took part in the alteration processes of the volcanic materials. The alteration of volcanic rocks by acidic sulfate solutions produced mainly silica, alunite, jarosite and kaolinite. This process has occasionally been related to the gold deposits in the area. On the other hand, neutral or slightly acidic or basic solutions would have caused the most important bentonite deposits in the area.
Guadix Basin: a giant clay store in central Betics (EUR 60.00)
Guadix Basin occupied during the Upper Miocene, Pliocene and Pleistocene about 4500 km2 in the central Betic Cordillera. The withdrawal of the sea 6.5 Ma ago allowed the area to be occupied by a series of river systems that were responsible for distributing the sediments produced by erosion of Sierra Nevada and other reliefs surrounding the basin. Finally, a phenomenon of river piracy turned the ancient lake in an area of external drainage, leading to the development of the scenic badland system that characterizes this semi-desertic exotic landscape in southern Europe. In this one-day trip we will recognize the pronounced paleogeographic control on the distribution of clays and the subsequent influence on the modeling of the current landscape. We will also know the main utilities given to the various types of clays in the region which was the savanah where the first European hominids inhabited.
The field is low to moderately demanding in terms of physical conditions. Most of the outcrops are less than 500 m far by walking. It is advisable to wear suitable walking shoes, hat/cap, sun glasses and sunscreen of factor 30. Special dietary needs should be communicated in advance.
Active Tectonics and Clay-rich sediments in Western Sierra Nevada (EUR 60.00)
Granada, Padul, Nigüelas, Lanjarón, Capileira – Granada to Las Alpujarras
Juan I. Soto (Professor in Geodynamics, Granada University)
The main objective of this field trip is to see the geological processes related to the uplift of the highest mountains in the Iberian Peninsula, the Sierra Nevada mountain range, with more than 3 thousand meters of elevation. Surface uplift is also related to active faults and shallow-seismicity in the Alpine folded belt of the Betics and Rif in the Western Mediterranean. We will visit the western and southern slopes of the Sierra Nevada mountain range, close to the Granada town, and some of the valleys of the Las Alpujarras region. Geological processes can be clearly distinguished here, because faults are cutting the topographic surface, bounding deep Neogene, sedimentary basins with marine to continental, clay-rich clastic sediments coming from the uplifting mountains. High mountains, active half-grabens, syn-sedimentary faults, and uplift since at least the Upper Miocene (also Messinian) will be the crucial observations of the trip, to finally unravel the latest evolution of the Sierra Nevada range and how the clay minerals record part of this amazing history.