Silicificación y paleokarstificación en depósitos evaporíticos continentales (Hoya de la Sima, Jumilla)

In the Northwest of the locality of Jumilla (Murcia, Spain) several evaporitic deposits with opaline cherts are found. The evaporites are mainly lenticular gypsums, which show, at the base, millimetric levels of micrites with ostracods and, at the top, a bioturbated carbonated gypsum bed. The opaline cherts are composed of quartz, opal CT and relics of host rocks (gypsum and calcite). A latter karstification affected these deposits and several karstic fillings with fragments of opaline cherts appear. The gypsums were deposited in a small, shallow (the presence of mammal tracks indicates a stage when the lakebed was exposed) and closed continental lake, between the Upper Miocene and the Pliocene. The opaline cherts were formed by early silicification of the bioturbated carbonated upper bed and by a "per descensum" silicification of the gypsums, mainly through fractures. The very rich silica solutions that produced the opaline cherts probably come from springs and fractures that are found in the zone