Gypsum crystal morphologies in lake sediments for paleoclimate reconstructions: a case study in Fuente de Piedra playa-lake (Málaga)

Gypsum (CaSO4∙2H2O) is one of the most common evaporitic minerals on Earth. Its crystals exhibit diverse morphologies that can provide insights into their depositional environment. We analyzed the morphologies of gypsum deposits in a 14 m sedimentary sequence of Fuente de Piedra playa-lake (Málaga, Spain) to link its variations to sedimentary facies and changes in the past lake level. Precipitation of primary prismatic crystals prevailed during lake highstand periods. In contrast, lenticular gypsum crystals are consistently present throughout the entire core and do not seem to be related to specific lake levels. An exception are macro-lenticular crystals, which seem to be correlated with dry periods and high salinity water. Subrounded gypsum grains, eroded from former primary crystals, are also abundant along the sequence and usually concentrate in facies related to stages of lake agitation during highstand periods. Gypsum is generally absent during lowstand periods, which may indicate relatively high dissolve organic matter or, more likely, less interaction of the lake with the saline groundwater aquifer beneath. Our results suggest that the occurrence of some gypsum morphologies can be used to infer paleo-lake levels.