Evaporite sedimentation in a tectonically active basin: The lacustrine Las Minas Gypsum unit (Late Tortonian, SE Spain)

Abstract

Evaporite successions may undergo significant lithostratigraphic changes laterally and vertically in tectonically-active basins. The Las Minas Gypsum, a lacustrine unit of Late Tortonian age and up to 160m thick in the Las Minas-Camarillas basin (SE Spain), consists of a number of shallowing-upward cycles. Each cycle is made up of a lower interval with marl and carbonate, and an upper interval with gypsum. In the upper interval, the base displays carbonate-gypsum laminites (couplets, yearly microcycles) showing a large variability of textures and fabrics; gypsum textures are cumulates and bottom-grown crystals. Laminites are overlain by selenitic gypsum. The carbonate is a primary dolomite induced by sulphate-reducing bacterial activity. Native sulphur was formed in early diagenesis and during exhumation was partly transformed into late diagenetic gypsum. The isotopic compositions of gypsum suggest that the sulphate mainly derived from chemical recycling of Triassic evaporites; however, marine sulphate was probably supplied by episodic marine incursions. A perennial saline lake characterized by irregular bottom topography and depositional settings with variable subsidence ratios is interpreted. In addition to climate, saline diapirism, Neogene volcanism, synsedimentary faulting and seismicity influenced the evaporitic deposition. Las Minas-Camarillas basin is an example of how in tectonically active zones different factors interplay to produce significant variability of the evaporitic sedimentation and cyclicity.