Sedimentary facies distribution and genesis of a recent carbonate-rich saline lake: Gallocanta Lake, Iberian Chain, NE Spain

Abstract

The study focuses on the Holocene sedimentary infill of the Gallocanta lacustrine basin in the Iberian Chain, NE Spain. The Gallocanta lake is a saline wetland with a maximum length of 7.5 km and a maximum width of 2.85 km. The water depth varies significantly, from a maximum depth of 2 m to completely dry. In the central areas (central subenvironment) sapropels and salts develop, with halite, gypsum, anhydrite, dolomite, aragonite, calcite, magnesite, and lesser amounts of quartz and clay minerals. Cyanobacteria filaments are related to the aragonite and dolomite crystals. The marginal subenvironment either has a gradual or a sharp change from that of the central subenvironment. An inner area with desiccated light grey lutites is present in this marginal subenvironment. In SEM and X-ray diffraction analyses, quartz, clay minerals, aragonite, calcite and small quantities of dolomite, gypsum, anhydrite and halite can be identified. This inner area is surrounded by an external fringe composed of light brown lutites and a high concentration of Salicornia meadwod and microbial mats. This zone is only occasionally submerged and contains sandy and conglomerate islets. Active palustrine areas are flood zones, where grey lutites with a significant quantity of vegetation, such as reeds, are common. In general, this entire sector is being modified by human action. Five sedimentary facies have been defined, and this has enabled the identification of three distinct stages in the general evolution of the basin. The first stage is an alluvial period, developing during an arid climate. After this, a more humid stage facilitated the installation of a shallow carbonate-rich lake. A reduction of the water level, probably due to a more arid stage, induces a salinity increase of the lacustrine brine and the change to the third stage, which corresponds to the present conditions. The water level experienced frequent oscillations, and alternations between humid conditions with a high production of organic matter, which favors carbonate formation, and water level dropdowns, even to total dryness, with saline sedimentation.