Modern sedimentation processes in Laguna de Medina, southern Spain, derived from lake surface sediment and catchment soil samples

Modern processes influencing sediment composition in the endorheic lake Laguna de Medina, southern Spain, are disentangled by analysis of 46 lake surface sediment and 32 catchment soil samples. Based on statistical analysis of the mineralogical, geochemical, elemental, and granulometric compositions of all samples, the lake surface sediments can be divided into six provinces of individual composition and depositional processes. High quartz contents and coarse grain sizes, reflecting input from ancient terraces of the Guadalete River that are exposed in the adjacent hinterland, characterize the lake sedimentation close to the northern shore. At the south-eastern shore, sedimentation is characterized by terrestrial input of the Triassic Keuper facies via the most important inlet, the Arroyo Fuente Bermeja, as reflected by high relative intensities of Ti, K, Al, Fe, Mg, Rb. Sediments close to the northern shore are characterized by high calcite contents, reflecting predominant sediment supply from the adjacent Cretaceous 'capas rojas', a series of Subbetic deep-water marlstones and limestones. Close to the western shore, relatively high gypsum contents presumably are due to precipitation from upwelling ground water. Anthropogenic influence is only indicated in the north-western and central eastern parts of the lake, where the surface sediments are significantly enriched in TOC and TN, reflecting enhanced primary production due to terrestrial organic matter supply from anthropogenic areas in the respective catchment. The central part of the lake is characterized by distal hemipelagic sedimentation, with high concentrations of clay and silt and a chemical and mineralogical composition that reflects a mixture of the sediment sources characterizing individual parts of the lake shores. The results of this study shed new light on the depositional processes and their potential spatial heterogeneity in small endorheic lakes. Furthermore, they will provide important information concerning the interpretation of the climate-controlled sedimentary processes through time, which are reflected in a 25.7 m long sediment record (Co1313) that was recovered in the lake centre in 2014 and 2015.