Petrology of a barrage tufa system (Pleistocene to recent) in the Ruidera Lakes Natural Park (Central Spain)

Abstract

The Ruidera Lakes Natural Park, Central Spain, contains a well-exposed Pleistocene to Recent freshwater carbonate succession in a fluvio-lacustrine setting. Carbonate precipitation continues today and is manifested in active phytoherm barrage constructions, marginal lacustrine stromatolitic terraces, lacustrine lime muds, and sand-grade detrital tufa. Phytoherm barrage deposits consist of coarse sparite fringe in vigorous flow areas associated with phytoherm framestones, and alternating sparite and micrite fringes, which are most common in areas with lower velocity flow. Holocene lake margin deposits consist of laterally growing mammilate stromatolites. These are developed as pinnacle stromatolites at the foot of overhangs associated with the lake margins. Pre-Holocene marginal lacustrine terraces have no associated stromatolite rims but contain abundant oncoidal deposits close to their base. In some ephemeral channels and pools located on the active phytoherm barrages stromatolitic pavements are developed which are comprised of elongate domes composed of fibrous calcite crystals encrusting cyanobacteriaI filaments. The erosion of phytoherms and continous rain of fragments from pinnacles, pavement and marginal stromatolites in the active system provides abundant detrital tufa. These allochthonous detrital tufas are volumetrically the most important carbonate deposits in Ruidera Lakes and dominate the lower reaches of the Upper Guadiana River valley. The lake depocentres accumulate carbonate muds, which are locally rich in Chara.