Pleistocene microfossils (charophytes and ostracods), vertebrates and mollusks from Aguada de Lomas and Sacaco (Arequipa, Peru): palaeoecological interpretations

ADRIANA, GARCIA; RODOLFO, SALAS; THOMAS, DEVRIES; MARIO, URBINA; FRANÇOIS, PUJOS; MARINA, AGUIRRE

Robertson, New South Wales, Australia

Congreso; 4th International Symposium on Extant and fossils Charophytes; 2004

    A rich fauna of vertebrates including mammals and birds, charophytes, ostracods and molluscs has been discovered in sediments from Aguada de Lomas and Sacaco (Arequipa, Perú) of Late Pleistocene age. The palaeo-wetlands or ‘humedales’ of Aguada de Lomas and Sacaco developed parallel to the Peruvian coast, on lower areas excavated by wind and water onto marine sediments of Miocene and Pliocene age later inundated by ocean or ground water. These Late Pleistocene environments are evaporitic, formed by whitish-grey silty clayish sediments, tuffaceous sandstones and gypsum, with intercalations of tuff and volcanic ash. The sequence is elevated up to +50 m, with the gypsum reaching up to 3 m thick in some areas. Sediments from Sacaco provided the more abundant populations of microfossils. Eighty per cent of the vertebrates are horses (Equus (A.) santaeelenae) indicating a savanna with long grasses typical from coastal plains with sandy sediments, while Lama guanicoe indicates drier environments, with development of shrubs.    The charophyte present in Aguada de Lomas and Sacaco, is Chara hornemannii Wallman, a current inhabitant of coastal saline lakes from tropical to subtropical areas of the American continent (Brazil, Cuba and USA) (Wood and Imahori, 1964-65; Daily, 1967). C. hornemannii is commonly found at water depths of 0.5 m up to 2 m, and salinities between 2 g L-1 and 20 g L-1. García (1999) described Quaternary gyrogonites of C. hornemannii from Salina del Bebedero, Argentina, but the species has not been found yet living in that country. The ostracod is a species of Limnocythere sp., a cosmopolitan genus found in temporary to permanent water bodies with variable salinity (fresh to 30 g L-1). The molluscs are Planorbis sp. and Littoridina australis, the last one adapted to environments with changing salinity, with optimum development between 8-22 g L-1). The association described indicates an environment of evaporative wetlands within a desert area, similar to the modern humedales along the Peruvian coast, e.g. the humedal de Villa, in Lima.