The Mar Chiquita Lake: An indicator of intraplate deformation in the central plain of Argentina

The Mar Chiquita saline lake is located in the lowest part of one of the largest endorreic saline basins of South America. With a surface area of 6000–6500 km2, the lake is located in a tectonic depression with an asymmetric cross section. The Sierras Pampeanas foothills, (with altitudes near 1500 m) are to the west and a 100-m topographic high (San Guillermo high) is to the east whose western border is bounded by a buried Middle Pleistocene fault (the Tostado-Selva Fault). The main tributary of the lake is the Dulce River, which flows from north to south. The southward flow of the river was impeded by an obstacle that closed the Dulce Valley, generating the Mar Chiquita Lake. The megafans of the Primero, Segundo, and Tercero Rivers deposited a large amount of sediment against the faulted border of the San Guillermo high, generating an obstacle that impeded the normal flow of the rivers and diverted the Dulce and the Salado Rivers to their present positions. Precise data concerning the age of the impounding of Mar Chiquita does not exist, but lacustrine conditions are undoubtedly younger than the uplift of the San Guillermo high, which occurred in the Middle Pleistocene. The well-preserved dry valley of the Dulce River, located southward of Mar Chiquita, is still visible in satellite images and confirms the youth of the impounding. The observations introduced in this paper allow us to understand the origin of a significant feature of the central plains of South America. The generation of Mar Chiquita Lake and upstream wetlands produced a pronounced environmental change in the arid Chaco-Pampeana Plain, which favored human life by introducing changes in vegetation and fauna.