Miocene to recent history of the western Altiplano in northern Chile revealed by lacustrine sediments of the Lauca basin (18�15??18�40? S/69�30??69�05?W)

The intramontane Lauca Basin at the western margin of the northern Chilean Altiplano lies to the west of and is topographically isolated from the well-known Plio-Pleistocene lake system of fluvio-lacustrine origin that covers the Bolivian Altiplano from Lake Titicaca to the north for more than 800 km to the Salar de Uyuni in the south. The Lauca Basin is filled by a sequence of some 120 m of mainly upper Miocene to Pliocene elastic and volcaniclastic sediments of lacustrine and alluvial origin. Volcanic rocks, partly pyroelastic, provide useful marker horizons. In the first period (6–4 Ma) of its evolution, the ‘Lago Lauca’ was a shallow ephemeral lake. Evaporites indicate temporarily close…