Sedimentary and Structural Evolution of the Salar de Atacama Depression

Abstract

The Salar de Atacama Depression is part of the northern Preandean Depression, a SSW-NNE striking morphological low situated between the Western Cordillera de los Andes and the Chilean Precordillera. The Cordillera de la Sal is a small SSW-NNE striking intrabasinal foldbelt within the Salar de Atacama Depression and provides the best outcrops of the sedimentary record of the Preandean Depression. It is built mainly of continental red beds (San Pedro Formation, Oligo-Miocene), locally more than 3 km thick. These sediments were deposited in a playa environment and contain large amounts of evaporites (gypsum, anhydrite, glauberite, and, especially, halite). First fossil findings (charophytes, gastropods, ostracods) indicate intervals with an oligohaline lacustrine environment in the north. Towards the west, the San Pedro Formation interfingers with an alluvial fan sequence (Tambores Formation). The sediments of the Salar de Atacama Depression overlie unconformably folded Upper Cretaceous-Eocene sediments of the Purilactis Formation. The origin of the observed complicated structural pattern is considered to be a result of the combination of compressional and sinistral strike slip movements. The most evident tectonic elements within the sediments of the Salar de Atacama Depression are: (1) NNE-SSW striking folds with doubly plunging axes; (2) a complex pattern of nearly vertical small scale normal, reverse and strike slip faults; (3) NNE-SSW striking low angle reverse faults; (3) N-S to NW-SE striking vertical tension fissures; (4) effects of gravitational lateral spread of thick halite deposits.