Late Miocene slope calcareous tufa, Atacama Desert, Chile: the role of faults, groundwater movement, and climate

This study enhances our understanding of Late Miocene-Pliocene climate in the Atacama Desert of the Antofagasta Region in northern Chile. Field relations, petrography, and geochemistry from two previously undescribed, fossil springs within the Calama Basin’s Opache Formation demonstrate similarities between the springs, such as laminated crystalline carbonate, including freshwater aragonite botryoids, but differences in trace element and δ13C values. One location contains stromatolites, oncolites, and sedimentary structures indicative of flowing water including ripple marks and microterracettes, whereas such features are generally absent at the other site. Both study areas are associated with fault systems that transferred groundwater from regional aquifers to the surface, bringing water rich in strontium, magnesium, iron, and manganese, to coprecipitate with CaCO3 as either aragonite or calcite. This correlation between springs and tectonics is becoming more widely recognized in other continental settings.