Mesozoic and Cenozoic Stratigraphy and Tectonic Events of Puno-Santa Lucia Area, Department of Puno, Peru

Abstract

The Puno-Santa Lucia area is in the higher parts of the Andes in southern Peru. The oldest rocks in the area are quartzite and shale of the lower Paleozoic Cabanillas Group, more than 2,000 m thick. The Jurassic Lagunillas Group is divided into three units with an aggregate thickness of 1,505 m. The Cretaceous rocks are included in the Huancane Group and the Moho Group, the combined thickness of which is 410 m. The Ayavacas Limestone, upper member of the Moho Group, contains fossils of Cenomanian age. Trachytes of Cretaceous age are present near Juliaca and on the Capachica Peninsula. Redbeds, Cotacucho, Vilquechico, and Munani Formations, mapped by Newell within the Tertiary Puno Group, are considered here to be Late Cretaceous on the basis of their stratigraphic positio . Apparently these formations were deposited in a closed basin between the Cordillera Occidental and Cordillera Oriental. The Puno Group of probable Tertiary age consists of two units: the Saracocha Formation below, consisting mainly of conglomerate, is widely distributed in the southwestern part of the area, but is absent in the northeast; and the Tacaza Formation above, a volcanic sequence, also present in the southwestern part, shows the thickest sections along the Cordillera Occidental with thinning toward the east. Olivine basalt flows and tuffs of the Sillapaca Formation unconformably overlie the Puno Group. Three orogenies have been identified.