Geochronology and paleogeographic of the Tertiary intermontaneous basin of northern Iglesia, Andes of San Juan, Argentina

Abstract

The northern Iglesia nonmarine basin, piggyback to the Precordillera thrust belt and east of the main Andean ranges, is subdivided into 5 sub-basins by north-trending structural highs. We combine stratigraphic data from seismic reflection and surface geology with magnetic polarity stratigraphy and fission-track zircon dates on intercalated volcanic deposits to determine ages, correlations and paleogeographic evolution among the sub-basins. Two distinct stratigraphic units fill the basin. Sequence 1, with strong and seemingly proximal volcanic influence accumulated approximately 17 Ma when the Iglesia basin was narrow and elongate, but not internally disrupted. Sequences 2 through 11 accumulated between 9 and 4 Ma in a depocenter that first broadened through time simultaneous with sub-division into the structural sub-basins, and then became restricted to the western structural sub-basin. Whereas it is clear that Sequences 2-11 correspond to the Iglesia Group, the proper stratigraphic assignment of Sequence l is less certain.