Provenance studies in the Lower Devonian Villavicencio siliciclastic unit of the southern region of the Argentine Precordillera, Mendoza, Argentina.

CINGOLANI, MANASSERO, BASEI, URIZ

Sao Paulo

Congreso; 6to-Congreso Latinoamericano de Sedimentología; 2013

Instituto de Geociencias.San Pablo

The Lower Devonian siliciclastic Villavicencio Formation crops out in the Mendoza Province, Argentina as a part of the southern section of the Tertiary Precordillera thrust-fold-belt. The best outcrops are located to the East of Uspallata-Caracoles de Villavicencio and San Isidro Creek. A graptolite Ordovician sequence is developed under this unit with a fault contact. The upper contact is an unconformity with the Permo-Triassic volcanic rocks and in some places the Villavicencio Fm is intruded by Permian granitoids (Cacheuta region). It is composed by massive dark grey sandstones alternating with laminated mud beds, and laminated sandy heterolithic facies showing wave action. Rip-up clasts of fine dark grey mudrock at the base of beds; reflect the relatively high energy environment. Facies are typical of marine shallow shelf sands. Some beds have plant debris that is current aligned suggesting short transport with low energy deposition. Several levels with endemic land plant fossils (Rhyniophytoids) were described as developed during the Lochkovian age. Palynological data (spores) provide an early Devonian age (Pragian-Emsian). Sandstone petrography shows mixing of Recycled Orogen and Continental Block provenances for these feldspathic-lithic wackes. Paleocurrent data has great dispertion with E-W and NW-SE bidirectional trends. U-Pb ages (LA-ICP-MS) on detrital zircons show a Mesoproterozoic dominant mode suggesting mainly sources of ‘Grenville-age’ (more than 50% of the analyzed zircons) probably located to the east of the study area. The youngest zircon ages are c.429 Ma (Silurian).