Comparative sedimentary provenance analysis of Upper Ordovician siliciclastic rocks from the San Rafael Block (Pavón Fm) and from the eastern side of the Cordillera Frontal (Las Lagunitas Fm), Mendoza-Argentina

Abstract

The San Rafael Block as a southern part of the Cuyania-Precordillera terrane is characterized by a Grenvillian-type basement overlain by Lower Paleozoic carbonate-siliciclastic rocks. During the Late Ordovician siliciclastic detritus was deposited as a marine clastic wedge within a foreland basin, after the drowning of the carbonate platform to conform the siliciclastic Pavón Fm bearing Sandbian graptolites (Manassero et al., 1999; Cingolani et al., 2003). On the other hand it was discovered recently (Tickyj et al., 2009) in the black shales of the Las Lagunitas Formation outcropped at the eastern side of the Cordillera Frontal the same graptolite fauna. This unit is located between the Diamante and Tunuyán River. The studied section at the Cortaderas creek is a clastic sequence comprising levels of well-sorted, coarse- to medium-grained sandstones and conglomeratic sandstones; coarse- to fine-grained wackes and medium- to fine-grained sandstones, intercalated with black shales. Within this profile the sandstone petrography of the studied samples shows quartz-feldspathic arenites with abundant undulate monocrystalline quartz, policrystalline quartz, metamorphic rock fragments, albite twined plagioclase, potassium feldspars and detrital flexures muscovite as accessory mineral. It is interesting to note that the Pavón and Lagunitas Fms show coherent sedimentary provenance from a continental block and recycled orogen sources. The new findings help to suggest that the Lagunitas Fm could be a western extension of the lithofacies of the Pavón Fm, in the Cordillera Frontal (Chilenia terrane) with source areas located to the East of the study area. Geochemical, isotopic analyses and detrital zircon ages are in progress.