PALEOZOIC BASIN EVOLUTION DURING TECTONIC AND CLIMATIC TRANSITIONS IN THE EASTERN PRECORDILLERA OF ARGENTINA

The Precordillera of western Argentina displays a complex pre-Andean stratigraphic record related to Paleozoic plate convergence along the southwestern margin of Gondwana. Sedimentologic and U-Pb detrital zircon and igneous geochronological results for the Silurian-Devonian Rinconada Formation and Carboniferous Jejenes Formation of the eastern Precordillera provide insight into basin evolution, drainage reorganization, and climatic and tectonic interactions during Paleozoic deformation and glaciation. Measured sections and lithofacies analyses indicate Silurian-Devonian deposition of sediment gravity flows and mass-transport deposits in a submarine fan environment. Flexural subsidence was induced by shortening in the adjacent Famatinian orogenic belt. The foreland basin was then deformed during the Late Devonian Chanic orogeny, prior to glacial incision of remnant topography during the Late Paleozoic Ice Age. Analyses of unconformities, cross-cutting relationships, and lithofacies within a Carboniferous paleovalley (Quebrada Grande, Sierra Chica de Zonda) indicate four facies associations within a fjord setting governed by glacial advance and glacial retreat, including deposition in fjord-head delta, distal fjord, fan-delta, and subglacial fan environments. Detrital zircon U-Pb geochronological results for seven Paleozoic sandstone samples (840 individual grain analyses) signify sediment derivation from western Pampean basement with progressive shifts during the Carboniferous, indicating drainage expansion to include the Famatinian magmatic arc and eastern Sierras Pampeanas provinces. The transition from a Silurian-Devonian deep marine foreland basin to an isolated Carboniferous fjord reflects major orogenic and climatic transitions in SW Gondwana. Late Ordovician-Silurian (Famatinian) and Late Devonian (Chanic) shortening created elevated topography that was subsequently beveled by glacial erosion during the Late Paleozoic Ice Age. We suggest that deformation related to subduction and terrane collision helped drive changes in Paleozoic basin configuration, sediment dispersal, and depositional environments. However, profound climate changes during regional glaciation further regulated the depositional processes and spatial extent of late Paleozoic clastic deposition across the Precordillera.