CONICET | Buscador de Institutos y Recursos Humanos

The western Gondwana margin underwent a complex geodynamic history during the early Paleozoic, and major uncertaintiesremain as to the role of tectonism in sedimentary dynamics. This study focuses on the lower part Santa Rosita Formation andthe coeval Guayoc Chico Group (Cordillera Oriental; Northwest Argentina), ranging from the late Cambrian (Furongian; Age10) to Early Ordovician (early Tremadocian; Tr1). This stratigraphic interval has been previously interpreted as depositedin an extensional basin to a retro-arc basin without major regional tectonic-induced deformation during its deposition, onlyrecording long-term relative sea-level fluctuations. Four areas (Sierra de Cajas, Angosto del Moreno, Quebrada de Trancas,and Quebrada de Moya) were chosen because they host the most complete and temporally well-constrained stratigraphicsections of the Cordillera Oriental. Throughout the stratigraphic sections, four main facies zones are described and attributedto deposition in estuarine, foreshore-shoreface, delta-front, and offshore environments. Trilobite biozones are used as thebiostratigraphic framework. By integrating sedimentary facies analysis, biostratigraphy, and sequence stratigraphy from thefour selected sections, a new scenario showcasing the evolution of the basin is proposed. This scenario interprets a tectonicallyinduced deformation during the deposition of the Santa Rosita Formation and the coeval Guayoc Chico Group. Thenewly acquired sedimentological data show that physiographical changes took place during the Cambrian-Ordovician transitionand are expressed in various localities. This major change is recorded in the stratigraphic architecture, where extensive wave-ravinement surfaces and sedimentary hiatus are the result of local, syn-depositional basement uplifts. The initiation of the Puna-Famatinian volcanic arc during the Early Ordovician on the western margin was likely responsible for deformationin the retro-arc basin and the proposed scenario is consistent with the stratigraphic evolution in other areas of the CordilleraOriental (e.g., Sierra de Mojotoro) and the Sierra de Famatina. Therefore, this study helps to constrain the evolution of thewestern Gondwana margin during the early Paleozoic, showing changes in the stratigraphic architecture and basin evolutionfrom an extensional to a retro-arc style.