Early Ordovician Aguada de la Perdiz Formation, northern Chile: Stratigraphy, provenance and regional tectonic setting

Abstract

The Early Ordovician Aguada de la Perdiz Formation of northern Chile is one of the oldest unmetamorphosed sedimentary units in Chile. Graptolites indicate a late Floian to early Dapingian age of the formation at the Aguada de la Perdiz type locality and small nearby outcrops in Chile. Correlative outcrops on the Argentinian side occur at Huaitiquina, Filo Pircas, Sierra de Guayaos and Lever Mucar. Graptolites are associated with scarce occurrences of brachiopods and conodonts in some outcrops. In the Argentinian Puna the correlative units were assigned to the Coquena Formation. All outcrops consist mainly of volcaniclastic turbidite and ash-rich flow deposits with intercalations of bimodal lavas, volcanic breccias and reworked felsic tuffs. The lithological assemblage reflects deposition in a marine volcaniclastic apron located on the eastern flank of the Famatinian magmatic arc. We propose to collectively group all respective outcrops in the Aguada de la Perdiz Formation thus respecting precedence of its first definition by García et al. (1962) because of the common characteristics of the formation on both sides of the international border. New U-Pb detrital zircon ages of a sample (n=124) from the Huaitiquina locality range between 3,530 and 550 Ma and reflect a common polycyclic provenance from older Amazonian sources. The youngest U-Pb zircon age corresponds to the Ediacaran and predates the biostratigraphically defined depositional age by ca. 80 Myr. Thus, the synsedimentary Famatinian felsic volcanism, otherwise common in coeval units, is not reflected in the detrital zircon age record at Huaitiquina. The absence of Famatinian ages may indicate that sediment delivery from the Famatinian arc line source bypassed this site and that erosion of the arc had locally dissected the volcanic edifices and had progressed to access the pre-Pampean Neoproterozoic arc basement.