The present chapter deals with provenance analysis of a carbonate-siliciclastic Ordovician sedimentary unit of the San Rafael block, named the Ponón Trehué Formation (Darriwilian to Sandbian). This is the only sequence which exhibits a direct contact with the Mesoproterozoic basement through an unconformity, not only within the San Rafael block, but rather for the entire Cuyania terrane. When combining different provenance proxies, such as petrography, whole-rock geochemistry, Sm–Nd data, Pb–Pb analyses, and detrital zircon dating, it can be deduced that the source rocks are characterized by: (i) an upper continental crust composition, (ii) a subordinated influence of a more depleted composition, (iii) a dominantly Mesoproterozoic age, (iv) sedimentary recycling did not conspicuously affected the detrital source, and (v) weathering was relatively strong. All these characteristics point to the Mesoproterozoic Cerro La Ventana Formation basement as a main source of detritus to a restricted basin infilled during the Ordovician.Centro de Investigaciones Geológicas