An extensive diamictite-bearing unit is present within the lower Palaeozoic siliciclastic sequence of the Central Andes. A review of its lithostratigraphy, sedimentology and biostratigraphy allows to differentiate two subunits according to their provenance and age. The correlative San Gabán Formation (Perú), Cancañiri Formation (Bolivia) and Zapla Formation (NW Argentina), of Hirnantian(?)-Llandovery age, presents evidence for resedimentation from a glaciated tectonically-active source area located to the west and south. It includes granitoid boulders, and large olistoliths of late Ordovician units. In central Bolivia, the lowermost Kirusillas Formation (early Wenlock) presents evidence for resedimentation of shallow shelf deposits from a nearby source located to the east and north. It includes olistoliths of the Sacta Limestone Member (earliest Wenlock). Only careful sedimentology and biostratigraphy may discern between the two units when both are present in the same section