Discussion on ‘The Neoproterozoic glacial record in the Río de la Plata Craton: a critical reappraisal'

Abstract

In a recent article, Pazos et al . (2008, p. 343) claim that ‘the Zanja del Tigre Formation (Uruguay) represents a glacial influenced succession deposited during the Neoproterozoic, correlative with one of the glaciations described in the Kalahari Craton, prior to Kalahari–Rio de la Plata assembly in the proto-western Gondwana margin'. However, we question the two lines of evidence that Pazos et al . (2008) put forth in their paper to constrain the age of this unit and to support a glacial event. Pazos et al . (2008, p. 350, and fig. 4) consider the Zanja del Tigre Formation as part of the Lavalleja Group. This view, however, is incompatible with existing interpretations. According to the latest compilations of the geology of Uruguay (Bossi et al . 1998; Bossi & Ferrando 2001), the Zanja del Tigre Formation is part of the Carape Group, which is stratigraphically below the Lavalleja Group. In fact, the Carape and the Lavalleja groups have long been considered independent lithostratigraphic units (e.g. Bossi & Navarro 1991), perhaps even belonging to different ‘terranes' or ‘blocks' (Gaucher et al . 2004). A recent geochronological study (not available to Pazos et al . 2008, at the time of writing) based on detrital …