The Record of the Varanger Glaciation at the Rio De La Plata

PAZOS, P. J. ; LEDA SÁNCHEZ BETTUCCI; TOFALO, O. R.

GONDWANA RESEARCH

Elsevier

Año: 2003 vol. 6 p. 65 - 77

1342-937X

A sedimentary succession included in the lower section of the Playa Hermosa Formation from the Playa Verde Basin,Uruguay, is described. Two facies associations, one mainly coarse- to medium-grained and other one fine-grained, havebeen defined (FA 1-11). In the first one, breccias, conglomerates, sandstones and minor mudstones were deposited in asubaqueous depositional setting (proximal) suggesting slope instability and resedimentation processes. The second onecontains diamictites, rhythmites, sandstones and mudstones and presents abundant evidence of soft-deformation, alsointerpreted to be deposited in a subaqueous environment (distal). Dropstones, clast layers, diamictites, rhythmites andvarve-like deposits are interpreted as ice rafting processes generated during a glacial episode. This glacial-relatedsuccession constitutes the first record from the Varanger glaciation at the Rio de la Plata Craton of the late Neoproterozoicage and also represents one of the oldest sedimentary records after the collision of the Rio de la Plata and Kalahari Cratons.A combined interaction of extensional faulting and glaciation in a tectonically active basin with locally high subsidence rates,resulted in high rates of sedimentation and resedimentation processes. As a whole, the sedimentary succession sets a relevantdatum to be used in future paleogeographic reconstructions of the Vendian glacial record in southern South America.