Paleontology and geological aspects from the end of Neogene successions in southwestern Rio Grande do Sul state, Brazil

Abstract

Three fluvial generated sucessions from southwestern Brazil are discussed in its litostratigraphic and paleontological aspects. The fossil content suggests distinct ages between the end of Pliocene and Holocene, sometimes contradictory with the absolute ages. Its correlation with other South American places is also furnished. The Guterres Alloformation is a fi ne to coarse sand and conglomeratic unit that contains only fossil wood logs and is here proposed to correspond to Salto and Salto Chico Formations, respectively from Uruguay and Argentina. However, thermoluminescence ages suggest a Late Pleistocene age, more coherent with the corresponding El Palmar, Argentina, and Touro Passo Formations. To the Touro Passo outcrops are proposed three architectural units, of channel, lateral accretion and flood plains, the last one exclusive from the Barranca Grande locality, also unique in contain autochnous and parauthoctonous mammal rests. The fossil content, with Tupinambis, Hydrochoerus, Tapirus and Tayassu, indicates an Upper Pleistocene age and points to a more warm and wet climate, that could be compared with those that marks the deposition from the northern areas from Uruguay and Argentina (Sopas and Yupói/Toropi Formations). The same correlation could be made to the Sanga da Cruz locality, but with little younger ages and characterized by typical Pampean elements, like Propraopus cf. P. grandis, Glyptodon, Pampaterium typum, and Macrauchenia patachonica.

Key words: Quaternary, fluvial deposits, vertebrates, woods, age, South Brazil.