Sedimentologia e Estratigrafia dos sistemas de leques deltaicos (Fan Deltas) do grupo Itararé (Bacia do Paraná) entre Butiá e Rio Pardo (RS)

Abstract

The Itararé Group is interpreted as a glacial-influenced unit filling glacial valleys in the central-eastern region of Rio Grande do Sul. The present work detail the filling of one of these depressions, known as Leão depression, between Butiá and Rio Pardo cities. The methods used for this investigation were the faciological and geophysical well-log analysis and the elaboration of stratigraphic sections from six stratigraphic wells. Two sections were elaborated from these wells: NW-SE-E and SW-NE oriented. From the faciological analysis, this unit was interpreted as the evolution of a fan delta system comprised by four units or facies associations: (A1) Distal delta front and slope; (A2) Pro-delta; (B) Proximal and distal shelf systems; (C) Estuaries. The stratigraphic evolution can be unraveled by the faciological and gamma rays stacking patterns. It was observed that the development of this depositional system presents a hierarchical progradational–retrogradational stacking pattern in three systems tracts: Lowstand, transgressive and highstand system tracts. Data integration do not indicate a direct relationship between the ice action and the filling of this valley. Otherwise, glacial influence is attested only by dropstones at restricted stratigraphic levels, interpreted as some floating ice blocks along the sedimentation.