Stratigraphic reconsideration of the late Paleozoic in the surrounding of the Los Sauces dam, La Rioja.

Abstract

Upper Paleozoic outcrops located around to Los Sauces dam, La Rioja Province, constitute an important sedimentary depocenter at the north of Paganzo Basin. The geologic column is grain and bed fining-upward; distinctive lithological features allow dividing the succession in two lithostratigraphic units: Libertad and Sauces Formations. This proposal modifies partially a previous stratigraphic scheme. The Libertad Formation, Late Carboniferous, is formed by sets of grey greenish and purple conglomerates and sandstone, which are interbedding with black siltstone and mudstone. These fine sediments were mined during last decades as refractory argillite. The Sauces Formation is formed by orange red sandstones and siltstones with a few proportions of conglomerates. Main outcrops of Sauces Formation are present at NNW, NE and SSE side of the valley and isolated outcrops appear as small islands in the modern lake. Some characteristic species of the megaflora collected in the basal and middle sections of the Libertad Formation indicate a Late Carboniferous age. On the other hand palynologic studies performed in samples collected in the Sauces Formation indicate an Early Permian age.