The silty shale Taquaral Member of the early Permian Irati Formation (Paraná Basin, Brazil). Paleontology and paleoenvironments

Abstract

Two facies are recognized in the Taquaral Member, base of the Artinskian Irati Formation, Parana Basin, Brazil: (1) The sandstone and conglomerate facies, mostly present in the lower part of the member, is thin, commonly 10 cm, exceptionally 1 m thick; and (2) the silty shale facies overlaying the former. Some sandy lenticular beds may occur in the lowermost shale strata. The silty shale facies is thicker (5–30 m), more homogeneous and more widespread than the sandy facies. Facies has yielded crustaceans and fish remains as the only recovered fossils. Other taxa reported by previous authors without formal descriptions and illustrations were never found by later researches. The scrutiny of the paleontological content of the silty shale is here presented by the first time and constitutes one of the purposes of this contribution. The fossil content allowed the proposition of a paleoenvironment of deposition, without a direct connection to open ocean. Some of the species may have been adapted to the new conditions, brackish, from older marine taxa, not yet discovered or stripped off by erosion.