ICNOFOSSEIS NO ARENITO DO GUAMA (PARA, BRASIL): POTENCIAIS REGISTROS SILURIANOS

Ichnofossils of the Guama Sandstone (Para, Brazil): potential Silurian records. The Guama Sandstone is a unit restricted to the Bragantina Platform in the northeast Para State. It is characterized by thick layers of well-rounded, well-sorted, medium-grained quartzsandstone with textural and compositional maturity. In general, the layers exhibit few preserved primary sedimentary structures. The facies association indicates a sandy coastal paleoenvironment comprising the foreshore and shoreface zones. We found in the Guama Sandstone the ichnospecies Psammichnites isp., cf. Schaubcylindrichnus coronus, Skolithos isp., Skolithos linearis and V-shaped vertical excavations, which commonly compose a mixture of the Cruziana and Skolithos ichnofacies. On the basis of the regular distribution alternating between Skolithos and Psammichnites in the sandstone layers, and the low ichnodiversity and local abundance, we suggest that periodic changes in energy and sedimentation rate occurred. These characteristics of the Guama Sandstone ichnoassemblage are similar to those of the Ipu (Parnaiba Basin) and Nhamunda (Amazon Basin) formations, although only Skolithos occurs in both units.