A comparative study of Conophyton stromatolites of the Ribeira and Brasilia bels

Abstract

The Conophyton stromatolites were described in the Ribeira (C. garganicum) and Brasília (C. metulum and C. cylindricum) belts, in lithostratigraphic unities attributed to the Mesoproterozoic. Conophyton garganicum occurs in the Ribeira Belt (Itaiacoca Group) in the Itapeva region (São Paulo). In the Itaiacoca Group, the Conophyton garganicum forms have also been found at Abapã (Paraná). They are similar to the other coniform stromatolites described in Itapeva, but differ from the other forms in the Brasília belt, including C. cylindricum and C. metulum. In the Brasília Belt two occurrences of Conophyton are described in the Vazante Group in Minas Gerais, in the Cabeludo (C. cylindricum) and Lagamar (C. metulum) regions and one in the Paranoá Group near Cabeceiras (Goiás) (C. cylindricum). Conophyton from Cabeludo differs from the Lagamar´s in laminar thickness, as well as the regularity degree and laminar heritage of the axial zone. Otherwise, the Conophyton from Cabeceiras is similar to the Cabeludo´s in laminar thickness and configuration. The significant differences between the Conophyton from Brasília and Ribeira belts indicate distinct depositional environments and/or ages. Conophyton shows Late Mesoproterozoic and Early Neoproterozoic ages from Vazante, Paranoá and Itaiacoca groups, which is consistent with available radiometric ages.