Title: Petrografia de arenitos e minerais pesados de depósitos cretáceos (Grupo Itapecuru), Bacia de São Luís-Grajaú, norte do Brasil
Abstract:Petrography, heavy minerals and quartz analyses, palaeocurrent data revaled the sedimentary story and potential source areas of sandstones of the Itapecuru Group in the southern margin of the São Luís...Petrography, heavy minerals and quartz analyses, palaeocurrent data revaled the sedimentary story and potential source areas of sandstones of the Itapecuru Group in the southern margin of the São Luís-Grajaú Basin. The studied deposits consist of quartzarenites with heavy mineral assemblage consisting of tourmaline, zircon, staurolite, rutile and kyanite with a wide variety of forms, mechanical surface textures, and colors. The predominance of rounded zircon and tourmaline grains suggests a strong contribution from recycled sediments from sedimentary and metassedimentary rocks. Quartz grains exhibit irregular forms, monocrystaline and polycrystalline types and surface textures similar to the heavy minerals grains. The modal composition in a Q-F-Lt plot suggests their origin from continental block and recycled orogen. The potential sources were mainly sedimentary rocks, as well as medium -to high-grade metamorphic and granitic rocks. The studied profile was subdivided into four stratigraphic levels A, B, C and D, through palaeocurrent data and RuZi index, which indicate change in source areas. Palaeocurrent pattern suggests that the Zone A, at the base of the succession, were sourced from the northern and northeastern regions, including the São Luís Craton, Gurupi Belt, and northwestern portion of the Borborema Province. Sediments of the zones B, C and D were supplied from the southern, southwestern and southeastern regions, including the Amazonian Craton, Araguaia Belt, and Borborema Province.Read More