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Título

PALEOGEOGRAPHIC RECONSTRUCTION DURING THE APTIAN-ALBIAN IN THE GRAJAÚ AND ARARIPE BASINS.

Texto do resumo

The tectonic evolution of the Equatorial Atlantic Margin (EAM) throughout the Early Cretaceous had global implications. The fragmentation of western Gondwana played a significant role in marine ingression into the interior basins of Northeast Brazil causing environmental changes due to its influence on ocean chemistry, nutrient distribution and water mass circulation. However, the moment of this entry and the extent of these inland seas are still a subject of discussion and little known.Contrasting paleogeographic reconstructions suggest that marine ingression occurred via different routes, i.e. (1) from the north, through the São Luís and Parnaíba basins; (2) from the northeast, passing through the Potiguar Basin, and (3) from the southeast, crossing the limits of the Sergipe-Alagoas Basin.
The environmental changes caused by marine ingressions are recorded in the black shales, limestones, evaporites of the Codó Formation (Aptian) of the Grajaú Basin, evaporites of the Ipubi Formation and shales and carbonates of the Romualdo Formation (Upper Aptian), Araripe Basin - Northeast Brazil .
Two outcrops representative of the many found in the Grajaú and Araripe basins were used for this research, to correlate the Aptian-Albian of the two basins. In the Grajaú Basin, in the town of Chorado Mine in the city of Grajaú-MA, gypsum mining takes place where the Codó Formation was described. In the Araripe Basin, a stratigraphic section was built in the Ipubi Formation and the Romualdo Formation at Campevi Mining. Analysis of satellite images and magnetometric and gravimetric maps helped with the structural interpretation of the area.
The described Codó Formation is composed of three Sequences: A lower sequence composed of black shales interbedded with ostracodal calcarenites and limestones. An intermediate sequence composed of evaporites (gypsum and subordinate anhydrites) and an upper sequence with shales, marls and limestones.
The Ipubi Formation is essentially composed of gypsum, sometimes forming two sequences, separated by black shales and calcarenites. The Romualdo Formation is composed of black shales, reddish shales, sandstones with channeled cross-stratification, humocky, small “waves”, limestones with fish and coquinas. For some authors, it records the last marine ingression into the interior basins of the Cretaceous of the Northeast.
Although the stratigraphic analysis shows a lithological correlation, Tetian faunal affinities and similarities in the paleoenvironments between the two basins in the Aptian-Albian, the connection through the Parnaíba Basin is not supported by the existing structural framework, in view of structural features such as the Transbrasilian Lineament that it formed a structural high, forming a drainage divide between the Araripe Basin and the Grajaú Basin.
During the Aptian, marine ingression extended into the interior of Northeastern Brazil, reaching the Araripe and Grajaú basins. It is suggested that in the Grajaú Basin the marine entry occurred from the north, at the opening of the EAM, forming an extensive Gulf, limited by the Xambioá Arch, while in the Araripe Basin the marine entry, also through the opening of the EAM, filled the several blocks formed along NE-SW shear zones, resulting in frequent mixing and coexistence of marine, brackish and non-marine environments

Palavras Chave

Grajau Basin; Carbonates; paleoenvironment; marine incursion; equatorial conjugate margins