CONTROLE ESTRUTURAL DA DEPOSIÇÃO MESOZOICA NAS BACIAS DA MARGEM CONTINENTAL BRASILEIRA

H. E. ASMUS

Resumo


The sedimentary fill of the Brazilian marginal basins is made up, when complete, of three suites reflecting the evolutionary stages of the continental margin: (1) the lower clastic non-marine suite was deposited in two stages, the basal section in a pre-rift stage, and the upper section in a rift-valley stage: (2) the middle suite, including the evaporitic section and the overlying shelf carbonates, was deposited in a stage of tectonic quiescence; (3) the upper marine suite, including some paralic and continental sediments, was deposited in a stage of vertical differential movements along flexure lines. The Upper Jurassic non-marine sediments of the basal section in Brazil (Sergipe-Alagoas, Recôncavo, and Almada Basins), correlate well with those of West Africa (Gabon and Congo Basins) showing a symmetric areal distribution. The absence of this Upper Jurassic section, south of the Jequitinhonha Basin in Brazil and the Cuanza Basin in West Africa is probably due to non-deposition in uplifted areas coinciding with sites of Early Cretaceous volcanic activity. The juxtaposition of the uplifted-volcanic areas in Brazil and Africa in a pre-drift arrangement suggests the existence of a hot-spot, active in Late Jurassic-Early Cretaceous times. An earlier rifting in the uplifted areas is suggested by the presence of Wealdian evaporites in the Santos and of Aptian marine sediments in the Pelotas Basin. Both sediment types are older than their lithological - environmental counterparts along the continental margin from the Campos to the Sergipe Basin. Along the northern margin, from the Amazon delta to the Potiguar Basin, the pre-rift and rift-valley stages are not well known. There is evidence of Early Cretaceous rifting in aborted rift-valleys [v.g. the São Luiz Basin) and also of Late Cretaceous compressional forces. The relationship between, and the duration of the tensional and compressional forces are still unclear.

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