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The Espirito Santo basin lies in the eastern continental margin of Brazil, as a member of an assemblage of Cretaceous/Tertiary basins correlatable by close stratigraphic and structural analogies. It is considered as the most complete model of this group of basins, and can serve as a pattern for a study of their origin and evolution.
The basin originated by Early Cretaceous tectonism that fractured the original cratonic mass into elongated grabens bounded by normal faults. Immature fluviolacustrine sediments were deposited in this tectonically active rift valley.
Sea-floor spreading caused the subsequent widening of the basin, and allowed the first marine transgression that formed a long and narrow embayment--the primitive South Atlantic Ocean. Here, due to restrictive conditions, an evaporitic section was deposited.
The combined effect of the enlargement of this embryonic ocean by eastward migration of the Mid-Oceanic Ridge since Late Cretaceous time, and basin tilting due to detumescence of the pre-rift arching, determined the deposition of a thick, predominantly marine section with deltaic sedimentation near the Doce River area, and of shallow-platform carbonates in the central and eastern parts of the basin.
This upper marine section, although only weakly structured by the progressively decreasing reactivation of the Early Cretaceous faulting, underwent adiastrophic movements by growth faulting and halokinesis.
Late Cretaceous to middle Eocene submarine volcanic activity built up the framework of a 30,000-sq km accretion to the preexisting continental shelf.
The process of origin and evolution, and the structural and stratigraphic characteristics of the Espirito Santo basin, cause consideration of the basin as potentially petroliferous, and warrant the exploration program that is being carried out.
The accumulated knowledge of the Espirito Santo basin, that reflects the regional situation of the whole Brazilian continental margin, affords an important clue to the study of continental drift of South America and Africa.
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