SEDIMENTOS SUPERFICIAIS DA MARGEM CONTINENTAL NORDESTE BRASILEIRA

AUGUSTO M. C. FRANÇA, PAULO N. COUTINHO, COLIN P. SUMMERHAYES

Resumo


Sedimentation on the narrow, shallow shelf of NE Brazil reflects source geology, climate, drainage and tectonic setting. Because of the tropical climate and negligible terrigenous sedimentation, biogenic carbonates dominate most of the middle shelf from Maceió to Macau and the entire outer shelf. In contrast with other tropical shelves, corals are virtually absent from the sediments as also are ooids and other precipitated forms of carbonate. Despite the absence of coral, these sediments are very similar to the reef-like sediments from shallow banks on the Yucatán and Sahul shelves. The terrigenous sediments are largely relict, except off the São Francisco and Jaguaribe deltas where modern sedimentation occurs within 10 km of the coast. The composition of the relict sediments suggests that Pleistocene climates were similar to those of the present days. Arkosic sands with an illitic clay fraction occur off the semi-arid northern coast, and were locally supplied to the east coast by the São Francisco, which is the only cast coast river to drain the arid hinterland. During low sea level times the east coast climate may have been somewhat less humid than at present, as montmorillonitic rather than kaolinitic clays were deposited on the continental slope during low stands of sea level.


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