Nilo Chagas de Azambuja Filho¹, Alvaro H. Arouca de Castro², Armando A. Scarparo Cunha³, Carlos Roberto Becker⁴, Clovis Francisco Santos⁵, José Guilherme R. da Silva⁶, José M. Cronemberger Mendes⁷, Maria do Carmo G. Severino¹, Paulo R. C. Cunha¹, and Ricardo Latge M. de Azevedo⁸. (1) EXPLORATION, PETROBRAS, Av. Republica do Chile, 65, 13 floor, Rio de Janeiro, 22290-240, Brazil, phone: 55-21-3224-9955, fax: 55-21-3224-3806, niloazambuja@petrobras.com.br, (2) EXPLORATION, PETROBRAS, Av. Republica do Chile, 65, Rio de Janeiro, Brazil, (3) CENPES, PETROBRAS, Ilha do Fundão, Quadra 7, Rio de Janeiro, (4) EXPLORATION, PETROBRAS, Av. Republica do Chile, 65, Rio de Janeiro, 22290-240, Brazil, (5) EXPLORATION, PETROBRAS, Rio de Janeiro, Brazil, (6) EXPLORATION, PETROBRAS, Vitória, Brazil, (7) EXPLORATION, PETROBRAS, Huston, (8) PETROBRAS, PETROBRAS, Av. Republica do Chile, 65

Significant climatic fluctuations can be observed in the Brazilian sedimentary basins, ranging in age from Paleozoic to Quaternary. These climate changes have been directly related to Milankovitch forcing. For example, during the opening of the South Atlantic, both lacustrine and marine sediments preserved climate cycles. From the Late Jurassic through Aptian, seven major climatic fluctuations have been interpreted from lithological and palynological data; four represent changes from arid to semi-arid conditions and three from semi-humid to humid conditions. These climatic changes have been strongly linked to higher frequency Milankovitch oscillations (precession-scale events). In the Albian, carbonates of Campos and Santos basins contain ten thick intervals composed of cycles varying from 0.3 to 1.4 my, and at least seventy thinner intervals with shorter periodocities. In the Oligocene and Miocene of these basins, carbonate-siliciclastic intervals display well defined eccentricity and precession cycles, as well. Devonian reservoir and source rocks in the Amazonas basin show depositional cycles with strong control by eccentricity (100 kyr). This has permitted the accuracy of age estimation to improve from 106 to 105 years. In the Solimões basin, the carbonate-evaporitic succession of Pennsylvanian age display well developed cyclic sedimentation deposited as 4th and 5th order cycles, and related to relative sea-level variations induced by eccentricity and precession cycles.