Ages and Tectonics of South Atlantic Salt Basins

Davison, Ian¹, Robert Wynn Jones² (1) Earthmoves Ltd, Camberley, Surrey, United Kingdom (2) BP, Sunbury on Thames, United Kingdom

The South Atlantic salt province contains separate basins of differing ages: Ceará, Sergipe-Alagoas, and south Bahia-Espírito Santo-Campos-Santos in Brazil and; the Doula, Rio Muni, and Gabon-Congo-Angola Basin in Africa. The Ascension Fracture Zone may have separated Rio Muni from the main African salt. The southern termination of the main African basin is the deep Namibe Rift which never evaporated. The Sergipe-Alagoas Basin is sepa­rated from Camamu by Jacuípe- a sediment-starved hole that never dried up. African salt basins were probably separated from Brazil by sub-aerial spreading ridges exposed by evap­oration drawdown.

Angolan salt was deposited ca. 123-124 Ma, as early Aptian algeriana–cabrizone plank­tonic foraminifera occur above salt (DSDP well 364; undisclosed shelfal well), and early Aptian spores, pollen and ostracods occur below. Sergipe-Alagoas evaporites occurs in two intervals; Paripueira Member deposited during zones P-230 (Inaperturopollenites crisopolensis) to P-260 (Inaperturopollenites turbatus); and the Ibura Member, restricted to upper P-270 zone (Sergipea variverrucata). Top Paripuera salt is older than 114.5 Ma, according to the Graciansky et al. (1998) time-scale, and pre-dates the first appearance of Ticinella bejaouaensis. The oldest Angolan salt is younger than the Paripuera Member, as it post-dates the last appearance of Inaperturopollenites crisopolensis. The Gabon evaporites are equivalent to the Ibura Member. On the Florianopolis High (S. Brazil) Ariri Formation anhydrite, equivalent of Santos salt lies on volcanics dated at 113.2 ± 0.1 Ma. It is still not clear whether the observed diachronism is within, or between salt basins, or both.