The paleogeography conditions of pre-salt Aptian units of Namibe Basin, Angola.
Abstract
The depositional environment of Aptian pre-salt carbonate rocks remains an open question with regard to the evolution of the South Atlantic. The paleogeographic reconstruction obtained by understanding the geological setting and the main controls on deposition soon after rifting and separation could provide the bridge linking the Brazilian and Angolansides of the early South Atlantic. Angolan coast is one of the best regions to study the Aptian record of the basins developed on the Brazil-Africa conjugate margins. The exposures are excellent, with little tectonic deformation and minimal weathering and erosion processes have affected these rocks. Namibe Basin is the southernmost of the Angolan Atlantic margin basins, bordered to the south by the volcanic Walvis Ridge and to the North by the Benguela Basin. The continuous geological exposures observed in dry canyons and unvegetated hills allow recognition of the Aptian stratigraphy, their contact relationships and lateral variation of beds. In the Carunjamba Valley the basal section of the pre-salt successionis dominated by the Cangulo Formation, an alluvial fan conglomerate deposited in valleys in the continental granitic basement. Tumbalunda Formation is mainly composed of sandstones and siltstones of a lacustrine system, with some limestones near to the transition with the gypsum beds of the Bambata Formation. Piambo Valley is characterized by travertine mounds developed over volcanic rocks of Paraná-Etendeka Province and Bero Complex. The pre-salt units are thinner here but the limestones are more expressive than in the Carunjamba region. Bero Valley is located in the southern portion of the exposed onshore outcrops.The pre-salt units are thicker, with limestones again showing microbial facies related to an evaporitic system near the top. Despite the limited thickness of pre-salt carbonate units in the Namibe Basin which are non-comparable with the huge carbonate successions of the Santos and Campos basins, the geological setting still affords an ideal opportunity to study and comprehend the lacustrine system developed during the Aptian, including the paleogeography of depositional systems and facies distribution.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP41C1583C
- Keywords:
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- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 1051 Sedimentary geochemistry;
- GEOCHEMISTRY;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL;
- 4912 Biogeochemical cycles;
- processes;
- and modeling;
- PALEOCEANOGRAPHY