Magmatically driven hydrocarbon generation and fluid flow in the Namibe Basin of Angola

Edoardo Fiordalisi, B E van Dongen, Julian Moore, Nathan Rochelle-Bates, Vladimir Machado, Richard Dixon, Ian R. Sharp, Stefan Schröder

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Abstract

The Namibe Basin of Angola formed in the Cretaceous as part of the South Atlantic rift and was affected by syn-rift and post-rift magmatic events, which had variable effects on the petroleum system in the basin. Here, bitumen is observed within both Pre- and Post-Salt stratigraphic sections. In the Pre-Salt, fluorescent bitumen has a lacustrine signature and is associated with calcite and quartz cements. Onshore Pre-Salt units are thermally immature, and therefore the source rock that generated the Pre-Salt bitumen is likely located offshore. Hydrocarbons migrated or re-migrated via magmatically-driven fluids, reaching the present-day onshore. Closer to magmatic units, non-fluorescent pyrobitumen was instead observed, evidencing hydrocarbon cracking processes following emplacement. In the Post-Salt, bitumen is in-situ and shows marine-like signatures compatible with an immediate Post-Salt source rock depositional environment. In the immediate Post-Salt, units with very high Total Organic Carbon (TOC; up to 13.8 %) and excellent source rock properties (Hydrogen Index > 600 mg HC/g TOC) have reached thermal maturation. Within the Namibe Basin these Post-Salt source units lie in proximity to major Turonian-Coniacian-Santonian volcanic centres and associated shallow intrusions, which are likely to have caused thermally forced maturation processes and generation of the Post-Salt hydrocarbons.
Original languageEnglish
Title of host publicationThe impacts of igneous systems on sedimentary basins and their energy resources
PublisherGeological Society
Publication statusAccepted/In press - 2023

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