Geochronology of volcanically associated hydrocarbon charge in the Pre-Salt of the Namibe Basin, Angola

In volcanic rifted margins, the timing of hydrocarbon charge is difficult to predict, but important in understanding fluid genesis. We investigate whether igneous activity was linked to hydrocarbon charge in the prolific South Atlantic Pre-Salt petroleum system. To do this, we apply in-situ carbonate U-Pb geochronology, a relatively novel tool for dating hydrocarbon migration, to bituminous veins in Pre-Salt travertines from the rifted onshore Namibe Basin (Angola). To test if fluid-flow is synchronous to known volcanic pulses, we also
present new 40Ar/39Ar geochronology of a nearby volcanic complex. Bitumen is associated with calcite in a first generation of veins and vugs, and with dolomite in younger veins. The dated calcite veins yield a pooled U-Pb age of 86.2 ± 2.4 Ma, 25 which overlaps the volcanism 40Ar/39Ar age of 89.9 ± 1.8 Ma. The overlapping dates, and localized bitumen occurrence around the dated volcanic center, show a clear genetic relationship between Late Cretaceous igneous activity and hydrocarbon charge. The dolomite was dated at 56.8 ± 4.8 Ma, revealing a previously unknown Paleocene/Eocene fluid flow phase in the basin.