Completed Study
Uplift and Thermal History of the West African Passive Margin: a Kwanza Basin Perspective
Coastal uplift and erosional unroofing of passive margins renews gravity spreading and rejuvenates supply of sediments to distal offshore regions, where they form reservoir facies and enhance hydrocarbon maturation. We constrain the timing and magnitude of uplift in the Inner Kwanza Basin, Angola, by combining an analysis of Tertiary hiatuses with new results from apatite fission-track analysis. Planktonic foraminiferal biozones in wells from the north of the basin show five major hiatuses: lower Oligocene (34 Ma), upper Oligocene (29 Ma), lower Miocene (16 Ma), mid-Miocene (12 Ma), and Plio-Pleistocene. Between hiatuses all Oligo-Miocene strata were marine, which refutes the idea of a massively elevated (1-2 km) "altiplano" coastal plateau in the mid-Tertiary. Fission-track results suggest three regional synchronous thermal events: (1) rift-related extensional and volcanic event at ~150 Ma, (2) a contractional and volcanic event at 100-70 Ma, and (3) a mild advective event at 20-10 Ma during uplift of the continental shelf, which renewed gravity spreading in the Outer Kwanza Basin.
More complex histories are also possible. During rifting, the adjoining basement was uplifted by >3700 m. Cumulative uplift of the basement since the mid-Jurassic is >7000 m. Along its eastern rim, the basin was unroofed by a total of up to 1200 m. In some southern regions, the Inner Kwanza Basin was unroofed by 500-800 m. In contrast, total uplift in the center and west of the northern Inner Kwanza Basin was only a few hundred meters at most. Fission-track results suggest ~15°C of Neogene heating by rising hot fluids, which enhanced hydrocarbon maturity.
For more information, please contact Michael Hudec. Telephone 512-471-1428. E-mail
August 2003