--> --> Abstract: Exhumation and Uplift History of Namibia’s Atlantic Margin, by Paul F. Green, Roger Swart, Jurgen Jacob, John Ward, and Brian Bluck; #90082 (2008)

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Exhumation and Uplift History of Namibia’s Atlantic Margin

Paul F. Green1, Roger Swart2, Jurgen Jacob3, John Ward4, and Brian Bluck5
1Geotrack International, Melbourne, VIC, Australia
2Consultant, Windhoek, Namibia
3Namdeb, Oranjemund, Namibia
4Gem Diamonds, Johanesburg, South Africa
5Dept of Geographical and Earth Sciences, University of Glasgow, Glasgow, United Kingdom

Published thermochronology data from Namibia have been interpreted as revealing widespread exhumation beginning in the Early Cretaceous (~130 Ma), with ~5 km of section removed from coastal locations since that time, decreasing inland to ~1 km. This is difficult to reconcile with geological constraints, such as the presence of the Early Cretaceous Etendeka volcanics, which show that many of the sampled locations must have been near surface in the Early Cretaceous. Preservation of the early Jurassic Kalkrand volcanics also argues against erosion of thick basement sections. We have obtained AFTA data from outcropping basement rocks collected with reference to key landscape elements, in order to provide a more integrated interpretation. Results show three key cooling episodes, which are also recognised in adjacent regions. Samples between the coast and the Fish River cooled below ~110°C around 110-100 Ma. Cooling at this time is recognised along the West African Margin from the Orange River to Equatorial Guinea, where it is clearly associated with a decrease in heat flow, and a similar origin is inferred for this cooling episode along the Namibian margin. Samples inland of the Fish River cooled below ~110°C around 65 to 60 Ma, while samples towards the coast also show cooling at this time but from lower temperatures, 80 to 100°C. We interpret this episode as the onset of exhumation across the region. This interpretation is more consistent with evidence from landscape studies and sediment supply within the Orange River drainage system, as well as evidence for Early Cenozoic exhumation from AFTA in offshore wells. Regional exhumation during the Early Cenozoic has major implications for hydrocarbon prospectivity, including potential disruption of accumulations and reservoir occurrence.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery