Completed Study
Regional Restoration Across the Kwanza, Basin, Angola
Michael R. Hudec and Martin P. A. Jackson
Restoration of a 375-km-long section across the Kwanza Basin, Angola, shows three stages of deformation detached on Aptian salt, each caused by basement activity. First, tilting related to postrift thermal subsidence initiated early Albian deformation, shortly after salt deposition ended. Deformation waned in the late Albian, probably owing to thinning of salt lubricant beneath the extensional province. The second phase of deformation was triggered by hitherto unrecognized crustal uplift beneath the continental rise around 75 Ma (Campanian). Uplift of the thick salt plateau led to salt extrusion and seaward advance of the Angola Salt Nappe over the abyssal plain.
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Exposure of the nappe toe removed the buttress provided by abyssal-plain cover, which rejuvenated seaward translation. Third, Miocene basement uplift below the shelf steepened the bathymetric slope and greatly accelerated downslope translation. This deformation is now slowing because thickening sediments on the abyssal plain have reduced the relief of the system and blocked salt-napped advance.
Minor changes in basin configuration led to profound changes in detached deformation. Miocene uplift was only a few hundred meters on the shelf, but this was sufficient to destabilize the system and cause the translation rate to increase from 300 to 3200 m/m.y. Deposition of 600 m of sediment on the abyssal plain in the upper Miocene shifted contractional deformation 150 km landward. We conclude that driving and resisting forces have been precariously balanced for much of the Kwanza Basin's history.
For more information, please contact Michael Hudec. Telephone 512-471-1428. E-mail
August 2003