Summary

The Karoo Basin of South Africa is a Carboniferous-Jurassic retroarc foreland fill, developed in front of the Cape Fold Belt in relation to subduction of the paleo-Pacific plate underneath the Gondwana plate. During orogenic loading, within the foreland area episodes of subsidence and increase in accommodation space adjacent to the orogen correlated to episodes of uplift and decrease in accommodation space away from the thrust-fold belt. During orogenic unloading the reverse occurred. The two tectonic settings with reciprocal flexural behaviour correspond to the foredeep (proximal) and forebulge (distal), and are separated by the foreland basin hingeline. Sedimentary sequences are preserved within both foredeep and forebulge settings, but with distinct stratigraphic signatures and contrasting facies due to the out of phase history of base-level changes in the two areas. Based on stratigraphic evidence the hingeline was shown to migrate northwards, away from the orogenic load, during the Late Carboniferous-Permian interval in response to thrust sheet advance (increase and progradation of orogenic load) in the Cape Fold Belt. During the Triassic-Middle Jurassic interval the hingeline moved south in response to the visco-elastic relaxation of the foreland lithosphere.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas