The Maputaland-Zululand passiv margin, a record of the South African Plateau uplift
Résumé
The Maputaland-Zululand oblique passive margin records the evolution of its inland topography: the South African Plateau. In this study, we aim at characterise and quantify the different periods of uplift of the plateau, using both seismic and field sequence stratigraphy. Onshore, we mapped the main truncations, incised valleys and their relationships with the downward shift of facies. These discontinuities have been dated using high resolution biostratigraphy, based on ammonites. Offshore, we define major periods of accommodation space removal from the migration of the offlapbreak. From this, we quantified the uplift based on the accommodation space removal, corrected from the long term subsidence and eustasy using the Haq et al. (1987) and Miller et al. (2005) curves. From Late Barremian to Maastrichtian (-127 to 65 My), the Maputaland-Zululand sedimentary record is controlled by fluvial-dominated deltas, punctuated (at Milankovitch-scale cycle scale) by storm-dominated condensed carbonate deposits (marine flooding). The main period of uplift occurred during Late Cretaceous times, between Middle Cenomanian and Middle Coniacian (95-88 Myr), probably around the Cenomanian/Turonian boundary (93 My). The Coniacian to Palaeocene (88 to 56 My) period corresponds to an overall aggradational trend with onlap on the upstream basement. Other minor uplift movements occurred during Early Cretaceous times, at the Aptian-Albian (112 My) transition and during Middle Albian (about 105 My). Those uplift are coeval with periods of siliciclastic sediments fluxes increases. We discuss the consequences of the uplift on the long term subsidence history of the margin.