Uplift history of a transform continental margin revealed by the stratigraphic record: The case of the Agulhas transform margin along the Southern African Plateau

Guillaume Baby (1) , François Guillocheau (1) , Carl Boulogne (1, 2) , Cécile Robin (1) , Massimo Dall'Asta (2)

1 GR - Géosciences Rennes
2 TotalFinaElf

The south and southeast coast of southern Africa (from 28°S to 33°S) forms a high-elevated transform passive margin bounded to the east by the Agulhas-Falkland Fracture Zone (AFFZ). We analysed the stratigraphic record of the Outeniqua and Durban (Thekwini) Basins, located on the African side of the AFFZ, to determine the evolution of these margins from the rifting stage to present-day. The goal was to reconstruct the strike-slip evolution of the Agulhas Margin and the uplift of the inland high-elevation South African Plateau. The Agulhas transform passive margin results from four successive stages: (1) Rifting stage, from Late Triassic to Early Cretaceous (~200?–134 Ma), punctuated by three successive rifting episodes related to the Gondwana breakup; (2) Wrench stage (134–131 Ma), evidenced by strike- and dip-slip deformations increasing toward the AFFZ; (3) Active transform margin stage (131–92 Ma), during which the Falkland/Malvinas Plateau drifts away along the AFFZ, with an uplift of the northeastern part of the Outeniqua Basin progressively migrating toward the west; (4) Thermal subsidence stage (92–0 Ma), marked by a major change in the configuration of the margin (onset of the shelf-break passive margin morphology).Two main periods of uplift were documented during the thermal subsidence stage of the Agulhas Margin: (1) a 92 Ma short-lived margin-scale uplift, followed by a second one at 76 Ma located along the Outeniqua Basin and; (2) a long-lasting uplift from 40 to 15 Ma limited to the Durban (Thekwini) Basin. This suggests that the South African Plateau is an old Upper Cretaceous relief (90–70 Ma) reactivated during Late Eocene to Early Miocene times (40–15 Ma).

Mots clés: Transform passive margin; South African Plateau uplift; Sequence stratigraphy

Domaines: Stratigraphie; Tectonique

Guillaume Baby, François Guillocheau, Carl Boulogne, Cécile Robin, Massimo Dall'Asta. Uplift history of a transform continental margin revealed by the stratigraphic record: The case of the Agulhas transform margin along the Southern African Plateau. Tectonophysics, 2018, 731-732, pp.104-130. ⟨10.1016/j.tecto.2018.03.014⟩. ⟨insu-01739509⟩