Hyper-extended crust in the South Atlantic: in search of a model

The discovery of giant hydrocarbon reservoirs in the pre-salt sequence of the deep-water Brazilian rifted margin together with the new acquisition of high-quality reflection and refraction seismic surveys across many rifted margins worldwide has attracted the interest of industry and researchers to deep-water rifted margins. For the first time, the new data sets enable the imaging and description of the pre-salt structures, which indicate that deep-water rifted margins are very different from what classical models had predicted thus far. Instead of the expected fault-bounded basins and a sharp ocean–continent boundary, the new data suggest the existence of a sag basin lying on hyper-extended crust with little indication for brittle high-angle faulting, a transitional domain between continental and oceanic crust showing neither characteristics of oceanic nor continental material, and very asymmetrical distal conjugate rifted margins. These observations raise significant doubts on the validity of the classical concepts used in rheology, mechanics and isostasy to explain extensional systems leading to seafloor spreading. They also require new concepts and more data in order to understand how these rifted margins evolved in time and space. This has important implications for the exploration and evaluation of petroleum systems in the frontier areas of hydrocarbon exploration.

In this study we publish two multi-channel seismic sections across the Angola and conjugate Brazilian rifted margins that we consider as ‘type’ sections for hyper-extended magma-poor rifted margins in the South Atlantic. The aim of this study is to discuss various possible interpretations and models to explain the high-resolution seismic images presented in this paper.