Structural, stratigraphic and sedimentological characterisation of a wide rift system: The Triassic rift system of the Central Atlantic Domain

Our tectono-stratigraphic model suggests that initial strain was accommodated in a Central Segment by inherited faults during the Early and Middle Triassic. During the Carnian, the rift domain was increasingly extended with the development of half-graben basins in the Central Segment and some in the Northern Segment. In both segments, the initial strain re-activated inherited faults and later the rift zones evolved towards significantly wider basins marked by the presence of a major erosional truncation surface across the basins and followed by lacustrine sedimentation that eventually overlapped paleo-topographic highs. Subsidence of such regional extent is likely driven by thermal processes following a phase of extreme lithospheric thinning and lower crustal removal associated with mantle uplift. The architecture of the Triassic rifting has the characteristics of the wide rift mode (very large basins with some active faults) for which subsidence is driven by lower crustal flow within a high heat-flow region. Nevertheless some faults were active during Late Triassic sedimentation but accounted for a relatively minor part of the overall subsidence. Pulses of active subsidence and topographic rejuvenation led to fluvial dominated deposition within basins. Non-rejuvenation of hinterland led to more lacustrine dominated sedimentation and eventual connection of basins across topographic highs due to regional (thermal) subsidence. During the latest Rhaetian, basins with the lowest elevations were possibly “flooded” by marine waters resulting in precipitation of thick salt deposits.