Meta‐analysis of the long‐term stratigraphic evolution of rifted margin basins: The GeoDyNamical Analysis approach applied to the South Atlantic Ocean

Abstract

Models of the formation of rifted margins have significantly evolved over the last decades by identifying new styles of crustal thinning and magmatic production. However, the expression of these different processes in the depositional environments of the overlying basins remains to be determined. Using only published data, we integrated the sedimentary evolution of 21 basins of the Equatorial, Central and South segments of the South Atlantic that record various styles of crustal thinning and magmatic production. To compare these basins that underwent rifting at different times, we developed a new type of analysis allowing to evaluate statistically the (dis)similarities in depositional environment trends by normalizing them to the tectonic phases of the basin (syn‐rift, transition and post‐rift) rather than the stratigraphic or absolute ages: The GeoDyNamical Analysis. We show that the timing of the long‐term retrograding mega‐sequence driven by lithosphere thinning depends on the deformation style and magma production. Along oblique margins of the Equatorial Segment, deepening initiated during syn‐rift because their narrow crustal thinning style favours rapid tectonic subsidence surpassing sediment supply. Along wide margins of the Central Segment, deepening is initiated later, at the end of the transition phase, because depth‐dependent thinning favours slow tectonic subsidence and late break‐up. Along magma‐rich margins of the South Segment, deepening is initiated during the transition phase, after volcanics stopped filling accommodation created by subsidence. In the Central Segment, evaporites accumulated during the second half of the transition phase, when crustal thinning ceased in the proximal margin and migrated to its distal part. Immediately before and during evaporites accumulation, sediments recorded continental and coastal depositional environments resulting from the limited thermal subsidence in the proximal margin domain. Evaporite deposition lasted until the initiation of retrograding mega‐sequence, at the onset of the post‐rift phase and the end of crustal thinning in the distal margin.

2‐D Geodynamic Modeling of the Central South Atlantic Wide Rifted Margins, Implications for Evaporite Deposition

“…Early post-evaporite deposits (Albian to Cenomanian) are mainly shallow water carbonates and distal mudstones (e.g., Marton et al, 2000;Rebelo et al, 2021;Séranne & Anka, 2005). After the Cenomanian, sedimentation evolved from carbonate-to more clastic-dominated and deeper depositional environments (Beglinger et al, 2012a;Coward et al, 1999;Laspatzis et al, 2022). Ostracods studies suggest that the Walvis ridge was not fully breached by global ocean circulation until Cenomanian-Turonian times and kept the central South Atlantic isolated before then (e.g., Bate, 1999;Dingle, 1996).…”

“…The last phase of syn‐rift deposition, called the “sag phase,” and the deposition of evaporites record the transition from continental to a fully marine depositional environment. The sag phase and the evaporite deposition period form the “transition phase” whose deposits extend from the proximal to the distal margin with broadly parallel, mostly unfaulted layers, except in the extreme distal margin (e.g., Beglinger et al., 2012b; Karner & Gambôa, 2007; Karner et al., 2003; Laspatzis et al., 2022; Moulin et al., 2005). The correlation of pre‐evaporite strata is complicated by the lack of direct observations of their sedimentary facies and biostratigraphy in the distal margin (e.g., Anka et al., 2009; Laspatzis et al., 2022).…”

“…The sag phase and the evaporite deposition period form the "transition phase" whose deposits extend from the proximal to the distal margin with broadly parallel, mostly unfaulted layers, except in the extreme distal margin (e.g., Beglinger et al, 2012b;Karner & Gambôa, 2007;Karner et al, 2003;Laspatzis et al, 2022;Moulin et al, 2005). The correlation of pre-evaporite strata is complicated by the lack of direct observations of their sedimentary facies and biostratigraphy in the distal margin (e.g., Anka et al, 2009;Laspatzis et al, 2022). Absolute ages used below are recalibrated using the latest chart of the International Commission on Stratigraphy (Cohen et al, 2013(Cohen et al, , 2023.…”