In this study case published in an article for the Geological Society of America Bulletin (link HERE), we show that a pre-kinematic salt layer forces the pre-rift sediments to glide along low-angle & long-offset normal faults. It results in forming a totally different geometry and tectono-stratigraphic record of rifting (Fig. 1 for comparing basement-cover coupled Vs decoupled rift basins).
From a structural point of view, the basement-cover mechanical decoupling due to the pre-kinematic salt implies that the thin-skinned counterpart of the basement (hyper-)stretching is transferred aside along the margins of the rift basin where salt tectonics can additionally be recorded (Fig. 1 C & E). At the basin depocenter, the tectonic subsidence related to crustal thinning controls the formation of accommodation space in addition of the salt removal. This basement-cover decoupled way to accommodate crustal thinning and hyper-extension is therefore reconciling the observed crustal thinning with the “hided” brittle crustal stretching enabling to make crustal and basin balanced sections.
Numerous implications arise from this work (table 1 for differences between coupled & decoupled hyper-extended rift basins). This mode of deformation implies that the pre-kinematic sedimentary units are remarkably preserved within the basin depocenter where the basement is usually extremely stretched. Where basement extension and the sedimentary cover are mechanically coupled (e.g. the Alpine counter-examples of supra-detachment basins), pre-kinematic units are usually stretched as extensional allochthons and are therefore barely preserved along the distal domains of rifted margins. Such a continuity of pre-kinematic layers at the basin depocenters can lead to a severe underestimation of the actual stretching of the crust underneath rift basins what has strong impacts on the actual subsidence, facies architecture and thermal record. We think that many instances of the so-called syn-rift “sag basins” worldwide (unfaulted but strongly subsiding syncline-shaped basins) can actually result from a basement-cover decoupling.
See more details in the paper HERE. Don’t hesitate to contact us for more details or to visit outcropping field analogues (e.g. Fig. 2) ! 😉