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Basin-scale salt flow and the evolution of salt structures in rift basins is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward-directed driver for salt tectonics. We designed a new experimental analogue apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup, demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting, and extension combined with tilting. Digital image correlation of top-view stereoscopic images was applied to reveal the 3D displacement and strain patterns. The results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement; i.e. the amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional faults developed as a result of gravity gliding. A comparison with natural examples reveals that such fault zones can also be observed at the margins of many salt-bearing rift basins indicating that gravity gliding played a role in these basins.

As a primary driving force, margin tilting is crucial for gravity-driven thin-skinned salt tectonics. We investigated how instant versus progressive margin tilting mechanisms influence salt tectonics using an analogue modeling setup where tilting rate could be controlled. Instant tilting resulted in initially high deformation rates, triggering widely distributed upslope extension and downslope contraction. Later, both the extensional and contractional domains migrated upslope as early extensional structures were successively deactivated, while deformation rates decreased exponentially. In contrast, progressive tilting led to downslope migration of the extensional domain by sequentially formed, long-lived normal faults. Contraction localized on a few, long-lived thrusts before migrating upslope. We attribute the distinct structural evolution of thin-skinned deformation, especially in the extensional domain, in the two tilting scenarios mainly to mechanical coupling between the brittle overburden and underlying viscous material. The coupling effect in turn is largely controlled by the deformation rate. By demonstrating the spatiotemporal variations of structural style and kinematic evolution associated with instant versus progressive tilting, we suggest that such variation is identifiable in nature and therefore can provide a new way to analyze margin tilting histories.

Sediment progradation and spreading is a key process during gravity-driven, thin-skinned deformation in salt-bearing passive margins. However, to what degree the size and shape of a progradational ...

Sediment spreading is a key process during gravity-driven deformation in salt-bearing passive margins. Whether and how progradational sedimentary wedges control gravity-spreading is still under deb...

Basin-scale salt flow and the evolution of salt structures in rift basin is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward directed driver for salt tectonics. We designed a new experimental analog apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting and extension combined with tilting. Digital image correlation of top view stereoscopic images was applied to reveal the 3D displacement and strain patterns. Results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement, i.e. amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional fault developed, which resemble fault zones observed on basin flanks offset from the central graben zone.

During the process of sediment mobilisation unconsolidated sediments are deformed due to fluid overpressure. Structures formed by sediment mobilisation can serve as high permeable pathways for vertical fluid migration through a low-permeable seal layer and, therefore, have to be considered in the risk assessment of CO2 storage sites. In our study, we designed and conducted physical sandbox models to investigate structural characteristics and the dynamic evolution of sediment mobilisation resulting from pore fluid overpressure. Preliminary results show that basically two different modes of cover deformation occur: uplift in cohesive sediment and pipe formation in low-cohesive sediments.

Current gravitational tectonics models illustrating the structural style of passive margin salt basins typically have domains of upslope extension and corresponding downslope contraction, separated by a domain of rather undeformed mid-slope translation. However, such a translational domain is rarely observed in natural systems where extensional and contractional structures may interfere in the mid-slope area. In this study, we use sandbox analogue modelling analyzed by 4D digital image correlation (DIC) to investigate how the pre-kinematic layer thickness, differential sediment loading and sedimentation rate control the structural evolution of translational domains. As in nature, experimental deformation is driven by slowly increasing gravitational forces associated with continuous basal tilting. The results show that a translational domain persists throughout the basin evolution when the pre-kinematic layer is evenly distributed, although a thin (1 mm in the experiment, 100 m in nature) pre-kinematic layer can render the translational domain relatively narrow when comparing to settings with a thicker (5 mm) pre-kinematic layer. In contrast, early differential sedimentary loading in the mid-slope area creates minibasins intervened by salt diapirs overprinting the translational domain. Similarly, very low sedimentation rate (1 mm per day in the experiment, equates to

Salt flow in sedimentary basins is mainly driven by differential loading and can be described by the concept of hydraulic head. A hydraulic head in the salt layer can be imposed by vertically displacing the salt layer (elevation head) or the weight of overburden sediments (pressure head). Basement faulting in salt-bearing extensional basins is widely acknowledged as a potential trigger for hydraulic heads and the growth of salt structures. In this study, scaled analogue experiments were designed to examine the kinematics of salt flow during the early evolution of a salt structure triggered by basement extension. In order to distinguish flow patterns driven by elevation head or by pressure head, we applied a short pulse of basement extension, which was followed by a long-lasting phase of sedimentation. During the experiments viscous silicone putty simulated ductile rock salt, and a PVC-beads/quartz-sand mixture was used to simulate a brittle supra-salt layer. In order to derive 2-D incremental displacement and strain patterns, the analogue experiments were monitored using an optical image correlation system (particle imaging velocimetry). By varying layer thicknesses and extension rates, the influence of these parameters on the kinematics of salt flow were tested. Model results reveal that significant flow can be triggered in the viscous layer by small-offset basement faulting. During basement extension downward flow occurs in the viscous layer above the basement fault tip. In contrast, upward flow takes place during post-extensional sediment accumulation. Flow patterns in the viscous material are characterized by channelized Poiseuille-type flow, which is associated with subsidence in regions of "salt" expulsion and surface uplift in regions of inflation of the viscous material. Inflation of the viscous material eventually leads to the formation of pillow structures adjacent to the basement faults (primary pillows). The subsidence of peripheral sinks adjacent to the primary pillow causes the formation of additional pillow structures at large distance from the basement fault (secondary pillows). The experimentally obtained structures resemble those of some natural extensional basins, e.g. the North German Basin or the Mid-Polish Trough, and can aid understanding of the kinematics and structural evolution of sedimentary basins characterized by the presence of salt structures.

Basement faulting is widely acknowledged as a potential trigger for salt flow and the growth of salt structures in salt-bearing extensional basins. In this study, dynamically scaled analogue experiments were designed to examine the evolution of salt pillows and the kinematics of salt flow due to a short pulse of basement faulting and a long-lasting phase of successive sedimentation. Experiments performed in the framework of this study consist of viscous silicone putty to simulate ductile rock salt, and a PVC-beads-quartz sand mixture representing a brittle supra-salt layer. In order to derive 2-D incremental displacement and strain patterns, the analogue experiments were monitored by an optical image correlation system (Particle Imaging Velocimetry). By varying layer thicknesses and extension rates, the influence of these parameters on the kinematics of salt flow were tested. Model results reveal that significant strain is triggered in the viscous layer by minor basement faulting. During basement extension downward flow occurs in the viscous layer above the basement fault tip. In contrast, upward flow takes place during post-extensional sedimentation. Lateral redistribution of the viscous material during post-extensional sedimentation is associated with subsidence above the footwall block and uplift adjacent to the basement faults leading to the formation of pillow structures (primary pillows). Decoupled cover faulting and the subsidence of peripheral sinks adjacent to the primary pillow causes the formation of additional pillow structures at large distance from the basement fault (secondary pillows). Experimental results demonstrate that the development of salt pillows can be triggered by basement extension, but requires a phase of tectonic quiescence. The potential for pillow growth and the displacement rate in the viscous layer increase with increasing thickness of the viscous layer and increasing extension rate, but decrease with increasing thickness of the overburden. The experimentally obtained structures resemble those of some natural extensional basins, e.g. the North German Basin or the Mid-Polish Trough, and can help to understand the kinematics during the structural evolution.

We applied scaled physical analogue experiments to investigate the early development of salt diapirs induced by differential sedimentary loading in an intra-continental basin realm (e.g. the North German Basin). During the experiments, deformation in a salt-analogue viscous layer was initiated by variations in the thickness of an overlying brittle material and subsequent accumulation of the brittle material further sustained deformation. A 2D optical image correlation system was used to monitor the strain evolution in the salt analogue material. Our models indicate that the formation of salt pillow structures can be achieved by minimum variations in the overburden loading. The increase of differential loading by adding synkinematic layers in the subsided areas causes not only an active piercing of the viscous layer through the brittle overburden but also an additional uplift in the adjacent areas. These elevations, named “secondary structures”, act as origins for a successive generation of diapirs. Consequently, an initial perturbation of the salt–sediment-interface can lead to a lateral propagation temporally shifted diapirs. The linkage between primary and secondary structures is reflected in the synkinematic overburden layers such as overlapping peripheral sinks in the transition zone between two diapirs. These sinks, in turn, are a frequently observable phenomenon around salt structures of the North German basin indicating that “secondary diapirism” is an underestimated process – besides regional tectonic stresses – influencing the evolution of salt structures.