Growth folds above the upper tips of normal faults are ubiquitous in extensional settings, especially during the early phases of extension and in salt-rich basins. As slip accumulates on the underlying normal fault, the geometry and size of the fold changes. These changes reflect the dip, throw, displacement and propagation rate of the underlying normal fault, as well as the thickness and rheology of the overlying cover. These changes also have a marked impact on the architecture and distribution of synkinematic sediments, as well as the styles of secondary deformation accommodating strain within the growing fold. Here, we analyse a large dataset of natural, and physically- and numerically-modelled growth folds to: (i) characterise their diagnostic features; (ii) investigate the controls on their geometry, size and differences; and (iii) describe how they grow with increasing extensional strain. We demonstrate that larger fault throws and a thicker and weaker cover are associated with larger growth folds. In contrast, small fault throws as well as thin and strong brittle cover are associated with smaller growth folds. We show that the geometry and size of growth folds vary through time; the width (and thus, the wavelength) of the fold is established relatively early during fold growth, whereas fold amplitude increases gradually with increasing fault throw. Fold width and amplitude become increasingly similar during fold evolution, until the fold is breached by the underlying normal fault. We also derive a number of preliminary empirical relationships between readily observable structural and stratigraphic parameters in our dataset that may help estimate the geometry and size of poorly exposed (i.e. in the field) or imaged (i.e. in the subsurface) growth folds. In addition, we discuss how fault growth models (i.e. constant-length vs. propagating) may impact the three-dimensional evolution of growth folds. Finally, our work shows that growth folds are likely more common than previously thought. For example, although they are well-documented in areas characterised by weak, ductile cover strata and low strain rates, our dataset illustrates that growth folds may also occur in brittle, relatively strong rocks and in regions with high strain rates. However, the underlying controls on fold occurrence remain elusive.

We examine 3-D seismic reflection data from the Santos Basin, offshore Brazil to determine how, where and when do radial faults grow near a sub-circular salt diapir (stock). We show roof stretching alone cannot account for the large heights and lengths of the kilometre-scale radial faults, suggesting stock widening (‘stem push’), a mechanism implied in numerical models but not yet documented in natural examples, played a pivotal role in radial fault formation. We suggest that, when a diapir is covered by a roof, radial faults form in its overburden due to roof stretching, extending no further than the limit of the drape folding. The roof may then be shouldered aside and the faults buried along the stock flanks, exposing these strata to stem push-related stresses that may then reactivate pre-existing or form new radial faults. Radial faults, irrespective of how they formed, may dip-link with or offset one-another as salt continues to rise. We suggest the causal mechanism for radial fault formation will likely change as roof thickness varies during diapirism, with this reflecting the ratio between sedimentation rate and salt volumetric flux. Our findings are likely applicable to other diapirs, helping us not only to interpret the paleo-stress state of salt-bearing sedimentary basins, but also advancing our understanding of fracture distributions, potential fluid flow pathways, and reservoir compartmentalization around salt diapirs in basins where seismic reflection imaging is poor.

The structural style of salt-influenced rifts may differ from those formed in predominantly brittle crust. Salt can decouple sub- and supra-salt strain, causing sub-salt faults to be geometrically decoupled from, but kinematically coupled to and responsible for, supra-salt forced folding. Salt-influenced rifts thus contain more folds than their brittle counterparts, an observation often ignored in extension estimates. Fundamental to determining whether sub- and supra-salt structures are kinematically coherent, and the relative contributions of thin- (i.e. gravity-driven) and thick-skinned (i.e. whole-plate stretching) deformation to accommodating rift-related strain, is our ability to measure extension at both structural levels. We here use published physical models of salt-influenced extension to show that line-length estimates yield more accurate values of sub- and supra-salt extension compared to fault-heave, before applying these methods to seismic data from the Halten Terrace, offshore Norway. We show that, given the abundance of ductile deformation in salt-influenced rifts, significant amounts of extension may be ignored, leading to the erroneous interpretations of thin-skinned, gravity-gliding. If a system is kinematically coherent, supra-salt structures can help predict the occurrence and kinematics of sub-salt faults that may be poorly imaged and otherwise poorly constrained.

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Purpose: Flow-mediated dilation (FMD) provides a valid bioassay of vascular function in humans. Although water immersion induces hemodynamic effects that modify brachial artery shear stress, it is unclear whether water-based exercise modifies FMD. We hypothesised that exercise in 32°C water would decrease brachial artery shear and FMD relative to land-based exercise, whereas exercise in 38°C would increase brachial shear and FMD. Methods: Ten healthy participants (8 males; 23.9±3.3yrs) completed 30mins of resistance-matched cycle exercise in three separate conditions: Land, and in 32C and 38C water. Brachial artery shear rate area under the curve (SRAUC) was measured throughout each condition, with FMD measured pre and post exercise. Results: Brachial SRAUC increased during exercise in all conditions and was highest across the 38C condition compared to Land and 32°C conditions (38C:275078350 vs Land:99084738 vs 32°C:138405861 1/s, P<0.001). Retrograde diastolic shear was greater during 32°C than both Land and 38°C conditions (32°C:-38692198 vs Land:-16021334 vs 32°C:-10361754, P<0.01). FMD increased as a result of 38°C (6.21.9 vs 8.52.7%, P=0.03), with no change in the Land exercise (6.32.4 vs 7.72.4%, P=0.10) or 32°C condition (6.43.2 vs 6.73.2%, P=0.99).Conclusion: Our findings indicate that cycle exercise in hot water attenuates retrograde shear, increases antegrade shear, and FMD. Exercise in 32°C water induces central hemodynamic changes relative to land-based exercise, but these do not translate to increases in FMD in either condition, likely due to the impact of increased retrograde shear. Our findings indicate that modification of shear has direct acute impacts on endothelial function in humans.