ALBERT

Description: Highlights • Red Sea salt deposits are loaded by only 200–300 m hemipelagics in deep water • Internal growth stratigraphy shows that they were deforming while being deposited • Power spectra of their surface shows they are inverse power-law over 1–13 km scale • Variograms suggest that their surface is stochastic with average lengthscale of ~3 km • Their stochastic character rules out Rayleigh-Taylor models of diapirism here Rayleigh-Taylor models for diapirism predict that diapirs should develop with characteristic spacings, whereas other models predict varied spacings. The deep-water Miocene evaporites in the Red Sea provide a useful opportunity to quantify length scales of diapirism to compare with model predictions. We first review the stratigraphy of the uppermost evaporites in high-resolution seismic data, revealing tectonic growth stratigraphy indicating that halokinetic movements occurred while the evaporites were being deposited. In some places, movements continued after the Miocene evaporite phase. The S-reflection marking the top of the evaporites is an erosional surface, in places, truncating anticlines of layered evaporites. In others, reflections within the uppermost evaporites are conformable, suggesting a lack of erosion. The top of the evaporites therefore had relief at the end of the Miocene. We select for numerical analysis 14 long profiles of topography of the S-reflection. Variograms derived from them after detrending reveal minor periodicity, though with varied wavelength, and varied roughness of the surface. However, an average variogram computed from these profiles is nearly exponential, indicating that the evaporite surface is mostly stochastic with no uniform scale of diapirism. An exponential model fitted to that average variogram suggests a spatial range over which the S-reflection topography becomes decorrelated of 3 km, which is comparable with the mean vertical thickness of the evaporite body. Power spectra of the evaporite surface are flatter at long wavelengths, which we interpret as due to weakness of halite preventing large surface relief from developing. The results suggest only modest periodicity, so the Rayleigh-Taylor model does not explain deformation in the Red Sea evaporites studied here. Their topography may turn out to be useful for suggesting the vertical scales and lengthscales of relief to expect of early stages of other salt giants, such as that of the Santo Basin.