Comment on se-2021-153

Frank Peel

doi:10.5194/se-2021-153-rc1

Abstract

Archimedes' principle states that the upward buoyant force exerted on a solid immersed in a fluid is equal to the weight of the fluid that the solid displaces. In this 3D salt-reconstruction study we treat Zechstein evaporites in the subsurface of the Netherlands, Central Europe, as a pseudo-fluid with a density of 2.2 g/cm3, overlain by a lighter and solid overburden. 3D sequential removal (backstripping) of a differential sediment load above the Zechstein evaporites is used to incrementally restore the top Zechstein surface. Assumption of a constant subsurface evaporite volume enables the stepwise reconstruction of base Zechstein and the approximation of 3D salt-thickness change and lateral salt re-distribution over time. The salt restoration presented is sensitive to any overburden thickness change irrespective if caused by tectonics, basin tilt or sedimentary process. Sequential analysis of lateral subsurface salt loss and gain through time based on Zechstein isopach difference maps provides new basin-scale insights into 3D subsurface salt flow and redistribution, supra-salt depocentre development, the rise and fall of salt structures, and external forces' impact on subsurface salt movement. The 3D reconstruction procedure described can serve as a template for analyzing other salt basins worldwide and provides a stepping stone to physically sound fluid-dynamic models of salt tectonic provinces.

Highlights

Archimedes (c. 246 BC) proposed - in short - that the upward buoyant force exerted on a solid body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the solid body displaces
Any process that results in differential overburden thickness will be be balanced, as exemplarily shown for Late Cretaceous and Paleogene diapir growth likely triggered by inversion tectonics (Figs. 5, 6)
250 6 Conclusions 1. 3D backstripping based on the ancient Archimedes' principle restored through time variations in 3D subsurface evaporite thickness; 3D salt loss and gain; 3D subsurface salt movement; and long-term salt-flow rates

Summary

Introduction

Archimedes (c. 246 BC) proposed - in short - that the upward buoyant force exerted on a solid body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the solid body displaces. This study uses Archimedes' principle to reconstruct 3D subsurface salt flow through geological time by treating salt as a dense fluid phase (ρ = 2.2 g/cm3) in which lighter overburden rocks (solids) float (Fig. 1). Various modelling studies have treated subsurface salt as a pseudo-fluid flowing in the subsurface and consider its sedimentary overburden as solid (e.g. Jackson and Vendeville, 1994). This approach is supported by the observation that salt flows when loaded; and that faulting rather than folding characterizes deformation in the overburden (Davison 2009; Warren, 2016).

Findings

Poisson Ratio

190 5 Discussion