Abstract The detailed analysis of folding in rocks was in part pioneered by John Ramsay, and resulted in a range of techniques and criteria to define folds. Although folding of unlithified or ‘soft’ sediments is typically assumed to produce similar geometries to those in ‘hard rocks’, there has to date been little detailed analysis of such folds. The aim of this paper is therefore to investigate folds developed during soft-sediment deformation (SSD) by applying techniques established for the analysis of tectonic folds during hard-rock deformation (HRD). We use the Late Pleistocene Lisan Formation exposed around the Dead Sea as our case study, as the laminated lake sediments record intricacies of fold detail generated during seismically triggered slumping of mass transport deposits (MTDs) towards the depocentre of the basin. While it is frequently assumed that folds created during SSD are chaotic and form disharmonic structures, we provide analyses that show harmonic fold trains may form during slumping, although larger upright folds cannot be traced for significant distances and are more typically disharmonic. Our analysis also reveals a range of fold styles, with more competent detrital-rich layers displaying buckles (Class 1B), as well as upright Class 1A folds marked by thickened limbs. Class 1A buckle folds are generally considered to be created by flattening that overprints folds with an original Class 1B geometry. As thickened fold limbs are truncated by overlying erosive surfaces, the vertical flattening is considered to have occurred during the slump event. Different fold shapes may partially reflect variable flattening, depending on the original orientation of upright or recumbent folds, together with continued downslope-directed simple-shear deformation that modifies the fold geometry. Analysis of fold wavelength, amplitude and bed thickness allows us to plot strain contour maps, and indicates that beds defining slump folds display viscosity contrasts in the range of 50–250, which are similar to values estimated from folds created during HRD in metamorphic rocks. A range of refold patterns, similar to those established by John Ramsay in metamorphic rocks, are observed within slumps, and are truncated by the overlying sediments, indicating that they formed during a single progressive slump event rather than distinct ‘episodes’ of superimposed deformation. This study confirms that techniques developed for the analysis of folds created during HRD are equally applicable to those formed during SSD, and that resulting folds are generally indistinguishable from one another. Extreme caution should therefore be exercised when interpreting the origin of folds in the rock record where the palaeogeographical and tectonic contexts become increasingly uncertain, thereby leading to potential misidentification of folds created during SSD.

Abstract Considerable natural remanent magnetization of the calcareous rocks in the Mottled Zone, Israel, is commonly related to surface combustion metamorphism. The vector sum of inductive and remanent magnetization (effective magnetization) was determined based on a study of the magnetic properties of rocks and interpretation of T (the modulus of geomagnetic field vector) and ▵ Z (the increment of vertical component of geomagnetic field) anomalies. Ground multiscale magnetic measurements indicate that the high-grade metamorphic rocks of the Mottled Zone, which have a spotty distribution, are characterized by extensive variations in magnetic fields and susceptibility, with a median value of ∼200 × 10 −5 SI. This magnetic pattern is similar to other areas of combustion metamorphism. Low-temperature hydrothermal rocks have a relatively homogeneous magnetic susceptibility with the same median value. Relatively homogeneous and moderate magnetization also was observed in some outcrops of the Mishash formation, which underlies the Mottled Zone rocks. High-grade metamorphism and locally varying magnetization may be due to the burning of gases. The local aeromagnetic maxima observed within the Hatrurim Basin and quantitative interpretation of some magnetic anomalies suggest magnetic sources with relatively homogeneous and stable magnetization and greater area and depth. The formation of such bodies requires a regional source for magnetization processes (e.g., gas flow from depth along faults). A more detailed study, including a helicopter survey and special ground and laboratory analyses, must be performed for a complete characterization of the complex magnetic system.