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Soft sediment deformation in laboratory experiments

Siman-Tov S. (1), Siegal O. (1), Marco S. (2), Heifetz E. (2)

(1) Geological Survey of Israel, 32 Yesha'ayahu Leibowitz, Jerusalem 9692100, Israel

(2) The Department of Geosciences, Tel-Aviv University, Tel-Aviv 69978, Israel

Soft-sediment deformation structures, such as folds, faults, and breccia layers, are common in Lisan Formation outcrops along the margins of the Dead Sea Basin. These structures, often referred to as seismites, have been attributed to ground motion during seismic events. Several mechanisms have been proposed for their formation, including slumping on the lake floor and shear instability between sediment layers (Kelvin–Helmholtz instability), similar to the interaction between sheared fluid layers. In this study, we aim to reproduce similar deformed structures in the laboratory to better understand the critical conditions and mechanisms responsible for their formation. We carefully sampled aragonite and detritus layers from Pratzim Wadi, ensuring minimal mixing. These sediments were then experimentally deposited in a ring-shaped cell, forming alternating layers of aragonite and detritus. Interestingly, some experiments revealed fingering at the layer boundaries, suggesting that density differences between layers induce Rayleigh–Taylor instability. While these deformations appeared in centimeter-thick deposited layers, no deformation was observed after consolidation under low normal stress. However, after shaking the cell, buoyancy effects emerged, highlighting the role of density differences, with the less dense aragonite rising above the denser detritus. When rotary acceleration was applied, non-compacted layers exhibited oblique smearing during floating, though no clear folds formed. Preliminary results indicate that folds may develop in consolidated sediments under high accelerations. These initial findings suggest that material properties significantly influence the resulting deformation structures. Furthermore, compaction and cohesion, followed by liquefaction, may be critical in generating the observed structures.

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