Soft-sediment deformation structures

Soft-sediment deformation structures are folds, faults, and other disruptions formed in unconsolidated or partly consolidated sediment before lithification, through processes such as loading, liquefaction, or slumping.

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Liquefaction: A process in which saturated granular material loses strength as pore-water pressure rises and effective stress falls. Earthquake shaking or rapid loading can liquefy sediment and allow layers to deform.
Sediment: Loose mineral grains, rock fragments, or biological material deposited by water, wind, ice, or gravity. These structures form in deposited material before it becomes solid rock.
Seismite: A sedimentary layer or set of structures interpreted as evidence of earthquake-induced deformation. Some soft-sediment structures preserve seismic shaking, though alternative triggers must be assessed.
Soft-sediment deformation: The deformation of unconsolidated or partly consolidated sediment before lithification. This broader process includes the structures produced by loading, fluid escape, and downslope movement.
Load cast: A bulbous downward protrusion of a denser sediment layer into a softer underlying layer. Unequal loading creates these downward lobes at sedimentary layer boundaries.
Lithification: The processes, including compaction and cementation, that turn sediment into sedimentary rock. Deformation qualifies as soft-sediment deformation only when it precedes this conversion.
Paleoseismology: The study of prehistoric earthquakes using geological evidence and landforms. Deformed sediment layers can extend earthquake records beyond written history.
Tectonic deformation: The folding, faulting, or other alteration of rock caused by forces within Earth's crust. It generally affects lithified rock, unlike deformation formed within soft sediment.
Flame structure: A tongue-shaped upward protrusion of soft sediment into an overlying layer. Soft underlying sediment may rise between descending load casts.
Pore-water pressure: The pressure exerted by fluid within the pores of soil or sediment. Changes in this pressure alter sediment strength and can trigger deformation.