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A clastic dike containing unusually large clasts occurs in the Quaternary deposits that unconformably cover the Mesoproterozoic sediments in the Fangshan District, Beijing area, China. The material into which the dike intruded is also uncommon because it consists mainly of loess-type silts that were deposited by braided rivers. The intrusion of the dike is explained as the result of the expulsion of pore water into the coarse, gravel-containing layers of a braided river system. The large size of the clasts in the dike is explained by an exceptionally strong upwards-directed flow which owed its high energy to a high hydrostatic pressure that had been built up because pore water could not gradually seep through the impermeable silt-sized material during ongoing burial. This uncommon dike is compared with a second example, in similar Quaternary sediments covering the Mesozoic rocks in the Huairou District.

Late Quaternary deposits in the northeastern Brazil have been scarcely investigated, despite their relevance to the discussion of the post-rift evolution of the South American passive margin within the context of landform, sea level and tectonic deformation. Sedimentological, stratigraphic and morphological characterization of these deposits, referred as Post-Barreiras Sediments, led to their distinction from underlying Early/Middle Miocene strata. Based on optically stimulated luminescence (OSL) dating, two sedimentary units (PB1 and PB2) were recognized and related to the time intervals between 74.8 ± 9.3 and 30.8 ± 6.9 ka, and 8.8 ± 0.9 and 1.8 ± 0.2 ka, respectively. Unit PB1 consists of indurated sandstones and breccias either with massive bedding or complex types of soft sediment deformation structures generated by contemporaneous seismic activity. Unit PB2 is composed of massive sands or sands related to structures developed by dissipation of dunes. The present work, focusing on the Post-Barreiras Sediments, discusses landform, sea level and tectonics of the eastern South American passive margin during the latest Quaternary. Non-deposition and sub-aerial exposure related to the Tortonian worldwide low sea level combined with tectonic quiescence followed the Miocene transgression. Tectonic deformation in the latest Pleistocene created space to accommodate unit PB1 in downthrown faulted blocks and, perhaps, also synclines produced by strike–slip deformation. Although deposition of this unit was simultaneous with the progressive fall in sea level that followed the Last Interglacial Maximum, punctuated rises combined with land subsidence led to marine deposition close to the modern coastline. Renewed subsidence in the Holocene gave rise to accommodation of the Post-Barreiras Sediments. Most of unit PB2 was deposited during the Holocene Transgression, but it is not composed of marine sediments, which suggests either an insignificant rise in relative sea level or aeolian reworking of thin transgressive sands. The data presented here lead to a review of the evolution of the South American passive margin based on assumptions of uniform sedimentation and undeformed planation surfaces over a wide coastal area of the northeastern Brazil.

Soft-sediment deformation structures induced by seismic liquefaction and/or fluidization receive much attention in sedimentological, structural and palaeoseismic studies. The direct record of larger earthquakes is restricted to instrumental and historical data; the recognition of prehistoric earthquakes requires criteria to recognize seismites in the geological record. The areal distribution of seismites can sometimes be related to active faults since distances to the epicenter (for a given magnitude) tend to be related to the liquefaction effects of seismic shocks.The use of soft-sediment deformation structures for palaeoseismic studies has limitations, however. Hardly anything is known, for instance, about the effects that modern seismic events have on the sediments in most environments. Moreover, criteria for the recognition of seismites are still under discussion. The following characteristics seem, particularly in combination, the most reliable: (1) Soft-sediment deformation structures should occur in laterally continuous, preferably recurring horizons, separated by undeformed beds; (2) These deformation structures should be comparable with structures known to have been triggered by modern seismic activity; (3) The sedimentary basin should have experienced tectonic activity at the time when the deformations were formed; and (4) The intensity or abundance of the soft-sediment deformation structures in a presumed seismite should change laterally, depending on the distance to the epicenter. It turns out that all of these four criteria have important exceptions. (1) Soft-sediment deformation structures occurring over large lateral distances in a specific layer can be triggered also by other processes. Moreover, in environments with a low sedimentation rate, the time between successive earthquakes is often too short to allow accumulation of beds that remain undisturbed. Furthermore, total liquefaction of a sandy bed may result in the absence of deformation features. (2) No truly diagnostic soft-sediment deformation structures exist to prove seismic activity. Moreover, the final configuration of a soft-sediment deformation structure is independent of the type of trigger. (3) Seismites occur frequently in areas where seismic activity is low today. (4) The lateral changes in the intensity of soft-sediment deformation structures in seismites as a factor presumed to depend on the distances to the epicenter, pose a complicated problem. The 2012 Emilia earthquakes, for instance, affected sandy fluvial channels but not the fine-grained floodplains.It must thus be deduced that specific soft-sediment deformation structures cannot be used without additional evidence to identify seismites. In particular, the magnitude of seismic shocks and the recurrence time of main events (the most important features that allow recognition of seismites) seem to be sedimentological in nature: facies changes in space and time seem the parameters that most strongly control the occurrence, morphology, lateral extent and the vertical repetition of seismites.

The 9 February 1971 earthquake in the San Fernando Valley damaged the Lower Van Norman Dam severely enough to warrant draining the reservoir. In March 1972 the sediment deposited on the reservoir floor was examined to determine whether the 1971 earthquake had induced sediment deformation and, if so, what types. A zone of deformational structures characterized by small-scale loads and slightly recumbent folds associated with the 1971 earthquake was discovered, in addition to two older zones of load structures. Each of the zones has been tentatively correlated with an historic earthquake.

Soft sediment deformation structures in lower Miocene alluvial sediments of the High Plains include three distinct types: long projections with nearly circular cross-sections, short projections with reniform cross-sections and massive volcanic ash structures. These structures project more than one meter downward into more dense host sand. The morphology of each type of structure is described and each is related to associated structures in the host sand. The origin of the long projections is probably related to activity of plants and/or animals. These projections probably formed by fining of burrows or root casts by fluid-saturated volcanic ash. The short projections intermediate axes are coincident with the axes of loaded ripples and indicate that these structures probably formed by t ixotropic flow through ripple troughs. Volcanic masses within host sand are most difficult to explain. Laboratory experiments were conducted to duplicate these structures and suggest that they formed by movement of sand through a layer of volcanic ash. Collectively, these structures are unique and indicate probable formation in a braided stream environment with high fluctuation in discharge, biologic activity and rapid accumulation of sediment.

Soft-sediment deformational structures in subsurface glacial and proglacial beds of the Permo-Carboniferous Dwyka Formation include faults, folds, boudins, sigmoidally shaped laminae and sandstone/siltstone injections within specific zones ranging in thickness from 1 to 12 m. The zones consist of rhythmite, shale with ice-rafted debris, siltstone and minor sandstone and diamictite, but often the original character of the sediments is completely destroyed by the deformation. The deformation structures predominantly formed during extensional strain of the sediments and form part of complex shear zones, diapiric structures, load coasts and convolute lamination. The deformation zones are lithologically controlled and intimately associated with debris-flow deposits, indicating that gravitational forces giving rise to slumping were the predominant cause of the deformation. Excess pore-water pressures and subsequent liquefaction of the fine-grained sediments on oversteepened depositional slopes apparently generated the sheetlike slumps, but the possibility of grounded ice initiating slumps in the lowermost deformation zone cannot be excluded. A new type of coarse-grained, matrix-supported deposit, designed melange diamictite, which formed during slumping under a soft-sediment slab, is described for the first time.

Normally, a deposited granular sediment behaves as a ‘solid’ aggregate and is stable so long as the slope of the depositional surface remains below the angle of initial yield (Ch. 7). Such an aggregate is capable of withstanding an applied shear stress. By way of contrast, a quick condition is one where the shear strength of a sediment is zero, with the weight of the grains being borne by the interstitial pore fluid. Thus, if a water-saturated sand is subjected to ground vibrations such as cyclic earthquake shocks or to pressure fluctuations caused by water waves passing overhead (Ch. 24), it will tend to compact and decrease in volume as the grains attempt to find the closest possible packing (Seed amp; Lee 1966). Provided that the pore fluid cannot escape, or at least escapes slowly, an increase in the pore-water pressure results (Fig. 11.1). If the pore-water pressure increases to a level where it approaches the overburden pressure, then the sand liquefies (see also Ch. 7). Liquefaction in sands is possible only if the deposit is initially loosely packed. Tightly packed sands tend to expand under shear, a process known as dilatancy (Ch. 7).

Dish structure is defined by the presence of thin, subhorizontal, flat to concave-upward, argillaceous laminations in siltstone and sandstone units. It is commonly associated with vertical or nearly vertical cross-cutting columns and sheets of massive sand termed pillars. Both form commonly in sediment ranging in grain size from coarse-grained siltstone to coarse-grained, conglomeratic sandstone. In sedimentation units greater than about 0.5 m thick, dish structure is faint and neither cuts across nor is cross-cut by other sedimentary structures. In thinner units dish structures commonly cut across primary flat laminations, climbing-ripple cross-laminations, and convolute laminations. Dish and pillar structures form during the consolidation of rapidly deposited, underconsolidated or quick beds. During gradual compaction and dewatering, semi-permeable laminations act as partial barriers to upward-moving fluidized sediment-water slurries, forcing horizontal flow beneath the laminations to points where continued vertical escape is possible. As water seeps upward through the confining laminations, fine sediment, planar, and low-density grains are filtered out and concentrated in the sediment pore spaces. The resulting clay- and organic-enriched laminations are flat dishes that may be later deformed by the upward pressure of flow around their margins and central subsidence as underlying sediment and water escape. Pillars form during forceful, explosive water escape. It s suggested that the shapes of dishes and pillars within an individual bed can be related to its original water content, thickness, and grain size; to the rate and magnitude of dewatering including consideration of water entering the bed from underlying consolidating sediments; and to the types and distribution of earlier-formed sedimentary structures. Dish structures cannot be used directly to infer transport or depositional processes. Where dishes are associated with or cut across primary sedimentary structures, the latter indicate deposition from currents. The study, indicates that coarse-grained terrigenous sediments often have pronounced and complex consolidation histories. Many rapidly deposited beds undergo partial liquefaction and fluidization during consolidation but retain sufficient strength to resist wholesale downslope flowage in response to gravity.

Isostatic response of the Earth's crust as a consequence of the fluctuating extent of ice-sheet masses was accompanied by earthquakes probably due to local reactivation of pre-existing faults. Our study of a glacilacustrine and glacifluvial succession exposed on Rügen Island (SW Baltic Sea) indicates that some of the soft-sediment deformation structures within the succession must have formed shortly before the front of the Pleistocene Scandinavian Ice Sheet reached the study area (during the Last Glacial Maximum), thus during a stage of ice advance. Based on analysis of the textural and structural features of the soft-sediment deformation structures, the deformed layers under investigation are interpreted as seismites which formed as a result of seismically induced liquefaction and fluidisation.

Ladakh, situated in the tectonically active terrain, in the vicinity of the Indus Suture Zone (ISZ), Shyok Suture Zone (SSZ) and Karakoram Fault (KF), is rich in Quaternary deposits and is truly a treasure trove for Quaternary researchers. This work presents the palaeoseismic signatures as recorded in the Quaternary sediments of the Spituk-Leh (along ISZ) and the Khalsar palaeolakes (along SSZ and KF). These two palaeolakes were a result of a regional tectonic activity at 35,000-40,000 yrs BP. 9 levels of soft-sediment deformation structures (seismites) are recorded from a >27 m thick, clay, sand sequence of the Spituk-Leh palaeolake. The deformation levels are confined to the lower 13 m of the sequence (0.5, 2.7, 3.2, 3.6, 5.5, 8.1, 9.8, 12.2 and 13.1 m). The upper part of the paleolakes seems to have stable tectonic conditions. About 90 km north of this section and separated by the Ladakh batholith, in the ~11 m thick section of Khalsar palaeolake shows 8 levels of soft-sediment deformation structures at 1.2, 1.5, 4.2, 4.5, 5.4, 8.8, 9.2 and 10.8 m levels. Deformation sediments are composed of alternations of clay, silts and sand and are restricted to single stratigraphic layers bounded by undeformed beds suggesting synsedimentary deformation. They are simple and complex convolutes, pinch and swell bedding, microfolds and microfaults, flame-like structures, pseudonodules or cycloids, clay diapirs, ball and pillow structures, pillar structures, sedimentary dykes, mud lenses, etc. Lying in the vicinity of the active faults the ISZ, SSZ and KF, these two palaeolake systems record multiple phases of seismic tremors of magnitude >5 due to release of stress along these fault systems during the late Quaternary times.