Seismites

At the end of the Permian, the carbonate succession of the shallow Oman margin is characterized by disrupted beds reflecting a response to a specific rheological condition. Half cemented thin beds are suddenly floating in a fluidized lime mud due to earthquakes shaken. This seismite deposit can be followed kilometer-on along the Saiq Plateau in the Central Oman Mountains, laterally with intraformational breccia or distorted structures

Densely spaced GPR and complex resistivity measurements on a 30,000 square meters site in a region of enigmatic sinkhole occurrences in unconsolidated Quaternary sediments have featured unexpected and highlighting results from both a meteorite impact research and an engineering geology point of view. The GPR measurements and a complex resistivity/IP electrical imaging revealed extended subrosion











depressions related with a uniformly but in various degrees of intensity deformed loamy and gravelly ground down to at least 10 m depth. Two principle observations could be made from both the GPR high-resolution measurements and the more integrating resistivity and IP soundings with both petrophysical evidences in good complement. Subrosion can be shown to be the result of prominent sandy-gravelly intrusions and extrusions typical of rock liquefaction processes well known to occur during strong earthquakes. Funnel-shaped structures with diameters up to 25 m near the surface and reaching down to the floating ground water level at 10 m depth were measured. GPR radargrams could trace prominent gravelly-material transport bottom-up within the funnels. Seen in both GPR tomography and resistivity/IP sections more or less the whole investigated area is overprinted by wavy deformations of the unconsolidated sediments with wavelengths of the order of 5-10 m and amplitudes up to half a meter, likewise down to 10 m depth. Substantial earthquakes are not known in this region. Hence, the observed heavy underground disorder is considered the result of the prominent earthquake shattering that must have occurred during the Holocene (Bronze Age/Celtic era) Chiemgau meteorite impact event that produced a 60 km x 30 km sized crater strewn field directly hosting the investigated site. Depending on depth and size of floating aquifers local concentrations of rock liquefaction and seismic surface waves (probably LOVE waves) to produce the wavy deformations could develop, when the big disintegrated meteoroid (a loosely bound asteroid or a comet of roughly estimated 1 km size) hit the ground. The observations in the Chiemgau area emphasize that studied paleoliquefaction features and wavy deformations (e.g. seismites) need not necessarily have originated solely from paleoseismicity but can provide a recognizable regional impact signature.

Plain Language Summary

Geophysical measurements have revealed widespread heavy disturbances of underground rocks by the highly energetic collision of a big cosmic body with the earth's surface in a young meteorite impact event. Today, 2,500-3,000 years later, prominent sinkhole phenomena (sudden terrain collapses), for a long time enigmatic to geologists, are considered the "smoking gun" of the impact event. The impact-induced underground deformations do not basically differ from those that occur in strong earthquakes, which can be excluded for the local region of the investigation. Hence, geologists and seismologists may confuse the origin of such typical rock deformations when exposed in geologic outcrops.

Plain Language Summary
Geophysical measurements have revealed widespread heavy disturbances of underground rocks by the highly energetic collision of a big cosmic body with the earth's surface in a young meteorite impact event. Today, 2,500 - 3,000 years later, prominent sinkhole phenomena (sudden terrain collapses), for a long time enigmatic to geologists, are considered the "smoking gun" of the impact event. The impact-induced underground deformations do not basically differ from those that occur in strong earthquakes, which can be excluded for the local region of the investigation. Hence, geologists and seismologists may confuse the origin of such typical rock deformations when exposed in geologic outcrops.

The NW-trending Denizli basin of the SW Turkey is one of the neotectonic grabens in the Aegean extensional province. It is bounded by normal faults on both southern and northern margins. The basin is filled by Neogene and Quaternary terrestrial deposits. Late Miocene-Late Pliocene aged Kolankaya formation crops out along the NW trending Karakova uplift in the Denizli basin. It is a typical fluviolacustrine succession that thickens and coarsens upward, comprising poorly consolidated sand, gravelly sand, siltstone and marl. Various soft-sediment deformation structures occur in the formation, especially in fine-to medium grained sands, silts and marls: load structures, flame structures, clastic dikes (sand and gravely-sand dike), disturbed layers, laminated convolute beds, slumps and synsedimentary faulting. The deformation mechanism and driving force for the soft-sediment deformation are related essentially to gravitational instability, dewatering, liquefaction-liquidization, and brittle deformation. Field data and the wide lateral extent of the structures as well as regional geological data show that most of the deformation is related to seismicity and the structures are interpreted as seismites. The existence of seismites in the Kolankaya Formation is evidence for continuing tectonic activity in the study area during the Neogene and is consistent with the occurrence of the paleoearthquakes of magnitude >5.

Fault-bound half-graben-type Raniganj Basin in eastern peninsular India hosts thick sedimentary succession of the coal-bearing Barakar Formation (Early Permian), which constitutes a part of the Lower Gondwana Supergroup. Sedimentological attributes of the upper Barakar succession are portrayed in two predominant facies associations, viz., (i) the lower part characterized by meandering fluvial facies association with distributary channel systems and (ii) the upper part represented by a transgressive, tide-wave-influenced, fluvio-estuarine facies association. Distinct beds with various soft-sediment deformation structures (SSDSs) manifesting paleoseismic events are reported as seismites from the upper Barakar succession. The SSDSs include convolute laminae, complex deformations with folded strata, syn-sedimentary growth faults, pseudonodules, loop bedding, and various water-escape structures including sand–silt flows/dikes. The seismites are restricted at two distinct stratigraphic horizons (S1andS2) within the upper Barakar succession,separated by undeformed beds in between. The seismites record episodes of paleoearthquake events triggered by syn-sedimentary reactivation of basin marginal faults in the half-graben-type Raniganj Gondwana Basin.These demarcate phases of significant shift in the depositional conditions from fluvial dominated to a transgressive tide-wave-influenced estuarine
system,caused by post-glacial basinal adjustments in the peninsular Indian Gondwanaland.

Outcrops and cores from the top of the lacustrine Tipton Member and the base of the Wilkins Peak Member (~51.5 Ma) of the Eocene Green River Formation, Bridger Basin in southwestern Wyoming yield a wide variety of sedimentary deformation features many of which are laterally extensive for more than 50 km. They include various types of folds, load structures, pinch-and-swell structures, microfaults, breccias and sedimentary dikes. In most cases deformation is represented by hybrid brittle–ductile structures exhibiting lateral variation in deformation style. These occur in low-energy, profundal organic-rich carbonate mudstones (oil shales), trona beds, tuffs, and profundal to sublittoral silty carbonate deposited in paleolake Gosiute. The deformation is not specific to the depositional environment because sedimentary units stratigraphically higher with similar facies show no deformation.
The studied interval lacks any evidence for possible trigger mechanisms intrinsic to the depositional environment , such as strong wave action, rapid sediment loading, evaporite dissolution and collapse, or desiccation, so 'endogenic' causes are ruled out. Thus, the deformation features are interpreted as seismites, and change in deformation style and inferred increase in intensity towards the south suggest that the earthquakes were sourced from the nearby Uinta Fault System. The 22 levels exhibiting seismites recognized in cores indicate earthquakes with minimum magnitudes between 6 and 7, minimum epicentral intensity (MCS) of ~9, and varying recurrence intervals in the seismic history of the Uinta Fault System, with a mean apparent recurrence period of ~8.1 k.y. using average sedimentation rates and dated tuffs; in detail, however, there are two noticeably active periods followed by relative quiescence. The stratigraphic position of these deformed intervals also marks the transition between two distinct stages in lake evolution, from the balanced-filled Tipton Member to the overlying, underfilled Wilkins Peak Member. Thus, these seismites are evidence for regional-scale changes in lacustrine sedimentation of Eocene Lake Gosiute in response to syndepositional tectonic activity. Analysis of synsedimentary deformation features is, therefore, a promising yet under-utilized tool to trace the tectonic evolution of lacustrine deposits of the Green River Formation and other tectonically active marine and non-marine basins.

Early Holocene seismic activity triggered fluidization and clastic-dike emplacement within Late Pleistocene lacustrine Lisan Formation sediments in the Dead Sea basin (DSB). Hundreds of opening-mode clastic dikes were documented cross-cutting
the Lisan Formation in four distinct sites in relatively small (\5 km2) areas: Bet ha’Arava, Masada Plain, Ami’az Plain, and Nahal Amazyahu. The spatial distribution of clastic-dike sites, although limited to Lisan Formation outcrops, still indicates wide-scale distribution.
All sites were demonstrated similarly in site dimensions, geometric parameters, dike infill materials, anisotropy of magnetic susceptibility (AMS) fabrics, and spatial distribution
patterns of clastic dikes. Field observations and laboratory analyses (grain size, XRD, and AMS) indicate transport of clastics from source layers below, indicating that dike emplacement was associated with the fluidization of lower Lisan clay-rich sediments. In all of the sites, the clastic dikes show a wide range of directions with clustered orientations, which might have been dictated by the local stress field that prevailed during dynamic fracturing of the Lisan host rock. Peak ground velocities were calculated for the Ami’az Plain by using a range of earthquake magnitudes and epicentral distances. The analyses indicate that liquefaction of features such as clastic dikes is related to amplification of seismic waves in specific sites, and the sites locations are up to 60 km away from an
epicenter in moderate earthquakes (Mw B 6.5), and more than 60 km away from an epicenter in strong earthquakes (Mw[6.5). The injection of clastic dikes in distinct and relatively small areas in the Lisan Formation along the DSB may serve as evidence for a unique combination of three factors: (a) clay-rich sediments and high water table as favorable conditions for fluidization on the exposed surface following the Lake Lisan
regression; (b) the occurrence of moderate-to-strong earthquakes (Mw > 6) in the early Holocene after the deposition of the Lisan Formation; and (c) the local geological structure characterized by edge and basin effects, which can amplify seismic waves. The present study indicates that injection due to fluidization of clay-rich strata during earthquakes was dominant throughout the DSB. We suggest that the clastic dikes can serve as evidence for local amplification conditions following seismic processes that occur close to active faults.

Early Holocene seismic activity triggered fluidization and clastic-dike emplacement within Late Pleistocene lacustrine Lisan Formation sediments in the Dead Sea basin (DSB). Hundreds of opening-mode clastic dikes were documented cross-cutting
the Lisan Formation in four distinct sites in relatively small (\5 km2) areas: Bet ha’Arava, Masada Plain, Ami’az Plain, and Nahal Amazyahu. The spatial distribution of clastic-dike sites, although limited to Lisan Formation outcrops, still indicates wide-scale distribution.
All sites were demonstrated similarly in site dimensions, geometric parameters, dike infill materials, anisotropy of magnetic susceptibility (AMS) fabrics, and spatial distribution
patterns of clastic dikes. Field observations and laboratory analyses (grain size, XRD, and AMS) indicate transport of clastics from source layers below, indicating that dike emplacement was associated with the fluidization of lower Lisan clay-rich sediments. In all of the sites, the clastic dikes show a wide range of directions with clustered orientations, which might have been dictated by the local stress field that prevailed during dynamic fracturing of the Lisan host rock. Peak ground velocities were calculated for the Ami’az Plain by using a range of earthquake magnitudes and epicentral distances. The analyses indicate that liquefaction of features such as clastic dikes is related to amplification of seismic waves in specific sites, and the sites locations are up to 60 km away from an
epicenter in moderate earthquakes (Mw B 6.5), and more than 60 km away from an epicenter in strong earthquakes (Mw[6.5). The injection of clastic dikes in distinct and relatively small areas in the Lisan Formation along the DSB may serve as evidence for a unique combination of three factors: (a) clay-rich sediments and high water table as favorable conditions for fluidization on the exposed surface following the Lake Lisan
regression; (b) the occurrence of moderate-to-strong earthquakes (Mw > 6) in the early Holocene after the deposition of the Lisan Formation; and (c) the local geological structure characterized by edge and basin effects, which can amplify seismic waves. The present study indicates that injection due to fluidization of clay-rich strata during earthquakes was dominant throughout the DSB. We suggest that the clastic dikes can serve as evidence for local amplification conditions following seismic processes that occur close to active faults.

Trembling assisted soft-sediment deformation structures of Karewa Group exposed in Kashmir valley
have been studied to understand the depositional environment and deformational stability of the Karewa Basin in
space and time. The study reveals the dominance of lacustrine-fluvial depositional environment during the PliocenePleistocene time with interference of number of syn- and post- depositional trembling quakes of different intensities
in the basin. The association of such soft-sediment deformational structures along with major sedimentary features
distributed laterally and vertically supports the pronounce past-trembling quakesin Karewa Basin during PliocenePleistocene time resulted from southwest upliftment of Pir-Panjal range (4 Myr) during the post-Tertiary Himalayan
Orogeny. The present study of past-seismic characteristics and trends may be significant for prediction of future
earthquakes and also deduce the past-seismic intensities of great earthquakes.

Seismogenic sedimentary structures—seismites—provide an opportunity to understand the effects of syndepositional tectonics on lacustrine sedimentation. The lowermost Wilkins Peak Member (Eocene Green River Formation, Wyoming, USA) contains laterally extensive intervals displaying folds, load structures, mixed brittle–ductile deformation, microfaults, breccias and sedimentary dykes, which formed intrastratally in a low-energy, sublittoral lacustrine environment. They developed in situ by liquefaction and plastic or brittle behaviour of semi-lithified sediment, or by remobilization and injection of granular material. Their morphological attributes and lateral extent, zonation in deformation intensity, and the depositional setting all imply deformation triggered by earthquake-induced stresses in shallow-buried sediment. Their stratigraphic distribution coincides with a shift in hydrological conditions from a balanced-filled to an underfilled lake type, independent of climate change. This study is the first to ascribe seismites to a pulse of tectonic activity that caused a synchronous change in lacustrine evolution.

In 2012 and 2013 extensive sedimentological field work was conducted to study the depositional setting, the regional geology and facies relationships, and measure sections of the Green River Formation in all the subbasins, in Wyoming, Colorado and Utah (USA). Several pervasive horizons of seismically induced deformation structures were identified mainly in profundal lacustrine sediments. Deformation is represented by brittle and plastic behaviour, as well as sediment injection and mass transport. The deformed layers are confined by undeformed beds which implies sporadic short-lived events that affected only near-surface sediments with susceptible rheological state at the time.
Based on: (1) the tectonic setting of the lacustrine basins; (2) the sedimentary environment and sedimentological characteristics of the successions in which the deformed layers occur; (3) their lateral extent and proximity to known active fault systems during the time of the deposition of host sediments; (4) their recurrence at different stratigraphic levels, intervals showing large-scale sedimentary deformation structures are interpreted as result of in-situ loss of shear strength, formed by increased pore pressure and vertical or horizontal stress induced by seismic activity

The carbonate-rich sediments of the Eocene Green River Formation (53–43 Ma) were deposited in a complex lake system in present-day Wyoming, Colorado and Utah during the Laramide orogeny. Although syndepositional tectonic activity has been inferred previously for this interval, sedimentary deformation features linked to ancient earthquakes have never previously been studied.
Stratigraphic intervals with synsedimentary deformation features were studied at several locations in all the sub-basins to provide information on the paleotectonic history of the area. Laterally extensive deformed horizons are common in laminated deposits of Fossil Basin (WY), and include folds, water-escape structures, dikes, microfaults, and chaotically brecciated intervals that preserved flow structures. These indicate hydrofracturing, dewatering and the liquified state of sediments during deformation. Sediments deposited in sublittoral environments of the Bridger Basin (WY), at the boundary between the Tipton Shale and Wilkins Peak members, also show evidence of synsedimentary deformation. These features, some traceable laterally for tens of kilometers, imply tectonically influenced changes in sedimentary processes during that time. Pervasive deformation features are also present in the Mahogany Oil Shale Zone in the Piceance Creek and Uinta basins (CO, UT). Behavior ranges from brittle (fragmented laminites and faulted beds) to plastic (convolution, folds), to cm- to m-scale cracks filled with injected sediment. Deformation styles were controlled by the rheological properties of the host sediment.
All these structures resulted from increased pore pressures from cyclic loading, and vertical and horizontal stresses induced by ground motion. Typically, undeformed strata separate the deformed horizons, which indicates that brief (tectonically-driven) events affected only near-surface sediments that were rheologically susceptible to syndepositional deformation.

Synsedimentary deformation features in profundal oil shale deposits are classified and  interpreted according to their geometric characteristics at several locations in the sub-basins of the Eocene Green River Formation (Wyoming, Colorado and Utah). They have a wide range of morphology and size, and deformation style ranges from brittle (fragmented laminites and faulted beds) to plastic (convolution, folding), to sedimentary injection into cm- to m-scale cracks and dikes. The style of deformation was governed by the rheological state of the sediment, while the degree of ductility was controlled by the amount of organic matter. Deformed horizons are separated by undeformed strata, which implies sporadic short-lived events that affected only near-surface sediments with the appropriately susceptible rheological state at the time. Although not recognized as such, soft-sediment deformation structures have been described previously in profundal sediments (e.g. “streaked-and-blebby” oil shale). Intervals showing large scale brecciation and chaotic soft-sedimentary deformation structures like convolute bedding are commonly explained as downslope mass movements of unlithified sediments. However, they can be also related to in-situ loss of shear strength without the role of gravity. Other deformation structures (e.g. folds, microfaults and sedimentary dikes) are commonly associated with these beds and they indicate fluidization and soft-sediment deformation of the sediment. Based on the tectonic setting of the basin and the detailed characteristics of the these features, deformation structures are interpreted as having been developed as a result of increased pore pressure and vertical or horizontal stresses induced by seismic activity. As soft-sediment deformation features induced by earthquakes are indicative of synsedimentary tectonism, these deposits can provide information about the location and timing of the tectonic movements along the uplifting margins of the lake sub-basins. Small- and large-scale deformation features and deformed oil shale intervals may have significant effects on the horizontal and vertical permeability and connectivity of the oil shale beds. Moreover, large scale clastic dikes may affect local and regional hydrology of an area. Clearly, synsedimentary geformation is an important but hitherto neglected aspect of the petroleum geology of the Green River Formation.

Their typically heterolithic nature and deposition in an overall quiet-water environment make lacustrine deposits particularly suitable for the analysis of soft-sedimentary deformation features induced by shaking during ancient earthquakes. Lacustrine sediments of the Eocene Green River Formation (53 – 43 Ma) accumulated in an interconnected lake system of ponded basins in Wyoming, Utah and Colorado during the Laramide orogeny. Despite the known syndepositional tectonic activity, horizons of soft-sediment deformation in the Green River Formation have not previously been studied and linked to tectonic movements.

Synsedimentary deformation features were classified and interpreted according to their geometric characteristics at several locations in the various sub-basins. Laterally extensive deformed horizons are present in the laminated lacustrine deposits of Fossil Basin. Deformation features include folds, water escape structures, sedimentary dikes, microfaults, and chaotically brecciated intervals with flow structures indicating a fluidized state of sediment during the deformation event. The style of deformation was governed by the varying rheological properties of the sediment and the various driving forces.

Numerous deformation features were also found in the Mahogany Oil Shale Zone, an extensive stratigraphic marker present in the Piceance Creek and Uinta basins, which contains several petroliferous shale beds. Deformation style ranges from brittle (fragmented laminites and faulted beds) to plastic (convolution, folding), to sedimentary injection into cm- to m-scale cracks in the form of dikes and dikelets. The degree of ductility in these profundal deposits was controlled by the amount of organic matter in the sediment.

Based on the tectonic setting of the basin, the detailed characteristics of the deformed features, and the presence of undeformed layers adjacent to deformed horizons, these features are interpreted as having been developed as a result of increased pore pressure and vertical and horizontal stresses induced by seismic activity. As soft-sediment deformation features induced by earthquakes are indicative of synsedimentary tectonism, they provide information about the location and timing of the tectonic movements in or at the margins of the lake sub-basins.

Pervasive horizons of various kinds of soft-sediment deformation structures were identified in the lacustrine sediments of the Eocene Green River Formation, USA. These features are present in a variety of sediments deposited in paludal (coal, sand) to profundal (oil shale) environments. Deformation is represented by brittle and plastic behavior, as well as sediment injection, and the deformed layers are confined by undeformed beds with similar thickness and lithology to the deformed ones. Based on the (1) tectonic setting of the subbasins; (2) the sedimentary environment and sedimentological characteristics of the successions in which the deformed layers occur; (3) their lateral extent; (4) their recurrence at different stratigraphic levels; and (5) their similarity to those described as seismically induced deformation structures in other areas and reproduced experimentally, we interpret these features as having developed as a result of increased pore pressure and vertical or horizontal stresses induced by seismic activity.