Soft-sediment Deformation Structures Research Articles

A Re-Examination of Earthquakes in Mediterranean Archaeology in Light of Historical Sources

Interest in earthquakes in Mediterranean archaeology has distinct disciplinary origins. Since the inception of archaeoseismology—earthquake archaeology—in the 1980s, approaches to earthquake factors have been characterized by reliance on ancient historical sources. However, although texts have supported the identification of earthquake disasters in material destruction, documentary records extend far beyond particular events and experiences of disaster; diverse cultural perceptions of earthquakes as expressed in ancient textual sources also offer an alternative interpretation for Mediterranean archaeology. This study reviews the material-geological record of Helike in Greece—the victim of an infamous major earthquake in 373 BC—in order to assess the impact of seismic activity on the site from the third millennium BC to the fifth century AD. Evidence for such an impact includes archaeoseismic types of destruction, anti-seismic construction in architecture and stratigraphically associated soil micromorphological evidence of seismically triggered soft sediment deformation structures (SSDS). A reassessment of ancient accounts of the 373 BC event to explore Graeco-Roman cultural perceptions of earthquakes provides a new interpretive frame for the material-geological record of Helike. This alternative interpretation repositions earthquakes, traditionally perceived as ‘natural’ disasters implicated in ‘collapse’ and ‘catastrophe’, as social phenomena. The case of Helike demonstrates the value of documentary records for reframing the complex social and political dimensions of recurrent earthquakes and persistent geological hazards.

Seismic-aseismic impact on marine depositional dynamics and sedimentary architecture: Study on multilayer-multiscale SSDS in Proterozoic Rohtas Limestone, India

The present study explores a diverse suite of soft-sediment deformation structures (SSDSs) preserved at multiple levels within the Mesoproterozoic carbonate succession of Rohtas Limestone in the Vindhyan Supergroup of India. The carbonate succession shows lithological heterogeneity, characterized by a sharp change of facies association and depositional environment. Three layers of SSDS, traced over 57 km, demarcate the lower lagoonal from upper open shelf deposits. Contorted laminae, load casts and flame structures, convolute laminae, ball and pillow structures, accordion folds and pillar structures within the limestone beds infer liquefaction-fluidization and plastic deformation. The lateral continuity, vertical repetition and confinement of SSDS beds at the interface of lagoon and open shelf deposits indicate the role of seismicity on facies succession. The SSDS beds show lateral variation in thickness and structures, depending on the distance from epicenter. The seismic trigger was accompanied by sudden deepening of the depositional environment and related marine transgression. The coarsening up packages within the lagoonal succession comprise load cast and flame structures, syn-sedimentary faults and intraclastic conglomerates. The open shelf succession shows several fining up cycles, with multiple load and flame structures with intraclastic conglomerate at the top. Origin of SSDS in association of the coarsening up sequence, and fining up cycle infers that intrabasinal tectonics and storms were the triggering agents for lagoon and open shelf successions respectively. The seismite in the studied succession not only reveals the seismicity during the Proterozoic, but also changed the sedimentary facies association, which may use as a diagnostic criterion for the identification of seismite. This study also highlights that seismic and aseismic impacts on sedimentary architecture and paleoceanography evolution.

A continuous 18.6–10 ka record of seismic events revealed by Xinmocun lacustrine sediments at Diexi, eastern Tibetan Plateau

Five Ms 7.0 earthquakes (Wenchuan, Yushu, Lushan, Jiuzhaigou and Maudo) have occurred on the eastern Tibetan Plateau since 2008, and > 20 historical earthquakes (Ms ≥ 5.0) have also been recorded, demonstrating the strong seismic activity prevalent in this region. Owing to the geomorphology of the region, consisting of alpine valleys with a lack of Quaternary deposits, it is difficult to conduct paleo-earthquake research through the excavation of trenches. Lacustrine sediments are regarded as the most suitable archives for paleo-earthquake studies because they often comprise a detailed, long-term, and continuous environmental record. To assess the seismic activity of the Diexi, we studied a well-exposed outcrop of Xinmocun lacustrine sediments that included three sections (XMCⅠ (11.5 m), XMCⅡ (5.6 m), and XMCⅢ (11 m)) near Diexi Lake, moving from a lake shore to lake center environment, at the intersection between the Minjiang fault and Songpinggou fault. Taking into account the geodynamic setting of the area and its known tectonic activity, soft-sediment deformation structures, including load and flame structures, injection structures, ball structures, pseudo-nodules, boudinage structures, plunged sediment mixture, liquefied breccia and micro-faults, discovered within the sections are interpreted as seismites. High-resolution grain-size and magnetic susceptibility indicators were used to obtain a continuous record of the changes in physical properties within the three sections enabling the recognition of additional seismic events that did not result in soft-sediment deformation structures. Rapidly deposited layers with underlying soft-sediment deformation structures in the sections record five (XMCI, XMCII and XMCIII) seismic events; these comprise siliciclastic-enriched sandy sediment fluxes from earthquake-triggered landslides or dust of siliciclastic-enriched clastic materials. Isolated rapidly deposited layers (without underlying soft-sediment deformation structures) record 18 (XMCII), 12 (XMCI), and 21 (XMCIII) additional earthquake-induced inputs of detrital material into the lake. Optically stimulated luminescence and 14C dating of the XMCⅠ, XMCⅡ, and XMCⅢ sections indicate continuous sediment deposition from 19.4–9.9 ka, 15.5–10.1 ka, and 18.7–10.6 ka, respectively, and the seismic events recorded in these sections can be cross-correlated within the age error range. Hence, there are a total of 30 seismic events recorded within the Xinmocun sediments during the period 18.6–10 ka, suggests a weakly periodic pattern with an apparent recurrence time of ∼ 280 years. The Minjiang fault and Songpinggou fault are Holocene active faults with a risk of causing strong earthquakes. Due to the Diexi area is located at the intersection of the Minjiang fault and Songpinggou fault, and has frequent seismic activity, suggest a high seismic risk in the future.

Ice? Salt? Pressure? Sediment deformation structures as evidence of late-stage shallow groundwater in Gale crater, Mars

Persistence of near-surface water during the late evolution of Gale crater, Mars, would have been fundamental for maintaining a habitable environment. Sedimentation in aqueous conditions is evident during the early stages of crater infilling, where accumulation of lower Mount Sharp group strata is characterized by fluviolacustrine sedimentary rocks. The basal unit of the Siccar Point group—the Stimson formation—which unconformably overlies the Mount Sharp group and represents conditions postdating the exhumation of Aeolis Mons, is characterized by accumulation of aeolian strata under arid conditions. Water was largely absent near the surface during its deposition. At the Feòrachas outcrop, discovery of soft sediment deformation structures in aeolian Stimson strata challenges the notion that Gale crater was devoid of water during its later depositional phase. We identified deformed wind-rippled and vertically laminated sandstones, hosted within erosion-resistant ridges forming boxwork patterns. Broadly, these structures are diagnostic of water (as liquid or as ice) in the shallow subsurface. Comparison with Earth analogues suggests formation by subsurface fluid escape, freeze-thaw processes, or evaporite deformation. Regardless of the mechanism, these structures signify the presence of water at or near the surface much later than previously documented and may extend the habitability window in Gale crater.

Soft-sediment deformation structures or microbially induced sedimentary structures: the description and possible origin of the "loopites" in the Mesoproterozoic Wumishan Formation, North China

Soft-sediment deformation structures or microbially induced sedimentary structures: the description and possible origin of the "loopites" in the Mesoproterozoic Wumishan Formation, North China

Characteristics and geological significance of early carboniferous soft-sediment deformation structures in the Kushanhe section, southwest Tarim Basin, Northwest China

The early Carboniferous Kushanhe Formation and Hantiereke Formation in the Kushanhe section in the piedmont of the southwestern margin of Tarim Basin are in a medium-deep water sedimentary environment with a stratigraphic thickness of more than 500 m, and the sedimentary facies is slope-shelf facies. Among these deposits, soft-sediment deformation structures (SSDS) are common, dominated by various types of slumps. The appearance of SSDS is related to the geotectonic environment of early Carboniferous in southwest Tarim Basin. In the Early Carboniferous, the Paleo-Tethys ocean dived under the Tarim plate, forming a back-arc structure, and a structural slope break belt easily appeared along the basin edge, which provided topographic conditions for the development of marginal platform marginal belt and slope facies. Under this background, the ultra-thick volcanic rocks of Wulate Formation accumulate along the subduction zone, and earthquakes with M≥ 5.0 are prone to occur. Landslides related to earthquakes and corresponding SSDS are easily triggered at the outer edge of the slope break zone. The large earthquake induced by tectonic environment is an important trigger factor of early Carboniferous SSDS. Therefore, the appearance of early carboniferous SSDS in Kushanhe section is an important sedimentary response to the early carboniferous piedmont tectonic activities in southwestern Tarim.

Signatures of Syndepositional Seismic Effects in Aeronian Marine Clastic Sediments in Western Gorny Altai

Abstract ––The Aeronian clastic sediments in the Gorny Altai area bear signatures of past seismic effects (paleo-seismites). Sedimentary structures produced by brittle deformation (breccias) span the level of the upper convolutus graptolite zone and the lower sedgwicki zone. They coexist with soft-sediment deformation structures (SSDS), such as turbated and rolled layers, bumpy layer boundaries, etc. At the final deposition stage, the rocks were deformed during seismically-triggered landsliding and were shed into a submarine canyon, with formation of rolls (pseudo-conglomerate).

Architecture of lacustrine deposits in response to early Carboniferous rifting and Gondwanan glaciation, Nova Scotia, south‐east Canada

AbstractUpper Palaeozoic lacustrine basin deposits not only record local tectonism but are also an archive to evaluate global palaeoclimate changes linked to the Late Palaeozoic Gondwanan ice age. The Tournaisian Horton Group of Nova Scotia, south‐east Canada, accumulated in rift basins following the final accretion of peri‐Gondwanan terranes to the Appalachians. Sedimentology, mineralogy and geochemistry of the well‐exposed sandstones and shales at the classic Blue Beach section (ca 353.5 to 352 Ma) reveal the interplay of local tectonism and global climatic controls on lacustrine sedimentation. The lacustrine depositional environment gradually transitioned from deep water offshore at the base of the section to wave‐dominated and fluvial‐dominated nearshore at the top. Multiple small transgressive–regressive sedimentation cycles have an average 21 ka duration, likely related to Milankovitch cyclicity. Unusually abundant soft‐sediment deformation structures and landslides are the sedimentary responses to frequent earthquakes during the most active phase of rift subsidence. The overall succession shows changes from a shallowing‐up balanced‐filled to an overfilled lacustrine basin. The chemical weathering intensity index and the Th/K ratio show a longer‐term trend from dry and cool conditions low in the section to humid and warm conditions near the top, with rapid change in the transition period. The section records the peak of the global mid‐Tournaisian carbon isotope excursion and the corresponding cooling event (354 Ma to approximately 351 Ma). The sedimentary succession is a response to long‐term and short‐term climatic cycles influencing lake level and sediment supply during the time of maximum rift basin subsidence recorded by the soft‐sediment deformation structures.

Soft sediment deformation structures from the Brahmaputra Basin: A window to the eastern Himalayan paleoseismicity and tectonics

The Brahmaputra foreland basin, is one of the most dynamic in terms of tectonism and sediment load, revealed a variety of seismically generated soft sediment deformation structures (SSDS) in the form of clastic dikes, sand sills and related micro-faults. The qualitative and quantitative parameters of these SSDS in the study area such as dimension, angle of intrusion to capping layer, cross-cutting relations, wall shattering, sand sills, and micro-faults seem to be caused by multiple strong seismic events. The causative earthquake with intensity (VIII-X), paleo-peak ground acceleration (0.55 g) and magnitude (M ≥ 7.0) might have caused liquefaction features in the study area. Along with the geometry of various SSDS and Optically stimulated luminescence (OSL) dates derived for the clastic dikes indicate the oldest possible age for the seismic event as 0.94 ka. Further, the intensity and age obtained for the present study indicates a possible near seismic source like Kopili Fault Zone, Mishmi Thrust, and neotectonic lineament with trend NW-SE, which can be traced as micro faults and in clastic dikes. Liquefaction potential studies in the area indicate the likelihood of very high liquefaction potential (>45) with ground failures regardless of earthquake size or epicentral distance. The present study highlights the importance of SSDS for establishing paleoseismology in tectonically active regions where surface ruptures are sporadic due to dense alluvial cover and most of the active faults are blind.

Trace fossil evidences of an Early Miocene paleoseismic event and depositional regime change from the Kutch (Kachchh) Basin

Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures (SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation (KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS, the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity, its ichnologic signature, and the depositional regime change refer to a higher-resolution (i.e., lower-order) sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.

The Great Boundary Fault in the Indo-Gangetic foreland basin: A geomorphological perspective

Identifying active faults in alluvial plains with varying sedimentation rates, erosion, and extensive anthropogenic modifications is challenging. In tectonically active foreland basins, tectonics outweighs other controlling factors and produces a set of key fluvial geomorphic markers that are critical for precisely locating active faults. This study employs several key tectonic fluvial morphometric parameters, seismically induced soft-sediment deformation structures (SSDS) as seismites, and the displaced rocks of the Siwalik mountains to mark the surface positions of a buried basement fault system, namely the Great Boundary Fault (GBF) beneath the alluvial cover of the Indo-Gangetic foreland basin.The Great Boundary Fault (GBF) is a NE-SW trending, oblique-slip, branching reverse basement fault running from peninsular India to the Sub-Himalayas. About 400 km length of its NE segment is buried under thick sediments of the Indo-Gangetic foreland basin. This fault's surfaceward propagation deforms the overlying sediments via a network of subsidiary faults, resulting in 20 km wide broad fault zones. The extreme flatness of the Ganga plain conceals the primary faulting evidence but tectonic fluvial geomorphic signatures, the SSDS, and the laterally displaced Siwalik rocks, including south-verging thrusts at the frontal Himalayas, provide collective evidence of neotectonic activity along both fault branches. The primary objectives of this study are to characterise the GBF's buried segment in the Ganga plain through the geomorphic signatures and SSDS, to elucidate its extension up to the Main Boundary Thrust (MBT), and to understand the surfaceward propagation mechanism of its reverse faults through the alluvial-fills.Tectonic geomorphic parameters such as sinuosity spectra and knickpoints were analysed using ArcGIS and Matlab. Meander scar mapping was carried out using Google Earth Pro and Landsat imagery within ArcGIS to characterise the pattern of avulsions and adjustments of the floodplain linked to the tilting directions of the fault blocks.Fourteen prominent knickpoints of 4 to ≥6 m height were derived from the river profiles across the fault zone. Rivers on the up-thrown block possessed low sinuosity (as low as 1.1), whilst those on the down-thrown block had higher sinuosities (up to 3.1), indicating active uplift and rapid subsidence. The deflection of multiple river courses (Ganga, Ramganga, Burhiganga, Sot, Pangaili, and Deoha) and the presence of asymmetrical meander-belts demonstrate an eastward tilting of the tectonic block. The occurrence of liquefaction-induced SSDS close to the GBF corroborates its recent seismogenic nature. Field observation suggests these SSDS are likely related to the Usawan paleo-earthquake (estimated magnitude of 6.5–7.2), epicentered near the GBF. Based on the geometry and the venting characteristics, a new type of SSDS has been recognized, and the term “liquefaction vents” has been proposed for it. Their association with the other types of SSDS that are characteristically formed by >6.5 magnitude earthquakes suggests it is the minimum magnitude of earthquake required for the formation of liquefaction vents. The regional seismic record suggests a significant number of both large and moderate earthquakes around this fault.Finally, we synthesise the results to propose a growth model for the propagation of reverse faulting from the underlying basement bedrock through to the alluvial sediments and the surface of the Ganga plain.

A continuous 18-10.2 ka paleo-earthquake events revealed by the Luobozhai lacustrine sediments, eastern Tibetan Plateau

To assess the regional seismicity during the late Quaternary, we studied a well−exposed sequence of Luobozhai lacustrine sediments, 14.5 m thick, near Lake Diexi in the upper reaches of the Minjiang River, eastern Tibetan Plateau. High-resolution geochemical, grain-size, and magnetic susceptibility indicators were then used to obtain a continuous record of the changes in elemental and physical properties within the profile to determine additional seismic events that did not result in soft sediment deformation structures. Rapidly deposited layers with underlying soft sediment deformation structures in the Luobozhai section indicate 18 siliciclastic-enriched sandy sediment fluxes from earthquake-triggered landslides or dust of siliciclastic-enriched clastic materials; isolated rapidly deposited layers (without underlying soft sediment deformation structures) record 17 additional earthquake-induced inputs of detrital material into the lake. Hence, there are a total of 35 seismic events (M ≥ 5.0) recorded within the Luobozhai section, which probably reflects the frequent seismicity of Minjiang fault. Optically stimulated luminescence and 14C dating of the Luobozhai section indicates continuous sediment deposition from 18 to 10.2 ka, and had a mean recurrence interval of approximately 224 years. Heavy mineral analysis shows that event layers and non-event layers have different mineral compositions. This reflects changes in sedimentation pre, during, and post a seismic event, especially the co-seismic debris material (e.g., from landslides and/or dust storms) that controls changes in provenance within the drainage basin, and in turn affects the regional erosion rate and weathering patterns. This study opens up new avenues of paleo-earthquake research.

Volcanism-driven lacustrine redox fluctuations were responsible for the formation of the Jehol Lagerstätte: Evidence from a high-resolution Aptian sedimentary core, Northeast China

While a “volcanic Pompeii” model is well accepted as the cause of mass mortality and exceptional preservation of the Jehol Biota, no consensus has been reached thus far regarding the cause of mass mortality of fossils found in interbedded finely laminated sediments. We propose that volcanically driven, lacustrine redox fluctuations were responsible for the formation of the Jehol Lagerstätte, based on data obtained from a new drill core of Lower Cretaceous sedimentary rocks in the Chaoyang Basin, Northeast China. We found manganese-rich carbonates are interbedded with molybdenum-rich black mudstones and tuffs, and phosphatized fossils in the drill core. The elemental enrichment factors for molybdenum are much higher than for uranium in the black mudstones, suggesting the role of the manganese particulate-shuttle in deposition of this element. The manganese-rich carbonates are formed by the reaction of manganese oxides with organic matter, indicating an oxidized water column. This process accelerates the enrichment of molybdenum under anoxic non-sulfidic conditions. The interbedded manganese carbonates and molybdenum-rich mudstones thus record redox fluctuations in the lacustrine depositional environment. Given the numerous tephra in the black mudstones and soft-sediment deformation structures ostensibly associated with seismicity, we propose that the redox fluctuations were caused by lake eutrophication and turnover driven by volcanism that was ultimately related to the destruction of the North China Craton. These volcanically induced redox fluctuations, along with the toxicity of the volcanic gases, may have caused the simultaneous mass mortality of aquatic, terrestrial, and avian fauna. Micro-X-ray fluorescence, energy dispersive X-ray spectroscopy, and Raman mapping show that the preservation of fossils was mainly due to phosphatization. Fluctuating redox conditions facilitated phosphate enrichment in sediments. Both the oxic and anoxic non-sulfidic conditions were conducive to the preservation of organisms by phosphatization, and oxidation was favorable for phosphate mineralization, both contributing to the exceptional preservation of the Jehol Biota fossils.

The Maracangalha injectite complex: An overlooked hydrocarbon play in the Lower Cretaceous Recôncavo Basin, NE Brazil

The Recôncavo Basin is the third major natural gas producer in Brazil. Lower Cretaceous sandstones of the Maracangalha Formation (Caruaçu and Pitanga Members) hold the largest volumes of non-associated gas in this basin. However, these reservoirs are extremely complex due to a range of soft-sediment deformational process that modify the depositional architecture and impact on the original structure of the porous system. The cause of soft-sediment deformation is still contradictory because both mass movements and post-depositional fluidization has been proposed by previous studies. This uncertainty has drastic implications for reservoir predictability in the subsurface since mass-transport deposits and fluidization-remobilization complexes have very different architectures. To test these hypotheses, this study examines soft-sediment deformation structures (SSDS) in outcrop and core in order to interpret remobilization processes and to infer the main trigger mechanisms involved. Outcrop description was carried out in the coastal zone of the Todos os Santos Bay, NE Brazil, where the Maracangalha Formation is very well exposed. High-resolution core images from four producing fields located northward (Miranga, Jacuípe, Lamarão and Massapê) were also described. SSDS include a great variety of structures: 1) dish, 2) pillar, 3) consolidation lamination, 4) load structures, 5) tilted, convoluted, distorted and disrupted laminations, 6) flames, ball and pillow structures and pseudonodules, 7) large-scale mounded geometries, 8) penecontemporaneous faults and 9) sandstone intrusions/extrusions (dikes, sills, breccias and volcanoes). Intensely deformed sandstones are connected to sandstone intrusions that cut through finer-grained, low-permeability strata. Orientation of normal faults and sandstone intrusions suggests that they are genetically related. The Pitanga and Caruaçu Members are better described as facies, since they differ only by the degree of deformation. Pitanga facies is the product of remobilization of an undeformed (Caruaçu) facies. Unlike previous interpretations that indicated the action of slumps, we concluded that the upward movement of interstitial fluids (liquefaction and fluidization) was the main mechanism of remobilization, deformation and mixing of sediments. The overpressure of pore fluids and syn-rift faults propagation broke up seal-strata, releasing the fluids pressure and driving the upward movement of sediments. Key architectural elements of a sand complex are recognized in outcrop and core, including parent units, host-strata and sandstone intrusions. For the origin of this injectite complex we suggest a seismic trigger related to extensional tectonics of the rift system. The Maracangalha injectite complex comprises a new hydrocarbon play to be considered in further exploration and production (E&P) activities in the Recôncavo Basin.

Reconstructing depositional environments through cave interior facies: The case of Galería Complex (Sierra de Atapuerca, Spain)

This work showed that cave sediments are useful for geomorphologic studies and for reconstructing depositional environments. While the cave entrance facies have been extensively studied for their relationship with the fossil and archaeological record, the cave interior facies have received much less attention, although they can provide much information on the geomorphological evolution of the karst. This work presents the stratigraphic and sedimentological study of a section >6 m thick and 10 m long of cave interior sediments of Galería Complex (Sierra de Atapuerca, Spain). Galería Complex is a cavity infill of the Sierra de Atapuerca (Spain), composed of three sections filled by at least 30 m of Pleistocene sediments. This sequence is divided into 5 lithostratigraphic units named from bottom to top: GI – GV. GI unit is 19 m thick of interior facies in the base of the Galería Complex, divided into two sub-unit, GIa and GIb, by the Matuyama-Bruhnes paleomagnetic boundary. GI unit shows an issue with the chronology since has uncoherent between TT-OSL and ESR/U-series and paleomagnetism dates. This work has been done by combining field observation with laboratory sedimentary analysis to characterize the texture and structure of the sediments. Based on these studies, 12 layers and 9 sedimentary facies have been identified. The facies associations indicate a clear separation between GIa and GIb sub-units. GIa sub-unit is dominated by epiphreatic conditions and represents continuous relativity sedimentation during the Early Pleistocene; meanwhile, GIb shows important erosion events and facies with reworked materials that indicate vadose conditions during the Middle Pleistocene. This environmental change is related to the geomorphological evolution of the Arlanzón River. In addition, soft-sediment deformation structures have been described, including faults and low-angle folds. An important leaching process has been identified by the presence of phosphates that could explain the underestimated ages obtained in other works.

Concurrence of load-and-flame structures, balls-and-pillows, clastic injectites and shear deformation bands as indicator of seismicity in mixed siliciclastic-carbonate successions (Finale Ligure Basin, Italy)

The present research explores a diverse suite of soft sediment deformation structures (SSDS) combined with clastic dykes and shear deformation bands distributed throughout a Early Miocene-age mixed carbonate-siliciclastic coastal wedge located on the Ligurian coast (NW Italy) of the Mediterranean region. The studied Aquitanian-Serravallian successions of the Finale Ligure Basin are typified by the presence of lithologically heterogeneous units, internally characterized by abrupt changes of lithofacies distributions and associated interpreted depositional environments. The interface between the terrigenous base and the carbonate wedge in many places features SSDS. Here, we report the discovery of a multiform deformational pattern, ranging from small size (cm-to dm-scale) load-and-flame structures, ball-and-pillows and mini-slumpings, to outsized (several meters in height) chaotic contorted and folded stratigraphic intervals, sand intrusions and diapir- or tree-like water escape structures. Many of the SSDS are related to fast injection of overpressurized fluids after sand liquefaction, and occur in close association with disaggregation and phyllosilicate shear bands, and sand dykelets. The stratigraphic distribution and cyclic repetitions of SSDS-prone intervals unambiguously indicates syn-depositional seismicity, thus suggesting that juxtaposition of SSDS, diapiric injectites, and shear deformation bands can serve as a suitable diagnostic criteria for seismite identification in the field. Since these particular assemblages of deformation structures reflect seismic activity in the area, they provide compelling evidence for previously undocumented tectonic episodes in Langhian-Serravallian times, associated with the latest stages of the Liguro-Provençal Basin opening.

Soft-sediment deformation structures in the Mesoproterozoic Kaimur Sandstone, Vindhyan Supergroup (Central India), and their seismotectonic implications

The unequivocal identification of soft-sediment deformation structures (SSDS) is a significant attribute to constrain the effect of transient geological events in the spatio-temporal evolution of ancient sedimentary basins. This paper reports and discusses, for the first time, the occurrence of several cm- to dm-scale SSDS within sandstone successions of the Mesoproterozoic Kaimur Group (Vindhyan Supergroup), exposed at the Hanumandhara Hill of Chitrakoot-Satna border region, Madhya Pradesh State, India. The SSDS are confined to a deformed interval comprising seven individual sedimentary units of variable composition and texture, which are sandwiched between nearly horizontally undeformed sandstone beds. The SSDS consist of load structures (load casts, flame structures, pseudonodules and ball-and-pillow structures), contorted lamination, convolute lamination, boudins and pinch-and-swell structures, deformed cross-stratification, slump structures, clastic injections, fluid escape structures, and syn-sedimentary fractures/faults. The present study suggests that the formation of these SSDS is essentially related to a combination of processes (gravitational instability, liquefaction, fluidization, and fluid escape) predominantly induced by seismic shocks. In addition, the restricted occurrence of fractures/faults in these deformed layers emphasizes the passage of seismically-induced Rayleigh waves. Considering the observed types of SSDS, their lateral homogeneity and geographic distribution along with the geodynamic framework of the Vindhyan Basin, the whole area can be tentatively attributed to having experienced moderate- to high-magnitude (M ≥ 5) seismicity. The present study combined with earlier reports of seismically-induced SSDS, from other regionally disposed formations belonging to the Lower (e.g., Kajrahat Limestone, Chopan Porcellanite, Koldaha Shale, Rohtas Limestone, and Glauconitic Sandstone of the Semri Group) and Upper (e.g., Bhander Limestone of the Bhander Group) Vindhyan Supergroup, respectively, provides evidence for the constant regional-scale seismo–tectonic activity within the Paleo-Mesoproterozoic Vindhyan Basin. Importantly, this observation further suggests that the intracratonic basins can be active tectonically contrary to the earlier propositions.

Soft-sediment deformation structures of mottled clay in Huizhou Quaternary basin, coastal South China

Tectonically induced liquefaction and the resulting soft-sediment deformation structure (SSDS) can provide useful information on paleo-earthquakes, which is vital for the assessment of geohazard susceptibility in tectonically active regions. In this study, we combined sedimentary and chronological methods to the reveal detailed characteristics of the mottled clay in the Huizhou Quaternary Basin. The dating results suggest that mottled clay usually developed during the late Pleistocene, overlying the fluvial deposit or embedding homogeneous aeolian yellow silt. Mottled clay has a typical bimodal frequency distribution with modal sizes at 5 and 80–90 μm, which are identical to those of the yellow silt and the underlying fluvial sand, respectively. Micro-X-ray fluorescence mapping revealed high concentrations of Fe and Si in the red and white fraction, respectively. In addition, the red fraction of mottled clay has a high hematite content, similar to loess-like yellow silt, whereas the white fraction and the underlying fluvial sediments are dominated by goethite. This sedimentary evidence together suggests that the mottled clay could be an admixture of aeolian yellow silt and the underlying fluvial sand. Furthermore, diverse deformed structures (e.g., fragmented structures, sand veins, sand dykes and flame structures) were observed in mottled clay. Therefore, we suggest that the mottled clay structure in the Huizhou Basin is a product of liquefaction-induced SSDS. Tectonic activity was considered to have triggered the liquefaction and SSDS, which is supported by the close spatial relationship between the mottled clay and regional faults. We propose that the SSDS of mottled clay could be a potential indicator of paleo-earthquakes in the coastal Quaternary basins of the northern South China Sea.

Record of Late Neogene seismites in turbidite deposits of the Tafna Basin (NW Algeria)

The wide variety of soft-sediment deformation structures (SSDS) developed within deposits of the same age may hinder the interpretation of their origin. Some types of SSDS may appear similar though have different trigger mechanisms, while others may result from a specific mechanism. Furthermore, the development of particular SSDS may be influenced by several synchronous or semi-synchronous factors. This study deals with the recognition of SSDS trigger mechanisms with respect to lithological and deformational features of the deposits concerned. Turbidite deposits of late Neogene age in the Hadjret El Gat area (Tafna Basin) contain different types of SSDS associated with (1) slope processes (e.g., slump folds) and induced overburden pressure, coupled with broken beds and overloading structures, and (2) liquefaction and fluidisation phenomena, leading to the development of load structures, ball-and-pillow structures, water-escape structures and syndepositional faults. These two mechanisms of SSDS formation in the study area are thought to result from seismically-induced triggers. Recognition of a vertically-repeated, sandwich-like arrangement of deformed and undeformed layers along with the SSDS features ("trapped" within beds) suggests that these internally-deformed beds are seismites, the first recognized in the Tafna Basin of NW Algeria. Large earthquakes may trigger seismic waves energetic enough to deform strata and induce the development of SSDS. This hypothesis is supported here by tectonic evidence, given deposition of the Tafna Basin strata in the convergence zone between Africa and Eurasia, active since the late Neogene.

A palaeoearthquake event and its age revealed by the travertine layer along the Litang fault in the southeastern margin of the Qinghai-Tibetan plateau

The Litang fault (LTF), located in the southeast of the Qinghai-Tibetan Plateau, is known for its high level of present-day seismicity, whereas its Pleistocene activity has been scarcely documented. This study focused on a tract of banded travertine deposits precipitated from thermal waters along the NW–SE-trending LTF trace. The role of travertine deposits in recording neotectonic activity has been studied by identifying their internal structure. Typical soft-sediment deformation structures observed within the banded travertines include micro folds, liquefied breccia, and liquefied diapirs. These deformed structures, which are restricted to a single unit separated unconformably by undeformed layers, can be traced for tens of meters, indicating that they were formed by seismic shaking triggered by LTF activity. The deformation of the banded travertine layers is attributed to the combined effects of seismic shaking, liquefaction, and fluidization, and it can be related to a paleo earthquake event with a magnitude of MS ​> ​5. The U-series ages obtained from the banded travertine deposits perturbed by the earthquakes are in the range of 130.59–112.94 ka, indicating an important fault-assisted neotectonic activity that occurred during the Middle–Late Pleistocene. Analysis of such structures, in combination with the use of U-series dating methods, can yield a reliable timing of neotectonic activity and provide new evidence for understanding the seismotectonic setting of the Litang area.