Water-escape Structures Research Articles

Deformation structures as key hints for interpretation of ice sheet dynamics - A case study from northeastern Estonia

Late Pleistocene glaciolacustrine sediments in the northern part of Estonia show a wide spectrum of ductile and brittle deformation structures like: (1) injection structures, dish structures, load casts, pseudonodules, ball-and-pillow structures, flame structures and fragments of broken-up sandy laminae all occurring in three internally deformed layers separated by undeformed layers, (2) large-scale upright gentle folds of outcrop size, (3) faults and fractures, and (4) water-escape structures (hydrofractures). We investigate the potential trigger mechanisms for the development of these deformation structures, their relationship in space and time as well as the lithological and geometrical features of soft-sediment deformation structures necessary to recognise deformation mechanisms. Based on comprehensive geological and numerical investigations, we link their origin to two major processes: (1) glacial rebound of Earth's crust causing earthquakes and (2) proglacial and submarginal glaciotectonic processes related to local oscillation of the ice-sheet front. We suggest criteria which allow us to recognise these two trigger mechanisms and propose a new proxy for reconstructing glacigenic processes and environments based on recognised soft-sediment deformation structures and their interrelationships. Our findings also highlight the significance of water saturation levels in glacigenic sediments and their impact on deformation processes. Furthermore, we introduce new types of water-escape structures that develop in proglacial marginal and/or submarginal settings. Our results contribute to a more nuanced interpretation of glacial activity and environmental conditions during the Late Pleistocene period in the study area.

Опыт определения копромаркеров в отложениях археологических памятников (по материалам стоянки Сельунгур, Южный Кыргызстан)

Introduction. The article discusses the results of a study of ash layers from Holocene deposits at the Selungur (Surungur) Cave. Goals. So, the work attempts a practical evaluation of a method of identifying coprostanols in archaeological sediments. The investigation of Holocene deposits of the site was carried out in 2018 and 2021 field seasons. The study identifies a total of 7 Holocene layers that represent the typical ‘fumier’ facies of cave and rock shelter deposits connected to pastoralism and animal husbandry practices, and built up of stratified layers of burnt herbivore dung. The sequence contains a record of multiple earthquakes that disturbed the sediments and effected in water escape structures, plastic deformations, and faults. Nevertheless, the stratigraphy remains easily readable. Unfortunately, archaeological and paleofaunistic materials were never found but a series of ash-containing interlayers suggests that the cave was repeatedly visited by ancient humans. Materials. In the ash deposits, our micro charcoal analysis has identified areas of concentration of burnt dungs which was used for fire. Series of samples were taken throughout the section of Holocene deposits for gas mass spectrometry analysis. The research efforts have also included the analysis of modern dung from herbivores inhabiting the area, such as cows, sheep, goats, horses and donkeys, for the latter obtained data to serve as a reference collection. Results. Unfortunately, layer 7 of the Selungur Cave proved characterized by poor preservation of fire products, while layers 6–1 yielded somewhat rich data. The obtained results make it possible to identify coprosterols and determine that equine dung was used in layers 6-2 as a fuel, and goat dung — in the first layer. The most widespread distribution of equines in this region occurred during the existence of Dayuan (Parkan) state, in the third century BC and later in the Middle Ages. Most likely, during these periods the mountain corridor comprising the Selungur Cave could have been used as a pass of the Silk Road that connected the Fergana and Alay valleys. The accumulation of the upper layer, in our opinion, is associated with the modern era.

Aspidella and water escape structures from the ca 850 Ma (Tonian) Heavitree Formation, Amadeus Basin, Central Australia

The mid-Tonian-aged Heavitree Formation, the basal unit of the Amadeus Basin succession, has long been believed to be devoid of metazoan fossils. Since a recent review of isolated occurrences of purported metazoan traces and remains within the formation’s upper unit, however, that conclusion has been questioned and led to the identification of new fossil remains, including imprints of Aspidella reported herein. Previously, organic-looking structures encountered in rocks older than mid-Ediacaran (ca 580 Ma) were commonly interpreted as originating inorganically, primarily through water escape, but a recently examined outcrop of the upper unit of the Heavitree Formation revealed a variety of water escape structures in association with, but structurally distinct from, a suite of organic impressions.

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.

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.

Uplifting mountains and shaking deserts: volcano-tectonic earthquakes revealed by soft-sediment-deformation structures in Upper Cretaceous aeolian deposits

ABSTRACT During the last stages of Gondwana fragmentation, large regions of the newly formed South American continent were covered by extensive deserts. Some parts of this continental landmass were synchronously affected by pronounced tectonism and magmatism, which were responsible for reshaping the regional topography. In this context, the southwestern part of the Sanfranciscana Basin in central Brazil is a key area for understanding this particular period in the geodynamic evolution of the South American continent. Aeolian deposits of the Posse Formation in the basin occur in direct association with volcanic rocks of the Upper Cretaceous Mata da Corda Group. Here, we report evidence of synsedimentary magmatism in direct association with soft-sediment-deformation structures, including flame structures, load casts and pseudonodules, water-escape structures, convolute lamination, faults, breccias, and clastic dikes, developed exclusively in aeolian sandstone and siltstone facies. The deformation features are interpreted as indicative of liquefaction, fluidization, and brittle behavior of the loose to partially lithified, wet sandy–silty sediments. The Late Cretaceous aeolian sedimentation is contemporaneous with the uplift of the Paranaíba High and associated magmatism in the Minas–Goiás Alkaline Province. In this context, these significant volcano-tectonic activities are considered to have triggered ductile to brittle deformation in the reported aeolian deposits.

Sedimentology of the Ediacaran barite‐bearing cap dolostone from Gaolan, northern Three Gorges, South China

AbstractWhile Ediacaran cap dolostones research is a hot topic, detailed sedimentological analysis of barite‐bearing cap dolostones remains scarce. Here, new data are presented from Xiangerwan in northern Three Gorges, South China, to illustrate the sedimentary characteristics, depositional environment and formation mechanism of the barite‐bearing cap dolostone. In ascending order, the succession is divided into: (i) pebbly dolostone; (ii) dolostone with unusual sedimentary structures (for example, sheet cracks and tepee structures); and (iii) barite‐bearing facies. The gravels of the pebbly dolostone record the slow relative sea‐level rise during post‐glacial transgression, with a local terrestrial influence. Sheet cracks and tepee structures represent water escape structures in the supratidal and upper intertidal zone, and gently wavy stromatolites in barite‐bearing facies are deposits typical of the upper intertidal zone. In addition, primary radial length‐slow dolomite cements were originally precipitated at the seafloor. In general, the cap dolostone was formed in a shallow‐water ramp environment. The form and sedimentary characteristics of barites indicate a primary (syngenetic) origin and help to divide the barites into bladed (Type I) and needle‐like (Type II) variants. With the ongoing melting of the Marinoan glacier and water density stratification, the cap dolostone was gradually precipitated, accompanied by exotic gravels input. The stratification persisted, and special sedimentary structures were widely developed. Phosphorus and barium ions were brought up from the deep basin by upwelling, indicated by the flourishing stromatolites and barite fan deposition. Above the sediment–water interface, the Type I barite first grew upward from substrates, then the Type II barite could grow either in the reverse ‘V‐shape’ cavities between and within the Type I barite clusters, forming rhythm layers with bedded dolomite, or scattered in the laminae of stromatolites or surrounding dolomite. Finally, the formation of barite fans indicates the end of cap dolostone deposition and deeper water sedimentation.

Event- and biostratigraphic evidence for two independent Ries and Steinheim asteroid impacts in the Middle Miocene

For decades, the Nördlinger Ries and Steinheim Basin in southern Germany have been regarded as a textbook example of a terrestrial impact crater doublet, although the oldest crater lake deposits in both craters suggest a biostratigraphic age difference of ~ 0.5 to 1 Myr. We previously presented stratigraphic arguments that challenged the double impact scenario and favoured a model of two temporally independent impact events in the Mid-Miocene. We here present, for the first time, four localities within a distance of ~ 50–100 km from the Ries and ~ 50–70 km from the Steinheim crater that expose two independent seismite horizons, together unique within the Upper Freshwater Molasse of the North Alpine Foreland Basin, each one featuring impressive water escape structures. The seismite horizons are separated by ~ 10 to 15 m of undisturbed Molasse deposits and, biostratigraphically, by an entire European Land Mammal Zone, thus providing evidence for two independent major seismic events within a time span of ~ 0.5–1 Myr. Both the lower and the upper seismite horizons can be correlated litho- and biostratigraphically with the basal crater lake sediments at the Ries and Steinheim craters, respectively, deposited immediately after the impacts. From a biostratigraphic point of view, the impact event that formed the Steinheim Basin probably occured around 14 Ma, some 0.8 Myr after the ~ 14.81 Ma Ries impact event.

Soft-sediment deformation structures recognised in a reverse-drag associated with normal faulting (Lake Ifrah, Northwest Africa): Palaeoseismic assessment and neotectonic implications

Reverse-drags in extensional settings are emblematic structures that may provide imprints of (neo)tectonic pulses, and even evidence of palaeoseismic activity. The direct pieces of evidence of (neo)tectonic activity therein are mostly reported to be subsidiary grabens, synthetic and antithetic normal faults, and/or bed-parallel slips that brittlely deform newly deposited soft-sediments, therefor being classified as soft-sediment deformation structures (SSDSs). Liquidization-induced SSDSs are, reasonably, likely to occur in such tectonically active settings as well. Nonetheless, both SSDSs types have not gained enough interest from structural geologist and sedimentologist communities. We hereby address this gap by investigating brittle and liquidization-induced SSDSs from late Pleistocene-Holocene fluvio-lacustrine beds (Lake Ifrah, northern Morocco). Sedimentation and deformation occur upon a reverse-drag anticline connected to a master normal fault that borders a half-graben structure (Ifrah sub-basin) superimposed on a master basin (Ifrah Basin), itself connected to a major strike-slip fault (the Tizi n'Tretten Fault, TTF). Liquidization-induced SSDSs involve load structures and water-escape structures, whereas brittle deformations encompass shrinkage cracks, subsidiary grabens, neptunian dykes, and bed-parallel slip (BPS) and associated domino-style faults. The deformation mechanism for both SSDS types involves either loss of strength upon liquidization (load structures and water-escape structures) or an increase in applied (internal or external) shear (shrinkage cracks, faults). Facies analysis and conventional trigger assessment allowed deciphering endogenic from exogenic triggers for deformation. Liquidization has been inferred to be seismic-triggered whereby the deformed beds are considered seismites. While BPS deformed brittlely late Pleistocene deposits (probably Marine Isotope Stage 3, MIS-3) and subsidiary grabens and neptunian dykes involve Middle Holocene sediments, they are considered to be linked to two flexural-slip events of the reverse-drag during MIS-3? and the Middle Holocene, respectively.Scaling relationships between the structural entities of the hanging-wall-master fault-footwall system allowed estimation of the subsidence due to hanging-wall collapses, and thereby the initiation of the Ifrah sub-basin (at least since 260 kyr). The rhomboidal-shaped master basin was suggested to belong to a dilational quadrant of the associated strike-slip fault, the TTF, at a tip-damage region. Accordingly, we highlight structural isolation of a segment of the TTF that is synchronous with the Ifrah Basin initiation.

Soft sediment deformation features in Dauki Fault region: evidence of paleoearthquakes, Shillong Plateau, NE India

The northeastern region (NER) of India has several complex regional geological structures, out of which the Dauki fault (DF) is a prominent one. The E–W trending reverse DF, which is inferred to go through the southern margin of Shillong Plateau (SP), has played major role in the regional deformation of the adjoining areas and was believed to be active during the Late Quaternary time. Previous paleoseismological studies conducted on the eastern and western part of the DF, Bangladesh, revealed that the fault ruptured in AD 849–920 and AD 1548, respectively. However, there were no studies on the DF from southern side of the SP, India. For the first time, from Indian side, soft sediment deformation structures (SSDS) are reported from five trenches in and around the DF zone, SP. Close to the Dauki village, five trenches in the eastern part of the DF, SP, show micro faulting, sand dykes, disturbed strata, and water escape structures. The detailed investigation of SSDS indicates that the origin of deformation is seismic trigger. The 14C AMS dating of deformation structures generated by earthquakes suggests three seismic events occurred between 130 and 920 year BP, 5415 to 9140 year BP, and at about 4285 year BP. This study confirms that DF is indeed active, at least, since the mid-Holocene. More trenching and dating of seismically induced deformation features are needed to accurately calculate the recurrence interval of significant earthquakes that can strike the fast-expanding urban areas in India and Bangladesh.

Evidence for Upper Cretaceous seismites in the Abu Tartur area, Western Desert, Egypt

Upper Cretaceous tidal-flat sediments of the Abu Tartur region, Western Desert of Egypt, contain a variety of soft-sediment deformation structures (SSDSs) in the Mut Member of the Quseir Formation and the overlying Duwi Formation. Here, we document recognition of a set of SSDSs characterized by complex morphology and large size. The SSDS include: 1) water-escape structures, 2) minor recumbent, chevron, and slump folds, 3) syn-sedimentary minor faults, 4) neptunian dykes, 5) regular ball-and-pillow structures, flattened pseudo-nodules, and load casts, 6) syn-sedimentary undulations, 7) fractures and joints, 8) sand injectites, and 9) autoclastic breccia and brecciated siderite clasts. The dimensions of the SSDSs range from a few centimeters to several decimeters. Both extensional and contractional forces appear to have been involved in development of these structures. A detailed analysis of facies relationships, combined with consistent orientations of SSDSs and the regional tectonics of the target area suggests earthquakes as the triggering mechanism for sediment deformation and large-scale mass failure. The deformed strata are consistent with most of the well-known criteria of typical seismites. Thus, syn-sedimentary liquefaction was identified as the primary driving force in most of the observed deformation horizons for these Upper Cretaceous SSDSs in the Abu Tartur area.

Soft-sediment deformation structures in a lacustrine depositional context: An example from the Eocene Dongying Depression in the Bohai Bay Basin, East China

The study documents soft-sediment deformation structures (SSDSs) in the lacustrine Dongying Depression, a Paleogene synrift basin located in the southeastern corner of the Bohai Bay Basin, East China. The focus of this study is the lower part of the upper 4th member of the Eocene Shahejie Formation (Es4U), characterized by littoral to sublittoral deposits in the southwestern Dongying Depression. Nine lithofacies are grouped into the upper shoreface facies associations (FA1-1), lower shoreface facies associations (FA1-2), and sublittoral facies associations (FA2). Fine-grained calcareous sandstone was mainly deposited in FA1-1, with thinly alternating calcareous mudstone and siltstone or sandstone in FA1-2, while deposition in FA2 was dominated by mudstone, containing sediment gravity flow deposits. The SSDSs widely encountered in the lower Es4U can be classified into seven categories: (1) load structures, (2) water-escape structures, (3) folds and convolute lamination, (4) sediment-injection structures, (5) microfaults, (6) autoclastic breccias, and (7) slumps. Detailed observations of SSDSs from cores indicate liquefaction and fluidization as the main deformation mechanisms in the sands and muds. Moreover, rupturing of cohesive deposits also contributes to the soft-sediment deformation. The types and morphologies of the SSDSs are closely related to the rheologies of the sediments (e.g., the sand content), influenced by the facies that determine the lithologies and stratigraphic stacking patterns. Except for some deformation structures related to subaqueous sediment gravity flows (e.g., muddy debrite flows and slumps), most SSDSs are ascribed to rift-related seismicity due to the activity of the adjacent synsedimentary faults when the Dongying Depression underwent quick subsidence during the Eocene.

Aseismic and seismic impact on development of soft-sediment deformation structures in deep-marine sand-shaly Crocker fan in Sabah, NW Borneo

Soft-sediment deformation structures are present within the deep-marine fan of the West Crocker Formation, Sabah Basin, NW Borneo. Focus of this study is to highlight the impact of seismic and aseismic activities on the development of these structures and their distribution in deep-marine fan. Twenty-nine types of deformation structures were identified during the study of twelve exposed sections. These structures were grouped into five categories: i) water-escape structures, ii) sole marks, iii) clastic intrusions, iv) deformed laminations, and v) syn-depositional brittle and ductile deformation structures. The sediment deformation is interpreted to be caused either by aseismic processes like slope failure, gravity collapse, sediment overloading, density gradient, seismic induced mechanisms such as earthquakes, tectonic uplift, or combined effect of seismic and aseismic events. These structures are classified based on type of features developed during semi-consolidated phase of rock deposition. The seismite structures i.e., clastic intrusions, deformed laminations, and syn-depositional structures are correlated with active collisional tectonics during the Late Paleogene times in the Sabah Basin. In the present work, a generalized conceptual model has also been proposed for the development of soft-sediment deformation structures in a submarine fan environment. Dewatering structurers and rapid sedimentation features are associated with inner fan, load and flame structures are present within middle fan, while contorted layers, slumps and mass-transport deposits are linked with distal fan settings.

Badenian (middle Miocene) continental paleoenvironment in the Novohrad–Nógrád Basin (Central Paratethys): a volcano-sedimentary record from the Páris-patak Valley in Hungary

Two levels of volcaniclastics, comprising conglomerates, sandstones and mudstones, are interbedded with upper middle Miocene (upper Badenian) andesite pyroclastics near the Hungarian-Slovakian border in the distal region of the Central Slovakian Neogene Volcanic Field. Based on the field sedimentological investigations, the facies of the volcaniclastics (e.g., lateral and vertical grain size changes, sedimentary structures, textures, clast composition), their geometry and field relationships are documented herein with the aim of reconstructing the depositional environment. The silica-cemented volcaniclastics are mostly andesite clasts with only ~ 5% being granitoid, quarzitic, and tuff clasts as well as charred fossil wood fragments. The coarse-grained facies association includes crudely stratified, tabular or lenticular, clast-supported pebble-cobble conglomerates with erosive basal surfaces, b-axis imbrication, alternating with sets of cross-bedding. The fine-grained facies association comprises cross-bedded pebbly to medium-grained sandstone and lenses of tuffaceous clayey siltstone with rare horizontal lamination and water-escape structures. Rip-up mudstone clasts, with diametre up to 1 m, are present in both facies associations, revealing the co-existence of abandoned silty palaeo-channel plugs. Facies associations are arranged in several 0.5-4-m-thick, fining-upwards successions that likely formed in shallow channels as downstream- to laterally accreting longitudinal bars, extensive gravel sheets and bars that migrated in peak flow during floods. Palaeocurrent indicators (i.e., clast imbrication, direction of planar cross-bedding, orientation of petrified wood logs) show bedload transport by traction currents, initially towards ~S, and later towards ~W. Intermittently debris flows also occurred. Cross-bedded sandstones formed as in-channel transverse bars during medium/low discharge. Variation of grain size shows frequent discharge fluctuations during permanently wet conditions in the late Badenian. The 4-5-m-deep, low-sinuosity channels were part of a high-energy, gravel-bed braided-river system on the south-eastern foothills of the Lysec palaeo-volcano. Here, pyroclastics were reworked and redeposited as volcaniclastics during inter-eruption, high-discharge episodes.

Gravity flows: Types, definitions, origins, identification markers, and problems

Abstract This review covers 135 years of research on gravity flows since the first reporting of density plumes in the Lake Geneva, Switzerland, by Forel (1885). Six basic types of gravity flows have been identified in subaerial and suaqueous environments. They are: (1) hyperpycnal flows, (2) turbidity currents, (3) debris flows, (4) liquefied/fluidized flows, (5) grain flows, and (6) thermohaline contour currents. The first five types are flows in which the density is caused by sediment in the flow, whereas in the sixth type, the density is caused by variations in temperature and salinity. Although all six types originate initially as downslope gravity flows, only the first five types are truly downslope processes, whereas the sixth type eventually becomes an alongslope process. (1) Hyperpycnal flows are triggered by river floods in which density of incoming river water is greater than the basin water. These flows are confined to proximity of the shoreline. They transport mud, and they do not transport sand into the deep sea. There are no sedimentological criteria yet to identify hyperpycnites in the ancient sedimentary record. (2) A turbidity current is a sediment-gravity flow with Newtonian rheology and turbulent state in which sediment is supported by flow turbulence and from which deposition occurs through suspension settling. Typical turbidity currents can function as truly turbulent suspensions only when their sediment concentration by volume is below 9% or C < 9%. This requirement firmly excludes the existence of 'high-density turbidity currents'. Turbidites are recognized by their distinct normal grading in deep-water deposits. (3) A debris flow (C: 25-100%) is a sediment-gravity flow with plastic rheology and laminar state from which deposition occurs through freezing en masse. The terms debris flow and mass flow are used interchangeably. General characteristics of muddy and sandy debrites are floating clasts, planar clast fabric, inverse grading, etc. Most sandy deep-water deposits are sandy debrites and they comprise important petroleum reservoirs worldwide. (4) A liquefied/fluidized low (>25%) is a sediment-gravity flow in which sediment is supported by upward-moving intergranular fluid. They are commonly triggered by seismicity. Water-escape structures, dish and pillar structures, and SSDS are common. (5) A grain flow (C: 50-100%) is a sediment-gravity flow in which grains are supported by dispersive pressure caused by grain collision. These flows are common on the slip face of aeolian dunes. Massive sand and inverse grading are potential identification markers. (6) Thermohaline contour currents originate in the Antarctic region due to shelf freezing and the related increase in the density of cold saline (i.e., thermohaline) water. Although they begin their journey as downslope gravity flows, they eventually flow alongslope as contour currents. Hybridites are deposits that result from intersection of downslope gravity flows and alongslope contour currents. Hybridites mimic the "Bouma Sequence" with traction structures (Tb and Tc). Facies models of hyperpycnites, turbidites, and contourites are obsolete. Of the six types of density flows, hyperpycnal flows and their deposits are the least understood.

Glacial origin of the Cryogenian Nantuo Formation in eastern Shennongjia area (South China): Implications for macroalgal survival

The Cryogenian Period was characterized by global glaciations, imposing extreme environmental stresses on early multicellular organisms. Globally distributed diamictite deposits are the major evidence for these glaciation events, but the glacial origin of at least some of these diamictite deposits has been disputed, complicating interpretations of the environmental conditions influencing the evolution of life in the Cryogenian (~720–635 Ma). In this study, we conducted a systematic sedimentological investigation of the Marinoan-age (~650–635 Ma) Nantuo Formation in six sections representing a ~20-km-long, east–west transect in the eastern Shennongjia area of South China. The Nantuo Formation, which ranges in thickness from ~2 m in the east to ~300 m in the west, comprises diamictite, conglomerate, lonestone-bearing sandstone, green siltstone, and black shale facies. The eastern sections (e.g., Longxi and Wushanhu) consist mainly of diamictite facies exhibiting micro-scaled rotation structures, microshear, grain stacking, grain-to-grain contacts and water-escape structures, supporting their deposition in a subglacial setting. In contrast, the western sections (Shijiahe, Liziping and Songluo) consist of massive and graded diamictite and conglomerate facies, consistent with an origin as glacially induced submarine debris flows. Furthermore, the lonestone-bearing sandstone facies in these sections contain abundant dropstones and mud pellets within finely-laminated turbidites, indicating an ice-rafted origin with locally reworking by turbidity currents. The green siltstone and black shale facies lack glacigenic features and may represent late deglacial deposits. Based on thickness and facies variations among the study sections, we infer that the Nantuo Formation records glacial sedimentation on a complex paleotopographic surface that was incised into the underlying bedrock, with subglacial deposits to the east transitioning into glaciomarine deposits to the west of study area. The distal Songluo section likely records three cycles of glacial advance and retreat in the form of a facies alternation between diamictite and black shale, consistent with a dynamically fluctuating ice margin. In summary, our sedimentological investigation supports a glacial origin for the Nantuo Formation in the eastern Shennongjia area. The occurrence of the benthic macroalgal-dominated Songluo Biota in the black shale facies at Songluo suggests that strong glacial retreats provided niches for macroalgal survival in the Cryogenian glacial ocean.

Soft-sediment deformation structures in cave deposits and their possible causes (Kalacka Cave, Tatra Mts., Poland)

Clastic deposits in Kalacka Cave in the Tatra Mts. Show soft-sediment deformation structures (SSDS) rare for a cave environments. The poorly sorted allochthonous sediments were deposited within a cave sump under a fluvial regime, likely due to glacially initiated back-flooding during the Last Glacial. The structures include small-scale faults (normal and reverse), folds (upright symmetric anticlines, low-amplitude open folds, W-vergent folds and fault-propagation folds), and water-escape structures. A laboratory experiment is used to assess the possibile liquefaction of a thin soft-sediment filling in a limestone tube, including calculation of the site effects of resonance frequency and amplification coefficient and the site vulnerability index Kg. The calculations indicate that seismic waves can be amplified up to 10 times and the expected resonance frequency is ~17.05 Hz.We argue that the observed SSDS formed in two stages. First, brittle and ductile deformation structures developed due to gravity-induced slumping. Next, liquefaction produced water-escape structures. The studied SSDS were likely seismically triggered. Favorable conditions occurred during the withdrawal of the last glacier (MIS 2) when the sediments were oversaturated and the Tatra Mts. experienced a strong earthquake (M7.0). Alternatively, high-frequency microearthquakes could have been triggered by slope failure cutting into Kalacka Cave.

Large soft-sediment deformation structures (SSDS) in the Permian Barren Measures Formation, Pranhita-Godavari Valley, India: potential link to syn-rift palaeoearthquake events

Records of palaeoearthquakes in sedimentary rocks are often debated due to the potential confusion in distinguishing seismic versus aseismic trigger mechanisms causing liquefaction. The present paper documents some unique soft-sediment deformation structures (SSDS), characterized by their extremely large size, complex morphology and preservation in coarse-grained pebbly sandstone. The SSDS are present in the Permian Barren Measures Formation, a syn-rift depositional unit within the Lower Gondwana succession in the Pranhita-Godavari Valley, eastern Peninsular India. The ~ 210 m thick succession is represented by stacked fining-up retrogradational cycles, characterized by coarse-grained trough cross-stratified pebbly sandstones near the base and fine-grained heterolithic sandstones–mudstones at the top. Each cycle signifies a change from fluvial- to tidal-influenced depositional systems. Coarse-grained pebbly sandstone beds near the base of each cycle record most SSDS, including complexly deformed layers, pseudonodules, load and flame structures, various water-escape structures like vertical/inclined sediment columns (sedimentary dykes) and contorted beds, and syn-sedimentary faults. The deformed beds are underlain and overlain by the undeformed beds. Complexly deformed SSDS are often sharply truncated at the top by undeformed beds manifesting syn-sedimentary character, which signifies that deformation took place just after deposition of the affected beds, but before deposition of the overlying beds while sedimentation was continuous. Facies analysis reveals the absence of processes like storms/pounding waves, slumps, rapid dumping (massive beds), impact shaking, volcanisms, tsunami waves or sediment gravity flows in the study area, thus negating their possibility as triggering agents for the liquefaction. The complex nature and large size of the deformation structures imply extensive liquefaction near the sediment–water interface. In addition, the deformed beds comply with most of the criteria of typical seismites. In half-graben type Gondwana basins, such seismites can be linked to palaeoearthquakes, which signify the phases of syn-rift fault reactivation, basinal sagging and associated accommodation changes.

Liquefaction structures induced by the M5.7 earthquake on May 28, 2018 in Songyuan, Jilin Province, NE China and research implication

An earthquake of magnitude M5.7 occurred in Yamutu village, Songyuan City, Jilin Province, NE China (45°16′12″N/124°42′35″E) on May 28, 2018, with a focal depth of 13 km. The epicenter is located at the intersection of the Fuyu/Songyuan-Zhaodong Fault, Second Songhua River Fault and Fuyu North Fault which lies northwest of Tancheng-Lujiang Fault (Tan-Lu Fault). The earthquake-induced widespread liquefaction structures and ground surface fissures within 3 km from the epicenter, caused serious disasters to the local surroundings. The visible liquefied structures include sand volcanoes, liquefied sand mounds, sand dikes and sand sills. Sand volcanoes can be divided into sand volcano with a crater, sand volcano without a crater and water volcano (no sand). Other soft-sediment deformation structures (SSDS) induced by the earthquake include deformation lamination, load and flame structures, deformation folds, dish structures, convolute bedding and water-escape structures. The formation process of the sand volcanoes comprises three stages: (1) building up excess pore-fluid pressure in the liquefied layer, (2) cracking of the low-permeable overlying layer, and (3) mixture of sand-water venting out of the ground surface. During the upward movement, the liquefied sand is injected into the low-permeable layer to form sand veins, sand sills and various types of deformation structures. Vertical distribution of seismic liquefaction structure can be divided into four zones: the thoroughly liquefied zone, the lower liquefied zone with SSDS, the upper liquefied zone with SSDS, and the ground surface liquefied zone. The liquefaction occurred at a burial depth of 2–5 m, and the thickness of liquefied sand is 2 m. NE-SW (35°–215°) trending compressive stress is possibly the seismogenic trigger of the Songyuan M5.7 earthquake that caused the fault (Fuyu/Songyuan-Zhaodong Fault) to reactivate. The study of the Songyuan seismic liquefaction structures gives insight into the prediction of modern earthquakes and disaster-prone areas. Meanwhile it provides abundant basic material for studying earthquake-induced SSDS in both ancient and modern sediments. The research is obviously of great significance to reveal that the northern Tan-Lu Fault has entered a stage of active seismic activity since the twenty-first century.

Soft-sediment deformation: deep-water slope deposits of a back-arc basin (middle Eocene-Oligocene Kırkgeçit Formation, Elazığ Basin), Eastern Turkey

The Kirkgecit Formation (middle Eocene-Oligocene) is exposed in an approximately E-W direction around the city of Elazig, eastern Turkey. This unit represents marly and sandy deep-marine sediments deposited in a slope setting with channels and contain soft-sediment deformation structures (SSDSs). These SSDSs include slump folds, chaotic strata, load casts, flame structures, convolute laminations, clastic dykes, water-escape structures and syn-sedimentary faults. The main underlying deformation processes are liquefaction, fluidization and gravity-induced loading. Some of the SSDS could be interpreted as seismites, which originated due to earthquakes that also triggered high-density mass flows. This interpretation is consistent with the active tectonics in the Elazig back-arc basin. The SSDS in the study area are compared with SSDS in other regions, as well as with SSDS in other marine deposits. In this way, findings obtained from the study area are compared with SSDS at different locations in the marine Kirkgecit Formation around Elazig and with similar structures developed in marine settings worldwide, such as SE Crete and NW Africa.