With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at ...With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity;however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.展开更多
This study identified soft-sediment deformation structures (SSDS) of seismic origin from lacustrine sediments in the late Quaternary paleo-dammed lake at Tashkorgan, northeastern Pamir. The observed deformation stru...This study identified soft-sediment deformation structures (SSDS) of seismic origin from lacustrine sediments in the late Quaternary paleo-dammed lake at Tashkorgan, northeastern Pamir. The observed deformation structures include sand dykes, liquefied diapir and convolute structures, gravity induced SSDS, and thixotropic pillar and tabular structures. We conducted a preliminary study on the morphology, formation and trigger mechanisms of pillar and tabular structures formed by liquefaction of underlying coarse sand and thixotropy of the upper silty clay. The regional tectonic setting and distribution of lacustrine strata indicate that the most probable trigger for the SSDS in lacustrine sediments was seismic activity, with an approximate earthquake magnitude of M〉6.0; the potential seismogenic fault is the southern part of the Kongur normal fault extensional system. AMS ^4C dating results indicate that the SSDS were formed by seismic events occurring between 26050±100 yrBP and 22710±80 yrBP, implying intense fault activity in this region during the late Pleistocene. This study provides new evidence for understanding tectonic activity and regional geodynamics in western China.展开更多
Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, ...Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, such as convoluted bedding, liquefied sand veins, load and flame structures, slump structures and sliding-overlapping structures. Based on their genesis, soft-sediment deformation structures can be classified as three types: seismic induced structures, vertical loading structures, and horizontal shear structures. Based on their geometry and genesis analysis, they are seismic-induced structures. According to the characteristics of convoluted bedding structures and liquefied sand veins, it can be inferred that there were earthquakes greater than magnitude 6 in the study area during the middle Jurassic. Furthermore, the study of the slump structures and sliding- overlapping structures indicates that there was a southeastern slope during the middle Jurassic. Since the distance from the study area to the Altyn Mountain and the Altyn fault is no more than 10km, it can be also inferred that the Altyn Mountain existed then and that the AItyn strike-slip fault was active during the middle Jurassic.展开更多
Soft-sediment deformation structures are abundant in the Cambrian Zhushadong and Mantou formations of the Dengfeng area, Henan Province, China. Soft-sediment deformation structures of the Zhushadong Formation consist ...Soft-sediment deformation structures are abundant in the Cambrian Zhushadong and Mantou formations of the Dengfeng area, Henan Province, China. Soft-sediment deformation structures of the Zhushadong Formation consist of fluidized deformation, synsedimentary faults, seismo-folds and plastic deformation; the Mantou Formation is dominated by small-scale horst faults, intruded dikes, fluidized veins, and seismo-cracks. These structures are demonstrated to be earthquake-related by analysis of trigger mechanisms, and may indicate the activity of the Qinling tectonic belt during the early Cambrian. Furthermore, the assemblages of soft-sediment deformation structures altered with time: large-scale, intense deformation in the Zhushadong Formation alters to small-scale, weak deformation in the Mantou Formation. This striking feature may have been caused by changes in hypocentral depth from deep-focus to shallow-focus earthquakes, indicating that the Qinling tectonic belt developed from the subduction of the Shangdan Ocean to the extension of the Erlangping back-arc basin. This study suggests that soft-sediment deformation structures can be used to reveal the activity of a tectonic belt, and, more importantly, changes in deformation assemblages can track the evolution of a tectonic belt.展开更多
Detailed fieldwork carried out in the southern part of Bida Basin, Nigeria, allowed the documentation of soft sediment deformation structures (SSDS) in the Maastrichtian Patti Formation. The aim of this study is to ex...Detailed fieldwork carried out in the southern part of Bida Basin, Nigeria, allowed the documentation of soft sediment deformation structures (SSDS) in the Maastrichtian Patti Formation. The aim of this study is to examine the sedimentary successions, describe and analyse these deformation features, discuss their deformation mechanisms and potential triggers. The Maastrichtian Patti Formation is composed of lithofacies interpreted to have been deposited in tidal and fluvial sedimentary environments. Soft sediment deformation structures recognised in the tidal sediments were clastic dykes, load cast, isolated sand balls, dish-and-pillar structures, convolute lamination, diapiric structures and recumbent folds. Severely deformed cross beds, ring structures, associated sand balls, normal folds and recumbent folds were identified in the fluvial sediments. SSDS recognised were interpreted to have been caused by effects of liquefaction and fluidization. Field observations, facies analysis and morphology of the SSDS indicate that there are relationship between the depositional environments and SSDS. Endogenic processes are considered as the trigger agents and they are represented by rapid sedimentation and overloading, impact of breaking waves, pressure fluctuations caused by turbulent water flow, cyclic stress and current generated by storm waves and changes in water table. The present study did not identify exogenic processes as trigger agent. The occurrence of SSDS in southern Bida Basin strongly favoured a non-tectonic origin but a clear relationship high energy processes in tidal and fluvial depositional environments.展开更多
The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolu...The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic (or Mesoproterozoic as proposed by some researches), while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite (microcrystalline limestone) of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension (and/or layer-perpendicular flattening) of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.展开更多
Soft-sediment deformation structures(SSDS)have been the focus of attention for over 150 years.Existing unconstrained definitions allow one to classify a wide range of features under the umbrella phrase"SSDS".As a ...Soft-sediment deformation structures(SSDS)have been the focus of attention for over 150 years.Existing unconstrained definitions allow one to classify a wide range of features under the umbrella phrase"SSDS".As a consequence,a plethora of at least 120 different types of SSDS(e.g.,convolute bedding,slump folds,load casts,dish-and-pillar structures,pockmarks,raindrop imprints,explosive sandegravel craters,clastic injections,crushed and deformed stromatolites,etc.)have been recognized in strata ranging in age from Paleoproterozoic to the present time.The two factors that control the origin of SSDS are prelithification deformation and liquidization.A sedimentological compendium of 140 case studies of SSDS worldwide,which include 30 case studies of scientific drilling at sea(DSDP/ODP/IODP),published during a period between 1863and 2017,has yielded at least 31 different origins.Earthquakes have remained the single most dominant cause of SSDS because of the prevailing"seismite"mindset.Selected advances on SSDS research are:(1)an experimental study that revealed a quantitative similarity between raindrop-impact cratering and asteroid-impact cratering;(2)IODP Expedition 308 in the Gulf of Mexico that documented extensive lateral extent(〉12 km)of mass-transport deposits(MTD)with SSDS that are unrelated to earthquakes;(3)contributions on documentation of pockmarks,on recognition of new structures,and on large-scale sediment deformation on Mars.Problems that hinder our understanding of SSDS still remain.They are:(1)vague definitions of the phrase"soft-sediment deformation";(2)complex factors that govern the origin of SSDS;(3)omission of vital empirical data in documenting vertical changes in facies using measured sedimentological logs;(4)difficulties in distinguishing depositional processes from tectonic events;(5)a model-driven interpretation of SSDS(i.e.,earthquake being the singular cause);(6)routine application of the genetic term"seismites"to the"SSDS",thus undermining the basic tenet of process sedimentology(i.e.,separation of interpretation from observation);(7)the absence of objective criteria to differentiate 21 triggering mechanisms of liquefaction and related SSDS;(8)application of the process concept"high-density turbidity currents",a process that has never been documented in modern oceans;(9)application of the process concept"sediment creep"with a velocity connotation that cannot be inferred from the ancient record;(10)classification of pockmarks,which are hollow spaces(i.e.,without sediments)as SSDS,with their problematic origins by fluid expulsion,sediment degassing,fish activity,etc.;(11)application of the Earth's climate-change model;and most importantly,(12)an arbitrary distinction between depositional process and sediment deformation.Despite a profusion of literature on SSDS,our understanding of their origin remains muddled.A solution to the chronic SSDS problem is to utilize the robust core dataset from scientific drilling at sea(DSDP/ODP/IODP)with a constrained definition of SSDS.展开更多
During the past 30 years (1987-2016), a great progress has been made in researches of soft-sediment deformation structures (SSDS), seismites and pataeoearthquakes in China. However, the research thought of this ac...During the past 30 years (1987-2016), a great progress has been made in researches of soft-sediment deformation structures (SSDS), seismites and pataeoearthquakes in China. However, the research thought of this academic fietd is not open enough. It is atmost with one viewpoint or one voice, i.e., atmost art the papers pubtished in journals of China considered the layers with SSDS as seismites. On the other hand, the authors are very glad to learn that the professors and students of China University of Petroleum (East China) have proposed different academic viewpoints on the origin of SSDS in Lingshan Istand, Qingdao, Shandong Province, China. It is a very active academic atmosphere. The authors' ideas are as follows: (1) The SSDS are sedimentary structures with multi-origin. The term "SSDS" is a good sedimentary and geological term and shoutd be utilized continuat[y. (2) The term "seismites" is a term which is definitety assigned to the layers with SSDS induced by earthquakes. It is one type of the tayers with SSDS. It is not equal to SSDS. (3) Some geotogists suggested obsoleting the term "seismites". These suggestions are rational However, since the term "seismites" has been utilized for a long time in China and worldwide, to obsolete this term should be discussed and agreement should be acquired from numerous geologists in China and worldwide. It may be suitable that let the geological practice decide whether to obsolete it or not. (4) Hopefully, further progress will be made in the researches of SSDS.展开更多
The Mesoproterozoic Wumishan Formation, composed of dolomite is a widely distributed stratigraphic unit in the Beijing area. It was formed over a long period of time in the Yan-Liao aulacogen, a stable peritidal envir...The Mesoproterozoic Wumishan Formation, composed of dolomite is a widely distributed stratigraphic unit in the Beijing area. It was formed over a long period of time in the Yan-Liao aulacogen, a stable peritidal environment that was ideal for recording earthquakes in the form of soft-sediment deformation structures (SSDS). Numerous examples occur in the upper part of the Wumishan Formation, along the Yongding River Valley. In addition, brittle structures include intrastratal fault and seismically cracked breccias. The soft-sediment deformation structures include liquefied features (diapirs, clastic dykes, convolute bedding), compressional deformation features (accordion folds, plate-spine breccias, mound-and-sag structures), and extensional plastic features (loop-bedding). Based on the regional geological setting and previous research, movements along the main axial fault of the Yan-Liao aulacogen are considered as the triggers for earthquakes since the Early Mesoproterozoic. The number and distribution of the SSDS suggest the major earthquake frequency in the Wumishan Formation of 20 to 32 thousand years.展开更多
The study on soft-sediment deformation structures(SSDS) of Lingshan Island has been one of the hot topics of sedimentology researches in China in recent years,and SSDS developed in turbidite system in the Laiyang Grou...The study on soft-sediment deformation structures(SSDS) of Lingshan Island has been one of the hot topics of sedimentology researches in China in recent years,and SSDS developed in turbidite system in the Laiyang Group are widely known by domestic researchers.However,few studies were conducted on the SSDS in fan delta system in the Qingshan Group,Lingshan Island.This study analyzes the classification and characteristics of SSDS especially their lithofacies association and tithologic characteristics through field outcrops investigation and thin section analysis as well.A conclusion was acquired that the paleoenvironment was a fan delta system with occurrence of several volcanic eruptions,where the water became gradually shallower.The SSDS types in the Qingshan Group includes load and flame structure,ball and pillow structure,waterescape structure,hydroplastic deformation structure,plastic sandstone breccia structure,volcanic drop stone and V-shaped ground fissure mainly caused by volcanic earthquakes of three types:(1)seismic waves,(2)gravity and inertia effect of pyroclastic flows,(3)instant differential air pressure;which is different from slumping and tectonic earthquakes occurred in the Laiyang Group.In addition,with the lithofacies association analysis between pyroclastic flow and SSDS beds,a distribution model of SSDS related to volcanic earthquakes can be established:SSDS types changed gradually with their distance further away from the volcanic activity core.Brittle deformation which was common in the proximal zone disappeared gradually;liquefied and plastic SSDS continued to dominate in the medial zone;and slightly liquefied SSDS were developed in the distal zone.Meanwhile,the scale and size of SSDS is negatively correlated with the distance of SSDS depositional locations from the volcanic vent.展开更多
From the viewpoint of origins of soft-sediment deformation structures(SSDS), 7 papers(Ito et al.,2016; Jiang et al., 2016; Lunina and Gladkov, 2016; Moretti et al., 2016; Rana et al., 2016; Rodríguez-Pascua et...From the viewpoint of origins of soft-sediment deformation structures(SSDS), 7 papers(Ito et al.,2016; Jiang et al., 2016; Lunina and Gladkov, 2016; Moretti et al., 2016; Rana et al., 2016; Rodríguez-Pascua et al., 2016; Wheatley et al., 2016) selected from the special issue of "The environmental significance of softsediment deformation" of the Sedimentary Geology 344(2016) were reviewed.(1) The first paper(according to the published order) by Moretti et al. is a general review and introduction of this special issue. This special issue has made an important contribution to the study of sedimentary environments.(2) The fourth paper by Rodríguez-Pascua et al. is an excellent case study. All evidence of earthquake in this paper is reliable. The old Roman City(adjacent to Madrid, the capital of Spain) was definitely destroyed by an earthquake. This paper solved the problem that the archaeologists have not solved yet.(3) The 19 thpaper by Rana et al. is another excellent case study. It demonstrated that SSDS in the youngest modern sediments in the seismically active area, i.e., the Alaknanda Valley, Garhwal Himalaya, India, are of non-seismic origin, but with typically sedimentary origin. All evidence of sedimentary origin of SSDS in the study area is reliable.(4) The second paper by Lunina and Gladkov stated that SSDS(mainly clastic dikes) in epicentral areas of the recent earthquakes in southern Siberia were originated by earthquakes and that the clastic dikes are the most reliable indicators in the epicentral areas of earthquakes. This conclusion is right. However, it is not accurate to consider all clastic injections as "in-situ earthquake structures" in anywhere, because the clastic injections are with multiple origins.(5) The third paper by Wheatley et al. comprehensively stated the clastic pipes of the Jurassic in the Colorado Plateau, USA. However, the principal origin of the clastic pipes(columns) was possibly not originated by "palaeoseismic controls", but by "tectonic controls" or "tectonic uplifts".(6) The 10^(th) paper by Jiang et al.proposed that 6 types of SSDS of the Lixian Section in eastern Tibetan Plateau, i.e., in a tectonically and seismically active area, were originated by earthquakes. However, the evidence of seismic origin is not sufficient. Therefore, the origins of SSDS in the Lixian Section are worthy to be further discussed.(7) The"injectites" and "extrudites" in a Late Pliocene basin on the Boso Peninsula, Japan, from the 24^(th) paper by Ito et al., are non-SSDS and their origin is unreliable.The above viewpoints may be inappropriate. Criticisms and corrections are welcome.This paper is not only the author's brief review on 7 papers selected from the special issue of the Sedimentary Geology 344(2016), but also an invitation to geologists worldwide to write papers for a new special issue of "The origins of SSDS" of the Journal of Palaeogeography which is planned to be published in 2018.展开更多
A particular type of soft-sediment deformation structure, similar to imbricate structure, is developed in the Jurassic strata at Honggouzi, western Qaidam Basin, China. We refer to this structure as a duplex-like defo...A particular type of soft-sediment deformation structure, similar to imbricate structure, is developed in the Jurassic strata at Honggouzi, western Qaidam Basin, China. We refer to this structure as a duplex-like deformation structure, because it is inferred to have been formed by the action of fast-moving, submarine gravity current sediments gliding across a pre-existing semiconsolidated sedimentary layer. The layers of duplex-like structure crop out in the southeastern limb of the core of a medium-sized anticline. The average dip direction of the duplex-like structure is 301.2° and the average dip angle is 54.7°. Duplex-like deformed laminations are composed mainly of weakly metamorphosed, extremely poorly sorted, feldspathic lithic graywacke. Sericite can be observed along bedding planes. The duplex-like structure occurs within a sequence of river-channel fine conglomerate, interchannel carbonaceous mudstone(shale), shallow-water delta sand-shale, shallow-lake calcareous mudstone, olistostromes, and a turbidite. At the bottom of the sequence, we found brownish-red shallow-lake calcareous mudstone and carbonaceous mudstone and at the top olistostromes whose genesis is related to the slip and drag of a slumped body of submarine sediment. In combination with other symbiotic and associated structures, it is considered that the duplex-like structure was formed by the slumping and subsequent movement and traction of delta-front semiconsolidated sediments over the bottom sediments of a shore or shallow-lake sedimentary environment, probably triggered by an earthquake. The attitude of the duplex-like structure indicates that the direction of gliding was from NW301.2° toward SE121°, which is consistent with the current location of the Altun Mountains, indicating that the Altun Mountains existed in the Jurassic. The orogenesis of these mountains likely involved seismic activity, and an earthquake was the triggering factor in the formation of the duplex-like structure by causing the slumping/gliding of the olistostrome sediments.展开更多
基金supported by projects from the National Natural Science Foundation of China (41807298, 41702372, 41672211)the China Postdoctoral Science Foundation (2019M650788)+2 种基金National Key Research and Development Project of China (2016YFC0600310)the China Geological Survey (DD20160022, DD20190059)the Basic Research Funds (JYYWF201810) of the Institute of Geology, CAGS.
文摘With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity;however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.
基金financially supported by the National Natural Science Foundation of China (41702372)the Open Fund of State Key Laboratory of Earthquake Dynamics (LED2017B03)
文摘This study identified soft-sediment deformation structures (SSDS) of seismic origin from lacustrine sediments in the late Quaternary paleo-dammed lake at Tashkorgan, northeastern Pamir. The observed deformation structures include sand dykes, liquefied diapir and convolute structures, gravity induced SSDS, and thixotropic pillar and tabular structures. We conducted a preliminary study on the morphology, formation and trigger mechanisms of pillar and tabular structures formed by liquefaction of underlying coarse sand and thixotropy of the upper silty clay. The regional tectonic setting and distribution of lacustrine strata indicate that the most probable trigger for the SSDS in lacustrine sediments was seismic activity, with an approximate earthquake magnitude of M〉6.0; the potential seismogenic fault is the southern part of the Kongur normal fault extensional system. AMS ^4C dating results indicate that the SSDS were formed by seismic events occurring between 26050±100 yrBP and 22710±80 yrBP, implying intense fault activity in this region during the late Pleistocene. This study provides new evidence for understanding tectonic activity and regional geodynamics in western China.
基金The National Natural Science Fund(No:41172093)the research fund(No:2003042500820060425509)for the doctoral program of higher education from Ministry of Education for their financial support
文摘Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, such as convoluted bedding, liquefied sand veins, load and flame structures, slump structures and sliding-overlapping structures. Based on their genesis, soft-sediment deformation structures can be classified as three types: seismic induced structures, vertical loading structures, and horizontal shear structures. Based on their geometry and genesis analysis, they are seismic-induced structures. According to the characteristics of convoluted bedding structures and liquefied sand veins, it can be inferred that there were earthquakes greater than magnitude 6 in the study area during the middle Jurassic. Furthermore, the study of the slump structures and sliding- overlapping structures indicates that there was a southeastern slope during the middle Jurassic. Since the distance from the study area to the Altyn Mountain and the Altyn fault is no more than 10km, it can be also inferred that the Altyn Mountain existed then and that the AItyn strike-slip fault was active during the middle Jurassic.
基金granted by the doctor foundation of Henan Polytechnic University(NO:B2013-076)the National Nature Science Foundation of China(NO:4147208341440016)
文摘Soft-sediment deformation structures are abundant in the Cambrian Zhushadong and Mantou formations of the Dengfeng area, Henan Province, China. Soft-sediment deformation structures of the Zhushadong Formation consist of fluidized deformation, synsedimentary faults, seismo-folds and plastic deformation; the Mantou Formation is dominated by small-scale horst faults, intruded dikes, fluidized veins, and seismo-cracks. These structures are demonstrated to be earthquake-related by analysis of trigger mechanisms, and may indicate the activity of the Qinling tectonic belt during the early Cambrian. Furthermore, the assemblages of soft-sediment deformation structures altered with time: large-scale, intense deformation in the Zhushadong Formation alters to small-scale, weak deformation in the Mantou Formation. This striking feature may have been caused by changes in hypocentral depth from deep-focus to shallow-focus earthquakes, indicating that the Qinling tectonic belt developed from the subduction of the Shangdan Ocean to the extension of the Erlangping back-arc basin. This study suggests that soft-sediment deformation structures can be used to reveal the activity of a tectonic belt, and, more importantly, changes in deformation assemblages can track the evolution of a tectonic belt.
文摘Detailed fieldwork carried out in the southern part of Bida Basin, Nigeria, allowed the documentation of soft sediment deformation structures (SSDS) in the Maastrichtian Patti Formation. The aim of this study is to examine the sedimentary successions, describe and analyse these deformation features, discuss their deformation mechanisms and potential triggers. The Maastrichtian Patti Formation is composed of lithofacies interpreted to have been deposited in tidal and fluvial sedimentary environments. Soft sediment deformation structures recognised in the tidal sediments were clastic dykes, load cast, isolated sand balls, dish-and-pillar structures, convolute lamination, diapiric structures and recumbent folds. Severely deformed cross beds, ring structures, associated sand balls, normal folds and recumbent folds were identified in the fluvial sediments. SSDS recognised were interpreted to have been caused by effects of liquefaction and fluidization. Field observations, facies analysis and morphology of the SSDS indicate that there are relationship between the depositional environments and SSDS. Endogenic processes are considered as the trigger agents and they are represented by rapid sedimentation and overloading, impact of breaking waves, pressure fluctuations caused by turbulent water flow, cyclic stress and current generated by storm waves and changes in water table. The present study did not identify exogenic processes as trigger agent. The occurrence of SSDS in southern Bida Basin strongly favoured a non-tectonic origin but a clear relationship high energy processes in tidal and fluvial depositional environments.
基金This paper was sponsored by the National Natural Science Foundation of China(grant No.40272049)Doctor Research Foundation of China University of Petroleum(Project No.Y020109).
文摘The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic (or Mesoproterozoic as proposed by some researches), while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite (microcrystalline limestone) of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension (and/or layer-perpendicular flattening) of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.
文摘Soft-sediment deformation structures(SSDS)have been the focus of attention for over 150 years.Existing unconstrained definitions allow one to classify a wide range of features under the umbrella phrase"SSDS".As a consequence,a plethora of at least 120 different types of SSDS(e.g.,convolute bedding,slump folds,load casts,dish-and-pillar structures,pockmarks,raindrop imprints,explosive sandegravel craters,clastic injections,crushed and deformed stromatolites,etc.)have been recognized in strata ranging in age from Paleoproterozoic to the present time.The two factors that control the origin of SSDS are prelithification deformation and liquidization.A sedimentological compendium of 140 case studies of SSDS worldwide,which include 30 case studies of scientific drilling at sea(DSDP/ODP/IODP),published during a period between 1863and 2017,has yielded at least 31 different origins.Earthquakes have remained the single most dominant cause of SSDS because of the prevailing"seismite"mindset.Selected advances on SSDS research are:(1)an experimental study that revealed a quantitative similarity between raindrop-impact cratering and asteroid-impact cratering;(2)IODP Expedition 308 in the Gulf of Mexico that documented extensive lateral extent(〉12 km)of mass-transport deposits(MTD)with SSDS that are unrelated to earthquakes;(3)contributions on documentation of pockmarks,on recognition of new structures,and on large-scale sediment deformation on Mars.Problems that hinder our understanding of SSDS still remain.They are:(1)vague definitions of the phrase"soft-sediment deformation";(2)complex factors that govern the origin of SSDS;(3)omission of vital empirical data in documenting vertical changes in facies using measured sedimentological logs;(4)difficulties in distinguishing depositional processes from tectonic events;(5)a model-driven interpretation of SSDS(i.e.,earthquake being the singular cause);(6)routine application of the genetic term"seismites"to the"SSDS",thus undermining the basic tenet of process sedimentology(i.e.,separation of interpretation from observation);(7)the absence of objective criteria to differentiate 21 triggering mechanisms of liquefaction and related SSDS;(8)application of the process concept"high-density turbidity currents",a process that has never been documented in modern oceans;(9)application of the process concept"sediment creep"with a velocity connotation that cannot be inferred from the ancient record;(10)classification of pockmarks,which are hollow spaces(i.e.,without sediments)as SSDS,with their problematic origins by fluid expulsion,sediment degassing,fish activity,etc.;(11)application of the Earth's climate-change model;and most importantly,(12)an arbitrary distinction between depositional process and sediment deformation.Despite a profusion of literature on SSDS,our understanding of their origin remains muddled.A solution to the chronic SSDS problem is to utilize the robust core dataset from scientific drilling at sea(DSDP/ODP/IODP)with a constrained definition of SSDS.
文摘During the past 30 years (1987-2016), a great progress has been made in researches of soft-sediment deformation structures (SSDS), seismites and pataeoearthquakes in China. However, the research thought of this academic fietd is not open enough. It is atmost with one viewpoint or one voice, i.e., atmost art the papers pubtished in journals of China considered the layers with SSDS as seismites. On the other hand, the authors are very glad to learn that the professors and students of China University of Petroleum (East China) have proposed different academic viewpoints on the origin of SSDS in Lingshan Istand, Qingdao, Shandong Province, China. It is a very active academic atmosphere. The authors' ideas are as follows: (1) The SSDS are sedimentary structures with multi-origin. The term "SSDS" is a good sedimentary and geological term and shoutd be utilized continuat[y. (2) The term "seismites" is a term which is definitety assigned to the layers with SSDS induced by earthquakes. It is one type of the tayers with SSDS. It is not equal to SSDS. (3) Some geotogists suggested obsoleting the term "seismites". These suggestions are rational However, since the term "seismites" has been utilized for a long time in China and worldwide, to obsolete this term should be discussed and agreement should be acquired from numerous geologists in China and worldwide. It may be suitable that let the geological practice decide whether to obsolete it or not. (4) Hopefully, further progress will be made in the researches of SSDS.
文摘The Mesoproterozoic Wumishan Formation, composed of dolomite is a widely distributed stratigraphic unit in the Beijing area. It was formed over a long period of time in the Yan-Liao aulacogen, a stable peritidal environment that was ideal for recording earthquakes in the form of soft-sediment deformation structures (SSDS). Numerous examples occur in the upper part of the Wumishan Formation, along the Yongding River Valley. In addition, brittle structures include intrastratal fault and seismically cracked breccias. The soft-sediment deformation structures include liquefied features (diapirs, clastic dykes, convolute bedding), compressional deformation features (accordion folds, plate-spine breccias, mound-and-sag structures), and extensional plastic features (loop-bedding). Based on the regional geological setting and previous research, movements along the main axial fault of the Yan-Liao aulacogen are considered as the triggers for earthquakes since the Early Mesoproterozoic. The number and distribution of the SSDS suggest the major earthquake frequency in the Wumishan Formation of 20 to 32 thousand years.
文摘The study on soft-sediment deformation structures(SSDS) of Lingshan Island has been one of the hot topics of sedimentology researches in China in recent years,and SSDS developed in turbidite system in the Laiyang Group are widely known by domestic researchers.However,few studies were conducted on the SSDS in fan delta system in the Qingshan Group,Lingshan Island.This study analyzes the classification and characteristics of SSDS especially their lithofacies association and tithologic characteristics through field outcrops investigation and thin section analysis as well.A conclusion was acquired that the paleoenvironment was a fan delta system with occurrence of several volcanic eruptions,where the water became gradually shallower.The SSDS types in the Qingshan Group includes load and flame structure,ball and pillow structure,waterescape structure,hydroplastic deformation structure,plastic sandstone breccia structure,volcanic drop stone and V-shaped ground fissure mainly caused by volcanic earthquakes of three types:(1)seismic waves,(2)gravity and inertia effect of pyroclastic flows,(3)instant differential air pressure;which is different from slumping and tectonic earthquakes occurred in the Laiyang Group.In addition,with the lithofacies association analysis between pyroclastic flow and SSDS beds,a distribution model of SSDS related to volcanic earthquakes can be established:SSDS types changed gradually with their distance further away from the volcanic activity core.Brittle deformation which was common in the proximal zone disappeared gradually;liquefied and plastic SSDS continued to dominate in the medial zone;and slightly liquefied SSDS were developed in the distal zone.Meanwhile,the scale and size of SSDS is negatively correlated with the distance of SSDS depositional locations from the volcanic vent.
文摘From the viewpoint of origins of soft-sediment deformation structures(SSDS), 7 papers(Ito et al.,2016; Jiang et al., 2016; Lunina and Gladkov, 2016; Moretti et al., 2016; Rana et al., 2016; Rodríguez-Pascua et al., 2016; Wheatley et al., 2016) selected from the special issue of "The environmental significance of softsediment deformation" of the Sedimentary Geology 344(2016) were reviewed.(1) The first paper(according to the published order) by Moretti et al. is a general review and introduction of this special issue. This special issue has made an important contribution to the study of sedimentary environments.(2) The fourth paper by Rodríguez-Pascua et al. is an excellent case study. All evidence of earthquake in this paper is reliable. The old Roman City(adjacent to Madrid, the capital of Spain) was definitely destroyed by an earthquake. This paper solved the problem that the archaeologists have not solved yet.(3) The 19 thpaper by Rana et al. is another excellent case study. It demonstrated that SSDS in the youngest modern sediments in the seismically active area, i.e., the Alaknanda Valley, Garhwal Himalaya, India, are of non-seismic origin, but with typically sedimentary origin. All evidence of sedimentary origin of SSDS in the study area is reliable.(4) The second paper by Lunina and Gladkov stated that SSDS(mainly clastic dikes) in epicentral areas of the recent earthquakes in southern Siberia were originated by earthquakes and that the clastic dikes are the most reliable indicators in the epicentral areas of earthquakes. This conclusion is right. However, it is not accurate to consider all clastic injections as "in-situ earthquake structures" in anywhere, because the clastic injections are with multiple origins.(5) The third paper by Wheatley et al. comprehensively stated the clastic pipes of the Jurassic in the Colorado Plateau, USA. However, the principal origin of the clastic pipes(columns) was possibly not originated by "palaeoseismic controls", but by "tectonic controls" or "tectonic uplifts".(6) The 10^(th) paper by Jiang et al.proposed that 6 types of SSDS of the Lixian Section in eastern Tibetan Plateau, i.e., in a tectonically and seismically active area, were originated by earthquakes. However, the evidence of seismic origin is not sufficient. Therefore, the origins of SSDS in the Lixian Section are worthy to be further discussed.(7) The"injectites" and "extrudites" in a Late Pliocene basin on the Boso Peninsula, Japan, from the 24^(th) paper by Ito et al., are non-SSDS and their origin is unreliable.The above viewpoints may be inappropriate. Criticisms and corrections are welcome.This paper is not only the author's brief review on 7 papers selected from the special issue of the Sedimentary Geology 344(2016), but also an invitation to geologists worldwide to write papers for a new special issue of "The origins of SSDS" of the Journal of Palaeogeography which is planned to be published in 2018.
基金financially supported this research National Natural Science Foudation of China (No. 41172093)
文摘A particular type of soft-sediment deformation structure, similar to imbricate structure, is developed in the Jurassic strata at Honggouzi, western Qaidam Basin, China. We refer to this structure as a duplex-like deformation structure, because it is inferred to have been formed by the action of fast-moving, submarine gravity current sediments gliding across a pre-existing semiconsolidated sedimentary layer. The layers of duplex-like structure crop out in the southeastern limb of the core of a medium-sized anticline. The average dip direction of the duplex-like structure is 301.2° and the average dip angle is 54.7°. Duplex-like deformed laminations are composed mainly of weakly metamorphosed, extremely poorly sorted, feldspathic lithic graywacke. Sericite can be observed along bedding planes. The duplex-like structure occurs within a sequence of river-channel fine conglomerate, interchannel carbonaceous mudstone(shale), shallow-water delta sand-shale, shallow-lake calcareous mudstone, olistostromes, and a turbidite. At the bottom of the sequence, we found brownish-red shallow-lake calcareous mudstone and carbonaceous mudstone and at the top olistostromes whose genesis is related to the slip and drag of a slumped body of submarine sediment. In combination with other symbiotic and associated structures, it is considered that the duplex-like structure was formed by the slumping and subsequent movement and traction of delta-front semiconsolidated sediments over the bottom sediments of a shore or shallow-lake sedimentary environment, probably triggered by an earthquake. The attitude of the duplex-like structure indicates that the direction of gliding was from NW301.2° toward SE121°, which is consistent with the current location of the Altun Mountains, indicating that the Altun Mountains existed in the Jurassic. The orogenesis of these mountains likely involved seismic activity, and an earthquake was the triggering factor in the formation of the duplex-like structure by causing the slumping/gliding of the olistostrome sediments.