The sedimentary background and sedimentary environment of the Lower Cretaceous of Lingshan Island,Shandong,remain unclear.There is considerable controversy as to whether the sedimentary environment was marine or conti...The sedimentary background and sedimentary environment of the Lower Cretaceous of Lingshan Island,Shandong,remain unclear.There is considerable controversy as to whether the sedimentary environment was marine or continental.In this study,analyses were conducted with respect to indicators of paleosalinity,the chemical composition of clay,paleobiota,the characteristics of strata exhibiting salinization in eastern China during the Early Cretaceous,and the relationship between paleosalinity and paleoclimate.The results indicate that the sedimentary environment of the Lower Cretaceous Laiyang Group of Lingshan Island was that of a salified lake rather than a marine environment.This study not only provides a reference for determining the sedimentary environment of the Lower Cretaceous Laiyang Group of Lingshan Island but also offers a new perspective for the study of Cretaceous strata with salinization characteristics in eastern China.展开更多
Objective Understanding the dynamics of sediment gravity flows is of great importance to correctly interpret their related deposits. The discovery of supercritical sediment gravity flows provides some new viewpoints ...Objective Understanding the dynamics of sediment gravity flows is of great importance to correctly interpret their related deposits. The discovery of supercritical sediment gravity flows provides some new viewpoints for the explanation of controversial sediment gravity flow deposits. However, the dynamics, formation, evolution processes of supercritical sediment gravity flows and their recognition criteria from their associated deposits are still worldwide controversial. The supercritical hyperpycnal flow deposits recognized in the upper part of Early Cretaceous Lingshandao Formation provide a rare opporttmity to understand their sedimentary characteristics. This work is aimed at documenting the typical sedimentary structures associated with the supercritical hyperpycnal flow, and discussing the vertical stacking and its relationship with flow evolution.展开更多
Imbricate structure is a common sedimentary structure and is well developed in sandy sediments. Here, we report a lamina- controlled fine-sand-particle imbricate structure in a set of very fine grained sedimentary roc...Imbricate structure is a common sedimentary structure and is well developed in sandy sediments. Here, we report a lamina- controlled fine-sand-particle imbricate structure in a set of very fine grained sedimentary rocks （fine sandstone, siltstone, and mudstone） at the Dockyard and Qianceng Cliff areas of Lingshan Island, Qingdao, Shandong, China. Sets of up to 300 laminae are found in stratigraphic profiles in these areas. The laminae are generally less than 1 mm thick, with most being 0.3-0.4 mm thick and the thinnest being 〈0.1 ram. The dip angle of the imbricate structure varies widely, between 0° and 90°, with an av- erage dip angle of about 40°-50°, which is higher than that of imbricate riverbed gravels （about 34°）. The dip angle is a func- tion of the shape and sorting of the particles, as well as the hydrodynamic conditions under which these fine-grained sediments were deposited. Several profiles show well-developed multiscale, soft-sediment deformation structures. Flute casts, load casts, and groove casts are also common. Fragments of carbon remains occur widely and commonly constitute stringers several mil- limeters thick and up to 10 cm long, together with fine clasts. Vitrain lenticles are also common. Based on the imbricate struc- ture of the Lingshan Island deposits, it is shown that in addition to paleocurrent analysis, the imbricate structure can be used to infer information about fluid properties, transport characteristics, and sedimentary processes of the depositional environment. A near-bottom underflow, either of authigenic origin or derived from cold river water in winter in a delta interdistributary bay or delta-front environment, is inferred to have provided the hydrodynamic setting in which this imbricate structure formed. The imbricate structure, together with other sedimentary structures and features, shows that the sedimentary rocks on Lingshan Is- land were deposited in an inland, shallow-water environment, such as a delta, and not in a deep-water or submarine continen- tal-slope environment.展开更多
The Lingshan Island scientific drill confirms that two episodes(Laiyang period and Qingshan period) of rifting developed in the central Sulu orogenic belt(SOB) in Late Mesozoic. With a set of methods including fieldwo...The Lingshan Island scientific drill confirms that two episodes(Laiyang period and Qingshan period) of rifting developed in the central Sulu orogenic belt(SOB) in Late Mesozoic. With a set of methods including fieldwork, drilling, core logging, zircon U-Pb dating and whole rock geochemistry applied, the age, the depositional sequence and the deep dynamic mechanisms of rift evolution were unraveled. The stratigraphic sequence of the Laiyang-Qingshan Groups on Lingshan Island was composed of two different rifting sequences:(1) Laiyang Group(147–125 Ma), which consists of deep-water gravity flow deposits with interlayers of intermediate volcanic rocks;and(2) Lower Qingshan Group(125–119 Ma), which unconformably overlies the former sequence and contains subaerial volcanic deposits and terrestrial deposits. The tectonic environment changed during the evolution of these two episodes of rifting: the rift was in a NNW-SSE extensional environment in the Laiyang period and showed the typical passive rifting character that “lithospheric extension and rifting preceded volcanism”. The passive rifting period was ended by a short WNW-ESE compression at about 125 Ma. After that, the tectonic environment transferred to a strong NW-SE extensional environment and the rifting evolved into a volcanic arc basin in the Qingshan period. The igneous rocks are shoshonitic to high-K calc-alkaline trachyandesites to trachytes with a few intercalated lamprophyres and a rhyolite.The geochemical characteristics of the igneous rocks indicate that they are mantle-derived melts with a metasomatized mantle source and/or crustal contamination. In addition, an increased thinning of the lithosphere happened during the rifting episodes.The low-angle subduction of the Paleo-Pacific plate in the Jurassic weakened the thickened SOB lithospheric mantle. The rollback of the subducting plate started in late Jurassic to early Cretaceous, and the SOB lithospheric mantle was delaminated synchronously because of the gravity collapse. Thus, this caused passive rifting in the Laiyang period. Thereafter, the rollback and trench retreat of the high-angle subducting Paleo-Pacific plate would have achieved its climax, resulting in the strong regional extension. Passive rifting was ended by the crustal uplift caused by asthenospheric upwelling beneath the rift. The lower crust was heated by the upwelling asthenosphere and partially melted to form felsic melts, which were emplaced upwards and erupted explosively. The rift evolved into a volcanic arc basin in the Qingshan period and showed some characteristics of active rifting. Above all, a passive rifting in the Laiyang period and a volcanic arc basin in the Qingshan period developed successively in the Lingshan Island area(the central SOB). This records the transfer of the study area from the Paleo-Tethys tectonic domain to the circum-Pacific tectonic domain. The delamination of SOB lithospheric mantle and the upwelling of asthenospheric material were the deep dynamic mechanisms driving the development and evolution of two rift episodes. Additionally, the rift development was controlled remotely by the subduction of the Paleo-Pacific plate.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
The tectonic position of the southwest section of the Qinzhou Bay-Hangzhou Bay Tectonic Junction Zone(QHTJZ)can be determined by examining the Qinzhou-Fangcheng Junction Zone(QFJZ)in Guangxi.This zone is significant b...The tectonic position of the southwest section of the Qinzhou Bay-Hangzhou Bay Tectonic Junction Zone(QHTJZ)can be determined by examining the Qinzhou-Fangcheng Junction Zone(QFJZ)in Guangxi.This zone is significant because it was the location of the largest earthquake ever recorded in the inland region of South China,specifically the 1936 Lingshan M6^(3/4)earthquake in Guangxi.Therefore,this region serves as an optimal location for researching the origins of intraplate earthquakes in South China.This study presents a display of a broadband magnetotelluric(MT)prospecting profile that traverses the Guangxi QFJZ and the Lingshan earthquake zone,extending from the northwest(NW)to the southeast(SE).A resistivity structure model was generated using three-dimensional(3D)inversion technology along the profile.The main faults in QFJZ were analyzed in terms of their deep extension forms and tectonic attributes.This analysis was performed by integrating the results obtained from geology,gravity,wave velocity ratio,Global Position System(GPS),and geothermal flow.The results showed that(1)the Dongzhong-Xiaodong fault(DXf),the eastern Fangcheng-Lingshan fault(FLf2),and the eastern Hepu-Beiliu fault(HBf2)were all trans-crustal deep faults,and crust-mantle ductile shear zones developed in the deep part.Two electrical boundary zones,DXf and HBf2,were identified.DXf inclined towards the northwest,while HBf2 inclined towards the southeast.The FangchengLingshan fault(FLf)exhibits a tectonic style resembling a“flower”shape in the upper crust.In the deeper section,it is characterized by an electrical boundary zone that gradually slopes towards the southeast direction.(2)The Hunan-Guangxi Passive Continental Margin(HGPCM)on the NW side of DXf had a stratified resistivity structure and relatively stable Bouguer gravity anomalies,which conformed to the quasi-craton tectonic attribute of the local failure at the southeastern margin of the Yangtze Block(YB).The southeastern side of this block is marked by the presence of the QFJZ and Yunkai Magmatic Arc(YKMA).These areas exhibit varying Bouguer gravity anomalies,indicating a combination of high and low resistivity in their electrical structures.This suggests that this zone has undergone multiple stages of structural evolution and transformation.The giant high-resistivity body under the Qinzhou-Fangcheng Remnant Ocean Basin(QFROB)might be the trace left by the extinction of the South China Ocean and the collision orogeny between YB and the Cathaysian Block(CB).The presence of sublow-resistivity layers in the middle-lower crust between the Liuwandashan Magmatic Arc(LMA)and YKMA indicates that this particular zone is being influenced from a distance by magmatic activities originating from the Leiqiong mantle.(3)The focal area of the 1936 Lingshan earthquake was located in the brittle high-resistivity body with a low strain rate.Under the coupling action of NWW-SEE regional tectonic stress and deep thermodynamic force,the brittle high-resistivity body in the upper crust became the main body for accumulating the tectonic stress.The Lingshan earthquake occurred due to the dextral strike-slip fracture instability of FLf2,a rock layer with slightly lower strength in the sub-high-resistivity zone.This instability was triggered when the accumulated stress reached the ultimate rock strength.The unveiling of the seismogenic model of the Lingshan earthquake,as presented in this study,holds significant scientific importance in comprehending the factors contributing to intraplate earthquakes in the South China region.展开更多
基金supported by the Fund from the Key Laboratory of Stratigraphy and Palaeontology,Ministry of Natural Resources(Grant No.KLSP 190102)the Graduate Scientific and Technological Innovation Project Financially Supported by Shandong University of Science and Technology(Grant No.SDKDYC 190104)。
文摘The sedimentary background and sedimentary environment of the Lower Cretaceous of Lingshan Island,Shandong,remain unclear.There is considerable controversy as to whether the sedimentary environment was marine or continental.In this study,analyses were conducted with respect to indicators of paleosalinity,the chemical composition of clay,paleobiota,the characteristics of strata exhibiting salinization in eastern China during the Early Cretaceous,and the relationship between paleosalinity and paleoclimate.The results indicate that the sedimentary environment of the Lower Cretaceous Laiyang Group of Lingshan Island was that of a salified lake rather than a marine environment.This study not only provides a reference for determining the sedimentary environment of the Lower Cretaceous Laiyang Group of Lingshan Island but also offers a new perspective for the study of Cretaceous strata with salinization characteristics in eastern China.
基金the National Science Foundation of China (grant No.U1262203)the National Science and Technology Special Grant (grant No.2016ZX05006-007) for their financial support
文摘Objective Understanding the dynamics of sediment gravity flows is of great importance to correctly interpret their related deposits. The discovery of supercritical sediment gravity flows provides some new viewpoints for the explanation of controversial sediment gravity flow deposits. However, the dynamics, formation, evolution processes of supercritical sediment gravity flows and their recognition criteria from their associated deposits are still worldwide controversial. The supercritical hyperpycnal flow deposits recognized in the upper part of Early Cretaceous Lingshandao Formation provide a rare opporttmity to understand their sedimentary characteristics. This work is aimed at documenting the typical sedimentary structures associated with the supercritical hyperpycnal flow, and discussing the vertical stacking and its relationship with flow evolution.
基金financially supported by Research Fund for the Doctoral Program of Higher Education of China (Grant Nos. 20030425008, 20060425509)National Natural Science Foundation of China (Grant No. 41172093)Independent Innovation Foundation of China University of Petroleum (Grant No. R1301003A)
文摘Imbricate structure is a common sedimentary structure and is well developed in sandy sediments. Here, we report a lamina- controlled fine-sand-particle imbricate structure in a set of very fine grained sedimentary rocks （fine sandstone, siltstone, and mudstone） at the Dockyard and Qianceng Cliff areas of Lingshan Island, Qingdao, Shandong, China. Sets of up to 300 laminae are found in stratigraphic profiles in these areas. The laminae are generally less than 1 mm thick, with most being 0.3-0.4 mm thick and the thinnest being 〈0.1 ram. The dip angle of the imbricate structure varies widely, between 0° and 90°, with an av- erage dip angle of about 40°-50°, which is higher than that of imbricate riverbed gravels （about 34°）. The dip angle is a func- tion of the shape and sorting of the particles, as well as the hydrodynamic conditions under which these fine-grained sediments were deposited. Several profiles show well-developed multiscale, soft-sediment deformation structures. Flute casts, load casts, and groove casts are also common. Fragments of carbon remains occur widely and commonly constitute stringers several mil- limeters thick and up to 10 cm long, together with fine clasts. Vitrain lenticles are also common. Based on the imbricate struc- ture of the Lingshan Island deposits, it is shown that in addition to paleocurrent analysis, the imbricate structure can be used to infer information about fluid properties, transport characteristics, and sedimentary processes of the depositional environment. A near-bottom underflow, either of authigenic origin or derived from cold river water in winter in a delta interdistributary bay or delta-front environment, is inferred to have provided the hydrodynamic setting in which this imbricate structure formed. The imbricate structure, together with other sedimentary structures and features, shows that the sedimentary rocks on Lingshan Is- land were deposited in an inland, shallow-water environment, such as a delta, and not in a deep-water or submarine continen- tal-slope environment.
基金supported by the Key R&D Plan of Shandong Province (Grant No. 2017CXGC1608)the Project of Department of Science and Technology of Sinopec (Grant No. P20028)+1 种基金the Shandong Natural Science Foundation Youth Fund Project (Grant No. ZR2020QD026)the Fundamental Research Funds for the Central Universities (Grant Nos. 18CX06019A, 19CX05004A)。
文摘The Lingshan Island scientific drill confirms that two episodes(Laiyang period and Qingshan period) of rifting developed in the central Sulu orogenic belt(SOB) in Late Mesozoic. With a set of methods including fieldwork, drilling, core logging, zircon U-Pb dating and whole rock geochemistry applied, the age, the depositional sequence and the deep dynamic mechanisms of rift evolution were unraveled. The stratigraphic sequence of the Laiyang-Qingshan Groups on Lingshan Island was composed of two different rifting sequences:(1) Laiyang Group(147–125 Ma), which consists of deep-water gravity flow deposits with interlayers of intermediate volcanic rocks;and(2) Lower Qingshan Group(125–119 Ma), which unconformably overlies the former sequence and contains subaerial volcanic deposits and terrestrial deposits. The tectonic environment changed during the evolution of these two episodes of rifting: the rift was in a NNW-SSE extensional environment in the Laiyang period and showed the typical passive rifting character that “lithospheric extension and rifting preceded volcanism”. The passive rifting period was ended by a short WNW-ESE compression at about 125 Ma. After that, the tectonic environment transferred to a strong NW-SE extensional environment and the rifting evolved into a volcanic arc basin in the Qingshan period. The igneous rocks are shoshonitic to high-K calc-alkaline trachyandesites to trachytes with a few intercalated lamprophyres and a rhyolite.The geochemical characteristics of the igneous rocks indicate that they are mantle-derived melts with a metasomatized mantle source and/or crustal contamination. In addition, an increased thinning of the lithosphere happened during the rifting episodes.The low-angle subduction of the Paleo-Pacific plate in the Jurassic weakened the thickened SOB lithospheric mantle. The rollback of the subducting plate started in late Jurassic to early Cretaceous, and the SOB lithospheric mantle was delaminated synchronously because of the gravity collapse. Thus, this caused passive rifting in the Laiyang period. Thereafter, the rollback and trench retreat of the high-angle subducting Paleo-Pacific plate would have achieved its climax, resulting in the strong regional extension. Passive rifting was ended by the crustal uplift caused by asthenospheric upwelling beneath the rift. The lower crust was heated by the upwelling asthenosphere and partially melted to form felsic melts, which were emplaced upwards and erupted explosively. The rift evolved into a volcanic arc basin in the Qingshan period and showed some characteristics of active rifting. Above all, a passive rifting in the Laiyang period and a volcanic arc basin in the Qingshan period developed successively in the Lingshan Island area(the central SOB). This records the transfer of the study area from the Paleo-Tethys tectonic domain to the circum-Pacific tectonic domain. The delamination of SOB lithospheric mantle and the upwelling of asthenospheric material were the deep dynamic mechanisms driving the development and evolution of two rift episodes. Additionally, the rift development was controlled remotely by the subduction of the Paleo-Pacific plate.
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.
基金supported by the Science for Earthquake Resilience Program of the China Earthquake Administration(Grant Nos.XH24033B,XH22004YA)the Guangxi Scientific Research and Technology Development Plan Project(Grant Nos.1377002,14124004-4-8)the Earthquake Prediction Open Fund Project of China Earthquake Administration(Grant No.2021EF0F02)。
文摘The tectonic position of the southwest section of the Qinzhou Bay-Hangzhou Bay Tectonic Junction Zone(QHTJZ)can be determined by examining the Qinzhou-Fangcheng Junction Zone(QFJZ)in Guangxi.This zone is significant because it was the location of the largest earthquake ever recorded in the inland region of South China,specifically the 1936 Lingshan M6^(3/4)earthquake in Guangxi.Therefore,this region serves as an optimal location for researching the origins of intraplate earthquakes in South China.This study presents a display of a broadband magnetotelluric(MT)prospecting profile that traverses the Guangxi QFJZ and the Lingshan earthquake zone,extending from the northwest(NW)to the southeast(SE).A resistivity structure model was generated using three-dimensional(3D)inversion technology along the profile.The main faults in QFJZ were analyzed in terms of their deep extension forms and tectonic attributes.This analysis was performed by integrating the results obtained from geology,gravity,wave velocity ratio,Global Position System(GPS),and geothermal flow.The results showed that(1)the Dongzhong-Xiaodong fault(DXf),the eastern Fangcheng-Lingshan fault(FLf2),and the eastern Hepu-Beiliu fault(HBf2)were all trans-crustal deep faults,and crust-mantle ductile shear zones developed in the deep part.Two electrical boundary zones,DXf and HBf2,were identified.DXf inclined towards the northwest,while HBf2 inclined towards the southeast.The FangchengLingshan fault(FLf)exhibits a tectonic style resembling a“flower”shape in the upper crust.In the deeper section,it is characterized by an electrical boundary zone that gradually slopes towards the southeast direction.(2)The Hunan-Guangxi Passive Continental Margin(HGPCM)on the NW side of DXf had a stratified resistivity structure and relatively stable Bouguer gravity anomalies,which conformed to the quasi-craton tectonic attribute of the local failure at the southeastern margin of the Yangtze Block(YB).The southeastern side of this block is marked by the presence of the QFJZ and Yunkai Magmatic Arc(YKMA).These areas exhibit varying Bouguer gravity anomalies,indicating a combination of high and low resistivity in their electrical structures.This suggests that this zone has undergone multiple stages of structural evolution and transformation.The giant high-resistivity body under the Qinzhou-Fangcheng Remnant Ocean Basin(QFROB)might be the trace left by the extinction of the South China Ocean and the collision orogeny between YB and the Cathaysian Block(CB).The presence of sublow-resistivity layers in the middle-lower crust between the Liuwandashan Magmatic Arc(LMA)and YKMA indicates that this particular zone is being influenced from a distance by magmatic activities originating from the Leiqiong mantle.(3)The focal area of the 1936 Lingshan earthquake was located in the brittle high-resistivity body with a low strain rate.Under the coupling action of NWW-SEE regional tectonic stress and deep thermodynamic force,the brittle high-resistivity body in the upper crust became the main body for accumulating the tectonic stress.The Lingshan earthquake occurred due to the dextral strike-slip fracture instability of FLf2,a rock layer with slightly lower strength in the sub-high-resistivity zone.This instability was triggered when the accumulated stress reached the ultimate rock strength.The unveiling of the seismogenic model of the Lingshan earthquake,as presented in this study,holds significant scientific importance in comprehending the factors contributing to intraplate earthquakes in the South China region.
