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
Imbricate structure is a common sedimentary structure and is well developed in sandy sediments.Here,we report a laminacontrolled fine-sand-particle imbricate structure in a set of very fine grained sedimentary rocks(f...Imbricate structure is a common sedimentary structure and is well developed in sandy sediments.Here,we report a laminacontrolled 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 mm.The dip angle of the imbricate structure varies widely,between 0°and 90°,with an average dip angle of about 40°–50°,which is higher than that of imbricate riverbed gravels(about 34°).The dip angle is a function 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 millimeters thick and up to 10 cm long,together with fine clasts.Vitrain lenticles are also common.Based on the imbricate structure 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 Island were deposited in an inland,shallow-water environment,such as a delta,and not in a deep-water or submarine continental-slope environment.展开更多
A typical ancient karst cave is found in the Yijianfang Formation of Ordovician at Liuhuanggou,North Tarim Basin.With an entrance of 4.8 m wide and 20 m high,the Liuhuanggou ancient karst cave extends to NW 315° ...A typical ancient karst cave is found in the Yijianfang Formation of Ordovician at Liuhuanggou,North Tarim Basin.With an entrance of 4.8 m wide and 20 m high,the Liuhuanggou ancient karst cave extends to NW 315° and has been filled by sediments,which can be classified into three types according to their nature and origin:clastic sediments(gravels),chemical sediments(palaeotravertine),and mixed sediments.Among them,the Paleotravertine and gravels are most common.The palaeotravertine is laminated type and yellowish brown or black in color due to oil inside.When saturated with oil,the palaeotravertine is black.Under microscope,oil mainly accumulates in the cracks between calcite crystals.The filling period of the Liuhuanggou karst cave can be divided into three stages:mixed filling,chemical filling,and clastic(palaeotravertine breccia) filling.Numerous fractures are distributed on one side of the karst cave.The fractures can be as wide as 40 cm and over 40 m long.Fractures of different periods and sizes constitute a fracture network and are all filled with calcite veins.Oil can be found inside the fractures.In the chemical fillings,sulfur is also found,which can indicate the magma influence on karst caves.The existence of sulfur also confirms that the Liuhunggou karst cave was formed in ancient times rather than recently or nowadays.Different from normal sedimentary limestone,the ancient Liuhuanggou karst cave has a distinct isotope fractionation and the depletion of heavy carbon and oxygen isotope.Controlled by the northwest oriented vertical strike-slip shear fault,the karst cave is actually a dissolved vertical fault belt.展开更多
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 laminacontrolled 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 mm.The dip angle of the imbricate structure varies widely,between 0°and 90°,with an average dip angle of about 40°–50°,which is higher than that of imbricate riverbed gravels(about 34°).The dip angle is a function 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 millimeters thick and up to 10 cm long,together with fine clasts.Vitrain lenticles are also common.Based on the imbricate structure 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 Island were deposited in an inland,shallow-water environment,such as a delta,and not in a deep-water or submarine continental-slope environment.
基金supported by National Basic Research Program of China (Grant Nos.2006CB202401,2011CB201001)National Major Projects of Gas and Oil (Grant No. 2008ZX05014-002)
文摘A typical ancient karst cave is found in the Yijianfang Formation of Ordovician at Liuhuanggou,North Tarim Basin.With an entrance of 4.8 m wide and 20 m high,the Liuhuanggou ancient karst cave extends to NW 315° and has been filled by sediments,which can be classified into three types according to their nature and origin:clastic sediments(gravels),chemical sediments(palaeotravertine),and mixed sediments.Among them,the Paleotravertine and gravels are most common.The palaeotravertine is laminated type and yellowish brown or black in color due to oil inside.When saturated with oil,the palaeotravertine is black.Under microscope,oil mainly accumulates in the cracks between calcite crystals.The filling period of the Liuhuanggou karst cave can be divided into three stages:mixed filling,chemical filling,and clastic(palaeotravertine breccia) filling.Numerous fractures are distributed on one side of the karst cave.The fractures can be as wide as 40 cm and over 40 m long.Fractures of different periods and sizes constitute a fracture network and are all filled with calcite veins.Oil can be found inside the fractures.In the chemical fillings,sulfur is also found,which can indicate the magma influence on karst caves.The existence of sulfur also confirms that the Liuhunggou karst cave was formed in ancient times rather than recently or nowadays.Different from normal sedimentary limestone,the ancient Liuhuanggou karst cave has a distinct isotope fractionation and the depletion of heavy carbon and oxygen isotope.Controlled by the northwest oriented vertical strike-slip shear fault,the karst cave is actually a dissolved vertical fault belt.
