The Jurassic system of China—Main characteristics and recent advances in research

In China, the marine Jurassic is mainly distributed in the Qinghai-Tibetan Plateau, southwestern China and environs including southwestern Xinjiang and western Yunnan. Along the western palaeo-Pacific coast, marine Jurassic deposits, which usually intercalate with nonmarine strata, exist sporadically in eastern Heilongjiang, western Fujian, Hongkong, central Guangdong, western Jiangxi, eastern and southwestern Hunan Province, and probably also in western Taiwan. Nonmarine Jurassic strata are widely distributed in the whole of China except for southern Tibet area. They are commonly intercalated with volcanic rocks and contain volcanic materials in eastern China, and in southern Tibet. Marine strata yield various abundant fossils including ammonites, which were widespread in the Tethyan Realm even all over the world. Consequently, China is a critical region to attempt marine and non-marine Jurassic correlation. Through various investigations, both marine and non-marine Jurassic biozonations or assemblages have been established and by this the marine and non-marine Jurassic stratigraphic system and their correlation in China have been clarified.     

The discovery of Jurassic plants in Shenzhen of Guangdong,southern China and related significance

Investigations of major marine and non-marine geologic and biotic events across the Triassic-Jurassic transition rely predominantly on detailed stratigraphic frameworks and biodiversity analyses. The alternating sequences of marine and terrestrial Triassic-Jurassic for- mations in Guangdong Province represent one of the most remarkable coal-bearing series in southern China. The Lower Jurassic Jinji Formation is widely distributed in Guangdong, with continuously outcropped sections and rich marine and non-marine fossil fauna. However, as little research has been conducted on fossil plant remains in the Jinji Formation, it is difficult to understand the systematics, diversity, and floral aspects of the Jurassic. Here we report on the recent collection of rich fossil plants from the Jinji Formation in the Dapeng area of Shenzhen, southern Guangdong Province. Our studies demonstrate taxonomical affiliations, preservation status, and diversity features of these plant fossils, which are marked by the close associ- ation of densely preserved, pinnae and rachis connected leaves, and the bennettitalean reproductive organs of Wil- liamsoniella, which may represent an Early Jurassic plant community dominated by Otozamites of the bennettitales. This work not only represents the first discovery of fossil plants in the Shenzhen area, but is also the first docu- mentation of Jurassic plants in Guangdong and the Pearl River Delta regions. Research related to these plant fossils will be helpful in the correlation of the Early Mesozoiccoal-bearing strata in Guangdong, and will provide a dee- per understanding of variations in plant diversity of the Triassic and Jurassic transition in southern China. Addi- tionally, it will provide terrestrial plant evidence for explorations in Jurassic palaeoecology, palaeoclimatology, and palaeogeography of southern China.     

Jurassic and Cretaceous Cupedomorpha (Insecta: Coleoptera) faunas of China

Widespread non-marine Mesozoic deposits in China often contain abundant cupedomorpha fossils with significance for correlation. Based on the composition and characteristics of the cupedomorphs, at present, seven cupedid and ommatid assemblages are recognized from the Jurassic-Cretaceous rocks, of which three cupedid and two ommatid assemblages were recovered from North and northeast China: Middle Jurassic Tetrocupes-Hebeicupes cupedid assemblage from northern Hebei and Inner Mongolia (Yanliao fauna); Late Jurassic or Early Cretaceous Ovatocupes-Priacma cupedid and Amblomma-Sinocupes ommatid assemblages from western Liaoning (Jehol fauna); Early Cretaceous Lupicupes-Diluticupes cupedid and Monticupes ommatid assemblages from Beijing and adjacent areas. Both the Ovatocupes-Priacma and AmblommaSinocupes assemblages are important elements of the Jehol entomofauna. Remaining are the Late Jurassic or Early Cretaceous MesotricupesGansucupes cupedid assemblage from Jiuquan Basin, Gansu Province, NW China and the ForticupesPicticupes ommatid assemblage from Shandong Province. In southern China only one poorly preserved ommatid specimen, Zygadenia (=Notocupes) sp. occurs.     

Jurassic and Cretaceous Cupedomorpha (Insecta: Coleoptera) faunas of China

Widespread non-marine Mesozoic deposits in China often contain abundant cupedomorpha fossils with significance for correlation. Based on the composition and characteristics of the cupedomorphs, at present, seven cupedid and ommatid assemblages are recognized from the Jurassic-Cretaceous rocks, of which three cupedid and two ommatid assemblages were recovered from North and northeast China: Middle Jurassic Tetrocupes-Hebeicupes cupedid assemblage from northern Hebei and Inner Mongolia (Yanliao fauna); Late Jurassic or Early Cretaceous Ovatocupes-Priacma cupedid and Amblomma-Sinocupes ommatid assemblages from western Liaoning (Jehol fauna); Early Cretaceous Lupicupes-Diluticupes cupedid and Monticupes ommatid assemblages from Beijing and adjacent areas. Both the Ovatocupes-Priacma and AmblommaSinocupes assemblages are important elements of the Jehol entomofauna. Remaining are the Late Jurassic or Early Cretaceous MesotricupesGansucupes cupedid assemblage from Jiuquan Basin, Gansu Province, NW China and the ForticupesPicticupes ommatid assemblage from Shandong Province. In southern China only one poorly preserved ommatid specimen, Zygadenia (=Notocupes) sp. occurs.     

Focal depth research of earthquakes in Mainland China: Implication for tectonics

Focal depth data of earthquakes in Mainland China are processed and analyzed in this paper, as well as the relationship between the focal depths and large-scale tectonic structures. As a basic parameter for earthquakes, focal depth is used to investigate deep environment of seismogenic regions, tectonic backgrounds for concentration and release of seismic energy, the inner crustal deformation and its mechanic features. Depth data of 31282 ML≥2.0 events with 1st class and 2nd class precision in Mainland China from Jan. 1, 1970 to May 31, 2000 are used to get spatial features of earthquakes distributed with depth and to provide average depth for each grid area throughout China. Researches show that the average depth (D-) for all the earthquakes used in this paper is (16±7) km, and (13±6) km and (18±8) km for the events in eastern China and western China, respectively. The area with the deepest focal depth is located in southwest Xinjiang region, near the western and southwestern ends of the Tarim Basin. The focal depth related to large-scale tectonic structures, for instance, = (33±12), (21±10), (14±7), (11±5) and (10±4) km in Tibet plateau block, Xinjiang block, North China, Northeastern China and South China, respectively. The earthquakes are deeper at the bounders of the integrated tectonic blocks, including the southwestern and northern brims of the Tarim Basin, southern brim of the Zhunge'r Basin and that of the Alashan block, as well as the eastern and western sides of the Edos block and the western brim of the Sichuan Basin. The earthquakes at the newly ruptured belts are relatively shallower, for instance, at the southwestern Yunnan seismic belt and the Zhangjiakou-Bohai seismic belt. The mechanic behavior, deformation and features for the crust and mantle structures are also discussed.     

Radiometric dating of sediments derived from metamorphic rocks of the Dabie orogenic belt in the Jurasic and Early Cretaceous

Using isotopic dating of tuff, heavy mineral and lithofacies, correlation of Jurassic strata on the northern margin of the Dabie orogenic belt (DOB) has been enabled in the Fenghuangtai, Zhougongshan, Maotanchang and Jingangtai formations, which might be as young as Early Cretaceous. Depositional systems have been interpreted as mainly alluvial fan, braided stream and overbank, secondarily fan-delta and lacustrine. The palaeocurrent systems of the Jurassic-Cretaceous basins can be divided into two classes: one transverse adjacent to the southern margin, the other longitudinal close to the middle flowing from west to east. Mesozoic sedimentary source rocks are mainly from the DOB and, according to their geochemistry, experienced evolution in a volcanic arc tectonic setting. The Jurassic-Cretaceous strata have been subdivided into four Chronosomes, and their overlapping progressively from east toward west implies that exhumation of the DOB characterized diachronous. Based on stratigraphic evidence from eclogite conglomerates found in the Maotanchang and Fenghuangtai formations, the first exposure of UHP (ultrahigh pressure) rocks in the DOB occurred in Jurassic-Lower Cretaceous time. Further, phengites and Triassic zircons found in the Lower Jurassic Fanghushan Formation suggest that denudation began in the Early Jurassic.     

Radiometric dating of sediments derived from metamorphic rocks of the Dabie orogenic belt in the Jurasic and Early Cretaceous

Using isotopic dating of tuff, heavy mineral and lithofacies, correlation of Jurassic strata on the northern margin of the Dabie orogenic belt (DOB) has been enabled in the Fenghuangtai, Zhougongshan, Maotanchang and Jingangtai formations, which might be as young as Early Cretaceous. Depositional systems have been interpreted as mainly alluvial fan, braided stream and overbank, secondarily fan-delta and lacustrine. The palaeocurrent systems of the Jurassic-Cretaceous basins can be divided into two classes: one transverse adjacent to the southern margin, the other longitudinal close to the middle flowing from west to east. Mesozoic sedimentary source rocks are mainly from the DOB and, according to their geochemistry, experienced evolution in a volcanic arc tectonic setting. The Jurassic-Cretaceous strata have been subdivided into four Chronosomes, and their overlapping progressively from east toward west implies that exhumation of the DOB characterized diachronous. Based on stratigraphic evidence from eclogite conglomerates found in the Maotanchang and Fenghuangtai formations, the first exposure of UHP (ultrahigh pressure) rocks in the DOB occurred in Jurassic-Lower Cretaceous time. Further, phengites and Triassic zircons found in the Lower Jurassic Fanghushan Formation suggest that denudation began in the Early Jurassic.     

Chronostratigraphic units in the Jurassic and their boundaries: Definition, recognition and correlation, causal mechanisms

The historical development of the chronostratigraphic classification of the Jurassic into series, stages and zones is summarised. Traditionally, the series and stages are defined hierarchically in terms of the standard (ammonite) zones they contained but since Hedberg (1976)［1］ they have been defined by a basal boundary stratotype (GSSP). To date four Jurassic Stages have ratified GSSPs; progress with the others is outlined. The primary marker for the definition of the Stage boundaries is biochronology based on evolution of ammonites, with secondary markers based on biostratigraphy of other fossil groups, chemostratigraphy and magnetostratigraphy. Causal mechanisms for the environmental changes that caused ammonite evolution are reviewed and possible methods of correlation with nonmarine successions are briefly discussed.     

Chronostratigraphic units in the Jurassic and their boundaries: Definition, recognition and correlation, causal mechanisms

The historical development of the chronostratigraphic classification of the Jurassic into series, stages and zones is summarised. Traditionally, the series and stages are defined hierarchically in terms of the standard (ammonite) zones they contained but since Hedberg (1976)［1］ they have been defined by a basal boundary stratotype (GSSP). To date four Jurassic Stages have ratified GSSPs; progress with the others is outlined. The primary marker for the definition of the Stage boundaries is biochronology based on evolution of ammonites, with secondary markers based on biostratigraphy of other fossil groups, chemostratigraphy and magnetostratigraphy. Causal mechanisms for the environmental changes that caused ammonite evolution are reviewed and possible methods of correlation with nonmarine successions are briefly discussed.     

The spring soil moisture and the summer rainfall in eastern China

The relation between the soil moisture in spring and the rainfall in summer in eastern China is investi- gated. Results show that the summer rainfall in eastern China is closely related to the spring soil moisture in the area from North China to the lower reaches of Yangtze River (NCYR). When spring soil moisture anomalies over NCYR are positive, the summer precipitation exhibits positive anomalies in Northeast China and the lower reaches of Yangtze River, and negative anomalies in southern China and North China. The higher soil moisture over NCYR cools land surface and reduces the land-sea tem- perature gradient, which weakens East Asian summer monsoon. The western Pacific Subtropical High (WPSH) is located to the south and shifts westward, resulting in more rainfall in the lower reaches of Yangtze River and less in southern China and North China.     

The age of the plant fossil assemblage in the Liuqu Conglomerate of southern Tibet and its tectonic significance

The Liuqu Conglomerate, situated to the south of Yarlung Tsangbo Suture Zone (YTSZ), is a suit of molasse formed in a foreland basin of the Himalayan orogenic belt after the collision between the two plates of the Indian and Eurasion. It is of great significance in constraining the younger limit time of the collision of the two plates and providing stratigraphic evidence to reveal the post?collisional tectonic evolution and uplifting history of the Tibet plateau. However, the age of this molasse suit and its correlation to other synchronous strata distributed in southern Tibet have been in great disputes for a long time. Especially in recent years, argues on its ages are growing violently with the recognition of the great sedimentary tectonic significances of this molasse. During the field work carried out recently on this molasse suit, a lot of plant fossils were found preserved in fairly good conditions in the upper part of this strata, which is of great help in determining its age. By identification, the assemblage of the plant fossils belongs to a tropic to subtropic flora developed in the southern margin of the Northern Hemisphere supercontinent during the Middle to Later Eocene, which can provide good constraint on its formation age. This paper is to give a brief introduction of the plant assemblage and its age, and to discuss their tectonic significances.     

The potential of vertebrate microfossils for marine to non-marine correlation in the Late Jurassic

Fish (cartilaginous: elasmobranch and bony: osteichthyan actinopterygian) and reptile (crocodile) microfossils comprising scales and teeth have been examined from a series of limestone samples in the Upper Jurassic of France and Germany to gauge the possibilities of using them for correlation between fully marine and hypo-or hyper-saline (non-marine) deposits.     

Marine dinoflagellates from Lower Cretaceous Muling Formation of Jixi Basin,China and their palaeoenvironmental significance

Newly discovered marine dinoflagellates from the lower-middle parts of the Lower Cretaceous Muling Formation of the Jixi Basin, eastern Heilongjiang Province,China, were identified as Circulodinium cingulatum He et al.,C. attadalicum (Cookson et Eiscnack) Helhy, Palaeoperidinium cretaceum Pocock, Oligosphaeridium totum Brideaux and Sentusidinium sp. Most of these species are distributed in the marine Lower Cretaceous strata of Europe, North America,Africa, Australia and Asia. It demonstrates that a transgression occurred in eastern Heilongjiang Province during the deposition of the Muling Formation, which was previously considered to be a coal-bearing continental stratigraphic unit.The marine dinoflagellates indicated that the Muling Formation is Barremian in age. The Palaeogeographic framework of eastern HeUongjiang Province in Late Mesozoic era should be rebuilt through systematic facies analyses of the marine,paralic and terrestrial deposits.     

The potential of vertebrate microfossils for marine to non-marine correlation in the Late Jurassic

Fish (cartilaginous: elasmobranch and bony: osteichthyan actinopterygian) and reptile (crocodile) microfossils comprising scales and teeth have been examined from a series of limestone samples in the Upper Jurassic of France and Germany to gauge the possibilities of using them for correlation between fully marine and hypo-or hyper-saline (non-marine) deposits.     

Influences of the surface wave-induced mixing and tidal mixing on the vertical temperature structure of the Yellow and East China Seas in summer

After a classification of the physical processes which affect the vertical mixing, diffusivity induced by the surface wave momentum and tidal currents and its influence on the vertical temperature structure are discussed. Based on three mixing schemes, the vertical temperature structure of the Yellow and East China Seas (YECS) is simulated. Results show that in summer, the surface wave-induced mixing plays a key role in forming the upper mixed layer in the YECS. The tidal mixing controls the lower layers within 30 m above the bottom, which is the main factor in forming the platform-shaped temperature structure in the southern Yellow Sea (YS). Together with the strong surface wave-induced mixing, the tidal mixing makes the thermocline ventilate near the east coast of the southern YS. The double cold cores in the deeper layers of the East China Sea have different causes. The western one is the maintenance of the winter cold water, while the eastern one is configured by circulation. The simulated vertical temperature structure of the YECS with the surface wave-induced mixing and tidal mixing has similar features to the observations, which indicates that these mixing processes are key factors in simulating the thermocline and pycnocline of the coastal oceans.     

Occurrence of Sciadopitys-like fossil wood （Coniferales） in the Jurassic of western Liaoning and its evolutionary implications

The genus Sciadopitys, containing a single species (S. verticillata), is the only extant representative of the Family Sciadopityaceae (Coniferales), and is a remarkable living fossil. Although some leafy fossils have been ascribed to Sciadopityaceae, fossil xylem material with a close affinity to this family is very rare, and there have been no fossils found showing both pith and primary xylem structures, which are of great importance for wood identification. Thus, it has been difficult to use fossils for the understanding of wood anatomy evolution in the sciadopityaceous plants over geological time. In this note we briefly report on Sciadopitys-like fossil wood found in the Middle Jurassic of western Liaoning, which bears well-preserved Protosciadopityoxylon-type secondary xylem, endarch primary xylem and heterogeneous pith. This is the first report of fossil specimens of the Sciadopityaceae with such detailed preservation of wood structures. The discovery provides precise anatomical evidence for reconstructing the evolu- tionary history and geographical distribution of Sciadopityaceae, as well as contributing to understanding of the fossil diversity of the Jurassic Yanliao Flora in northern China.     

Discussion of gas enrichment mechanism and natural gas origin in marine sedimentary basin,China

There are abundant natural gas resources in Chinese marine sedimentary basin. The exploration hot shots of natural gas are the Palaeozoic marine strata here in recent years, and several large scale gas fields have been discovered. Chinese Palaeozoic high-post matured and coal measure hydrocarbon source rocks are mainly prone to gas generation in the present. This research considered that gas source rocks and TSR are the key cause of gas enrichment of marine strata. High-quality argillaceous and coal measure hydrocarbon rocks are distributed widely in the Palaeozoic marine strata, which have been in highly matured phase in the present. The argillaceous source rock generally contains various sulfates that could accelerate crude oil cracking to gas for TSR occurrence, and coal measure source rock mainly generates gas, so Chinese marine basin gives priority to accumulating gas. Marine strata have not founded oil reservoirs in the Sichuan Basin and Ordos Basin, and they consist mainly of dry gas. Marine natural gases are the mixed gases of oil cracking gas and coal-formed gas in a general way, oil cracking gases contain usually some H2S and CO2. Hydrocarbon carbon isotopes are very complicated, and methane and ethane isotopic values bear apparent reversal caused by thermal evolution and mixing among different genetic types of natural gas. Coal-formed gases are the main component of Chinese marine natural gas. The Upper Permian of the Sichuan Basin and the Carboniferous-Permian of the Ordos Basin coal measure hydrocarbon source rock present large hydrocarbon generation potential, which are the prospecting highlight of marine natural gas hereafter. Oil cracking gas exploration will be paid much attention to in the Tarim Basin because of the lack of coal measure hydrocarbon source rock.     

Geochemical characteristics and tectonic implications of HP-UHP eclogites and blueschists in southwestern Tianshan, China

Four rock assemblages in correspondence with two different tectonic settings have been recognized in the NEE-SWW extending HP-UHP metamorphic belt in southwestern Tianshan, northwest China. Eclogite assemblage EC1 is geochemically akin to alkaline within-plate oceanic island basalt (OIB). EC2 shows affinity to enriched mid-oceanic ridge basalt (EMORB). Rare earth element (REE) and other immobile trace element characteristics of blueschist assemblage BS1 resemble those of normal mid-oceanic ridge basalt (NMORB). These three assemblages are likely formed on a seamount setting, and the prevalent presence of carbonate minerals and omphacite quartzite stripes/gobbets suggests ancient pelagic sediments including marls are probably developed upon the basaltic seamount. Whereas the geochemical characteristics of BS2 assemblage are of volcanic arc basalt-type. The seamount with the pelagic sediments on it is brought into the subduction zone, and volcanic arc basalts formed on the active continental margin and trench sediments are eroded and enwrapped in the subducting mass, they are altogether subjected to high to ultrahigh pressure metamorphism and subsequent exhumation towards surface. The HP-UHP metamorphic belt is thus interpreted as a subduction-accretionary complex formed by tectonic juxtaposition and imbrication of seamount, seafloor, trench and volcanic arc sequences during oceanic crust subduction.     

^40Ar-^39Ar geochronology of Cenozoic Linzizong volcanic rocks from Linzhou Basin, Tibet, China, and their geological implications

Whole-rock and mineral separate Ar-Ar dating was carried out for the Linzizong volcanic rocks at Linzhou Basin in Tibet to constrain the time span of volcanism and the corresponding stratigraphic sequence. Sampling was based on detailed geologic mapping and stratigraphic sequence of Dianzhong, Nianbo, Pana Formations, systematically from the bottom to near the top. The results indicate that the Linzizong volcanic rocks erupted from Paleocene to middle of Eocene (64.43--43.93 Ma). Among them, the Pana Formation formed from ca. 48.73 to 43.9 Ma, the Nianbo Formation around 54 Ma and the Dianzhong Formation from 64.4 to 60.6 Ma. In combination with evidence from the geochemical characteristics of the volcanic rocks, and from stratigraphy in southern Tibet, it is postulated that the age of the lowest member in the Dianzhong Formation of the Linzizong volcanic rock, which overlies unconformably the Late Cretaceous Shexing Formation, likely corresponds to the inception of the collision between Indian and Asian continents in southern Tibet.