Bioturbation is well developed in the reservoir of the Neogene Sanya Formation in the northern Qiongdongnan Basin. Based on detailed observations of cores,quantitative characterization and connectivity analysis of the microscopic pores of reservoir rock samples with and without bioturbation were carried out using polarized light microscopy,scanning electron microscopy and micro-CT. The reservoir modification effect reflected by the Ophiomorpha-Thalassinoides ichnofabric was studied in detail. The results show that the Ophiomorpha-Thalassinoides ichnofabric in the Neogene Sanya Formation is well developed in northern Qiongdongnan Basin. The burrows obviously modified the initial sedimentary structure of the reservoirs,and the primary sedimentary bedding was destroyed. The burrows are mainly filled with quartz,feldspar,chlorite and a small amount of clay minerals. Many intergranular pores and a small amount of intra-grain dissolution pores developed,while the mud content of the surrounding rocks is high,and the pores were poorly developed. Quantitative analysis shows that the morphological characteristics of the pores and pore throats are consistent. The pore volume,pore area, equivalent radius of pore and throat area all present left-skewed unimodal distribution,while the equivalent radius of throat and throat length show approximate bimodal distribution. The number of large pores and throats,effective porosity,permeability and average coordination number of samples with bioturbation are significantly greater than those of samples without bioturbation. This reveals that the Ophiomorpha-Thalassinoides ichnofabric enhances the reserve capacity and connectivity of microscopic pores in the Sanya Formation reservoir. This study is of great significance for analyzing the modification effect of bioturbation on oil and gas reservoirs,increasing reserve capcity, production and recovery of oil and gas in the study area.

Because of the availability of plant fossil materials in the deep past,palaeoenvironment inversion using δ¹³C value of Paleozoic plant fossils is relatively poorly studied. In this paper,the stable carbon isotopes of some fossil plants are analyzed from the Lower Devonian Xujiachong Formation in Qujing area and from the Posongchong Formation in Wenshan area,Yunnan Province,China. The δ¹³C values of Drepanophycus from the Xujiachong Formation range from-29.0‰ to -22.8‰ with an average value of-24.5‰. The δ¹³C values of Zosterophyllum and Eophyllophyton from the Posongchong Formation range from -24.8‰ to -22.1‰ and -23.0‰ to -22.6‰,and their average values are -23.2‰ and -22.7‰,respectively. All values fall within the distribution range of the δ¹³C values of modern C3 plants. The δ¹³C values of different organs of Drepanophycus are dissimilar,and the δ¹³C value of the axis is 0.1‰ to 0.3‰ higher than that of the leaf. From the 57th to the 79th sedimentary cycles of the Xujiachong Formation,the δ¹³C value of Drepanophycus increases by about 2‰,which is interpreted as relating to a decrease in the palaeoatmospheric CO₂ concentration and to the climate cooling. The calculated C_i/C_a values of Drepanophycus and Zosterophyllum are relatively stable across the studied interval. Thus,it is inferred that these two plants are sensitive to the change of palaeoatmospheric CO₂ concentration and the palaeoclimate in Qujing area may be the present tropical savanna climate or tropical monsoon climate.

The Toarcian oceanic anoxic event(T-OAE,Early Jurassic)was an episode of profound environmental changes marked by a global carbon-cycle perturbation,marine mass extinctions,and black-shale deposits. Morphological description and inclusion analysis of fish coprolites collected from the Da’anzhai Member of the Lower Jurassic Ziliujing Formation in the northeast Sichuan Basin were carried out in this paper. We found that the interior of coprolites is composed of abundant organic matters,silts,incomplete clay minerals,phosphorous fossils,undigested fish bone,and a large number of ostracods. According to the morphology and microscopic examination of the coprolites,we speculate that they originated from lungfish. The fish coprolites were deposited in an intermediate to deep lake. During the Da’anzhai depositional period,the surface water of the Sichuan lake was enriched in oxygen,and the lake ecological system was healthy. The bottom of the lake was characterized by deposits of black shale,which implies an anoxic and reducing environment. The T-OAE fish coprolites may suggest a stratified water column in a Toarcian lake. The above results may provide a basis for the study of sedimentary response and ecological impact in the lake of Toarcian oceanic anoxic events of early Jurassic.

The continuous Permian-Triassic strata in West Qinling represent deep-marine deposits. In this paper,abundant trace fossils(seventeen ichnospecies,twelve ichnogenera)have been identified in the Upper Permian Maomaolong Formation in the Gannan area of the western Qinling orogen. As a new ichnologic method,ichnonetwork analysis focuses on the reconstruction of the community system composed of interconnected ichnotaxa,which provides useful means for studying the behavior and ecology of ichnocoenosis. In this study,an ichnonetwork analysis is conducted with trace fossils data obtained from the first hand filed trip. The results show that ichnocoenosisis structured in the Maomaolong Formaiton,and three ichnoassociations were controlled by palaeoenvironments: Palaeophycus-Lockeia-Arenicolites-Dictyodora-Planolites-Protovirgularia-Chondrites (C1,proximal turbidite zone),Palaeophycus-Lockeia-Arenicolites-Dictyodora-Protovirgularia-Phycodes-Chondrites-Helminthopsis (C2,turbidite transition zone-distal turbidite zone),and Palaeophycus-Nereites-Scolicia-Protovirgularia-Helminthopsis (C3,distal turbidite zone). The evolution from C1 to C3 in the Upper Permian Maomaolong Formation from the Gannan area of the West Qinling reveals the palaeoenvironmental changes from proximal turbidite zone to distal turbidite zone.

Based on the new findings of fossil fishes from the Silurian shallow marine red beds at the Gumushan section,Wuhan,Hubei Province,the lower Telychian(Llandovery)red beds are confirmed to be developed in southeastern Hubei. The original Fentou Formation in Wuhan area is emended and subdivided into two parts: the upper part is the emended Fentou Formation,while the lower part is called Qingshui Formation. The redefined Fentou Formation is characterized by yellowish-green,gray-green,and gray-yellow mudstones,argillaceous siltstones,and siltstones bearing abundant brachiopods,bivalves,gastropods,trilobites,and trace fossils. The lower part of the Qingshui Formation consists of purple-red,reddish-brown mudstones and argillaceous siltstones intercalated with quartz sandstones,while its upper part is dominated by purple-red and yellowish-green quartz sandstones intercalated with mudstones,argillaceous siltstones and siltstones containing lots of fossil fishes. Fishes from the upper part of the Qingshui Formation include the galeaspids Hanyangaspis guodingshanensis,Hongshanaspis inexpectatus,Jiangxialepis retrospina,and the chondrichthyans Sinacanthus and Neosinacanthus,all belonging to the Wentang Fish Assemblage of the Zhangjiajie Vertebrate Fauna. The galeaspid J. retrospina can be compared directly to J. jiujiangensis from the Qingshui Formation in Wuning area,Jiangxi Province,as members of the genus Jiangxialepis assignable to the family Shuyuidae,whose members are elements of the Silurian Lower Red Beds in South China. According to comprehensive analysis of the fish assemblage and stratigraphic sequence,the Lower Red Beds in Wuhan,with an age of early Telychian,can be correlated with the Houjiatang Formation in Anhui and Jiangsu,the Tangchiawu Formation in Zhejiang,the Qingshui Formation in Jiangxi,the Rongxi Formation in Hunan,and the Tataertag Formation in Tarim Region. In addition,the distribution pattern of the Silurian Lower Red Beds in the South China Block indicates that the Upper and Lower Yangtze seas were connected by a narrow shallow epeiric water during the early Telychian,which probably provides a precondition for the galeaspids dispersing and communicating between Wuning of Jiangxi and Wuhan of Hubei.

Western Guizhou plateau is an ideal place to reconstruct variations of the Southwest Monsoon since the Last Glacial Period. However,lack of continuous and high temporal resolution records obstacle understanding of evolution of the paleo-vegetation and the Southwest Monsoon. Here we present a palynology record since the Last Glacial Period,which was obtained from a drained paleo-lake in the western Guizhou plateau,with precise AMS¹⁴C date, to reconstruct the evolutionary history of vegetation and monsoon. Result shows that: On orbital scale during the stage of MIS3,the main vegetation comprised of arboreal and herbs,in which coniferous arboreal pollen percentage reach its maximum,and indicated a warm and humid climate,implying a strong Southwest Asia Monsoon. During MIS2,the arboreal forest decreased dramatically and the herbs and ferns extended,indicating that a cold and dry climate occurred in this area,implying a weaker Southwest Asia Monsoon,especially during the LGM. On millennium scale,Southwest Asia Monsoon of the western Guizhou plateau co-responded to the “ice drift events”in the North Atlantic,and the Heinrich(mainly H3 and H2)and LGM events resulted in weaker Southwest Asia Monsoon and the decrease of coniferous vegetation in western Guizhou plateau. Comparing with regional climate records reveal that the Southwest Monsoon and the East Asia Summer Monsoon changed synchronous on orbital or millennial scale. The in-phrase relationship implies variations of monsoon system attributed to insolation dynamics in north high latitude and the North Atlantic “ice sheets raft”. Between 19-18 cal ka BP,the research area underwent the driest and coldest climate since MIS2,the arboreal and herbal vegetation nearly disappeared,and the dominant vegetation were ferns,indicating the weakest Southwest Monsoon,while the East Asia Summer Monsoon began to strengthen,which testifies the out-phrase relationship of the two monsoon systems on sub-millennial scale.

In this paper,we studied composition,appearance and distribution of ichnofossils in the carbonates of the Upper Carboniferous-Lower Permian Taiyuan Formation in the western North China Basin,and analyzed the relationships between Sr contents, Sr/Ba values,1000×(Sr/Ca), and δ¹³C in some ichnofossils burrow and paleo-water-depth. Three types of ichnoassemblages with different water-depths were established: (1)Nereites-Chondrites ichnoassemblage occurred in the lower zone of the shallow sea below the redox interface;(2)Zoophycos-Teichichnus ichnoassemblage formed in the middle zone of the shallow sea between the wave base and redox interface;(3)Zoophycos-Thalassinoides ichnoassemblage occurred in the upper zone of the shallow sea(between the sea level and wave base)or lagoonal environments. Based on various characteristics of these ichnoassemblages in different sections,and paleo-water-depth changes in different area,two major transgressions can be identified in the Taiyuan Formation in the study area. This research provides ichnology basis for detailed studies on evolution of depositional environments and stratigraphic correlation of the Taiyuan Formation in the western North China.

Major biotic and environmental events in Earth history are often accompanied by palaeo-ocean redox condition changes,as biogenetic sedimentary structures in situ,trace fossils play a significant role in reconstructing palaeo-ocean redox conditions. This study analyzes and summarizes the previous ichnological parameters,and suggests the ichnodiversity,bioturbation degree,burrow size,and key ichnotaxa can be quantitatively used to indicate the palaeo-ocean redox conditions. Additionally,Lopingian trace fossils and bioturbation structures in South China are systematically analysed in order to reconstruct the redox conditions during the end-Permian mass extinction. The quantitative ichnological parameters reveal that the ocean anoxic event occurs in late Wuchiapingian,and the ocean anoxia is not permanent in Changhsingian,instead,obvious periodic fluctuations between anoxic/dysoxic and oxic can be observed. The high-resolution quantitative ichnological proxies at Meishan section suggest that ocean anoxia occurs in the top of Bed 24e in the Changhsing Formation,appears to correlate with the biotic mass extinction. The above examples show that the application of ichnological parameters in the reconstruction of palaeo-ocean redox conditions has broad prospects.

The overall occurrence,stratigraphical distribution,palaeoenvironmental and palaeobiogeographical significances of the ostracod faunas from the Upper Carboniferous Qijiagou Formation in the Qijiagou section of the Urümqi region,China,are documented in this study. Nineteen species belonging to 11 genera are identified and figured herein. The ostracod fauna in the Qijiagou Formation indicates an age of the Moscovian-Kasimovian. The ostracod assemblages from the Qijiagou Formation belong to palaeocopid and smooth-podocopid associations,and ecologically equivalent to the OA1-OA3 assemblages in the active plate margin. The changes of ostracod assemblages and sedimentary evidences from the Qijiagou section indicate littoral and shallow sea facies,and there was probably a regression when the Qijiagou Formation were being deposited in the Qijiagou section of the Urümqi region. The ostracods of the Qijiagou Formation have strong affinities with the taxa of Tarim,Junggar,central Tianshan and Urals,and also share some similarities with those from North America,West Europe and North China. This implies that the Junggar and Tarim blocks converged and were relatively close to the Laurasia during the Pennsylvanian(Late Carboniferous),and ostracods experienced faunal exchanges between Junggar-Tarim blocks and Laurentia. The above ostracods, further enriched the fossil materials of Qijiagou Formation, is of great sinificance for exploring the evolutionary characteristics of the acient Asian Ocean and regional mineral devdopment.

Many small inland sedimentary basins,rich in coal,uranium,hydrocarbon and others, developed during the Early Cretaceous in Beishan area at the Gansu and Inner Mongolia border area. However,the chaotic subdivision of lithological stratigraphic systems and unclear age determination have seriously hindered resource exploration in recent years. Based on the stratigraphical and palynological data collected from boreholes and outcrop sections,the Lower Cretaceous Laoshuwo Group of this area was divided into three formations in an ascending order,including the Tuomatan Formation,the Tianshuijing Formation(a new name)and the Mazongshan Formation(a new name). The former two formations are probably in an unconformity contact. The Tuomatan Formation is mainly composed of dark gray,dark gray-green coal-bearing mudstone,siltstone and coarse sandstone,containing Aequitriradites that are common in the early Early Cretaceous. Cicatricosisporites that are more common in middle Early Cretaceous are rare in the Tuomatan Formation indicating the age of this formation is the earliest Early Cretaceous(probably late Berriasian to early Valanginian). The Tianshuijing Formation is characterized by gray-green fine-grained mudstone and siltstone,and rich in Ephedripites and Cicatricosisporites,indicating an age of middle Early Cretaceous(probably Hauterivian-Barremian). The Mazongshan Formation is characterized by purple-red,light-gray fine-grained siltstone,in which a few tricolpate pollen records of early angiosperms indicate a late Early Cretaceous age(probably Aptian-Albian). This new stratigraphic system in the Beishan area at the Gansu and Inner Mongolia border area will provide reference for later resource exploration and basic research.

A series of tectonic movements during the Late Mesozoic greatly changed the topography and landform in eastern China,forming a geomorphic pattern of “high in the east and low in the west”. There is still a controversial issue on the existence of plateaus or mountains in eastern China during the Cretaceous,and thus the evolutionary processes,paleoaltitude and the extensional range of plateaus or mountains need further studies. In this paper,we collected the palynological data of xerophyte and disaccate pollen from vorious localities of China during the Cretaceous,and further discussed the paleovegetation succession and palaeoclimate evolution,which provides paleontological evidence for the interpretation of the geomorphology in eastern China at that time. The result shows that there were three climate zones in China during the Cretaceous: (i)the northeastern region was a warm and humid subtropical-warm climate zone;(ii)the northern region was a semi-arid tropical-subtropical transitional climate zone;(iii)the Tibet,Xinjiang and southern China were a hot and tropical-subtropical climate zone. The interpretation of the geomorphology shows that there was a high-altitude landform in northeast China during the early Early Cretaceous. Additionally,it is likely that coastal mountains existed in the Fujian and Zhejiang regions during the Early Cretaceous. In early Late Cretaceous,the range of coastal mountains in eastern China reached its maximum. From the late Late Cretaceous to Early Paleocene,the mountains in eastern China gradually collapsed,and by the Early Paleocene,the mountains were probably disappeared.

The palaeogeography in the northern South China Sea changed drastically in the Early Cenozoic era and the sedimentary environment underwent a transition from land to sea. The plant ecology methods are powerful in accurately revealing the transition time and processes,which is of great significance for the restoration of palaeogeography in this region. In this study,representative borehole samples are collected from the deep-water area of the Baiyun sag in the northern South China Sea to investigate the Paleogene transgression based on sporopollen algae analysis. The results show that the Baiyun sag was dominated by fluvial and lacustrine facies that was not affected by marine transgression of the Wenchang Formation in the Early to Middle Eocene. In the Enping Formation of Late Eocene,eastern and southeastern parts of the Baiyun sag developed into a shallow marine environment characterized as the development of a large number of marine sporopollen algae. The fluvial and lacustrine environments developed in the southern part in the early stage,and it transforms into marine and land transition environment. The northwestern part was dominated by large river delta environment. For the southern uplift zone of the Baiyun sag,it was characterized by fluvial lacustrine facies environment in the early stage,while it transformed into the marine and land transition environment in the late stage. The northwestern part of the depression was dominated by the large river delta environment. During the depositional period of the Zhuhai Formation in the Oligocene,it revealed a continental slope-deep sea environment in eastern and southeastern parts of the Baiyun sag,a transitional depositional environment occurred in northwestern and southern parts,and the large river delta appeared in the northwest part of the sag. Due to global sea level rise and sudden shift of the South China Sea spreading axis,most parts of the Baiyun sag were located in the continental slope environment in the early Miocene. Transgression initiated from the eastern and southeastern parts of the Baiyun sag and subsequently advanced towards the western areas,which is completely consistent with the gradual opening of the South China Sea oceanic crust from east to west.