Sedimentary systems of the Oligocene Huagang Formation in the central anticline zone of the Xihu Depression,East China Sea Shelf Basin

The Xihu Depression is the largest hydrocarbon-bearing depression of the East China Sea Shelf Basin(also referred to as the ECSSB).However,the depositional systems and reservoir distribution of the Oligocene Huagang Formation in the Xihu Depression are still controversial.Under the guidance of sedimentology and stratigraphy,this study documented a marine-terrestrial transitional environment in the restricted bay setting of the Oligocene Huagang Formation through core description,well logging,and seismic data analysis.This study also revealed that the Oligocene Huagang Formation is dominated by tidal delta,estuary,and gravity flow deposits in the central anticline zone of the Xihu Depression.The new understanding of the sedimentary systems and the discovery of the transgressive gap in the eastern Diaoyu Islands uplift explain the origin of fine-grained sediments and the EW-trending sand bodies in the central depression and the sand bodies parallel to shoreline in the west slope belt,which cannot be explained by previous study results,such as southern transgression or fluvial deltas and even lacustrine deposition.Moreover,the tidal channels,tidal sand flats,and gravity flow sand bodies formed by the transgressive tides are high-quality reservoirs.The study will provide a basis for well placement and serve as guidance for the selection of favorable hydrocarbon exploration areas in the Xihu Depression.

Method and Description of Sedimentary System Characterization Based on Sequence Stratigraphy

A Oilfield is the most representative mid to deep oil field in the Bohai Sea, with the main oil bearing intervals being the upper and middle Shahejie-3 sections of the Paleogene Shahejie Formation. By combining well seismic analysis, the middle section of Shahejie-3 is divided into high-level system tract and forced lake retreat system tract, corresponding to the II oil formation and I oil formation, respectively. Using sequence stratigraphy methods, based on seismic profiles and drilling lithological cycles, the high stand system tract is divided into 5 stages of delta progradation. The first and second stages are high angle S-type progradation with large sedimentary thickness, the third stage is oblique progradation, and the fourth and fifth stages are S-oblique composite progradation;By combining seismic data, we characterized the large-scale (8 small-scale) progradation bodies of 5 periods, clarified the distribution characteristics of reservoir planes, and laid the foundation for the later exploration of oilfield potential.

Holocene shelf-coastal sedimentary systems associated with the Changjiang River: An overview

The fate of the terrestrial sediment supplied by rivers is a critical issue for understanding the patterns of Holocene environmental change on continental shelves. The East China Sea is a typical broad continental shelf with abundant sediment supply from large rivers. Here, a variety of sedimentary records were formed during the Holocene period. The sedimentary systems associated with these records have unique charac- teristics in terms of spatial distribution, material composition, deposition rate and the timing of deposition, which are related to active sediment transport processes induced by tides and waves, shelf circulations and sediment gravity flows. The sedimentary records thus formed are high resolution slices, i.e., each record has a temporal resolution of up to 10^-10-1 a, but only covers a limited part of the Holocene time. In terms of the spatial distribution, these records are scattered over a large area on the shelf. Further studies of these systems are required to understand the underlying process-product relationships. In particular, the mid- Holocene coastal deposits on the Jiangsu coast, the early to middle Holocene sequences of the Hangzhou Bay, as well as the Holocene mud deposits off the Zhejiang-Fujian coasts, should be investigated in terms of the material supply （from both seabed reworking during the sea level rise event and river discharges）, transport-accumulation processes, the sediment sequences and the future evolution of the sedimentary systems. Advanced numerical modeling techniques should be developed to meet the needs of these studies.

A Cretaceous Desert-Playa Sedimentary System Controlled the Potash Formation in the Simao Basin

Objective The Simao Basin in Yunnan Province has developed Cretaceous evaporite-bearing clastic deposits, including the Mangang and Mengyejing Formations which were originally interpreted as fluvial and lacustrine deposits. The Mangang Fm. composed of well-rounded quartz sandstones, were commonly considered as the bottom part of the Mengyejing salt series. Dttring last decades,

Sedimentary system characteristics and depositional filling model of Upper Permian——Lower Triassic in South Yellow Sea Basin

In the South Yellow Sea Basin,Mesozoic–Paleozoic marine strata are generally well developed with large thickness,and no substantial breakthroughs have been made in hydrocarbon exploration.Through research,it is believed that the Upper Permian–Lower Triassic can be regarded as a long-term base-level cycle.Based on drilling data,characteristics of the lithology–electric property combination cyclicity,and the special lithology,the long-term base-level cycle was divided into five medium-term base-level cycles(MC1–MC5).On this basis,the Permian–Triassic sedimentary systems and their filling model were analyzed in accordance with the change of base-level cycle and transition of sedimentary environment,as well as characteristics of the drilling sedimentary facies and seismic facies.The results show that there were six sedimentary systems(fluvial,delta,tidal flat,open platform,restricted platform,and continental shelf)developed in the Upper Permian–Lower Triassic,the sedimentary systems were distributed such that the water was deep in the northwest and shallow in the southeast,and there were two base-level cycle filling models(a relatively stable tidal flat facies and a rapidly transgressive continental shelf facies to stable platform facies)developed in the Upper Permian–Lower Triassic.These models can provide a basis for evaluation of the Mesozoic–Paleozoic hydrocarbon geology in the South Yellow Sea Basin.

Paleogeomorphy,provenance system and sedimentary system of the Dongying formation in the Qikou sag

Reconstructed synsedimentary paleogeomorpholgy is an effective method in predicting the distribution of sandbodies and can provide valid evidence in the search for reservoirs. Based on a synsedimentary paleogeomorpholgy reconstruction of the third member of the Dongying formation (Ed3) in the Qikou sag,the basic paleogeomorphic characteristics of Ed3 are described and the spatial distributions of denudation and subsidence areas are discussed. Key boundary faults controlling the deposition of important sediment bodies are proposed and the interrelations among faulted slope-break belts or flexure belts,intra-depression uplifts and sags,sediment sources and sediments input points have been investigated.

Experimental Simulation Study of the Dominant Enrichment Area of Terrestrial Organic Matter in the Shallow-Delta Sedimentary System of the Yacheng Formation in the Qiongdongnan Basin

Shallow-delta sedimentary systems receive both terrestrial and marine organic matter. As oil and gas exploration activities determine that the source rocks of the deep-water area of the Qiongdongnan Basin, northern South China Sea, are generally rich in and even dominated by terrestrial organic matter, this has led many researchers to examine the rules governing terrestrial organic matter enrichment in shallow-delta sea sedimentary systems. However, the deep burial of source rocks in deep-water areas and the relatively small amount of drilling undertaken have greatly restricted the study of these rules. In this study, the ‘forward modeling' research method was used to observe and analyze the deposition and preservation of terrestrial organic matter through flume experiments, where the depositional results were carefully depicted and sampled. The total organic carbon content of selected samples was measured and when combined with qualitative observations and quantitative comparison results, the dominant enrichment areas of terrestrial organic matter were identified. The experimental results show that the overbank parts of the delta front, the dune countercurrent surface, the low-lying parts, the delta front slope area and the shallow-prodelta sea area are where terrestrial organic matter is predominantly enriched. This provides an important basis and guidance for the prediction of the development areas of marine source rocks with terrestrial input in the deep-water areas of the Qiongdongnan Basin.

The Sedimentary System and Evolution of the Early Tertiary in the Sunda Basin, Indonesia

The Sunda basin is located at the north of the Sunda Strait situated between Sumatra and Java islands, Indonesia. It is an early Tertiary typical half-graben basin, in which developed a series of terrigenous clastic sedimentation. Previous work suggested that the early Tertiary sediments were alluvial, fluvial, lacustrine and swamp deposits, of which the Banuwati formation was alluvial and lacustrine deposits, the Zelda member fluvial deposits, and Gita member fluvial and swamp deposits. In this paper, based on the integrated research on core lithology （including lithology succession and structure）, well log shape, and seismic reflection characteristics, a more detailed sedimentation system was set up as follows： l） In addition to the alluvial, lacustrine, fluvial and the swamp deposits presented in previous work, subaqeous fan, shore-shallow lacustrine, deep lacustrine and turbidite fan, fan delta and delta deposits also developed in this basin. 2） Alluvial fan, subaqeous fan and fan delta deposits occurred on the steep slope adjacent to the synrift boundary fault; while the deltaic depositional system usually distributed on the gentle slope of the basins. 3） The Zelda member that was interpreted as a fluvial deposit in previous work is now interpreted as a subaqueous fan, fan delta, delta and lacustrine deposit system. 4） From the point of view of sedimentology, the evolution of basin could be divided into four stages： the initial subsidence （matching the Banuwati formation）, the rapid subsidence （matching the low Zelda member of Talang Akar formation）, the steady subsidence or fluctuation （matching the middle Zelda member of Talang Akar formation）, and the uplifting （matching the upper Zelda member and the Gita member of Talang Akar formation）. At the initial subsidence stage, the alluvial fan, flood plain, braided stream deposits developed, and then subaqeous fan sedimentation; at the rapid subsidence stage, shore-shallow lacustrine and deep lacustrine deposits and turbidite fans occurred; at the steady subsidence stage, thick fan deltas and delta sandstones developed; and at the uplifting stage, came fluvial （including meandering fiver and the anastomosed stream） and swamp sediments. Sediment supply was mainly from the northwest, secondly from the east. From the beginning to the end of the terrigenous basin evolution, the area of sedimentation was gradually enlarged. The palaeo-topography became increasingly flat.

Sedimentary architecture of submarine channel-lobe systems under different seafloor topography:Insights from the Rovuma Basin offshore East Africa

Seafloor topography plays an important role in the evolution of submarine lobes.However,it is still not so clear how the shape of slope affects the three-dimensional(3-D)architecture of submarine lobes.In this study,we analyze the effect of topography factors on different hierarchical lobe architectures that formed during Pliocene to Quaternary in the Rovuma Basin offshore East Africa.We characterize the shape,size and growth pattern of different hierarchical lobe architectures using 3-D seismic data.We find that the relief of the topographic slope determines the location of preferential deposition of lobe complexes and single lobes.When the topography is irregular and presents topographic lows,lobe complexes first infill these depressions.Single lobes are deposited preferentially at positions with higher longitudinal(i.e.across-slope)slope gradients.As the longitudinal slope becomes higher,the aspect ratio of the single lobes increases.Lateral(i.e.along-slope)topography does not seem to have a strong influence on the shape of single lobe,but it seems to affect the overlap of single lobes.When the lateral slope gradient is relatively high,the single lobes tend to have a larger overlap surface.Furthermore,as the average of lateral slope and longitudinal slope gets greater,the width/thickness ratio of the single lobe is smaller,i.e.sediments tend to accumulate vertically.The results demonstrate that the shape of slopes more comprehensively influences the 3-D architecture of lobes in natural deep-sea systems than previously other lobe deposits and analogue experiments,which helps us better understand the development and evolution of the distal parts of turbidite systems.

Sedimentary elements,evolutions and controlling factors of the Miocene channel system:a case study of the deep-water Taranaki Basin in New Zealand

Deep-water channel systems are important petroleum reservoirs,and many have been discovered worldwide.Understanding deep-water channel sedimentary elements and evolution is helpful for deep-sea petroleum exploration and development.Based on high-resolution 3D seismic data,the Miocene channel system in the deep-water Taranaki Basin,New Zealand,was analyzed by using seismic interpretation techniques such as interlayer attribute extraction and strata slicing.The channel system was divided into five composite channels(CC-I to CC-V)according to four secondary level channel boundaries,and sedimentary elements such as channels,slump deposits,inner levees,mass transport deposits,and hemipelagic drape deposits were identified in the channel system.The morphological characteristics of several composite channels exhibited stark variances,and the overall morphology of the composite channels changed from relatively straight to highly sinuous to relatively straight.The evolution of the composite channels involved a gradual and repeated process of erosion and filling,and the composite channels could be divided into three evolutionary stages:initial erosion-filling,later erosion-filling(multistage),and channel abandonment.The middle Miocene channel system may have formed as a consequence of combined regional tectonic activity and global climatic change,and its intricate morphological alterations may have been influenced by the channel's ability to self-regulate and gravity flow properties.When studying the sedimentary evolution of a large-scale deep-water channel system in the Taranaki Basin during the Oligocene-Miocene,which transitioned from a passive margin to plate convergence,it can be understood how tectonic activity affected the channel and can also provide a theoretical reference for the evolution of the deepwater channels in areas with similar tectonic conversion environments around the world.

Sedimentary Environment and Mineralization of the Black Shale Polymetallic Layer in the Early Cambrian,SW China:Constraints from in situ LA-ICP-MS Analysis of Pyrite

A polymetallic layer is usually developed at the bottom of the early Cambrian black shale in Guizhou Province.The mineral that makes up the polymetallic layer is related to the sedimentary facies.To analyze the differentiation mechanism between polymetallic deposits(Ni-Mo and V),the Zhijin Gezhongwu profile located in the outer shelf and the Sansui Haishan V deposit located in the lower slope are selected to study the in situ sulfur isotopes and trace elements of pyrite.The results show that δ^(34)S values of pyrite vary widely from−7.8‰to 28‰in the Gezhongwu profile,while the δ^(34)S values are relatively uniform(from 27.8‰to 38.4‰)in the Haishan profile.The isotopic S composition is consistent with the transition that occurs in the sedimentary phase from the shelf to the deep sea on the transgressive Yangtze platform;this indicates that the δ^(34)SO_(4)^(2−)values in seawater must be differently distributed in depositional environments.The sulfur in the Ni-Mo layer is produced after the mixing of seawater and hydrothermal fluid,while the V layer mainly originates from seawater.Overall,the Ni-Mo and V deposits have been differentiated primarily on the basis of the combined effect of continental weathering and hydrothermal fluid.

Biogeochemistry of sedimentary organic matter in the Yongjiang River estuary in the southern part of Hangzhou Bay,China,since the Late Pleistocene

A sediment core(YJK19-02)collected from the southern outlet of Hangzhou Bay near the Yongjiang River estuary in East China was analyzed for grain size,lignin,bulk elemental composition,stable carbon isotope,and rare earth elements(REEs)to determine the sources and diagenesis of sedimentary organic matter(OM)of the estuary and adjacent areas since the Late Pleistocene.δ^(13)C values(-24.80‰–-23.60‰),total organic carbon/total nitrogen(TOC/TN)molar ratios(8.00–12.14),and light rare earth element/heavy rare earth element ratios(LREE/HREE=8.34–8.91)revealed the predominance of terrestrial sources of OM,mainly from the Changjiang(Yangtze)River.The lignin parameters of syringyl/vanillyl(S/V=0.20–0.73)and cinnamyl/vanillyl(C/V=0.03–0.19)ratios indicate the predominance of nonwoody angiosperms,and the vanillic acid/vanillin ratios[(Ad/Al)_(V)=0.32–1.57]indicate medium to high degrees of lignin degradation.An increasing trend ofΛ(total lignin in mg/100-mg OC)values from ca.14500 a BP to ca.11000 a BP reflected the increase in temperature during the Late Pleistocene.However,a time lag effect of temperature on vegetation abundance was also revealed.The relatively higher and stableΛvalues correspond to the higher temperature during the mid-Holocene from ca.8500 a BP to ca.4500 a BP.Λvalues decreased from ca.4000 a BP to the present,corresponding to historical temperature fluctuations during this time.Our results show that the vegetation abundance in the Yongjiang River Basin since the Late Pleistocene was related to the temperature fluctuation duo to climate change.

Distribution and sources of sedimentary organic matter in different aquaculture areas of northeastern Zhanjiang Bay using stable carbon and nitrogen isotopes

Zhanjiang Bay is a major aquaculture area in China with many types of mariculture products(such as oysters,fish,and shrimp).The culture area and shrimp output in Zhanjiang Bay are ranked first in China.We investigated the total organic carbon(TOC),total nitrogen(TN),TOC/TN ratio,and stable isotopes(δ^(13)C and δ^(15)N) of the fish and shrimp feed,fish and shrimp feces,and sedimentary organic matter(SOM) in and around different aquaculture areas of northeastern Zhanjiang B ay to study the impact of aquaculture activities on SOM.The average TOC contents of fish and shrimp feed were 39.20%±0.91% and 39.29%±0.21%,respectively.The average TOC content in the surface sediments of the oyster culture area,the mixed(fish and shrimp) culture area,and the cage fish farm area were 0.66%,0.88%±0.10%,and 0.58%±0.19%,respectively,which may indicate that mixed culture had a greater impact on SOM.The relatively high TOC and TN contents and relatively low TOC/TN ratios,and δ^(15)N values in the upper layer of the core sediment in the mixed culture area could also support the significant influence of mixed culture.The average δ^(13)C and δ^(15)N values of fish and shrimp feed were -20.6‰±2.2‰ and 1.8‰±1.2‰,respectively,which were different from the isotopic values of SOM in the study area.δ^(13)C and δ^(15)N values for SOM in different aquaculture areas were different from those of nearby reference stations,probably reflecting the influence of aquaculture.The δ^(13)C and δ^(15)N values in the oyster culture area(-25.9‰ and6.0‰,respectively) seemed to have reduced δ^(13)C and enriched δ^(15)N relative to those of the reference station(-24.6‰ and 5.8‰,respectively).This may reflect the influence of organic matter on oyster culture.The δ^(15)N value of the station in the mixed culture area(7.1‰±0.4‰) seemed to be relatively enriched in δ^(15)N relative to that of the reference station(6.6‰).Sedimentation and the subsequent degradation of organic matter from mixed cultures may have contributed to this phenomenon.The surface sediment at the cage fish farm area seemed to be affected by fish feces and primary production based on the indication of δ^(13)C and δ^(15)N values.The sediment core at the mixed culture region(NS6) had lower TOC/TN ratios and more positive δ^(13)C and δ^(15)N values than the sediment core at the oyster culture area,suggesting a higher proportionate contribution of marine organic matter in the mixed culture area.In summary,oyster culture,mixed culture,and cage fish culture in northeastern Zhanjiang Bay had a certain degree of impact on SOM,and mixed culture had more significant influences on SOM based on the high TOC contents and the significant vertical variations of TOC/TN ratio and δ^(15)N value in the sediment of this area.This study provides new insights into the impact of aquaculture activities on SOM content.

Application of 9-component S-wave 3D seismic data to study sedimentary facies and reservoirs in a biogasbearing area:A case study on the Pleistocene Qigequan Formation in Taidong area,Sanhu Depression,Qaidam Basin,NW China

To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment,based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China,a fourth-order isochronous stratigraphic framework was set up and then sedimentary facies and reservoirs in the Pleistocene Qigequan Formation in Taidong area of Qaidam Basin were studied by seismic geomorphology and seismic lithology.The study method and thought are as following.Firstly,techniques of phase rotation,frequency decomposition and fusion,and stratal slicing were applied to the 9-component S-wave seismic data to restore sedimentary facies of major marker beds based on sedimentary models reflected by satellite images.Then,techniques of seismic attribute extraction,principal component analysis,and random fitting were applied to calculate the reservoir thickness and physical parameters of a key sandbody,and the results are satisfactory and confirmed by blind testing wells.Study results reveal that the dominant sedimentary facies in the Qigequan Formation within the study area are delta front and shallow lake.The RGB fused slices indicate that there are two cycles with three sets of underwater distributary channel systems in one period.Among them,sandstones in the distributary channels of middle-low Qigequan Formation are thick and broad with superior physical properties,which are favorable reservoirs.The reservoir permeability is also affected by diagenesis.Distributary channel sandstone reservoirs extend further to the west of Sebei-1 gas field,which provides a basis to expand exploration to the western peripheral area.

Callovian-Oxfordian sedimentary microfacies in the middle of Block B on the right bank of the Amu Darya Basin,Turkmenistan

The right bank of the Amu Darya Basin enjoys abundant natural gas resources,on which the Callovian-Oxfordian strata in the middle of Block B serve as the major horizons for natural gas production.However,the characteristics and distribution patterns of the sedimentary microfacies in these strata are yet to be further explored.Based on the analysis of data on drilling,logging,cores,and thin sections from 29 typical wells,as well as the regional sedimentary background,this study inferred that the middle of Block B evolved from the Callovian ramp platform into the Oxfordian rimmed platform.Moreover,this study determined that the inner-ramp intertidal-subtidal shallow-water subfacies mainly developed during the Callovian and transitioned into the shallow shelf subfacies during the Oxfordian.This study identified eight sedimentary microfacies,namely reef knoll,reef-shoal complex,bioclastic shoal,psammitic shoal,bioherm,lime mud mound,intershoal(intermound),and static-water mud.Based on research into the high-precision sequence-sedimentary microfacies framework,this study built a geological model for the development of sedimentary microfacies in the study area.According to this geological model,the sedimentary microfacies in the study area are characterized by vertical alternation of reef-shoal complex,bioclastic(psammitic)shoal,bioherm,and intershoal microfacies.Moreover,they show the development of reef knoll,reef-shoal complex,bioclastic(psammitic)shoal,and bioherm(or lime mud mound)laterally from west to east,with the physical properties of the reservoirs deteriorating from west to east accordingly.The microfacies of reef-shoal complex and the bioclastic(psammitic)shoal predominate in the study area,and their deposition and development are controlled by sequence boundaries and are also affected by paleo-landforms.The Oxfordian reef-shoal complexes were largely inherited from the Callovian uplifts and show lateral seaward progradation.

Assessment of Radiological Hazards of Sedimentary, Igneous and Sediments Natural Rocks

Gamma-ray spectroscopy based on a 100% efficiency hyper-pure germanium detector was used to evaluate the activity concentrations of 226Ra, 232Th, and 40K natural radionuclides in sedimentary, conglomerate, igneous and sedi-ments rock samples collected from four different locations in Eastern desert in Egypt. The obtained activity concentrations are used to evaluate the radi-ological hazards indices, absorbed dose rate, annual effective dose equivalent in air, radium equivalent, external and internal hazard index, radiation level index, annual gonadal dose equivalent, excess lifetime cancer risk and expo-sure rate. The results show that 1) the absorbed dose rate depends on the rock type, 2) the annual effective dose equivalent in air in 71% of sample below 20 mSvy-1 (permissible limit for workers), 3) the conglomerate rocks show low radioactivity level, 4) sedimentary rocks are rich in radium while igneous rocks are rich in thorium and the sediments rocks are rich in both radium and thorium.

Investigation of the Petrological and Geochemical Characteristics of Siderite in the Early Cretaceous Sandstone of Lacustrine Sedimentary Sequence in the Erlian Basin from Northeastern China

Siderite is a prevalent authigenic mineral in siliciclastic rocks, which usually occurred in eodiagensis period and could be used as an indicator of sedimentary environment. Some siderite precipitated in burial depth with geochemical information of basin fluid evolution. The crystal morphology, geochemical composition, and isotope values are influenced by physical and geochemical environment of precipitation. In this study, samples from the Early Cretaceous of Erlian basin in the northwestern China were collected, and mineralogy, bulk and in-situ geochemistry, C and O isotopes were analyzed to comprehensively investigate the sedimentary and diagenetic environment that the sediments experienced. Six lithofaices with three types of crystal habits were recognized in the siderite-rich sandstone, bundle crystal in spherical forms, blocky rhombs in intergranular pore and cleavage of muscovite, and micro bundle and mosaic crystals aggregates in nodular. The siderite growth proceeds through micro bundle and mosaic crystals to bundle siderite aggregates and then into blocky rhombs. The crystal evolution is also reflected by geochemical composition. The micro bundle and mosaic crystals are Casiderite. The spheritic shaped bundle aggregates are Ca-Mn-siderite. The blocky rhomb siderite shows gray part and bight part with Ca, Mg and Mn varies. Increase of Ca in block rhomb siderite suggests burial and mesodiagenesis, the high content of Mn may have linkage with eogenetic effects. The relatively positive and slightly negative δ13C value indicates meteoric water domination and influence of organic matter evolution in shallow buried time. The narrow ranges negative δ18O value suggest a small span of temperature of siderite formation.

Reconstruction of paleo river systems and distribution of sedimentary facies of Shanxi and lower Shihezi formations in southern Ordos basin

The study area is located in the south of Huanxian county,in Yan'an and Puxian counties and to the north of Xi'an.The Shanxi and lower Shihezi formations are important gas-bearing formations.Given our analysis of the direction of rivers,the contents of stable heavy minerals and of feldspar of palaeo river systems,the study area is divided into six palaeodrainage patterns corresponding to six feldspar regions and six sedimentary facies regions.On this basis,the distribution of sedimentary facies was also analyzed.During the Shanxi stage,a delta front was deposited in the Huanxian region and delta plains and fronts were deposited in the Pingliang,Chunhua-Yaoxian and Hancheng-Chengcheng regions.In the Yan'an-Daning region,only a delta front was developed.The distribution of sedimentary facies in the earlier Shihezi stage originated from the Shanxi stage.A delta front was developed in the Huanxian region while a delta plain and front developed in the Pingliang-Zhenyuan region during the same time.Lakes originated only in the Zhenyuan-Huanxian-Huachi-Zhengning and Daning-Jixian zones.This analytical method shows that different palaeodrainage patterns can be effectively distinguished in order to forecast sedimentary facies.

Sedimentary characteristics of distributive fluvial system in arid area: A case study of the Shule River distributive fluvial system, NW China

Based on detailed investigation of the modern sedimentation of the distributive fluvial system of Shule River and the data of unmanned aerial vehicle(UAV)aerial photography and satellite remote sensing,the sedimentary characteristics and differences of distributive fluvial system in arid areas are analyzed.By comparing the changes in slope,river morphology and sedimentary characteristics in different sections from the apex to the toe,the distributive fluvial system of Shule River can be divided into three facies belts:"proximal","middle"and"distal".The proximal belt has the largest slope and strongest hydrodynamic condition,mainly appears as large-scale braided river deposits;the fluvial bars in this belt are mainly composed of gravels,the gravels have good roundness and certain directionality,and are medium-large boulders,with low sand content;the main microfacies in this belt are braided channel and flood plain.The middle belt with slope smaller than the proximal belt,is mainly composed of braided bifurcating river deposits.Due to branching and infiltration,this belt has weaker hydrodynamic conditions,so some of the distributive rivers dry up,appearing as ephemeral rivers.This belt has small lenticular sandbodies,fine to medium gravels,higher sand content,and mainly braided channel,flood plain and aeolian dune microfacies.The distal belt has the smallest slope and flat terrain,where the river begins to transform from braided river to meandering river,the sediment is mainly sand.Due to the influence of slope,this belt has weaker erosion toward source and stronger lateral erosion,and point bars developing around the edge of the active lobes.In this belt,the river is completely meandering,and the main microfacies are braided channel,meandering channel,flood plain,aeolian dune,lake and swamp.

Control of paleogeographic pattern on sedimentary differentiation of evaporite-carbonate symbiotic system:A case study of the sixth sub-member of Ordovician Majiagou Formation M5 Member in central-eastern Ordos Basin,NW China

The relationship between paleogeographic pattern and sedimentary differentiation of evaporite-carbonate symbiotic system is examined based on logging,core and thin section data,by taking the sixth sub-member of fifth member of Ordovician Majiagou Formation(M56)in the central-eastern Ordos Basin as an example.(1)Seven sub-geomorphic units(Taolimiao west low,Taolimiao underwater high,Taolimiao east low,Hengshan high,East salt low,North slope and Southwest slope)developed in the study area.(2)The“three lows”from west to east developed dolomitic restricted lagoon,evaporite evaporative lagoon and salt evaporative lagoon sedimentary facies respectively,the"two highs"developed high-energy grain beach and microbial mound,and the north and south slopes developed dolomitic flats around land.(3)The paleogeographic pattern caused natural differentiation of replenishment seawater from the northwest Qilian sea,leading to the eccentric sedimentary differentiation of dolomite,evaporite and salt rock symbiotic system from west to east,which is different from the classic“bull's eye”and“tear drop”distribution patterns.(4)As the Middle Qilian block subducted and collided into the North China Plate,the far-end compression stress transferred,giving rise to the alternate highland and lowland in near north to south direction during the sedimentary period of M56 sub-member.(5)Taolimiao underwater high and Hengshan high developed favorable zones of microbial mounds and grain shoals in south to north strike in M56 sub-member,making them favorable exploration areas with great exploration potential in the future.