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《Bulletin of Mineralogy, Petrology and Geochemistry》
JOPC 2022 Vol.24 Number 4
2022, Vol.24 Num.4
Online: 2022-08-01
LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY
SEQUENCE STRATIGRAPHY AND PALAEOGEOGRAPHY
PALAEOGEOGRAPHY AND MINERAL RESOURCES
QUATERNARY PALAEOGEOGRAPHY AND SEDIMENTOLOGY
HUMAN HISTORY PALAEOGEOGRAPHY
0
WU Shenghe, XIAN Benzhong, WANG Yuan, WANG Junhui
Foundation conference of the International Society of Palaeogeography was grandly held
2022 Vol. 24 (4): 0- [
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FENG Zengzhao
A report of application for founding International Society of Palaeogeography at congratulation meeting
2022 Vol. 24 (4): 1- [
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WU Shenghe
President speech in foundation conference
2022 Vol. 24 (4): 2- [
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Congratulatory messages and letters
2022 Vol. 24 (4): 3- [
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LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY
611
JI Youliang, REN Hongyan, ZHANG Shiqi, MA Zhengtao, NIU Jiayu, GUO Shanshan, GAO Chenxi, LIU Xiaoyu
Paleogene palaeogeography and oil and gas distribution in Bohai Bay Basin
The Bohai Bay Basin is a typical inner-continent rift basin characterized by six depressions,four uplifts,54 sub-depressions and 44 sub-uplifts. The hydrocarbon distributions are closely related to their palaeogeography. In this paper,integration of a large number of well logging,core,paleontological and seismic data in various depressions in Bohai Bay Basin,as well as a large number of published data,were used to correlate and build the Paleogene(including the Kongdian,Shahejie and Dongying Formations)stratigraphic framework in each depression in Bohai Bay Basin. On this basis,the sedimentary facies of each formation and member of the Paleogene in the Jizhong Depression,Jiyang Depression,and Dongpu sub-depression of Linqing Depression were analyzed,and the sedimentary system map of these areas was compiled. Combined with previously published palaeogeographic reconstruction of the Liaohe Depression,Huanghua Depression and the Bohai Sea area,the lithofacies palaeogeographic map of the Kongdian Formation,the Members 4,3,2,1 of Shahejie Formation,and Dongying Formation of the Paleogene in the Bohai Bay Basin were compiled. There are dozens of oil and gas-bearing sags in the Bohai Bay Basin. The deep lacustrine mudstone in the center of each sag constitutes the source rocks,while the nearshore sublacustrine fans,fan deltas,deltas,beach bars and other sand bodies on the sag margin are important reservoirs. Under favorable accumulation conditions,the source rock in the center of the sag supplies hydrocarbons to the surrounding interbedded reservoirs to form oil reservoirs. In the center of the sag,unconventional hydrocarbon resources such as shale oil,shale gas,and tight oil and gas are also developed. Therefore,each depression is the basic unit of oil and gas generation,migration and accumulation,and an independent oil and gas migration-accumulation system. The distribution of oil-generating sags and their palaeogeographic features control the planar distribution of oil and gas in the Paleogene in the Bohai Bay Basin.
2022 Vol. 24 (4): 611-633 [
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RAN Zongyuan, XIAO Qian, SHE Zhenbing, WANG Guoqing
Tempestite sequence of carbonate rocks of the Wumishan Formation in Zhoukoudian area,Beijing
The Mesoproterozoic Wumishan Formation is widely exposed in the Zhoukoudian area,Beijing. It mainly comprises of dolostones with abundant siliceous bands and intraclasts. The irregular shape of these intraclasts suggests that they were strongly deformed before deposition. Its genesis remains controversial,though they were interpreted as dewatering or scouring structures,seismites,or storm-related deposits(tempestites). Here we present results of detailed sedimentological studies on the Wumishan Formation in the Hengshunchang section located in the Zhoukoudian area. Based on systematic analysis of lithology and sedimentary structures,we interpret the studied unit as a typical carbonate tempestite sequence. Sedimentary cycles in the sequence can be divided into five units(A to E)from bottom to top. Unit A consists of a medium- to thick-layered dolo mudstone,as fair-weather deposits before the storm. Unit B is characterized by scouring surface with gutter casts and siliceous intraclasts,representing the product of storm surge. Unit C is composed of gray-banded siliceous dolostones,with continuous siliceous strips and well-developed parallel and cross beddings(including wavy cross bedding,hummocky and swaley cross stratification)that imply deposition during the storm attenuation period. Unit D is a gray-white,thin-layered dolo mudstone,interpreted as post-storm deposits. Unit E consists of dolostones with siliceous nodules,likely formed by local disturbance of seawater in fair-weather conditions. This distinct sedimentary sequence,combined with conspicuous scouring bottom surface,high content and extremely disorganized intraclasts,suggests that the Hengshunchang section represent an
in situ
tempestite and the study area was located near the tropics in the Mesoproterozoic period. At that time,the surface seawater temperature was likely relatively high. Tropical cyclones were prone to occur,which may have triggered frequent storm surges and eventually typical storm deposits formed at the Hengshunchang section. The research results not only supply the storm sedimentary records of the Wumishan Formation in Yanshan area,but also provide important sedimentological evidence for the paleogeography,paleolatitude and paleoclimate of North China plate in this period.
2022 Vol. 24 (4): 634-648 [
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649
LI Feiyang, ZHANG Lijun, LI Tairan, YANG Qiqi, NIU Yongbin, SONG Huibo
Sedimentary characteristics and palaeoenvironmental significance of the Permian-Triassic transition at Niejiagou section of Shaanxi in eastern Qinling
The marine carbonate strata of the Permian-Triassic transition were found in the Niejiagou section of Zhen'an,Shaanxi. It records the succession of biota and environmental changes of shallow-marine carbonate platform in the Permian-Triassic transition,and is a perfect area for studying the depositional response and palaeoenvironmental changes before and after the end-Permian mass extinction. Based on the detailed analysis of carbonate microfacies and biology combination in the Permian-Triassic transition of the Neijiagou section,11 microfacies types are identified,including patched agglomerates,stromatolites,oolitic-layered stromatolites,foraminiferal grainstone,algal-crinoid grainstone,wackestone containing coated and eroded bone debris particles,oolitic grainstone,aggregate grainstone,oolitic wackestone,mudstone and micrite. According to the characteristics of carbonate microfacies and sedimentary indicators,marginal shoal facies,open platform facies and restricted platform facies are divided in the Permian-Triassic transition. The microfacies characteristics reflect frequent sedimentary microfacies changes in the Permian-Triassic transition. The biological succession and stratigraphic sequence of the Permian-Triassic transition in the Niejiagou section have good uniformity correlation with other sections in South China. After the end-Permian mass extinction,low biodiversity and biological abundance,e.g.,small bivalves and crinoid,occur in the shallow-marine carbonate platform in the Early Triassic. The special microbial sedimentary structures dominated around the mass extinction event boundary. Afterwards,the microbialites disappeared and the bioclastic limestone reoccupied. This research can provide new understanding for the coevolution of organisms and the environment caused by the end-Permian mass extinction.
2022 Vol. 24 (4): 649-662 [
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663
ZHANG Xinyue, LI Ling, ZHANG Daofeng, YI Gang, WU Dongxu, ZHONG Shoukang, YANG Mengying, XIONG Ying, XIAO Di, TAN Xiucheng
Characteristics and genesis of quasi-stratified karst breccia of the Majiagou Formation in Ordos Basin
Karst breccia with complex structural characteristics is widely developed in the Ordovician Majiagou Formation in Ordos Basin. It is found that the classical model can not explain the fabric and distribution characteristics of breccia,and the genetic mechanism is required further studied. Based on observation of cores and thin sections,different types of breccias of upper Ordovician Majiagou Formation in the eastern Sulige Gas Field are summarized and identified to clarify the spatial distribution,sequence structure characteristics and the formation mechanism. The results showed that(1)five types of breccia can be identified according to the occurrence and origin,including nearly in situ dissociation breccia(B1),near surface accumulation breccia(B2),cave accumulation breccia(B3),height(wall)fractured breccia(B4)and solution breccia(B5). They are multilayer overlapping in the vertical direction and have the “quasi stratified”characteristics which can be comparable in the horizontal direction;(2)The vertical configuration and evolution of different breccias are related to the periodical upward shallower sedimentary sequence and exposure dissolution,which can be classified into three types: main development type of B1,combined development type of B2-B3-B4 and main development type of B5;(3)The quasi-stratified breccia formed in the early diagenetic stage and was controlled by the high frequency sea level change under the background of low geomorphic relief,the multi-cycle superposition in the vertical direction,transverse migration and interlocking process of exposed dissolution lens. The research is helpful for understanding the characteristics and genesis of diversified karst breccia in Majiagou Formation,Ordos Basin,which also provides new materials for the study of dolomite karstification at the early diagenesis period.
2022 Vol. 24 (4): 663-679 [
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680
HUANG Jiansong, ZHENG Jie, SONG Xiang, LIU Lei, YI Gang, YANG Ping
Sedimentary characteristics of Beichagou Sandstone in the Lower Permian Shanxi Formation in Ordos Basin and its effects on natural gas accumulation
Beichagou sandstone,which is the marker bed between Shanxi and Taiyuan Formations of Permian in North China Platform,is widely distributed in the Ordos Basin and acted as the significant Upper Paleozoic natural gas reservoir. Based on the outcrop investigation,exploration data,and previous studies of palaeostructure and lithofacies paleogeography,the sedimentary characteristics of Beichagou sandstone in the Ordos Basin were analyzed in detail. Due to the abundant supply of coarse clastics with high quartz content in the provenance area in a short time,the lithology of the Beichagou sandstone is mainly gravel bearing coarse-grained quartz sandstone with quartz content up to 90%. The sand bodies are closely overlapped and stable distributed,and there is rare mudstone interlayer between single sand bodies. The paleogeography is highest in the north,high in the south and low in the south central,making the alluvial fan,gravelly braided river,braided river delta plain,delta front and prodelta successively advanced from the north and south margin to the central area of the Ordos Basin. Four large scale sand belts of delta deposit developed in the north part of the deposition center,while six small scale sand belts developed in the south region. Influenced by the sandbody size,variation of mineral composition and diagenesis,the reservoir properties of each sand belt varies greatly. The largest sand body along Hangjinqi-Yulin-Zizhou-Qingjian-Yonghe-Jixian,which is characterized as the highest quartz content,and very high dissolution of feldspar and other soluble minerals under the action of acidic formation water,has the favorable reservoir properties and beneficial for the accumulation of natural gas. The Beichagou sandstone along Hangjinqi-Yulin-Zizhou-Qingjian-Yonghe-Jixian,is a favorable belt for further exploration and development of natural gas in the Ordos Basin.
2022 Vol. 24 (4): 680-696 [
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697
LI Changhao, GE Yu, JIN Xin, SHI Zhiqiang
Sedimentological evolution during the Early Jurassic Fuxian period in Ordos Basin: palaeoclimatic response to Toarcian Oceanic Anoxic Event
As a global geological event,the early Toarcian(Early Jurassic)Oceanic Anoxic Event(T-OAE)(~183.8 Ma)affected both the marine and terrestrial environments. The response of this event had been recorded in the Lower Jurassic Fuxian Formation in the Ordos Basin. Based on the field geological survey,scanning electron microscopy and thin section analysis,we studied the lithology,color changes and sedimentary sequence of the Fuxian Formation in the northeastern Order Basin. Together with the previous research results of literature,we revealed the lithofacies palaeogeography and sedimentary model of the Fuxian period. Our results show that the Ordos Basin had experienced the palaeoclimatic change from wet to drought during the Fuxian period. The white glutenite and black or gray mudstone/shale containing abundant plant fossils deposited in the humid conditions,which corresponds to the filling stage of valleys in the basin. After filling up,the variegated and red mudstone/shale containing few plant fossils deposited in the flat topographical condition during the late Fuxian period,corresponding to an arid climate pulse under the overall humid climate in the Early and Middle Jurassic periods. The changes of rock color and climate are interpreted as the continental response of the T-OAE,which can be used for the isochronous correlation of the Fuxian Formation. We interpret the “coarse Fuxian”was fluvial deposits filling the incised valleys,the “fine Fuxian”deposited in lake or flood plain environments,the “black Fuxian”and “white Fuxian”were sedimentary products of humid climate,while “variegated Fuxian”and “red Fuxian”deposited under drought climate condition after the T-OAE.
2022 Vol. 24 (4): 697-712 [
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YI Dinghong, SHI Yajun, LI Xiang, LONG Guohui, NI Xianglong, LI Jiyong, WANG Zhaobing, MA Xinmin
Sedimentary evolution and controlling factors of beach bar sand bodies of the Upper Ganchaigou Formation of Neogene in Zhahaquan area, western Qaidam Basin
The beach bar sand body,which is the significant reservoir for lithologic oil and gas reservoir exploration,has become an important exploration field of increasing reserves and production in China's lacustrine basin. In order to further evaluate the oil and gas exploration prospect of the beach bar sand bodies which developed in the shore-shallow subfacies in the Upper Ganchaigou Formation in Neogene in Zhahaquan area,western Qaidam Basin and predict the favorable exploration zone and target,based on the core observation and comprehensive analysis of drilling and logging data,combined with the analysis results of rock thin sections,cumulative particle size probability curves,dark mudstone mud-to-ground ratio and sand-to-ground ratio sensitive parameters,the development and evolution characteristics of shore-shallow lake beach-bar sand bodies and paleogeomorphology in the Upper Ganchaigou Formation in this area are studied in detail. The results show that: (1)The braided delta-shallow lake sedimentary system was developed in the Upper Ganchaigou Formation in Zhahaquan area. The beach bar sand body was developed,and the lithology was mainly lithic feldspar fine sandstone-ultrafine sandstone. The compositional maturity was medium-poor,and the sorting roundness was medium-good. The particle size probability curve was mainly composed of two-stage jump and suspension reflecting wave action. Sedimentary structure types are diverse,including wave sand ripple cross bedding,wavy bedding,hilly cross bedding and lenticular bedding. (2)During the sedimentary period of the Upper Ganchaigou Formation,the scale of beach bar sand body in the study area first increased and then decreased. From the early to the middle period,the scale of beach bar sand body continued to increase. Among them,the nearshore bar mainly expanded in the south and east directions,and distributed in the north-west direction. The farshore bar mainly expanded in the north-south direction,and distributed in the northwest-southeast direction. From the middle stage to the late stage,the development scale of beach bar sand body decreases continuously. Among them,the nearshore bar mainly shrinks in the north-south direction and extends eastward,and the distribution direction changes from southeast to northeast. The farshore bar mainly shrinks in the north-south direction. (3)During the deposition period of the Upper Ganchaigou Formation,the paleogeographic is characterized as high in the west and low in the east,low in the north and low in the south,and high in the middle part in the study area. From the early to the middle period,the paleogeomorphic high points continued to expand significantly to the east and southeast directions,and the scope was expanding. From the middle to the late period,the range of paleogeomorphology high points continued to shrink in the north and northwest directions,and the range of paleogeomorphology high points in the southeast corner of the study area continued to expand northward. Comprehensive analysis of the above results shows that the development and evolution of beach bar sand body of the Upper Ganchaigou Formation in Zhahaquan area is controlled by the source scale and the development of micropaleogeomorphology. Among them,the evolution of micropaleogeomorphology is the dominated factor for the development of beach bar sand body. The research results can provide reference for lithologic trap prediction of beach bar sand body under similar geological setting.
2022 Vol. 24 (4): 713-727 [
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SEQUENCE STRATIGRAPHY AND PALAEOGEOGRAPHY
728
WU Yinye, LI Guoxin, WU Luofei, XU Zhaohui, LONG Guohui, FANG Xiang, FU Lei, ZHANG Tianshu, TAO Shizhen
Advances on depositional systems tracts in large lake basins and shale oil and gas exploration in mid-western China
Detrital siliciclastics and carbonate deposits are widely distributed in China,and many new oil and gas fields have been discovered in petroliferous basins,especially in tight oil/shale oil exploration in recent years. It is suitable for studies of allo-cyclic sequences with genetic connections to explain the sequence stratigraphic unit according to the evolution of the sedimentary systems tract and accommodation changes. Through this approach,sequence evolution models could be built and oil and gas reservoirs could be predicted. The advances on systems tracts of deep-water systems are manifested in the introduction of the concept of forced regression(sea or lake),developing from the classical three-division systems tracts to the four systems tract and/or two systems tracts,and the distribution of internal relative comformity sequence and systems tract at different scales are closely related to naming. The falling stage systems tract(FSST)and forced regression wedge systems tract(FRW)are formed under different conditions. A-P-D parasequence stacking pattern analysis is used to analyze the Hyperpycnal and the sediment mechanism of normal fluid(Homopycnal and/or Hypopycnal),which improves the accuracy of systems tract identification and oil and gas reservoir prediction. Research examples of the Qaidam Basin and Sichuan Basin confirm that lacustrine transgressive systems tract develops as as lake level rises,shallow lake and semi-deep lake areas expand,the deltaic thin-bedded sands and deep-water turbidite fans and multi-cycle muddy shale-marl combinations are developed in depocenters. It is conducive to the development of shale oil and gas reservoirs and become the “sweet spots” of exploration target areas. Looking forward to the future,important progress will be made in the field of shale oil and gas exploration in the following aspects: (1)research on high-frequency cycle systems tract of deep-water depositional systems in salt lake basins; (2)study on mixed depositional systems of TST that are related to shale type and mixed sediment shale oil types; (3)sequence-paleogeographic studies at the scale of systems tract; (4)studies on source-sink systems and the distribution characteristics of ancient lakes under the framework of systems tract; (5)geochemical indexes analysis of paleo-water depth,paleo-climate and paleo-environment in lakes;(6)reservoir capacity of micro-nanoscale pore-fracture systems in organic-rich shales;(7)sedimentological research on the contribution rate of pure lacustrine mudstones and swamp mudstones to large-scale natural gas hydrocarbon resources.
2022 Vol. 24 (4): 728-741 [
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742
LI Dongwei, GONG Chenglin, WANG Jun, LI Yichao, LI Hong, GE Daoyao
Recognition and prediction of fluvial sand-bodies and their responses to paleoclimatic fluctuations: a case study in the Lower Member of Ming-huazhen Formation in southern Shijiutuo uplift,Bozhong Depression
The recognition and prediction of fluvial sand bodies and their responses to paleoclimatic fluctuations represent a hot topic of concern in fluvial sedimentology. Based on the seismic sedimentology approach,a three-step workflow used for delineation of fluvial sand bodies has been proposed(
i.e.
,seismic-well tie used for establishment of sequence stratigraphic framework,90° phase rotation to correlate with lithology to seismic events,and stratal slices used to identify sand bodies). This workflow was utilized to delineate fluvial sand bodies in the Lower Member of Neogene Minghuazhen Formation,southern Shijiutuo uplift,Bozhong Depression,Bohai Bay Basin,leading to the recognition of six main types of fluvial sand bodies(e.g.,straight and sinuous channel sandstones,channel-levee complexes,point bars,oxbows,river mouth bars,and crevasse splay). Paleoclimates during the deposition of the Lower Member of the Minghuazhen Formation were reconstructed,based on mudstone colours and records of algae species and sporopollens. Our results suggest that the early,middle,and late evolutionary stages of the Lower Member of the Minghuazhen Formation underwent humid-arid transition,dominantly humid,and predominantly arid conditions,respectively. The paleoclimatic evolution towards a humid condition led to the decrease in sandbody widths and channel sinuosity,and to the better development isolated channel fills characterized by ribbon-shape distribution patterns. The paleoclimatic evolution towards an arid condition led to the increase in sandbody widths and channel sinuosities,and to the better development of channel-levee complexes and river mouth bars characterized by band-shaped distribution patterns. The database and observations of this study provide reference for the recognition and prediction of fluvial sand bodies in other rift basins,and have practical implications for hydrocarbon exploration of fluvial sand bodies in the shrinking evolution period of lacustrine basins characterized by weak tectonic activities.
2022 Vol. 24 (4): 742-758 [
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PALAEOGEOGRAPHY AND MINERAL RESOURCES
759
ZHOU Jinghao, XIAN Benzhong, ZHANG Jianguo, ZHONG Qi, CHEN Peng
Organic matter enrichment law of lacustrine shale constrained by high resolution cyclostratigraphy: a case study from the lower sub-member of Member 3 of Paleogene Shahejie Formation,Dongying sag
The precise prediction of organic matter,which is closely related to palaeoclimate and palaeoenvironment,is the core and difficulty of petroleum geology research. In this study,cyclic stratigraphy and geochemical techniques were used to identify the high-frequency cyclic strata and analyze the palaeoenvironment,palaeoclimate,organic matter geochemistry and mineralogy of the lower sub-member of Member 3 of Shahejie Formation($Es_{3}^{L}$)in Well FY1,Dongying sag. The results show that: (1)Two 1.2 Ma long-term obliquity cycles,five 400 ka long eccentricity cycles,21 short eccentricity cycles of 96 ka,42 obliquity cycles of 51 ka and 103 precession cycles of 19 ka are identified in the $Es_{3}^{L}$ of the Paleogene in Dongying sag. Combined with the previous research results,based on the waveform curves of 1.2 Ma,400 ka and 96 ka,two long-term,six medium-term and 21 short-term base-level cycles were identified. (2)The correlation between the depositional environment of $Es_{3}^{L}$ and TOC data indicates a synchronization between palaeoclimate evolution and organic matter enrichment,which are controlled by the astronomical cycle. During the long obliquity or long eccentricity increased period,the climate become warmer and result in a raised base-level,enhanced reduced environment and favorable environment for organic matter accumulation. (3)The degree of organic matter enrichment depends mainly on the palaeo-productivity controlled by the wet climate and preservation condition controlled by paleo-lake depth. The long-term and medium-term scale cycle has a dominated control on organic matter enrichment. Therefore,the waveform curve of the long-term and medium-term scale cycle can be used to reconstruct the palaeoenvironment and locate the rich organic matter layer.
2022 Vol. 24 (4): 759-770 [
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YU Zhiyun, CHEN Shiyue, ZHANG Shun, LIU Xinjin, TANG Dong, YAN Jihua
Influence of diagenesis on reservoir performance of shale: a case study of the upper sub-member of Member 4 of Paleogene Shahejie Formation in Dongying sag
The pore structure characteristics and reservoir capacity of continental shale oil reservoirs are affected by the complex diagenetic alteration during burial,resulting in significant vertical differences. However,relevant researches are still limited. This work focuses on the typical continental organic-rich shale of the upper sub-member of Member 4 of Paleogene Shahejie Formation(E
s
4U
)in Dongying sag,using the multi-scale observation methods like core description,thin section and scanning electron microscopy(SEM)observations,X-ray diffraction,isotope geochemistry,physical property and energy spectrum analysis,to reveal the diagenesis characteristics and its controls on reservoir quality of the shale. Our work has identified that: (1)Seven types of diageneses that can affect reservoir quality. The constructive diagenesis is mainly calcite recrystallization,clay mineral transformation,and dolomitization. The E
s
4U
is overall in the middle diagenetic stage A. (2)Calcite recrystallization,clay minerals transformation,and dolomitization vary significantly in vertical. The sparry calcite caused by recrystallization is mainly developed in the $Ea^{4Ucs3}$ and the $Ea^{4Ucs2}$ layers. The intermediate and high pores formed by clay minerals transformation are mainly developed in the $Ea^{4Ucs2}$ layer. Based on the petrological characteristics,there are two types of dolomite identified in the study area. Among them,the argillaceous dolomite is mainly developed in the $Ea^{4Ucs3}$ layer,and the microcrystalline iron dolomite is mainly developed in the $Ea^{4Ucs1}$ layer and the $Ea^{4Ucs2}$ layer. (3)The combined actions of calcite recrystallization and clay mineral transformation generate a large number of micropores in the $Ea^{4Ucs2}$ layer. At the same time,moderate iron dolomite is a skeleton mineral to support the pores,conducive to preserving pores in a moderate-deep burial depth. It is the key for the $Ea^{4Ucs2}$ layer to become a high-quality shale-oil reservoir.
2022 Vol. 24 (4): 771-784 [
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785
CAO Shengtao, XIE Hong, ZHENG Lulin, WEI Huairui, ZHANG Lan
Study on metallogenic environment,mineralization and metallogenic model of the Xifeng phosphate deposits in central Guizhou Province,China
The Xifeng phosphate deposit is an important component of the Ediacaran Doushantuo phosphate deposits in Guizhou Province,Southwest China,which is characterized by a thick ore layer,a high quality,a developed fault system,and rich and unique stromatolites. We reveal that the Xifeng phosphorite rocks were formed in the foreshore and shoreface environments under the combined conditions of hot water,biological and normal seawater sedimentation. The Doushantuo Formation underwent a palaeoclimate shift from a warm and humid climate to a dry and hot climate,and to a hot and humid climate,related to transgression,regression,and transgression,respectively. Therefore,the metallogenic process of the Xifeng phosphate deposits also underwent three stages of mineralization related to the transgression,regression and transgression again. The lower ore layer formed during the early transgression stage of the Doushantuo Period,whereas the upper ore layer formed in the subsequent regression and transgression stages. The two ore layers are separated by dolomite on the margin of the palaeo-continent of central Guizhou. When the second transgression crossed the foreshore position of the first transgression,only the upper ore layer formed,namely the Kaiyang and Xifeng phosphorus deposits. The Wengfu phosphate deposit has two layers of ore bodies,corresponding to the foreshore and shoreface zone that experienced three stages of mineralization. The location elevation of Wengfu phosphate deposit during mineralization is significantly lower than the Xifeng phosphate deposit,and the Xifeng phosphate deposit was slightly lower than the Kaiyang phosphate deposit. During mineralization prediction and prospecting exploration of the phosphate deposits in the Doushantuo Period,the dynamic foreshore and shoreface environment in central Guizhou and its vicinity,similar to the Xifeng phosphorus deposit,is the prospecting target area. Meanwhile,using the characteristics of two intersecting ore layers formed by “three-stage mineralization”,mineralization prediction surrounding the known deposits,mineralized points and foreshore and shoreface zones can be efficiently performed.
2022 Vol. 24 (4): 785-801 [
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QUATERNARY PALAEOGEOGRAPHY AND SEDIMENTOLOGY
802
AN Yu, FAN Niannian, XU Zhiwei, LIU Xingnian
Estimation of dust source of Shimao loess in Loess Plateau-Mu Us junction area based on detrital zircon
There is still no consensus on the source of dust in the Chinese Loess Plateau,especially the contribution of deserts and rivers. Focusing on the Shimao section of Shenmu city in the eastern Mu Us Desert,this study analyzes the source of aeolian dust deposits and river sediments since the last deglaciation by using detrital zircon age,as well as Inverse Monte Carlo model to quantify the provenance distribution. The results of particle size distribution and Cathodoluminescence images show that Shimao loess is composed of typical aeolian deposits. The peak ages of coarse detrital zircons(>40 μm)in Shimao loess occur at 190~300 Ma,300~600 Ma,1700~1900 Ma and 2300~2600 Ma,demonstrating that the proximal(local bedrock detritus),intermediate(Yellow River sediments)and the distal(Alashan Desert)sources all contribute to the detrital zircon ages;quantitative calculations show that the three source areas contribute 71%,21% and 8% of the aeolian coarse particles,respectively. For the proximal and intermediate sources,the Yellow River and its tributaries eroded the bedrock and transported the deposited floodplain materials,which became the transfer station for dust transportation and provided the main material source for the formation of loess. The results of optically stimulated luminescence dating show that the river sediments and the overlying loess in the Shimao sectoin were formed in the penultimate deglaciation and the last deglaciation respectively. This in turn suggests that the sedimentary discontinuity between the river sediments and the overlying loess layer may indicate the erosion events from the last glacial to deglaciation period,which led to the exposure of river floodplain materials and the formation of potential local dust sources. These results indicate that river systems including the Yellow River and its tributaries have an important provenance contributions to dust loess.
2022 Vol. 24 (4): 802-812 [
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HUMAN HISTORY PALAEOGEOGRAPHY
813
WANG Ying, LIU Dezheng, ZHANG Yongzhan
Influence of environmental changes on departure ports of Northern Maritime Silk Road in Yangtze River Delta region,China
Being an important waterway for trade between China and East Asian countries in ancient times,the Northern Maritime Silk Road promoted the great development of the Maritime Silk Road during Song to Yuan Dynasties,and achieved the glory of the great navigation in the Ming Dynasty. It is of great significance to study the changes and causes of the departure port for the improvement of the “Maritime Silk Road Research System”and the construction of the “21
st
Century Maritime Silk Road”,but so far there is little research. Based on the records of ancient Chinese books,local chronicles and historical maps,combined with the previous understanding of China's environmental changes in the historical period,this paper studies the changes and causes of the main departure ports of the northern MSR in the Yangtze River Delta region from the Sui and Tang dynasties to Ming and Qing dynasties. The results show that: (1)During the Sui-Tang and Ming-Qing Dynasties,three main departure ports of the northern MSR emerged successively in the Yangtze River Delta region. The Yangzhou port flourished during the Sui and Tang dynasties,the Shanghai Port rose in Tang and Song dynasties,and the Mingzhou port(now Ningbo port)thrived during the Song and Yuan dynasties;(2)As the climate became cooler,the northern ethnic minorities were committed to invading the south,the economic and political center of Central China moved southwards. As a result,the departure port of the northern MSR moved from the Dengzhou(now Penglai)in northern Shandong peninsula to the Yangtze River Delta region; (3)With the accumulation of sediment,the echelon-shaped shoals developed,the estuary branched eastward and moved southwards,and the river-mouth coastlines of the Yangtze River evolved from a trumpet-shaped estuary to a delta. That is the key reason for the departure port to move eastwards from the Yangzhou port to Shanghai port and even to abandon the Yangtze River mouth and shift to Mingzhou port at the Hangzhou Bay,
i.e.
the Qiantangjiang River estuary;(4)The development of shoals in the mouth of the Yangtze River has also caused changes in the water systems in the areas of the Yangzhou port and Shanghai port,so that the specific positions of the ports are constantly adjusted following the changes of river conditions when these two ports are used as the main departure ports of northern MSR; (5)Changes in foreign trade policies also played a certain role in promoting or hindering the changes of the main departure port.
2022 Vol. 24 (4): 813-824 [
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