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	JOPC 2022 Vol.24 Number 6
	2022, Vol.24 Num.6
	Online: 2022-12-01

	LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY BIOPALAEOGEOGRAPHY AND PALAEOECOLOGY GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS QUATERNARY PALAEOGEOGRAPHY AND SEDIMENTOLOGY

LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY

	1037	YU Xinghe, LI Shunli, SUN Hongwei

		Coupling effect of “mass-slope” from source to sink in clastic rock deposition
		The three-dimensional spreading characteristics of clastic rock deposition and their genesis mechanisms are the key to establish the depositional models and predict sand distribution,which is a key scientific problem in sedimentology research. Most domestic and abroad scholars considered that the planar geometry and profile filling pattern were closely related to the slope gradient,and grain-size of their deposits. Their quantitative relationships have not been uniformly and clearly understood so far. However,establishing quantitative relationships between grain-size and slope in different types of depositional systems is essential for predicting the movement patterns and their distribution of different particles in sediment bodies. In this paper,the geological characteristics of the source,transport and sink areas were analyzed. Based on the force analysis of unidirectional water flow on different masses of particles at rest / in motion and the general topographic slope setting before deposition, the trajectories of different clastic particles in the longitudinal profile were systematically analyzed,deduced,and simulated,which shows a parabolic change with the set slope shape,reflecting the transformation of sediment-routing agent and its response characteristics with the change of slopes. The quantitative equations of flow velocity and slope of the longitudinal profile of the terrestrial clastic depositional systems were established. It is clearly pointed out that the flow velocity or regime of sediments defines their depositional mode, and general rule of the accretion pattern and sediment distribution in the sink area is clarified. In this paper,the “mass-slope” coupling effect of clastic depositional systems and its main connotation are proposed,and the geological response of the “mass-slope” coupling effect on the distribution of sediment types and their spatial morphological characteristics of various depositional systems is described from various dimensions and source-to-sink segments.
		2022 Vol. 24 (6): 1037-1057 [Abstract] ( 328 ) [HTML 1KB] [PDF 5685KB] ( 323 )

	1058	SHAN Xin, LI Shunli, SHI Xuefa, TAN Chengpeng

		A review of strait sedimentology
		The strait is distinguished from delta or shelf in having unique sedimentary processes and sediment distribution. Straits show a wide variety of shapes,with a length ranging from a few kilometers to several hundred kilometers and a depth ranging from several tens of meters to more than one kilometer. The strait shows a mouth shape toward open sea and becomes wider and deeper seaward. When ocean current flow through the narrow end of strait,the flow velocity increases and erosions occur here. After the flow through the narrowest part of strait,the oceanic currents enter a wider zone,causing a decreased flow velocity and deposition in this zone. Tidal processes are probably the most important transport agents for shallow-water strait. Other processes include uni-directional oceanic current and sediment gravity flow. Deep-water strait is dominated by oceanic currents and sediment gravity flows. High-energy zones predominantly comprise gravel lags and cross-bedding,whereas low-energy zone is featured by current ripples and muddy deposits. When sea level is low,the strait is exposed in which fluvial processes are dominant. During transgression,river evolves to delta/estuary,bay and strait.
		2022 Vol. 24 (6): 1058-1072 [Abstract] ( 307 ) [HTML 1KB] [PDF 9114KB] ( 254 )

	1073	LI Weiru, LI Zhihua, LI Shengli, LI Shunli, SHAO Jiashu

		Sedimentary characteristics and model of barrier island-lagoon: an example from the Upper Pleistocene-Holocene in Plum island,USA
		Plum island is the largest barrier island in the Gulf of Maine in the northeastern United States. On the continental side of Plum island are the largest lagoon and salt marsh in New England,which are the sedimentary responses to the late Quaternary glacial and coastal processes. Through the description of 160 boreholes in the Upper Pleistocence-Holocene the Plum island study area,eight types of sediments were identified: peat,glacial clay,clay,silt,fine sand,medium-coarse sand,gravel and dropstone. According to the characteristics of sediments and deposition phenomena,the sedimentary microfacies of Plum island can be divided into eight types: barrier dune,beachface deposits,offshore sand sheet deposits,salt marsh,fluvial channel,tidal inlet channel,lagoon and tidal flat. During the Last Glacial Maximum(MIS2),the study area was covered by the Laurentide Ice Sheet and glacial landform developed. Glacial clay accumulated above the bedrock and formed the basal deposits. During the Post-Glacial period(MIS1),the ice sheet melted and the sea level changed in New England,forming sand bars near the drumlins of the glacier landform,and finally evolving into a barrier island-lagoon environment. The lagoon was connected with the open sea through tidal inlet channels.
		2022 Vol. 24 (6): 1073-1083 [Abstract] ( 427 ) [HTML 1KB] [PDF 6401KB] ( 297 )

	1084	FU Chao, YU Xinghe, LI Shengli, LI Shunli, GAO Mingxuan, PENG Zixiao, ZHAO Haiquan

		Lacustrine sequence patterns under different accommodation space settings and the responding delta morphology: a comparison of Poyang Lake and Daihai Lake
		Nowadays,stratigraphic stratigraphy has gradually moved toward quantification,and its standardization has become a consensus in the sedimentological community. As one of the essential parameters in stratigraphic standardization,it has received more and more attention in recent research. In this study,two typical lacustrine deltas in China were selected for comparative study,including the Ganjiang River delta of Poyang Lake with a relatively slope(dip angle<1°),and the deltas around Daihai lake with a relatively slope slope(dip angle 3°~10°). Based on the interpretation of satellite photographys of different water levels in the past 30 years and the interpretation of modern outcrop/trench profiles,this study examines their sedimentary evolution and points out their facies distribution pattern: (1)In the high accommodation space area,the changes of lake shoreline are relatively stable in a setting of rapid increase of accommodable space,but the planar influence range is limited. The responding delta mainly developed a broom-shaped or fan-shaped geometry during the low lake-level systems tract(LST),and lobate shape(high sedimentary supply rate)or bird-foot shape(low sedimentary supply rate)during the transgression systems tract(TST)and high lake level systems tract(HST). (2)The lake shoreline changes drastically in a low accommodation space area,and the influence range is more extensive. The responding deltas are observed to show a bird-foot shape in the low lake-level regression systems tract(RST),and are dominated by finger-sharped bars. In contrast,in the transgression systems tract(TST)period,the deltas are bird-foot-shaped and are dominated by offshore bars. Based on the above observations,the results of forward simulation,as well as insights from the classical stratigraphic sequence and shoreline migration process,this study establishes corresponding stratigraphic stacking pattern-deltaic development modes for high and low accommodation space settings,respectively. Furthermore,the controlling factors of sequence-sedimentary evolution in different accommodation settings are analyzed from the persepctive of long-term and short-term scales.
		2022 Vol. 24 (6): 1084-1098 [Abstract] ( 327 ) [HTML 1KB] [PDF 8849KB] ( 570 )

	1099	CUI Hang, ZHU Shifa, SHI Zhensheng, SUN Shasha, CHANG Yan, SUO Yihu

		Sedimentary characteristics and development model of lacustrine fine-grained hybrid sedimentary rocks in the Jurassic Da'anzhai Member,northern Sichuan Basin
		Water eutrophication occurred during the depositional period of Jurassic Da'anzhai Member in Sichuan Basin,forming lacustrine hybrid sedimentary strata of fossiliferous carbonate and shale. It provides a “natural laboratory”for the study of depositional mechanism of mixed sedimentary strata. In this paper,the lithologic classification and sedimentary facies distribution of Da'anzhai Member in Yilong-Yingshan area located at the northern Sichuan Basin are studied based on core and well logging data,and the depositional process and controlling factors of the mixed sedimentary strata are also discussed. The results show that the lacustrine mixed sedimentary strata was composed of intermixing and alternation of bivalves,ostracods components and fine-grained siliceous debris(including clay minerals). The shell beach was widely distributed in the depositional stage of Da₁ and Da₃ sub-member,while Da₂ sub-member was dominated by semi-deep and deep lacustrine subfacies,which forms a complete lacustrine transgressive-regressive sedimentary cycle. Additionally,shallow-water coquina can be transported and re-deposited in deep-water environment driven by gravity flow. The lacustrine mixed depositional process was mainly facies mixing model and punctuated mixing model. The mixing depositional process was controlled by lake level fluctuation,provenance,geological agent, etc. The fluctuation of lake level controls the distribution of different sedimentary microfacies. Gravity flow caused by triggering mechanisms such as earthquakes,storms and waves,prompted the mixing of sediments from different material source and microfacies(terrigenous detrital transportation,bio-chemical carbonate deposition,suspended deposition of fine particles,etc.),increasing the internal disorder degree and expanding the spatial distribution scope of hybrid sedimentary rocks. Finally,the depositional mechanism model of lacustrine hybrid sedimentary rocks in Da'anzhai Member of Yilong-Yingshan area was established,which can provide theoretical support for the exploration of continental shale oil and gas and can provide reference for the study of hybrid sedimentary rocks under similar geological setting.
		2022 Vol. 24 (6): 1099-1113 [Abstract] ( 281 ) [HTML 1KB] [PDF 17056KB] ( 202 )

	1114	ZHAO Shike, SHI Xiaoying, SUN Longfei, XIE Baozeng, TANG Dongjie

		Hematized microbial mats thrived in terminal Paleoproterozoic shallow seawaters: identification and implications
		Microbially mediated iron oxidation has been considered as one of the most important mechanisms for the formation of Precambrian iron formation and marine red bed. However,the evidence of microbial mediation is rarely recorded through Earth history. To reveal the potential roles of microbes in the Precambrian iron cycling,we chose microbially induced sedimentary structure(MISS)from the late Paleoproterozoic Dahongyu Formation,North China,as target,and conducted a comprehensive investigation in sedimentology and mineralogy. In this formation,sand cracks are the dominated type of MISS,indicating the existence of abundant microbial mats on the intertidal to supratidal zones previously. Microscopic observations show that the non-microbial mat layer contains abundant in situ to shortly transported glauconite,indicating suboxic and iron-rich shallow seawater and porewater chemistry. In contrast,the microbial mats show significant hematization,indicative of more oxygenated conditions. Considering the differences in microbial activity and mineralogy between the microbial mat and adjacent non-microbial mat layers,we propose that microbial mediation is an important mechanism leading to the oxidation of Fe(Ⅱ)in the weakly oxygenated ferruginous shallow seawater. This study provides important evidence for microbial mediation in Fe(Ⅱ)oxidation and may shed light on the formation of Precambrian marine red bed and iron formation.
		2022 Vol. 24 (6): 1114-1129 [Abstract] ( 257 ) [HTML 1KB] [PDF 25338KB] ( 266 )

	1130	LI Xiangdong, CHEN Hongda, CHEN Haiyan, WEI Zeyi

		Genesis mechanism analysis of convolute laminations of the Upper Ordovician Lashenzhong Formation in western margin of Ordos Basin
		Convolute lamination,which has very complicated genesis processes,is an important type of soft-sediment deformation structures. In deep-water deposition environments,there are very important significance both in understanding the formation mechanism of convolute laminations and improving the identification of internal-wave and internal-tide deposits by revealing the relationship between them. The convolute laminations were found in blocked turbidity current deposits of Upper Ordovician Lashenzhong Formation have been carried out in Zhuozishan area,Inner Mongolia,in the north of western Ordos Basin. It could be divided into two categories according to the morphology: vergent regular convolute laminations and cyclotron-like convolute laminations. The former type is characterized as tight anticlines,flat synclines and sand nuclear underlying anticline,which is frequently associated with bi-directional cross-beddings. The latter type,which is belonged to intra-stratal contortion,is often restricted to layers with truncation surface and is associated with sedimentary structures of combined-flow deposits and wave-ripple laminations. Based on the comprehensive research on sedimentary characteristics,convolute lamination features,associated sedimentary structures and other related research results,it can be inferred that the vergent regular convolute lamination is mainly induced by internal-tides and the density inversion occured during liquefaction. The deformation driven by Rayleigh-Taylor instability and subsequent modification due to continued horizontal shear imposed by flow. The cyclotron-like convolute lamination is mainly induced by short period internal waves which includes random internal-waves produced by reflected turbidity currents and internal solitary waves distorted from internal-tides. It is characterized as syn-depositional stratified liquefaction rather than density inversion. The deformation occurs induced by Kelvin-Helmholtz instability and further modification of horizontal shear imposed by flow.
		2022 Vol. 24 (6): 1130-1148 [Abstract] ( 330 ) [HTML 1KB] [PDF 10447KB] ( 206 )

	1149	WU Chenxiao, YAO Zongquan, DELEQIATI·Janatayi , DENG Gaoshan, LI Tianming, HAO Jia, LIU Yu, WANG Xiaohong, SHUGELA·Mahaxi Xiaohong

		Tectonic setting analysis of provenance area of the Permian Jiamuhe Formation on western slope of Shawan sag,Junggar Basin
		It is very controversial on the provenance system and the depositional system of the Permian Jiamuhe Formation in Shawan sag of the Junggar Basin. In this paper,cluster analysis,multidimensional scaling analysis and principal component analysis were used to analyze the contents of heavy minerals and trace elements,and it was found that it is rich in quartz(35.41%),feldspar(43.2%)and poor in rock debris(18.71%)of conglomerate clastic particles in Permian Jiamuhe Formation in Shawan sag. The average value of rare elements equal 139×10^-6,which is close to the average value in the continental upper crust(i.e.,148.14×10^-6),the diagram of Hf-La/Th and La/Sc-Co/Th ratio indicate that the Jiamuhe Formation belongs to the acidic island arc region. The distribution pattern of REE shows a right-leaning distribution pattern,which is characterized as rich in LREE and poor in HREE,indicating that the source rocks are mainly feldspathic volcanic rocks. There are four provenance areas including Wells XG1-ZJ6 area,Wells CP10-ZH4-ZJ3 area,Wells CP10-CP005-CP26 area,and Well CP5 area. The discriminant diagram of tectonic setting reveals that the Jiamuhe Formation was formed in continental island arc environment. This study will be helpful for the reliable estimation of sedimentary system and ancient river system of the western slope area in Shawan sag and the accurate prediction of oil and gas reservoirs in prospective areas.
		2022 Vol. 24 (6): 1149-1161 [Abstract] ( 279 ) [HTML 1KB] [PDF 4777KB] ( 168 )

BIOPALAEOGEOGRAPHY AND PALAEOECOLOGY

	1162	LI Da, HE Xitong, XING Zhifeng, QI Yong'an, ZHENG Wei, FU Jian

		Symbiotic characteristics of wrinkle structure and trace fossils in the Second Member of Miaolingian Mantou Formation in western Henan
		Since the Ediacaran period,the microbes and metazoan were interacted,but microbial induced sedimentary structures(MISS)and metazoan bioturbation structures coexisted temporarily in the Cambrian Miaoling age. In this paper,two types of microbially induced sedimentary structures,including wrinkle structures and microbial mat-crack structures,are identified in the lower part of the Second Member of the Mantou Formation in western Henan Province. The symbiotic relationship between MISS and trace fossils was classified,and three models of the symbiotic relationship between the wrinkle structures and metazoans and ecological evolution model of microbial mat and metazoan were established, including the trackways(Monomorphichnus henanensis)and the grazing trace(Jinningichnus badaowanensis)on the microbial mat, Planolites montanus under microbial mat, and the burrows in mudstone substrate. It showed that some organisms with special environmental tolerance coexisted with microbial mats in the tidal environment with relatively sufficient food sources,revealing the short period of harmonious coexistence relationship between microbial mat and metazoans not only continued the partial symbiotic characteristics during the Ediacaran,but also developed in the mixground-dominated Phanerozoic ecological environment.
		2022 Vol. 24 (6): 1162-1178 [Abstract] ( 281 ) [HTML 1KB] [PDF 28462KB] ( 181 )

	1179	WANG Hailin, ZHANG Bin, SONG Huibo, WANG Changzheng, HU Bin, ZHANG Lijun

		Assemblages of lebensspuren and distribution characteristics in tidal flat of Luanhe delta
		The characteristics,distribution and assemblage of lebensspuren and their relationships with sedimentary environment and sediment properties are significant for the study of trace fossils and palaeoenvironment. However,the research on lebensspuren started late and few related work is found in China. The paper discussed the composition,assemblage and distribution characteristics of lebensspuren in tidal flat of Luanhe delta,and analyzed the relationship between the biological assemblage and the sedimentary environments. The results are as follows: (1)The lebensspuren at the surface of bedding mainly include the repichnia and trails made by arthropoda,annelida and gastropods,and the lebensspuren in the bedding include the burrows approximately perpendicular and parallel to bedding plane,in which the domichnia is dominant with high abundance and various types. (2)Three kinds of biological assemblages are established. Type I is characterized by Y-shaped and vertical tubular burrows with locally high abundance. The epigenic burrows and trails on the bedding plane are less,and the trace makers mainly include Nereis succinea and Brachyura. The bottom of the sediments are characterized as high sand content,high intensity hydrodynamics and low organic matter content,indicating the sandy delta tidal flat sedimentary environment. Type II is characterized as various burrows in the substrate and numerous trails on the surface of bedding. The burrows in the substrate include vertical tubular,J-shaped,U-shaped,Y-shaped and branched burrows with high abundance,and the trace makers mainly include Nereis succinea and Brachyura. The lebensspuren on the formation surface mainly include repichnia and trackways,e.g., Nereis succinea,Brachyura,Glossaulax didyma and Paguridae. The substrate sediments are characterized as high muddy content,high water content and high organic matter content,forming in the middle and lower tidal area of delta tidal flat. Type Ⅲ is characterized by the burrows approximately perpendicular and parallel to the bedding plane and motion traces on the bedding surface. The burrows in the substrate include vertical tubular,J-shaped,U-shaped,Y-shaped and complex branched burrows,which are mainly made by Brachyura,mud beetles and their larvaes. The burrows parallel to bedding plane are mainly made by Cryllotalpa,mud beetles and their larvaes. The motion traces on the bedding surface include the trackways made by Brachyura and footprint made by birds. The substrate sediments for type Ⅲ assemblage showed the characteristics of high muddy content,low water content,high organic matter content and high degree of consolidation,indicating the high tidal area of delta tidal flat. (3)Based on the analyses of lebensspuren assemblage,distribution characteristics and the relationship with the substrate sediments properties and sedimentary environment,a sedimentary environment distribution model of lebensspuren in deltaic tidal flat was established. The research results can not only acted as a basis for the identification of the sedimentary environment of the ancient delta tidal flat,but also provide evidence for the sedimentary environment restoration of similar relic fossil assemblages.
		2022 Vol. 24 (6): 1179-1192 [Abstract] ( 268 ) [HTML 1KB] [PDF 16032KB] ( 205 )

GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS

	1193	HUANG Tianhai, XIAO Di, TANG Hao, LI Shuangjian, ZHENG Jianfeng, ZHOU Li, TAN Xiucheng

		Sedimentary environment identification and hydrocarbon source significance of black shale of the Ordovician Meitan Formation at Banqiao section in Zunyi,Guizhou
		The Lower Ordovician Meitan Formation in the Upper Yangtze area of South China is characterized as the thick mud shale deposits,in which the black shale is well developed. However,there is a great controversy on its sedimentary environment. Taking the Banqiao section of Zunyi as an example,this paper focuses on the comprehensive study on the sedimentary characteristics and geochemistry of the black shale and the associated rocks,especially the relative water depth,sedimentary hydrodynamics and physical and chemical properties of palaeo-seawater during the deposition of black shale of Meitan Formation. The results show that: (1)The black shale of Meitan Formation is characterized as the dark color and well-developed horizontal bedding,without macroscopically paleontological fossils. The interlayer of bioclastic limestone and calcareous siltstone with different thickness developed,indicating that the black shale of Meitan Formation was not the sedimentary product of deep-water environment,but deposited in the low-energy shallow muddy lagoon environment in the mixed platform. (2)The bioclastic limestone that is interbedded with the black shale section mostly develops the inverse grain structure with the fine grain at the bottom and the coarse grain at the top,and iron oxides can be seen at the top,while the calcareous siltstone,interbedded with black shale,mostly develops wave cross bedding and biological drilling,showing shallow water deposition characteristics. (3)The average values of V/(V+Ni),Th/U,V/Cr and Ni/Co of black shale are 0.71,5.52,1.07 and 2.04,respectively,indicating the hypooxidation-oxidation environment. The Sr/Ba ratio ranges from 0.11 to 2.20,with an average value of 0.55,indicating the fresh water-brackish water environment;(4)Macroscopically,obvious erosion surface can be seen in some sections of bioclastic limestone,and karst development can be seen through microscopic observation. At the same time,the REE distribution pattern tends to be horizontal,and the ∑ REE value is higher and Y/Ho is lower,showing the exposed karst environment. (5)TOC values of black shale ranged from 0.09% to 1.05%,with an average value of 0.39%. TOC values of original black shale ranged from 0.28% to 3.16%,with an average value of 1.25. The average value of R_O is 2.095,and the organic matter is mainly sapropelic. Based on the above analysis,it shows that the black shale of Meitan Formation in Banqiao section of Zunyi is a set of effective hydrocarbon source rocks formed in a shallow water and suboxidation-oxidation environment and high paleoproductivity is the main reason for the organic matter enrichment. The research results provides strong evidence for identifying the sedimentary environment and hydrocarbon generation potential of black shale rocks series in Meitan formation in southern Sichuan,and also provides a new example for the identification of shallow-water sedimentary environment conditions of black shale.
		2022 Vol. 24 (6): 1193-1209 [Abstract] ( 279 ) [HTML 1KB] [PDF 12509KB] ( 534 )

	1210	WANG Guoquan, SUN Beilei, LIU Chao, WU Jie, PAN Xinyu, $\boxed{\hbox{ZENG Fangui}}$

		Paleo-peat sedimentary environment and controlling on trace elements: example from the 11# coal seam in Donglutian Coalmine of Ningwu Coalfield
		The paleopeat-forming environments plays an important role in the enrichment of trace elements in coal. Coal facies and related geochemical parameters are important indicators for the paleopeat environmental condition. In this paper,the coal facies parameters,geochemical parameters and mineralogical characteristics were used to reconstruct the paleopeat-forming environments of the 11# coal seam in Donglutian Coalmine from Pingshuo district,Ningwu Coalfield, and the influence of paleopeat-forming environments on trace element enrichment was discussed. The results show that: 1)The coal facies of the Donglutian Coalmine 11# coal seam include three types,i.e.,the low swamp of the barrier island lagoon,lower delta plain and upper delta plain. Under the influence of transgression,the pH,paleosalinity,redox degree and hydrodynamic conditions of marsh water show the periodic variation. 2)The contents of Li with an average value of 133.50μg/g,Zr with an average value of 198.12μg/g and Pb with an average value of 60.76μg/g in 11# coal seam are much higher than those of the hard coal in the world. 3)In the profile of coal seam,trace elements in 11# coal seam show two different assemblages, i.e.,Li-Zr-Nb-Ta-Hf and Pb-Cu-Ga-Ge-Tl-REY. The former assembly is mainly enriched in DLT-11-2,DLT-11-6 and DLT-11-10,which are characterized by similar sedimentary environments,i.e.,seawater,anoxic to euxinic conditions,strong hydrodynamic conditions,with relatively low sulfur content,the low swamp facies in the barrier island-lagoon. The latter assembly is mainly enriched in DLT-11-0、DLT-11-4 and DLT-11-8,which are characterized by similar sedimentary environments,i.e.,seawater,alkaline,oxic or anoxic conditions,weak hydrodynamic conditions,with relatively high sulfur content,lower swamp facies of the lower delta plain. These results would provide valuable theoretical basis for reasonable mining target selection of metal mineral resources and clean utilization of coal resources in other coal-bearing basins.
		2022 Vol. 24 (6): 1210-1223 [Abstract] ( 311 ) [HTML 1KB] [PDF 6480KB] ( 182 )

QUATERNARY PALAEOGEOGRAPHY AND SEDIMENTOLOGY

	1224	WANG Ting, ZOU Chunhui, MAO Longjiang, ZHOU Yulong, MO Duowen

		Sediment grain size end-member analysis and its response to climate and sea-level changes in CZ01 borehole on west coast of Bohai Bay
		Located on the west coast of the Bohai Bay where land and sea interact,the Cangzhou region is vulnerable to sea level changes and extreme weather events and is very sensitive to the response to global climate change. A non-parametric end-member analysis model was applied to classify the sediment grain size of CZ01 borehole in Cangzhou region into six end-members since the late Mid-Pleistocene and analyze their sources,and to reveal the response of each end-members to climate and sea-level changes at different time scales in conjunction with the existing geological record. The results show that: (1)EM1(5.01 μm)is mainly a remote wind-dust input,EM2(13.18 μm)and EM3(39.81 μm)are sediments carried by the ancient Yellow River,EM4(69.18 μm)and EM5(138.04 μm)are marine sediments,EM6(275.42 μm)may indicate extreme climate events such as paleofloods. (2)During the Marine Oxygen Isotope Stages(MIS)Ⅰ,the climate is warm and humid,and the EM4+5 indicates that the sea-level of the Bohai Sea is wavelike rising and gradually reaches the modern sea level. During this period,the Bohai Sea level stagnates or decreases slightly after a steady state of rise due to the Younger Dryas impact hypothesis around 11.5 ka BP and a dry-cold climate event around 5.1 ka BP,while around 9.5 ka BP,7.5 ka BP,5.8 ka BP and 1.7 ka BP,the Bohai Sea level rises due to increased precipitation caused by strengthening East Asian summer monsoon. (3)The cold and dry climate in the Northern Hemisphere in MIS Ⅵ stage,and the regional subsidence center transfer caused by the weakening of Himalayaorogeny around 150~132 ka BP resulted in the increase of Bohai Sea surface. In MIS Ⅴ stage,the climate fluctuated dramatically: during the warm period of interglacial period(5a,5c and 5e),the climate was warm and humid,and the sea-level of Bohai Sea rose, and the sea level height of the Bohai Sea during MIS5b and 5d is lower. Compared with the end of MIS5a,the sea-level in MIS Ⅳ decreased suddenly and then tended to be stable. Several small-scale transgression events occurred during the period,which may be related to the frequent changes of East Asian summer monsoon. From the MIS Ⅲ stage to the Last Glacial Maximum,the sea-level decreased significantly with periodic fluctuations,and a large-scale transgression occurred at about 46 ka BP. MIS Ⅱ stage showed a slight decreased sea-level compared with MIS Ⅲ stage,which was a low sea-level period. Due the termination of the glacier period around 15 ka BP,and the strengthened East Asian summer monsoon, sea-level began to rise again. The sedimentary records of the Bohai Sea since 180 ka BP are consistent with the geological records in the northern hemisphere and even worldwide,which are closely related to the glacier melts caused by solar radiation fluctuation and the change of East Asian summer monsoon.
		2022 Vol. 24 (6): 1224-1237 [Abstract] ( 285 ) [HTML 1KB] [PDF 2977KB] ( 179 )

	1238	WU Zhilei, FANG Xiuqi, YE Yu

		Reconstruction of historical cropland cover using settlement relics in eastern part of northern China's farming-pastoral zone
		Northern China's farming-pastoral transitional zone presents the characteristic of half farming and half animal husbandry. For such areas,because of its unique environment and socio-economic development process,it is difficult to accurately reconstruct cropland cover. Utilizing settlement relics that can indicate the spatio-temporal location of agricultural activities to reconstruct historical cropland cover is one of the effective ways to improve the reliability of the reconstruction results. The study area falls within the eastern part of northern China's farming-pastoral zone. We reconstructed the 5'×5'cropland cover change at 4 time points using the settlement relics of the study area during Liao,Jin,Yuan,and Ming dynasties. The main conclusions are as follows: (1)From Liao dynasty to Ming dynasty,the total cropland area decreased by 98.0%,and the cropland area in Yuan and Ming dynasties was significantly less than that in Liao and Jin dynasties,indicating that the area had undergone a fundamental transformation from half farming and half animal husbandry to animal husbandry;(2)The coverage of cropland was the largest in Liao dynasty,and it was somewhat reduced in Jin dynasty,which presented a mosaic distribution pattern. However,the coverage of cropland was sharply reduced in Yuan dynasty,and only scattered cropland was distributed in Ming dynasty;(3)The cropland cover change in the study area was influenced by both climate change and human factors. During Liao and Jin dynasties,the climate was relatively warm and humid,and the rulers attached great importance to agricultural development. In contrast,during Yuan and Ming dynasties,the climate was cold and dry,and the national was accustomed mainly to animal husbandry. To sum up,the reconstruction of historical cropland cover based on settlement relics not only reproduces the mosaic distribution pattern of cropland,but also depicts the process of land use change from farming to animal husbandry in study area.
		2022 Vol. 24 (6): 1238-1248 [Abstract] ( 274 ) [HTML 1KB] [PDF 2328KB] ( 193 )

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