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	JOPC 2024 Vol.26 Number 6
	2024, Vol.26 Num.6
	Online: 2024-12-01

	HUMAN HISTORY PALAEOGEOGRAPHY LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY PALAEOGEOGRAPHY AND MINERAL RESOURCES GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS

HUMAN HISTORY PALAEOGEOGRAPHY

	1287	FANG Xiuqi

		On perspectives of the Anthropocene
		The Anthropocene is regarded as a unique geological era dominated by humans. Over more than 20 years since the concept was proposed,the Anthropocene has not only been increasingly used within the Earth Science,but also rapidly adopted by many disciplinaries such as society and humanities. This paper aims to review the Anthropocene,regarding the similarities,differences and interrelationships in understanding the Anthropocene among the disciplinaries,from three perspectives of Earth System Science, Geology and Humanities. It has been suggested that the 1950s was the beginning of the Anthropocene, when was called the Great Acceleration of human activities that has changed the Earth System dramatically. The Anthropocene from an Earth System Science perspective focuses on the new Earth System state driven by humans. The Anthropocene from a geological perspective focuses on the geological signals in the strata indicating the start of a new geological era. The Anthropocene from a social and humanistic perspective focuses on human responsibility to cope with the global environment crises by industrial civilization and to make a hopeful promise to the human future. No matter the Anthropocene to be into the geochronological system,it will be an issue focused by the Earth Science and the Social Sciences in the long-term future.
		2024 Vol. 26 (6): 1287-1304 [Abstract] ( 194 ) [HTML 1KB] [PDF 3253KB] ( 27 )

LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY

	1305	QI Kening, KUANG Hongwei, LIU Yongqing, PENG Nan, WANG Yuchong, CHEN Xiaoshuai

		Sedimentary characteristics of the Cryogenian Nantuo Formation and stratigraphic attribution of red beds in central Yunnan, southwestern margin of Yangtze Craton
		In the central Yunnan region of the Yangtze Craton,the “red beds” that develop in the transitional section between the Nantuo Formation and the Doushantuo Formation of the Neoproterozoic,are still debated among scholars. This study carried out detailed stratigraphic and sedimentological studies on the Nantuo Formation in the Lunacun and Feidatian sections in the central Yunnan region. The sections were located on the southwestern margin of the Yangtze craton. The conglomerate member and its overlying red mudstone member of the Nantuo Formation exhibit typical glacial sedimentary features such as striae,dropstone,and rhythmic laminae,base on which,four sedimentary subfacies can be divided,i.e.,subglacial lag,periglacial channel,pre-glacial delta front,and pre-glacial shoreline subfacies,reflecting different stages of glaciation. The youngest detrital zircon age at the top of the red mudstone is 636Ma,indicating that the deposition time of the top of the purple-red fine sandstone in the upper member of the Nantuo Formation may be later than 636Ma. The regional stratigraphic comparison reveals that the spatial distribution of the conglomerate and mudstone members of the Nantuo Formation in central Yunnan is stable;it represents accumulation of conglomerates under glacier ice,transitioning upwards to the conglomerates of periglacial river channels,and then upwards to the mudstones and fine sandstone of the pre-glacial delta front and the pre-glacial shoreline,exhibiting a pattern of gradual melting of glaciers and marine invasion. In summary,this study suggests that the Nantuo Formation should be divided into two parts,with the lower member consisting of conglomerate and the upper member consisting of purple-red mudstone. The boundary between the Nantuo Formation and the Doushantuo Formation should be placed at the top of the red layer. This study deepens the understanding of the Cryogenian palaeogeography,the southwestern margin of the Yangtze craton. It provides new sedimentological data for improving the isochronous stratigraphic framework from the Cryogenian to Ediacaran,and assists in deep oil and gas exploration in the Sichuan Basin and its surrounding areas.
		2024 Vol. 26 (6): 1305-1324 [Abstract] ( 134 ) [HTML 1KB] [PDF 19433KB] ( 32 )

	1325	DONG Yan, WANG Meiling, CHEN Bin, SHI Zhiqiang

		Characteristic and formation cause of white sandstones in the Jurassic outcrop area of burnt rocks in northern China
		Burnt rocks are widely distributed across northern China,often formed by the spontaneous combustion of Jurassic coal beds during the Mesozoic and Cenozoic. White sandstones are commonly accompanied with the red burnt rocks caused by the spontaneous combustion of Jurassic coals in these areas. These white sandstones have received little attention,and their formation remains poorly understood. In this study,the white sandstones accompanied with burnt rocks are observed at the Jurassic outcrops in the margins of Yili,Junggar,Tuha and Ordos Basins. White sandstone samples were collected and analyzed through thin section identification,scanning electron microscopy(SEM),and energy spectrum analysis to examine their petrological and mineralogical characteristics. The results show that the white sandstones in the Jurassic coal-bearing sequence are distributed at the top,bottom or alongside of burnt rocks,with light-grey white color,loose structure,and well-developed porosity. The clastic grains are mainly quartz and feldspar minerals,and the interstitial material is mainly kaolinite. Unique pore structures caused by fluid movement are also observed. According to the spatial correlation with burnt rocks,we propose that the cause of these white sandstones is closely related to the spontaneous combustion of Jurassic coals. The massive production of kaolinite,removement of nonferrous metals and vanishment of organic matter are likely caused by coal combustion process,which result in the formation of white sandstones. Thus,these white sandstones represent a special type of low-temperature baked rock. Three genetic models are proposed for the formation of these white sandstones: (A)valley incision type,(B)fissure incision type and(C)hill infiltration type.
		2024 Vol. 26 (6): 1325-1337 [Abstract] ( 91 ) [HTML 1KB] [PDF 19423KB] ( 25 )

	1338	XU Zhenhua, DENG Hang, WU Shenghe, YUE Dali, LIU Yuming, LI Qing

		Depositional architecture and formative mechanism of dendritic bars within river-dominated shallow-water delta front
		River-dominated shallow-water delta front sands can be categorized into distributary-bar and bar-finger types based on combination relationships between distributary channel and mouth bar. Scholars paid more attention to delta front sands of lobate distributary-bar type and bird-foot bar-finger type. However,the dendritic sand bars that composed of multiple bar fingers has been largely overlooked,and its depositional architecture and formative mechanism are still unclear. This paper focuses on the Rimaozhou deposits in Poyang Lake to explore the depositional architecture and formative mechanisms of the dendritic bars in river-dominated shallow-water deltas,utilizing satellite imagery,Ground Penetrating Radar(GPR)profiles,shallow core sampling,and sedimentary numerical simulations. The findings indicate that dendritic bars consist of a complex network of bifurcating and confluent bar fingers. Distributary channels incise mouth bars,as like walking on the bar. Distributary bays nestle among these bar fingers. According to width,distributary channels within dendritic bars can be divided into chief branches and side branches,where the formers are wide,cover a small number,and distributed at central sand bars;instead,the latter are narrow,cover a large number,and distributed at sides and terminal of sand bars. The development of dendritic bars is driven by the supply of fine-grained,cohesive sediments and high discharge levels. Fine-grained and cohesive sediments contribute to the growth of stable levees and the formation of bar fingers,while high discharge encourages the bifurcation and avulsion of distributary channels,facilitating the formation of dendritic bar fingers. Dendritic bars in river-dominated shallow-water delta reservoirs exhibit low lateral connectivity. The most promising reservoir locations are typically found at the central mouth bar,characterized by distributary channel sands and proximal mouth bar sands.
		2024 Vol. 26 (6): 1338-1351 [Abstract] ( 96 ) [HTML 1KB] [PDF 22548KB] ( 28 )

	1352	ZHANG Wenmiao, XIAN Benzhong, JI Hancheng, MA Guofu, XIAO Wenhua, TIAN Rongheng, CHEN Sirui, YANG Baizhi

		Depositional model of fan deltas based on analysis of sedimentary processes: a case study of the Lower Cretaceous Xiguayuan Formation in Sangyuan outcrop of Luanping Basin
		Flood flow types and variable discharge are the critical controls on fan delta morphology and depositional characteristics. However,characteristics of depositional units formed by variable flow types are still poorly understood. This study focuses on the well-exposed Sangyuan outcrop of the Lower Cretaceous Luanping Basin,which was measured in detail. Based on the classification of lithofacies,flow types and depositional processes are interpreted,with corresponding depositional units determined. Depositional models are constructed in response to various types of flood flow. Three types of flood flow are identified based on the classification of lithofacies associations,containing debris flow,hyperconcentrated flood flow and sheet flood flow. According to the processes and geometry,eight types of depositional units are identified,including subaerial debris-flow tongue deposits,hyperconcentrated flood flow-dominated braided channels,subaqueous debris-flow tongue deposits,high-density turbidite channels,subcritical-flow dominated subaqueous distributary channels,high-density turbidite lobes,subaqueous sheet flood dominated lobes,and slump deposits. During the debris flow-dominated phase of fan delta development,multistorey debris-flow tongue deposits gradually prograded into the lacustrine basin. In the hyperconcentrated flood flow-dominated phase,braided channels were formed in the fan delta plain,while high-density turbidity currents,transformed from hyperconcentrated flood flow,generated high-density turbidite channels and lobes in the fan delta front. During the sheet flood flow-dominated phase,unconfined sheet flood flow is developed when flood flows exit the incised channels,generating subaqueous sheet flood dominated lobe in the fan delta front. The rapid deposition of sandstones in the fan delta front during flood flow stage leads to the instability of sediment and the development of slumps. During base flow stage,subaerial braided channels and subaqueous distributary channels dominated by subcritical-flow structures are developed. This study sheds light on the sandbody geometry and depositional architecture of fan delta formed by variable types of flood flow.
		2024 Vol. 26 (6): 1352-1371 [Abstract] ( 92 ) [HTML 1KB] [PDF 82005KB] ( 32 )

	1372	HUANG Leqing, HU Nengyong, WEN Chunhua, MENG Fanxing, CHEN Xu, XIANG Ke, ZENG Guangqian, JIAO Peng, WANG Lingjue

		Quantitative reconstruction and implications of the Cretaceous Aeolian bedform architecture in Chayong Basin,the hinterland of South China
		The Cretaceous strata in the Chayong Basin,located in the hinterland of South China,are characterized by ancient desert sediments with diverse dune morphology. These features reflect a complex interplay of tectonic activity,hydrological conditions,and palaeoclimatic changes. Despite their significance,research on this topic remains limited,hindering our understanding of the evolution of the paleodesert environment. This study employs the innovative End-Member Modeling by Grain Size Analysis(EMMA)with traditional dune morphology analysis to investigate paleoaeolian morphologies and quantitatively reconstruct bedform configurations. The results indicate that the Cretaceous dunes in the Chayong Basin are exceptionally large,with morphological parameters surpassing global averages for typical fault basins. This suggests an initial arid or desert basin state comparable to the Cretaceous dunes of the Ordos Basin's or the modern dunes of the Taklamagan Desert. EMMA identified four end-members that are indicative of aeolian dunes,sand sheets,and moist interdune areas. The reconstructed paleowind direction was predominantly north-northeast,influenced by the westerlies of the Northern Hemisphere. The sedimentary configurations exhibit a variety of forms,including compound crescentic and complex transverse dunes. The southern part of the basin is characterized by a dry-moist interdune system,presenting internal arid-moist interdunes and small-medium crescentic dunes. In contrast,the northern part develops a dry interdune aeolian system dominated by giant compound dunes. Tectonic uplift and fluvial development surrounding the basin have provided abundant sediment sources,resulting in secondary erosion,migration,and deposition driven by wind action. The subsidence of the fault-basin basement and fluctuations in the groundwater table,has created accommodation space for the accumulation and preservation of aeolian sediments. This study,based on aeolian sedimentary geological records,offers a new perspective on the large-scale dynamics of the Chayong Basin during the Cretaceous period,enhancing our comprehension of the coupled processes of aeolian/fluvial sedimentation,basin tectonics,and paleoclimatic evolution in the hinterland of South China.
		2024 Vol. 26 (6): 1372-1395 [Abstract] ( 89 ) [HTML 1KB] [PDF 14763KB] ( 16 )

	1396	DU Yan, XU Huan, DING Jiaxiang, HE Keheng, ZHAO Xiaoran, XIA Lei, YUAN Tingyuan, ZHANG Bihui, LIU Gaozheng

		Late Cretaceous aeolian sedimentary association in Gonjo Basin, eastern Tibet: implications for palaeoclimate and palaeogeography
		During the Late Cretaceous period,aeolian deposits were widely distributed in East Asia,exhibiting significant zonal variation. However,there are few reports on aeolian deposits in the central region of the Tibet Plateau,which shares the same paleo-latitude as South China. In recent years,previous magnetic stratigraphy studies have redefined the Paleogene aeolian sedimentary age in the Gonjo Basin of eastern Tibet as Late Cretaceous. This finding presents a new opportunity to investigate the palaeogeographic and palaeoclimatic conditions prior to the uplift of the Tibet Plateau during this period. The aeolian sedimentary sequence,aeolian interface and sedimentary system of the Gonjo Formation were investigated in detail through field profile investigation,rock and mineral identification using a polarizing microscope,scanning electron microscopy and energy spectrum analysis. The findings indicate that the aeolian sedimentary association of the Gonjo Basin is primarily situated at the base of the Gonjo Formation,predominantly concentrated along the western margin of the basin,and is mainly composed of desert,alluvial fan and fluvial deposits. Aeolian sediments are characterized by large trough,wedge-shaped cross-bedding,and steep-angled plate cross-bedding. Additionally,typical features such as grainflow strata,grainfall laminea,wind-ripple strata and wind-ripple marks are observable within the layers. The clastic particles of the eolian sandstone are primarily medium to fine sand,exhibiting high structural maturity and compositional maturity. The edges of the quartz particles display a “desert varnish” structure. Under a scanning electron microscope,typical crescent and dish-shaped impact craters were observed on the surface of quartz grains,indicating the origin of aeolian deposition. Vertically,the aeolian sedimentary association demonstrates a clear interaction between lower eolian and hydrogenic deposits,with central aeolian deposits prevailing and an increase in upper hydrogenic deposits. This pattern suggests fluctuations in the groundwater level caused by sudden precipitation or flooding in an arid climate context. The formation and evolution of aeolian sediments at the end of the Cretaceous in the Gonjo Basin is closely linked to the “rain shadow” effect resulting from the Late Cretaceous uplift of the Gangdise Mountains,as well as to the global mid-Maastrichtian warming event. These findings are significant for understanding the palaeogeographic patterns and palaeoclimatic conditions preceding the uplift of the Tibetan Plateau at the end of the Cretaceous.
		2024 Vol. 26 (6): 1396-1419 [Abstract] ( 87 ) [HTML 1KB] [PDF 23808KB] ( 32 )

PALAEOGEOGRAPHY AND MINERAL RESOURCES

	1420	LI Yanhe, WANG Baoyu, LIU Shunxi, NI Xiaoming, WANG Juan, HU Bin

		Sedimentary environment of coal-bearing strata and its control on accumulation of coal measure gas in Pingdingshan mining area,Henan Province
		In recent years,a new breakthrough has been made in the exploration and development of coal measures gas in the Pingdingshan mining area of Henan Province. The daily production per well in mining area,goal area and unmining area reached 40 500 m³,20 000 m³ and 4 500 m³,respectively. To better understand the sedimentary background of coal measure gas generation and occurrence,this study applies stratigraphy and sedimentology research methods to conduct a detailed analysis of strata,sedimentary characteristics,and sedimentary sequences,along with gas logging data. This reveals the sedimentary environment controlling the generation and occurrence of coal measure gas(coalbed methane,shale gas,and tight sandstone gas)in the Shanxi Formation and Xiashihezi Formation. Specifically,the sedimentary environment of peat swamp(peat flat)on tidal flat,delta interdistributary bay swamp and distributary channel control the accumulation of coal measure gas. According to the vertical variation of stratigraphic and sedimentary characteristics,nine different sedimentary sequence types are classified,and the sedimentary environment model of coal measure gas occurrence in the Shanxi Formation and Xiashihezi Formation in Pingdingshan area is proposed. The study also shows that the content change of coal measure gas and its regional distribution characteristics are not only closely related to the spatio-temporal variation of coastal tidal flat marsh,delta distributary channel sand body and interdistributary bay marsh,and are also related to the variation of reservoir thickness. The results can provide a scientific basis for the future design,deployment and production of coal measure gas exploration and development wells in Pingdingshan area. Moreover,the findings offer important reference significance for the development of coal measures gas in the similar coal-bearing strata in North China.
		2024 Vol. 26 (6): 1420-1434 [Abstract] ( 137 ) [HTML 1KB] [PDF 9783KB] ( 15 )

	1435	LIU Hengyu, LIU Mingjie, HAO Zhilei, REN Yin, WU Enyu, XU Han, ZHONG Shoukang, TAN Xiucheng, ZENG Wei, LIAN Chengbo, DAI Hongming

		Pore formation and preservation mechanisms of ancient deep tight sandstone reservoirs: a case study of the Mesoproterozoic Changcheng System in Ordos Basin
		To investigate the pore formation and preservation mechanisms of ancient deep tight sandstone reservoirs,a combination of core,thin section,scanning electron microscopy,X-ray diffraction and fluid inclusion analysis techniques was used to systematically analyze the sedimentary environment,petrology,reservoir space,porosity and diagenesis of the deep sandstone reservoirs of the Changcheng System in the central and eastern Ordos Basin. On this basis,the mechanisms of pore formation and preservation was clarified. The results show that the Changcheng System mainly develops quartz sandstone and lithic quartz sandstone in tidal channel sedimentary environment,with medium textural maturity and high compositional maturity. The reservoir space is dominated by residual intergranular pores and intragranular dissolution pores of rock fragments,with an average porosity of 6.6%. The compaction of the Changcheng System sandstone is generally strong,and it is mainly composed of quartz and illite cementation. The acidic dissolution of rock fragment is the most developed,followed by alkaline dissolution of quartz. The results indicate that the coarse grain size,good sorting and low matrix content are the main reasons for the primary pore development in the Changcheng System tidal channel sandstones,which formed under strong hydrodynamic conditions. The Changcheng System sandstone reservoirs have experienced leaching dissolution of meteoric fresh water during the early stage,organic acids dissolution during the middle stage and alkaline dissolution of quartz during the late stage,which provides favorable conditions to the formation of secondary pores. The pore preservation of the Changcheng System sandstone reservoirs is mainly attributed to the rich in rigid compressive quartz grains,coarse grain size and good sorting,the quartz cementation inhibited by early authigenic clay coating and the burial process of early long-term shallow burial and rapid deep burial in the later stage.
		2024 Vol. 26 (6): 1435-1451 [Abstract] ( 87 ) [HTML 1KB] [PDF 12453KB] ( 18 )

	1452	JIN Hui, CUI Junfeng, YANG Guiru, YANG Wei, XIAO Dianshi, WANG Zhihong, WANG Min, WU Xueqiong, BO Dongmei

		Classification and origin of tight sandstone reservoirs of the 3rd Member of Xujiahe Formation in central and western Sichuan Basin
		Due to the complex rock composition and strong heterogeneity in pore throat structure of the Upper Triassic Xujiahe Formation in central and western Sichuan Basin,the gas content and productivity show rapid changes. Therefore, it is urgent to clarify the reservoir types,formation mechanisms,and their distribution characterization. Taking the tight sandstone reservoirs of the 3rd Member of the Xujiahe Formation as the object,this study conducts microscopic analysis of pore structure through thin section,physical properties,mercury intrusion,and nuclear magnetic resonance,establishes reservoir classification standards,and then reveals the control of diagenesis and rock composition on the formation of various reservoir types. The results show that there are five types of reservoir spaces developed in the 3rd Member of the Xujiahe Formation,including microcracks,primary intergranular pores,residual intergranular pores,dissolution pores,and intercrystalline pores,among which the development of the intergranular pore throats is the key to reservoir quality. Based on the fractal features,the pore throat system is divided into five intervals,and combined with parameters such as the proportion of meso to macro pore throats and main flow throat radius,four types of tight reservoirs are finely divided. Type Ⅰ reservoirs feature “weak compaction and strong dissolution”,which is related to high percentage of quartz particles,low percentage of mudstone and carbonate rock fragments,and moderate volcanic rock debris; Type Ⅱ reservoirs exhibit “strong compaction and strong dissolution”,with a large amount of impurities,low percentage of mudstone debris,and high percentage of feldspar particles as the material basis for their formation;Both Type Ⅲ and Type Ⅳ reservoirs have strong cementation characteristics,calcite cementation was developed due to the high content of calcareous rock debris in Type Ⅲ reservoirs,while significant reduction of pore size related to the matrix in Type Ⅳ reservoirs. This research can not only guide the study of the formation mechanism of tight reservoirs in the study area,but also provide certain reference for the correlation between the classification and genetic of tight reservoirs.
		2024 Vol. 26 (6): 1452-1466 [Abstract] ( 90 ) [HTML 1KB] [PDF 21592KB] ( 19 )

	1467	WANG Yan, WANG Nuoyu, YANG Debin, ZHANG Heng, ZHANG Juan, ZHANG Changjian, ZHANG Xiao

		Characteristics and evolution mode of the Ordovician paleodrainage system architecture in northwestern Tahe oilfield,Tarim Basin,China
		The deep surface water system structure developed in the Middle and Lower Ordovician in the northwest of Tahe Oilfield has a significant impact on the development of karst fractures and caves on both sides of the water system. Therefore,it is crucial to quantitatively describe the water system structure and conduct researches on its evolution mode. Based on three-dimensional seismic data,seismic attribute extraction technology was utilized to identify paleokarst platform and paleokarst surface water systems. In addition,the planar and vertical morphologic structure parameters of the surface drainage system were quantitatively characterized. Consequently,the formation and evolution patterns of paleokarst surface water systems was explored,and the relationship between surface water system evolution and paleokarst cave-fissure development was analyzed as well. The research results indicate that: (1)Three paleokarst paltform and a deep meandering gorge type surface watershed structure are developed from east to west in the northwest of Tahe Oilfield. The main water system in this basin flows in a north-south direction,while the branch water system flows in an east-west direction,exhibiting an asymmetric distribution pattern. (2)The curvature rate of a single river bend in the water system is greater than 1.5,exceeding the critical value for defining the curvature rate of a meander bend,and featuring typical meander characteristics. The curvature rate of the east-west meander belt is 2.42,and the curvature rate of the north-south meander belt is 1.78. (3)The east-west water system mainly has a single V shape,while the north-south water system has a composite V shape. The incision depth of the water system in the three paleokarst platform gradually deepens from east to west,and the average width to depth ratios of the water system are 4.06,3.52,and 3.03,respectively. (4)The paleokarst surface water system in the study area experienced two stages: free meandering and entrenched meandering, reflecting the lateral and vertical erosion processes of the water system, respectively. Among them,vertical erosion of the water system occurs gradually,adapting to the gradual uplift of the three paleokarst paltform. (5)Deep meandering is the lowest drainage reference level in a region,controlling the development of large karst underground rivers on both sides of the river. Each karst platform has an independent water circulation structure,and the gradual uplift of the karst platform promotes the differential evolution of the water system,thereby controlling the differences in the scale and type of karst underground rivers. The understanding of the paleokarst water system structure and its evolution in the research area provides important reference basis for the study of the development characteristics and distribution patterns of paleokarst fracture cave storage space.
		2024 Vol. 26 (6): 1467-1482 [Abstract] ( 92 ) [HTML 1KB] [PDF 5413KB] ( 15 )

GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS

	1483	KONG Fanxing, ZHANG Zheyuan, XU Fangjian, DONG Jiang, LI Anchun, GU Yu, HU Limin, CHEN Tianyu, LIU Xiting

		Fate of reactive iron in inner shelf sediments of the East China Sea in response to environmental evolution since the last deglaciation
		The reactive iron in shelf sediments plays an important role in the marine iron biogeochemical cycle,however,its response mechanism to the evolution of shelf sedimentary environments is still unclear. This study focuses on shelf sediments of core EC2005 from the East China Sea inner shelf to explore the influence of sedimentary environmental evolution on the fate of reactive iron since the last deglaciation. The average ratio of total iron to aluminum(Fe_T/Al)in core EC2005 sediments is 0.54,and the average ratio of reactive iron to total iron(Fe_HR/Fe_T)is 0.29,indicating that terrigenous fine-grained sediments input from the Changjiang River are the main source of particulate iron in the study area. The average content of reactive iron speciation from high to low is easily reducible(oxyhydr)oxide iron(Fe_ox1,0.64%),pyrite iron(Fe_py,0.32%),reducible(oxyhydr)oxide iron(Fe_ox2,0.23%)and carbonate iron(Fe_carb,0.09%). The relative contents of Fe_py and Fe_carb exhibit opposite trends along the core depth,indicating competition between carbonate(bicarbonate)ions and sulfide ions for ferrous iron during the early diagenetic process. This competition is primarily controlled by the sedimentary environment and redox state of the East China Sea inner shelf since the last deglaciation. Fe_ox1 is closely related to the change of organic carbon content and plays an important role in controlling the variations of Fe_py and Fe_carb contents. In continental environments(17.3-13.1 ka),Fe_ox1 is mainly converted into Fe_carb,and Fe_py content is almost zero. In transitional environments(13.1-7.3 ka),Fe_carb content decreases accompanied by an increase in Fe_py content. In marine environments(7.3 ka to present),Fe_py content reaches a maximum,and Fe_carb content increases significantly in the surface layers. Our findings highlight the control of the sedimentary environment on the fate of reactive iron in shelf sediments,providing a new perspective for studying modern and deep-time marine C-S-Fe biogeochemical cycles.
		2024 Vol. 26 (6): 1483-1497 [Abstract] ( 149 ) [HTML 1KB] [PDF 2241KB] ( 24 )

	1498	ZHANG Yaru, ZHANG Guanglu, YANG Jun, ZHAO Yanyan, GUAN Hongxiang, LIU Sheng

		A Study on mineralogical and in-situ geochemical characteristics of pyrite under different sedimentary environments in the South China Sea
		Pyrite is a common mineral in sediments and sedimentary rocks,and its geochemical characteristics can clearly indicate the surrounding sedimentary environment. However,the differences in geochemical characteristics of pyrite and the controlling factors of its formation are still unclear. This study uses scanning electron microscope and laser ablation inductively coupled plasma mass spectrometry to study the morphology and in-situ geochemical characteristics of pyrite in different sedimentary environments in the South China Sea. The results show that the contents of pyrite and δ³⁴S values at site SH-CL38 exhibit a mirror-image relationship,representing the pyrite formed in a normal marine sedimentary environment,which is controlled by organoclastic sulfate reduction;The extremely low δ¹³C value(-45.55‰)of authigenic carbonate particles at site F indicates methane seepage,and the formation of pyrite is related to sulfate-driven anaerobic oxidation of methane process. There are significant differences in the geochemical distribution of pyrite micro-areas between the two sites: the contents of Mn,Co,Ni,Mo,and Sb in pyrite at site SH-CL38 are higher than those at site F,which may be caused by the reducing dissolution of iron and manganese(hydrogen)oxide. In contrast,the content of Cu,V,As,and Cd in pyrite at site F is higher than that at site SH-CL38,which may be influenced by organic matter mineralization. The Ca and Mg content of pyrite particles indicate that,under methane seepage condition at the site F,authigenic calcite with low Mg and high Ca was preferentially precipitated,resulting in the later precipitated pyrite having high Mg and low Ca characteristics. The differences in morphology and trace element content of pyrite in two different sedimentary environments indicate that the mineralogical and geochemical characteristics of pyrite can be used to identify methane seepage.
		2024 Vol. 26 (6): 1498-1515 [Abstract] ( 95 ) [HTML 1KB] [PDF 4129KB] ( 20 )

	1516	LI Songhan, ZHANG Junna, ZHANG Xiaohu, ZHAO Haitao, ZHAO Bolun, HAN Zinan

		Significance of palaeoclimate indicators of geochemical indexes of palaeoflood profiles in Luoyang Basin,China
		In paleoclimate studies,geochemical indexes are predominantly employed in the analysis of loess,lake and other sediment types. However,the role of chemical elements in indicating palaeoclimate conditions in river sediments has been rarely investigated,primarily due to significant variations in sedimentary dynamics. In this paper,the significance of paleoclimate indicators derived from the geochemical index of the late Longshan Paleoflood section(SQ)dating from 4 to 3.8 ka BP in the Luoyang Basin. The analysis reveals a significant correlation between the chemical elements in the SQ profile and the median particle size. After accounting for the influences of provenance,sedimentary recycling and diagenetic potassium metasomatism on the chemical elements,the chemical elements were grouped based on the correlation coefficients with median particle size. Subsequently,we established chemical element parameter indexes according to the migration strength of the elements within the same group. The results are consistent with the CIA particle size effect correction findings,both indicating low values in the paleoflood layer,which suggests a dry and cool climate. Based on the results of palynology in this profile,it is concluded that the relatively mild,warm and cool climate in the Luoyang Basin serves as a significant environmental background for the occurrence of paleoflood events around 4 000 years ago. However,the complexity of the river deposition process presents limitations for this study. The method of grouping parameters offers a valuable approach to exploring the palaeoclimatic significance of chemical element indicators found in river sediments.
		2024 Vol. 26 (6): 1516-1530 [Abstract] ( 94 ) [HTML 1KB] [PDF 7217KB] ( 35 )

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