The modern pollen assemblages of surface lake sediments and topsoils in northwestern China were studied to understand the relationship of modem pollen data with contemporary vegetation and climate, and the differences...The modern pollen assemblages of surface lake sediments and topsoils in northwestern China were studied to understand the relationship of modem pollen data with contemporary vegetation and climate, and the differences between the pollen assem- blages of surface lake sediments and topsoils. The results show that Chenopodiaceae and Artemisia are dominant elements in the pollen assemblages of northwestern China. Additionally, Ephedra, Cyperaceae, Asteraceae, Poaceae, Picea, Pinus, and Betula are also important pollen taxa. Both pollen assemblages and principal component analysis indicate that pollen data from surface lake sediments and topsoils can be used to differentiate the main vegetation types of this region （desert, steppe, mead- ow and forest）. However, differences exist between modern pollen assemblages of the two types of sediments due to the dif- ferent relevant source areas of pollen and degrees of pollen preservation. For example, the larger relevant source area of sur- face lake sediment results in a higher abundance of Betula in pollen assemblage from surface lake sediment, whereas the ten- dency to disintegrate thin-walled pollen types in topsoil leads to a higher proportion of resistant pollen, such as Asteraceae. Linear regression analysis indicates that the Artemisia/Chenopodiaceae （A/C） ratio in pollen assemblages of surface lake sedi- ments can be used to indicate humidity changes in the study area. However, the A/C ratio in topsoils should be used carefully. Our results suggest that pollen data from surface lake sediments would be better references for interpreting the fossil pollen assemblages of lake cores or lacustrine profiles.展开更多
Modern pollen analysis is the basis for revealing the palaeovegetation and palaeoclimate changes from fossil pollen spectra.Many studies pertaining to the modern pollen assemblages on the Tibetan Plateau have been con...Modern pollen analysis is the basis for revealing the palaeovegetation and palaeoclimate changes from fossil pollen spectra.Many studies pertaining to the modern pollen assemblages on the Tibetan Plateau have been conducted,but little attention has been paid to pollen assemblages of surface lake sediments.In this study,modern pollen assemblages of surface lake sediments from 34 lakes in the steppe and desert zones of the Tibetan Plateau are investigated and results indicate that the two vegetation zones are dominated by non-arboreal pollen taxa and show distinctive characteristics.The pollen assemblages from the desert zone contain substantially high relative abundance of Chenopodiaceae while those from the steppe zone are dominated by Cyperaceae.Pollen ratios show great potential in terms of separating different vegetation zones and to indicate climate changes on the Tibetan Plateau.The Artemisia/Chenopodiaceae ratio and arboreal/non-arboreal pollen ratio could be used as proxies for winter precipitation.Artemisia/Cyperaceae ratio and the sum of relative abundance of xerophilous elements increase with enhanced warming and aridity.When considering the vegetation coverage around the lakes,hierarchical cluster analysis suggests that the studied sites can be divided into four clusters:meadow,steppe,desert-steppe,and desert.The pollen-based vegetation classification models are established using a random forest algorithm.The random forest model can effectively separate the modern pollen assemblages of the steppe zone from those of the desert zone on the Tibetan Plateau.The model for distinguishing the four vegetation clusters shows a weaker but still valid classifying power.It is expected that the random forest model can provide a powerful tool to reconstruct the palaeovegetation succession on the Tibetan Plateau when more pollen data from surface lake sediments are included.展开更多
Carbon isotopic compositions of individual n-alkanols and sterols in modern sediments from the Nan-sha Islands sea area are measured after derivatization to trimethylsilyl ethers by the new isotopic analytical techniq...Carbon isotopic compositions of individual n-alkanols and sterols in modern sediments from the Nan-sha Islands sea area are measured after derivatization to trimethylsilyl ethers by the new isotopic analytical technique of GC/C/IRMS. The effects of the three added silyl carbon atoms in every alcohol molecule on these compound isotopic compositions and the characteristics of their carbon isotopic compositions are studied. Then their biological sources are discussed using their carbon isotopic compositions.展开更多
The Cretaceous sedimentary successions in NE China are largely incomplete as the basins are inverted and younger strata are eroded.Except for the Songliao Basin,whose depositional record has remained relatively intact...The Cretaceous sedimentary successions in NE China are largely incomplete as the basins are inverted and younger strata are eroded.Except for the Songliao Basin,whose depositional record has remained relatively intact,the burial record to the east was interrupted in the late Early or Late Cretaceous.There is still controversy on the possible connection between the Songliao Basin and the eastern basin group,as well as the extent of the previously suggested“pan-Sanjiang”proto-basin that covered most current eastern satellite basins.To address these questions,we studied modern river catchments of variable sizes from sediment-supplying basement highs that cover most of eastern NE China to track the intense denudation events and provenance changes through the Cretaceous.We found a great inconsistency between detrital age patterns of the modern river sands and the spatial proportions of the source units.The detrital age distributions allow to re-evaluate the basement units that are mostly composed of the Triassic–Jurassic igneous suite and some metasedimentary units with Paleozoic ages,but the contribution from Proterozoic formations is negligible.Combining the newly dated modern catchment detrital U-Pb ages,the region-wide compilation of the basement emplacement ages,and the U-Pb ages in the Cretaceous formations in NE China,we systematically refine the Cretaceous provenance history.In the Early Cretaceous,the eastern satellite basins accumulated sediments from the Lesser Xing’an range(LXR)in the west,Zhangguangcai range(ZGCR)in the south,and the Nadanhada terrane(NT)in the east.The sediment of the southern Songliao Basin derived from the North China Craton(NCC)and from ZGCR but barely from the Great Xing’an Range(GXR).The Jiamusi uplift(JU)did not provide sediments to the eastern satellite basins and the Songliao Basin.In the Late Cretaceous,the eastern satellite basins received sediments from the exhumed JU but barely from ZGCR and LXR.The Songliao Basin still accumulated the sediments from the NCC,some so展开更多
The content and isotopic compositions of different sulphur species in pore-water and solid phases have been examined on five sediment cores taken from muddy sediment region in the Yellow Sea and the East China Sea. Re...The content and isotopic compositions of different sulphur species in pore-water and solid phases have been examined on five sediment cores taken from muddy sediment region in the Yellow Sea and the East China Sea. Relationships among these data have been investigated with the combination of morphology of mineral pyrite and organic matter so as to role out the diagenetic behaviour of sulphur species at the early stage of diagenesis in modern marine sediment and the origin of pyrite formation.展开更多
High performance liquid chromatography (HPLC) has the advantages of rapid analysis and high sensitivity. In the present study a suitable analytical condition has been established for HPLC, and the LAS in modern sedime...High performance liquid chromatography (HPLC) has the advantages of rapid analysis and high sensitivity. In the present study a suitable analytical condition has been established for HPLC, and the LAS in modern sediments from core Zhu-9 at the Pearl River mouth has been determined by HPLC. The concentrations of C12-LAS homologues are the highest. The sedimentation flux of C12-LAS was correlated with the average flow of the Xijiang and Beijiang rivers: the higher the flow rate, the larger the C12-LAS sedimentation flux. This shows that the more rapidly the river flows, the shorter the LAS will stay in freshwater, the less the extent of biodegradation, the larger the C12-LAS sedimentation flux in the core Zhu-9.展开更多
The aim of this paper is to study the REE geochemistry of the Shenzhen Bay (SZB) and Dapeng Bay(DPB) modern sediments, discuss their REE distribution patterns, reveal the REE geochemical difference between the two bay...The aim of this paper is to study the REE geochemistry of the Shenzhen Bay (SZB) and Dapeng Bay(DPB) modern sediments, discuss their REE distribution patterns, reveal the REE geochemical difference between the two bays which share the same material source but are deposited in different sedimentary environments, and expound their dynamic changes.It can be concluded that the SZB and DPB sediments are essentially of continental source.Their REE distribution patterns are quite different from those of Pacific pelagic sediments, but are very similar to those of South Chi-na granites.Because of different sedimentary environments prevailing in the SZB and DPB, some REE fractionation would have taken place in the sediments of the two bays.展开更多
基金supported by the National Basic Research Program of China(Grant No.2012CB956102)the National Natural Science Foundation of China(Grant Nos.41071126,41125006,41401227)the China Postdoctoral Science Foundation(Grant No.2014M550822)
文摘The modern pollen assemblages of surface lake sediments and topsoils in northwestern China were studied to understand the relationship of modem pollen data with contemporary vegetation and climate, and the differences between the pollen assem- blages of surface lake sediments and topsoils. The results show that Chenopodiaceae and Artemisia are dominant elements in the pollen assemblages of northwestern China. Additionally, Ephedra, Cyperaceae, Asteraceae, Poaceae, Picea, Pinus, and Betula are also important pollen taxa. Both pollen assemblages and principal component analysis indicate that pollen data from surface lake sediments and topsoils can be used to differentiate the main vegetation types of this region （desert, steppe, mead- ow and forest）. However, differences exist between modern pollen assemblages of the two types of sediments due to the dif- ferent relevant source areas of pollen and degrees of pollen preservation. For example, the larger relevant source area of sur- face lake sediment results in a higher abundance of Betula in pollen assemblage from surface lake sediment, whereas the ten- dency to disintegrate thin-walled pollen types in topsoil leads to a higher proportion of resistant pollen, such as Asteraceae. Linear regression analysis indicates that the Artemisia/Chenopodiaceae （A/C） ratio in pollen assemblages of surface lake sedi- ments can be used to indicate humidity changes in the study area. However, the A/C ratio in topsoils should be used carefully. Our results suggest that pollen data from surface lake sediments would be better references for interpreting the fossil pollen assemblages of lake cores or lacustrine profiles.
基金the National Natural Science Foundation of China(Grant Nos.41671202&41690113)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA20070101)the National Key Research and Development Program of China(Grant No.2016YFA0600501)。
文摘Modern pollen analysis is the basis for revealing the palaeovegetation and palaeoclimate changes from fossil pollen spectra.Many studies pertaining to the modern pollen assemblages on the Tibetan Plateau have been conducted,but little attention has been paid to pollen assemblages of surface lake sediments.In this study,modern pollen assemblages of surface lake sediments from 34 lakes in the steppe and desert zones of the Tibetan Plateau are investigated and results indicate that the two vegetation zones are dominated by non-arboreal pollen taxa and show distinctive characteristics.The pollen assemblages from the desert zone contain substantially high relative abundance of Chenopodiaceae while those from the steppe zone are dominated by Cyperaceae.Pollen ratios show great potential in terms of separating different vegetation zones and to indicate climate changes on the Tibetan Plateau.The Artemisia/Chenopodiaceae ratio and arboreal/non-arboreal pollen ratio could be used as proxies for winter precipitation.Artemisia/Cyperaceae ratio and the sum of relative abundance of xerophilous elements increase with enhanced warming and aridity.When considering the vegetation coverage around the lakes,hierarchical cluster analysis suggests that the studied sites can be divided into four clusters:meadow,steppe,desert-steppe,and desert.The pollen-based vegetation classification models are established using a random forest algorithm.The random forest model can effectively separate the modern pollen assemblages of the steppe zone from those of the desert zone on the Tibetan Plateau.The model for distinguishing the four vegetation clusters shows a weaker but still valid classifying power.It is expected that the random forest model can provide a powerful tool to reconstruct the palaeovegetation succession on the Tibetan Plateau when more pollen data from surface lake sediments are included.
基金Project supported by the National Natural Science Foundation of China and Project of the Multidisciplinary Oceanographic Expedition of Chinese Academy of Sciences to Nansha Islands
文摘Carbon isotopic compositions of individual n-alkanols and sterols in modern sediments from the Nan-sha Islands sea area are measured after derivatization to trimethylsilyl ethers by the new isotopic analytical technique of GC/C/IRMS. The effects of the three added silyl carbon atoms in every alcohol molecule on these compound isotopic compositions and the characteristics of their carbon isotopic compositions are studied. Then their biological sources are discussed using their carbon isotopic compositions.
基金support by the Geoscience Center of the Georg-August-University Göttingen.Y.J.Liu acknowledges the National Key R&D(2022YFF0800400-2)National Natural Science Foundation of China(Grant No.42130305)+4 种基金Taishan Scholars(ts20190918)Qingdao Leading innovation talents(19-3-2-19-zhc)S.Z.Li acknowledges Marine S&T Fund of Shandong Province for Laoshan Laboratory(Qingdao)(No.2022QNLM050302)Taishan Scholars(tspd20210305)study has been performed at the Geoscience Center Göttingen.J.P.Zhou acknowledges China Scholarship Council(2016094678)。
文摘The Cretaceous sedimentary successions in NE China are largely incomplete as the basins are inverted and younger strata are eroded.Except for the Songliao Basin,whose depositional record has remained relatively intact,the burial record to the east was interrupted in the late Early or Late Cretaceous.There is still controversy on the possible connection between the Songliao Basin and the eastern basin group,as well as the extent of the previously suggested“pan-Sanjiang”proto-basin that covered most current eastern satellite basins.To address these questions,we studied modern river catchments of variable sizes from sediment-supplying basement highs that cover most of eastern NE China to track the intense denudation events and provenance changes through the Cretaceous.We found a great inconsistency between detrital age patterns of the modern river sands and the spatial proportions of the source units.The detrital age distributions allow to re-evaluate the basement units that are mostly composed of the Triassic–Jurassic igneous suite and some metasedimentary units with Paleozoic ages,but the contribution from Proterozoic formations is negligible.Combining the newly dated modern catchment detrital U-Pb ages,the region-wide compilation of the basement emplacement ages,and the U-Pb ages in the Cretaceous formations in NE China,we systematically refine the Cretaceous provenance history.In the Early Cretaceous,the eastern satellite basins accumulated sediments from the Lesser Xing’an range(LXR)in the west,Zhangguangcai range(ZGCR)in the south,and the Nadanhada terrane(NT)in the east.The sediment of the southern Songliao Basin derived from the North China Craton(NCC)and from ZGCR but barely from the Great Xing’an Range(GXR).The Jiamusi uplift(JU)did not provide sediments to the eastern satellite basins and the Songliao Basin.In the Late Cretaceous,the eastern satellite basins received sediments from the exhumed JU but barely from ZGCR and LXR.The Songliao Basin still accumulated the sediments from the NCC,some so
基金Project supported by the National Natural Science Foundation of China.
文摘The content and isotopic compositions of different sulphur species in pore-water and solid phases have been examined on five sediment cores taken from muddy sediment region in the Yellow Sea and the East China Sea. Relationships among these data have been investigated with the combination of morphology of mineral pyrite and organic matter so as to role out the diagenetic behaviour of sulphur species at the early stage of diagenesis in modern marine sediment and the origin of pyrite formation.
文摘High performance liquid chromatography (HPLC) has the advantages of rapid analysis and high sensitivity. In the present study a suitable analytical condition has been established for HPLC, and the LAS in modern sediments from core Zhu-9 at the Pearl River mouth has been determined by HPLC. The concentrations of C12-LAS homologues are the highest. The sedimentation flux of C12-LAS was correlated with the average flow of the Xijiang and Beijiang rivers: the higher the flow rate, the larger the C12-LAS sedimentation flux. This shows that the more rapidly the river flows, the shorter the LAS will stay in freshwater, the less the extent of biodegradation, the larger the C12-LAS sedimentation flux in the core Zhu-9.
文摘The aim of this paper is to study the REE geochemistry of the Shenzhen Bay (SZB) and Dapeng Bay(DPB) modern sediments, discuss their REE distribution patterns, reveal the REE geochemical difference between the two bays which share the same material source but are deposited in different sedimentary environments, and expound their dynamic changes.It can be concluded that the SZB and DPB sediments are essentially of continental source.Their REE distribution patterns are quite different from those of Pacific pelagic sediments, but are very similar to those of South Chi-na granites.Because of different sedimentary environments prevailing in the SZB and DPB, some REE fractionation would have taken place in the sediments of the two bays.
