The intensified monsoon increases summer rainfall and creates wet conditions in the Asian summer monsoon region during the early Holocene. Along with millennial-scale changes of the monsoon intensity, it is still uncl...The intensified monsoon increases summer rainfall and creates wet conditions in the Asian summer monsoon region during the early Holocene. Along with millennial-scale changes of the monsoon intensity, it is still unclear whether the boundary of the monsoon region changes according to monsoon variability. Investigations into the early Holocene environment in monsoon marginal zones are crucial for understanding the monsoon boundary changes. Zhuye Lake is located at the northwest edge of the Asian summer monsoon, the northern Qilian Mountains, which are less affected by modern summer monsoon water vapor. Previous studies have reached different conclusions regarding the early Holocene climatic and environmental changes based on different dating methods（^14C and OSL（optically stimulated luminescence）） and materials（shells, carbonate, pollen concentrates and bulk organic carbon）. In this study, we synthesized 102 ^14C dates and 35 OSL dates from ten Holocene sedimentary sections and ten paleo-shorelines in the lake basin. A comparison between ages from different dating methods and materials generally shows that carbon reservoir effects are relatively slight in Zhuye Lake while the disordered chronologies are mainly related to the erosion processes and reworking effects. In addition, proxy data, including lithology, pollen, total organic carbon and carbonate, were collected from different sites of Zhuye Lake. According to the new synthesis, the early Holocene environment was relatively humid, associated with high runoff and lake water levels. The result indicates that the monsoon boundary moves to the north during the period of the intensified monsoon. A typical arid-area lake was formed during the mid-Holocene when carbonate accumulation and high organic matter contents were the main features of this period. The lake retreated strongly during the late Holocene, showing a drought trend. Overall, the lake evolution is generally consistent with the Holocene Asian summer monsoon change, showing the monsoon infl展开更多
Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction a...Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction and peat fraction) of the bulk peat samples were investigated by AMS-dating and which fraction is better to help construct an age framework for the boreholes were compared and discussed. The results indicated that the peat fraction give a good dating results sequence in the boreholes, compared with the corresponding organic sediment fraction. And the dating results of organic sediment fraction show 161-6 702 years older than corresponding peat fraction, which was caused by marine influence. Then, we suggest an experience formula as y =0.99 x-466.5 by the correlation analysis for correcting the marine influenced organic sediment ages within the conventional ages between 4 000 to 9 000 yrs BP, and more study should be carried out for the AMS ^(14)C dating of the bulk organic sediments.展开更多
自然环境变迁影响古代文明的发展与更替,被越来越多的学者所关注和认可。本文对陕西省商洛市东龙山遗址从仰韶、龙山文化至夏、商、周代时期连续的文化遗存和全新世黄土-古土壤序列进行了磁化率测量、孢粉分析、动物化石分类鉴定,考古...自然环境变迁影响古代文明的发展与更替,被越来越多的学者所关注和认可。本文对陕西省商洛市东龙山遗址从仰韶、龙山文化至夏、商、周代时期连续的文化遗存和全新世黄土-古土壤序列进行了磁化率测量、孢粉分析、动物化石分类鉴定,考古遗址调查和^(14)C加速器测年,为的是进一步探讨环境变迁与考古文化更替之间的内在联系。在该遗址区域内分别选定3个全新世黄土-古土壤剖面和考古遗址采集样品,进行高精度^(14)C加速器测年,根据测年数据建立合适的贝叶斯校正模型,以此进行^(14)C系列样品的贝叶斯校正,首次建立了该地区全新世黄土-古土壤地层和考古遗址的^(14)C年代序列。马兰黄土与全新世黄土-古土壤交界处的^(14)C年龄为9470~9130 cal BP,复合古土壤下部形成时期为8020~7940 cal BP:复合古土壤上部形成时期为4970~4840 cal BP;新黄土开始堆积时间为2960~2840 cal BP。仰韶文化始于复合古土壤下部形成之后:龙山文化始于复合古土壤上部形成时期;夏、商代始于4080~3840 cal BP;周代始于新黄土开始堆积时间。通过对东龙山地区环境代用指标的分析,揭示了该地区进入全新世初期时,气候逐渐转暖,此后古土壤开始发育,仰韶文化、龙山文化和夏代、商代文化繁盛期的出现均与温暖湿润的气候环境相关联,自周代以后,气候转为干冷,开始堆积新黄土。而在仰韶文化与龙山文化交替时段(5000 cal BP),龙山文化与夏代、商代交替时段(4000 cal BP)以及周代晚期(3000 cal BP)发生的降温事件在全球均有记录,这3次短暂而突然的气候降温事件的交替出现,导致温度和降水逐渐下降和减少,促进了古人类文明发展的兴衰更替。展开更多
The Monards Marsh is located on the northeastern bank of the Gironde Estuary in France. Lithological, sedimentolngical and mi- cropalacontological investigations were made on four cores to determine the evolution of H...The Monards Marsh is located on the northeastern bank of the Gironde Estuary in France. Lithological, sedimentolngical and mi- cropalacontological investigations were made on four cores to determine the evolution of Holocene sedimentary environments and processes in this area over the last 6 000 a. Three main lithological facies are distinguished from bottom to top： （ 1 ） grey laminated silty-sandy clay ; （2） homogeneous dark grey silty clay ; and （ 3 ） compact silty clay. About 26 benthic foraminifera species are identified and divided into six groups according to their ecological characteristics. In association with lithology, sedimentary structures and grainuiometry, the distribution of foraminifera group is used to define external slikke, internal slikke, external schorre, internal schorre, and continental marsh facies. Combined with 14C（AMS） dating, these data indicate four successive paleoenvironments in the Monards Marsh： （ 1 ） Holocene transgression resuited in the development of a basal schorre facies overlying fluvial deposits that transformed to slikke facies sedimentation; the transgression maximum occurred around 5 600 to 5 4430 a BP and was inferred to be associated with the last phase of the rapid Holocene sea-level rise; （2） post-trangressive maximum sedimentation resuited in a regressive sequence of deposits prograding towards the estuary, corresponding to the stahilisation of sea level after 5 4430 a BP; （3） a slight positive tendency in the sea level around 2 800 a BP recorded in the central part of the marsh; and （4） the wetland to a continental marsh environment. The sequential pattern for the evolution of wetlands in this estuarine area during the Holocene is fluvial facies - blackish schorre facies - slikke facies - blackish schorre facies - continental marsh facies. Characteristics of sedimentary facies distribution and evolution reveal that the development of Holocene salt marsh in this area was controlled by the sea-level change and tidal range. The se展开更多
The origin and quality of groundwater in the Southeastern region （belongs to Southern Plain） were identified by using isotopic techniques and geochemical analysis. Groundwater samples were collected from 7 aquifers...The origin and quality of groundwater in the Southeastern region （belongs to Southern Plain） were identified by using isotopic techniques and geochemical analysis. Groundwater samples were collected from 7 aquifers： the Holocene, upper Pleistocene, middle Pleistocene, lower Pleistocene, upper Pliocene, middle Pliocene and Miocene aquifers. The water isotopic compositions （82H and 8180） were determined to elucidate the origin and the interaction between surface water and groundwater studies. Transit time （age） of the groundwater samples was determined to explain the direction of groundwater flow. The dating techniques included 3H and ^14C isotopes measurement, followed by a correction for the initial ^14C-activity by the ^13C-composition （^13C） in TDIC （Total Dissolved Inorganic Carbon）. Geochemical parameters of the groundwater samples were measured either directly in the field or in the laboratory. The results showed that the groundwater from the Holocene and upper Pleistocene aquifers was most recharged from the local meteorological and hydrological systems, including local precipitation, fiver and reservoirs. Thus, it has short transit time and its stable isotopic composition is spread around the local meteoric waterline and lines for rivers or reservoirs water. The groundwater in the deeper aquifers： middle and lower Pleistocene, and Neogene aquifers has old age up to 22.5 ka BP. Its water seems to be recharged from the areas with an altitude from 600 to 700 m higher to the Neogene deposit layer altitude. The groundwater in the SE SP （South-Eastern Southern Plain） region has a high quality. The water type is Na-Ca-Mg-HCO3 with low content of chloride and TDS （Total Dissolved Solids）. Calcite/dolomite and gypsum dissolution, organic matter decomposition and sequence of red-ox reactions proceeding through different electron acceptors sediment were controlled the chemistry of the groundwater in the study region.展开更多
基金supported by the National Natural Science Foundation of China (41371009)the Fundamental Research Fund for the Central Universities (lzujbky-2013-127)
文摘The intensified monsoon increases summer rainfall and creates wet conditions in the Asian summer monsoon region during the early Holocene. Along with millennial-scale changes of the monsoon intensity, it is still unclear whether the boundary of the monsoon region changes according to monsoon variability. Investigations into the early Holocene environment in monsoon marginal zones are crucial for understanding the monsoon boundary changes. Zhuye Lake is located at the northwest edge of the Asian summer monsoon, the northern Qilian Mountains, which are less affected by modern summer monsoon water vapor. Previous studies have reached different conclusions regarding the early Holocene climatic and environmental changes based on different dating methods（^14C and OSL（optically stimulated luminescence）） and materials（shells, carbonate, pollen concentrates and bulk organic carbon）. In this study, we synthesized 102 ^14C dates and 35 OSL dates from ten Holocene sedimentary sections and ten paleo-shorelines in the lake basin. A comparison between ages from different dating methods and materials generally shows that carbon reservoir effects are relatively slight in Zhuye Lake while the disordered chronologies are mainly related to the erosion processes and reworking effects. In addition, proxy data, including lithology, pollen, total organic carbon and carbonate, were collected from different sites of Zhuye Lake. According to the new synthesis, the early Holocene environment was relatively humid, associated with high runoff and lake water levels. The result indicates that the monsoon boundary moves to the north during the period of the intensified monsoon. A typical arid-area lake was formed during the mid-Holocene when carbonate accumulation and high organic matter contents were the main features of this period. The lake retreated strongly during the late Holocene, showing a drought trend. Overall, the lake evolution is generally consistent with the Holocene Asian summer monsoon change, showing the monsoon infl
基金Supported by the China Geological Survey(No.121201006000182401)the National Natural Science Foundation of China(Nos.41476074,41372173)
文摘Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction and peat fraction) of the bulk peat samples were investigated by AMS-dating and which fraction is better to help construct an age framework for the boreholes were compared and discussed. The results indicated that the peat fraction give a good dating results sequence in the boreholes, compared with the corresponding organic sediment fraction. And the dating results of organic sediment fraction show 161-6 702 years older than corresponding peat fraction, which was caused by marine influence. Then, we suggest an experience formula as y =0.99 x-466.5 by the correlation analysis for correcting the marine influenced organic sediment ages within the conventional ages between 4 000 to 9 000 yrs BP, and more study should be carried out for the AMS ^(14)C dating of the bulk organic sediments.
文摘自然环境变迁影响古代文明的发展与更替,被越来越多的学者所关注和认可。本文对陕西省商洛市东龙山遗址从仰韶、龙山文化至夏、商、周代时期连续的文化遗存和全新世黄土-古土壤序列进行了磁化率测量、孢粉分析、动物化石分类鉴定,考古遗址调查和^(14)C加速器测年,为的是进一步探讨环境变迁与考古文化更替之间的内在联系。在该遗址区域内分别选定3个全新世黄土-古土壤剖面和考古遗址采集样品,进行高精度^(14)C加速器测年,根据测年数据建立合适的贝叶斯校正模型,以此进行^(14)C系列样品的贝叶斯校正,首次建立了该地区全新世黄土-古土壤地层和考古遗址的^(14)C年代序列。马兰黄土与全新世黄土-古土壤交界处的^(14)C年龄为9470~9130 cal BP,复合古土壤下部形成时期为8020~7940 cal BP:复合古土壤上部形成时期为4970~4840 cal BP;新黄土开始堆积时间为2960~2840 cal BP。仰韶文化始于复合古土壤下部形成之后:龙山文化始于复合古土壤上部形成时期;夏、商代始于4080~3840 cal BP;周代始于新黄土开始堆积时间。通过对东龙山地区环境代用指标的分析,揭示了该地区进入全新世初期时,气候逐渐转暖,此后古土壤开始发育,仰韶文化、龙山文化和夏代、商代文化繁盛期的出现均与温暖湿润的气候环境相关联,自周代以后,气候转为干冷,开始堆积新黄土。而在仰韶文化与龙山文化交替时段(5000 cal BP),龙山文化与夏代、商代交替时段(4000 cal BP)以及周代晚期(3000 cal BP)发生的降温事件在全球均有记录,这3次短暂而突然的气候降温事件的交替出现,导致温度和降水逐渐下降和减少,促进了古人类文明发展的兴衰更替。
文摘The Monards Marsh is located on the northeastern bank of the Gironde Estuary in France. Lithological, sedimentolngical and mi- cropalacontological investigations were made on four cores to determine the evolution of Holocene sedimentary environments and processes in this area over the last 6 000 a. Three main lithological facies are distinguished from bottom to top： （ 1 ） grey laminated silty-sandy clay ; （2） homogeneous dark grey silty clay ; and （ 3 ） compact silty clay. About 26 benthic foraminifera species are identified and divided into six groups according to their ecological characteristics. In association with lithology, sedimentary structures and grainuiometry, the distribution of foraminifera group is used to define external slikke, internal slikke, external schorre, internal schorre, and continental marsh facies. Combined with 14C（AMS） dating, these data indicate four successive paleoenvironments in the Monards Marsh： （ 1 ） Holocene transgression resuited in the development of a basal schorre facies overlying fluvial deposits that transformed to slikke facies sedimentation; the transgression maximum occurred around 5 600 to 5 4430 a BP and was inferred to be associated with the last phase of the rapid Holocene sea-level rise; （2） post-trangressive maximum sedimentation resuited in a regressive sequence of deposits prograding towards the estuary, corresponding to the stahilisation of sea level after 5 4430 a BP; （3） a slight positive tendency in the sea level around 2 800 a BP recorded in the central part of the marsh; and （4） the wetland to a continental marsh environment. The sequential pattern for the evolution of wetlands in this estuarine area during the Holocene is fluvial facies - blackish schorre facies - slikke facies - blackish schorre facies - continental marsh facies. Characteristics of sedimentary facies distribution and evolution reveal that the development of Holocene salt marsh in this area was controlled by the sea-level change and tidal range. The se
文摘The origin and quality of groundwater in the Southeastern region （belongs to Southern Plain） were identified by using isotopic techniques and geochemical analysis. Groundwater samples were collected from 7 aquifers： the Holocene, upper Pleistocene, middle Pleistocene, lower Pleistocene, upper Pliocene, middle Pliocene and Miocene aquifers. The water isotopic compositions （82H and 8180） were determined to elucidate the origin and the interaction between surface water and groundwater studies. Transit time （age） of the groundwater samples was determined to explain the direction of groundwater flow. The dating techniques included 3H and ^14C isotopes measurement, followed by a correction for the initial ^14C-activity by the ^13C-composition （^13C） in TDIC （Total Dissolved Inorganic Carbon）. Geochemical parameters of the groundwater samples were measured either directly in the field or in the laboratory. The results showed that the groundwater from the Holocene and upper Pleistocene aquifers was most recharged from the local meteorological and hydrological systems, including local precipitation, fiver and reservoirs. Thus, it has short transit time and its stable isotopic composition is spread around the local meteoric waterline and lines for rivers or reservoirs water. The groundwater in the deeper aquifers： middle and lower Pleistocene, and Neogene aquifers has old age up to 22.5 ka BP. Its water seems to be recharged from the areas with an altitude from 600 to 700 m higher to the Neogene deposit layer altitude. The groundwater in the SE SP （South-Eastern Southern Plain） region has a high quality. The water type is Na-Ca-Mg-HCO3 with low content of chloride and TDS （Total Dissolved Solids）. Calcite/dolomite and gypsum dissolution, organic matter decomposition and sequence of red-ox reactions proceeding through different electron acceptors sediment were controlled the chemistry of the groundwater in the study region.
