Sediment grain size is a conventional proxy of climatic changes. Larger sediment grain size is often interpreted to indicate dry climate during lower lake level while smaller sedi- ment grain size implies wet climate ...Sediment grain size is a conventional proxy of climatic changes. Larger sediment grain size is often interpreted to indicate dry climate during lower lake level while smaller sedi- ment grain size implies wet climate during higher lake level. Through detailed study on sediment grain sizes in Lake Erhai and Lake Chenghai, this paper reveals the different indication signifi- cances of sediment grain sizes in different time scales, different resolution investigations. For long time-scale and low resolution (102a or 103a) studies, larger sediment grain size indicates lower lake level, smaller lake area and drier climate while smaller sediment grain size indicates higher lake level, larger lake area and wetter climate. For short time-scale and high resolution (a or 10a) studies, larger sediment grain size reflects more rainfall and wetter climate while smaller sediment grain size reflects less rainfall and drier climate. Environmental information revealed by lacustrine sediment records is often different in different time scales because of the variance of sedimentation resolution, sampling resolution and dating precision. Therefore, paleoclimate im- plications of environmental proxies in long time-scale and low resolution investigations could not be mechanically applied to short time-scale and high resolution studies. Only after synthetically analyzing the influence manner and extent of all factors on the sediment records in different time scales, can credible conclusions be obtained.展开更多
The changes of magnetic susceptibility(κ) are correlated with those of corresponding sedimentological, geochemical, mineralogical and biological results, which verifies thatκ can be taken as one of the environmental...The changes of magnetic susceptibility(κ) are correlated with those of corresponding sedimentological, geochemical, mineralogical and biological results, which verifies thatκ can be taken as one of the environmental proxies. However, usually the exact origin of magnetic signal is poorly understood, and is difficult to relate with the environmental evolution. Magnetic properties of material derived from the catchment and sedimentary environment may affect the accumulation, preservation, or authigenesis and diagenesis of magnetic minerals. In the Lake Hulun region in Inner Mongolia, it is found that muddy sediments, deposited during high water level period (corresponding to humid climate), have comparatively highκ values. In contrast, the sandy sediments, deposited during low water level period (corresponding to arid climate), have lowκ values. Detailed rock magnetic investigation confirms that detrital magnetite derived from volcanic rocks in the catchment exists in both muddy and sandy sediments. During high water level period, secondary ferrimagnetic iron sulphide was produced in muddy sediments under relatively reductive conditions. Ferrimagnetic iron sulphide, coexisting with detrital magnetite, predominates the magnetic properties of muddy sediments, resulting in increasingκ. This paper reveals the significance of authigenic ferrimagnetic iron sulphide produced after sediment deposition.展开更多
河套盆地西缘与北缘发育一系列山前台地,台地沉积物记录了盆地环境变化。高台地沉积物记录了"吉兰泰—河套"古大湖形成过程,而低台地记录了古大湖的消退过程。盆地东部与西部低台地沉积特征不同,东部低台地由全新世冲洪积物组...河套盆地西缘与北缘发育一系列山前台地,台地沉积物记录了盆地环境变化。高台地沉积物记录了"吉兰泰—河套"古大湖形成过程,而低台地记录了古大湖的消退过程。盆地东部与西部低台地沉积特征不同,东部低台地由全新世冲洪积物组成,西部狼山山前低台地由晚更新世晚期—全新世(14 C年龄(15 260±60)a cal BP与(9 810±40)a cal BP)湖相沉积组成。低台地沉积特征及测年结果表明,1.5万年至1.0万年前后,河套盆地东部湖泊消失,而西部仍发育湖泊,古湖经历了自东向西的退却过程。古湖消退受盆地周缘断裂活动的差异性控制,1.5万年至1.0万年前后,盆地周缘断裂活动性总体上东强西弱,东部大青山山前断裂活动速率较高,大量碎屑物质进入盆地,呼和坳陷湖泊萎缩甚至消失,西部狼山山前断裂活动速率较低,进入盆地碎屑物质较少,临河坳陷大部分地区发育湖泊。展开更多
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sciences(Grant No.KZCX2-105)the National Natural Science Foundation of China(Grant Nos.403030140 and 49894170).
文摘Sediment grain size is a conventional proxy of climatic changes. Larger sediment grain size is often interpreted to indicate dry climate during lower lake level while smaller sedi- ment grain size implies wet climate during higher lake level. Through detailed study on sediment grain sizes in Lake Erhai and Lake Chenghai, this paper reveals the different indication signifi- cances of sediment grain sizes in different time scales, different resolution investigations. For long time-scale and low resolution (102a or 103a) studies, larger sediment grain size indicates lower lake level, smaller lake area and drier climate while smaller sediment grain size indicates higher lake level, larger lake area and wetter climate. For short time-scale and high resolution (a or 10a) studies, larger sediment grain size reflects more rainfall and wetter climate while smaller sediment grain size reflects less rainfall and drier climate. Environmental information revealed by lacustrine sediment records is often different in different time scales because of the variance of sedimentation resolution, sampling resolution and dating precision. Therefore, paleoclimate im- plications of environmental proxies in long time-scale and low resolution investigations could not be mechanically applied to short time-scale and high resolution studies. Only after synthetically analyzing the influence manner and extent of all factors on the sediment records in different time scales, can credible conclusions be obtained.
文摘The changes of magnetic susceptibility(κ) are correlated with those of corresponding sedimentological, geochemical, mineralogical and biological results, which verifies thatκ can be taken as one of the environmental proxies. However, usually the exact origin of magnetic signal is poorly understood, and is difficult to relate with the environmental evolution. Magnetic properties of material derived from the catchment and sedimentary environment may affect the accumulation, preservation, or authigenesis and diagenesis of magnetic minerals. In the Lake Hulun region in Inner Mongolia, it is found that muddy sediments, deposited during high water level period (corresponding to humid climate), have comparatively highκ values. In contrast, the sandy sediments, deposited during low water level period (corresponding to arid climate), have lowκ values. Detailed rock magnetic investigation confirms that detrital magnetite derived from volcanic rocks in the catchment exists in both muddy and sandy sediments. During high water level period, secondary ferrimagnetic iron sulphide was produced in muddy sediments under relatively reductive conditions. Ferrimagnetic iron sulphide, coexisting with detrital magnetite, predominates the magnetic properties of muddy sediments, resulting in increasingκ. This paper reveals the significance of authigenic ferrimagnetic iron sulphide produced after sediment deposition.
文摘河套盆地西缘与北缘发育一系列山前台地,台地沉积物记录了盆地环境变化。高台地沉积物记录了"吉兰泰—河套"古大湖形成过程,而低台地记录了古大湖的消退过程。盆地东部与西部低台地沉积特征不同,东部低台地由全新世冲洪积物组成,西部狼山山前低台地由晚更新世晚期—全新世(14 C年龄(15 260±60)a cal BP与(9 810±40)a cal BP)湖相沉积组成。低台地沉积特征及测年结果表明,1.5万年至1.0万年前后,河套盆地东部湖泊消失,而西部仍发育湖泊,古湖经历了自东向西的退却过程。古湖消退受盆地周缘断裂活动的差异性控制,1.5万年至1.0万年前后,盆地周缘断裂活动性总体上东强西弱,东部大青山山前断裂活动速率较高,大量碎屑物质进入盆地,呼和坳陷湖泊萎缩甚至消失,西部狼山山前断裂活动速率较低,进入盆地碎屑物质较少,临河坳陷大部分地区发育湖泊。
