中国东部全新世自然环境演变

最近一万年来,我国东部自然环境演变十分明显,主要表现为:10500—9000a.B.P.气温、海面快速回升、沟谷加快填平、冰川萎缩、冻土北移或上移、森林扩展、阔叶树增多;9000—6000a.B.P.高温高海面及6000—4000a.B.P.最宜环境中,出现新高温期与新冰期交替,亚热带常绿阔叶林扩展与减缩。北方针叶林北撤与南侵、喜暖的微体古生物—有孔虫化石富集与缺失,降水丰歉、泥炭发育与停止等一系列变化;4000a.B.P.以来,这是气温与海面趋向下降的环境,气候变温干,常绿阔叶树减少,海面降低引起河口外移,沟谷重新受切割,地面冲刷,堆积次生黄土,气候波动频率加快,变幅减弱,环境变差。     

北疆全新世环境变迁研究的新进展

新疆全新世环境变迁前人研究较少。作者在国家自然科学基金的资助下,主要对北疆巴里坤湖ZK0024孔、ZK00A孔及湖滨浅滩剖面尤其对A孔进行了较深入的研究。通过全新世剖面0.5cm间距的沉积地层学、生物地层学(孢粉、微体古生物)、沉积地球化学特征、氧、碳同位素及年代学的研究(古地磁磁偏角、~(14)C、~(210)Pb、树木年轮),提取了生物、物理、化学过程相互作用的信息。初步探讨了     

内蒙古正蓝旗地区全新世古环境变迁的孢粉记录

通过对正蓝旗闪电河剖面孢粉资料的分析,重建了内蒙古中部地区全新世以来古植被及古气候的演变过程。全新世早期气候温凉略干,为草原型植被或稀疏草原型植被;中期气候相对暖湿,为森林型植被;后期气候温凉偏干或凉爽偏干,为稀疏草原型植被或草原型植被。     

陕西榆林风沙滩区全新世气候和环境变迁

榆林长城沿线处于环境变化敏感带,其风沙滩区沉积剖面的磁化率和粒度分析结果显示,该区全新世早期11500～10000aBP随着全球气候的逐渐转暖,磁化率、黏粒和粉沙含量逐渐增高;全新世中期的10000～45003BP气候相对比较湿润,植被覆盖度增大,风沙活动减弱,地表沉积物当-中粉沙和黏土成分含量显著增大,风化成壤作用增强,地表发育沙质弱古土壤;全新世中期后段的4500～3000aBP期间,气候以比较温和湿润为主,但在4200～4000aBP出现一个气候干旱事件,风沙活动强烈;近3000a以来,气候显著干旱化,波动频繁,地表风沙沉积物显著变粗,表现出有5次沙漠扩张。该区生态环境演化、人文历史变迁基本上是自然因素与人为活动综合作用的结果,以自然演化为主,近代人为因素对环境变化起着加强和放大作用。     

中国西部地区全新世自然环境演变序列与特征

根据湖泊、山地冰川、黄土与古土壤序列、泥炭及沙漠演变等多种地质记录的综合对比分析，重建和恢复了我国酉部地区全新世以来的自然环境演变序列及特征。全新世期间我国西部地区环境演变存在着以水热配置关系不同为突出特征的两种不同的演变模式：即以新疆北部地区为代表的西风型和以青海湖及青藏高原为代表的季风型模式。其成因同区域性特征及大气环流形势密切相关。并划分出我国西部地区全新世自然环境演变过程中的几个重要时间界线，即距今１２ｋａ或１０ｋａ、９ｋａ、３ｋａ和０．５ｋａ。众多地质记录间良好的对比关系对于深入理解我国西部全新世气候环境的演变过程，预测其变化趋向具有十分重要的意义。     

白洋淀地区全新世以来的气候环境变化

白洋淀是华北平原最大的淡水湖泊,是研究全新世气候变化的理想区域。文章选择白洋淀东垒头剖面（厚382 cm）,在8个AMS-¹⁴C测年数据基础上,通过对其189个样品的地球化学元素、粒度和磁化率等指标分析,高分辨率地揭示了白洋淀地区全新世气候变化过程。研究结果显示：1）11335~10300 cal.a B.P.期间,CaO/MgO比值（多高于4.8）、（CaO+K₂O+Na₂O）/Al₂O₃比值（多高于1.3）、CaCO₃含量（多高于12%）和中值粒径（多高于15 μm）均为整个剖面最大值,干旱指数（平均约为0.019）为剖面次高值,CIA值（多低于45）、Ti含量（多低于0.38%）和低频磁化率值（多低于10×10^-8 m³/kg）为整个剖面的最低值,指示气候冷干,受新仙女木事件影响较大;2）10300~8500 cal.a B.P.期间,CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值、干旱指数和中值粒径明显下降,CIA值、Ti含量、低频磁化率值均不同程度上升,指示气候向暖湿发展;3）8500~6000 cal.a B.P.期间,气候总体温暖湿润,干旱指数（平均达0.014）为剖面的最小值,CIA值和Ti含量较高,CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值较低;但该阶段所有指标波动剧烈,8200 cal.a B.P.和6800 cal.a B.P.左右CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值、干旱指数、CaCO₃含量出现高峰值,CIA值和Ti含量出现低峰值,指示2次明显冷干事件;4）6000~4200 cal.a B.P.期间,CaCO₃含量最低,但干旱指数较高,CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值均有不同程度上升,指示气候湿润度有所下降;其中4500 cal.a B.P.为一次明显冷干事件,干旱指数呈现高峰值;5）4200~1035 cal.a B.P.期间,砂含量（多低于2%）、中值粒径（多低于10 μm）为剖面最小值;干旱指数、CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值、CaCO₃含量明显升高,指示气候向着凉干方向发展;干旱指数在2800 cal.a B.P.呈现高峰值,指示一次明显冷干事件,同时,该时段受人类活动影响,低频磁化率值（多高于20×10^-8 m³/kg）明显高于其他时段。

     

祁连山摆浪河全新世冰量变化初探

采用祁连山老虎沟12号冰川2009年RTK测量生成的数字高程模型(DEM), 建立现代冰川表面横截面拟合的二次方程, 结合差分GPS测量的冰碛垄形态, 运用于祁连山摆浪河上游14号冰川和16号冰川全新世以来冰量变化的估算. 结果表明: 新冰期以来冰储量减少0.38 km³, 小冰期以来14号冰川和16号冰川的冰储量分别减少0.016 km³和0.047 km³; 根据祁连山全新世各个时期最大冰川范围的时间, 估计了全新世以来14号和16号冰川冰储量的减少速率, 新冰期以来为12.2×10^-5~15.0×10^-5 km³·a^-1, 小冰期以来分别为4.0×10^-5~5.3×10^-5 km³·a^-1, 11.75×10^-5~15.7×10^-5 km³·a^-1.     

泸沽湖地区晚全新世气候和环境演变

泸沽湖地区受人类活动影响较小、对气候变化较为敏感,是开展古气候研究的理想区域。本文以孢粉为重要研究手段,对采自泸沽湖草海地区103cm的浅钻沉积物开展研究,采样间距2cm,共取得52块样品用于孢粉分析。沉积物年龄采用AMS-~(14)C测定,经校正之后钻孔底部年龄为3455cal.a BP。经实验分析之后,所有样品均含有丰富的孢粉类群,反映的植被组成主要以松(Pinus)林为主,铁杉(Tsuga)也较为常见,被子植物中则以栎属(Quercus)占绝对优势,栗属(Castanea)和木犀科(Oleaceae)植物也频繁出现,而草本植物则以禾本科(Gramineae)为主,蓼科(Polygonaceae)、菊科(Asteraceae)和莎草科(Cyperaceae)植物也是重要的组成成分,林下生长有大量的蕨类的植物,主要以紫萁属(Osmunda)、石松属(Lycopodium)和膜蕨科(Hymenophyllaceae)等为主,另外,采样点草海为季节性湿地,水生植物主要以香蒲属(Typha)和藻类植物中的双星藻(Zygnema)和水绵(Spirogyra)最为常见。为了获得该地区晚全新世以来的气候变化曲线,本研究采用共存分析法分别对划分的四个孢粉带进行了古气候的定量重建,年均温和年均降水量分别为:3455cal.a BP至2585cal.a BP,MAT(mean annual temperature)=11.5~18.6℃,MAP(mean annual precipitation)=797.5~1484.3mm;2585cal.a BP至1699cal.a BP,MAT=11.7~18.6℃,MAP=617.9~1523.1mm;1699cal.a BP至595cal.a BP,MAT=8.5~18.6℃,MAP=797.5~1484.3mm;595cal.a BP至今,MAT=5.7~18.6℃,MAP=617.9~1484.3mm。结果显示该地区3455cal.a BP以来气候经历了略微变暖-变凉-持续变凉-回暖四个阶段。本研究还将变化曲线与其他地区同时代的研究结果进行了对比分析,显示年均温的变化趋势与格陵兰冰芯δ~(18)O以及祁连山敦德冰芯所反映的温度变化趋势基本一致,并可观察到中世纪暖期、晚全新世小冰期及现代温暖期。     

Holocene river development and environmental change in Upper Wharfedale,Yorkshire Dales,England

This paper provides the first radiometrically dated evidence of Holocene alluvial landform development in Upper Wharfedale, Yorkshire Dales. Four river terraces are identified. Terraces 1 and 2 are closely linked to Late Devensian and early Holocene environmental change, with gravel reworked from local glacial and periglacial sources prior to cementation by carbonate‐rich waters. U‐series dating of cement provides age estimates for cementation of between ca. 5.1–7.4 kyr BP for Terrace 1 and ca. 3.6–>8.0 kyr BP for Terrace 2. U‐series dating of tufas overlying Terraces 1 and 2 produced ages of ca. 4.2–4.5 kyr BP and ca. 2.1–2.2 kyr BP respectively, and provide upper age limits for terrace formation. Terrace 3 marks a change in sediment calibre, supply and sedimentation style, and ¹⁴C dating suggests that the principal source of fine‐grained material may be agricultural expansion in the Yorkshire Dales from ca. ad 600 (1350 cal. yr BP). Radiocarbon dates indicate that Terrace 4 was deposited from the eleventh century, with initiation of the contemporary floodplain between the fifteenth and seventeenth centuries ad. Both these lowest units contain sediments contaminated with heavy metals as a result of mining activities within the catchment. The evidence presented in this study is comparable to that of research undertaken in upland environments elsewhere in northern and western Britain, thereby adding to the corpus of information currently available for evaluating the fluvial geomorphological response to climate and vegetation change during the Holocene. Copyright © 2000 John Wiley & Sons, Ltd.     

辽河三角洲LZK03孔全新世环境演变

根据辽河三角洲LZK03孔岩心的地层、孢粉、~(14)C测年及粒度分析结果,重建了该孔全新世以来的沉积环境演变历史,划分了4个时期:1湖沼期,地层埋深22.70~18.35m,晚更新世晚期约8000cal BP,起始时间早于全新世底界年龄,一直持续到全新世海侵到达该地区;2海侵期,18.35~13.55m,8000~3000cal BP,全新世海侵(辽东湾命名为盘山海侵)于8000cal BP到达该地区,湖沼发育结束,随着海侵向陆扩展,形成了海相潮坪沉积;3海退期,13.55~7.50m,约3000cal BP开始海退,河流携带的泥砂成为主要物源;4盐沼期,7.50~0m,500cal BP时海水已退至LZK03孔向海一侧,经常暴露于地表的氧化环境使盐沼沉积呈黄棕色,被高潮海水淹浸的时间减少。     

Late Pleistocene and Holocene environmental changes in the coastal zone of northwestern Portugal

This paper examines the Quaternary changes in the coastal zone of northwestern Portugal through the relationship between sediments and landforms. By interpolating the available data from geomorphology, lithostratigraphy, sedimentology and geochronology, it was possible to reconstruct existing palaeoenvironments, the oldest of which date back to the last interglacial. The main landforms are a high and a low platform bounded by scarps. River sands and silty sediments formed in a lacustrine environment (Antas Formation, MIS 5) are associated with the high platform. Two deposits are associated with the low platform: the Cepães Formation (MIS 3) consisting of a lower set of river sand beds and an upper gravel beach bed, and the Aguçadoura Formation (MIS 1) consisting of Holocene lagoonal beds. Copyright © 2006 John Wiley & Sons, Ltd.     

长江三峡库区全新世环境考古研究进展

充分利用长江三峡工程文物抢救性发掘的宝贵机会,通过对重庆市忠县中坝遗址、丰都县玉溪遗址等典型遗址和神农架大九湖泥炭地层环境考古研究,摸索出了一套利用年代学、沉积学、重矿物组分鉴定、锆石形态统计、地球化学和环境磁学方法辨别考古遗址地层中古洪水沉积的方法;建立了该区地表孢粉-气候的转换函数,并将其用于对神农架大九湖泥炭地层的研究,弄清了该区全新世以来环境演变的背景,并将自然沉积地层环境演变记录与典型考古遗址地层古洪水事件作了对比分析。遗址时空分布研究表明:长江三峡库区旧石器时代至宋代677处遗址时空分布总趋势是从西往东、从高往低逐渐增加的,遗址多沿江河分布,且在河流交汇处呈聚集状态,这与人类多选择河流1～2级阶地为生、河流交汇处鱼类资源丰富有关。研究表明:中坝遗址能延续5000a的原因一方面与其盐业遗址的属性有关,另一方面与其长期具有良好生态环境有关。从该遗址T0202探方出土近20万件动物骨骼的分类统计证明了这一点。7.6kaBP以来,水位在吴淞高程147.024m以上的古洪水至少在玉溪遗址T0403探方中留下了16次沉积记录。神农架大九湖297cm厚的泥炭及其148个孢粉样品和10个AMS14C测年数据表明,该泥炭地层为本项目提供了理想的全新世自然环境演变背景,尤其8.2kaBP前后的降温事件很明显,6.7～4.2kaBP为中全新世最适宜期,4.2kaBP前后由暖湿转为凉干,3.5～0.9kaBP季风降水整体较弱,0.9kaBP前后转为较凉湿。根据对中坝和玉溪两处遗址地层的研究,在8.2～6.7kaBP期间出现有10个古洪水层;在6.7～4.2kaBP全新世最适宜期遗址地层中出现有8个古洪水层;在3.5～0.9kaBP降水减少的时期,中坝遗址中仅出现2个洪水层(即西周时期的37-1和战国早期的第21层);在0.9kaBP以来降水较多的时期,中坝遗址中存在3个洪水层(即宋代中期的11C-1层、清代的5-1层和1981年的2B-2层)。这表明,8.2～6.7kaBP的洪水在三峡地区次数是最多的,6.7～4.2kaBP的洪水数量次之。长江三峡库区的这一古洪水发生规律或许可以解释长江中游的江汉平原在7.8～5.1kaBP期间遗址数量偏少的原因。     

Punctuated environmental change along the Holocene (<6 ka) bank margin of south-west Exuma Sound, Bahamas

Characteristics of environmental change along the Holocene (<6 ka BP) bank margin of south‐west Exuma Sound, Bahamas, are defined by comparing mineral, isotope and lithologic stratigraphic patterns in deep‐water (1081 m) slope strata in ODP Hole 631A (Exuma Sound) with proximal (≈6 km) shoal‐water and insular geology of the Lee Stocking Island (LSI) region. After platform submergence, a bank‐top transition from non‐skeletal‐ to skeletal‐dominated deposition occurred in the LSI region by ≈3·8 ka, and is recorded in the adjacent slope sediments by a contemporaneous change in the abundance of transported allochems. The transition at Site 631 is punctuated by an anomalous shift in foraminiferal δ¹³C (–1‰) and δ¹⁸O (–3‰), which may represent a period of climate change that established a brackish coastal zone at least 6 km wide, coincident (≈3·8–4 ka) with bank‐top erosion and pedogenesis. Non‐skeletal allochems reappeared in Hole 631A sediments as the dominant transported allochem type by ≈2·4 ka, then again over the last several hundred years, and are contemporaneous with periods of increased platform‐margin circulation in the LSI region. Such rejuvenation of platform circulation may have resulted from rapid relative rises in sea level, superimposed on the net gradual post‐glacial rise. At Site 631, a prominent (25%) decline in aragonite abundance occurred during the period from 2·4 ka to the last few hundred years, and coincided with an increase in magnesian calcite and skeletal debris, and a positive shift in foraminiferal δ¹⁸O values. These patterns lend support to the hypothesis that, during this period, the LSI margin was barred by skeletal shoals, allowing bank‐top trapping of aragonite and hypersaline water, with increased coastal salinity (resulting from reflux of hypersaline waters through the shoals) and/or cooled coastal waters (caused by reduced exchange of warmed bank‐derived water relative to wind‐generated upwelling). Along the Exuma slope, a diagenetic overprint may further enhance the recent decline in aragonite accumulation. Integration of Holocene deep‐water slope and bank‐top stratigraphies along the bank margin of south‐west Exuma Sound reveals a pattern of punctuated environmental change superimposed on longer term development of interglacial conditions.     

成都平原中—晚全新世环境考古研究进展*

自20世纪80年代以来,成都平原环境考古工作在聚落选址与地理环境、古气候与古蜀文明发展、灾变事件研究及史前人地关系综合研究等方面取得重要进展。研究表明: 成都平原史前城址群的出现与当时的地理环境应有很大关系;成都平原中—晚全新世以来气候整体温暖湿润,其中有多次气候波动和降温事件发生;古洪水、古地震等自然灾害与古蜀文明发展的关系很密切;基于成都平原诸多先秦遗址的人地关系综合研究表明,河流、地貌、气候等因素与史前聚落变迁有很大关系。总体上,成都平原环境考古工作经历了3个发展阶段。受限于研究材料和方法,目前仍然缺乏高分辨率古环境演变规律的研究成果;自然灾害与成都平原先秦时期古文化演变的一些重要节点的耦合关系仍不明确;今后还需要加强与河流地貌有关的聚落环境考古研究;利用地理信息系统和遥感技术分析环境变迁与人类活动关系以及定量和模型化研究史前人地关系也将是未来成都平原环境考古工作的重要内容。     

关于里下河地区水文业务工作的思考

里下河地区水文情势复杂,既有腹部的水网区、又有沿海垦区,水文站点众多.随着大规模的水利建设,河道、水系水利工程化程度不断提高,原有水系的水文特征已有所改变,传统水文工作的发展受到了一定程度的制约.针对该地区水文业务工作的实际情况,本文就如何调整水文监测站网、提高自动测报能力、加强技术分析研究,使水文业务发展适应区域经济社会发展的需要等进行了有益探讨.     

Late Quaternary environmental changes on Pacific islands: controversy,certainty and conjecture

The late Quaternary history of the Pacific islands is poorly known. Most details about Pleistocene history come from studies of ocean-floor sediments, although a few insular pollen records extend back into the last glacial stage. There is limited evidence for Last Glacial Maximum (LGM) aridity and a rise in LGM–early Holocene precipitation associated with strengthening of the Southern Oscillation. The middle Holocene warming is best represented by sea-level records, which, from all parts of the Pacific, now show a contemporary maximum ca. 5000–3000 yr BP. Late Holocene cooling and precipitation increase were probably more widespread than available data suggest. The advent of humans into Pacific island environments, mostly during the late Holocene, is critically reviewed. Vegetation change may have, at least in part, been the result of climate change. Many Pacific island grasslands may be climatogenic rather than anthropogenic. Fires may have occurred naturally long before people arrived on Pacific islands. Ideas about early human impacts on Pacific island enviroments need to be critically reviewed. © 1997 John Wiley & Sons, Ltd.