郧县前坊村剖面黄土-古土壤序列风化成壤及古气候研究

秦岭作为我国南方和北方地理、气候、自然环境的天然分界线,并当作是黄土高原的南屏障。汉江上游谷地地区位于秦岭南侧,属于北亚热带气候区域,受季风气候活动影响强烈。为了探讨该地区在亚热带气候背景下,风成黄土成壤改造对气候变化的响应机制,通过对汉江上游谷地前坊村（QFC）剖面磁化率、烧失量、粒度、Rb/Sr等理化性质进行研究。结果表明:①末次冰期以来沙尘暴很有可能越过秦岭在其南侧堆积,黄土-古土壤剖面地层序列从上到下依次为:MS-L₀-S₀-Lt-L₁-AD;这些沉积物完整记录了一级阶地上晚更新世气候变化信息,地层单元受到各个时期不同程度成壤强度的改造。②前坊村剖面中,理化性质在不同地层单元有显著差异。例如磁化率、烧失量、Rb/Sr指标平均含量的高值出现在古土壤层中,低值出现在黄土层;而Zr/Rb含量变化正好相反;这些理化性质表明,在古土壤发育期,水热条件进入最适宜期,沉积物的风化成壤作用显著;在黄土堆积期,气候寒冷干燥,主要以粉尘堆积为主,沉积物的风化成壤作用较弱。③秦岭南侧北亚热带汉江上游前坊村一级阶地剖面化学风化强度变化揭示了黄土-古土壤环境气候变化的规律:末次冰期以来（大约18.0～11.5 ka B.P.）,气候干冷,沙尘暴频繁出现,沉积物以黄土堆积为主,成壤作用微弱,形成马兰黄土（L₁）;全新世早期（约11.5～8.5 ka B.P.）,气候由干冷向暖湿方向转变,但主要以干冷为主,形成过渡层（Lt）;在全新世大暖期（8.5～3.1 ka B.P.）,气候条件达到最优阶段,水热配合较好,生物活动活跃,成壤作用十分显著,发育了古土壤S₀;到了全新世晚期以来（3.1 ka B.P.）气候又由暖湿向干冷方向转变,成壤作用明显减弱,沙尘暴出现较为频繁,形成了以黄土堆积为主的全新世黄土（L₀）。现代表土层（MS）是在（1.5 ka B.P.）以来气候转暖,加之人类长期农业耕作扰动,在全新世黄土L₀顶部叠加而形成的。     

黄河源区第四纪地质研究的新进展

通过对黄河源区的钻孔、自然露头的研究, 建立了黄河源区的第四纪地层层序。第四纪地层可划分为下更新统、中更新统、上更新统和全新统。下更新统为河湖相沉积; 中更新统主要有湖积物、冰碛物和冰水沉积物; 上更新统主要有湖积物、冰碛物、冰水沉积物、洪积物和河流沉积物; 全新统主要由河流沉积物、洪积物和湖积物构成。黄河源区的冰期可划分为3期, 即末次冰期、倒数第二次冰期、倒数第三次冰期, 末次冰期又可分为2个冰阶。黄河源区的湖泊演化可划分为早更新世、中更新世和晚更新世—全新世3个阶段: 早更新世的湖泊范围小; 中更新世的湖泊范围明显扩大, 在位置上也较早更新世的湖泊南移; 晚更新世的湖泊经历了两次的扩张—收缩变化, 到了全新世, 除现今还发育的几个湖泊外, 大多数地区的湖水已退出, 基本上转变为河流环境。在晚更新世末期到全新世初期, 封闭黄河源区的多石峡被切开, 湖水外泄, 现今的黄河形成了, 同时发生了袭夺长江水系的水流。     

华北区第四纪植被演替与气候变化

文中华北区是指燕山、辽南一线以南、吕梁山以东、渭河谷地与准阳丘陵以北地区。该区属暖温带,即蒙古和东北寒温带、温带区域与华中和华东亚热带区域之间的过渡地带,故第四纪冰期、间冰期气候的变化,对本区的影响表现得很强烈,它引起第四纪植被的明显演替,是我国第四纪植被变化较大的两个区域之一(另一为青藏区)。     

Pollen‐ and diatom based environmental history since the Last Glacial Maximum from the Andean core Fúquene‐7, Colombia

The late Pleistocene–Holocene ecological and limnological history of Lake Fúquene (2580 m a.s.l.), in the Colombian Andes, is reconstructed on the basis of diatom, pollen and sediment analyses of the upper 7 m of the core Fúquene‐7. Time control is provided by 11 accelerator mass spectrometry (AMS) ¹⁴C dates ranging from 19 670 ± 240 to 6040 ± 60 yr BP. In this paper we present the evolution of the lake and its surroundings. Glacial times were cold and dry, lake‐levels were low and the area was surrounded by paramo and subparamo vegetation. Late‐glacial conditions were warm and humid. The El Abra Stadial, a Younger Dryas equivalent, is reflected by a gap in the sedimentary record, a consequence of the cessation of deposition owing to a drop in lake‐level. The early Holocene was warm and humid; at this time the lake reached its maximum extension and was surrounded by Andean forest. The onset of the drier climate prevailing today took place in the middle Holocene, a process that is reflected earlier in the diatom and sediment records than in the pollen records. In the late Holocene human activity reduced the forest and transformed the landscape. Climate patterns from the Late‐glacial and throughout the Holocene, as represented in our record, are similar to other records from Colombia and northern South America (the Caribbean, Venezuela and Panama) and suggest that the changes in lake‐level were the result of precipitation variations driven by latitudinal shifts of the Intertropical Convergence Zone. Copyright © 2003 John Wiley & Sons, Ltd.     

Quaternary glaciation of Mt. Qomolangma-Xixabangma region

The uplift of the Himalaya and Qinghai-Xizang plateau began at the end of Pliocene to the beginning of Early Pleistocene, changing the atmospheric circulation in Asia, enhancing the South Asian monsoon and enormously effecting the climatic conditions and glacial development.According to the evidence of glacial deposits, geomorphology, paleobiology, paleopedology, etc., at least four glaciations can be recognized. The uplift of the Himalayas was earlier than that of other mountains, so that the glaciation occurred in Early Pleistocene, forming small piedmont glaciers on the N slope, whilst at the same time there were wide short valley glaciers on the S slope. During the Middle Pleistocene, the height of Himalaya was about 4000 m a s l, the monsoon was strong, and much water vapour reached the interior of the plateau, the most favourable period for glacial development. Great piedmont glaciers and small ice caps formed on the mountains N of Himalayas and great valley glaciers occurred on the S slope, but no great ice sheet covered the plateau.During the early Late Pleistocene, the Himalayas had risen to over 5000 m asl, forming a barrier against the incursion of the Indian monsoon, so that the precipitation decreased sharply on the plateau N of Himalayas, thus diminishing the extent of the glaciation. But on the high mountains of the S part of Xizang and on several high mountains of the S slope of the Great Himalaya, the precipitation increased and the extent of glaciation reached a maximum. Since Last Glaciation, the precipitation of the alpine zone has decreased more sharply, the climate has become drier and colder, becoming unfavourable for glacial development.During the Holocene, three stages may be distinguished, i.e. the recession in Early Holocene (10,000-8000 BP); the disappearance of most glaciers in the Hypsithermal period in Middle Holocene, (8000-3000 BP); and the neoglacial fluctuations in Late Holocene (3000 BP up to present). The glaciers of the Neoglaciation advanced several hundred meters or even 3–5 km farther than existing glaciers.     

龙门山古冰川作用

汶川地震中央区域龙门山主山九顶山海拔4 984 m,山脊北坡有三处成排分布不少规模较小的冰斗-冰川谷地形,恢复当时雪线高度在4 100 m高度。根据其形态保存程度、古今雪线高度差等情况判断,应当是2阶段冰川作用遗存。据气温和降水资料,现在九顶山雪线高度在5 000 m,刚好超出九顶山顶部。故而九顶山3 800 m以上目前处于冰缘环境,石冰川、石环、融冻泥流等冰缘现象比较突出。九顶山不存在更老的冰川作用及其地貌遗存,是青藏高原以东5 000 m上下的高山只是在末次冰期时抬升跨越冰期雪线而发育冰川这一新观点的又一证据,也是青藏高原第四纪晚期剧烈抬升的又一证据。     

The impact of climate changes during the Holocene on vegetation in northern French Guiana

The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C₄ savannas) occurred in northern French Guiana during the Holocene. We measured variations in the δ¹³C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C₄ savannahs or C₄ forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the ¹³C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties.     

南海北部陆坡高速堆积体沉积物稀土元素特征及其物源意义

对南海北部陆坡MD05-2905站9个沉积物样品稀土元素进行分析,结果显示MD05-2905站沉积物中稀土含量总量(ΣREE)变化范围较大,其分布范围为60.66×10-6～350.37×10-6,平均值为174.59×10-6,其中全新世样品的稀土含量总量明显低于末次冰期样品,其球粒陨石分布模式与上地壳基本一致。对比发现,其ΣREE平均值相对接近中国黄土和珠江口,而与深海粘土中稀土元素的丰度相差较大,说明其主体可能来自陆源。稀土元素分馏参数δEu和δCe以及富集因子(EF)和判别函数(DF)揭示南海北部MD05-2905站沉积物与黄土、珠江口和台湾浅滩都有联系,显示了多物源多传输方式的特征。另外发现富集因子(EF)和判别函数(DF)数值在末次冰期时期与全新世时期差别相对较大,末次冰期时期黄土、珠江口和台湾浅滩的DF值都远远小于全新世时期,这可能反映末次冰期时黄土、珠江口和台湾浅滩对南海北部的物源贡献更大,也反映末次冰期与全新世期间各个物源供给/传输方式可能发生变化。     

Quaternary glaciation of the North Slope of Karakorum mountains

Three kinds of moraines can be found in the Muztagh valley on the N slope of Mount K2, Karakorum: an old calco-cement moraine lying at the altitude of 5000 m asl, a hilly moraine lying at the altitude of 4200–4800 m asl and a new lateral moraine, lying on both sides of the present river valley. According to the moraines’ geomorphology, they are referred to the Middle Pleistocene Glaciation, the Late Pleistocene Glaciation and the Post-Glacial Period respectively. The lowest level of glacial cirques at 4200–4000 m asl, corresponding to the largest Glaciation, belongs to the Middle Pleistocene (Riss). The ancient cirques at this altitude in the Shaksgam and Yargand valleys are poorly preserved while at the piedmont of the West Kunlun mountains they are represented in better shape. This means that these ancient cirques had been submerged and almost removed by the main ice flow of the valleys. Old cirques, however, are well shaped (or reshaped) where associated with younger cirques at 4600 m als; they could be considered as the product of the Last Glaciation (Würm). Thus, the equilibrium line altitude (ELA) decreased to 1600 m during the Riss Glaciation and to 1000 m during the Würm Glaciation. On the basis of the ELA decrease and existence of complex morainic deposits found at the piedmont of the West Kunlun mountains at about 2200 m asl, the author adheres to the opinion that Riss Glaciation had developed an ice cover (ice sheet), with the central ice area located in Karakorum and reaching up to the high peaks of the Kunlun mountains, and down to the piedmont region. During the Last Glaciation an immense ice cap covered the upper parts of the Shaksgam and Yarkant valleys. The paper also deals with the relations between glaciations and tectonic uplift, indicating that topographic and climatic conditions were favourable for the large-scale ice development in the Middle and Late Pleistocene. The uplift may have reached 600–800 m during the Postglacial period. The uplift rates are often reflected by the glaciostatic in the Postglacial Age.     

西藏阿里阿伊拉日居山脉第四纪冰川作用

在西藏阿里阿伊拉日居山脉南北两麓及切割山脉的各沟谷中,分布着4套早更新世以来的冰川沉积物。根据这些冰川沉积物的地层层序和冰川沉积物的电子自旋共振(ESR)年龄测定结果,将阿伊拉日居山脉南北两麓所发生的4次早更新世以来的冰川作用,分别命名为札达冰期(1161-952 ka BP)、阿伊拉日居冰期(762-730 ka BP)、学朗冰期(336-211 ka BP)和弄穷冰期(105-15 ka BP),并与青藏高原及其他地区冰期进行了对比。各次冰期的冰川性质分别为大型山岳冰川、冰帽、山麓冰川和中小型山谷冰川。全新世时期,现代冰川有过冰川推进。近期冰川则发生了明显的后退。     

Stratigraphy of Pleistocene glaciations in the St Elias Mountains,southwest Yukon,Canada

At least five Middle to Late Pleistocene advances of the northern Cordilleran Ice Sheet are preserved at Silver Creek, on the northeastern edge of the St Elias Mountains in southwest Yukon, Canada. Silver Creek is located 100 km up‐ice of the Marine Isotope Stage (MIS) 2 McConnell glacial limit of the St Elias lobe. This site contains ~3 km of nearly continuous lateral exposure of glacial and non‐glacial sediments, including multiple tills separated by thick gravel, loess and tilted lake beds. Infrared‐stimulated luminescence (IRSL) and AMS radiocarbon dating constrain the glacial deposits to MIS 2, 4, either MIS 6 or mid‐MIS 7, and two older Middle Pleistocene advances. This chronology and the tilt of the lake beds suggest Pleistocene uplift rates of up to 1.9 mm a^?1 along the Denali Fault since MIS 7. The non‐glacial sediment consists of sand, gravel, loess and organic beds from MIS 7, MIS 3 and the early Holocene. The MIS 3 deposits date to between 30–36 ¹⁴C ka BP, making Silver Creek one of the few well‐constrained MIS 3‐aged sites in Yukon. This confirms that ice receded close to modern limits in MIS 3. Pollen and macrofossil analyses show that a meadow‐tundra to steppe‐tundra mosaic with abundant herbs and forbs and few shrubs or trees, dominated the environment at this time. The stratigraphy at Silver Creek provides a palaeoclimatic record since at least MIS 8 and comprises the oldest direct record of Pleistocene glaciation in southwest Yukon.     

On the early history of the wild reindeer (Rangifer tarandus L.) in Finland

This paper discusses the early migration of the wild reindeer into Finland. Reindeer bones found in dated archaeological contexts suggest that the two subspecies, the mountain reindeer ( Rangifer tarandus tarandus L.) and the forest reindeer ( Rangifer tarandus fennicus Lönnb.), were part of our fauna as early as c. 9000 BP and 7000 BP, respectively. The mountain reindeer may be descended from the European Pleistocene reindeer, and may have migrated into northern Finland via the west coast of Norway. The forest reindeer invaded Finland directly from the east, from its glacial refugia in Siberia. During the Holocene, the distribution ranges of these two subspecies fluctuated in accordance with climatic and vegetational changes in northern Finland.     

An outline of physical geography including Pleistocene glacial landforms of Eastern Tibet (provinces Sichuan and Qinghai)

The relief of the expedition area in NW-Sichuan and SE-Qinghai can simply be separated into two main areas: the catchment area of the Yangtze with deeply incised rivers in narrow V-shaped valleys up to about 3,000 m and the plateau area with old peneplains in the Huang He catchment with meandering rivers up to more than 4,000 m. Precipitation and temperature decrease towards the NW. All zonal boundaries, eg the vegetation boundaries or the snowline, are ascending in elevation towards the interior of the plateau. The natural vegetation, especially the forests, are modified by anthropo-zoogenic influences. Within the zone of alpine meadows and the uppermost region of natural forest as well as in the Red Basin evidence of pasture and agriculture goes back by at least 2,000 years. During the last 20 years within the transition zone of the deeply incised valleys towards the plateau one third of the forests have been cut down.The main investigation area of Nianbaoyeze is built up by a granite-dome being about 500 to 800 m higher than the surrounding peneplains. The extent of Pleistocene glaciations can be mapped by the distribution of terminal and lateral moraines and erratic granite boulders on the slopes of the surrounding schists. The altitude of terminal moraines indicates a snowline of the last glaciation at about 4,300 m, which is about 800 m below the present snowline. Three main Pleistocene glaciations can be separated due to palaeosols, the overlying stratum being either aeolian sandy silt or solifluction debris. The ice free areas shows several Pleistocene terraces and in addition loess deposits with palaeosols in the deeper basins. In summary there is a rising of the snowline of the last glaciation at the E margin of the Tibetan Plateau from about 4,000 m in the E (Minshan) to 4,300 m at Nianbaoyeze and to about 4,700 m in the W (Bayan Har Shan). The hypothesis of an extensive plateau glaciation could not be verified for this region.     

Topographic and climatic influences on accelerated loess accumulation since the last glacial maximum in the Palouse, Pacific Northwest, USA

Topographic and climatic influences have controlled thick loess accumulation at the southern margin of the Palouse loess in northern Oregon. Juniper and Cold Springs Canyons, located on the upwind flank of the Horse Heaven Hills, are oriented perpendicular to prevailing southwesterly winds. These canyons are topographic traps that separate eolian sand on the upwind side from thick accumulations (nearly 8 m) of latest Pleistocene to Holocene L1 loess on the downwind side. Silt- and sand-rich glacial outburst flood sediment in the Umatilla Basin is the source of eolian sand and loess for the region. Sediment from this basin also contributes to loess accumulations across much of the Columbia Plateau to the northeast. Downwind of Cold Springs Canyon, Mt. St. Helens set S and Glacier Peak tephras bracket 4 m of loess, demonstrating that approximately 2500 g m⁻² yr⁻¹ of loess accumulated between about 15,400–13,100 cal yr B.P. Mass accumulation rates decreased to approximately 250 g m⁻² yr⁻¹ from 13,100 cal yr B.P. to the present. Tephrochronology suggests that the bulk of near-source Palouse loess accumulated in one punctuated interval in the latest Pleistocene characterized by a dry and windy climate.     

Geology of the dry creek site; a stratified early man site in Interior Alaska

The Dry Creek archeologic site contains a stratified record of late Pleistocene human occupation in central Alaska. Four archeologic components occur within a sequence of multiple loess and sand layers which together form a 2-m cap above weathered glacial outwash. The two oldest components appear to be of late Pleistocene age and occur with the bones of extinct game animals. Geologic mapping, stratigraphic correlations, radiocarbon dating, and sediment analyses indicate that the basal loess units formed part of a widespread blanket that was associated with an arctic steppe environment and with stream aggradation during waning phases of the last major glaciation of the Alaska Range. These basal loess beds contain artifacts for which radiocarbon dates and typologic correlations suggest a time range of perhaps 12,000–9000 yr ago. A long subsequent episode of cultural sterility was associated with waning loess deposition and development of a cryoturbated tundra soil above shallow permafrost. Sand deposition from local source areas predominated during the middle and late Holocene, and buried Subarctic Brown Soils indicate that a forest fringe developed on bluff-edge sand sheets along Dry Creek. The youngest archeologic component, which is associated with the deepest forest soil, indicates intermittent human occupation of the site between about 4700 and 3400 ¹⁴C yr BP.     

A late quaternary record of eolian silt deposition in a maar lake, St. Michael Island, western Alaska

Recent stratigraphic studies in central Alaska have yielded the unexpected finding that there is little evidence for full-glacial (late Wisconsin) loess deposition. Because the loess record of western Alaska is poorly exposed and not well known, we analyzed a core from Zagoskin Lake, a maar lake on St. Michael Island, to determine if a full-glacial eolian record could be found in that region. Particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian. Silt deposition took place from at least the latter part of the mid-Wisconsin interstadial period through the Holocene, based on radiocarbon dating. Based on the locations of likely loess sources, eolian silt in western Alaska was probably deflated by northeasterly winds from glaciofluvial sediments. If last-glacial winds that deposited loess were indeed from the northeast, this reconstruction is in conflict with a model-derived reconstruction of paleowinds in Alaska. Mass accumulation rates in Zagoskin Lake were higher during the Pleistocene than during the Holocene. In addition, more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape. The thinner loess record on land may be due to the sparse, herb tundra vegetation that dominated the landscape in full-glacial time. Herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height. The lack of abundant, full-glacial, eolian silt deposition in the loess stratigraphic record of central Alaska may be due, therefore, to a mimimal ability of the landscape to trap loess, rather than a lack of available eolian sediment.     

The Lateglacial and Holocene in Central Europe: a multi‐proxy environmental record from the Bohemian Forest,Czech Republic

The Hercynian mountain ranges were islands of mountain glaciation and alpine tundra in a Central European ice‐free corridor during the Late Pleistocene. Today they are notable areas of glacial landforms, alpine‐forest free areas, peatlands and woodlands. However, our knowledge of the Lateglacial and early Holocene environmental changes in this region is limited. We present a new multi‐proxy reconstruction of a mid‐altitude environment in the Bohemian Forest spanning this period. A core (5.2 m length) in the ?erné Lake cirque (1028 m a.s.l.) was subjected to lithological, geochemical, pollen and macrofossil analysis supplemented by two optically stimulated luminescence (OSL) and 10 AMS radiocarbon dates. We determined the impact of regional and supraregional climate changes on the environment. The two most significant changes in sedimentation during the Lateglacial (17.6 and 15.8–15.5 cal. ka BP) were synchronous with regional glacial chronostratigraphy. Unlike Central European mountain ranges, in the Bohemian Forest the Younger Dryas was not coincident with glacier re‐advance, but was a dry, cold episode with low lake levels, which prevailed until the early Preboreal. Plant macrofossils indicate local establishment of Betula nana and Betula pendula/pubescens at 15.4–13.4 cal. ka BP. Comparison with Holocene records from Central Europe shows a similar immigration history of vegetation at mid and higher altitudes. The tree line exceeded an altitude of ~1000 m a.s.l. around 10.5 cal. ka BP and coincided with rapid geochemical changes in the sediment. The 8.2 ka BP event did not have any response in the sedimentary record, but corresponded to stabilization of the Picea abies population and expansion of Fagus. Fagus colonized the Bohemian Forest earlier than other Hercynian mid‐mountains, but never predominated in the composition of the forest at higher elevations. Abies alba was the last tree species that immigrated to the study area.     

Würm glaciation of Lake Issyk-Kul area,Tian Shan Mts.: A case study in glacial history of Central Asia

Recent field research and modeling experiments by the authors suggest that Würm glaciation of Tian Shan Mountains had much larger extent than it was previously believed. Our reconstruction is based upon the following evidence: 1. a till blanket with buried glacier ice occurring on mountain plateaus at altitudes of 3700 to 4000 m asl; 2. trough valleys with U-shaped profiles breaching the border ridges and thus attesting to former outlet glaciers spreading outwards from the plateaus; 3. morphologically young moraines and ice-marginal ramps which mark termini of the outlet glaciers at 1600–1700 m asl (near Lake Issyk-Kul shores) and farther down to 1200 m asl (in Chu River valley); 4. clear evidence of impounding the Chu River by former glaciers and turning Lake Issyk-Kul into an ice-dammed and iceberg-infested basin; 5. radiocarbon dates attesting to the Late Pleistocene age of the whole set of glacial phenomena observed in the area.Our data on past glaciation provide a solution for the so called paleogeographical puzzle of Lake Issyk-Kul, in particular they account for the lake-level oscillations (by ice dam formations and destructions), for the origin of Boam Canyon (by impact of lake outbursts), and the deflection of Chu River from Lake Issyk-Kul (by incision of the canyon and build-up of an ice-raft delta near the lake outflow).The Würm depression of regional snowline was found to be in the range of 1150–1400 m. While today's snowline goes above the plateaus of Tian Shan touching only the higher ridges, the Würmian snowline dropped well below plateau surfaces making their glacierization inevitable. The same change in snowline/bedrock relationship was characteristic of the interglacial-to-glacial climate switches on the Tibetan Plateau resulting in similar changes of glaciation. The whole history of central Asian glaciations seems to be recorded in the Chinese loess sequences.A finite-element model was used to test two climate scenarios — one with a gradual and another with an abrupt change in snow-line elevation. The model predicted that an equilibrium ice cover would form in 19,000 (first scenario) or 15,000 (second scenario) years of growth. It also yielded ice thicknesses and ice-marginal positions which agreed well with the data of field observations.     

Late Quaternary loess deposition in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland and its palaeoclimatic implications

The piedmont aeolian sediment in Central Asia is has been widely used for Quaternary palaeoclimatic reconstructions. Here we present detailed sedimentological and rock magnetic investigations on 188 samples from the ~9.4‐m‐thick Urumqi River section (URS) in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland. Optically stimulated luminescence (OSL) dating constrains the time‐span of the URS loess sedimentation from c. 28 to c. 6.8 ka. This chronology implies that the onset of the URS loess sedimentation is approximately synchronous with the Shangwangfeng Glaciation (MIS 2) in the headwaters of the Urumqi River. Analyses of sediment grain size and rock magnetic parameters indicate that sediment grain‐size composition controls magnetic properties of the URS loess, i.e. the wind intensity model, distinct from the pedogenic model interpreting the variations in magnetic properties of the loess in the Chinese Loess Plateau (CLP). Overall, the variations in sediment grain size and magnetic properties throughout the URS indicate that the present study area was dominated by a climate of strengthened wind associated with gradually intensified aridity during the latest Pleistocene. In contrast, the intensity of aridity and coldness during the early Holocene gradually became relatively weakened.     

鲁北平原晚第四纪地层结构及沉积演化

以54个浅层新钻孔和多个野外露头为研究对象,综合沉积物粒度、薄片、微体古生物、孢粉、14C测年及静力触探等资料,分析了鲁北平原晚第四纪的地层结构和沉积类型,总结了晚更新世晚期以来的沉积演化。研究表明,末次冰期盛冰期到冰后期,受地势、气候条件控制的黄河河道迁移和海水进退是影响地层结构和沉积特征的主要因素,南北地层结构差异明显,发育古河道、湖沼、黄土、三角洲、潮坪和滨浅海等沉积类型,其中古河道分布面积最广,自下而上可划分为三期。晚更新世晚期至早全新世早期,受干冷气候影响,发育第Ⅰ期古河道,小清河以南沉积黄土层;早全新世晚期至中全新世,气候转暖导致海平面升高,沿海地区形成海侵层和三角洲,内陆地区继承性发育第Ⅱ期古河道和湖沼沉积;中全新世末期或晚全新世以来,受黄河泛滥影响,沉积第Ⅲ期古河道和现代黄河三角洲。地层结构和沉积物分布的研究对于分析地下水位的变化规律,以及选择合适的地震激发层等均有重要的指导意义。