Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau

The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd.     

The Upper Pleistocene to Holocene sediments on the Mediterranean island of Lampedusa (Italy)

The island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic–environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central‐southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd.     

洛川黄土-红粘土序列铁氧化物组成及其古气候指示

对洛川黄土、古土壤和红粘土中磁性矿物组成、成因和相关系进行了研究。结果表明:黄土磁性矿物以风尘磁铁矿为主,少量的成土赤铁矿和成土磁赤铁矿;古土壤磁性矿物以成土磁赤铁矿为主,成土赤铁矿次之,少量的风尘磁铁矿和赤铁矿;红粘土磁性矿物以成土赤铁矿为主,风尘磁铁矿和成土磁赤铁矿次之,少量风尘赤铁矿。黄土、古土壤和红粘土磁性矿物组成差异,反映了其形成期不同的古气候特性以及不同气候条件下生物地球化学作用强度的差异。干冷的冰期,黄土弱成土作用形成了以粗颗粒的风尘磁铁矿核 赤铁矿边的磁化率载体。间冰期的温暖湿润的古气候最有利于生物活动,强烈生物活动导致古土壤中大量纳米超细磁赤铁矿/磁铁矿产生,形成以磁赤铁矿为主,风尘磁铁矿核 赤铁矿边为辅的磁化率载体。红粘土成壤期,强降雨强蒸发的长干短湿的高温炎热的古气候使得红粘土化学风化强烈,生物地球化学活动较弱,形成以磁铁矿核 赤铁矿边和磁赤铁矿核 赤铁矿边的磁化率载体。黄土、古土壤和红粘土磁性矿物组成、磁性矿物相关系是其形成期独特的古气候指示。     

安徽宣城地区中晚更新世风成堆积与环境变迁

通过对宣城向阳中晚更新世沉积剖面的综合研究,认为该剖面与中国北方同时代的黄土—古土壤剖面相比较,虽然长江下游以南地区中晚更新世多个冰期中风成堆积的单层厚度与累积厚度,亦即风成物质的沉积通量与沉积速率均比北方黄土区要小,但它们所反映的气候与环境的变化具有明显的可比性。     

黄、渤海海岸风沙地貌类型及其分布规律和发育模式

于１９９０－１９９４年，对黄，渤海海岸风沙地貌，风沙沉积，风沙灾害和土地沙漠化现象进行详细的外业调查，测量和填图，在此基础上，利用ＧＩＳ技术原理，对海岸岗沙地貌进行系统的分类研究，对海岸风沙地貌分布规律和发育模式进行较深入的探讨，结果表明，研究区风沙地貌，风沙灾害和土地沙漠化现象主要分布在冬，春季气候干旱，风力强而持久，砂源丰富的渤海海岸和山东半岛半岸的砂质海岸地区，海岸沙丘和风成砂地总面积达７０     

垣曲盆地最高阶地风尘堆积形成时代及其构造意义

对垣曲盆地原土坪阶地剖面进行了详细的沉积学和磁性地层学研究,结果表明,原土坪剖面地层自下而上由水下河湖相-漫滩相-风尘堆积构成,整个剖面记录了一个水位下降、由水下沉积环境转变为气下环境的连续堆积过程。剖面地层记录的1.84～1.62MaB.P.期间由河湖相沉积环境转变为典型风尘堆积的沉积转型及风尘堆积反映出的1.21MaB.P.前后古气候变化事件是对青藏高原青藏运动C幕和昆黄运动的区域沉积响应。开始于1.62MaB.P.的典型风尘堆积底界年龄代表了该级阶地的形成时代,表明该段黄河至少在此时已经形成。     

也论成都粘土的成因

为了解成都粘土的成因机制，在总结前人资料的基础上，从分析成都粘土的分布、结构、矿物组成等特征入手，客观地展示了成都粘 本质，进而将其与我国北方的马兰黄土和长江中下游的下蜀粘土之间的特性进行比较以及对龙门山和成都平原第四纪晚更新世的古环境的分析，最终得出典型的成都粘土的成因是属于风成“黄土”的结论。     

长江中下游地区下蜀黄土成因研究的回顾

为了进一步认识下蜀黄土的成因及其在我国东部环境演为研究中的意义，回顾了20世纪30年代以来下蜀黄土研究的主要成果，系统地评述了下蜀黄土的风成说、水成说和多成因说。下蜀黄土的成因，从营力的先后及主交看，风成应是第一位的。因此，在利用下蜀黄土保存的古环境信息研究我国东部变化时，应慎重选择剖面，以获得良好的结果。     

The rate of grain release by pore-ice sublimation in cold-aeolian environments

Pore‐ice sublimation is a prerequisite for aeolian activity in cold environments where surface sediments hold significant amounts of frozen water. Few quantitative studies have defined the rate of grain release from cemented surfaces by pore‐ice sublimation. In 1996–1997, controlled field experiments at Presqu'ile Beach, Ontario, were implemented to measure sediment release from frozen surfaces. The release rates were compared to the local wind regime, ambient temperature and humidity. In additional field experiments, the effect of sediment water content on grain release by sublimation was examined. From the experimental results, an equation which predicts grain release based on local wind speed, ground temperature, humidity, and surface water content is proposed. Predicted release rates show reasonable agreement with natural deflation measured on the beach at Presqu'ile Provincial Park.     

Simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel

Topographic interactions generate multidirectional and unsteady air?ow that limits the application of velocity pro?le approaches for estimating sediment transport over dunes. Results are presented from a series of wind tunnel simulations using Irwin‐type surface‐mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp‐crested model dunes. Findings complement existing theories on secondary air?ow effects on stoss transport dynamics and provide new information on the in?uence of lee‐side air?ow patterns on dune morphodynamics. For all speeds investigated, turbulent unsteadiness at the dune toe indicates a greater, more variable surface shear, despite a signi?cant drop in time‐averaged measurements of streamwise shear stress at this location. This effect is believed suf?cient to inhibit sediment deposition at the toe and may be responsible for documented intermittency in sand transport in the toe region. On the stoss slope, streamline compression and ?ow acceleration cause an increase in ?ow steadiness and shear stress to a maximum at the crest that is double that at the toe of the isolated dune and 60–70 per cent greater than at ?ow reattachment on the lower stoss of closely spaced dunes. Streamwise ?ow accelerations, rather than turbulence, have greater in?uence on stress generation on the stoss and this effect increases with stoss slope distance and with incident wind speed. Reversed ?ow within the separation cell generates signi?cant surface shear (30–40 per cent of maximum values) for both spacings. This supports ?eld studies that suggest reversed ?ow is competent enough to return sediment to the dune directly or in a de?ected direction. High variability in shear at reattachment indicates impact of a turbulent shear layer that, despite low values of time‐averaged streamwise stress in this region, would inhibit sediment accumulation. Downwind of reattachment, shear stress and ?ow steadiness increase within 6 h (h = dune height) of reattachment and approach upwind values by 25 h. A distance of at least 30 h is suggested for full boundary layer recovery, which is comparable to ?uvial estimates. The Irwin sensor used in this study provides a reliable means to measure skin friction force responsible for sand transport and its robust, simple, and cost‐effective design shows promise for validating these ?ndings in natural dune settings. Copyright © 2003 John Wiley & Sons, Ltd.