An early Holocene erosion phase on the loess tablelands in the southern Loess Plateau of China

A Holocene loess profile to the west of Xi'an China was studied multi-disciplinarily to investigate the relationships between soil erosion and monsoonal climatic change. The proxy data obtained from this aeolian loess and palaeosol sequence indicate large-scale variations of climate in the southern Loess Plateau since the last glaciation. A rainwash bed, indicative of a wetter climate, excessive runoff and erosion on the loess tablelands, was identified relating to the early Holocene before the onset of the “climatic optimum”. This is synchronous with the early Holocene physiographic erosional stage identified in the valleys in North China. It means that severe erosion took place when the region was undergoing climatic amelioration during the early Holocene. The evidence presented in this paper shows that the erosion occurred as a regional response to a monsoonal climatic shift in the southern Loess Plateau. During the last glaciation, prior to the erosion phase, the land surface on the tablelands had been largely stable except for the rapid accumulation of aeolian dust and the resultant increase in its elevation. Relatively slow dust accumulation and intensive bio-pedogenesis responding to the Holocene “climatic optimum” followed the erosion phase. The loess tablelands were most vulnerable to erosion during the large-scale monsoonal climatic shift from dry-cold glacial to humid-warm post-glacial conditions in the southern Loess Plateau.     

陕北黄土丘陵沟壑区土壤侵蚀驱动力及驱动机制分析（英文）

This paper analyzes the spatial variation in soil erosion in the loess hilly-gully region of northern Shaanxi Province, China. It sums up existing research, describes the factors that drive soil erosion, and uses geodetection to investigate the factors individually and in pairs.Our results show that soil erosion in the loess hilly-gully region of northern Shaanxi is mainly hydraulic erosion. There are significant spatial differences in the severity of soil erosion in the region. Generally, it is more severe in the north and west and less severe in the south and east. Individual factor detection results show that the major risk factors affecting soil erosion are human population distribution, precipitation, land-use type, elevation, and soil type. Interactive detection results show that interacting factors play much bigger roles in soil erosion than do individual factors. Based on forced detection results from different periods of time, we can see that forest and grass coverage, urbanization, and economic development in the study area all clearly inhibit soil erosion.     

阿拉善地区古水下沉积物与风沙沉积物磁学特征及意义

风力搬运过程中存在的物质分选极可能导致沉积区与物源区沉积物性质出现差异,对于研究物源示踪具有重要的意义。选取阿拉善地区古水下沉积物和风沙沉积物,进行磁学参数测定,调查分选作用对沉积物性质的影响,并探讨对中国黄土高原黄土物源研究的启示。结果表明：古水下沉积物与风沙沉积物的细砂组分磁学性质基本一致,但粉砂组分则存在明显差别,古水下沉积物的磁性矿物浓度显著低于风沙沉积物,风力分选作用可能是风沙沉积物粉砂组分磁性强的主要原因;古水下沉积物中高矫顽力矿物浓度较低,受沉积后改造作用微弱,指示古水下沉积物可用于黄土物源示踪研究。阿拉善地区沉积物和黄土高原黄土的磁学性质对比表明：风沙沉积物与黄土高原黄土磁学性质存在明显差别,但古水下沉积物与黄土高原黄土磁学性质却十分相似。这一地质证据支持阿拉善地区是黄土高原黄土沉积物的重要物源区,同时暗示古水下沉积物在黄土物源示踪方面的巨大潜力。     

The Late Ordovician deglaciation sequence of the SW Murzuq Basin (Libya)

Rocks of Late Ordovician to Silurian age are well exposed on the western rim of the Murzuq Basin (Ghat‐Tikiumit area, Libya) where seismic‐scale exposures allow spectacular insights into the growth and decay of the Late Ordovician (Hirnantian) ice sheet. The final deglaciation left a complex topography with a combination of subglacial morphologies and proglacial depositional systems. This paper documents the glacial and proglacial palaeo‐topography that controls the accumulation of a postglacial transgressive depositional system and the Rhuddanian (Early Silurian) shales. The glacial relief directly contributed to an important hiatus, with the Rhuddanian deposits at the base of the remnant glacial troughs being 3 Ma older than at the top of the topographic highs. The source‐rock in the Murzuq Basin is of Early Rhuddanian age, so it is present only in the deepest part whereas geomorphic traps are formed within the highs of the relict postglacial topography. The transgressive system, recognised for its good reservoir potential, is considered to play a key‐role in the petroleum system, linking the source rock deposited in the ancient topographic lows with the reservoir rocks in the topographic highs. This study aims to demonstrate the importance of palaeo‐glaciological reconstructions for petroleum exploration of the Ordovician–Silurian in North Africa.     

Inconsistent palaeomagnetic recording of the Blake event in Chinese loess related to sedimentary environment

Three loess sequences located east of the Liupan mountain region, China, were studied to obtain records of the Blake polarity event. Palaeomagnetic records from the appropriate stratigraphic interval of these three sequences, however, record the Blake event poorly in one case and not at all in the other two cases. It is important to understand why these loess sequences miss the Blake event, whereas others record it quite well. We conclude that regional variations in the sedimentary environment over the Chinese loess plateau are responsible for the inconsistent recording of the Blake event. The palaeomagnetic records suggest a threefold subdivision of the Chinese loess plateau into (1) the central and southern portions of the part of the plateau that lies east of the Liupan Mountains, where the primary record of the Blake event has been severely smoothed or wiped out by pedogenic processes during palaeosol (S1) formation; (2) the northern margin of the loess plateau to the east of the Liupan Mountains, where frequent, severe dust storms have resulted in discontinuous records with a high probability of missing the Blake event; and (3) the region west of the Liupan Mountains, where loess sequences are deposited rapidly and nearly continuously with only minor pedogenesis, and are thus capable of recording short events like the Blake.     

GEOMORPHOLOGICAL CHARACTERISTICS AND REGIONAL DIFFERENTIATION OF LANDSCAPE OF NORTH SHAANXI

I.TectonicBasisNoIthShaaim,lytl1gbforco135'll'Nand39u34'Nfl-o111lo7"28'EtollI"I5'E,ll1dudesYan'anandYLIlinprefedures.n1elmpOnisIocatedol1h1eErdosSN1dine,aSubdivisionofNoIthChinaShieldl3].n1esps1clineisa1ci1cledbydapal1dgrffitfaLilts.Nogreatfaultsandreicso…     

新疆西风区黄土与古土壤磁化率变化特点

在东部季风区的黄土研究中,磁化率是反映季风区气候变化的重要替代性指标之一,但关于中国西风区黄土磁化率的研究至今仍然为空白。通过对新疆典型的西风区——伊犁地区现代土壤和两个典型剖面黄土与古土壤序列磁化率研究发现,两个剖面黄土与古土壤磁化率特征存在差别。地处荒漠草原地带的则克台黄土剖面中马兰黄土的磁化率值略高于弱成壤层,末次间冰期古土壤层的上部磁化率也低于黄土,与东部季风区相比黄土磁化率偏高;而位于草原地带的库尔德能布拉克剖面黄土磁化率为低值,古土壤为高值,表现出与东部季风区类似的变化特点。两个黄土剖面所反映的磁化率的区域差异在一定程度上揭示了气候对磁化率变化的控制作用,但另一方面也反映了该区磁化率物理意义的复杂性。提出虽然在西风区黄土记录研究中不能简单套用东部季风区的方法,但磁化率和碳酸盐含量在西风区可指示湿度变化。     

巴丹吉林沙漠东南缘查格勒布鲁剖面CGS1层段粒度特征及其指示的全新世千年尺度气候变化

位于巴丹吉林沙漠东南缘的查格勒布鲁剖面CGS1层段记录了全新世以来显示风力强弱的沙丘砂与黄土堆积旋回。以Md（Φ）、Mz（Φ）的5 Φ（31.5 μm）为界,可以划分出10个“C1-C10”明显的和1个“C11”较弱的（<5 Φ）旋回变化。其中,有7个属于沙丘砂与之上覆黄土或古土壤构成的旋回。这些旋回在Md（Φ）、Mz（Φ）上显示出多谷峰波动的形式。不仅如此,粒度的σ、SC/D值和>63 μm含量亦随之响应。研究认为,CGS1层段粗粒和细粒层位Md（Φ）等参数和>63 μm含量的变化分别代表了东亚冬夏季风的作用过程;冬季风时期的C1与北大西洋IRD事件的冷期B0和B1,C2、C3、C4依次与B2、B3、B4,C7、C9、C10依次与B5、B6、B7在时间-气候性质上具有很好的对应;北大西洋B8冷期在CGS1中没有明显表现,但仍然能够在Md（Φ）、Mz（Φ）曲线上看到这是一个<5 Φ的低值时期,而>63 μm的含量相应增高;C5、C6和C8寒冷时段虽未见于北大西洋,但在中国一些地点却有发现。这些由若干粒度指标反映出来的寒冷事件表明,在全新世东亚夏季风活动盛行的总的形势下还存在频繁的千年尺度的冬季风波动。而尤为重要的是这些寒冷事件存在的与北大西洋寒冷事件的遥相关的关系表明,除C5、C6和C8以外的CGS1粒度记录的寒冷事件都隐含了北大西洋的强烈信号。从这个意义上来说,笔者讨论的内容可为全新世北半球的D/O震荡及其形成机制提供一个比较理想的东亚季风变化与中国沙漠区域环境响应的地质证据。     

北疆地区全新世气候波动与水热组合特点

湖沼沉积、黄土沉积和冰积等地质记录的研究表明,北疆地区全新世气候受地理位置和大气环流影响,气候变化较为复杂。整个北疆地区早全新世气候暖干,中全新世至现代,气候特点因地因时而异。受西风控制地区,代表暖干环境的黄土沉积可一直延伸到晚全新世,而可能受夏季风影响的地区和偏北的阿尔泰山,环境的好转早于西风区,并且气候的波动也较西风区更为频繁。     

地表物质组成与土地沙漠化

土地沙漠化是在干旱、半干旱地区,由于特定的自然条件和人类不合理地利用自然资源,所引起的环境退化过程。随着这个过程的进一步发展对人类的不利影响越来越大。因此,对土地沙漠化的问题,也越来越得到人们的普遍重视。在内蒙伊克昭盟及宁夏、陕北地区,沙漠化的土地面积,分别占总土地面积的32%、25.2%和45.9%。这说明了在上述地区土地沙漠化是相当严重的。造成土地沙漠化的自然因素,除气候的干旱、多风外,地表物质的组成是其物质基础。而地表物质组成与沉积条件密切相关,因此,不同的沉积环境形成不同的沉积物,其质地性质差异很大。这些不同的沉积物,对土地沙漠化的发生及发展速度、类型和治理措施都有直接关系。因此,研究地表物质组成与土地沙漠化之间的关系是极为重要。     

Role of fluvial and structural processes in the formation of the Wahiba Sands, Oman: A remote sensing perspective

The Wahiba Sands in northeastern Oman are bordered on the north, south and west by highlands. Remote sensing data are used to characterize the region between 19–23.5°N and 56.5–60°E by mapping surface and near-surface drainage, faults and fractures and aeolian features. It is suggested that the sands were originally deposited with surface runoff from the principal wadis and fluvially reworked fault zones, which define the northeastern and southwestern margins. These fluvial processes resulted in the accumulation of the vast groundwater resources now stored there. During dry climates, wind became the principal modification regime and it began to sort and shape the sediments into the dune forms that characterize today's Wahiba region. The thickness of the sands reflects the depth of the basin in which they lie. The center of the basin is filled with the thickest sand (the High Sands) and contains the highest groundwater concentrations. Presently, aeolian reworking dominates in the Wahiba region, although the Low and the Peripheral Sands continue to experience some fluvial action from occasional, seasonal rainfall. Even though dry conditions dominate today, it is clear that similar to the Sahara of North Africa, the surface sands of the Wahiba basin are indicators of groundwater occurrence.     

天山黄土记录的古尔班通古特沙漠形成演化

沙漠形成演化是第四纪古气候、古环境研究的重要内容之一。通过位于古尔班通古特沙漠下风向天山北坡河流最高阶地上的厚层风成黄土的形成时代和>63 μm砂含量变化的研究,确定古尔班通古特沙漠最迟在0.8 Ma前已经存在。0.8 Ma以来沙漠发育经历了基本稳定期(0.8~0.4 Ma)、强烈波动扩展期(0.4~0.13 Ma)和收缩稳定期(0.13~0 Ma)三个阶段。昆黄运动造成东亚大气环流形势的改变,使准噶尔、塔里木盆地等我国西北地区降雨减少,气候显著变干及冬季风强化,盆地中湖泊萎缩消失、大片河湖相松散物质裸露产生的丰富物源为沙漠形成提供了充足的条件,沙漠开始广泛发育,沙漠主体形成。     

Derivation of the chalk superficial deposits of the North Downs, England: an application of discriminant analysis

Stepwise discriminant analysis was used on particle size and heavy mineral data from 276 sediment samples, including 39 from published sources, to distinguish between Palaeocene and Plio–Pleistocene deposits, found above the Cretaceous Chalk in southeast England, and to determine parent materials of the soils and superficial deposits of the central North Downs. Of 71 known cases (in situ deposits), 85.9% were correctly classified using textural data (sig. 99.9%), and 89.7% of 29 known cases (sig. 99.9%), using heavy mineral data. The best textural discriminating variables were %sand, graphic mean, %clay and graphic skewness, and the best heavy mineral discriminants were %kyanite plus staurolite, %andalusite and %garnet. Discriminant analysis has achieved good differentiation between marine Plio–Pleistocene sands, Clay-with-flints, loess and Palaeocene groups, and allowed objective classification of sediments of unknown origin. The distribution of parent materials revealed, strongly upholds the earlier interpretation [Z. Geomorphol. 39 (1995) 433] that in the central North Downs, except where Palaeocene residuals survive, the superficial cover above the Chalk consists of in situ Clay-with-flints sensu stricto, beneath Plateau Drift and loess. Clay-with-flints is seen as residual, and Plateau Drift as a Pleistocene soliflucted deposit. Textural affinities of Reading Beds Clay and Clay-with-flints elicited by a third discriminant analysis, using additional published data from 22 samples, suggest their common derivation from Chalk residua.     

Seismic reflection measurements behind the Hikurangi convergent margin, southern North Island, New Zealand.

Summary. The active Australian-Pacific plate boundary passes through New Zealand. In the north, the Pacific plate subducts beneath the Australian plate with an accretionary wedge forming the eastern continental (Hikurangi) margin of the North Island. The structure of the region behind the Hikurangi margin changes from the extensional back-arc basin under central North Island to a postulated crustal downwarp under the southern North Island. A 100 km long multichannel seismic reflection profile was recorded across the region of crustal downwarp. The data show discontinuous coherent reflectors dipping westwards at the east end of the profile, and east dipping reflectors at the west end, from depths of 9 to 15 s two way time. Simple hand migration of these events indicate that the east dipping reflectors, interpreted as the base of the Australian plate crust, abut against the west dipping reflectors which are interpreted as marking the top of the subducted Pacific plate. Detailed earthquake hypocentre locations in the area show a dipping zone of high seismicity, the top of which coincides closely with the west dipping events, thus supporting this interpretation.     

新疆伊犁黄土和古土壤形成环境的差异性分析

通过粒度和元素地球化学分析研究方法,对伊犁盆地昭苏剖面黄土和古土壤形成环境的差异性进行了对比研究。结果发现,伊犁古土壤层中＞30 μm、＞40 μm和＞63 μm等粗粒径组分含量较黄土层稍高,尤其是＞63 μm组分更为显著;伊犁古土壤形成时期,西风环流较强,导致古土壤层中存在大量粗颗粒的近源堆积物,气候存在突变性,是一个环境变化不稳定的时期;而黄土堆积时,西风较弱,气候变化相对稳定;古土壤形成时期虽降水相对较多,但气候较冷,导致其风化成壤作用并不强,而黄土堆积时降水与古土壤形成时期相当或者较少,但由于气候总体较为温暖,风化成壤作用相对较强。不同时期水热组合形式及其各自权重不同均会对伊犁黄土和古土壤风化作用产生不同程度的影响。     

新疆伊犁黄土的物性指标、动力学特性与滑坡

分析了伊犁谷地28个黄土样品的粒径、密度、含水量和孔隙比,测试了震陷、湿陷、动弹模量和塑性指数,探讨了伊犁谷地黄土的物性、动力学特征,讨论了它们与滑坡之间的关系。伊犁谷地的原生黄土主要以粉粒为主,含量为74%,大于75μm的颗粒含量为10%,小于5μm的颗粒含量为15%;黄土天然含水量为4%~16.1%,谷地东部的黄土明显地比谷地西部的更细,伊犁黄土的孔隙比在0.832~0.907之间,有相当的湿陷性。在含水量低于20%时,还会有湿陷。黄土的塑性指数为9左右,比较小,粘粒含量低,易损性大,抗震性能差,具有较强的震陷性。在同样的动应变下,伊犁黄土的动模量较小,随着动应变的增大,其动模量衰减较快。冻融季节是伊犁地区滑坡的多发季节,构造活动强烈的地段也是地质灾害的多发地段。     

A call for Australian loess: discussion and commentary

A study of loess in Australia brings the idea of 'desert' loess back into view. Production of particles in deserts still presents problems, but deserts do make adequate storage regions for loess particles – usually produced in adjacent mountains. Straightforward for Central Asia or China (a particle source in High Asia and convenient deserts en route to eventual deposition), but the Sahara and Australian deserts traditionally present problems. If loess material is allowed to be silt-sized clay agglomerate particles as well as the usual clastic primary minerals, then loess in Australia seems reasonable. Loess acquires its remarkable loessic qualities via aeolian deposition – the nature of the particles is perhaps of lesser importance. A more generalised approach to airborne sediments might be attempted, with two major types of suspension material recognised: large dust (maybe coarse and very coarse silt, say 20–60 µm, or perhaps 4–6 phi) and small dust (fine and very fine silt, 2–8 µm, 7–9 phi). Loess is made from large dust.     

山东地区黄土研究综述

山东地区黄土开始堆积时期普遍较晚,目前已见的剖面中,以青州傅家庄剖面堆积厚度最大(30 m以上),起始堆积时间最早,出露的最老层位为L9,TL测年时间约为0.8 Ma B.P.。山东地区黄土成因类型多样,物质来源广泛,其岩性特征与其他地区的黄土有明显的差别;在本地区内部,黄土的差异也比较明显,大体可分为两大成因分布区:渤海湾滨海与岛屿区和鲁中山前区。前者黄土粒度较粗,且普遍含有海相微体化石,其物质来源主要为末次冰期时期出露的渤海陆架物质,西北气流携带而来的内陆远源物质占次要地位。而后者黄土类型成因多样,东部的潍坊、青州黄土分布区,受到末次冰期时强劲冬季风的影响,物质来源主要为北部出露的渤海湾,向西至淄博、济南地区则已逐渐过渡为西北内陆风尘物质成分占据主导。     

上海春季沙尘与非沙尘天气大气颗粒物粒度组成与矿物成分

上海春季典型沙尘天气的湿降尘和非沙尘天气总悬浮颗粒物、自然降尘的粒度分析结果表明,沙尘天气湿降尘几乎全部由<63 μm的颗粒组成（99.45%）,其中10~50 μm、5~10 μm和<5μm的含量分别占49.02%、21.75%和27.14%,平均粒径为13.57 μm,分选差。这一粒度特征与马兰黄土和下蜀黄土很相似。非沙尘天气总悬浮颗粒物的粒度分布范围和均值与湿降尘很接近,自然降尘颗粒则明显较粗。矿物X—衍射物相及半定量分析结果表明,上述三种大气颗粒物都由粘土矿物、石英、钾长石、斜长石、方解石、白云石、石膏、角闪石等组成,所不同的是湿降尘中含有较多来自西北干旱半干旱区远源输入的矿物颗粒;而非沙尘天气总悬浮颗粒物中石膏含量较高（达14.59%）,推测为溶解在大气中的气态污染物 SO2与方解石作用形成的二次污染颗粒。     

我国水土流失典型区土壤表土结皮敏感性

表土结皮是降雨与土壤共同作用下的产物,某一土壤是否结皮、结皮的敏感程度如何,取决于该土壤的性质及所处地区的降雨情况。我国广泛分布着多种理化性质迥异的土壤,尤其是黄土、紫色土、红壤和黑土分布在我国水土流失严重的区域。但是,土壤发育表土结皮的敏感性很少见报道。本文通过分析模拟降雨试验结果及前人研究结论,提出了影响表土结皮发育敏感性的3个关键因素,并基于此对我国四大水土流失典型区土壤表土结皮的敏感性进行了分析。研究表明:细颗粒,尤其是粉粒是表土结皮发育的物质基础;团聚体稳定性是表土结皮发育快慢及程度的决定因素;高强度降雨是表土结皮发育的必要条件。黄土高原地区土壤极易发育表土结皮,四川紫色土区土壤发育表土结皮的概率大,南方红壤区除花岗岩、页岩外其他母岩上发育的土壤很难发育表土结皮,东北典型黑土不发育表土结皮,而非典型黑土易发育表土结皮。