Discovery and significance of Quaternary aqueously deposited aeolian sandstones in the Sanhu area, Qaidam Basin, China

Influenced by neo-tectonic movement, the Sanhu area of China＇s Qaidam Basin formed in the Quaternary in response to migration of its depocentre. A study of core material from the Qijia 1 Well reveals novel Quaternary aqueously deposited aeolian sandstones in the Qigequan Formation of the Sanhu area. Here we report the sedimentary petrology and geochemistry data of these deposits that constrain their depositional history. Evidence for aeolian influence during deposition includes： sorting and roundness, pure quartz sand with single mode grain size distribution and few suspension materials,very fine sand grain size distribution indicating sorting by saltation and suspension transport, dish-shaped and crescentshaped pits in grain surfaces indicating aeolian transport and chemical composition similar to that observed in active or recent dune deposits, namely enrichment in Si O_2, Na_2 O, and Mg O relative to the sand dam sediment in the lakeshore.Identification of these aqueously deposited aeolian sandstones expands the range of sedimentary deposit types found in the Sanhu area and improves understanding of its paleoclimatic history.

Holocene climatic change reconstructed from trace elements of an aeolian deposit in the southeastern Mu Us Desert, northern China

In semi-arid and arid desert regions of northern China, aeolian deposits document the framework variation of an Asian monsoon during the late Quaternary. However, there is still a lack of detailed data pertaining to Holocene Asian monsoonal variation especial in the modern Asian summer monsoonal boundary belt. In this study, we reconstructed Holocene millennial-scale climatic changes in the Mu Us Desert, northern China, through systematic analysis of the variation of trace elements(324 samples) in different lithological units of the palaeosol-aeolian sand deposit, in combination with14 C and OSL chronology. Statistical results, correlation and clustering analysis indicate that the high content of 11 trace elements(V, Y, Cr, Nb, P, Mn, Cu, Zr, As, Ni and Rb, represented by P) and lower Sr content corresponding to periods of palaeosol development, marked increase of vegetation, weathering degree, and enhanced Asian summer monsoonal strength. In contrast, their opposed variation are coincident with accumulated aeolian sand layers, implying weaker summer monsoons and less geochemical weathering and degraded vegetation. These associations can be considered as signaling regional humid and dry changes of the Holocene environment. Accordingly, relatively arid conditions dominated the region before 7.2 ka, and there was an optimal humid climate in 7.2-4.6 ka. Afterwards, the climate became obviously dry, accompanied with several cycles of relatively wet and dry, such as relatively wet intervals around 4.1-3.7 ka, 3.5-3.3 ka and 2.5 ka. In addition, six millennial-scale dry events were recorded, and these events were consistent with weaker Asian summer monsoonal intervals in low latitudes, declined palaeosol development and precipitation in middle latitudes, as well as increased winter monsoon and periodic ice-rafting events in high latitudes of the Northern Hemisphere, within limits of accuracy of existing dating ages. This possibly suggests a noteworthy synchronism between millennial-scale climatic changes in this region and on a global scale.

Effects of an oasis protective system on aeolian sediment deposition:a case study from Gelintan oasis,southeastern edge of the Tengger Desert,China

Desert-oasis ecotones are boundary areas between oases and desert ecosystems.Large efforts to control sediment and stabilize these boundaries depend on understanding sedimentary processes,especially aeolian transport and deposition.Previous studies on aeolian sediment deposition have focused primarily on a single land surface type or a single engineering approach.Few studies have considered deposition in a multi-layer oasis protective system.A complete oasis protective system consists of an outer bare sand area,a sand barrier zone,a shrub and herbaceous plant zone,and a farmland shelter zone.This study used sedimentary analysis to quantify grain-size characteristics in samples from the four land surfaces under different types of weather conditions in the Gelintan oasis of the Tengger Desert,the fourth largest desert in China.The results showed that aeolian sediment deposition decreased from the outer bare sand area through the oasis protective system and into the interior.The four land surface types showed significant differences in deposition volume(P<0.05).Deposited sediment showed gradual decrease in dominant grain-size from sand to silt,but sediment deposited during dust weather contained a larger coarse-grained fraction.From the outer desert to the inner oasis,transport mechanisms shifted from saltation(sand)to suspension(silt and smaller)in non-dust weather.During dust weather,deposition primarily occurs from near-surface aeolian sand transport with saltation.Sediment sorting decreased from exterior to interior zones of the protective system while skewness and kurtosis showed no significant change(P<0.05).These results can help inform strategies for stabilizing and protecting desert-oasis ecotones in this region and other localities.

鄂尔多斯盆地西南部下白垩统铀矿化砂岩中有机质特征及其与铀成矿的关系

鄂尔多斯盆地西南部下白垩统铀矿找矿在近几年取得了重大突破,在镇原、彭阳等地区发现了新的铀矿产地,白垩系铀矿化主要赋存于洛河组与环河组,少部分赋存于泾川组和罗汉洞组,这些赋矿层位原生沉积均处在干旱环境条件下,其中缺乏肉眼可见的有机质。但在钻孔岩心中,铀矿化砂岩中往往富含浸染状的有机质,这类有机质的性质及其与铀成矿的关系目前还缺乏系统的研究。文章以鄂尔多斯盆地西南部镇原地区铀矿化砂岩为研究对象,通过岩心观察与室内研究,厘定了赋矿砂岩中的有机质类型,探讨了有机质的来源及其铀成矿的关系。研究结果表明:赋矿砂岩中的原生沉积炭屑有机质十分稀少,有机质主要为充填于砂岩微孔隙中、具有流动特征、低演化程度的大分子有机质,可能主要来源于“延7”段烃源岩。铀矿化与固体炭屑有机质关系不大,而主要与“可溶性”流动状有机质密切相关。研究区白垩系铀成矿特征具有“渗出”砂岩型铀矿成矿作用的特点。

长江武汉段天兴洲低滩沉积物粒度端元对河流-风成沙丘沉积环境的指示意义

河床沙波向风成沙丘演变的过程具有特殊的沉积动力机制。笔者等以68份长江武汉段天兴洲洲头低滩沉积物的粒度分布数据为例,利用端元分析方法从每个粒度分布中分离提取4个粒度端元组分(EM1、EM2、EM3和EM4),探讨了河流—风成沙丘不同沉积环境中粒度端元的异同。研究结果表明:EM1和EM3组分在粒度分布中占比与沉积物粒度中值分别呈较好的线性正相关和负相关;河流沉积物主要由EM1、EM2和EM3组成的跳跃方式搬运,对应滚动次总体的EM4组分占比5%~10%,少悬浮搬运;风成沙纹沉积物主要包括两段跳跃次总体,以EM2组分为主、EM1和EM3组分为辅,少EM4组分;沙丘背风面沉积物主要靠颗粒流顺坡滑塌,以EM2组分为主、EM1和EM3组分为辅,含占比约为5%的EM4组分;未被风成沙纹覆盖的沙丘波谷沉积物记录了河流和小型滞水洼地的沉积特征,代表滚动次总体的EM4组分占比7%~15%,悬浮次总体占比可达20%。本文提取的沉积物粒度端元为弱风环境中河道内局部小型河流—风成沙丘的沉积环境和演化过程研究提供了参考。

藏东贡觉盆地白垩纪末期风成沉积组合及其古气候和古地理意义

晚白垩世,东亚地区风成沉积分布广泛,具有显著的纬向分带特征,然而,与华南地区处于相同古纬度的青藏高原中部地区却鲜有风成沉积的报道。近年来,前人依据磁性地层学研究结果将藏东贡觉盆地原古近纪风成沉积时代重新厘定为白垩纪末期,这为研究该时期青藏高原隆升前的古地理和古气候条件创造了新的契机。通过野外剖面考察/实测、样品薄片偏光显微镜岩矿鉴定、扫描电子显微镜观察和能谱分析等,本研究对贡觉盆地贡觉组风成沉积序列、风成界面和沉积体系开展了详细研究。研究结果表明,贡觉盆地风成沉积组合主要位于贡觉组底部,集中分布在盆地西缘,主体由沙漠、冲积扇与河流沉积组成。其中,风成沉积以大型槽状层理、楔状层理和高角度板状交错层理为特征,层系中可见典型的颗粒流层、颗粒飘落层和风成沙波层,层面上可见风成波痕。风成砂岩中的碎屑颗粒以中、细砂为主,普遍表现出高结构成熟度和高成分成熟度特征,石英颗粒边缘具有“沙漠漆”结构。扫描电镜下,石英颗粒表面发育典型的新月形和碟形撞击坑,很好地指示了风成沉积成因。垂向上,风成沉积组合中显示出明显的下部风成与水成沉积交互、中部风成沉积主导、上部水成沉积增多的沉积序列特征,反映了干旱气候背景下突发性的降水/洪水引发地下水位的波动。认为贡觉盆地白垩纪末期风成沉积的形成演化与冈底斯山晚白垩世隆升形成的“雨影”效应密切相关,同时也与全球马斯特里赫特中期升温事件存在着一定联系。研究结果对于理解白垩纪末期青藏高原隆升前的古地理格局和古气候条件具有重要意义。

Optically stimulated luminescence dating of sandy deposits from Gulang county at the southern margin of the Tengger Desert, China

Aeolian deposits from the deserts in northern China have been used for palaeoenvironmental research to understand aeolian sedimentology and its dynamic connection to past climate conditions. The Tengger Desert in China is sensitive to the waxing and waning of the monsoonal system. In response to past climate change, the southern margin of the Tengger Desert has evolved significantly since the last glacial period. However, previous attempts to date aeolian deposits in this region were mainly based on radiocarbon dating, which has problems when applied to aeolian deposits. Moreover, sedimentary records are limited. Accordingly, past aeolian activity in this desert remains poorly understood. In the present study, we dated sand samples from Gulang county at the southern margin of the Tengger Desert using optically stimulated luminescence (OSL) to understand the history of aeolian activity in this region. Our samples represented well-sorted aeolian sands and sandy loess. Aeolian sands are evidence of dune field buildup and sparse vegetation cover whereas sandy loess is evidence of improved stabilization of sand dunes resulting from ameliorated vegetation cover. Certain samples showed a decline in the equivalent dose (D e ) values when successive integration intervals were applied, which resulted from unstable OSL signals from non-fast components in the initial part of the decay curve. In order to obtain reliable D e estimates, we investigated component-resolved and different background subtraction approaches, and compared the resultant D e estimates. We adopted the early background subtraction method to derive D e values. Luminescence chronologies and sedimentary records indicated that sand dunes accumulation occurred before 10 ka, and sandy loess developed between 9.5 and 7.6 ka when sand dunes were stabilized as a result of increased effective moisture levels. The transition between sand dune mobilization and stabilization emphasizes the significance of an effective moisture threshold in controlling aeolian activity. Mobilization of sand dunes at ~2.3 ka might be related to an increased aridity during the Late Holocene.

Holocene Moisture Variation Recorded by Aeolian Sand-Palaeosol Sequences of the Gonghe Basin, Northeastern Qinghai-Tibetan Plateau, China

The northeastern Qinghai-Tibetan Plateau(QTP) of China is located at the triple junction of the Asian winter and summer monsoons and the westerlies, where paleoclimatic evolution has an important scientific significance for recognizing the spatial-temporal pattern of Asian monsoons in the past and predicting environmental change in the future. Nevertheless, the framework of the Holocene moisture variation and related mechanisms remain controversial, owing to complex hydroclimatic conditions triggered by the landform of the large mountain-arid basin. Here, we employed geochemical proxies from typical aeolian sand-palaeosol sequences in the Gonghe Basin, northeastern QTP, together with Optically Stimulated Luminescence(OSL) dating, to reconstruct the pattern of effective moisture variation and associated mechanisms in this region. Our results indicate that the regional effective moisture was at its lowest until 9–8 ka, and approached a maximum during 8–4/3 ka of the middle Holocene. Afterwards, the climate became relatively dry in general, but with a transient humid interval around 2–1 ka. Our geochemical evidence indicates that the dry early Holocene probably can be attributed to a strong winter monsoon forced by remnant ice sheet, combined with the high evaporation caused by solar insolation. Also, shifts of humid-dry are closely linked to the Asian summer monsoonal strength and therefore the balance of evaporation-precipitation in the middle and late Holocene. Thus, the pattern of the Holocene effective moisture variation is characterized as the ‘monsoon model’ in a closed intermontane arid and semi-arid basin near the western Asian monsoonal limit.

Grain-size Characteristics of Sediment in Daniugou Peatland in Changbai Mountains,Northeast China:Implications for Atmospheric Dust Deposition

The grain-size distribution characteristics and grain-size parameters of sediment in two vertical sections of Daniugou peatland in the Changbai Mountains were systematically investigated.A comparative analysis of the sediment granularity using a discriminative function with Hongyuan peat,red clay,loess-paleosol,fluvial deposit as well as lacustrine deposit was also conducted.It turns out that the vertical section of Daniugou peat ash is primarily constituted by clay and silt particles,and the content of sand is relatively small.Grain-size frequency curves generally show a single-peak modality while a bimodal pattern is detected in the upper layer.The grain-size component and peak pattern of grain-size frequency curves also illustrate that peat ash materials were transported to the peatland by long-range aeolian dust during the deposition process,while there existed short-distance dust influence in peat deposition of the upper layer.Comparisons of grain-size parameters and the discriminative Y-value of Daniugou peat ash with those of typical aeolian sediments show close similarities,suggesting the possibility that atmospheric dust transport processes were involved in the accumulation of peat again.Moreover,the variations of grain-size distribution suggest the local environmental deterioration which is just the driving force of local dust elevation.Grain-size analysis of peatland sediment is demonstrated to be one effective method to extract information about regional and global environmental evolution,and more attention should be paid to current local ecological environment and to seeking a balance between economic development and environmental protection in Northeast China.

华南衡阳盆地上白垩统黄土类似物的初步研究

中国新生代黄土序列具有沉积速率高、连续性好等特点,记录了东亚地区持续的古气候动力学演化和重大地质事件信息。受区域构造-地貌和大气环流格局影响,中生代晚期华南发育了众多盆山型古沙漠系统且出露了巨厚的风成砂,但几乎未有学者提及黄土/黄土类似物的存在。本文通过粒度端元解析、野外露头的构型分析等手段,对衡阳盆地上白垩统红花套组进行了初步研究,识别出风成砂丘、砂席和泥滩等环境类型;并在泥滩环境中提取到黄土类似物的粒度组分信号,同时提出了黄土类似物的风成成因,总结了其形成-堆积过程。这项工作旨在探索白垩纪黄土类似物存在的可能性,为未来开展华南陆块中生代风尘记录研究提供契机。

古尔班通古特沙漠南缘沉积记录的全新世环境演变

古尔班通古特沙漠南缘处在风、水两相营力作用的交汇区域,沉积环境独特,对气候变化响应敏感,是研究中国西北沙区全新世环境演变的理想区域。选取古尔班通古特沙漠南缘荒漠-绿洲过渡带3个风积-冲积交互地层剖面,在实地观察岩性特征、沉积序列的基础上,通过光释光(OSL)测年建立年代标尺,结合粒度参数、磁化率和石英颗粒表面微形态特征的对比分析,综合判别研究区全新世以来的沉积环境演化过程。结果表明:研究区地层序列主要反映了河流过程和风沙过程的消长,并且表现出同期异相特征。约11.8~10.2 ka,天山北麓冲积作用活跃,辫状河深入沙漠,局部发育河流沉积;约10.2~6.0 ka,研究区进入全新世适宜期,沙漠北退,河湖、湿地广泛发育;约6 ka至今,研究区冲积作用减弱,风沙活动频繁,沙漠环境与河流环境交替出现。近千年以来,研究区沉积环境表现出风沙活动增强、河流冲积萎缩的特点,古尔班通古特沙漠总体上有南侵扩张趋势。本区全新世湿润环境的出现主要受制于西风环流的强弱变化和位置变动,此外,北半球夏季太阳辐射与天山冰川的耦合作用及北大西洋冷事件引发的气候波动可能也是影响本区全新世沉积环境变迁的重要因素。

渭河盆地南缘早更新世风成相和湖相沉积环境演化

受地球轨道参数诱导的太阳辐射变化和两极冰盖消长的共同影响,第四纪气候环境演化表现出阶段性变冷及显著的冰期-间冰期波动特征。位于亚洲季风区关键地带的渭河盆地堆积了新生代以来巨厚的河湖相沉积以及风成沉积,是研究第四纪环境演化的重要区域。盆地堆积的下更新统三门组河湖相地层被认为和古三门湖有密切联系,但目前对于三门组地层年龄和古三门湖演化及其与区域活动演化是否有联系尚未达成共识。相比单一沉积载体研究,选取渭河盆地南缘阎峪风成相黄土和武家堡湖相沉积2种沉积载体进行对比分析,探讨了同期异相沉积记录的粒度和磁化率变化特征,重建了渭河盆地南缘早更新世(距今2.6~1.6 Ma)沉积环境演化。结果表明,阎峪记录的黄土-古土壤序列平均粒径和磁化率变化良好地记录了东亚冬、夏季风的盛衰演化历史;武家堡指示的盆地南缘沉积环境在距今1.95 Ma由湖相转变为风成相沉积,湖相沉积粒径和磁化率变化呈正相关关系,敏感响应湖平面高低波动。风成相与湖相记录揭示了渭河盆地边缘早更新世环境演化经历了[2.6,1.95)Ma的湖盆演化和[1.95,1.6]Ma的湖盆萎缩-风成相堆积,湖盆萎缩受黄河贯通影响强烈。

西太平洋海山盆地沉积物黏土矿物特征及其指示意义

深海沉积物中的黏土矿物组合特征能反映物源区古气候与古环境的变化。前人已有较多关于马里亚纳海沟以西太平洋沉积物黏土矿物组合特征方面的研究,但对马里亚纳海沟以东黏土矿物组合特征的研究较少,从而限制了对亚洲大陆风尘输入与太平洋深海沉积环境之间关系的深入认识。本文以2019年大洋54航次在西太平洋马尔库斯-威克海山区采集到的31个表层样和1个柱状样为研究对象,结合收集到的西太平洋海域及附近地区的数据,开展了黏土矿物组成与分布特征、物质来源等研究。结果表明,研究区表层沉积物中的黏土矿物类型以伊利石为主,含量平均值为69%;绿泥石和高岭石次之,含量平均值分别为16%与11%;蒙脱石最少,含量平均值为3%。柱状样黏土矿物组合与表层沉积物基本一致,但在250 cm深度以下,蒙脱石含量明显增高,伊利石含量相对减少。物源分析表明,亚洲风尘是研究区伊利石的主要物源,高岭石和绿泥石的主要物源可能也是亚洲风尘,东亚冬季风是这些风尘物质的主要搬运营力。沉积物中的蒙脱石则主要由海底火山物质风化形成。P04柱上部伊利石含量增加而蒙脱石含量降低的变化响应了中更新世以来亚洲风尘输入量增加的过程。

渭河盆地新生代沉积相研究

渭河盆地位于鄂尔多斯地块南缘与秦岭造山带的交接部位,为一新生代盆地,古近系和新近系沉积厚度几千米,沉积类型多样,通过钻井及大量野外剖面的详细观察及实测,开展了地层、沉积相及岩相古地理学的研究。对渭河盆地新生代地层单位进行了重新厘定,并根据沉积特征划分为冲积扇沉积、河流沉积、湖泊沉积、三角洲沉积及风成沉积5种沉积类型。研究认为:整个沉积过程,盆地边断、边陷、边充填,纵向上极不对称,沉积中心偏南,平面上西窄东宽,盆地边部以冲积扇沉积为主,向中心由三角洲沉积逐渐过渡为湖相沉积。盆地从始新世开始沉积,渐新世后期抬升并存在沉积间断,中新世冷水沟期接着开始沉积,水体逐渐扩大,寇家村期湖泊广泛发育,至灞河期沉积范围达到最大,上新世游河期盆地存在西安、固市两大沉积凹陷区,边部开始出现风成沉积,第四纪西部隆起,湖泊沉积范围开始缩小,中更新世至全新世,盆地内湖泊萎缩成区域上的小型洼地。

新疆东天山地区地球化学勘查方法技术研究

系统研究了与新疆东天山地区地球化学勘查方法技术有关的干扰物质及其干扰程度以及在表生条件下风成沙、土壤和盐积层的分布特点、元素分布规律,为地球化学勘查方法制定奠定了理论基础。通过试点测量取得了良好效果。

乌兰布和沙漠的形成与环境变化

在对乌兰布和沙漠进行野外考察的基础上,通过地貌学、沉积学和年代学的研究,为恢复该地区全新世以来沙漠的形成与演化找到了新的证据。乌兰布和沙漠西南部的吉兰泰盐湖周围及沙漠南部丘间低地湖相地层下部风成砂的系统OSL测年结果表明,乌兰布和沙漠的形成年代约在7ka BP前后。此外,该沙漠腹地众多的干盐湖,大量含有蓝蚬的湖岸堤,以及丘间低地中的湖相地层和植物根系等的存在,证明了沙漠腹地大古湖的存在。乌兰布和沙漠的形成,可以归因于吉兰泰古湖面积的不断缩小和干涸,湖泊周围松散沉积物的风蚀、搬运及选择性堆积过程。

青海湖湖区风成沙堆积

通过对青海湖现代沉积环境与沉积相研究，并结合古代沉积盆地进行对比分析，认为风成堆积相是湖泊环境在内陆于煤气候条件下湖盆沉积的一种重要类型。本文讨论了湖泊环境中风成堆积相沉积的气候特征、形成过程、分布范围、沉积及储层岩石特征等。最后，结合国内外风成砂岩油气藏储集特征描述，指出湖盆中风成砂作为油气储集层具有良好的储集性能，这种沉积类型的分布具有一定的石油地质意义。

沙坡头铁路防护体系内风沙沉积的粒度特征

包兰铁路沙坡头段铁路防护体系内，由于下垫面性质发生变化，流沙区至人工植被带地表沉积物中表层土壤的黏粒和粉沙含量显著增大，平均粒径减小，颗粒分选性显著变差。防护体系内表层沉积物中的粉沙含量与地表相对高程反相关，黏粒含量与地形起伏没有直接关系，颗粒平均粒径、分选性与地表相对高程正相关。在土层垂直方向上，表层0-5cm内土壤粉沙含量较高，颗粒分选性差；5cm以下深度内土壤粉沙含量减少，颗粒分选性变好。在防护体系内沙丘地貌的不同部位，沙尘沉积速率不同。据此估算表明防护体系内固定沙丘迎风坡顶部沉积速率为0．147cm／a左右；背风坡和丘间地平均堆积速率大于0．588cm／a。

末次冰期鄱阳湖西南缘地区的风尘堆积

鄱阳湖湖滨沙山是末次冰期特定气候条件下季风活动所产生的风成沙丘沉积体。在调查鄱阳湖沙山的过程中,发现位于鄱阳湖南部沙山下风方向的丰城—樟树—新余一带岗丘顶部几米厚的第四纪堆积地层,虽然颜色明显偏红,但地层性状及沉积学特征却与北方风成黄土及宁镇下蜀黄土有着很大的相似性。通过对具代表性的新余打鼓岭剖面进行分析,确认其成因系风力搬运而成的粉尘堆积。结合冬季风路径上沉积物粒度的空间变化特征,初步提出鄱阳湖沙山与新余一带风尘红土堆积是在末次冰期特定气候条件下,冬季风作用所形成的风沙-风尘堆积系统。鄱阳湖风成沙丘及其西南缘风尘沉积的发育是晚更新世末期江南鄱阳湖区气候环境恶化的佐证,也是对我国西北地区沙漠-黄土堆积过程的区域响应。

陕北风沙区含砾石工程堆积体坡面产流产沙试验

采用室内人工模拟降雨方法,研究了陕北风沙区含砾石工程堆积体边坡的产流产沙过程。结果表明：1砾石存在改变了坡面入渗速率,径流系数受入渗速率的影响,随砾石含量的增加先线性递减后线性递增,并在10%砾石含量处存在阈值;径流系数随降雨强度的增加线性递增。2含砾石堆积体坡面流速较纯土堆积体降低,且随雨强增大,砾石延缓径流流动的作用越显著;雨强对径流流速的影响随砾石含量增加持续减弱。3土壤剥蚀率在产流24~33 min后显著增加,砾石主要对显著增加后的平均剥蚀率产生影响。4雨强1.0 mm/min时,砾石存在促进降雨侵蚀,产沙量增大;雨强大于1.0 mm/min时,砾石具有显著的减沙效应。