Stratigraphy,geochemistry, and thermoluminescence ages of lower Mississippi Valley loess

Four periods of loess deposition in the Lower Mississippi Valley can be identified on the basis of geochemical and mineralogical criteria, radiocarbon dating, and thermoluminescence dating. These are designated Loess Units 1,2,3, and 4 in order of increasing age. Carbonate-rich Unit 1 loess comprises more than 70 per cent of the thickness of the loess profiles. ¹⁴C and TL dates indicate this loess was deposited between 9 000 and 20 000 years ago. A maximum sedimentation rate of 2.17 mm yr^?1 has been recorded near Vicksburg just after the last Laurentide glacial maximum, between 17 190 and 15 580 years ago. The Unit 2 loess, which is thin and partly decalcified, was deposited slowly between about 25 000 and 20 000 years ago. The Unit 3 and Unit 4 loess formations, which are both highly weathered, have yielded TL ages of 76 000–85 000 years and 119 000- > 132 000 years, suggesting they were deposited during the Altonian Substage of the early Wisconsinan and the Illinoian glacial stage respectively. The four loess units are stratigraphically equivalent to the Peoria, Farmdale, Roxana, and Loveland loess formations previously recognized in Illinois. The source of dust in both areas was glacial outwash in the Mississippi Valley. During interglacials and interstadials, when the supply of glacial debris was reduced and the Mississippi River changed from a braided to a meandering regime, dust sedimentation in southern Mississippi virtually ceased, allowing weathering and pedogenesis to proceed.     

Cenozoic tectonic and geomorphic evolution of the Longxi region in northeastern Tibetan Plateau interpreted from detrital zircon

The Longxi region contains different kinds of Cenozoic sediments, including eolian deposits, reworked loess, fluvial and lacustrine deposits. The provenance evolution of these sediments is of great significance in exploring the uplift, tectonic deformation and associated with geomorphic evolution of the Northeastern Tibetan Plateau. In this paper, we used the single-grain zircon provenance analysis to constrain the provenances for the Paleogene alluvial conglomerates and for the Neogene fluvial-lacustrine sediments, and compared them with results from the loess deposits since the Miocene. The results show that: (1) the Paleogene alluvial conglomerates contain a large number of detrital zircons ranging from 560 to 1100 Ma that were derived from the Yangzi Block. However, the sediments of early Miocene have much fewer zircons of this age span, which are characterized by an abundance of zircon ages in the ranges of 200–360 Ma. This indicates that the Paleogene alluvial conglomerates mainly come from the middle and/or southern West Qinling, and the early Miocene sediments are primarily from the northern West Qinling; (2) Late Neogene fluvial sediments (11.5 Ma onward) in Tianshui-Qinan region are dominated by zircon ages of 380–450 Ma. This zircon population is similar to that of the exposed intrusive rocks of southern part of the Liupan Mountains, implying that the southern part of Liupan Mountains probably had already uplifted by 11.5 Ma; (3) Late Miocene lacustrine sediments in Tianshui region have a zircon age spectra that is remarkably different from coeval fluvial deposits, but is similar to the zircon age distributions of the Miocene loess in Qinan region, late Miocene-Pliocene Hipparion red clay and Quaternary loess. This indicates that fine particles within these Miocene lacustrine sediments in Tianshui region may be dominated by aeolian materials. This study reveals that provenance changes of Cenozoic sediments in Tianshui-Qinan region and its geomorphic evolution are closely related to the multi-stage uplift of the Northeastern Tibetan Plateau. In particular, the major uplift of the Northern Tibetan Plateau during late Oligocene-early Miocene may have not only provided the source areas and wind dynamic conditions for the deposits of the Miocene loess, but also provided the geomorphic conditions for its accumulation.     

三门峡盆地晚新生代沉积物磁性载体类型

对三门峡盆地晚新生代沉积岩样品进行岩石磁学研究,通过三轴饱和等温剩磁和剩磁矫顽力实验、交变退磁和热退磁实验及磁化率测定,发现黄土-古土壤、河湖相灰绿层和冲洪积层3种不同岩性的磁载体存在显著差异.即黄土-古土壤以磁铁矿为主,赤铁矿和磁赤铁矿很少;河湖相灰绿色沉积磁性矿物含量较低,主要为赤铁矿和磁铁矿,但磁铁矿较多,此外还有一些不稳定磁性矿物(如针铁矿、菱铁矿等);冲洪积物以磁铁矿和赤铁矿为主,磁铁矿相对较多.     

ReOSL dating of aeolian and fluvial sediments from Nihewan Basin,northern China and its environmental application

The Nihewan Formation, consisting of thick fluvio–lacustrine sediments with abundant mammalian faunas and Paleolithic remains, is widely distributed in the Nihewan Basin, northern Hebei Province, China. In this study the fluvio–lacustrine sediments of the Nihewan Formation and the loess–paleosol sequence evident in the Haojiatai Section were dated by recuperated OSL (ReOSL) of fine-grained quartz (Wang, X.L., Lu, Y.C., Wintle, A.G., 2006a. Recuperated OSL dating of fine-grained quartz in Chinese loess. Quaternary Geochronology 1, 89–100.). The preliminary ReOSL dating results show that: (i) the loess–paleosol sequence in the upper part of the profile started to develop at about 128 ka ago; (ii) the unconformity separating the loess–paleosol from the underlying Nihewan Formation represents a sedimentation break of about 130 ka. On the basis of the ReOSL dates and related stratigraphic evidence it is proposed that the ancient Lake Nihewan dried shortly after about 266 ka.     

Upper Pleistocene‐Holocene geomorphic changes dictating sedimentation rates and historical land use in the valley system of the Chifeng region,Inner Mongolia,northern China

This study focuses on the late Quaternary landscape evolution in the Chifeng region of Inner Mongolia, China, its relations to the history of the Pleistocene‐Holocene loess accumulation, erosion and redeposition, and their impact on human occupation. Based on 57 optically stimulated luminescence (OSL) ages of loess sediments, fluvial sand and floodplain deposits accumulated on the hill slopes and floodplains, we conclude that during most of the Pleistocene period the region was blanketed by a thick layer of aeolian loess, as well as by alluvial and fluvial deposits. The loess section is divided into two main units that are separated by unconformity. The OSL ages at the top of the lower reddish loess unit yielded an approximate age of 193 ka, roughly corresponding to the transition from MIS 7 to 6, though they could be older. The upper gray loess unit accumulated during the upper Pleistocene glacial phase (MIS 4–3) at a mean accumulation rate of 0·22 m/ka. Parallel to the loess accumulation on top of the hilly topography, active fans were operating during MIS 4–2 at the outlet of large gullies surrounding the major valley at a mean accumulation rate of 0·24 m/ka. This co‐accumulation indicates that gullies have been a long‐term geomorphic feature at the margins of the Gobi Desert since at least the middle Pleistocene. During the Holocene, the erosion of the Pleistocene loess on the hills led to the burial of the valley floors by the redeposited sediments at a rate that decreases from 3·2 m/ka near the hills to 1–0·4 m/ka¹ in the central part of the Chifeng Valley. This rapid accumulation and the frequent shifts of the courses of the river prevented the construction of permanent settlements in the valley floors, a situation which changed only with improved man‐made control of the local rivers from the tenth century AD. Copyright © 2010 John Wiley & Sons, Ltd.     

Preliminary ESR dating results on loess samples from the loess–paleosol sequence at Luochuan, Central Loess Plateau, China

The quartz Al centre has been used in pioneering studies for ESR dating of sediments. Acceptable age estimates could be obtained for a range of deposits using this centre after estimating the residual level. To inspect the feasibility and reliability of ESR dating of windblown sediments, six loess samples from the loess–paleosol sequences of Luochuan profile on central Loess Plateau, China, were dated by ESR with regeneration method using the quartz Al centre measured at 115 K. The samples were exposed to sunlight for 430 h. Only about 25% signal intensity was bleached. According to our preliminary results, ESR age estimates increased with the depth along the loess profile, however, the ESR age of each sample is only about a half of the reference age of the corresponding strata. For example, the ESR age of a sample from the top of L₈ loess near B/M boundary (a known age of 780 ka) yields an age of only 385 ka. It seems that ESR dating using quartz Al centre with dose regeneration protocol may have the potential for dating of loess and other aeolian deposits, but the studies on the nature of the quartz Al centre and experiment protocols have to be studied further.     

贵州省麦岗水库沉积物磁性特征及其与粒度的关系

对贵州省麦岗水库沉积物环境磁性特征的研究表明,亚铁磁性矿物主导了沉积物矿物磁性特征,但同时也存在反铁磁性矿物等其他矿物,超顺磁颗粒在沉积物中广泛存在.在所选矿物磁性参数中,χlf、χfd、SOFT与粒度不相关;χARM、SIRM、F300与粒度相关,但相关系数不高;χARM/χlf、χARM/SIRM和粒度显著相关,可以作为粒度的代用指标.研究结果显示,磁性参数确实可以作为粒度的代用指标.但对比研究表明,在不同沉积环境,甚至相似沉积环境的沉积物中,矿物磁性参数和粒度的关系可能不同,在特定沉积环境中,利用磁性参数作为粒度的代用指标应该在充分研究的基础上进行,使研究结果更为可靠.     

Trapping of airborne dust by mosses in the Negev Desert,Israel

Airborne silt and clay containing calcium carbonate, quartz, clays, marine nannoplankton, and aquatic diatoms are trapped among stems of mosses in the Negev Highlands Desert. The mosses were studied in an area with 70 mm mean annual rainfall. They grow over the particles covering them and trap additional dust as it comes, resulting in the accumulation of loess sediments. The mosses protect the accumulated soil from erosion by wind or water. Remnants of the moss leaves and stems were found at a depth of 15 mm and more. No particles or minerals typical to basalt were found in the moss-trapped soil. The function of cushiony mosses may be used to explain the processes of loess trapping and protection in larger areas in moister areas such as the Northern Negev. Microscopic fossils in the dust may be used as guides to the origin of the (aeolian) sediments.     

The provenance of Gansu Group in Longxi region and implications for tectonics and paleoclimate

The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of paleo-atmospheric circulation,and the regional tectonics and geomorphic evolution during the Miocene.Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin,and compare them with those of surrounding eroded mountain(such as the West Qinling Mountains and Liupan Mountains)materials and Quaternary loess derived from the Asian inlands.The results reveal that(1)the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region,but very similar to the Quaternary loess deposits.This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess,and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary.(2)The detrital-zircon age spectrum of the fluvial deposits(with age about 11.5 Ma)from Tianshui region is different from the eroded materials of West Qinling Mountains,but similar with that of the Liupan Mountains to the east,which may suggest that the Liupan Mountains have already been exhumed by11.5 Ma.     

甘肃西山坪遗址岩石磁学性质及其研究意义探讨

对甘肃西山坪遗址剖面样品进行磁化率、频率磁化率、热磁分析、非磁滞剩磁和等温剩磁等一系列岩石磁学实验测试,分析环境磁学参数特征变化,试图探讨西山坪遗址研究意义,为今后深入研究该沉积序列蕴含的古环境记录提供了岩石磁学基础.结果表明：西山坪遗址剖面沉积物中磁性矿物主要以低矫顽力的磁铁矿和磁赤铁矿为主,高矫顽力磁性矿物赤铁矿含量极其有限,越向剖面表层,强磁性矿物含量逐渐增加.磁性矿物颗粒表现出黄土的典型特征,以单畴、准单畴为主,含有一定量的超顺磁颗粒,颗粒度越向剖面表层越细.从物源上看,遗址沉积物主要来自近源的黄土风尘堆积,主要是风成堆积,并混合大量人类活动信息,给今后综合研究岩石磁学与人类活动特征的关系有一定借鉴意义.     

Luminescence chronology of fluvial and aeolian deposits in the Russian Altai (Southern Siberia)

Geomorphological investigations in the Russian Altai Mountains provide evidence for the extent and timing of Late Quaternary glaciations and aeolian sediments. Infrared optically stimulated luminescence (IR-OSL) and thermoluminescence (TL) dating of aeolian sediments from the central part of the Russian Altai were carried out on silty and sandy sediments that cover fluvial and glacio-fluvial terraces. Most samples from loess, loess-like sediments and sandy loess taken from different terrace sequences within the Altai Mountains provide IRSL ages suggesting a main aeolian deposition period between 25 and 15 ka. These data are consistent with those from the adjacent Mongolian Altai. Sand and silt layers within moraines yielded IRSL age estimates between 22 and 19 ka and correlate to the ice margins of the Last Glacial Maximum. Aeolian dune sands overlying or neighbouring the loess-like sediments and the fluvial terraces at some places provide evidence for Late Glacial (around 15 ka) and Early Holocene (around 9 ka) aeolian activity. The youngest sand sheets gave deposition ages of about 1.5 ka. These sediments covered graves and are related to overgrazing. They provide evidence for the significant human impact on the environment. Fluvial sediments, including silt and sandy gravel intermingled with charcoal, yielded contradicting radiocarbon and luminescence ages. IRSL age estimates obtained for the silty layers range from 19 to 18 ka and are significantly older than the radiocarbon ages, which gave sub-recent ages between 1170 and 910 BP. These data indicate fluvial sedimentation of debris and mudflows in a period of deforestation and strong soil erosion related to mining activities during the 9th and 10th century.     

Arsenic in the Yellow river,China

Data collected since 1973 show high levels of arsenic in the Yellow River, very largely from natural sources. Average and peak concentrations, and the downstream distribution of the arsenic suggest the most likely source as the loess which provides 90 per cent of the river's suspended load. Arsenic is strongly absorbed by the silt and clay in the river: some of it is deposited in reservoirs and delta sediments but most is carried out to sea.     

Can Hydraulic Conductivity of Fluvial Sediments be Informed by Spectral Reflectance?

Water Resources - This study explores the statistical relationship between spectral reflectance and hydraulic conductivity (K) of fluvial sediments in two Nebraska rivers. The spectral reflectance...     

Oxygen isotope compositions of quartz grains (4—16μm) from Chinese eolian deposits and their implications for provenance

In recent years, the researches of inland Asia aridification since late Cenozoic have attracted much attention in the paleoclimate community. Rea et al.[1] studied a 12 Ma eolian record in North Pacific and associated it with the aridification of northwes…     

Characterisation and sediment–source linkages of intertidal sediment of the UK’s north Sefton Coast using magnetic and textural properties: findings and limitations

Sediment pathways and links to offshore processes are considered in the textural and magnetic characteristics of sediments of the intertidal flats and salt marshes of the north Sefton Coast, UK. In addition, sediment from a range of intertidal, marine and fluvial locations within the northwest region has similarly been characterised. Subsequently, the characteristics of these regional sediments, using a multivariate statistical approach of R- and Q-mode factor analyses, have been used to investigate the sediment transport pathways of the north Sefton Coast sediment. The benefits of fractionating sediment samples have been observed, and by using combinations of textural and isothermal remanent magnetic measurements, specific environments within the research have been successfully differentiated and characterised. Linkages between potential sediment source areas have also been established on a particle size-related basis.     

新疆泥火山发育区场地震陷灾害机理探讨

粒度组分是影响黄土震陷的重要因素之一.通过采集新疆艾其沟泥火山泥质碎屑喷出样品和泥火山发育区域出露的沉积剖面泥质碎屑样品,利用激光粒度分析测试的实验方法对样品进行粒度测试,分别对样品中值(Md)、均值(Mz)、标准偏差(σφ)、偏度(SK1)、峰度(KG)等粒度参数进行分析.研究结果显示:艾其沟泥火山泥质沉积物粒度组分...     

Origin and evolution of mid-Cretaceous, garnet-bearing, intermediate and silicic volcanics from Canterbury, New Zealand

The Mt Somers Volcanics are part of a suite of mid-Cretaceous (89 ± 2 Ma) intermediate to silicic volcanics, erupted onto an eroded surface of Torlesse sediments. Rock types vary from basaltic andesite to high-silica rhyolite. Andesites are medium- to high-K with phenocrysts of plagioclase, orthopyroxene and pigeonite. Dacites are peraluminous and commonly contain granulite facies xenoliths and garnet xenocrysts. Equilibrium mineral assemblages indicate metamorphic pressures of close to 6 kbar at 800°C. Rhyolites are peraluminous with phenocrysts of quartz, sanidine, plagioclase, biotite, garnet and orthopyroxene. The ferromagnesian phases show textural evidence of magmatic crystallization and are chemically distinct from xenocryst phases in dacites. Equilibrium assemblages indicate that early magmatic crystallization occurred at close to 7 kbar (20 km depth) at above 850°C, with melt-water contents of less than 3.5%. Major-element contents, trace-element contents and an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7085 indicate that the rhyolites formed by partial melting of dominantly quartzo-feldspathic Torlesse sediments, leaving a granulite-facies residue. The chemical variation displayed by the rhyolites is best explained by fractional crystallization of the observed high-pressure phenocryst assemblage. Most elements show a compositional gap between rhyolite and dacite. The major-element, trace-element and Sr isotope compositions of the intermediate lavas are best explained by assimilation of lower crustal material combined with fractional crystallization in mantle-derived tholeiitic magmas. Magmatism was the result of heat and magma flux from the mantle, during the change from compressive to extensional tectonics after the culmination of the Rangitata Orogeny.     

青藏高原可可西里库赛湖年纹层石英颗粒表面形态特征研究

湖泊是风成沉积的理想载体,利用扫描电镜分析石英砂的表面微结构特征,可以用于判断石英颗粒被风或水流搬运的相对距离和湖泊的水动力条件,从而判断其沉积环境与演化历史.库赛湖位于青藏高原北部可可西里地区,是青海省沙尘天气频发的地区之一,为进一步证实库赛湖年纹层粗颗粒层的风成成因,以库赛湖沉积年纹层为研究对象,结合青藏高原北部典型沙丘沉积、库赛湖冰面风成沉积、典型河流沉积和库赛湖湖滨相水成粗颗粒沉积样品,利用扫描电镜对上述沉积物石英颗粒表面特征进行观察研究,并统计35种特征的出现频率.结果表明:库赛湖地区典型风成物石英颗粒表面具有圆形轮廓、中低浮雕、翻板、新月型撞击坑、球根状边缘、直形阶梯、弓形阶梯、碟形坑等微形貌特征;典型水成物石英颗粒表面具有V型撞击坑、小型和中型贝壳状断口、少量溶蚀坑等微形貌特征;库赛湖年纹层粗颗粒层石英颗粒表面具有圆形轮廓、低浮雕、翻板、新月形撞击坑、球根状边缘、碟形坑等明显风成特征,与研究区风成物的石英颗粒表面特征相似,而与研究区典型水成物的石英颗粒表面特征差别很大.因此,库赛湖年纹层中的粗颗粒层是由风成作用形成的.     

洛川黄土-古土壤剖面环境剂量率测量的对比

如何准确测量环境剂量率是释光和电子自旋共振测年技术的关键之一.本文选择了几种环境剂量率的主要室内测量方法,对洛川黄土-古土壤这个典型的均匀剖面进行测量对比研究,同时检验Daybreak公司生产的厚源ZnS Alpha计数仪的测量精度.     

Niveo-aeolian deposits and denivation forms,with special reference to the great Kobuk Sand Dunes,Northwestern Alaska

The geomorphology, lithology and chronostratigraphy of extensive, late Pleistocene inland and river dune sands, aeolian sand sheets (‘cover sands’) and loess deposits of periglacial origin in northwestern Europe are well known. However, the idea that some of these aeolian sediments result from niveo-aeolian processes is still an open question, as no diagnostic sedimentary features have yet been reported. Moreover, actual niveo-aeolian sediments and related denivation forms, reported from various cold-climate regions, are not suitable analogues. Recent observations in active dune fields in northwestern Alaska indicate that interstratification of wind-driven snow and sand preferentially occurs on slip faces of transverse, barchanoid or parabolic dune ridges. Annual denivation forms develop: e.g. snow ramparts, sinkholes, snow hummocks, snow meltwater fans and tensional cracks. The surface consists of a cracked wet sand layer with a dimpled surface and spongy structure. Although the preservation potential of these features is low in this specific case, similar features may be observed in ancient sediments elsewhere and provide useful palaeoclimatic indicators. The niveo-aeolian concept should therefore not specifically be related to late Pleistocene cover sand deposition in northwestern Europe, as previously assumed.