Microstructural analyses of a Middle Pliocene till from the James Bay Lowlands,Canada—evidence of “potential” fast ice streaming

Sediment from the Attawapiskat area near James Bay, Northern Ontario was sampled for micromorphological analyses. The sediment is a glacial diamicton (till) of subglacial origin. The till contains entrained and scavenged sediments of proglacial and/or subglacial glaciofluvial/glaciolacustrine origin from a subglacial deforming layer that was emplaced due to both stress reduction and/or porewater dissipation. Evidence of porewater escape, clay translocation and other microstructures all point to emplacement under active subglacial bed deformation. The limited number of edge to edge (ee) grain crushing events, however, point to lower stress levels than might anticipated under a thin fast ice lobe of the James Bay during the Middle Pliocene. Microstructures of Pleistocene tills were quantitatively compared with the Attawapiskat till and the limited number of ee events at Attawapiskat further highlighted that grain to grain contact was curtailed possibly due to high till porosity, high porewater pressures and low strain rates or alternatively due to a high clay matrix component reducing grain crushing contact events. It is suggested that this Middle Pliocene till may be indicative of sediments emplaced under ice lobe surging conditions or fast ice stream subglacial environments. This proposal has significant implications for the glaciodynamics of this part of the Middle Pliocene James Bay lobe. This research highlights a crucial link between subglacial conditions, till microstructural analyses and glaciodynamics.     

Microsedimentology of ice stream tills from the Eastern Alps,Austria – a new perspective on till microstructures

This study of tills from the Eastern Alps, Austria, illustrates the insights obtained using microsedimentology on subglacial tills in the context of palaeogeographical reconstructions of glacier advances. Investigations of several sites with tills derived from both local glaciers and the ice‐sheet streaming of the Inn Glacier during the Last Glacial Maximum and its termination reveal a detailed picture of subglacial sedimentology that provides evidence of soft sediment subglacial deformation under polythermal conditions. All the tills exhibit microstructures that are proxy evidence of significant changes in till rheology. The tills originate from multiple sources, incorporating older tills and other deposits picked up by the subglacial deformation within a polythermal but dominantly warm temperate subglacial thermal regime. The analyses of till microstructures reveal a direct relationship between basal ice strain conditions and their development. A hypothesis is derived, from the various microstructures observed in these Austrian tills formed under soft sediment deforming basal ice conditions, that suggests that with basal thermal changes and fluctuations in clay content, pore‐water content and pressure, microstructures form in a non‐random manner. It is postulated that in clay‐deficient sediments, edge‐to‐edge events are most likely to occur first; and where clay content increases, grain stacks, rotation structures, deformation bands and, finally, shear zones are likely to evolve in an approximate sequential manner. After repeated transport, emplacement, reworking and, probably, further shearing and deformation events, an emplaced ‘till’, as observed in these Austrian tills, will form that carries most, if not all of these microstructures, in varying percentages. Finally, the impact of the Inn Glacier Ice Stream on these tills is not easily detected and/or differentiated, but indications of high pore water and probable dilatant events leading to reductions in the number of edge‐to‐edge events point to the impact of fast or thick ice upon these subglacial tills.     

关于风化壳建造、古风化壳建造及其形成机理问题

现代风化作用形成风化壳物质,经过迁移就位以后形成风化壳建造;第四纪以前的古风化作用则形成古风化壳物质,经过迁移就位以后形成古风化壳建造。它们既不同于海相沉积,也不同于陆相沉积,与板块构造也无关系。但是它们有相同的风化作用形成机理;有大同小异的风化矿物、结构构造,以及颗粒大小不一,排列杂乱的产出特征,也有相同的迁移就位特征。是一个独特的建造,值得讨论。     

黄土高原红粘土与黄土古土壤粒度特征对比--红粘土风成成因的新证据

对黄土高原具有代表意义四个剖面的晚第三纪红粘土样品进行了粒度分析,并将结果与典型风成黄土古土壤样品的粒度特征进行详细对比,得到红粘土是风成成因的沉积学证据。结果表明,黄土高原红粘土与其上覆第四纪古土壤形成环境相似,红粘土是在相对于黄土堆积搬运风动力变幅小的条件下沉积的,在沉积之后受到较强的风化成壤改造作用。     

干旱绿洲区运积物发育土壤的地球化学特征—以新疆焉耆盆地为例

土壤的矿物及其地球化学特征是指示其风化特征的重要依据.为理解干旱绿洲区土壤发育特征,本文选取新疆焉耆盆地两个土壤剖面对其粒度、矿物、元素地球化学特征进行分析,结果表明:两剖面沉积物的粒度主要以黏粒、粉粒为主,矿物主要为石英、长石和黏土矿物,石英/长石多数小于1,长石以斜长石类为主,化学风化作用极弱.两剖面的化学蚀变指数...     

贵州普定碳酸盐岩上覆松散堆积物的沉积环境初探

通过对贵州省普定县马官地区不同地貌部位的4个剖面进行详细的粒度分析,把粒度参数以及频率曲线与各种沉积环境的特征进行对比,排除了河流沉积、风成沉积的可能性。研究区域各剖面的粒度分布特征表明其沉积环境属于碳酸盐岩溶蚀残余风化,同时还有坡面流水和地下水作用的参与。     

黄土高原黄土．和红粘土10Be地球化学特征

充分认识元素和同位素在不同环境条件下的地球化学行为,是运用元素和同位素示 踪环境变化的前提。对来自于黄土高原的黄土、古土壤和红粘土样品的宇宙成因核素¹⁰Be测量和化学成分分析,以及各种化学淋溶实验表明：¹⁰Be主要以吸附状态赋存于粉尘沉积物粘粒矿物的表面,部分已结合进自生的粘土矿物中;在粉尘沉积物风化过程中¹⁰Be与⁹Be和～的活动性相似,基本没有发生迁移,其原因是连续沉积的粉尘含有大量的碱性物质,阻止了…Be的解吸附和淋滤;沉积和风化作用导致了¹⁰Be浓度与化学指标在黄土-古土壤和红粘土剖面中的协同变化。     

碳酸盐岩酸不溶物作为贵州岩溶区红色风化壳主要物质来源的证据

贵州岩溶区红色风化壳是中国南方红色负化壳的重要组成部分，本文根据部分红色风化壳剖面野外特征、矿物学、地球化学及土壤物理学等的研究结果，对其物源及成因进行了探讨。各剖面，尤其邻近剖面显著的矿物学、地球化学差异排除了远程风成沉积物、火山灰、上覆或者高处碎屑岩层作为统一且重要物源的可能。极低的石英含量表明贵州常见的长石石英砂岩不是其主要物源，具有中稀土（MREE）富集的特征也排除了粘土岩、页岩作为主要物源的可能。风化壳剖面间的差异性均可从基岩酸不溶物的差异性得到很好解释，表明它们是下伏碳酸盐岩风化、酸不溶物（准）原地堆积的结果。部分剖面甚至显示了典型风化壳剖面的一些特征，具有正常风化序列的剖面结构特征。     

黔北新蒲红色风化壳剖面的粒度分布特征--兼论岩溶区上覆土层的物质来源

粒度分析在风化壳物源示踪方面是一种新的尝试,具有指示直接的特点。尤其当常规的地球化学、矿物学等方法难以直观反映母岩的不均一性对风化壳的影响时,粒度分布特征却可以建立两者的对应关系,从而更为合理地指示风化壳和下伏基岩的关系。黔北新蒲剖面的下伏基岩为局部夹碎屑岩薄层的连续型碳酸盐岩,本文通过对其酸不溶物及上覆红色风化壳粒度分布特征的研究,表明基岩的垂向不均一,导致上覆风化壳粒度分布特征的差异性,同时存在与下伏不同基岩酸不溶物粒度分布特征相对应的风化壳,指示了碳酸盐岩为其上覆风化壳的成土母岩。化学风化指标在剖面的变化也支持了粒度分析结果,即风化壳母岩的不均一性。从碎屑岩夹层和碳酸盐岩对风化壳提供物源的相对份额中指出碳酸盐岩的酸不溶物对上覆风化壳的优势贡献。从粒度参数角度进一步诠释了连续型碳酸盐岩风化残积成土的现实性,为正确理解中国西南岩溶区红色风化壳的成因提供了新的探索手段。综合资料显示,碳酸盐岩特别是连续型碳酸盐岩酸不溶物构成中国西南岩溶区上覆红色风化壳的主要物质来源也是可能的。     

Late Pleistocene glaciation of the Kleiner Arbersee area in the Bavarian Forest,south Germany

During Pleistocene mountain glaciation of the Bavarian Forest, south Germany, the Wurmian Kleiner Arbersee glacier left behind glacial landforms and sediments which are described, classified and interpreted using a combination of geomorphological, sedimentological, pedological, surveying and absolute dating methods. The latest Kleiner Arbersee glacier with a maximum length of 2600 m, a minimum width of 800 m and a thickness of 115 m formed an elongated cirque, four lateral moraines, one divided end moraine, one recessional moraine, a proglacial lake and a basin in which lake Kleiner Arbersee was established after deglaciation. Beyond the glacial limit the landscape is denuded by periglacial slope deposits which are differentiated from the glacigenic sediments based upon clast fabrics, clast shapes and sediment consolidation. Within the glacial limit sandy–gravelly to silty–gravelly tills are widely distributed, whereas glaciolacustrine sediments are restricted to a small area north of the lake. Small variations in the sand and silt fraction of the tills are explained by melt-out processes. Quartz, mica and chlorite derived from gneiss bedrock are dominant in the clay mineral spectrum of tills, but also gibbsite as a product of pre-Pleistocene weathering is present giving evidence of glacially entrained saprolites. An IRSL-date of glaciolacustrine sediments (32.4±9.4 ka BP) confirms the Wurmian age for the glaciation and radiocarbon ages of the basal sediments (12.3±0.4 and 12.5±0.2 ka BP uncalibrated) in the lake Kleiner Arbersee prove that the basin was ice-free before the Younger Dryas.     

The role of climate and local regolith–landscape processes in determining the pedological characteristics of æolian dust deposits across south-eastern Australia

Fine-grained æolian sediments are an important component of many loessic soil–landscape systems across south-eastern Australia. These loessic soils are commonly related to the deposition of ‘parna’, a red, clayey, calcareous material proposed to have been transported predominantly as silt-sized pellets and companion silt grains. However, it is apparent that loessic soils of south-eastern Australia do not necessarily exhibit or retain the morphological features regarded as typical of parna. This may be due to variations in post-depositional pedogenic processes operating over long periods of time. It is important to understand this inconsistency in loessic soil expression because the physico-chemical and structural attributes of these profiles may significantly affect catchment-wide processes such as salinisation and erosion. In this paper, the pedological features of a range of previously identified loessic profiles occurring across south-eastern Australia are examined to assess the relative importance of climate and local landscape processes on profile characteristics. Most of the sampling sites occur in mid- to upper-slope positions, while the annual average rainfall of the sites ranges from 440 mm to 650 mm. The deepest profiles in the driest locations tend to yield whole-coloured, slightly alkaline, slightly saline and sodic subsoils with moderate cation exchange capacities. Profiles in the wettest locations are generally characterised by smaller cation exchange capacities, are acidic, non-saline and non-sodic, and feature prominent mottling and sesquioxide nodules. Measurements and predictions of the structural attributes of the profiles indicate that all topsoils are quite stable to wetting, whereas subsoils exhibit variable stabilities, depending on physico-chemical properties. These results appear to demonstrate a broad climosequence effect on loessic soil attributes. The climosequence effect was compared to the changes in loessic profile characteristics down a case study toposequence in southern New South Wales. The toposequence indicates that local landscape features such as slope and drainage have also been important in determining the properties of these materials, as has re-working by colluvial processes. We conclude that to explain adequately the current characteristics of profiles containing fine-grained æolian sediments, particularly their salinisation potential and stability to erosion, it is critical to consider both the past and present climate and the local soil-forming processes.     

Weichselian in central South Norway: the Gudbrandsdal Interstadial and the following glaciation.

Present knowledge of sub-till sediments found in the valleys in the Mid-Gudbrandsdal area and the stratigraphy of the overlying basal tills is summarized. The existence of widespread waterlain sediments which are thought to have been depostied in a cold ice-free period of Middle/Early Weichselilan age, the Gudbradnsdal Interstadial, gives evidence of surprisingly modest ice erosion during the last ice age, even in valleys close to the highest mountains. Judging by the nearly total evacuation of older deposits from the tributaries, the ice-free period seems to have lasted for a long time, with very strong slope processes. Huge quantities of proglacial sandur sediments accumulated in the main valleys indicate that the last inland ice sheet grew slowly. By comprehensive analyses the authors have succeeded in correlating the overlying tills with four regional glacial phases of the last ice age reconstructed mainly through analyses of striae. It is found that the conservation of the sediments, as well as the distribution of different tills, was dependent on the relative location of the ice divide.     

A consideration of some hidden hydromorphic effects on the fines of glacial tills in the Kuhmo-Suomussalmi area, eastern Finland

The silt and clay-size (minus 0.063 mm) fractions of 766 samples of glacial tills from the Kuhmo-Suomussalmi area in eastern Finland were analyzed for 8 trace and minor elements (Co, Cr, Cu, Mn, Ni, Pb, Zn, Fe) by AAS after hot 7 mol/I HNO, dissolution treatment. The results were treated statistically. Threshold values were calculated separately for those tills overlying gneissic basement on the one hand and greenstone belt on the other. The results show that the overall element levels for the metals in the area are lower than elsewhere in Finland by a factor which varies between 1 and 46. The reason for the differences may be the absence of preglacial weathering material in the till fines which elsewhere enhance element levels. Marked differences in the element levels over each bedrock subunit show up in the overlying tills. Correlation, regression and factor analyses show that the elements have high mutual correlations suggestive of hydromorphic alteration, even though the macroscopically hydromorphic samples were omitted from the statistical analyses. The effect is weak, however, and does not suppress the primary correlation, which results in the emergence of two factors in factor analysis of the geochemical data of the greenstone belt tills, the Co-Cr-Cu-Mn-Ni-Fe and Pb-Zn factors, the latter corresponding to one of the two known types of mineralization encountered in the underlying bedrock.     

Stratigraphy and geochemistry of a sequence of Quaternary palaeosols in the Lower Teleki Valley,Mount Kenya,East Africa — Implications for interregional correlations

The relative weathering of a sequence of five palaesols formed in different parent materials, including bedrock of phonolitic composition, is described and assessed. The three lower palaeosols (units 3–5) are considered to be of interglacial origin. The saprolite (unit 5), in phonolite, formed prior to deposition of the lower Brunhes-age till, is considered to be as old as the Brunhes Matuyama boundary (0.73 myr). The other two palaeosols in this group (units 3 and 4), derived from loess and till, respectively, formed over middle to late Brunhes time under palaeoclimates that were wetter (and presumably warmer), and of sufficient leaching power to move clay, as well as organically complexed extractable Fe and Al. The palaeosols in unit 3 are more complex than the lower ones. Their upper and lower horizons have about the same chemical composition as the lowest two palaeosols, while the middle horizons are similar to the upper two palaeosols (units 1 and 2). Radiocarbon dates for unit 3 are considered to be too young to account for the strong weathering in the upper and lower horizons. This interpretation is supported by high D/L ratios of aspartic acid. Overlying sediments, emplaced by episodic colluvial (unit 2) and slope wash (unit 1) processes, are less weathered; the lower colluvial unit in this group was emplaced during the late stade of the last glaciation. The surface sediments were emplaced more recently during the same interval and weathered mainly during the post-glacial period. Tentative correlations with core 82PCS18 from the Canary Basin show that upper unit 3 is probably equivalent to Isotope Stage 5e, lower unit 3 to Isotope Stage 7, unit 4 to Isotope Stage 8, and unit 5 to Isotope Stage 9. Units 1 and 2 are firmly correlated with Isotope Stage 2.     

Formation of subglacial till under transient bed conditions: deposition, deformation, and basal decoupling under a Weichselian ice sheet lobe, central Poland

A multi-proxy approach involving a study of sediment architecture, grain size, grain roundness and crushing index, petrographic and clay mineral composition, till fabric and till micromorphology was applied to infer processes of till formation and deformation under a Weichselian ice sheet at Kurzetnik, Poland. The succession consists of three superposed till units overlying outwash sediments deformed at the top. The textural characteristics of tills vary little throughout the till thickness, whereas structural appearance is diversified including massive and bedded regions. Indicators of intergranular bed deformation include overturned, attenuated folds, boudinage structures, a sediment-mixing zone, grain crushing, microstructural lineations, grain stacking and high fabric strength. Lodgement proxies are grooved intra-till surfaces, ploughing marks and consistently striated clast surfaces. Basal decoupling by pressurized meltwater is indicated by undisturbed sand stringers, sand-filled meltwater scours under pebbles and partly armoured till pellets. It is suggested that the till experienced multiple transitions between lodgement, deformation and basal decoupling. Cumulative strain was high, but the depth of (time-transgressive) deformation much lower (centimetre range) than the entire till thickness ( ca 2 m) at any point in time, consistent with the deforming bed mosaic model. Throughout most of ice overriding, porewater pressure was high, in the vicinity of glacier floatation pressure indicating that the substratum, consisting of 11 m thick sand, was unable to drain subglacial meltwater sufficiently.     

黄土高原黄土和红粘土~(10)Be地球化学特征

充分认识元素和同位素在不同环境条件下的地球化学行为,是运用元素和同位素示踪环境变化的前提。对来自于黄土高原的黄土、古土壤和红粘土样品的宇宙成因核素10Be测量和化学成分分析,以及各种化学淋溶实验表明：10Be主要以吸附状态赋存于粉尘沉积物粘粒矿物的表面,部分已结合进自生的粘土矿物中;在粉尘沉积物风化过程中10BC与9Be和Al的活动性相似,基本没有发生迁移,其原因是连续沉积的粉尘含有大量的碱性物质,阻止了10Be的解吸附和淋滤;沉积和风化作用导致了10Be浓度与化学指标在黄土－古土壤和红粘土剖面中的协同变化。     

Effects of grain size distribution on mineralogical and chemical compositions: a case study from size‐fractional sediments of the Huanghe (Yellow River) and Changjiang (Yangtze River)

The influence of hydrodynamics on the chemical composition of sediments is based on the uneven distribution of element abundances in different size fractions. In this study, 72 size‐fractional sediments from the Huanghe (Yellow River) and Changjiang (Yangtze River) riverbeds were measured with XRD, SEM, ICP‐AES and ICP‐MS. The analysis results show that the mineral and chemical characteristics change with grain size in the Huanghe and Changjiang sediments. According to the principal components analysis, three independent geochemical factors were found. The first factor elements, Zr, Hf, Th, U, Y, La and TiO₂ are influenced by the existence of heavy minerals. The second factor elements, Al₂O₃, alkalis, alkaline earth (excluding Ca and Sr) and most of the transitional metals are dominated by clay minerals. The third factor group includes Ca and Sr, which were controlled by calcium‐bearing mineral contents and chemical weathering intensities. The various grain size distributions greatly affect the mineralogical and chemical compositions of bulk sediments. Compared to other size fractions, the 5–6PHI size fractions of the Huanghe and Changjiang sediments have special mineralogical and chemical compositions, and intermediate volume percentages. Weight or volume percentage of each size fraction may be more suitable than mean grain‐size of the bulk sediment to elucidate the grain size effects. Chemical Index of Alteration (CIA) values increase steeply with decreasing grain size, while Weathering Index of Parker (WIP) values are relatively stable. Because of the big influence of the abundance of clay minerals on CIA values, it is questionable to use CIA as a proxy of weathering intensity. Considering the clay mineral effects, stability in values and heterogeneous material properties, WIP has the potential to indicate the chemical weathering intensity of sediments. Copyright © 2014 John Wiley & Sons, Ltd.     

Saalian sediments of the Belchatów outcrop, central Poland

The deposits of six glacial episodes, including five till beds and fluvial deposits of one temperate substage, stratigraphically lying between the Holsteinian and Eemian Interglacials have been recognized in the geological record of the Kleszczów Graben, central Poland. Two other temperate substages have been recognized on the basis of well-developed weathering horizons on the tills. The depositional environments and general petrological features of these sediments are described and their stratigraphical position is discussed. The Saalian Complex of the Kleszczów Graben has been subdivided into the Older Saalian (three glacial episodes), the Pilica Interstadial and the Younger Saalian (three glacial episodes and two presumed interstadials). This sequence cannot be simply correlated with other Saalian stratigraphic sequences in Europe, although the pre-Odranian and Odranian (=main Drenthe) tills most probably belong to the Older Saalian, and the Wartanian (Warthe) tills to the Younger Saalian. The geological record presented here suggests that reforestation phases occurred during the Saalian. This contradicts recently developed continental stratigraphics.     

30 ka以来东阿拉伯海U1456站位粘土粒级碎屑沉积物来源及其古环境意义

通过对国际大洋发现计划U1456站位沉积物AMS 14C年代、粘土矿物、常量元素及粒度组成的综合分析,探讨了东阿拉伯海粘土粒级碎屑沉积物的源-汇过程及其古环境指示意义.30 ka以来U1456站位的粘土矿物组合以蒙脱石和伊利石为主,并含有少量的绿泥石和高岭石.物源分析结果表明粘土粒级碎屑沉积物主要来自于印度河与德干高原.30 ka以来西南季风很可能是影响喜马拉雅山脉以及印度大陆风化剥蚀的重要因素.在西南季风减弱的阶段,印度河物源端元对研究区的输入量减少,这可能与此时热带辐合带的南移及末次冰盛期喜马拉雅山脉冰川覆盖面积的增加有关,从而导致印度河径流量及喜马拉雅山脉可供风化剥蚀的区域减少.K/Al比值指示的源区大陆化学风化作用强度与前人重建的西南季风记录间较为同步,在东阿拉伯海可以作为晚第四纪以来西南季风演化的有效重建指标.