南极纳尔逊冰帽前缘地冰前沉积物的结构和地球化学特征研究

本文对现代南极纳尔逊冰帽边缘的冰前沉积物结构和地球化学特征进行了详细研究。冰前沉积物的粒度分布具有冰川成因沉积物的典型特征 ,显著不同于风成和湖泊沉积物。另外 ,冰前沉积物的粒度分布是分形的 ,其分形维值大约为 2 .9,该值可以作为粒度分布的另外一个统计参数。因为矿物分离和冰川作用过程的影响 ,冰前沉积物的绝对元素含量之间的相关性很差 ,但不同元素与 Rb的比值具有显著的统计相关性 ,这说明元素与 Rb比值降低或消除了沉积物形成过程中来自于冰川作用对元素地球化学变化所造成的影响 ,这对于处理冰前沉积物的地球化学数据和…     

一种新的粒度指标:沉积物粒度分维值及其环境意义

根据分形理论，对1000个不同类型沉积物样品的粒度分形结构及其分维值作了定量计算。结果表明：各类型沉积物都具有良好的统计自相似性，并且各自有着不同的分维值。粒度分维值的大小与分选好坏密切相关。没有经过外力搬运与分选的风化破碎物质(碎屑物)——断层泥、冻土的粒度分维值接近于碎形体的分维值2．60左右；经过外力搬运但分选作用较弱的冰碛物、水石流、泥石流堆积物的粒度分维值也接近2．60；而经过强烈外力分选作用的河床、湖泊沉积物、潮滩及海底沉积物的分维值明显偏小。鉴于此，本认为分维值可以作为沉积物类型判别的重要参数之一。     

西藏樟木滑坡群的分形特征及其意义

根据分形理论，以西藏樟木滑坡群为例，详细分析了滑坡活动时空结构的信息维特征和滑动带土粒度分布的分形结构特征。结果表明，滑坡活动具有很好的分形现象；滑动带土的粒度分维值一般在２～３之间，其平均值约为２．８，分维可作为描述滑动带土粒度成分的参数。在此基础上，探讨了分维的研究意义     

西藏樟木滑坡群的分形特征及其意义

根据分形理论，以西藏樟木滑坡群为例，详细了分析了滑坡活动时空结构的信息维特征和滑动带土粒度分布的分形结构特征。结果表明，滑坡活动具有很好的分形现象，滑动带土的粒度分维值一般在２～３之间，其平均值约为２．８分维可作为描述滑动带土粒度成分的参数。在此基础上，探讨了分维的研究意义。     

软弱层带夹泥粒度成分的分形研究

应用分形几何理论，对软弱层带夹泥粒度成分的研究表明，粒度分布具有分形结构特征，其分维值在２－３之间。分维值可作为定量描述夹泥粒度成分的参数。分维值的大小，不仅能表征夹泥所处的演化阶段及环境条件，而且还与夹泥的粘粒含量，粘土矿物成分及物理力学特征等密切相关。     

甘肃黄土的粒度分维特征及意义

依据分形理论分析了甘肃黄土粒度分布的分形结构特征。黄土具有良好的统计自相似性。随着空间位置和黄土形成时代的不同,黄土的分形结构特征有明显的变化特征,其分维值介于2.29至2.56之间;且粒度分维值的大小与分选好坏密切相关,即:分选系数大则分维值大,反之则分维值小。这表明黄土的粒度分维在一定程度上可以反映黄土的形成演化特征。在此基础上进一步研究了黄土粒度分维与干密度、孔隙比、湿陷系数之间的定量关系,指出黄土分维值可以定量表征黄土的物理、水理性质。与地形地貌、水文和气候等因素一样,它也可作为自然区划的一个主要指标。     

滑坡滑动带土的分维特征及其意义

本文据分形理论分析了滑坡滑动带土粒度分布的分形结构特征。探讨了分维的研究意义。结果表明，滑动带土的分维在２和３之间，平均值约为２．８５。分维的大小揭示了作为自组织系统的滑动带土的形成演化特征。     

南京下蜀黄土颗粒分形研究

根据分形理论,研究了南京下蜀黄土粒度分形结构特征,发现在双对数坐标下粒径和粒度含量之间存在明显的线性关系,表明粒度组成具有分形结构。通过对下蜀黄土颗粒分形的计算,结果显示颗粒分维值随着粘粒含量的增大而增大,且与不均匀系数和曲率系数有良好的非线性关系。在此基础上,讨论了粒度分维所具有的工程地质意义。最后指出粒度分维体现了土体工程地质性质的本质,可以考虑作为土体分类的一个合理指标。     

冻土粒度成分的分形结构特征及其意义

本据分形理论，研究了冻土粒度成分的分形结构特征，结果表明，冻土的分维介于２和３之间，平均值为２．６左右。分维的大小揭示了作这自组织系统的冻土的形成演化特征，分维可作为描述冻土粒度成分的参数。     

活动断裂的分形结构特征

依据分形理论分析了活动断裂带几断裂系，水系及断层泥粒度分布的分形结构特征，指出断裂系及水系分维值的大小体现了活动断裂的结构复杂程度和构造活动性特征，探讨论了断层泥分维值同断层运动特征与基物理力学性质的关系，分维是定量研究活动断裂的一种度量指标。     

Textural and Geochemical Characteristics of Proglacial Sediments: A Case Study in the Foreland of the Nelson Ice Cap, Antarctica

This paper presents a detailed study on the textural and geochemical characteristics of the proglacial sediments near the edge of modern Nelson Ice Cap, Antarctica. The grain size distributions of the proglacial sediments are characteristic of glacigenic deposits, but very different from those of aeolian and lacustrine sediments. Moreover, the grain size distributions of the proglacial sediments are fractal with a dimension of about 2.9, and the fractal dimensions can be used as another summary statistical parameter for quantifying the relative amounts of coarse and fine materials. Correlations between the absolute element abundances of the proglacial sediments are very weak due to mineral partitioning and other effects of glacial processes, but correlations between the element/Rb ratios are statistically significant. This finding indicates that element/Rb ratios can be used to reduce or eliminate the effects of glacial processes, evaluate geochemical data and determine the sediment provenance in the for     

Late Pleistocene and early Holocene drainage events in the eastern Fehmarn Belt and Mecklenburg Bight,SW Baltic Sea

The Fehmarn Belt is a key area for the Late Pleistocene and Holocene development of the Baltic Sea as it was a passage for marine and fresh water during its different stages. The pre‐Holocene geological development of this area is presented based on the analysis of seismic profiles and sedimentary gravity cores. Late Pleistocene varve sediments of the initial Baltic Ice Lake were identified. An exceptionally thick varve layer, overlain by a section of thinner varves with convolute bedding in turn covered by undisturbed varves with decreasing thicknesses is found in the Fehmarn Belt. This succession, along with a change in varve geochemistry, represents a rapid ice‐sheet withdrawal and increasingly distal sedimentation in front of the ice margin. Two erosional unconformities are observed in the eastern Mecklenburg Bight, one marking the top of the initial Baltic Ice Lake deposits and the second one indicating the end of the final Baltic Ice Lake. These unconformities join in Fehmarn Belt, where deposits of the final Baltic Ice Lake are missing due to an erosional hiatus related to a lake‐level drop during its final drainage. After this lake‐level drop, a lowstand environment represented by river deposits developed. These deposits are covered by lake marls of Yoldia age. Tilting of the early glacial lake sediments indicates a period of vertical movements prior to the onset of the Holocene. Deposits of the earliest stages of the Baltic Sea have been exposed by ongoing erosion in the Fehmarn Belt at the transition to the Mecklenburg Bight.     

Glacial advance,occupation and retreat sediments associated with multi‐stage ice‐dammed lakes: north‐central Alberta,Canada

Ice sheets that advance upvalley, against the regional gradient, commonly block drainage and result in ice‐dammed proglacial lakes along their margins during advance and retreat phases. Ice‐dammed glacial lakes described in regional depositional models, in which ice blocks a major lake outlet, are often confined to basins in which the glacial lake palaeogeographical position generally remains semi‐stable (e.g. Great Lakes basins). However, in places where ice retreats downvalley, blocking regional drainage, the palaeogeographical position and lake level of glacial lakes evolve temporally in response to the position of the ice margin (referred to here as ‘multi‐stage’ lakes). In order to understand the sedimentary record of multi‐stage lakes, sediments were examined in 14 cored boreholes in the Peace and Wabasca valleys in north‐central Alberta, Canada. Three facies associations (FAI–III) were identified from core, and record Middle Wisconsinan ice‐distal to ice‐proximal glaciolacustrine (FAI) sediments deposited during ice advance, Late Wisconsinan subglacial and ice‐marginal sediments (FAII) deposited during ice‐occupation, and glaciolacustrine sediments (FAIII) that record ice retreat from the study area. Modelling of the lateral extent of FAs using water wells and gamma‐ray logs, combined with interpreted outlets and mapped moraines based on LiDAR imagery, facilitated palaeogeographical reconstruction of lakes and the identification of four major retreat‐phase lake stages. These lake reconstructions, together with the vertical succession of FAs, are used to develop a depositional model for ice‐dammed lakes during a cycle of glacial advance and retreat. This depositional model may be applied in other areas where meltwater was impounded by glacial ice advancing up the regional gradient, in order to understand the complex interaction between depositional processes, ice‐marginal position, and supply of meltwater and sediment in the lake basin. In particular, this model could be applied to decipher the genetic origin of diamicts previously interpreted to record strictly subglacial deposition or multiple re‐advances.     

MIS 3时期青藏高原东南部稻城古冰帽冰进事件研究

深海氧同位素3阶段（Marine Isotope Stage 3,MIS 3）是全球气候演化过程中特殊的时期,对深入认识区域古气候、古环境演变具有重要意义。青藏高原东南部稻城古冰帽是第四纪冰川作用历史和古气候研究的理想区域,许多学者在该区进行了冰川地貌学和年代学研究。目前,该区域在MIS 3阶段是否存在冰川前进事件仍存在争论。现着重从洞穴石笋、高原冰芯、海洋沉积、古湖孢粉等记录来总结我国MIS 3阶段的气候环境状况,并搜集高原及周边地区MIS 3阶段冰进事件的记录,结合稻城古冰帽区已发表的MIS 3阶段的年代数据来探讨稻城古冰帽区MIS 3阶段的冰川前进的可能性。结果表明：稻城古冰帽区MIS 3阶段（43~53 ka）发生了大规模冰进事件,这可能是由于该冰帽区处于相对冷湿环境且受到了西南季风的影响。本研究可为区域气候重建与环境演变提供新的依据。     

Time‐transgressive tunnel‐valley infill revealed by a three‐dimensional sedimentary model,Hamburg, north‐west Germany

Deep, elongated incisions, often referred to as tunnel valleys, are among the most characteristic landforms of formerly glaciated terrains. It is commonly thought that tunnel valleys were formed by meltwater flowing underneath large ice sheets. The sedimentary infill of these features is often highly intricate and therefore difficult to predict. This study intends to improve the comprehension of the sedimentology and to establish a conceptual model of tunnel‐valley infill, which can be used as a predictive tool. To this end, the densely sampled, Pleistocene tunnel valleys in Hamburg (north‐west Germany) were investigated using a dataset of 1057 deep wells containing lithological and geophysical data. The stratigraphic correlations and the resulting three‐dimensional lithological model were used to assess the spatial lithological distributions and sedimentary architecture. The sedimentary succession filling the Hamburg area tunnel valleys can be subdivided into three distinct units, which are distinguished by their inferred depositional proximity to the ice margin. The overall trend of the succession shows a progressive decrease in transport energy and glacial influence through time. The rate of glacial recession appears to have been an important control on the sedimentary architecture of the tunnel‐valley fill. During periods of stagnation, thick ice‐proximal deposits accumulated at the ice margin, while during rapid recession, only a thin veneer of such coarse‐grained sediments was deposited. Ice‐distal and non‐glaciogenic deposits (i.e. lacustrine, marine and terrestrial) fill the remaining part of the incision. The infill architecture suggests formation and subsequent infill of the tunnel valleys at the outer margin of the Elsterian ice sheet during its punctuated northwards recession. The proposed model shows how the history of ice‐sheet recession determines the position of coarse‐grained depocentres, while the post‐glacial history controls the deposition of fines through a progressive infill of remnant depressions.     

Refining the pattern and style of Cordilleran Ice Sheet retreat: palaeogeography,evolution and implications of lateglacial ice‐dammed lake systems on the southern Fraser Plateau,British Columbia,Canada

Decay of the last Cordilleran Ice Sheet (CIS) near its geographical centre has been conceptualized as being dominated by passive downwasting (stagnation), in part because of the lack of large recessional moraines. Yet, multiple lines of evidence, including reconstructions of glacio‐isostatic rebound from palaeoglacial lake shoreline deformation suggest a sloping ice surface and a more systematic pattern of ice‐margin retreat. Here we reconstructed ice‐marginal lake evolution across the subdued topography of the southern Fraser Plateau in order to elucidate the pattern and style of lateglacial CIS decay. Lake stage extent was reconstructed using primary and secondary palaeo‐water‐plane indicators: deltas, spillways, ice‐marginal channels, subaqueous fans and lake‐bottom sediments identified from aerial photograph and digital elevation model interpretation combined with field observations of geomorphology and sedimentology, and ground‐penetrating radar surveys. Ice‐contact indicators, such as ice‐marginal channels, and grounding‐line moraines were used to refine and constrain ice‐margin positions. The results show that ice‐dammed lakes were extensive (average 27 km²; max. 116 km²) and relatively shallow (average 18 m). Within basins successive lake stages appear to have evolved by expansion, decanting or drainage (glacial lake outburst flood, outburst flood or lake maintenance) from southeast to northwest, implicating a systematic northwestward retreating ice margin (rather than chaotic stagnation) back toward the Coast Mountains, similar in style and pattern to that proposed for the Fennoscandian Ice Sheet. This pattern is confirmed by cross‐cutting drainage networks between lake basins and is in agreement with numerical models of North American ice‐sheet retreat and recent hypotheses on lateglacial CIS reorganization during decay. Reconstructed lake systems are dynamic and transitory and probably had significant effects on the dynamics of ice‐marginal retreat, the importance of which is currently being recognized in the modern context of the Greenland Ice Sheet, where >35% of meltwater streams from land‐terminating portions of the ice sheet end in ice‐contact lakes.     

The Dubawnt Lake palaeo-ice stream: evidence for dynamic ice sheet behaviour on the Canadian Shield and insights regarding the controls on ice-stream location and vigour

We report evidence for a major ice stream that operated over the northwestern Canadian Shield in the Keewatin Sector of the Laurentide Ice Sheet during the last deglaciation 9000–8200 (uncalibrated) yr BP. It is reconstructed at 450 km in length, 140 km in width, and had an estimated catchment area of 190000 km². Mapping from satellite imagery reveals a suite of bedforms ('flow-set') characterized by a highly convergent onset zone, abrupt lateral margins, and where flow was presumed to have been fastest, a remarkably coherent pattern of mega-scale glacial lineations with lengths approaching 13 km and elongation ratios in excess of 40:1. Spatial variations in bedform elongation within the flow-set match the expected velocity field of a terrestrial ice stream. The flow pattern does not appear to be steered by topography and its location on the hard bedrock of the Canadian Shield is surprising. A soft sedimentary basin may have influenced ice-stream activity by lubricating the bed over the downstream crystalline bedrock, but it is unlikely that it operated over a pervasively deforming till layer. The location of the ice stream challenges the view that they only arise in deep bedrock troughs or over thick deposits of 'soft' fine-grained sediments. We speculate that fast ice flow may have been triggered when a steep ice sheet surface gradient with high driving stresses contacted a proglacial lake. An increase in velocity through calving could have propagated fast ice flow upstream (in the vicinity of the Keewatin Ice Divide) through a series of thermomechanical feedback mechanisms. It exerted a considerable impact on the Laurentide Ice Sheet, forcing the demise of one of the last major ice centres.     

Palaeoenvironmental record of glacial lake evolution during the early Holocene at Sokli,NE Finland

The development of a glacial lake impounded along the retreating, northeastern ice margin of the Fennoscandian Ice Sheet during the last deglaciation and environmental conditions directly following the early Holocene deglaciation have been studied in NE Finland. This so‐called Sokli Ice Lake has been reconstructed previously using topographic and geomorphologic evidence. In this paper a multiproxy approach is employed to study a 3‐m‐thick sediment succession consisting of laminated silts grading into gyttja cored in Lake Loitsana, a remnant of the Sokli Ice Lake. Variations in the sediment and siliceous microfossil records indicate distinct changes in water depth and lake size in the Loitsana basin as the Sokli Ice Lake was drained through various spillways opening up along the retreating ice front. Geochemical data (XRF core‐scanning) show changes in the influence of regional catchment geochemistry (Precambrian crystalline rocks) in the glacial lake drainage area versus local catchment geochemistry (Sokli Carbonatite Massif) within the Lake Loitsana drainage area during the lake evolution. Principal component analysis on the geochemical data further suggests that grain‐size is an additional factor responsible for the variability of the sediment geochemistry record. The trophic state of the lake changed drastically as a result of morphometric eutrophication once the glacial lake developed into Lake Loitsana. The AMS radiocarbon dating on tree birch seeds found in the glaciolacustrine sediment indicates that Lake Loitsana was deglaciated sometime prior to 10 700 cal. a BP showing that tree Betula was present on the deglaciated land surrounding the glacial lake. Although glacial lakes covered large areas of northern Finland during the last deglaciation, only few glaciolacustrine sediment successions have been studied in any detail. Our study shows the potential of these sediments for multiproxy analysis and contributes to the reconstruction of environmental conditions in NE Finland directly following deglaciation in the early Holocene.     

Late Quaternary record of sea-level changes in the Antarctic

The Late Quaternary sediment sequence of the continental margin in the eastern Weddell Sea is well suited for palaeoenvironmental reconstructions. Two cores from the upper slope, which contain the sedimentary record of the last 300 ky, have been sedimentologically investigated. Age models are based on lithostratigraphy and are correlated with the stable isotope record. As a result of a detailed analysis of the clay mineral composition, grain size distributions and structures, this sedimentary record provides the first marine evidence that the Antarctic ice sheet extended to the shelf edge during the last glacial.The variations in volume and size of the ice sheet were also simulated in numerical models. Changes in accumulation rate and ice temperature are of some importance, but the model revealed that fluctuations are primarily driven by changes in eustatic sea-level and that the ice edge extended to the shelf edge during the last glacial maximum. This causal relationship implies that the maximum ice extension strongly depends on the magnitude and duration of the sea-level depression during a glacial period. The results of the sedimentological investigations and of the numerical models show that the Antarctic ice sheet follows glacial events in the northern hemisphere by teleconnections of sea level. Correspondence to: H. Grobe