中国西南山区第四纪冰川堆积物工程地质分类探讨

中国的大陆冰川堆积物几乎都属于巨粒土或块石（漂石）土、碎石土,但因复杂的物质组成和组构特征,各地或同一地区不同成因类型（冰碛、冰水）的堆积物具有极为不同的工程地质性质,其地质体稳定性和地质灾害的易发性存在着显著的差异。我国已有的工程分类框架不能满足当代冰川堆积物甚至其他碎石土（巨粒土）的工程地质和地质灾害研究的需要。中国西南山区冰川堆积物的物质成分、细观结构等的野外调查和室内测试分析结果表明,冰川堆积物的物质成分和组构特征主要表现为:颗粒组成的不均一性和多元性、组构单元的双元性、结构的无序性和胶结性等。冰川堆积物的物质成分和组构特征与其工程性质具有密切的关系,是冰川堆积物工程地质分类的基础。本文探讨了中国西南山区冰川堆积物的工程地质分类问题,提出基于胶结程度和粒度组成的二级分类方案,对冰川堆积物及其他块（漂）石土的工程地质研究和工程实践具有一定指导意义。     

Using postglacial sea level, crustal velocities and gravity-rate-of-change to constrain the influence of thermal effects on mantle lateral heterogeneities

Lateral heterogeneities in the mantle can be caused by thermal, chemical and non-isotropic pre-stress effects. Here, we investigate the possibility of using observations of the glacial isostatic adjustment (GIA) process to constrain the thermal contribution to lateral variations in mantle viscosity. In particular, global historic relative sea level, GPS in Laurentide and Fennoscandia, altimetry together with tide-gauge data in the Great Lakes area, and GRACE data in Laurentide are used. The lateral viscosity perturbations are inferred from the seismic tomography model S20A by inserting the scaling factor β to determine the contribution of thermal effects versus compositional heterogeneity and non-isotropic pre-stress effects on lateral heterogeneity in mantle viscosity. When β = 1, lateral velocity variations are caused by thermal effects alone. With β < 1, the contribution of thermal effect decreases, so that for β = 0, there is no lateral viscosity variation and the Earth is laterally homogeneous. These lateral viscosity variations are superposed on four different reference models which differ significantly in the lower mantle viscosity. The Coupled Laplace Finite Element method is used to predict the GIA response on a spherical, self-gravitating, compressible, viscoelastic Earth with self-gravitating oceans, induced by the ICE-4G deglaciation model.Results show that the effect of β on uplift rates and gravity rate-of-change is not simple and involves the trade-off between the contribution of lateral viscosity variations in the transition zone and in the lower mantle. Models with small viscosity contrast in the lower mantle cannot explain the observed uplift rates in Laurentide and Fennoscandia. However, the RF3S20 model with a reference viscosity profile simplified from Peltier's VM2 with the value of β around 0.2–0.4 is found to explain most of the global RSL data, the uplift rates in Laurentide and Fennoscandia and the BIFROST horizontal velocity data. In addition, the changes in GIA signals caused by changes in the value of β are large enough to be detected by the data, although uncertainty in other parameters in the GIA models still exists. This may encourage us to further utilize GIA observations to constrain the thermal effect on mantle lateral heterogeneity as geodetic and satellite gravity measurements are improved.     

Laurentia crustal motion observed using TOPEX/POSEIDON radar altimetry over land

A new method to estimate the vertical crustal motion from satellite altimetry over land was developed. The method was tested around Hudson Bay, where the observed vertical motion is largely caused by the incomplete glacial isostatic adjustment (GIA) as a result of the Laurentide ice sheet deglaciation since the last glacial maximum (LGM). Decadal (1992–2003) TOPEX/POSEIDON radar altimetry data over land surfaces were used. The results presented here are improved compared to a previous study (Lee, H., Shum, C.K., Kuo, C.Y., Yi, Y., Braun, A., 2008. Application of TOPEX altimetry for solid Earth deformation studies. Terr. Atmos. Ocean. Sci. 19, 37–46. doi:10.3319/TAO.2008.19.1-2.37(SA).) which estimated vertical motion only over relatively flat land surfaces (standard deviation of the height variation <40 cm). In this study, we extended the concept of traditional 1-Hz (one-per-frame) radar altimeter ocean stackfiles to build 10-Hz (10-per-frame) land stackfiles over Hudson Bay land regions, and succeeded in obtaining vertical motion estimates over much rougher surfaces (standard deviation of the height variation <2 m). 90-m C-band Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) is used as a reference surface to select an optimal waveform retracker, to correct surface gradient errors, and to calculate land surface anomalies. Here, we developed an alternative retracker, called the modified threshold retracker, resulting in decadal vertical motion time series over a 1500 km by 1000 km region covering northern Ontario, northeastern Manitoba, and the Great Lakes region which is at the margin of the former Laurentide ice sheet. The average of the estimated uncertainties for the vertical motion is 2.9 mm/year which is comparable to 2.1 mm/year of recent GPS solutions. The estimated vertical motion is compared with other geodetic observations from GPS, tide gauge/altimetry, GRACE, and several GIA models. The data agree best with the laterally varying 3D GIA model, RF3S20 (β = 0.4) whereas the combination of land altimetry solution with other measurements match best with the models RF3S20 (β = 0.0) or RF3S20 (β = 0.2) in terms of mean and standard deviation of the differences. It is anticipated that this innovative technique could potentially be used to provide additional constraints for GIA model improvement, and be applied to other geodynamics studies.     

Ice ages and nuclear waste isolation

The greatest natural threats to the integrity of the geological barriers to nuclear wastes isolated in cavities mined at depths between 400 and 800 m are likely during rapid retreats of future ice sheets. The next major glacial retreat is expected at ca 70 ka, well within the lifetime of high grade nuclear waste, but it is not yet clear how long man's greenhouse effect may delay it.

This contribution discusses the potential problems posed to European waste isolation sites during erosion by ice and over-pressurizing of meltwater and gasses in a lithosphere flexed by major ice sheets. These depend on the target rocks and the location of the site with respect to the ice-streams and margins of future ice sheets of particular size.

No sites are planned under the centres of future ice sheets in Europe where end-glacial earthquakes can be expected to reactivate major faults, nor where ice can be expected to deepen and lengthen fjords along the Atlantic coast. Sites in the Alps may be vulnerable to radical changes in the patterns of glacial troughs. The stability and geohydrology of sites in coastal areas beyond future ice margins are threatened by river gorges when sea level falls ca 125 m or, in enclosed basins like the Mediterranean, ever lower. The greatest problems are likely in lowland regions exposed by the rapid retreat of thick ice fronts where large lakes on or under thick warm-based ice are dammed by more distal cold-based ice. Groundwater in subhorizontal fractures dilated by glacial unloading may reach over-pressures capable of hydraulically lifting megablocks of bedrock with fracture permeability and/or the ice damming them so that less permeable substrates are susceptible to incisions eroded to depths of ca 360 at locations controlled mainly by ice topography, kinematics and history.     

Glacial–interglacial records of the reflectance of sediments from the Norwegian–Greenland–Iceland Sea (Nordic seas)

 The reflectance of sediments (gray level) were measured on 11 sediment cores from the Norwegian–Greenland–Iceland Sea (Nordic seas). The analyzed time interval covers the past five glacial–interglacial cycles. Although the results demonstrate that the gray-level method has a potential for stratigraphic purposes, it is indicated that gray-level changes in the Nordic seas are not necessarily driven by variations in the content of biogenic calcite. A detailed comparison of gray-level values with contents of total CaCO₃ (carbonate) and total organic carbon (TOC) reveals no overall causal link between these proxies. However, specific glacial core sections with layers containing organic-rich sediment clasts as a consequence of iceberg-rafting seem to correlate well with law gray-level values. Of those cores which show relatively high and comparable carbonate values in the last three main interglacial intervals (stages 11, 5.5, and 1), stage 11 is always marked by the highest gray-level values. A close inspection of the surface structure of the foraminiferal tests as well as the conduction of reflectance measurements on these tests leads to the conclusion that enhanced carbonate corrosion occurred during stage 11. The test corrosion not only affected the reflectance of the tests by making them appear whiter, it also seems responsible for the comparatively high gray-level values of the total sediment in stage 11. In contrast, the relatively low gray-level values found in stages 5.5, and 1 are not associated with enhanced test corrosion. This observation implies that variable degrees of carbonate corrosion can have a profound effect on total sediment reflectance. Received: 6 September 1998 / Accepted: 4 April 1999     

1990—2020年中国冰湖变化特征及影响因素

本文基于505 景 Landsat 卫星影像,通过自动化冰湖边界提取与人工目视解译相结合的方法调查了 2000 和 2020年中国境内冰湖的分布与变化,并结合 1990 年冰湖编目数据,分析中国冰湖变化特征及影响因素。 研究表明,19902020 年中国冰湖面积增加(180.1±0.1) km²,增加了 17.9%。 其中,冰川补给湖面积扩张最显著,为 22.9%,而非冰川补给湖的面积仅扩张 4.9%。 1990 2020 年冰湖面积在较高海拔带呈现增长快速的趋势,其中,在海拔 5500 m 以上冰湖面积扩张最大,达 30.5%。 在区域尺度,非冰川补给湖的变化主要受降水量和蒸发量变化的影响,其中蒸发量变化对非冰川补给湖更为显著;气温升高与冰川普遍退缩则是导致冰川补给湖普遍快速扩张的主要原因。     

中国末次冰盛期以来湖泊水量变化及古气候变化机制解释

中国古湖泊数据库收录的42个湖泊,提供的湖泊水量每千年变化的空间信息,可以用来系统分析中国区域末次冰盛期以来大气环流变化的状况.研究结果表明:我国西部从末次冰盛期以来直至全新世中期均为较湿润的气候状况,推测冰期内的湿润条件主要与西风带的降水以及低温低蒸发密切相关,而全新世主要为夏季风降水增加所致;全新世晚期气候趋干明显.我国东部的大部分区域在冰盛期和晚冰期较为干旱;只是在全新世有效降水状况才有大幅度的改善,全新世中期夏季风降水的效应仍然相当显著,控制的范围可达整个中国西部,同时位于现代季风气候区的中国东部,有效降水的峰值区的变化似乎存在从北往南的穿时性,南方有效降水峰值出现在晚全新世.而西南季风区湿润状况的明显改善发生在晚冰期,比东南季风区发生的早,显然这与两个季风系统的相互消长有一定的关系.我国东北区的湿润状况改善的也较早,显示了独特的季风气候机制.     

长江三角洲末次盛冰期的气候波动

通过对长江三角洲东部地区鹤鸣孔第一硬黏土层的孢粉、藻类分析,研究了该地区末次盛冰期的气候波动。结果表明,鹤鸣孔第一硬黏土层含种类较丰富的孢子、花粉和藻类化石,并可以划分为3个孢粉、藻类组合,代表了该地区末次盛冰期气候变化的3个阶段,反映了该地区末次盛冰期并不是一个持续的干冷状况,第一硬黏土层沉积的早期和晚期气候较温暖湿润,针阔叶混交林发育,而中期阶段气候偏冷,植被贫乏。     

沙鲁里山更新世冰川作用及西南季风波动对末次冰期冰川作用的影响

地处南亚季风区的沙鲁里山地区保留有丰富的第四纪冰川作用遗迹。文章通过ESR对冰碛物直接定年,结合冰碛地貌形态及其风化程度差异,结果表明沙鲁里山地区可能经历了4次规模较大的冰川作用。它们的ESR年代大约为19～16kaB.P.,48～43kaB.P.,135kaB.P.和571kaB.P.,分别与深海氧同位素第2、第3、第6、第16阶段对应。自沙鲁里山最早冰川作用(571kaB.P.)以后,该区经历了较大规模的抬升作用。MIS2和MIS4期间西南季风微弱,降水稀少,气温严寒,南亚季风区冰川发育受到一定限制。MIS3早期和晚期夏季风强盛,降水丰富,温度较高,水热平衡状况有利于冰川发育;MIS3中期气温较低,夏季风较强盛,降水较丰富,这种冷湿组合的气候条件有利于冰川发育。南亚季风区,MIS3期间的冰川前进规模不亚于甚至在某些区域超过了末次盛冰期,其主要原因可能是受制于夏季风的降水差异。     

末次冰期最盛期以来长江扬中段古河谷的沉积环境

选择长江扬中段古河谷作为研究对象, 探讨末次冰期最盛期以来的沉积环境.搜集整理了扬中—泰州长江大桥地质勘探钻孔28个, 根据钻孔资料, 绘制了长江古河谷的地质剖面示意图.在其中2个钻孔采集了粒度样品、磁化率样品, 分别用Mastersizer 2000激光粒度仪、BartingtonMS2磁化率仪进行了分析; 在4个钻孔采集了¹⁴C年代样品, 利用液体闪烁计数仪进行测定, 得出了27个年代数据.结果表明: 扬中地区长江古河谷约-61 m以上沉积为末次冰期最盛期以来的沉积; 末次冰期最盛期、晚冰期早期(约12 000 a B.P.), 河流滞留沉积与溯源堆积形成了厚约24 m的河床相砂砾层; -23~-37 m为12 000 a B.P.-8 000 a B.P.时的河漫滩相沉积, 沉积物主要为粉砂及粉砂质黏土, 局部细砂; 8 000 a B.P.-4 000 a B.P.为河口湾环境, 形成河口湾-浅海沉积, 厚度为-17~-23 m, 沉积物主要为粉砂夹粉砂质黏土; -17 m以上为4 000年以来的河口坝、汊道河床沉积及三角洲形成以来的河床、河漫滩沉积.