The Southern Margin of the Late Cainozoic Ice Cap on the Central Plateau of Tasmania

The easternmost extremity of the ice cap that developed in the Tasmanian Central Highlands during the time of most extensive Late Cainozoic glaciation lay on the doleritecapped Central Plateau east and north-east of Lake St Clair. During the Last Glacial Maximum (LGM), the more restricted ice cover included a small discrete ice cap (probably less than 250-300 m thick) that formed on the Central Plateau. The LGM ice limits on the southern part of the Central Plateau, including all five southern outlet valleys, are reported here. Earlier ice limits have been identified in two of these valleys, but on the plateau proper earlier glacial deposits have been generally extensively reworked beyond the LGM limit, such that confirmation of a glacial origin for diamictons on slopes is difficult. South of the plateau, the oldest deposits flooring lower reaches of two outlet valleys indicate that ice flowed southwards directly from the plateau, but later deposits indicate diffluent flow from the Derwent Glacier.     

PEDOGENESIS IN LATE PREHISTORIC INDIAN MOUNDS,UPPER MISSISSIPPI VALLEY

Inceptisols are developed on silt loam, loam, and sandy loam Indian mounds at the Keller Mound Group and Bluff Top Mound in northeastern Iowa. The mounds date to the Allamakee Phase of the Late Woodland Period (ca. 1650–1250 B.P.) and are built with fill obtained from the A, E, and upper B horizons of pre-existing soils (Alfisols). Differences in the morphologic and chemical characteristics of soils on different mounds are attributed to textural differences of the mounds' fill. Coarse-textured mound fill is pedogenically altered at a faster rate than fine-textured fill, but total carbon percentage of the A horizon attains a steady state faster in fine-textured mound fill. Total phosphorus content is used to determine from which horizons of pre-existing soils the specific layers of mound fill originated. Rates and pathways of pedogenesis in mound fill may not provide good analogues for the early stages of soil development in materials that have not undergone previous weathering and subsequent modification by humans. Nevertheless, mound soils are useful benchmarks for some pedologic studies since they provide time lines for evaluating minimum rates for development of argillic and albic horizons, as well as attainment of the Alfisol order.     

末次冰盛期东亚夏季风变化的重庆石笋记录

基于重庆小山岩洞XSY1石笋的5个²³⁰Th年龄和582个氧同位素数据,重建了23134~19345 a B.P.期间分辨率约6.5 a的东亚夏季风变化历史。此石笋δ¹⁸O记录的长期趋势逐渐负偏,在其上叠加了一系列千年-百年尺度季风振荡,呈现为4谷3峰的结构形态。重庆XSY1和南京MSD石笋δ¹⁸O记录在数百年尺度的反相关系表明冰盛期时东亚大陆东部水汽并非来自印度洋。与北高纬记录对比显示东亚季风的增强与减弱基本对应格陵兰温度的升高与降低时期,暗示在冰量最大时期东亚季风与北高纬气候仍密切联系。此外,XSY1的δ¹⁸O与冰芯¹⁰Be通量亦存在明显的对应关系,表明太阳活动对东亚季风的调控作用受冰量边界条件影响较小。功率谱分析结果显示出1011 a、722 a、460 a、337 a和163 a的周期,与太阳活动周期相近,进一步确认太阳活动对东亚季风的驱动作用。石笋XSY1与澳大利亚石笋MC-S2 δ¹⁸O记录在千年尺度呈反相位变化,表明冰盛期时东亚季风与全球其他气候系统的动力联系。

     

Non-classical types of loess

The purpose of this contribution is to describe the sequence of physical and chemical processes resulting in the sediment-type named loess, a fine-grained sediment deposit of universal occurrence. Owing to historical causes, loess has been (and still is) implicitly linked to glacial/periglacial environments among most naturalists. However it is known today that most eolian dust is deflated from tropical deserts. Hence, that sequence of processes is more comprehensive than the former narrow cold scenario. Six examples of different “non-classical” cases (from South America and Europe) that fit well to the loess definition are developed: 1) volcanic loess in Ecuador: pyroclastic eruptions/valley wind/mountain praire/silica structuring; 2) tropical loess in northeastern Argentina, Brazil and Uruguay: deflation of river and fan splays/savanna/iron sesquioxide structuring; 3) gypsum loess in northern Spain: destruction of anhydrite/gypsiferous layers in a dry climate/valley wind/Saharian shrub peridesert/gypsum structuring; 4) trade-wind deposits in Venezuela and Brazil: deflation in tidal flats/trade wind into the continent/savanna/iron hydroxide structuring; 5) anticyclonic gray loess in Argentina: continental anticyclone on plains/anti-clockwise winds and whirls/steppe/carbonate structuring. All these non-classical types conform to the accepted loess definitions and they also share the most important field characteristics of loess such as grain size, friability, vertical or sub-vertical slopes in outcrops, subfusion and others. Other cases can probably be recognized when systematically scrutinized.     

驳施雅风“冰臼”“负球状风化”成因论

施雅风院士最近撰文指出笔者等近年来在中国东部发现的若干"冰臼"并非冰川遗迹,而是花岗岩经"负球状风化"而成。然而,他所谓的"负球状风化说"与当地的气候环境条件和客观存在的事实完全相悖。冰臼是地表负地形之一,现今是"堆积区"而不是"侵蚀区",以现代常见的侵蚀作用产生冰臼的所谓"风说"、"壶说"、"风雨说"、"差异风化说"、"负球状风化"等,都是不可能的。这些假说是对过去业己形成冰臼群进行不同成因推断,是对冰臼群成因的最大误解。冰臼只能由大量冰川融水沿冰川裂隙自上向下,以滴水穿石的方式形成滚流水钻,强烈冲击下伏基岩产生。从河流流水动力学特点上看,急流旋涡主要产生水平力为主,而冰臼的形成主要是垂直力才有可能产生,因此河流流水也是无法产生冰臼的。     

末次冰期亚洲季风千年尺度事件的频谱特征分析

基于神农架永兴洞3支石笋氧同位素记录,拼接重建了末次冰期88~22 ka B.P.平均分辨率达70 a的东亚季风演变序列。本文以小波诊断技术为基础,对去除65°N夏季太阳辐射和72 ka异常事件影响的石笋δ¹⁸O进行了多时间尺度分析。小波频谱分析结果表明,末次冰期亚洲季风具有明显的近8 ka、4 ka、2 ka左右的周期。其中近8 ka周期是唯一一个贯穿整个末次冰期的显著周期。小波方差分析结果也显示该时段仅有1个突出的峰值,对应时间约为7.7 ka。进一步分析发现这个周期组分其实也出现在格陵兰冰芯δ¹⁸O和南极温度变化中,可能被年龄误差和异常事件所掩盖。已有的千年尺度机制难以有力地解释该周期组分,我们利用外差法对轨道参数的周期进行分解,获得16 ka周期,这个周期的一半刚好与发现的8 ka周期相匹配。因此,地球轨道参数单独或共同作用,引起海表温、大冰盖、海洋/大陆生态系统的变化,通过大气、大洋等环流作用,从而产生地球气候系统轨道和千年尺度的振荡。

     

国际油气井钻头进展概述（二）——FuseTek融合钻头与Pexus组合钻头

NOV公司2013年向市场推出FuseTek融合钻头。它将PDC钻头的高钻速与孕镶金刚石钻头的耐磨性结合于一体,适宜于钻进中硬—坚硬、高研磨性地层。FuseTek钻头已广泛应用于刚果、厄瓜多尔、中国、哥伦比亚等国家。应用表明,该新型组合钻头比PDC钻头或牙轮钻头钻进效率提高许多,工作寿命增加1～3倍或更多。Shear Bits公司于2014年推出Pexus组合钻头。该钻头广泛应用于加拿大冰川冰碛物钻进。地层上部硬卵砾石层利用可转动硬质合金齿钻进,下部软砂岩与页岩则运用PDC碎岩。整个冰碛物地层用一个Pexus钻头一钻到底。所述3类组合式钻头（含Kymera钻头）对于未来实现“一个钻头,一口井”的目标有重要意义。     

Dissolved oxygen variations in alpine glacial meltwaters

Recent models of chemical weathering in alpine glacial meltwaters suggest that sulphide oxidation is a major source of solute in the distributed component of the subglacial hydrological system. This reaction requires O₂, and may lower dissolved oxygen levels to below saturation with respect to the atmosphere. This should result in an inverse association between SO₇^2- and dissolved oxygen saturation. However, measurements of O₂ saturation in bulk meltwaters draining the Haut Glacier d'Arolla, Switzerland, show that there is a positive association between SO₄^2- and O₂ saturation. The O₂ content of glacial meltwaters depends on the initial content of snow and icemelt, which may be controlled by the rate of melting, and the kinetic balance between O₂ losses (e.g. sulphide oxidation, microbial respiration) and gains (e.g. diffusion of O₂ into solution).     

东海舟山QZ504孔古生物组合特征及地层划分

东海残留沉积区舟山ＱＺ５０４孔未发现上海地区普遍存在的全新世暗绿色硬粘土层。但通过对该孔微体古生物组合特征的分析与对比，划分了全新世与更新世的更线，反映了气候的变化，证实了滚流对本区的影响。