Isolating quartz-dominated OSL signal of rock slice by using pulsed stimulation: Implications for dating burial age of cobbles

Although the OSL signal sourced from quartz is expected to be more stable and bleached more rapidly than the IRSL signal sourced from feldspar in a general sense, the former is much less investigated than the latter for rock surface related luminescence dating. It is mainly due to the difficulty in isolating quartz-dominated OSL signals from rock slices, and the low sensitivity and non-fast component dominated OSL signals for quartz in most of rocks. In merit of the sub-conduction band transition of trapped electrons of feldspar under both green light stimulation and IR stimulation at elevated temperature (Jain and Ankjӕrgaard, 2011), it is expected that the contribution of feldspars to the green light stimulated luminescence could be substantially reduced by a prior IR stimulation at elevated temperature. Meanwhile, more fast-component dominated quartz OSL signal (if there is any) could be obtained by green light stimulation (Bailey et al., 2011). Therefore, in this study, we investigated the feasibility of using the post-IR pulsed green stimulation, which is performed at 25 °C (PGLSL₂₅) following two IR stimulations (IR₅₀IR₂₂₅), to isolate the quartz-dominated OSL signals from rock slices of granite cobbles for burial dating. The decay characteristics of stimulation curve, characteristic saturation dose and thermal stability of the pIR₅₀IR₂₂₅ PGLSL₂₅ signal suggest that this signal is quartz-dominated, but still not fast-component dominated. We tentatively validated the equivalent dose (D_e) measurement protocol by dose recovery experiment. The luminescence-depth profiles show that the bleaching depths of pIR₅₀IR₂₂₅ PGLSL₂₅ signals are slightly smaller than or close to that of the IR₅₀ signals, while they are much shallower for the pIR₅₀IR₂₂₅ signals. The pIR₅₀IR₂₂₅ PGLSL₂₅ procedure enables multiple D_e values determined from luminescence signals, with different bleachabilities and stabilities, from both feldspars and quartz in one measurement, which is of potential for buried age dating of cobbles.     

Dating of megaflood deposits in the Russian Altai using rock surface luminescence

Catastrophic drainage of ice-dammed lakes in the Altai Mountains has been inferred from geomorphological evidence in the Katun Valley (Russia), and is presumed to have occurred during the Pleistocene. The sedimentary features have been difficult to date directly, due to the absence of organic carbon, and the improbability that luminescence signals in sand grains would be reset during transport. However, the development of rock-surface luminescence dating provides a new opportunity to date the features: clasts have a different transport history to sand grains, and their luminescence depth profiles can be inspected for evidence of bleaching before burial. Here we investigate two sites in the Altai Mountains, and use rock-surface luminescence burial dating to constrain the age of the megaflood deposits. In the Katun Valley, we sampled granite cobbles from a frozen sediment clast emplaced as a dropstone within a massive megaflood gravel terrace. Burial ages for the clasts range from 16.7 to 21.4 ka, with a mean age of 19.8 ± 1.5 ka. This represents the depositional age of the fluvial sediments that preceded the lake outburst flood, (and hence places a maximum age on the catastrophic flood). Clasts sampled from mega-ripples in the Kurai Basin are shown to have a mid-to-late Holocene burial age, which is not consistent with the possible origin of these features during a catastrophic drainage of a glacier-dammed lake. Instead, the burial age of the Kurai Basin sediments may reflect local-scale periglacial or seismic processes along the Kurai Fault Zone.     

软土地区双线区间盾构隧道施工对周边地表以及建筑物沉降的影响

研究盾构隧道施工对周围地面以及建筑物沉降造成的影响,是软土地区盾构隧道安全施工和正常运营的基础课题。为了分析宁波轨道交通5号线同德路站—石碶站区间双线盾构隧道施工对周边地表和建筑物的影响,本文在建立盾构隧道动态施工过程三维有限元模型的基础上,基于地表以及建筑物沉降数值模拟结果与现场监测值的对比,分析了隧道开挖对隧道周围地表沉降与建筑物沉降的影响。结果表明,掘进完成时,开挖方向沉降槽往上行线隧道方向偏移、呈现倒梯形形态,横断面影响区域为距离双线隧道轴线中心小于3倍隧道直径;上行线在下行线开挖后并不会增加地表沉降,但增大了沉降槽宽度;下行线到达前产生的沉降占最终累计沉降的67%;当盾构掘进面刚到达建筑物时、建筑物的倾斜方向与盾构掘进方向一致,当盾构掘进面离开建筑物时、建筑物将沿着盾构掘进的反方向倾斜;建筑物两侧沉降值较中部沉降值降低了83%;双线贯通后建筑物沉降呈“U”形分布,最大沉降量发生在远离隧道一侧距建筑物中心0.5 m处。     

四川昭觉县中部乡镇表层土壤硒地球化学特征

硒元素是人体必需的微量元素之一,食用富硒农产品是人体获取和补充硒元素的主要途径,调查区域硒地球化学特征是有效地利用富硒土地资源以及开发富硒农副产品的重要依据。本文选择四川省昭觉县域内较为重要的农耕乡镇采集表层土壤样品,采用原子荧光光谱法、X射线荧光光谱法、电感耦合等离子体质谱/发射光谱法等方法测定1328件土壤、19件玉米及20件土豆中硒等地球化学指标含量,利用相关分析与统计学等方法,结合距离加权反比插值法,探讨研究区硒含量、分布和影响因素等地球化学特征,评价土壤与作物的富硒情况及安全性。结果表明：(1)研究区表层土壤硒含量范围为0.04～1.50mg/kg,平均值为0.33mg/kg,划定富硒土壤面积为7.23km~2,占全区土壤面积的30.31%,玄武岩发育的土壤硒含量最高,平均值为0.4mg/kg,表明区内地质背景与土壤硒含量密切相关,区内富硒土壤主要受含玄武岩夹苦橄岩、凝灰质砂泥岩的峨眉山玄武岩组地层控制;(2)不同的用地类型和土壤类型对硒元素的富集能力不同,人为农业活动导致土壤对硒的吸附能力下降,黄棕壤土层中黏粒或铁氧化物等易与硒结合富集;酸性土壤中硒含量与pH值成反比;土壤...     

基于机器学习的表层土壤成矿元素空间预测: 以稀有金属铷元素为例

近些年随着土地质量地球化学调查工作的开展,获取了大量表层土壤样品数据。然而,这些数据也存在一个明显的缺陷,即1∶50 000大比例尺表层土壤数据往往缺少成矿元素。鉴于土壤成矿元素含量对于矿产资源勘查的重要指示作用,尝试基于现有数据对大比例尺表层土壤成矿元素含量提供一个补全方案。以稀有金属铷元素为例,采用随机森林算法把同一区域2 548组1∶250 000小比例尺表层土壤数据按照8∶2的比例随机分为两组,用80%的数据进行训练建模,20%的数据对模型进行验证。采用变量重要性度量排序和构建学习曲线的组合方法优选了8种元素(K、B、Ni、V、Zn、As、Co、Cu)作为预测变量,模型对训练数据和测试数据的拟合优度R²分别达到0.983 2和0.895 6,说明预测变量的优选方法是有效的。随后将1∶50 000表层土壤的上述预测变量数据作为输入变量导入模型中,得到预测的Rb元素含量,预测结果比较符合实际特征。本研究表明将大数据机器学习随机森林算法引入表层土壤地球化学元素含量空间定量预测具有可行性,可进一步拓展土地质量地球化学数据的服务应用维度。     

From pollen percentage to vegetation cover: evaluation of the Landscape Reconstruction Algorithm in western Norway

The Landscape Reconstruction Algorithm (LRA) with the two models REVEALS and LOVE is developed to transform pollen percentage data to vegetation cover. This paper presents the first study to evaluate LRA in a region with large topographic variations within a short distances. The REVEALS model estimates regional vegetation abundance based on pollen assemblages from large lakes (100–500 ha). Pollen surface samples from one large and 28 small lakes are used together with a combination of regionally derived pollen productivity estimates and available estimates from other regions of Europe. The results show a good relationship between REVEALS‐estimated forest cover and vegetation abundance based on the CORINE land‐cover data. The REVEALS results using various sets of pollen assemblages from small lakes were comparable to those using one large lake. Local vegetation abundance using the LOVE model was estimated around 26 lakes. For common taxa, such as Pinus and Poaceae, the LOVE‐based estimates of plant abundance match well with the distance‐weighted plant abundances based on vegetation maps. Our results indicate that the LRA approach is effective for reconstruction of long‐term vegetation changes in western Norway and other regions with high topographic relief when no major gradients exist in the pollen data.     

地表水渗漏对娘子关岩溶泉泉水水质的影响

娘子关泉水作为阳泉市主要的供水水源,受特定地质结构与人为污染等因素的影响,水质呈现逐年恶化的趋势,部分组分含量目前已处于超标或临界超标状态。在分析泉域岩溶水系统地质结构基础上,通过泉域内各主要河流渗漏量实测与水化学测定,采用物理混合方法评价河流渗漏途径对娘子关泉水水质的污染影响程度。     

龙门山晚新生代地表剥蚀量的定量估算

龙门山是青藏高原周边山脉中地形梯度变化最大的山脉.利用数字高程模型(digital elevation models, DEM),采用三维残余面法恢复龙门山晚新生代古残余面DEM,并与现代地形面做差值运算,得到研究区域的剥蚀量地形,进而定量估算青衣江、岷江、沱江和涪江主要水系流域晚新生代的地表剥蚀量.结果表明:龙门山晚新生代地表剥蚀总量为80 500~92 800 km3;岷江流域对龙门山地区剥蚀量贡献率约33.9%~37.1%,其次为涪江(33.6%~38.4%)、青衣江(24.1%~31.9%),沱江流域贡献率为0.4%~0.6%;类似2008年“5·12”汶川地震的次生灾害引发的地表快速剥蚀,是青藏高原东缘龙门山造山带晚新生代地表剥蚀的主要原因.      

pH值对适于页岩气储层的SDBS压裂液性能的影响研究

在低渗、低孔隙率页岩气储层压裂改造过程中,压裂液体系的pH值直接影响地层中的造缝、稳缝效果。pH值对阴离子表面活性剂压裂液的粘度、表面张力和页岩膨胀抑制性影响很大。通过改变阴离子表面活性剂的浓度,测定了在不同pH值条件下压裂液体系基本性能的变化。研究表明：SDBS压裂液体系的粘度随着pH值的增加先增大后减小,在pH值=9时达到最大;体系在pH值=5时降低体系表面张力的能力最好;页岩的膨胀量随着pH值的增大逐渐增大,在pH=7时膨胀量最大,且随着pH值的进一步增大,页岩膨胀量先减小后增大,在pH值=9时膨胀量最小;当体系的pH值一定时,SDBS在临界胶束浓度状态能够最大程度抑制页岩的膨胀。从化学微观角度上分析了pH值对SDBS压裂液性能的影响,有利于SDBS压裂液体系配方优化。     

PDC钻头切削齿布齿设计的新思路

切削齿布齿设计是PDC钻头设计的关键。为提高PDC钻头的钻进效率,综合考虑PDC钻头切削齿的设计特点和切削先后顺序等因素,并且通过对PDC钻头单切削齿实验结果进行分析,提出了以冠部轮廓法线为基准的切削齿布齿设计方法。