Environmental magnetic studies of sediment cores from Gonghai Lake: implications for monsoon evolution in North China during the late glacial and Holocene

Environmental magnetic studies were conducted on a 9.42-m-long sediment core from Gonghai Lake, North China. Radiocarbon dating indicates that the record spans the last 15,000 cal year BP. The principal magnetic mineral in the sediments is pseudo-single domain magnetite of detrital origin with minimal post-depositional alteration. Although the variations in the concentration of detrital magnetic minerals and their grain size throughout the core reflect inputs from both soil erosion and eolian dust, it is shown that their climatic and environmental significance changes with time. In the lowermost part of the core, ~15,000–11,500 cal year BP, the magnetic minerals were supplied mainly by bedrock erosion, soil erosion and dust input when climate ameliorated after the cold and dusty last glacial maximum. The increasing magnetic susceptibility (χ) in this interval may indicate a combination of changes in the lake environment together with catchment-surface stabilization and a decreasing proportion of dust input. In the central part of the core, ~11,500–1,000 cal year BP, the detrital magnetic minerals mainly originated from dust inputs from outside the catchment when the lake catchment was covered by forest, and catchment-derived sediment supply (and thus the lake sediment accumulation rate) were minimal. The generally low concentration of magnetic minerals in this part of the core reflects the highest degree of soil stability and the strongest summer monsoon during the Holocene. In the uppermost part of the core, the last ~1,000 years, detrital magnetic minerals mainly originated from erosion of catchment soils when the vegetation cover was sparse and the sediment accumulation rates were high. Within this part of the core the high magnetic susceptibility reflects strong pedogenesis in the lake catchment, and thus a strong summer monsoon. This scenario is similar to that recorded in loess profiles. Overall, the results document three main stages of summer monsoon history with abrupt shifts from one stage to another: an increasing and variable summer monsoon during the last deglacial, a generally strong summer monsoon in the early and middle Holocene and a weak summer monsoon in the late Holocene. The results also suggest that different interpretational models may need to be applied to lake sediment magnetic mineral assemblages corresponding to different stages of environmental evolution.     

“数字测图原理与方法”卓越课程改革与实践

围绕"数字测图原理与方法"本科卓越课程建设,针对课程教学改革、课程实施方案和教学质量评价等方面进行介绍和讨论,对本科卓越课程建设中所涉及的教学理念、教学思路、教学方法和综合实践能力培养进行有益的探讨与实践。     

西安市PM2.5城乡差异及与城市热岛的关联研究

依据一种基于建筑用地比例和土地利用信息熵的城乡站点划分方法,将西安市环境与气象站点划分为城区、郊区和两类乡村站,讨论其PM_2.5的城乡分布特征及与城市热岛效应强度(Urban Heat Island Intensity,UHII)间的相关关系。结果表明,不同季节西安市呈现不同的PM_2.5城乡分布特征和日变化特征,两类乡村站点PM_2.5差异明显且下风向乡村站点(乡村D)对应的UHII_D对城区和乡村的影响程度大于上风向乡村站点(乡村U)对应的UHII_U。在城区较多本地排放的影响下,乡村PM_2.5浓度与 UHII_U(或UHII_D)相关系数均大于城区。随着UHII_D的增加,城乡PM_2.5相对浓度差值(RUPII_D)整体呈下降趋势且UHII_D与RUPII_D在春夏秋季显著负相关。UHII_D增大,城区近地面PM_2.5的水平扩散能力减弱,但PM_2.5的垂直扩散能力较乡村更强,从而UHII_D通过影响PM_2.5的传输扩散特征,进一步影响西安市RUPII_D。     

利用FY-4A卫星光学数据对中国近地面PM2.5浓度的估算和检验分析

对FY-4A卫星的气溶胶光学厚度（AOD）产品进行检验,并根据卫星相关观测资料,通过改进后的PMRS方法,反演得到中国近地面PM_2.5质量浓度网格化分布。结果表明,FY-4A卫星反演不同站点AOD与地基观测网（AERONET）观测结果吻合较好,但存在一定的低估或高估现象,相关系数区间为0.54—0.87。将细粒子比（FMF）以0.4为界进行划分,FMF＞0.4时,拟合结果较FMF≤0.4时更接近于AERONET观测结果;但FMF≤0.4时,卫星反演的AOD稳定性优于FMF＞0.4时。通过引入AOD的大小,改进FMF＞0.4时对细粒子柱状体积消光比（VE_f）的估算算法,并通过改进后的PMRS方法对中国近地面PM_2.5浓度进行逐时反演,其反演结果和地面观测结果相关较好,其中,乌鲁木齐、石家庄和徐州观测点的相关系数均高于0.7,但数值上仍存在高估或低估,误差结果由多种因素决定。空间分布中,卫星反演的中国2019年近地面PM_2.5浓度月均值与近地面观测的结果有较好的对应关系,二者逐月演变趋势基本一致,基本可以反映出中国近地面大气细粒子的空间分布,特别是秋、冬季京津冀周边区域、汾渭平原等污染高值区均与地面观测对应较好。      

舟曲县南峪沟松散固体物源及其对泥石流的补给特征

南峪沟地处特殊的构造部位,特定的地层经长期的内外营力共同作用,形成泥石流松散固体物源。物源类型有重力堆积物和沟床中下游段松散堆积物,其分布相对较集中,对泥石流补给方式表现为坡面冲刷、崩塌、滑坍和流体冲刷;沟域面积和沟道长度与物源量没有明显的对应关系,决定泥石流补给量的主要因素是沟谷形态和山体岩石类型。     

Holocene palaeoflood events recorded by slackwater deposits along the lower Jinghe River valley,middle Yellow River basin,China

Palaeoflood slackwater deposits (SWDs), are the natural record of overbank flooding and are often found within aeolian loess‐soil profiles along the river valleys of the middle Yellow River basin. These pedo‐stratigraphic sequences are studied using a multi‐disciplinarily approach to reconstruct Holocene hydro‐climatic variations. Our field investigations along the lower Jinghe River valley have identified palaeoflood SWDs at several sites along the riverbanks based on sedimentological criteria. Analytical results, including magnetic susceptibility, particle‐size distribution and concentrations of chemical elements, indicate that these well‐sorted palaeoflood SWD beds were deposited from the suspended sediment load in floodwaters. We identify two episodes of extraordinary palaeoflood events along the Jinghe River valley. These hydro‐climatic events were dated to 4200–4000 and 3200–2800 a BP, by using the optically stimulated luminescence method in combination with archaeological dating of retrieved anthropogenic remains, and with pedo‐stratigraphic correlations with the previously studied Holocene pedo‐stratigraphy in the Jinghe River drainage basin. The flooding events are therefore considered to be a regional expression of known climatic events in the northern hemisphere and demonstrate Holocene climate was far from stable. This study provides important data in understanding the interactions between regional hydro‐climatic systems and global change in semi‐arid and sub‐humid regions. Copyright © 2012 John Wiley & Sons, Ltd.     

中天山巴仑台地区变形花岗岩类LA-ICP-MS-U-Pb年代学及其构造意义

本文对巴仑台地区中天山南北边缘的变形花岗岩体进行了详细的锆石LA-ICP-MS-U-Pb年代学研究。中天山北缘花岗质片麻岩中岩浆锆石结晶年龄为630.0±5.0 Ma,代表了中天山微陆基底的新元古代岩浆事件年龄;其变质增生锆石边的年龄为440.9±3.3 Ma,精确限定了中天山北缘洋盆闭合与碰撞造山作用的时代为早志留世。中天山南缘糜棱岩化花岗闪长岩中岩浆锆石结晶年龄为389.5±3.2 Ma,指示出中天山南缘洋壳在中泥盆世向北俯冲形成陆缘岩浆弧;其变质增生锆石边的年龄为362.1±4.3 Ma,精确限定了中天山南缘洋盆闭合与碰撞造山作用的时代为晚泥盆世末期。研究结果还表明中天山微陆块具有年龄为2.5Ga和1.8Ga的古老结晶基底。     

水平井分段完井不同分段模式优化研究

运用势的叠加原理和镜像反映原理,导出了水平井任意分段模式下井筒与油藏渗流耦合产能计算模型,用该模型可以计算任意分段模式下来平井的产能,通过对比不同分段模式下的水平井产能,可以对分段进行优化,从而指导分段完井方案的制定.研究结果表明:当打开程度一定时,不同分段模式对产量影响不大;产量随着打开程度的提高而增加,但当打开程度大于40％时,产量增幅趋于平缓,因此,打开程度必须大于打开临界程度,这样既减小了因分段而牺牲的产量又达到了分段的目的;井筒摩阻对产量影响较大,在进行分段优化时,必须考虑井筒摩阻的影响,从而优选盲管段的位置.     

煤层受古河流冲刷的预测及探讨

古河流冲刷是影响煤矿规划、设计、开采方式不同的常见原因之一,并直接影响煤炭回收率、原煤质量。本文系统地分析其产生的原因及其危害,并结合生产实践,提出三种比较合理的预测方法。三种不同方法预测的综合利用,使之能更好的为生产服务。