Geochemical and isotopic characterization of trace fossil infillings: New insights on tracemaker activity after the K/Pg impact event     

《Cretaceous Research》2016

Geochemical and isotopic analyses of the Cretaceous–Paleogene (K/Pg) boundary deposits were conducted at the Caravaca section (External Subbetic, southeast of Spain) in order to evaluate the recovery of the macrobenthic tracemaker community and the bioturbational disturbance. Samples from the infilling material of several lower Danian dark-colored trace fossils (Chondrites, Planolites, Thalassinoides and Zoophycos) located in the uppermost 8-cm of the light upper Maastrichtian strata, as well as samples from the host sedimentary rock of these trace fossils, were analyzed and compared with data from the lower Danian deposits. The values of element ratios indicative of extraterrestrial contamination (Cr/Al, Co/Al and Ni/Al) are higher in the infilling trace fossil material than in the upper Maastrichtian and lower Danian deposits, which suggests a contribution of the ejecta layer. Regarding the isotope composition, the δ¹³C values are lower in the infilling material than in the Maastrichtian host sedimentary rocks surrounding the traces, while the δ¹⁸O are higher in the infilling material. The geochemical and isotopic compositions of the infilling material evidence the unconsolidated character of the sediment, including the red boundary layer. Softground conditions confirm a relatively rapid recovery by the macrobenthic tracemaker community, starting a few millimeters above the K/Pg boundary layer. The mixture of the infilling material of the trace fossils moreover reveals a significant macrobenthic tracemaker activity affecting K–Pg boundary transition sediments that may have significantly altered original signatures.  相似文献   

Landscape pattern and transition under natural and anthropogenic disturbance in an arid region of northwestern China     

《International Journal of Applied Earth Observation and Geoinformation》2016

There is a pressing need to determine the relationships between driving variables and landscape transformations. Human activities shape landscapes and turn them into complex assemblages of highly diverse structures. Other factors, including climate and topography, also play significant roles in landscape transitions, and identifying the interactions among the variables is critical to environmental management. This study analyzed the configurations and spatial-temporal processes of landscape changes from 1998 to 2011 under different anthropogenic disturbances, identified the main variables that determine the landscape patterns and transitions, and quantified the relationships between pairs of driver sets. Landsat images of Baicheng and Tekes from 1998, 2006 and 2011 were used to classify landscapes by supervised classification. Redundancy analysis (RDA) and variation partitioning were performed to identify the main driving forces and to quantify the unique, shared, and total explained variation of the sets of variables. The results indicate that the proportions of otherwise identical landscapes in Baicheng and Tekes were very different. The area of the grassland in Tekes was much larger than that of the cropland; however, the differences between the grassland and cropland in Baicheng were not as pronounced. Much of the grassland in Tekes was located in an area that was near residents, whereas most of the grassland in Baicheng was far from residents. The slope, elevation, annual precipitation, annual temperature, and distance to the nearest resident were strong driving forces influencing the patterns and transitions of the landscapes. The results of the variation partitioning indicated complex interrelationships among all of the pairs of driver sets. All of the variable sets had significant explanatory roles, most of which had both unique and shared variations with the others. The results of this study can assist policy makers and planners in implementing sustainable landscape management and effective protection strategies.  相似文献   

泥河湾侯家窑遗址古河流及环境考古意义     

李蕾  黄华芳  王健  许清海  张聪聪 《沉积学报》2016,34(1):111-119

侯家窑遗址位于泥河湾盆地西北部,自发现至今,历经40余年,但遗址年代和古人类生存环境问题仍悬而未决。本文基于地质地貌观测、电阻率测深、高程测量等工作,试图通过遗址区地层结构和古河流发育情况研究,阐释上述问题。结果如下:①伴随着泥河湾古湖的快速萎缩,在侯家窑遗址区发育了一条源自北部熊耳山、宽逾1 km的古河流。它形成于240 ka B.P.前,消亡于晚更新世初,发育历史贯穿了侯家窑古人类生存阶段的始终。②遗址古文化遗存不是埋藏在湖相泥河湾层中,而是埋藏于距今约224~161 ka的牛轭湖沉积层和壤化黏土层内,表明古人类在此倚河而居长达6万年。③遗址区面向东南的宽阔圈椅状地形,为古人类生存造就了相对温和舒适的地理环境;古河流既为古人类提供了水源,良好的流域生态环境也给古人类提供了富足的食物;熊耳山既是古河流源地,也是优质石料产地,古河流将石料搬运至遗址附近,石器制作便利。因此,在寒冷气候条件下生活的古人类,选择生境较好的侯家窑遗址区倚河而居势成必然。④遗址区古河流发育在易遭侵蚀的泥河湾湖相沉积层之上,河水泥沙含量高、浑浊,唯有遗址附近的牛轭湖区水流缓滞、清澈,而且植物繁茂,是各类动物优先猎食和饮水的地方。但牛轭湖独特的地貌特点,使动物们在急迫情况下难以逃脱,古人类此地围猎,远较他地成功率高。  相似文献   

变化环境下渭河流域水文干旱演变特征剖析   总被引：4，自引：0，他引：4       下载免费PDF全文

任立良  沈鸿仁  袁飞  赵崇旭  杨肖丽  郑培丽 《水科学进展》2016,27(4):492-500

环境变化影响区域水资源的可持续开发利用,导致水文过程出现非平稳特征,需发展非平稳水文干旱评估方法。选取渭河流域为研究区,依据流域内2个水文站、62个雨量站和24个气象站1961-2013年数据,基于可变下渗容量模型定量分离气候变化和人类活动对径流衰减的贡献;采用标准化径流指数（Standardized Runoff Index, SRI）剖析水文干旱时空演变特征;提出多种SRI参数化方案,对比评定各方案表征非平稳干旱的合理性以及环境变化对干旱演变的影响作用。结果表明:自1991年以来渭河流域年径流量呈显著衰减趋势,人类活动是径流演变的主要因素,对咸阳和华县站径流量变化的贡献率分别为-66.7%和-71.0%;时变参数方案计算的干旱指数能合理重建历史水文干旱序列;人类活动是渭河流域1991年以来短历时水文干旱发生的主导因素,气候变化主要影响长历时旱涝的演变趋势。  相似文献   

中国大陆降水时空变异规律——Ⅲ. 趋势变化原因          下载免费PDF全文

任国玉  柳艳菊  孙秀宝  张莉  任玉玉  徐影  张华  战云健  王涛  郭艳君  陈峪  唐国利  郭军 《水科学进展》2016,27(3):327-348

中国大陆现代降水表现出若干长期变化特征,对现代降水趋势性变化的原因,目前还没有很好了解。结合多种资料分析以及前人研究成果,对中国大陆近几十年降水变化趋势的原因进行了探讨,得到以下初步认识:① 现代降水量变化趋势具有明显的地域性差异,全国平均没有表现出显著增加或减少的长期变化,但强降水事件频率和降水量出现明显增多,而小雨事件特别是痕量降水事件显著减少。② 再分析资料表明,最近几十年全国水汽净收支量在一定程度上增加了,实际观测资料显示近地面和对流层中下层空气比湿或大气可降水量出现较明显上升趋势。③ 代用资料序列分析显示,全国大部地区近几十年降水变化仍处于晚近历史时期正常自然波动范围内;近百年观测的降水量序列也表明,黄淮海地区降水具有多重时间尺度相互叠加作用特点,低频自然气候变异的影响信号有清晰表现。④ 人类活动引起的大气中温室气体浓度增加对全国或东部季风区现代降水变化影响的信号,目前仍难以识别;区域性近地面风速减弱导致的雨量观测系统偏差以及大范围气溶胶浓度增加,可能是东部季风区大多数台站观测到的强降水事件频率增加和小雨频率显著减少的两个重要原因。⑤ 主要与城市化影响相关的地面观测资料系统偏差,可以部分解释现有分析表明的短历时强降水事件频率和累计降水量增加现象,同时也很可能是城市台站小雨和痕量降水事件频率明显下降的另一重要原因。  相似文献   

MASNUM-WAM海浪模式集合Kalman滤波同化研究-I.风场扰动对海浪模拟影响   总被引：1，自引：1，他引：0  

孙盟  尹训强  杨永增  吴克俭 《海洋与湖沼》2016,47(6):1091-1100

模式集合样本的代表性和观测信息的可靠性是制约数据同化效果的重要因素,而前者对海浪模式同化的影响尤为显著。由于海浪模式对初始场的敏感性较弱,来自大气的风输入源函数是海浪的重要能量输入,如何合理地对风输入进行扰动,构造海浪的集合模式运行,是实现和改进海浪模式集合Kalman滤波同化的关键问题。为了实现海浪模式集合运行,本文提出了风场的三种集合扰动方案,分别为：纯随机数、随机场和时间滞后的风场扰动方法。本研究利用2014年1月ECMWF全球风场,基于这三种风场扰动方法开展了集合海浪模式的集合运行实验,并统计分析了海浪特征要素（有效波高）和二维波数谱对风场扰动的响应。结果表明,随机场集合扰动方案所构造的风场集合效果最佳,所得海浪模拟结果的集合样本发散度适中,能够较为合理地反映背景误差的统计特征,可用于进一步的集合Kalman滤波海浪数据同化实验。  相似文献   

人为干扰对滨海湿地生态系统的影响   总被引：1，自引：1，他引：0  

杨杰峰  张曼胤  康晓明  李伟  雷茵茹  崔丽娟 《湿地科学与管理》2016,(1):42-45

对滨海湿地生态系统的主要人为干扰方式进行了系统辨识,详细阐述了不同人为干扰方式对滨海湿地生态系统结构、功能及服务的影响。综合分析了人为干扰造成的滨海湿地生态系统的结构改变、功能破坏、服务减少,其中,城市化、工业化进程干扰对滨海湿地生态系统的影响最为严重,并提出了滨海湿地保护对策。  相似文献   

华蓥山中段地区地下水资源量评价   总被引：1，自引：1，他引：0  

康小兵  罗声  许模  刘宏 《中国岩溶》2018,37(4):527-534

四川华蓥山中段地区水流失比较严重,供需矛盾突出,水环境持续恶化,不但影响到居民正常的生产和生活,而且严重影响了该地区国民经济的建设和发展。通过野外调查和综合分析现场收集的资料,总结出华蓥山中段地区地下水资源量流失情况:该区每年流失的水资源量约为0.914 4亿m3,且华蓥山褶皱西翼水流失总量大于东翼,而西翼北端是区内水流失量最严重的区域,其水资源量流失的影响因素主要为气候、社会发展及人类活动等。   相似文献   

Spatiotemporal change patterns of urban lakes in China’s major cities between 1990 and 2015     

Cong Xie  Leiguang Wang  Xing Fang  Wenzhi Liao 《International Journal of Digital Earth》2018,11(11):1085-1102

China has experienced unprecedented urbanization in the past decades, resulting in dramatic changes in the physical, limnological, and hydrological characteristics of lakes in urban landscapes. However, the spatiotemporal dynamics in distribution and abundance of urban lakes in China remain poorly understood. Here, we characterized the spatiotemporal change patterns of urban lakes in China’s major cities between 1990 and 2015 using remote-sensing data and landscape metrics. The results showed that the urban lake landscape patterns have experienced drastic changes over the past 25 years. The total surface area of the urban lakes has decreased by 17,620.02?ha, a decrease of 24.22%, with a significant increase in the landscape fragmentation and a reduction in shape complexity. We defined three lake-shrinkage types and found that vanishment was the most common lake-shrinkage pattern, followed by edge-shrinkage and tunneling in terms of lake area. Moreover, we also found that urban sprawl was the dominant driver of the lake shrinkage, accounting for 67.89% of the total area loss, and the transition from lakes to cropland was also an important factor (19.86%). This study has potential for providing critical baseline information for government decision-making in lake resources management and urban landscape design.  相似文献   

Examining human heat stress with remote sensing technology     

Yang Song 《地理信息系统科学与遥感》2018,55(1):19-37

Heat stress as an environmental hazard which can seriously affect productivity, health, or even survival of individuals has long been studied. Despite the endeavors that have been made to address the issue quantitatively with various heat stress indices, they are often measured at scatter sites. This research devotes to revealing human heat stress within continuous space with remote sensing technology. The study began with the retrieval of dry-bulb temperature from land surface temperature (LST) with empirical models. As wet-bulb temperature was calculated from dry-bulb temperature and relative humidity, discomfort index (DI) as an indicator of heat stress was revealed for the study area at 1 km spatial resolution for three summer days. Results indicated that DI can be derived within continuous space with remotely sensed data, and its spatial distribution can be dramatically affected by relative humidity. Further comparison between DI and LST indicated that LST as a widely utilized indicator of surface thermal condition fails to address human heat stress as environmental factors such as relative humidity are not taken into account.  相似文献