Evidence for Heinrich event 1 in the British Isles     

Marshall McCabe  Jasper Knight  Stephen McCarron 《第四纪科学杂志》1998,13(6):549-568

In the north Irish Sea basin (ISB), sedimentary successions constrained by AMS ¹⁴C dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle. (i) Marine muds (Cooley Point Interstadial) dated to between 16.7 and 14.7 ¹⁴C kyr BP record a major deglaciation of the ISB following the Late Glacial Maximum (LGM). (ii) Terminal outwash and ice-contact landforms (Killard Point Stadial) were deposited during an extensive ice readvance, which occurred after 14.7 ¹⁴C kyr BP and reached a maximum extent at ca.14 ¹⁴C kyr BP. At this time the lowlands surrounding the north ISB were drumlinised. Coeval flowlines reconstructed from these bedforms end at prominent moraines (Killard Point, Bride, St Bees) and indicate contemporaneity of drumlinisation from separate ice dispersal centres, substrate erosion by fast ice flow, and subglacial sediment transfer to ice-sheet margins. In north central Ireland bed reorganisation associated with this fast ice-flow phase involved overprinting and drumlinisation of earlier transverse ridges (Rogen-type moraines) by headward erosion along ice streams that exited through tidewater ice margins. This is the first direct terrestrial evidence that the British Ice Sheet (BIS) participated in Heinrich event 1 (H1). (iii) Regional mud drapes, directly overlying drumlins, record high relative sea-level (RSL) with stagnation zone retreat after 13.7 ¹⁴C kyr BP (Rough Island Interstadial). Elsewhere in lowland areas of northern Britain ice-marginal sediments and morainic belts record millennial-scale oscillations of the BIS, which post-date the LGM advance on to the continental shelf, and pre-date the Loch Lomond Stadial (Younger Dryas) advance in the highlands of western Scotland (ca. 11–10 ¹⁴C kyr BP). In western, northwestern and northern Ireland, Killard Point Stadial (H1) ice limits are reconstructed from ice-flow lines that are coeval with those in the north ISB and end at prominent moraines. On the Scottish continental shelf possible H1-age ice limits are reconstructed from dated marine muds and associated ice marginal moraines. It is argued that the last major offshore ice expansion from the Scottish mountains post-dated ca. 15 ¹⁴C kyr BP and is therefore part of the H1 event. In eastern England the stratigraphic significance of the Dimlington silts is re-evaluated because evidence shows that there was only one major ice oscillation post-dating ca.18 ¹⁴C kyr BP in these lowlands. In a wider context the sequence of deglacial events in the ISB (widespread deglaciation of southern part of the BIS → major readvance during H1 → ice sheet collapse) is similar to records of ice sheet variability from the southern margins of the Laurentide Ice Sheet (LIS). Well-dated ice-marginal records, however, show that during the Killard Point readvance the BIS was at its maximum position when retreat of the LIS was well underway. This phasing relationship supports the idea that the BIS readvance was a response to North Atlantic cooling induced by collapse of the LIS. © 1998 John Wiley & Sons, Ltd.  相似文献   

广州市居民网络购物频率的影响因素及其空间差异   总被引：1，自引：1，他引：0  

邓清华  薛德升  龚建周 《地理科学》2020,40(6):928-938

基于广州市居民网络购物行为调查问卷和电子地图兴趣点（POI）数据,从全市和不同区位2个空间尺度,运用有序多分类Logistic回归模型探讨了个人社会经济属性、商品特征、空间环境及物流快递4类因素对居民网购频率的影响。研究发现：① 影响因素在不同空间尺度和不同区位产生作用的因子个数、作用强度和作用方向存在差异。影响因子数量在全市域范围最多,远郊区最少。各因子总体上在近郊区和全市域作用强度大,在远郊区最弱。退货服务重要性在近郊区和中心区作用方向相反;② 部分空间环境因子对网购频率有影响,城市化水平、商业中心可达性在全市域范围有影响,居住地城市化水平越高、离商业中心距离越近的居民网购频率越高,支持了创新扩散假说。快递点数量在中心区有影响,居住地快递点数量越多的居民网购频率越高。其它空间环境因子没有显著影响。③ 个人社会经济属性因素对网购频率影响较大,性别、年龄是最重要的影响因子,其次是学历、职业,月收入影响最小。商品特征、快递物流因素各因子在不同区域对网购频率产生较大影响。  相似文献   

星历精度对动态GPS精密单点定位的精度影响分析     

李辉  李建文  朱建华  安治国  李伟峰 《测绘科学》2012,37(3):186-187

不同的精密星历,其精度对GPS动态精密单点定位结果会产生影响,达到什么程度至今还没有确切的答案。本文利用IGS网站给出的不同精密星历数据结合钟差数据,采用GrafNav软件进行不同的组合计算,得出了一些有益的结论。  相似文献   

激光扫描技术在规划竣工测量中的应用   总被引：1，自引：1，他引：0  

孟志义 《北京测绘》2012,(1):64-66,76

规划监督测量包括验线测量和竣工测量两个阶段,本文以竣工测量为研究对象,结合实际工程项目,研究探讨三维激光扫描技术在规划监督测量中应用的可行性,具体流程、质量控制等关键技术。  相似文献   

Controls on mineral deposit occurrence inferred from analysis of their spatial pattern and spatial association with geological features   总被引：4，自引：0，他引：4  

Emmanuel John M. Carranza   《Ore Geology Reviews》2009,35(3-4):383-400

In this paper, point pattern analysis, fractal analysis and Fry analysis were employed to study the spatial pattern of known occurrences of mineral deposits of the type sought, whereas distance distribution method was applied to study the spatial associations between various geological features and known occurrences of mineral deposits of the type sought. In the Aroroy district (Philippines), the results of the applications of these spatial analytical techniques support a conceptual model of district-scale mechanism of geologic controls on low-sulphidation epithermal Au mineralization, which involves a more-or-less regular mesh of interlinked zones of extension faults/fractures at and/or around intersections of NNW- and NW-trending strike-slip faults/fractures. Integration of spatial evidential data layers representing these structural controls and surficial geochemical anomalies, via knowledge-guided application of data-driven evidential belief functions, results in delineation of prospective areas occupying about 25% of the district, in which there is about 70% likelihood of undiscovered occurrences of low-sulphidation epithermal Au deposits.  相似文献   

Mechanisms of hydrogen incorporation and diffusion in iron-bearing olivine   总被引：1，自引：1，他引：0  

Sylvie Demouchy  Stephen Mackwell 《Physics and Chemistry of Minerals》2006,33(5):347-355

The incorporation and diffusion of hydrogen in San Carlos olivine (Fo₉₀) single crystals were studied by performing experiments under hydrothermal conditions. The experiments were carried out either at 1.5 GPa, 1,000°C for 1.5 h in a piston cylinder apparatus or at 0.2 GPa, 900°C for 1 or 20 h in a cold-seal vessel. The oxygen fugacity was buffered using Ni–NiO, and the silica activity was buffered by adding San Carlos orthopyroxene powders. Polarized Fourier transform infrared (FTIR) spectroscopy was utilized to quantify the hydroxyl distributions in the samples after the experiments. The resulting infrared spectra reproduce the features of FTIR spectra that are observed in olivine from common mantle peridotite xenoliths. The hydrogen concentration at the edges of the hydrogenated olivine crystals corresponds to concentration levels calculated from published water solubility laws. Hydrogen diffusivities were determined for the three crystallographic axes from profiles of water content as a function of position. The chemical diffusion coefficients are comparable to those previously reported for natural iron-bearing olivine. At high temperature, hydrogenation is dominated by coupled diffusion of protons and octahedrally coordinated metal vacancies where the vacancy diffusion rate limits the process. From the experimental data, we determined the following diffusion laws (diffusivity in m² s⁻¹, activation energies in kJ mol⁻¹): for diffusion along [100] and [010]; for diffusion along [001]. These diffusion rates are fast enough to modify significantly water contents within olivine grains in xenoliths ascending from the mantle.  相似文献   

新近系研究进展简介   总被引：12，自引：5，他引：7  

王伟铭  邓涛 《地层学杂志》2005,29(2):104-108

新近系各阶全球层型剖面和点位( GSSP)的选定工作近年来取得了许多实质性的进展,至今上新统3个阶的GSSP已全部获得批准,中新统有3个阶获批准、2个阶有望在2 0 0 4年获得通过、1个阶的指示事件尚未确定,有待进一步的工作。除介绍新近系各个阶最新的GSSP内容外,还就中国陆相新近系建阶工作的进展和研究重点作了简要的回顾与展望,认为上新统麻则沟阶、高庄阶和中新统谢家阶有望在命名剖面定义底界的界线层型和点位,中新统保德阶、通古尔阶和山旺阶的底界有待在甘肃临夏盆地、兰州盆地和秦安地区寻找。中国陆相新近系建阶工作的开展与完成,会给中国地层学研究工作带来积极而又深远的影响。  相似文献   

基于PPP和双差网解法的GNSS水汽反演效果分析          下载免费PDF全文

吴琼  涂满红 《气象与减灾研究》2023,46(4):296-303

基于2021年5—7月GPS卫星资料,采用精密单点定位(Precise Point Positioning,PPP)和双差网解两种算法进行了大气可降水量（Precipitable Water Vapor,PWV）反演,利用同址探空水汽资料,对比分析了PPP算法与双差网解法计算的PWV反演精度。结果表明,PPP算法和双差网解法反演出的PWV随时间变化的趋势基本一致。两种算法反演出的PWV结果合理,与探空PWV相比,采用PPP和双差网解两种算法反演的PWV相对偏差均小于2.4 mm、绝对偏差在4 mm以下,均方差约4 mm,与探空PWV相关系数均在0.87以上,均能较好地反映大气中水汽含量的变化情况,两种算法均具备较强的水汽反演能力,双差网解法反演的PWV在相关性、精度上略优于PPP算法。PPP算法可实现单站水汽高时间分辨率反演,对于获取台站高时效、高精度的大气水汽探测产品具备优势。  相似文献   

Searches for small-scale anisotropies from neutrino point sources with three years of IceCube data     

《Astroparticle Physics》2015

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Demonstration of a virtual active hyperspectral LiDAR in automated point cloud classification   总被引：2，自引：0，他引：2  

Juha Suomalainen  Teemu HakalaHarri Kaartinen  Esa Räikkönen  Sanna Kaasalainen 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(5):637-641

In this paper, a measurement system for the acquisition of a virtual hyperspectral LiDAR dataset is presented. As commercial hyperspectral LiDARs are not yet available, the system provides a novel type of data for the testing and developing of future hyperspectral LiDAR algorithms. The measurement system consists of two parts: first, backscattered reflectance spectra are collected using a spectrometer and a cutting-edge technology, white-light supercontinuum laser source; second, a commercial monochromatic LiDAR system is used for ranging. A virtual hyperspectral LiDAR dataset is produced by data fusion. Such a dataset was collected on a Norway spruce (Picea abies) sample. The performance of classification was tested using an experimental hyperspectral algorithm based on a novel combination of the Spectral Correlation Mapper and a region growing algorithm. The classifier was able to automatically distinguish between needles, branches and background, in other words, perform a difficult task using only traditional TLS data.  相似文献