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121.
滇西新生代兰坪盆地和剑川盆地分别位于哀牢山–红河断裂带两侧,青藏高原东构造结内,其沉积过程和构造变形对青藏高原东南缘的构造演化有重要的启示意义。通过对这两个盆地古近纪沉积和构造过程的研究,我们发现兰坪盆地和剑川盆地及邻区的构造变形分为三期:始新世早期的强烈挤压变形、始新世中晚期的伸展变形、渐新世的走滑变形。始新世早期的挤压变形主要表现为兰坪地区的褶皱–冲断系统、哀牢山-红河断裂的逆冲活动和剑川盆地的宽缓褶皱。沉积方面,古新统勐野井组(E_1m)较为稳定的细粒滨湖相沉积转变为始新统宝相寺组(E_2b)较粗的具有前陆盆地性质的河流相沉积,特别是宝相寺组底部发育的一套快速堆积的磨拉石建造,可能是对始新世强烈挤压环境下的沉积响应。始新世中晚期伸展变形体现在盆地的构造环境由早期的挤压环境变为伸展环境和该时期大量富钾岩体和岩脉的侵入,沉积学上,下始新统宝相寺组的河流相转变为中始新统金丝厂组(E_2j)具有快速堆积磨拉石特征的曲流河沉积,极可能是对构造体制变革的沉积响应。渐新世的走滑变形则体现在渐新统的缺失和哀牢山–红河断裂的早期左行走滑。因此,我们认为剑川–兰坪地区在始新世中期和渐新世均发生了显著的运动学转换,这一认识也得到了始新世中期兰坪和剑川盆地物源明显变化的支持。结合青藏高原东南部始新世中晚期岩浆的活动,渐新世大型剪切带(崇山剪切带、高黎贡剪切带)的强烈走滑和保山块体的旋转,我们推测青藏高原东南缘古近纪的构造演化为古新世-始新世早期的挤压、始新世中晚期的伸展、渐新世的转换压缩。 相似文献
122.
地下水硝酸盐(NO3-)污染是一个全球性的环境问题,尤其在农业区普遍存在。地下水中NO3-可以通过交互作用进入地表水中,是地表水NO3-的潜在来源。研究地下水中NO3-的来源及其贡献率对防治周边地表水NO3-污染具有重要意义。本研究以四川盆地农业区河流型水库周边地下水为研究对象,综合运用水文地球化学、多种稳定同位素(δD-H2O和δ18O-H2O,δ15N-NO3-和δ18O-NO3-)、贝叶斯同位素混合模型(SIAR)和人类健康风险评价(HHRA)解析地下水中NO3-的来源与转化过程、不同NO3-来源的贡献率及潜在的人类健康风险。结果表明:丰、枯水期地下水中NO3--N浓度分别为1.24~42.91和0~42.96 mg/L,61%和40%的地下水样品超过了饮用水限值(10 mg/L)。δ15N-NO3-和δ18O-NO3-表明,研究区地下水中NO3-的主要来源为粪肥/生活污水。硝化作用可能是研究区地下水中重要的氮循环过程,存在加剧地下水NO3-污染的风险。SIAR模型得出丰、枯水期地下水中NO3-的主要来源为粪肥/生活污水,贡献率分别为50%和38%。HHRA表明长期饮用研究区NO3-浓度较高的地下水对人类健康具有潜在风险。 相似文献
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124.
黄淮地区一次冷锋暴雨天气过程的预报分析 总被引:1,自引:0,他引:1
利用常规天气图、地面加密资料、数值预报产品、卫星云图和多普勒天气雷达资料等,对2007年7月18-19日出现在黄淮地区的暴雨天气过程进行了综合分析.结果表明:暴雨是高空西风槽、冷锋和副热带高压边缘强盛的西南暖湿急流共同作用产生的;强降水产生在地面中尺度辐合线附近.在高层干冷、低层暖湿的大气不稳定条件下,地面冷空气的侵入触发了不稳定能量的释放,同时低层辐合、高空辐散的高低空配置,引发了强降水的产生.卫星云图和多普勒天气雷达资料在暴雨临近预报中起着重要作用. 相似文献
125.
SONG Bowen ZHANG Kexin CHEN Ruiming WANG Chaowen LUO Mansheng ZHANG Jianyu JIANG Shangsong 《《地质学报》英文版》2013,87(2):528-539
The thick, Eocene to Pliocene, sedimentary sequence in Qaidam Basin at the northern margin of the Tibetan Plateau records the surface uplift history of the northeastern Tibetan plateau. In this study, we present detailed geochemistry, heavy mineral, and clay mineralogy data of the well preserved sedimentary record in the Dahongou section in the northeast of the Qaidam Basin. The results suggest that the sedimentary sequence recorded a 30 Ma young uplift/unroofing event in the northern edge of the Qaidam Basin, which is characterized by high ZTR index value and chlorite content, and low CIW`. The results are consistent with previous sedimentological studies of the Qaidam Basin, which indicated rapid increase of the accumulation rates around 30 Ma. Based on past thermochronological data from the mountains around the Qaidam Basin and the accumulation rates of the Cenozoic basins in the northeastern Tibetan Plateau, we infer a regional uplift and denudation event along the northeastern Tibetan Plateau during early Oligocene (~30 Ma), indicating that the Tibetan Plateau had expanded north-eastward of the study area at that time. 相似文献
126.
岩房湾铅锌矿位于陕西省太白县境内。文章通过矿床的成矿流体及地球化学特征研究,对比同属于风太矿田的八方山—二里河、铅硐山、银母寺等大型铅锌矿,认为岩房湾铅锌矿床成矿流体为中-低盐度、中-低温、含有CO2,N2,CH4等气体的还原性流体体系,并显示出热卤水成因特点。流体包裹体主要包括水溶液包裹体、CO2-H2O-NaCl包裹体、纯CO2包裹体3种类型,为不混溶包裹体群,均一温度高于八方山—二里河等铅锌矿,可能与西坝岩体的侵入有关。氢、氧同位素特征显示成矿流体为岩浆水与变质水的混合,碳、氧同位素特征显示成矿过程中碳质来源于泥盆纪正常海相碳酸盐岩,铅同位素特征显示出造山带与上地壳混合来源的特点。岩房湾铅锌矿成矿流体和同位素特征与同区大型SEDEX型铅锌矿存在着一些差异,不宜笼统将其与同区热水沉积成因大型铅锌矿床归为同一类型。 相似文献
127.
128.
Liu Yonghe Zhang Kexin Zhang Wanchang Shao Yuehong Pei Hongqin Feng Jinming 《Theoretical and Applied Climatology》2013,111(1-2):37-50
Multifractal analysis can provide parameters associated with different scales of rainfall, which may be useful for setting up parsimonious downscaling models of rainfall, or for revealing climate-specific properties. Time series of rain rate with 1-min resolution collected from ten stations over a monsoon watershed in eastern China were used to study the multifractal properties. The power spectra estimated by fast Fourier transform (FFT) and discrete Haar wavelet transform (DWT) showed three scaling regimes: the sub-hourly scaling regime with β?≈?1.2, the scaling regime from 1 h to 1 day with β close to 0.6, and the low-frequency spectra plateau with β?≈?0.1. From the hyperbolic tails of exceeding probability distributions, the estimated values of parameter q c are in 2–2.5, which were consistent with the critical order of K(q) curves. The statistical moments display two main scaling regimes: the high-frequency regime from 3 min to 5 days and the scaling regime beyond 5 days. The scales of 5–10 days seem a transitional regime. The reason that the regimes, revealed by the power spectra, disagree with the statistical moments may be that both FFT and DWT power spectra have limited abilities of analyzing low-frequency scaling but are sensitive to the properties in high-frequency scales. The H values estimated for the regime of sub-hourly scales are larger than 0.4, and the values for the regime 1 h–1 day are close to 0.1. For the low-frequency scales beyond 1 day, negative H is obtained by DWT power spectra. The parameters of universal multifractal models were also estimated. The values of α for the scaling range of 1 min–5 days are 0.486?±?0.047, and for the low-frequency scaling range, its values are 0.808?±?0.323. For the high- and low-frequency scaling ranges, the values of C 1 are 0.5 and 0.169, respectively, which is different from the values for daily rainfall series collected at the same rain gages. 相似文献
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130.
This study provides a reconstruction of the environmental evolution since 128 ka recorded by the lipid biomarkers of the C15–C35
n-alkanes, the C13–C33
n-alkan-2-ones and the C12–C30
n-alkanols isolated from the Tawan loess section, Northwest China. Variations in paleoenvironment are reconstructed from the
values of the carbon preference index (CPI), the average chain length (ACL), the L/H (ratio of lower-molecular-weight to higher-molecular-weight homologues), the n-alkane C27/C31 ratios, and the n-alkan-2-one C27/C31 ratio. These parameters indicate the dominance of grasses over the west Chinese Loess Plateau (CLP) during the late Pleistocene.
Lower values of the CPI and the ACL values, respectively, indicate stronger microbial reworking of organic matter and changes
in plant species, which are both indicative of a warmer-wetter environment. Furthermore, the fluctuations of environment recorded
in the Tawan section exhibit ten phases that show obvious cycles between warm periods and cold intervals. This study reveals
that changes in the biomarker proxies agree well with changes in the magnetic susceptibility and grain size, and it indicates
a huge potential for paleoenvironmental reconstructions by using the n-alkan-2-one and n-alkanol proxies. 相似文献