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71.
Studies of Recent ostracodes around the area of South America shed little light on the paleoenvironmental interpretation of Miocene assemblages. Consequently, interpretations of the Miocene ostracode assemblages must be supplemented using evidence from better documented taxa. Benthic foraminifera in samples from the Lower to Middle Miocene Brasso Formation at Brasso Village, Trinidad, have previously been used to distinguish three sample groupings (Beneath, Within and Above) around an oxygen minimum zone (OMZ), this being a layer of water within which dissolved oxygen concentrations can be as low as 0.1–1.0 mL/L. Using these same samples and the foraminiferal assemblage demarcations relative to the OMZ, this paper examines the associated and rich ostracode fauna of the Brasso Formation.The mean recovery of ostracode valves per sample was approximately three times greater in the Within OMZ sample group than in either of the Beneath OMZ or Above OMZ groups, perhaps reflecting the exclusion of macro-predators from within the OMZ. Individual rarefaction of species richness S to N = 300 valves was conducted for each sample group. This showed that S did not differ between the sample groups, ranging from 22.4 to 24.8. We used all ostracode species to model group separation. Based upon the Mahalanobis’ criterion, we obtained significant group separation using a model with four taxa: Munseyella ex gr. minuta, Argilloecia posterotruncata, Munseyella sp. and Xestoleberis sp., while a fifth, Argilloecia spp., provided a significant but minor increase in separation probabilities over all groups. The two most abundant species (Bradleya sp., Gangamocytheridea reticulata) were thus not the best species for detecting the OMZ. Platycopid ostracodes of the genus Cytherella were found throughout the section, rather than concentrated within the OMZ, which contradicts the Platycopid Signal Hypothesis that OMZs are characterized by platycopid dominance. The total distribution and turnover of both ostracodal and foraminiferal assemblages were compared and contrasted quantitatively using a total assemblage turnover index (ATI) and the paleoenvironmental importance evaluated. The correlated between-sample ATI is for both groups lowest within the OMZ. 相似文献
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文章在计算水溶液化学组份平衡分布及其pH值的基础上,分析和讨论了封闭系统中CaCO3溶解或沉淀所引起的水化学后果,并依据计算数据和借助作图的办法得出了如下结论,即CaCO3溶解会使水溶液pH值增大,H2CO3含量减少;相反,CaCO3沉淀会使水溶液pH值减小,H2CO3含量增多。 相似文献
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依据文本对勘的方法,从图片和文字两个方面对《北京西山地质志》中、英文本进行比较研究。图片方面,英文本作了大量的增补和解说,内容更为详实准确。文字方面,中、英文本目录存在明显差异。英文本序言和注释有其独到的价值和意义。中文本正文的细节增补,应是吸收了当时的最新研究成果。中、英文本比较研究为认识《北京西山地质志》的价值与地位提供了准确可靠的学术依据。 相似文献
77.
Satellite remote sensing provides an alternative to time-consuming and labor intensive in situ measurements of biophysical variables in agricultural crops required for precision agriculture applications. In orchards, however, the spatial resolution causes mixtures of canopies and background (i.e. soil, grass and shadow), hampering the estimation of these biophysical variables. Furthermore, variable background mixtures obstruct meaningful comparisons between different orchard blocks, rows or within each row. Current correction methodologies use spectral differences between canopies and background, but struggle with a vegetated orchard floor. This background influence and the lack of a generic solution are addressed in this study.Firstly, the problem was demonstrated in a controlled environment for vegetation indices sensitive to chlorophyll content, water content and leaf area index. Afterwards, traditional background correction methods (i.e. soil-adjusted vegetation indices and signal unmixing) were compared to the proposed vegetation index correction. This correction was based on the mixing degree of each pixel (i.e. tree cover fraction) to rescale the vegetation indices accordingly and was applied to synthetic and WorldView-2 satellite imagery. Through the correction, the effect of background admixture for vegetation indices was reduced, and the estimation of biophysical variables was improved (ΔR2 = 0.2–0.31). 相似文献
78.
地形地表的不规则起伏对雷电电磁场传输的影响 总被引:2,自引:0,他引:2
为了研究地形地表的不规则起伏(简称粗糙地表)对雷电电磁场传播的影响,首先利用二维分形方法模拟了粗糙地表,然后利用Barrick表面阻抗理论和Wait近似算法研究了粗糙地表对雷电电磁场传播的影响。结果表明,粗糙地表对地闪首次回击垂直电场的影响较小,但对继后回击存在明显的影响。随着粗糙度的增加,继后回击垂直电场峰值的衰减程度明显增加,且时域脉冲波形上升沿时间增大。如继后回击电磁场传播100 km,均方高为30 m的粗糙地表(电导率σ=0.1 S/m)引起时域电磁场波形上升沿时间额外增约1.5μs,电场峰值额外减小约12%,且其影响随着地面电导率的减小而增大。因此,在实际工作中应考虑复杂地形地表对闪电定位系统探测精度和效率的可能影响。 相似文献
79.
K. M. Hiremath 《Journal of Astrophysics and Astronomy》2006,27(2-3):367-372
We use 130 years data for studying correlative effects due to solar cycle and activity phenomena on the occurrence of rainfall
over India. For the period of different solar cycles, we compute the correlation coefficients and significance of correlation
coefficients for the seasonal months of Jan–Feb (JF), Mar–May (MAM), June–Sept (JJAS) and Oct–Dec (OND) and,annual mean data. We find that: (i) with a moderate-to-high significance, Indian rainfall is correlated with the sunspot activity and,
(ii) there is an overall trend that during the period of low sunspot activity, occurrence of rainfall is high compared to
the period of high sunspot activity.
We speculate in this study a possible physical connection between the occurrence of the rainfall and the sunspot activities
and, the flux of galactic cosmic rays. Some of the negative correlations between the occurrences of the sunspot and rainfall
activities obtained for different solar cycle periods are interpreted as effects of aerosols on the rain forming clouds due
to either intermittent volcanic eruptions or due to intrusion of interstellar dust particles in the Earth’s atmosphere. 相似文献
80.