中生代火山岩铀矿与重力场的关系

本文在综合整理中国东南沿海一带区域物化探资料的基础上,对羊洲-下桐市-火轩市-酒港一带中生代火山岩铀矿化与深层构造和物化探异常的关系进行了研究。讨论了莫霍面、区域重力场和深层构造的关系;重力梯度带与火山岩铀矿的关系;重力梯度带内浅部重力异常与铀矿的关系。提出了中生代火山岩型铀成矿带与上地幔变异带、重力梯度带之间有密切相关的分布规律,重力梯度带内的浅部重力异常可以确定铀矿的空间位置等看法。此外,水系沉积物的分析结果也反映出Cu、Pb、Zn、Ag以及Ni、Cr、Co等元素的异常,在重力梯度带内有着特定的展布规律,其空间分布与铀元素也具有密切的联系。     

A review of mathematical models of river planform changes

Different mathematical models of river planform changes exist or are being developed. They are reviewed here by discussing a two-dimensional depth-averaged model, various meander models and a model for the braided Brahmaputra-Jamuna River in Bangladesh. Much emphasis is placed on topics where further research is needed. It is concluded that the models help in understanding the underlying processes, but cannot yet be considered generally valid and easy-to-use software packages. In the hands of experienced geomorphologists or river engineers, however, some of the models do already form valuable tools which allow better predictions of future river planforms.     

GRADIENT MEASUREMENTS OF METHANE FLUX IN LIN''''AN RICE PADDIES

From July to September of 1990,CH_4 flux measurements were made in Lin'an rice paddies using gradient profiletechniques.Some characteristics of the turbulence structure under the stable conditions have been verified in the surfacelayer according to the in situ measurements.The semi-empirical turbulent parameters β_m,β_h and β_c and their changeswith the stability parameter Ri are given.Observed results indicate that CH_4 flux in the rice-paddy is mainly decided bythe methnogenesis and the process of CH4 transport from internal soils to the atmosphere,and that the CH_4 verticaltransfer is depressed in the stable surface layer.The CH_4 flux shows that its obvious diurnal changes,and the meanCH_4 flux are higher in nighttime and lower in daytime,and the peaks appear at about 2000 BST at night and 0300 BSTin the early morning,respectively.The mean value of CH_4 flux is about 4.18±2.3 mg/m~2 h.     

GRADIENT MEASUREMENTS OF METHANE FLUX IN LIN’AN RICE PADDIES*

From July to September of 1990,CH₄ flux measurements were made in Lin'an rice paddies using gradient profile techniques.Some characteristics of the turbulence structure under the stable conditions have been verified in the surface layer according to the in situ measurements.The semi-empirical turbulent parameters β_m,β_h and β_c and their changes with the stability parameter Ri are given.Observed results indicate that CH₄ flux in the rice-paddy is mainly decided by the methnogenesis and the process of CH₄ transport from internal soils to the atmosphere,and that the CH₄ vertical transfer is depressed in the stable surface layer.The CH₄ flux shows that its obvious diurnal changes,and the mean CH₄ flux are higher in nighttime and lower in daytime,and the peaks appear at about 2000 BST at night and 0300 BST in the early morning,respectively.The mean value of CH₄ flux is about 4.18±2.3 mg/m² h.     

外界条件变化对天然气水合物相平衡曲线及稳定带厚度的影响

目前，有关天然气水合物的相关研究越来越多，而天然气水合物相平衡曲线和稳定带厚度的研究也变得越来越重要.本文利用Sloan的CSMHYD程序研究了外界条件变化对天然气水合物相平衡曲线及稳定带厚度的影响.研究结果表明：当天然气水合物中含有其他气体时，除了氮气会使水合物稳定存在的区域变小外；其他气体都会使稳定区域变大，且甲烷含量越少，水合物越容易形成；对于本文中所提到的几种气体，丙烷和硫化氢对相平衡曲线的影响最大；另外，水合物稳定存在的区域会随着盐度增加而变小.地温梯度、水深、海底温度、气体组成和孔隙水盐度对稳定带厚度的影响不同，其中稳定带厚度与地温梯度呈指数相关关系，与水深呈对数相关关系，与海底温度、水合物中甲烷含量及气体组成呈线性相关关系.水深从1 000 m增加到4 000 m时，稳定带厚度增加了大约400 m；水深2 000 m情况下，地温梯度从0.02℃/m到0.1℃/m变化时，稳定带厚度减薄了大约660 m；底水温度从0~17℃的变化过程中，稳定带厚度减薄了大约1000m；在水合物中气体组成从纯甲烷到含20%乙烷时，稳定带厚度增加了大约170m；盐度在0~4.5 wt％的变化中，稳定带厚度减薄了大约130 m.由此可见，在这几种因素中，地温梯度和底水温度对稳定带厚度的影响较大.     

Bedform morphology of salmon spawning areas in a large gravel-bed river

While the importance of river channel morphology to salmon spawning habitat is increasingly recognized, quantitative measures of the relationships between channel morphology and habitat use are lacking. Such quantitative measures are necessary as management and regulatory agencies within the Pacific Northwest region of the USA, and elsewhere, seek to quantify potential spawning habitat and develop recovery goals for declining salmon populations. The objective of this study was to determine if fall Chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Snake River, Idaho, USA, were correlated with specific bedform types at the pool–riffle scale. A bedform differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool–riffle units that were independent of discharge. The vertical location of thalweg points within these units was quantified with a riffle proximity index. Chinook salmon spawning areas were mapped and correlated with the pool–riffle units through the use of cross-tabulation tables. The results indicate that 84% of fall Chinook salmon spawning areas were correlated with riffles (χ² = 57.5, df = 3, p < 0.001), with 53% of those areas located on the upstream side of riffle crests. The majority of Snake River fall Chinook salmon spawning occurred at elevations greater than 80% of the difference in elevation between the nearest riffle crest and pool bottom. The analyses of bedform morphology will assist regional fish managers in quantifying existing and potential fall Chinook salmon spawning habitat, and will provide a quantitative framework for evaluating general ecological implications of channel morphology in large gravel-bed rivers.     

Morphology of step-pools in a wilderness headwater stream: The importance of standardizing geomorphic measurements

The morphology of step-pools and cascades reflect the geological and climatic factors affecting channels in mountain watersheds. This study uses longitudinal and cross-section surveys to describe a headwater stream in the Boston Mountains of the Ozarks Plateau region in Arkansas and develop morphological relationships for comparisons with other regions. In the Bowers Hollow Creek watershed (3.5 km²), located within the boundaries of the Upper Buffalo Wilderness Area, step height and wavelength relationships are generally similar to those reported from other regions. Step-pool reaches were widely distributed in a discontinuous manner throughout the watershed. Average values of the sampled reaches are: reach slopes, 0.105 m/m; width, 6.10 m; crest particle sizes, 440 mm; step heights, 0.87 m; and step wavelengths, 6.62 m. The mean step steepness for the watershed was 0.13, whereas the mean length of a reach step to height ratio was 9:1. A comparison of morphological definitions found that the values of step height and steepness can vary by > 30% according to how step parameters are defined. Step height is particularly sensitive; thus, comparison of step height-based relationships from published data requires great care.     

论"单位涌水量就是导水系数"

单位涌水量是井抽水水位降深换算为1 m时的单井出水量;导水系数是含水层宽度为1 m时,地下水水力坡度为1时的单宽流量.二者之间从定义上看毫无关系,但它们的单位(m3/d·m)(m2/d)是相同的.笔者经过多年探讨和初步试验后发现,单位涌水量就是管井抽水所利用含水层的导水系数.     

Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal

We use daily satellite estimates of sea surface temperature (SST) and rainfall during 1998–2005 to show that onset of convection over the central Bay of Bengal (88–92°E, 14–18°N) during the core summer monsoon (mid-May to September) is linked to the meridional gradient of SST in the bay. The SST gradient was computed between two boxes in the northern (88–92°E, 18–22°N) and southern (82–88°E, 4–8°N) bay; the latter is the area of the cold tongue in the bay linked to the Summer Monsoon Current. Convection over central bay followed the SST difference between the northern and southern bay (ΔT) exceeding 0.75°C in 28 cases. There was no instance of ΔT exceeding this threshold without a burst in convection. There were, however, five instances of convection occurring without this SST gradient. Long rainfall events (events lasting more than a week) were associated with an SST event (ΔT ≥ 0.75°C); rainfall events tended to be short when not associated with an SST event. The SST gradient was important for the onset of convection, but not for its persistence: convection often persisted for several days even after the SST gradient weakened. The lag between ΔT exceeding 0.75°C and the onset of convection was 0–18 days, but the lag histogram peaked at one week. In 75% of the 28 cases, convection occurred within a week of ΔT exceeding the threshold of 0.75°C. The northern bay SST, T _N , contributed more to ΔT, but it was a weaker criterion for convection than the SST gradient. A sensitivity analysis showed that the corresponding threshold for T _N was 29°C. We hypothesise that the excess heating (∼1°C above the threshold for deep convection) required in the northern bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient.     

Fossil nothofagaceous leaves from the Eocene of western Antarctica and their bearing on the origin, dispersal and systematics of Nothofagus

Fossil leaves resembling Nothofagaceae have been investigated from the Eocene of western Antarctica and a new form genus Nothofagofolia is proposed for these kinds of fossils. Some new specimens belonging to this form genus are described. They were collected from the Fossil Hill locality of Fildes Peninsula, King George Island, South Shetland Islands, western Antarctica. Two new species, two new combinations and an unnamed species are reported. A number of published Nothofagus leaf fossils from the same locality are discussed and revised. As a result of these studies of Nothofagus leaf morphology, we conclude that (1) Nothofagus probably originated in high latitudes of the Southern Hemisphere during the middle-late Late Cretaceous and diversified, dispersed gradually to the lower latitudes of the same hemisphere; (2) leaf morphological characters are significant for the systematics of the family Nothofagaceae, especially at the intrageneric level; and (3) extant species of Nothofagus known from southern temperate areas have more primitive leaf morphological characters and lower leaf ranks than those from tropical mountains as well as those of the Fagaceae and Betulaceae. Supported by the Foundation of State Key Laboratory of Palaeobiology & Stratigraphy, Nanjing Institute of Geology and Palaoentology, Chinese Academy of Sciences (Grant No. 013106), the National Natural Science Foundation of China (Grant No. 30670159) and the Fund of Innovation Program by Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences