A note on 10Be‐derived mean erosion rates in catchments with heterogeneous lithology: examples from the western Central Andes

Millennial catchment–mean erosion rates derived from terrestrial cosmogenic nuclides are generally based on the assumption that the lithologies of the parent rock each contain the same proportion of quartz. This is not always true for large catchments, in particular at the edge of mountainous plateaus where quartz‐rich basement rocks may adjoin sedimentary or volcano‐sedimentary rocks with low quartz content. The western Central Andes is an example of this type of situation. Different quartz contents may be taken into account by weighting the TCN production rates in the catchment. We recall the underlying theory and show that weighting the TCN production rate may also lead to bias in the case of a spatial correlation between erosion rate and lithology. We illustrate the difference between weighted and unweighted erosion rates for seven catchments (16 samples) in southern Peru and northern Chile and show variations up to a factor of 2 between both approaches. In this dataset, calculated erosion rates considering only granitoid outcrops are better correlated with catchment mean slopes than those obtained without taking into account the geological heterogeneity of the drained watershed. This dataset analysis demonstrates that weighting erosion rates by relative proportions of quartz is necessary to evaluate the uncertainties for calculated catchment–mean erosion rates and may reveal the correlation with geomorphic parameters. Copyright © 2015 John Wiley & Sons, Ltd.     

New constraints from the Hα line for the temperature of the transiting planet host star OGLE‐TR‐10

The spectroscopic analysis of systems with transiting planets gives strong constraints on planetary masses and radii as well as the chemical composition of the systems. The properties of the system OGLE‐TR‐10 are not well‐constrained, partly due to the discrepancy of previous measurements of the effective temperature of the host star. This work, which is fully independent from previous works in terms of data reduction and analysis, uses the Hα profile in order to get an additional constraint on the effective temperature. We take previously published UVES observations which have the highest available signal‐to‐noise ratio for OGLE‐TR‐10. A proper normalization to the relative continuum is done using intermediate data products of the reduction pipeline of the UVES spectrograph. The effective temperature then is determined by fitting synthetic Hα profiles to the observed spectrum. With a result of T_eff = 6020 ± 140 K, the Hα profile clearly favours one of the previous measurements. The Hα line is further consistent with dwarf‐like surface gravities as well as solar and super‐solar metallicities previously derived for OGLE‐TR‐10.The Hα line could not be used to its full potential, partly because of the varying shape of the UVES échelle orders after flat field correction. We suggest to improve this feature when constructing future spectrographs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Assessing impervious area ratios of grid-based land-use classifications on the example of an urban watershed

ABSTRACT

When applying a distributed hydrological model in urban watersheds, grid-based land-use classification data with 10 m resolution are typically used in Japan. For urban hydrological models, the estimation of the impervious area ratio (IAR) of each land-use classification is a crucial factor for accurate runoff analysis. In order to assess the IAR accurately, we created a set of vector-based “urban landscape GIS delineation” data for a typical urban watershed in Tokyo. By superimposing the vector-based delineation map on the grid-based map, the IAR of each grid-based land-use classification was estimated, after calculating the IARs of all grid cells in the entire urban watershed. As a result, we were able to calculate the frequency distribution of IAR for each land-use classification, as well as the spatial distribution of IARs for the urban watershed. It is evident from the results that the reference values of IAR for the land-use classifications were estimated very roughly and inherited errors of between about 7% and 70%, which corresponds to more than 100 mm increase of direct runoff for the 1500 mm annual average precipitation.

Editor D. Koutsoyiannis; Guest editor E. Volpi     

A test of the isochron burial dating method on fluvial gravels within the Pulu volcanic sequence,West Kunlun Mountains,China

Isochron burial dating with cosmogenic nuclides is used in Quaternary geochronology for dating sediments in caves, terraces, basins, and other depositional environments. However, the method has seldom been rigorously tested against an independent chronology. Here, we report a direct comparison of isochron burial dating with K-Ar and ⁴⁰Ar/³⁹Ar bracketing ages on volcanic flows that sandwich a fluvial gravel layer in the Xinjiang province of northwestern China. The ages agree to within analytical uncertainty, validating the assumptions and physical constants used in the isochron burial dating method.     

鄂尔多斯盆地上三叠统延长组长10油层组沉积特征及物源*

鄂尔多斯盆地上三叠统延长组为大型拗陷湖盆沉积,长10油层组为延长组初始期沉积物。但其物源特征、沉积体系划分、沉积相类型等基础问题尚不清楚,严重制约了全盆地长10油层组的勘探发现。针对这些问题,作者采用了轻重矿物、锆石测年等分析方法,明确了长10油层组主要发育东北、西北、西南三大物源,根据物源特征沉积体系划分为东北、西北和西南沉积体系。综合野外露头、岩心、钻井、测井等资料揭示了长10主要发育河流-三角洲沉积,其中,西北沉积体系主要发育辫状河沉积,东北沉积体系发育曲河流-三角洲沉积,西南沉积体系发育辫状河-三角洲沉积,沉积中心位于太白-宜君一带,为浅湖相沉积。     

Charnock dynamics: a model for the velocity structure in the wave boundary layer of the air–sea interface

We present a unified model of the air–sea boundary layer, which takes account of the air–sea momentum exchange across the sea surface. The recognition of the importance of the velocity shears in the water (which comprise a frictional shear and the Stokes shear due to the wave motion) in determining the sea surface roughness is a distinctive feature of the analysis, which leads to a prediction of the Charnock constant (α) in terms of two independent parameters, namely the wave age and the ratio of the Stokes shear to the Eulerian shear in the water. This expression is used to interpret the large observational variability of the Charnock constant. The 10-m drag coefficient can also be expressed using similar reasoning, and the introduction of a relation in which the ratio of the frictional shear in the water to the frictional shear in the air decreases with the friction velocity yields predictive relations for the variation of the 10-m drag coefficient at very high wind speeds both in the open ocean and in wind–wave tanks. The physical interpretation of this relation is that the production of spray essentially returns momentum from the ocean to the atmosphere, and this process becomes progressively more important as the wind speed increases.     

乌鲁木齐大气污染物的空间分布及地面风场效应

通过对1999—2001年乌鲁木齐市监测站3种污染物浓度的分析,比较深入地掌握了乌鲁木齐市区不同季节污染物的空间分布状况,得出城市首要污染物是PM10,污染物主要在乌鲁木齐市天山区堆积;利用乌鲁木齐城郊地面风场资料、海拔1 000 m高度探空风场资料分析了地面风场常年特征、季节变化特点,得出冬季城中偏南和偏北有辐合性流场,夏季整个城市为辐散性流场;近地层冬季静风频率高;结合污染物的空间分布和高空风场特征,从一个方面解释了乌鲁木齐冬季、夏季污染物浓度变化的原因。     

鄂尔多斯盆地志靖-安塞地区延长组长10储层特征及评价

利用岩心资料、岩石薄片、铸体薄片、压汞资料、扫描电镜、X衍射及核磁共振等资料,对志靖-安塞地区长10储层进行分析,结果显示,志靖-安塞地区长10储层岩性主要为长石砂岩、岩屑质长石砂岩,孔隙类型以粒间孔、长石溶孔以及浊沸石溶孔为主,物性较好,孔隙度、渗透率分别为11.4%、2.35 mD,但非均质性较强.通过对东西部物性差异性形成机理进行研究,认为区内东部地区储层物性优于西部地区,主要是由于东部地区具有良好的物质基础以及来自长9烃源岩更多的酸性物质,促使其溶蚀空隙更为发育造成的.志靖-安塞地区可划分为4类储层,其中Ⅰ、Ⅱ类储层主要发育在东部地区,西部地区少见或不发育,Ⅲ类储层分布面积广,但物性较差,Ⅳ类储层大部分为非有效储层.     

湖南桃源瓦尔岗剖面层序地层框架下的寒武系第10阶旋回地层学研究

很多地层学与沉积学特征,如显生宙较高的海平面位置以及最高的大气圈二氧化碳含量、全球性温暖的气候(温室效应条件)、后生动物骨骼生物礁的贫乏、三叶虫的主导性、典型的方解石海、SPICE碳同位素事件所代表的大洋缺氧事件和大气圈增氧事件,将寒武纪芙蓉世特征化。经过多年的努力,一个全新的芙蓉统年代地层格架已经得到了系统的确立,芙蓉统可以进一步划分为排碧阶、江山阶和没有得到最后定义的第10阶。湖南桃源县瓦尔岗剖面,以丰富的斜坡相三叶虫的发育著称,是全球寒武系芙蓉统第10阶底界GSSP的候选剖面。为了配合第10阶层型剖面的年代地层学研究,在层序地层学框架内,对该剖面第10期地层为主的地层序列进行了较为系统的旋回地层学研究。基于基本的岩相和沉积相的观察与研究,将该剖面沈家湾组中主要归为第10期的大部分地层归为一个三级沉积层序,并进一步划分为两个四级海平面变化层序;该三级沉积层序大致包含48个准层序级别的六级米级旋回,这些米级旋回常常4个一组构成五级旋回(准层序组)而表现出明显的沉积旋回的1∶4的叠加样式,成为较为典型的米兰柯维奇旋回属性而可以作为代表性的"定时器"。结果表明,第10期地层的形成时限大致为4.80Myr(百万年),稍大于地球化学测年得出的4.10Myr(~495.0-489.5Ma);而且层序界面代表的沉积环境变化要超前于阶的界面代表的生物变化。因此,层序地层学框架内的旋回地层学研究,丰富了瓦尔岗剖面的地层学内容。