Climatically relevant periodicities in the thickness of biogenic carbonate varves in Spooensee, Switzerland (9740-6870 calendar yr BP)

Accurate determination of the thicknesses of 2717 biogenic carbonate varves from a Swiss lake (Soppensee), spanning the period from about 9740 to 6870 calendar yr BP, allowed the computation of a power spectrum using classical FFT methods. The presence of pronounced peaks at 40-50 and 20-25 yr agrees with the results of other studies on varve thickness and D¹⁴C which have been interpreted as indicating an association between solar forcing and varve thickness. The presence in the Soppensee varve series of an additional peak at 10.9 yr, corresponding to the Schwabe sunspot cycle, lends further support to this hypothesis. Because the Soppensee varves are of biogenic rather than clastic origin, any influence fluctuations in solar irradiance may have had on sedimentation rates is likely to have been exerted via primary production.     

Natural hazards in British Columbia: an interdisciplinary and inter-institutional challenge

 Although British Columbia experiences many natural hazards, there is as yet no unified policy to promote natural hazard management in the province. The problem is not in the quantity and quality of geoscience assessment of natural hazards, but instead, it is suggested, in the isolation of that work from broader risk perspectives and in the lack of clarity of division of responsibilities between various levels of government. The example of recent changes in perception of the terrain stability problem illustrates how natural hazard problems are driven by social and political priorities rather than by geoscience priorities. Received: 22 November 1998 / Accepted: 22 November 1998     

The relationship between formation structure and thickness in the Permo-Triassic succession of the Southern Coalfield, Sydney Basin, New South Wales, Australia

Using trend-surface analysis, the patterns of formation structure and thickness variation in the Permo-Triassic succession of the Southern Coalfield, Sydney Basin, are resolved into geologically meaningful large- and small-scale features. The structural trends correspond to the regional syncline of the southern Sydney Basin and the negative and positive residual domains to smaller-scale structures including the South Bulli and Douglas Park Synclines and the Bulli and Kemira Anticlines. The results of trend-surface analysis and simple linear regression reveal an inverse relationship between structural elevation (relative to sea level) and formation thickness on both a regional and a local scale. This relationship is strongest for the Bulli Coal and the Bald Hill Claystone. In the case of the Bulli Coal, the present-day structural trends and formation thickness trends show a strong inverse correlation and the residuals show a moderate inverse correlation; the correlations between the inferred Middle Triassic structure of the Bulli Coal and formation thickness are even stronger than those involving the present-day structure. These results indicate that structures which were active during the Permo-Triassic and which influenced sedimentation have been preserved in the present-day structure. The persistence of the patterns of structure and thickness variation upward through the Permo-Triassic sequence suggests that sedimentation was controlled by contemporaneous basement subsidence, rather than by short-lived compaction-induced subsidence patterns.     

Sea ice thickness measurement and its underside morphology analysis using radar penetration in the Arctic Ocean

Sea ice, as an important component of the Arctic climate system, has drawn significant sci-entific interest. Sea ice thickness and its morphology have dramatic impacts on ocean-atmos- phere-ice interactions[1—4], which directly affect the exchange proces…     

基于压差式水位传感器的冰层厚度自动监测系统

本自动监测冰厚装置原理,是通过测量冰层底面与冰下水中一固定端之间垂直距离来实现的。该距离是一只浮桶从固定端运动到冰层底面的行程。随浮桶一起运动的压差式水位传感器分别给出浮桶位于固定端和冰层底面的位置,而浮桶的运动则依靠数据采集仪控制浮桶内水泵排吸水改变浮桶的重力来实现,并且该仪器能够记录传感器的信号和设置水泵开关的开、闭时间。为了避免浮桶对冰层厚度变化的影响且浮桶不至于与冰层底面冻结,浮桶只是在测量行程时上浮到冰层底面,其他时间均在固定端位置。文中给出系统的工作原理和现场实测结果的初步分析。     

南海晚新生代地层结构特征、沉积厚度及沉积模式

本文综合地震、钻井及区域地质资料，通过分析地震相参数等，研究南海晚新生代（E3-Q）地层结构特征和沉积厚度变化，建立了晚新生代沉积模式，所取得的研究成果可为南海油气的进一步勘探开发提供有效的基础资料。     

中国西北地区云的分布及其变化趋势

利用1983年7月—2001年9月ISCCP D2云的月平均资料,针对西北地区15种不同类型云的分布特征进行了分析,给出了中、低云量之和以及高云量在3个气候子区的多年变化趋势,初步探讨了其形成机制。结果表明:水层云、冰层云、水雨层云、冰雨层云和深对流云的光学厚度和云水路径值最大;水层云主要出现在天山山区、北疆地区和陕西南部,冰层云主要出现在北疆地区,水雨层云、冰雨层云和深对流云以及水高层云、冰高层云、卷层云的云量高值区在天山—昆仑山—祁连山一带以及陕南和/或陇南地区,因此上述地区也是有利于人工增水作业的地区。近20年中,高云量在3个气候区都呈明显下降趋势,中、低云量之和则呈上升趋势。西北地区云与地气系统之间可能存在这样一个过程:地面气温的升高,促使地面蒸发加剧,从而导致中、低云量增多而使降水增多,同时高云云量减少。     

地质学方法估算准噶尔盆地西山窑组剥蚀厚度

综合利用地层对比法和沉积速率法估算了准噶尔盆地西山窑组剥蚀厚度，用全盆地34条二维区域地震测线资料，估算了西山窑组剥蚀厚度的平面分布特征。利用单井的地质分层和精细年代格架数据，估算了西山窑组的单井剥蚀厚度。对比结果表明，两者剥蚀厚度的估算结果相近，绝对误差最大不超过50m，相对误差在20％以内。估算结果表明，准噶尔盆地腹部西山窑组剥蚀厚度为100-400m，且自北东向南西，剥蚀厚度逐渐增大，在南部剥蚀厚度可大于400m。     

Prediction of Apparent Equivalent Thickness Using the Spontaneous Potential Method and Its Application to Oilfield Development

The upper spontaneous potential produced by oil and gas accumulation is of a stable potential field, and its intensity is directly proportional to the content of the source and inversely proportional to the radius apart from the source. Theoretical research and practical results show that anomalies of spontaneous potential can indicate oil-bearing sandstone bodies and locate the areas of oil and gas accumulation. In oil areas which have fewer reservoir beds, the petroleum reservoir thickness can be predicted by determining the linear relationship between potential intensity and apparent equivalent thickness. In the Weixing （卫星） oilfield, which is devoid of sufficient reservoir beds, its apparent equivalent thickness can be predicted by the linear equation h= -0.19x＋0.74. On the basis of geological research, we use the spontaneous potential method to predict the equivalent thickness, helping in the selection of the most appropriate drill sites to enhance the probability of successful well boring so as to serve the next round development of the oilfield.     

Turbidite bed thickness distributions: methods and pitfalls of analysis and modelling

Turbidite bed thickness distributions are often interpreted in terms of power laws, even when there are significant departures from a single straight line on a log–log exceedence probability plot. Alternatively, these distributions have been described by a lognormal mixture model. Statistical methods used to analyse and distinguish the two models (power law and lognormal mixture) are presented here. In addition, the shortcomings of some frequently applied techniques are discussed, using a new data set from the Tarcău Sandstone of the East Carpathians, Romania, and published data from the Marnoso‐Arenacea Formation of Italy. Log–log exceedence plots and least squares fitting by themselves are inappropriate tools for the analysis of bed thickness distributions; they must be accompanied by the assessment of other types of diagrams (cumulative probability, histogram of log‐transformed values, q–q plots) and the use of a measure of goodness‐of‐fit other than R², such as the chi‐square or the Kolmogorov–Smirnov statistics. When interpreting data that do not follow a single straight line on a log–log exceedence plot, it is important to take into account that ‘segmented’ power laws are not simple mixtures of power law populations with arbitrary parameters. Although a simple model of flow confinement does result in segmented plots at the centre of a basin, the segmented shape of the exceedence curve breaks down as the sampling location moves away from the basin centre. The lognormal mixture model is a sedimentologically intuitive alternative to the power law distribution. The expectation–maximization algorithm can be used to estimate the parameters and thus to model lognormal bed thickness mixtures. Taking into account these observations, the bed thickness data from the Tarcău Sandstone are best described by a lognormal mixture model with two components. Compared with the Marnoso‐Arenacea Formation, in which bed thicknesses of thin beds have a larger variability than thicknesses of the thicker beds, the thinner‐bedded population of the Tarcău Sandstone has a lower variability than the thicker‐bedded population. Such differences might reflect contrasting depositional settings, such as the difference between channel levées and basin plains.