Expanding the spectrum of shallow‐marine,mixed carbonate–siliciclastic systems: Processes,facies distribution and depositional controls of a siliciclastic‐dominated example

Most of the present knowledge of shallow‐marine, mixed carbonate–siliciclastic systems relies on examples from the carbonate‐dominated end of the carbonate–siliciclastic spectrum. This contribution provides a detailed reconstruction of a siliciclastic‐dominated mixed system (Pilmatué Member of the Agrio Formation, Neuquén Basin, Argentina) that explores the variability of depositional models and resulting stratigraphic units within these systems. The Pilmatué Member regressive system comprises a storm‐dominated, shoreface to basinal setting with three subparallel zones: a distal mixed zone, a middle siliciclastic zone and a proximal mixed zone. In the latter, a significant proportion of ooids and bioclasts were mixed with terrigenous sediment, supplied mostly via along‐shore currents. Storm‐generated flows were the primary processes exporting fine sand and mud to the middle zone, but were ineffective to remove coarser sediment. The distal zone received low volumes of siliciclastic mud, which mixed with planktonic‐derived carbonate material. Successive events of shoreline progradation and retrogradation of the Pilmatué system generated up to 17 parasequences, which are bounded by shell beds associated with transgressive surfaces. The facies distribution and resulting genetic units of this siliciclastic‐dominated mixed system are markedly different to the ones observed in present and ancient carbonate‐dominated mixed systems, but they show strong similarities with the products of storm‐dominated, pure siliciclastic shoreface–shelf systems. Basin‐scale depositional controls, such as arid climatic conditions and shallow epeiric seas might aid in the development of mixed systems across the full spectrum (i.e. from carbonate‐dominated to siliciclastic‐dominated end members), but the interplay of processes supplying sand to the system, as well as processes transporting sediment across the marine environment, are key controls in shaping the tridimensional facies distribution and the genetic units of siliciclastic‐dominated mixed systems. Thus, the identification of different combinations of basin‐scale factors and depositional processes is key for a better prediction of conventional and unconventional reservoirs within mixed, carbonate–siliciclastic successions worldwide.     

Environmental controls on soil frost activity in the Western Cape mountains,South Africa

This study aims to analyse the environmental controls on soil frost processes in the Western Cape mountains of South Africa. Two microclimatic monitoring stations were established on different substrates at about 1900 m a.s.l. recording air and soil temperature, soil moisture and precipitation over periods of five and two years respectively. Other data available are snow cover estimations and soil textural data. Results show the region to experience surficial diurnal frost only. The frequency of effective frost days in the sandstone areas is extremely limited due to insulation by snow cover and vegetation, effectiveness of the zero-curtain effect and high albedo values of the surface. Irrespective of climatic controls, sandstone-derived sediments are found to be too coarse to develop segregation ice. These strata underlie over 90 per cent of the Western Cape mountains over 1000 m a.s.l. Monitoring on shales indicates 12 and 16 diurnal frost cycles for needle-ice growth for 1993 and 1994, respectively. © 1998 John Wiley & Sons, Ltd.     

湖、库水体N2O排放研究进展

湖、库水体是重要的N₂O排放源,在全球氮素循环及全球气候变化中具有重要作用.本文综述了目前有关湖、库水体N₂O排放研究进展,重点介绍湖、库水体N₂O产生和排放的过程、不同时空尺度的排放特征、N₂O排放的影响因子框架及监测方法.湖、库水体N₂O不仅源于内部微生物硝化作用、反硝化作用、硝化-反硝化耦合作用、脱氮作用以及极少数底栖无脊椎动物代谢过程,同时流域上游河流汇入、地表径流输入、污水排放以及地下水排泄等构成湖、库水体N₂O的重要外源,但目前对内源/外源的相对贡献的定量化研究不足;湖、库水体N₂O排放方式包括扩散、植物传输及少量气泡排放,对水库而言,大坝下游水电涡轮机形成的脱气作用可能是N₂O排放的潜在途径.对文献综合分析表明,湖、库水体N₂O排放通常呈现明显的季节变化（夏季>冬季）和日变化,同时在全球（一般低纬度>高纬度）、区域及水体内部等不同尺度上表现出显著的空间变异性;这种时空变异特征主要受到湖、库自身理化因子（温度、营养盐、溶解氧、C/N、水文）、生物因子（水生植物、藻华）以及陆域人类活动（污水排放、农业活动以及城市化等）的影响;湖、库N₂O排放不同监测方法的差异也是潜在的影响因素,传统的漂浮箱法和薄边界层法均可能低估水体N₂O排放通量,未来需将传统的监测方法与新型的涡度相关法相结合,减小监测方法的不确定性.结合当前湖、库水体N₂O排放的研究不足,建议未来可以从湖、库N₂O产生的微生物机制,区域尺度上人类活动与湖、库群N₂O排放的耦合关系,水陆交错带的产、排过程,变化环境下的湖、库N₂O排放以及监测方法等方面深入研究.     

地壳破裂型式和幔根构造间断面形成的成矿控制(英文)

尽管地壳最上部的构造、岩性和地球化学条件控制着内生金属矿床的就位,然而最大量金属富集的地点和空间分布却常被幔根构造间断面（ｍａｎｔｌｅ ｒｏｏｔｅｄｓｔｒｕｃｔｕｒａｌｄｉｓｃｏｎｔｉｎｕｉｔｙ）所控制。这些构造间断面延长几百到几千ｋｍ,这表明它们是在比地壳最上部更为均质环境的应力分布下产生的。这些构造间断面与其它的近于垂直的深部构造的交切面界定了主要的岩石圈块体并提供了热、岩浆和成矿流体上升的通道。金属趋向于富集在这些块体的角上,以及构造间断面与板块边缘、裂谷构造或造山带的穿插部位。对上述组合型式的幔根构造间断面和它们在地表地质投影的识别,可确定金属聚集有较大潜力的靶区。文章还提供了来自不同地质环境的实例。     

Lithostratigraphic and structural controls of ‘tsavorite’ deposits at Lemshuku,Merelani area,Tanzania

The first study of the Lemshuku ‘tsavorite’ mining district is presented. From bottom to top, the lithostratigraphic column corresponds to a metasedimentary sequence composed of quartzite, fine-grained graphitic gneiss, kyanite-graphite gneiss, biotite-almandine gneiss, metasomatized graphitic gneiss and dolomitic marble. ‘Tsavorite’ occurs in quartz veins and rarely as nodular concretions. Two factors control mineralization: (1) lithostratigraphy, with ‘tsavorite’ in association with pyrite and graphite confined to quartz veins within the metasomatized graphitic gneiss; and (2) structure, with the mineralized veins characteristically controlled by tight isoclinal folds associated with shearing.     

前陆盆地冲断带构造分段特征及其对油气成藏的控制作用

以中国中西部典型前陆盆地为例,分析了典型前陆盆地前陆冲断带的构造分段特征,总结构造分段的主控因素主要包括构造动力学背景、调节构造、构造变形期次与构造叠加、滑脱层与构造变形强度的影响等。中国中西部前陆冲断带的油气勘探成果表明,构造分段特征对不同构造段油气成藏具有明显的影响和控制作用,主要表现为:不同构造段的油气富集层位不同;不同构造段的油气成藏时间及成藏期次特征存在差异,主成藏期也不同。     

Local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern Mount Isa Inlier, Australia: Review and analysis with autocorrelation and weights of evidence

Although major crustal lineaments may play an important role in mineralisation, the relationship between lineaments and mineral deposits can be quite cryptic, and structural controls may vary as a function of scale along lineaments. Major lineaments alone may be of limited use for detailed target generation. The Cloncurry Lineament in the Eastern part of the Mount Isa Inlier is a crustal scale structure defined by potential field-derived ‘worms’. Weights-of-evidence quantifies the association between mineral occurrences and this lineament. Autocorrelation is used to recognise structural controls on mineralisation at different scales, by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot. The weights-of-evidence analysis shows that Au, Au–Cu, Cu–Au and Cu deposits have a positive spatial correlation to the Cloncurry Lineament, which suggests it that acted as a primary crustal scale control on the localisation of Cu and Au through focussing mineralisation systems on a broad scale. However, autocorrelation defines a variety of local structural controls, which can be interpreted as shear zones, variably oriented fault sets, en echelon fault arrays, and potentially the orientation of bedding and/or iron formations which localise fluid flow and mineral deposition at finer scales. The results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the Mt Isa Inlier.     

GPS RTK测量精度定位与质量控制方法

在GPS RTK观测实验和误差分析的基础上,对RTK测量的平面和高程精度进行了定位;针对RTK测量的特点,对其可靠性进行了分析,并针对性地提出了相应的质量控制方案。     

冀中坳陷深县凹陷的生长断层特点及其对沉积的控制作用

众所周知,构造控制沉积,沉积控制储层,但多数沉积相图的编制并没有系统考虑构造对沉积的控制作用,因而造成沉积相或古地理图与同生构造格局不匹配的严重缺陷。这里所指的构造主要是生长断层,而活动方式会对沉积地层有明显的控制作用。深县凹陷的生长断层可以划分为4种模式:晚期活动模式、持续活动模式、间歇活动模式及深部扩展模式。在此基础上,本文根据断层的活动变化特点并结合区域物源分析,系统地讨论了深县地区的生长断层对该区沉积格局的控制作用,在总体沉积格局表现为"南部水下扇、北部三角洲"的基础上,两大沉积体系前缘的同生断层分布控制砂体的进一步展布,呈现出平面顺断朵状分布、剖面垂向楔形叠加的沉积特点。