西藏长青温池波弄贡变质带片麻岩锆石 ELA-ICP-MS U-Pb年龄及地质意义

西藏林芝至通麦一带出露大面积变质岩,变质岩中含长柱状锆石。长柱状锆石晶体形态特征、矿物包裹体、CL图像及Th/U比值在0.1～0.4之间,表明锆石主要来自火山岩,受后期变质流体改造。长柱状锆石ELA-ICP-MSU-Th-Pb年龄为(40.7±0.3)Ma,MSWD=2.35。变质流体改造边缘部分年龄和核部年龄基本一致。长柱状锆石特征及年龄表明长青温池至通麦一带片麻岩原岩为新生代含火山物质的沉积岩而不是元古宙变质基底。     

Reversing buoyancy in turbidity currents: developing a hypothesis for flow transformation and for deposit facies and architecture

A turbidity current that contains fresher or otherwise less dense water than its surroundings may initially be denser than the ambient and propagate as a bottom-hugging flow, but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient seawater. It is proposed that this reversal in buoyancy may be a significant mechanism controlling the structure and facies of turbiditic deposits. Buoyancy reversal followed by lofting may directly affect the relative distribution of fine and coarse material in the deposit, while buoyancy reversal itself may mediate the transformation between dilute and highly-concentrated suspension flows, particularly in distal regions, and thus lead to the formation of complex turbiditic beds: in particular, the generation of distal co-genetic debrites may be expected. Similar transformations occur within dilute pyroclastic density currents, where a mobile, basal concentrated flow, termed a surge-derived pyroclastic flow, develops through rapid sedimentation from the suspended load of the overlying surge. The physical mechanisms involved in these processes are discussed, leading to the proposal of some associated facies models; these are compared with field data from the Northern Apennines, with some striking similarities being noted as well as some differences. On the basis of this discussion, some directions are suggested for future experimental and modelling work on the topic.     

生物硅的生成与溶解速率的研究——以胶州湾为例

营养盐的含量与元素间的比值直接控制着生态系统的生产力和浮游植物的种类组成.近岸海区硅藻可占初级生产的75%,但其生长速率受Si(OH)4含量的限制.胶州湾浮游植物的物种组成以硅藻为主.用29Si同位素示踪培养方法,采用四极杆质谱同位素稀释技术同时测定了胶州湾硅的生成速率与溶解速率.胶州湾生物硅(BSi)的含量为0.90～1.14 μmol/L,岩成硅(LSi)的含量为46.3～52.3 μmol/L.岩成硅是生物硅的约50倍.胶州湾BSi的含量处于世界近岸海区的低值范围,LSi的含量与LSi/BSi的比值均处于高值区.BSi的绝对生成速率为4～6 nmol/L*d,比生成速率为6～17/d.BSi的绝对溶解速率为<9 nmol/d,比溶解速率为<23/d.进一步开展胶州湾不同季节水体中BSi的生成速率与溶解速率的研究,是深入认识海湾浮游植物生长限制及其资源可持续利用的基础.     

高分辨率合成孔径雷达卫星反演风场资料在中国近海风能资源评估中的应用研究

由于海上测风非常昂贵,实地测风资料严重不足,而卫星反演海面风场资料可以有效地弥补这一缺陷,对近海风能资源评估具有至关重要的意义。近年来,欧洲太空局2002年3月发射的Envisat卫星搭载合成孔径雷达（SAR）图像产品在欧洲近海风能资源评估中得到了广泛应用。文中探讨了空间分辨率约1 km×1 km的SAR卫星反演海面风场资料应用于杭州湾近海风能资源评估的技术方法,通过杭州湾海域的实测风速与SAR卫星反演海面风速数据的对比分析发现：（1）14个实测站点中13个站的相对误差小于20%,其中7个站的相对误差小于10%,平均标准差为2.29 m/s;（2）以SAR卫星反演风速数据为基础计算的风能参数（形状参数和尺度参数）与实测数据计算结果的一致性较高;（3）将该数据同化进入WRF数值模式中,与控制试验相比,大部分检验站点的风速相关系数明显提高,标准差和相对误差也得到改善。SAR卫星反演风场资料可用于中国的近海风能资源评估。     

Measurements and Modelling of the Wind Speed Profile in the Marine Atmospheric Boundary Layer

We present measurements from 2006 of the marine wind speed profile at a site located 18 km from the west coast of Denmark in the North Sea. Measurements from mast-mounted cup anemometers up to a height of 45 m are extended to 161 m using LiDAR observations. Atmospheric turbulent flux measurements performed in 2004 with a sonic anemometer are compared to a bulk Richardson number formulation of the atmospheric stability. This is used to classify the LiDAR/cup wind speed profiles into atmospheric stability classes. The observations are compared to a simplified model for the wind speed profile that accounts for the effect of the boundary-layer height. For unstable and neutral atmospheric conditions the boundary-layer height could be neglected, whereas for stable conditions it is comparable to the measuring heights and therefore essential to include. It is interesting to note that, although it is derived from a different physical approach, the simplified wind speed profile conforms to the traditional expressions of the surface layer when the effect of the boundary-layer height is neglected.     

Contaminant fluxes from point and diffuse sources from abandoned mines in the River Tamar catchment, UK

Acid mine waters have the potential to seriously impair the environmental quality of aquatic systems long after mining activities have ceased. This detailed study of dissolved and particulate metal fluxes from adits, drains and streams in the River Tamar catchment, southwest England, showed that seven specific sources, of the 25 adits and streams surveyed, accounted for more than 75% each of the 13 t a^− 1 Fe, 4.3 t a^− 1 Mn, 4.2 t a^− 1 Cu, 3.6 t a^− 1 Zn and 1.4 t a^− 1 As that we estimated to be discharged annually from the abandoned metalliferous mining area centred around Calstock and Gunnislake. Upstream of this study area, widespread multi-metallic mineralisation contributed to the flux of Fe, Mn, As, Co, Cu and Zn within the River Tamar. Simple mass balance calculations indicated that a large proportion (≥ 50% for most dissolved and particulate metals) of the metal flux in the River Tamar was unaccounted for by our survey, and therefore is likely to have an important diffuse component, which is subject to ongoing investigations. Potential impacts of mine contamination on the estuarine environment are discussed. The study provided information necessary to prioritise monitoring and remediation efforts in the context of sustainable catchment management.     

Impact of earthquakes on agriculture during the Roman-Byzantine period from pollen records of the Dead Sea laminated sediment

The Dead Sea region holds the archives of a complex relationship between an ever-changing nature and ancient civilisations. Regional pollen diagrams show a Roman-Byzantine period standing out in the recent millennia by its wetter climate that allowed intensive arboriculture. During that period, the Dead Sea formed laminites that display mostly a seasonal character. A multidisciplinary study focused on two earthquakes, 31 BC and AD 363, recorded as seismites in the Ze’elim gully A unit III which has been well dated by radiocarbon in a previous study. The sampling of the sediment was done at an annual resolution starting from a few years before and finishing a decade after each earthquake. A clear drop in agricultural indicators (especially Olea and cereals) is shown. These pollen indicators mostly reflect human activities in the Judean Hills and coastal oases. Agriculture was disturbed in large part of the rift valley where earthquake damage affected irrigation and access to the fields. It took 4 to 5 yr to resume agriculture to previous conditions. Earthquakes must be seen as contributors to factors damaging societies. If combined with other factors such as climatic aridification, disease epidemics and political upheaval, they may lead to civilisation collapse.     

Palaeoecological,archaeological and historical data and the making of Devon landscapes. I. The Blackdown Hills

This paper presents the first systematic study of the vegetation history of a range of low hills in SW England, UK, lying between more researched fenlands and uplands. After the palaeoecological sites were located bespoke archaeological, historical and documentary studies of the surrounding landscape were undertaken specifically to inform palynological interpretation at each site. The region has a distinctive archaeology with late Mesolithic tool scatters, some evidence of early Neolithic agriculture, many Bronze Age funerary monuments and Romano‐British iron‐working. Historical studies have suggested that the present landscape pattern is largely early Medieval. However, the pollen evidence suggests a significantly different Holocene vegetation history in comparison with other areas in lowland England, with evidence of incomplete forest clearance in later‐Prehistory (Bronze?Iron Age). Woodland persistence on steep, but poorly drained, slopes, was probably due to the unsuitability of these areas for mixed farming. Instead they may have been under woodland management (e.g. coppicing) associated with the iron‐working industry. Data from two of the sites also suggest that later Iron Age and Romano‐British impact may have been geographically restricted. The documented Medieval land management that maintained the patchwork of small fields, woods and heathlands had its origins in later Prehistory, but there is also evidence of landscape change in the 6th–9th centuries AD. We conclude that the Blackdown Hills area was one of many ‘distinctive subregions’, which due to a combination of edaphic, topographic and cultural factors could qualify as an eco‐cultural region or ‘pays’. It is argued that the use of such eco‐culturally distinctive regions or pays can provide a spatial and archaeological framework for palaeoecology, which has implications for landscape research, designation and heritage management.     

Creek enlargement in a low‐energy degrading saltmarsh in southern England

A low‐energy saltmarsh in the Beaulieu River Estuary, southern England was investigated. A geomorphological survey revealed that the creek bank geometry was characterized by the presence of cantilevers, a result of the protection provided by roots over the upper part of the bank. The saltmarsh deposits, consisting mainly of clay and organic matter, have a high resistance to flow‐induced erosion. Short‐term hydrographic deployments revealed that the tidal currents and waves recorded were insufficient to cause erosion of the bank surface. However, pin measurements over a 2‐year period revealed that the tidal creeks within the saltmarsh did experience bank erosion, particularly below the cantilevers, in spite of this low‐energy setting. Bank face erosion was therefore considered to be related to long‐term processes. The bases of the cantilevers were found to be located at a precise level, in relation to the tides. Water level data over a 2‐year period were examined against erosion measured below the cantilevers. The results suggest that the erosion on the bank faces, particularly below the cantilevers, is associated with the frequency of water level variations and long‐term submergence/emergence cycles, which can decrease the bonds between the particles and enable erosion by low tidal and wind‐wave currents within this low‐energy environment. This mechanism is probably responsible for tidal creek enlargement via erosion of the bank face and subsequent bank failure, a process which acts over a long temporal scale (1–10 years). Copyright © 2010 John Wiley & Sons, Ltd.