Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

Redistribution of fallout radionuclides in Enewetak Atoll lagoon sediments by callianassid bioturbation

The lagoon sediments of Enewetak Atoll in the Marshall Islands contain a large selection of fallout radionuclides as a result of 43 nuclear weapon tests conducted there between 1948 and 1958. Studies of the burial of fallout radionuclides have been conducted on the islands and in several of the large craters, but studies of their vertical distribution have been limited to about the upper 20 cm of the lagoon sediments. We have found elevated fallout radionuclide concentrations buried more deeply in the lagoon sediments and evidence of burrowing into the sediment by several species of callianassid ghost shrimp (Crustacea: Thalassinidea) which has displaced highly radioactive sediment. The burrowing activities of callianassids, which are ubiquitous on the lagoon floor, facilitate radionuclide redistribution and complicate the fallout radionuclide inventory of the lagoon.     

Increased dissolved oxygen in Pacific intermediate waters due to lower rates of carbon oxidation in sediments

Concentrations of dissolved oxygen in the ocean seem to correlate well with climate instabilities over the past 100,000 years. For example, the concentration of dissolved oxygen in Pacific intermediate waters was considerably higher during Pleistocene glacial periods than it is today. This has been inferred from the presence of bioturbated sediments, implying that oxygen levels were sufficient for burrowing organisms to live. Today, basins in the northeastern Pacific Ocean are floored by laminated sediments implying lower oxygen levels, which may be explained by reduced ventilation. Here we report a recent return to bioturbated sediments in the northeastern Pacific Ocean since the late 1970s. From the carbon isotope composition of benthic foraminifers living in the sediment, we infer a twofold decrease in the carbon oxidation rate occurring within sediments, equivalent to an increase in dissolved oxygen concentration of 15-20 micromoles per litre. These changes, at the edges of the Santa Barbara, Santa Monica and Alfonso basins, are coincident with a change in North Pacific climate which has reduced upwelling by 20-30% and increased sea surface temperatures by 1.5-3 degrees C. This suggests that climate effects on surface productivity, reducing the supply organic matter to sediments, may have had a greater effect on benthic oxygen levels than changes in ocean circulation patterns.     

基于邮件协议的NAT穿越远程升级与控制系统

提出了一种新的实现网络地址转换(NAT)穿越的方案:利用邮件服务器的POP3和SMTP协议传递相关IP地址和端口等信息,并通过"打洞"技术,实现客户端和设备结点之间的UDP连接.相比于利用程序服务器进行"打洞"从而实现NAT穿越的方案,该方案运营成本更低,系统稳定性更高,系统可移植性更强.基于该NAT穿越方案,结合多设备结点、多种网络环境的情况,引入固件升级模块,设计与实现了一个物联网智能设备的远程升级和控制系统,并对系统的稳健性进行了探讨.     

Robust judgement of inter-object distance by an arthropod

Animals use several strategies for depth vision, reflecting the constraints imposed by body size, the structure of the visual system and the visual geometry of the environment. Arthropods in particular have restricted depth perception, because they are small and possess closely set, low-resolution compound eyes. Yet, here we show that fiddler crabs defending their burrows from conspecifics can judge how close other crabs are to their burrow. When confronted with small dummy crabs, the burrow owners assess the dummy's position and motion relative to their burrow and not relative to themselves--in other words, by using an allocentric rather than an egocentric frame of reference. Irrespective of their own distance from the dummy, the likelihood that the crabs rush back to defend their burrow increases strongly as the dummy approaches the burrow. In addition, the mean dummy-burrow distance at which the crabs respond is constant and independent of the dummy's direction of approach. We propose that to solve this sophisticated task of relative distance judgement, the crabs combine visual information on dummy position and direction with information on burrow location acquired during path integration. In doing so, the crabs, like humans, make clever use of the visual geometry of their environment.     

不同底播时间和苗种规格的魁蚶潜沙率差异性分析

【目的】了解魁蚶(Scapharca broughtonii)生物学特性,为更好地开展魁蚶底播增殖工作提供数据支持。【方法】采用围格实验生态学方法研究4种规格魁蚶在4个不同底播时间下的潜沙率差异性。【结果】不同底播时间下,在实验开始前24h内,1cm、1.5cm和2cm组魁蚶潜沙率差异不显著,但均高于2.5cm组;在底播36h后4种规格魁蚶潜沙率无显著差异。底播时间选在9:00、13:00和17:00时,同规格的魁蚶潜沙率无明显差异,均高于在21:00时底播。【结论】在底播时应选取潜沙速率快且潜沙率较为稳定的规格作为埋栖型贝类的底播规格,根据实验结果建议选择2cm魁蚶做为底播苗种;底播时间应根据当地海区潮汐情况确定,选择平流期开展底播,最佳底播时间应选取17:00,尽量避开夜间底播。     

Eocene lizard from Germany reveals amphisbaenian origins

Amphisbaenia is a speciose clade of fossorial lizards characterized by a snake-like body and a strongly reinforced skull adapted for head-first burrowing. The evolutionary origins of amphisbaenians are controversial, with molecular data uniting them with lacertids, a clade of Old World terrestrial lizards, whereas morphology supports a grouping with snakes and other limbless squamates. Reports of fossil stem amphisbaenians have been falsified, and no fossils have previously tested these competing phylogenetic hypotheses or shed light on ancestral amphisbaenian ecology. Here we report the discovery of a new lacertid-like lizard from the Eocene Messel locality of Germany that provides the first morphological evidence for lacertid-amphisbaenian monophyly on the basis of a reinforced, akinetic skull roof and braincase, supporting the view that body elongation and limblessness in amphisbaenians and snakes evolved independently. Morphometric analysis of body shape and ecology in squamates indicates that the postcranial anatomy of the new taxon is most consistent with opportunistically burrowing habits, which in combination with cranial reinforcement indicates that head-first burrowing evolved before body elongation and may have been a crucial first step in the evolution of amphisbaenian fossoriality.     

Hydrothermal recharge and discharge across 50 km guided by seamounts on a young ridge flank

Hydrothermal circulation within the sea floor, through lithosphere older than one million years (Myr), is responsible for 30% of the energy released from plate cooling, and for 70% of the global heat flow anomaly (the difference between observed thermal output and that predicted by conductive cooling models). Hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 Myr old. But in view of the relatively impermeable sediments that cover most ridge flanks, it has been difficult to explain how these fluids transport heat from the crust to the ocean. Here we present results of swath mapping, heat flow, geochemistry and seismic surveys from the young eastern flank of the Juan de Fuca ridge, which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km. Our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops. We find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies.     

Host-parasite 'Red Queen' dynamics archived in pond sediment

Antagonistic interactions between hosts and parasites are a key structuring force in natural populations, driving coevolution. However, direct empirical evidence of long-term host-parasite coevolution, in particular 'Red Queen' dynamics--in which antagonistic biotic interactions such as host-parasite interactions can lead to reciprocal evolutionary dynamics--is rare, and current data, although consistent with theories of antagonistic coevolution, do not reveal the temporal dynamics of the process. Dormant stages of both the water flea Daphnia and its microparasites are conserved in lake sediments, providing an archive of past gene pools. Here we use this fact to reconstruct rapid coevolutionary dynamics in a natural setting and show that the parasite rapidly adapts to its host over a period of only a few years. A coevolutionary model based on negative frequency-dependent selection, and designed to mimic essential aspects of our host-parasite system, corroborated these experimental results. In line with the idea of continuing host-parasite coevolution, temporal variation in parasite infectivity changed little over time. In contrast, from the moment the parasite was first found in the sediments, we observed a steady increase in virulence over time, associated with higher fitness of the parasite.     

Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system

Continental erosion controls atmospheric carbon dioxide levels on geological timescales through silicate weathering, riverine transport and subsequent burial of organic carbon in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins is however limited by the organic carbon load capacity of the sediments and organic carbon oxidation in continental margins. At the global scale, previous studies have suggested that about 70 per cent of riverine organic carbon is returned to the atmosphere, such as in the Amazon basin. Here we present a comprehensive organic carbon budget for the Himalayan erosional system, including source rocks, river sediments and marine sediments buried in the Bengal fan. We show that organic carbon export is controlled by sediment properties, and that oxidative loss is negligible during transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the organic carbon is recent organic matter captured during transport, which serves as a net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon buried in oceanic sediments. High erosion rates in the Himalayas generate high sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the observed extreme organic carbon burial efficiency. Active orogenic systems generate enhanced physical erosion and the resulting organic carbon burial buffers atmospheric carbon dioxide levels, thereby exerting a negative feedback on climate over geological timescales.     

Metamorphic devolatilization of subducted marine sediments and the transport of volatiles into the Earth's mantle

Volatiles, most notably CO2, are recycled back into the Earth's interior at subduction zones. The amount of CO2 emitted from arc volcanism appears to be less than that subducted, which implies that a significant amount of CO2 either is released before reaching the depth at which arc magmas are generated or is subducted to deeper depths. Few high-pressure experimental studies have addressed this problem and therefore metamorphic decarbonation in subduction zones remains largely unquantified, despite its importance to arc magmatism, palaeoatmospheric CO2 concentrations and the global carbon cycle. Here we present computed phase equilibria to quantify the evolution of CO2 and H2O through the subduction-zone metamorphism of carbonate-bearing marine sediments (which are considered to be a major source for CO2 released by arc volcanoes). Our analysis indicates that siliceous limestones undergo negligible devolatilization under subduction-zone conditions. Along high-temperature geotherms clay-rich marls completely devolatilize before reaching the depths at which arc magmatism is generated, but along low-temperature geotherms, they undergo virtually no devolatilization. And from 80 to 180 km depth, little devolatilization occurs for all carbonate-bearing marine sediments. Infiltration of H2O-rich fluids therefore seems essential to promote subarc decarbonation of most marine sediments. In the absence of such infiltration, volatiles retained within marine sediments may explain the apparent discrepancy between subducted and volcanic volatile fluxes and represent a mechanism for return of carbon to the Earth's mantle.     

Mechanisms of particle vertical diffusion in sediment-laden flows

Diffusion coefficient of natural sediments andeffects of lift force and gradient in particle velocity fluctua-tions were investigated through using a closed kinetic model.Comparison against experimental data of Einstein ＆ Chien(1955) validated the model. The diffusion coefficient εyy ofmedium and large sediments distinctly exceeds fluid eddyviscosity V^tf, while εyy of fine sediments approximately equals V^tf. In the measured region of 0.03＜y/H＜0.4, εyy/V^tf increaseswith the distance from the wall decreasing. Combined effectsof lift force and gradient in particle velocity fluctuationschange sediment gravitational settling remarkably below y/H=0.2, and need to be accounted for describing sedimentdiffusion in this region.     

水力吸泥-离心脱水疏浚过程的环境特征分析

城市建成区的中、小河道底泥污染特征为重金属和有机污染富集于浮动性表层底泥中，以水力吸泥－离心脱水组合疏浚工艺用于清理此种底泥的环境特征分析，采用现场疏浚操作时，同步进行相关物流与水体采样监测的方法进行，结果显示：水力吸泥的疏浚泥浆其污染物组成与原状底泥一致；泥浆经离心脱水后，805以上的颗粒物可回收于含固率谪于70％的脱水泥饼中；脱水泥饼颗粒物的污染程度显著低于原状底泥；离心上清液浓缩了底泥中的各种污染物，其直接排入河道是造成水力疏浚过程水体水质损害的最主要因素；离心上清液可经混凝－澄清－过滤过程有效地净化，研究证明该组合疏浚工艺配套离心上清液澄清后，可符合相关类型受污梁底泥疏浚的环境保护要求，且大部分疏浚物流可就地利用于浸地或农田。     

Extracellular electron transfer via microbial nanowires

Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(iii) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(iii) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(iii) reducers in many environments, must directly contact Fe(iii) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, to aid in establishing contact with the Fe(iii) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(iii) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell-cell interactions, and for bioengineering of novel conductive materials.     

缢蛏稚贝的爬行行为及盐度对其钻穴能力的影响

缢蛏稚贝的爬行行为可分成扭动、滑行和转动三种类型,其中以扭动最典型。这些运动方式不仅有利于稚贝的钻穴生活,对其漂移行为也有一定的意义,当低盐度培养的稚贝移至较“高盐度”培养时,其钻穴能力受到明显的抑制,而较“高盐度”条件下培养的稚贝,盐度的变化对钻穴活动的影响不明显。文中还探讨了蛏苗生产应注意的问题。     

Methane formation from long-chain alkanes by anaerobic microorganisms.

Biological formation of methane is the terminal process of biomass degradation in aquatic habitats where oxygen, nitrate, ferric iron and sulphate have been depleted as electron acceptors. The pathway leading from dead biomass to methane through the metabolism of anaerobic bacteria and archaea is well understood for easily degradable biomolecules such as carbohydrates, proteins and lipids. However, little is known about the organic compounds that lead to methane in old anoxic sediments where easily degradable biomolecules are no longer available. One class of naturally formed long-lived compounds in such sediments is the saturated hydrocarbons (alkanes). Alkanes are usually considered to be inert in the absence of oxygen, nitrate or sulphate, and the analysis of alkane patterns is often used for biogeochemical characterization of sediments. However, alkanes might be consumed in anoxic sediments below the zone of sulphate reduction, but the underlying process has not been elucidated. Here we used enrichment cultures to show that the biological conversion of long-chain alkanes to the simplest hydrocarbon, methane, is possible under strictly anoxic conditions.     

Retarding and manipulating of DNA molecules translocation through nanopores

Nanopores are emerging sensitive sensors that can detect and analyze single charged molecule. Nanopores present a promising approach for sequencing human gen- ome below US$1,000 because of its superior performance, such as high throughput and low cost. However, a dominant bottleneck, that is, the high translocation speed of DNA molecules, has to be overcome. This property decreases accuracy of nanopore sensors to the single-base level. In this review, we mainly introduce the recent research works of retarding and manipulating of DNA motion through nanopores by actively control of three forces, which are the driving force, interaction force between nanopore and molecule, and exterior drag force. Lastly, conclusion and further outlook are presented pore-based DNA sequencing on future directions of nano- technology.     

The abundance threshold for plague as a critical percolation phenomenon

Percolation theory is most commonly associated with the slow flow of liquid through a porous medium, with applications to the physical sciences. Epidemiological applications have been anticipated for disease systems where the host is a plant or volume of soil, and hence is fixed in space. However, no natural examples have been reported. The central question of interest in percolation theory, the possibility of an infinite connected cluster, corresponds in infectious disease to a positive probability of an epidemic. Archived records of plague (infection with Yersinia pestis) in populations of great gerbils (Rhombomys opimus) in Kazakhstan have been used to show that epizootics only occur when more than about 0.33 of the burrow systems built by the host are occupied by family groups. The underlying mechanism for this abundance threshold is unknown. Here we present evidence that it is a percolation threshold, which arises from the difference in scale between the movements that transport infectious fleas between family groups and the vast size of contiguous landscapes colonized by gerbils. Conventional theory predicts that abundance thresholds for the spread of infectious disease arise when transmission between hosts is density dependent such that the basic reproduction number (R(0)) increases with abundance, attaining 1 at the threshold. Percolation thresholds, however, are separate, spatially explicit thresholds that indicate long-range connectivity in a system and do not coincide with R(0) = 1. Abundance thresholds are the theoretical basis for attempts to manage infectious disease by reducing the abundance of susceptibles, including vaccination and the culling of wildlife. This first natural example of a percolation threshold in a disease system invites a re-appraisal of other invasion thresholds, such as those for epidemic viral infections in African lions (Panthera leo), and of other disease systems such as bovine tuberculosis (caused by Mycobacterium bovis) in badgers (Meles meles).     

山东小清河流域黄土的发现及勘探意义

通过钻孔取样、野外考察、粒度分析等方法对山东小清河流域浅层的沉积物特征进行研究。结果表明:小清河流域南部浅层沉积物以泥质粉砂和粉砂质泥为主,富含钙质结核和蜗牛化石等黄土标志物,发育明显的黄土-古土壤沉积旋回;南部粒度特征与青州黄土、北京降尘、西峰黄土等典型的风成沉积物相似,具有中国黄土的典型双峰特征,粒度分布明显粗于北京降尘和西峰黄土,而与邻近的青州黄土相似或较其稍粗,体现近物源的特性;末次冰期时裸露的渤海陆架是研究区黄土的主要物源区,中国东部季风和流域以南的山脉为黄土的形成提供搬运动力和地形条件;流域最北端发育古河道沉积,黄土与古河道间存在一个过渡带,沉积特征的差异和流域内南高北低的地势致使南部潜水面深度远大于北部,最终导致油气地震勘探中北部的地震激发效果明显优于南部。     

香港沉积物氧化过程对铅的约束作用

本项研究通过了３２ｄ（天）的连续充气实验,探索硫含量变化对Ｐｂ的影响,结果表明：沉积物充气氧化过程引起ＡＶＳ的迅速减少,同时,Ｐｂ,Ｅｈ,ＤＯ,ｐＨ也发生了明显的变化趋势。