Carbonate stromatolites from a Messinian hypersaline setting in the Caltanissetta Basin, Sicily: petrographic evidence of microbial activity and related stable isotope and rare earth element signatures     

ELVIRA OLIVERI  RODOLFO NERI  ADRIANA BELLANCA  ROBERT RIDING†  Associate Editor: Tracy Frank 《Sedimentology》2010,57(1):142-161

Lower Messinian stromatolites of the Calcare di Base Formation at Sutera in Sicily record periods of low sea‐level, strong evaporation and elevated salinity, thought to be associated with the onset of the Messinian Salinity Crisis. Overlying aragonitic limestones were precipitated in normal to slightly evaporative conditions, occasionally influenced by an influx of meteoric water. Evidence of bacterial involvement in carbonate formation is recorded in three dolomite‐rich stromatolite beds in the lower portion of the section that contain low domes with irregular crinkly millimetre‐scale lamination and small fenestrae. The dominant microfabrics are: (i) peloidal and clotted dolomicrite with calcite‐filled fenestrae; (ii) dolomicrite with bacterium‐like filaments and pores partially filled by calcite or black amorphous matter; and (iii) micrite in which fenestrae alternate with dark thin wispy micrite. The filaments resemble Beggiatoa‐like sulphur bacteria. Under scanning electron microscopy, the filaments consist of spherical aggregates of dolomite, interpreted to result from calcification of bacterial microcolonies. The dolomite crystals are commonly arranged as rounded grains that appear to be incorporated or absorbed into developing crystal faces. Biofilm‐like remains occur in voids between the filaments. The dolomite consistently shows negative δ¹³C values (down to ?11·3‰) and very positive δ¹⁸O (mean value 7·9‰) that suggest formation as primary precipitate with a substantial contribution of organic CO₂. Very negative δ¹³C values (down to ?31·6‰) of early diagenetic calcite associated with the dolomite suggest contribution of CO₂ originating by anaerobic methane oxidation. The shale‐normalized rare earth element patterns of Sutera stromatolites show features similar to those in present‐day microbial mats with enrichment in light rare earth elements, and M‐type tetrad effects (enrichment around Pr coupled to a decline around Nd and a peak around Sm and Eu). Taken together, the petrography and geochemistry of the Sutera stromatolites provide diverse and compelling evidence for microbial influence on carbonate precipitation.  相似文献   

左江洪涝特征分析   总被引：1，自引：0，他引：1  

张健 《气象研究与应用》2005,26(3):24-26

台风是造成左江洪涝的主要影响系统,后汛期洪涝频率明显高于前汛期,洪水汇流量与降雨性质、地形地貌、土壤含水量有关,依不同降雨量径流量不同的原理及洪涝特征估测洪水量、洪峰流量较接近实况,具有应用价值。  相似文献   

The water regime of the Monegros playa-lakes as established from ground and satellite data     

Carmen Castaeda  Juan Herrero 《Journal of Hydrology》2005,310(1-4):95-110

The Monegros playa-lakes are isolated saline wetlands, locally named ‘saladas’, situated in a vulnerable semi-arid territory where agricultural expansion threatens the natural hydrologic cycle with regular artificial flooding, risking the survival of a valuable natural resource. This study aims to examine the water regime of these playa-lakes from climate data and available hydrologic records. These records are historical and limited to a series of weekly measurements of depth and of water extent extracted from Landsat imagery. We have characterized the hydrological behavior of the playa-lakes by treating ground and satellite data separately. For this purpose, the playa-lakes are first grouped according to the water occurrence episodes. Then their hydrologic status is related to the previous rainfall and also to ET₀, since there is a lack of local records of wind as well as brine or fresh water evaporation. The northern playa-lakes respond to rain faster than the southern ones. All playa-lakes have a significant relationship between water occurrence and rainfall accumulated within 180 days prior to an observation. A significant relationship between ET₀ and water occurrence was found for a shorter 15-day accumulation period. Quantifying the current water regime now is critical for monitoring the effects of expanding irrigation in adjacent lands. Remote sensing is well-suited to an environmental assessment for regions of difficult access with the added benefit of lowered field measurement cost. The hydrological data from the Monegros playa-lakes could be integrated with other playa environments worldwide to compare regionally specific climate conditions.  相似文献   

Vulnerability from storm surges and cyclone wind fields on the coast of Andhra Pradesh,India   总被引：2，自引：0，他引：2  

A. D. Rao  P. Chittibabu  T. S. Murty  S. K. Dube  U. C. Mohanty 《Natural Hazards》2007,41(3):515-529

The results presented here are from a study conducted for the government of the state of Andhra Pradesh (GOAP) in India, as part of a World Bank project on cyclone mitigation. A set of detailed maps were prepared depicting the Physical Vulnerability (PV), specifically storm surge inundation zones are shown for frequent occurrence, 50-year return period, likely scenario for global warming and extreme global warming. Similarly vulnerable areas from strong wind field from tropical cyclones (TCS) are also presented for the same four parameters. Vulnerability zones are presented from a social point of view also based upon certain socio-economic parameters that were included in determining the overall vulnerability of each Mandal in a coastal district (a Mandal represents a group of villages and towns) include: population, senior citizens, women, children under different age groups, type of housing, income level, cyclone shelters, hospitals and medical centres, schools and caste based population. The study is about scenarios that could happen if global warming and the predicted intensification of TCS actually occur as predicted by some numerical models.  相似文献   

Drainage and flooding in karst terranes     

Wanfang Zhou 《Environmental Geology》2007,51(6):963-973

Flooding in karst terranes is a commonly occurring geo-hazard. It causes damage to property, businesses, and roadways. It can lead to the formation of cover-collapse sinkholes and groundwater contamination. Generally, three types of flooding or their combinations are related to karst: recharge-related sinkhole flooding, flow-related flooding, and discharge-related flooding. Understanding of the type of flooding is essential for solving the flooding problem. Areas prone to karst flooding should be recognized, and restrictions and laws on land use should be implemented. Runoff and erosion control plans should address the unique characteristics of karst features. Digging out clogged sinkholes, creating retention basins, or installing Class V Injection Wells are possible solutions to improve drainage of storm water. Solutions to flooding problems in karst areas should also be coordinated with the water quality control to prevent groundwater contamination.  相似文献   

Past and present state of the ichthyofauna of Lake Lugano     

Rudolf Müller  Hans Jürg Meng 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):338-350

The evolution of the ichthyofauna of Lake Lugano (Lago di Lugano) during the past 120 years is characterized by the introduction of eight new fish species and by the possibly natural addition of the blenny (Blennius fluviatilis) in recent years. Introduced Salmonids such as charr (Salvelinus alpinus) and whitefish (Coregonus sp.) have established strong populations during the first half of this century, but have declined drastically thereafter. Likewise, the population of the native shad (Alosa fallax lacustris) has diminished significantly. A hydroacoustic survey of the pelagic fish stock of Lake Lugano in 1989 revealed the presence of a dense bleak (Alburnus albidus) population at 0 to 14 m depth. No other fish were found to be present in the pelagic zone. Oxygen and temperature distributions seem to confine the bleak to the uppermost layer in summer. In winter, very few fish were located by echosounding. Growth of bleak and roach (Rutilus rubilio) was difficult to interpret since data for comparison are lacking. Growth of perch (Perca fluviatilis) in the littoral zone was found to be slower than in other eutrophic lakes, for no obvious reason. Possible ways of restructuring the pelagic fish community are discussed.  相似文献   

Aquatic system response to climatic and human changes: Productivity,bottom water oxygen status,and sapropel formation in Lake Lugano over the last 10 000 years     

F. Niessen  L. Wick  G. Bonani  C. Chondrogianni  C. Siegenthaler 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):257-276

The Holocene record of Lake Lugano (southern basin: surface area 20.3 km², maximum depth 87 m) comprising organic carbon-rich sediments (sapropels), is divided into eight intervals based on radiocarbon- and varve-dating. The content of organic carbon, inorganic carbon, and biogenic silica, as well as the benthic remains of ostracods and oligochaetes, are converted into accumulation rates and benthic abundances in order to assess past production rates and bottom water oxygen status, respectively. The results suggest three periods of distinct palaeolimnological character: (i) low primary production combined with shifts between aerobic and anaerobic profundal conditions (prior to ca. 3000 BC), (ii) moderate rates of production combined with a relatively high profundal oxygen content (after ca. 1500 BC), and (iii), high production rates (460 g C m^–2 a^–1) combined with anaerobic profundal conditions (present eutrophic state). Corresponding organic carbon contents in the sediments are: up to 5% (i), 4% (ii), and 8% (iii). Until the beginning of this century, the flux of autochthonous sediments to the lake floor correlated with the fluctuations in the allochthonous sediment accumulation rate, indicating that catchment erosion largely controlled lacustrine production during the Holocene history of Lake Lugano. Pollen data show catchment-vegetational transformations at ca. 3500 BC (change from fir to beech forests), at 1400 BC (onset of cereal vegetation) and at ca. A.D. 450 (strong increase in various cultural plants). The first two changes had a relatively large imprint on lacustrine sedimentation. At ca. 3500 BP, erosion increase in the catchment was triggered by vegetation changes in the mountain zone above ca. 1000 m a. s. l., which may have been induced by climatic and human alteration (drop in the treeline altitude). Maximum catchment erosion occurred at ca. 1400 BC which was clearly dominated by human cultivation during the Bronze Age. More oxygenated profundal conditions in the lake after ca. 3000 BC are possibly related to a better mixing of the lake waters during the winter season by increased wind activity.  相似文献   

Density structure and tritium-helium age of deep hypolimnetic water in the northern basin of Lake Lugano     

A. Wüest  W. Aeschbach-Hertig  H. Baur  M. Hofer  R. Kipfer  M. Schurter 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):205-218

Long-term stratification of the deep hypolimnetic waters of the northern basin of Lake Lugano (Lago di Lugano) has resulted in a lack of deep-water renewal which has persisted for decades. Tritium-helium age measurements reveal that deep water has not been in contact with the atmosphere since the 1960s. Higher primary production associated with the significant increase in phosphorus concentration which occurred at this time resulted in greater autochthonous gross sedimentation rates, increasing the rate of mineralization and, consequently, the rate of release of dissolved solids (mainly HCO ₃ ^- and Ca²⁺) into the deep hypolimnion. This gave rise to an intensification of the stratification and to a consequent reduction in the vertical exchange of hypolimnetic water layers. Today, the density stabilizing effect of ion release due to mineralization in the deep water is four to five times greater than the destabilizing effect of the geothermal heat flux from the earth's interior. It is known from laboratory experiments that such small density gradient ratios are likely to give rise to double-diffusive instabilities. However, even rudimentary mass balance calculations of biogeochemical components indicate that shear-induced turbulence, most likely generated by bottom currents, mixes far more efficiently than double diffusion. In the future, the biogenic density stratification is likely to persist in the deep water, unless the upward ion flux, driven by primary production, decreases by a factor of four to five.  相似文献   

The dynamic model Seemod applied to the Southern Basin of Lake Lugano   总被引：1，自引：1，他引：1  

F. Zamboni  A. Barbieri  B. Polli  G. Salvadè  M. Simona 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):367-380

The dynamic model Seemod developed at the EAWAG (Imboden and Gächter, 1978) and modified by Bührer (Ambühl and Bührer, 1984), was adapted to the South Basin of the Lake of Lugano (Lago di Lugano). The model can predict the evolution of the state of the lake, described by the concentrations of dissolved phosphorus, dissolved oxygen particulate phosphorus and organic particulate carbon, in function of phosphorus load and taking into account physical and biochemical initial- and boundary conditions. The model parameters were chosen through measurements and calibrations by short runs. A 10-year-long simulation was done, starting from the data of 1980, and its results agree quite well with the measurements. Then some 15-year-long simulations were done, which corresponded to different scenarios related to a progressive linking up of sewage systems to water treatment plants. The model predicts that a satisfactory water quality level can only be reached by reducing the total phosphorus input to less than 25 t/a.  相似文献   

支持向量机在水淹层测井识别中的应用   总被引：2，自引：1，他引：1  

赵军  程鹏飞  刘地渊  徐卫东 《物探与化探》2008,32(6)

支持向量机(SVM)算法是特别适合于用有限已知样本训练建模,进而预报未知样本属性的模式识别新算法。笔者尝试将Vapnik提出的支持向量机算法用于水淹层测井识别。总结了P油田水淹层的声波时差、自然电位、深感应电阻率、中感应电阻率及密度测井曲线与水淹程度的对应关系,建立了基于支持向量分类机的识别模型,并将上述参数作为训练样本的输入,油气特征作为训练样本的输出,对支持向量机进行训练。对于P油田水淹层的实际预测结果表明:支持向量机可以成为一种用于水淹层识别的有效工具。  相似文献