Climatically induced lake level changes during the last two millennia as reflected in sediments of Laguna Potrok Aike,southern Patagonia (Santa Cruz,Argentina)

The volcanogenic lake Laguna Potrok Aike, Santa Cruz, Argentina, reveals an unprecedented continuous high resolution climatic record for the steppe regions of southern Patagonia. With the applied multi-proxy approach rapid climatic changes before the turn of the first millennium were detected followed by medieval droughts which are intersected by moist and/or cold periods of varying durations and intensities. The total inorganic carbon content was identified as a sensitive lake level indicator. This proxy suggests that during the late Middle Ages (ca. AD 1230–1410) the lake level was rather low representing a signal of the Medieval Climate Anomaly in southeastern Patagonia. At the beginning of the Little Ice Age the lake level rose considerably staying on a high level during the whole period. Subsequently, the lake level lowered again in the course of the 20th century.     

Exposing metal and silicate charges to electrical discharges: Did chondrules form by nebular lightning?

In order to investigate the hypothesis that dust aggregates were transformed to meteoritic chondrules by nebular lightning, we exposed silicatic and metallic dust samples to electrical discharges with energies of 120 to 500 J in air at pressures between 10 and 10⁵ Pa. The target charges consisted of powders of micrometer-sized particles and had dimensions of mm. The dust samples generally fragmented leaving the major fraction thermally unprocessed. A minor part formed sintered aggregates of 50 to 500 μm. In a few experiments melt spherules having sizes ?180 μm in diameter (and, generally, interior voids) were formed; the highest spherule fraction was obtained with metallic Ni. Our experiments indicate that chondrule formation by electric current or by particle bombardment inside a discharge channel is unlikely.     

ESO's new CCD Testbench

During the forthcoming years, ESO will implement a large number of CCDs in optical instruments for the Paranal and La Silla observatories. An important step in this process is the CCD characterization and optimization that is done after the device is received from the manufacturer. In order to accommodate the new large CCDs and to interface to the new FIERA controller, ESO is building a new CCD testing facility in Garching. Among the measurements that will be made with this new facility are: quantum efficiency, conversion factor, charge transfer efficiency, dark current, read out noise and cosmetic quality.     

Cosmic rays and the primordial gas

One of the most-outstanding problems in the gravitational collapse scenario of early structure formation is the cooling of primordial gas to allow for small-mass objects to form. As the neutral primordial gas is a poor radiator at temperatures   T ≤ 10⁴ K  , molecular hydrogen is needed for further cooling down to temperatures   T ∼ 100 K  . The formation of molecular hydrogen is catalyzed by the presence of free electrons, which could be provided by the ionization due to an early population of cosmic rays (CRs). In order to investigate this possibility, we developed a code to study the effects of ionizing CRs on the thermal and chemical evolution of primordial gas. We found that CRs can provide enough free electrons needed for the formation of molecular hydrogen, and therefore can increase the cooling ability of such primordial gas under following conditions. A dissociating photon flux with   F < 10⁻¹⁸ erg cm⁻² Hz⁻¹ s⁻¹  , initial temperature of the gas  ∼10³ K  , total gas number densities   n ≥ 1 cm⁻³  , and cosmic-ray sources with     .     

Cenomanian–Turonian carbonate platform deposits in west central Jordan

We studied upper Albian to Turonian shallow-marine shelf deposits (Ajlun Group) of west central Jordan along a NNE-SSW running transect. The carbonate-dominated succession includes few siliciclastic intercalations, claystones and shales, and can be subdivided into five formations. The Naur, Fuheis and Hummar Formations of upper Albian to upper Cenomanian age represent shallow subtidal to supratidal platform environments. The uppermost Cenomanian to middle Turonian Shueib Formation includes deeper water deposits of the inner/mid-shelf and locally TOC-rich black shales. Shallow-marine platform environments once again dominate the Wadi As Sir Formation (middle-upper Turonian). A new multibiostratigraphic framework is based on ammonites (mainly of the middle Cenomanian rhotomagense Zone to the middle Turonian woollgari Zone) and calcareous nannofossils (biozones CC 9–CC 11), supplemented by benthic and planktonic foraminifers and ostracods. It forms the base of a sequence stratigraphic subdivision, containing eight sedimentary sequences (S1–S8), which are separated by four Cenomanian sequence boundaries (CeJo1–CeJo4) and three Turonian sequence boundaries (TuJo1–TuJo3). This scheme allows the correlation of the platform succession from distal to proximal shelf areas in contrast to previous correlations using lithologic units. Furthermore, comparisons between the platform successions and sequence patterns of west central Jordan and those from neighbouring areas allow to differentiate local, regional, and global controlling factors of platform development within the study area.     

Rill development and soil erosion: a laboratory study of slope and rainfall intensity

A total of 15 rainfall simulation experiments were conducted in a 1 m by 2 m box varying slope (10, 20, 30%) and rainfall intensity (60, 90, 120 mm h^?1). The experiments were performed to study how rill networks initiate and evolve over time under controlled conditions with regard to the treatment variables considered, and to allow for input in a computer simulation model. Runoff and sediment yield samples were collected. Digital elevation models were calculated by means of photogrammetry for several time steps of most experiments. The soil used in the experiments was a basal till derived Cambisol typical for the Swiss Plateau. While significant differences were found for sediment yield, runoff did not vary significantly with treatment combinations. Increasing rainfall intensity had a larger effect on sediment yield than increasing slope. Rill density and energy expenditure decreased with time, suggesting that energy expenditure was a useful parameter to describe the emergence of rill network at the laboratory scale. Copyright © 2010 John Wiley & Sons, Ltd.     

Erosion and Flooding—Threats to Coastal Infrastructure in the Arctic: A Case Study from Herschel Island,Yukon Territory,Canada

Arctic coastal infrastructure and cultural and archeological sites are increasingly vulnerable to erosion and flooding due to amplified warming of the Arctic, sea level rise, lengthening of open water periods, and a predicted increase in frequency of major storms. Mitigating these hazards necessitates decision-making tools at an appropriate scale. The objectives of this paper are to provide such a tool by assessing potential erosion and flood hazards at Herschel Island, a UNESCO World Heritage candidate site. This study focused on Simpson Point and the adjacent coastal sections because of their archeological, historical, and cultural significance. Shoreline movement was analyzed using the Digital Shoreline Analysis System (DSAS) after digitizing shorelines from 1952, 1970, 2000, and 2011. For purposes of this analysis, the coast was divided in seven coastal reaches (CRs) reflecting different morphologies and/or exposures. Using linear regression rates obtained from these data, projections of shoreline position were made for 20 and 50 years into the future. Flood hazard was assessed using a least cost path analysis based on a high-resolution light detection and ranging (LiDAR) dataset and current Intergovernmental Panel on Climate Change sea level estimates. Widespread erosion characterizes the study area. The rate of shoreline movement in different periods of the study ranges from ?5.5 to 2.7 m·a^?1 (mean ?0.6 m·a^?1). Mean coastal retreat decreased from ?0.6 m·a^?1 to ?0.5 m·a^?1, for 1952–1970 and 1970–2000, respectively, and increased to ?1.3 m·a^?1 in the period 2000–2011. Ice-rich coastal sections most exposed to wave attack exhibited the highest rates of coastal retreat. The geohazard map combines shoreline projections and flood hazard analyses to show that most of the spit area has extreme or very high flood hazard potential, and some buildings are vulnerable to coastal erosion. This study demonstrates that transgressive forcing may provide ample sediment for the expansion of depositional landforms, while growing more susceptible to overwash and flooding.     

有机组分土-水分配系数的确定(英文)

有机组分的土水分配系数(Kd)是描述有机组分在地下系统中吸附特征的重要参数。同时,它也是物质运移模拟和环境评价中的主要参数之一。影响Kd的因素可概括为三个方面:土壤性质、有机组分本身特征及水相的物理化学性质。一般而言,对于非极性和弱极性有机组分,土壤中的有机质含量(foc )是影响Kd的最主要因素。但是,对于极性有机组分(POCs), 特别是在土壤有机质含量较低的情况下,土壤中矿物的种类和含量、水化学组分特征(pH、离子力等)经常在吸附过程中起重要作用。实验室内测定Kd的方法包括批实验和柱实验方法。批实验法适用于研究Kd较高情况下的吸附。在Kd较低的情况下,如低有机质土壤对极性有机污染物的吸附,土柱色谱法(SCC)是更适宜的选择。另外,可用土柱色谱法快速了解各种因素对吸附过程的影响,并获取详细的吸附和解吸信息。应用土柱色谱法时应当注意非平衡吸附和可能的柱堵塞问题。很多文献中提到结合柱实验和已有的吸附数据来预测土壤有机碳标准化的分配系数Koc(=Kd/foc)。但是,如果没有考虑吸附中特定的作用过程(如矿物吸附),对极性有机组分Koc的预测将会产生很大的误差。在环境评价中,将从一种土壤测定的Koc 应用到不同性质的土壤中,可能会导致错误的认识。在进行室内实验时,应把标准土(如Eurosoi     

Magmatic-dominated fluid evolution in the Jurassic Nambija gold skarn deposits (southeastern Ecuador)

The Jurassic (approximately 145 Ma) Nambija oxidized gold skarns are hosted by the Triassic volcanosedimentary Piuntza unit in the sub-Andean zone of southeastern Ecuador. The skarns consist dominantly of granditic garnet (Ad_20–98) with subordinate pyroxene (Di_46–92Hd_17–42Jo_0–19) and epidote and are spatially associated with porphyritic quartz-diorite to granodiorite intrusions. Endoskarn is developed at the intrusion margins and grades inwards into a potassic alteration zone. Exoskarn has an outer K- and Na-enriched zone in the volcanosedimentary unit. Gold mineralization is associated with the weakly developed retrograde alteration of the exoskarn and occurs mainly in sulfide-poor vugs and milky quartz veins and veinlets in association with hematite. Fluid inclusion data for the main part of the prograde stage indicate the coexistence of high-temperature (500°C to >600°C), high-salinity (up to 65 wt.% eq. NaCl), and moderate- to low-salinity aqueous-carbonic fluids interpreted to have been trapped at pressures around 100–120 MPa, corresponding to about 4-km depth. Lower-temperature (510–300°C) and moderate- to low-salinity (23–2 wt.% eq. NaCl) aqueous fluids are recorded in garnet and epidote of the end of the prograde stage. The microthermometric data (Th from 513°C to 318°C and salinity from 1.0 to 23 wt.% eq. NaCl) and δ¹⁸O values between 6.2‰ and 11.5‰ for gold-bearing milky quartz from the retrograde stage suggest that the ore-forming fluid was dominantly magmatic. Pressures during the early retrograde stage were in the range of 50–100 MPa, in line with the evidence for CO₂ effervescence and probable local boiling. The dominance of magmatic low-saline to moderately saline oxidizing fluids during the retrograde stage is consistent with the depth of the skarn system, which could have delayed the ingression of external fluids until relatively low temperatures were reached. The resulting low water-to-rock ratios explain the weak retrograde alteration and the compositional variability of chlorite, essentially controlled by host rock compositions. Gold was precipitated at this stage as a result of cooling and pH increase related to CO₂ effervescence, which both result in destabilization of gold-bearing chloride complexes. Significant ingression of external fluids took place after gold deposition only, as recorded by δ¹⁸O values of 0.4‰ to 6.2‰ for fluids depositing quartz (below 350°C) in sulfide-rich barren veins. Low-temperature (<300°C) meteoric fluids (δ¹⁸O_water between −10.0‰ and −2.0‰) are responsible for the precipitation of late comb quartz and calcite in cavities and veins and indicate mixing with cooler fluids of higher salinities (about 100°C and 25 wt.% eq. NaCl). The latter are similar to low-temperature fluids (202–74.5°C) with δ¹⁸O values of −0.5‰ to 3.1‰ and salinities in the range of 21.1 to 17.3 wt.% eq. CaCl₂, trapped in calcite of late veins and interpreted as basinal brines. Nambija represents a deep equivalent of the oxidized gold skarn class, the presence of CO₂ in the fluids being partly a consequence of the relatively deep setting at about 4-km depth. As in other Au-bearing skarn deposits, not only the prograde stage but also the gold-precipitating retrograde stage is dominated by fluids of magmatic origin.     

大别山超高压变质带层析地震调查

１９９７年３月中德合作进行了大别山科学钻探选址区层析地震调查,研究结果揭示出大别山超高压变质带（ＵＨＰ）地壳精细结构。郯庐断裂带近垂直延伸至Ｍｏｈｏ界面（可能更深）,在Ｍｏｈｏ界面以上郯庐断裂带西侧大别山地壳物质没有迁移进入其东侧。在主测线（横中至潜山镇）２０ｋｍ深度发现一个由西向东倾斜的强反射层,推测可能是一个大的滑脱层。超高压变质岩石（或地幔物质）可能由地幔深处通过郯庐断裂带再沿此滑脱层析返到