Contributions of mineral and organic components to tidal freshwater marsh accretion

Vertical accretion in tidal marshes is necessary to prevent submergence due to rising sea levels. Mineral materials may be more important in driving vertical accretion in tidal freshwater marshes, which are found near the heads of estuaries, than has been reported for salt marshes. Accretion rates for tidal freshwater marshes in North America and Europe (n = 76 data points) were compiled from the literature. Simple and multiple linear regression analyses revealed that both organic and mineral accumulations played a role in driving tidal freshwater marsh vertical accretion rates, although a unit mass of organic material contributed ∼4 times more to marsh volume than the same mass input of mineral material. Despite the higher mineral content of tidal freshwater marsh soils, this ability of organic matter to effectively hold water and air in interstitial spaces suggests that organic matter is responsible for 62% of marsh accretion, with the remaining 38% from mineral contributions. The organic material that helps to build marsh elevation is likely a combination of in situ production and organic materials that are deposited in association with mineral sediment particles. Regional differences between tidal freshwater marshes in the importance of organic vs. mineral contributions may reflect differences in sediment availability, climate, tidal range, rates of sea level rise, and local-scale factors such as site elevation and distance to tidal creeks. Differences in the importance of organic and mineral accumulations between tidal freshwater and salt marshes are likely due to a combination of factors, including sediment availability (e.g., proximity to upland sources and estuarine turbidity maxima) and the lability of freshwater vs. salt marsh plant production.     

A study of lignin degradation in leaf and needle litter using C-labelled tetramethylammonium hydroxide (TMAH) thermochemolysis: Comparison with CuO oxidation and van Soest methods

We studied the degradation of lignin in leaf and needle litter of ash, beech, maple, pine and spruce using ¹³C-labelled tetramethylammonium hydroxide (¹³C TMAH) thermochemolysis. Samples were allowed to decompose for 27 months in litter bags at a German spruce forest site, resulting in a range of mass loss from 26% (beech) to 58% (ash). In contrast to conventional unlabelled TMAH thermochemolysis, ¹³C-labelling allows thermochemolysis products from lignin, demethylated lignin and other polyphenolic litter compounds (e.g. tannins) to be distinguished. Proxies for lignin degradation (phenol yield; acid/aldehyde ratio of products) changed considerably upon correction for the contribution of non-lignin sources to the thermochemolysis products. Using the corrected values, we found increasing acid/aldehyde values as well as decreasing or constant yield of lignin derived phenols normalised to litter carbon, suggesting pronounced lignin degradation by wood-rotting fungi. No indication for build up of demethylated lignin through the action of brown rot fungi on ring methoxyls was found. The results were compared with those of other analytical techniques applied in previous studies. Like ¹³C-TMAH thermochemolysis, CuO oxidation showed increasing lignin oxidation (acid/aldehyde ratio) and no/little enrichment of lignin derived phenols in the litter. Molecular lignin degradation patterns did not match those from analysis of total acid unhydrolysable residues (AURs). In particular, the long assumed selective preservation of lignin during the first months of litter decomposition, based on AUR analysis, was not supported by results from the CuO and ¹³C TMAH methods.     

Seasonal variation of Titan's atmospheric structure simulated by a general circulation model.

The seasonal variation of Titan's atmospheric structure with emphasis on the stratosphere is simulated by a three-dimensional general circulation model. The model includes the transport of haze particles by the circulation. The likely pattern of meridional circulation is reconstructed by a comparison of simulated and observed haze and temperature distribution. The GCM produces a weak zonal circulation with a small latitudinal temperature gradient, in conflict with observation. The direct reason is found to be the excessive meridional circulation. Under uniformly distributed opacity sources, the model predicts a pair of symmetric Hadley cells near the equinox and a single global cell with the rising branch in the summer hemisphere below about z = 230 km and a thermally indirect cell above the direct cell near the solstice. The interhemispheric circulation transports haze particles from the summer to the winter hemisphere, causing a maximum haze opacity contrast near the solstice and a smaller contrast near the equinox, contrary to observation. On the other, if the GCM is run under modified cooling rate in order to account for the enhancement in nitrites and some hydrocarbons in the northern hemisphere near the vernal equinox, the meridional cell at the equinox becomes a single cell with rising motions in the autumn hemisphere. A more realistic haze opacity distribution can be reproduced at the equinox. However, a pure transport effect (without particle growth by microphysics, etc.) would not be able to cause the observed discontinuity of the global haze opacity distribution at any location. The stratospheric temperature asymmetry can be explained by a combination of asymmetric radiative heating rates and adiabatic heating due to vertical motion within the thermally indirect cell. A seasonal variation of haze particle number density is unlikely to be responsible for this asymmetry. It is likely that a thermally indirect cell covers the upper portion of the main haze layer. An artificial damping of the meridional circulation enables the formation of high-latitude jets in the upper stratosphere and weaker equatorial superrotation. The latitudinal temperature distribution in the stratosphere is better reproduced.     

Late orogenic rebound and oblique Alpine convergence: New constraints from subsidence analysis of the Austrian Molasse basin

Subsidence analysis of 16 wells in the Austrian Molasse basin documents major spatial and temporal changes in tectonic subsidence as well as a late-stage surface uplift. The timing of the main phase of tectonic subsidence shifted from early Oligocene in the western part of the peripheral foreland to the early Miocene in the eastern part. These temporal and spatial changes in tectonic subsidence reflect a change from oblique dextral to sinistral convergence between the Alpine nappe stack and its foreland. The main phase of sediment accumulation was delayed to the early Miocene and led to the infill of the basin and a major second, sediment-load driven phase of basement subsidence. Sediment accumulation rates in the basin reflect the build-up of topography in the Alpine mountain chain. Since approximately 6 Ma a pronounced regional uplift of the entire Molasse basin has taken place, marking the transition from lateral extrusion to orthogonal contraction within the Alpine system and deep-seated changes in geodynamic boundary conditions, possibly due to delamination of previously thickened lithosphere. Surface uplift is contemporaneous with similar processes in extra-Alpine Central Europe, where it is interpreted to reflect intra-plate stress changes.     

黑龙江省嫩江地区科洛杂岩隆升时代

科洛杂岩出露于黑龙江省嫩江县大兴安岭北段,构造解析指示其为一大型伸展滑脱构造,整体反映杂岩体向南东伸展滑脱的特征。依据杂岩体显微构造特征,推测科洛地区伸展滑脱变形带变形温度约为300～450 ℃。滑脱带中变形花岗片麻岩样品中黑云母单矿物的 ⁴⁰Ar/³⁹Ar 年龄为118.39～117.37 Ma,指示伸展滑脱带形成时代为早白垩世晚期。结合大兴安岭地区中生代岩浆活动特征和南北变质核杂岩对比研究,认为大兴安岭整体经历了早白垩世中晚期的快速隆升,形成一系列变质核杂岩,发育大规模伸展变形作用,与松辽盆地坳陷期具有良好的耦合关系。     

In-situ zircon U-Pb age and Hf-O isotopic constraints on the origin of the Hasan-Robat A-type granite from Sanandaj–Sirjan zone,Iran: implications for reworking of Cadomian arc igneous rocks

Mineralogy and Petrology - The Lower Permian Hasan-Robat syenogranite occurs as a single pluton and intruded the Upper Carboniferous–Lower Permian sandstones and dolomitic limestones in the...     

药品和膳食补充剂中金属含量的分析——NexION 300 ICP-MS在执行USP 232法案中的应用

美国药典(USP)提议的通用章节USP 232将替代原来的USP 231.在食品和膳食补充剂中使用的有效药物原料不可避免地包含许多元素,因此现代检测实验室已开始使用各种手段应对不断增加的食品和膳食补充剂产品中元素的检测需要.电感耦合等离子体质谱仪(ICP-MS)能够分析元素周期表中绝大多数的元素,而且检测浓度范围为μg/g～mg/g,这样的检测浓度范围表明在一次分析中可以对痕量污染物和重要的营养元素同时进行测定,因此是满足以上需求的理想选择.     

Metagranitoids from the eastern part of the Central Rhodopean Dome (Bulgaria): U–Pb, Rb–Sr and 40Ar/39Ar timing of emplacement and exhumation and isotope-geochemical features

Summary Geochronological data (U–Pb, Rb–Sr and ⁴⁰Ar/³⁹Ar) are used to unravel the Late Alpine high-grade metamorphism, migmatisation and exhumation of Variscan granitoids within the core of the Central Rhodopean dome, Bulgaria. The age of the granitoid protolith is 300±11Ma, as determined by U–Pb analyses on single zircons selected from the core of the dome structure.Rb–Sr whole rock data define an errorchron with a large scatter of the data points due to the Late Alpine metamorphic overprint. The slope of the reference line indicates a Variscan magmatic event. Strontium characteristics are used to discriminate the samples most influenced by metamorphism from those, which reflect possible differences in the protolith age of the granitoids.Petrological-geochemical data, the initial strontium ratio of 0.708±0.001, and _Hf zircon values ranging from –2.58 to –3.82 point to a mixed, but crust-dominated origin of the Variscan magmas; young crustal material and mantle fragments were sources for the I-type metagranitoids.The exhumation of the granitoids from depths greater than 20–25km to about 5km below the surface was a rapid geological process. It started with the formation of granitic eutectic minimum melts at the temperature peak of metamorphism. Monazite crystallisation at about 650°C continued during isothermal decompression to possible depths of about 10–12km. An age of 35.83±0.40Ma was determined using conventional U–Pb isotope methods on four multigrain monazite fractions. A maximum average age of 36.6–37.5Ma (assuming same error uncertainties) for crystallisation of the metamorphic monazites was calculated assuming 10 to 20% monazite resetting during the subsequent Oligocene volcanism and hydrothermal activity in the region of the Central Rhodopean Dome. The rocks were then cooled to about 350–300°C at 35.35±0.22Ma according to ⁴⁰Ar/³⁹Ar ages of biotites and below 300°C at 35.31±0.25Ma (Rb–Sr data), as indicated by crystallisation of adularia in an open vein subsequent to pegmatite intrusion. A minimum exhumation rate of 3–5km per 1 million years can therefore be calculated for the exhumation of the metagranitoids during the period from 38–35Ma.     

Early Palaeozoic tectonothermal events in basement complexes of the eastern Greywacke Zone (Eastern Alps): evidence from U–Pb zircon data

Field observations and U-Pb zircon data yield evidence that the Kaintaleck Complex represents a distinct crystalline basement unit of the eastern Greywacke Zone and contrasts partly with other pre-Alpine basement complexes of the Eastern Alps. The age data indicate possible Late Archean rock formation, several magmatic and metamorphic events in the Early Palaeozoic (ca. 520-490 and ca. 400-360 Ma), and low-grade metamorphic overprint in the Cretaceous. Zircons from a garnet gneiss layer in a plagioclase gneiss and amphibolite sequence yield an upper intercept age of ca. 2.55 Ga which is interpreted as a possible protolith age. The lower intercept age at 514 Ma represents either (1) a magmatic event or (2) a metamorphic overprint within amphibolite facies conditions. Magmatic zircons derived from granitic orthogneiss boulders of the Kalwang Conglomerate, which covers the crystalline basement, crystallised at ca. 500 Ma. The lower discordia intercepts of the orthogneiss boulders mark the Cretaceous low-grade metamorphic overprint. The lower intercept age of paragneiss zircons from another slice of the Kaintaleck Complex suggests a likely Devonian metamorphic event at ca. 390-400 Ma. The new data demonstrate that the Kaintaleck Complex experienced several stages of tectonothermal evolutions, which are in contrast to the evolution of the main mass of the Austroalpine basement. The data constrain linkages of this part of the Austroalpine basement to the Cordillere Ligérienne and Cadomian block within West-European Variscides.