Selected samples of dissolved organic matter (DOM) isolated by ultrafiltration (UDOM) have been analyzed by thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH). This technique cleaves ester and ether bonds of bio‐ and geological macromolecules and releases monomer subunits and methylates them in situ as their methyl ethers and methyl esters. Compared with conventional pyrolysis, TMAH thermochemolysis avoids decarboxylation of preexisting carboxylic moieties and produces aromatic acids as their methyl esters. Various phenolic derivatives, which might originate from incorporated lignin‐derived structures, from the highly aliphatic and resistant biopolymer cutan and also from proteinaceous materials, were identified among the products produced from UDOM upon thermochemolysis. The presence of lignin derivatives in UDOM indicates input of organic matter derived from terrestrial sources. Various aromatic acids, perhaps representing the final steps in the oxidation of the side‐chain during microbial oxidation of lignin, were released upon TMAH thermochemolysis, suggesting they are structural constituents of the UDOM. Different ratios of lignin‐derived materials, commonly determined using the CuO oxidation method, such as the Δ value, indicative of the amount of lignin present, the acid/aldehyde ratio (Ad/Al)G, indicative of the extent of oxidative degradation of the lignin component, and the syringyl/guaiacyl (S/G) and p‐hydroxyphenyl/guaiacyl (P/G) ratios, indicative of the contribution for the different types of lignin, were determined. 相似文献
Serpentinized rocks closely associated with Paleoproterozoic eclogitic metabasites were recently discovered at Eseka area in the northwestern edge of the Congo craton in southern Cameroon. Here, we present new field data, petrography, and first comprehensible whole-rock geochemistry data and discuss the protolith and tectonic significance of these serpentinites in the region. The studied rock samples are characterized by pseudomorphic textures, including mesh microstructure formed by serpentine intergrowths with cores of olivine, bastites after pyroxene. Antigorite constitutes almost the whole bulk of the rocks and is associated (to the less amount) with tremolite, talc, spinel, and magnetite. Whole-rock chemistry of the Eseka serpentinites led to the distinction of two types. Type 1 has high MgO (> 40 wt%) content and high Mg# values (88.80) whereas Type 2 serpentinite samples display relatively low MgO concentration and Mg# values (< 40 and 82.88 wt%, respectively). Both types have low Al/Si and high Mg/Si ratios than the primitive mantle, reflecting a refractory abyssal mantle peridotite protolith. Partial melting modeling indicates that these rocks were derived from melting of spinel peridotite before serpentinization. Bulk rock high-Ti content is similar to the values of subducted serpentinites (> 50 ppm). This similarity, associated with the high Cr contents, spinel-peridotite protolith compositions and Mg/Si and Al/Si ratios imply that the studied serpentinites were formed in a subduction-related environment. The U-shaped chondrite normalized-REE patterns of serpentinized peridotites, coupled with similar enrichments in LREE and HFSE, suggest the refertilized nature due to melt/rock interaction prior to serpentinization. Based on the results, we suggest that the Eseka serpentinized peridotites are mantle residues that suffered a high degree of partial melting in a subduction-related environment, especially in Supra Subduction Zone setting. These new findings suggest that the Nyong series in Cameroon represents an uncontested Paleoproterozoic suture zone between the Congo craton and the São Francisco craton in Brazil.
This work presents new 87Sr/86Sr and δ88/86SrSRM987 isotopic values of thirteen mineral, vegetal and animal reference materials. Except for UB‐N, all our results are consistent with previously published data. Our results highlight intermediate precisions among the best presently published and a non‐significant systematic shift with the calculated δ88/86SrSRM987 mean values for the three most analysed reference materials in the literature (i.e., IAPSO, BCR‐2 and JCp‐1). By comparison with the literature and between two distinct digestions, a significant bias of δ88/86SrSRM987 values was highlighted for two reference materials (UB‐N and GS‐N). It has also been shown that digestion protocols (nitric and multi‐acid) have a moderate impact on the δ88/86SrSRM987 isotopic values for the Jls‐1 reference materials suggesting that a nitric acid digestion of carbonate can be used without significant bias from partial digestion of non‐carbonate impurities. Different δ88/86SrSRM987 values were measured after two independent Sr/matrix separations, according to the same protocol, for a fat‐rich organic reference material (BCR‐380R) and have been related to a potential post‐digestion heterogeneity. Finally, the δ88/86SrSRM987 value differences measured between animal‐vegetal and between coral‐seawater reference materials agree with the previously published results, highlighting an Sr isotopic fractionation along the trophic chain and during carbonate precipitation. 相似文献
Atmospheric dust is an integral component of the Earth system with major implications for the climate, biosphere and public health. In this context, identifying and quantifying the provenance and the processes generating the various types of dust found in the atmosphere is paramount. Isotopic signatures of Pb, Nd, Sr, Zn, Cu and Fe are commonly used as sensitive geochemical tracers. However, their combined use is limited by the lack of (a) a dedicated chromatographic protocol to separate the six elements of interest for low‐mass samples and (b) specific reference materials for dust. Indeed, our work shows that USGS rock reference materials BHVO‐2, AGV‐2 and G‐2 are not applicable as substitute reference materials for dust. We characterised the isotopic signatures of these six elements in dust reference materials ATD and BCR‐723, representatives of natural and urban environments, respectively. To achieve this, we developed a specific procedure for dust, applicable in the 4–25 mg mass range, to separate the six elements using a multi‐column ion‐exchange chromatographic method and MC‐ICP‐MS measurements. 相似文献
Large proportions of rainwater and snowmelt infiltrate into the subsurface before contributing to stream flow and stream water quality. Subsurface flow dynamics steer the transport and transformation of contaminants, carbon, weathering products and other biogeochemistry. The distribution of groundwater ages with depth is a key feature of these flow dynamics. Predicting these ages are a strong test of hypotheses about subsurface structures and time-varying processes. Chlorofluorocarbon (CFC)-based groundwater ages revealed an unexpected groundwater age stratification in a 0.47 km2 forested catchment called Svartberget in northern Sweden. An overall groundwater age stratification, representative for the Svartberget site, was derived by measuring CFCs from nine different wells with depths of 2–18 m close to the stream network. Immediately below the water table, CFC-based groundwater ages of already 30 years that increased with depth were found. Using complementary groundwater flow models, we could reproduce the observed groundwater age stratification and show that the 30 year lag in rejuvenation comes from return flow of groundwater at a subsurface discharge zone that evolves along the interface between two soil types. By comparing the observed groundwater age stratification with a simple analytical approximation, we show that the observed lag in rejuvenation can be a powerful indicator of the extent and structure of the subsurface discharge zone, while the vertical gradient of the age-depth-relationship can still be used as a proxy of the overall aquifer recharge even when sampled in the discharge zone. The single age stratification profile measured in the discharge zone, close to the aquifer outlet, can reveal the main structure of the groundwater flow pattern from recharge to discharge. This groundwater flow pattern provides information on the participation of groundwater in the hydrological cycle and indicates the lower boundary of hydrological connectivity. 相似文献
Damage to the top of coal seams, caused by incorrect blast stand-off distances, results in coal losses of up to 10–15% to the Australian open cut coal mining operations. This is a serious issue to be addressed. Here we propose to use a new forward-looking imaging technique based on the borehole radar technology to predict the coal seam top in real time while drilling blast holes. This is achieved by coupling the conventional borehole radar waves on to a steel drill rod to induce a guided wave along the axial drill rod. The drill rod ahead of the borehole radar behaves as a forward-looking antenna for the guided waves. Both numerical modelling and field trials simulating a drill rod as an antenna are used to investigate the feasibility of the proposed technique for prediction of the coal top under typical open cut environments. Numerical modelling demonstrated that conductivity of the overburden is the most important factor affecting our ability to see coal seams ahead of the drill bit, the guided borehole radar waves could be used for top coal prediction and a theoretical prediction error less than 10 cm and a forward-looking capability of 4–6 m can be achieved. Field trials at Australian open cut coal mines also demonstrated that guided borehole radar waves can be observed and used for prediction of coal top ahead of drill bit during blast-hole drilling in resistive, open cut environments (the average resistivity should be higher than 75 Ωm). 相似文献
Recently, the interest in PS-converted waves has increased for several applications, such as sub-basalt layer imaging, impedance estimates and amplitude-versus-offset analysis. In this study, we consider the problem of separation of PP- and PS-waves from pre-stacked multicomponent seismic data in two-dimensional isotropic medium. We aim to demonstrate that the finite-offset common-reflection-surface traveltime approximation is a good alternative for separating PP- and PS-converted waves in common-offset and common shot configurations by considering a two-dimensional isotropic medium. The five parameters of the finite-offset common-reflection-surface are firstly estimated through the inversion methodology called very fast simulated annealing, which estimates all parameters simultaneously. Next, the emergence angle, one of the inverted parameters, is used to build an analytical separation function of PP and PS reflection separation based on the wave polarization equations. Once the PP- and PS-converted waves were separated, the sections are stacked to increase the signal-to-noise ratio using the special curves derived from finite-offset common-reflection-surface approximation. We applied this methodology to a synthetic dataset from simple-layered to complex-structured media. The numerical results showed that the inverted parameters of the finite offset common-reflection-surface and the separation function yield good results for separating PP- and PS-converted waves in noisy common-offset and common shot gathers. 相似文献