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81.
To study the crystal chemistry of bernalite, Fe(OH)3, and the nature of the octahedral Fe3+ environment, Mössbauer spectra were recorded from 80 to 350 K, optical spectra were recorded at room temperature and a sample was studied using transmission electron microscopy. The Mössbauer spectrum of bernalite consists of a single six-line magnetic spectrum at 80 K. A broadened six-line magnetic spectrum with significantly less intensity is observed at higher temperatures, and is attributed to a small fraction of bernalite occurring as small particles. The variation of hyperfine magnetic field data for bulk bernalite with temperature is well described by the Weiss molecular field model with parameters of H
0 = 55.7±0.3 T and T
N = 427±5K. The centre shift data were fitted to the Debye model with parameters 0=0.482±0.005 mm/s (relative to -Fe) and M=492±30 K. The quadrupole shift is near zero at 300 K, and does not vary significantly with temperature. Absorption spectra in the visible and near infrared range show three crystal field bands of Fe3+ at 11 300, 16000 and 23 200 cm-1, giving a crystal field splitting of 14 570 cm-1 and Racah parameters of B=629 cm-1 and C=3381 cm-1. Infrared reflection spectra show two distinct OH-stretching frequencies, which could correspond to two structurally different types of OH groups. A band was also observed at 2250 cm-1, suggesting the presence of molecular CO2 in the large cation site. Analytical transmission electron microscopy indicates that Si occurs within the bernalite structure as well as along domain boundaries. Electron diffraction and imaging show that bernalite is polysynthetically twinned along {100} planes with twin domains ranging from 3 to 20 nm in thickness. Results are discussed with respect to the nature of the octahedral Fe3+ site, and compared with values for other iron oxides and hydroxides. 相似文献
82.
The population and distribution of carbon-oxidizing and sulfate-reducing bacteria in the soils of the Mozhaisk Reservoir are studied. 相似文献
83.
Weidong Sun Jin-tuan Wang Li-peng Zhang Chan-chan Zhang He Li Ming-xing Ling Xing Ding Cong-ying Li Hua-ying Liang 《中国地球化学学报》2017,36(1):9-15
Copper is a moderately incompatible chalcophile element. Its behavior is strongly controlled by sulfides. The speciation of sulfur is controlled by oxygen fugacity. Therefore, porphyry Cu deposits are usually oxidized (with oxygen fugacities > ΔFMQ +2) (Mungall 2002; Sun et al. 2015). The problem is that while most of the magmas at convergent margins are highly oxidized, porphyry Cu deposits are very rare, suggesting that high oxygen fugacity alone is not sufficient. Partial melting of mantle peridotite even at very high oxygen fugacities forms arc magmas with initial Cu contents too low to form porphyry Cu deposits directly (Lee et al. 2012; Wilkinson 2013). Here we show that partial melting of subducted young oceanic slabs at high oxygen fugacity (>ΔFMQ +2) may form magmas with initial Cu contents up to >500 ppm, favorable for porphyry mineralization. Pre-enrichment of Cu through sulfide saturation and accumulation is not necessarily beneficial to porphyry Cu mineralization. In contrast, re-melting of porphyritic hydrothermal sulfide associated with iron oxides may have major contributions to porphyry deposits. Thick overriding continental crust reduces the “leakage” of hydrothermal fluids, thereby promoting porphyry mineralization. Nevertheless, it is also more difficult for ore forming fluids to penetrate the thick continental crust to reach the depths of 2–4 km where porphyry deposits form. 相似文献
84.
The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). ThreeGCs (NGC 6341, NGC 7078, and ω Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galactic disk. The passage of any one of these three GCs through the disk could potentially have initiated the formation of the Gould Belt. 相似文献
85.
86.
G. T. Bloomfield 《New Zealand geographer》1967,23(1):90-91
Book reviewed in this article:
GEOGRAPHY, ITS SCOPE AND SPIRIT. By J. O. M. Broek
GEOGRAPHY AS HUMAN ECOLOGY: METHODOLOGY BY EXAMPLE. Edited by S. R. Eyre and G. R. J. Jones
A PREFACE TO ECONOMIC GEOGRAPHY. By H. H. McCarty and J. B. Lindberg
A PROLOGUE TO POPULATION GEOGRAPHY. By W. Zelinsky 相似文献
GEOGRAPHY, ITS SCOPE AND SPIRIT. By J. O. M. Broek
GEOGRAPHY AS HUMAN ECOLOGY: METHODOLOGY BY EXAMPLE. Edited by S. R. Eyre and G. R. J. Jones
A PREFACE TO ECONOMIC GEOGRAPHY. By H. H. McCarty and J. B. Lindberg
A PROLOGUE TO POPULATION GEOGRAPHY. By W. Zelinsky 相似文献
87.
Biogeochemical records of paleoenvironmental changes in Nainital Lake,Kumaun Himalayas,India 总被引:1,自引:0,他引:1
Preetam Choudhary Joyanto Routh Govind J. Chakrapani Bhishm Kumar 《Journal of Paleolimnology》2009,42(4):571-586
Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns
about sediment and water pollution. Lead-210 dated sediment cores from the lake represent ~95 years of accumulation and yield
a mean sedimentation rate of ~4.7 mm year−1. Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (δ13C, δ15N, and δ34S), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC
flux varies from 1.0 to 3.5 g m−2 year−1. Sediments are anoxic (Eh −328 to −187 mV) and have low (0.10–0.30 g m−2 year−1) N, but high (0.37–1.0 g m−2 year−1) S flux. Shifts in δ13C, δ15N, and δ34S suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain
hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of
the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the
lake has remained largely unchanged, and the perceived human-induced impacts are limited. 相似文献
88.
89.
N. V. Makarova V. M. Makeev T. V. Sukhanova P. S. Miklyaev A. L. Dorozhko I. V. Korobova 《Moscow University Geology Bulletin》2012,67(4):209-217
The neotectonic structures of the Lower Oka (Nizhneokskii) Region formed under different geodynamic conditions. This is attested by the morphology, orientation, internal structure, and jointing of the structures. The Oka-Tsna arc formed under the effect of tension from an inner source on the one hand and stress from the Alpian belt on the other hand. The latitudinally-oriented structures of the northwestern slope of the Tokmovo arc emerged as a result of uplift and widening. Both types of structure are combined within the limits of the Oka-Murom trough, which is a geodynamically active zone. 相似文献
90.
Janice Brahney John J. Clague Brian Menounos Thomas W. D. Edwards 《Journal of Paleolimnology》2008,40(1):489-505
The level of Kluane Lake in southwest Yukon Territory, Canada, has fluctuated tens of metres during the late Holocene. Contributions
of sediment from different watersheds in the basin over the past 5,000 years were inferred from the elemental geochemistry
of Kluane Lake sediment cores. Elements associated with organic material and oxyhydroxides were used to reconstruct redox
fluctuations in the hypolimnion of the lake. The data reveal complex relationships between climate and river discharge during
the late Holocene. A period of influx of Duke River sediment coincides with a relatively warm climate around 1,300 years BP.
Discharge of Slims River into Kluane Lake occurred when Kaskawulsh Glacier advanced to the present drainage divide separating
flow to the Pacific Ocean via Kaskawulsh and Alsek rivers from flow to Bering Sea via tributaries of Yukon River. During periods
when neither Duke nor Slims river discharged into Kluane Lake, the level of the lake was low and stable thermal stratification
developed, with anoxic and eventually euxinic conditions in the hypolimnion. 相似文献