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131.
Iron (II) oxide in 50 mg samples of silicate rocks, deposits, and soils is measured after digestion with HF and HCl in the presence of ICl. The iodine produced is measured spectrophotometrically. Results are presented for the eighteen available USGS geochemical reference standards including the GXR series. 相似文献
132.
Bruce D LaZerte 《Geochimica et cosmochimica acta》1981,45(5):647-656
A model is constructed to predict the stable carbon isotope ratio of the total dissolved CO2 in aquatic sediments and laboratory reactors. The major parameters of the model are the fractionation between CO2 and CH4 as well as the intra-molecular fractionation of acetate, the relative production of CH4 from CO2 reduction versus acetate fermentation, the net production ratio of CO2 to CH4 and the stable carbon isotope ratio of the source organic carbon. The model is fitted to published data and to date from the littoral sediments of Lake Memphremagog, Quebec, Canada. The inclusion of the intra-molecular fractionation factor of acetate in the model provides a good fit to the data; without this factor, the values of the other parameters necessary for a good fit appear unreasonable. 相似文献
133.
Electron paramagnetic resonance (EPR) spectroscopy analysis of marine samples from different environments appears to differentiate
between adsorbed and structural Mn (II) and Fe (III) sites in the sediment. This suggests that EPR may provide a means of
distinguishing different environmental influences on sediment. Acid extract solutions from sediment samples exhibit clearly
defined EPR spectra due to Mn(II), Ti(III), Fe(III), and VO(IV), which are amenable to qualitative and quantitative analysis
at concentrations below one part per million. Spectra of several shellfish vary considerably, both between species, and within
a species, depending on sampling localities. Resonances from Mn(II), Mo(V), and Fe(III) can be obtained. Mn(II) is substituted
for Ca(II) in the calcite structure of some shells.
The low detection limits, small sample size, required and identification of oxidation states by EPR complement other analytical
techniques and may prove useful in marine systems. 相似文献
134.
A combination of both water chemistry and sedimentological information was used to investigate the carbonate-producing mechanism
in Littlefield Lake, a small lake located in Isabella County, central Michigan. Data on temperature, dissolved oxygen, pH,
calcium carbonate (CaCO3) saturation, alkalinity, calcium, and magnesium were obtained on a monthly basis over a 13-month period, with each parameter
determined at 1m intervals over a depth range of 20m. The loss of dissolved carbon dioxide (CO2) from warm surface waters during direct degassing, and to a lesser extent during photosynthetic uptake by lacustrine macrophytes
and phytoplankton during the summer, results in massive precipitation of the low-magnesium calcite which predominates in all
Littlefield Lake sedimentary facies However, despite the fact that carbonate precipitation in this rather typical temperate-region
marl lake is directly related to, and may be driven by, seasonal variation in these physiochemical parameters, most calcite
forms as encrustations around cyanophytic and chlorophytic macrophytes. Such relationships demonstrate that carbonate precipitation
in marl lakes may result from complex interactions between both biochemical and physiochemical processes. As such, marl formation
in this, and probably many other calcareous lake systems, can not be simply ascribed to one or the other of these two general
mechanisms. 相似文献
135.
Chemical partitioning data are of fundamental interest to exploration geochemists. This paper is one of the few studies which has investigated the relative proportions of the rare elements in various soil extracts. The dispersion of trace elements from weathering pegmatites in Powhatan Country, Virginia, was found to be restricted to the immediate vicinity of the pegmatites. A sequential extraction procedure was used to measure the distribution of Be, La, Nb, Sn, U, Li, and Ni,among the following fractions of the B soil horizons: exchangeable, Fe and Mn oxyhydroxide, residual, and aqua regia digestion. The elements Sn, Be, Li, and U were found to be associated with soils over the complex Herbb No. 2 pegmatite, whereas La and Ni were generally associated with the background soils.A geochemical exploration model was developed using stepwise discriminant function analysis to determine the combination of elements and soil extracts that best differentiates between complex pegmatitic, simple pegmatitic, and background soils. Log-transformed aqua regia extract concentrations of Sn, La, U, and Li were the most effective variables when used to separate complex pegmatitic from simple pegmatitic soils. 相似文献
136.
John Cushing Marla Daily Elmer Noble V. Louise Roth Adrian Wenner 《Quaternary Research》1984,21(3):376-384
Mammoth remains on Santa Cruz Island, one of the four Northern Channel Islands of California, are very sparse, in marked contrast to those reported from Santa Rosa and San Miguel Islands of the same island group. A probable major reason for this scarcity is that Quaternary deposits are greatly restricted on Santa Cruz Island. It is proposed, contrary to popular opinion, that fossils found on Santa Cruz Island were derived from animals which died on the island, and were not transported there by humans. Reasons for this conclusion are that the size and geological context of the fossils are similar to those of the largest mammoth fossils of Santa Rosa Island, and that, in spite of extensive investigations by many persons, mammoth remains have not been found in middens, either on the islands or on the adjacent mainland. 相似文献
137.
G. J. Redhammer G. Roth W. Paulus G. André W. Lottermoser G. Amthauer W. Treutmann B. Koppelhuber-Bitschnau 《Physics and Chemistry of Minerals》2001,28(5):337-346
Single crystals of Li-aegirine LiFe3+Si2O6 were synthesized at 1573?K and 3?GPa, and a polycrystalline sample suitable for neutron diffraction was produced by ceramic sintering at 1223?K. LiFe3+Si2O6 is monoclinic, space group C2/c, a=9.6641(2)?Å, b= 8.6612(3)?Å, c=5.2924(2)?Å, β=110.12(1)° at 300?K as refined from powder neutron data. At 229?K Li-aegirine undergoes a phase transition from C2/c to P21 /c. This is indicated by strong discontinuities in the temperature variation of the lattice parameters, especially for the monoclinic angle β and by the appearance of Bragg reflections (hkl) with h+k≠2n. In the low-temperature form two non-equivalent Si-sites with 〈SiA–O〉=1.622?Å and 〈SiB–O〉=1.624?Å at 100?K are present. The bridging angles of the SiO4 tetrahedra O3–O3–O3 are 192.55(8)° and 160.02(9)° at 100?K in the two independent tetrahedral chains in space group P21 /c, whereas it is 180.83(9)° at 300?K in the high-temperature C2/c phase, i.e. the chains are nearly fully expanded. Upon the phase transition the Li-coordination changes from six to five. At 100?K four Li–O bond lengths lie within 2.072(4)–2.172(3)?Å, the fifth Li–O bond length is 2.356(4)?Å, whereas the Li–O3?A bond lengths amount to 2.796(4)?Å. From 57Fe Mössbauer spectroscopic measurements between 80 and 500?K the structural phase transition is characterized by a small discontinuity of the quadrupole splitting. Temperature-dependent neutron powder diffraction experiments show first occurrence of magnetic reflections at 16.5?K in good agreement with the point of inflection in the temperature-dependent magnetization of LiFe3+Si2O6. Distinct preordering phenomena can be observed up to 35?K. At the magnetic phase transition the unit cell parameters exhibit a pronounced magneto-striction of the lattice. Below T N Li-aegirine shows a collinear antiferromagnetic structure. From our neutron powder diffraction experiments we extract a collinear antiferromagnetic spin arrangement within the a–c plane. 相似文献
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