Precambrian microbial fossils show carbonaceous cellular structure, which often resemble in shape and size cyanobacteria and other prokaryotes. Morphological taxonomy of these minute, simple, and more or less degraded fossils is, however, often not enough to determine their precise phylogenetic positions. Here we report the results of micro-FTIR spectroscopic analyses of well-preserved microfossils in 850 Ma and 1900 Ma stromatolites, together with those of 8 species of extant prokaryotes and 5 of eukaryotes for comparison. These Proterozoic fossils have low CH3/CH2 absorbance ratios (R3/2 < 0.5) of aliphatic CH moieties, suggesting selective preservation of long, straight, aliphatic carbon chains probably derived from bacterial membrane lipids. All the observed R3/2 values of coccoids, filaments and amorphous organic matter resemble lipid fractions of extant Bacteria including cyanobacteria, but not Archaea. The results indicate that Proterozoic microfossils belong to Bacteria, which is consistent with the cyanobacterial origin inferred from morphology. Moreover, the R3/2 value of fossilized cell would reflect chemical composition of its precursor membrane lipid, thus could be a useful new tracer for distinguishing Archaea, Bacteria and possibly Eucarya for fossilized and extant microorganisms. 相似文献
We present oxygen and carbon isotope ratios and the morphological structure of the cultured freshwater pearl mussel (Hyriopsis sp., Unionidae) shell and pearl. The number of first-order fluctuations of δ18O of the outer shell layer along the maximum growth axis was consistent with the number of cultured years. The dominant factor
controlling annual δ18O fluctuations was water temperature with a minor contribution from the variation in δ18O of ambient water, especially during the rainy season. The δ13C values were approximately constant throughout the life of the mussel, suggesting that the contributions of body size to
δ13C of the shell were minor. We observed nine distinct disturbance rings on the outer surface of the shell. Five rings coincided
with the five winter peaks of the δ18O profile, indicating winter growth cessation below approximately 10°C, probably because of either inactive growth at low
water temperatures or reproduction. Summer disturbance rings were not observed in all years. Moreover, some summer rings showed
discontinuity in the inner structure. These findings suggest that summer growth cessation may be caused by occasional events
such as heavy rains, as the decrease of dissolved oxygen concentration. The δ18O profile and shell structures indicated that shell aragonite was precipitated at close to equilibrium conditions with respect
to the oxygen isotope composition of the ambient water. Hyriopsis sp. shells can potentially be used for reconstruction of past hydrologic conditions. The δ18O of a pearl indicated that calcification occurred over a temperature range of at least 13–23°C. The optimal temperature for
pearl calcification in this species is lower than that for marine pearl calcification. 相似文献
A test environment to evaluate the seismic performance of gusset plate connections intended for steel braced frames is proposed. The developed test method combines the substructuring techniques with finite element analysis methods in an on‐line hybrid scheme. Numerical substructure analysis is conducted on bracing members, while bracing connections are treated as experimental substructures. A force‐displacement combined control imposed with the aid of 2 jacks ensures physical continuity between the analysis and test. The rotational behavior of gusset plate connections subjected to large inelasticity and varying axial loading until fracture is investigated. Two gusset plate details were designed and tested to verify the efficiency of the proposed method. The test method is rational, and smooth operation is achieved. The test results revealed the advantage of the developed on‐line hybrid test method in exploring the ultimate capacity of bracing connections. 相似文献
A corundum-bearing mafic rock in the Horoman Peridotite Complex, Japan, was derived from upper mantle conditions to lower crustal conditions with surrounding peridotites. The amphiboles found in the rock are classified into 3 types: (1) as interstitial and/or poikilitic grains (Green amphibole), (2) as a constituent mineral of symplectitic mineral aggregates with aluminous spinel at grain boundary between olivine and plagioclase (Symplectite amphibole) and (3) as film-shaped thin grains, usually less than 10 μm in width, at grain boundary between olivine and clinopyroxene (Film-shaped amphibole). The Film-shaped amphibole is rarely associated with orthopyroxene extremely low in Al2O3, Cr2O3 and CaO (Low-Al OPX). These minerals were formed by infiltration of SiO2- and volatile-rich fluids along grain boundaries after the rock was recrystallized at olivine-plagioclase stability conditions, i.e. the late stage of the exhumation of the Horoman Complex.
Chondrite-normalized rare earth element patterns and primitive mantle-normalized trace-element patterns of the Green amphibole and clinopyroxene are characterized by LREE-depleted patterns with Eu positive and negative anomalies of Zr and Hf. These geochemical characteristics of the constituent minerals were inherited from original whole-rock compositions through a reaction involving both pre-existing clinopyroxene and plagioclase. We propose that the fluids were originally rich in a SiO2 component but depleted in trace-elements. Dehydration of the surrounding metamorphic rocks in the Hidaka metamorphic belt, probably related to intrusion of hot peridotite body into the Hidaka crust, is a plausible origin for the fluids. 相似文献
Abstract Permian basalt showing typical spinifex texture with >10 cm-long olivine pseudomorphs was discovered from the Jurassic Tamba accretionary complex in southwest Japan. The spinifex basalt occurs as a river boulder accompanied by many ferropicritic boulders in a Permian chert-greenstone unit. Groundmass of this rock is holocrystalline, suggesting a thick lava or sill for its provenance. Minor kaersutite in the groundmass indicates a hydrous magma. The spinifex basalt, in common with the associated ferropicritic rocks, is characterized by high high field strength element (HFSE) contents (e.g. Nb = 62 ppm and Zr = 254 ppm) and high-HFSE ratios (Al2O3/TiO2 = 3.9, Nb/Zr = 0.24 and Zr/Y = 6.4) unlike typical komatiites. The spinifex basalt and ferropicrite might represent the upper fractionated melt and the lower olivine-rich cumulate, respectively, of a single ultramafic sill (or lava) as reported from the early Proterozoic Pechenga Series in Kola Peninsula. Their parental magma might have been produced by hydrous melting of a mantle plume that was dosed with Fe- and HFSE-rich garnet pyroxenite. The spinifex basalt is an evidence for the Pechenga-type ferropicritic volcanism taken place in a Permian oceanic plateau, which accreted to the Asian continental margin as greenstone slices in Jurassic time. 相似文献
Abstract— We measured concentrations and isotopic ratios of noble gases in enstatite (E) chondrites Allan Hills (ALH) 85119 and MacAlpine Hills (MAC) 88136. These two meteorites contain solar and cosmogenic noble gases. Based on the solar and cosmogenic noble gas compositions, we calculated heliocentric distances, parent body exposure ages, and space exposure ages of the two meteorites. The parent body exposure ages are longer than 6.7 Ma for ALH 85119 and longer than 8.7 Ma for MAC 88136. The space exposure ages are shorter than 2.2 Ma for ALH 85119 and shorter than 3.9 Ma for MAC 88136. The estimated heliocentric distances are more than 1.1 AU for ALH 85119 and 1.3 AU for MAC 88136. Derived heliocentric distances indicate the locations of parent bodies in the past when constituents of the meteorites were exposed to the Sun. From the mineralogy and chemistry of E chondrites, it is believed that E chondrites formed in regions within 1.4 AU from the Sun. The heliocentric distances of the two E chondrite parent bodies are not different from the formation regions of E chondrites. This may imply that heliocentric distances of E chondrites have been relatively constant from their formation stage to the stage of exposure to the solar wind. 相似文献
To clarify the beneficial roles of naturally occurring organic ligands on the growth of phytoplankton in newly upwelled water,
phytoplankton culture experiments using disphotic zone water were conducted to discriminate between the effects of EDTA in
the detoxification of certain toxic metal ions and increasing the availability of essential metals. Culture media were prepared
by adding EDTA and Chelex-100, separately or in combination, to disphotic zone water samples. Our proposed working hypothesis
is that phytoplankton growth can be enhanced by removing toxic metal ions from culture media by Chelex-100 and by detoxification
of toxic metal ions or increasing the availability of essential metals by EDTA. A shortening of the lag period and an increase
of the specific population growth rate were clearly observed after the addition of Chelex-100; nd EDTA. The effects of EDTA
were more considerable than those of Chelex-100; a 17 to 44% in shortening the lag period and a 35 to 56% increase in the
growth rate, when comparing the effects of Chelex-100 with those of EDTA. The similar effects of removing toxic metal ion
by Chelex-100 as those of detoxification by EDTA suggested that EDTA has a role not only of detoxification but also of increasing
the availability of essential metals. The present study suggests that the low productivity in newly upwelled water observed
by Barber and Ryther (1969) can be ascribed to both toxic metal ions and a lack of available forms of essential metals because
of their low contents of free natural organic ligands. 相似文献
The hypothesized reaction mechanisms for U reduction by the dehydrogenation of hydroxyl groups and aliphatic hydrocarbonaceous moieties of lignite were verified by kinetic U reduction experiments using simple alcohols (1-octadecanol and 2-propanol) and aliphatic hydrocarbons (n-octacosane). The rate constants and activation energies for U reduction by these alcohols are similar to those obtained for U reduction by lignite. The rate-determining step for U reduction by both simple and natural organic matter is hypothesized to be controlled by oxygen diffusion through U oxides. The equilibria of the system lignite-aqueous uranyl have been used to calculate standard free energy changes ΔG° for lignite dehydrogenation. Their comparison with those for the dehydrogenation of simple organic molecules supports the proposed reactions thermodynamically. 相似文献