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461.
KURT BOSTRÖM DAVID E. FISHER 《Boreas: An International Journal of Quaternary Research》1972,1(4):275-288
Boström, K., & Fisher, D. E.: Lateral fluctuations in pelagic sedimentation during the Pleistocene glaciations. Boreas, Vol. 1, pp. 275–288. Oslo, 1st December, 1972.
A total of 308 sediment samples of dated cores from 7 different locations have been analyzed for several major and trace elements. Our results, as well as previously published ones, show that during the Pleistocene the pelagic sediments have high concentrations of Mn, Cu, Co, REE, etc., in deposits of glacial age and low concentrations in corresponding interglacial ones; for hemipelagic sediments the situation is reversed. This shows that the boundary between reducing hemipelagic sediments and well-oxidized pelagic sediments has been migrating laterally back and forth due to climatic variations. Such sediment sequences may be easily confused with deposits where postdepositional migration of Mn and other elements has taken place. 相似文献
A total of 308 sediment samples of dated cores from 7 different locations have been analyzed for several major and trace elements. Our results, as well as previously published ones, show that during the Pleistocene the pelagic sediments have high concentrations of Mn, Cu, Co, REE, etc., in deposits of glacial age and low concentrations in corresponding interglacial ones; for hemipelagic sediments the situation is reversed. This shows that the boundary between reducing hemipelagic sediments and well-oxidized pelagic sediments has been migrating laterally back and forth due to climatic variations. Such sediment sequences may be easily confused with deposits where postdepositional migration of Mn and other elements has taken place. 相似文献
462.
Triclinic KFeSi3O8, iron-microcline, has been synthesized fromoxide mixes and by complete conversion of monoclinic KFeSi3O8,iron-sanidine. Iron-microcline is triclinic, C, a=8?68?0?01?, b=13?10?0?01, c=7?34?0?01, =90? 45'?10', ß=116?03'?10', =86?14'?10'. The optical properties (Na light) are:=1?585?0?002, ß=1?596?0?002, =1?605?0?002, 2V=85?(calc.), Xb, Z c=20??5?. A reversible phase transition betweentriclinic and monoclinic KFeSi3O8 occurs at 704??6? C at 2000bars total pressure. Iron-microcline is the low-temperaturepolymorph; no intermediate polymorphs were observed in eitherhydrothermal or dry heating experiments. 相似文献
463.
DAVID W. SCHOLL 《Sedimentology》1963,2(2):156-163
Three methods, (a)dessication, (b)gas extraction and (c)immiscible-liquid extraction, are described and evaluated for removing interstitial water from coarse-grained sedi- ments for semi-quantitative and quantitative chemical analyses. The dessication method is useful for chlorinity or chlorosity determinations and (with a correction of 5%) gives results probably accurate to within about ± 2O% Extraction of interstitial water with gas of high relative humidity gives results which are correct to within an error of ± l.O% The chlorosity of interstitial water extracted by forcing a high- viscosity epoxy plasticizer (immiscible with water) through the sediment falls within about ± 0.1% of the correct value. The immiscible-extraction method is therefore recommended for work requiring quantitative knowledge of interstitial water chemistry. 相似文献
464.
Surface textures of quartz grains have been examined from five samples from the Laurentian Fan and Sohm Abyssal Plain, representing varied transport distances and power of the depositing turbidity current. The grains retain their primary irregular shape derived from glacial erosion, and glacial surface textures are preserved in dish-shaped depressions. These features have been superimposed by a slight rounding of edges and an abundance of collision-induced markings, particularly mechanical V-forms. The most intense current modification of this sort occurs in mid-Wisconsinan or earlier sands that have been transported over 1000 km to the distal Sohm Abyssal Plain by turbidity currents. Collision textures probably develop during grain flow on the steep continental slope: delicate resedimented shelf foraminifera are preserved in the same turbidites and most have been transported exclusively in suspension. 相似文献
465.
NICOLAS J. RAWLENCE DAVID J. LOWE JAMIE R. WOOD JENNIFER M. YOUNG G. JOCK CHURCHMAN YU‐TUAN HUANG ALAN COOPER 《第四纪科学杂志》2014,29(7):610-626
Palaeoenvironmental DNA (PalEnDNA) is defined as ancient DNA (aDNA) originating from disseminated genetic material within palaeoenvironmental samples. Sources of PalEnDNA include marine and lake sediments, peat, loess, till, ice, permafrost, palaeosols, coprolites, preserved gut contents, dental calculus, tephras, and soils as well as deposits in caves/rockshelters and at archaeological sites. PalEnDNA analysis provides a relatively new tool for Quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions, testing hypotheses regarding megafaunal extinctions, human–environment interactions, taxonomic studies, and studies of DNA damage. Because PalEnDNA samples comprise markedly different materials, and represent wide‐ranging depositional and taphonomic contexts, various issues must be addressed to achieve robust, reproducible findings. Such issues include climatic and temporal limitations, the biological origin and state (free versus bound) of PalEnDNA, stratigraphic reliability, sterile sampling, ability to distinguish modern from aDNA signals, DNA damage and PCR amplification, DNA extraction methods, and taxonomic resolution. In this review, we provide a non‐specialist introduction to the use of PalEnDNA for Quaternary and archaeological researchers, assess attributes and limitations of this palaeoenvironmental tool, and discuss future prospects of using PalEnDNA to reconstruct past environments. 相似文献
466.
ACOSTA-VIGIL ANTONIO; LONDON DAVID; MORGAN GEORGE B. VI; DEWERS THOMAS A. 《Journal of Petrology》2006,47(2):231-254
We have conducted experiments on dissolution of quartz, albite,orthoclase, and corundum into H2O-saturated haplogranite meltat 800°C and 200 MPa over a duration of 1201488 hwith the aim of ascertaining the diffusive transport propertiesof granitic melts at crustal anatectic temperatures. Cylindersof anhydrous starting glass and a single mineral phase (quartzor feldspar) were juxtaposed along flat and polished surfacesinside gold or platinum capsules with 10 wt % added H2O. Concentrationprofiles in glass (quenched melt) perpendicular to the mineralglassinterfaces and comparison with relevant phase diagrams suggestthat melts at the interface are saturated in the dissolvingphases after 384 h, and with longer durations the concentrationprofiles are controlled only by diffusion of components in themelt. The evolution of the concentration profiles with timeindicates that uncoupled diffusion in the melt takes place alongthe following four linearly independent directions in oxidecomposition space: SiO2, Na2O, and K2O axes (Si-, Na-, and K-eigenvectors,respectively), and a direction between the Al2O3, Na2O, andK2O axes (Al-eigenvector), such that the Al/Na molar ratio isequal to that of the bulk melt and the Al/(Na + K) molar ratiois equal to the equilibrium ASI (= mol. Al2O3/[Na2O + K2O])of the melt. Experiments in which a glass cylinder was sandwichedbetween two mineral cylindersquartz and albite, quartzand K-feldspar, or albite and corundumtested the validityof the inferred directions of uncoupled diffusion and exploredlong-range chemical communication in the melt via chemical potentialgradients. The application of available solutions to the diffusionequations for the experimental quartz and feldspar dissolutiondata provides diffusivities along the directions of the Si-eigenvectorand Al-eigenvector of (2·02·8) x 1015m2/s and (0·62·4) x 1014 m2/s, respectively.Minimum diffusivities of alkalis [(39) x 1011m2/s] are orders of magnitude greater than the tetrahedral componentsof the melt. The information provided here determines the rateat which crustal anatexis can occur when sufficient heat issupplied and diffusion is the only mass transport (mixing) processin the melt. The calculated diffusivities imply that a quartzo-feldspathicsource rock with initial grain size of 23 mm undergoinghydrostatic, H2O-saturated melting at 800°C (infinite heatsupply) could produce 2030 vol. % of homogeneous meltin less than 110 years. Slower diffusion in H2O-undersaturatedmelts will increase this time frame. KEY WORDS: chemical diffusion; haplogranite; mineral dissolution experiments; crustal anatexis 相似文献
467.
The Role of Pre-existing Mechanical Anisotropy on Shear Zone Development within Oceanic Mantle Lithosphere: an Example from the Oman Ophiolite 总被引:4,自引:0,他引:4
Structural and fabric analysis of the well-exposed Hilti mantlesection, Oman ophiolite, suggests that shear zone development,which may have resulted from oceanic plate fragmentation, wasinfluenced by pre-existing mantle fabric present at the paleo-ridge.Detailed structural mapping in the mantle section revealed agently undulating structure with an eastwest flow direction.A NWSE strike-slip shear zone cuts across this horizontalstructure. The crystal preferred orientation (CPO) of olivinewithin the foliation is dominated by (010) axial patterns ratherthan more commonly observed (010)[100] patterns, suggestingthat the horizontal flow close to the Moho involved non-coaxialflow. Olivine CPO within the shear zone formed at low temperatureis characterized by (001)[100] patterns and a sinistral senseof shear. The olivine CPO becomes weaker with progressive mylonitizationand accompanying grain size reduction, and ultimately developsinto an ultra-mylonite with a random CPO pattern. The olivine[010]-axis is consistently sub-vertical, even where the horizontalfoliation has been rotated to a sub-vertical orientation withinthe shear zone. These observations suggest that the primarymechanical anisotropy (mantle fabric) has been readily transformedinto a secondary structure (shear zone) with minimum modification.This occurred as a result of a change of the olivine slip systemsduring oceanic detachment and related tectonics during cooling.We propose that primary olivine CPO fabrics may play a significantrole in the subsequent structural development of the mantle.Thus, the structural behavior of oceanic mantle lithosphereduring subduction and obduction may be strongly influenced byinitial mechanical anisotropy developed at an oceanic spreadingcenter. KEY WORDS: mantle lithosphere; anisotropy; shear zone; olivine CPO; Oman ophiolite 相似文献
468.
DAVID J. CULLEN 《Sedimentology》1988,35(3):421-428
By far the commonest consituents of insular phosphate deposits are calcium phosphates of the apatite series of minerals, especially varieties that contain structural carbonate in their crystal lattices, e.g. francolite and dahllite. This reflects the fact that the vast majority of described insular phosphate deposits occur in low latitudes, where they have formed, in a tropical environment, by metasomatic replacement of carbonate in coral substrates by phosphate derived either from avian excrement or from phosphorus-enriched lagoonal/lacustrine waters. Thin, recently-formed guano accumulations on islands of the subantarctic Bounty group differ radically in that they consist principally of struvite, a hydrated ammonium magnesium phosphate that is better known as a component of human/mammalian urinary stones and enteroliths, and of bat guano in sheltered speleothems. Apatite occurs only in an accessory role in the Bounty Islands guano. This contrast in mineralogy, and the somewhat anomalous survival of soft, unstable struvite in a totally exposed environment on the Bounty Islands, are attributed to climatic factors and to the nature of the granodioritic rock substrate. 相似文献
469.
Mawpyut igneous suite in Jaintia Hills of Meghalaya plateau comprises differentiated suite of ultramafic–mafic rocks. The
complex differs from other ultramafic–alkaline–carbonatite igneous emplacements of Shillong plateau and Mikir Hills like Jesra,
Sung, Samchampi complexes, by the absence of alkaline–carbonatite rocks as major litho-units. Melanite garnet-bearing nepheline
syenite, occurs as late phase minor intrusion in Mawpyut igneous complex, posseses alkaline character and shows inubiquitous
relation with the host ultramafic–mafic rocks. On the other hand, this alkaline intrusive bodies of the Mawpyut igneous complex
shows chemico-mineralogical resemblance with garnet-bearing nepheline syenite, ijolite litho-members of Jesra, Sung, Samchampi
complexes of the region. It is interpreted that melanite garnet-bearing nepheline syenite intrusion in Mawpyut is contemporaneous
with Jesra, Sung, Samchampi ultramafic–alkaline–carbonatite complexes and the host rocks of Mawpyut complex is an earlier
magmatic activity possibly from a comparatively least enriched source. 相似文献
470.
A COMPARATIVE STUDY OF GLAUCONITE AND THE ASSOCIATED CLAY FRACTION IN MODERN MARINE SEDIMENTS 总被引:1,自引:0,他引:1
The crystallinity and mineralogy of both the glauconite and the clay fraction of samples from six contemporary marine environments were investigated by X-ray diffraction. In those areas where glauconite is now forming, the mineralogy and the degree of crystallinity of both the glauconite pellets and the associated clay fraction are similar. In contrast, detrital and relic glauconites are observed to have mineralogies that are different from their clay fractions. No consistent relationship was observed between degree of crystallinity and color of the pellets. Further, only two classes of glauconite as defined by BURST (1958) were common: expandable, interlayered clays and two or more clay minerals in a mixed assemblage. Based on the clay fraction-glauconite similarities and other supporting evidence, glauconite on the Scotia Ridge is concluded to be authigenic. Glauconite from Santa Monica Bay, California and from the continental shelf off Morocco appear to be detrital. Glauconite pellets in the shelf sediments off Guinea and the southeastern Atlantic Shelf of the United States are both detrital and authigenic. The poor crystallinity exhibited by the Chatham Rise glauconite is in contrast to the well-crystallized associated clay fraction and indicates that they are not genetically related. However, the origin of this glauconite remains in doubt. 相似文献