Analysis Of Individual Grains Research Articles

OPTICAL DATING OF SINGLE AND MULTIPLE GRAINS OF QUARTZ FROM JINMIUM ROCK SHELTER, NORTHERN AUSTRALIA: PART II, RESULTS AND IMPLICATIONS*

Quartz sediments from the floor deposit at Jinmium rock shelter have been investigated using the multiple‐grain and single‐grain optical dating methods described by Galbraith et al. (1999, this volume). Here we present the results of this dating programme and argue that the artefact‐bearing sediments were deposited within the last 10000 years. This time interval is consistent with the radiocarbon chronology but is much younger than previous claims for initial human occupation during the Pleistocene. Analysis of individual grains revealed also that the characteristic saturation doses of some grains are unusually high, which may permit dating of deposits older than a few hundred thousand years. Such grain‐to‐grain differences raise doubts, however, about the validity of using multiple‐grain samples to investigate the phenomenology of quartz luminescence.

Identification of Active Crystalline Phase in La-K-Cu-V Mixed Oxide for the Simultaneous Removal of Nitrogen Oxides and Diesel Soot

Abstract The oxide catalyst having an overall metal composition of La/K/Cu/V = 9/1/7/3 (denoted as LKCVO) showed an excellent selectivity to NOx reduction into N2 in the simultaneous NOx-soot removal reaction, though it was a mixture of several crystalline phases. In order to identify the real active phase, LKCVO was characterized by X-ray diffraction (XRD) and by elemental analysis of individual grains in a transmission electron microscope (TEM) equipped with an energy dispersive spectrometer (EDS). LKCVO was found to be composed of CuO and mixed metal oxides analogous to La2CuO4, LaVO4, and La3VO7. By comparing the catalytic activity of LKCVO with those of single-phase oxides synthesized according to the results of XRD and TEM/EDS, (La2−xKx)(Cu0.95V0.05)O4 with 0.05 ≤ x ≤ 0.1 was identified to be the real active phase in LKCVO for the simultaneous NOx-soot removal reaction.

Variations in REE and Sr-isotope chemistry of carbonate gangue, Castellanos Zn–Pb deposit, Cuba

Abundances of REEs and Sr, the magnitudes of the positive Eu anomalies (Eu/Eu *) and 87Sr/ 86Sr values in carbonate gangue of the Late Jurassic Castellanos SEDEX Zn–Pb deposit vary both laterally and, to a lesser extent, vertically. At the vent-distal site Sr, La and Eu/Eu *, determined by laser ablation microprobe analyses of individual grains, increase slightly from the base of the deposit upward. The La/Lu ratio only increases significantly in the upper part of the section. Both Sr/(Sr+Ca) and La/(La+Ca) in total carbonate, determined by ICP spectrometry, remain relatively constant or increase slightly from the base upward at the vent-distal location. Values of Sr/(Sr+Ca) correlate reasonably well with La/(La+Ca) throughout most of the vent-distal section. The Sr content and Eu/Eu * are higher and La much lower at the vent-proximal location and all three exhibit very large within-sample variations. La does not correlate with Sr at the vent-proximal site. The 87Sr/ 86Sr values at both distal and proximal sites lie between that for Jurassic (Oxfordian) seawater and that of a hydrothermal fluid with a 87Sr/Sr 86 value estimated from 87Sr/ 86Sr in the carbonate gangue of Cu mineralization in a nearby feeder channel beneath a small Zn–Pb deposit similar to Castellanos. Mixing of the REE- and Sr-enriched hydrothermal component with seawater in proportions calculated from the Sr-isotope data will explain the small vertical variations throughout most of the vent-distal section. However, the very low La abundances, the decoupling of the La from Sr and Eu/Eu * and the extreme micro-scale heterogeneity of REE distribution at the vent-proximal site suggest extensive leaching, redistribution and removal of REEs from early-stage carbonates by late-stage hydrothermal fluids at that location.

Luminescence dating of rock art and past environments using mud-wasp nests in northern Australia

Mud-nesting wasps are found in all of the main biogeographical regions of the world1,2,3, and construct nests that become petrified after abandonment. Nests built by mud-dauber and potter wasps in rock shelters in northern Australia1,4 often overlie, and occasionally underlie, prehistoric rock paintings. Mud nests contain pollen, spores and phytoliths from which information about local palaeovegetation can be gleaned. Here we report a new application of optical dating5,6,7, using optically stimulated luminescence (OSL), and accelerator mass spectrometry (AMS) 14C dating of pollen8 to determine the ages of mud-wasp nests associated with rock paintings in the Kimberley region of Western Australia9,10. Optical dating of quartz sand (including the analysis of individual grains) embedded in the mud of fossilized nests shows that some anthropomorphic paintings are more than 17,000 years old. Reconstructions of past local environments are also possible from the range of pollen and phytolith types identified. This approach should have widespread application to studies of rock-art dating and late Quaternary environmental change on continents where mud-wasps once lived and other sources of palaeoecological information are absent.

A Highly Reliable Al Line with Controlled Texture and Grain Boundaries

AbstractIn order to clarify the relationship between Al line reliability and film microstructure, especially grain boundary structure and crystal texture, we have tested three kinds of highly textured Al lines, namely, single-crystal Al line, quasi-single-crystal Al line and hypertextured Al line, and two kinds of conventional Al lines deposited on TiN/Ti and on SiO2. Consequently, the empirical relation between the electromigration (EM) lifetime of Al line † and the (111) full width at half maximum (FWHM) value ω is described by † ∝ ω-2 [1]. This improvement of Al line reliability results from as following reasons; firstly, homogeneous microstructure and high activation energy of 1.28eV for the single-crystal Al line (ω=0.18°); secondly, sub-grain boundaries which consisted of dislocation arrays found in the quasi-single-crystal Al line (ω=0.26°) has turned out to be no more effective mass transport paths because dislocation lines are perpendicular to the direction of electron wind. Although there exist plural grain boundary diffusion paths in the newly developed hypertextured Al line (ω=0.5°) formed by using an amorphous Ta-Al underlayer {1], the vacancy flux along the line has been suppressed to the same order of magnitude of single crystal line. It has been clarified that the decrease of FWHM value has promoted the formation of sub-grain boundaries and low-angle boundaries with detailed orientation analysis of individual grains in the hypertextured film. The longer EM lifetime for the hypertextured Al line is considered to be due to the small grain boundary diffusivities for these stable grain boundaries, and this diffusivity reduction resulted in the suppression of void/hillock pair in the Al lines. These results have confirmed that controlling texture and/or grain boundary itself is a promising approach to develop reliable Al lines which withstand higher current densities required in future ULSIs.

Diverse metal sources of Archaean gold deposits: evidence from in situ lead-isotope analysis of individual grains of galena and altaite in the Ross and Kirkland Lake deposits, Abitibi Greenstone belt, Canada

Lead isotope compositions for individual grains of galena and altaite (PbTe) were determined in situ using a secondary ion mass spectrometer (SIMS). Galena was collected from the Ross deposit and altaite from the Kirkland Lake (KL) deposits in the southern Abitibi greenstone belt, Superior Province of Canada. The samples from KL are more radiogenic than those from the Ross deposit. Isotopic compositions vary significantly between different grains in each deposit and form broad linear arrays in 207Pb/204Pb-206Pb/204Pb and 208Pb/204Pb-206Pb/204Pb diagrams. The linear arrays of Pb-isotope data are attributed to mixing of Pb from different sources. At least two sources are required for individual deposits: one with low U/Pb and Th/Pb ratios and the other with high ratios. Lead minerals occurring with Au are less radiogenic than those that are not obviously associated with Au, suggesting that Au was supplied from low U/Pb sources such as sulphides or older ultramafic-mafic rocks. While most data are consistent with the derivation from local rocks, highly radiogenic Pb with relatively low 207Pb/206Pb ratios recorded at KL require post-Archaean mineralization or derivation of the Pb from an unusual crustal source with low μ. The latter interpretation is favored because of the lack of textural evidence and because it is difficult to dissolve and precipitate altaite at low temperatures. The presence of a Pb reservoir with low μ is also inferred from the data of Archaean banded iron formations and volcanogenic massive sulphide deposits. Different isotopic patterns of the two deposits suggest different sources of metals in the two deposits. While this conclusion does not reject the derivation of fluids from the lower crust or mantle, the data are not in accord with conceptual models invoking a common source reservoir for metals. The study suggests that fluids, which may have a common origin, leached metals and other constituents from the upper crustal rocks during their ascent. The proposed model, different origins for different constituents, explains much of the conflicting evidence presented by Archaean Au deposits, including provinciality of mineralogy and relatively uniform fluid inclusion and C-isotope data from many Au deposits.

SEM Study of Chemical Variations in Western U.S. Fly Ash

ABSTRACTScanning electron microscope/electron microprobe chemical analyses of individual grains of several western fly ashes have shown an inter-grain variation in composition for ashes derived from both lignite and subbituminous western coals. SRM 2689 (a Class F fly ash from a bituminous coal) and SRM 2691 (a Class C fly ash from a subbituminous coal) have been included in the study and also show inter-grain chemical variation. A classification scheme of fly ash grain compositions has been developed and has proven to be useful in illustrating the differences and similarities of the ashes. There is a positive correlation, for example, between grains rich in SiO2 and Al2O3 and the Na2O content of the grains in lignite and subbituminous coal derived fly ashes. There is also a positive correlation between grains rich in CaO and the MgO content of the grains in both classes of fly ashes.

Rare earth elements in chondritic phosphates—implications for 244Pu chronology

In stony meteorites of the chondrite class, phosphates (comprising about 0.6% of the whole) act as host for rare-earth elements (REE) and for Pu which was present at the time of formation. For the purpose of Pu–Xe dating it has been suggested that, in the absence of a stable Pu isotope, measured Xe abundances may be related to REE concentrations, on the grounds of presumed similarity in the geochemical behaviour of Pu and REE1. There are two phosphate phases in chondrites, apatite and merrillite (or whitlockite), which are difficult to separate from each other for analysis. Recent results based on grain-size discrimination2 indicate similar REE concentrations in both phosphates, whereas Pu favours merrillite3. Direct in situ analyses of individual grains by the ion-probe technique, however, show REE concentrations to be about five times higher in merrillite. The use of REE in the role of Pu analogue thus appears a better prospect than suggested by the previous indirect evidence.

Palaeomagnetism and magnetomineralogy of a Holocene lake sediment from Vågsøy, western Norway

Stable remanent directions encountered in three oriented lake-sediment cores, covering 6 m of gyttja deposits, reveal declination swings with amplitudes of the order of ± 50°. Anomalously low inclinations, scattered around the horizontal in the upper 2 m of core, is attributed to compressional disturbances of the alignment of magnetic grains during the coring procedure. Four 14C dates obtained (1250, 1940, 4600 and 6330 y B.P.) have enabled a correlation with features ‘c’–‘g’ of the British Geomagnetic Master Curve). For the older part of the curve, features ‘h’ and ‘i’, the correlation is questionable. Magneto-mineralogical parameters and qualitative chemical analysis of individual grains by secondary X-ray emission analysis reveal the presence of pure magnetite grains. Scanning electron micrographs show a dominant proportion of concoidal slightly elongated grains (10–80 μm). A few almost-perfect octahedral magnetite crystals can be related to outcrops of augen gneisses in the vicinity confirming a detrital origin of these grains.