Composition and Textual Characterization of Platinum-group Mineral (PGM) in Chromites from Zedang Ophiolite in Tibet, China

<正>1 Introduction Platinum-group elements(PGE)are mainly concentrated in some specific minerals known as PGMs,which commonly occur in podiform chromites of ophiolites.In-situ PGM assemblages in chromites can provide valuable information on the physico-chemical nature of the parental melt(s)from which chromitite     

The pre-Landnám fauna of Iceland: a palaeontological contribution

The origins of the Icelandic biota are discussed with particular reference to recent work on Coleopteran (beetle) and Trichopteran (caddis fly) fossils from deposits which are earlier than the arrival of man (Landnám) in the country. The hypothesis of survival through Pleistocene glaciations in refugia is discounted in favour of immigration on ice floes during Late Glacial/Early Holocene deglaciation. Consideration of the nature of the insect fauna and the extent of Late Glacial ice sheets, with the evidence from ocean circulation patterns, suggests a source area in the fjords of south-west Norway. The model is applicable to the origins of the biota on all the North Atlantic islands, east of the Davis Strait.     

PRINCIPAL COMPONENTS REGRESSION FOR ROUTINE MULTICOMPONENT UV DETERMINATIONS: A VALIDATION PROTOCOL

A validation protocol for multicomponent spectroscopic assays based on principal componentsregression is described. Factorial design and hypothesis tests are used to establish the linearity andabsence of interaction between components in the regression model. Testing considers multiple responsevariables simultaneously so that correlation between residuals is properly treated. Assay reproducibilityand sensitivity to related substances are evaluated.     

MIXTURE ANGLYSIS USING FACTOR ANGLYSIS I: CALIBRATION AND QUANTITATION

One of the major application areas of factor analysis, multivariate calibration and quantitation, is coveredin this review. The algorithms, methodologies and applications covered include principal componentregression, target transformation factor analysis, singular value decomposition and rank annihilationfactor analysis. Many important areas of research having relevance to multivariate calibration andquantitation problems are also covered in this review, including background correction, measurementerror, rank determination, cross-validation, figures of merit, detection of invalid samples, experimentaldesign, sample selection, statistical inference and wavelength selection.     

The latest vertebrates are the earliest

The teeth, or elements, ofconodonts are among the most important Palaeozoic microfossils. Despite this, the biological relationships of conodonts have long remained enigmatic. Recent evidence of their soft anatomy, and of the ultrastructure of the elements, has finally revealed that they are vertebrates. These discoveries push vertebrate origins firmly back into the Cambrian and add a large cohort of specialists to the ranks of the vertebrate palaeontologists.     

Age, Origin and Cooling History of the Coronel Joao Sa Pluton, Bahia, Brazil

In north-east Brazil, Archean and Paleoproterozoic cratonicblocks are enclosed within a network of Brasiliano-age (0·7–0·55Ga) metasedimentary foldbelts. The unfoliated Coronel JoãoSá granodiorite pluton, which contains magmatic epidoteand strongly resorbed clinopyroxene, intrudes the SergipanoFoldbelt. Zircons yield a concordant U–Pb crystallizationage of 625 ± 2 Ma; titanite ages are approximately 621Ma. Discordant zircons suggest inheritance from at least twomagma sources of ages <1·8 and >2·2 Ga.Model calculations based on diffusion parameters and Rb–Srisotope data from separated minerals indicate that the plutoncooled at a rate of 36°C/Myr. Whole-rock element compositionsand initial Sr–Nd isotopic compositions that are heterogeneouson all length scales suggest magma mixing. Trace-element concentrationsand Nd isotope data argue against a contribution from a contemporaneousmantle-derived magma. Values of magmatic _Nd (at 625 Ma) resemblecontemporary _Nd for local supracrustal rocks and basement, compatiblewith anatexis of a crustal source. In north-east Brazil, cratonicblocks could have amalgamated with foldbelts that originatedas: (1) a mosaic of island arcs and arc basins (traditionalallochthonous model), or as (2) extensional continental sedimentarybasins (but not oceanic crust) later involved in collision (autochthonousmodel). The Coronel João Sá isotopic and chemicaldata support an autochthonous origin. KEY WORDS: Brasiliano Orogeny; granodiorite pluton; Rb–Sr isotopes, Sm–Nd isotopes; U–Pb isotopes, magma cooling rate     

A Comparison of Growth Biomarkers for Assessing Sublethal Effects of Cadmium on a Marine Gastropod, Nassarius festivus

The effect of cadmium on the growth of an intertidal marine gastropod, Nassarius festivus, was investigated using a number of biomarkers namely conventional measurements in terms of increase in shell length or body weight, scope for growth (SfG) and RNA/DNA ratio. After eight days of cadmium exposure, the no observable effect concentration (NOEC) and lowest observable effect concentration (LOEC) for the rate of increase in wet weight were 1.00 and 1.38 mg/l, respectively, while those for shell length did not show any significant difference from the control until day 16. After 16 days of cadmium exposure, the LOEC for both shell length and wet weight measurements was 0.22 mg/l. The 8-day SfG test was sensitive to cadmium stress, showing a significant decrease at 0.16 mg/l cadmium when compared to the control. The NOEC and LOEC of RNA/DNA ratio determination were 0.52 and 0.93 mg/l, respectively. An assessment based on sensitivity and technical complexity suggests that Scope for Growth is the most sensitive growth biomarker, followed by the RNA/DNA ratio, and then the conventional growth measurement based on shell size and body weight.     

Unusual intraclastic limestones in Lower Triassic carbonates and their bearing on the aftermath of the end-Permian mass extinction

Flat pebble conglomerates were a common carbonate facies in Cambrian to Early Ordovician open marine settings, but they become extremely rare in these environments after this time. However, the Early Triassic witnessed an anachronistic reappearance of flat pebbles, together with other intraclast types, in a range of carbonate depositional settings. In south China, flat pebble conglomerates are encountered in storm-dominated, platform carbonates to deep basinal settings, while prefossilized bivalve intraclasts and flat pebbles are common in mid-ramp facies of northern Italy. The emplacement mechanisms of the intraclast-bearing beds appear to have been diverse and to have included basinal turbidity flows and storm-generated hyperconcentrated flows: true storm beds, deposited under combined flow conditions, are rare. The cause of the widespread early lithification implied by the Early Triassic intraclasts appears to have been twofold: suppression of bioturbation, allowing the preservation of thin beds, and rapid submarine lithification. Both features appear to be a response to the widespread development of benthic dysoxia/anoxia during and following the end-Permian mass extinction. This event appears to have temporarily recreated the conditions that pertained in Cambro-Ordovician shelf seas. Flat pebble conglomerates may, therefore, constitute a proxy indicator of stressed environmental conditions associated with global anoxic/dysoxic events.     

ESTIMATING RATES OF DENUDATION USING COSMOGENIC ISOTOPE ABUNDANCES IN SEDIMENT

We propose, as a testable hypothesis, a basin-scale approach for interpreting the abundance of in situ produced cosmogenic isotopes, an approach which considers explicitly both the isotope and sediment flux through a drainage basin. Unlike most existing models, which are appropriate for evaluating in situproduced cosmogenic isotope abundance at discrete points on Earth's surface, our model is designed for interpreting isotope abundance in sediment. Because sediment is a mixture of materials, in favourable cases derived from throughout a drainage basin, we suggest that measured isotope abundances may reflect spatially averaged rates of erosion. We investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed.