1,720,981 research outputs found
Rapid chemical analysis of the
No full textScanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis of smear slides of oriented <2 µm clay fractions is shown to be a reliable and rapid analytical technique for providing chemical data on clay mineral mixtures. Such smear slides are routinely prepared for clay mineral analysis by X-ray diffraction and the only additional treatment required for chemical analysis by EDS is carbon-coating to form an electronically conductive surface. Using standard clays, mixtures of standard clays, and sediment samples, it is shown that sample thickness, sample heterogeneity and surface roughness do not introduce significant analytical errors, although the presence of non-clay mineral phases such as calcite, dolomite, quartz and pyrite may introduce minor discrepancies. Chemical data complement the XRD analyses and increase their accuracy and reliability
Alteration mineralogy of Cretaceous basalt from ODP Site 1001, Leg 165 (Caribbean Sea)
No full textSecondary clay minerals observed in the two uppermost basalt lava flows at ODP Site 1001, in the Caribbean Sea, drilled from the large igneous province of Cretaceous age, result from low-temperature alteration processes. Alteration mainly proceeds by circulation and diffusion of sea water. Six different types of clay mineral assemblage were recognized. Initial alteration with oxygenated sea water involves Fe and K fixation, creating visible oxidation halos parallel to the sides of cracks and fissures. A saponite/beidellite mixture, interstratified smectite-glauconite, interstratified glauconite-nontronite and Fe oxyhydroxides are obtained depending on the distance from fluid conduits. The presence of beidellite may be due to enhanced Al mobilization resulting from high fluid flux. These early minerals are cross-cut by thin veins of pure celadonite or glauconite with further vesicle infill. Late-stage alteration is typified by the formation of saponite and takes plac
Palaeo-flux records from electron microscope studies of Holocene laminated sediments, Saanich Inlet, British Columbia
No full textHolocene varved sediments recovered from Saanich Inlet, ODP Leg 169S, have been analysed using high-resolution scanning electron microscope techniques. The individual centimetre-scale varves form couplets, comprising diatom ooze/diatomaceous mud deposited during spring to autumn and silty clay deposited during winter. Each individual varve may contain up to 19 laminae, recording sub-seasonal to seasonal-scale processes. These intra-annual laminae contain a range of components, including pelagic faecal pellets and aggregates of diatomaceous material. The combination of these individual components in varying proportions with a heterogeneous sediment, leads to a range of laminae fabrics. These include intact monospecific Skeletonema costatum and Thalassiosira pacifica diatom oozes and highly fragmented, aggregate- and faecal pellet-dominated diatom oozes which are typically Chaetoceros spp.-dominated. Additional laminae fabrics include diatomaceous mud, stringer-type diatomaceous mud which contains discrete diatom aggregates, homogeneous and pelleted silty clay. The varved diatom succession typically commences in early spring with Thalassiosira spp./Chaetoceros spp., followed by Chaetoceros spp. in late spring. During late spring/early summer blooms of S. costatum may be recorded, and summer to autumn production is characterised by one to several Chaetoceros spp.-dominated blooms. Inter-annual variability in diatom flux typically comprises the presence/absence of Thalassiosira spp. and S. costatum. In addition, resting spores of Chaetoceros spp., Thalassiosira nordenskioeldii and Leptocylindricus danicus are intermittently recorded. There is a major change in varve thickness from thinner varves prior to approximately 2100 yr BP to thicker varves after this date, which is attributed to increased terrigenous input throughout the varve. The identification of laminae fabrics, diatom successions and a unique massive interval has enabled an inter-site correlation between sites 1033B and 1034B
High-resolution stratigraphic framework for Mediterranean sapropel S5: defining temporal relationships between records of Eemian climate variability
No full textA high-resolution stratigraphic framework is presented for sapropel S5, which represents the low-mid latitude climate optimum of the previous interglacial period (Eemian). The framework is based on three sites along a transect from west to east through the eastern Mediterranean, and is further validated using a fourth site. This method allows expression of S5-based proxy records of Eemian climate variability along a standardised depth scale that offers unprecedented possibilities for assessment of spatial gradients and signal leads and lags in an interval where high-resolution (radiocarbon-style) dating cannot be performed. Our lateral comparison of S5 sapropels suggests that the onset of S5 in ODP site 967C (Eratosthenes seamount) was 1–6 centuries delayed relative to the onsets in more westerly sites
Paleo-sediment trap insights into the significance of subsurface production for ocean flux
No full textCalcium and sulphur distribution in fired clay brick in the presence of a black reduction core using micro X-ray fluorescence mapping
Full text linkA new finding of the observation of an elemental gradient or zoning of calcium and sulphur in fired brick bodies is described, that does not appear to have been reported in the literature before. Many raw clays used in brickmaking and pottery contain sulphur and calcium evenly distributed in low amounts in the unfired clay body. However, when the clay body is fired in the kiln at 1050 °C, the elements sulphur and calcium appear to combine to a compound, most probably calcium sulphate. The formation of calcium sulphate, visualised using energy dispersive imaging micro X-ray fluorescence (?-XRF), only occurs around a so-called reduction core, also known as ‘black core’, caused by reduced magnetite Fe3O4 in the centre of the brick body. The presence of a black reduction core appears to cause the formation of a calcium sulphate layer around the black reduction core. This research contributes to the understanding of phenomena like salt formation, efflorescence and durability in solid clay brick bodies. Large sums are spent on building conservation by national economies and improvement of bricks is of key interest to them.<br/
Intracellular mineral grains in the xenophyophore Nazareammina tenera (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)
No full textXenophyophores, a group of large agglutinated foraminifera, are characterized by the presence of numerous intracellular barite grains, termed granellae, the function and origin of which is unclear. The recently described xenophyophore Nazareammina tenera (Gooday et al., in press), from abyssal depth (4300 m) in the Nazaré Canyon contains an unusually dense concentration of mineral grains in its cytoplasm. Uniquely among known xenophyophores, the intracellular grains in this species comprise a variety of different mineral types in addition to barite. They exhibit a wide range of morphologies and energy dispersive X-ray analysis indicated that they include Ti-bearing minerals, many of them rod-shaped (probably rutile), as well as those containing Fe and Ti (possibly ilmenite and anatase), and Al and Si (probably clay minerals). While the function of intracellular particles in xenophyophores remains unclear, the presence of numerous particles of various types in the cytoplasm suggests that they originate from the sediment. This suite of intracellular mineral grains is completely different from that used to construct the agglutinated test of N. tenera, suggesting that this species is able to discriminate between different kinds of particles. A second xenophyophore species, Reticulammina cerebreformis (Gooday et al., in press), which is abundant at the same site as N. tenera, is devoid of intracellular particles, suggesting that their presence in N. tenera is a species-specific characteristic
Mid to Late Holocene climate change in north central Mongolia as recorded in the sediments of Lake Telmen
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