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111.
OLE BENNIKE JØRN BO JENSEN PETER B. KONRADI WOLFRAM LEMKE JAN HEINEMEIER 《Boreas: An International Journal of Quaternary Research》2000,29(4):272-286
Shallow seismic profiling indicated the presence of a drowned lagoon-barrier system formed during the transgression of the southern Kattegat, and investigations of core material have confirmed this. Studies of plant and animal macrofossils show that the lagoonal sediments contain a mixture of marine, brackish, lacustrine, telmatic and terrestrial taxa, and analyses of foraminifers indicate brackish-water conditions. Low oxygen isotope values obtained on shells of marine molluscs also point to lowered salinity. The lagoonal sediments are situated at depths between 24 and 35 m below present sea level. They are dated to between c. 10.5 cal. ka BP and c. 9.5 cal. ka BP, and reflect a period characterized by a moderate relative sea level rise. The lagoonal sediments are underlain by lateglacial glaciomarine clay and silt, which are separated from the Holocene deposits by an unconformity. The earliest Holocene sediments consist of littoral sand with gravel, stones and shells; these sediments were formed during the transgression of the area before the barrier island-lagoon system was developed. The lagoonal sediments are overlain by mud, which contains animal remains that indicate increasing water depths. 相似文献
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The Neoproterozoic Aries kimberlite was emplaced in the centralKimberley Basin, Western Australia, as a NNNE-trendingseries of three diatremes infilled by lithic-rich kimberlitebreccias. The breccias are intruded by hypabyssal macrocrysticphlogopite kimberlite dykes that exhibit differentiation toa minor, high-NaSi, olivinephlogopiterichteritekimberlite, and late-stage macrocrystic serpentinediopsideultramafic dykes. Mineralogical and geochemical evidence suggeststhat the high-NaSi, olivinephlogopiterichteritekimberlite was derived from the macrocrystic phlogopite kimberliteas a residual liquid following extended phlogopite crystallizationand the assimilation of country rock sandstone, and that themacrocrystic serpentinediopside ultramafic dykes formedas mafic cumulates from a macrocrystic phlogopite kimberlite.Chemical zonation of phlogopitebiotite phenocrysts indicatesa complex magmatic history for the Aries kimberlite, with theearly inheritance of a range of high-Ti phlogopitebiotitexenocrysts from metasomatized mantle lithologies, followed bythe crystallization of a population of high-Cr phlogopite phenocrystswithin the spinel facies lithospheric mantle. A further oneto two phlogopitebiotite overgrowth rims of distinctcomposition formed on the phlogopite phenocrysts at higher levelsduring ascent to the surface. Ultra-violet laser 40Ar/39Ar datingof mica grain rims yielded a kimberlite eruption age of 815·4± 4·3 Ma (95% confidence). 40Ar/39Ar laser profilingof one high-Ti phlogopite-biotite macrocryst revealed a radiogenic40Ar diffusive loss profile, from which a kimberlite magma ascentduration from the spinel facies lithospheric mantle was estimated(assuming an average kimberlite magma temperature of 1000°C),yielding a value of 0·232·32 days for thenorth extension lobe of the Aries kimberlite. KEY WORDS: 40Ar/39Ar; diamond; kimberlite; mantle metasomatism; phlogopitebiotite 相似文献
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The concept of sediment sorting extending from the Bagnold constitutive relationship for sediment under shear is examined in the context of beach placer formation. The traditional interpretation of shear sorting is found to be inconsistent with data from new granular flow experiments. A binary mixture satisfying the shear equivalence relationship displayed pronounced segregation during shear. This observation is contrary to shear sorting as applied in the literature where no such segregation for this pairing of mineral species is expected. Further experiments minimizing the potential of grain percolation of smaller grains or kinetic sieving also demonstrated sorting patterns inconsistent with the existing shear sorting interpretation. Consequently, the shear sorting process, as currently formulated, may not be an appropriate means to describe beach placer formation. Kinetic sieving appears to be a more likely mechanism in this context, enhanced by the shearing and dilation of the granular‐fluid flow. 相似文献
116.
By RALPH KAHN REAS PETZOLD MANFRED WENDISCH EIKE BIERWIRTH TILMAN DINTER MICHAEL ESSELBORN MARCUS FIEBIG BIRGIT HEESE PETER KNIPPERTZ DETLEF MÜLLER ALEXANDER SCHLADITZ WOLFGANG VON HOYNINGEN-HUENE 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):239-251
Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006 field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite's larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05–0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR's ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away. 相似文献
117.
PETER J. VINCENT TOM C. LORD MATT W. TELFER PETER WILSON 《Boreas: An International Journal of Quaternary Research》2011,40(1):105-115
Vincent, P. J., Lord, T. C., Telfer, M. W. & Wilson, P. 2010: Early Holocene loessic colluviation in northwest England: new evidence for the 8.2 ka event in the terrestrial record? Boreas, 10.1111/j.1502‐3885.2010.00172.x. ISSN 0300‐9483. Twelve new samples of loessic silts from widely spaced locations on the karst uplands of northwest England have yielded Optically Stimulated Luminescence (OSL) dates that fall within or overlap with (within uncertainties) the early to mid‐Holocene period (11.7–6.0 ka), and support three already‐published Holocene ages from similar sediment from this region. Nine of the 15 dates are coincident with the hypothesized climatic deterioration at 8.5–8.0 ka in the North Atlantic region and eight are coincident with the 8.2 ka event. These dates demonstrate that the silts are not primary air‐fall loesses of deglacial/Lateglacial age (c. 18.0–11.7 ka) but have been reworked and now consist of loess‐derived colluvial deposits; we consider the ages to be reliable as there is no compelling evidence to indicate that the samples are partially bleached. There is no substantive archaeological or palynological evidence for Late Mesolithic hunter‐gatherers having had a major impact on the landscape, and it is considered highly unlikely that these people triggered colluviation. We estimate that during the 8.2 ka event there was a reduction in mean annual air temperature at these upland locations of ~2.6–4.6 °C, and proxy evidence from other sites indicates a shift to wetter conditions. It is inferred that there was greater snow accumulation in winter, that the snowpack survived for longer periods, and that there was an increase in the magnitude and frequency of frost‐related processes and meltwater flooding. Together, these changes in climate and their associated (sub)surface processes were responsible for the reworking of the loess. The OSL dates indicate climatically induced landscape dynamism in Great Britain during the latter half of the ninth millennium. 相似文献
118.
STEFAN LAUTERBACH ACHIM BRAUER NILS ANDERSEN DAN L. DANIELOPOL PETER DULSKI MATTHIAS HÜLS KRYSTYNA MILECKA TADEUSZ NAMIOTKO BIRGIT PLESSEN ULRICH VON GRAFENSTEIN DECLAKES PARTICIPANTS 《Boreas: An International Journal of Quaternary Research》2011,40(1):57-72
Lauterbach, S., Brauer, A., Andersen, N., Danielopol, D. L., Dulski, P., Hüls, M., Milecka, K., Namiotko, T., Plessen, B., von Grafenstein, U. & DecLakes participants 2010: Multi‐proxy evidence for early to mid‐Holocene environmental and climatic changes in northeastern Poland. Boreas, 10.1111/j.1502‐3885.2010.00159.x. ISSN 0300‐9483. We investigated the sedimentary record of Lake Hańcza (northeastern Poland) using a multi‐proxy approach, focusing on early to mid‐Holocene climatic and environmental changes. AMS 14C dating of terrestrial macrofossils and sedimentation rate estimates from occasional varve thickness measurements were used to establish a chronology. The onset of the Holocene at c. 11 600 cal. a BP is marked by the decline of Lateglacial shrub vegetation and a shift from clastic‐detrital deposition to an autochthonous sedimentation dominated by biochemical calcite precipitation. Between 10 000 and 9000 cal. a BP, a further environmental and climatic improvement is indicated by the spread of deciduous forests, an increase in lake organic matter and a 1.7‰ rise in the oxygen isotope ratios of both endogenic calcite and ostracod valves. Rising δ18O values were probably caused by a combination of hydrological and climatic factors. The persistence of relatively cold and dry climate conditions in northeastern Poland during the first one and a half millennia of the Holocene could be related to a regional eastern European atmospheric circulation pattern. Prevailing anticyclonic circulation linked to a high‐pressure cell above the retreating Scandinavian Ice Sheet might have blocked the influence of warm and moist Westerlies and attenuated the early Holocene climatic amelioration in the Lake Hańcza region until the final decay of the ice sheet. 相似文献
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By BERND HEINOLD INA TEGEN MICHAEL ESSELBORN KONRAD KANDLER PETER KNIPPERTZ DETLEF MÜLLER ALEXANDER SCHLADITZ MATTHIAS TESCHE BERNADETT WEINZIERL ALBERT ANSMANN DIETRICH ALTHAUSEN BENOIT LAURENT REAS MASSLING THOMAS MÜLLER REAS PETZOLD KERSTIN SCHEPANSKI ALFRED WIEDENSOHLER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):307-324
The regional dust model system LM-MUSCAT-DES was developed in the framework of the SAMUM project. Using the unique comprehensive data set of near-source dust properties during the 2006 SAMUM field campaign, the performance of the model system is evaluated for two time periods in May and June 2006. Dust optical thicknesses, number size distributions and the position of the maximum dust extinction in the vertical profiles agree well with the observations. However, the spatio-temporal evolution of the dust plumes is not always reproduced due to inaccuracies in the dust source placement by the model. While simulated winds and dust distributions are well matched for dust events caused by dry synoptic-scale dynamics, they are often misrepresented when dust emissions are caused by moist convection or influenced by small-scale topography that is not resolved by the model. In contrast to long-range dust transport, in the vicinity of source regions the model performance strongly depends on the correct prediction of the exact location of sources. Insufficiently resolved vertical grid spacing causes the absence of inversions in the model vertical profiles and likely explains the absence of the observed sharply defined dust layers. 相似文献