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MARK D. BATEMAN PAUL C. BUCKLAND MARTIN A. WHYTE ROBERT A. ASHURST CLAIRE BOULTER EVA PANAGIOTAKOPULU 《Boreas: An International Journal of Quaternary Research》2011,40(4):573-584
Bateman, M. D., Buckland, P. C., Whyte, M. A., Ashurst, R. A., Boulter, C. & Panagiotakopulu, E. 2011: Re‐evaluation of the Last Glacial Maximum typesite at Dimlington, UK. Boreas, 10.1111/j.1502‐3885.2011.00204.x. ISSN 0300‐9483. Recent erosion has allowed re‐examination of the stratigraphy and sampling for both optically stimulated luminescence dating and palaeoecological analysis of the key sections in the Last Glacial Maximum deposits at Dimlington in East Yorkshire, England. Both stratigraphy and fossil insect evidence support a subaerial origin for laminated and cross‐bedded sediments between two diamictons previously interpreted as synchronous. The fossil biota indicates conditions similar to those of a pond on sandur in the high Arctic, with little or no vegetation cover. The existence of distinct oscillations of the ice front is indicated. The first, within the period 21.7–16.2 ka, appears coincident with climate warming, as deduced from Greenland ice‐core evidence, and is interpreted as an ice stream associated with changing flow patterns within the British–Irish Ice Sheet (BIIS). The second, dating between 16.2 and 15.5 ka, appears to coincide with a climatic cooling, although current models show that the BIIS had by this period already retreated back to ice centres. This new evidence supports the view that the eastern sector of the BIIS did not reach its maximal extent synchronously with other parts of the BIIS. 相似文献
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CORDIER CAROLE; CLEMENT JEAN-PHILIPPE; CAROFF MARTIAL; HEMOND CHRISTOPHE; BLAIS SYLVAIN; COTTEN JOSEPH; BOLLINGER CLAIRE; LAUNEAU PATRICK; GUILLE GERARD 《Journal of Petrology》2005,46(11):2281-2312
This study is based on a set of coarse-grained igneous rockscollected from two zoned plutons located in the central partof Tahiti Nui and Raiatea. The Ahititera pluton (central depressionof Tahiti Nui) comprises a great diversity of rocks, rangingfrom ultrabasic to felsic in composition. It shows a concentriczonation with nepheline-free rocks in its periphery and nepheline-bearingrocks in its central part. The Faaroa pluton (central depressionof Raiatea) is entirely mafic and includes only gabbros andtheralites. The two plutons have variable Nd–Sr isotopicsignatures, especially the Ahititera rocks, which are subdividedinto three groups based on their mineralogy, geochemistry andisotope composition. The isotopic variability probably reflectslocal heterogeneities in the Society mantle plume. Petrographicand isotopic data have been used to define two magmatic suitesin Ahititera, identifiable from their degree of Si undersaturation.The evolution of the mildly Si-undersaturated suite is controlledby simple fractional crystallization, whereas the strongly Si-undersaturatedsuite requires additional H2O influx. The third isotopic groupincludes only theralites. The rare earth element (REE) compositionsof the mafic rocks from both plutons do not correlate with theirisotopic signature. The REE patterns of the most Si-undersaturatedrocks are systematically characterized by steeper slopes. Suchfeatures are also observed in lavas from seamounts located withinthe present-day hotspot area. It appears that REE concentrationsin Society lavas and intrusives are probably mainly governedby variable degrees of partial melting of a garnet-free mantlesource and are independent of their isotopic signature. KEY WORDS: cumulates; fractional crystallization; partial melting; French Polynesia; plutonic rocks; Society Islands; Tahiti; Raiatea 相似文献
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Classification and analysis of palynodebris from the Palaeocene sediments of the Forties Field 总被引：3，自引：0，他引：3
Sedimentary organic matter behaves as sedimentary particles and this study attempts to interpret its occurrence in the Palaeocene sands and mudstones of the Forties Field of the North Sea. New nomenclature and classification of this palynodebris are presented and are used to make quantitative counts of the palynodebris from nearly 600 samples of known sedimentary character. The new categories are further refined by objective testing of the data by Principal Components Analysis and Cluster Analysis. It is argued that two types of sedimentary organic matter are of particular value because they are preferentially deposited in different environments: palynowafers are most commonly deposited in the submarine fan lobes and channel complexes and amorphous matter occurs mostly in the lower energy basin plain sediments. 相似文献
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MICHAEL C. BOULTER 《Geology Today》1997,13(3):102-106
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C.A. BOULTER 《Geology Today》1986,2(4):106-111
The Pilbara is an important region for the study of early Earth history, primarily because it contains large areas of volcanics and sediments, as old as 3550 million years, that are commonly extremely well preserved as a result of an exceptionally heterogeneous tectonic overprint during cratonisation. This latter event was completed by 2800 million years ago and hence much of the cover sequence up to the classic Hamersley banded iron formation is Archean in age. 相似文献
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