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Kaare L. Rasmussen Hans J. F. Olsen Raymond Gwozdz Evgeniy M. Kolesnikov 《Meteoritics & planetary science》2001,36(7):1001-1006
Abstract— Jull et al. propose an alternative interpretation of our depth vs. 14C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable. 相似文献
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Rajmund Gwozdz Hans J. Hansen Kaare L. Rasmussen 《Geostandards and Geoanalytical Research》2001,25(1):159-166
The collapse of a section of the cliff at Stevns Klint, Denmark in 1986 provided a unique opportunity to collect about 50 kg of Fish Clay representing the Cretaceous-Tertiary (K-T) boundary layer. In this paper, details of the preparation of this sample are presented, together with preliminary analytical results to support the development of this sample as a reference material, particularly for the determination of iridium and the other platinum-group elements in clays and sediments associated with K-T boundary studies and in other environmental samples collected to study the effects of automobile exhaust catalysts. 相似文献
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Lithium was analysed in 392 basalts and related igneous rocks from the North Atlantic Tertiary-Recent province using activation analysis and ?erenkov counting.Monotonous Li values of 5.5±2 ppm in NE Atlantic basalts define a low-Li geochemical province which has persisted for 60 million years, over 20° of latitude and regardless of basalt type and chemistry. This low-Li province and the increasing Li contents of ocean-ridge tholeiites into the S Atlantic are believed to monitor Li heterogeneity in the underlying mantle.Li, like Na, increases gently during the differentiation of several basalt series. No whole-rock coherence is observed between Li and Mg, K, Rb or Ca. Mantle phlogopite is considered to play an insignificant rôle in controlling the Li levels of NE Atlantic basalts. 相似文献
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Uranium is significantly enriched (up to two orders of magnitude) in the Danish Cretaceous-Tertiary boundary beds relative to the underand overlaying sediments. Both the predominant oxic and some anoxic deposits have a high uranium content. To investigate the geochemical behaviour of the element, a series of sections was analysed for uranium by means of the delayed-neutron counting technique. Uranium contents in the carbonate rocks from different parts of the Danish Sub-basin are generally low but show slight regional trends. Experiments that involve cold acid extractions suggest that uranium is associated with the non-carbonate residues. The uranium distribution with depth in the offshore drill core from the Central Graben area (North Sea) suggests that the element is associated with clay in the Danian part. Cretaceous-Tertiary boundary beds from Stevns Klint and other localities in the Danish sub-basin have anomalously high uranium contents compared with the values for chalk. Uranium is not correlated with iron, non-carbonate carbon or aluminium. The highest uranium values within boundary sections are not found in the lower part of the sections as is the case for iridium. The only boundary beds that show typical anoxic depositional affinity have a total uranium accumulation that is one order of magnitude lower than that found in the oxic sections. High amounts of uranium within Cretaceous-Tertiary boundary beds are suggested to be related to diagenetic processes such as compaction and dehydration. Uranium is thought not to cause the extinctions at the Cretaceous-Tertiary boundary because of the relatively low contents found at the actual extinction level. 相似文献
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Li was analysed by activation analysis in 363 whole-rock samples and 53 minerals from a 200 m drill core through aegirine lujavrite I, Ilímaussaq intrusion. The rocks are interpreted as cumulates and Li is dominantly located in the intercumulus material which is thought to represent the coexisting magma with 540 ppm: whole-rock contents generally range from 80–260 ppm Li and reflect variations in the amount of intercumulus material from 25–48 wt. %. The proportion of intercumulus material is lowest in the deeper parts of the drill core, in layers with a moderate density stratification resulting from showers of near-liquidus crystals and in compressed cumulates beneath a large naujaite xenolith from the roof. Intercumulus arfvedsonite with an average of 2200 ppm Li contains the bulk of Li in most samples, but nearly every sample contains Li (0–176 ppm) outside the rock-forming minerals (Li-ORFM) which was unlocated by conventional mineral separation. Li-ORFM formed during late-magmatic crystallization (a) from the final residues of intercumulus magma which crystallised as accessory Li-mica and alteration products and (b) during in situ zeolitization of arvedsonite which released Li. A later, more intense zeolitization released Li from the rocks of the drill core. Naujaite xenoliths contain 42–130 ppm Li, except where Li-metasomatised, and are associated with low Li values in adjacent lujavrites. Shearing of consolidated lujavrite allowed mobilization of the Li and its reprecipitation along narrow channels (< 10 cm). Li is not concentrated in late hydrothermal coatings. 相似文献
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