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761.
Mu Ramkumar Doris Stüben Zsolt Berner Jens Schneider 《Journal of Earth System Science》2010,119(1):1-17
The Ariyalur-Pondicherry sub-basin of the Cauvery basin comprises a near complete stratigraphic record of Upper Cretaceous-Lower
Tertiary periods. Earlier studies have documented variations of clay mineral assemblages, change in microtexture of siliciclasts
and many geochemical and stable isotopic anomalies far below the Cretaceous-Tertiary boundary (KTB) in these strata. This
paper documents the occurrences of two positive 87Sr/86Sr anomalies preceding K-T boundary in this basin and discusses plausible causes. Analysis of trace elemental and stable isotopic
profiles, sedimentation history, petrography and mineralogy of the rocks reveal that while both the anomalies may be due to
increased detrital influx caused by sea level and climatic changes, the second anomaly might have been influenced by Deccan
volcanism which in turn predated KTB. Record of such anomalies preceding K-T boundary supports the view of multi-causal step-wise
extinction of biota across KTB. 相似文献
762.
Maarten Haest Jens Schneider Christophe Cloquet Kris Latruwe Frank Vanhaecke Philippe Muchez 《Mineralium Deposita》2010,45(4):393-410
Base metal–Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed
during two episodes. Subeconomic Cu–Pb–Zn–Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520 Ma ago)
in a set of E–W- and NE–SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic
composition (206Pb/204Pb = 18.07–18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides
were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE–SW-oriented faults into a
chalcocite-dominated Cu–Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of
lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the 207Pb/204Pb vs. 206Pb/204Pb diagram (206Pb/204Pb = 18.66–23.65; 207Pb/204Pb = 15.72–16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead
and uranium during a young fluid event possibly c. 100 Ma ago. The Pb isotope systematics of local host rocks to mineralisation
also indicate some comparable young disturbance of their U–Th–Pb systems, related to the same event. They could have provided
Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu–Pb–Zn–Fe polysulphides,
whereas the U most likely originated from external sources. Local metal sources are also suggested by the 208Pb/204Pb–206Pb/204Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate
host rocks on the chalcocite-dominated Cu–Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu
Plateau clearly record a diachronous evolution. 相似文献
763.
Historical and proxy records document that there is a substantial asynchronous development in temperature, precipitation and
glacier variations between European regions during the last few centuries. The causes of these temporal anomalies are yet
poorly understood. Hence, highly resolved glacier reconstructions based on historical evidence can give valuable insights
into past climate, but they exist only for few glaciers worldwide. Here, we present a new reconstruction of length changes
for the Glacier des Bossons (Mont Blanc massif, France), based on unevaluated historical material. More than 250 pictorial
documents (drawings, paintings, prints, photographs, maps) as well as written accounts have been critically analysed, leading
to a revised picture of the glacier’s history, especially from the mid-eighteenth century up to the 1860s. Very important
are the drawings by Jean-Antoine Linck, Samuel Birmann and Eugène Viollet-le Duc, which depict meticulously the glacier’s
extent during the vast advance and subsequent retreat during the nineteenth century. The new glacier reconstruction extends
back to AD 1580 and proves maxima of the Glacier des Bossons around 1610/1643, 1685, 1712, 1777, 1818, 1854, 1892, 1921, 1941,
and 1983. The Little Ice Age maximum extent was reached in 1818. Until the present, the glacier has lost about 1.5 km in length,
and it is now shorter than at any time during the reconstruction period. The Glacier des Bossons reacts faster than the nearby
Mer de Glace (glacier reconstruction back to AD 1570 available). The Mont Blanc area is, together with the valley of Grindelwald
in the Swiss Alps (two historical glacier reconstructions available back to AD 1535, and 1590, respectively), among the two
regions that are probably best-documented in the world regarding historical glacier data. 相似文献
764.
Alexander Lorenz Hermann Held Eva Bauer Thomas Schneider von Deimling 《Climate Dynamics》2010,34(5):719-734
Greenland ice-core data containing the 8.2 ka event are utilized by a model-data intercomparison within the Earth system model
of intermediate complexity, CLIMBER-2.3 to investigate their potential for constraining the range of uncertain ocean diffusivity
properties. Within a stochastic version of the model (Bauer et al. in Paleoceanography 19:PA3014, 2004) it has been possible to mimic the pronounced cooling of the 8.2 ka event with relatively good accuracy considering the timing
of the event in comparison to other modelling exercises. When statistically inferring from the 8.2 ka event on diffusivity
the technical difficulty arises to establish the related likelihood numerically per realisation of the uncertain model parameters:
while mainstream uncertainty analyses can assume a quasi-Gaussian shape of likelihood, with weather fluctuating around a long
term mean, the 8.2 ka event as a highly nonlinear effect precludes such an a priori assumption. As a result of this study
the Bayesian Analysis leads to a sharp single-mode likelihood for ocean diffusivity parameters within CLIMBER-2.3. Depending
on the prior distribution this likelihood leads to a reduction of uncertainty in ocean diffusivity parameters (e.g. for flat
prior uncertainty in the vertical ocean diffusivity parameter is reduced by factor 2). These results highlight the potential
of paleo data to constrain uncertain system properties and strongly suggest to make further steps with more complex models
and richer data sets to harvest this potential. 相似文献
765.
766.
Zhaohua Wu Edwin K. Schneider Ben P. Kirtman E. S. Sarachik Norden E. Huang Compton J. Tucker 《Climate Dynamics》2008,31(7-8):823-841
In climate science, an anomaly is the deviation of a quantity from its annual cycle. There are many ways to define annual cycle. Traditionally, this annual cycle is taken to be an exact repeat of itself year after year. This stationary annual cycle may not reflect well the intrinsic nonlinearity of the climate system, especially under external forcing. In this paper, we re-examine the reference frame for anomalies by re-examining the annual cycle. We propose an alternative reference frame for climate anomalies, the modulated annual cycle (MAC) that allows the annual cycle to change from year to year, for defining anomalies. In order for this alternative reference frame to be useful, we need to be able to define the instantaneous annual cycle: we therefore also introduce a new method to extract the MAC from climatic data. In the presence of a MAC, modulated in both amplitude and frequency, we can then define an alternative version of an anomaly, this time with respect to the instantaneous MAC rather than a permanent and unchanging AC. Based on this alternative definition of anomalies, we re-examine some familiar physical processes: in particular SST re-emergence and ENSO phase locking to the annual cycle. We find that the re-emergence mechanism may be alternatively interpreted as an explanation of the change of the annual cycle instead of an explanation of the interannual to interdecadal persistence of SST anomalies. We also find that the ENSO phase locking can largely be attributed to the residual annual cycle (the difference of the MAC and the corresponding traditional annual cycle) contained in the traditional anomaly, and, therefore, can be alternatively interpreted as a part of the annual cycle phase locked to the annual cycle itself. In addition to the examples of reinterpretation of physics of well known climate phenomena, we also present an example of the implications of using a MAC against which to define anomalies. We show that using MAC as a reference framework for anomaly can bypass the difficulty brought by concepts such as “decadal variability of summer (or winter) climate” for understanding the low-frequency variability of the climate system. The concept of an amplitude and frequency modulated annual cycle, a method to extract it, and its implications for the interpretation of physical processes, all may contribute potentially to a more consistent and fruitful way of examining past and future climate variability and change. 相似文献
767.
Literature data show that refractory-lithophile elements in most chondrite groups are unfractionated relative to CI chondrites; the principal exception is the EL-chondrite group whose observed falls (all of which are type 6) are depleted in Ca and light REE. In contrast, literature data and our new INAA data on EL3 PCA 91020, EL3 MAC 88136 and EL4 Grein 002 show that some replicates of these samples have nearly flat REE patterns (unlike those of EL6 chondrites); other replicates exhibit fractionated REE patterns similar to those of EL6 chondrites. Petrographic examination shows that many EL6 (and some EL3 and EL4) chondrites are impact-melt breccias or contain impact-melted portions. We suggest that the same impact processes that formed these breccias and produced melt are responsible for the observed bulk compositional fractionations in refractory-lithophile elements, i.e., EL6 chondrites were produced from initially unequilibrated EL3 material. When large amounts of impact heat were deposited, plagioclase and/or oldhamite (CaS) (the major REE carriers in enstatite chondrites) may have been melted and then transported appreciable (>10 cm) distances. EL6 chondrites represent the residuum that is depleted in REE (particularly in LREE) and Ca. Unlike the case for EL chondrites, our new INAA data on ALH 84170, EET 87746 and SAH 97096 (all EH3) show some scatter but are consistent with the EH group having uniform refractory-lithophile abundances. 相似文献
768.
769.
R. C. Nichol R. K. Sheth Y. Suto A. J. Gray I. Kayo R. H. Wechsler † F. Marin G. Kulkarni M. Blanton A. J. Connolly J. P. Gardner B. Jain C. J. Miller A. W. Moore A. Pope J. Pun D. Schneider J. Schneider A. Szalay I. Szapudi I. Zehavi N. A. Bahcall I. Csabai J. Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,368(4):1507-1514
770.
The evolution of a perfect fluid perturbation is considered in the radiation dominated period and in the dust epoch. In the investigation we make use of the general formalism developed in previous papers.It turns out that the evolution tendency is predicted by the state of the cosmic background. The radiation dominated universe does not stimulate growing processes of the perturbation, whereas the dust dominated universe causes a growing tendency of small perfect fluid formations. The results of this work are in accordance with these obtained by the present writers in a previous work. 相似文献