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101.
M. J. C. Walker M. Berkelhammer S. Björck L. C. Cwynar D. A. Fisher A. J. Long J. J. Lowe R. M. Newnham S. O. Rasmussen H. Weiss 《第四纪科学杂志》2012,27(7):649-659
This discussion paper, by a Working Group of INTIMATE (Integration of ice‐core, marine and terrestrial records) and the Subcommision on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS), considers the prospects for a formal subdivision of the Holocene Series/Epoch. Although previous attempts to subdivide the Holocene have proved inconclusive, recent developments in Quaternary stratigraphy, notably the definition of the Pleistocene–Holocene boundary and the emergence of formal subdivisions of the Pleistocene Series/Epoch, mean that it may be timely to revisit this matter. The Quaternary literature reveals a widespread but variable informal usage of a tripartite division of the Holocene (‘early’, ‘middle’ or ‘mid’, and ‘late’), and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology. We propose an Early–Middle Holocene Boundary at 8200 a BP and a Middle–Late Holocene Boundary at 4200 a BP, each of which is linked to a Global Stratotype Section and Point (GSSP). Should the proposal find a broad measure of support from the Quaternary community, a submission will be made to the International Union of Geological Sciences (IUGS), via the SQS and the ICS, for formal ratification of this subdivision of the Holocene Series/Epoch. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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A. Gelinas D. A. Kring L. Zurcher J. Urrutia‐Fucugauchi O. Morton R. J. Walker 《Meteoritics & planetary science》2004,39(6):1003-1008
Abstract— The spatial distribution and amount of material transferred from the bolide involved in the Cretaceous/Tertiary (K/T) event to the target rocks at Chicxulub is still poorly constrained. In this study, Re‐Os isotopic analyses of impact melt breccias and lithic clasts from the Yaxcopoil‐1 (Yax‐1) borehole were used to determine the distribution and proportion of the bolide component in the target rocks. Because of the much greater concentration of Os in chondritic meteorites compared to the target rocks, little addition of the bolide component would be necessary to greatly perturb the Os concentration and isotopic composition of target rocks. Hence, this is a very sensitive means of examining bolide contributions to the target rocks. For the examined suite of samples, the initial 187Os/188Os ratios vary from 0.19 to 2.3. Conservative mixing calculations suggest that the bolide component comprised as much as approximately 0.1%, by mass, of some samples. Most samples, however, have negligible contributions from the bolide. No samples have Os that is dominated by the bolide component, so for this suite of samples, it is impossible to fingerprint the chemical nature of the bolide using relative abundances of siderophile elements. These results suggest that the bolide did not contribute a significant amount of material to the target rocks. This may, in turn, indicate that most of the bolide was vaporized upon impact or otherwise ejected without mixing with the melt from the target. 相似文献
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Sergey L. Gratiy Andrew C. Walker David B. Goldstein Laurence M. Trafton 《Icarus》2010,207(1):394-408
Conflicting observations regarding the dominance of either sublimation or volcanism as the source of the atmosphere on Io and disparate reports on the extent of its spatial distribution and the absolute column abundance invite the development of detailed computational models capable of improving our understanding of Io’s unique atmospheric structure and origin. Improving upon previous models, Walker et al. (Walker, A.C., Gratiy, S.L., Levin, D.A., Goldstein, D.B., Varghese, P.L., Trafton, L.M., Moore, C.H., Stewart, B. [2009]. Icarus) developed a fully 3-D global rarefied gas dynamics model of Io’s atmosphere including both sublimation and volcanic sources of SO2 gas. The fidelity of the model is tested by simulating remote observations at selected wavelength bands and comparing them to the corresponding astronomical observations of Io’s atmosphere. The simulations are performed with a new 3-D spherical-shell radiative transfer code utilizing a backward Monte Carlo method. We present: (1) simulations of the mid-infrared disk-integrated spectra of Io’s sunlit hemisphere at 19 μm, obtained with TEXES during 2001-2004; (2) simulations of disk-resolved images at Lyman-α obtained with the Hubble Space Telescope (HST), Space Telescope Imaging Spectrograph (STIS) during 1997-2001; and (3) disk-integrated simulations of emission line profiles in the millimeter wavelength range obtained with the IRAM-30 m telescope in October-November 1999. We found that the atmospheric model generally reproduces the longitudinal variation in band depth from the mid-infrared data; however, the best match is obtained when our simulation results are shifted ∼30° toward lower orbital longitudes. The simulations of Lyman-α images do not reproduce the mid-to-high latitude bright patches seen in the observations, suggesting that the model atmosphere sustains columns that are too high at those latitudes. The simulations of emission line profiles in the millimeter spectral region support the hypothesis that the atmospheric dynamics favorably explains the observed line widths, which are too wide to be formed by thermal Doppler broadening alone. 相似文献
106.
Near liquidus experiments on peridotite and other olivine normative compositions from 1.7 to 6 GPa confirm the applicability of exchange-based empirical models of Ni and Co partitioning between olivine and silicate liquids with compositions close to the liquidus of peridotite. Given that most estimates of lunar bulk composition are peridotitic, the partitioning models thus lend themselves to calculation of olivine compositions produced during the early stages of magma ocean crystallization. Calculation of olivine compositions produced by fractional crystallization of a model lunar magma ocean, initially 700 km deep, reveals a prominent maximum in Ni concentration versus fraction crystallized or Mg’ (molar MgO/(MgO + FeO)), but a pattern of monotonically increasing Co concentration. These patterns qualitatively match the puzzling patterns of Ni and Co concentrations observed in lunar rocks in which forsteritic olivines in magnesian suite cumulates have lower Ni and Co abundances than do less magnesian olivines from low-Ti mare basalts, and olivines from the ferroan anorthosite suite (FAS) have lower Ni, but similar Co to mare basalt olivines.The Ni and Co abundances in olivines from the magnesian suite cumulates can be reconciled in terms of fractional crystallization of a deep magma ocean which initially produces a basal dunite comprised of the hottest and most magnesian olivine overlain by an olivine-orthopyroxene (harzburgite) layer that is in turn overlain by an upper zone of plagioclase-bearing cumulates. The ultramafic portion of the cumulate pile overturns sending the denser harzburgite layer, which later becomes a portion of the green glass source region, to the bottom of the cumulate pile with Ni- and Co-rich olivine. Meanwhile, the less dense, but hottest, most magnesian olivines with much lower Ni and Co abundances are transported upward to the base of the plagioclase-bearing cumulates where subsequent heat transfer leads to melting of mixtures of primary dunite, norite, and gabbronorite with KREEP (a K-REE-P enriched component widely believed to be derived from the very latest stage magma ocean liquid). These hybrid melts have Al2O3, Ni, and Co abundances and Mg’ appropriate for parent magmas of the magnesian suite. Ni and Co abundances in the FAS are consistent with either direct crystallization from the magma ocean or crystallization of melts of primary dunite-norite mixtures without KREEP. 相似文献
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109.
Two high value species, yellowtail kingfish (Seriola lalandi) and hāpuku (groper, Polyprion oxygeneios), have been identified as suitable new candidates for New Zealand aquaculture. This paper reviews the research by NIWA and collaborators conducted to test the biological, technological and economic feasibility of farming these two species. NIWA now has the capability to produce sufficient kingfish fingerlings per year to meet the needs of the early stages of an industry. Advances in hāpuku aquaculture have also been significant, from spawning in captivity through to the selection of juveniles for improved growth. Recently, the first spawning of captive hāpuku F1 broodstock and production of F2 eggs, larvae and juveniles was achieved. Although hāpuku larval survival remains variable, the ability to close the life cycle, and the availability of domesticated broodstock, provide a significant step forward and increase the chances of this species being commercially farmed. 相似文献
110.
Neha Singh Ravi Prakash Singh Saumitra Mukherjee Kyle McDonald K. J. Reddy 《Environmental Earth Sciences》2014,72(1):111-118
A study was conducted to understand the hydrogeological processes dominating in the North 24 Parganas and South 24 Parganas based on representative 39 groundwater samples collected from selected area. The abundance of major ions was in the order of Ca2+ > Na+ > Mg2+ > K+ > Fe2+ for cations and HCO3 ? > PO4 3? > Cl? > SO4 2? > NO3 ? for anions. Piper trilinear diagram was plotted to understand the hydrochemical facies. Most of the samples are of Ca-HCO3 type. Based on conventional graphical plots for (Ca + Mg) vs. (SO4 + HCO3) and (Na + K) vs. Cl, it is interpreted that silicate weathering and ion exchange are the dominant processes within the study area. Previous studies have reported quartz, feldspar, illite, and chlorite clay minerals as the major mineral components obtained by the XRD analysis of sediments. Mineralogical investigations by SEM and EDX of aquifer materials have shown the occurrence of arsenic as coating on mineral grains in the silty clay as well as in the sandy layers. Excessive withdrawal of groundwater for irrigation and drinking purposes is responsible for fluctuation of the water table in the West Bengal. Aeration beneath the ground surface caused by fluctuation of the water table may lead to the formation of carbonic acid. Carbonic acid is responsible for the weathering of silicate minerals, and due to the formation of clay as a product of weathering, ion exchange also dominates in the area. These hydrogeological processes may be responsible for the release of arsenic into the groundwater of the study area, which is a part of North 24 Parganas and South 24 Parganas. 相似文献