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91.
Study of 10 volatile elements (and non-volatile Co) in co-existing light and dark portions of 5 gas-rich chondrites indicates patterns of distinct but non-uniform enrichment of volatile elements. Only Cs is enriched in all samples; Hi and Tl enrichments covary. The observed enrichments are inconsistent with prior suggestions of admixture of C1 or C2 chondritic matter, whether pristine or partly devolatilized, but suggest that both light and dark portions of each chondrite represents a compositionally more extended sampling of parental nebular material than hitherto known. 相似文献
92.
93.
Steven D. Bussey Paul M. Taufen Bart J. Suchomel Malcolm Ward 《Journal of Geochemical Exploration》1993,47(1-3)
The Bell Springs deposit is a bulk-tonnage, low-grade gold deposit, formed in a hot-spring environment, that is hosted by middle Miocene weakly peralkaline, high-silica rhyolite ash flows and rheomorphic tuffs. Ore grade mineralization over about 460 × 460 m was controlled by northeast- and northwest-trending structures. Sixty-nine soil samples collected along a traverse across the Bell Springs deposit, screened into six mesh size fractions, +10, −10+35, −35+80, −80+120, −120+200, and −200, were treated by low-detection-limit acid digestion/organic extraction procedures, and analyzed by ICP or graphite furnace techniques for Au, Ag, As, Bi, Cd, Cu, Ga, Hg, Mo, Pb, Sb, Se, Te, Tl, and Zn. Twenty-five stream-sediment samples were collected from a drainage crossing mineralization and from a nearby tributary. Sediment size fractions of −200 mesh and −10+200 mesh were analyzed by the same procedures used for soils. In addition, analyses of bulk leachable gold via cyanide leach method (BLEG) was done on bulk −10 mesh sediments.Anomalous Au, Ag, As, Sb, and Mo in all soil size fractions revealed the underlying ore. Areas with anomalous Sb and As were about three times larger than areas with anomalous Au and Ag. Analyses of fine-fractions of stream sediments provided the best-defined Au anomalies in drainages. A multi-element factor calculated by multiplying Au, As, Sb, and Mo reinforced anomalous Au in drainages and correlated well with Bell Springs mineralization. 相似文献
94.
Stabilizing greenhouse gas concentrations at low levels: an assessment of reduction strategies and costs 总被引:2,自引:8,他引:2
Detlef P. van Vuuren Michel G. J. den Elzen Paul L. Lucas Bas Eickhout Bart J. Strengers Bas van Ruijven Steven Wonink Roy van Houdt 《Climatic change》2007,81(2):119-159
On the basis of the IPCC B2, A1b and B1 baseline scenarios, mitigation scenarios were developed that stabilize greenhouse
gas concentrations at 650, 550 and 450 and – subject to specific assumptions – 400 ppm CO2-eq. The analysis takes into account a large number of reduction options, such as reductions of non-CO2 gases, carbon plantations and measures in the energy system. The study shows stabilization as low as 450 ppm CO2-eq. to be technically feasible, even given relatively high baseline scenarios. To achieve these lower concentration levels,
global emissions need to peak within the first two decades. The net present value of abatement costs for the B2 baseline scenario
(a medium scenario) increases from 0.2% of cumulative GDP to 1.1% as the shift is made from 650 to 450 ppm. On the other hand,
the probability of meeting a two-degree target increases from 0%–10% to 20%–70%. The mitigation scenarios lead to lower emissions
of regional air pollutants but also to increased land use. The uncertainty in the cost estimates is at least in the order
of 50%, with the most important uncertainties including land-use emissions, the potential for bio-energy and the contribution
of energy efficiency. Furthermore, creating the right socio-economic and political conditions for mitigation is more important
than any of the technical constraints. 相似文献
95.
In solution thermodynamics, and more recently in surface chemistry, it is well established that relationships can be found between the free energies of formation of aqueous or surface metal complexes and thermodynamic properties of the metal ions or ligands. Such systematic dependencies are commonly termed linear free energy relationships (LFER). A 2 site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model has been used to model “in house” and literature sorption edge data for eleven elements: Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Eu(III), Am(III), Sn(IV), Th(IV), Np(V) and U(VI) to provide surface complexation constants for the strong sites on montmorillonite. Modelling a further 4 sets of sorption isotherms for Ni(II), Zn(II), Eu(III) and U(VI) provided complexation constants for the weak sites. The protolysis constants and site capacities derived for the 2SPNE SC/CE model in previous work were fixed in all of the calculations. Cation exchange was modelled simultaneously to provide selectivity coefficients. Good correlations between the logarithms of strong SKx−1 and weak W1Kx−1 site binding constants on montmorillonite and the logarithm of the aqueous hydrolysis constants OHKx were found which could be described by the following equations: Strong (≡SSOH) sites:
SlogKX−1=8.1±0.3+(0.90±0.02)logOHKX 相似文献
96.
Douglas?W.?WaplesEmail author May?Ritt?Pedersen Peter?Kuijpers 《Natural Resources Research》2004,13(4):229-239
An equation for correcting log-derived temperatures measured at well depths between 1200 and 5400 m has been derived by comparing log-derived temperatures from wells in the Danish Central Graben (North Sea) with DST temperatures, from the same wells, that are believed to represent true formation temperatures. Equations developed previously using data over different depth ranges from Malaysia and Mexico yield fair results when applied to the North Sea. However, a better fit to the Danish data was obtained using new equations that are similar to those published in the earlier studies. The correction method here is based principally on time since end of circulation (TSC), but it also includes a small dependence on depth. In this study the true subsurface temperature (Ttrue) (°C) is given by
where the correction factor f = 3.07·TSC(–0.09)/(0.47·Z(0.175)), Tsurf is the seafloor temperature in °C, Tmeas is the measured log temperature in °C, TSC is in hours, and Z is the depth below seafloor in meters. When TSC is not known, maximum probable, minimum probable, and most likely values can be estimated from the observed trend of TSC with depth.An estimate of the uncertainty in the corrected temperature can be obtained from the equation
where is the standard deviation of the error in the correction factor f. This approach can be modified to include the additional uncertainty associated with unspecified TSC. 相似文献
97.
T. Nielsen L. De Santis K.I.T. Dahlgren A. Kuijpers J.S. Laberg A. Nygrd D. Praeg M.S. Stoker 《Marine and Petroleum Geology》2005,22(9-10):1149
The present paper provides an overview of glacial related seabed features and sedimentary sequences found along the formerly glaciated NW European margin and compare it with those found on contemporary glaciated margins from both the Southern and Northern Hemispheres. A brief review of the seabed physiography and strata architecture of the margins under consideration is followed by comparison of the most relevant similarities and differences. Comparison of the present-day bathymetric setting of both former and contemporary glaciated margins reveals no clear link to the effect of neither ice sheet or sediment load. Three different types of glacially eroded shelf transverse troughs have been identified, while marginal troughs seem connected to similar geological settings everywhere. Beyond the shelf edge interaction between downslope and alongslope processes has occurred resulting, amongst others, in the formation of large sedimentary mounds on the rise. More frequent large-scale mass wasting occurs on the former glaciated NW European margin than the Greenland and Antarctic margins in the latest Neogene to recent times. A two-stage evolution of the shelf prograding wedges is observed on all margins under consideration, which may reflect a general development of an ice cover from an initial phase of non- to restricted glaciation, evolving to a mature stage of expansive glaciation. 相似文献
98.
Side-scan sonar and sub-bottom profiling investigations of the Iceland-Faeroe Ridge have revealed the widespread presence
of iceberg plowmarks at water depths between 750 and 860 m. This is well beyond the maximum water depth reported for ice scouring
in the adjacent areas of the North Atlantic. An exceptionally deep iceberg plowmark was found at the southern flank of the
ridge, which could be traced down to 940 m water depth. Supported by published nearby sediment core data, a Saalian (MIS 6)
age of that iceberg plowmark is suggested. Considering a glacial sea level of 120 m below present, the paleo-draft of this
iceberg is estimated to have been at least 820 m. The keel depth of such giant icebergs drifting in the glacial northern North
Atlantic significantly exceeds the draft dimensions of large icebergs seen today in the Antarctic. The most likely source
area for this extreme deep-draft type of iceberg is inferred to be southern Greenland. Plowmark direction, which in our case
indicates iceberg entrainment by the North Atlantic Current, is suggested to be a useful indicator of (sub)surface paleo-circulation
during late Pleistocene iceberg surging and deglaciation episodes. 相似文献
99.
During a recent (2006) cruise of RV ‘Dana’ high resolution side-scan sonar and sub-bottom profiling was carried out on selected shelf and slope transects offshore Disko Bugt, central West Greenland. Available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c. 1100 m water depth. The newly acquired side-scan sonar data reveal the presence of giant iceberg plow marks extending (sub)parallel to the slope between about 800 and 1085 m water depth. The height difference between bottom of the scours and rim crest is up to 40 m. The largest plow marks are about 750 m wide. To date no observed modern icebergs including those from Antarctica have drafts in excess of c. 500 m. Taking into account maximum glacial sea level lowering of c. 120 m, the paleo-iceberg keel depth was at least 950 m. Due to the presence of the relatively shallow (< 700 m) sill of Davis Strait to the south, calving of these paleo-icebergs is thought to have occurred from an ice margin in the Baffin Bay region (Jakobshavn Isbræ paleo-ice stream?). The depth of occurrence (> 1000 m) and dimensions of the plow marks are concluded to be exceptional, and comparable to glacial scouring features reported from the Arctic Ocean. 相似文献
100.
Earlier studies suggest that once population growth and market integration reach a certain critical level, traditional practices of work sharing tend to degenerate or disappear altogether. Work sharing has, however, survived to date in small-scale fisheries in Kerala, India. Artisanal fishermen strongly favor the system, for ethical reasons as well as for their personal benefit. Besides, boat owners appear not to be hindered by the system. Contrary to observations in crop production, work sharing has not inhibited the introduction of modern technologies like motorization. 相似文献