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91.
A unique troilite-iron-cohenite-rich lens was found on a ledgein the sediment-contaminated Kitdlit dyke on Disko. The lensdisplays a mineralogical diversity and extreme liquid evolutionnot previously described from any single magmatic sulphide ormetal liquid system. It was deposited at 1200 ?C and fo2 = 1013as two immiscible liquidsa sulphide liquid and a C-richmetal liquidwhich solidified from about 1100? to 300?C as a closed system in a thermal gradient. The lower iron-rich half of the lens formed by crystallizationof iron, cohenite, troilite, schreibersite and w?stite (in thatorder), with trace amounts of the phases found in the upperhalf of the lens. The approximate crystallization order of theupper troilite-rich half of the lens was: iron, cohenite, troilite,chromite, w?stite, fayalite (pseudomorphosed), high-T chalcopyrite,high-T heazlewoodite (beta-(Ni, Fe, Cu, Co)3+?S2)and, finally, lead minerals. The latter comprise native lead,galena, altaite (PbTe), shandite (Ni3Pb2S2) and an unidentifiedphase. Additional immiscible liquids were formed during solidification.Oxysulphide liquid (roughly FeO with a minor FeS-component)exsolved from metal and sulphide liquid in equilibrium withiron and cohenite below 1100 ?C. Later, FeO-rich silicate liquid,and Pb-rich liquid with Ni, Cu, S and Te, exsolved from thesulphide liquid. Segregation of oxysulphide and Pb-rich liquidmay occur during core formation in planetoids, and there arethus important cosmochemical implications. 相似文献
92.
A model for the conservation of geological remains as documents 总被引:1,自引:0,他引:1
Geological remains are conserved mainly either together with living beings for the sake of the integrity of nature or for
their economical or aesthetic value. However, they also have scientific value for the geologist to reconstruct the earth's
past. For this reason we propose a model which is an application of marginal utility theory in economics and takes into account
the informational utility of geological remains. Informational utility of geological remains ranges over their geological significance which is induced by the importance of the geological processes that produce them, and over their spatial extensiveness. Our model takes into account also the cost and budget of conservation and proposes to solve the differential equations of informational utility and cost simultaneously in order
to obtain the optimum quantity of the remains to be conserved.
Received: 9 January 1998 · Accepted: 4 February 1998 相似文献
93.
94.
By N. KAADEN A. MASSLING A. SCHLADITZ T. MÜLLER K. KANDLER L. SCHÜTZ B. WEINZIERL A. PETZOLD M. TESCHE S. LEINERT C. DEUTSCHER M. EBERT S. WEINBRUCH A. WIEDENSOHLER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):51-63
The Saharan Mineral Dust Experiment (SAMUM) was conducted in May and June 2006 in Tinfou, Morocco. A H-TDMA system and a H-DMA-APS system were used to obtain hygroscopic properties of mineral dust particles at 85% RH. Dynamic shape factors of 1.11, 1.19 and 1.25 were determined for the volume equivalent diameters 720, 840 and 960 nm, respectively.
During a dust event, the hydrophobic number fraction of 250 and 350 nm particles increased significantly from 30 and 65% to 53 and 75%, respectively, indicating that mineral dust particles can be as small as 200 nm in diameter. Log-normal functions for mineral dust number size distributions were obtained from total particle number size distributions and fractions of hydrophobic particles. The geometric mean diameter for Saharan dust particles was 715 nm during the dust event and 570 nm for the Saharan background aerosol.
Measurements of hygroscopic growth showed that the Saharan aerosol consists of an anthropogenic fraction (predominantly non natural sulphate and carbonaceous particles) and of mineral dust particles. Hygroscopic growth and hysteresis curve measurements of the 'more' hygroscopic particle fraction indicated ammonium sulphate as a main component of the anthropogenic aerosol. Particles larger than 720 nm in diameter were completely hydrophobic meaning that mineral dust particles are not hygroscopic. 相似文献
During a dust event, the hydrophobic number fraction of 250 and 350 nm particles increased significantly from 30 and 65% to 53 and 75%, respectively, indicating that mineral dust particles can be as small as 200 nm in diameter. Log-normal functions for mineral dust number size distributions were obtained from total particle number size distributions and fractions of hydrophobic particles. The geometric mean diameter for Saharan dust particles was 715 nm during the dust event and 570 nm for the Saharan background aerosol.
Measurements of hygroscopic growth showed that the Saharan aerosol consists of an anthropogenic fraction (predominantly non natural sulphate and carbonaceous particles) and of mineral dust particles. Hygroscopic growth and hysteresis curve measurements of the 'more' hygroscopic particle fraction indicated ammonium sulphate as a main component of the anthropogenic aerosol. Particles larger than 720 nm in diameter were completely hydrophobic meaning that mineral dust particles are not hygroscopic. 相似文献
95.
An on‐line solid phase extraction method for the preconcentration and determination of Cu(II) by flame atomic absorption spectrometry has been described. The procedure is based on the retention of Cu(II) ions at pH 6.0 on a minicolumn packed with Amberlite XAD‐1180 resin impregnated with chrome azurol S. After preconcentration, Cu(II) ions adsorbed on the impregnated resin were eluted by 1 mol L?1 HNO3 solution. Several parameters, such as pH, type of eluent, flow rates of sample and eluent solutions, amount of resin were evaluated. At optimized conditions, for 3.5 min of preconcentration time, the system achieved a detection limit of 1.0 µg L?1, and a relative standard deviation of 1.2% at 0.2 µg mL?1 copper. An enrichment factor of 56‐fold was obtained with respect to the copper determination. The proposed method was successfully validated by the analysis of standard reference material (TMDA 54.4 lake water) and recovery studies. The method was applied to the preconcentration of Cu(II) in natural water samples. 相似文献
96.
CHRISTIAN BETZLER JUAN C. BRAGA DAVID JARAMILLO‐VOGEL MIRIAM RÖMER CHRISTIAN HÜBSCHER GERHARD SCHMIEDL SEBASTIAN LINDHORST 《Sedimentology》2011,58(3):643-669
Post‐glacial, neritic cool‐water carbonates of the Western Mediterranean Sea were examined by means of hydroacoustic data, sediment surface sampling and vibrocoring to unravel geometries and to reconstruct sedimentary evolution in response to the last sea‐level rise. The analysed areas, located on the Alboran Ridge, in the Bay of Oran, and at the southern shelf of the island of Mallorca, are microtidal and bathed by oligotrophic to weakly mesotrophic waters. Seasonal water temperature varies between 13 °C and 27 °C. Echosounder profiles show that the Bay of Oran and the southern shelf of Mallorca are distally steepened ramps, while the Alboran Ridge forms a steep‐flanked rugged plateau around the Alboran Island. In the three areas, an up to 10 m thick post‐glacial sediment cover overlies an unconformity. In Oran and Mallorca, stacked lowstand wedges occur in water depths of 120 to 130 m. On the Alboran Ridge and in the Bay of Oran, highstand wedges occur at 35 to 40 m. Up to 5 m long cores of upper Pleistocene to Holocene successions were recovered in water depths between 40 and 81 m. Deposits contain more than 80% carbonate, with mixed carbonate‐volcaniclastics in the lower part of some cores in Alboran. The carbonates consist of up to 53% of aragonite and up to 83% of high magnesium calcite. Radiocarbon dating of bivalve shells, coralline algae and serpulid tubes indicates that deposits are as old as 12 400 cal yr bp . The carbonate factories in the three areas are dominated mostly by red algae, but some intervals in the cores are richer in bivalves. A facies rich in the gastropod Turritella, reflecting elevated surface productivity, is restricted to the Mallorca Shelf. Rhodoliths occur at the sediment surface in most areas at water depths shallower than 70 m; they form a 10 to 20 cm thick veneer overlying rhodolith‐poor bioclastic sediments which, nonetheless, contain abundant red algal debris. This rhodolith layer has been developing for the past 800 to 1000 years. Similar layers at different positions in the cores are interpreted as reflecting in situ growth of rhodoliths at times of reduced net sedimentation. Sedimentary successions in the cores record the post‐glacial sea‐level rise and the degree of sediment exposure to bottom currents. Deepening‐upward trends in the successions are either reflected by shallow to deep facies transitions or by a corresponding change of depth‐indicative red algae. There are only weak downcore variations of carbonate mineralogy, which indicate that no dissolution or high magnesium to low magnesium calcite neomorphism occurs in the shallow subsurface. These new data support the approach of using the Recent facies distribution for interpretation of past cool‐water, low‐energy, microtidal carbonate depositional systems. Hydroacoustic data show that previous Pleistocene transgressive and highstand inner ramp deposits and wedges were removed during sea‐level lowstands and accumulated downslope as stacked lowstand wedges; this suggests that, under conditions of high‐amplitude sea‐level fluctuations, the stratigraphic record of similar cool‐water carbonates may be biased. 相似文献
97.
98.
99.
Kaare L. RASMUSSEN Henning HAACK Finn ULFF‐M
LLER 《Meteoritics & planetary science》2001,36(7):883-896
Abstract— Metallographic cooling rates have been calculated for all five members of the iron meteorites group IIF using two different techniques. We have determined cooling rates of ~5 °C/Ma based on Ni profiles through the taenite rim enclosing kamacite spindles. Ni profiles through the kamacite phase are less precise cooling rate indicators, but suggest a cooling rate of ~1 °C/Ma within an order of magnitude at lower temperatures (360–400 °C). Based on the kamacite bandwidth and the Ni profiles through the taenite, we estimate that the kamacite nucleated 130–200 °C below the temperature predicted from the phase diagram. The size of and the distance between the large kamacite spindles is found to be consistent with the thermal history that we have determined on the basis of Ni profiles in kamacite and taenite. We find that previously published kamacite bandwidth cooling rates for the five group IIF members are most likely in error because of the presence of large schreibersite spindles in some kamacite spindles and because undercooling of kamacite was ignored. Contrary to previous workers we find that the metallographic cooling rates are consistent with cooling in a common core. 相似文献
100.
ÓLAFUR INGÓLFSSON ASTRID LYSÅ SVEND FUNDER PER MÖLLER SVANTE BJÖRCK 《Boreas: An International Journal of Quaternary Research》1994,23(4):447-458
The Late Quaternary ( c . 130,000–10,000 BP) glacial history of the central west coast of Jameson Land, East Greenland, is reconstructed through glacial stratigraphical studies. Seven major sedimentary units are described and defined. They represent two interglacial events (where one is the Holocene). one interstadial event and two glacial events. The older interglacial event comprises marine and fluvial sediments, and is correlated to the Langelandselv interglacial, corresponding to oxygen isotope sub-stage 5e. It is followed by an Early Weichselian major glaciation during the Aucellaelv stade, and subsequently by an Early Weichselian interstadial marine and deltaic event (the Hugin Sø interstade). Sediments relating to the Middle Weichselian have not been recognized in the area. The Hugin Sø interstade deposits have been overrun by a Late Weichselian ice advance, during the Flakkerhuk stade, when the glacier, which probably was a thin, low gradient fjord glacier in Scoresby Sund, draped older sediments and landforms with a thin till. Subsequent to the final deglaciation, some time before 10,000BP, the sea reached the marine limit around 70 m a.s.l., and early Holocene marine, fluvial and littoral sediments were deposited in the coastal areas. 相似文献