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1.
Determinations of spatial and temporal variations in organic matter and nutrient dynamics in water and sediments are crucial for understanding changes in aquatic bodies. In this study, we (i) determine the spatial dynamics of dissolved inorganic nutrients, during the transition from the dry to the rainy season, and (ii) provide future productivity predictions for the Rufiji Delta mangroves, Tanzania, based on the input of various nutrients. Water samples were collected from six locations, three times per year between April 2012 and January 2014, and analysed for dissolved nutrients, total organic and inorganic carbon, chlorophyll a, chlorophyll b and total carotenoids. The prediction of future net primary productivity in the Rufiji mangroves was undertaken using the software STELLA. The mean nutrient concentrations were of the order: nitrate > phosphate > ammonium > silica > dissolved organic carbon. The study revealed that high nutrient concentrations occurred in the northern part of the Rufiji Delta as a result of anthropogenic influence in the watershed. Modelling of nutrient inputs into the delta indicated enhanced primary productivity, which is expected to increase the vulnerability of water quality in the near future due to eutrophication. 相似文献
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湖北铜绿山矿床石英闪长岩的矿物学及Sr-Nd-Pb同位素特征 总被引：11，自引：8，他引：3
铜绿山是长江中下游鄂东南矿集区最重要的、大型夕卡岩型Cu-Fe(Au)矿床。本文对该矿区中与成矿密切的石英闪长岩进行了详细的矿物成分、地球化学及Sr-Nd-Pb同位素研究。结果表明:岩石中斜长石主要为更长石(An=21～31);角闪石贫Ti(0.2),高Mg/(Mg+Fe)(0.5),属于富镁角闪石;而黑云母为镁质黑云母。岩石的地球化学具有高硅(58.86%～67.71%),富碱(Na2O+K2O=5.67%～9.63%),富集轻稀土元素(LREE)和大离子亲石元素(LILE),并强亏损元素Nb、Ta、Ti等特征。岩石的(87Sr/86Sr)i为0.7055～0.7069,εNd(t)为-7.65～-3.44;(206Pb/204Pb)i=17.66～18.00,(207Pb/204Pb)i=15.49～15.56,(208Pb/204Pb)i=37.73～38.19。矿物成分、地球化学和同位素特征说明,铜绿山岩体与阳新岩体为同源岩浆的产物,源区为深度大于40km的富集地幔,经下地壳的混染及分离结晶作用形成。岩浆熔体形成的温度应大于889℃。角闪石和黑云母的温度计估算岩浆结晶温度分别为650～800℃和500～630℃,黑云母开始结晶温度略低于角闪石结晶结束温度,压力为1.49kbar,对应侵位深度约4.9km。岩浆具有利于Cu、Fe、Au等成矿元素进入熔体的条件,可能与板块俯冲作用相关。 相似文献
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Morris RV Golden DC Bell JF rd Lauer HV Adams JB 《Geochimica et cosmochimica acta》1993,57(19):4597-4609
We have examined a Hawaiian palagonitic tephra sample (PN-9) that has spectroscopic similarities to Martian bright regions using a number of analytical techniques, including Mossbauer and reflectance spectroscopy, X-ray diffraction, instrumental neutron activation analysis, electron probe microanalysis, transmission electron microscopy, and dithionite-citrate-bicarbonate extraction. Chemically, PN-9 has a Hawaiitic composition with alkali (and presumably silica) loss resulting from leaching by meteoric water during palagonitization; no Ce anomaly is present in the REE pattern. Mineralogically, our results show that nanophase ferric oxide (np-Ox) particles (either nanophase hematite (np-Hm) or a mixture of ferrihydrite and np-Hm) are responsible for the distinctive ferric doublet and visible-wavelength ferric absorption edge observed in Mossbauer and reflectivity spectra, respectively, for this and other spectrally similar palagonitic samples. The np-Ox particles appear to be imbedded in a hydrated aluminosilicate matrix material; no evidence was found for phyllosilicates. Other iron-bearing phases observed are titanomagnetite, which accounts for the magnetic nature of the sample; olivine; pyroxene; and glass. By analogy, np-Ox is likely the primary pigmenting agent of the bright soils and dust of Mars. 相似文献
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敦煌三危山地区白垩纪OIB型基性岩墙的特征及地质意义 总被引：4，自引：3，他引：1
本文首次报道甘肃敦煌三危山地区早白垩世玄武质岩浆活动的记录。在三危山附近,基性岩墙侵入于敦煌群TTG和表壳岩大理岩和片岩中。全岩的K-Ar年龄为136.00±11.56Ma到99.11±6.35Ma,形成时代属于早白垩世。基性岩墙SiO2含量变化范围较小,集中在47.95%~50.65%之间,以富TiO2 (2.07%~2.35%,平均为2.21%)、MgO(6.03 %~6.51%,平均为6.32%)、贫K2O(<1.29%),Na2O>K2O, Mg#值中等且比较稳定(48.9~53.1,平均为51.7)为特征。基性岩相容元素含量相对较低,Ni含量变化相对较小,分布在112.7×10-6~182.7×10-6之间。而V含量变化较大,介于184×10-6~267×10-6之间,表明岩浆早期可能发生了一定的以橄榄石和单斜辉石为主的分离结晶作用。基性岩富集LREE((La/Yb)N ＝3.97~4.66)和LILE,无Eu负异常,较高的Fe/Mn比值等,具有与洋岛玄武岩(OIB)相似的特征。微量元素比值等特征表明其来源与富集地幔关系密切,玄武质岩浆的形成可能与岩石圈的减薄和软流圈的上涌有关。 相似文献
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华北地台南缘张士英岩体的锆石SHRIMP U-Pb测年、Hf同位素组成及其地质意义 总被引：6，自引：3，他引：3
张士英岩体位于华北地台南缘,岩石类型包括钾长花岗岩、似斑状花岗岩和石英斑岩脉,其中只在钾长花岗岩中发育有暗色岩石包体,在包体和寄主岩中发育反映岩浆混合作用的岩石结构。钾长花岗岩、似斑状花岗岩和石英斑岩脉的SHRIMP锆石U-Pb年龄分别为107.3±2.4Ma、106.7±2.5Ma和101±3Ma。锆石Hf同位素分析结果显示,钾长花岗岩的锆石εHf(t)为-15.96～-20.80,单阶段模式年龄(tDM1)为1396～1643Ma,两阶段模式年龄(tDM2)为1880～2018Ma;似斑状花岗岩的锆石εHf(t)为-18.97～-22.18,tDM1为1512～1640Ma,tDM2为1925～2080Ma;除了一粒年龄为2.6Ga的锆石具有εHf(t)为-0.71、tDM1为2943Ma和tDM2为3036Ma的组成,石英斑岩的锆石εHf(t)为-23.41～-27.95,tDM1为1678～1896Ma,tDM2为2144～2330Ma。这些数据暗示,除了存在少量太古宙地壳物质的贡献外,张士英岩体的物质来源可能主要为1.9～2.3Ga期间形成的新生地壳,但也不排除古老地壳与富集地幔源混合的可能。综合分析前人研究成果表明,在太平洋板块俯冲方向发生转变的过程中,先存断裂带发生拉张。张士英岩体与中国东部同期岩浆活动一起可能形成于这种受断裂带控制的伸展环境。 相似文献
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We present moderate-resolution (lambda/delta lambda = 300 to 370) reflectance spectra of Mars from 2.04 to 2.44 micrometers that were obtained at UKIRT during the 1993 opposition. Seven narrow absorption features were detected and found to have a Mars origin. By comparison with solar and Mars atmospheric spectra, five of these features were attributed all or in part to Mars atmospheric CO2 or CO(2.052 +/- 0.003, 2.114 +/- 0.002, 2.150 +/- 0.003, 2.331 +/- 0.001, and 2.357 +/- 0.002 micrometers). Two of the bands (2.331 +/- 0.001 and 2.357 +/- 0.002 micrometers) appear to have widths and depths that are consistent with additional, nonatmospheric absorptions, although a solar contribution cannot be entirely ruled out. Two other weak bands centered at 2.278 +/- 0.002 and 2.296 +/- 0.002 micrometers may be at least partially mineralogic in origin. The data provide no conclusive identification of the mineralogy responsible for these absorption features. However, examination of terrestrial spectral libraries and previous moderate spectral resolution mineral studies indicates that the most likely origin of these features is either (bi)carbonate or (bi)sulfate anions in framework silicates or (Fe, Mg)-OH bonds in sheet silicates. If the bands are caused by phyllosilicate minerals, then an explanation must be found for the extremely narrow widths of the cation-OH features in the Mars spectra as compared to terrestrial minerals. 相似文献
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Elizabeth M. Truswell 《Australian Journal of Earth Sciences》2013,60(3-4):343-356
Fifty‐three sea‐floor samples close to Antarctica collected by Douglas Mawson during the Australasian Antarctic Expedition of 1911–1914 have beeen analysed for recycled palynomorphs. The distribution of the recycled microfossils provides a broad guide to the position of hidden sedimentary sequences on the Antarctic continental margin. The samples were dredged off the East Antarctic coast between 91°E and 146°E. In three distinct ‐areas, concentrations of recycled palynomorphs suggest the presence nearby of eroding sedimentary sequences. Near the western edge of the Shackleton Ice Shelf the recycled suite suggests Early to Late Permian, Late Jurassic to mid‐Cretaceous, and Late Cretaceous to Early Tertiary sediments, with evidence for marine influence only in the Tertiary. Samples from the outer edge of the continental shelf and slope east of Cape Carr indicate Early Cretaceous and Late Cretaceous to Early Tertiary sequences, and the same age span is suggested by samples from the western side of the Mertz Glacier Tongue; in this area radio echosounding has suggested that inland sedimentary basins intersect the coast. The sedimentary sequence predicted for the Shackleton Ice Shelf area probably faced the open Indian Ocean, at least since the Mesozoic. Cretaceous sequences predicted for the other localities occur at points on the Antarctic coast where they would be expected on the basis of most reconstructions. The area east of Cape Carr has as its conjugate’ coast part of the Great Australian Bight Basin; that off the Mertz Glacier, the area west of the Otway Basin. At both these areas on the southern Australian margin thick Cretaceous rift‐valley sequences occur. 相似文献
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Measurements of NH4, NO3, urea and HCO3 uptake using 15N and 13C stable isotope tracers were undertaken in Saldanha Bay, South Africa, between January 2012 and January 2013. These studies provide the first direct measurements of N utilisation by the plankton in the bay. Primary production in the bay is driven predominantly by the advection of nutrients from the neighbouring shelf environment during upwelling events, with terrestrial and other sources providing minor inputs. New production (NO3-based) was calculated from the f-ratio and total primary production and was used to provide estimates of potential carrying capacity for bivalve culture. Despite the apparent light limitation of NO3 uptake in the winter, the availability of NO3 appeared to exert the major influence on new production throughout the year. In addition, new production was modulated by NH4 availability as shown by the suppression of NO3 uptake by concentrations higher than 1?1.5?mmol m?3. The estimated areal new production of 0.60?g C m?2 d?1 yielded a bay-wide annual estimate of 9 811 t C ha?1 y?1, slightly higher than previous calculations based on physical models. It is estimated that the total annual production of mussels and oysters, respectively, for a 1 000-ha cultivation area is approximately 40 000–53 000 t y?1 (mainly Mytilus galloprovincialis) and 4 600–6 000 t y?1 (Crassotrea gigas). The combined total production figures constitute only 24–31% of the surplus new production. A combined harvestable carrying capacity of 74 000–82 000 t y?1 can be calculated from this surplus. However, from a management and ecological perspective, bivalve culture should be limited to well below this theoretical maximum. Even with this constraint, there appears to be considerable scope for expansion of bivalve farming over the modest, present levels with little jeopardy to ecological integrity. 相似文献
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A basal section of the Lower Proterozoic Transvaal Dolomite from the northern Cape has been re-examined. Numerous associations of stromatolites and other structures have been distinguished in it. Forms of domical stromatolite dominate the structures, but columns, and associations built around spheroidal forms, are also represented. This material accumulated in a telescoped range of environments through the intertidal to a high-energy agitated zone and out into the subtidal.Columnar forms and flat domes from the intertidal zone appear to be remarkably similar to features described from Hamelin Pool at Shark Bay, Western Australia. The subtidal elongate domes and mounds increase in size with depth to reach dimensions of 40 by 10 m, heights of 13 m and relief of 2.5 m. Minor structures on these subtidal forms reflect decreasing energy outwards; included within them are columnar forms in the shallow subtidal zone.It is suggested that deposition within an epeiric sea was away from a headland on a relatively steeply shelving floor affected by currents at right angles to the shore. There are indications that an arid to semi-arid climate existed at that time. 相似文献