Nitrogen isotopic composition of sinking particles from the southern Bay of Bengal: Evidence for variable nitrogen sources     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(10):1658-1676

An 8-year record of N fluxes and δ¹⁵N of sinking particles from the deep southern Bay of Bengal, northern Indian Ocean, is presented. Fluxes and δ¹⁵N vary between ∼0.1 and 3 mg m⁻² day⁻¹ and ∼2‰ and 8‰, respectively. The seasonal variation is determined mainly by oceanographic processes coupled to the Indian monsoon system. The annual pattern of δ¹⁵N is characterized by minima during spring intermonsoon (∼March–May), when nutrient inputs to the euphotic zone should be low because of stratification, and lighter nitrate/particulate matter is expected to be advected from the central Bay. Highest δ¹⁵N are associated with peak fluxes during southwest monsoon (∼June–September), when the southern Bay comes under the influence of the SW monsoon current, which appears to advect particulate matter with distinctly higher δ¹⁵N. The impact of this process, however, varies interannually under the influence of factors such as ENSO and the Indian Dipole Mode. Weakened advection leads to relatively low N fluxes and reduced δ¹⁵N. The data highlight the necessity of multi-annual studies to comprehend the natural variability of a system.  相似文献   

河南镇平秋树湾矿区铜、钼矿床地质特征及深部找矿潜力分析   总被引：7，自引：1，他引：6  

张智慧  秦明  方荣  唐杰  翟东旭 《矿产与地质》2008,22(2):107-110

秋树湾矿区是一座中型规模的铜、钼矿床。在水平方向上矿区具北铜南钼的分布特征,即北山铜矿床和南山钼矿床;从垂向上看,北山铜矿床深部赋存有规模较大的钼矿体,并具垂直分带现象,即上铜下钼。这主要是矿区成矿后,构造活动使南山赋矿区向上逆冲,使其上部的铜矿体被剥蚀,而北山赋矿区上部的矿体则保存了下来。因此,研究认为,在北山铜矿区的下部及南山钼矿区中深部寻找隐伏钼矿床具有较大潜力。  相似文献   

实验变差函数计算方法的研究与运用   总被引：1，自引：0，他引：1  

李章林  王平  李冬梅 《国土资源信息化》2008,(2):10-14

本文系统、详尽地分析讨论了不同样品数据条件下实验变差函数的计算方法。在实验变差函数计算流程的设计和有效样品搜索域的确定方面提出了自己独特的见解。最后用一个矿山的控矿工程教据对文中介绍的方法进行了测试。结果表明,利用本文的方法,容易得到稳健、准确、信息量高的实验变差函数。  相似文献   

Multi-stage emerald formation during Pan-African regional metamorphism: The Zabara,Sikait, Umm Kabo deposits,South Eastern desert of Egypt     

《Journal of African Earth Sciences》2008,50(2-4):168-187

The genesis of gem-quality deep green emeralds of Zabara, Sikait and Umm Kabo (South Eastern Desert, Egypt) is to date a controversial topic. The emerald-bearing biotite schists and quartz lenses are interpreted alternatively as a product of (i) thrust-fault-shear zone – controlled large scale alkali-metasomatism driven by post-magmatic fluid flow or of (ii) a large scale interaction between syntectonic pegmatitic magma or hydrothermal fluids with pre-existing basic to ultrabasic rocks, or of (iii) a syn- to post-tectonic regional metamorphism and small scale blackwall metasomatism. Detailed microstructural and chemical analyses of the Egyptian emeralds and their host rocks show that three generations of beryl can be distinguished: a colourless pegmatitic beryl; a pale green Cr-poor beryl crystallized from pegmatite-related hydrothermal fluids; and a deep green Cr- and Mg-rich emerald. The crystallization of the Cr- and Mg-rich emerald was controlled by the very local availability of Cr, Mg and Be-rich metamorphic fluids during the Pan-African tectono-thermal event. Emerald-rich quartz lenses demonstrate that those fluids locally did mobilize quartz, too. The pale green emeralds found within the pegmatites in association with colourless beryl are the product of a mobilization of colourless pegmatitic beryl and/or phenakite by late pegmatitic fluids slightly enriched in Cr by an interaction with the Cr-rich country rocks. The late pegmatitic fluids are typically Na-rich as is demonstrated by the pervasive albitization of the pegmatites. The complex interplay of magmatic and regional metamorphic events during the genesis of the Egyptian emeralds/beryls makes it impossible through stable oxygen isotope data to relate their genesis to the one or the other event.  相似文献   

Fluid–Sediment Interaction in a Marine Shallow-Water Hydrothermal System in the Wakamiko Submarine Crater, South Kyushu, Japan     

Miwako Nakaseama    Jun-Ichiro Ishibashi    Keita Ogawa    Hiroshi Hamasaki    Keiko Fujino  Toshiro Yamanaka 《Resource Geology》2008,58(3):289-300

The Wakamiko submarine crater is a small depression located in Kagoshima Bay, southwest Japan. Marine shallow‐water hydrothermal activity associated with fumarolic gas emissions at the crater sea floor (water depth 200 m) is considered to be related with magmatic activity of the Aira Caldera. During the NT05‐13 dive expedition conducted in August 2005 using remotely operated vehicle Hyper‐Dolphine (Japan Agency for Marine‐Earth Science and Technology), an active shimmering site was discovered (tentatively named the North site) at approximately 1 km from the previously known site (tentatively named the South site). Surface sediment (up to 30 cm) was cored from six localities including these active sites, and the alteration minerals and pore fluid chemistry were studied. The pore fluids of these sites showed a drastic change in chemical profile from that of seawater, even at 30 cm below the surface, which is attributed to mixing of the ascending hydrothermal component and seawater. The hydrothermal component of the North site is estimated to be derived from a hydrothermal aquifer at 230°C based on the hydrothermal end‐member composition. Occurrence of illite/smectite interstratified minerals in the North site sediment is attributed to in situ fluid–sediment interaction at a temperature around 150°C, which is in accordance with the pore fluid chemistry. In contrast, montmorillonite was identified as the dominant alteration mineral in the South site sediment. Together with the significant low potassium concentration of the hydrothermal end‐member, the abundant occurrence of low‐temperature alteration mineral suggests that the hydrothermal aquifer in the South site is not as high as 200°C. Moreover, the montmorillonite is likely to be unstable with the present pore fluid chemistry at the measured temperature (117°C). This disagreement implies unstable hydrothermal activity at the South site, in contrast to the equilibrium between the pore fluid and alteration minerals in the North site sediment. This difference may reflect the thermal and/or hydrological structure of the Wakamiko Crater hydrothermal system.  相似文献   

The paleoclimatic records and the relevance with the formation of hydrocarbon source rocks:A case study of Huanghekou depression,Bohaiwan basin     

Zhanhong LIU  Sitian LI  Renchen XIN  Changgui XU  Jianchun CHENG 《Frontiers of Earth Science》2008,2(1):73-82

Bohaiwan basin, covering an area of 200 000 km², is one of the most important oil-bearing basins in Eastern China. Rifting processes formed the basin, and two evolution phases can be recognized. The rifting phase developed in Paleogene, and post-rifting phase occurred in Neogene. More than 200 oil fields have been found in the onshore and offshore area in Bohaiwan basin in recent years. The distribution of the oil fields is closely related to the rich hydrocarbon depressions, and the Huanghekou depression is one of these rich hydrocarbon depressions. A number of large and medium-sized oil and gas fields have been found in this area, such as BZ25-1, BZ34 etc., and the hydrocarbon was mainly from the Huanghekou depression. The formation of rich hydrocarbon source rocks depended on the tectonic setting of rapid subsidence, favorable paleoclimatic conditions and paleolimnology environments. The effects of paleoclimatic condition on hydrocarbon source rocks are the focus of this paper. __________ Translated from Geological Bulletin of China, 2007, 26(7): 830–840 [译自: 地质通报]  相似文献   

Carbon isotope stratigraphy using carbonate cements in the Triassic Sherwood Sandstone Group: Corrib Field,west of Ireland     

《Chemical Geology》2006,225(1-2):137-155

Carbon stable isotopes from carbonate minerals (mainly dolomite) from six wells from the Lower Triassic Sherwood Sandstones of the Corrib Gas Field, Slyne Basin, west of Ireland, allow stratigraphic correlation. The results also provide information on palaeoenvironmental change during the deposition of these continental redbed sedimentary rocks. The Triassic reservoir rocks have been buried to > 4000 m and heated to > 165 °C and now contain methane-rich gas. Although the oxygen isotopic signal has been at least partially reset during burial and heating, a primary carbon isotopic signal appears to have survived diagenesis. The carbon isotope ratio varies from − 3.2‰ to + 2.1‰. All six wells show similar stratigraphic changes when all the carbon isotope data are plotted relative to a major playa horizon. δ¹³C increases from about − 3‰ at the base of the Sherwood to about + 2‰ 170 m above the base. δ¹³C then decreases to about − 2‰ for the next 70 m and remains steady for the following 50 m. The top 20 m of the Sherwood contains carbonate with a δ¹³C values decreasing to about − 3‰. The occurrence of a stratigraphically-correlatable carbon isotope pattern implies that the primary evolution signal has been preserved. The change in δ¹³C correlates with indicators of aridity and biological stress such that the highest δ¹³C values are in sedimentary rocks deposited in a playa lake (arid times); these rocks contain the greatest quantity of dolomite cement. Conversely, the lowest δ¹³C values correspond to sedimentary rocks deposited from well-developed rivers (relatively humid times) from the lowest quantity of dolomite cement. The same carbon isotope evolution has been found in another well in the Slyne basin and in Belgium, suggesting that the palaeoenvironmental isotope signal in the Triassic sedimentary rocks of the Corrib Field may have a regional significance.  相似文献   

Variations in chemical composition and particle size of dune sediments along the west coast of Jutland,Denmark     

《Sedimentary Geology》2006,183(3-4):217-242

Geochemical and textural variations in frontal dune sediments along the western coast of Jutland, Denmark, have been investigated in order to identify possible sediment ‘provinces’ and transport pathways. An understanding of sediment sources and sinks is important for both for an understanding of the nature of sedimentary environments and for applied coastal engineering and management purposes. Four coastal sectors were identified on the basis of geochemical composition. One sector is compositionally different from the other three units, having higher concentrations of the trace elements Ni, Cr, V, Sc, Zn, Pb, Ba, Zr and many rare earth elements. Dune sediments on this section of coast also have higher Al₂O₃ to K₂O ratios and lower Al₂O₃ to Fe₂O₃ ratios, reflecting a lower content of feldspar and higher content of heavy minerals. It is inferred that different, or additional, sediment source(s) have supplied sediment to this section of coast. Beach nourishment has contributed to the observed compositional differences, but previous data obtained from the Lodbjerg area indicate that aeolian sands on this section of coast naturally have a relatively high Si, Fe and Ti content, reflecting high quartz / feldspar ratio and relatively high content of heavy minerals, compared with those on other sections of the coast. Frontal dunes along the most northern section show high abundances of K₂O, Rb and Ba, reflecting a relatively high K-feldspar content derived from local sources. Alongshore trends were also identified in the mean particle size and sorting of the frontal dunes, although there is no direct correspondence with the observed geochemical differences. Three coastal units can be identified on the basis of particle size. Frontal dune sediments in the middle section are relatively coarser and less well-sorted than those to the north and south, probably reflecting both the addition of beach nourishment material and greater exposure to strong westerly winds, which are a capable of transporting a wide range of particle sizes. The three units defined on this basis do not correlate directly with the units defined on the basis of geochemical composition.  相似文献   

Zircon SHRIMP U–Pb dating,C and O isotopes for impure marbles from the Jiaobei terrane in the Sulu orogen: Implication for tectonic affinity     

《Precambrian Research》2006,144(1-2):1-18

Middle Neoproterozoic carbonates are found in the western part of Shandong Pennisula (i.e., the Jiaobei terrane) that is located in the northwestern part of the Sulu orogen in east-central China. For the first time, a successful SHRIMP U–Pb dating, coupled with CL imaging, was conducted on two samples of impure marble from the Fenzishan Group in this tectonic unit. The results yield consistent ages of 786 ± 67 and 240 ± 44 Ma for igneous and metamorphic zircons, respectively. Positive δ¹³C values as high as +5.6‰ are measured for both pure and impure marbles, consistent not only with the worldwide Neoproterozoic limestones in connection with the Sturtian ice-age, but also with the marbles associated with UHP metamorphic eclogites in the Dabie orogen. O isotope fractionation between calcite and garnet from one sample gave a temperature of 680 °C, pointing to upper amphibolite-facies metamorphic conditions. These results indicate that protolith of the marbles is a kind of limestone that was synchronously deposited with volcaniclastic rocks in the mid-Neoproterozoic rift basin of continental margin. Like the UHP metamorphic rocks in the Dabie-Sulu orogenic belt, both mid-Neoproterozoic magmatism and Triassic metamorphism are recorded in the impure marbles. Therefore, protolith of the impure marbles corresponds to the sedimentary limestone of rift basin developed during the mid-Neoproterozoic breakup of supercontinent Rodinia, but it was the sedimentary cover along the northern margin of the South China Block prior to its Triassic subduction. The occurrence of the mid-Neoproterozoic limestone with the Triassic metamorphism in the southern margin of the North China Block thus indicates tectonic overthrust by a crustal detachment between the sedimentary cover and the Precambrian basement during the continent subduction. As a result, the marbles in affinity to the South China Block were northward thrusted over the basement of the North China Block.  相似文献   

Combined investigations of fluid inclusions in opaque ore minerals by NIR/SWIR microscopy and microthermometry and synchrotron radiation X-ray fluorescence     

《Applied Geochemistry》2006,21(5):813-819

An alternative IR microscopy system in the NIR (near infrared, up to 10 μm) and SWIR (short wavelength infrared, up to 1.4 μm) ranges has been developed for the study of opaque ore minerals. The system uses either IR LED or IR light bulb sources depending on the degree of opacity of the investigated minerals. This paper presents the methodology and the promising results obtained in studies of opaque ore minerals such as Ag minerals (pyrargyrite) from epithermal deposits and Nb-tantalates (columbite) from pegmatites. It also presents results on the internal features of hematites from Fe ore banded formations and tungstates from granite–greenstone belt deposits. The data obtained on fluid inclusions from pyrargyrite and hematite crystals have been integrated by complementary information from X-ray fluorescence analysis using synchrotron radiation (μ-SXRF) under conditions specifically designed for the study of opaque ore minerals.  相似文献