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61.
62.
《Chemie der Erde / Geochemistry》2015,75(2):219-236
The formation of iron sulphide minerals exerts significant control on the behaviour of trace elements in sediments. In this study, three short sediment cores, retrieved from the remote Antinioti lagoon (N. Kerkyra Island, NW Greece), are investigated concerning the solid phase composition, distribution, and partitioning of major (Al, Fe) and trace elements (Cd, Cu, Mn, Pb, and Zn). According to 210Pb, the sediments sampled correspond to depositions of the last 120 years. The high amounts of organic carbon (4.1–27.5%) result in the formation of Fe sulphides, predominantly pyrite, already at the surface sediment layers. Pyrite morphologies include monocrystals, polyframboids, and complex FeS–FeS2 aggregates. According to synchrotron-generated micro X-ray fluorescence and X-ray absorption near-edge structure spectra, authigenically formed, Mn-containing, Fe(III) oxyhydroxides (goethite type) co-exist with pyrite in the sediments studied. Microscopic techniques evidence the formation of galena, sphalerite and CuS, whereas sequential extractions show that carbonates are important hosts for Mn, Cd, and Zn. However, significant percentages of non-lattice held elements are bound to Fe/Mn oxyhydroxides that resist reductive dissolution (on average 60% of Pb, 46% of Cd, 43% of Zn and 9% of Cu). The partitioning pattern changes drastically in the deeper part of the core that is influenced by freshwater inputs. In these sediments, the post-depositional pyritization mechanism, illustrated by overgrowths of Fe monosulphides on pre-existing pyrite grains, results in relatively high degree of pyritization that reaches 49% for Cd, 66% for Cu, 32% for Zn and 7% for Pb. 相似文献
63.
Aro V. Arakel 《Geodinamica Acta》2013,26(4):169-184
AbstractContemporary layered halite in the Hutt Lagoon, Western Australia, forms distinct precipitational and clastic fades, which are ascribed to seasonal ponding and playa development in the lagoon respectively. Field and laboratory documentation of the halite types and monitoring of surface water chemistry for several annual hydrologic cycles indicate that following evaporative concentration of ponded seawater halite layers, characterized by zoned and clear halite crystal varieties, are developed. During early stages of annual playa development, vadose solution and precipitation appear to be most active within and above the capillary fringe zone, causing diagenetic modification of the halite textures, fabrics and structures. Ultimately, clastic halite facies are produced by wind reworking of the earlier deposits, in response to progressive evaporative drawdown of the brine level in the main depression area of the lagoon.The co-existence of the halite precipitates and clastites is related to a dynamic equilibrium in the water budget of the Hutt Lagoon. This equilibrium is best exemplified by limitation of brine level fluctuations to a narrow repetitive zone. Identification of similar early diagenetic features, such as vadose solution, precipitation, overgrowth, replacement and mechanical reworking of surface halite sediments, in ancient evaporite deposits may aid in a better understanding of the role of brine level fluctuation on genesis and diagenesis of subaqueous/subaerial halite. 相似文献
64.
甘肃老虎山闪长岩的地球化学特征及其成因 总被引:6,自引:6,他引:6
位于北祁连造山带东端的老虎山闪长岩侵位在晚奥陶统阴沟群砂板岩中,闪长岩的单颗粒锆石U-Pb年龄为423.5±2.8Ma,是中志留世侵位的。老虎山闪长岩属于钙碱性岩系,富集LREE和大离子亲石元素(LILE),Ce/Yb比值大于13,Th/Ta比值大(13~42),在微量元素分布图中呈现明显的Nb负异常,具岛弧或活动陆缘环境的特征。虽然老虎山闪长岩具有岛弧地球化学特征,但并不能认为它就产于岛弧环境,因为,在奥陶纪末期,早古生代的北祁连洋盆已经发生闭合,华北板块与柴达木板块已发生碰撞。因此,老虎山闪长岩是造山后侵位的,其成因可能与岩石圈拆沉作用有关。 相似文献
65.
S. White 《Environmental Geology》1994,23(4):248-255
Most studies of karst landscapes and their processes have been concerned with consolidated, often well-jointed limestones. There are particular problems involved in the study of karst procesess in softer, less-compact limestones such as chalk, coral reefs, and aeolian calcarenite. Previous studies in aeolian calcarenite indicated these problems and a scheme was developed of speleogenesis in aeolian calcarenite. A study of karst processes in aeolian calcarenite at Bats Ridge in western Victoria has developed this scheme further. The karst features and processes at Bats Ridge are an integral part of the landscape of a mid-Pleistocene calcarenite dune system. The resolution of problems of the rapid subaerial speleogenesis in the area is achieved by the synthesis of the known karst features of the ridge and the geology and geomorphology of the area. Karst development on this aeolianite ridge depends on lithological conditions as well as the availability of aggressive water capable of solution. The diagenesis of the calcarenite is occurring now and must have been occurring by the mid-Pleistocene. This simultaneous lithification of the carbonate dunes into aeolian calcarenite rock and the development of solutional karst features in the dunes is the characteristic feature of the speleogenesis in this area. It is the formation of a hardened kankar layer (cap rock) in the dunes of sufficient compressive and tensile strength to support cavities, which is the result of these interrelated factors, that has strongly determined the formation of the karst features. 相似文献
66.
V. Paul Wright 《Geological Journal》1986,21(2):139-149
Palaeosols may be modified in a variety of ways during burial diagenesis but significant alteration can take place during the earliest phases of burial caused by rising groundwaters. A calcrete palaeosol, the Heatherslade Geosol, from the Lower Carboniferous of South Wales, contains abundant pyrite which overprinted the original soil fabrics. The pyrite is interpreted as the product of anaerobic conditions caused by drowning during the early stages of a marine transgression. Unusual diamond-shaped forms of pyrite occur which possibly represent pseudomorphs after gypsum. 相似文献
67.
矿床产于中元古代地层中。矿区内酸性脉岩发育,常密集成带,矿床受穿过脉岩带的构造破碎带控制。矿化岩石主要为构造碎裂岩和角砾岩,其原岩为长英质脉岩、变石英砂岩、变安山岩、板岩及粉砂岩等。矿化以裂隙充填为主,对围岩化学成分的选择性不大。围岩蚀变有:绢云母化、硅化、钾长石化、黑云母化、黄铁矿化、赤铁矿化及水合多水高岭石化等。铀矿物主要为沥青铀矿、铀黑、铀石,其次有钛铀矿、水铀矾,含铀矿物有锐钛矿、金红石、赤铁矿、水合多水高岭石和褐铁矿等;其它金属矿物主要有辉钼矿、黄铁矿、方铅矿和黄铜矿。矿石具脉状、角砾状、块状和浸染状构造,沥青铀矿具胶状结构。矿床中钼的储量远大于铀,铀矿体产于钼矿体之中或其边部。通过室内、外研究,可以认为本矿床为与中酸性小侵入体有关的中-低温热液成因的钼-铀型复合矿床。 相似文献
68.
利用1994年度《甘青交界祁连山西段水文地质工作空白区1∶50万区域水文地质调查》成果,结合空白区外以往资料,采用大气降水入渗法、地下水径流模数法和排泄量统计法等方法,对祁连山西段地下水天然资源进行了概算。结果是祁连山西段地下水天然资源总量为16.93亿m3/a,其中山地11.68亿m3/a,盆地5.25亿m3/a(已扣除重复量)。 相似文献
69.
通过柴窝堡铜矿带区域沉积环境、构造环境及岩浆活动分析,认为矿带具备铜矿成矿地质条件.具体阐述了铜沟─庙儿沟铜矿田的成矿地质地球化学特征和矿化富集规律,认为铜沟─庙儿沟铜矿区的矿床属沉积─热液叠加改造型层控矿床. 相似文献
70.
The primary factors that control the concentration of total reduced (inorganic) sulfide in coastal sediments are believed
to be the availability of reactive iron, dissolved sulfate and metabolizable organic carbon. We selected nine sites in shallow
(<3 m), close to sub-tropical, estuaries and bays along the central Texas coast that represented a range in sediment grain
size (a proxy for reactive iron), salinity (a proxy for dissolved sulfate), and total organic carbon (a proxy for metabolizable
organic carbon). Based on these parameters a prediction was made of which factor was likely to control total reduced sulfide
at each site and what the relative total reduced sulfide concentration was likely to be. To test the prediction, the sediments
were analyzed for total reduced sulfide, acid volatile sulfide, and citrate dithionate-extractable, HCl-extractable and total
Fe in the solid phase. Using solid-state gold–mercury amalgam microelectrodes and voltammetry, we determined pore water depth
profiles of Fe(II) and ΣH2S and presence or absence of FeS(aq). At five of the nine sites the calculated degree of sufildization of citrate dithionite-reactive-iron was close to or greater
than 1 indicating that rapidly reactive iron was probably the limiting factor for iron sulfide mineral formation. At one site
(salinity = 0.9) dissolved Fe(II) was high, ΣH2S was undetectable and the total reduced sulfide concentration was low indicating sulfate limitation. At the last three sites
a low degree of sulfidization and modest total reduced (inorganic) sulfide concentrations appeared to be the result of a limited
supply of metabolizable organic carbon. Fe(II)–S(-II) clusters (FeS(aq)) were undetectable in 10 out of 12 bay sediment profiles where ΣH2S was close to or below detection limits, but was observed in all other porewater profiles. Acid volatile sulfide, but not
total reduced sulfide, was well correlated with total organic carbon and ranged from being undetectable in some cores to representing
a major portion of total reduced sulfide in other cores. Although predicted controls on total reduced sulfide were good for
very low salinity water or sandy sediments, they were only right about half the time for the other sediments. The likely reasons
for the wrong predictions are the poor correlation of total organic carbon with grain size and differing fractions of metabolizable
organic carbon in different sedimentary environments. Differences in sediment accumulation rates may also play a role, but
these are difficult to determine in this region where hurricanes often resuspend and move sediments. This study demonstrates
the need to examine more complex and often difficult to determine parameters in anoxic “normal marine” sediments if we are
to understand what controls the concentration and distribution of sulfides. 相似文献