共查询到20条相似文献，搜索用时 331 毫秒
1.
Gordeev V. V. Shevchenko V. P. Korobov V. B. Kochenkova A. I. Starodymova D. P. Belorukov S. K. Lokhov A. S. Yakovlev A. E. Chultsova A. L. Zolotykh E. O. Lobkovsky L. I. 《Doklady Earth Sciences》2021,500(1):787-793
Doklady Earth Sciences - The results of four years of continuous investigations (from May 2015 through April 2019) of the elemental composition of the water of the Northern Dvina River are... 相似文献
2.
The homogenization of inhomogeneities in the elemental composition of the interstellar medium due to stellar evolution and weak mixing are inevitably related to the action of shocks. This paper considers the influence of variations in the elemental composition on the thermal and ionizational evolution of a collisional gas with the solar metallicity that is cooled behind a shock front with a velocity of 50–120 km/s. The intensities of lines of heavy elements in plasma cooling behind a shock front depend not only on variations in the elemental composition, but also on the shock velocity, due to the different values of the critical density for the transition to the equilibrium level populations in atoms and ions of heavy elements. This circumstance can be used to determine the elemental composition of cool and warm gas of the interstellar medium, as well as the thermal history of the gas. 相似文献
3.
R. B. Seyful-Mulyukov 《Doklady Earth Sciences》2016,467(1):246-248
The quantum matrix of the hydrocarbon (HC) molecule is substantiated. On the basis of its properties and behavior, the genesis of oil is explained as a process of self-evolution of oil and preservation of molecules of different composition and generation time. Individual HC molecules are generated in nanoseconds, and the period of the genesis of oil is comparable with that of migration of the HC fluid from the mantle to the deposit. A model of subatomic abiogenic genesis of oil is presented. Hydrocarbon (HC) molecules of various structure and composition are formed due to interaction of the valency electron orbitals of C and H atoms, the elemental particles of which are quantum objects and carriers of information. On the basis of this, the term quantum matrix of the HC molecule, the properties and behavior of which explain the genesis of oil as a process of its self-evolution and preservation of the molecules of various composition and the period of generation of oil, is substantiated. It is proved that individual HC molecules are generated within nanoseconds and the period of origin of the entire assemblage of more than 500 molecules of oil of various types is comparable with the period of migration of the HC fluid from the mantle to the deposit. 相似文献
4.
The elemental composition of suspended particles in surface waters of Lake Baikal has been studied by ICP MS along a transect of the zone affected by the Selenga River. The amount of terrigenous suspension in water was estimated from Al content, which decreases in a saltatory manner along the transect: 6.5–8.3 km offshore it decreases by an order of magnitude; 11–14 km offshore, by other 20 times; in the pelagic zone it remains almost unchanged. During the study period (late June 2001), the distribution limit of suspension from the Selenga River in the lake’s surface waters lays 11–14 km offshore.It has been found that pelagic suspension is more than 20 times richer in Ca, P, Zn, Cu, Ni, Sn, Mo, Bi, S, and Cd than littoral one (6.5 km offshore) in the zone affected by the Selenga River. This is mainly due to fine suspension (<1.2 μm), which was considerably richer in Ca, P, Zn, Cu, Ni, Sn, Mo, Sb, and Cd than coarser ones in the river.Fine suspension in Lake Baikal, both in the zone affected by the river and in the pelagic zone, is considerably (2–35 times) richer in most elements, except for typical terrigenous ones, than river one. This suggests that element enrichment takes place in the lake, probably owing to bioaccumulation and chemisorption. These processes may be affected by additional factors, because fine suspension from the zone affected by the river differs significantly from pelagic one in elemental composition. 相似文献
5.
The chemical structure of refractory marine dissolved organic matter (DOM) is still largely unknown. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) was used to resolve the complex mixtures of DOM and provide valuable information on elemental compositions on a molecular scale. We characterized and compared DOM from two sharply contrasting aquatic environments, algal-derived DOM from the Weddell Sea (Antarctica) and terrigenous DOM from pore water of a tropical mangrove area in northern Brazil. Several thousand molecular formulas in the mass range of 300-600 Da were identified and reproduced in element ratio plots. On the basis of molecular elemental composition and double-bond equivalents (DBE) we calculated an average composition for marine DOM. O/C ratios in the marine samples were lower (0.36 ± 0.01) than in the mangrove pore-water sample (0.42). A small proportion of chemical formulas with higher molecular mass in the marine samples were characterized by very low O/C and H/C ratios probably reflecting amphiphilic properties. The average number of unsaturations in the marine samples was surprisingly high (DBE = 9.9; mangrove pore water: DBE = 9.4) most likely due to a significant contribution of carbonyl carbon. There was no significant difference in elemental composition between surface and deep-water DOM in the Weddell Sea. Although there were some molecules with unique marine elemental composition, there was a conspicuous degree of similarity between the terrigenous and algal-derived end members. Approximately one third of the molecular formulas were present in all marine as well as in the mangrove samples. We infer that different forms of microbial degradation ultimately lead to similar structural features that are intrinsically refractory, independent of the source of the organic matter and the environmental conditions where degradation took place. 相似文献
6.
运用区域大规模采样方法,对内蒙古中南部地区所采样品进行元素丰度值加权计算,这是建立区域地壳模型的基础工作之一,同时也为化探异常的检出提供较为准确的背景值。研究区涉及内蒙古地轴和内蒙古中部造山系2个构造单元。采用加权求平均值的方法,得到内蒙古中南部出露地壳10种常量元素氧化物和40种微量元素的丰度值。经地表热流值、地震平均波速和元素比值方法检验后证明所得结果合理。计算所得内蒙古中南部出露地壳平均成分为花岗闪长质,与目前一般认为的结论相同。将结果与其他地区进行比较分析后可知,内蒙古中南部出露的地壳与全球上地壳的组成基本一致。由微量元素、稀土元素的图解和内蒙古中南部出露地壳的元素丰度与中国东部出露地壳元素丰度的对比可以看出,整体上,内蒙古中南部具有较强的壳内分异作用和地壳增生作用(地幔物质加入)。 相似文献
7.
运用区域大规模采样方法,对内蒙古中南部地区所采样品进行元素丰度值加权计算,这是建立区域地壳模型的基础工作之一,同时也为化探异常的检出提供较为准确的背景值。研究区涉及内蒙古地轴和内蒙古中部造山系2个构造单元。采用加权求平均值的方法,得到内蒙古中南部出露地壳10种常量元素氧化物和40种微量元素的丰度值。经地表热流值、地震平均波速和元素比值方法检验后证明所得结果合理。计算所得内蒙古中南部出露地壳平均成分为花岗闪长质,与目前一般认为的结论相同。将结果与其他地区进行比较分析后可知,内蒙古中南部出露的地壳与全球上地壳的组成基本一致。由微量元素、稀土元素的图解和内蒙古中南部出露地壳的元素丰度与中国东部出露地壳元素丰度的对比可以看出,整体上,内蒙古中南部具有较强的壳内分异作用和地壳增生作用(地幔物质加入)。 相似文献
8.
Graham E. Forrester 《Estuaries and Coasts》2005,28(6):974-981
Site-specific variation in the trace element composition of fish otoliths can be used to identify fish to source, but the
mechanisms controlling elemental composition are poorly understood. Environmental influences on the deposition of barium (Ba),
copper (Cu), manganese (Mn), and strontium (Sr) in the otoliths of mudsuckers (Gillichthys mirabilis) were tested using a reciprocal field transplant experiment, in which fish from 3 estuaries were transplanted to each of
the 3 estuaries. Fish originating from the 3 estuaries showed no differences in otolith chemistry that might reflect acclimation
to past conditions in their home estuary or genetic differences among populations, which simplifies the interpretation of
otolith chemistry. Cu and Mn concentrations in otoliths differed according to the site of transplant. Cu in otoliths showed
the same pattern of difference among estuaries as did Cu in sediments, but there was no correspondence between Cu in otoliths
and dissolved Cu. Ranked differences among estuaries in otolith Mn matched the ranking of estuary-specific differences in
dissolved Mn, and there was no correspondence between the concentration of Mn in otoliths and sediments. Fish transplanted
to different estuaries showed no differences in otolith concentrations of Ba or Sr, and the concentrations of Ba and Sr in
the water column showed a similar lack of difference among estuaries. This study provides field evidence supporting the conclusion
that the elemental composition of otoliths reflects environmental conditions to which fish have been recently exposed, but
whether that correlation is with trace elements in the sediment or water column can vary. 相似文献
9.
The Upper Permian Castile Formation of the Delaware Basin in northwest Texas and New Mexico consists of up to 600 m of evaporites and is subdivided into units of anhydrite overlain by halite. The Castile Formation has commonly been interpreted as a deep-water, deep-basin deposit in which sediments were laid down in several hundred metres of water or brine. Recent textural observations within anhydrite units, in which the thick-bedded anhydrite horizons have been interpreted as being of shallow-water origin, have challenged this assumption. This geochemical study of the oldest anhydrite unit in the Castile Formation (the Anhydrite 1 Member) attempts to resolve some of the problems regarding brine depth and evolution in the basin. The Anhydrite 1 Member has been subdivided into five major cycles on the basis of the distribution of stratigraphic units of thick-bedded anhydrite.
Stable isotopic analyses of sulphur from anhydrite, and oxygen and carbon from calcite show that the basin waters were chemically homogeneous during precipitation of anhydrite, and do not indicate any significant input of meteoric, continental-derived waters. Throughout the section studied progressive enrichment of 18O upwards within cored intervals indicates continuous evaporation of the water body. Carbon isotopes appear to indicate fluctuations in organic activity within the cycles. Trace elemental analyses of Fe, Mg, Sr, Mn, Al, Ba, Zn, Pb and Cu from the sulphate fraction of the samples show a very high variability. There is a distinct increase in trace elemental abundances at the tops of cycles which may indicate variations in precipitation kinetics. Analyses of texturally defined cycles show that up-core trends for many of the trace elements correlate with changes in δ18O, indicating a progressive increase in the influence of evaporation. In addition, cyclical variations in trace elemental composition indicate changes in basin conditions with around a 350-year cyclicity. These changes are independent of δ18O values. The geochemical data do not provide conclusive proof of water depth during deposition of the Castile Formation. The data are interpreted as reflecting small-scale changes in conditions of deposition, despite the fact that water input remained essentially constant in terms of chemical composition. 相似文献
10.
Geochemistry of dust aerosol over the Eastern Pamirs 总被引：1，自引：0，他引：1
The Pamirs are situated in the inner part of the Asian continent, a region which plays a critical role in Asian dust emission and transport. This study measured the elemental composition of atmospheric dust aerosol samples collected during the period between July 2004 and April 2006 at Mt. Muztagata, Eastern Pamirs, at a high-altitude (38°17′N, 75°01′E, 4430 m). The Muztagata aerosol samples show Ca/Al (∼0.7) and Fe/Al (∼0.7) ratios that are distinguishable from those from other sites. The La/Th ratios (averaging 2.30-2.36) and Th/U ratios (averaging 2.75-3.11) indicate typical eolian deposition. The dust aerosol samples have very similar rare earth element (REE) patterns, with relative enrichment of light REE, a slight depletion of heavy REE, and a strongly negative europium anomaly (δEu values averaging 0.65). The Muztagata dust shows homogeneity of composition during the sampling period, with minor variations due to seasonal effects and possible different air mass, suggesting the possibility of a well-mixed atmospheric background dust on a regional scale. The zonal Westerlies dominate and the longitude circulations are relatively very weak for dust transport dynamics in the Pamirs and Tien Shan regions. Our results demonstrate a distinct difference in elemental composition between dust over the Eastern Pamirs and that over Inilchek, Central Tien Shan, indicating that the Asian dust emission regions have great variations in their chemical properties, and provide a better constraint on the climatic impact of Asian dust. 相似文献
11.
Xiaona Li Gregory A. Cutter Eric Tappa Timothy W. Lyons Mary I. Scranton 《Geochimica et cosmochimica acta》2011,75(1):148-332
The biogeochemistry of iron sulfide minerals in the water column of the Cariaco Basin was investigated in November 2007 (non-upwelling season) and May 2008 (upwelling season) as part of the on-going CARIACO (CArbon Retention In A Colored Ocean) time series project. The concentrations of particulate sulfur species, specifically acid volatile sulfur (AVS), greigite, pyrite, and particulate elemental sulfur, were determined at high resolution near the O2/H2S interface. In November 2007, AVS was low throughout the water column, with the highest concentration at the depth where sulfide was first detected (260 m) and with a second peak at 500 m. Greigite, pyrite, and particulate elemental sulfur showed distinct concentration maxima near the interface. In May 2008, AVS was not detected in the water column. Maxima for greigite, pyrite, and particulate elemental sulfur were again observed near the interface. We also studied the iron sulfide flux using sediment trap materials collected at the Cariaco station. Pyrite comprised 0.2-0.4% of the total particulate flux in the anoxic water column, with a flux of 0.5-1.6 mg S m−2 d−1.Consistent with the water column concentration profiles for iron sulfide minerals, the sulfur isotope composition of particulate sulfur found in deep anoxic traps was similar to that of dissolved sulfide near the O2/H2S interface. We conclude that pyrite is formed mainly within the redoxcline where sulfur cycling imparts a distinct isotopic signature compared to dissolved sulfide in the deep anoxic water. This conclusion is consistent with our previous study of sulfur species and chemoautotrophic production, which suggests that reaction of sulfide with reactive iron is an important pathway for sulfide oxidation and sulfur intermediate formation near the interface. Pyrite and elemental sulfur distributions favor a pathway of pyrite formation via the reaction of FeS with polysulfides or particulate elemental sulfur near the interface. A comparison of thermodynamic predictions with actual concentration profiles for iron sulfides leads us to argue that microbes may mediate this precipitation. 相似文献
12.
S. Huang 《Geochimica et cosmochimica acta》2009,73(1):65-39
Elemental composition of the particle flux at the Oceanic Flux Program (OFP) time-series site off Bermuda was measured from January 2002 to March 2005. Eighteen elements (Mg, Al, Si, P, Ca, Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd, Ba and Pb) in sediment trap material from 500, 1500 and 3200 m depths were quantified using fusion-HR-ICPMS. Positive Matrix Factorization (PMF) was used to elucidate sources, elemental associations and processes that affect geochemical behavior in the water column.Results provide evidence for intense elemental cycling between the sinking flux material and the dissolved and suspended pools within mesopelagic and bathypelagic waters. Biological processing and remineralization rapidly deplete the sinking flux material in organic matter and associated elements (N, P, Cd, Zn) between 500 and 1500 m depth. Suspended particle aggregation, authigenic mineral precipitation, and chemical scavenging enriches the flux material in lithogenic minerals, barite and redox sensitive elements (Mn, Co, V, Fe). A large increase in the flux of lithogenic elements is observed with depth and confirms that the northeast Sargasso is a significant sink for advected continental materials, likely supplied via Gulf Stream circulation.PMF resolved major sources that contribute to sinking flux at all depths (carbonate, high-Mg carbonate, opal, organic matter, lithogenic material, and barite) as well as additional depth-specific elemental associations that contribute about half of the compositional variability in the flux. PMF solutions indicate close geochemical associations of barite-opal, Cd-P, Zn-Co, Zn-Pb and redox sensitive elements in the sinking flux material at 500 m depth. Major reorganizations of element associations occur as labile carrier phases break down and elements redistribute among new carrier phases deeper in the water column.Factor scores show strong covariation and similar temporal phasing among the three trap depths and indicate a tight coupling in particle flux compositional variability throughout the water column. Seasonality in flux composition is primarily driven by dilution of the lithogenic component with freshly-produced biogenic material during the late winter primary production maximum. Temporal trends in scores reveal subtle non-seasonal changes in flux composition occurring on month long timescales. This non-seasonal variability may be driven by changes in the biogeochemical properties of intermediate water masses that pass through the region and which affect rates of chemical scavenging and/or aggregation within the water column. 相似文献
13.
The biogeochemistry of sedimentary sulfur was investigated on the continental shelf off central Chile at water depths between 24 and 88 m under partial influence of an oxygen minimum zone. Dissolved and solid iron and sulfur species, including the sulfur intermediates sulfite, thiosulfate, and elemental sulfur, were analyzed at high resolution in the top 20 cm. All stations were characterized by high rates of sulfate reduction, but only the sediments within the Bay of Concepción contained dissolved sulfide. Due to advection and/or in-situ reoxidation of sulfide, dissolved sulfate was close to bottom water values. Whereas the concentrations of sulfite and thiosulfate were mostly in the submicromolar range, elemental sulfur was by far the dominant sulfur intermediate. Although the large nitrate- and sulfur-storing bacteria Thioploca were abundant, the major part of S0 was located extracellularly. The distribution of sulfur species and dissolved iron suggests the reaction of sulfide with FeOOH as an important pathway for sulfide oxidation and sulfur intermediate formation. This is in agreement with the sulfur isotope composition of co-existing elemental sulfur and iron monosulfides. In the Bay of Concepción, sulfur isotope data suggest that pyrite formation proceeds via the reaction of FeS with polysulfides or H2S. At the shelf stations, on the other hand, pyrite was significantly depleted in 34S relative to its potential precursors FeS and S0. Isotope mass balance considerations suggest further that pyritization at depth includes light sulfide, potentially originating from bacterial sulfur disproportionation. The δ34S-values of pyrite down to −38‰ vs. V-CDT are among the lightest found in organic-rich marine sediments. Seasonal variations in the sulfur isotope composition of dissolved sulfate indicated a dynamic non-steady-state sulfur cycle in the surface sediments. The 18O content of porewater sulfate increased with depth at all sites compared to the bottom water composition due to intracellular isotope exchange reactions during microbial sulfur transformations. 相似文献
14.
Available data on synthesis, input, and decomposition of organic matter (OM) in the water column and recent bottom sediments of the World Ocean are generalized. The most reliable values of OM production and masses in the ocean, the total supply of organic carbon, and the input of terrigenous OM with coastal erosion, river runoff, and eolian matter are estimated. Maps of fossilization coefficients, distribution, and accumulation of OM in recent bottom sediments of the World Ocean are presented. A numerical expression is proposed for the main circumcontinental pattern of OM accumulation in the ocean. The group and elemental compositions of living matter of the ocean, land, and the Earth as a whole and the organic composition of bottom sediments are briefly considered. 相似文献
15.
O. P. Taran V. V. Boltenkov N. I. Ermolaeva E. Yu. Zarubina I. V. Delii R. E. Romanov V. D. Strakhovenko 《Geochemistry International》2018,56(3):256-265
The paper presents data on sapropels from ten lacustrine systems at the Barabinsk and Kulunda plains in Novosibirsk region. The sapropels are classified according to the type of the biological contribution to their origin and the content of organic matter. The sapropel of lakes Kachkulnya and Barchin, which are rich in organic matter and differ by the type of their origin (macrophytogenic and planktonogenic), were studied in much detail with the application of the following techniques: X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), and elemental (CHNSO) analysis. Groups of organic compounds contained in the organic matter were determined by successive extraction, and the monosaccharide composition was studied by high-performance liquid chromatography (HPLC). The organic matter of sapropel with different type of boilogical contribution was discovered to differ in elemental (CHNSO) composition, group of organics, and the monosaccharide compositions. Our results led us to conclude that the genesis of sapropel significnalty imprints the composition of its organic matter. 相似文献
16.
17.
Solar wind (SW) helium, neon, and argon trapped in a bulk metallic glass (BMG) target flown on NASA’s Genesis mission were analyzed for their bulk composition and depth-dependent distribution. The bulk isotopic and elemental composition for all three elements is in good agreement with the mean values observed in the Apollo Solar Wind Composition (SWC) experiment. Conversely, the He fluence derived from the BMG is up to 30% lower than values reported from other Genesis bulk targets or in-situ measurements during the exposure period. SRIM implantation simulations using a uniform isotopic composition and the observed bulk velocity histogram during exposure reproduces the Ne and Ar isotopic variations with depth within the BMG in a way which is generally consistent with observations. The similarity of the BMG release patterns with the depth-dependent distributions of trapped solar He, Ne, and Ar found in lunar and asteroidal regolith samples shows that also the solar noble gas record of extraterrestrial samples can be explained by mass separation of implanted SW ions with depth. Consequently, we conclude that a second solar noble gas component in lunar samples, referred to as the “SEP” component, is not needed. On the other hand, a small fraction of the total solar gas in the BMG released from shallow depths is markedly enriched in the light isotopes relative to predictions from implantation simulations with a uniform isotopic composition. Contributions from a neutral solar or interstellar component are too small to explain this shallow sited gas. We tentatively attribute this superficially implanted gas to low-speed, current-sheet related SW, which was fractionated in the corona due to inefficient Coulomb drag. This fractionation process could also explain relatively high Ne/Ar elemental ratios in the same initial gas fraction. 相似文献
18.
《Russian Geology and Geophysics》2015,56(10):1367-1383
New data on the mineral composition and the first data on the geochemical composition of ores of the Rogovik gold-silver deposit (Omsukchan ore district, northeastern Russia) have been obtained. Study of the regularities of the spatial distribution of ore mineralization shows that the deposit ores formed in two stages. Epithermal Au-Ag ores of typical poor mineral and elemental compositions were generated at the early volcanic stage. The major minerals are low-fineness native gold, electrum, acanthite, silver sulfosalts, kustelite, and pyrite. The typomorphic elemental composition of ores is as follows: Au, Ag, Sb, As, Se, and Hg. The content of S is low, mostly < 1%. Silver ores of more complex mineral and elemental compositions were produced under the impact of granitoid intrusion at the late volcanoplutonic stage. The major minerals are high-Hg kustelite and native silver, silver sulfosalts and selenides, fahlore, pyrite, chalcopyrite, galena, and sphalerite. The typomorphic elemental composition of ores is as follows: Ag, As, Sb, Se, Hg, Pb, Zn, Cu, and B. The content of S is much higher than 1%. The ores also have elevated contents of Mo, Ge, F, and LREE (La, Ce, and Nd). At the volcanoplutonic stage, polychronous Au-Ag ores formed at the sites of the coexistence of silver and epithermal gold-silver mineralization. Their specific feature is a multicomponent composition and a strong variability in chemical composition (both qualitative and quantitative). Along with the above minerals, the ores contain high-Hg gold, hessite, argyrodite, canfieldite, orthite, fluorapatite, and arsenopyrite. At the sites with strongly rejuvenated rocks, the ores are strongly enriched in Au, Ag, Hg, Cu, Pb, Zn, Ge, Se, La, Ce, Nd, S, and F and also contain Te and Bi. The hypothesis is put forward that the late silver ores belong to the Ag-complex-metal association widespread in the Omsukchan ore district. A close relationship between the ores of different types and their zonal spatial distribution have been established. In the central part of the Rogovik deposit, epithermal Au-Ag ores are widespread in the upper horizons, Ag ores are localized in the middle horizons, and rejuvenated polyassociation Au-Ag ores occur at the sites (mostly deep-seated) with ore-bearing structures of different ages. 相似文献
19.
Franois De Vleeschouwer Brigitte Van Vliët Lano Nathalie Fagel 《Applied Geochemistry》2008,23(12):3819-3839
This paper presents geochemical profiles of a tephra-bearing minerotrophic peat column from NE-Iceland obtained using various elemental analyses of the solid phase and the pore water. The influence of tephra grain size, thickness and composition of each tephra on the peat geochemistry was investigated. Interpretations are supported by a statistical approach, in particular by autocorrelation, and by microscopy observations. Minerotrophic peat geochemistry may be strongly dependent upon post-depositional mobilization and possible leaching of elements as demonstrated by Fe and trace metal concentration profiles. Chemical elements, and more specifically potentially harmful metals, can be slowly leached out of volcanic falls during their weathering and re-accumulate downwards. It is emphasised that a tephra deposit can act as an active geochemical barrier, blocking downward elemental movements and leading to the formation of enriched layers. In this study, the formation of poorly amorphous Fe phases above the Hekla 3 tephra is shown. These poorly crystalline Fe phases scavenged Ni. 相似文献
20.
《Chemical Geology》2006,225(1-2):61-76
The boron geochemical cycle has been simulated using a time-dependent geochemical box model that was coupled to a one-dimension model of seawater–oceanic crust interactions. Boron elemental and isotopic compositions of oceanic rocks as a function of depth were calculated by mass balance, using the temperature and porosity profiles of the crust as well as the available experimental and empirical distribution coefficients and fractionation factors between mineral and water. Ranges of boron elemental and isotopic variations of seawater were calculated for crust–seawater interactions that take place from the ridge-axis to the off-axis closure of the hydrothermal system. The present-day δ11B of seawater (40‰) could represent a steady-state value. However, depending on crustal permeability, lifetime of water–rock interactions, and expansion rate of the oceanic ridge, the δ11B of seawater may vary from 30‰ to 50‰ at the 10 million year scale.Some boron isotope compositions of Cretaceous biogenic carbonates and ophiolitic serpentinites from Oman are comparable to modern rock samples, suggesting that the δ11B of Cretaceous seawater was close to the present-day value. Low δ11B values of some biogenic carbonates cannot be attributed to low pH values of past seawater, but more probably to δ11B variations of seawater or diagenetic alteration by crustal aqueous fluids. Boron isotope composition of hydrothermally altered serpentines could be considered as a promising proxy of the seawater composition. 相似文献