首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
The chemical composition of organic matter (Corg, Norg, δ13C, δ15N, and n-alkanes) was studied in the top layer of bottom sediments of the East Siberian Sea. Possible ways were proposed to estimate the amount of the terrigenous component in their organic matter (OM). The fraction of terrigenous OM estimated by the combined use of genetic indicators varied from 15% in the eastern part of the sea, near the Long Strait, to 95% in the estuaries of the Indigirka and Kolyma rivers, averaging 62% over the sea area.  相似文献   

2.
Complex biogeochemical studies including the determination of isotopic composition of Corg in both suspended particulate matter and surface horizon (0–1 cm) of sediments (more than 260 determinations of δ13C-Corg) were carried out for five Arctic shelf seas: White, Barents, Kara, East Siberian, and Chukchi. The aim of this study is to elucidate causes that change the isotopic composition of particulate organic carbon at the water-sediment boundary. It is shown that the isotopic composition of Corg in sediments from seas with a high river runoff (White, Kara, and East Siberian) does not inherit the isotopic composition of Corg in particles precipitating from the water column, but is enriched in heavy 13C. Seas with a low river runoff (Barents and Chukchi) show insignificant difference between the value of δ13C-Corg in both suspended load and sediment because of a low content of the isotopically light allochthonous organic matter (OM) in particulates. Complex biogeochemical studies with radioisotope tracers (14CO2, 35S, and 14CH4) revealed the existence of specific microbial filter formed from heterotrophic and autotrophic organisms at the water-sediment boundary. This filter prevents the mass influx of products of OM decomposition into water column, as well as reduces the influx of a part of OM contained in the suspended particulate matter from water into sediment.  相似文献   

3.
The paper reviews data (acquired in 2007–2016) on aliphatic and polycyclic aromatic hydrocarbons in comparison with data on concentrations of lipids, Corg, and chlorophyll a in the water and bottom sediments the river–sea geochemical barrier (for the Northern Dvina, Ob, Yenisei, and Lena rivers). It was established that the concentrations of anthropogenic hydrocarbons decrease and these compounds precipitate like other organic compounds and particulate matter, where riverine and marine waters mix. Relatively pure water flows in the pelagic zones of seas. In spite of low temperatures in the Arctic, anthropogenic hydrocarbons transform so rapidly that natural compounds dominate in the water and bottom sediments: autochthonous in the seawater and allochthonous in the bottom sediments.  相似文献   

4.
We use the evolution of river sediment characteristics and sedimentary Corg from the Himalayan range to the delta to study the transport of Corg in the Ganga-Brahmaputra system and especially its fate during floodplain transit.A detailed characterisation of both mineral and organic particles for a sampling set of river sediments allows taking into account the sediment heterogeneity characteristic of such large rivers. We study the relationships between sediment characteristics (mineralogy, grain size, specific area) and Corg content in order to evaluate the controls on Corg loading. Contributions of C3 and C4 plants are estimated from Corg stable isotopic composition (δ13Corg). We use the evolution of δ13Corg values from the Himalayan range to the delta in order to study the fate of Corg during floodplain transit.Ganga and Brahmaputra sediments define two distinct linear relations with specific area. In spite of 4-5 times higher specific area, Ganga sediments have similar Corg content, grain size and mineralogy as Brahmaputra sediments, indicating that specific area does not exert a primary control on Corg loading. The general correlation between the total Corg content and Al/Si ratio indicates that Corg loading is mainly related to: (1) segregation of organic particles under hydrodynamic forces in the river, and (2) the ability of mineral particles to form organo-mineral aggregates.Bed and suspended sediments have distinct δ13Corg values. In bed sediments, δ13Corg values are compatible with a dominant proportion of fossil Corg derived from Himalayan rocks erosion. Suspended sediments from Himalayan tributaries at the outflow of the range have low δ13Corg values (−24.8‰ average) indicating a dominant proportion of C3 plant inputs. In the Brahmaputra basin, δ13Corg values of suspended sediments are constant along the river course in the plain. On the contrary, suspended sediments of the Ganga in Bangladesh have higher δ13Corg values (−22.4‰ to −20.0‰), consistent with a significant contribution of C4 plant derived from the floodplain. Our data indicate that, during the plain transit, more than 50% of the recent biogenic Corg coming from the Himalaya is oxidised and replaced by floodplain Corg. This renewal process likely occurs during successive deposition-erosion cycles and river course avulsions in the plain.  相似文献   

5.
The group composition of organic matter (OM) was studied in the channel sediments of the Pakhra River under natural condition and in the zone affected by the town of Podol’sk, Moscow oblast. It was found that the natural alluvium is poor in OM (Corg = 0.65%), the composition of which is dominated by humus acids (81.8% of Corg) at minor fractions of residual OM (16.7%) and lipids (1.5%). Anthropogenic muds formed in the river channel in the zone affected by urban pollution are conspicuous in high OM content (Corg = 1.26–2.60%), the composition of which is enriched in lipids (up to 10–20%) and residual OM (up to 27.3–48.6%), whereas the fraction of humus acids decreases to 29.6–57.1%. The muds are most significantly enriched in lipids (their specific concentration increases by factors of 6–59 compared with the natural alluvium) and residual OM (by factors of 3–11). The amount and character of the group composition of OM from anthropogenic muds are controlled by the specific features of the sources of sedimentary material in the river and the character of the environment of alluvium sedimentation in the zone affected by an industrial town.  相似文献   

6.
The presence of rocks capable of generating hydrocarbons (HC) in the section of sedimentaryrock basins is an essential criterion for their qualification as structures with oil and gas pools. Although organic matter (OM) is always present as dissemination in genetically different sediments, it is believed that rocks enriched with OM of the sapropel series (2 to 3% Corg) can generate a significant amount of liquid HC. However, rock sequences with the Corg ranging from 3–5 to 15–20% are considered oil source formations. The rock section of large petroliferous basins usually includes one or two source sequences, which generated liquid and gaseous HCs after submergence to high temperature and pressures zones. In the basin confined to the Arctic slope of Alaska, one of the main producers of liquid HC is represented by the Upper Triassic clays and limestones of the Shublik Formation. In the Barents Sea and North Sea basins, such rocks are represented by the Spekk Formation and the Kimmeridge Clay, respectively; in the West Siberian basin, by the Bazhenovo Formation; in the Persian Gulf, by the Fahlian, Sargelu, and Garau formations; in basins of the Caribbean region, by marls and clayey limestones of the La Luna Formation. In perioceanic basins of the South Atlantic, the major source sequences are represented by the Neocomian and Barremian clays and marls. The source rocks are identified as the Lagoa Feia Formation in the Campos and Santos basins. They are cognized as the Black Marlstone or Bukomazi Formation in the Lower Congo, Kwanzaa-Cameroon, and Angola basins.  相似文献   

7.
Oil source rocks represent sequences with the Corg content ranging from 3–5 to 15–20%. Sedimentary sections of large petroliferous basins usually include one or two such sequences, which generated liquid and gaseous hydrocarbons (HCs) during their long-term subsidence to the elevated temperature zone. The middle episode of the Late Cretaceous was marked by the accumulation of sediments with a high Corg content in different areas of the World Ocean. However, truly unique settings favorable for accumulation of the sapropelic organic matter (OM) appeared at continental margins that primarily faced the Tethys Ocean. The La Luna Formation is one of the best known source rock sequences responsible for the generation of liquid HCs in basins of the Caribbean region. In the Persian Gulf, the Kazhdumi Formation composed of marls and clayey limestones is considered the main oil-generating sequence. In the Paleogene after closure of the Tethys, the Pacific continental margins became the main domains that accumulated source rocks. The maximal deposition of sapropelic OM in this region corresponded to the early-middle Eocene. In the Neogene, the accumulation of source sediments was associated with deltas and submarine fans of large rivers and with upwelling zones. In basins of the Californian borderland, the main oil-generating sequences are represented by siliceous rocks of the Monterey Formation. They were deposited in a regional upwelling zone related to the cold California Current.  相似文献   

8.
We compared the degradation behaviour of amino sugars (ASs) and amino acids (AAs) during sedimentation in two lakes. Concentrations of individual ASs and AAs were measured in plankton, sediment trap and sediment samples from Lake Zug (LZ; eutrophic, stratified, permanently anoxic below 170 m) and Lake Brienz (LB; oligotrophic, oxic throughout the water column). In the plankton samples AAs comprised 37–50% of the organic carbon (Corg) and 41–65% of the N. With increasing water depth the fraction of Corg and N as AAs almost halved in both lakes. At the sediment surface the contribution of AAs to the Corg pool was slightly greater, but in the sediments the proportion further decreased downwards to values of 1% of the Corg pool in LB and 8% in LZ, and 3% and 17% of the N pool, respectively. ASs contributed to a smaller extent to the planktonic organic matter (OM). Within the water column, the contribution decreased in both lakes. In contrast, in the sediments the contribution of ASs to the Corg and N pools increased slightly with depth, indicating AS accumulation. We applied degradation indices based on ASs, AAs and chlorins, which all revealed transformation with OM sedimentation. However, some indices were more sensitive to early degradation (e.g. reactivity index) and others to an intermediate level of degradation (e.g. chlorin index and non-protein AAs). Despite the different trophic status and redox conditions, the general pattern of degradation was similar in both lakes, but was more pronounced in the sediments of the eutrophic LZ.  相似文献   

9.
This paper addresses the problem of relationships between the chemical composition and color of Quaternary marine sediments using the data of X-ray fluorescence analysis for the region of the Mendeleev Rise (Arctic Ocean). The contributions of sedimentation and diagenetic factors to color formation were estimated. It was shown that lithostratigraphic correlations should be performed (with certain limitations) using only sediment layers of dark brown and pink color.  相似文献   

10.
The normative mineral composition is reported on source rocks of metasediments from the granulite belt of the Baltic Shield. The primary composition, CIA index, and position of data points of studied rocks in discriminant diagrams indicate that a significant part of the studied rocks formed from immature sediments (graywackes and subgraywackes). The material supplied to sedimentation paleobasins was obtained from different (ultrabasic, basic, intermediate, and acid) rocks. The paleobasin was characterized by organic activity and reducing environment in the bottom layer. Correlation found between some elements, e.g., (Rb, Ba, Pb)–K; Sr–(Na, Ca), and so on, is also typical of Phanerozoic deposits. The possible contents of OM (Corg) and U were reconstructed in source rocks of metasediments of the Lapland–Kolvitsa granulite belt of the Baltic Shield.  相似文献   

11.
The contribution of soil organic matter (SOM) to continental margins is largely ignored in studies on the carbon budget of marine sediments. Detailed geochemical investigations of late Quaternary sediments (245-0 ka) from the Niger and Congo deep-sea fans, however, reveal that Corg/Ntot ratios and isotopic signatures of bulk organic matter (δ13Corg) in both fans are essentially determined by the supply of various types of SOM from the river catchments thus providing a fundamentally different interpretation of established proxies in marine sciences. On the Niger fan, increased Corg/Ntot and δ13Corg (up to −17‰) were driven by generally nitrogen-poor but 13C-enriched terrigenous plant debris and SOM from C4/C3 vegetation/Entisol domains (grass- and tree-savannah on young, sandy soils) supplied during arid climate conditions. Opposite, humid climates supported drainage of C3/C4 vegetation/Alfisol/Ultisol domains (forest and tree-savannah on older/developed, clay-bearing soils) that resulted in lower Corg/Ntot and δ13Corg (< −20‰) in the Niger fan record. Sediments from the Congo fan contain a thermally stable organic fraction that is absent on the Niger fan. This distinct organic fraction relates to strongly degraded SOM of old and highly developed, kaolinite-rich ferallitic soils (Oxisols) that cover large areas of the Congo River basin. Reduced supply of this nitrogen-rich and 12C-depleted SOM during arid climates is compensated by an elevated input of marine OM from the high-productive Congo up-welling area. This climate-driven interplay of marine productivity and fluvial SOM supply explains the significantly smaller variability and generally lower values of Corg/Ntot and δ13Corg for the Congo fan records. This study emphasizes that ignoring the presence of SOM results in a severe underestimation of the terrigenous organic fraction leading to erroneous paleoenvironmental interpretations at least for continental margin records. Furthermore, burial of SOM in marine sediments needs more systematic investigation combining marine and continental sciences to assess its global relevance for long-term sequestration of atmospheric CO2.  相似文献   

12.
  相似文献   

13.
Surface sediment samples were collected from the Squamish River Delta, British Columbia, in order to determine the role of sediment surface area in the preservation of organic matter (OM) in a paralic sedimentary environment. The Squamish Delta is an actively prograding delta, located at the head of Howe Sound.Bulk total organic carbon (TOC) values across the Squamish Delta are low, ranging from 0.1 to 1.0 wt.%. The carbon/total nitrogen ratio (Corg/N) ranges from 6 to 17, which is attributed to changes in OM type and facies variations. The <25-μm fraction has TOC concentrations up to 2.0 wt.%, and a Corg/N ratio that ranges from 14 to 16. The 53–106-μm fraction has higher TOC concentrations and Corg/N ratios relative to the 25–53-μm fraction. The Corg/N ratio ranges from 9 to 18 in the 53–106-μm fraction and 5.5–10.5 in the 25–53-μm fraction. Surface area values for bulk sediments are low (0.5–3.0 m2/g) due to the large proportion of silt size material. Good correlation between surface area and TOC in bulk samples suggests that OM is adsorbed to mineral surfaces. Similar relationships between surface area and TOC were observed in size-fractionated samples. Mineralogy and elemental composition did not correlate with TOC concentration.The relationships between surface area, TOC and total nitrogen (TN) can be linked to the hydrodynamic and sedimentological conditions of the Squamish Delta. As a result, the Squamish Delta is a useful modern analogue for the formation of petroleum source rocks in ancient deltaic environments, where TOC concentrations are often significantly lower than those in source rocks formed in other geological settings.  相似文献   

14.
Geochemical and isotopic data for the uppermost 1.2 m of the sediments of the central Santa Monica Basin plain were examined to better understand organic matter deposition and recycling at this site. Isotopic signatures (Δ14C and δ13C) of methane (CH4) and dissolved inorganic carbon (DIC) indicate the occurrence of anaerobic oxidation of CH4 that is fueled by CH4 supplied from a relict reservoir that is decoupled from local organic carbon (Corg) degradation and methanogenesis. This finding was corroborated by a flux budget of pore-water solutes across the basal horizon of the profile. Together these results provide a plausible explanation for the anomalously low ratio between alkalinity production and sulfate consumption reported for these sediments over two decades ago. Shifts in Δ14C and δ13C signatures of Corg have previously been reported across the 20-cm depth horizon for this site and attributed to a transition from oxic to anoxic bottom water that occurred ~350 years BP. However, we show that this horizon also coincides with a boundary between the base of a hemipelagic mud section and the top of a turbidite interval, complicating the interpretation of organic geochemical data across this boundary. Radiocarbon signatures of DIC diffusing upward into surface sediments indicate that remineralization at depth is supported by relatively 14C-enriched Corg within the sedimentary matrix. While the exact nature of this Corg is unclear, possible sources are hemipelagic mud sections that were buried rapidly under thick turbidites, and 14C-rich moieties dispersed within Corg-poor turbidite sections.  相似文献   

15.
We present an organic geochemical study of surface sediments of Lake Sarbsko, a shallow coastal lake on the middle Polish Baltic coast. The aim was to provide evidence concerning the origin of the organic matter (OM) and its compositional diversity in surface deposits of this very productive, highly dynamic water body. The content and composition of the OM in the bottom sediments were investigated at 11 sampling stations throughout the lake basin. OM sources were assigned on the basis of bulk indicators [total organic carbon (TOC), total nitrogen (TN), δ13CTOC and δ15N and extractable OM yield], biomarker composition of extractable OM and compound-specific C isotope signatures. The source characterization of autochthonous compounds was verified via phytoplankton analysis. The distribution of gaseous hydrocarbons in the sediments, as well as temporal changes in lake water pH, the concentration of DIC (dissolved inorganic carbon) and δ13CDIC were used to trace OM decomposition.The sedimentary OM is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition. However, the presence of CH4 and CO2 in the bottom deposits provides evidence for microbial degradation of sedimentary OM. The transformation of organic compounds in surface, bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of CaCO3.The data enhance our understanding of the relationships between the composition of sedimentary OM and environmental conditions within coastal ecosystems and shed light on the reliability of OM proxies for environmental reconstruction of coastal lakes.  相似文献   

16.
Isotopic compositions of organic (δ13C-Corg) and carbonate (δ13C-Ccarb) carbon were analyzed in the particulate matter (hereafter, particulates) and sediments from the North and Middle Caspian basins. Isotopic composition of Corg was used for assessing proportions of the allochthonous and autochthonous organic matter in the particulates. Difference between the δ13C-Corg values in surface sediments and particulates is explained by the aerobic and anaerobic diagenetic transformations. Isotopic composition of Corg in sediments may be used as a tool for reconstructing the Quaternary transgressive-regressive history of the Caspian Sea.  相似文献   

17.
A series of layers rich in organic matter (sapropelites) is known in the upper Ypresian deposits of the northeastern Peri-Tethys. Study of formainifers and quantitative analysis of their different ecological groups showed that proportion of infauna is considerably grater in sapropelic layers than in host deposits. In distinction from infauna, tests of species not burrowing into sediments (epifauna) are partially dissolved. The analyzed paleocoenoses of benthic foraminifers imply that sapropelites have been formed most likely in dysoxic environments, under conditions of the bottom waters contamination by carbon dioxide in response to a high Corg influx, weakened water circulation and low oxygen concentration. The comparison of foraminiferal assemblages with paleocoenoses studied previously in the Paleocene/Eocene boundary sapropelic interbed suggests that deposits rich in Corg originated under the same hydrogeochemical environments.  相似文献   

18.
A close relation of the organic carbon (Corg) content with major has been established for rocks of the Upper Jurassic–Lower Cretaceous Bazhenov Formation. Applying the method of multiple linear regression, it has been demonstrated that the Corgcontent in rocks of the Bazhenov Formation is stringently controlled by its bulk chemical composition. This inference is consistent with the existing ideas regarding a close interrelation between the following main components of rocks: organic carbon and authigenic quartz formed on remains of Radiolaria; pyrite formed in a highly reducing medium of Corg-rich sediments; and terrigenous clayey material diluting the authigenic siliceous–carbonaceous–pyritic matrix. These components chiefly determine the spectrum of major elements in the Bazhenov Formation. The establishment of the close relation between the Corgcontent and the group of major elements refutes the suggestion of some authors that siliceous material was supplied to nonlithified sediments of the Bazhenov sea by hydrothermal solutions, because this mechanism would have inevitably upset geochemical relations between elements in the studied rocks.  相似文献   

19.
Lithology and Mineral Resources - The results of petrographic, petrogeochemical and isotopic studies of sedimentary rocks obtained from bedrock outcrops of the Alpha–Mendeleev Rise, Arctic...  相似文献   

20.
The paper presents the first results of a comparative study of the composition and distribution of organic matter (OM) (Corg, n-alkanes, Pr, Phy) in samples of the ferromanganese nodule–sediment–pore water system taken at a single site in the Clarion–Clipperton Fracture Zone, Pacific Ocean. Samples were taken during Cruise 120 of R/V James Cook in 2015. The results of the comparison of organogeochemical parameters in the lipid fraction of OM in ferromanganese nodules of different size and morphology with the underlying sediment (0–1 cm) and pore water revealed both principle genetic affinity of OM therein and significant discrepancies between the processes of diagenesis during the formation and growth of each individual ore sample.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号