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1.
The molecular distributions of homologous aliphatic lipid compounds (n-alkanes, n-alkanoic acids, n-alkanols, n-alkanals and n-alkan-2-ones) were investigated in sediments of Lake Bera, Malaysia as well as in plant waxes from the vicinity using gas chromatography-mass spectrometry. In addition, triterpenoids of the oleanane, ursane, lupane and friedelane series, and their diagenetic products were also identified. Using the aquatic proxy Paq, it was found that the n-alkanes present in surface sediments S1, S5 and S6 correspond to an input from emergent macrophytes, whereas in sediments collected from open water (S2, S3 and S4) they correspond to input from submerged/floating macrophytes. The presence of n-alkan-2-ols, a commonly found homologous series in the sediments as well as in the plant wax, is novel here. In addition, the presence of 24-methylcycloart-22-enol and 24-ethylcycloart-22-enol in sediments as well as the plant wax of Pandanus helicopus, a dominant reed around the lake, also supports the input of plant biomarkers to the sediments. The occurrence of 5-membered ring triterpenoid derivatives as major diagenetic products of the triterpenoids identified (e.g. friedelan-2,3-dione) shows that the degradation of the organic matter in the sediments occurs mainly under oxic conditions. Also, the presence of ring-A degraded triterpenoids (dihydroputranjivic acid, 3-nor-2,4-seco-friedelane, 4α- and 4β-3-norfriedelanes, A-norfriedel-10-one, and A-norfriedel-8-en-10-one) and the aromatized triterpenoid hydrocarbons (mono- and triaromatic derivatives) as minor diagenetic products indicates photochemical and microorganism-mediated alteration reactions of natural products in the sediments. Additional novel polyfunctional friedelane derivatives, namely friedelane-2,3-dione, friedelane-1,3-diol-2-one and friedel-1(10)-ene-1,3-diol-2-one were identified for the first time in this study. These novel polyfunctional triterpenoids were inferred to derive from the oxidation of the triterpenoids from higher plants in this oxic tropical environment. For future reference purposes, the mass spectra of the identified polar triterpenoids are also presented here. This study provides important data on the biogeochemistry of organic matter in a tropical lake of SE Asia.  相似文献   

2.
Herein, lipid biomarker analysis is applied to surface sediments from the southeastern Niger Delta region for the quantitative determination of aliphatic lipids, steroids and triterpenoids in order to differentiate between natural (autochthonous vs. allochthonous) and anthropogenic organic matter (OM) inputs to this deltaic environment. This ecosystem, composed of the Cross, Great Kwa and Calabar Rivers, is receiving new attention due to increased human and industrial development activities and the potential effects of these activities impacting its environmental health. While the presence of low molecular weight n-alkanes (<C22) and the fossil biomarkers pristane and phytane in all samples, are indicative of a minor petroleum related input, the total extractable organic component of the surface sediments of these rivers remains predominantly of a natural origin as characterized by the variety and predominance of lipid classes that are mainly derived from the epicuticular waxes of vascular plants and include n-alkanes, n-alkanols, n-alkan-2-ones, n-alkanoic acids, steroids and triterpenoids. In addition, recent OM inputs from microorganisms are indicated by the presence of lower molecular weight n-alkanoic acids (Cmax = 16), while the major triterpenoids of the sediments, taraxerol and friedelin, and the major sterol, sitosterol, indicate recent OM inputs from vascular plants. Plankton-derived sterols, such as fucosterol and dinosterol, are also found in sediments from the Cross and Great Kwa Rivers and likely originate from autochthonous primary productivity. Furthermore, the coprosterols coprostanol and 24-ethylcoprostanol are present in most samples and indicate measurable anthropogenic contributions from domestic untreated sewage inputs and agricultural run-off, respectively. Of the three rivers studied, the Cross River system was excessively influenced by human and industrial development activities, including drivers such as urbanization and population center growth, land-use change to support agricultural production and animal husbandry, and petroleum exploration and production. These influences were found to be regionally specific as controlled by point sources of pollution based on the relative distributions measured and on the fact that the molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.  相似文献   

3.
The concentrations of polar organic compounds including n-alkanoic acids, n-alkanols, steroids and triterpenoids were determined in extracts of shallow sediments from the Mesopotamian marshlands of Iraq. The sediments were collected by a stainless steel sediment corer, extracted with a dichloromethane and methanol mixture (3:1 v:v) by ultrasonic agitation and then analyzed by gas chromatography–mass spectrometric (GC–MS). The analysis results showed that the n-alkanoic acids ranged from C8 to C20 with concentrations of 7.8 ± 1.2 μg/g sample, whereas the concentrations of n-alkanols, which ranged from C12 to C39 were from 28.6 ± 4.3 to 121.7 ± 18.3 μg/g sample. The steroids and triterpenoids included stenols, stanols, stenones, stanones, tetrahymanol, tetrahymanone and extended ββ-hopanes. The total concentrations of steroids and triterpenoids ranged from 26.8 ± 4.1 to 174.6 ± 26.2 μg/g and from 0.74 ± 0.11 to 11.2 ± 1.7 μg/g sample, respectively. The major sources of these lipids were from natural vegetation, microbial (plankton) residues and bacteria in the sediments, with some contribution from anthropogenic sources (livestock, sewage and petroleum). Further studies of these wetlands are needed to characterize the input rate, transformation and diagenesis of the organic matter and to assess its various sources.  相似文献   

4.
The black shale samples collected from two Neogene formations in the Klias Peninsula area, West Sabah, have been assessed and characterized in details by gas chromatography, gas chromatography-mass spectrometry and a variety of organic geochemical parameters. The aims of this study are to describe the characteristics of organic matter of these sediments in terms of source/type of the organic matter, assess its thermal maturity and paleoenvironment of deposition, based primarily on biomarker distributions. The results of both formations do not reveal significant differences within the rock extracts. The gas chromatograms of the saturated hydrocarbon fractions of the Setap Shale and the Belait formations displayed monomodal n-alkane distributions and nearly identical regular sterane compositions with a predominance of C27 regular steranes. These are consistent with open marine depositional environments dominated by marine biological matter. Another related feature of these rock extracts is the presence of a high relative abundance of gammacerane, indicating anoxic marine hypersaline source depositional environment. The relatively high abundance of common land plant-derived biomarkers, such as bicadinanes and oleananes, is a clear indication of a major terrigenous input to the source of the extractable organic matter. The predominance of oleanane biomarkers in both formations is indicative of angiospermis input and Tertiary source rocks. The high C29/C30 hopane ratios, moderate development of C33–C35 hopanes, high abundance of tricyclic terpanes and a slight predominance of C27 regular sterane over C28 and C29 steranes are characteristic features tending to suggest a significant marine influence on these source rocks, thereby suggesting a mixed source input. The 22S/(22S+22R)C32 hopane ratio has reached equilibrium, and this is supported by the high maturity level as indicated by the 22S/22SC31–33 extended hopane ratios and 20S/(20S+20R)C29 regular steranes ratios.  相似文献   

5.
With the purpose of tracing the variations of the organic matter sources of sediments, a sample column (25.96 m in size) from the Hemudu Area of Hangzhou Bay was put through AMS14C dating and biogeochemical analysis. TOC and TN presented similar variation trends, suggesting the same and stable sources of organic matter; the bad correlation between the grain size and TOC content indicated that the organic matter occurrence was neither controlled by the grain size nor the surface absorption of the fine particles, but it may has something to do with the complicated sedimentary hydrodynamic force, the input of organic matter and microbial action. Judging on the basis of C/N ratio and δ13CTOC, the organic carbon in sediments was a mixture of terrigenous and marine organic carbon, testifying to the land-sea interaction characteristic of the study area. The indexes experienced abrupt changes at about 6.5 ka BP, when the lighter terrigenous organic carbon made an increased proportion to the heavier marine organic carbon. The phenomenon reflected the enclosure of the lagoon and the reduced exchange interactions with the seawater of open seas.  相似文献   

6.
Here we report on the temporal changes in the composition of dissolved organic carbon (DOC) collected in the tidal freshwater region of the lower Mississippi River. Lignin-phenols, bulk stable carbon isotopes, compound-specific isotope analyses (CSIA) and 13C nuclear magnetic resonance (NMR) spectrometry were used to examine the composition of high molecular weight dissolved organic matter (HMW DOM) at one station in the lower river over 6 different flow regimes in 1998 and 1999. It was estimated that the annual input of DOC delivered to the Gulf of Mexico from the Mississippi River was of 3.1 × 10−3 Pg, which represents 1.2% of the total global input of DOC from rivers to the ocean. Average DOC and HMW DOC were 489 ±163 and 115 ± 47 μM, respectively. 13C-NMR spectra revealed considerably more aliphatic structures than aromatic carbons in HMW DOC. Lignin phenols were significantly 13C-depleted with respect to bulk HMW DOM indicating that C4 grass inputs to the HMW DOM were not significant. It is speculated that C4 organic matter in the river is not being converted (via microbial decay) to HMW DOM as readily as C3 organic matter is, because of the association of C4 organic matter with finer sediments. The predominantly aliphatic 13C NMR signature of HMW DOM suggests that autochthonous production in the river may be more important as a source of DOC than previously thought. Increases in nutrient loading and decreases in the suspended load (because of dams) in the Mississippi River, as well as other large rivers around the world, has resulted in significant changes in the sources and overall cycling of riverine DOC.  相似文献   

7.
The comprehensive biomarker characteristics from previously undescribed Middle Jurassic clays of Poland are presented. The molecular composition of the organic matter (OM) derived from clays of Aalenian to Callovian age has not changed significantly through time. High relative concentrations of many biomarkers typical for terrestrial material suggest a distinct dominance of OM derived from land plants. Increasing concentrations of C29-diaster-13(17)-enes towards the northern part of the basin indicate an increase in terrestrial input. This terrestrial material would have originated from the enhanced transport of organic matter from land situated at the northern bank of the basin, i.e., the Fennoscandian Shield. The organic matter was deposited in an oxic to suboxic environment, as indicated by relatively low concentrations of C33–C35 homohopanes, moderate to high Pr/Ph ratio values, an absence of compounds characteristic for anoxia and water column stratification, such as isorenieratane, aryl isoprenoids and gammacerane, as well as common benthic fauna and burrows. δ18O measurements from calcitic rostra of belemnites suggest that the mean value of the Middle Jurassic sea-water temperature of the Polish Basin was 13.1 °C. It is suggested that this mirrored the temperature of the lower water column because belemnites are considered here to be necto-benthic. The organic matter from the Middle Jurassic basin of Poland is immature. This is clearly indicated by a large concentration of biomarkers with the biogenic configurations, such as ββ-hopanes, hop-13(18)-enes, hop-17(21)-enes, diasterenes and sterenes. The identification of preserved, unaltered biomolecules like ferruginol, 6,7-dehydroferruginol and sugiol in Protopodocarpoxylon wood samples from these sediments present particularly strong evidence for the presence of immature OM in the Middle Jurassic sediments. Moreover, the occurrence of these polar diterpenoids is important due to the fact that they are definitely the oldest known natural products detected in geological samples.  相似文献   

8.
This study characterizes organic carbon (Corganic) and phosphorus (P) geochemistry in surface sediments of the Sacramento-San Joaquin Delta, California. Sediment cores were collected from five sites on a sample transect from the edge of the San Francisco Bay eastward to the freshwater Consumnes River. The top 8 cm of each core were analyzed (in 1-cm intervals) for Corganic, four P fractions, and redox-sensitive trace metals (uranium and manganese). Sedimentary Corganic concentrations and Corganic: P ratios, decreased, while reactive P concentrations increased moving inland in the Delta. The fraction of total P represented by organic P increased inland, while that of authigenic P was higher bayward than inland reflecting increased diagenetic alteration of organic matter toward the bayward end of the transect. The redox indicator metals are consistent with decreasing sedimentary suboxia inland. The distribution of P fractions and C:P ratios, reflect the presence of relatively labile organic matter in upstream surface sediments. Sediment C and P geochemistry is influenced by site-specific particulate organic matter sources, the sorptive power of the sedimentary material present, physical forcing, and early diagenetic transformations presumably driven by Corganic oxidation.  相似文献   

9.
Benzene extractable aliphatic hydrocarbons from the New Albany Shale in the Illinois Basin were characterized by gas chromatography and mass spectrometry, and the total organic matter of the shale was characterized by solid state carbon-13 cross polarization magic angle spinning nuclear magnetic resonance. Core samples from a northwest-trending cross-section of the Illinois Basin were studied. Gas chromatography (GC) and gas chromatography-mass spectrometric analysis (GC/MS) data indicate a regional variation of the aliphatic composition of the shale extracts. A positive, linear relationship between the two ratios, pristane/n-C17 and phytane/n-C18, is indicated. The NMR results indicated that organic matter deposited in northwestern Illinois shale is relatively high in aliphatic hydrocarbon content while, in contrast, organic matter found in southeastern Illinois shale is relatively low in aliphatic hydrocarbon content. Our findings suggest that the organic variation of the shale is mainly due to the differences in thermal maturity of the shale organic matter and the use of pristane/n-C17 ratio as a thermal parameter in the study of oil may be extended to the study of the ancient sediments.  相似文献   

10.
Multidisciplinary analysis of the carbonaceous sediments of Warkalli Formation (Mio-Pliocene) from the Warkalli cliff section has been done to assess the source of organic matter, palaeodepositional settings and the hydrocarbon potential. The n-alkane distribution from n-C12 to n-C33 along with bimodal distribution indicates significant organic matter contribution from microbial activity and higher plants. The contribution from angiosperm source vegetation is indicated by the oleanane type of triterpenoids. The hopanes distribution indicates the immature stage of the organic matter, which is in agreement with the Tmax (av. 401 °C) and huminite reflectance (av. 0.28% Rr) values. The total organic carbon (TOC) contents vary between 0.8 and 6.72 wt. % in the studied sediments. Hydrogen index and oxygen index values range from 16 to106 mg HC/g TOC, and 113 to 344 mg CO2/g TOC, respectively. The maceral content is low, being dominated by the detrohuminite submaceral and the mineral matter accounts for 68 to 77% of the total composition. The phytoclast group (63–87%) is dominant with subordinate amorphous organic matter (4–35%). The study shows that the sediments were deposited in a marginal suboxic basin with intermittent variations. All the parameters unequivocally suggest that the studied sequence holds the potential to generate gaseous hydrocarbons.  相似文献   

11.
Organic matter contained in particulate matter in Lake Michigan waters and sediments has been characterized by CN ratios and by distributions of biomarker fatty acids, alkanols, sterols, and aliphatic hydrocarbons. Differences in organic constituents of particulate matter from various depths and distances from shore indicate a complex interaction of production, transformation, and destruction of the organic matter contained in sinking particles. Near-surface material contains important contributions of landderived organic matter, presumably of eolian input. Midwater particles have predominantly aquatic organic material of algal origin. At the sediment-water interface, selective suspension of the finer fractions of surficial sediments enriches bottom nepheloid layers with these sediment size classes. As a result, near-bottom particulate matter has an aquatic biomarker character. Organic matter associated with sinking particles undergoes substantial degradation during passage to the bottom of Lake Michigan, and aquatic components are selectively destroyed relative to terrigenous components.  相似文献   

12.
分子有机地球化学与古气候、古环境研究   总被引：30，自引：5，他引：30  
分子有机地球化学可以从分子级水平研究地质体中有机分子化合物的演化规律。本文报道了应用生物标志化合物指标探讨古气候和古环境,例如探讨古生物(含古植物)的输入,淡水、半咸水和高盐度水古环境的判识以及大气飘尘的来源和成因等。  相似文献   

13.
Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C14-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K2qn1) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST.  相似文献   

14.
The biomarker composition and stable isotope (C, O) ratio values of organic matter (OM) and carbonate from sediment cores from the oligotrophic Lake Brienz and the eutrophic Lake Lugano (both in Switzerland) are compared, in order to obtain information about OM sources and transformation processes. Eutrophic conditions at Lake Lugano are reflected in elevated total organic carbon (TOC) content and hydrogen index (HI) values, as well as higher lipid concentrations. Parallel down core trends in δ13C values of TOC and calcite in the Lake Lugano sediments reflect bioproductivity cycles. Variations in δ18O values of calcite are consistent with changes in mean summer temperature over the time interval covered by the core. In contrast, such a correlation does not exist for Lake Brienz and there the stable isotope composition of calcite reflects its allochthonous origin. In the sediments of both lakes, fatty acid (FA) distributions and the composition of n-alkanols and n-alkanes indicate highly variable proportions of autochthonous OM sources (algae, zooplankton, bacteria) and OM from land plants. Enhanced in situ microbial synthesis during sediment deposition in Lake Lugano is suggested by the higher TOC-normalised concentrations of branched chain FAs (C15–C17), hopanoic acids and triterpenoid alcohols (i.e. tetrahymanol, diplopterol). Variations in the concentrations of cholesterol are related to contributions from zooplankton and/or green algae, while sitosterol concentrations reflect the input of vascular plants. Periods of increased input of OM from diatoms are evidenced by high 24-methylcholesta-5,22-dien-3β-ol (either epibrassicasterol or brassicasterol) and/or highly branched isoprenoid (HBI) alkenes concentrations. High relative concentrations of diplopterol in Lake Lugano sediments are consistent with the predominance of cyanobacteria commonly observed in eutrophic lakes. The presence of archeol and hydroxyarcheol in very low concentrations in the Lugano sediments argues for the activity of methanogens and/or anaerobic methanotrophs.Differences in OM degradation processes are reflected in higher chlorin index values in the Brienz sediments but higher saturated vs. unsaturated n-FAs in the core from Lugano. Higher concentrations of branched chain FAs and 16:1ω7 n-FA, as well as enhanced 18:1ω7/18:1ω9 n-FA, are consistent with enhanced bacterial biomass in the Lugano water column or sediments. The preservation of phytol seems to be enhanced in sediments with a high relative contribution of land plant OM. Major factors affecting OM accumulation in the lakes are differences in OM sources (i.e. terrestrial OM vs. autochthonous production), extent of bacterial activity and most likely oxygen availability in the water column.  相似文献   

15.
The molecular composition of fossil resins from early to middle Eocene coal from northeast India, has been analyzed for the first time to infer their paleobotanical source. The soluble component of fossil resin was analyzed using gas chromatography–mass spectrometry (GC–MS). The resin extracts are composed of cadalene-based C15 sesquiterpenoids and diagenetically altered triterpenoids. The macromolecular composition was investigated using pyrolysis gas chromatography-mass spectrometry (Py-GC–MS) and Fourier transform infrared (FTIR) spectroscopy. The major pyrolysis products are C15 bicyclic sesquiterpenoids, alkylated naphthalenes, benzenes and a series of C17–C34 n-alkene-n-alkane pairs. Spectroscopic analysis revealed the dominance of aliphatic components. The presence of cadalene-based sequiterpenoids confirms the resin to be Class II or dammar resin, derived from angiosperms of Dipterocarpaceae family. These sesquiterpenoids are often detected in many SE Asian fluvio-deltaic oils. Dipterocarpaceae are characteristic of warm tropical climate suggesting the prevalence of such climate during early Eocene in northeast India.  相似文献   

16.
River runoff and atmospheric fallout (dust and air particulate matter) are major input sources of natural and anthropogenic terrestrial organic and inorganic components to the Arabian seas. In this study, we report on the various lipid tracer compounds that might be transported to the Arabian Gulf by rivers, dust, and air particulate matter. These are based on geochemical analysis of sediment, dust, and particulate samples collected from Iraq, Kuwait, and Saudi Arabia. The samples were extracted with a dichloromethane/methanol mixture and analyzed by gas chromatography-mass spectrometry. The extractable organic compounds (lipids) in the samples include n-alkanes, n-alkanoic acids, n-alkanols, methyl n-alkanoates, steroids, triterpenoids, carbohydrates, and petroleum hydrocarbons. The steroids and triterpenoids were major components in river and wetland samples. The major sources of these lipids were from natural vegetation, microbial (plankton and bacteria) residues in the sediments, sand, and soils, with some contribution from anthropogenic sources. Accordingly, these sources could be major inputs to the Arabian seas besides the autochthonous marine products. Future studies of the organic and inorganic biogeochemistry on river, dust, and coastal areas are needed to characterize the various regional sources, transformation, and diagenetic processes of the organic matter en route to the marine environment.  相似文献   

17.
The Eocene Maoming oil shale from Guangdong Province occurs as a laterally uniform stratigraphic section, typically 20–25 m thick, from which the aliphatic hydrocarbon constituents of six representative samples were investigated using GC and C-GC-MS. The sediments evaluated included the basal lignite, a vitrinite lens from the overlying claystone, and four intervals from the massive oil shale bed. As expected, the lignite and vitrinite differ markedly from the oil shales. The lignite is dominated by bacterial hopanoids and components of higher plant origin, including C29 steroids and triterpenoids such as oleanenes. Visually, the oil shale samples show corroded and degraded phytoclasts, spores, wispy particles of fluorescent organic material attributable to dinoflagellates and, especially in the uppermost sample, colonial algal bodies. The distributions of biological markers in the oil shales show many features in common, notably a dominance of dinoflagellate-derived 4-methylsteroids, and a significant proportion of higher-plant derived n-alkanes with marked odd-over-even carbon number predominance. Overall, they exhibit several features that resemble characteristics of the Messel shale. The hydrocarbons of the lowest shale horizon suggest that there may have been a gradual transition between deposition of the original peat and the subsequent oil shales. The aliphatic hydrocarbons of the uppermost shale are dominated by a number of C31 and C33 botryococcane homologues and other unusual branched alkanes possibly derived from green algae. All of the samples are immature. Overall, molecular and microscopic examination of the stratigraphic succession of the Maoming oil shale suggests a shallow, lacustrine environment within which peats were deposited. This lake subsequently deepened to support abundant algal populations, especially dinoflagellates, culminating in a dominance of botryococcoid algae.  相似文献   

18.
In this study, the molecular composition and biomarker distribution of lacustrine sediments from Val-1 drillhole in the central zone of the western part of the Valjevo-Mionica basin were investigated at depth interval of 0–400 m. Former investigations have shown that the core material can be separated into six depth intervals based on bulk geochemical, mineralogical and sedimentological characteristics. Concerning the quality of organic matter, presence of specific minerals, and high salinity and anoxicity, or alkalinity, three zones are of highest interest, defined at depth intervals of 15–75 m (A), 75–200 m (B) and 360–400 m (F). The first aim of the study was to identify which biomarkers characterize these specific intervals. The second aim, addressing the transitions zones of these intervals, was to extend the changes in the characteristics of the organic substance, to reflect the changes of conditions in the depositional environment as well as to define biomarker parameters which are the most sensitive sedimentological indicators.The sediments from the hypersaline anoxic and alkaline environment show high contribution of algal precursor biomass, what is in accordance with the good quality of organic substances in the sediments from these zones. High squalane content and low content of regular isoprenoid C25 are typical for hypersaline anoxic environment, whereas sediments from alkaline environment have high regular isoprenoid C25 content.Transition to specific sedimentation zones is characterized by change in total organic matter content, and of both free and pyrolysis-derived, and change in hydrogen index value. In the biomarker distributions, more significant changes were detected in distributions of n-alkanes and isoprenoids, compared to polycyclic alkanes. The most intensive changes in alkane distribution are reflected in changes in n-C17 content compared to n-C27, and phytane compared to n-C18. In addition, significant sensitivity was seen in ratios between squalane and n-alkane C26 (hypersaline depositional environment), or isoprenoid C25 and n-alkane C22 for high alkalinity environment.This study showed that Sq/n-C26 ratio can be used to assess the quality of organic substance in immature lacustrine sediments.  相似文献   

19.
In order to understand the distribution characteristics of biomarkers in source rocks,which may be related to organic input,Quaternary sediments from the Caohai Basin and the Chaiwobu Lake were analyzed for sterols,As a result,various sterols,have been found in the sediments.The composition of sterols in the sediments revealed that cholesterols and cholestadienols are more abundant than their C29 counterparts in the Chaiwobu Lake sediments and that C29 sterols are more abundant in the peats from the Caohai Basin,It is also found that stanol/sterol ratios in clays are higher than in peats.Studies show that organic input to the Chaiwobu Lake is mainly plankton and zooplankton and to the Caohai Basin is mainly terrestrial high plant.The authors have proposed that the relative abundance of C27 or C29 sterane in source rocks may reflect input characteristics to some extent and the stanol/sterol ratios may reflect the redox conditions of the depositional environments.  相似文献   

20.
The geochemical composition of lake bed sediments of a tropical reservoir in Brazil have been investigated. The C, N, P composition showed almost no variation between the different sampling points. All samples contained inorganic phosphorus (IP) ranging from 52 to 70%. The Redfield ratios show that the lake is without significant anthropogenic inputs. Most of the organic matter is composed by higher plants decomposition revealed in the total organic carbon (TOC):nitrogen (N) ratio ranging from 15.4 to 57.2. Also, TOC:organic phosphorus (OP) ranged from 265.3 to 933.6, suggesting that most of the organic matter has terrestrial origin from wood plants. The ratios suggest that most organic matter is influenced by the terrestrial characteristics of the watershed. Furthermore, the relative abundance of n-alkane homologues in the sediments was investigated. All samples have been analyzed for the n-alkanes C8 to C40. The sediments were dominated by n-alkanes C25–C38. It is concluded that n-alkane in sediments mainly come from terrestrial plants, however there is a contribution of submerged aquatic plants, especially in those sites in deeper areas of the lake. On the basis of Paq index the n-alkanes in sediments comes from terrestrial plants, however there is a contribution from emerged/floating plants.The investigated lake seems to be considered as meso to eutrophic. Because of the relatively high primary productivity in the lakes, there is a substantial organic-matter flux to the sediments, which rapidly becomes anoxic. According to the pristine/phytane ratio the sediments represent an anoxic environment with values found between 0.38 and 1.72.  相似文献   

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