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1.
Certain features of the distributions of sedimentary 4-methyl steroid hydrocarbons have been investigated: (i) competitive dehydration experiments with stanols adsorbed on a shale suggests a possible explanation for the low abundance of 4-methyl sterenes relative to their desmethyl counterparts in immature sediments, (ii) a 4-methyl spirostene which is a minor product of the backbone rearrangement of 4-methylcholest-4-ene in the laboratory has been tentatively assigned; its presence in a Toarcian black shale with a second isomer provides further evidence that the sedimentary backbone rearrangement of 4-methyl sterenes is analogous to that of their desmethyl counterparts and (iii) the major C30 4-methyl steranes in Semécourt shale (Toarcian, Paris Basin) differ from those in an Eocene lacustrine shale from China; this indicates the potential complexity of C30 steroidal alkanes (both 4-methyl and desmethyl) which can occur in sedimentary organic matter and shows that care must be taken in using m/z 217 mass chromatograms alone for routine input and maturity assessment using steroidal alkanes. 相似文献
2.
晋县凹陷赵芯2井（2459m,Ezk）低熟蒸发岩样品中检出了异常分布的C22-C27甾烯和C24-C30四环萜烷（17,21-断藿烷）,但在同井更深、成熟度相对更高的沉积物中并未检出。实测镜质组反射率R^0=0．43％以及芳烃馏分中有高丰度的苯并噻吩和多烷基化的二苯并噻吩,说明热催化作用成因是不可能的,微生物参与成为最可能的生成途经。沉积抽提物未显示出常规生物降解的痕迹,因此这些化合物很可能是在早期成岩阶段特定微生物作用的结果。该区油样中检出的C21-C29甾烷的特征与同时检出的C22-C27甾烯特征一致,进一步表明微生物作用的可能性;高丰度的C24-C30四环萜烷（17,21-断藿烷）和常规藿烷、甲基藿烷相匹配,以及高丰度的C22-C27甾烯和规则甾烷缺失相匹配,特别是芳烃馏分中多取代二苯并噻吩类有机含硫化合物的检出,均表明异常分布的C22-C27甾烯与C24-C30四环萜烷类似,很可能是早期成岩阶段微生物改造作用下的产物。 相似文献
3.
Sections of a 42 cm core from one area and surface sediments from two other areas of Buzzards Bay, Massachusetts were analyzed for sterols. The distribution of sterols in surface sediments appears to be influenced by benthic faunal composition or factors controlling this composition. A comparison of sterols extracted by Soxhlet-extraction with sterols extracted after subsequent saponification of the sediment showed that the former sterols decrease in concentration while the latter saponified sterols increase in concentration with depth. In both fractions, the individual sterol compositions are similar. A transformation between Soxhlet-extractable and non-Soxhlet-extractable saponified sterols appears to be occurring over the 130 yrs sampled by the core. This transformation is probably due to chemical/physical processes rather than biological processes. Comparison with fatty acid data shows that early diagenesis of sterols is slower than early diagenesis of fatty acids. 相似文献
4.
The South China Sea(SCS) is one of the most productive and accumulative marginal shelves of organic carbon in the world. To expound the transformation and preservation of organic carbon in the Northeast SCS, where abundant oil and gas resources have been reported, compound specific sterols in free(FR), base hydrolytic(BH), and acid hydrolytic(AH) forms were analyzed in surface and columnar sediments in May, 2016. The results showed that the total contents of sterols detected ranged from 0.15 to 3.74 ppm dry weight in the surface sediments, and gradually decreased from 3.41 to0.17 ppm dry weight from surface to deep sediments, in which cholesterol(27~(△5)) was the most abundant component. Sterols mainly existed in the BH form(54.51%-74.20%), followed by the FR form(25.50%-45.49%) and then the AH form(0-3.77%) in turn, in the surface sediments. BH and FR sterols accounted for 0-49.08% and 50.92%-100% in the columnar sediments, while AH sterols were undetectable. The contents of specific sterols indicated that, the primary source of marine organic carbon was about 5 times as much as that from terrestrial input. More and more FR sterols transformed into BH sterols with increasing sedimentary depth, and BH sterols absolutely dominated in sediment depths under 25 cm. The forms of Sterols C27 were maintained at a relative consistence state, but Sterols C28 to C30 degraded gradually during the sedimentation process. It was suggested that the stability of sterols, based on the chemical structures, might be the primary factor controlling their degradation and preservation in deeper sediments. These results would help to understand the organic carbon(OC) transformation in a hydrate formation area in a marginal sea. 相似文献
5.
6.
The aliphatic, aromatic and polar (NSO) fractions of seabed petroleums and sediment bitumen extracts from the Guaymas Basin hydrothermal system have been analyzed by gas chromatography and gas chromatography-mass spectrometry (free and silylated). The oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolyzates that have migrated to the seafloor by hydrothermal fluid circulation. The downcore sediments are representative of both thermally unaltered and thermally altered sediments. The survey has revealed the presence of oxygenated compounds in samples with a high degree of thermal maturity. Phenols are one class of oxygenated compounds found in these samples. A group of methyl-, dimethyl- and trimethyl-isoprenoidyl phenols (C27-C29) is present in all of the seabed NSO fractions, with the methyl- and dimethyl-isoprenoidyl phenols occurring as major components, and a trimethyl-isoprenoidyl phenol as a minor component. A homologous series of n-alkylphenols (C13-C33) has also been found in the seabed petroleums. These phenols are most likely derived from the hydrothermal alteration of sedimentary organic matter. The n-alkylphenols are probably synthesized under hydrothermal conditions, but the isoprenoidyl phenols are probably hydrothermal alteration products of natural product precursors. The suites of phenols do not appear to be useful tracers of high temperature hydrothermal processes. 相似文献
7.
Core sections from coastal bay, continental slope, and continental rise surface sediments of the western North Atlantic were analyzed for sterols. Changing rate or type of sediment input, bioturbation, and chemical conversion appear to be processes important in controlling the distribution of sterols in these sediments. Comparisons of individual sterol distributions and variations in the ratio of Soxhlet-extractable to non-extractable saponified sterols indicate that for the western North Atlantic, the extent to which each process is dominant varies with proximity to shore. Evidence is presented to show that sterols in the deep sea may be at least partially terrigenous in origin and not all biogenically derived in the surface waters. These sterols, and by analogy other labile organic compounds, may serve as a source of carbon for benthic organism metabolism. 相似文献
8.
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
9.
Trace element analyses have been carried out on hydrothermally altered pillow basalts of greenschist facies dredged from the median valley of the Mid-Atlantic Ridge. Sr is leached from the rock, and its behavior is apparently controlled by the same reactions as Ca. Cu is also leached from the basalt, but often shows local precipitation in veins as sulfides. Fe, B, Li, Ba, Mn, Ni and Co show sufficient variations in concentration and location within the altered basalts to indicate that some mobilisation occurs, but there may be subsequent uptake or precipitation into the secondary mineral assemblages. V, Y, Zr and Cr do not appear to be affected by hydrothermal alteration.The production of a metal-enriched solution by hydrothermal alteration and subsequent precipitation of metal salts to form metalliferous sediments is indicated, as is precipitation of metal sulfides in the basaltic basement. 相似文献
10.
A. A. Beus 《Journal of Geochemical Exploration》1979,11(2):195-208
Emerald-bearing deposits in the Cordillera Oriental are structurally controlled, localized at the intersection of two fault systems. At these intersections zones of intense fracturing affected by sodium and carbonate metasomatism host the emerald mineralization. Albitization, carbonatization and hydrothermal leaching of potassium and trace metals are characteristics of the metasomatically altered Cretaceous black shales which compose the emerald-bearing tectonic zones.Stream sediments collected in areas which have metasomatically altered shales in the drainage basin have a low K/Na ratio. It is possible to use this ratio, or the sodium content of the sediments, to locate areas worthy of further exploration. 相似文献
11.
The distributions of free 4-desmethyl sterols in sediments from the Peru coastal zone at 15°S have been determined. Major free sterols in the surface sediments include cholesterol, which is mainly derived from zooplankton, and two C28 sterols: 24-methylcholesta-5,24(28)-dien-3β-ol and 24-methylcholesta-5,22E-dien-3β-ol both of which are derived fro diatoms. Their concentrations decrease by almost an order of magnitude in the top 20 cm of sediment depth, indicating that free sterols are rapidly degraded in this sedimentary environment. Lipids from higher plants were also detected: long chain fatty acids and alcohols and various triterpenoid alcohols, including taraxerol, lupeol and α- and β-amyrin. The concentrations of most terrigenous lipids varied by less than a factor of 3 over the same depth, and these changes were not correlated with changes in the concentrations of total organic carbon. Below 3 cm, lipids from higher plants predominated in the extractable lipid distributions due to the more rapid degradation of marine lipids. We postulate that there are significant marine sources of the higher plant sterols 24-ethylcholesterol, 24-ethylcholesta-5,22E-dien-3β-ol and 24-methylcholesterol in these sediments. A high proportion of many of the terrigenous lipids in these sediments are probably transported into the coastal zone by rivers, rather than from the atmosphere, and then redistributed by bottom currents. 相似文献
12.
热水沉积作用的概念和几个岩石学标志 总被引：29，自引：7，他引：29
热水沉积作用系指沉积界面之下循环流动的热水喷溢出界面以后发生的沉积作用,以及界面之下的围岩的交代(蚀变)充填作用。本文讨论了三个重要的岩石学标--与沉积物同期(准同期)的交代、充填作用;具对称分布趋势的喷溢条带和纹层及礁硅岩套。 相似文献
13.
The abundance of sterols in sediment depth profiles is determined by variations in input source abundances and diagenesis. Deconvolution of these variables would permit accurate estimation of degradation rates and initial input source contributions of sterols to the sediments. In this study we have demonstrated the application of a simple mathematical approach to the estimation of the relative stabilities of a range of sterols in a microbially-poor temperate intertidal sediment. The results indicate that st-5-enols and possibly 4-methyl sterols are less stable than other sterols in this environment. Since dehydration reactions of sterols would be favoured by both a 4-methyl substituent and a C5,6 double bond, whilst other processes would not be as selective, it seems probable that this abiological process predominates in the Corner Inlet sediments. 相似文献
14.
W.G Meinschein 《Geochimica et cosmochimica acta》1976,40(3):323-330
The sterol contents of plankton and sediment samples have been determined. Cholesterol, 22-dehydrocholesterol, brassicasterol, campesterol, 24-methylenecholesterol, stigmasterol, and β-sitosterol are the major sterols in these samples. Systematic variations have been observed in the compositions of the sterols from bay and Gulf of Mexico plankton and from sediments collected in the mouth of the Aransas River, Capano Bay, Aransas Bay, Corpus Christi Bay and the Gulf near Port Aransas. The concentration of cholesterol increases as the concentration of β-sitosterol decreases in the sample sequence of river inlet sediments-bay sediments-Gulf sediments-bay and Gulf plankton. Calculations based on either the cholesterol or the β-sitosterol contents of the sterol fractions of the fresh water sediments and the Gulf plankton and sediments suggest that 34% of the sterols in the Gulf sediments are derived from terrigenous sources. 相似文献
15.
Capillary gas chromatography-mass spectrometry (C-GC-MS) and Iatroscan thin layer chromatography-flame ionisation detection (TLC-FID) were used to study hydrocarbon distributions in a sediment core from Ace Lake, a saline, meromictic lake in the Vestfold Hills of Antarctica. Hydrocarbons were abundant in most core sections (up to 125/μg/g dry wt), particularly in near-surface samples, and the distributions were very complex. Major constituents were identified as phytane, 2,6,10,15,19-pentamethyleicosane, tetrahydrosqualene, a mixture of phytenes, cholesta-3,5-diene and fern-7-ene. Smaller amounts of sterenes and hopenes were also present. The predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present.Phytenes were abundant in all core sections, and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria. Phytadienes were minor constituents at all depths studied. An unusual feature of some distributions was the high concentrations of fern-7-ene which was the major hydrocarbon in the 20–25 cm core section. This alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments. A possible source might be from purple non-sulphur bacteria. High concentrations of straight-chain C29 and C34 alkenes were also found in these sediments but their origin has not been determined. Major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago. The present condition of permanent anoxic bottom waters probably developed only in the last 1000 years. 相似文献
16.
Beyene G.Haile Urszula Czarniecka Kelai Xi Aleksandra Smyrak-Sikora Jens Jahren Alvar Braathen Helge Hellevang 《地学前缘(英文版)》2019,10(2):629-649
Sedimentary basins containing igneous intrusions within sedimentary reservoir units represent an important risk in petroleum exploration. The Upper Triassic to Lower Jurassic sediments at Wilhelm?ya(Svalbard) contains reservoir heterogeneity as a result of sill emplacement and represent a unique case study to better understand the effect of magmatic intrusions on the general burial diagenesis of siliciclastic sediments. Sills develop contact metamorphic aureoles by conduction as presented in many earlier studies. However, there is significant impact of localized hydrothermal circulation systems affecting reservoir sediments at considerable distance from the sill intrusions. Dolerite sill intrusions in the studied area are of limited vertical extent(～12 m thick), but created localized hydrothermal convection cells affecting sediments at considerable distance(more than five times the thickness of the sill)from the intrusions. We present evidence that the sedimentary sequence can be divided into two units:(1) the bulk poorly lithified sediment with a maximum burial temperature much lower than 60-70 ℃,and(2) thinner intervals outside the contact zone that have experienced hydrothermal temperatures(around 140 ℃). The main diagenetic alteration associated with normal burial diagenesis is minor mechanical plastic deformation of ductile grains such as mica. Mineral grain contacts show no evidence of pressure dissolution and the vitrinite reflectance suggests a maximum temperature of ～40 ℃. Contrary to this, part of the sediment, preferentially along calcite cemented flow baffles, show evidence of hydrothermal alteration. These hydrothermally altered sediment sections are characterized by recrystallized carbonate cemented intervals. Further, the hydrothermal solutions have resulted in localized sericitization(illitization) of feldspars, albitization of both K-feldspar and plagioclase and the formation of fibrous illite nucleated on kaolinite. These observations suggest hydrothermal alteration at T 120-140 ℃ at distances considerably further away than expected from sill heat dissipation by conduction only, which commonly affect sediments about twice the thickness of the sill intrusion. We propose that carbonate-cemented sections acted as flow baffles already during the hydrothermal fluid mobility and controlled the migration pathways of the buoyant hot fluids. Significant hydrothermally induced diagenetic alterations affecting the porosity and hence reservoir quality was not noted in the noncarbonate-cemented reservoir intervals. 相似文献
17.
Mitsugu Nishimura 《Geochimica et cosmochimica acta》1977,41(12):1817-1823
Significant quantities of solvent-inextractable geolipids, obtained by saponification of solvent extracted sediments, were found in various sedimentary samples including soils, river inlet sediment and lake sediments from Lake Suwa.The carbon isotopic composition () of extractable and inextractable geolipids from the same sediment sample were similar. Moreover, the carbon number distributions of sterols in the two geolipid fractions from the same sediment were also similar.Whereas the ratios of both lipids and sterols to total organic carbon for the extractable geolipids in the lake sediments decreased with depth, the former ratio for inextractable giolipids tends to increase with depth and the latter remains fairly constant. On the other hand, the stanol to stenol ratio of the extractable fraction increased with depth but that of the inextractable fraction was lower than that of the extractable fraction and was fairly constant irrespective of sediment depth.The transformation of extractable sterols into inextractable ones was not observed during incubation for 1200 days of sterols with Suwa sediments.Thus, the following conclusions were made: (1) the extractable and inextractable geolipids have similar origins, (2) some constituents of the latter may be protected from chemical or microbiological degradation and transformation in the sediments, and (3) the transformation of some constituents of the former into the inextractable ones virtually does not occur after incorporation into Suwa sediments.These results suggest that some constituents of the inextractable geolipid fraction may provide fundamental information on early diagenetic alteration of geolipids in lake sediments and on the relatively recent paleoenvironment. 相似文献
18.
The provenance of organic matter in surface sediments from the northern Gulf of Mexico was investigated by analyzing the compositions of lipid biomarkers (n-alkanes, fatty acids, sterols) liberated after a series of chemical treatments designed to remove different organo-mineral matrix associations (i.e. freely extractable, base-hydrolyzable, unhydrolyzable). Bulk analyses of the organic matter (carbon content, carbon:nitrogen ratios, stable and radiocarbon isotopic analyses) were also performed on the intact sediments and their non-hydrolyzable, demineralized residue. We found recognizable lipids from distinct sources, including terrestrial vascular plants, bacteria and marine algae and zooplankton, within each of the isolated fractions. Based on the lipid signatures and bulk compositions, the organic matter within the unhydrolyzable fractions appeared to be the most diagenetically altered, was the oldest in age, and had the highest abundance of terrigenous lipids. In contrast, the base-hydrolyzable fraction was the most diagentically unaltered, had the youngest ages and was most enriched in N and marine lipids. Our results indicate that fresh, autochthonous organic matter is the most important contributor to base-hydrolyzable lipids, whereas highly altered allochthonous sources appear to be predominant source of unhydrolyzable lipids in the surface sediments from the Atchafalaya River shelf. Overall, the lipid biomarker signatures of intact sediments were biased towards the autochthonous source because many of the organic compounds indicative of degraded, terrigenous sources were protected from extraction and saponification by organo-mineral matrices. It is only after these protective matrices were removed by treatment with HCl and HF that these compounds became evident. 相似文献
19.
Hong Lu Tengshui Chen Kliti Grice Paul Greenwood Ping’an Peng Guoying Sheng 《Organic Geochemistry》2009,40(8):902-911
An unusual series of C22–C27 monounsaturated sterenes and C24–C30 tetracyclic terpanes (17,21-secohopanes) were detected in relatively high concentrations in an immature evaporitic marl sediment of the Jinxian Sag, Bohai Bay Basin, North China. The site of unsaturation in these novel sterenes is assigned tentatively to the D ring on the basis of mass spectral interpretation, which also distinguishes them from reported unsaturated sterenes. Other hydrocarbon biomarker or stable isotope characteristics are indicative of microbial (e.g. methyl hopanes), phytoplankton or higher plant (depleted δ13C values of isoprenoids and hopanes) inputs and an anoxic carbonate depositional environment (hexacyclic hopanes; tetracyclic terpanes). The hydrocarbon composition showed no obvious biodegradation and the relatively high concentration of unsaturated terpenoids (e.g. gammacerene) and low values of other established maturity parameters (Ts/Tm = 0.23; Ro = 0.44%; Tmax = 417 °C), are consistent with sediments of low maturity. The novel, low molecular weight sterenes and the tetracyclic terpanes may be early diagenetic products of microbial sources in a carbonate environment. 相似文献
20.
Organic materials in lacustrine sediments are from multiple terrestrial and aquatic sources. In this study, carbon (δ13C) and hydrogen isotopic compositions (δD) of phytol, various sterols, and major n-fatty acids in sediments at Lake Haruna, Japan, were determined in their solvent-extractable (free) and saponification-released forms (bound). The δ13C-δD distributions of these lipid molecules in sediments are compared with those of terrestrial C3 and C4 plants, aquatic C3 plants, and plankton to evaluate their relative contributions. δ13C-δD of free phytol in sediments is very close to that of phytol in plankton samples, whereas δ13C-δD of bound phytol in sediments is on a mixing line between terrestrial C3 plant and plankton material. Unlike phytol, no significant δ13C-δD difference between free and bound forms was found in sterols and n-fatty acids. δ13C-δD values of algal sterols such as 24-methylcholesta-5,22-dien-3β-ol in sediments are close to those of plankton, whereas δ13C-δD of multiple-source sterols such as 24-ethylcholest-5-en-3β-ol and of major n-fatty acids such as n-hexadecanoic acid in sediments are between those of terrestrial C3 plants and plankton samples. Thus, δ13C-δD distributions clearly indicate the specific source contributions of biomarkers preserved in a lacustrine environment. Free phytol and algal sterols can be attributed to phytoplankton, and bound phytol, multiple source sterols, and major n-fatty acids are contributed by both terrestrial C3 plants and phytoplankton. 相似文献