南海北部油气缓释环境沉积物脂类化合物组成特征

认识沉积环境有机碳留存状况是阐述油气形成过程中有机碳早期成岩的关键内容。以南海珠江口盆地及其邻近海域为背景,通过研究表层沉积物中脂类化合物的形态组成,认识脂类有机碳的来源和留存状态,阐述特征脂类分子的早期成岩特征。结果表明,研究区域表层沉积物有机碳含量为0.22%～0.66%,有机碳稳定同位素分布在-20.88‰～-22.93‰之间,表现为显著的海源特征。沉积物中共检测出21种脂肪酸、6种脂肪醇、8种甾醇和植醇;总脂肪酸、脂肪醇、甾醇和植醇含量分别为12.57～40.27μg/g、5.35～8.98μg/g、0.15～3.75μg/g和0.01～3.99μg/g干重,总体表现为靠近珠江口和台湾海峡略高。脂类化合物的存在形态以游离态(FR)和碱性水解态(BH)为主,酸性水解态(AH)贡献较低;其中植醇和甾醇呈现显著的BH优势,植醇中未检出AH组分的贡献。脂类化合物主要来自于海洋现场生产,海洋微藻和细菌的相对贡献率分别为21.18%～33.78%和11.02%～15.64%,陆源高等植物贡献低于5%。来源于硫酸盐还原菌的支链脂肪酸在靠近珠江口海域高达1.79～2.62μg/g,占总脂肪酸的5.14%～6.50%,并与硫酸盐还原过程相关的古菌分布相一致。     

Marine and terrigenous lipids in coastal sediments from the Peru upwelling region at 15°S: Sterols and triterpene alcohols

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.     

Environmental changes in Saginaw Bay,Lake Huron recorded by geolipid contents of sediments deposited since 1800

Changes in organic materials preserved within sediments of Saginaw Bay deposited over the past two centuries record corresponding periods in the environmental history of this part of Lake Huron and its watershed. Sediments deposited since 1940 show an increasingly greater input of aquatic organic matter in response to accelerating cultural eutrophication of Saginaw Bay. Concentrations of fatty acids, sterols, fatty alcohols, and aliphatic hydrocarbons are higher in these modern sediments than in deeper ones. Molecular distributions of these geolipids reflect less aquatic material deeper in the sediments. Prior to 1875, sediment organic matter appears to be diluted by mineral matter from enhanced erosion caused by clearing of the watershed for farming and settlement. During this period there is better preservation of carbonate minerals due to quicker burial. Since 1875, petroleum components comprise over 90% of the total aliphatic hydrocarbon content of these sediments, reflecting the advent and continued existence of chronic, low-level petroleum contamination of this part of the Great Lakes.     

Early diagenesis of organic matter in the water column and sediments: Microbial degradation and resynthesis of lipids in Lake Haruna

Particulate matter, sediment trap, and surface sediment samples collected in freshwater Lake Haruna were studied to understand early diageesis of organic materials in the water column and in bottom sediments. The samples were analyzed for biomarkers, including aliphatic and aromatic hydrocarbons, fatty alcohols, saturated and unsaturated fatty acids, β- and ω-hydroxyacids, and α,ω-dicar☐ylic acids. Decreases in concentrations of autochthonous saturated C₁₂–C₁₉ fatty acids and polyunsaturated C₁₈ acids relative to TOC occured with the settling of organic matter ot the lake bottom, whereas the amounts of terrestial saturated C₂₀–C₃₀ acids remained almost constant. Conversely, the concentrations of monosaturated fatty acids, branched chain fatty acids, and β- and ω-hydroxyacids, which are probably produced by microbial activity, increased. These results indicate that preferential degradation of algal lipids accompanies microbial resynthesis of lipids during settling, however, terrigenous lipids are relatively stable.     

Hydrothermal petroleum in the sediments of the Andaman Backarc Basin,Indian Ocean

Recent sediments of the Andaman Backarc Basin, Indian Ocean, between the Andaman Nicobar islands and the Malay Peninsula have been analyzed for biomarker lipids. Three cores were selected: one each from the fault zone in a deep basin (a graben between two fault systems), another from a location adjacent to the fault, and the third from the topographic high in the rift valley. The molecular composition of the lipid classes (n-alkanes, isoprenoids, alkylbenzenes, alkylcyclohexanes, hopanoids, polycyclic aromatic hydrocarbons, steranes, alcohols, sterols and fatty acids) was examined by gas chromatography (GC) and GC/mass spectrometry to understand the nature and source of the hydrocarbons present and the processes of maturation of organic matter. The data show that the hydrocarbons are of hydrothermal origin, derived from thermal alteration of sedimentary organic matter, consisting of a mixture predominantly of marine-derived components with some terrestrial inputs. Normal alcohols and fatty acids also corroborate the distribution of n-alkanes. The distribution profiles and various parameters computed from the concentration of the target compounds suggest that oxidative reactions and microbial degradation in this environment are insignificant. Triterpane and PAH compositions indicate that the thermal maturity of the bitumen in the samples is comparable to or lower than that found at other hydrothermal regions such as the Northern Juan de Fuca Ridge, Guaymas Basin and Escanaba Trough.     

Characterization of sedimentary humic matter by alkaline hydrolysis

Humic matter fractions from modern sediments of Lake Huron and Lake Michigan have been compared. Large yields of saccharinic acids from alkaline hydrolysis suggest that these fractions contain large portions of carbohydrate materials. Evidence for contributions of aquatic lipid (C-16 fatty acids) and of liginin (phenolic acids) to these sediments is also present in the hydrolysis products. Qualitative differences among fulvic acid, humic acid and humin from the same lake are minor, suggesting common (or similar) organic sources for these fractions. The lability of sedimentary humic matter to alkaline hydrolysis is inversely related to its degree of exposure to oxidative weathering. Lability may also be related to diagenetic state as fulvic acids generally yield greater quantities of hydrolysis components than humic acids which in turn yield more than humin.     

Hydrocarbons and fatty acids in two cores of Lake Huron sediments

Compositions of aliphatic hydrocarbons and of fatty acids were analyzed in two half-meter cores of postglacial Lake Huron sediment. One core represents a continuous record of the past 450 yr of sediment accumulation; the other consists of a surficial layer of modern sediment overlying 40 cm of 11,000–12,000 yr-old sediment. Concentrations of hydrocarbons are higher in the younger core than in the older one. Based upon n-alkane distributions, this reflects a smaller input of terrigenous material to Lake Huron 11,000 yr ago rather than diagenetic losses. Most of the hydrocarbons present in the 450 yr-old core are allochthonous while half are autochthonous in the older core. Fatty acids are primarily of aquatic character in both cores, and their concentrations decrease rapidly with depth. Unsaturated acids disappear more quickly than do their saturated analogs. Fatty acid degradation occurs mostly in the biologically active zone of these sediments, and little further alteration of fatty acids appears to happen over times as long as 12,000 yr.     

The importance of atmospheric input of terrestrial organic material to deep sea sediments

The concentrations of lipids were determined in atmospheric particle, gas and rain samples collected from the tropical North Pacific to assess lipid sources, transport mechanisms and fluxes to the ocean surface. Four lipid compound classes (aliphatic hydrocarbons, fatty alcohols, fatty acid esters, and salts) all unequivocally show a terrestrial vascular plant source. These aerosol lipids originate from wind erosion of Asian and American soils and direct emission from vegetation. The major fluxes result from rain rather than dry deposition. These fluxes are large enough to have a major potential impact on the inventory of terrestrially derived lipid material found in deep-sea sediments. This has been showm for n-alkanes, fatty alcohols, fatty acids, total lipids and for organic carbon. By comparing atmospheric and sediment trap fluxes with sediment accumulation rates, it is suggested that some biogenic terrestrial material is more protected from degradation than marine-derived material.     

Biotransformation and assimilation of dietary lipids by Calanus feeding on a dinoflagellate

Stage V and adult females of the marine copepod Calanus helgolandicus were fed in the laboratory on the dinoflagellate Scrippsiella trochoidea at three concentrations calculated to represent pelagic ocean to ‘bloom’ conditions. The identification and quantification of sterols, fatty acids and alcohols present in the algal diet, copepods and their faecal pellets were then carried out using computerized gas chromatography- mass spectrometry (C-GC-MS). The grazing rates of animals were measured and the data then combined with those of lipid distributions in the diet and faecal pellets in order to determine quantitatively the fate of each lipid during its passage through the gut of Calanus. The results showed marked differences in the proportion of the three lipid classes removed, with highest values found for fatty acids and the lowest for sterols. Up to 97% of ingested algal fatty acids were removed by the copepod, with a preference towards the removal of polyunsaturated acids. Algal sterols were also removed by Calanus; the percentage composition and concentration of sterols in faecal pellets differing from the algal diet at all three food levels. Evidence that the removal of lipids from the diet represented assimilation by the copepods was provided by the further finding that during the feeding period (20 hr) all three lipid classes increased in animal tissues. Quantitative measurements of individual sterols revealed that significant amounts of 4-methyl and 4-desmethyl sterols having the 8(14) and 17(20) unsaturation were removed at all dietary levels. In contrast, ring-saturated stanols were not removed and appear to pass through the gut quantitatively.     

Organic geochemistry of Walvis Bay diatomaceous ooze—I. Occurrence and significance of the fatty acids

Diatomaceous ooze of the shelf off Walvis Bay (S.W. Africa) was analysed for lipid material. The lipids from the sediment consist of a mixture of hydrocarbons, alcohols, ketones, fatty acids, sterols, carotenoid pigments and chlorophylls. The total fatty acid mixture has been analysed by capillary gas chromatography mass spectrometry and shown to consist of straight chain, iso-, anteiso- and isoprenoid acids. The environmental setting of the S.W. African shelf (Walvis Bay) makes it possible to discuss these fatty acids as markers for the fate of organic matter. The acids in the sediment point to a generation during passage of algal lipids through levels of microbial activity either on or slightly above the burial surface.     

Organic geochemistry of suspended and settling particulate matter in Lake Michigan

Organic matter contained in particulate matter in Lake Michigan waters and sediments has been characterized by $\text{C}\text{N}$ 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.     

Early diagenesis of fatty acids in lacustrine sediments—III. Changes in fatty acid composition in the sediments from a brackish water lake

A 3-m sediment core taken from Lake Suigetsu, in which a shift from fresh to brackish water occurred about three hundred years ago, has been examined for variation with depth of organic carbon and fatty acids. From the difference in total amounts of sulphur between sediments under fresh and brackish water environments, the surface sediments above approximately 35 cm depth were deduced to be accumulated under a brackish water environment. The total contents of organic carbon and fatty acids, and percentage composition of fatty acids gave discontinuous profiles above and below the 35–40 cm sediment layer. At a depth of 12.5 cm, the distribution in chain length of the fatty acids changed from a unimodal (the predominance of C₁₂-C₁₈ over C₂₀-C₃₄) to a bimodal pattern, which was mirrored by the composition diversity index (CDI).Although the fatty acids in the surface sediments (0–40 cm) from Lake Suigetsu seemed to suffer milder degradation through microbial activity than those in a core (0–150 cm) from Lake Suwa, a freshwater eutrophic lake, both lacustrine sediments showed similar trends in the alteration of fatty acid composition with depth.     

Early diagenesis of fatty acids and isoprenoid alcohols in estuarine and coastal sediments

Fatty acids and isoprenoid alcohols were analyzed in river, estuarine, and coastal sediment cores: (1) to investigate the distribution of these lipids among the unbound phase. those bound or closely associated with humic substances, and those bound or closely associated with the huminkerogen and clay mineral matrix. (2) to investigate the diagenetic changes of these lipids with depth in the sediments. and (3) to obtain information on the use of these compounds as organic tracers in marine sediments.Results confirm earlier observations that fatty acids are rapidly altered in marine sediments Both the total and the individual fatty acids decrease in concentration with depth in the sediments: unsaturated acids decrease faster than saturated acids and unbound acids decrease faster than bound acids Approximately 8–62% of the fatty acids were unbound. 2–22% were associated with humic substances. and 38–86% were associated with the residual organic-mineral matrix. Qualitative differences also exist between the fatty acids associated with the unbound, humic, and residual fractions. The ratio of trans/cis geometric isomers of the fatty acids generally increases downcore. with no rearrangement of the double bond positions within the molecules. Either the cis isomer is being preferentially degraded with depth in the sediments, or there is a low temperature, clay catalyzed conversion of the cis isomers to the trans isomers occurring down the cores.Phytol was the major alcohol present in the sediments and does not appear to be altered as rapidly as the fatty acids. Less than 10% of the total phytol (PHY) plus dihydrophytol (DHP) was present as DHP and no trend could be discerned between PHY and DHP with depth or with unbound, humic, and residual material in the cores. All of the isolated DHP appeared to be present as the RRR stereoisomer. Along with the absence of phytane in the cores, this observation suggests that the reduction of phytol to dihydrophytol is microbially mediated in the upper layer of the sediment.     

The lipid chemistry of an interfacial sediment from the Peru Continental Shelf: Fatty acids,alcohols, aliphatic ketones and hydrocarbons

A sample of the sediment-water column interface which lies on the continental shelf under the Peru upwelling regime, has been examined for fatty acids, fatty alcohols, ketones and hydrocarbons. Fatty acids were the most abundant compound class, ranging from C₁₂-C₂₄, with 16:0 as the major component (765.5 μg/g dry sediment). The alcohols were dominated by 3,7,11,15-tetramethylhexadeca-2-en-ol (phytol), with even-chain n-alcohols in the range C₁₄-C₂₀. The ketones consisted of C₃₇-C₃₉ di- and tri-unsaturated alken-2-ones and alken-3-ones. Both alkanes and alkenes were present in the hydrocarbon fraction; the alkanes ranging from C₁₃ — C₂₀ and comprising both straight chain and isoprenoid compounds; the alkenes consisting of isomeric pairs of C₂₅ branched trienes and tetraenes. The data indicate that the organic content has been contributed very largely from marine sources (probably mainly from phytoplankton and bacteria), showing little terrigenous influence. The presence of labile compounds such as polyunsaturated fatty acids (with two to six double bonds), implies that the sediment has undergone very little diagenetic alteration, and the lipids are probably largely unchanged from the state in which they actually reached the sediment. They may therefore serve as a useful baseline in assessing diagenesis in older sediments, where diagenetic transformations are more advanced.     

Fatty acids of bacterial origin in contemporary marine sediments

Contributions by bacteria to recent sediments have been recognized as one important source of input for the extractable lipids. It has, however, proved difficult so far to conclusively relate the components identified to the contributing bacteria. This fact is primarily related to the lack of information on both the lipid chemistry of marine bacteria, and of detailed structures of the sedimentary lipids. In this paper a study of the fatty acids from a tropical marine sediment selected because of its high biomass content is reported, and relationships between the sedimentary extracts of the surface layer to fatty acid components of bacteria cultured from the sediment sample are detailed. By selecting specific structural features, a group of fatty acids have been identified as valid markers for bacteria in this environment: these include iso- and anteiso-branched chain acids; 10-methylpalmitic acid; cyclopropyl 17:0 and 19:0 acids of which ▽19:0 (11,12) is unique to bacteria; cis-vaccenic acid; and the 15:1, 17:1 ω6 and ω8 isomers especially when these occur in pairs; iso Δ7–15: 1 and iso Δ9–17:1 are branched unsaturated acids apparently unique to bacteria. Trans-monoene fatty acids are likely to be a direct bacterial input, and the hydroxy acids identified are probably of bacterial cell wall origin. This study, whilst emphasizing the necessity for detailed structural information on fatty acids in order to use them validly as biological markers, considerably extends the range of fatty acids as markers of bacterial input to contemporary sediments.     

Tightly bound aliphatic acids in Lake Biwa sediments: Their origin and stability

Tightly bound geolipids were separated from a 200 m sediment core of Lake Biwa by a second saponification of sediments from which unbound and bound lipids had been extracted. Tightly bound fatty acids, β-hydroxy acids, ω-hydroxy acids and α,ω-dicarboxylic acids were released; their concentrations ranged from 4.7–31.5, 5.6–60.5, 3.4–9.5 and 0.2–5.4 μg/g dry sediment, respectively. These geolipids were considered to be incorporated in humic substances.Tightly bound fatty acids showed a unimodal distriution with a peak at C₁₆, suggesting that they originate from algae and bacteria and that they are more stable than unbound and bound fatty acids in the sediments. Most of the total β-hydroxy acids, which probably originate from bacteria, were found in the tightly bound fraction. This suggests that a large portion of tightly bound geolipids are formed in the water column and in surface sediments as a result of microbial alteration dead algae. Each class of tightly bound lipids showed higher concentrations between depths of 3 and 15 m in the sediments, where primary production was thought to be enhanced in the past.     

白令海陆架区柱样沉积物脂类分子特征及其气候变化响应

为探究全球变暖对于高纬度海洋生态环境的影响,对中国第5次北极科学考察在白令海陆架区采集的BL16柱样沉积物中的脂类进行了研究.沉积物中检测到丰富的饱和烃和脂肪酸等化合物,其组成和分布显示,该沉积柱中有机质为陆源和海源混合输入.其中长链正构烷烃和长链饱和正构脂肪酸主要来源于陆源高等植物,饱和异构和反异构脂肪酸主要来源于海洋自生细菌,短碳链正构烷烃、反异构烷烃和烷基环戊烷烃的浓度相互间有较好的相关性,表明其来源较为一致,主要来源于海洋浮游藻类和细菌.海源短链正构烷烃与陆源长链正构烷烃的比值∑C_15-21/∑C_23-33在0.14~0.90之间,表明该沉积柱中正构烷烃主要以陆源输入为主.沉积柱中短链正构烷烃、反异构烷烃和烷基环戊烷浓度,以及脂肪酸中异构、反异构脂肪酸组分与长链饱和正构脂肪酸组分的相对变化与总有机碳含量（TOC）、总氮含量（TN）变化一致,尤其在20世纪70年代以来明显升高,可能反映了海洋初级生产力持续增加的趋势,并且对全球变暖做出了灵敏的响应.      

An isotopic biogeochemical study of Neoproterozoic and Early Cambrian sediments from the Centralian Superbasin, Australia

Organic matter from Neoproterozoic and Early Cambrian sediments of the Amadeus and Officer basins of the Centralian Superbasin, Australia, has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons. These sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the Cambrian. Hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially-dominated ocean to the early stages of metazoan radiation. In particular, carbon isotopic data for n-alkyl and isoprenoid lipids presented here, and in earlier studies, showed a reversal in carbon isotopic ordering between the Proterozoic and Phanerozoic. By comparison with the delta 13C of kerogen, n-alkyl lipids from deep-water Proterozoic sediments were enriched in 13C and appear to be derived mainly from heterotrophs whilst open marine Phanerozoic counterparts are 13C depleted and evidently derived mainly from autotrophs. Data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean, possibly aided by the innovation of faecal pellets.     

Maturation related changes in the distribution of ester bound fatty acids and alcohols in a coal series from the New Zealand Coal Band covering diagenetic to catagenetic coalification levels

A rank series of lignites and coals of low to moderate maturation levels (vitrinite reflectance (R₀): 0.27–0.8%) from the New Zealand Coal Band were investigated using alkaline ester cleavage experiments to reveal compositional changes of ester bound components (fatty acids and alcohols) during increasing maturation. Ester bound alcohols are found to be present in highest amounts in the very immature lignite samples (R₀: 0.27–0.29%), but show a rapid decrease during early diagenesis. Ester bound fatty acids also show an initial exponential decrease during diagenesis, but reveal an intermittent increase during early catagenesis before decreasing again during main catagenesis. This intermittent increase was related to the short chain fatty acids. To obtain a maturity related signal and to eliminate facies related scattering in the amounts of fatty acids in the coal samples, the carbon preference index of fatty acids (CPI_FA) parameter is introduced here. For the long chain fatty acids (C₂₀–C₃₂) originating from terrigenous plant debris, the CPI_FA decreases with increasing maturity, showing a strong maturation related signal. During diagenesis, the same trend can be observed for the short chain fatty acids, but the intermittent increase in the amounts of short chain fatty acids is also accompanied by high CPI_FA values. This indicates less altered organic biomass at this advanced maturation level and is in contrast to the mature CPI_FA signal of the long chain fatty acids of the same samples. One possible reason for this discrepancy could be extremely different amounts of short and long chain fatty acids in the original source organic matter of these samples. However, another intriguing explanation could be the incorporation of immature bacterial biomass from deep microbial communities containing C₁₆ and C₁₈ fatty acids as main cell membrane components. Deep microbial life might be stimulated at this interval by the increasing release of thermally generated potential substrates from the organic matrix during early catagenesis. In contrast to the fatty acids, the high amounts of alcohols in the immature lignite samples are also visible in the alkene distribution from the open system pyrolysis experiments of the organic matrix before and after saponification.     

Short chain ladderanes: Oxic biodegradation products of anammox lipids

Anammox, the microbial anaerobic oxidation of ammonium by nitrite to produce dinitrogen gas, has been recognized as a key process in both the marine and freshwater nitrogen cycles, and found to be a major sink for fixed inorganic nitrogen in the oceans. Ladderane lipids are unique anammox bacterial membrane lipids that have been used as biomarkers for anammox bacteria in recent and past environmental settings. However, the fate of ladderane lipids during diagenesis is as of yet unknown. In this study, we performed oxic degradation experiments (at 20-100 °C) with anammox bacterial biomass to simulate early diagenetic processes occurring in the water column and at the sediment-water interface. Abundances of C₁₈ and C₂₀ ladderane lipids decreased with increasing temperatures, testifying to their labile nature. The most abundant products formed were ladderane lipids with a shorter alkyl side chain (C₁₄ and C₁₆ ladderane fatty acids), which was unambiguously established using two-dimensional NMR techniques on an isolated C₁₄-[3]-ladderane fatty acid. The most pronounced production of these short-chain lipids was at 40 °C, suggesting that degradation of ladderane lipids was microbially mediated, likely through a β-oxidation pathway. An HPLC-MS/MS method was developed for the detection of these ladderane alteration products in environmental samples and positively tested on various sediments. This showed that the ladderanes formed during degradation experiments also naturally occur in the marine environment. Thus, short-chain ladderane lipids may complement the original longer-chain ladderane lipids as suitable biomarkers for the detection of anammox processes in past depositional environments.