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1.
Organic matter degradation in sediments of the York River estuary: Effects of biological vs. physical mixing 总被引：1，自引：0，他引：1
We investigated the influence of biological and physical seabed disturbance on the degradation of bulk organic matter and source specific lipid biomarker compounds by measuring downcore changes in bulk elemental composition, bulk stable isotopic (δ13C and δ15N) signatures, and lipid biomarker compounds in sediment cores collected from two sites in the York River, a subestuary of the Chesapeake Bay, USA. One site (LY) is influenced by biological mixing (bioturbation), restricted to the upper 15-20 cm, while the other site (POD) experiences intense, episodic physical mixing events that penetrate 50-100 cm into the sediment. We utilized a suite of auxiliary measurements to constrain the sources of organic matter, depositional environments, and general ages of the cores. Diagenetic modeling of total organic carbon and total nitrogen in sediments yielded higher apparent rate constants for POD than LY suggesting that the physical mixing regime promotes enhanced degradation of bulk organic matter. Apparent rate constants for select lipids representing distinct sources of organic matter were also higher at POD than LY for all but the most labile (i.e., diatom-derived fatty acids) biomarkers. Differences in stanol/stenol ratios also supported enhanced diagenesis of stenols at POD. The source-specific biomarkers, while useful in qualitatively identifying the sources of sedimentary organic matter, likely do not represent the full spectrum of its reactivity. However, based on our results, we hypothesize that the intense sediment disturbance at POD promotes degradation of more recalcitrant organic material, due to prolonged exposure to oxygen and other electron acceptors (e.g., NO3−, Mn and Fe oxides). In contrast, the degradation of more labile constituents is equally facilitated by biological and physical disturbance. 相似文献
2.
The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the moun-tainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux.We analyzed flu-vial sediments from two SMRs and compared the results with two large mountain rivers(LMRs)in Nepal.We investigated the organic matter(OM),its compositional variability,and seasonal export using a suite of lipid biomarkers,namely n-alkanes,n-alkanoic acids,n-alkanols,and sterols.The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability.The LMRs showed a dis-tinct contrast in the distribution of lipids in suspended sediments.Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the sus-pended load.Functional lipids(n-alkanoic acids and n-alkanols)were the major constituents in SMR sed-iments,indicating better preservation.In contrast,n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs.The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs.A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs.Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems.Topsoil colonized by fungal species under moist acidic condi-tions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs.In LMRs,the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of n-alkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool.The differences in lipid concentrations,their distribution,seasonality,and the size of rivers suggest differential preserva-tion/degradation of the organic matter pool and their importance in contributing to the carbon budget. 相似文献
3.
4.
Although fatty acids and alcohols in plant polyesters can be useful indicators of organic matter provenance in soils and sediments, interpretation is limited by uncertainty in: (i) the distribution of lipids among plant species and their organs (e.g. leaves and roots) and (ii) the extent to which plant lipid composition is recorded in soils and sediments. In this study, we compare lipids in leaves, roots and soils from 11 temperate tree species. Base hydrolysis was used to release ester-bound lipids and solvent extraction was then used to recover both hydrolysable and “free” lipids. Leaf and root lipid composition varied substantially among the tree species and we highlight differences among evergreen conifers, deciduous broadleaved angiosperms and a deciduous conifer (Larix decidua). Some of the variation appears to be linked to the morphology and lifespan of leaves and roots. Soils preserved much of the variation in the leaf and root lipid composition of the overlying tree species. Yet, the concentration of some lipids in soil diverged from their concentration in tree leaves and roots, reflecting an undocumented input from understory plants and other plant organs (e.g. seeds) or variation in the extent of lipid preservation in soil. Finally, by comparing leaf and root lipid composition, our results help constrain the attribution of lipids to each of these plant organs. This allowed us to evaluate the utility of leaf-derived lipids as plant type biomarkers and to document a substantial contribution of root-derived lipids to soil beneath all 11 tree species. 相似文献
5.
Yann Hautevelle Raymond Michels Fabrice Malartre Marcel Elie Alain Trouiller 《Applied Geochemistry》2007
The Callovo-Oxfordian claystones located at 500 m depth at Bure (Meuse, France) are currently being investigated by Andra (the French National Radioactive Waste Management Agency) for testing the feasibility of long-term and deep geological nuclear waste disposal. In order to evaluate its potential as a geological barrier, it is very important to study, assess and describe its physico-chemical variability. The molecular biomarker composition of 150 samples of these claystones and their surrounding limestones carry diverse information on the sources of the sedimentary organic matter, the chemistry of the depositional environment, the preservation and diagenesis conditions. It also allows assessing the degree of lateral and vertical variability of the organic matter within these sedimentary series. The abundance of unsaturated biomarkers, the distribution of steroids and hopanoids and CPI values >2 prove the thermal immaturity of the organic matter. The co-occurrence of plankton, bacteria and land plant biomarkers indicate that the organic matter is a mixture of marine and continental contributions. The data also reveal that the organic matter was deposited under oxic and open-sea conditions except for a brief event of photic zone anoxia at the beginning of the Middle Callovian. In the claystones, the geosynthesis of diasterenes is favored to the detriment of the formation of steranes, especially in smectite-rich levels, and the organic matter is rapidly isolated from oxidizing then reducing conditions after the deposition due to the protective effect of clays. On the scale investigated, the claystones are characterized by a unique molecular facies and are thus homogenous from their organic content point of view. Yet, detailed investigation of specific molecular families indicates changes related to major claystone–limestone transitions. The homogeneity of these claystones can be explained by the paleogeographic position of their depositional setting and the plane and sub-horizontal paleotopography on which they were deposited. This study demonstrates the efficiency of organic geochemistry in the assessment of the variability of geological barriers. 相似文献
6.
As a contribution to a project on the role of aerobic heterotrophic bacteria in the organic matter turnover within cyanobacterial mats, we investigated selected lipid classes of five morphologically different microbial mats from the intertidal area of Abu Dhabi, United Arab Emirates. The mats thrive under extreme environmental conditions as they are exposed to salinity up to 200 and shadowless sunshine for nearly 12 h per day. The total extractable organic matter is characterised by heavy δ13C values of −17‰ to −10‰, suggesting CO2 limitation. The lipids reflect the biomass of the principal mat-building phototrophic and heterotrophic microorganisms. Moderate amounts of hydrocarbons, mainly cyanobacterial n-heptadecane, short chain monomethyl alkanes and diploptene were detected in all the mats. The ubiquitous n-hexadecanoic acid is dominant amongst the free and ester-bound phospholipid fatty acids (PLFAs), whereas the overall acid composition varies due to differences in the extreme environmental conditions. Additionally, the top layers of two of the five mats were analysed separately to compare their lipid compositions with those of the whole mats. As would be expected, the concentrations of cyanobacterial biomarkers exceed those found in the total mats. Noteworthy is the presence of n-heneicosadiene as predominant hydrocarbon in the top layer of the so called gelatinous mat, which thrives under the locally most extreme conditions. As the n-alkadiene was present to a much lesser extent in the intact mat, it may provide a new biomarker for a so far unknown important aerobic organism. 相似文献
7.
Moritz F Lehmann Stefano M BernasconiAlberto Barbieri Judith A McKenzie 《Geochimica et cosmochimica acta》2002,66(20):3573-3584
The carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments. In order to reconstruct past environmental changes from sedimentary organic matter, it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments.In a series of oxic and anoxic incubation experiments, we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation. The decomposition rates determined with a double-exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions. However, under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions. Within three months of incubation the δ13C of bulk organic matter decreased by 1.6‰ with respect to the initial value. The depletion can be attributed to the selective preservation of 13C-depleted organic compounds. During anoxic decay, the δ15N values continuously decreased to about 3‰ below the initial value. The decrease probably results from bacterial growth adding 15N-depleted biomass to the residual material. In the oxic experiment, δ15N values increased by more then 3‰ before decreasing to a value indistinguishable from the initial isotopic composition. The dissimilarity between oxic and anoxic conditions may be attributed to differences in the type, timing and degree of microbial activity and preferential degradation. In agreement with the anoxic incubation experiments, sediments from eutrophic Lake Lugano are, on average, depleted in 13C (−1.5‰) and 15N (−1.2‰) with respect to sinking particulate organic matter collected during a long-term sediment trap study. 相似文献
8.
Carme Huguet Jung-Hyun Kim Gert J. de Lange Jaap S. Sinninghe Damsté Stefan Schouten 《Organic Geochemistry》2009,40(12):1188-1194
One of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis. However, studies have shown that oxic degradation of biomarker lipids can affect their relative distribution. We tested the diagenetic stability of the and TEX86 palaeothermometers upon long term oxygen exposure. For this purpose, we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) in different sections of turbidites at the Madeira Abyssal Plain (MAP) that experienced different degrees of oxygen exposure. Sediments were deposited anoxically on the shelf and then transported by turbidity currents to the MAP, which has oxic bottom water. This resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water. Concentrations of GDGTs and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts, indicating substantial degradation. High-resolution analysis of the Pleistocene F-turbidite showed that the index of long chain alkenones increased only slightly (0.01, corresponding to <0.5 °C) in the oxidized part of the turbidite, suggesting minor preferential degradation of the C37:3 alkenone, in agreement with previous studies. TEX86 values showed a small increase (0.02, corresponding to ～2 °C) in the F-turbidite, like , while for other Pliocene/Miocene turbidites it either remained unchanged or decreased substantially (up to 0.06, corresponding to ～6 °C). Previous observations showed that the BIT index, a proxy for the contribution of soil organic matter to total organic carbon, was always substantially higher in the oxidized part in all the turbidites, as a result of preferential degradation of marine-derived GDGTs. This relative increase in soil-derived GDGTs affects TEX86, as the isoprenoid GDGT distribution on the continent can be quite different from that in the marine environment. Our results indicate that the organic proxies are affected by long term oxic degradation to different extents; this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation. 相似文献
9.
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
10.
滇黔交界地区玄武岩铜矿中有机质的生物标志物特征及其地质意义 总被引：7，自引：1，他引：6
滇黔交界地区玄武岩中赋存的自然铜矿化与沥青密切相伴,玄武岩层间含碳沉积岩中的自然铜矿化发育大量碳质。本文采用有机质抽提、族组分定量及饱和烃色-质分析等方法对这两种产状的铜矿石中有机质的族组分含量和生物标志物进行了研究,并对其地质意义进行了探讨。通过研究取得如下认识：①含沥青铜矿石和含碳质铜矿石虽然产状明显不同,其有机质成因有明显差异,但其有机质族组分含量及生物标志物特征十分类似,反映它们经历了类似的地质作用;②有机质族组分及其生物标志物提供的来源信息较混乱,这可能是成矿流体循环改造导致的;③生物标志物特征表明,含沥青铜矿石及含碳质铜矿石中有机质经历了类似的较还原的高盐度环境,这可能是高盐度成矿流体及还原的成矿条件的指示;④生物标志物特征及氯仿沥青“A”低含量特征表明两类铜矿石中有机质成熟度高,这可能是成矿流体的热力对有机质改造的结果;⑤有机质生物标志物特征显示两类铜矿石中有机质生物降解作用不强,表明沥青的形成是原油受成矿热液热力影响发生热裂解的结果。 相似文献
11.
从生物脂类化合物到沉积有机质的变化及其对正演烃源岩有机质形成的启示 总被引：2，自引：2，他引：0
现代海洋生物有机组分的动态变化过程是利用正演法评价海相优质烃源岩的重要中间环节, 可以为估算沉积过程中有机质的损耗提供参考.从化学组成来看, 生物体的脂类与原油成分最为接近, 而且与其他生化组分相比, 脂类的化学性质相对稳定, 可以长期保存在地层中, 因此脂类是最重要的生油母质.温度、盐度、CO2等环境条件以及生物的种类和生长阶段对生物脂类组成有重要影响, 不同环境条件和不同种类的生物对烃源岩有机质的贡献也不同.海水中的有机质在沉积过程中受原始生产力和氧化还原条件的影响.在特定生境中, 在一定的生产力范围内, 沉积有机质的通量与生产力有正相关关系.超过此范围, 沉积有机质通量与生产力关系不大.氧化条件下有机质降解速度快, 而还原条件则有利于沉积有机质的保存.生物膜的形成不仅使有机质更容易沉积, 而且降低了有机质被降解的机会.地质历史时期生物膜的识别对研究烃源岩有机质的保存具有重要意义. 相似文献
12.
Effects of oxygen and redox oscillation on degradation of cell-associated lipids in surficial marine sediments 总被引：2，自引：0，他引：2
Ming-Y.i Sun Robert C. AllerCindy Lee Stuart G. Wakeham 《Geochimica et cosmochimica acta》2002,66(11):2003-2012
Degradation patterns of sedimentary algal lipids were tracked with time under variable redox treatments designed to mimic conditions in organic-rich, bioturbated deposits. Uniformly 13C-labeled algae were mixed with Long Island Sound surface muddy sediments and exposed to different redox regimes, including continuously oxic and anoxic, and oscillated oxic: anoxic conditions. Concentrations of several 13C-labeled algal fatty acids (16:1, 16:0 and 18:1), phytol and an alkene were measured serially. Results showed a large difference (∼10×) in first-order degradation rate constants of cell-associated lipids between continuously oxic and anoxic conditions. Exposure to oxic conditions increased the degradation of cell-associated lipids, and degradation rate constants were positive functions (linear or nonlinear) of the fraction of time sediments were oxic. Production of two new 13C-labeled compounds (iso-15:0 fatty acid and hexadecanol) further indicated that redox conditions and oxic: anoxic oscillations strongly affect microbial degradation of algal lipids and net synthesis of bacterial biomass. Production of 13C-labeled iso-15:0 fatty acid (a bacterial biomarker) was inversely proportional to the fraction of time sediments were oxic, rapidly decreasing after 10 days of incubation under oxic and frequently oscillated conditions. Turnover of bacterial biomass was faster under continuously or occasionally oxic conditions than under continuously anoxic conditions. 13C-labeled hexadecanol, an intermediate degradation product, accumulated under anoxic conditions but not under oxic or periodically oxic conditions. The frequency of oxic: anoxic oscillation clearly alters both the rate and pathways of lipid degradation in surficial sediments. Terminal degradation efficiency and lipid products from degradation of algal material depend on specific patterns of redox fluctuations. 相似文献
13.
Manzur Ahmed Herbert Volk Simon C. George Mohinudeen Faiz Linda Stalker 《Organic Geochemistry》2009,40(7):810-831
Organic geochemical and petrological assessment of coals/coaly shales and fine grained sediments, coupled with organic geochemical analyses of oil samples, all from Permo–Triassic sections of the Southern Sydney Basin (Australia), have enabled identification of the source for the widely distributed oil shows and oil seeps in this region. The Permian coals have higher hydrogen indices, higher liptinite contents, and much higher total organic matter extract yields than the fine grained sediments. A variety of source specific parameters obtained from n-alkanes, regular isoprenoids, terpanes, steranes and diasteranes indicate that the oil shows and seeps were generated and expelled predominantly from higher plant derived organic matter deposited in oxic environments. The source and maturity related biomarkers and aromatic hydrocarbon distributions of the oils are similar to those of the coals. The oil-coal relationship also is demonstrated by similarities in the carbon isotopic composition of the total oils, coal extracts, and their individual n-alkanes. Extracts from the Permo–Triassic fine grained sediments, on the other hand, have organic geochemical signatures indicative of mixed terrestrial and prokaryotic organic matter deposited in suboxic environments, which are significantly different from both the oils and coal extracts. The molecular signatures indicating the presence of prokaryotic organic matter in some of the coal extracts and oils may be due to thin sections of possibly calcareous lithologies interbedded within the coal measures. The genetic relationship between the oils and coals provides new evidence for the generation and expulsion of oils from the Permian coals and raises the possibility for commercial oil accumulations in the Permian and Early Triassic sandstones, potentially in the deeper offshore part of the Sydney Basin. 相似文献
14.
Iatroscan TLC-FID combines the separatory capabilities of thin-layer chromatography (TLC) (on silica coated chromarods) with the possibility of quantitation by flame ionization detection (FID). It can be used to separate lipid extracts into classes of compounds ranging from neutral to polar products. The rapidity with which this system provides lipid class profiles from small samples makes it particularly useful in oceanographic studies where routine analyses of large numbers of samples are required. Lipid classes were analysed in 4 marine bacterial strains grown on various substrates and 10 microalgae isolated from the marine environment and grown in batch cultures. Data on lipid composition of these microorganisms were obtained and compared to literature data. Results show that ratios between classes of compounds within the different groups of microorganisms were characteristic enough to constitute a good print of bacterial or phytoplankton sources in organic matter in sea water. In a preliminary study, phospholipid classes from a bacterial strain and a microalga were separated. Results show that the determination of ratios between phospholipid classes in organic matter could represent an improvement in the utilization of lipid classes as biomarkers. 相似文献
15.
通过岩芯观察、岩石薄片粒度分析,在鄂尔多斯盆地南缘铜川地区三叠系延长组9段识别出了浊积岩,并揭示了其垂向上典型鲍马序列组合及沉积特征。同时,对鄂尔多斯盆地延长组长9段的油页岩、富有机质泥岩等样本进行TOC、热解测试,分析了该段浊积岩特征及对有机质富集的特征及影响。结果表明:半深湖--深湖区油页岩、泥岩干酪根类型以Ⅱ1型为主,浊积岩上下层位的泥岩、泥页岩、粉砂质泥岩等干酪根类型主要为Ⅲ型和Ⅱ2型。长9段浊积岩对含油页岩段的有机质富集具有一定影响,浊积岩AB及ABC序列对底部沉积的泥岩、泥页岩有机质含量影响最大,其有机碳含量相对较低;浊积岩DE序列对底部沉积的泥岩、泥页岩有机质含量影响相对较小,有机质含量相对较高。 相似文献
16.
Sedimentary biomarker distributions can record ocean productivity and community structure, but their interpretation must consider alteration during organic matter (OM) export and burial. Large changes in the water column redox state are known to impact on the preservation of biomarkers, but more subtle variation in sediment redox conditions, characteristic of major modern ocean basins, have been less thoroughly investigated. Here we evaluate changes in biomarker distributions during sinking and burial across a nearshore to offshore transect in the southwestern Cape Basin (South East Atlantic), which includes a range of sedimentary environments. Biomarker concentrations and distributions in suspended particulate matter from the upper water column were determined and compared with underlying sedimentary biomarker accumulation rates and distributions. Biomarker distributions were similar in surface and subsurface waters, indicating that the OM signature is exported from the ocean mixed layer with minimal alteration. We show that, while export production (100 m) is similar along this transect, 230Thxs-corrected biomarker accumulation rate varies by over an order of magnitude in sediments and is directly associated with sedimentary redox conditions, ranging from oxic to nitrogenous–ferruginous. Biomarker distributions were dominated by sterols in surface water, and by alkenones in underlying sediments, which we propose to be primarily the result of selective preservation. Notably, the difference in sediment O2 penetration depth was associated with relative biomarker preservation. Subtle variation in sedimentary redox conditions has a dramatic impact on the distribution of preserved biomarkers. We discuss mechanisms for preferential degradation of specific biomarkers within this setting. 相似文献
17.
This study demonstrates that intracrystalline organic matter in coral skeletons is well preserved over century timescales. The extent of preservation of organic matter in coral skeletons was investigated by measuring total organic carbon (TOC), total hydrolyzable amino acid (THAA), chloropigment, and lipid concentrations in 0-300 year old annual growth bands from Montastraea annularis (Florida Keys) and Porites lutea (Red Sea). Organic matter intrinsic to the calcium carbonate mineral (intracrystalline) was analyzed separately from total skeletal organic matter. The Red Sea coral had less TOC (0.02-0.04 wt%) than the Florida Keys coral (0.04-0.11 wt%), but a higher percent of intracrystalline organic matter in all annual bands measured. Carbon in the form of THAA, most likely from mineral-precipitating proteins, contributed 30-45% of the TOC in both corals. Carbon in lipids represented about 3% of the TOC in the coral skeletons. Chlorophyll-a and b were present in annual bands where endolithic algae were present, but these compounds were minor contributors to TOC. The distribution of specific organic compounds showed that organic matter was well preserved throughout the time period sampled in both the total and intracrystalline pools. Variations in THAA were not correlated with TOC over time, suggesting that organic matter that is involved in biomineralization, like amino acids, may be deposited in response to different environmental factors than are other components of skeletal organic matter. Differences in the quantity and composition of organic matter between the two corals investigated here were assessed using principal components analysis and suggest that location, species and skeletal structure may all influence organic matter content and possibly the degree of physical protection of organic matter by the coral skeleton. Further, our study suggests that intracrystalline organic matter may be better protected from diagenesis than non-intracrystalline organic matter and may therefore be a more reliable source of organic matter for paleoceanographic studies than total skeletal organic matter. 相似文献
18.
Sources of organic matter (OM) and lipids were assessed and factors affecting OM degradation were studied for two sediment cores representing distinct depositional regimes (i.e., the oscillating oxic to suboxic/anoxic western basin and oxic Zaka Bay) for eutrophic Lake Bled, NW Slovenia. Lower surface organic carbon (OC) concentration was determined in the western basin than for Zaka Bay sediments (5.1 vs. 5.4 wt% dry sediment, respectively), but one order of magnitude greater total lipid concentration was observed in the former. Also, there was a higher proportion of autochthonous OM in the western basin (77% vs. 66%) on the basis of atomic C/N ratios. Lipid-based origin assessment suggested a similar contribution of autochthonous OM in the western basin (64–77%), but a lower one in Zaka Bay (<50%). It seems that redox potential is the main factor governing OM degradation in the western basin. In contrast, a contribution from more refractory terrestrial OM, via the surface inflow in Zaka Bay, and higher sedimentation rates may surpass redox effects in Zaka Bay. Overall, oxygen may play a more important role in degradation of the more labile pool (i.e., lipids) than bulk OM. Higher apparent degradation rate constants (k′) for lipids also suggested a greater lability than for OC, while respective k′ values were higher in the oxic than anoxic environment. 相似文献
19.
Methylhopanoids are organic compounds synthesized by certain bacteria, that when preserved in sediments act as molecular fossils or biomarkers for organic matter inputs from specific bacterial sources. Two series of methylhopanoids occur, each mainly deriving from a distinct bacterial source: cyanobacteria (2-methyl) and methanotrophic bacteria (3-methyl). The abundance and composition of methylhopanoids within sediments of modern depositional environments varies widely, apparently due to different bacterial communities contributing to the sedimentary organic matter. Comparable molecular characteristics are found in oils and their source rocks. Consequently, methylhopanoids are valuable in oil-oil and oil-source rock correlations, distinguishing between samples related to different depositional environments. In particular, abundant 3β-methylhopanoids (from methanotrophic bacteria or an additional unknown bacterial source) are characteristic of some modern alkaline saline lake environments. Comparable compositional features in the methylhopanes of oils allow the assignment of lacustrine oils offshore West Africa to two distinct lacustrine source rock facies, and to distinguish between different marine source facies, thus refining oil-source rock correlation. 相似文献
20.
Wang Hongmei Ma Xiangru Liu Deng Yang Xiaofen Li Jihong 《Frontiers of Earth Science》2007,1(4):399-404
Understanding the dynamics of organic matter in modern marine water columns greatly favors the geobiological evaluation of
hydrocarbon source rocks. Biolipids could make great contribution to petroleum hydrocarbons due to their comparable chemical
components and the slightly refractory characteristics of biolipids during the microbial/thermal degradation. A variety of
environmental factors such as temperature, CO2 and salinity could affect the biochemical contents in microorganisms. As a result, microorganisms living in a changing environmental
condition might have a different contribution to the petroleum formation. Organic carbon flux is shown to bear a positive
correlation with the primary productivity only within a certain range of biomass volumes in a specific biohabitat. Furthermore,
organic matter is degraded much quickly in a water column with oxic conditions. Therefore, the anoxic condition, along with
the enhanced biological productivity, would be one of the significant factors in the formation of high-quality hydrocarbon
source rocks. The formation of biofilms and microbial mats favors the preservation of sedimentary organic matter by decreasing
the degradation rate of organic matter. Identification of biofilms and microbial mats in sedimentary rocks will thus greatly
help to understand the depositional processes of organic matter finally preserved in hydrocarbon source rocks.
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Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 748–754 [译自: 地球科学—中国地质大学学报 相似文献