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1.
通过分析研究东海西部OR_1井的资料及南黄海北部田横岛东南方向的柱状取心资料,发现东海及南黄海近代沉积物中姥鲛烷/植烷比值均小于1,平均值为0.28—0.35。而古代海相沉积岩中有机质的姥鲛烷/植烷比值一般都在0.5—3.0之间。从而得出:姥鲛烷/植烷比值的大小可能与沉积物中有机质的成熟度(演化程度)有关。  相似文献   

2.
The Late Cretaceous sedimentary record of the North American Western Interior Seaway is characterized by cyclic deposition of organic carbon-rich sediments. One notable interval during the late Coniacian-Santonian is recorded by the Niobrara Formation. The organic carbon-rich interval within the Niobrara Formation has been identified as Oceanic Anoxic Event (OAE) 3. Understanding the reason for this distribution of organic carbon within the Niobrara Formation requires a refined understanding of the source and maturity of the organic matter. In this study, we present lipid biomarker records from the USGS Portland #1 core (Cañon City, CO) to constrain the thermal maturity of the organic matter and the differing contributions of organic matter sources. Sterane and hopane thermal maturity indices indicate that the samples are somewhat immature with respect to oil formation and that there is strong agreement between different proxies for thermal maturity. Based on the distribution of n-alkanes, steranes, and hopanes, there is a significant increase in the contribution of algal organic matter during and after OAE 3, coeval with increased organic carbon accumulation. Although a consistent terrestrial contribution is observed, it is only a minor source of organic matter at the Portland core location and does not drive increased organic matter accumulation during OAE 3. Of particular note is the consistent influence of even-over-odd predominantly mid-chain length (C21 to C25) organic matter. This observation within the brackish to marine, not methanogenic WIS represents an expansion of the depositional settings in which even-over-odd predominance has been observed in mid-chain length n-alkanes. Pristane (Pr) and phytane (Ph) abundances are inconsistent with a redox control on Pr/Ph ratios and suggest an increase in the delivery and/or preservation of phototrophic organic matter as the source for pristane and phytane in the Portland core.  相似文献   

3.
The objectives of our study were to assess the thickness, lateral extent, organic richness and maturity of the potential source rocks in Hungary and to estimate the volumes of hydrocarbons generated, in order that potential shale gas and shale oil plays could be identified and characterised.The Upper Triassic Kössen Marl in south-west Hungary could represent the best potential shale gas/shale oil play, due to its high organic richness, high maturity and the presence of fracture barriers. The area of gas- and oil-generative maturity is around 720 km2 with the unexpelled petroleum estimated to be up to 9 billion barrel oil-equivalent.The Lower Jurassic sediments of the Mecsek Mountains and under the Great Plain contain fair quality gas-prone source rocks, with low shale gas potential, except for a thin Toarcian shale unit which is richer in organic matter. The latter could form a potential shale gas play under the Great Hungarian Plain, if it is thicker locally.The Lower Oligocene Tard Clay in north-east Hungary could represent the second best potential shale oil play, due to its organic richness, favourable maturity and large areal extent (4500 km2) with around 7 billion barrel oil-equivalent estimated in-place volume of petroleum.Middle Miocene marine formations could represent locally-developed shale gas plays; they have fair amounts of organic matter and a mixture of type II/III kerogen, but their vertical and lateral variability is high.The Upper Miocene lacustrine Endrőd Marl contains less organic matter and the kerogen is mainly type III, which is not favourable for shale gas generation. The high carbonate and clay content, plus the lack of upper and lower fracture barriers would represent additional production challenges.  相似文献   

4.
Sixty crude oils from the Termit Basin (Eastern Niger) were analysed using biomarker distributions and bulk stable carbon isotopic compositions. Comprehensive oil-to-oil correlation indicates that there are two distinct families in the Termit Basin. The majority of the oils are geochemically similar and characterized by low Pr/Ph (pristane to phytane ratios) and high gammacerane/C30 hopane ratios, small amounts of C24 tetracyclic terpanes but abundant C23 tricyclic terpane, and lower δ13C values for saturated and aromatic hydrocarbon fractions. All of these geochemical characteristics indicate possible marine sources with saline and reducing depositional environments. In contrast, oils from well DD-1 have different geochemical features. They are characterized by relatively higher Pr/Ph and lower gammacerane/C30 hopane ratios, higher amounts of C24 tetracyclic terpane but a low content of C23 tricyclic terpane, and relatively higher δ13C values for saturated and aromatic hydrocarbon fractions. These geochemical signatures indicate possible lacustrine sources deposited under freshwater, suboxic-oxic conditions. This oil family also has a unique biomarker signature in that there are large amounts of C30 4α-methylsteranes indicating a freshwater lacustrine depositional environment.The maturity of the Termit oils is assessed using a number of maturity indicators based on biomarkers, alkyl naphthalenes, alkyl phenanthrenes and alkyl dibenzothiophenes. All parameters indicate that all of the oils are generated by source rocks within the main phase of the oil generation stage with equivalent vitrinite reflectance of 0.58%–0.87%.  相似文献   

5.
To understand the origin and biogeochemistry of the organic matter in surface sediments of Lake Shihwa and Lake Hwaong, organic nitrogen, inorganic nitrogen, labile organic carbon, and residual organic carbon contents as well as stable isotope ratios for carbon and nitrogen were determined by KOBr-KOH treatment. Ratios of organic carbon to organic nitrogen (Corg/Norg) (mean = 24) were much higher than ratios of organic carbon to total nitrogen (Corg/Ntot) (mean=12), indicating the presence of significant amounts of inorganic nitrogen in the surface sediments of both lakes. Stable isotope ratios for organic nitrogen were, on average, 5.2‰ heavier than ratios of inorganic nitrogen in Lake Shihwa, but those same ratios were comparable in Lake Hwaong. This might be due to differences in the origin or the degree of degradation of sedimentary organic matter between the two lakes. In addition, stable isotope ratios for labile organic carbon were, on average, 1.4‰ heavier than those for residual organic carbon, reflecting the preferential oxidation of13C-enriched organic matter. The present study demonstrates that KOBr-KOH treatment of sedimentary organic matter can provide valuable information for understanding the origin and degradation state of organic matter in marine and brackish sediments. This also suggests that the ratio of Corg/Norg and stable isotope ratios for organic nitrogen can be used as indexes of the degree of degradation of organic matter.  相似文献   

6.
Organic matter in cobalt-rich crust(CRC) from the Marcus–Wake Seamounts of the western Pacific Ocean, Sample CM1D03, has been analyzed to understand the source, geochemistry and mineralization of organic matter, and the mineralization environment. Biomarkers, including n-alkanes, isoprenoids, terpanes and sterols, have been detected in various layers of the CRC sample, using gas chromatography(GC) and gas chromatography–mass spectrometry(GC–MS). The content of organic carbon(OC) and its stable isotope(δ13C), and the combined features of the biomarkers show that the mineralized organic matter in CM1D03 CRC was mainly derived from microorganisms and lower plankton(e.g., bacteria and algae, respectively) from marine surface water, with some terrestrial higher plant components. The ratio of chloroform bitumen "A": OC was high in the CRC, between 10.51 and 20.66, showing significant migration characteristics of n-alkanes. Four mineralization categories of organic matter were recognized based on GC chromatograms of n-alkane molecules:(1) primitive type(bacteria and algae), which is characterized by moderately mature of n-alkanes preserving the original characteristics of the organic matter from microorganisms and lower plankton;(2) microbial degradation type, which is characterized by low contents of n-alkanes and rising baseline in the chromatogram, with the "bulge" being the products of organic matter by biodegradation;(3) organic matter migration type, which is characterized by low carbon number of n-alkanes with n C18 as the main peak carbon, without odd even predominance, and low concentrations of isoprenoids and hydrocarbons with high carbon number; and(4) organic matter hydrothermal type, which is characterized by relatively low concentration of small molecular weight n-alkanes, pristane, and phytane, accompanied by higher concentration of n-alkanes with carbon number greater than n C18. This study shows that biomarkers can record controlling factors of mineralization and their variation.  相似文献   

7.
Recent data on the sources of organic carbon buried in the ocean have emphasized the probable importance of terrigenous organic matter in burial budgets of deltaic depocenters. The many markers used to assess relative importance of marine vs. terrestrial sources each have ambiguities. We use the ratio of bromine to organic carbon (Br:OC) as a source indicator for organic matter in the Mississippi delta. Progressive increases in bromine concentrations from the river to the slope indicate increasing content of marine-derived organic matter. Quantitative estimates of marine vs. terrigenous organic matter using Br:OC ratios in a two-endmember mixing model are consistent with recent estimates using a combination of three other source markers [Gordon, E.S., Goñi, M.A. 2003. Sources and distribution of terrigenous organic matter delivered by the Atchafalaya River to sediments in the northern Gulf of Mexico. Geochim. Cosmochim. Acta, 67:2359–2375]. The Br:OC vs. δ13C relationship indicates seaward increase in δ13C without proportionate incorporation of marine organic matter, consistent with recent arguments that isotopically depleted terrestrial detritus derived from C3 plants is separated from C4-derived terrigenous organic matter during transport. Decreasing Br:OC ratios downcore at many sites that have significant amounts of marine organic matter indicate that the marine organic matter is preferentially lost during burial diagenesis. This preferential loss constrains the contribution of organic matter burial in deltaic environments to global removal of Br.  相似文献   

8.
Variations in elemental and isotopic ratios of suspended particulate matter (SPM) were investigated in the Guayas River Estuary Ecosystem (GREE) that empties into the Gulf of Guayaquil, Ecuador. Detritus in the system was identified on the basis of extremely high carbon:chlorophyll aratios (>1000). This material had mean δ13C of −26·4±0·3, δ15N of +4·8±0·2, and (C:N)atomicof 14·1±0·9. The isotopic data were comparable to measurements reported for fresh and degrading mangrove leaves, whereas the elemental ratio was comparatively enriched in nitrogen. Isotope measurements of SPM throughout the GREE were more similar to values for riverine material and detritus compared with that for the coastal end-member. Values indicative ofin situproduced algae, sewage and shrimp pond effluent were only found at selected sites. Bacterial bioassays, which were used to document potential sources of dissolved organic matter in the GREE, were isotopically similar to SPM. This correspondence coupled with the relatively low (C:N)aof SPM could be explained by bacterial immobolization of nitrogen onto detritus. Finally, tidal variations of (C:N)aand δ13C at a brackish mangrove site were similar in magnitude to spatial variations encountered throughout the GREE. Based on these results, the authors caution that care must be taken when samples are taken for food-web studies in these systems.  相似文献   

9.
Late Jurassic organic-rich shales from Shabwah sub-basin of western Yemen were analysed based on a combined investigations of organic geochemistry and petrology to define the origin, type of organic matter and the paleoenvironment conditions during deposition. The organic-rich shales have high total sulphur content values in the range of 1.49–4.92 wt. %, and excellent source rock potential is expected based on the high values of TOC (>7%), high extractable organic matter content and hydrocarbon yield exceeding 7000 ppm. The high total sulphur content and its relation with high organic carbon content indicate that the Late Jurassic organic-rich shales of the Shabwah sub-basin were deposited in a marine environment under suboxic-anoxic conditions. This has been evidenced from kerogen microscopy and their biomarker distributions. The kerogen microscopy investigation indicated that the Late Jurassic organic-rich shales contain an abundant liptinitic organic matter (i.e., alginite, structureless (amorphous organic matters)). The presence of alginite with morphology similar to the lamalginite alga and amorphous organic matter in these shale samples, further suggests a marine origin. The biomarker distributions also provide evidence for a major contribution by aquatic algae and microorganisms with a minor terrigenous organic matter input. The biomarkers are characterized by unimodal distribution of n-alkanes, low acyclic isoprenoids compared to normal alkanes, relatively high tricyclic terpanes compared to tetracyclic terpanes, and high proportion of C27 and C29 regular steranes compared to C28 regular sterane. Moreover, the suboxic to anoxic bottom water conditions as evidenced in these Late Jurassic shales is also supported based on relatively low pristane/phytane (Pr/Ph) ratios in the range of 0.80–1.14. Therefore, it is envisaged here that the high content of organic matter (TOC > 7 wt.%) in the analysed Late Jurassic shales is attributed to good organic matter (OM) preservation under suboxic to anoxic bottom water conditions during deposition.  相似文献   

10.
Because organic matter originating in the euphotic zone of the ocean may have a distinctive nitrogen isotope composition (15N/14N), as compared to organic matter originating in terrestrial soils, it may be used to evaluate the relative nitrogen contribution to marine and estuarine sediment. The nitrogen isotope ratios of 42 sediment samples of total nitrogen and 38 dissolved pore-water ammonium samples from Santa Barbara Basin sediment cores were measured. The range of δ15N values for total nitrogen was +2.89 – +9.4‰ with a mean of +6.8‰ and for pore water ammonium, +8.2 – +12.4‰ with a mean of 10.2‰.The results suggest that the dissolved ammonium in the pore water is produced from bacterial degradation of marine organic matter. The range of δ15N values for total nitrogen in the sediment is interpreted as resulting from an admixture of nitrogen derived from marine (+10‰) and terrestrial (+2‰ marines. The marine component of this mixture, composed principally of calcium carbonate with smaller amounts of opal and organic matter, contains ～ 1.0% nitrogen. The terrestrial component, which comprises over 80% of the sediment, contains ～ 0.1% organically bound nitrogen and accounts for > 25% of the total nitrogen in Santa Barbara Basin sediment.  相似文献   

11.
Origin of sedimentary organic matter in the north-western Adriatic Sea   总被引：1，自引：0，他引：1  
In order to evaluate the origin and the transformation of organic matter on the shallow shelf of the NW Adriatic Sea, organic carbon, total nitrogen and stable isotope ratios of organic carbon were analysed in riverine suspended matter and sediments as well as in marine suspended and sedimentary organic matter, in marine phytoplankton and zooplankton.The deposition of organic matter is influenced by fine sediment concentration. Surface sediments were characterised by highly variable biogeochemical conditions on the sea floor, whereas sub-surface sediments showed a more homogeneous hypoxic/anoxic environment.Low Corg/N ratio and high organic carbon and nitrogen concentrations in riverine suspended organic matter indicate an important contribution of freshwater phytoplankton within rivers, particularly during low flow regimes, which adds to the marine phyto- and zooplankton at shelf locations.In order to evaluate the importance of terrestrial, riverine and marine sources of OM in shelf sediments, a three end-member mixing model was applied to shelf surface sediments using 13C/12C values for organic matter and N/C ratios. The model showed an elevated contribution of terrestrial organic substances at intermediate depths (10–15 m), mostly corresponding to an area of coarser grain-size, whereas the riverine and marine organic fractions were mainly accumulating near the coast and offshore, respectively.  相似文献   

12.
Late Turonian, Coniacian and Santonian source rock samples from a recently drilled well (Tafaya Sondage No. 2; 2010) in the Tarfaya Basin were analyzed for quantity, quality, maturity and depositional environment of the organic matter (OM). To our knowledge such a thick sequence of organic matter-rich Turonian to Santonian source rocks was investigated in that great detail for the first time. Organic geochemical and organic petrological investigations were carried out on a large sample set from the 200 m thick sequence. In total 195 core samples were analyzed for total organic carbon (Corg), total inorganic carbon contents and total sulfur (TS) contents. Rock-Eval pyrolysis and vitrinite reflectance measurements were performed on 28 samples chosen on the basis of their Corg content. Non-aromatic hydrocarbons were analyzed on selected samples by way of gas chromatography–flame ionization detection (GC–FID) and GC–mass spectrometry (GC–MS). The organic matter-rich carbonates revealed a high source rock potential, representing type I kerogen and a good preservation of the organic matter, which is mainly of marine (phytoplankton) origin. HI values are high (400–900 mg/g Corg) and in a similar range as those described for more recent upwelling sediments along the continental slope of North Africa. TS/Corg ratios as well as pristane over phytane ratios indicate variable oxygen content during sediment deposition. All samples are clearly immature with respect to petroleum generation which is supported by maturity parameters such as vitrinite reflectance (0.3–0.4%), Tmax values (401–423 °C), production indices (S1/(S1 + S2) > 0.1) as well as maturity parameters based on ratios of specific steranes and hopanes.  相似文献   

13.
A combined geochemical and molecular characterization of a wide selection of oils from the major Brazilian offshore basins has been undertaken. The elemental (sulphur, nickel and vanadium) and bulk (oAPI and δ13C) properties of each sample been considered, together with its molecular composition determined using liquid and gas chromatography, and quantitative biological marker investigations using gas chromatography-mass spectrometry for alkanes.The results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups. The distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils. Each group is correlated tentatively with source rocks laid down in a specific depositional regime, namely lacustrine freshwater, lacustrine saline water, marine evaporitic, marine carbonate or marine deltaic. The diagnostic features that allow this classification are: the relative abundance and carbon number distributions of n-alkanes; pristane/phytane ratios; sulphur, nickel and vanadium contents; carbon isotope data; the absolute concentrations of hopanes and steranes, and their abundance relative to 4-methylsteranes and, also the occurrence and abundance of several specific biological markers, including 18α(H)-oleanane, gammacerane, β-carotane, tricyclic terpanes, higher acyclic isoprenoids, 28, 30-bisnorhopane and 25, 28, 30-trisnorhopane. This investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils.  相似文献   

14.
中国海域及邻区某些盆地生油岩的有机地球化学特征   总被引：1，自引：0，他引：1  
本文根据有机地球化学资料,研究和探讨了中国海域及邻区某些盆地生油岩的有机质丰度、可溶有机质的组成特征和不溶有机质的性质。结果表明,绝大多数生油岩有机碳含量大于0.90％,氯仿沥青“A”含量平均值大于600ppm,总烃大于200ppm。母质类型为腐殖—腐泥型和腐泥—腐殖型。  相似文献   

15.
The chloroform-extractable ‘lipid’ fraction of dissolved organic matter in seawater was analyzed by gravimetry, liquid chromatography, gas chromatography (GC), and gas chromatography—mass spectrometry (GC—MS). Gravimetric concentrations of dissolved lipids in the Gulf of Mexico were in the range of 60–160 μg 1?1 in near-surface waters and 61–116 μg 1?1 in near bottom waters and accounted for ～4% of the dissolved organic carbon. Over a 12-h sampling period and a 5-d sampling period extensive variability in dissolved lipid quantity and quality were observed. The major percentage of extractable weight was collected in the polar liquid chromatographic fraction (55–95%). Gas chromatographic concentrations of the aliphatic fractions were in the range of 0.014-0.187 μg 1?1. Concentrations derived from gas chromatography were consistently lower than gravimetrically-derived concentrations. A number of compounds were tentatively identified by a combination of GC, GC—MS, and authentic standards. The major components of the analyzable dissolved lipids were n-alkanes (C16C32), pristane, phytane, methyl, ethyl and propyl esters of fatty acids. Minor components included olefins and cycloalkanes, aromatics, short-chained acids, and possibly a lactone and an alcohol. All concentrations and compounds were indicative of a fairly pristine environment. The n-alkane distribution appears to be the result of marine and terrestrial inputs superimposed on a chronic low-level background of oil pollution. It is suggested that the fatty acid esters and other fragment molecules are the résult of the degradation of humic substances. A number of potential indicators of source were isolated.  相似文献   

16.
The C/N and stable C and N isotope ratios (δ13C, δ15N) of sedimentary and suspended particulate matter were determined in the Schelde Estuary. Suspended matter was divided into 2 to 5 size fractions by centrifugation. Four major pools of organic matter were recognized: riverine, estuarine, marine and terrestrial materials. Terrestrial organic matter (δ13C≈−26‰, δ15N≈3.5‰, C/N≈21) is important for the sedimentary pool, but suspended matter is dominated by the marine (δ13C≈−18‰, δ15N≈9‰, C/N≈8), riverine (δ13C≈−30‰, δ15N≈9‰, C/N≈7.5) and estuarine (δ13C≈−29‰, δ15N≈15‰, C/N≈8) end-members. In the upper estuary, the suspended matter size fractions vary systematically in their carbon and nitrogen biogeochemistry, with the small particles having low C/N ratios, depleted δ13C and enriched δ15N values relative to large particles. Moreover, sedimentary and suspended matter differ significantly in terms of C/N ratios (17 vs. 8.9), δ13C (−26.3 vs. −28.9‰) and δ15N (+6.9 vs. 12.0‰). In the lower estuary, suspended matter fractions are similar and sedimentary and suspended organic matter differ only in terms of δ13C (−23.5 vs. −20.1‰). Our data indicate that autochthonous organic matter contributes significantly to the total suspended matter and that the suspended organic matter composition cannot be explained in terms of conservative mixing of riverine and terrestrial sources on the one hand and marine sources on the other hand.  相似文献   

17.
2015年夏季开展了大亚湾悬浮颗粒有机物碳（POC）、氮含量（PN）及其同位素组成的研究,结果表明,δ13CPOC和δ15NPN的变化范围分别为-25.7‰~-17.4‰和-6.3‰~10.4‰,平均值分别为-20.2‰和8.2‰。大亚湾悬浮颗粒有机物含量及其碳氮同位素组成的空间变化反映了不同有机质来源的影响:喜洲岛附近海域表现出高POC、PN、δ13CPOC和δ15NPN的特征,指征着浮游植物水华的主导贡献;东北部范和港附近海域具有高POC、PN、低δ13CPOC和高δ15NPN的特征,反映了河流/河口水生有机物的影响;湾顶白寿湾附近海域的δ13CPOC和δ15NPN出现低值,体现了陆源有机质和人类污水排放的影响。借助δ13CPOC和δ15NPN的三端元混合模型,定量出海洋自生有机质、陆源有机质、河流/河口水生有机质等3个来源的贡献平均分别为70%、13%和17%,其中海洋自生有机质是夏季大亚湾悬浮颗粒有机物的最主要来源。从这3种来源颗粒有机物含量的空间变化看,海洋自生有机质含量由湾内向湾外减少,与初级生产力的空间变化相对应;河流/河口水生有机质含量在大亚湾东北部出现高值;陆源有机质含量在表、底层出现不同态势,表层陆源有机物含量在湾中部海域最低,而底层则呈现出自湾内向湾口增加的趋势,主要受控于离岸距离和珠江冲淡水、粤东沿岸上升流输送的影响。  相似文献   

18.
The quantitative characterization of carbon isotopes of n-alkanes is commonly carried out in organic geochemical studies. Possible controls on carbon isotopes include source organic matter, maturity, fractionation during oil expulsion and migration, and the mixing of different oils. In this study of the origin of crude oils in the western Pearl River Mouth Basin, the influences of all of these factors have been considered in reaching a conclusion. Carbon isotopes of n-alkanes in the crude oils, and the extracts of the two effective source rocks (the Wenchang and Enping formations) in the basin, exhibit clear differences. The Wenchang source rocks have heavy δ13C values that remain almost constant or become slightly heavier with increasing carbon number. The Enping source rocks have light δ13C values that become lighter with increasing carbon number. Two groups of oils in this area were identified based on the carbon isotopes of the n-alkanes; groupIoils are similar to extracts of the Wenchang source rocks. However, the groupIIoils are different from both the Wenchang and Enping source rocks and the carbon isotopic profiles of their n-alkanes exhibit a “V” feature with increasing carbon number. The results of artificial thermal maturation experiments indicate that, from the early stage to the peak stage of oil generation (with EasyRo between 0.64% and 1.02%), the δ13C values of n-alkanes in the pyrolysis oils become heavier by about 3‰ with increasing thermal maturity, but the shape of the carbon isotopic profiles are not significantly changed. Calculated δ13C values of n-alkanes in “mixed” artificial pyrolysis oils indicate that the mixture of oils generated from the same source rocks with different maturities could not change the carbon isotopic profile of the n-alkanes, however, a mixing of the Wenchang and Enping oils could give the “V” feature in the profiles, similar to the groupIIoils in this area. The groupIIoils appear to be mixed Wenchang and Enping oils, the latter being the dominant component in the mixture. We conclude that the source organic matter and the degree of mixing are the main factors controlling the carbon isotopic characteristics of n-alkanes in crude oils in the western Pearl River Mouth Basin.  相似文献   

19.
The Cuu Long Basin (Mekong Basin) is a rift basin off southern Vietnam, and the most important petroleum producing basin in the country. However, information on petroleum type and characteristics has hitherto been largely unavailable to the public. This paper presents petroleum geochemical data on nine oil samples from four different producing fields in the Cuu Long Basin: the Dragon (Rong), Black Lion (Sutu-Den), Sunrise (Rang ?ong) and White Tiger (Bach Ho) Fields. The oils are highly paraffinic with bimodal normal alkane distributions and show moderate pristane to phytane ratios and a conspicuous hyperbolic decrease in abundance with increasing carbon number of hopane homologues from C30 to C35. The TPP-index of Holba et al. (Holba, A.G., Dzou, L.I., Wood, G.D., Ellis, L., Adam, P., Schaeffer, P., Albrecht, P., Greene, T., Hughes, W.B., 2003. Application of tetracyclic polyprenoids as indicators of input from fresh–brackish water environments. Organic Geochemistry 34, 441–469) is equal to 1 in all samples which in combination with tricyclic triperpane T26/T25 ratios >1 and the n-alkane and hopane distributions mentioned above provide a strong indication of an origin from lacustrine source rocks. This is supported by the absence of marine C30 desmethyl steranes (i.e. 24-n-propylcholestanes) and marine diatom-derived norcholestanes. Based on the overall biological marker distributions, the lakes probably belonged to the overfilled or balanced-fill types defined by Bohacs et al. (Bohacs, K.M., Carroll, A.R., Neal, J.E., Mankiewicz, P.J., 2000. Lake-basin type, source potential, and hydrocarbon character. An integrated sequence-stratigraphic–geochemical framework. AAPG Studies in Geology 46, 3–34). The oils were generated from source rocks at early- to mid-oil-window maturity, presumably Oligocene lacustrine shales that are present in the syn-rift succession. Oils from individual fields may, however, be distinguished by a combination of biological marker parameters, such as the oleanane index, the gammacerane index, the relative abundance of tricyclic terpanes, the proportions of diasteranes and 28-norspergulane, complemented by other parameters. The oils of the Cuu Long Basin show an overall similarity to the B-10 oil from the Song Hong Basin off northern Vietnam, but are markedly different from the seepage oils known from Dam Thi Nai on the coast of central Vietnam.  相似文献   

20.
样品于1992年采自山东广饶盐场，用气相色谱和气质联用等方法对样品进行有机分析。结果表明，盐田表层上（包括藻席）中存在大量的烷烃和芳烃类生物标志物，低Pr／Ph比值（＜0．25）反映植烷存在于姥鲛烷之前，大量不饱和化合物的存在显示了有机质演化的初始状态，也反映了表层土的氧化还原性质。不同层位样品中烷烃和芳烃的含量变化很大，同一剖面烷烃含量最大变幅为：1.73×10-5（表层藻垫）至4.10×10-5（表层下3．5－8.5cm土样），说明有机质在常温常压下即开始了演化过程。大量常见生物标志物的存在，说明生物有机质的最初演化是比较容易的。研究生物有机质在常压常温条件下的演化，也许对生物标志物的研究和油气的地质成因有重要意义。  相似文献   

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