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1.
对北京地区具代表性的环境功能区土壤剖面中的藿烷、甾烷、芳香甾烷类分子标志物含量及组成变化进行了分析。在10个土壤剖面中都检测到了不同浓度的藿烷与甾烷系列化合物,其中水稻田（B9）和城区绿地（B7）这些化合物的含量最高,在农田（B6、B9）和城区绿地（B7）表层土壤中还检测到了少量的三芳甾烷。土壤剖面中藿烷和甾烷含量随深度的增大而降低,在表层30 cm深度范围内的变化较大,30 cm以下其含量波动甚微,但不同深度土层中藿烷和甾烷化合物的指纹特征相近。表明表层土壤均不同程度受到了化石燃料及其衍生物的影响,并且土壤剖面不同深度土壤中藿烷和甾烷具有相关性,受石油类燃烧污染源的影响较大,煤燃烧污染影响的比重相对较小,而且深部土壤的藿烷与甾烷主要来源于表层土壤。 相似文献
2.
根据原油和烃源岩中三芳甾烷及甲基三芳甾烷组成特征,结合稳定碳同位素值,分析了苏北盆地溱潼凹陷红庄油田古近系凝析油的油源特征。结果表明,红庄油田凝析油主要来源于溱潼凹陷深部烃源岩,而并非来自于古近系烃源岩。应用储层岩石流体包裹体测试技术,根据油气包裹体特征及盐水包裹体均一化温度,结合地层埋藏史,分析了红庄油田S245井戴一段砂岩储层流体成藏期次。研究表明,与烃类包裹体共生的盐水包裹体均一化温度分布范围主要介于80～110℃,油气充注时期为新近纪中新世晚期,开始充注的时间大约为6 Ma。 相似文献
3.
借助色谱质谱仪,对黔南坳陷和黔北坳陷凯里残余油藏凯棠剖面液态石油、岩孔古油藏中的热裂解焦沥青和研究区发育的震旦系陡山沱组、下寒武统牛蹄塘组、上奥陶统五峰组和下志留统龙马溪组四套高演化烃源岩的饱和烃和芳烃馏分进行了分析研究。尽管已有研究认为凯里残余油藏和岩孔古油藏的油源岩均是下寒武统牛蹄塘组,但它们具有完全不同的三芳甾类分布与组成。如凯里残余油藏凯棠剖面的液态原油中C28三芳甾烷优势明显,其含量相当于C26+C27三芳甾烷之和的一倍,且三芳甲藻甾烷在甲基三芳甾烷中的含量极低,它与其他甲基三芳甾烷的比值介于0.02~0.05;而在岩孔古油藏的焦沥青中,C26-28三芳甾烷的相对含量呈现C27 >C28 >C26的趋势,三芳甲藻甾烷丰富,它与其他甲基三芳甾烷的比值约为0.50,即比前者高一个数量级,这与研究区四套高演化烃源岩中三芳甾类标志物的分布与组成十分相似。值得注意的是与常规甾、萜烷生物标志物一样,三芳甾类标志物的分布与组成在四套高演化烃源岩中也出现了明显的趋同现象,从而失去了其在油源研究中的实用价值。因此,在利用常规甾、萜烷和三芳甾类标志物开展油源研究时,应尽可能在成熟度相近的地质样品之间进行,且样品的成熟度应限制在生油窗范围内。 相似文献
4.
塔北隆起雅克拉油气田原油成因特征 总被引：1，自引：0，他引：1
针对雅克拉油气田多个含油气层位的原油,进行了一系列的地球化学测试分析,对雅克拉油气田原油的地球化学特征、成因特征进行了解剖。研究结果表明,雅克拉油气田深浅不同层位原油轻烃组成与轻烃单体烃碳同位素、类异戊二烯烷烃组成以及原油与馏分碳同位素组成具有明显的海相原油特征;深浅层原油三环萜烷、C28甾烷、三芳甾烷和甲基三芳甾烷以及原油与馏分碳同位素组成皆具有典型上奥陶统来源油的特征,与寒武-下奥陶统来源油特征差异明显,暗示雅克拉油气田原油来源于上奥陶统烃源层。 相似文献
5.
Two oil families in Ordovician reservoirs from the cratonic region of the Tarim Basin are distinguished by the distribution of regular steranes, triaromatic steroids, norcholestanes and dinosteroids. Oils with relatively lower contents of C28 regular steranes, C26 20S, C26 20R + C27 20S and C27 20R regular triaromatic steroids, dinosteranes, 24-norcholestanes and triaromatic dinosteroids originated from Middle–Upper Ordovician source rocks. In contrast, oils with abnormally high abundances of the above compounds are derived from Cambrian and Lower Ordovician source rocks. Only a few oils have previously been reported to be of Cambrian and Lower Ordovician origin, especially in the east region of the Tarim Basin. This study further reports the discovery of oil accumulations of Cambrian and Lower Ordovician origin in the Tabei and Tazhong Uplifts, which indicates a potential for further discoveries involving Cambrian and Lower Ordovician sourced oils in the Tarim Basin. Dinosteroids in petroleum and ancient sediments are generally thought to be biomarkers for dinoflagellates and 24-norcholestanes for dinoflagellates and diatoms. Therefore, the abnormally high abundance of these compounds in extracts from the organic-rich sediments in the Cambrian and Lower Ordovician and related oils in the cratonic region of the Tarim Basin suggests that phytoplankton algae related to dinoflagellates have appeared and might have flourished in the Tarim Basin during the Cambrian Period. Steroids with less common structural configurations are underutilized and can expand understanding of the early development history of organisms, as well as define petroleum systems. 相似文献
6.
LI Sumei 《中国地质大学学报(英文版)》2002,13(4)
31 samples of shales and mudstones developed in reducing hypersaline and freshwater setting and 20 oil samples of Bamianhe oilfield, Bohai Bay basin were collected for a detailed study of petroleum system. Composition and distribution, especially significance of steroids, are discussed as a part of those. Abundant steroidal biomarkers, including C27-29 regular steranes, C28-30 4-methyl steranes, dinosteranes and aromatic steranes, were detected. Results show that the composition and distribution of the steroids in samples studied are functions of thermal maturity, organic source, paleoenvironment and lithology of potential source rocks. Alga-rich Es4 shales (brackish water) developed in the south slope of depocenter (Niuzhuang sag) were found particularly rich in steroidal biomarkers including C30 4-methyl steranes and dinosteranes. Es3 mudstones (fresh water) were found devoid of dinosteranes. Distribution patterns of regular steranes are completely different from methyl steranes indicating different origins of the specific compounds of the fraction. Diagnostic distribution of steranes in rock extracts of diverse intervals makes the compounds to be essential indictors of source-rock tracing. Methyl steranes prove to be much more useful in oil-source rock correlation than regular steranes. Results also show that alga-rich Es4 shales located in the south slope are not likely the primary source rock responsible for the oils discovered based on the composition and distribution of steroids. 相似文献
7.
对渤海湾盆地一系列生物降解原油的色谱-质谱分析结果表明,庙西凹陷PL15-8D与PL9-4井四个严重生物降解原油三环萜烷系列分布较为异常,主要表现为以C23为主峰的后峰型、C20与C23为主峰的微弱双峰型以及以C20与C24为主峰的双峰型分布模式。强烈的生物降解作用导致C19~C23三环萜烷优先于C24+三环萜烷被不同程度地侵蚀,是形成这一异常分布的根本原因。三环萜烷系列相对丰度与绝对浓度的变化规律表明,不同碳数三环萜烷的生物降解作用同时发生,但其降解速率有明显差别,即抗生物降解能力不同。三环萜烷系列化合物（除C20三环萜烷以外）的抗生物降解能力具有随碳数增加而增强的趋势,而C20三环萜烷抗降解能力似乎强于C21~C23三环萜烷。原油中未检测到脱甲基三环萜烷,表明三环萜烷的降解并非通过微生物的脱甲基化作用,推测其降解途径是微生物氧化三环萜烷C环支链末端的甲基,形成对应的羧酸化合物。四个原油样品甾烷、藿烷与三环萜烷被微生物严重侵蚀,不能用于油源对比研究,而三芳甾烷未受生物降解影响,可作为研究区严重生物降解原油油源对比的有效指标。 相似文献
8.
为了探讨热力作用对原油中甾烷类化合物形成和分布的影响,对塔里木盆地26个典型海相原油样品和1个热模拟样品进行系统的地球化学研究。结果表明:不同演化阶段原油中甾烷类化合物组成和分布的变化较为明显。高熟阶段原油的热裂解作用导致了甾烷类化合物含量大幅降低,过熟阶段甾烷类化合物含量的短暂升高则与原油中高分子量的烃类化合物裂解有关。随着热演化程度的增加,C27和C29规则甾烷在生成和裂解速率上的不同,致使C27/C29规则甾烷的值呈现先减小后增大的趋势,所以C27/C29规则甾烷的值在成熟-高熟阶段不能用于物源方面评价。同样由于热稳定性差异的影响,原油C29甾烷异构化参数在高熟阶段发生“倒转”,因此可利用甾烷异构化参数倒转的特征来判断原油的热演化阶段。而原油中重排甾烷/规则甾烷的值与成熟度具有较好的正相关性,可作为原油在成熟-高熟阶段有效的成熟度评价参数。 相似文献
9.
烃源岩中C19~C29甾烷系列和25 降藿烷系列的检出及其地质意义 总被引：1，自引：1，他引：0
沉积有机质中通常可检测到C21（孕甾烷）、C22（升孕甾烷）和C27~C29甾烷,但C19、C20和C23~C26甾烷并不常见。在三塘湖盆地芦草沟组黑色页岩中检出了完整的C19~C29甾烷系列和25 降藿烷系列。如此完整且丰度较高的此类化合物,尚无文献报道。这一新的资料可能蕴含着丰富的油气地球化学信息。初步认为这2个系列的化合物指示:其古环境为干旱和咸化水体环境;有机质以藻类和浮游生物等低等水生生物来源为主,在沉积初期遭受强烈的生物降解作用;原始有机质与细菌降解的产物共存,成为生烃先质。 相似文献
10.
借助色谱- 质谱（GC- MS）和色谱- 质谱- 质谱（GC- MS- MS）分析,对黔南坳陷凯里残余油藏凯棠和洛棉剖面上储层沥青中的烃类组成进行了系统分析,以判断其所遭受生物降解作用的程度,探寻在极端降解原油中是否还存在原生生物标志物,为这类原油的油源研究开拓新的途径和方法。结果表明：凯棠剖面上的储层沥青中尽管仍可检测到较为完整的C19- 30三环萜烷和C27- 35藿烷系列,但C19- 29脱甲基三环萜烷系列和C26- 34 25- 降藿烷系列丰富而完整,甾烷系列中C21- 22低分子量甾烷和重排甾烷优势明显,这一系列特征表明这些沥青遭受了剧烈生物降解作用的改造。但三芳甾类仍保存完好,依据原油生物降解程度的评判标准,判断其生物降解级别介于8~9级之间。洛棉剖面上的储层沥青中藿烷系列基本消失殆尽,三环萜烷系列及其脱甲基产物和25- 降藿烷系列的分布因极端生物降解作用而发生显著变异,某些化合物如C23T、C24T、C23NTE和C28- 29NH成为优势成员;甾烷系列中C21- 22低分子量甾烷占绝对优势,三芳甾类完全消失,据此判断该剖面上沥青的生物降解级别已达到10级或更严重。由于这两个剖面上的沥青遭受了极端生物降解作用的改造,常用的甾、萜类生物标志物完全失去了实用价值。但是,在所分析的这些沥青中都检测到三个系列的C27- 35 8,14- 开环藿烷系列,它们与塔里木盆地塔中地区海相端元油中存在的同类标志物的分布特征相似。正常海相端元油和极端生物降解沥青中同时检测到这三个系列的8,14- 开环藿烷,这一事实表明这类生物标志物在成因上具有原生性,而与生物降解作用无关。此外,在极端生物降解作用沥青中的完好保存,表明它们具有极强的抗生物降解能力,因而它们在此类原油的油源研究中可能具有潜在的实用价值。 相似文献
11.
Jürgen Rullkötter Baruch Spiro Arie Nissenbaum 《Geochimica et cosmochimica acta》1985,49(6):1357-1370
A detailed GC/MS study of biological marker compounds in the saturated and aromatic hydrocarbon fractions of oils and asphalts from the Dead Sea area, Israel, provided decisive information to the solution of a long-lasting controversy by showing that the asphalts are products of early generation in an immature stage from the same type of carbonate source rock which generated more mature oils. The asphalts are not biodegraded residues of the oils.Oils from six different wells, and asphalts from wells, outcrops, and a floating block from the Dead Sea all have very similar sterane and triterpane patterns. They all lack rearranged steranes (diasteranes) indicating a carbonate source matrix and compare reasonably well with a sample of Upper Cretaceous bituminous chalk from Nebi Musa. The main difference between the oils and the asphalts is a significantly higher triaromatic to mono- plus triaromatic steroid hydrocarbon ratio in the former. This is explained as a result of rapid subsidence and heating of their source rock close to the deep parts of the Dead Sea graben. The oils thus were generated in the more deeply buried source rock blocks under the graben fill, whereas the asphalts either originate from an immature source rock section closer to the graben rims or represent an earlier phase of generation and expulsion.This study also provides general information on the evolution of biological markers in carbonate source rocks. Low-activation-energy processes, like isomerisation of steranes, appear to occur much faster at low temperatures than in shales. The high sulfur content and less cross-linking of the biogenic organic matter into a complex kerogen structure are suggested to be responsible for this. Care should be taken when using only sterane isomerisation to assess the maturity of hydrocarbons from carbonate rocks and of carbonate-derived oils. 相似文献
12.
《International Geology Review》2012,54(9):805-812
Chemical biosignatures may consist of biomarkers or nonrandom mixtures of lipids or other compounds that could not have been assembled by abiogenetic processes. The most obvious of these are repeating structural subunits, reflecting the biosynthetic assemblage of lipids. Biosignatures may eventually be a critical component in recognizing extraterrestrial life. Taxon-specific biomarkers (TSBs) are recognized as complex biosynthetic molecules (biomarkers) that are utilized or synthesized by one specific group of organisms. Thus, they are signature compounds with demonstrated efficacy for tracing evolutionary history and the early development of the Earth's biosphere. Examples of TSBs and how they are used are exemplified by steranes (earliest eukaryotes), 2-methylhopanes (oxygenetic photosynthesis), 24-n-propylcholestanes (chrysophyte algae), triaromatic and saturate dinosteroid hydrocarbons (dinoflagellates), triaromatic 23,24-dimethylcholesteroids (dinoflagellates, haptophyles), 24-isopropylcholestanes (porifera), 24-norcholestanes (diatoms), and oleananes (angiosperms). Occurrence of TSBs before the recognized appearance of the taxa they represent is viewed as a new opportunity to obtain an early record of evolution. When applied to major taxa, important information about Earth's ancient environments can be determined. 相似文献
13.
为明确白云凹陷目前发现原油的成因及来源,系统分析取自珠江口盆地不同类型原油中各类生物标志物的分布与组成特征,发现番禺低隆起北部构造及番禺4洼的原油具有姥植比低(2.0),指示陆源有机质输入的奥利烷含量中等,基本缺乏达玛树脂贡献的双杜松烷,各类重排构型甾藿含量较低,而指示沟鞭藻贡献的C_(30)4-甲基甾烷异常丰富的特点。C_(30)4-甲基甾烷与C_(29)规则甾烷的比值2.1,且其三环萜烷系列C_(19-26)呈现以C_(21)为主峰的正态分布,指示其原始生烃母质以藻类为主,表明这类原油与文昌组湖相烃源岩具有较好的可比性;而番禺低隆起南部构造及白云凹陷的凝析油具有姥植比高(4.0),明显富含奥利烷和双杜松烷,各类重排构型甾藿烷含量较高,缺乏C_(30)4-甲基甾烷的特点,且其三环萜烷C_(19-26)呈现阶梯状依次降低的特点,表明陆源有机质是其主要原始生烃母质,这符合白云凹陷发育恩平组煤系烃源岩的石油地质背景。 相似文献
14.
通过色谱-质谱分析,对海拉尔盆地贝尔凹陷35个原油样品进行聚类分析,将之分成4类.Ⅰ类原油是贝尔凹陷原油主体,占分析样品的77%,特点足菲系列含量高,平均值为64.7%,三芳甾类化合物和三芴类化合物含量次之,分别为11.42%和11.81%.Ⅱ类原油为高三芳甾类原油,三芳甾类化合物占芳烃化合物的53.9%,是该类原油的主要成份,非系列化合物含量较低,为32.5%,萘系列含量和三芴化合物含量最低,分别为0.6%和3.54%.Ⅲ类原油为高菲系列和高萤蒽含量原油,菲系列为64%,萤蒽含量高达11%,是其它原油的16倍以上.Ⅳ类原油具有高萘、高三芴化合物和低菲系列化合物的特点,分别占原油芳烃馏分的30%、32%和26%,三芳甾类化合物含量低,占3.6%.这充分说明海拉尔箍地烃源岩沉积期间有不同的沉积环境,原油有不同的牛烃母质.Ⅱ类原油以藻类为主要生烃母质,Ⅲ类原油以高等植物为主,Ⅰ类原油介于Ⅱ类和Ⅲ类原油之间,为混合型生烃母质.Ⅳ原油沉积环境和前三类原油明显不同,为咸水强还原湖相沉积环境. 相似文献
15.
《Applied Geochemistry》2005,20(2):367-381
Several series of saturated, diaromatic, triaromatic C-ring cleaved and triaromatic diterpenoids and triterpenoids have been detected in 4 immature coal and mudstone samples. A number of these compounds appear to represent intermediates in a series of postulated pathways for progressive aromatization of biogenic diterpenoids and triterpenoids. Diagenetic pathways for the formation of tricyclic aromatic hydrocarbons from abietane and pimarane type diterpenoid precursors and for the formation of diaromatic, triaromatic C-cleaved and triaromatic hydrocarbons from β-amyrin and other triterpenoid precursors are proposed. Saturated and aromatized abietanes, pimaranes and phyllocladanes, which are the most abundant compounds in all 4 samples, indicate a predominant higher plant input which can be related to the Coniferales group but not to individual plant families. β-Amyrin and other triterpenoid-derived triaromatic and triaromatic C-ring cleaved hydrocarbons with triterpenoid structures are thought to be characteristic for angiosperms. The relative concentrations of the triaromatic and triaromatic C-ring cleaved hydrocarbons are higher in samples 9602 (mudstone) and 9603 (coal) than samples 9601 (coal) and 9604 (mudstone) indicating samples 9602 (mudstone) and 9603 (coal) contain relatively more angiosperm derived organic matter than samples 9601 (coal) and 9604 (mudstone). The distribution patterns and the relative concentrations of saturated and aromatic diterpenoids and triterpenoids thus are valuable markers for the determination of the relative contents of biological sources of organic material in geological samples. 相似文献
16.
Jari Nobrega Cardoso Francisco Radler De Aquino Neto Ren Rodrigues Luiz A.F. Trindade 《Organic Geochemistry》1986,10(4-6)
The distributions of polycyclic alkanes were monitored in a Neocomian sequence (well 1-ESS-34) from the Espirito Santo Basin, southeast Brazil. The profiles included, apart from regular hopanes, significant concentrations of 18α(H), 28,30-bisnorhopane and subordinate amounts of gammacerane. Sterane concentrations, normally with hopane/sterane <5, were compatible with other geochemical data indicating a predominantly planktonic/microbial source of the deposited organic matter. Sample maturities ranged from very immature to the onset of oil generation, allowing biomarker distributions to be followed along a broad maturation range. The ability of certain molecular ratios (e.g. C27 17α(H)/17β(H)hopanes) to reflect a maturity sequence with depth in the closely-spaced strata of the immature upper levels (Jiquiá Stage) showed the value of molecular techniques over classical geochemical methods (e.g. vitrinite reflectance) for the study of immature sequences. The presence in the oils of southern Espirito Santo of 28,30-bisnorhopane, gammacerane and methyl steranes in similar concentrations as in extracts of the deepest levels of the 1-ESS-34 well qualify the Jiquia Stage as the probable source rock of oils accumulated in the basin. 相似文献
17.
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
18.
C.M. Ekweozor 《Organic Geochemistry》1986,10(4-6)
The major steranes of the non-asphaltene fraction of Nigerian tar sand bitumen (maltene) are the c27-c29 diasteranes [13β(H),17α(H); 20R + S] and C28-C29 regular steranes [14β (H),17β (H); 20S]. The reducing metal reaction products of the corresponding asphaltenes (maltene-I) contain mainly C27-C29 regular steranes with the 14β(H),17β(H); 20R + S and 14α(H),17α(H); 20R + S configurations as well as the corresponding diasteranes having the 13β(H),17α(H); 20R + S configuration. These sterane distributions suggest that maltene-I corresponds to an unaltered oil whilst the maltene is equivalent to the product of severe biodegradation of maltene-I. This is consistent with maltene-I being the remnant of “original oil” trapped within the asphaltene matrix and protected from the effect of in-reservior biodégradation.Degradation of Nigerian asphaltenes by refluxing with ferric chloride-acetic anhydride or methanolic potassium hydroxide also releases soluble reaction products having the characteristics of unaltered oil such as the presence of n-alkanes having an unbiased distribution. These methods appear to be milder and more suitable than reducing metal reactions for releasing hydrocarbons occluded by asphaltenes. 相似文献
19.
Twenty-seven heavy crude oils of diverse origin were geochemically assessed with respect to both bulk and mlecular composition for the purpose of identifying and quanttfying valid biomarker parameters for low maturity oils. The low thermal maturity level of many of these oils is evident from the bulk and alipathic chromatographic data, and oil sourced from both marine and terrigenous organic matter are represented. Selective metastable ion monitoring (SMIM) was employed to measure separately the distribution of C27, C28, and C29 sterane isomers. The useful maturity indicators include the C29 5α(H) 20S/20R ratio, the relative quantity of the biological sterane configuration in each of the total normal C27, C28, and C29 steranes, and the rearranged to normal sterane ratio. In addition, C27 rearranged steran es appear to form at a faster rate than C28 or C29 rearranged steranes. However, the isomerization of the C27 biological component appears to occur at a slower rate than the C29 counterpart suggesting that the former may be used as a maturity parameter at higher levels of thermal maturation. In the triterpane distributions, the C27 trisnorhopane isomers and the moretane to hopane ratios appear to be both source and maturity related and cannot be used as successful maturity parameters in oils unless they share a common source. The C31+ hopane 22S/22R equilibrium ratio appears to increase with increasing molecular weight (C31–C34). 相似文献
20.
In a previous study, oils in the Potwar Basin (Upper Indus) of Pakistan were correlated based on the dissimilarity of source and depositional environment of organic matter (OM) using biomarkers and bulk stable isotopes. This study is aimed at supporting the classification of Potwar Basin oils into three groups (A, B and C) using the distribution of alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, alkyldibenzofurans, alkylfluorenes, alkylbiphenyls, triaromatic steroids, methyl triaromatic steroids, retene, methyl retenes and cadalene. The higher relative abundance of specific methyl isomers of naphthalene and phenanthrene and the presence of diagnostic aromatic biomarkers clearly indicate the terrigenous and oxic depositional environment of OM for group A oil. Group B and C oils are of marine origin and the aforementioned heterocyclic and polycyclic aromatic hydrocarbons (HCs) differentiate them clearly into two different groups. The relative percentages of heterocyclic aromatic HCs reveal that the distribution of these compounds is controlled by the depositional environment of the OM. Sulfur-containing heterocyclic aromatic HCs are higher in crude oils generated from source rocks deposited in suboxic depositional environments, while oxygen-containing heterocyclic aromatic HCs in combination with alkylfluorenes are higher in marine oxic and deltaic oils. Biomarker and aromatic HC parameters do not indicate significant differences in the thermal maturity of Potwar Basin oils. Triaromatic and methyl triaromatic steroids support the division of Potwar Basin oils into the three groups and their relative abundances are related to source OM rather than thermal maturity. Significantly higher amounts of C20 and C21 triaromtic steroids and the presence or absence of long chain triaromatic steroids (C25, C26, C27, and C28) indicates that these compounds are probably formed from different biological precursors in each group. Different isomers of methyl substituted triaromatic steroids are present only for short chain compounds (C20–C22) and the origin of these compounds may be short chain methyl steranes from unknown biological precursors. 相似文献