加拿大阿萨巴斯卡地区Mildred泥炭柱脂类化合物的组成特征

利用气相色谱-质谱联用仪(GC-MS)系统地分析了阿萨巴斯卡地区Mildred泥炭柱37个样品的脂类化合物,研究了它们的组成特征及可能来源。结果表明,样品中检出的正构烷烃、正烷酮、正烷醛、正烷醇、脂肪酸和脂肪酸甲酯均由高碳数化合物构成,并具明显的奇碳或偶碳优势,GC-MS质量色谱图中甾类和萜类极性化合物呈现显著的高峰。根据泥炭分子地球化学分析,Mildred泥炭柱沉积有机质主要来源于原地堆积的高等植物,苔藓类、水生植物对泥炭有机质也有一定程度的贡献,其中松柏、杜鹃花科等木本植物、莎草科草本植物以及泥炭藓类是主要的成炭植物。萜类和甾类极性化合物的分布存在明显差异,萜类化合物主要集中于剖面的上部,其形成与泥炭藓类植物存在联系;甾类化合物来源不具专属性,多与高等植物的输入有关,也可能是受微生物的改造作用而形成。     

原油裂解过程中正构烷烃的组成变化特征及其地球化学意义

采用高温模拟技术,对原油样品进行模拟实验,并对其裂解过程中正构烷烃的组成和变化特征进行了地球化学研究。结果表明,原油大量裂解生成气态烃之前,原油中的高分子量正构烷烃已经开始裂解,以C1+5烃类裂解成C6～C14化合物为主。随成熟度的增加,C6～C14化合物进一步转化为C1～C5化合物,并伴随苯系物的产出,最终形成甲烷和裂解沥青。在正构烷烃的裂解过程中,苯及其同系物的丰度呈明显增加趋势,可以作为原油裂解程度的潜在判识标志。此外,利用同样的实验条件对正十六烷进行了对比模拟实验,其产物的组成和变化特征与原油中正构烷烃的基本相同。     

青藏高原东北部全新世泥炭正构烷烃的生物记录

通过对正构烷烃分布特点的系统分析,恢复了青藏高原东北部全新世以来泥炭的生物记录。正构烷烃nC25和nC31相对含量在泥炭序列中呈现的规律性变化揭示出,在全新世期间因气候的变化幅度不同而引起了生物形态种或化学种的取代,即当气候变化幅度大时,沼泽地可能出现了水生植物和陆生植物群落之间的相互演替;当气候波动小时,则出现了分子（化学）种之间的相互取代。将这一研究结果与同一地区的孢粉资料对比、验证,分析了它们之间的差异性,提出了类脂分子化石可作为恢复植被的有效工具,与孢粉相结合,可获取更为全面的植被演化历史。这一研究为青藏高原地区全新世以来的有关生物学信息提供了新的证据。     

晚全新世以来福建仙山泥炭钻孔的正构烷烃记录

通过对福建仙山泥炭钻孔中正构烷烃的分析,探讨了研究区近千年以来的气候特征。分析显示:正构烷烃分布范围主要为C16~C35,且以奇碳链为主,奇偶优势明显。正构烷烃与有机质含量(TOC)密切相关,在典型的泥炭层,TOC含量高,长碳链的C27,C29和C31正构烷烃占优势,揭示有机质主要来源于草本或木本等高等植物,盆地处于相对干的沉积环境; 在非泥炭层,TOC含量低,钻孔中多含粗砂或粉砂,中碳链的C21或C23正构烷烃占优势,揭示有机质主要来源于水生植物或苔藓植物,表明相对较湿的沉积环境。钻孔中正构烷烃 C23/C27 比值与前人提出的 C23/C29 和Paq.等参数呈同向变化,可以作为区域干-湿变化的代用指标。结合地层的年代序列,利用正构烷烃重建了区域距今1400年以来的植被演化和气候变化历史。结果显示,福建仙山地区气候存在3次相对湿润和4次相对较干的时段。在钻孔358~280cm(约公元600~910年),气候相对较干,在280~40cm(约公元910~1640年),降水较多,气候湿润,但中间存在两次变干的阶段; 在40~0cm(约公元1640年至今),降水相对较少,气候转干。TOC含量和正构烷烃 C23/C27 序列与南方旱涝频率序列、石笋和硅藻记录对比显示,研究区在中世纪暖期气候相对较干,而小冰期则相对湿润,揭示出仙山泥炭沉积记录的气候信息具有区域一致性,为认识季风在短时间尺度的变化特征提供了依据。     

正烷烃在石油地球化学中的作用

The possibility is explored of using the characteristics of n-alkane distribution as an indicator of oll generating rocks and as indices for some other interesting aspects concerning the secondary migration of oil. It is suggested that the upper limit of the n-alkane OEP value of oil generating rocks should be considered as a function of the age of oil formation rather than a constant regardless of the difference in age. For a given stratum in a given region, it possesses a fixed value which can be defined through analyses and calculations with respect to the known oil generating rocks within rids stratum.     

柴达木盆地咸湖相生油岩正构烷烃分布特征及其成因

柴达木盆地西部第三系咸水湖相生油岩样品分析资料表明，不同沉积相带生油岩正构烷烃系列有三种碳数分布模式。深湖相生油岩在C18－C28范围呈明显的偶碳数优势，而＞C28范围无碳数优势；滨浅湖相样品在整个碳数范围内呈奇碳数优势分布；过渡相带地层正构烷烃在中碳数范围呈偶碳数优势分布，而高碳数（＞C23）部分为奇碳数优势分布。经不同沉积相带样品之间的沉积环境地球化学指标和碳酸盐含量比较发现，本区咸湖相生油岩正构烷烃的分布不取决于沉积环境的氧化还原性和岩石的矿物组成，而主要与沉积相带中的有机质生源组成有关。偶碳数优势分布的正构烷烃成因并非如常规观点解释的那样，由正构脂肪酸、醇类的还原作用或经碳酸盐催化发生β断裂而来，而可能来源于咸化湖泊中的某种嗜盐细菌或其他微生物。     

加拿大阿萨巴斯卡地区泥炭脂类分子记录的古气候信息

为了进一步了解泥炭中脂类分子化合物的分布与植被演化和气候变化的响应关系,对采自加拿大阿尔伯塔省东北部阿萨巴斯卡地区的JPH4、Mildred和McMurray泥炭柱样品中的脂类分子进行测定。根据正构烷烃、正烷酮、甾类和萜类等分子化合物的地球化学分析,结合年代学资料,重建了研究区近千年来的古气候演化过程。现代暖期以来(1990年以来),区内大范围的锈色泥炭藓发育,指示温暖干旱的气候条件;现代暖期早期(1900年以来),陆源高等植物和狭叶泥炭藓共存于干-湿交替的气候环境下;JPH4泥炭柱记录了小冰期期间寒冷干旱的气候环境,该时期莎草科等陆生维管植物发育;上述结论与前人记录的区域植被和气候变化具有较好的可比性。研究区发育的锈色泥炭藓种类特殊,多形成于干旱环境且具有C₃₁正构烷烃优势分布,ACL、P_aq、C₂₃/(C₂₇+C₃₁)正构烷烃指标能够有效表征植被输入特征和气候变化。正烷酮主要来源于相应正构烷烃的微生物氧化作用,正烷酮指标CPI-ket、ACL-ket和(K₂₃     

一种可能的煤成油母质——泥炭藓煤的有机地球化学特征

形成于贫营养型高地沼泽的云南金所泥炭藓软褐煤的链烃主要由正烷烃组成，异戊二烯类烃含量甚低，含少量陆源三萜烯。芳烃馏分主要由三芳，四芳三萜类和两个未知化合物组成。前者具典型陆源输入的奥利烷或乌散烷分子骨架，褐煤Rren^0仅0.24%，但芳构化作用已十分强烈，且芳烃主要由芳构化陆源三萜类组成。     

柴达木盆地昆特依地区晚更新世正构烷烃分布特征及其环境变迁

为探讨柴达木盆地晚更新世的环境变迁,同时为青藏高原隆升对气候变化的影响提供基础资料,对柴达木盆地昆特依地区ZK1404钻孔沉积物中的正构烷烃分布特征以及ASM¹⁴C测年数据进行了分析。结果显示,昆特依地区晚更新世沉积物的正构烷烃总体上呈现以高碳数为主的分布特征,多数样品以nC₂₇、nC₂₉为主峰,部分以nC₃₁为主峰,呈现出显著的奇碳优势。少数样品中低于nC₂₁的短链正构烷烃相对丰度较高,主要以nC₁₇、nC₂₀为主峰碳数,无明显的奇偶优势。根据正构烷烃分布特征、AMS¹⁴C测年数据、区域地质调查资料及沉积环境判断,柴达木盆地昆特依地区晚更新世（33600~26370a B.P.）气候环境以温凉干旱与温凉干旱偏湿交替出现为特征,与现代大陆性干旱荒漠气候截然不同。     

黄土高原西部地区现代植被及其表土正构烷烃分布模式研究

由于现代木本、草本植物正构烷烃主峰分布的研究结果存在一定的差异,从而导致黄土沉积中利用正构烷烃主峰分布进行古植被恢复时存在较大争议,尤其是松科植物主峰分布的不同。因此,采集黄土高原西部地区常见木本和草本植物及其表土,包括研究区常见松科植物,利用GC分析,开展现代植物及其表土正构烷烃主峰分布的研究。结果发现,黄土高原西部地区常见10种木本植物正构烷烃的主峰分布均以C27或C29为主峰,3种草本植物以C31为主峰,与分子有机地球化学研究结果一致,研究区3种常见松科植物均以C29为主峰,并无C31为主峰的分布; 研究区现代表土正构烷烃的结果显示,表土正构烷烃主峰分布与上覆植被输入量有直接关系,对于不同景观的采样点,由于其木本、草本植物输入量的差异而导致正构烷烃分布存在差异,对于有机质来源较为多元化的地区,分析要十分慎重。同一种植物腐叶与新鲜叶片正构烷烃主峰分布是一致的,说明植物叶片的腐烂过程对其正构烷烃主峰分布没有产生影响。对同一种植物不同地区的对比分析发现,木本植物正构烷烃主峰分布特征受生长环境影响较小,主峰分布不变,但是对于草本植物受生长环境影响较大,主峰分布会产生变化。因此,对于黄土沉积中利用正构烷烃主峰分布特征进行的古植被恢复在开展现代过程研究的基础上是较为可靠准确的。     

Qualitative fatty acid and n-alkane stratigraphy of the Lake Turkana Basin,Kenya

In order to improve understanding of the stratigraphy of the Lake Turkana Basin, one of the important sites in the evolution of early man, this study evaluates the usefulness of organic biological marker compounds, n-alkanes and fatty acids, for correlation of isolated sedimentary strata.Eighty-five paleosol samples were collected from well-defined sedimentary horizons in two regions (Area 103 and Area 130) of the Koobi Fora area of Lake Turkana. Results indicate that most of the organic matter present was derived from terrestrial plant waxes. In sediments where extensive diagenesis has occurred, microbial input of organic matter may have been substantial. Algae were either not an important source of organic matter, or their marker compounds have been removed or altered by degradative processes.The fate of the original paleosol organic matter has been governed to some extent by weathering processes, especially in Area 130. Weathering decreased the amount of extractable lipids, particularly fatty acids and the low molecular weight alkanes (C₁₇C₂₀); produced or retained relatively large amounts of alkanes greater than C₂₁ within a unimodal distribution; and lowered CPI values. Consequently, stratigraphic correlation by unique alkane and fatty acid distributions has been confined to short distances (many meters).Both n-alkanes and fatty acids have been retained better by association with clay minerals than by sand matrices. The alkane distribution of sandstones differs from that of clay organics in having a narrower carbon chain length distribution and lower CPI values. In Area 103, where weathering was less severe, compositional variations with stratigraphic position indicate that lipid material has been retained within each of the facies examined.     

Hopane,sterane and n-alkane distributions in shallow sediments hosting high arsenic groundwaters in Cambodia

The presence of elevated As in ground waters exploited for drinking water and irrigation in South-East Asia is causing serious impacts on human health. A key mechanism that causes the mobilization of As in these waters is microbially mediated reductive transformation of As-bearing Fe(III) hydrated oxides and the role of degradable organic matter (OM) in this process is widely recognized. A number of different types of OM that drive As release in these aquifers have been suggested, including petroleum derived hydrocarbons naturally seeping into shallow sediments from deeper thermally mature source rocks. However, the amount of information on the characteristics of the OM in South-East Asian aquifers is limited. Here the organic geochemical analyses of the saturated hydrocarbon fractions and radiocarbon analysis, of two additional sites in SE Asia are reported. The results show that the OM in a given sedimentary horizon likely derives from multiple sources including naturally occurring petroleum. The importance of naturally occurring petroleum as one of the sources was clearly indicated by the n-alkane CPI of approximately 1, the presence of an unresolved complex mixture, and hopane (dominated by 17α(H),21β(H) hopanes) and sterane distribution patterns. The results also indicate that the OM in these aquifers varies tremendously in content, character and potential bioavailability. Furthermore, the presence of petroleum derived OM in sediments at both sites doubles the number of locations where their presence has been observed in association with As-rich, shallow aquifers, suggesting that the role of petroleum derived OM in microbially mediated As release might occur over a wider range of geographical locations than previously thought.     

Relation between n-alkane distributions and effective coalification temperatures in some Permian shales

In Permian shales of the Sydney Basin, Australia, n-alkane distributions have been compared with effective coalification temperatures (ECTs) estimated from vitrinite reflectivities. The upper, non-marine part of the section shows evidence of progressive cracking (shift of n-alkane maximum toward shorter chains and tendency to eliminate longer chains) as depth and ECT increase; but this trend is not maintained in the underlying marine section.All samples show lack of a maximum in the longer-chain n-alkane distribution. Possible reasons discussed are (i) a cracking rate of long chains greater than their formation rate; (ii) a need for higher temperatures than the rock has so far undergone to produce a new crop of long chains; or (iii) exhaustion of the straight-chain generating potential of the kerogen. Pyrolysis experiments may be effective in testing these possibilities.The linking of ECTs to alteration stages of sediment hydrocarbons opens the possibility of comparing these stages among formations which differ in age and organic and inorganic composition, and among basins of diverse geological history.     

东北地区以泥炭为信息载体的全新世气候变迁研究进展

泥炭作为一种地质信息载体,在全球环境变化研究中起着越来越重要的作用.我国东北地区地处全球变化的敏感区,泥炭地研究的意义更为显著.笔者针对近年来东北地区泥炭地研究的多种成果,对该区全新世以来泥炭沉积和区域气候变迁历史进行了系统分析.得出:①东北地区泥炭有三次沉积高峰,分别始于早全新世、中全新世与晚全新世初期;②该区10000a以来大体上经历了冷湿-温暖适宜-凉湿-温暖偏干-冷干-寒冷略湿-变暖这样一个气候变迁过程.     

天目山泥炭有机碳同位素特征及其古环境意义

通过对浙江天目山泥炭剖面的高密度采样和有机碳同位素分析,重建了该地区4 ka BP以来的古植被特征和古环境演化历史.天目山3200 a BP之前,气候温和适度,晚期变冷变干,为中全新世末气候波动的过渡时期.3200~700 a BP,有机碳δ13Corg值在波动中降低,气候出现多次急剧冷暖变化,指示了几次温暖与寒冷事件.700 aBP以来,有机碳同位素迅速正偏,表明又一暖期的出现,到了后期气温又有所降低,植被转化为草原草甸景观.天目山地区近4 ka以来的气候变化与国内外不同区域的研究资料相一致,但又有区域的差异性.     

加拿大Athabasca地区下白垩统McMurray组沉积特征分析

在前人研究基础上,通过钻井岩心描述和测井曲线对比,根据岩石学特征、沉积相标志、测井相标志等对加拿大Athabasca地区下白垩统McMurray组进行了沉积特征分析。McMurray组主要发育了河流相、三角洲相和滨海沉积,总体呈海平面相对上升变化。纵向上,中下部层序以河流相为主,沉积物多为来自盆地周边的近物源,以西部物源为主。短河流汇入盆地后可沿盆地长轴南北发育,成为北部区块的长物源。上部层序受西北方向海侵的影响,自北向南发育滨海-河口湾-三角洲相沉积。     

Effect of leaf litter degradation and seasonality on D/H isotope ratios of n-alkane biomarkers

During the last decade, compound-specific hydrogen isotope analysis of plant leaf-wax and sedimentary n-alkyl lipids has become a promising tool for paleohydrological reconstructions. However, with the exception of several previous studies, there is a lack of knowledge regarding possible effects of early diagenesis on the δD values of n-alkanes. We therefore investigated the n-alkane patterns and δD values of long-chain n-alkanes from three different C3 higher plant species (Acer pseudoplatanus L., Fagus sylvatica L. and Sorbus aucuparia L.) that have been degraded in a field leaf litterbag experiment for 27 months.We found that after an initial increase of long-chain n-alkane masses (up to ∼50%), decomposition took place with mean turnover times of 11.7 months. Intermittently, the masses of mid-chain n-alkanes increased significantly during periods of highest total mass losses. Furthermore, initially high odd-over-even predominances (OEP) declined and long-chain n-alkane ratios like n-C₃₁/C₂₇ and n-C₃₁/C₂₉ started to converge to the value of 1. While bulk leaf litter became systematically D-enriched especially during summer seasons (by ∼8‰ on average over 27 months), the δD values of long-chain n-alkanes reveal no systematic overall shifts, but seasonal variations of up to 25‰ (Fagus, n-C₂₇, average ∼13‰).Although a partly contribution by leaf-wax n-alkanes by throughfall cannot be excluded, these findings suggest that a microbial n-alkane pool sensitive to seasonal variations of soil water δD rapidly builds up. We propose a conceptual model based on an isotope mass balance calculation that accounts for the decomposition of plant-derived n-alkanes and the build-up of microbial n-alkanes. Model results are in good agreement with measured n-alkane δD results. Since microbial ‘contamination’ is not necessarily discernible from n-alkane concentration patterns alone, care may have to be taken not to over-interpret δD values of sedimentary n-alkanes. Furthermore, since leaf-water is generally D-enriched compared to soil and lake waters, soil and water microbial n-alkane pools may help explain why soil and sediment n-alkanes are D-depleted compared to leaves.     

新疆哈拉奇地区地球化学分区特征及地质意义

水系沉积物测量是勘查地球化学一种重要方法。随着勘查地球化学的深入发展,有关地球化学异常圈定的方法已成为人们关注的焦点。采用R型因子分析方法,对哈拉奇地区水系沉积物测量所取得的数据进行统计处理,提取了具有代表性的5种因子组合类型,同时以因子得分为综合指标,绘制了因子得分等值线图并制作了元素组合分区图。通过综合分析,地球化学分区图反映了不同地段中以相应的元素组合类型为主的地球化学异常及地质成因信息,同时与主要控矿因素的空间分布比较一致,为研究区地质找矿提供新方向。     

内蒙古道郎山地区花岗岩的地质地球化学特征及其意义

内蒙古道郎山位于华北板块北缘,区内出露的花岗岩主要为燕山期岩体,岩石类型主要为黑云母花岗岩。岩石地球化学特征表现为强过铝质、富硅贫钙。岩石的里特曼指数平均值为1.80,碱度指数AR平均值为2.6,属于钙碱性系列岩石。岩体分异指数高,结晶演化程度高;稀土总量偏低,具有明显Eu负异常。推测岩体是由成熟度较高的泥质岩类在较低的温度下部分熔融形成的。