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1.
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2.
Nine rock samples from three Jurassic stratigraphic units of a shallow core from NW Germany were analyzed by pyrolysis-gas chromatography. The units contain a mixed Type-II/III kerogen (Dogger-α), a hydrogen-rich Type-II kerogen (Lias-), and a hydrogen-poor Type-III kerogen (Lias-δ). All of the kerogen was immature (Ro = 0.5%). Two sets of kerogen concentrates (“AD”: HCl/HF followed by a density separation, and “A”: only acid treatment) prepared from the rock samples were also analyzed to make a detailed comparison of the pyrolysates of rock and corresponding kerogen-concentrates.Hydrogen-index (HI) values of the kerogen concentrates prepared from organic-carbon poor rock were nearly 200% higher than HI values of the rock samples. Changes in HI were minimal for the samples containing Type-II kerogen. The A and AD samples from the Corg-poor rock yielded pyrolysates with n-alkane series of very different molecular lengths. Pyrograms of the rock samples had n-alkane series extending to n-C14; the chromatograms of the A samples reached the n-C14-nC20 range. The AD samples from Corg-poor rock and all three sample types from the Corg-rich rock had n-alkane series up to n-C29. The benzene/hexane and toluene/heptane ratios for the Corg-poor rock and A samples were far higher than for the AD samples, which had ratios similar to those of all three sample types from the Corg-rich rocks. These results indicate that choice of kerogen preparation method is critical when Corg-poor samples are analyzed.  相似文献   

3.
Moss covered, high latitude wetlands hold large amounts of terrestrial organic matter (OM), which may be vulnerable to expected climate warming. Molecular analysis of fluvially transported material from these regions can distinguish between different sources of terrestrial OM. Sphagnum moss may represent one of the major sources. This study aimed to quantitatively establish a molecular proxy for identifying Sphagnum-derived OM from high latitude peatlands in the sub-Arctic coastal ocean. We collected and analyzed Sphagnum species throughout northern Sweden and Finland. Results show that the C25/(C25 + C29) n-alkane ratio is most suitable for terrestrial OM source apportionment in these coastal regions since, compared to other n-alkane Sphagnum proxies, it shows (i) the least variation between species, (ii) the most constant values for different latitudinal regimes and (iii) the largest dynamic range to the higher plant end member in two-source mixing models. Application of the proxy to surface sediments and suspended particulate matter in the sub-Arctic northern Baltic Sea shows that 68–103% of the terrestrial OM fraction is derived from Sphagnum-rich peatland. We recommend that future studies on terrestrial OM fluxes into (sub-)Arctic regions should apply the C25/(C25 + C29) proxy to improve insight into the contribution of Sphagnum-derived terrestrial OM from climate-vulnerable, high latitude wetlands.  相似文献   

4.
We investigated the latitudinal changes in atmospheric transport of organic matter to the western Pacific and Southern Ocean (27.58°N-64.70°S). Molecular distributions of lipid compound classes (homologous series of C15 to C35n-alkanes, C8 to C34n-alkanoic acids, C12 to C30n-alkanols) and compound-specific stable isotopes (δ13C of C29 and C31n-alkanes) were measured in marine aerosol filter samples collected during a cruise by the R/V Hakuho Maru. The geographical source areas for each sample were estimated from air-mass back-trajectory computations. Concentrations of TC and lipid compound classes were several orders of magnitude lower than observations from urban sites in Asia. A stronger signature of terrestrial higher plant inputs was apparent in three samples collected under conditions of strong terrestrial winds. Unresolved complex mixtures (UCM) showed increasing values in the North Pacific, highlighting the influence of the plume of polluted air exported from East Asia. n-Alkane average chain length (ACL) distribution had two clusters, with samples showing a relation to latitude between 28°N and 47°S (highest ACL values in the tropics), whilst a subset of southern samples had anomalously high ACL values. Compound-specific carbon isotopic analysis of the C29 (−25.6‰ to −34.5‰) and C31n-alkanes (−28.3‰ to −37‰) revealed heavier δ13C values in the northern latitudes with a transition to lighter values in the Southern Ocean. By comparing the isotopic measurements with back-trajectory analysis it was generally possible to discriminate between different source areas. The terrestrial vegetation source for a subset of the southernmost Southern Ocean is enigmatic; the back-trajectories indicate eastern Antarctica as the only intercepted terrestrial source area. These samples may represent a southern hemisphere background of well mixed and very long range transported higher plant organic material.  相似文献   

5.
Lipids extracted from lacustrine deposits in the paleolake Qarhan of the Qaidam basin in the northeastern Tibetan Plateau were determined by conventional gas chromatography-mass spectrometry. Several series of biomarkers were identified, mainly including n-alkanes, n-alkan-2-ones, n-alkanoic acids, branched alkanes, triterpenoids and steroids, indicative of various biogenic contributions. On the basis of cluster analysis, the n-C15, n-C17, n-C19 alkanes were proposed to be derived from algae and/or photosynthetic bacteria, the n-C21, n-C23, n-C25 homologues from aquatic plants, and the n-C29, n-C31 homologues from vascular plants. In contrast, the n-C27 alkane is not categorized in the n-C29 and n-C31 group of alkanes, probably due to more complex origins including both aquatic and vascular plants, and/or differential biodegradation. Stratigraphically, layers-2, 4 and 5 were found to show a close relationship in n-alkane distribution, associated with a positive shift in carbon isotope composition of bulk organic matter (δ13Corg), inferring a cold/dry period. Layers-1 and 6 were clustered together in association with a negative δ13Corg, excursion, probably indicating a relatively warm/humid climate. The potential coupling between the n-alkane distributions and δ13Corg, suggests a consequence of vegetation change in response to climate change, with the late MIS3 being shown to be unstable, thought to be the climatic optimum in the Tibetan Plateau. Our results suggest that the cluster analysis used in this study probably provides an effective and authentic method to investigate the n-alkane distribution in paleolake sediments.  相似文献   

6.
Hydrocarbon distributions and stable isotope ratios of carbonates (δ13Ccar, δ18Ocar), kerogen (δ13Cker), extractable organic matter (δ13CEOM) and individual hydrocarbons of Liassic black shale samples from a prograde metamorphic sequence in the Swiss Alps were used to identify the major organic reactions with increasing metamorphic grade. The studied samples range from the diagenetic zone (<100°C) to amphibolite facies (∼550°C). The samples within the diagenetic zones (<100 and 150°C) are characterized by the dominance of C<20n-alkanes, suggesting an origin related with marine and/or bacterial inputs. The metamorphic samples (200 to 550°C) have distributions significantly dominated by C12 and C13n-alkanes, C14, C16 and C18n-alkylcyclopentanes and to a lesser extend C15, C17 and C21n-alkylcyclohexanes. The progressive 13C-enrichment (up to 3.9‰) with metamorphism of the C>17n-alkanes suggests the occurrence of cracking reactions of high molecular weight compounds. The isotopically heavier (up to 5.6‰) C<17n-alkanes in metamorphic samples are likely originated by thermal degradation of long-chain homologous with preferential release of isotopically light C1 and C2 radicals. The dominance of specific even C-number n-alkylcyclopentanes suggests an origin related to direct cyclization mechanism (without decarboxylation step) of algal or bacterial fatty acids occurring in reducing aqueous metamorphic fluid conditions. The regular increase of the concentrations of n-alkylcycloalkanes vs. C>13n-alkanes with metamorphism suggests progressive thermal release of kerogen-linked fatty acid precursors and degradation of n-alkanes. Changes of the steroid and terpenoid distributions are clearly related to increasing metamorphic temperatures. The absence of 18α(H)-22,29,30-trisnorneohopane (Ts), the occurrence of 17β(H)-trisnorhopane, 17β(H), 21α(H)-hopanes in the C29 to C31 range and 5α(H),14α(H),17α(H)-20R C27, C29 steranes in the low diagenetic samples (<100°C) are characteristic of immature bitumens. The higher thermal stress within the upper diagenetic zone (150°C) is marked by the presence of Ts, the disappearance of 17β(H)-trisnorhopane and thermodynamic equilibrium of the 22S/(22S + 22R) homohopane ratios. The increase of the ααα-sterane 20S/(20S + 20R) and 20R ββ/(ββ + αα) ratios (from 0.0 to 0.55 and from 0.0 to 0.40, respectively) in the upper diagenetic zone indicates the occurrence of isomerization reactions already at <150°C. However, the isomerization at C-20 (R → S) reaches thermodynamic equilibrium values already at the upper diagenesis (∼150°C) whereas the epimerisation at C-14 and C-17 (αα → ββ) arrives to constant values in the lower anchizone (∼200°C). The ratios Ts vs. 17α(H)-22,29,30-trisnorneohopane [(Ts/(Ts + Tm)] and 18α(H)-30-norneohopane (C29Ts) vs. 17α(H),21β(H)-30-norhopane [C29Ts/(C29Ts + C29)] increase until the medium anchizone (200 to 250°C) from 0.0 to 0.96 and from 0.0 to 0.44, respectively. An opposite trend towards lower values is observed in the higher metamorphic samples.The occurrence of specific hydrocarbons (e.g., n-alkylcyclopentanes, cadalene, hydrogenated aromatic compounds) in metamorphic samples points to kerogen degradation reactions most probably occurring in the presence of water and under reducing conditions. The changes of hydrocarbon distributions and carbon isotopic compositions of n-alkanes related to metamorphism suggest that the organic geochemistry may help to evaluate the lowest grades of prograde metamorphism.  相似文献   

7.
The geochemical composition of lake bed sediments of a tropical reservoir in Brazil have been investigated. The C, N, P composition showed almost no variation between the different sampling points. All samples contained inorganic phosphorus (IP) ranging from 52 to 70%. The Redfield ratios show that the lake is without significant anthropogenic inputs. Most of the organic matter is composed by higher plants decomposition revealed in the total organic carbon (TOC):nitrogen (N) ratio ranging from 15.4 to 57.2. Also, TOC:organic phosphorus (OP) ranged from 265.3 to 933.6, suggesting that most of the organic matter has terrestrial origin from wood plants. The ratios suggest that most organic matter is influenced by the terrestrial characteristics of the watershed. Furthermore, the relative abundance of n-alkane homologues in the sediments was investigated. All samples have been analyzed for the n-alkanes C8 to C40. The sediments were dominated by n-alkanes C25–C38. It is concluded that n-alkane in sediments mainly come from terrestrial plants, however there is a contribution of submerged aquatic plants, especially in those sites in deeper areas of the lake. On the basis of Paq index the n-alkanes in sediments comes from terrestrial plants, however there is a contribution from emerged/floating plants.The investigated lake seems to be considered as meso to eutrophic. Because of the relatively high primary productivity in the lakes, there is a substantial organic-matter flux to the sediments, which rapidly becomes anoxic. According to the pristine/phytane ratio the sediments represent an anoxic environment with values found between 0.38 and 1.72.  相似文献   

8.
Biodegraded oils are widely distributed in the Liaohe basin, China. In order to develop effective oil-source correlation tools specifically for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils and their asphaltene pyrolysates have been determined using the gas chromatography–isotope ratio mass spectrometry technique. No significant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyrolysates of oil asphaltenes was found for anhydrous pyrolysis carried out at temperatures below 340°C. This suggests that the stable carbon isotopic distribution of n-alkanes (particularly in the C16–C29 range) in the asphaltene pyrolysates can be used as a correlation tool for severely biodegraded oils from the Liaohe Basin. Comparison of the n-alkane isotopic compositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the differentiation of organic facies variation and post-generation alterations.  相似文献   

9.
A Pliocene oil shale (Pula, Hungary), a C3 plant Triticum aestivum and a C4 plant Zea mays were compared using isotopic composition of bulk organic matter, along with distributions and individual carbon isotope ratios of n-alkanes from organic extracts. The microalga Botryococcus braunii (A race) was thus shown to be the main source of the predominant 27, 29 and 31 n-alkanes of Pula sediment Therefore, the dominance of odd carbon-numbered n-alkanes in the range C25–35 in extracts from immature sediments shall not be systematically assigned to higher plant contribution but algal input is also possible. In fact, the long chain n-alkanes with an odd predominance previously observed in extracts of various immature sediments are likely to be derived at least partially, from algae.  相似文献   

10.
Anhydrous non-isothermal heating experiments were conducted under controlled compressive stress on cylindrical plugs of six oil shales from Permian through Eocene age. The objective of this study was to compare the distribution of acyclic paraffins in initial, residual and expelled organic matter and to highlight causes of compositional differences resulting from expulsion. Pristane generation from kerogen is highest in the Eocene Messel shale and affects the pristane / phytane (pr / ph) ratio commonly used as a redox proxy. The isoprenoid to n-alkane ratios (pr / n-C17, ph / n-C18) decrease during generation and are lowest in the residual bitumen due to preferential generation and retention of n-alkanes. The n-alkane distribution shows that only lacustrine shales produce high wax oils. Evaporative fractionation leads to loss of n-alkanes up to n-C20 with boiling points below 350 °C. This demonstrates that lacustrine and marine shales may lead to accumulation of low wax oils due to evaporative fractionation after expulsion.  相似文献   

11.
Precise indices based on n-alkane signatures were developed in order to determine the sources and composition of sedimentary organic matter (SOM) in coastal systems. The Arcachon Bay (France), a well-studied temperate lagoon, was used as an example of a complex coastal system sheltering a wide diversity of OM sources. Three main groups of sources were well discriminated from their n-alkane signatures: seagrass (Zostera sp.) produced mainly n-C17, n-C19, n-C21, n-C23 and n-C25 alkanes, algae (Rhodophyta, Chlorophyta) produced n-C15 and n-C17 and the terrigenous input [Quercus sp., Spartina sp. and river suspended particulate OM (SPOM)] was characterized by n-C25, n-C27, n-C29, n-C31 and n-C33. From the above and literature n-alkane fingerprints, we developed a set of indices (n-alkane ratios) to quantify the contribution of these three major sources of the SOM. At the Arcachon Bay scale, they indicated that SOM was composed mainly of seagrass (ca. 53 ± 19%) and terrestrial (ca. 41 ± 17%) material, followed by algae (ca. 6 ± 9%). Moreover, the new n-alkane indices exhibited more relevant spatial patterns than classical ones – the TAR (C27 + C29 + C31/C15 + C17 + C19; terrestrial to aquatic ratio) and the Paq (C23 + C25/C23 + C25 + C29 + C31; aquatic plant %) – with a greater contribution from marine sources in the central part of the lagoon where a high density of Zostera seagrass was observed. Therefore, the development of precise indices adapted to the local diversity of OM sources is needed when using n-alkanes for quantifying the source composition of SOM in complex coastal systems.  相似文献   

12.
We measured hydrogen isotope compositions (δD) of high-molecular-weight n-alkanes (C27-C33) from grasses grown in greenhouses and collected from the US Great Plains. In both cases, n-alkanes from C4 grasses are enriched in D by more than 20‰ relative to those from C3 grasses. The apparent enrichment factor (εC29-GW) between C29n-alkane and greenhouse water is −165 ± 12‰ for C3 grasses and −140 ± 15‰ for C4 grasses. For samples from the Great Plains, δD values of C29n-alkanes range from −280 to −136‰, with values for C4 grasses ca. 21‰ more positive than those for C3 grasses from the same site. Differences in C3 and C4 grass n-alkane δD values are consistent with the shorter interveinal distance in C4 grass leaves, and greater back-diffusion of enriched water from stomata to veins, than in C3 grass leaves. Great Plains’ grass n-alkane isotopic ratios largely reflect precipitation δD values. However, the offset or apparent fractionation between n-alkanes and precipitation is not uniform and varies with annual precipitation and relative humidity, suggesting climatic controls on lipid δD values. The dryer sites exhibit smaller absolute apparent fractionation indicative of D-enrichment of source waters through transpiration and/or soil evaporation. To explore the relationship between climate and n-alkane δD values, we develop three models. (1) The ‘direct analog’ model estimates δDC29 values simply by applying the apparent enrichment factors, εC29-GW, observed in greenhouse grasses to precipitation δD values from the Great Plains. (2) The ‘leaf-water’ model uses a Craig-Gordon model to estimate transpirational D-enrichment for both greenhouse and field sites. The transpiration-corrected enrichment factors between C29 and bulk leaf-water, εC29-GW, calculated from the greenhouse samples (−181‰ for C3 and −157‰ for C4) are applied to estimate δDC29 values relative to modeled bulk leaf-water δD values. (3) The ‘soil- and leaf-water’ model estimates the combined effects of soil evaporation, modeled by analogy with a flow-through lake, and transpiration on δDC29 values. Predictions improve with the addition of the explicit consideration of transpiration and soil evaporation, indicating that they are both important processes in determining plant lipid δD values. D-enrichment caused by these evaporative processes is controlled by relative humidity, suggesting that important climatic information is recorded in leaf wax n-alkane δD values. Calibration studies such as this one provide a baseline for future studies of plant-water-deuterium systematics and form the foundation for interpretation of plant wax hydrogen isotope ratios as a paleo-aridity proxy.  相似文献   

13.
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.  相似文献   

14.
This study provides a reconstruction of the environmental evolution since 128 ka recorded by the lipid biomarkers of the C15–C35 n-alkanes, the C13–C33 n-alkan-2-ones and the C12–C30 n-alkanols isolated from the Tawan loess section, Northwest China. Variations in paleoenvironment are reconstructed from the values of the carbon preference index (CPI), the average chain length (ACL), the L/H (ratio of lower-molecular-weight to higher-molecular-weight homologues), the n-alkane C27/C31 ratios, and the n-alkan-2-one C27/C31 ratio. These parameters indicate the dominance of grasses over the west Chinese Loess Plateau (CLP) during the late Pleistocene. Lower values of the CPI and the ACL values, respectively, indicate stronger microbial reworking of organic matter and changes in plant species, which are both indicative of a warmer-wetter environment. Furthermore, the fluctuations of environment recorded in the Tawan section exhibit ten phases that show obvious cycles between warm periods and cold intervals. This study reveals that changes in the biomarker proxies agree well with changes in the magnetic susceptibility and grain size, and it indicates a huge potential for paleoenvironmental reconstructions by using the n-alkan-2-one and n-alkanol proxies.  相似文献   

15.
The aliphatic hydrocarbon composition (acyclic isoprenoids, hopanoids and steroids) of oils from the most productive fields in the southern geological Province of Cuba have been studied. This province is defined by its position with respect to the Cretaceous overthrust belt generated during the formation of oceanic crust along the axis of the proto-Caribbean Basin. The relative abundances of 18α(H)-22,29,30-trisnorneohopane, gammacerane and diasteranes suggest that Pina oils are related to the carbonate oils from the Placetas Unit in the northern province (low Ts/(Ts+Tm) and C27,29 rr/(rr+sd) ratios). The Cristales and Jatibonico oils exhibit some differentiating features such as higher Ts/(Ts+Tm) and absence of gammacerane. The oils from this province do not exhibit significant differences in either hopane, C32 22S/(S+R) and C30 αβ/(αβ+βα), or sterane, C29 αα 20S/(S+R), maturity ratios. However, the relative content of 5α(H),14β(H),17β(H)-cholestanes (C29 ββ/(ββ+αα) ratio) indicates that Pina oils are more mature than Cristales and Jatibonico oils. Several of these oils (Cristales, Jatibonico and Pina 26) are heavily biodegraded, lacking n-alkanes, norpristane, pristane and phytane (the two former oils do not contain acyclic isoprenoid hydrocarbons). Other biodegradation products, the 25-norhopanes, are found in all the oils. Their occurrence is probably due to mixing of severely biodegraded oil residues with undegraded crude oils during accumulation in the reservoir.  相似文献   

16.
We present a systematic study of chain-length distributions and D/H ratios of n-alkyl lipids (both n-alkanes and n-alkanoic acids) in a wide range of terrestrial and aquatic plants around and in Blood Pond, Massachusetts, USA. The primary goal is to establish a model to quantitatively assess the aquatic plant inputs of the mid-chain length n-alkyl lipids to lake sediments and to determine the average hydrogen isotopic ratios of these lipids in different plants. Our results show that middle-chain n-alkyl lipids (C21-C23n-alkanes and C20-C24n-alkanoic acids) are exceptionally abundant in floating and submerged aquatic plants, in contrast to the dominance of long-chain n-alkyl lipids (C27-C31n-alkanes and C26-C32n-alkanoic acids) in other plant types, which are consistent with previously published data from Mountain Kenya and the Tibetan Plateau. Combining available data in different environmental settings allows us to establish statistically robust model distributions of n-alkyl lipids in floating/submerged macrophytes relative to other plant types. Based on the model distributions, we established a multi-source mixing model using a linear algebra approach, in order to quantify the aquatic inputs of mid-chain n-alkyl lipids in lake sediments. The results show that ∼97% of the mid-chain n-alkyl lipids (C23n-alkane and C22n-acid (behenic acid)) in Blood Pond sediments are derived from floating and submerged macrophytes. In addition, D/H ratios of C22n-acid and C23n-alkane in the floating and submerged plants from Blood Pond display relatively narrow ranges of variation (−161 ± 16‰ and −183 ± 18‰, respectively). Our study demonstrates that mid-chain n-alkyl lipids such as C23n-alkane and C22n-acid could be excellent recorders of past lake water isotopic ratios in lakes with abundant floating and submerged macrophyte inputs.  相似文献   

17.
Bulk geochemical characterization (total organic carbon, grain size distribution, carbon isotope composition) and molecular biomarkers (lignin phenols, straight chain aliphatic hydrocarbons, glycerol dialkyl glycerol tetraethers) were analyzed for a 21 m core from the Bohai Sea (North China), spanning ca 21 ka BP. These paleo-proxies presented remarkable differences between the late glacial period and the Holocene, reflecting continental and coastal environments, respectively. Two peat layers were deposited during the period of ca 9000-8460 yr BP. Thereafter the core site has been consistently covered by seawater until recent reclamation of land from the sea. The occurrence of a total organic carbon maximum from ca 6000-3800 yr BP was attributed to delivery of organic carbon enriched sediments via the Yellow River, consistent with increased vegetation density and higher development of soil under warm and humid mid-Holocene climate conditions. The distributions of lignin phenol compositions and C31/C29n-alkane ratio suggested the largest expansion of woody plants between ca 5300 and 4000 yr BP, corresponding to the extremely favorable climatic conditions. Since ca 3800 yr BP, an abrupt increase in the C31/C29n-alkane ratio suggested higher abundance of grasses, consistent with a drying climate trend after the mid-Holocene. Since our coastal sediments close to the Yellow River outflow contain catchment-integrated environmental signals of the river basin, molecular proxies demonstrate that the variability of vegetation distributions in the Holocene is a widespread phenomenon in those areas adjacent to Yellow River Basin.  相似文献   

18.
The lower part of Shayi Member (Es1x Sub-Member) composed mainly of dark mudstones and shales is the dominant source rocks for the Lixian Slope. Based on organic petrology, organic and inorganic geochemistry analyses of several mudstone and shale samples selected from Es1x Sub-Member, this research provides an overview on type, origin and thermal maturity of organic matters, as well as depositional environment of Es1x Sub-Member. Kerogen microscopy observation shows that the macerals are dominated by sapropelinite with a significant mixture of vitrinite and inertinite, indicating that aquatic algal-bacterial organic matter inputs are dominate with a significant contribution of terrigenous organic matter inputs. This statement is supported by n-alkane patterns distribution characteristics, high (n-C21 + n-C22)/(n-C28 + n-C29) values (average = 1.77), the plot of high Ph/n-C18 values (average = 4.15) versus low Pr/n-C17 values (average = 1.13), and high proportion of C27 sterane and C29 sterane (average = 37.7 and 42.0%, respectively). In addition, the rather low Pr/Ph values (average = 0.38), high gammacerane index values (average = 0.30), high V/Ni and V/(V + Ni) values (average = 11.84 and 0.89, respectively), high Sr/Ba and Sr/Cu values (average = 8.54 and 108, respectively), indicative of a saline water condition and a anoxic depositional environment. The low C29 sterane ααα 20S/(20S + 20R), C29 sterane αββ/(αββ + ααα), C31 homohopane 22S/(22S + 22R), C32 homohopane 22S/(22S + 22R), Ts/(Ts + Tm) values and relatively high moretane/hopane values show that the level of thermal maturity of organic matters in Es1x Sub-Member are low.  相似文献   

19.
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ASM~(14)C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nC_(27)、nC_(29)为主峰,部分以nC_(31)为主峰,呈现出显著的奇碳优势。少数样品中低于nC_(21)的短链正构烷烃相对丰度较高,主要以nC_(17)、nC_(20)为主峰碳数,无明显的奇偶优势。根据正构烷烃分布特征、AMS~(14)C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。  相似文献   

20.
To constrain seasonal changes in the long-range atmospheric transport of land-derived lipid biomarker compounds, we investigated the compound-specific stable isotopic composition of marine aerosol n-alkanes collected from 1990 to 1993 at a remote island, Chichi-Jima (27°04′N, 142°13′E), in the western North Pacific. Compound-specific isotope analysis revealed, in particular, strong seasonal changes in the δ13C values of the C29 and C31n-alkanes (biomarkers for higher plants). Lighter δ13C values were observed in winter (typically −32 to −34‰), with a transition to heavier values in summer (typically −28 to −31‰). Using a mixing equation and typical end members for C3 and C4 plants, we found that this is due to relative increases in the contributions from C4 plants in the summer season. Using backward air-mass trajectory analyses, it was shown that the Asian continent was the major source region for C3 plant material during winter/spring, whereas Indonesia/Australia and possibly the Americas were the major source regions for C4 material during the summer/autumn. Also observed was an enhanced atmospheric transport of n-alkanes from C4 plants in 1991 summer/autumn during a strong El Nino event, which was associated with forest and bushfires in Indonesia and Australia. In addition to providing information on contemporary processes, this study also provides a base for future paleoclimatological work in ocean sediments.  相似文献   

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