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1.
Detailed compositional data for the sterols isolated from a surface, Unit I, sediment from the Black Sea are reported. A procedure based on digitonin precipitation has been used to separate the more abundant free sterols from those occurring in esterified forms. Saponification of the solvent extracted sediment residue liberated only a small quantity of residual bound sterols in contrast to studies of other sediments. 4-Methylsterols are much more abundant than 4-desmethylsterols in both the free and esterified sterol fractions which we attribute to a major dinoflagellate input, as in deeper Unit II sediment. The desmethylsterol fraction appears to derive from a variety of sources including dinoflagellates, coccolithophores, diatoms, terrigenous detritus and perhaps invertebrates. 5α(H)-Stanols are particularly abundant in the free sterol fraction. An analysis of the stanol/stenol ratios suggests that the 4-desmethyl-5α(H)-stanols are the result of specific microbial reductions of Δ5-sterols and/or the reflection of a contribution of stanol containing source organisms.  相似文献   

2.
C26, C27, C28 and C29 sterols, including Δ5-, Δ22- and Δ5,22-sterols and both 5α- and 5β-stanols, have been identified in the contemporary lacustrine sediment of Rostherne mere (Cheshire, England). Amounts of total sterols decrease from ca. 400 ppm extracted sediment dry weight for the 0–7 cm sediment section to ca. 40 ppm for the corresponding 18–30 cm section. 5α-stanols are of far greater abundance than the 5α-stanol isomers. The carbon number distributions of unsaturated and saturated sterols and the increase in stanol: Δ5-sterol ratio with sediment depth provide indirect evidence for the operation of a sterol hydrogenation process. C29 sterols preponderate at lower sediment depths, suggesting a predominantly higher plant input, whereas C27 sterols are more abundant in the surface sediment.  相似文献   

3.
In order to study the first steps of incorporation of lipids in recent organic-rich sediments into free and bound fractions, we have selected the Santa Barbara Basin, off California. This basin with a maximum of 590 m water depth is characterized by high phytoplankton production in surface waters and a low oxygen content in bottom waters. Sediments show the following features: high sedimentation rate ≈ 4 mm/yr, no bioturbation, and development of a bacterial mat community at the surface with predominance of sulphur-oxidizing bacteria trapping particles, thus preventing re-distribution of sediment, which permit a unique observations of organic sedimentation on a new few years basis.A sediment core has been divided into 2 cm thick slices corresponding to a time resolution of ≈5 years, from 1835 up to 1987. Samples have been analyzed using a multi-parameter approach, such as for plankton species identification, carbon stable isotope ratios and, as reported here, for lipid organic tracers. Organic tracers have been analyzed in the sterol and fatty series for both free and bound compounds by gas chromatography and gas chromatography/mass spectrometry.The incorporation processes of sterols with depth appear different for free and bound compounds. Total free sterol concentrations show high values in surface sediments (≈ 100 μg/g dry sediment), rapidly decrease up to ≈ 10 cm depth and remain at a constant value of 30–40 μg/g. Total bound sterol concentrations show low values in surface sediment (13.6 μg/g), and vary irregularly with depth up to a value of 55 μg/g at 7.3 m, and then remain constant at 25–26 μg/g.Profiles of evolution with depth of free C27, C28 sterols show a regular decrease, whereas C29 sterols show an irregular decrease with anomalies at 7.3 cm (approximately age: 1977–1978) and at 14.1 cm (1962–1964). Profiles of bound compounds are rather different, very regular for C28 sterols, irregular with oscillations for C27 and C29 sterols at 7.3, 12.2 and 18.0 cm (1954–1956), suggesting a different mode of incorporation and probably different inputs for C27, C29 and C28 sterols.The study of the kinetics of degradation of sterols between surface (1987) and 10.5 cm (1968–1972) shows that C27 compounds are degraded at a slight higher rate (0.53 μg/μg of initial C27 concentration/ year) than are C28 and C29 compounds (0.047 μg/μg of initial concentration/year). An intermediate value is found for brassicasterol: 0.049 μg/μg/year.  相似文献   

4.
本文以油苗抽提物的饱和烃色谱-质谱分析为基础,剖析了羌塘盆地昂达尔错地区油苗的生物标志化合物特征,探讨了其沉积环境和成熟度指示意义。昂达尔错油苗含有丰富的正构烷烃、类异戊二烯烃、萜类化合物和甾类化合物。正构烷烃轻烃组分含量较高,无明显的奇偶优势。Pr/Ph比小于1,显示一定的植烷优势。萜类化合物中五环三萜烷相对含量最高,四环萜烷含量最少,并有一定的伽马蜡烷和升藿烷分布。规则甾烷相对含量为C27C29C28,呈不对称"V"字形分布,异构化成熟度参数值较高,且4-甲基甾烷化合物普遍存在。昂达尔错油苗母源岩沉积于具有较高盐度的还原环境,以藻类、菌类等海相有机质输入为主,油苗有机质处于成熟阶段。  相似文献   

5.
Significant quantities of solvent-inextractable geolipids, obtained by saponification of solvent extracted sediments, were found in various sedimentary samples including soils, river inlet sediment and lake sediments from Lake Suwa.The carbon isotopic composition (δ13C) of extractable and inextractable geolipids from the same sediment sample were similar. Moreover, the carbon number distributions of sterols in the two geolipid fractions from the same sediment were also similar.Whereas the ratios of both lipids and sterols to total organic carbon for the extractable geolipids in the lake sediments decreased with depth, the former ratio for inextractable giolipids tends to increase with depth and the latter remains fairly constant. On the other hand, the stanol to stenol ratio of the extractable fraction increased with depth but that of the inextractable fraction was lower than that of the extractable fraction and was fairly constant irrespective of sediment depth.The transformation of extractable sterols into inextractable ones was not observed during incubation for 1200 days of sterols with Suwa sediments.Thus, the following conclusions were made: (1) the extractable and inextractable geolipids have similar origins, (2) some constituents of the latter may be protected from chemical or microbiological degradation and transformation in the sediments, and (3) the transformation of some constituents of the former into the inextractable ones virtually does not occur after incorporation into Suwa sediments.These results suggest that some constituents of the inextractable geolipid fraction may provide fundamental information on early diagenetic alteration of geolipids in lake sediments and on the relatively recent paleoenvironment.  相似文献   

6.
Esters of phytol or related isoprenoid acids and fatty acid esters of pentacyclic triterpenoid alcohols and sterols have been isolated from lacustrine sediments varying in age from contemporary to c. 50,000 years old. The esters were analysed by C-GC-MS and identified by GC retention data and mass spectral interpretation based on comparison with authentic compounds.In surface sediment of a productive lake, phytyl and steryl esters are biochemical markers of input from algal and Zooplankton sources. Esters of pentacyclic triterpenols detected in an older, peat-derived sediment may reflect constituents of peat-forming plant species. In sediments derived mainly from terrestrial organic matter, steryl esters containing the same acyl group showed a lower stanol/Δ5-stenol ratio than did the corresponding free sterols.  相似文献   

7.
Steroids with unconventional side chains have increasingly been applied as diagnostic markers for geological source and age assessments. However, one of the most distinctive characteristics, the abnormal abundance of pregnane and homopregnane in ancient sediments and petroleum, remains unresolved. Higher pregnane and homopregnane, as well as C23–C26 20-n-alkylpregnanes, relative to the regular steranes were observed in samples collected from different petroleum basins in China. These included Precambrian marine carbonate-derived petroleum (NW Sichuan Basin), Lower Paleozoic marine marl derived crude oils (Tarim Basin), and Eocene hypersaline lacustrine carbonate source rocks and associated petroleum (Bohai Bay Basin). However, all of the samples have many common biomarker characteristics, such as pristane/phytane ratios < 1, low amounts of diasteranes and high C29/C30 hopane (∼0.6–1), C35/C34 hopane (mostly ⩾ 1) and dibenzothiophene/phenanthrene (DBT/PHEN, mostly 0.5–1) ratios revealing a contribution from anoxic carbonate/marl source rocks deposited in restricted, clastic-starved settings. We suggest that 5α,l4β,l7β-pregnane and homopregnane, as well as their higher C23–C26 homologues, are geological products derived from steroids bound to the kerogen by a sulfurized side chain. Carbon or carbonate minerals are considered to be natural catalysts for this cracking reaction via preferential cleavage of the bond between C-20 and C-22. Similar distributions occur in the short chain analogues of 4-methylsterane, triaromatic steroid and methyltriaromatic steroid hydrocarbons, providing circumstantial evidence for this proposal. The ratio of pregnane and homopregnane to the total regular steranes and the ratio of C27 diasteranes to cholestanes can be sensitive indicators of sedimentary environments and facies. In general, high diasteranes and low pregnanes (with homologues) indicate an oxic water column or significant input of terrigenous organic matter in clay rich source rocks and some organic lean carbonate rocks. Low diasteranes with high pregnanes implies restricted, sulfur rich conditions, typical of anoxic carbonate source rocks. Furthermore, the two ratios may be useful to assess the variation of mineralogy and openness of source rock depositional settings.  相似文献   

8.
The black shale samples collected from two Neogene formations in the Klias Peninsula area, West Sabah, have been assessed and characterized in details by gas chromatography, gas chromatography-mass spectrometry and a variety of organic geochemical parameters. The aims of this study are to describe the characteristics of organic matter of these sediments in terms of source/type of the organic matter, assess its thermal maturity and paleoenvironment of deposition, based primarily on biomarker distributions. The results of both formations do not reveal significant differences within the rock extracts. The gas chromatograms of the saturated hydrocarbon fractions of the Setap Shale and the Belait formations displayed monomodal n-alkane distributions and nearly identical regular sterane compositions with a predominance of C27 regular steranes. These are consistent with open marine depositional environments dominated by marine biological matter. Another related feature of these rock extracts is the presence of a high relative abundance of gammacerane, indicating anoxic marine hypersaline source depositional environment. The relatively high abundance of common land plant-derived biomarkers, such as bicadinanes and oleananes, is a clear indication of a major terrigenous input to the source of the extractable organic matter. The predominance of oleanane biomarkers in both formations is indicative of angiospermis input and Tertiary source rocks. The high C29/C30 hopane ratios, moderate development of C33–C35 hopanes, high abundance of tricyclic terpanes and a slight predominance of C27 regular sterane over C28 and C29 steranes are characteristic features tending to suggest a significant marine influence on these source rocks, thereby suggesting a mixed source input. The 22S/(22S+22R)C32 hopane ratio has reached equilibrium, and this is supported by the high maturity level as indicated by the 22S/22SC31–33 extended hopane ratios and 20S/(20S+20R)C29 regular steranes ratios.  相似文献   

9.
Evidence of a changing environment in the catchment area of a small pond (Lansquenet, Lorraine, France) during the last millennium was provided by coupling palynology data and organic ratios [terrestrial to aquatic ratio: TAR(HC); the C29 vs. C27 sterols, C29/C27(ST); average chain length, ACL and aquatic/macrophytes ratio, Paq]. The depositional and alteration conditions of organic matter (OM) were provided by the 5α(H)-stanols/Δ5-sterols ratio. This study shows that quite simple organic ratios clearly allow identification of the different evolution steps of a watershed, from a swamp to the progressive settlement of a pond. During the swampy period, the C/N(at) (ca. 11.1), TAR(HC) (ca. 36.8), C29/C27(ST) (ca. 8.7) and Paq (<0.3) show a high contribution of allochthonous OM associated with the presence of particular aquatic and mesohygrophilous species. A woody level dated to the XIIIth century reflects the period of the settlement of the pond in a more oxic environment [5α(H)-stanol/Δ5sterol ratio <0.2]. Then, the progressive increase in aquatic input and the development of submerged and floating macrophytes are evidenced by low C/N(at) (<7.6), TAR(HC) (ca. 2.7), C29/C27(ST) (ca. 2) and high Paq (ca. 0.5), suggesting an increase in the water level and eutrophication of the pond. A second oxic event [5α(H)-stanols/Δ5sterols ratio averaging 0.16], associated with extensive OM degradation, corresponds to the most recent dredging in 2002 and reflects an important disturbance of sediments due to pond management.  相似文献   

10.
Based on the compositions and distributions of biomarkers in thirty-five representative oil samples, oils from the Tarim Basin of northwestern China are mainly divided into two oil families. One oil family contains relatively low amounts of C15-C20 isoprenoid hydrocarbons and shows pristane predominance with Pr/Ph ratios ranging from 1.50 to 3.00. The GC/MS analytical data of these oils show the occurrence of abundant hopanes, and low concentrations of steranes and tricyclic terpanes with hopanes/steranes ratios from 6.25 to 12.24 and tricyclic terpanes/hopanes ratios from 0.03 to 0.24. These oils contain low drimane relative to homodrimane (C15/C16 < 1.0) and abundant rearranged bicyclanes in bicyclic sesquiterpanes. They are dominated by low carbon number (C19-C21) compounds in the tricyclic terpanes, and are rich in rearranged hopanes, C29Ts and an unknown C30 compound in pentacyclic triterpanes. These geochemical characteristics suggest that the oils were generated mainly from terrigenous organic matter. The other oil family shows remarkably different biomarker compositions and distributions. The oils revealed Pr/Ph ratios of about 1.0, high drimane/homodrimane ratios (>1.0), low hopanes/steranes ratios (0.65–2.50), high tricyclic terpanes/hopanes ratios (0.30–2.00) and a dominant peak at C23 in tricyclic tepanes, suggesting a marine organic origin. Oil-source rock correlation indicates that these two oil families seem to have been derived from Mesozoic Jurassic-Triassic terrestrial source rocks (shales and coal seams) and Lower Paleozoic Ordovician-Cambrian marine source rocks, respectively.  相似文献   

11.
It is essential to have suitable tools able to trace the fate of manure organic matter in the environment to assess whether manure disposal on the soils of catchments could affect the organic quality of rivers. Sterol compounds – mainly expressed as C29 + 28/C27 and 5β/C27 ratios – have been shown to be specific molecular tracers of pig, dairy and poultry manures in soils. The objective of this study was to measure C29 + 28/C27 and 5β/C27 ratios in five Brittany rivers (Elorn, Yar, Léguer, Min Ran and Couesnon) draining agricultural catchments receiving massive annual inputs of pig, poultry and dairy manures and compare these ratios with ratios published for enriched soils and manure samples. The particulate organic fractions from the studied rivers yielded steroid signatures typical of animal manures. More specifically, a stanol compound diagnostic of pig slurry – the 5β-stanol known as coprostanol – was found to be very widespread, with particularly high concentrations in one of the rivers (Elorn). The C29 + 28/C27 and 5β/C27 ratios of the particulate fractions of the rivers were compared with ratios measured directly in pig, dairy and poultry manure samples, as well as with the breeding activities on river catchments. These comparisons show that the steroid profiles of the five investigated rivers correlate closely with the types of manure (i.e. pig, poultry or dairy) spread on soils in their catchments. For instance, the C29 + 28/C27 and 5β/C27 ratios in the Elorn river are similar to the values typical of pig slurry (e.g. 5β/C27 > 4); compared with other catchments, the soils in this area receive by far the largest amount of pig slurry. By contrast, the Yar river drains a catchment receiving only poultry and dairy manures, and its soils exhibit C29 + 28/C27 and 5β/C27 ratios similar to those of dairy and poultry manures (e.g. 5β/C27 ∼ 1). Thus, this study indicates that the organic quality of rivers is modified in catchments where there is intense manure spreading on soils. It also provides evidence that rivers draining areas receiving different manure types may exhibit differences in the long-term evolution of their OM content. Indeed, two of the investigated river catchments receive dominantly dairy and poultry manure, and exhibit clear long-term upward trends in OM. On the other hand, one catchment receiving high proportions of pig slurry clearly shows a long-term downward trend in OM contents. A survey of the literature shows that the relative amount of OM and N received by soils in agricultural catchments could be the key parameter in determining the direction of the long-term OM trend of the river, rather than the absolute amount and/or type of manure that is applied to the soil. In any case, the present study suggests that sterol/stanol compounds may be of diagnostic value in determining whether a stream or a river is undergoing contamination by manure-derived organic matter.  相似文献   

12.
Biomarker compositions of particulate organic matter (POM) from the oligotrophic Lake Brienz and the eutrophic Lake Lugano (both Switzerland) are compared, in order to obtain information about organic matter (OM) production and transformation processes in relation to water column stratification. Eutrophic conditions in Lake Lugano are reflected by enhanced alkalinity, elevated total organic carbon (TOC) and chlorin contents compared with Lake Brienz. Lower δ13C values of dissolved inorganic carbon (DIC) in Lake Lugano reflect enhanced OM respiration in the water column.Differences in OM dynamics between both lakes, as well as seasonal variations, are evidenced by TOC-normalised concentration profiles of total fatty acids (FAs) and total neutrals. In Lake Brienz, the results reflect the relative contributions of primary productivity and refractory, allochthonous OM to POM, governed by particle load and interflows due to density stratification. The depth trends at Lake Lugano are a result of high primary productivity, water column stratification and associated particle load in the upper layers, as well as microbially induced degradation close to the chemocline and greater preservation under anoxic conditions. Minor differences exist with regard to the OM composition. In both lakes, FA distributions and the composition of n-alkanols indicate a predominant autochthonous OM source (algae, zooplankton, bacteria). Inputs of OM from diatoms are reflected in highly-branched isoprenoid (HBI) alkenes, 16:1 n-FAs and 24-methylcholesta-5,22-dien-3β-ol (either epibrassicasterol or brassicasterol). Differences in relative proportions of n-C16 vs. n-C18 FAs and alkanols, respectively, as well as in the percentages of C27, C28 and C29 sterols relative to the sum of sterols are related to differences in the abundances of chrysophytes, diatoms and green algae within the euphotic zone of both lakes as well as in bacterial activity and soil in-wash. High relative proportions of cholesterol in the autumn samples, most pronounced at Lake Lugano, were attributed to an increased input from zooplankton grazing in the water column.Differences in OM degradation processes are reflected in slightly higher chlorin index values and higher relative proportions of saturated vs. unsaturated n-FAs in Lake Lugano. Higher contents of branched chain FAs, 16:1ω7 n-FA, and enhanced 18:1ω7/18:1ω9 n-FA ratios suggest enhanced bacterial biomass in the water column of Lake Lugano close to the chemocline. Increasing proportions of saturated n-FAs and n-alkanols with increasing water depth, most distinct in the autumn for both lakes, argue for intensified bacterial activity and degradation of OM during autumn. High relative contents of sterols and low n-alkanol concentrations in POM close to the chemocline at Lake Lugano during spring are interpreted to reflect higher primary productivity in the photic zone, OM export to the deeper parts and enhanced degradation rates of more labile constituents (i.e. C13–C20 n-alkanols), as compared to Lake Brienz.  相似文献   

13.
Organic matter contained in particulate matter in Lake Michigan waters and sediments has been characterized by CN ratios and by distributions of biomarker fatty acids, alkanols, sterols, and aliphatic hydrocarbons. Differences in organic constituents of particulate matter from various depths and distances from shore indicate a complex interaction of production, transformation, and destruction of the organic matter contained in sinking particles. Near-surface material contains important contributions of landderived organic matter, presumably of eolian input. Midwater particles have predominantly aquatic organic material of algal origin. At the sediment-water interface, selective suspension of the finer fractions of surficial sediments enriches bottom nepheloid layers with these sediment size classes. As a result, near-bottom particulate matter has an aquatic biomarker character. Organic matter associated with sinking particles undergoes substantial degradation during passage to the bottom of Lake Michigan, and aquatic components are selectively destroyed relative to terrigenous components.  相似文献   

14.
《Applied Geochemistry》2001,16(1):95-108
Bottom sediments and suspended matter from the shelf and slope areas off northeastern Taiwan were analyzed for sterol, n-alkanol and n-alkane compositions. The Σ(algal sterols/cholesterol) ratios (mean±1σ) were 1.00±0.31 (n=7) for the shelf sediments, 3.29±0.61 (n=7) for the slope sediments, and 1.54±0.19 (n=3) for the suspended matter. The much higher proportion of cholesterol in the shelf sediments is most likely derived from mollusks in the relict sediments. An additional sterol source for the shelf sediments probably is suspended matter in the water column although the shelf has no apparent sedimentation. Results from phytol and n-alkanols suggest recent inputs of lipids from the water column to the shelf. The stanol/stenol ratios are lower for the older shelf sediments than for the younger slope sediments.  相似文献   

15.
The Qinjiatun and Qikeshu oilfields are new Mesozoic petroleum exploration targets in Lishu Fault Depression of Songliao Basin, northeastern China. Currently, researches on geochemistry of crude oils from Qinjiatun and Qikeshu oilfields have not been performed and the genesis of oils is still uncertain. Based on bulk analyses, the crude oils in the Qinjiatun and Qikeshu oilfields of Lishu Fault Depression from the Lower Cretaceous can be classified as three types. TypeⅠoils, from Quantou and Denglouku formations of Qikeshu oilfield, are characterized by high C24tetracyclic terpane/C26tricyclic terpanes ratios, low gammacerance/C30hopane ratios, tricyclic terpanes/hopanes ratios, C29Ts/C29norhopane ratios and 17α(H)-diahopane/17α(H)-hopane ratios, indicating a brackish lacustrine facies. TypeⅡoils, from Shahezi Formation of Qikeshu oilfield show low C24tetracyclic terpane/C26tricyclic terpanes, high gammacerance/C30hopane ratios, tricyclic terpanes/hopanes ratios, C29Ts/C29 norhopane and C30diahopane/C30hopane ratios, thus suggesting that they originated from source rocks deposited in a weak reducing brackish lacustrine environment, or clay-rich sediments. Type oilsⅢ, from some wells of Qikeshu oilfield have geochemical characteristics intermediate between those two types and may be mixture of typeⅠand Ⅱoils.  相似文献   

16.
General characteristics and biomarker distributions of Lower Permian coal-measure source rocks in northeastern Ordos Bsain have been analyzed in this paper. The results show that the source rocks are type III kerogen, thermally mature, with high content of total organic carbon. The extracts of the source rock samples with different lithologies from Well Su 27 feature high Pr/Ph ratios, high C19TT and C24Te, high rearranged hopanes, a predominance of C29 sterane in regular steranes, and the absence of C30 4-methylsteranes. These data suggest that the source rocks were deposited in suboxic to oxic conditions with dominantly terrigenous higher plant input. In contrast, the source rocks from wells Shuang 1 and Yu 20, are characterized by low Pr/Ph ratios, low C19TT and C24Te, high C23TT, similar content of C27 sterane and C29 sterane, and the presence of C30 4-methylsteranes, showing that the source rocks were deposited in reducing environment with algae and/or microorganisms and terrigenous higher plant input.  相似文献   

17.
青海湖沉积物中的甾醇及其演化   总被引：3，自引：0，他引：3  
Ｃ２７，Ｃ２８和Ｃ２９甾醇（△５.２２，△２２，△５和△５.２４（２８）和５α－甾烷醇）在青海湖三孔近代沉积物（ＱＨ，ＱＥ和ＱＯ）中被检出。其中以Ｃ２９甾醇占优势。在ＱＥ和ＱＧ孔沉积物中还检出了低浓度的三个Ｃ３０甾醇（４α，２３，２４－三甲基－５α－胆甾－２２Ｅ－烯醇（甲藻甾醇），４α－甲基－２４－乙基－５α－胆甾－２２Ｅ－烯醇和４α－甲基－２４－乙基－５α－胆甾烷醇］。在ＱＨ和ＱＧ孔上部层段沉积物中，Ｃ２７，Ｃ２９.饱和的和不饱和的甾醇的碳数分布的平行性，甾烷醇/△５－甾醇及△２２－/△５.２２－甾醇的比值随沉积物埋深而增加提供了甾酸氢化作用的间接证据。青海湖沉积物中的甾醇主要来自湖区丰富的高等植物和湖中的藻类等。在ＱＧ孔８０～１００ｃｍ和１２０～１４０ｃｍ层段沉积物中，５ａ－胆甾烷醇浓度迅速增加可能反映特殊的生物（介形类）对该二层段沉积物中高浓度的胆甾烷醇的贡献。  相似文献   

18.
The Bulonggoer paleo-oil reservoir (BPR) on the northwest Junggar Basin is the first Devonian paleo-oil reservoir discovered in North Xinjiang, China. Solid bitumens occur within sandstone pores and as veins filling fractures. Samples of both types were analyzed using stable carbon isotope and reflectance measurements, as well as molecular biomarker parameters.The extremely positive δ13C values and biomarker indicators of depositional environment/lithology, such as pristane/phytane (Pr/Ph), C29/C30 hopane, diasteranes/regular steranes and dibenzothiophene/phenanthrene ratios, indicate a siliciclastic source for the BPR and their deposition in a highly reducing hypersaline environment. The presence of long chain n-alkanes and abundant tetracyclic diterpanes, C20–C21 tricyclic terpanes and perylene are indicators of higher plant organic matter input. Moreover, the bimodal distribution of C27 > C28 < C29 regular steranes and abundant methyltriaromatic steroids also support a contribution of microalgae as well as higher plants organic matter. The similar molecular composition and thermal maturity parameters indicate that the reservoir and veined solid bitumens were altered from a common paleo-petroleum, which originated from peak oil window matured source rocks.All solid bitumens from the BPR are characterized by relatively low bitumen reflectance values (Rb% < 0.7), suggesting that they were generated from low temperature processes rather than oil thermal cracking. Comparatively, the Rb% values for veined bitumens are higher than reservoir bitumens, indicating that the veined bitumens occurred earlier and experienced higher thermal conditions.  相似文献   

19.
Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C14-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K2qn1) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST.  相似文献   

20.
辽宁金羊盆地羊D1井油砂地球化学特征及意义   总被引：2，自引：1，他引：1  
在中国地质调查局沈阳地质调查中心实施的"羊D1"井的中侏罗统髫髻山组火山岩中见多处油气显示,取得了油气新发现。对该井已发现的2件油砂样品中的原油采用气相色谱-质谱技术(GC-MS)进行了分析测试,结果显示,2个油砂样品的地球化学特征一致,表现为链烷烃呈现出单峰态的分布,主峰碳数分别为C_(21)和C_(22),无明显奇碳数优势,姥植比值低;萜类化合物表现为,三环萜烷以C_(23)为主峰呈正态分布,C_(24)四环萜烷与C_(26)三环萜烷丰度相当,伽马蜡烷含量较高;甾类化合物表现为规则甾烷相对含量关系为C_(27)C_(29)C_(28),以C_(27)甾烷占优势的不对称"V"形分布。这些指标总体指示,原油为成熟油,对应烃源岩沉积于偏还原性的湖相环境,母质来源主要为藻类等低等水生生物,陆源高等植物也具有一定贡献。通过和周边的北票组烃源岩进行油岩对比研究发现,油砂样品中的原油可能来自于盆地内下伏的下侏罗统北票组烃源岩的贡献。研究结果说明,北票组在金羊盆地分布广泛,其烃源岩可能具有较好的生油潜力,金羊盆地是一个具有勘探潜力的含油气盆地。  相似文献   

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