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1.
In order to confirm the tentative structure of a dithiane sulfide with a bicyclic squalene hydrocarbon skeleton representing the predominant alkyl sulfide in Shell Beach samples from the Monterey Formation (Miocene, CA) and also occurring in various immature sulphur-rich sediments [Schouten, S., Sinninghe Damsté, J.S., de Leeuw, J.W., 1995. A novel triterpenoid carbon skeleton in immature sulphur-rich sediments. Geochimica et Cosmochimica Acta 59, 953–958], synthesis of a reference compound bearing two thiochromane moieties has been carried out. The product was obtained as a diastereomeric mixture appearing in the form of five peaks (partly) resolved in gas chromatography (GC). This is in sharp contrast with the geochemical compound, which appears as a single broad peak in GC. Co-elution experiments showed that none of the peaks from the synthetic mixture coelute in GC with that of the geochemical sulfide. Furthermore, the different synthetic isomers have identical mass spectra, which are clearly distinct from that of the naturally-occurring compound. The results unambiguously indicate that the natural compound is not the dithiane triterpenoid originally envisaged. Instead, we propose that the compound has a structure of a bicyclic squalene derivative bearing two “S-spiro”-type moieties as is the case for other sulfides related to regular polycyclic polyprenoids and hopanoids in Monterey sediments.  相似文献   

2.
The concentrations of Br and I in marine sediments have been used to categorize the sedimentary environments of different coastal regions of the world with respect to organic matter contents. The present study uses the concentrations of Br, I and P2O5 of different marine settings as a new proxy to interpret the depositional environments. A total of 150 coastal lagoon sediment samples (suspended sediments, surface sediments and sediment cores) were analyzed for Br, I and P2O5 concentrations by X-ray fluorescence spectrometry. They were compared with the Br, I and P2O5 concentrations of the 2004 Indian Ocean tsunami sediments. Sediments from various sources are separately clustered in I–Br plot and a trivial negative correlation is found for the whole plot. A similar correlation pattern exists in the I–P2O5 diagram. This correlation is explained by the distribution of marine plants (higher and lower) in different sedimentary environments of the coastal profile. Therefore, the concentration of I and its relation to P2O5 can be used as a tool to identify sediment depositional environments in marine settings.  相似文献   

3.
Soils and recent marine sediments contain a complex polycyclic aromatic hydrocarbon assemblage. The many series of alkylhomologs have a similar molecular weight distribution, and it varies little over a wide range of depositional environments. It is suggested that these hydrocarbons are formed in natural fires, are dispersed and mixed by air transport and eventually deposited into surface sediments. The analytical, geochemical and environmental implications of these findings are discussed.  相似文献   

4.
Due to the apparent rhythmic characteristics of the stratigraphically complex unit formed of deltaic and mostly lacustrine deposits in Qianjiang depression (Jianghan basin), we used the seismic pattern proxies inside a seismic sequence, by analyzing the character of reflections (amplitude, continuity, and configuration) to detect the different seismic facies and to predict their depositional environmental settings. The depression fills are characterized by a distinct upward change in seismic facies; beginning with a fan facies in the bottom, followed by free facies occurring where thick salt sediments were presented, then convergent base-lapping facies, succeeded by chaotic facies and overlain by parallel to sub-parallel facies. The convergent base-lapping facies is the most common and the parallel and draping facies is restricted to slope areas shallower than 1000 m in water depth. Three depositional environments that range from fluvial, delta, to marine (lake) are predicted too. This paper lays the foundation for the development of a seismic sequence stratigraphic framework, and contributing to better understanding of the potential evaluation of hydrocarbon occurrence in the Eastern center of China.  相似文献   

5.
The Gulf of Suez is characterized by the presence of many hydrocarbon-bearing fields including reservoirs ranging in age from the Palaeozoic to the Tertiary. East Morgan oil field is one of the promising oil fields which are located in the southern part of the Gulf of Suez and tapping hydrocarbon deposits and potentials of the Miocene age. The purpose of this work is to evaluate the Miocene sediments of the Asl and Hawara Formations in East Morgan oil field (western sub-basin) through carrying out an integrated petrophysical, seismic structural and sequence stratigraphy study. Quantitative well logging analyses are carried out over Asl and Hawara Formations to throw light over their hydrocarbon potentiality. Good oil saturation is exhibited by the sand sections of Asl Formation, and fair to good are assigned for those of Hawara Formation in the Belayim dip province. On the other hand, a little hydrocarbon saturation is represented by both formations to the south of the study area in the Morgan accommodation zone (MAZ). The estimated petrophysical parameters of Asl reservoir throughout the study area range between 4 % and 10 % for effective porosity, 18 % and 89 % for shale volume and 2 % and 48 % for hydrocarbon saturation. Meanwhile, the ranges of 1–8 %, 20–98 % and 2–32 % are given for Hawara Formation for effective porosity, shale volume and hydrocarbon saturation, respectively. The lateral distribution maps show that the central and the western parts of the MAZ attain the best petrophysical parameters and hydrocarbon potentiality. Seismic facies analysis, structural framework and depositional history of the study area were studied through interpreting the seismic reflection data of 27 seismic profiles. A number of geo-seismic cross sections are constructed and interpreted to investigate the structural setting of the study area and clarify the main structural elements that affect the hydrocarbon bearing reservoirs. A group of simple NW–SE step-like normal faults, parallel to the Clysmic trend, is found cutting through the reservoir rocks at the bottom layers of the section (Rudeis Formation) and extending upwards to overlying layers (Zeit Formation). Some graben- and horst-shaped structures are found and usually bounded by two sets of oppositely dipping normal step-like cross faults. The seismic facies and sequence analysis revealed that the Miocene rocks are subdivided into two major third-order depositional sequences (S1 and S2), separated by two major depositional sequence boundaries (DSB1 and DSB2). The first sequence (S1, Lower–Middle Miocene rocks) is of prime interest, as it encounters the main hydrocarbon reservoirs in the study area (Asl and Hawara Formations that are equivalent to Rudeis Formation). The seismic facies of this sequence are characterized by low to moderate amplitude, discontinuous horizons and bounded by the depositional sequence boundary (DSB1) at the top. The reflection geometry at the cycle boundaries is considered as erosional truncation, toplaps and even concordant along the upper boundary of the cycle. The external form of these sediments is considered as sheet-like and wedge-shaped units. The entrapment of hydrocarbons seems to be of a combined effect of the stratigraphic and structural elements. It appears clear that both of the step-like structural fault system and the lateral variation of facies are the key parameters that control the accumulation of hydrocarbon in this area and in East Morgan field as a whole.  相似文献   

6.
The Chaudian sediments composing the Pekla and Tuzla sections are characterized by a variable lithology and transgressive structure. Their basal part is mainly composed of coarse terrigenous varieties with diverse structures indicating different depositional settings in the accumulation zone (shelf and upper part of the submarine slope). These sediments are characterized by strong lithification probably in subaerial environments under the influence of atmospheric precipitation. The Chaudian basin was a large brackish-water depression populated by malacofauna of the Caspian type.  相似文献   

7.
The geochemistry of sediments is primarily controlled by their provenances, and different tectonic settings have distinctive provenance characteristics and sedimentary processes. So, it is possible to discriminate provenances, depositional environments and tectonic settings in the development of a sedimentary basin with the geochemistry of the clastic rocks. The analytical results of the present paper demonstrate that sediments in the Songliao prototype basin are enriched in silica (SiO2=66.48-80.51 %), and their ΣREE are 30-130 dmes of that of chondrite with remarkable Eu anomalies. In discriminating diagrams of Eu/Eu vs eeeeeREE and (La/Yb)N vs ΣREE, most samples locate above the line Eu/ Eu=l, on the right of the line Eu/Eu/ΣREE=1 and under the line La/Yb)N/eeeeeREE=1/8, which indicates that the depositional environment of sediments in the basin was oxidizing. In addition, variations of MgO, TiO2, A12O3, FeO+Fe2O3, Na2O and CaO vs SiO2 reflect a tendency of increasing mineral maturity of sediments  相似文献   

8.
This study explored the relationship between high-Arctic fiord depositional environments and the natural thermoluminescence (TL) signal of sediments. The energy and duration of light exposure during transportation and deposition controls the TL level of silicate mineral grains in the sediment. The TL signal of sediments rapidly decreases within c. 0·5 km of a glacier sediment source. The highest TL levels are from tills and ice-proximal glacial-marine sediments, which receive little or no light exposure during transportation and deposition. Intermediate and consistent TL levels are recorded for ice-distal glacialmarine muds, c. 0·5–5·0 km from the glacier front, reflecting slower sedimentation rates. The lowest TL levels are for littoral and sublittoral sediments which receive extended light exposure with shoaling. The granulometry of the sediments is fairly homogeneous and is not diagnostic of a sedimentary environment with most samples dominated by silt and clay; littoral and ice-proximal samples exhibit peak abundances in sand. These results suggest that the relative TL signal of sediments is sensitive to a depositional environment, particularly for environments proximal (within 0·5 km) to a glacier terminus and in shallow water, less than 15 m deep.  相似文献   

9.
Arnold, L. J. & Roberts, R. G. 2011: Paper I – Optically stimulated luminescence (OSL) dating of perennially frozen deposits in north?central Siberia: OSL characteristics of quartz grains and methodological considerations regarding their suitability for dating. Boreas, Vol. 40, pp. 389–416. 10.1111/j.1502‐3885.2011.00209.x. ISSN 0300?9483. Optically stimulated luminescence (OSL) dating of coarse‐grained quartz is increasingly being used as the main chronological tool in late Quaternary palaeoenvironmental reconstructions of Siberia. However, relatively little information has been published on the suitability of OSL dating for the various types of perennially frozen sediments found in this region. Here we provide a systematic examination of the quartz luminescence characteristics of 21 perennially frozen samples from the Taimyr Peninsula and adjacent coastal lowlands of north‐central Siberia, and discuss their implications for the reliability of single‐grain and multi‐grain OSL chronologies in such contexts. The results of this study suggest that the quartz luminescence characteristics of these samples are, in principle, favourable for OSL dating but, in practice, require that a series of validation checks are made of the chosen experimental conditions. If these tests are satisfied, then reliable OSL chronologies should be obtained for sedimentary deposits in this region. Importantly, however, the single‐grain and multi‐grain aliquot equivalent dose (De) distribution characteristics for our samples reveal that there are advantages in targeting certain types of depositional settings for OSL dating studies of Siberian sediments. We also show that samples from the same depositional settings, and even from the same sites, do not necessarily display similar De distribution characteristics. The latter complication favours the use of single‐grain analysis to unravel the bleaching and burial histories of young (mid‐ to late Holocene) sediments in these Arctic environments.  相似文献   

10.
Weathering intensity changes due to climatic variability across tectonically stable portions of continental crust can generate a thick and extensive weathered cover, resulting in regolith-dominated terrains (RDTs). Mineral exploration in RDTs is challenging because of the lack of bedrock outcrop, and the difficulty of linking surface regolith geochemistry to the geology at depth. Complex weathering obscures the expression of the basement geochemistry in the regolith, and therefore the footprints of mineral systems are difficult to detect. The southeast of the Yilgarn Craton and the Albany–Fraser Orogen (AFO) in the south of Western Australia is an RDT that extends along the coastline and the Eucla basin.This study proposes a landscape evolution model of the AFO, driven by transgression–regression sea-level changes that resulted in the formation of numerous islands and development of estuarine zones. This model contrasts with the river system-dominated landscape evolution present in the Yilgarn Craton. This difference has significant implications for mineral exploration and geochemical interpretation of the regolith in this region.Weathering profiles developed “on inland” and “on island” are thicker and more mature than those developed in sea-inundated areas. Even if in the Yilgarn Craton local areas display reworking of weathering profiles and other complexities from Permian, non-marine Tertiary sediments and Quaternary fluvial and aeolian sediments, at a regional scale, if vertical geochemical mobility of elements has occurred, “on inland” and “on island” are more reliable for understanding geochemical anomaly-basement relationships, whereas the “marine inundated” areas require a more detailed investigation, because of the role of marine reworking of weathering profiles and possible mixture of sediments from different provenances.Landscape changes from the topographically high, dissected Yilgarn environment with thick saprolite development and uneven basement topography, to the nearly flat regions dominated by sand dunes and thin saprolite development at the coastline. These regions are the result of the erosional and depositional effects of successive sea-level transgression–regression cycles. Within this framework, the following four different regolith settings have been identified in a progressive change from Yilgarn Craton environments to the modern coastline: (1) Albany; (2) Kalgoorlie–Norseman; (3) Esperance; and (4) Neale.Mapping the palaeocoastlines, islands and estuarine zones, as well as the region of influence of marine limestones and sediments, can significantly improve the understanding of how surface geochemistry relates to the landscape, and how it links with the geology at depth, and therefore, how it may reflect the presence of mineral systems. Understanding the difference in the landscape evolution between the AFO and Yilgarn Craton is essential to properly calibrate mineral exploration protocols in both regions.  相似文献   

11.
Capillary gas chromatography-mass spectrometry (C-GC-MS) and Iatroscan thin layer chromatography-flame ionisation detection (TLC-FID) were used to study hydrocarbon distributions in a sediment core from Ace Lake, a saline, meromictic lake in the Vestfold Hills of Antarctica. Hydrocarbons were abundant in most core sections (up to 125/μg/g dry wt), particularly in near-surface samples, and the distributions were very complex. Major constituents were identified as phytane, 2,6,10,15,19-pentamethyleicosane, tetrahydrosqualene, a mixture of phytenes, cholesta-3,5-diene and fern-7-ene. Smaller amounts of sterenes and hopenes were also present. The predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present.Phytenes were abundant in all core sections, and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria. Phytadienes were minor constituents at all depths studied. An unusual feature of some distributions was the high concentrations of fern-7-ene which was the major hydrocarbon in the 20–25 cm core section. This alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments. A possible source might be from purple non-sulphur bacteria. High concentrations of straight-chain C29 and C34 alkenes were also found in these sediments but their origin has not been determined. Major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago. The present condition of permanent anoxic bottom waters probably developed only in the last 1000 years.  相似文献   

12.
大王北洼陷烃源岩有机地球化学特征   总被引：3，自引：0，他引：3  
根据烃源岩可溶抽提物的色谱和色谱- 质谱分析结果,对大王北洼陷沙四段、沙三段和沙一段烃源岩的饱和烃和芳烃生物标志化合物组合特征进行了对比研究,揭示了三套烃源岩在沉积环境和有机母源输入的不同特征,总结了应用生物标志化合物鉴别三套烃源岩的组合参数特征,为精细的油源对比奠定了基础。研究表明,沙四段烃源岩具有较低的Pr /Ph,4-甲基甾烷同类物中C28 4-甲基系列含量最低、较高的甲藻甾烷含量、较低的重排甾烷含量、异常的C35 升藿烷含量、高伽马蜡烷异常指数、含一定量的奥利烷和较高的硫芴系列化合物含量等特征,反映了沙四段烃源岩形成于高盐度含硫强还原沉积环境,低等水生生物为主,高等植物有明显贡献的混合母源特征。沙三段烃源岩具有较高的Pr /Ph,4-甲基甾烷同类物中C29 4-甲基系列含量最低、几乎不含甲藻甾烷、较高的重排甾烷含量、基本正常的升藿烷分布、低伽马蜡烷异常指数和较低的奥利烷含量等特征,反映了沙三段烃源岩形成于半咸水的一般还原环境,低等水生生物为主,有一定量高等植物有机输入的混合母源特征。沙一段烃源岩具有极低的Pr /Ph,4-甲基甾烷同类物中C28 4-甲基系列含量最低、较高的甲藻甾烷含量、很低的重排甾烷含量、异常的C33 升藿烷含量、高伽马蜡烷异常指数、极低的奥利烷含量和较高的脱羟基维生素E 含量等特征,反映了沙一段烃源岩形成于高盐度强还原沉积环境,低等水生生物占绝对优势的有机母源特征。对研究区烃源岩生物标志化合物成熟度参数随深度的变化进行了分析,结果表明在不同层系中成熟度参数的演化存在显著差异,沉积埋藏历史和沉积环境可能是导致这些差异的原因,为此在应用这些参数进行烃源岩乃至生成石油的成熟度评价时,应使用不同的标准。  相似文献   

13.
Analyses of the lipid constituents of three temperate lacustrine sediments (Rostherne Mere, Esthwaite Water and Grasmere, Great Britain) and three sub-tropical lagoonal/tidal flat sediments (U.S. Virgin Islands, Rockhampton, Qld., Australia and Port Moresby, Papua, New Guinea) indicate the presence of straight-chain components attributable to autochthonous and allochthonous sources. Despite broad similarities in carbon-number distributions, minor differences observed in the respective hydrocarbon and in the respective fatty-acid compositions of the various sediments reflect differences in the sedimentary environments. Lipid constituents obtained by organic solvent extraction following acid hydrolysis appear to include a larger bacterial contribution than that observed in the lipids extracted by solvent alone.  相似文献   

14.
In the Gargaf area, the stratigraphic architecture of the Late-Ordovician glacial drift results from successive glacial erosion events, with the location of the main glacial valleys partly controlled by inherited Panafrican structural trends, and by the existence of glacio-isostatically induced fault-related depocentres. Four laterally discontinuous, depositional units correspond to the filling of palaeovalleys. Each of the corresponding basal bounding surfaces was incised during a major ice front advance, reaching at least the northern Gargaf (>28°S). The bulk of the glacial record is made up of fluvial to shallow-marine sediments deposited in relatively distal glacial environments. Each unit, which recorded a glacial-interglacial climatic cycle, can be used for correlation throughout the Murzuq Basin and even at the scale of the North Gondwana platform. To cite this article: J.-F. Ghienne et al., C. R. Geoscience 335 (2003).  相似文献   

15.
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16.
Arnold, L. J., Roberts, R. G., MacPhee, R. D. E., Haile, J. S., Brock, F., Möller, P., Froese, D. G., Tikhonov, A. N., Chivas, A. R., Gilbert, M. T. P. & Willerslev, E. 2010: Paper II – Dirt, dates and DNA: OSL and radiocarbon chronologies of perennially frozen sediments in Siberia, and their implications for sedimentary ancient DNA studies. Boreas, Vol. 40, pp. 417–445. 10.1111/j.1502‐3885.2010.00181.x. ISSN 0300‐9483 The sedimentary ancient DNA (sedaDNA) technique offers a potentially invaluable means of investigating species evolution and extinction dynamics in high‐latitude environments. An implicit assumption of the sedaDNA approach is that the extracted DNA is autochthonous with the host deposit and that it has not been physically transported from older source deposits or reworked within the sedimentary profile by postdepositional mixing. In this paper we investigate whether these fundamental conditions are upheld at seven perennially frozen wetland sites across the Taimyr Peninsula and coastal lowlands of north‐central Siberia. Optically stimulated luminescence (OSL) and radiocarbon (14C) dating are used to constrain the ages of both the inorganic and organic fractions of perennially frozen deposits from which sedaDNA of extinct and extant species have been recovered. OSL and 14C age/depth profiles, as well as single‐grain equivalent dose (De) distribution characteristics, are used to assess the stratigraphic integrity of these sedaDNA sequences by (i) identifying the presence of primary or reworked organic and inorganic material, and (ii) examining the types of depositional and postdepositional processes that have affected specific sedimentary facies. The results of this study demonstrate that even though DNA preservation and stratigraphic integrity are commonly superior in perennially frozen settings, this does not, in itself, guarantee the suitability of the sedaDNA approach. The combined OSL and 14C chronologies reveal that certain perennially frozen sites may be poorly suited for sedaDNA analysis, and that careful site selection is paramount to ensuring the accuracy of any sedaDNA study – particularly for ‘latest appearance date’ estimates of extinct taxa.  相似文献   

17.
Besshi-type Cu deposits are strata-bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents. Although there are numerous Besshi-type deposits in the Sanbagawa metamorphic belt, Japan, their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints. We report Re-Os data for the Iimori deposit, one of the largest Besshi-type deposits in western Kii Peninsula, in order to examine the robustness of the Re-Os isotope system for dating sulfide minerals in the high-P/T metamorphic belt and to elucidate the primary depositional environment of the Iimori sulfide ores. An 11-point Re-Os isochron plot yields an age of 156.8 ± 3.6 Ma. As this Re-Os isochron age is significantly older than the timing of the Sanbagawa peak metamorphism (110-120 or ∼90 Ma) and a well-defined isochron was obtained, the Re-Os age determined here is most likely the primary depositional age. Despite high-grade metamorphism at up to 520 ± 25 °C and 8-9.5 kbar, the Re-Os isotope system of the Iimori sulfides was not disturbed. Hence, we consider that the whole-rock Re-Os closure temperature for the Iimori sulfide ores was probably higher than 500 °C. As the accretion age of the Sanbagawa metamorphic belt is considered to be 120-130 or 65-90 Ma on the basis of radiolarian and radiometric ages, we estimated the time from the Iimori sulfide deposition on the paleo-seafloor to its accretion at the convergent plate boundary to be greater than 25 Myr. Consequently, the depositional environment of the Iimori sulfide ores was not in the marginal sea, but was truly pelagic.  相似文献   

18.
Upper Callovian to Tithonian (late Jurassic) sediments represent an important hydrocarbon reservoir in the Kopet‐Dagh Basin, NE Iran. These deposits consist mainly of limestone, dolostone, and calcareous mudstone with subordinate siliciclastic interbeds. Detailed field surveys, lithofacies and facies analyses at three outcrop sections were used to investigate the depositional environments and sequence stratigraphy of the Middle to Upper Jurassic interval in the central and western areas of the basin. Vertical and lateral facies changes, sedimentary fabrics and structures, and geometry of carbonate bodies resulted in recognition of various carbonate facies related to tidal flats, back‐barrier lagoon, shelf‐margin/shelf‐margin reef, slope and deep‐marine facies belts. These facies were accompanied by interbedded beach and deep marine siliciclastic petrofacies. Field surveys, facies analysis, parasequences stacking patterns, discontinuity surfaces, and geometries coupled with relative depth variation, led to the recognition of six third‐order depositional sequences. The depositional history of the study areas can be divided into two main phases. These indicate platform evolution from a rimmed‐shelf to a carbonate ramp during the late Callovian–Oxfordian and Kimmeridgian–Tithonian intervals, respectively. Significant lateral and vertical facies and thickness changes, and results obtained from regional correlation of the depositional sequences, can be attributed to the combined effect of antecedent topography and differential subsidence related to local tectonics. Moreover, sea‐level changes must be regarded as a major factor during the late Callovian–Tithonian interval. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

19.
Modern sediments of Mono Lake show marked variation in lipid composition with depositional environment. Constituents derived from the drainage basin, characterized by high molecular weight alkane hydrocarbons (C25–C31), and the steroids β-sitosterol and brassicasterol, predominate in near-shore environments. In the deepest part of the lake, sediments exhibit a combination of externally-derived constituents, and lipids derived from the lake biota; the latter characterized by low molecular-weight alkanes and alkenes (C15–C17), phytane, and the steroids ergost-7-en-3β-ol and 24-ethylcholest-7-en-3-β-ol. Steranes, 4-methylsteranes, and the C18 and C19 isoprenoids appear to be forming in the intensely reducing bottom sediments at the present time.The compositions of samples from the Pleistocene succession of Mono Basin suggest that sample-to-sample variation within the same stratum is negligible so long as unweathered samples from the same depositional environment are compared. Sediments having equivalent lithologies may or may not have similar compositions, but sediments having similar fossil contents do show similar lipid compositions. Subaerial weathering of sediments causes a marked decrease in the amount of extractable organic material, as well as distinct changes in its hydrocarbon composition. Specifically, weathered sediments exhibit a decrease in relative content of low molecular weight hydrocarbons and a relative increase in nC22.Organic composition of sediments from the Pleistocene stratigraphie column cannot be correlated with depth of burial. Compositional changes with stratigraphie position are probably related to paleo-ecological factors such as population or productivity rather than depth of burial. Lithology and organic composition provide mutually-corroborating evidence regarding glacial advances in the adjacent Sierra Nevada Mountains. During glaciations, the lake sediments are rich in sandstones, and the organic composition shows a predominance of externally-derived debris, with no evidence for contributions from the lake biota.  相似文献   

20.
Four typical distribution patterns of pentacyclic triterpenoid hydrocarbons (types A-D) are distinguished in the low-mature source rocks from eastern China. Type A has a relatively high content of pentacyclic triterpenes. It exists in immature sediments and the distribution and abundance of triterpenes vary with the maturity of the sediments. An unknown C30 triterpene (UCT2) has also been detected in very shallow sediments. This compound is very unstable and disappears rapidly with the increase of depth. Type B is characterized by a relatively high amount of 17α(H), 21β(H)-30-homohopane. This kind of distribution pattern is common in coals and terrestrial sediments of low maturity. Type C has a relatively high content of diahopane and neohopane series. The analysis shows that this distribution pattern may have an indirect relationship with the input of higher plants despite its microbial source. There are C30-unconfirmed triterpane (UCT2) and a relatively high content of C35 hopane in type D. The dist  相似文献   

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