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1.
This paper presents isotopic, bulk geochemical and biomarker data measured on organic matter accumulated in a narrow extensional basin developed at the oceanward margin of the huge Triassic carbonate platform in the Alps–Appenines domain. The integration of isotope signatures, organic petrographical and biomarker evidence together with the composition of kerogen pyrolysates suggests immature organic matter predominantly of algal origin with a minor, but not negligible, higher plant derived and moderate bacterial contribution for the entire sequence. The mineral sources are dominated by platform-derived subtidal Dachstein limestone with a minor palaeosol input and a moderate contribution of autochtonous quartz. Nevertheless, parallel variations observed in the mineral content, as well as in the amount and the quality of the organic matter reflect variations in the palaeoenvironment. The increased humidity, existing in the period of the accumulation of the upper section of the sequence, led to the restriction of dolomitization. A slightly greater higher plant derived contribution, in this section, is evidenced by the composition of bitumen and the results on GC and GC/MS analyses on the non-aromatic hydrocarbon fraction of bitumen. Moreover, the climate-induced weathering enchanced the primary productivity and resulted in a pronounced increase in the TOC content. The average estimated value of the planktonic productivity is about three times higher for the calcite-rich sequence than the dolomite-rich one, being 44.2 and 15.3 tCorg/m2/Ma, respectively. The low to moderate planktonic productivity shows that anoxic conditions, observed for the entire succession, are a consequence of the stagnant water stratification rather than high planktonic productivity. Depth trends in the data measured on kerogens (HI, OI, δ13Corg values, composition of pyrolysate) together with the δ18O excursions and Δδ13C values appear to be controlled by sea-level fluctuations. Consistent with the high abundance of alkyltiophenes in kerogen pyrolysates, the high Sorg/C ratios (ranging between 0.05 and 0.10) suggest the importance of natural sulfurization in the formation of the sulfur-rich type-II-S kerogen occurring in all of the samples.  相似文献   

2.
In this study, progradation and the subsequent retrogradation of a late Paleocene isolated carbonate platform (Galala Mountains, Eastern Desert, Egypt) is demonstrated by variations of distinct facies associations from the platform margin in the north to the hemipelagic basin in the south. A combination of a sea-level drop and tectonic uplift at around 59 Ma (calcareous nannofossil biozone NP5) favored the initiation of the carbonate platform. From this time onwards, the facies distribution along the platform–basin transect can be subdivided into five facies belts comprising nine different facies associations. Their internal relationships and specific depositional settings are strongly coupled with the Maastrichtian–Paleocene seafloor topography, which resulted from local tectonic movements. Patch reefs and reef debris were deposited at the platform margin and the horizontally bedded limestones on the upper slope. Slumps and debris flows were stored on the lower slope. In the subhorizontal toe-of-slope facies belt, mass-flow deposits pass into calciturbidites. Further southwards in the basin, only hemipelagic marls were deposited. Between 59 and 56.2 Ma (NP5–NP8), the overall carbonate platform system prograded in several pulses. Distinct changes in facies associations from 56.2 to 55.5 Ma (NP9) resulted from rotational block movements. They led to increased subsidence at the platform margin and a coeval uplift in the toe-of-slope areas. This resulted in the retrogradation of the carbonate platform. Furthermore the patch-reef and reef-debris facies associations were substituted by the larger foraminifera shoal association. The retrogradation is also documented by a significant decrease in slump and debris-flow deposits on the slope and calciturbidites at the toe of slope.  相似文献   

3.
Palynological analysis were done on 12 rock samples for Ratawi Formation from Rumailah well 131 and eight samples for the same formation from Zubair well 47, South Iraq, to extract sedimentary organic matters. Microscopic examination led to diagnose large numbers of spores, pollen, dinoflagellates (proximat, cavate, and chorate), foraminifera, melanogen, hylogen, and amorphogen. Three palynological facies were determined on the bases of percentages of sedimentary organic matter and palynomorphs from two sections. Analysis of these palynofacies clarified Ratawi Formation as deposited from environments ranging from delta and lagoon (suboxic–dysoxic) to shelf facies (anoxic near the shore–suboxic) with the presence of some layers deposited from semideep open marine environment (bathyal). Organic geochemical analysis of total organic carbon and Rock Eval pyrolysis were done to determine quantity, quality, and degree of maturation of the kerogen. Poor to medium proportion of total organic carbon of kerogen types II and III within a catagenesis stage are recorded in these rocks, and hence, poor hydrocarbon generation could be suggested for these strata.  相似文献   

4.
Petrographic studies indicate that lateral variations in the decomposition levels of peat are associated with the predominantly occurring peat macerals. Source Rock Analyzer (SRA) results indicate lateral variation in peat organic matter types from type II to III and back again to type II, occurring laterally within the top 0-m to 0.5-m layer at the basin margin to the midsection and further towards the near-center areas of the peat dome. This variation is most likely caused by a combination of factors: (a) Horizontal zonation and lateral variation of the dominant species of plant assemblages (b) Fibric (marginal) peats and hemic to sapric peats associated with type II organic matter (kerogen). Sample organic matter (coal-equivalent kerogen) typing indicates that the relative abundance of phytoclasts and palynomorphs generally supports the organic matter classification obtained by the SRA method. Lateral variations in the peat organic matter types may support the lateral vegetation variation concept. The classification of peat organic matter types (interpreted from visual analyses of palynological slides) occurring from the basin periphery to the mid-section and further towards the basin center yields organic matter of type II to type III and mixed types II to III (coal kerogen-equivalent), respectively.  相似文献   

5.
The Avengco Basin is located in the western part of the Tibetan Plateau and is similar to the Nima Basin in the central part of the plateau and the Lunpola Basin in the eastern part in terms of sedimentary characteristics and tectonic settings, which are well known to provide a good source rock potential. However, the organic geochemical characteristics of the Paleocene-Eocene potential source rocks in the Avengco Basin have been under debate. Thirty-four marl and mudstone outcrop samples of the Niubao Formation in the Avengco Basin were collected and subjected to the following analyses: total organic carbon (TOC), Rock–Eval pyrolysis, stable carbon isotopes of kerogen, gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). Here, we present the results indicating the organic matter of the upper Niubao Formation is mainly composed of Type II kerogen with a mixed source, which is dominated by algae. However, the lower Niubao Formation has the less oil-prone Type II–III kerogen, and the sources of the organic matter are mainly terrestrial plants with less plankton. In addition, the samples are thermally immature to marginally mature. The Niubao Formation was deposited in an anoxic–oxic environment which was brackish with an imperceptible stratified water column. The upper Niubao Formation has a medium to good hydrocarbon-generating potential. However, the lower Niubao Formation has a zero to poor hydrocarbon-generating potential.  相似文献   

6.
Carboniferous black mudrocks with known petroleum potential occur throughout Northern Germany. However, despite numerous boreholes exploring for conventional hydrocarbons, the potential for shale gas resources remains uncertain. Therefore, an integrated investigation was conducted to elucidate the shale gas potential for three different Carboniferous facies incorporating baseline parameters from sedimentological and organic-geochemical analyses. Tournaisian–Namurian fine-grained rocks of the Culm-facies, with Type II + III kerogen were deposited in the basin center. TOC contents of up to 7 % occur in the Lower Alum Shale (3.6 % VRr) and up to 6 % in the Upper Alum Shale (4.4 % VRr). Bands of organic-rich black shales, reflecting sea-level variations controlled by global eustatic cycles, occur within the Tournaisian–Visean “Kohlenkalk”-facies north of the Rhenish Slate Mountains and in the Rügen island area. In both areas the organic matter is characterized by a kerogen Type II + III with TOC contents of up to 7 % and maturities of up to 4.2 and 1.8 % VRr, respectively. Black hemipelagites intercalated with coarser-grained silt- and sandstones occur in the Synorogenic Flysch Formation of the Namurian A along the southern basin margin. TOC contents vary from 0.5 to 2.0 % with Type III kerogen dominated organic matter and maturities of up to 2.5 % VRr. The baseline parameters presented in this paper indicate a shale gas potential for the sediments of the Culm-facies on the southern basin margin and of the “Kohlenkalk”-facies in the Rügen area.  相似文献   

7.
The Krishna–Godavari (KG) basin, a passive margin Late Carboniferous to Holocene basin along the rifted east coast of India, includes the deltaic and inter-deltaic regions of the Krishna and Godavari rivers onshore and extends into the offshore. It is one of India’s premier hydrocarbon-bearing basins. In an attempt to better understand the thermal history of the basin, apatite fission track (AFT) data has been obtained from six exploration wells (five onshore and one offshore). AFT thermal history models as well as other thermal indicators e.g. vitrinite reflectance (VR), Rock–Eval Tmax data reveal that the host rocks are currently at their maximum post-depositional temperatures and that any possible heating related to small-scale tectonism or rifting episodes in the basin bears little significance on the maturation of the sediments. In the case of one borehole (M-1) however, the organic maturity data reveals a period of Oligocene cooling across an unconformity when ∼1000 m of section was eroded due to falling sea-level. This information offers the potential for improved basin modeling of the KG basin.  相似文献   

8.
柳广弟  高岗 《沉积学报》1999,17(3):482-485
通过碳酸盐岩地层中的纯碳酸盐岩、缝合线缝隙物和泥质条带有机质含量和残留烃量分析表明,碳酸盐岩地层中不同的组成部分之间有机质的分布是不均匀的,其中缝合线缝隙物和泥质条带具有高的TOC值和较低的S1/ TOC 值,而纯碳酸盐岩TOC值则很低,但其S1/ TOC 却很高。这说明缝合线缝隙物和泥质条带发生了明显的排烃作用,而纯碳酸盐岩排烃作用不明显。因此可以认为高有机质丰度的缝合线缝隙物和泥质条带是碳酸盐岩地层烃源的主要贡献者。压溶作用对碳酸盐岩的排烃起重要作用。  相似文献   

9.
The ratio of the abundance of the C19:1 isoprenoids 1-pristene and 2-pristene to the abundance of (nC17:1 + nC17:0) is significantly lower in pyrolysates of kerogens from highly anoxic depositional environments than in pyrolysates of kerogen if similar types and levels of catagenesis from more oxic organic facies. 13C-NMR analysis shows that the occurrence of lower relative concentrations of isoprenoid precursors also correlates with the occurrence of low proportions of oxygen-bonded carbon and high proportion of aliphatic carbon in kerogens. The ratio of 1-pristene to (n-C17:1 + nC17:0) can be correlated laterally and statigraphically within a basin. There is no clearly discernible dependence of relative isoprenoid concentration of kerogen type for oil-generative kerogens, although immature lignites have high 1-pristene/(nC17:1 + nC17:0) ratios.The 1-pristene/(nC17:1 + nC17:0) ratios in kerogens pyrolysates from the same organic facies decrease logarithmically with increasing catagenesis and can be correlated directly with measured vitrinite reflectance values. Geologic and experimental data imply that 1-pristene precursors are lost from kerogen more rapidly than the precursors of the C18 isoprenoid.The lower relative isoprenoid concentrations observed in anoxically deposited kerogens appear to be the result of the enhanced preservation of normal alkyl groups and the enhanced formation of free isophrenoids early in the sequence of kerogen alteration. These results are significant to the use of isoprenoids as geochemical marker oils, bitumens, and kerogens and to the determination of the structure and diagenesis of isoprenoid precursors.  相似文献   

10.
鄂尔多斯盆地下奥陶统碳酸盐岩有机相类型及生烃潜力   总被引：26，自引：0，他引：26  
夏新宇  张文正 《沉积学报》1999,17(4):638-643
对鄂尔多斯盆地下奥陶统马家沟组碳酸盐岩的各种沉积环境的有机相特征进行了研究,结果表明平均有机碳丰度最高的是陆缘斜坡相碳酸盐岩(0.26%),其次是膏盐湖(0.22%)、膏云坪(0.21%),而开阔海、云坪和滩等环境的碳酸盐岩有机碳平均含量较低(<0.20%);碳酸盐岩干酪根样品多数为富氧、贫氢,显示其有机质类型较差;岩石地球化学特征和生物化石特征反映出陆缘斜坡处于相对还原的环境,而其他沉积环境则为氧化环境。鄂尔多斯盆地下奥陶统的大部分碳酸盐岩处于生烃潜力较差的C～D相。从有机质数量、有机相类型来判断,鄂尔多斯盆地下奥陶统碳酸盐岩不是好烃源岩,难以形成具有一定规模的气田。  相似文献   

11.
The international interest in shale oil has recently provoked special attention to the Russian unconventional oil-source formations, including the Bazhenov Formation of West Siberia, domanik deposits in the Volga–Ural region, and the lower Maikop Group of the Cis-Caucasus. High contents of para-autochthonous soluble organic matter (bitumen) in clayey–carbonate, clayey–siliceous, carbonate–clayey–siliceous rocks with low filtration–capacity properties results in significant uncertainties in the identification of the generation potential of organic matter (OM). Examination of a large database on the OM of the Bazhenov Formation allowed us to propose an optimum complex technique for study of the source rock potential and assessment of the amount of produced hydrocarbons in the kerogen-rich sediments. The investigations include a combination of Rock Eval pyrolysis prior to and after extraction with different solvents, the comparison of bituminological and pyrolytic characteristics, and the determination of the group composition of soluble organic matter, as well as chromatography and chromato-mass spectrometry.  相似文献   

12.
为了探讨南海碳酸盐台地的发育过程及控制因素, 采用有机分子化合物指标方法对其进行了研究.有机分子化合物指标BIT(branched isoprenoid tetraether)是沉积物中源自陆源的细菌膜脂支链甘油双烷基链甘油四醚(branched glycerol dialkyl glycerol tetraethers,简称bGDGTs)与主要来自海洋泉古菌中的类异戊二烯GDGTs(isoprenoid GDGTs,简称iGDGTs)的含量之比,在古环境研究中,用来区分沉积物有机质的来源、判断沉积环境.通过对西科1井的数据研究发现,西科1井BIT指数随深度呈现三段式规律性变化,从下到上呈现高-低-高的变化,反映了中中新世以来南海海平面变化及碳酸盐台地生长发育的过程:在中中新世晚期,受全球及区域海平面变化下降影响,西沙地区碳酸盐台地形成礁-滩交互的沉积地层,由于大气淡水的影响,造成BIT指数呈现高值;到晚中新世至上新世,全球及区域海平面出现持续上升,有利于西沙碳酸盐台地的生长发育,使该井沉积环境以礁内泻湖相为主,造成BIT指数呈现低值;在第四纪冰期,全球及区域海平面出现总体下降趋势,西沙碳酸盐台地又频繁暴露于地表,造成BIT指数又呈现高值.研究表明,西沙地区碳酸盐台地受区域相对海平面变化影响更大,说明南海海平面变化既受全球海平面变化的影响,也受南海区域构造沉降的控制.   相似文献   

13.
胡建中  承金  潘永胜 《现代地质》2001,15(3):261-265
内蒙古固阳渣尔泰山群增隆昌组晚期沉积环境演化为碳酸盐岩台地。重点研究了台前斜坡碳酸盐角砾岩的岩性、岩相和相序特征 ,识别出重力滑动、浊流和风暴重力流成因的角砾岩 ,探讨了不同成因的角砾岩与海平面变化的响应关系。研究表明 ,角砾岩主要形成于海平面的上升速率减慢或最大静止期 ,此时台地碳酸盐岩产率过剩 ,大量的碳酸盐岩由地震、重力、风暴流带入斜坡和坡底 ,形成异地角砾岩。  相似文献   

14.
The sources and enrichment of organic matter in a sediment core in the first member of the Xiagou Formation (K1g1) from the Chang 2-2 borehole of the Jiuquan Basin, NW China, have been examined using Rock–Eval, maceral, carbon isotopes and biomarker data. This data indicates that highly variable organic matter sources and preservation conditions in response to climate change. TOC content, HI, and δ13C value were strongly correlated with the abundance of gammacerane, woody organic matter content, steranes/hopanes ratio, and C29 sterane content. This correlation demonstrates the importance that the control of the salinity of the depositional environment and organic matter sources can have upon the enrichment, type, and carbon isotopic composition of organic matter. In the Jiuquan Basin’s relatively high temperature and arid climate, high salinity lakes with high primary productivity of algae, planktons, and bacteria, and good organic matter preservation conditions (anoxic bottom water) resulted in the enrichment of isotopically-light algae-bacterial organic matter. In the Jiuquan Basin’s regions with a relatively low temperature and wet climate, fresh lakes with low primary productivity of algae, planktons, and bacteria received significant terrigenous high plants input, resulting in the deposition of a low abundance of isotopically heavier terrestrial organic matter.  相似文献   

15.
沉积有机质中稳定碳同位素逆转现象初探   总被引：7，自引：3，他引：7  
本文研究了沉积有机质的可溶部分（抽提物）和不溶部分（干酪根）及抽提物的族组分（饱和烃、芳烃、非烃、沥青质）的碳同位素组成特征。通过其δ13C的分布为:干酪根>抽提物;沥青质 >非烃 >芳烃 >饱和烃。研究表明由于生源物质的不同,沉积环境的差异可构沉积有机质碳同位素组成异常。如非烃 >沥青质 >芳烃 >非烃、本文称为沉积有机质碳同位素局部逆转。当沉积有机质可溶部分>干酪根时,称之为总体逆转。湖沼相或河间湖相高等植物来源常为正常组或型;经细菌强烈改造生源以高等植物为主有低等生物为类脂组分加入常形成局部逆转的碳同位素组成。总体逆转则常现于有机质演化程度很高的海相沉积岩中。  相似文献   

16.
Organic-rich (18.2%) Monterey Formation diatomite from California was studied. The organic matter consist of 94% bitumen and 6% kerogen. Biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter. While 17 alpha(H), 18 alpha(H), 21 alpha(H)-28,30-bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes, it was not detected in the pyrolysates of the kerogen. A C40-isoprenoid with "head to head" linkage, however, was present in pyrolysates of both kerogen and asphaltenes, but not in the bitumen from the diatomite. The maturation level of the bitumen, based on the extent of isomerization of steranes and hopanes, was that of a mature oil, whereas the pyrolysate from the kerogen showed a considerably lower maturation level. These relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock. We consider the possibility, however, that some of the 28,30-bisnorhopane-rich Monterey Formation oils have not been generated through thermal degradation of kerogen, but have been expelled from the source rock at an early stage of diagenesis.  相似文献   

17.
The Bowland Basin (northern England) contains a series of carbonates and terrigenous mudstones deposited during the Ivorian to early Brigantian. Two regional depositional environments are indicated by facies and facies associations. Wackestone/packstone and calcarenite facies indicate deposition in a carbonate ramp environment, while lime mudstone/wackestone, calcarenite and limestone breccia/conglomerate facies, often extensively slumped, represent a carbonate slope environment. Stratigraphic relations suggest that the depositional environment evolved from a ramp into a slope through the Dinantian. Two main sediment sources are indicated by the sequence; an extra-basinal terrigenous mud source and a supply of carbonate from the margins of the basin. Deposition from suspension and from sediment gravity flows, in situ production and remobilization of sediment during sedimentary sliding were important processes operating within the basin. Periods of enhanced tectonic activity in the late Chadian to early Arundian and late Asbian to early Brigantian are indicated by basin-wide horizons of sedimentary slide and mass flow deposits. Both intervals were marked by a decline in carbonate production resulting from inundation and uplift/emergence. The first of these intervals separates deposition on a seafloor with gentle topography (carbonate ramp) from a situation where major lateral thickness and facies variations were present and deposition took place in a carbonate slope environment. The second interval marks the end of major carbonate deposition within the Bowland Basin and the onset of regional terrigenous sedimentation.  相似文献   

18.
四川盆地龙潭组烃源岩R°值主要变化在2.0％～3.0％范围,干酪根H/C原子比值多数集中在0.3～0.5之间,有机质热演化达到过成熟阶段.它们的各类饱和烃生物标志物组成和分布大都发生了异常变化,限制了其地球化学应用.其芳烃组分和干酪根碳同位素及S、N元素组成还包含着标志有机质生源及沉积环境的信息.川东南地区近海湖沼相含...  相似文献   

19.
A stepped combustion technique, incremental heating in oxygen, has been used to study the carbon isotopic composition of carbonaceous sediments. This technique can afford data on the organic matter of the sediment and can give information on the structure, namely the variations in the isotopic composition of different portions, of the kerogen. Green River shale has been used as a model material and results indicate that it contains two distinct carbonaceous components, a carbonate and kerogen. Isotopic compositions for the kerogen measured by stepped combustion closely match those obtained by normal methods following preconcentration of the kerogen by mineral removal and solvent extraction.The variation in isotopic composition with combustion temperature has been used to investigate relationships with maturity and to look at its use as a possible correlation tool.  相似文献   

20.
The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South China, documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata, exquisitely preserved fossils have been discovered： the Weng＇an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng＇an section of a carbonate platform （shelf of the Yangtze Platform, Guizhou Province） from the Songtao section and Nanming section of a transition belt （slope of the Yangtze Platform, Guizhou Province） and from the Yanwutan section （basin area of the Yangtze Platform, Hunan Province）. Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon （mean δ^13Corg = -35.0‰） from the uppermost Nantuo Formation are followed by an overall increase in δ^13C up-section. Carbon isotope values vary between -9.9‰ and 3.6‰ for carbonate and between -35.6‰ and -21.5‰ for organic carbon, respectively. Heavier δ^13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity （such as the Weng＇an biota）. The δ^13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin, reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.  相似文献   

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