首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 97 毫秒
1.
Sulphur isotope compositions and S/C ratios of organic matter were analysed in detail by combustion-isotope ratio monitoring mass spectrometry (C-irmMS) in eastern Mediterranean sediments containing three sapropels of different ages and with different organic carbon contents (sapropel S1 in core UM26, formed from 5–9 ka ago with a maximum organic carbon content of 2.3 wt%; sapropel 967 from ODP Site 160-967C, with an age of 1.8 Ma and a maximum organic carbon content of 7.4 wt%; and sapropel 969 from ODP Site 160-969E, with an age of 2.9 Ma and a maximum organic carbon content of 23.5 wt%). Sulphur isotopic compositions (34S) of the organic matter ranged from -29.5 to +15.8 and the atomic S/C ratio was 0.005 to 0.038. The organic sulphur in the sediments is a mixture of sulphur derived from (1) incorporation of 34S-depleted inorganic reduced sulphur produced by dissimilatory microbial sulphate reduction; and (2) biosynthetic sulphur with an isotopic signature close to seawater sulphate. The calculated biosynthetic fraction of organic sulphur in non-sapropelic sediments ranges from 68–87%. The biosynthetic fraction of the organic sulphur of the sapropels (60–22%) decreases with increasing organic carbon content of the sapropels. We propose that uptake of reduced sulphur into organic matter predominantly took place within sapropels where pyrite formation was iron-limited and thus an excess of dissolved sulphide was present for certain periods of time. Simultaneously, sulphide escaped into the bottom water and into sediments below the sapropels where pyrite formation occurred.  相似文献   

2.
The Toolebuc Formation, which is a potentially important source of oil shale in the Eromanga Basin of NW Qld, exhibits a marked gamma‐ray response that has long beeen used as a stratigraphic marker. At Julia Creek, a large area of the Formation contains low‐grade oil shale that is accessible to mining. Detailed investigation, by gamma‐ray spectrometry and neutron activation analysis, of drill core samples from this deposit and from the type section of the Toolebuc Formation at Boulia (BMR Boulia 3A stratigraphic drill hole) show that the Toolebuc gamma‐ray anomaly in the northern Eromanga Basin is due to the presence of uranium. Analyses for organic carbon and phosphorus show that the uranium is associated primarily with organic matter in the oil shales and with phosphatic skeletal fish debris in the accompanying coquinites.

Drill core samples from Tibooburra, N.S.W. were also analysed (BMR Urisino‐1 stratigraphic drill hole) to investigate whether the gamma‐ray anomalies observed in the Bulloo Embayment on the southern margin of the Eromanga Basin (possibly correlative with the Toolebuc Formation) might also be indicative of oil shale. The results show that the much weaker anomaly at this locality is due principally to potassium and reflects the presence of an argillaceous siltstone within glauconitic sandstones.  相似文献   

3.
杨平  汪正江  谢渊  杜秋定  陈厚国  贺永忠 《地质通报》2012,31(11):1910-1921
为研究黔北地区下寒武统牛蹄塘组烃源岩母质来源和沉积环境,开展了生物标志化合物分析,结果表明：①正构烷烃OEP接近1.0,无明显奇偶优势,受轻微生物降解影响,正构烷烃多表现为双峰型(C18/C25),(nC21+nC22)/(nC28+nC29)值为0.54~1.01,显示重烃组分占绝对优势;Pr/Ph值范围在0.51~0.82之间,具有植烷优势。②烃源岩样品组成相对丰度五环三萜烷>三环萜烷>四环萜烷,三环萜烷中C21、C23、C24呈倒V字形分布,Ts/(Tm+Ts)为0.45~0.50。③C27规则甾烷/C29规则甾烷略小于1或者接近1,芳烃化合物DBT/P为0.05~0.09。根据这些特征并结合干酪根同位素及正构烷烃同位素组成和变化规律,认为该区域下寒武统牛蹄塘组烃源岩形成于浅海还原环境,且有机质主要来源于细菌、藻类等低等水生生物,有机质热演化程度较高。根据常量、微量元素指标并结合有机地化指标刻划出从灯影组到牛蹄塘组和明心寺组沉积时期的水体环境,将牛蹄塘组烃源岩的形成分为3个阶段,第一阶段为早寒武世初始快速海侵阶段,第二阶段为深水还原高有机质产力阶段,第三阶段为海水缓慢变浅高有机质产力阶段,而到了明心寺组沉积时期为浅水氧化非烃源岩阶段。  相似文献   

4.
山东临朐山旺地区中新世山旺组硅藻土极为发育。通过对该地区硅藻土纹层的研究,确定其分类和成因,为进一步确立年纹层的存在、利用其进行高分辨率测年、探讨高频古气候旋回奠定基础。山旺组硅藻土的单层纹层厚度一般为100μm左右。依据纹层的物质成分,单层纹层可分为硅藻纹层、有机纹层和粘土纹层三种类型。各类单层纹层组合成为明暗相间的层偶,层偶厚度一般为100～400μm,常常表现为浅色的硅藻纹层逐渐向深色的粘土纹层或有机质纹层渐变过渡。纹层层偶可分为:薄层硅藻纹层-有机质层偶,厚层藻纹层-有机质层偶,薄层粘土纹层-有机质层偶,厚层粘土纹层-有机质层偶和硅藻纹层-粘土纹层层偶。山旺组硅藻土中不同类型的单层纹层以及层偶的形成主要受控于当时湖盆内粘土物质的沉积速率、硅藻的繁盛程度和有机物质的沉积和保存条件。  相似文献   

5.
The study of the composition and depositional environments of sediments from the Mar’yanovo Formation (Upper Jurassic-Lower Cretaceous Bazhenov and Georgiev horizons) recovered by boreholes Vostok-1 and Vostok-3 in the southeastern part of the West Siberian Sea Basin revealed the following fact: in the latter hole located closer to the basin boundaries as compared with the former one, they are characterized by lower organic carbon and pyrite contents, indicating reduced salinity of the basin and higher oxidation degree of sediments. The same trend is derived from comparison of rocks from the Mar’yanovo Formation in both holes with the over- and underlying strata. In Borehole Vostok-4, the closet one to the former shoreline of the basin, the Mar’yanovo Formation is indistinguishable. Intense chemical weathering of rocks in provenances during their deposition noted by Kontorovich et al. (1971) is considered a most important factor responsible for its composition and formation conditions. Elevated influx of dissolved weathering products into the sea basin intensified its biogenic activity and stimulated the accumulation of high organic matter concentrations. This inference is valid for all Upper Jurassic-Lower Cretaceous organic carbon-rich sediments that are synchronous to the Mar’yanovo Formation and developed over a spacious area of the West Siberian basin.  相似文献   

6.
Analyses of organic carbon, nitrogen, sulfur and iron have been performed in order to understand sources and preservation of organic matter in black shale of the Buxin Formation (Early Paleogene) from the Sanshui Basin. The C/N ratios show that the organic matter is characterized by a mixture of terrestrial and phytoplanktonic contributions. The relative importance of different sources depend on climate conditions and most of organic matter is of terrestrial origin. The relationships between C, S and Fe indicate that the brackish environment with alternation of anoxia and low-O2 developed in the bottom waters during the deposition of these organic-rich sediments as a result of a mixed setting of thermal stratification and salinity stratification, the latter being the consequence of intermittent sea water incursion. Bacterial sulfate reduction is the most effective early diagenesis affecting the preservation of organic matter. The intensity of sulfate reduction is related to the relative proportion of met  相似文献   

7.
The Cenomanian-Turonian oceanic anoxic event(C/T OAE) is developed in southern Tibet.Organic geochemical study of the Cenomanian-Turonian sediments from the Gamba and Tingri aress shows that the mid-Cretaceous black shales in southern Tibet are enriched in organic carbon.Te molecular analyses of organic matter indicate marine organic matter was derived from algae and bacteria.In the Gamba area,the organic matter is characterized by abundant tricyclic terpanes and pregane,which are predominant in 191 and 217 mass chromatograms,respectively,Pristane/phytane(Pr/Ph)ratios in the C/T OAE sediments are less than 1, demonstrating the domination of phytane.The presence of carotane can be regarded as a special biomarker indicating oxygen depletion in the C/T OAE sediments in the Tethyan Himalayas.In anoxic sediments,β-carotane and γ－carotane are very abundant.The β-and γ-carotane ratios relative to nC17 in the Cenomanian-Turonian anoxic sediments vary from 32.28-42.87and 5.10-11.01.  相似文献   

8.
Lignin oxidation products and 13C/12C ratios were compared as indicators of land-derived organic matter in surface sediments from the western Gulf of Mexico. Whole sediments were reacted with cupric oxide to yield phenolic oxidation products that indicated the types and relative amounts of the lignins that were present.Measurements of lignin concentration and carbon isotope abundances both indicated a sharp offshore decrease of land-derived organic matter in most areas of the western Gulf. This decrease results primarily from mixing of terrestrial and marine organic matter. The terrestrially derived material in these sediments has a lignin content similar to that of grasses and tree leaves. Flowering plants contribute most of the sedimented lignin compounds. These lignins apparently occur in the form of well-mixed plant fragments that are transported to sea by rivers and deposited primarily on the inner continental shelf.  相似文献   

9.
The Maikop Formation, deposited in eastern Azerbaijan during Oligocene and Early Miocene times, contains prolific source rocks with primarily Type II organic matter. Paleontological analyses of dinoflagellate cysts revealed a Lower to Upper Oligocene age for the investigated succession near Angeharan. A major contribution of aquatic organisms (diatoms, green algae, dinoflagellates, chrysophyte algae) and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n-alkane distribution patterns, composition of steroids and δ13C of hydrocarbon biomarkers. Microbial communities included heterotrophic bacteria, cyanobacteria, chemoautotrophic bacteria, as well as green sulfur bacteria. Higher inputs of terrigenous organic matter occurred during deposition of the Upper Oligocene units of the Maikop Formation from Angeharan mountains. The terpenoid hydrocarbon composition argues for angiosperm dominated vegetation in the Shamakhy–Gobustan area.High primary bioproductivity resulted in a stratified water column and the accumulation of organic matter rich sediments in the Lower Oligocene units of the Maikop Formation. Organic carbon accumulation during this period occurred in a permanently (salinity-) stratified, mesohaline environment with free H2S in the water column. This is indicated by low pristane/phytane ratios of all sediments (varying from 0.37–0.69), lower methylated-(trimethyltridecyl)chromans ratio in the lower units and their higher contents of aryl isoprenoids and highly branched isoprenoid thiophenes. Subsequently, the depositional environment changed to normal marine conditions with oxygen deficient bottom water. The retreat of the chemocline towards the sediment–water interface and enhanced oxic respiration of OM during deposition of the Upper Oligocene Maikop sediments is proposed.Parallel depth trends in δ13C of total OM, n-alkanes, isoprenoids and steranes argue for changes in the regional carbon cycle, associated with the changing environmental conditions. Increased remineralisation of OM in a more oxygenated water column is suggested to result in low TOC and hydrocarbon contents, as well as 15N enriched total nitrogen of the Upper Oligocene units.  相似文献   

10.
A significant resource of vanadium and molybdenum exists near Julia Creek, Australia, where the middle Cretaceous organic-rich Toolebuc Formation lies between 0 and 25 m of the surface. We present and discuss a comprehensive geochemical study of the Toolebuc Formation and its enclosing stratigraphy near Julia Creek to understand this ore deposit. V and Mo contents in fresh facies are strongly associated with total organic carbon (TOC) contents, but not with Al or CaCO3; this suggests that V and Mo were originally concentrated in the organic fraction. However, chemical extractions using H2O2 indicate that Mo was originally concentrated in pyrite. The data also suggest that V was mobilised from organic matter during early diagenesis and became associated with clays as little V was extracted by H2O2 in the fresh samples. TOC contents in the Toolebuc Formation were removed during weathering, residually enriching trace metals including V and Mo, and as a result, the TOC relationship with V and Mo disintegrates. With weathering, both V and Mo predominantly became associated with iron oxide/hydroxide phases (and possibly other unidentified phases) as these elements in the weathered facies were highly soluble in the sodium citrate–sodium dithionite digestion. Large shale-hosted V and Mo deposits such as Julia Creek offer a potentially viable alternative to the currently mined magnetite-hosted deposits. A thorough understanding of the formation and host mineral phases for V and Mo of these shale deposits, however, is critical to ensure that these valuable metals can be feasibly extracted.  相似文献   

11.
华南下扬子巢湖地区孤峰组黑色硅质岩中富含有机质,是中国油气和页岩气勘探的潜在源岩,研究孤峰组有机质富集规律对开展油气勘探工作具有重要意义。文章对巢湖平顶山地区中二叠统孤峰组硅质岩进行总有机碳含量（TOC）和饱和烃分子标志物特征分析,探讨其中有机质富集规律。结果表明孤峰组有机质热成熟度参数C29 ααα甾烷20S/(20S+20R)比值分布在0.37 至0.46 之间,C31升藿烷22S/(S+R)比值分布在0.53 至0.59 之间,热成熟度水平处于生油窗的早期。有机质正构烷烃主峰为C18,以短链烷烃为主,藿烷含量较高,甾烷以C27 ααα 20R 胆甾烷为主,有机质主要来自海洋浮游藻类和细菌。孤峰组有机质Pr/Ph 比值小于0.6,伽玛蜡烷指数平均值为0.2,说明古沉积水体为中等分层缺氧环境。孤峰组普遍富含有机质可能与炎热气候下古沉积水体长期分层和缺氧有关。随着气候在孤峰组沉积早期和晚期突然变冷,高强度的海洋洋流上涌提高了初级生产力水平,造成有机质更大规模的富集。  相似文献   

12.
华南下扬子巢湖地区孤峰组黑色硅质岩中富含有机质，是中国油气和页岩气勘探的潜在源岩，研究孤峰组有机质富集规律对开展油气勘探工作具有重要意义。文章对巢湖平顶山地区中二叠统孤峰组硅质岩进行总有机碳含量（TOC）和饱和烃分子标志物特征分析，探讨其中有机质富集规律。结果表明孤峰组有机质热成熟度参数C29 ααα甾烷20S/(20S+20R)比值分布在0.37 至0.46 之间，C31升藿烷22S/(S+R)比值分布在0.53 至0.59 之间，热成熟度水平处于生油窗的早期。有机质正构烷烃主峰为C18，以短链烷烃为主，藿烷含量较高，甾烷以C27 ααα 20R 胆甾烷为主，有机质主要来自海洋浮游藻类和细菌。孤峰组有机质Pr/Ph 比值小于0.6，伽玛蜡烷指数平均值为0.2，说明古沉积水体为中等分层缺氧环境。孤峰组普遍富含有机质可能与炎热气候下古沉积水体长期分层和缺氧有关。随着气候在孤峰组沉积早期和晚期突然变冷，高强度的海洋洋流上涌提高了初级生产力水平，造成有机质更大规模的富集。  相似文献   

13.
Eocene organic-rich sediments are widespread in the Amasya region of north-central Turkey and have been studied in outcrop. Detailed data from thick Eocene sediments (Derealan Formation) made it possible to construct an organic-facies framework using different zonations.

Organic matter is composed predominantly of autochthonous algal and amorphous material, with a minor contribution of allochthonous terrestrial material. Kerogen in the deposits is primarily Type I, as indicated by organic petrographic observations and Rock-Eval data. Total organic-carbon content (TOC) of this deposit decreases from over 54% in limestone and shale to less than 2% in the other deposits of the Derealan Formation. Tmax values vary between 441 ° and 456° C, confirming the increase in maturation trends indicated by vitrinite reflectance data.

Both organic petrographic and geochemical maturation parameters place the Eocene sediments of the Northern Gumushacikoy (Amasya) region within the B organic facies. According to the organic-carbon/sedimentation-rate relationship, the preservation of matter took place under anoxic conditions.  相似文献   

14.
Chemical and radiometric analyses have been made on core samples from 15 drill holes intersecting the Toolebuc Formation at Julia Creek. The holes are located in the vicinity of the St Elmo Structure and include intersections of a potentially economic oil shale deposit west of this structure as well as non‐economic mixed coquinite/shale intersections to the east. The gamma ray activity of the formation is due largely to uranium in the shales. Wire‐line gamma ray logs, available for eight of these holes, reflect the distribution of organic carbon. Despite this, there is poor correlation between uranium and organic carbon in the oil shales as a result of remobilization of uranium from organic matter into phosphate during diagenesis. In consequence wire‐line gamma ray logs have no potential for evaluating oil yield. Density, on the other hand, is a good indicator of oil potential. On a hole by hole basis, the correlation between uranium and organic carbon in the formation ranges from 0.22 west of the St Elmo Structure (the potential oil shale resource) to 0.95 east of the structure. This reflects a systematic change in sedimentology from oil shale that is thick and well separated from coquinite (low correlation) to laterally equivalent but finely interbedded coquinite and shale (high correlations). Such trends could be used in exploratory drilling to indicate favourable areas elsewhere in the Toolebuc Formation.  相似文献   

15.
文章以修水地区下寒武统王音铺组至观音堂组下部富铀黑色页岩地层钻孔样品（U含量为9.37×10-6~202×10-6） 为研 究对象,进行了细致的显微观察和分析,并对该区下寒武统地层中U含量与沉积环境因素（沉积盆地中的生物生产力、底 层水体的氧化还原状态、及盆地与广海间的流通性） 之间的关系进行了探讨。结果表明,这些钻孔样品显示明显的沉积成 岩特征,未发现明显热液叠加/淋积作用现象,说明本区下寒武统地层只经历了沉积成岩作用,而没有经历过明显的热液作 用或者淋积作用。研究地层大部分样品中的U含量与TOC含量呈正相关,王音铺组上部U含量最高（202×10-6） 的样品沉积 时的初级生物生产力也最高。经扫描电镜观察和电子探针分析,发现其中有机质中包裹着沥青铀矿,两者关系密切,推测 U与有机质很可能是一起沉积-成岩富集的;在缺氧硫化的强还原沉积环境下沉积的王音铺组地层的U含量,明显高于在 缺氧非硫化环境下沉积的观音堂组下部地层中的U含量,而且在强还原硫化环境下,沉积时盆地处于开放流通性程度较高 时期的样品,其U含量明显高于盆地处于开放程度较低时期的样品。综合这些观察和分析得出,早寒武世王音铺组上部地 层沉积时,高生物生产力所形成的有机质降解时大量耗氧,导致底层水沉积环境处于强还原硫化状态,同时,沉积盆地处 于适当的开放程度,与广海之间水流交换使盆地上层含U氧化水体得到补充,U最终在底层水体强还原硫化环境下沉淀于 沉积物中,可达到较高程度的富集乃至矿化的水平。  相似文献   

16.
Time and tectonic processes involved in docking of the Argentine Precordillera (Cuyania terrane) against SW Gondwana has been a matter of much debate. A paleomagnetic study on the Early Caradoc Pavón Formation, exposed in the San Rafael block, province of Mendoza, Argentina, is presented. After detailed thermal and alternating field demagnetizations two geologically significant magnetic components were defined. A widespread post-tectonic component (A) is present in most sites of the Pavón Formation, with dual polarities, and is coincident with the characteristic remanence isolated from a Permo-Triassic rhyolitic dome intruding the sediments. Its pole position (83.7°S, 271.0°E, dp = 6.8°, dm = 9.0° N = 11 sites) falls on the Late Permian-Early Triassic South American reference poles suggesting that this component was acquired during the Choiyoi magmatic phase. A second component (B) also shows dual polarities and a positive fold test suggesting a primary origin. Unblocking temperatures and rock magnetic experiments indicate that B is carried either by hematite or magnetite at different sites. Anisotropy of magnetic susceptibility results suggest a depositional fabric and no remanence distortion due to deformation or compaction. A paleomagnetic pole computed from this remanence (PV) falls on 3.6°N, 346.4°E (dp = 2.9°, dm = 4.6° n = 22 samples). It indicates a paleolatitude around 26°S for deposition of Pavón sediments and constrains the paleogeographic evolution of Cuyania during the Ordovician, which was still at subtropical latitudes by the Early Caradoc. PV is consistent with the Laurentian Late Ordovician reference pole if Cuyania remains attached to SE Laurentia for the Early Caradoc, while it shows a significant cw rotation with no paleolatitude anomaly respect to the Gondwana reference pole when kept in its present position in SW South America. These comparisons are interpreted in three possible alternatives for the paleogeographic and tectonic setting of Cuyania in the Late Ordovician.  相似文献   

17.
为研究黔北地区下寒武统牛蹄塘组烃源岩母质来源和沉积环境,开展了生物标志化合物分析,结果表明：④正构烷烃OEP接近1．0,无明显奇偶优势,受轻微生物降解影响,正构烷烃多表现为双峰型（c18／c25）,（nC2＋nC22）／（nC28＋nC29）值为0．54～1．01,显示重烃组分占绝对优势;Pr／Ph值范围在0．51-0．82之间,具有植烷优势。②烃源岩样品组成相对丰度五环三萜烷〉5-g,萜烷〉四环萜烷,三环萜烷中C21、C23、C24呈倒V字形分布,Ts／（Tm＋Ts）为0．45-0．50。⑧C27规则甾烷／c∞规则甾烷略小于1或者接近1．芳烃化合物DBT／P为0．05-0．09。根据这些特征并结合干酪根同位素及正构烷烃同位素组成和变化规律,认为该区域下寒武统牛蹄塘组烃源岩形成于浅海还原环境,且有机质主要来源于细菌、藻类等低等水生生物,有机质热演化程度较高。根据常量、微量元素指标并结合有机地化指标刻划出从灯影组到牛蹄塘组和明心寺组沉积时期的水体环境,将牛蹄塘组烃源岩的形成分为3个阶段。第一阶段为早寒武世初始快速海侵阶段,第二阶段为深水还原高有机质产力阶段,第三阶段为海水缓慢变浅高有机质产力阶段,而到了明心寺组沉积时期为浅水氧化非烃源岩阶段。  相似文献   

18.
自然界中有机质分布广泛、类型多样且性质各异,不论在水体还是在沉积物(岩)中都扮演着重要的角色。因此,探讨各类型有机质聚集和沉积过程的差异性,对深化认识有机质沉积特征和演化规律具有重要的意义。生物体在生长过程中产生了许多有机质,包括生物体自身、生物残体、动物排泄物以及生物分泌的有机分子等,各类型有机质的性质差异极大。由于研究方法的不同,可将海洋中有机质划分为颗粒有机质(particulate organic matter,POM)和溶解有机质(dissolved organic matter,DOM),而DOM又可划分为胶体有机质(colloidal organic matter,COM)和真溶解有机质;从聚合体形式上看,又有海雪和悬浮体等存在形式。进一步分析发现有机质的形态包括生物体、生物残体、排泄物和有机质聚合体等,并且各类型有机质与无机矿物以不同的形式共存。此外,DOM与POM间存在一定的转化关系。这些性质和特征架起了不同类型有机质间聚集和沉积的桥梁。在沉积物(岩)中通过粒度或密度分级分离及孢粉相分析,也发现不同类型的有机质,如生物体、生物残体和无定形等,它们常与特定的无机矿物共生,如无定形多富集在黏粒级颗粒中,而生物体和生物残体多富集在粗颗粒中。进一步溯源发现沉积物(岩)中的各类有机质与生物有机质或海洋中有机质的类型极具相似性,这些特征展现各类型有机质在沉积过程中的差异性。综合有机质的形态、性质以及与矿物共生关系,认为有机质可通过机械沉积、化学沉积和生物沉积等3种不同的方式沉积保存,其中机械沉积的有机质以惰性的生物残体为主,化学沉积的有机质以活性极强的无定形为主,生物沉积有机质以活性较强的微生物和粘附物为主。有机质沉积方式及有机质特征、矿物—有机质间关系和保存条件的差异,决定了有机质的演化命运的不同,进而对有机质生烃以及碳循环产生重要的影响,因而应引起人们的高度关注。  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.
Sedimentary pyrite formation: An update   总被引：1，自引：0，他引：1  
Sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time. The amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter, dissolved sulfate, and reactive detrital iron minerals. Organic matter appears to be the major control on pyrite formation in normal (non-euxinic) terrigenous marine sediments where dissolved sulfate and iron minerals are abundant. By contrast, pyrite formation in non-marine, freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic-rich fresh water shales from marine shales. Under marine euxinic conditions sufficient H2S is produced that the dominant control on pyrite formation is the availability of reactive iron minerals.Calculations, based on a sulfur isotope model, indicate that over Phanerozoic time the worldwide average organic carbon-to-pyrite sulfur ratio of sedimentary rocks has varied considerably. High CS ratios during Permo-Carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time. Low CS ratios, compared to today, during the early Paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean. The latter could have been due to lower oceanic oxygen levels and/or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号