塔河油田稠油中25-降苯并藿烷的检出及其意义

与苯并藿烷相比,25-降苯并藿烷的研究较少,目前这类化合物仅检出于加拿大和我国川西北的降解沥青中。本研究在塔河油田井下奥陶系储层稠油中检测到了完整系列的25-降苯并藿烷（C31-C34）,发现25-降苯并藿烷与苯并藿烷的比值与现有的生物降解评价参数有较好的可比性,且该参数在不同降解程度原油中的差别比其他参数更大,故今后有必要对其开展更深入的研究,以便更精细地评价原油的生物降解程度。     

A complete series of C31–C34 25-norbenzohopanes in the Devonian and Jurassic bitumen sands,NW Sichuan Basin

A complete series of C₃₂–C₃₅ benzohopanes and corresponding C₃₁–C₃₄ 25-norbenzohopanes were tentatively identified in Devonian and Jurassic bitumen sands from the northwestern Sichuan Basin in southwestern China. Although other origins cannot be excluded, the relative distributions of C₃₂–C₃₅ benzohopanes and C₃₁–C₃₄ 25-norbenzohopanes, along with other biomarker parameters, suggest that the 25-norbenzohopanes formed by demethylation of the corresponding benzohopanes.     

桂西北晚古生代地层中的毗连不整合研究

桂西北右江地区广泛发育碳酸盐岩孤立台地,台地边缘发育大量沉积岩脉、角砾岩体、台地边缘同沉积正断层、及局部地层缺失造成的特殊界面,各要素之间的成因关系一直有争论。毗连不整合是指因同沉积断层作用使平坦地形变成强烈起伏的陡坡地形,粗碎屑物质快速沉积于地形凹处,新沉积的地层与早先坡下的较老基岩横向相接,因此造成新老地层之间的不整合,多形成于构造不稳定地区。国外地质学家最初将其识别为普通的角度不整合、陆架边缘不整合或者台地边缘不整合等等,国内地质学家也注意到了这类特殊界面,但在一些野外露头上观察其为断层面,而在另一些露头上观察其为侵蚀间断（不整合）面,由此产生争论：这类特殊界面是断层还是不整合？并产生很多名称：同构造沉积不整合、碳酸盐岩台地边缘围限断裂带、角度不整合接触带、陡崖式假不整合、事件沉积不整合、超覆不整合、构造窗和飞来峰等等,迄今为止没有统一。笔者等在研究广西晚古生代孤立碳酸盐岩台地边缘沉积岩脉和角砾岩体的过程中,发现特殊界面与沉积岩脉和角砾岩体关系密切,并发现如果将这些特殊界面归类于传统不整合面,均有与地质事实相矛盾的地方,因而认为其应重新归类。随着研究的深入：笔者等在凤山剖面的同一露头上观察到关键地质现象：特殊界面下部具断层特征,上部具溶蚀间断特征,因此认为其是遭受溶蚀的同沉积断层面。其成因是：同沉积构造十分活跃,使同沉积断层面上部来不及被新沉积物掩埋而遭受水下溶蚀,从而形成巨大地形起伏,造成新老地层横向相接,与Davis毗连不整合概念吻合,据此将这类特殊界面统一命名为毗连不整合。随即发现桂西北晚古生代地层内部广泛发育毗连不整合,并且发现晚古生代地层与下伏寒武系、及上覆三叠系之间也是毗连不整合接触,这是桂西北晚古生代地层及相关寒武系和三叠系的基本特色,由于毗连不整合代表区域地质构造活动强烈,表明桂西北地质构造从古生代到中生代一直处于活动状态,地层—构造活动记录与古特提斯域特征相似,属古特提斯洋的东沿部分。从而结束特殊界面是断层还是不整合的争论,为桂西北地层与构造的深入研究及其大地构造归属提供了新证据。     

Chertification histories of some Late Mesozoic and Middle Palaeozoic platform carbonates

A consistent pattern for the silica sources, depositional environments and timing of chertification was observed in a diverse suite of five Late Mesozoic and Middle Palaeozoic carbonate sequences; the (1) Upper Greensand (Cretaceous) and (2) Portland Limestone (Jurassic) of southern England, (3) the Ramp Creek Formation (Mississippian) of southern Indiana, and the (4) lower Helderberg Group (Devonian) and (5) Onondaga Limestone (Devonian) of New York State. Nodular chert formation in all five limestone sequences occurred in sediments that were largely uncemented. Ghosts of pre-chertification carbonate cements are present in some chert nodules but are volumetrically minor. In every limestone sequence except the Upper Greensand, chertification occurred after burial to a depth sufficient for intergranular pressure solution and mechanical grain deformation of carbonate sand. Nodular chert is most abundant in subtidal, normal marine wackestones and mudstones that were deposited at or below fair-weather wave base, and is absent or rare in supratidal, intertidal and high-energy subtidal limestones and dolomites. An intraformational sponge spicule silica source for chert nodules is suggested by direct evidence, such as calcitized sponge spicules in the host limestone, and circumstantial evidence, such as ghosts of sponge spicules in chert nodules and a correlation of chert abundance with depositional environment. Most molds of siliceous sponge spicules were apparently obliterated by post-chertification intergranular compaction. We propose that these general trends for the depositional environments, silica sources and timing of chertification are representative of most Mesozoic to Middle Palaeozoic platform limestones.     

Paleoclimatic reconstruction in northern Oman based on carbonates from hyperalkaline groundwaters

A paleoclimatic reconstruction for the past 35,000 years for northern Oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs. High-pH groundwaters (pH up to 11.9) discharge from the mantle sequence of the Oman Ophiolite as the product of modern, low-temperature serpentinization. Under arid climatic conditions, hyperalkaline discharge occurs at the surface. Uptake of atmospheric CO₂ precipitates characteristic laminated travertines, accompanied by strong kinetic depletion of ¹³C and ¹⁸O. Pluvial climates supporting a shallow bicarbonate-groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite-replaced roots and stems. All such carbonates have modern initial ¹⁴C contents, allowing radiocarbon dating and paleoclimatic reconstruction for the late Pleistocene and Holocene. Our reconstruction shows a dominantly wet late Pleistocene up to 19,000 yr B.P., when a phase of climatic deterioration began, leading to a period of hyperaridity which dominated from ca. 16,300 to 13,000 yr B.P. The early Holocene pluvial occurred from 12,500 to ca. 6500 yr B.P. and was followed by renewed climatic deterioration and the current phase of hyperaridity. Comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the A'Rub al Khali of central Saudi Arabia and the summer insolation-driven monsoon record of east Africa and the Arabian Sea is remarkably good.     

The occurrence and distribution of phenylphenanthrenes,phenylanthracenes and binaphthyls in Palaeozoic to Cenozoic shales from China

The distributions of phenylphenanthrenes, phenylanthracenes and binaphthyls in sediment extracts have been investigated in a set of lacustrine shales from the Eocene Shahejie Formation (well SG 1) in the western Depression of Liaohe Basin, East China. All isomers of these phenyl substituted polycyclic aromatic hydrocarbons (PAHs) have been identified in the m/z 254 mass chromatograms by comparison of the mass spectra and standard retention indices with those published elsewhere. The 2,2′-binaphtyl/1,2′-binaphthyl ratio values show a linear increase with increasing maturity, and have a good correlation with T_max (°C). Therefore, they can be used as an effective maturity indictor for source rocks in this study. In the main phase of the oil generation window, the 3-phenylphenanthrene and 2-phenylphenanthrene prevail over other isomers, and some thermodynamically unstable isomers including all phenylanthracenes, 4-phenylphenanthrene and 1,1′-binaphthyl are present at very low concentrations or below the detection limit in the m/z 254 mass chromatograms. The absolute concentrations of individual phenylphenanthrene and binaphthyl isomers were obtained by comparison of the peak areas with that of internal standard phenanthrene-d10. All isomers are present at low concentrations at low maturity stages and then show an abrupt increase at a depth of ≈3100 m, corresponding to the onset of the intensive C₁₅₊ hydrocarbon generation. The Phenylphenanthrene Ratio (2- + 3-PhP)/[(2- + 3-PhP) + (4- + 1- + 9-PhP)] shows a reverse change with increasing maturity at the low maturity stage. It displays a drastic increase at a depth of ≈3100 m and then remains at a nearly constant value. This study can expand the understanding of the formation and distribution of phenyl substituted PAHs in sedimentary organic matter deposited in various environments.     

Manganese removal from mine waters – investigating the occurrence and importance of manganese carbonates

Manganese is a common contaminant of mine water and other waste waters. Due to its high solubility over a wide pH range, it is notoriously difficult to remove from contaminated waters. Previous systems that effectively remove Mn from mine waters have involved oxidising the soluble Mn(II) species at an elevated pH using substrates such as limestone and dolomites. However it is currently unclear what effect the substrate type has upon abiotic Mn removal compared to biotic removal by in situ micro-organisms (biofilms). In order to investigate the relationship between substrate type, Mn precipitation and the biofilm community, net-alkaline Mn-contaminated mine water was treated in reactors containing one of the pure materials: dolomite, limestone, magnesite and quartzite. Mine water chemistry and Mn removal rates were monitored over a 3-month period in continuous-flow reactors. For all substrates except quartzite, Mn was removed from the mine water during this period, and Mn minerals precipitated in all cases. In addition, the plastic from which the reactor was made played a role in Mn removal. Manganese oxyhydroxides were formed in all the reactors; however, Mn carbonates (specifically kutnahorite) were only identified in the reactors containing quartzite and on the reactor plastic. Magnesium-rich calcites were identified in the dolomite and magnesite reactors, suggesting that the Mg from the substrate minerals may have inhibited Mn carbonate formation. Biofilm community development and composition on all the substrates was also monitored over the 3-month period using denaturing gradient gel electrophoresis (DGGE). The DGGE profiles in all reactors showed no change with time and no difference between substrate types, suggesting that any microbiological effects are independent of mineral substrate. The identification of Mn carbonates in these systems has important implications for the design of Mn treatment systems in that the provision of a carbonate-rich substrate may not be necessary for successful Mn precipitation.     

极端生物降解沥青中8,14- 开环藿烷系列及其地球化学意义

借助色谱- 质谱（GC- MS）和色谱- 质谱- 质谱（GC- MS- MS）分析,对黔南坳陷凯里残余油藏凯棠和洛棉剖面上储层沥青中的烃类组成进行了系统分析,以判断其所遭受生物降解作用的程度,探寻在极端降解原油中是否还存在原生生物标志物,为这类原油的油源研究开拓新的途径和方法。结果表明：凯棠剖面上的储层沥青中尽管仍可检测到较为完整的C19- 30三环萜烷和C27- 35藿烷系列,但C19- 29脱甲基三环萜烷系列和C26- 34 25- 降藿烷系列丰富而完整,甾烷系列中C21- 22低分子量甾烷和重排甾烷优势明显,这一系列特征表明这些沥青遭受了剧烈生物降解作用的改造。但三芳甾类仍保存完好,依据原油生物降解程度的评判标准,判断其生物降解级别介于8~9级之间。洛棉剖面上的储层沥青中藿烷系列基本消失殆尽,三环萜烷系列及其脱甲基产物和25- 降藿烷系列的分布因极端生物降解作用而发生显著变异,某些化合物如C23T、C24T、C23NTE和C28- 29NH成为优势成员;甾烷系列中C21- 22低分子量甾烷占绝对优势,三芳甾类完全消失,据此判断该剖面上沥青的生物降解级别已达到10级或更严重。由于这两个剖面上的沥青遭受了极端生物降解作用的改造,常用的甾、萜类生物标志物完全失去了实用价值。但是,在所分析的这些沥青中都检测到三个系列的C27- 35 8,14- 开环藿烷系列,它们与塔里木盆地塔中地区海相端元油中存在的同类标志物的分布特征相似。正常海相端元油和极端生物降解沥青中同时检测到这三个系列的8,14- 开环藿烷,这一事实表明这类生物标志物在成因上具有原生性,而与生物降解作用无关。此外,在极端生物降解作用沥青中的完好保存,表明它们具有极强的抗生物降解能力,因而它们在此类原油的油源研究中可能具有潜在的实用价值。     

The occurrence of calcified planktonic green algae in freshwater carbonates

Phacotus and Coccomonas, two carbonate-secreting, non-marine, planktonic chlorophyte genera, are important sediment contributors mainly in hard water lakes. The calcite loricae of these flagellate algae exhibit characteristic features easily recognizable under the microscope, making Phacotus and Coccomonas important facies fossils for the recognition of ancient non-marine environments. The fossil record of Phacotus can be traced back to the Miocene and it is probable that further research could extend this record into pre-Tertiary periods.     

Potential field imaging of Palaeozoic orogenic structure in northern and central Europe

The Trans-European Suture Zone (TESZ) is the most fundamental lithospheric boundary in Europe, separating the ancient crust of the Fennoscandian Shield–East European Craton from the younger crust of central Europe, and extending deep into the mantle. Geophysical potential field images provide an overview of the entire Palaeozoic orogenic system of northern and central Europe for the first time. The TESZ is largely concealed by sedimentary basins of Permian–Cenozoic age; geological observations are largely restricted to local basement highs and deep boreholes, and the coverage of deep seismic surveys is widely spaced, despite experiments recently acquired within the EUROPROBE programme. By contrast, the potential field data offer a relatively detailed coverage of standardised observations throughout the TESZ. While some features of the images may be sourced in the near surface, particularly in the gravity image, much of their content reflects the structure of the underlying Palaeozoic basement. At the scale presented, the images highlight the most fundamental features of the crustal structure of the TESZ. These include the strong contrast between the highly magnetic crust of the East European Craton and the less magnetic Palaeozoic-accreted terranes of central Europe; the lateral continuity of terranes and their internal structure, particularly where arc-magmatic complexes are involved; and the location and geometry of the terrane boundaries (oceanic sutures and strike-slip zones) that separate them.     

Geochemical characteristics and geological significance of the Neoproterozoic carbonates from northern Anhui Province,China

Petrographical and geochemical studies were carried out of the Neoproterozoic carbonates from northern Anhui Province, China. These carbonates can be subdivided into two types, including purified limestone (PL) and mixed limestone and siliclastic rocks (MLS). PLs are low in Si, Al, Zr and total REE but high in CaO compared with MLSs. Correlations between Zr, Fe2O3, P2O5 and total REE are also less remarkable, indicating that they were not obviously contaminated by continental materials but directly precipitated from seawater. So they can be used for the inversion of paleo-seawater REE patterns. The inversed results indicated that the REE pattern of Neoproterozoic seawater was similar to that of the modern seawater except for the lack of Ce depletion, which was probably affected by the reduced hydrothermal solution. In combination with previous studies, the geochemical trending of these carbonatic samples towards the continental arc in the La- Th-Sc and Th-Sc-Zr/10 diagrams is interpreted as the contamination of arc volcanism. The tectonic background of the southern margin of the North China Craton in the Neoproterozoic was probably related to the Grenville orogeny during the convergence of the Rodinia supercontinent, rather than an intra-plate environment.     

Petrogenesis of the Late Cretaceous northern Alberta kimberlite province

At present, 48 Late Cretaceous (ca. 70–88 Ma) kimberlitic pipes have been discovered in three separate areas of the northern Alberta: the Mountain Lake cluster, the Buffalo Head Hills field and the Birch Mountains field. The regions can be distinguished from one another by their non-archetypal kimberlite signature (Mountain Lake) or, in the case of kimberlite fields, primitive (Buffalo Head Hills) to evolved (Birch Mountains) magmatic signatures.

The dominant process of magmatic differentiation is crystal fractionation and accumulation of olivine, which acts as the main criteria to distinguish between primitive and evolved Group I-type kimberlite fields in the northern Alberta. This is important from the viewpoint of diamond exploration because the majority (about 80%) of the more primitive Buffalo Head Hills kimberlites are diamondiferous, whereas the more evolved Birch Mountains pipes are barren of diamonds for the most part. Petrographically, the Buffalo Head Hills samples are distinct from the Birch Mountains samples in that they contain less carbonate, have a smaller modal abundance of late-stage minerals such as phlogopite and ilmenite, and have a higher amount of fresh, coarse macrocrystal (>0.5 mm) olivine. Consequently, samples from the Buffalo Head Hills have the highest values of MgO, Cr and Ni, and have chemistries similar to those of primitive hypabyssal kimberlite in the Northwest Territories. Based on whole-rock isotopic data, the Buffalo Head Hills K6 kimberlite has ⁸⁷Sr/⁸⁶Sr and _Nd values similar to those of South African Group I kimberlites, whereas the Birch Mountains Legend and Phoenix kimberlites have similar _Nd values (between 0 and +1.9), but distinctly higher ⁸⁷Sr/⁸⁶Sr values (0.7051–0.7063).

The lack of whole-rock geochemical overlap between kimberlite and the freshest, least contaminated Mountain Lake South pipe rocks reflects significant mineralogical differences and Mountain Lake is similar geochemically to olivine alkali basalt and/or basanite. Intra-field geochemical variations are also evident. The K4 pipe (Buffalo Head Hills), and Xena and Kendu pipes (Birch Mountains) are characterized by anomalous concentrations of incompatible elements relative to other northern Alberta kimberlite pipes, including chondrite-normalized rare-earth element distribution patterns that are less fractionated than the other kimberlite samples from the Buffalo Head Hills and Birch Mountains. The Xena pipe has similar major element chemical signatures and high-Al clinopyroxene similar to, or trending towards, the Mountain Lake pipes. In addition, K4 and Kendu have higher ⁸⁷Sr/⁸⁶Sr and lower _Nd than Bulk Earth and plot in the bottom right quadrant of the Nd–Sr diagram. We suggest, therefore, that the K4 and Kendu pipes contain a contribution from old, LREE-enriched (low Sm/Nd) lithosphere that is absent from the other kimberlites, are affected by crustal contamination, or both.

Based on xenocryst populations, the northern Alberta kimberlite province mantle is dominated by carbonate-saturated lherzolitic mantle. Higher levels of melt depletion characterize the Buffalo Head Hills mantle sample. Despite high diamondiferous to barren pipe ratios in the Buffalo Head Hills pipes, mineral indicators of high diamond potential, such as G10 garnet, diamond inclusion composition chrome spinels and high-sodium eclogitic garnet, are rare.     

Methane-derived authigenic carbonates from the northern Gulf of Mexico — MD02 Cruise

Authigenic carbonates were sampled in piston cores collected from both the Tunica Mound and the Mississippi Canyon area on the continental slope of the northern Gulf of Mexico during a Marion Dufresne cruise in July 2002. The carbonates are present as hardgrounds, porous crusts, concretions or nodules and shell fragments with or without carbonate cements. Carbonates occurred at gas venting sites which are likely to overlie gas hydrates bearing sediments. Electron microprobe, X-ray diffraction (XRD) and thinsection investigations show that these carbonates are high-Mg calcite (6–21 mol% MgCO₃), with significant presence of framboidal pyrite. All carbonates are depleted in ¹³C (δ¹³C = − 61.9 to − 31.5‰ PDB) indicating that the carbon is derived mainly from anaerobic methane oxidation (AMO). Age estimates based on ¹⁴C dating of shell fragments and on regional sedimentation rates indicate that these authigenic carbonates formed within the last 1000 yr in the Mississippi Canyon and within 5500 yr at the Tunica Mound. The oxygen isotopic composition of carbonates ranges from + 3.4 to + 5.9‰ PDB. Oxygen isotopic compositions and Mg²⁺ contents of carbonates, and present in-situ temperatures of bottom seawater/sediments, show that some of these carbonates, especially from a core associated with underlying massive gas hydrates precipitated in or near equilibrium with bottom-water. On the other hand, those carbonates more enriched in ¹⁸O are interpreted to have precipitated from ¹⁸O-rich fluids which are thought to have been derived from the dissociation of gas hydrates. The dissociation of gas hydrates in the northern Gulf of Mexico within the last 5500 yr may be caused by nearby salt movement and related brines.     

藏北羌塘中部早古生代蛇绿岩堆晶岩中斜长花岗岩的地球化学特征

桃形湖蛇绿岩是龙木错－双湖缝合带近期的重要发现。这一发现回答了龙木错－双湖缝合带中不存在完整蛇绿岩剖面的质疑,是该缝合带存在的重要证据,也是古特提斯洋早期裂解时间确定的主要依据之一。其中斜长花岗岩的岩石地球化学特征反映出洋脊花岗岩的属性,包括Al2O3含量较高,准铝质至过铝质（12.56％～16.19％）,富Na2O,贫K2O（Na2O／K2O＞3）,主量元素、微量元素和稀土元素含量较低等,但是其稀土元素配分曲线、微量元素蛛网图又与标准大洋斜长花岗岩有所区别,表现为轻重稀土元素分异很明显,具强烈的Eu正异常（Eu／Eu?鄢=1.92～9.19,均值为5.18）,初步推测原因是岩浆迅速上升过程中Ca分离不完全和样品中石榴子石分布不均匀。结合斜长花岗岩的野外产状及以往的研究成果,初步结论是：桃形湖蛇绿岩中的斜长花岗岩形成于近洋脊或准洋脊环境,岩浆源自地幔,与桃形湖蛇绿岩中的变质橄榄岩、堆晶辉长岩、基性熔岩的岩浆同源,是基性—超基性岩浆分异的残余,应属桃形湖蛇绿岩中的浅色岩组分,是蛇绿岩的端元岩石。     

藏北羌塘中部早古生代蛇绿岩堆晶岩中斜长花岗岩的地球化学特征

桃形湖蛇绿岩是龙木错－双湖缝合带近期的重要发现。这一发现回答了龙木错－双湖缝合带中不存在完整蛇绿岩剖面的质疑,是该缝合带存在的重要证据,也是古特提斯洋早期裂解时间确定的主要依据之一。其中斜长花岗岩的岩石地球化学特征反映出洋脊花岗岩的属性,包括Al2O3含量较高,准铝质至过铝质（12.56％～16.19％）,富Na2O,贫K2O（Na2O／K2O＞3）,主量元素、微量元素和稀土元素含量较低等,但是其稀土元素配分曲线、微量元素蛛网图又与标准大洋斜长花岗岩有所区别,表现为轻重稀土元素分异很明显,具强烈的Eu正异常（Eu／Eu?鄢=1.92～9.19,均值为5.18）,初步推测原因是岩浆迅速上升过程中Ca分离不完全和样品中石榴子石分布不均匀。结合斜长花岗岩的野外产状及以往的研究成果,初步结论是：桃形湖蛇绿岩中的斜长花岗岩形成于近洋脊或准洋脊环境,岩浆源自地幔,与桃形湖蛇绿岩中的变质橄榄岩、堆晶辉长岩、基性熔岩的岩浆同源,是基性—超基性岩浆分异的残余,应属桃形湖蛇绿岩中的浅色岩组分,是蛇绿岩的端元岩石。     

The Early Palaeozoic break-up of northern Gondwana,new palaeomagnetic and geochronological data from the Saxothuringian Basin,Germany

Early Palaeozoic volcanic and sedimentary rocks from the Saxothuringian Basin (Franconian Forest, northern Bavaria) have been subjected to detailed radiometric and palaeomagnetic studies in order to determine the tectonic environment and geographic setting in which they were deposited. Two hand samples were collected from the as yet undated pyroclastic flow deposits for ²⁰⁷Pb/²⁰⁶Pb age dating. Radiometric results for these samples, obtained by the single-zircon evaporation technique, are identical within error, and the mean age of all measured grains is 478.2ǃ.8 Ma (n=11). This age is considered to be primary and firmly constrains the eruption of the ignimbrites and formation of the subaqueous pyroclastic flows as having occurred in Early Ordovician (Arenig) times. Palaeomagnetic studies were carried out on these Early Ordovician volcanic rocks, and also on the biostratigraphically dated, Late Ordovician (Ashgillian) Döbra sandstones. The volcanic rocks carry up to three directions of magnetisation. The poorly defined, low and intermediate unblocking temperature directions are thought to represent secondary overprint directions of post-Ordovician age. The high temperature component, however, identified at temperatures of up to 580 °C, is of mixed polarity and passes the fold test with 99% confidence. The overall mean direction after bedding correction is 189°/76°, !₉₅=11.6°, k=44.7 (25 samples, five sites), and is considered to be primary and Early Ordovician in origin. It yields a palaeo-south pole at 24°N and 007°E, which translates into palaeolatitudes of 63°+21.7°/-17.3° S for the Saxothuringian Terrane. Samples from the Late Ordovician Döbra sandstone are generally very weakly magnetised. A high temperature D component of magnetisation can be identified in some samples and yields a mean direction of 030°/-58°, !₉₅=18.5°, k=25.7 (15 samples, four sites) after bedding correction. The Arenig palaeomagnetic results indicate high palaeolatitudes, but separation from northern Gondwana. This is in basic agreement with data from elsewhere in the Armorican Terrane Assemblage, all of which suggest high southerly palaeolatitudes in the Early Ordovician. The geochemical signatures of these rocks indicate emplacement in an extensional environment. These new data, therefore, are interpreted as marking the onset of rifting of Saxothuringia from the north African margin of Gondwana, and the start of the relative northward migration of the Saxothuringian Terrane. Although the Late Ordovician palaeomagnetic results presented here are only poorly constrained, they suggest an intermediate palaeolatitude for Saxothuringia in Ashgillian times, in good agreement with Late Ordovician palaeomagnetic data from the Barrandian.     

Sedimentology and isotope geochemistry of Riphean carbonates in the Kharaulakh Range of northern East Siberia

Stable carbon isotope variations in primarily offshore Proterozoic carbonates of the Eselekh, Neleger, and Sietachan Formations in the Kharaulakh Range of northern East Siberia provide important information on the depositional history of the Riphean complexes and allow an age estimate to be made for potentially petroliferous Precambrian strata in the northeast of the Siberian Platform. The results of petrographic, geochemical, and isotopic studies of the measured samples demonstrate that the carbonates are recrystallized without substantial postdepositional alteration of the carbon isotope system and that the acquired 5¹³C values are accurate and can be used for the purposes of chemostratigraphy. The Riphean strata of the Kharaulakh Range are characterized by mostly high (5.5-8.6%c) 5¹³C values. Based on carbon isotope data, the studied section could not be correlated with Mesoproterozoic strata of the Anabar and Olenek Uplifts but occupies a rather higher stratigraphic position. It can be correlated with the Baikal Group of the West Pre-Baikal Area and the Dal’nyaya Taiga Group of the Patom Upland; specifically, the negative shift in the uppermost Sietachan Formation possibly corresponds to the Zhuya negative excursion. Comparison with the model curve of carbon isotope evolution in the Precambrian ocean suggests that the age of the studied section does not exceed 820 Ma. Most likely, the studied strata are younger than 635 Ma (i.e., postdate the Marino glaciation) but older than the Gaskiers glaciation (580 Ma).     

藏北羌塘盆地羌资1井中侏罗统沥青脉生物标志化合物分布特征及其意义

藏北羌塘盆地羌资1井中侏罗统沥青脉生物标志化合物含有丰富的正烷烃、类异戊二烯烷烃、萜类化合物和甾类化合物。正烷烃图谱形态以单峰形态占优势,主碳峰以nC₁₆、nC₁₇、为主,次为nC₁₈、nC₂₀、nC₁₅,轻烃组分占有绝对优势,OEP值介于0.69-1.22之间,平均值为0.96,偶碳数优势不明显;Pr/Ph值介于0.35~0.78之间,平均值为0.59,具有明显的植烷优势。萜烷相对丰度表现为五环三萜烷 > 三环萜烷 > 四环萜烷,γ-蜡烷普遍存在,但相对含量较低;甾烷主要为规则甾烷,少量孕甾烷,规则甾烷Σ(C₂₇+C₂₈) > ΣC₂₉,ΣC₂₇/ΣC₂₉介于0.61~2.18之间,平均值为1.06,显示弱的C₂₇甾烷优势或弱的C₂₉甾烷优势。有机质母质构成中,除有丰富的藻类等低等水生生物外,可能还有陆生高等植物输入混合。成熟度参数和镜质体反射率均显示沥青脉中的有机质处于成熟-过成熟阶段。沥青脉形成环境为还原环境。另外,除饱和烃和芳烃含量上有明显差别外,中侏罗统夏里组砂泥岩中的沥青脉与布曲组碳酸盐岩中的沥青脉的生物标志化合物无明显区别。