Oil source rocks at mesozoic and cenozoic continental margins: Communication 2. Oil source rocks at continental margins in the second half of the cretaceous and in the Cenozoic

Oil source rocks represent sequences with the C_org content ranging from 3–5 to 15–20%. Sedimentary sections of large petroliferous basins usually include one or two such sequences, which generated liquid and gaseous hydrocarbons (HCs) during their long-term subsidence to the elevated temperature zone. The middle episode of the Late Cretaceous was marked by the accumulation of sediments with a high C_org content in different areas of the World Ocean. However, truly unique settings favorable for accumulation of the sapropelic organic matter (OM) appeared at continental margins that primarily faced the Tethys Ocean. The La Luna Formation is one of the best known source rock sequences responsible for the generation of liquid HCs in basins of the Caribbean region. In the Persian Gulf, the Kazhdumi Formation composed of marls and clayey limestones is considered the main oil-generating sequence. In the Paleogene after closure of the Tethys, the Pacific continental margins became the main domains that accumulated source rocks. The maximal deposition of sapropelic OM in this region corresponded to the early-middle Eocene. In the Neogene, the accumulation of source sediments was associated with deltas and submarine fans of large rivers and with upwelling zones. In basins of the Californian borderland, the main oil-generating sequences are represented by siliceous rocks of the Monterey Formation. They were deposited in a regional upwelling zone related to the cold California Current.     

Hydrocarbon source rocks in sedimentary basins of continental margins in the Middle-Late Paleozoic

The second half of the Paleozoic was marked by amalgamation of large continental blocks. The collision between the Laurentia and Baltica continents in the Devonian culminated in the formation of Laurussia. This event was followed by accretion of the Siberian and Kazakhstan continental blocks after the closure of the Uralian marine basin in the terminal Carboniferous-initial Permian. These processes were responsible for the formation of the Pangea supercontinent at the end of the Permian Period. They were accompanied by climate changes reflected in the alternation of warming and cooling epochs. One of these cooling epochs was terminated by large-scale glaciation of Gondwana at the end of the Carboniferous Period. Nevertheless, the most significant process, which drastically changed the existing paleogeographic situation, was colonization of continents by plants and animals, and, thus, accumulation of coaliferous formations in them. The lacustrine and sea basins also accumulated humic and mixed humic/sapropel organic matter (OM) in addition to pure sapropelic sediments.     

Oil source rocks at the mesozoic and cenozoic continental margins: Communication 1. Oil source rocks at continental margins in the Triassic-Jurassic and Neocomian-Aptian

The presence of rocks capable of generating hydrocarbons (HC) in the section of sedimentaryrock basins is an essential criterion for their qualification as structures with oil and gas pools. Although organic matter (OM) is always present as dissemination in genetically different sediments, it is believed that rocks enriched with OM of the sapropel series (2 to 3% C_org) can generate a significant amount of liquid HC. However, rock sequences with the C_org ranging from 3–5 to 15–20% are considered oil source formations. The rock section of large petroliferous basins usually includes one or two source sequences, which generated liquid and gaseous HCs after submergence to high temperature and pressures zones. In the basin confined to the Arctic slope of Alaska, one of the main producers of liquid HC is represented by the Upper Triassic clays and limestones of the Shublik Formation. In the Barents Sea and North Sea basins, such rocks are represented by the Spekk Formation and the Kimmeridge Clay, respectively; in the West Siberian basin, by the Bazhenovo Formation; in the Persian Gulf, by the Fahlian, Sargelu, and Garau formations; in basins of the Caribbean region, by marls and clayey limestones of the La Luna Formation. In perioceanic basins of the South Atlantic, the major source sequences are represented by the Neocomian and Barremian clays and marls. The source rocks are identified as the Lagoa Feia Formation in the Campos and Santos basins. They are cognized as the Black Marlstone or Bukomazi Formation in the Lower Congo, Kwanzaa-Cameroon, and Angola basins.     

大别山周缘盆地物源研究:新结果及运用

叙述单颗粒碎屑矿物在大别山周缘盆地物源分析中的运用。现代河流沉积与大别山源区的对比研究表明碎屑石榴石、K 白云母和电气石的化学组成可以有效地被用于物源分析。它们在侏罗纪—白垩纪—古近纪沉积中的特征揭示了大别山源区岩石组成的复杂性,由扬子大陆深俯冲折返所形成的高压—超高压变质岩在白垩纪—古近纪逐渐向东南缘盆地提供了重要的物源, 在侏罗纪时期主要分布在大别山北缘盆地的源区。石炭纪时期大别山北缘盆地中碎屑Cr 尖晶石的化学组成和碎屑锆石U Pb年龄结构指示源区岩石组成主要为早古生代华北大陆南缘活动大陆边缘的特征;此外,锆石U Pb年龄指示源区岩石也具有扬子大陆的特征。     

Tectonic and climate control of oil shale deposition in the Upper Cretaceous Qingshankou Formation (Songliao Basin, NE China)

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.     

雅鲁藏布江缝合带日喀则群的蛇绿岩质海底扇及其板块构造意义

沿雅鲁藏布江缝合带分布的日喀则群(K_2TK)砂泥质细粒复理石中发育着一种独特的沉积单元——蛇绿岩质砂砾质海底扇。这些扇体规模小,内扇和中扇相序典型。无论是内扇还是中扇,水道都特别发育,而且水道游荡作用明显。盛行砂砾质高密度浊流和粘性碎屑流沉积,沉积物粒度粗,含大量卵石级以上的粗碎屑,具有近源、快速堆积的特点。其碎屑组分为世界现代和古代海底扇沉积所罕见,主要是蛇绿岩碎屑,并含少量岛弧火山-岩浆岩碎屑和老地层的碎屑。这些扇体具有活动边缘型海底扇的典型特征,但又有其特殊性,它们发育在雅鲁藏布洋盆闭合、印度板块与藏北板块开始碰撞时的残留复理石盆地边缘。板块碰撞导致蛇绿岩质杂岩体和洋壳物质逆冲、抬升形成一个外弧造山带。该外弧造山带成为这些扇体的主要物源区。同时,强烈的逆掩和纳布作用也可将部分岛弧岩和老地层带到残留盆地边缘,一起作为来源母岩。     

Petroliferous basins at continental margins of Paleozoic paleoseas: Communication 1. Petroliferous basins at margins of Iapetus and Panthalassa

Although large marine basins governing the fabric of our planet in the Paleozoic disappeared later (whether or not they were oceans is a debatable issue), sedimentary basins formed at continental margins at that time played a crucial role as depositories of various fossil minerals, including ores, salts, phosphorites, coal, bauxites, and construction materials. Many of these basins are oil- and gas-bearing structures. Their oldest representatives are confined to margins of Proterozoic/Paleozoic paleoseas (Iapetus and Panthalassa), whereas other basins appeared after opening of the Central Asian, Uralian, and Rheic (Paleotethys) deep-marine basins. Study of specific features of the sedimentary cover of such basins, rock composition therein, rocks and associated oil- and gas-bearing systems revealed that the Paleozoic planet was divided into two parts: Gondwana, with the major portion confined to high latitudes of the Southern Hemisphere; and other smaller near-equatorial continents. This pattern significantly governed the composition and mode of post-sedimentary transformations of natural reservoirs, as well as age and spatial distribution of the major hydrocarbon (HC) source sequences. Most Paleozoic oil- and gas-bearing basins make up specific belts because of their confinement to continental margins in paleoseas of that time.     

Amino acids and hexosamines in the Hess Rise core during the past 220,000 years

Core sediment samples collected from the Hess Rise, North Pacific, were analyzed for 20 common amino acids (AA) and two hexosamines (HA) to understand the relation between glacial–interglacial variations and deposition/preservation of sedimentary organic matter (OM). The sediments are predominantly carbonaceous (carbonates 35–80%). AA-based parameters—aspartic acid/glycine ratio and serine+threonine relative mole content—suggest that calcareous plankton was the major source of OM in these sediments. This inference is supported by the similarity in distribution patterns of AA and HA contents with that of organic carbon. Low values of AA/HA and glucosamine/galactosamine ratios (average 4.4 and 1.1, respectively) imply that much of the planktonic OM was replaced by microbial OM. The relative molar concentration of two nonprotein AA (β-alanine and γ-aminobutyric acid) varied with age of sediments; i.e., they were less abundant in recent sediments and more abundant in the oldest sediments. This trend is an indicator of extremely slow but continuous enzymatic degradation of proteinaceous OM within the sediments. So far, bulk OM has been believed to be one of the best proxies for estimation of primary productivity. However, it may be an underestimate, even for the late Quaternary sediments. Comparison of AA and HA content variations with SPECMAP stack revealed their enhanced deposition and preservation during glacial periods relative to interglacial periods. This, in turn, affected not only the planktonic production in surface waters but also the benthic community, including bacteria on the seafloor.     

Paleoenvironmental Characteristics of Paleogene Lacustrine Source Rocks in the Western Bozhong Sag, Bohai Bay Basin, China: Evidence from Biomarkers, Major and Trace Elements

The organic matter (OM) enrichment mechanisms and depositional environment characteristics of lacustrine source rocks in the western Bozhong Sag, Bohai Bay Basin in Northeast China remain controversial. To address these issues, based on Rock-Eval pyrolysis, kerogen macerals, H/C and O/C ratios, GC-MS, major and trace elements, the Dongying Formation Member (Mbr) 3 (E3d3), the Shahejie Formation mbrs 1 and 2 (E2s1+2), and the Shahejie Mbr 3 (E2s3) source rocks in the western Bozhong Sag were studied. The above methods were used to reveal their geochemical properties, OM origins and depositional environments, all of which indicate that E2s1+2 and E2s3 are excellent source rocks, and that E3d3 is of the second good quality. E3d3 source rocks were formed under a warm and humid climate, mainly belong to fluvial/delta facies, the E3d3 sediments formed under weakly oxidizing and freshwater conditions. Comparatively, the depositional environments of E2s1+2 source rocks were arid and cold climate, representing saline or freshwater lacustrine facies, and the sediments of E2s1+2 belong to anoxic or suboxic settings with large evaporation and salinity. During the period of E2s3, the climate became warm and humid, indicating the freshwater lacustrine facies, and E2s3 was characterized by freshwater and abundant algae. Moreover, compared with other intervals, the OM origin of E3d3 source rocks has noticeable terrestrial input. The OM origin of the E2s1+2 and E2s3 are mainly plankton and bacteria. Tectonic subsidence and climate change have affected the changes of the depositional environment in the western Bozhong Sag, thus controlling the distribution of the source rocks, the geochemical characteristics in the three intervals of lacustrine source rocks have distinct differences. Overall, these factors are effective to evaluate the paleoenvironmental characteristics of source rocks by biomarkers, major and trace elements. The established models may have positive implications for research of lacustrine source rocks in offshore areas with few drillings.     

Genesis of oil: A fundamental problem of geology (the current state of the problem)

The current state of the problem of oil genesis is discussed. The biogenic (sedimentary-migration theory) of oil genesis is shown to be valid based on the analysis of present-day data on the composition and properties of oil, the composition and distribution of organic matter (OM) in sedimentary rocks, and numerous calculations of the balance of oil-and-gas generation at different stages of catagenetic evolution. The confinement of oil and gas fields to sedimentary basins, as well as the relation of oil and/or gas reserves to volumes of oil-and-gas source rocks, which occur (or occurred) in the generation center, and/or to extremely high potential of oil source formations also indicate of the relationship between oil-and-gas fields and the “life” of former geological epochs.     

The Antarctic margin and its possible hydrocarbon potential

Geological and geophysical data over the Antarctic margin are reviewed to define those areas where thick sedimentary sequences occur which may have potential to source hydrocarbons. Where possible, the Waples-Lopatin model has been used to calculate whether the degree of maturation of the sediments is sufficient for hydrocarbons to have been generated.Significant sedimentary sequences occur along the continental margins of Wilkes Land, western Dronning Maud Land, Antarctic Peninsula and Ellsworth Land and, as basins or troughs, on the continental shelf of Prydz Bay, Weddell Sea and Ross Sea. Maturation assessments are possible for western Dronning Maud Land, eastern Weddell Sea, western Antarctic Peninsula, Ellsworth Land and Ross Sea regions. Within the great limitations of the data, only western Weddell Sea and Ross Sea basins have maturation values sufficient for the generation of hydrocarbons.     

Permian intermontane basin sedimentation in southern Scotland

Towards the end of the Carboniferous period, several isolated basins were eroded into Carboniferous sediments lying within the Lower Palaeozoic Southern Uplands massif. Eruption of basaltic lava flows ensued, followed by deposition of thin pediment breccias as desert conditions became established, leading to the development of extensive aeolian sands which interfinger with alluvial fan breccias at the basin margins. Such intermontane desert basins have rarely been documented in the stratigraphic record and the Permian deposits are here compared to similar deposits and processes operating in Recent intermontane desert basins. A number of breccia types have been distinguished, some attributable to secondary reworking of deflation areas on alluvial fans, and the deposits of streamfloods, braided streams, sheetfloods and desert-floor ephemeral streams have been recognised.     

青藏高原古近纪-新近纪隆升与沉积盆地分布耦合

根据在高原及邻区近7年完成的1∶250000地质填图资料, 划分出青藏高原及邻区古近系-新近系残留盆地共92个.沉积范围大且序列完整的盆地分布在高原周缘和腹地.在高原的南、北和东缘, 沿区域性大断裂带分布许多走滑拉分盆地.古新世—始新世海相地层仅分布在藏南和新疆叶城地区.藏南半深海-深海沉积沿江孜-萨嘎-郭雅拉-桑麦一线分布, 其海水东浅西深, 西部为活动型, 反映新特提斯洋闭合的时间从东向西变新, 地壳抬升首先开始于东侧.晚白垩世隆起区主要分布在研究区东北部, 高原总体地貌格局为东北高, 西南低.古新世—始新世出现了腾冲-班戈、库牙克-格尔木新的隆起带, 西昆仑隆起带向东拓展, 祁连隆起带加宽, 松潘-甘孜隆起区范围向东有所萎缩.渐新世期间, 冈底斯和喜马拉雅带掘起, 昆仑-阿尔金-祁连的进一步隆起, 造成了整个高原的周缘为山系、而腹地为盆的宏观地貌格局.中-上新世期间, 冈底斯和喜马拉雅带、喀喇昆仑-西昆仑地区进一步较大幅度隆起;高原从渐新世及其以前的东高西低格局, 经历了中新世—上新世全区的不均衡隆升和拗陷, 最终在上新世末铸就了西高东低的地貌格局, 青藏做为一个统一的高原发生了重大的地貌反转事件.青藏高原新生代的隆升过程以多阶段、不均匀、非等速为特征, 具有强烈的时空差异性.      

Erosion of the Laurentide region of North America by glacial and glaciofluvial processes

Collection of seismic reflection data from continental margins and ocean basins surrounding North America makes it possible to estimate the amount of material eroded from the area formerly covered by Laurentide ice sheets since major glaciation began in North America. A minimum estimate is made of 1.62 × 10⁶ km³, or an average 120 m of rock physically eroded from the Laurentide region. This figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift, Cenozoic marine sediments, and modern sediment loads of rivers. Most of the sediment produced during Laurentide glaciation has already been transported to the oceans. The importance of continental glaciation as a geomorphic agency in North America may have to be reevaluated. Evidence from sedimentation rates in ocean basins surrounding Greenland and Antarctica suggests that sediment production, sediment transport, and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps, such as the Laurentide. Low rates of sediment survival from the time of the Permo-Carboniferous and Precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust.     

雅鲁藏布中新生代深水沉积盆地形成和演化(Ⅱ)——喜马拉雅碳酸盐台地动力演化

喜马拉雅地区的碳酸盐台地产生、发展和消亡与特提斯造山带形成的动力演化息息相关。三叠纪时,碳酸盐台地较稳定地在聂拉木陆架边缘发展起来,主要受陆源碎屑强烈干扰,碳酸盐台地在其生长面附近发育。早、中侏罗世,碳酸盐台地受构造沉降和海平面变化强烈影响,从潮下低能带向高能变浅的镶边台地旋回性发展。在台地边缘斜坡—盆地中发育一套特殊的碳酸盐“喷溢流”沉积。晚侏罗世,碳酸盐台地受被动大陆边缘初期快速热沉降影响,被黑色页岩覆盖,台地被淹没死亡。早白垩世,陆架边缘台地可能以孤立台地为特征,相当多的碳酸盐台地碎裂或崩塌,靠大陆一侧则主要为末端变陡缓坡。晚白垩世开始,碳酸盐台地主要在岗巴一带发育,发育向上变深的沉积序列,为受前陆挠曲影响产物。第三纪初,碳酸盐台地主要为缓坡,属于前陆盆地远离造山带一侧的碳酸盐台地沉积。喜马拉雅碳酸盐台地的最终消亡是由于造山抬升暴露。     

被动大陆边缘构造演化对深水区烃源岩形成的控制

以世界被动大陆边缘含油气盆地构造演化、油气田资料为基础,采用地质综合分析方法,探讨了不同类型被动大陆边缘盆地在不同构造演化阶段深水区烃源岩的形成条件:开阔海型被动大陆边缘盆地群裂谷阶段发育大型局限湖盆,区域分布的厚层湖相富生油黑色泥页岩为主力烃源岩;边缘海型被动大陆边缘盆地群裂谷阶段发育受河流—波浪控制的大型三角洲,海陆过渡相富生气炭质泥页岩和煤系为主力烃源岩;被动大陆边缘阶段盆地群发生持续性海侵,在高水位体系域缺氧环境下的富有机质海相泥页岩为盆地重要的烃源岩。     

Late Ordovician evolution of the intracratonic basins in north-west Gondwana

The Palaeozoic intracratonic basins in northwest Gondwana, i.e. the Amazonas, Parnaiba and Acera basins, probably opened during late Caradoc and Ashgill times. The fluviatile sedimentation later changed to littoral at the basinal margins. A transgression from the north-west region of Gondwana slowly overlapped the margins of the intracratonic basins. The transgression reached its maximum in the Rawtheyan (late Ashgill), as evidenced by fossiliferous shallow marine sediments in the Amazonas Basin. The Hirnantian glaciation in north Gondwana lowered the sea level, and in the Amazonas Basin a littoral sedimentation followed on shallow marine strata. From the opening of the basins onwards, a shallow sea probably existed close to the epicontinental basins in north-west Gondwana. The basins were connected via a narrow passage between the Guayana and Ivorian cratons.     

前陆盆地层序地层与油气聚集

从区域构造的观点看, 同板块碰撞有关的前陆盆地是油气聚集的有利地区。两个板块的相互碰撞形成一系列的造山带, 而在相对稳定板块的前缘常常形成前陆盆地。由于前陆盆地的特点, 使它对油气的生成、运移、聚集和保存都十分有利, 世界上前陆盆地是油气最富集的一类盆地。前陆盆地层序地层学是将层序地层学理论应用于褶冲带和前陆盆地的一个特例, 假定物源供给稳定, 前陆盆地可容空间的变化主要受控于构造作用和全球海平面变化。本文通过概括前陆盆地不同级别的地层层序、旋回及其成因, 揭示造山带构造运动、盆地沉积作用和海平面变化之间的内在联系, 进一步研究前陆盆地的沉积一构造演化, 提出前陆盆地的油气潜力主要取决于早期被动边缘发育程度和保存条件, "薄皮"逆掩断层带具一定油气潜力, 具有多种类型油气圈闭, 以及盆地晚期的前缘沉积有利于早期沉积的埋藏、成熟和保存等四项前陆盆地与油气关系的结论和认识, 为油气资源勘探提供理论依据。      

Lithology and late postglacial stratigraphy of bottom sediments in isolated basins of the White Sea coast exemplified by a small lake in the Chupa settlement area (Northern Karelia)

The complex lithological, geochemical, geochronological, and micropaleontological (diatoms, spores, pollen) investigations of stratified bottom sediments that constitute facies-variable sedimentary sequences in a small isolated lake located near the upper limit of the sea on the White Sea coast made it possible to define lithostratigraphic units (LSU) forming the complete sedimentary succession in deep parts of isolated basins. It is shown that stratigraphy of heterogeneous sequences is determined by two regional transgressive–regressive cycles in relative sea level fluctuations: alternating late Glacial and Holocene transgressions and regressions. The lower part of a clastogenic clayey–sandy–silty sequence successively composed of freshwater (LSU 1) and brackish-water (LSU 2) sediments of the ice-marginal basins and marine postglacial facies (LSU 3) was formed during the late Glacial glacioeustatic marine transgression. Its upper part formed in different isolated basins at different stages of the Holocene is represented depending on its altimetric position on the coastal slope by costal marine sediments (LSU 4) and facies of the partly isolated inlet (LSU 5). The organogenic sapropelic sequence, which overlies sediments of the marine basin and partly isolated bay, corresponds to lithostratigraphic units represented by Holocene sediments accumulated in the meromictic lake (LSU 6), onshore freshwater basin (LSU 7), and freshwater basin with elevated water mineralization (LSU 8) deposited during maximum development of Holocene transgression and lacustrine sediments (LSU 9) formed in coastal environments during terminal phases of the Holocene. The defined lithostratigraphic units differ from each other in lithological, micropaleontological, and geochemical features reflected in structural and textural properties of their sediments, their composition, inclusions, and composition of paleophytocoenoses and diatom assemblages.     

Occurrence of rare borate minerals: Veatchite-A,tunellite, teruggite and cahnite in the Emet borate deposits,Turkey

The Emet borate deposits were formed in two separate basins, possibly part of an interconnected lacustrine playa lake, in areas of volcanic activity, fed partly by thermal springs and partly by surface streams. The borates are interlayered with tuff, clay and marl. Limestone occurs above and below the borate lenses. Sediments in both basins are similar but borate minerals show different mineralogical and geochemical features in the two basins.The Emet borate deposits are the only deposits known to contain any of the minerals veatchite-A, tunellite, teruggite and cahnite. Principal minerals are colemanite, with minor ulexite, hydroboracite and meyerhofferite.Thermal springs associated with local volcanic activity are thought to be the source of the borates. The initial brines from which the borates crystallized are deduced to have been high in sulphite and sulphate, low in chloride, and hence it is assumed that the initial brines were fed at all times by abundant calcium and boron with minor amounts of arsenic, strontium and sulphur. Realgar, celestite and native sulphur are almost ubiquitous in borates and sediments, and appear to have formed at all stages during deposition and diagenesis.The early colemanite, meyerhofferite, ulexite and teruggite nodules were probably formed directly from brines penecontemporaneously within the unconsolidated sediments below the sediment/water interface, and continued to grow as the sediments were compacted. Later generations of colemanite occur in vugs, veins and as fibrous margins to colemanite nodules. Tunellite appears to have formed during diagenesis with enrichment of Sr in some places. Diagenetic alterations include the partial replacement of colemanite by veatchite-A, cahnite, hydroboracite and calcite.