Geochemistry and isotope chemistry of CaNaCl brines in Silurian strata,Michigan Basin,U.S.A.

Formation waters from Silurian-aged reefs in the northern and southern trends of lower Michigan were collected and analyzed for major, minor and isotope compositions. The results were combined with an analysis of an exceptionally concentrated (TDS 640 g/l) Silurian brine reported by Case in 1945 to determine the origin and possible evolutionary pathways for the chemical and isotope components of the brines. The waters are extremely concentrated(TDS> 450g/l) CaNaCl brines. Bromide values support that they originated from seawater concentrated into the MgSO₄ and possibly the KCl salt facies. The brines have, however, evolved considerably from an expected seawater composition and now contain a dominant CaCl composition. Dolomitization appears to have been very important in the brine evolution, but this process cannot explain all the Ca present in these brines. Four scenarios may explain the enrichment in Ca: (1) halite dissolution accompanied by the exchange of Na for Ca; (2) reactions involving aluminosilicate minerals, carbonates and halite; (3) an input of CaCl₂ solutions derived from altered MgCl₂ fluids released during the metamorphism of carnallite into sylvite; and (4) a pre-existing enrichment of CaCl in the Early Paleozoic seawater that filled the basin. All four are possible, but the favored explanation involves the diagenesis of the Salina A-1 potash salts. The isotope composition of the waters is consistent with evaporated seawater, perhaps enriched by exchange with carbonates or by the input of hydration water from evaporite minerals. The isotopic evolution, however, is equivocal but the brine composition does not indicate they have been diluted with meteoric water. This implies the waters have remained isolated from surface-controlled hydrological systems.     

鄂尔多斯盆地奥陶系盐下白云岩储层特征、成因及分布

奥陶系盐下白云岩储层是鄂尔多斯盆地中东部天然气勘探的重要接替领域.基于钻井岩心、微观薄片、物性分析及地球化学特征等资料,应用微区多参数实验分析方法,对奥陶系盐下白云岩储层特征、成因与分布开展了系统研究.结果表明:①奥陶系盐下主要发育颗粒滩白云岩和微生物白云岩储层,其中颗粒滩白云岩储层岩性为砂屑白云岩、鲕粒白云岩和粉—细...     

Late Paleozoic remagnetization of the Trenton Formation in Ordovician petroleum reservoirs of southwestern Ontario

A paleomagnetic study of subsurface core samples from dolomitized carbonates of two producing reservoirs in the Upper Ordovician Trenton Formation, collected from four wells in southwestern Ontario yielded a paleomagnetic direction of D = 152.3°, I = − 12.3° (N = 49, α₉₅ = 8.7). This characteristic remanent magnetization (ChRM) direction was azimuth-corrected by aligning the viscous remanence magnetization (VRM) with the present Earth's magnetic field direction. A drilling-induced magnetization (VRMdi) was present in less than half the specimens sampled in this study. In addition, where the VRM correction could not be made, a paleolatitudinal arc calculated from the inclination-only mean of I = − 9.0° (N = 34, α₉₅ = 3.0°) intersected the apparent polar wander path in the Late Permian–Early Triassic. These paleodirections are similar to the paleomagnetic directions observed in Ordovician Trenton carbonates from the Michigan Basin and New York State, U.S.A., suggesting a related regional late Paleozoic remagnetization.     

Petrographic and geochemical characterization of coal from Talcher coalfield,Mahanadi Basin,India

In the present study an attempt has been made to characterize the coals of Talcher coalfield employing petrographic and geochemical techniques on a large number of coal samples. Pillar coal samples were collected from all the six workable coal seams, which occur in the Karharbari (Seam-I) and the Barakar (Seams II, III, IV, V and IX) formations.     

Migration,filling history and geochemical characteristics of Ordovician natural gases in the Tahe Oilfield,Tarim Basin,Northwest China

Ordovician natural gases in the Tahe Oilfield are composed predominantly of hydrocarbon gases dominated by methane with a significant amount of heavy hydrocarbon gas component. The non-hydrocarbon gases include N₂, CO₂ and minor H₂S. The Ordovician natural gases are believed to have originated from the same source rocks, and are composite of gases differing in thermal maturity. Carbon dioxide was derived from thermal metamorphism of Ordovician carbonate rocks. The generation of natural gases involves multiple stages from mature normal oil and condensate-associated gas to thermally cracked gas at the maturity to over-maturity stages. In the main part of the Tahe Oilfield, the Ordovician natural gases appear to be filled in two major phases with a typical petroleum-associated gas from southeast to northwest and from east to west in the early stage; and a thermally cracked gas from east to west in the late stage. At the same time, the oil/gas filling boundary has been primarily established between the two stages.     

塔里木盆地满加尔凹陷西北缘上奥陶统铁热克阿瓦提组海相砂体类型与储集性

通过对羊屋2井、跃南2井、吉南1井等5口井岩心的精细描述、单井沉积微相与测井相分析及350 km地震剖面解释,认为在满加尔凹陷西北缘上奥陶统铁热克阿瓦提组海相砂泥岩沉积地层中发育5种重要的海相砂体,即滨岸（临滨-前滨）砂体、内陆棚沙脊砂体、内陆棚沟槽砂体、风暴砂体与潮道砂体。在等时地层格架内,研究区西部羊屋与哈得井区,铁热克阿瓦提组最底部分布着具有正韵律特点的、发育海侵砾岩与冲刷面的内陆棚沟槽砂体,其上为正反韵律均有且冲刷面不发育的较细粒内陆棚沙脊砂体,上部则是发育平行层理和冲洗交错层理的具明显反韵律特征的滨岸（临滨-前滨）砂体,顶部发育非均质性较强的风暴层砂体。在东部的吉南井区,下部发育内陆棚沙脊砂体,上部发育潮下带潮道砂体及潮间带砂坪沉积。受奥陶纪末期全球海平面下降影响,砂体分布范围逐步增大。铁热克阿瓦提组海相砂岩储集体以次生孔隙为主,非均质性比较强,导致储集层非均质性的主要原因是不均匀胶结作用、溶解作用以及局部发育有裂缝。对比5种类型海相砂体的储集性,按优差排序依次是内陆棚沙脊砂体、滨岸（临滨-前滨）砂体、内陆棚沟槽砂体、潮道砂体与风暴沉积砂体。
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Geological evolution of the Ishpeming Greenstone Belt,Michigan, U.S.A.

The Ishpeming Greenstone Belt is an Archean belt in the southern part of the Canadian Shield in the Upper Peninsula of Michigan, U.S.A. Two volcanic cycles are preserved in it. The oldest formation, and basal to the first cycle (the Kitchi Schist), consists of mafic metavolcanics, has a major serpentinized ultramafic body near its base, and grades upward to a coarse felsic volcanic breccia at the top of the cycle. This unit in turn is overlain by a sequence of mafic flows that grades upward to interbedded mafic flows and exhalites of the Mona Schist. This sequence has been intruded by the Dead River Pluton.The Ishpeming Greenstone Belt probably represents the keel of a previously much more extensive Greenstone Belt.Gold mineralization occurs associated with mafic basaltic volcanic rocks and serpentinized ultramafics low in the succession, and with carbonate-rich quartz-chlorite-sericite schists and exhalites higher in the sequence. No mineral deposits are now being exploited here.     

Origin of dolomite in the Late Jurassic platform carbonates,Bolkar Mountains,Central Taurides,Turkey: Petrographic and geochemical evidence

The Late Jurassic-early Senonian Cehennemdere Formation extending in an E-W direction in a wide area at the south of the Bolkar Mountains (Central Taurides, Turkey) is composed of platform carbonates. The formation was deposited in an environment that was being transformed from a shallow carbonate platform to an open shelf and a continental slope, and was buried until late Paleocene uplift. The formation, with a thickness of about 360 m, was chiefly developed as textures consisting of mudstone and wackestone and has been commonly dolomitized. Based on petrographic and geochemical properties, four types of replacement dolomites and two types of dolomite cements were distinguished. Replacement dolomite (RD), which is cut by low-amplitude stylolites developed as (1) fine crystalline planar-s dolomite (RD1); (2) medium crystalline planar-s dolomite (RD2); (3) medium-coarse crystalline planar-e dolomite (RD3) and; (4) coarse crystalline planar-s (e) dolomite (RD4). Two types of dolomite cements (CD) observed in low abundance and overlie low-amplitude stylolites: (1) coarse crystalline dolomite cement (CD1) filling dissolution voids and fractures in RD1 dolomites, and; (2) rim dolomite cement (CD2) that commonly develops on the space-facing surfaces of RD4 dolomite. Replacement dolomites are non-stoichiometric (Ca_54–59Mg_41–46), have similar geochemical properties, and are generally dull red/non luminescent in appearance. Replacement dolomite is represented by δ¹⁸O values from −4.5 to −0.5‰ VPDB, δ¹³C values of −0.7 to 2.7‰ VPDB, and ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.707178 to 0.707692. Petrographic and geochemical data indicate that replacement dolomite (particularly RD2, RD3, and RD4 dolomite) was formed at shallow-intermediate burial depths during the Late Jurassic-Early Cretaceous, from seawater and/or from slightly modified seawater. The replacement dolomite (RD) was then recrystallized at increased burial depths and temperatures. Dolomite cements are similar to replacement dolomites in that they are non-stoichiometric (Ca₅₅Mg₄₅) and have similar trace element compositions. CD1 dolomite, which cuts low-amplitude stylolites, was formed during intermediate to deep burial following stylolite development. CD2 dolomite was precipitated in intercrystal pores in association with RD4 dolomite. Remaining pore space was filled with bitumen.     

贵州泥堡金矿床构造蚀变体岩相学及地球化学特征

贵州泥堡金矿构造蚀变体(SBT)为产出于茅口组(P_2m)和龙潭组(P_3l)或峨眉山玄武岩(P_3β)之间沉积间断面-不整合界面附近的一套硅质蚀变岩石组合。采用光学显微镜及ICP-MS研究SBT样品岩相学及元素地球化学特征,结果显示,SBT矿石样品中主要矿物有石英、黄铁矿、褐铁矿、萤石、白云石和辉锑矿等,蚀变类型主要为黄铁矿化、白云石化和硅化,微观结构主要为砂状、岩屑-凝灰碎屑结构、交代结构等,构造主要有浸染状、块状、角砾状、条带状和脉状构造。SBT微量元素标准化曲线以Au、As、Sb、Hg、Te的强烈富集,Li、Sc、Cr的亏损和Cd、Ta的富集为特征。稀土元素CI球粒陨石标准化配分模式图表现为轻稀土富集的右倾型,LREE/HREE为6. 98～19. 91,"四分组"效应明显,重稀土分馏不明显,解释为受热液作用强烈; SBT微量元素标准化图及稀土元素配分曲线均表现出与围岩相似,表明继承了原岩的元素组成;δEu为0. 80～1. 84,显示Eu从明显负异常到明显的正异常;δCe为0. 72～1. 25,显示Ce从明显负异常到弱正异常,认为流体来源于深部或至少经历过对富含斜长石源区的水-岩反应,而不是含矿地层的改造热液。     

Petrochemistry of the Fish Cove rhyolite,Keweenaw peninsula,Michigan, U.S.A.

A small (360 × 180 m) rhyolitic intrusive body in the lower portion of the Portage Lake Lava Series of Michigan's Keweenaw peninsula was mapped and sampled in detail. The rhyolite is one of a number of similar bodies which make up less than 1% of the total volume of this thick Late-Precambrian plateau basalt pile. The rock is a low-calcium rhyolite with fine-grained homogeneous texture and sparse phenocrysts of plagioclase and quartz. Analyses of selected trace and major elements for 21 samples taken from the body reveal a chemical zonation consisting of a core zone enriched in K, Rb and Ba, and a border zone relatively poor in these elements. Little areal difference is found with respect to other elements tested (Mn, Sr, Zr, Ca, Ti, and Fe). This apparently primary zonation seems to result from the migration of K, Rb and Ba during crystallization of the shallow intrusive. Though zoned, the trace-element chemistry of the Fish Cove body is distinct from that of eight other rhyolites in the Portage Lake Lava Series, and suggests that fingerprinting by trace elements might be a fruitful method for identifying and correlating the sources of numerous rhyolitic pebbles in conglomerates interbedded with the basaltlava flows of the Portage Lake Series.     

鄂尔多斯盆地奥陶系马家沟组马五段白云岩的同位素地球化学特征

鄂尔多斯盆地中央气田奥陶系马家沟组马五段白云岩是重要的油气储集层,多年来,马家沟组白云岩的成因问题一直是地质研究者讨论的热点话题.对马五段白云岩的C、O、Sr同位素地球化学资料的分析表明,孔洞充填的白云石(含鞍状白云石)和白云岩的δ13C、δ18O值极其近似,且白云岩的δ18OPDB值比奥陶纪海水值要偏负1.752‰～4.395‰(平均2.911‰);成岩流体(水)的占δ18OSMOW平均值为+8‰,比当时海水值偏正;87Sr/86Sr比值比奥陶纪海水87Sr/86Sr比值要高.从C、O同位素数据上看,形成白云岩和沉淀于孔洞中的白云石(含鞍状白云石)的流体为同源流体;造成白云岩的δ18O值偏负的原因主要是埋藏条件的"温度效应";87Sr/86Sr比值偏高可能是交代流体来自或流经了富含放射成因Sr的铝硅酸盐基底或硅质碎屑岩.这些特征表明马五段白云岩很可能形成于埋藏环境.     

Petrographic and geochemical characteristics of the Paleogene sedimentary rocks from the North Jiangsu Basin,Eastern China: implications for provenance and tectonic setting

The petrography and geochemistry (major, trace, and rare earth elements) of clastic sedimentary rocks from the Paleogene Dainan Formation (E₂ d) in the North Jiangsu Basin, eastern China, are investigated to trace their provenance and to constrain their tectonic setting. The studied samples are characterized by LREE enrichment, flat HREE, and negative Eu anomaly similar to the upper continental crust composed chiefly of felsic components in the source area. Petrographic observation indicates that the sandstones contain predominant metamorphic and sedimentary clasts that were derived from peripheral recycled orogen and intrabasinal materials. The trace element ratios (Co/Th, La/Sc, La/Th, and Th/U) and the La-Th-Sc ternary plot further confirm that the sandstones are derived from granitic gneiss sources from recycled orogen and the intrabasinal mixed sedimentary provenance. The granitic gneiss source rocks may have derived from the Proterozoic granitic gneiss denuded in the eastern Dabie-Sulu orogen; and the intrabasinal provenance may come from the underlying strata during the Late Paleocene Wubao movement. The chemical index of alteration (CIA) and A-CN-K plot show that these source rocks may have experienced weak to medium chemical weathering. Analysis on tectonic setting of the source area suggests an active continental margin, which is intimate with tectonic feature of the Dabie-sulu orogen and the Yangtze block. In summary, we suggest that the North Jiangsu Basin is an ideal site for the study of the coupling between the uplift of the orogen and the subsidence of the foreland basin.     

松辽盆地白垩系青山口阶缺氧事件层的有机地球化学特征

松辽盆地白垩系青山口阶下部广泛分布一套富含有机碳的黑色泥岩、页岩沉积,它具有干酪根碳同位素正偏、重排甾烷含量低,普遍存在伽马蜡烷生物标志化合物等有机地球化学特征,代表了白垩纪温室效应时间窗内古湖泊贫氧环境条件下的沉积产物。结合生物地层研究成果,认为青山口阶下部曾发生过古湖泊缺氧事件,其层位大体可与白垩纪古海洋Cenomanian-Turonian界线事件层进行对比,由此提出了松辽盆地青山口阶下部的时代归属于晚白垩世Cenomanian晚期—Turonian早期的新观点。     

The geochemical characteristics and genetic types of crude oils in the western depression of the Liaohe Basin,China

The physical properties and group compositions of crude oils in the western depression of the Liaohe Basin possess such characteristics as to increase gradually in density, viscosity and wax contents, and decrease in saturated hydrocarbon and non-hydrocarbon and bitumen contents from the deep level to the shallow level and from the center of the depression to its boundary. Saturated hydrocarbons have various spectra, such as single peak and double peak patterns, front peak and rear peak patterns, and smooth peak and serated peak patterns, as well as the chromatograms of biodegraded n-alkanes. The ratios of Pr/Ph in crude oils from the southern part of the depression are generally higher than those in the northern part. The distribution of regular steranes C₂₇–C₂₉ is predominantly of the ramp type, and only a few samples have relatively high C₂₈ contents in the southern part of the depression. As viewed from their physical properties and geochemical characteristics, crude oils in the study area can be divided into two types (I and II) based on oil-generating sources and sedimentary environments, and then further divided into three sub-types (I_a, I_b and I_c:II_a, II_b and III_c, respectively) based on their degrees of maturation and secondary transformation. This will provide the reliable basis for oil-source correlation and petroleum exploration and prediction.     

Molecular Geochemical Evidence for the Origin of Natural Gas from Dissolved Hydrocarbon in Ordovician Formation Waters in Central Ordos Basin

1IntroductionTheOrdosBasinisthesecondlargestoilandgas bearingbasininChina .ItislocatedinthePaleo zoicplatformandbelongstoacratonbasin ,whichisincongruencewiththePaleozoicdepressionattheedgesoftheplatformandtheMesozoic Cenozoicdepressionwithintheplatform .SincethediscoveryofnaturalgasesinWellShancan 1andWellYu 3in 1989,theassessmentandexplorationofOrdovicianweatheringcrustnaturalgasesintheOrdosBasinhaveattractedextensiveatten tion (YangJunjieetal.,1996 ;DaiJinxingetal.,1997) .Thecentral…     

塔里木盆地下奥陶统白云岩类型及其成因*

下奥陶统白云岩是塔里木盆地最现实的重点勘探领域。文中在分析塔里木盆地早奥陶世构造、沉积及古气候等地质背景的基础上,以前人对白云岩的结构分类为基础,从白云岩发育产状出发,将塔里木盆地下奥陶统白云岩划分为灰岩中零散白云石、灰岩中斑状白云石、层状白云岩和沿断裂分布白云岩4类,白云石含量层位上自下而上具有总体减少的趋势。各类白云岩在岩石学特征和发育分布上具有较为明显的差异,局部可重叠出现。灰岩中零散白云石和斑状白云石的岩石学和地球化学及发育分布特征均反映其主要由浅埋藏白云石化作用形成;层状白云岩和沿断裂分布白云岩形成于中深埋藏白云石化作用;各类白云岩的产状特征差异受控于沉积期海平面变化、海水性质及埋藏条件等因素。沿断裂分布白云岩的形成和分布与断裂密切相关,是重要的储集岩石类型。白云岩储集层的形成主要是后期改造的结果,埋藏白云石化作用并未对大规模白云岩储集层的形成起到建设性作用,伴生或后期流体再运移导致的溶蚀作用为其主要成因。     

望天鹅火山岩石地球化学特征及其成因

东北吉林望天鹅新生代火山岩（7．04—1．86Ma）主要由玄武粗安岩和碱性流纹岩组成。玄武粗安岩的SiO2介于49．38％-53．31％之间;K2O＋Na2O为4．27％-7．72％;∑REE为163．69×10^-6-258．55×10^-6,Eu异常不明显,δEu为0．72～1．17;碱性流纹岩具高SiO2（70．39％～71．49％）含量,高碱（K2O＋Na2O为9．28％～9．49％）,高稀土总量（∑REE介于309．30×10^-6～465．03×10^-6之间）,明显的Eu负异常,3Eu为0．52～0．71。碱性流纹岩的微量元素含量较玄武粗安岩高,且具有明显的Sr、P、Ti负异常。望天鹅火山岩的^87Sr／^86Sr比值在0．705156-0．709029之间,而^144Nd／^143Nd比值变化较小,介于0．512295～0．512602之间;放射性成因Pb同位素变化范围也较小,^206Ph／^204Pb为17．254～18．090,^207Ph／^204Pb为15．460～15．507,^208Pb／^204Ph为37．278—38．048。综合分析火山岩的主量元素、微量元素和Sr-Nd—Pb同位素特点,初步认为望天鹅火山的玄武粗安岩和碱性流纹岩具有相同的地幔源区。玄武粗安岩起源于微弱富集上地幔,在上升过程中结晶分异形成了碱性流纹岩。     

Degradation and Metamorphic Differentiation of the Keweenawan Tholeiitic Lavas of Northern Michigan, U.S.A.

The Portage Lake Lava Series of the Keweenaw Peninsula, northernMichigan, is composed of over 5000 m of tholeiitic lava flows.Chemical and petrologic study of thin undifferentiated flowsfrom this sequence shows that the bulk of the flows are olivinetholeiites; highly ironenriched tholeiites comprise up to 10per cent of the volume. In addition, a few small rhyolitic intrusives,exceedingly rich in alkalis, are exposed in the region. Duringburial the amygdular tops of each flow acted as channelwaysfor migrating fluids during a regional metamorphic event thatproduced a progressive sequence of secondary phases within theflow tops. In the upper part of the stratigraphic section, laumontite,analcime, albite, and chlorite dominate assemblages characteristicof the zeolite facies. Stratigraphically deeper. flow tops arecharacterized by metamorphic assemblages of the prehnite-pumpellyitefacies. Within the higher rank facies, rocks along fractureshave been transformed to calcium-rich monomineralic domains(metadomains) of epidote or pumpellyite. These metadomains gradeoutward through incompletely reconstituted rocks containingalbitized feldspars, and finally, in flow centers, to basaltdisplaying few signs of mineralogical readjustment. Extremechemical disparity exists within the altered flow tops, particularlywith respect to calcium and sodium content. Calculations revealthat bulk compositions of metamorphically adjusted flow topsare similar to unaltered basalts. Thus, the chemical variationdisplayed by the metamorphic rock types resulted from localizedmetamorphic differentiation. The Keweenawan sequence displays progressive dehydration fromthe top to the base of the stratigraphic section. At the topchlorite (H₂O = 12 per cent) and pumpellyite (H₂O = 6 per cent)metadomains formed by dehydration. The fact that most of theserocks were hydrated strongly suggests that fluid pressures wereless than total pressures during the metamorphic event. In rocksundergoing hydration in the uper part of the stratigraphic section,therefore, water pressures decreased away from channelways.As a result, the most hydrous rock types formed in these regions.Conversely, in rock undergoing dehydration water pressures increasedaway from channelwasys, so that the most dehydrated rocks formedin such regions. Water content of an individual rock is dependenton both position in the stratigraphic pile and position withrespect to fluid channelways.     

Petrographic characteristics of the Proterozoic Vempalle carbonates,Cuddapah Basin,India and their implications

The Vempalle Formation of the Proterozoic Cuddapah basin has a well developed sequence of carbonate rocks, which are interbedded with shales, siltstones and chert. The stromatolitic carbonates are conspicuous at many places but the oolitic carbonates are less prominent and are present only in some areas. All the carbonates are pervasively dolomitized. Petrographic examination of these carbonates revealed that they are predominantly made up of fine grained micrite with patchy development of sparite and chert/quartz. The stromatolitic carbonates show distinct banding of alternate carbonate and cherty layers. The latter are rich in organic matter indicating prevalence of profuse biogenic activity. The oolitic carbonates comprise of ooids showing both concentric and radial patterns and made up of carbonate/chert and cemented by micro/mega quartz or carbonate itself. Diagenetic and post depositional features are reflected in cementation, recrystallization, compaction, stylolite formation and silicification processes. Various stages of cementing material are observed. Secondary vein fillings of carbonate or quartz traverse the carbonate/cherty groundmass. Intraclasts present suggest occasional erosional destruction of associated sediments, short lived transport and local redeposition. Accessory silicate minerals represent terrigenous influx during deposition. Dolomitization of the carbonates was fabric retentive and early diagenetic. The environmental conditions were characterised by low energy, within a shallow water zone, in occasional higher energy events and turbulence. The carbonates appear to have been deposited on a shallow water ramp within a tidal regime.     

百色盆地东部坳陷古近系那读组烃源岩的地质及地球化学特征

百色盆地东部坳陷古近系那读组的那一段上亚段和下亚段以及那二段广泛发育厚度很大的暗色泥岩,累计厚度可达200～1000m。在东部坳陷的绝大部分地区三段地层暗色泥岩的有机碳含量都在1．0％以上,是好的烃源岩。三套高效源岩的干酪根均以ⅡA型为主,次为ⅡB型和Ⅲ型,干酪根类型分布受控于沉积环境。那一段泥岩的Ro值为0．4％～0．65％,处于未成熟一低成熟阶段;那二段在较深部位的Ro值为0．7％～0．8％或更高,处于成熟阶段的早期。该坳陷的暗色泥岩厚度高值区、半深湖区、有机碳含量高值区、Ro高值区是一致的;沉积中心、沉降中心与生烃中心吻合。那二段成熟度相对较高,已达到成熟阶段早期,源岩厚度、沉积环境、有机质丰度和类型等也比较有利,因此,那二段应是本区的最主要的高效烃源岩。田东沉积区面积较大、泥岩厚度较大、半深湖区范围较大、有机碳含量较高、有机质类型较好、有机质的成熟度也相对较高,因此,田东沉积区比田阳沉积区更具有生、排烃的潜力。