煤相参数在煤层层序划分中的应用——以新疆准东煤田帐南西矿区为例

运用层序地层学原理和方法,利用钻探和测井资料以及煤的显微组分和煤相参数分析,对新疆准东煤田西山窑组的层序单元进行了划分,特别对煤层中的准层序进行了确定。研究结果表明:西山窑组为 1个三级层序,并由低位、湖扩和高位体系域构成;在煤层中确定了水进型、水退型 2种准层序类型以及缓慢水进型准层序组和相对快速水进型准层序组;湖扩体系域由水进型和水退型煤层构成,高位体系域由水退型煤层构成;煤层煤相总体为干燥森林沼泽。      

Changes to depositional palaeoenvironments within the Qikou depression (Bohaiwan Basin,China): carbon and oxygen isotopes in lacustrine carbonates of the Palaeogene Shahejie Formation

This paper reports the carbon and oxygen isotope compositions of lacustrine carbonate sediments from the Palaeogene Shahejie Formation, Qikou depression, Bohaiwan Basin, with the aim of determining the palaeoenvironmental conditions in the region. Results from Es₂, the second member of the Shahejie Formation, showed values of δ¹³C and δ¹⁸O from –1.2‰ to +2.4‰ (average +0.6‰) and from –6.8‰ to –4.7‰ (average –5.7‰), respectively, suggesting a relatively hot climate attending deposition. The slightly closed nature of the lake, which contains brackish water, resulted in higher carbonate δ¹³C and δ¹⁸O values than in a meteoric environment. The values of δ¹³C and δ¹⁸O preserved within the carbonates of the overlying lower Shahejie I (Es₁) varied between +1.3‰ and +4.9‰ (average +3.2‰) and from ?4.4‰ to ?1.8‰ (average ?3.1‰), respectively, indicating that the climate became colder at that time. Subsequently, a marine transgression caused the salinity of the lake water to increase. The values of δ¹³C and δ¹⁸O were controlled by salinity. The high δ¹³C values were also influenced by the rapid burial of the lake organisms and by algal photosynthesis. Values of δ¹³C and δ¹⁸O from carbonates in upper Es₁ ranged from ?8.0‰ to +11.0‰ (average +10.1‰) and from ?5.0‰ to ?1.5‰ (average ?3.4‰), respectively, indicating a slight increase in the temperature over time. In the closed and reducing environment, extremes in δ¹³C values resulted from biochemical fermentation. The positive δ¹³C excursion recorded in the carbonates of the Shahejie Formation in the Qikou depression indicates that the palaeoclimate underwent a significant transformation during the Eocene and the Oligocene.     

Carbon- and Oxygen-Isotopic Behavior of Carbonate Rocks of the Phosphatic Gramame Formation,Pernambuco-Paraíba Coastal Basin,Northeastern Brazil

In the basal section of the carbonates of the Maastrichtian Gramame Formation in the Pernambuco-Paraiba coastal basin of northeastern Brazil, major phosphate concentrations (P₂O₅ > 10%) were deposited in shallow-marine environments (inner shelf). In contrast, dolomite-associated phosphates are characterized by low P₂O₅ concentrations (<10%) and were deposited in the relatively deep water of a platform ramp, under conditions of limited oxygen availability. Calcite is the main carbonate phase remaining after the diagenesis that affected the phosphorite. A positive δ¹³C (up to +2%_PDB), coupled with a positive MgO-δ¹⁸0 correlation in the phosphate-enriched carbonates, suggests that upwelling currents were the early phosphogenic vectors during marine transgression, in contrast to warm superficial seawater that prevailed during the Maastrichtian elsewhere. The major phosphate concentrations are related to reworking and diagenesis in a shallow shelf environment during a regression pulse of sea level, followed by a dramatic drop of δ¹³C to negative values (down to ?6%_PDB). This study suggests that carbon and oxygen isotopes can be used as potential tools for phosphorite prospecting elsewhere.     

塔里木盆地玉尓吐斯组高频层序沉积充填演化特征及控烃作用

结合9个野外剖面和17口井,对塔里木盆地玉尔吐斯组沉积演化及其对烃源岩的制约作用进行了系统研究和分析。在精细对比后发现,塔里木盆地下寒武统玉尔吐斯组可分为2个三级层序(SQ1、SQ2)、5个四级层序(sq1—sq5),其中三级层序SQ1可分为3个四级层序,SQ2可分为2个四级层序。SQ1发生在寒武纪初期,海进速度较慢,影响范围相对局限,而SQ2的海进则相对迅速,影响范围较大。四级层序sq1发生在第一次海侵初期,水体浅,主要沉积紫红色白云岩、灰黑色砂屑白云岩,起填平补齐的作用;sq2、sq4发生在海侵—海退的转换时期,是两套深水的沉积,岩性以黑色泥岩、硅质泥岩和硅质岩为主,局部发育泥岩与条带状白云岩互层;sq3、sq5是海退过程中的浅水沉积,主要发育灰色白云岩和藻白云岩,局部有泥质夹层。利用Mn、Fe、Ti、Rb、K、Sr、Ba、Cu、U、V、Mo等元素及其比值进行沉积环境分析表明,sq2时期,水体深度大、盐度低、气候温暖湿润,有利于生物发育,并且其硫化缺氧的环境极其有利于有机质的保存;sq4时期,水体深度较大,盐度相对较小,气候相对温暖湿润,较为适合生物生存,并且其硫化缺氧夹次氧化的环境,较为适合有机质保存。高频海平面变化与沉积环境演化影响着玉尔吐斯组的烃源岩分布与品质,sq2时沉积的烃源岩品质优于sq4,但是其分布范围小于sq4。     

Multiple Dolomitization and Fluid Flow Events in the Precambrian Dengying Formation of Sichuan Basin,Southwestern China

The Precambrian Dengying Formation is a set of large-scale, extensively dolomitized, carbonate reservoirs occurring within the Sichuan Basin. Petrographic and geochemical studies reveal dolomitization was a direct result of precipitation by chemically distinct fluids occurring at different times and at different intensities. Based on this evidence, dolomitization and multiple fluid flow events are analyzed, and three types of fluid evolution models are proposed. Results of analysis show that Precambrian Dengying Formation carbonates were deposited in a restricted peritidal environment(630–542 Ma). A high temperature and high Mg~(2+) concentration seawater was a direct result of dolomitization for the micrite matrix, and for fibrous aragonite in primary pores. Geochemical evidence shows low δ~(18)O values of micritic dolomite varying from-1.29‰ to-4.52‰ PDB, abundant light rare earth elements(REEs), and low dolomite order degrees. Microbes and meteoric water significantly altered dolomite original chemical signatures, resulting in algal micritic dolomite and the fine-grained, granular, dolosparite dolomite having very negative δ~(18)O values. Finely crystalline cement dolomite(536.3–280 Ma) and coarsely crystalline cement dolomite have a higher crystallization degree and higher order degree. The diagenetic sequence and fluid inclusion evidence imply a linear correlation between their burial depth and homogenization temperatures, which closely resemble the temperature of generated hydrocarbon. Compared with finely crystalline dolomite, precipitation of coarsely crystalline dolomite was more affected by restricted basinal fluids. In addition, there is a trend toward a more negative δ~(18)O value, higher salinity, higher Fe and Mn concentrations, REE-rich. Two periods of hydrothermal fluids are identified, as the exceptionally high temperatures as opposed to the temperatures of burial history, in addition to the presence of high salinity fluid inclusions. The early hydrothermal fluid flow event was characterized by hot magnesium-and silicon-rich fluids, as demonstrated by the recrystallized matrix dolomite that is intimately associated with flint, opal, and microcrystalline quartz in intergranular or intercrystalline pores. This event was likely the result of a seafloor hydrothermal chimney eruption during Episode I of the Tongwan Movement(536.3±5.5 Ma). In contrast, later hydrothermal fluids, which caused precipitation of saddle dolomite, were characterized by high salinity(15–16.05 wt% NaCl equivalent) and homogenization temperatures(250 to 265°C), δ~(18)O values that were more enriched, and REE signatures. Geochemical data and the paragenetic sequence indicate that this hydrothermal fluid was related to extensive Permian large igneous province activity(360–280 Ma). This study demonstrates the presence of complicated dolomitization processes occurring during various paleoclimates, tectonic cycles, and basinal fluids flow; results are a useful reference for these dolomitized Precambrian carbonates reservoirs.     

准噶尔盆地中部2区块高分辨层序地层研究

根据沉积相序变化、准层序叠加样式、测井曲线特征,运用关键坡折带知识,通过伴生的低水位域底界面的识别及附近的超失、削截特征分析,仔细追踪和查明了准噶尔盆地腹部地区中部2区块9条关键界面.进行了侏罗系的高分辨层序地层的划分。研究表明C1井区J_1b_2-J_2t沉积时期可划分出8个三级层序,均具有完整的三分结构:LST、TST和HST;共划分出27个体系域,共识别出准层序组56个,准层序118个。单个层序的厚度105.6～176.8 m,平均140.7 m;单个准层序组平均24.9 m;单个准层序平均11.8 m。     

四川龙门山马角坝地区石炭纪层序地层及海平面变化研究

在沉积学、生物地层学研究之基础上，结合沉积地球化学资料，对龙门山马角坝地区石炭系进行了露头层序地层学研究。首次识别出９个三级层序和若干个四至五级高频层序。在三级层序中，岩关组２个、大塘组３个、威宁组２个、马平组２个，它们均可作区域性对比。其中，四个层序分别与冈瓦纳大陆晚古生代五次冰川事件中四次间冰期－冰期旋回相对应，表明其成因与冰川型全球海平面变化有关。显然，研究区石炭纪层序主要受控于全球海平面升降旋回，具有全球对比意义。     

Sedimentology and stratigraphy of Geli Khana Formation (Anisian–Ladinian), a contourite depositional system in the northeastern passive margin of Arabian plate,northern Iraq-Kurdistan region

The Middle Triassic Geli Khana Formation of the northeastern part of the Arabian plate marks the establishment of the Neo-Tethys passive margin. The indication of bottom-current activities, within the lower and middle parts of the formation, gives the opportunity to study Middle Triassic facies and depositional settings in northern Iraq. Three sections (two outcrops and one subsurface) were selected to study the sedimentology and stratigraphy of Geli Khana succession. Petrographic investigations of the carbonate and siliciclastic beds on 140 thin sections show both skeletal and non-skeletal grains. The skeletal grains reveal deposition in deep open marine and in shallow warm water, within a gently slope ramp setting. Twelve microfacies were recognized. In the northern thrust zone, these facies were subdivided, according to their environmental interpretation, into three basic types of facies associations: outer ramp/basinal, middle ramp/slope, and inner ramp/lagoon (open and restricted). Restricted lagoon and tidal flat facies association is suggested for the Geli Khana Formation in Well Jabal Kand-1. Typical contourite deposits associated with turbidites are recognized for the first time in the Middle Triassic Geli Khana Formation in the northern thrust zone, northern Iraq, Kurdistan region. The contourites are characterized by thin beds and occasional lenses of sandy limestones, siltstones to fine-grained sandstones with current ripples, laminations (planar and cross), and erosional surfaces. These current structures are associated with thin-bedded (5–25 cm) limestones and shales. Deformation structures are characteristic feature of the formation inferring syndepositional slumping and turbidite influence too.     

High-resolution sequence stratigraphy of a complex, incised valley succession, Cobequid Bay — Salmon River estuary, Bay of Fundy, Canada

The post-glacial succession in the Cobequid Bay — Salmon River incised valley contains two sequences, the upper one incomplete. The lower sequence contains only highstand system tracts (HST) deposits which accumulated under microtidal, glacio-marine deltaic conditions. The upper sequence contains two, retrogradationally stacked parasequences. The lower one accumulated in a wave-dominated estuarine environment under micro-mesotidal conditions. It belongs to the lowstand system tract (LST) or early transgressive system tract (TST) depending on the timing and location of the lowstand shoreline, and contains a gravel barrier that has been overstepped and preserved with little modification. The upper parasequence accumulated in the modern, macrotidal estuary, and is assignable to the late TST. Recent, net progradation of the fringing marshes indicates that a new HST has begun. The sequence boundary separating the two sequences was formed by fluvial incision, and perhaps also by subtidal erosion during the relative sea level fall. Additional local erosion by waves and tidal currents occurred during the transgression. The base of the macrotidal sands is a prominent tidal ravinement surface which forms the flooding surface between the backstepping estuarine parasequences. Because fluvial deposition continued throughout the transgression, the fluvial-estuarine contact is diachronous and cannot be used as the transgressive surface. The maximum flooding surface will be difficult to locate in the macrotidal sands, but is more easily identified in the fringing muddy sediments. These observations indicate that: (1) large incised valleys may contain a compound fill that consists of more than one sequence; (2) relative sea level changes determine the stratal stacking patterns, but local environmental factors control the nature of the facies and surfaces; (3) these surfaces may have complex origins, and commonly become amalgamated; (4) designation of the transgressive surface (and thus the LST) is particularly difficult as many of the prominent surfaces in the valley fill are diachronous facies boundaries; and (5) the transgression of complex topography may cause geologically instantaneous changes in tidal range, due to resonance under particular geographical configurations.     

四川盆地东北部长兴组层序地层与储层分布

四川盆地东北部的二叠系长兴组为一套碳酸盐岩地层。宣汉盘龙洞剖面详尽研究表明,长兴组可分为两个三级层序:第1层序的海侵体系域由开阔台地滩间相沉积组成,高位体系域为台地边缘礁滩相沉积;第2层序的海侵体系域为浅滩沉积,高位体系域为暴露浅滩相-蒸发潮坪相沉积。长兴组中层序界面主要有水下间断不整合面和暴露侵蚀不整合面两类,相当于PeterVail的II类层序界面。在层序地层研究的基础上,对长兴组储层的时空分布特点进行了系统研究。研究发现,储层与层序地层关系密切,储层主要发育在层序的高水位体系域中:礁滩相储层位于第1层序的高位体系域中,而暴露浅滩-蒸发潮坪储层则主要产在第2层序的高水位体系域中。长兴组层序地层格架图以及层序高水位体系域沉积相平面图的编制,成为预测储层二维空间分布的基础。结果表明,礁滩相储层分布于通江—开县碳酸盐台地的东西两侧,暴露浅滩-蒸发潮坪储层遍布于通江—开县的碳酸盐台地及其东西两侧地区之中。两个层序高位体系域中的储层岩石孔隙丰富,储集条件较好,分布面积较广,从而成为研究区域油气勘探的重要目的层。     

北京西山潭柘寺地区石炭—二叠纪层序地层与聚煤作用研究

通过露头剖面及钻孔岩心数据,对北京西山潭柘寺地区石炭—二叠纪陆相及海陆过渡相含煤岩系进行了层序地层和聚煤作用研究。依据区域不整合面（古风化壳）、下切河道砂体底面、生物缺失带、海侵方向转换面以及岩性突变面等特征辨认出8个层序界面,据此将研究区石炭—二叠系划分为7个三级层序,分别对应于本溪组及太原组M6煤层底板以下、太原组中上部、山西组、下石盒子组、红庙岭组下段、红庙岭组上段、双泉组。根据岩相及沉积环境变化特征,可将每个三级层序进一步划分为低位体系域、海侵体系域和高位体系域。区内可采煤层（如M4）形成于下三角洲平原沉积环境,在三级层序内一般位于最大海泛面附近。     

藏北雁石坪地区中侏罗统玛托组高频层序及海平面变化分析

西藏北部雁石坪地区晚巴柔—早巴通期玛托组是一个以砂岩、泥岩为主夹少量灰岩组成的混积型陆棚环境的沉积。含有介壳的凝缩段、下超面及沟蚀面,它们是划分体系域的关键界面。体系域具有二元结构特征,即海侵—高水位体系域,且TST沉积旋回厚度>HST,准层序类型有3种,分别是以砂岩为主的准层序、以泥岩为主的准层序和以潮坪体系向上变浅的准层序,准层序叠置构成进积型和退积型准层序组。采用沉积体系分析方法,初步建立研究区玛托组相对海平面变化曲线,并与藏南及全球海平面曲线进行对比分析,结合碳、氧同位素和磁化率资料,探讨研究区晚巴柔—早巴通期玛托组海平面变化控制因素。研究认为全球海平面变化控制了雁石坪地区晚巴柔早期海平面变化,而班公湖—怒江逢合带向北俯冲构造活动引起的区域洋盆容积变化是晚巴柔晚期—早巴通期海平面变化的主要因素。     

蜀南地区飞仙关组高精度层序地层研究

针对四川盆地下三叠统飞仙关组层序地层存在多种不同划分方案,以高精度层序地层学理论与方法为指导,以蜀南地区飞仙关组台地相碎屑岩和碳酸盐岩为研究对象,以野外露头剖面、岩芯、钻井、测井、地震等资料为基础,综合应用岩性突变面、沉积相转换面、沉积物空间堆积样式的变化、早期成岩变化、电测井曲线特征以及地震反射特征等标志,识别出不同级次的11个层序界面,据此将本区飞仙关组划分为2个三级层序(TSQ1和TSQ2)和10个四级层序,其中TSQ1可细分出6个四级层序,TSQ2可再分出4个四级层序,并将其与传统地层单位进行对比:三级层序TSQ1和TSQ2分别对应于飞一段+飞二段地层和飞三段+飞四段地层。通过层序地层对比和层序地层格架的建立,指出这些层序在全区均具有良好的可对比性和等时性,每个层序均具有快速海侵到缓慢海退的特点,均由海侵体系域和高位体系域构成,未发现低位体系域和凝缩段。层序与储层关系的研究表明,四级层序Ⅲ和Ⅷ是台内鲕滩这种有利储集相带的主要发育层位,所形成的滩相鲕粒灰岩储层与高位体系域的向上变浅序列和早期暴露及其所导致的大气淡水淋溶改造有关,平面上集中分布于中东部地区。     

From Basin Black Shales to Platform Carbonate Rocks： A Study on Sequence Stratigraphy for the Lower Cambrian of the Upper-Yangtze Region in South China

In the Upper-Yangtze region,especially in Guizhou Province and its adjacent areas,the Lower Cambrian is well developed and is marked by a succession from black shales of the basin facies to carbonate rocks of the platform facies.The drowning event of the platform occurring at the turn from Sinian to Cambrian resulted in a set of black shales,i.e.the Niutitang Formation,which makes up the bottom part of the Lower Cambrian.With the shoaling of the sedimentary environment,a set of carbonate rocks,i.e.the Qingxudong Formation,was formed in the top part of the Lower Cambrian.Thus,the Lower Cambrian in the study area makes up one second-order sequence that can be further subdivided into five third-order sequences,and forms a regularly cyclic succession of transgression-regression.There is a regularly vertical stacking pattern for the third-order sequences in the second-order sequence.From bottom to top,the succession of the"CS(condensed section) HST(high-stand system tract)"of the third-order sequences is changed into the succession of the"TST(transgressive system tract) CS HST".Correspondingly,the drowning-type sequence boundary is changed into the exposure-type one.Therefore,both the second-order and the third-order sequences have similar sedimentary-facies architectures.A concomitant with these temporal changes, the Lower Cambrian with a thickness of 1000m that contains five third-order sequences is changed into a condensed succession that cannot identify third-order sequences toward the southeast with the deepening of the sedimentary environment.According to the elementary features of the third-order sequences,i.e.the regularity o sedimentary-facies successions in space and the synchronism of sedimentary-environment changes in time,the detailed division of the third-order sequences at main logged sections in different paleogeographical background becomes the basis to establish the sequence-stratigraphic framework that can demonstrate two types of facies-changing surface and two types of diachronism in the stratigraphic records.This sequence-stratigraphic framework shows a growing process of the carbonate platform from the base of the condensed succession formed by black shales of basin facies.Resulting from the rapid transgression at the turn from Sinian to Cambrian the ecological space became open,which formed the antecedent condition of paleogeographical setting for"the Cambrian Biological Explosion".Ultimately,the genetic relationship between the depositional events and the biological-diversity events is very complex and there remain lots of problems that need further research in the future.     

川东北地区飞仙关组层序地层特征及演化模式

在对川东北地区飞仙关组沉积构造背景认识的基础上,采用野外露头、岩心、测井及地震剖面等多种分析手段,通过对层序界面、相序、叠置结构、测井曲线及地震层序等标志的综合识别分析,将川东北地区飞仙关组划分为2个三级层序,认识到它们都发育有低位体系域、海侵体系域和高位体系域。进一步,通过层序地层格架剖面的建立,运用层序地层原理,在对层序地层控制因素分析的基础上,建立了川东北地区飞仙关组层序地层演化模式,从层序演化的角度上探讨了滩体的发育分布规律,对于下一步的油气勘探具有重要指导意义。     

上扬子地区五峰组-龙马溪组页岩层序地层及演化模式

学者们在页岩层序划分与构成等方面还存在较大分歧;其次,现有研究中针对页岩非均质性在层序格架内的变化特征及成因规律方面亦有不足.五峰组-龙马溪组页岩是上扬子地区重要的页岩气勘探层位之一,通过钻井岩心、露头剖面、常规测井、能谱测井和地球化学参数等资料,对上奥陶统五峰组-下志留统龙马溪组黑色页岩层序地层学进行了定量分析.在五峰组-龙马溪组识别出3个三级层序,其中五峰组为一个三级层序,进一步划分出海侵体系域（五峰组下部黑色页岩）和高位体系域（五峰组上部观音桥段）;龙马溪组一段作为一个三级层序,进一步划分出海侵体系域、早期高位和晚期高位体系域;龙马溪组二段和三段为一个三级层序,进一步划分出低位体系域、海侵体系域和高位体系域.以不同体系域为单元分析了五峰组-龙马溪组层序发育与沉积环境特征,揭示了各体系域内古生产力与水体氧化还原条件对有机质富集的控制机理,总结并提出了系统的五峰组-龙马溪组黑色页岩层序地层垂向演化模式.      

高分辨露头层序地层学的研究基础──准层序的识别

以塔里木盆地西南缘下石炭统和什拉甫组为例，将微相分析及古生态分析应用于准层序研究之中。在此基础之上，分析沉积层序及其内部各体系域、各种界面的沉积特征。同时，根据准层序垂直叠加的特征来寻找沉积层序内部更高级次的旋回，以达到提高沉积层序的分辨率之目的，恢复该地区维宪期多级次古海平面变化特征。强调准层序分析是高分辨露头层序地层学的研究基础。     

Multistage dolomitization and distribution of dolomitized bodies in Early Jurassic carbonate platforms (Southern Alps,Italy)

The Early Jurassic dolomitized carbonates are a hydrocarbon exploration target in Northern Italy. Of these carbonates, the Liassic Albenza Formation platform and the overlying Sedrina Formation shelf were studied to define a pervasive dolomitization model and to shed light on dolomite distribution in the sub‐surface. Field work, as well as analyses of well cores, stable isotopes, trace elements and fluid inclusions, was carried out on the outcropping thrust belt and sub‐surface deformed foreland of the Southern Alps. Petrographic analyses showed a first, pervasive, replacement dolomitization phase (D1) followed by volumetrically less important dolomite cement precipitation phases (D2, D3 and D4). The δ¹⁸O values fall between ?8·2‰ and 0·1‰ Vienna‐Pee Dee Belemnite with the more depleted samples belonging to dolomite cement‐rich dolostones; the δ¹³C ranges from 2·6‰ to 3·7‰ Vienna‐Pee Dee Belemnite. Analysis of trace elements showed different Fe and Mn contents in the sub‐surface and outcropping dolostones, and a higher Fe in the younger dolomite cements. An increase in the precipitation temperature (up to 130 °C from fluid inclusion data) and a decrease in diagenetic fluid salinity (from sea water to brackish) are observed from the first pervasive replacement dolomite to the dolomite cement phases. Field observations indicate that, in the Albenza Formation, dolomitization was limited to palaeohighs or faulted platform margins in the Early Jurassic carbonates. The pervasive replacement phase is interpreted based on a ‘compaction model’; the formation fluids expelled from compacting basinal carbonates could have funnelled along faults into permeable palaeohighs. The high homogenization temperature of the dolomite cements and decreased salinities indicate precipitation at great depth with an influx of meteoric water. These data, along with the thermal history, suggest that the dolomite cements precipitated according to the ‘tectonic squeegee’ dolomitization model. The dolomite precipitation temperature was set against the thermal history of the carbonate platform to interpret the timing of dolomite precipitation. The dolomite precipitation temperatures (90 to 100 °C) were reached in the studied formations first in the thrust fold belt (Early Tertiary, 60 Ma), and then in the foreland succession during the Late Tertiary (10 Ma). This observation suggests that the dolomite precipitation fronts moved southwards over time, recording a ‘diagenetic wave’ linked to the migration of the orogenic system. Observations suggest that the porosity increased during the first phase of replacement dolomitization while the dolomite cementation phases partially occluded the pores. The distribution of porous dolomitized bodies is therefore linked to the ‘compaction dolomitization’ model.     

Oxygen and carbon isotope composition of Gordon Group carbonates (Ordovician), Florentine Valley,Tasmania, Australia

The Gordon Group carbonates consist of biota of the Chlorozoan assemblage, diverse non‐skeletal grains and abundant micrite and dolomite, similar to those of modern warm water carbonates. Cathodoluminescence studies indicate marine, meteoric and some burial cements. Dolomites replacing burrows, mudcracks and micrite formed during early diagenesis.

δ¹⁸O values (‐5 to ‐7%ō PDB) of the non‐luminescent fauna and marine cement are lighter than those of modern counterparts but are similar to those existing within low latitudes during the Ordovician because of the light δ¹⁸O values of Ordovician seawater (‐3 to ‐5%o SMOW). The δ¹⁸O difference (2%o) between marine and meteoric calcite indicates that Ordovician meteoric water was similar to that in modern subtropics. Values of δ¹³C relative to δ¹⁸O indicate that during the Early Ordovician there were higher atmospheric CO₂ levels than at present but during the Middle and Late Ordovician they became comparable with the present because of a change from ‘Greenhouse’ to glacial conditions. δ¹⁸O values of Late Ordovician seawater were heavier than in the Middle Ordovician mainly because of glaciation.

Dolomitization took place in marine to mixed‐marine waters while the original calcium carbonate was undergoing marine to meteoric diagenesis.     

塔里木盆地柯坪地区中下奥陶统碳酸盐岩露头层序地层学研究

在前人岩石地层、生物地层、年代地层研究基础上,作者运用层序地层学理论结合沉积微相分析,对柯坪地区中下奥陶统露头碳酸盐岩进行了层序地层解剖。研究区共识别出二种界面类型 (暴露层序不整合界面和淹没层序不整合界面 )、三种准层序组构特征 (潮坪、浅滩和滩下陆棚 )和两种主要类型的体系域构成 (海侵体系域和高位体系域 ),在此基础上把该套碳酸盐岩划分为 7个三级层序,其中Sq1～ 2对应于蓬莱坝组地层、Sq3～ 6对应于鹰山组地层和Sq7对应于大湾沟组地层。Sq1～ 2三级层序由潮坪旋回的藻纹层白云岩、细粉晶白云岩和灰岩组成;Sq3～ 4三级层序由潮坪旋回的藻纹层灰岩和颗粒灰岩组成;Sq5～ 6三级层序由潮下浅滩相旋回的颗粒灰岩组成;Sq7三级层序由滩下陆棚环境藻灰岩和泥质瘤状灰岩组成