Alluvial-fan-carbonate facies with evaporites, Eocene Guarga Formation, Southern Pyrenees, Spain

Continental carbonates of the basal part of the Guarga Formation, Upper Eocene, have been studied in the field and in the laboratory. Both geographic pattern and vertical sequences served as a basis for sedimentary models. The pattern reveals that carbonate deposition was greater in the western part of the Tremp-Graus Basin than in the eastern part. Studies of slabs and thin sections suggest high energy deposition in the eastern part of the basin and low energy deposition in the western part. Gross lithology, petrography, and faunal/floral associations indicate sedimentary environments which include calcimorphic palaeosoils, caliche nodule zones, solid caliche nodule zones, caliche crusts, fluvial carbonates, paludal carbonates, and pond/lake carbonates. Distribution pattern of the carbonate bodies and lithologies seem to be controlled by alluvial-fan processes. They are typical fining-upward sequences in the sense of Collinson (1978) which furthermore can be assigned to a channel-bound group and a succession independent of fluvial channels. Referring to fan-physiography the sequences can be subdivided into fluvial proximal interchannel, fluvial distal interchannel, lacustrine distal interchannel, nearshore lacustrine-paludine, and lacustrine offshore carbonate facies. The two last categories are distal alluvial plain and/or fan-edge associations. The presence of especially charophyte oogonia adjacent to pseudomorphs of lenticular gypsum in the lacustrine carbonates of the western Tremp-Graus Basin indicates that their depositional environment was that of shallow lakes with alternating salinities. Diagenetic alterations consist of three major phenomena: (a) general cementation of the carbonates by low-Mg calcite, (b) pseudomorphs of lenticular gypsum, and (c) silification. The relationship of gypsum and silica diagenesis to the regional distribution of lacustrine carbonates suggests early diagenetic processes for their formation. Gypsum pseudomorphs are small and are found to be replaced by Fe-calcite throughout the whole area, or are large and replaced preferentially by silica in the west only. There is experimental evidence (Cody, 1979) that distribution of gypsum morphology and crystal sizes can be related to increased salinities and increased organic production in the west. Chert-gypsum fabrics from that area resemble the ‘silex nectique’ of Cayeux (1929). The occurrence of this noteworthy type of chert together with length-slow chalcedony is an indication of relatively early silification of the gypsum. It is suggested that the sediments containing the silicified lenticular gypsum hosted brines of partly marine origin which alternately became brackish or fresh. An attempt was made to check the influence of evaporation during carbonate deposition by determining the stable isotope composition of the carbonates and of the chert. The data show no distinct variations with respect to the presumed palaeoenvironments. The ranges in the carbonates (δ¹³C ? 5,0 to ?7,9; δ¹⁸ O ?4,5 to ?7,7) fit among the data given in the literature. The values derived from chert (δ¹⁸O 26,9 to 31 SMOW) support a concept of alternating salinities. Distribution of carbonate lithofacies indicate a systematic change in sedimentation from fluvial/ephemeral to permanent lacustrine from east to west. Diagenetic alterations suggest an increase of salinities of pore waters in the same direction. In addition the lacustrine limestones in the west were due to frequent changes in pore-water salinity. Similar sequences lacking subtidal and/or lagoonal fossil associations but including pseudomorphs of carbonate and chert after lenticular gypsum were described from the Lower Purbeckian of Dorset (West, 1964, 1975, 1979), and from the Tertiary of the Paris Basin (Fontes, 1968). Guarga limestone environments of especially the western Tremp-Graus Basin probably resembled the modern semi-arid ephemeral saline lakes in Australia (Burne, Bauld & De Dekker, 1980). Gypsum precipitation in these environments can be compared to the one in modern sabkhas from the Mediterranean coast of Egypt (West, Ali & Hilmy, 1979; Ali West & Hilmy, 1980).     

辽西义县组碳酸盐岩夹层及其环境意义

义县组是热河生物群最繁盛的层位,它承载了热河生物群演化的重要信息,开展义县组沉积环境的深入研究是认识和恢复热河生物群生活环境的有效途径.辽西地区义县组中夹有多层碳酸盐岩沉积层,所含沉积环境信息丰富.通过碳酸盐岩的研究,获取碎屑岩中丢失的环境信息,并与碎屑岩沉积层的研究相结合,为恢复辽西地区义县期热河生物群的古地理、古气...     

Climatic and tectonic controls on carbonate deposition in syn‐rift siliciclastic fluvial systems: A case of microbialites and associated facies in the Late Jurassic

This work provides new insights to assess the factors controlling carbonate deposition in the siliciclastic fluvial systems of rift basins. Sedimentological and stable‐isotope data of microbialites and associated carbonate facies, along with regional geological information, are shown to reveal the influence of climate and tectonics on the occurrence and attributes of carbonate deposits in these settings. The Vega Formation – a 150 m thick Lower Kimmeridgian siliciclastic fluvial sequence in Asturias Province (northern Spain) – constitutes a candidate for this approach. This unit includes varied facies (stromatolites; rudstones, packstones and wackestones containing oncoids, intraclasts, charophytes and shell bioclasts; marlstones and polygenic calcareous conglomerates) that formed in a low‐gradient fluvial–lacustrine system consisting of shallow, low‐sinuosity oncoid‐bearing channels and pools within marshy areas, with sporadic coarse alluvial deposition. The sedimentological attributes indicate common erosion by channel overflow and rapid lateral changes of subenvironments caused by water‐discharge variations. The carbonate fluvial–lacustrine system developed near uplifted marine Jurassic rocks. The occurrence of the system was conditioned by normal faults (active during the deposition of the unit) that favoured: (i) springs of HCO₃–Ca‐rich water from a Rhaetian–Sinemurian carbonate rock aquifer; and (ii) carbonate deposition in areas partially isolated from the adjacent siliciclastic fluvial system. The microbialite δ¹³C and δ¹⁸O values support deposition in a hydrologically open system, fed by ambient‐temperature meteoric water, with riparian vegetation. Three types of lamination in the stromatolites and oncoids reflect distinct morphological types of cyanobacterial communities. The textural pattern of lamination parallels δ¹³C and δ¹⁸O changes, suggesting short‐term cycles of precipitation and temperature. A moderately to strongly contrasted seasonal and/or pluriannual precipitation regime is inferred from the cyclic δ¹³C pattern of the lamination and from the discontinuous and asymmetrical growth of oncoids. Thus, the isotopic and sedimentological attributes of the carbonate deposits were linked to short‐term climate changes associated with semi‐arid conditions, consistent with the studied climatic zone.     

Dolomitization of Carbonate Periplatform Deposit,Machari Formation (Middle to Late Cambrian),Korea

The petrography, the geochemistry and the burial history all constrain the origin and modification history of dolomites in an ancient periplatform carbonate slope deposit,the Machari Formation (late Miclclle to early Late Cambrian),Korea. The formation is mainly composed of rhythmic bedding. laminated to bedded lime mudstone alternating with argillaceous lime mudstone. The rhythmic bedding is a product of the deposition of offshore periplatform ooze and hemipelagic clay on a periplatform slope. This formation also shows minor and intermittent influx of other lithofacies including the bioclastic-peloidal packstone, peloidal wackestone, and intraclasts deposited as turbidites. Five types of dolomite occur in the Machari Formation, whose occurrence.texture and geochemistry provide an insight into origin and modification history.     

含气岩系的组成及其形成环境

含气岩系是讨论天然气形成的地质基础，它的组成包括气源岩层、储集岩层和盖层三部分。不同地区、不同时代含气岩系的组合类型及其分布特点各异。含气岩系的形成与地质历史时期的沉积环境密切相关，最有利于形成含气岩系的气源岩层、储集岩层和盖层的沉积环境，应为海洋沉积相域的滨岸沼泽相至浅水台地相，少数在浅海开阔台地沉积环境中.陆盆沉积相域多在浅湖相，少数位于半深湖相环境中，它的生、储、盖层组合及其形成次序是形成天然气藏的决定因素。     

柴达木盆地西部新生界陆相湖盆碳酸盐岩沉积环境与沉积模式*

利用野外露头、岩心、测井录井和分析化验资料,对柴达木盆地西部(简称“柴西地区”)新生界干柴沟组湖相碳酸盐岩进行了研究,划分了其沉积微相类型,研究了其分布规律,分析其形成环境和控制因素,并建立了相应沉积模式。该区湖相碳酸盐岩在垂向上与碎屑岩频繁互层,湖相碳酸盐岩包括颗粒灰岩、藻灰岩、泥晶灰岩和混积岩4大类11种,划分出了灰泥坪、颗粒滩、藻丘(礁)、浅湖湾以及(半)深湖泥灰岩相等5种沉积微相。通过分析不同碳酸盐岩及其微相时空展布特征,认为其发育主要受控于湖盆构造运动、湖平面变化、陆源碎屑注入、古气候与古水介质条件、古地貌与古水深环境,并在此基础上建立了柴西湖相碳酸盐岩的沉积模式。研究认为柴达木盆地西部干柴沟组沉积时期,湖盆为典型咸化湖盆,构造活动相对稳定,湖平面上升达到峰值。碳酸盐岩主要发育在湖侵期,高频湖平面变化形成了碳酸盐岩与碎屑岩频繁互层。在枯水期,盆地坡折处发育碎屑岩滩坝或三角洲前缘沉积;在湖侵期,盆地坡折处发育了鲕粒滩及藻灰岩,盆地洼陷区发育泥灰岩或灰质泥岩。     

通南巴地区上三叠统须家河组沉积体系及其主控因素

近年来的勘探实践表明,通南巴地区上三叠统须家河组具有良好的油气勘探前景。通过野外剖面及岩心观察,结合测井和各种分析鉴定资料以及沉积相标志的综合分析,识别出冲积扇、河流、湖泊三角洲、湖泊（受间歇性海水改造）和海相三角洲5种沉积体系,建立了海陆过渡三角洲、冲积扇-辫状河三角洲-湖泊两种沉积演化模式。研究结果还显示,本区沉积体系主要受控于古气候、构造运动和物源区母岩性质:古气候控制着须家河组煤系地层特殊的砂、泥间互的沉积结构及生储盖组合;构造运动控制着各沉积时期的沉积体系类型及砂体展布;不同物源区母岩性质影响沉积物的组分与结构。      

Petrography and geochemistry of intraclastic manganese–carbonates from the ∼2.2 Ga Nsuta deposit of Ghana: Significance for manganese sedimentation in the Palaeoproterozoic of West Africa

Intraclastic Mn carbonate rocks occur in the marginal areas of the manganese–carbonate orebody (manganesestone) of the Palaeoproterozoic Nsuta deposit in the Birimian of Ghana. Macroscopically the intraclastic rocks display graded bedding and are typified by a matrix-supported fabric with subangular to subrounded particles less than a millimetre to ∼1.5 × 0.5 cm. Both clasts and matrix consist mainly of varying proportions of microcrystalline and microconcretionary carbonates, quartz, muscovite and subordinate pyrite. Within individual intraclasts, carbonate minerals (including distinctly zoned microconcretions) are essentially Mg kutnahorite and Mg–Ca rhodochrosite, similar to the carbonate minerals in the manganesestone. Whole rock chemistry of the intraclastic carbonates shows significant variability in the amounts of SiO₂, Al₂O₃, MnO, MgO, CaO, Na₂O and, to a lesser extent, K₂O. Major element contents of the manganesestone similarly vary widely, except that these have, in particular, comparably higher MnO but less SiO₂ and Al₂O₃ than the intraclastic carbonates and host rock Mn phyllite. Rare earth element (REE) concentrations in the intraclastic carbonates are approximately an order of magnitude higher than in the manganesestone. Whereas both rocks exhibit positive Eu anomalies, only the manganesestone shows a discernibly negative Ce anomaly. Petrographic and geochemical features suggest that the intraclasts are fragments of reworked Mn carbonate sediments derived from intraformational erosion and subsequent (mass flow) deposition as carbonate “turbidite” mud. Processes such as submarine slumping, sliding and other sediment gravity flows may have likely interrupted Mn sedimentation and transported partially consolidated manganiferous sediments down slopes into the early Birimian ocean.     

Manganese deposits in a Carboniferous paleokarst profile,Um Bogma region,west-central Sinai,Egypt

The Carboniferous carbonates of the Um Bogma Formation of the west-central Sinai include two rock successions. The lower succesion consists of karstic carbonates, intrakarstic products, weathering varieties, manganese deposits, and soil cover. The lower karstic rocks and the associated soil cover are preserved under a rhythmic alternation of dolostone and shale forming the upper rock succession of the Um Bogma Formation. The all over congruent relations between the manganese deposits and the fossilized karst profile, karst products, and the associated pedogenesis demonstrate the role of weathering in the accumulation of these deposits during Carboniferous karstification. It is clear that the manganese oxides were deposited during the mature stage of Carboniferous karstification, i.e., during the soil formation, preceeding initial diagenetic change of the karstic rocks and final deposition of the related late-diagenetic caliche cement. The geochemical behavior of Mn during the karstification and the microbiological processes involved in pedogenesis played an essential role in the concentration of the manganese ore in the subsoil horizon of the paleokarst profile. The Um Bogma Formation has been subjected to another episode of karstification during the Quaternary and resulted in lowering of the landforms of the Carboniferous carbonates and destruction of the Carboniferous karst and the associated manganese deposits in some localities.     

东营凹陷沙河街组湖相碳酸盐岩碳氧同位素组分及其古湖泊学意义

湖相碳酸盐岩的碳、氧稳定同位素分析能提供重要的环境信息。山东东营凹陷沙河街组湖相碳酸盐岩主要分布在沙一段和沙四段。对47个碳酸盐岩样品碳、氧同位素组分的分析表明:沙一段、沙四中和沙四上亚段下部沉积时期东营湖均是程度不同的封闭型湖泊。古盐度和蒸发／降雨:沙四中亚段和沙四上亚段下部沉积时期＞沙一段沉积时期＞沙四上亚段上部沉积时期;古湖水面:沙四上亚段上部沉积时期＞沙一段沉积时期＞沙四中亚段和沙四上亚段下部沉积时期;古生产力:沙一段沉积时期＞沙四上亚段上部沉积时期＞沙四中亚段和沙四上亚段下部沉积时期。     

山东平邑盆地古近系湖相微生物碳酸盐岩形成机理*

微生物碳酸盐岩是当前沉积学的研究热点之一,但关于古近系湖相微生物碳酸盐岩的报道还非常少。为探讨山东平邑盆地古近系官庄组中段湖相微生物碳酸盐岩的形成机理,笔者进行了野外实测以及室内偏光显微镜和扫描电镜观察。研究结果认为：（1）研究区微生物碳酸盐岩主要有核形石、叠层石和凝块石;（2）在核形石、叠层石和凝块石内部均发现了球状微生物化石、席状体和凝块状泥晶等微生物成因的显微组构,表明了它们形成过程中共同的生长、粘结和钙化等微生物作用;（3）微生物作用对环境变化比较敏感,水体较小、变化频繁的湖泊环境,对微生物碳酸盐岩结构和形态的发育有很大影响;核形石、叠层石和凝块石的形成环境大致呈现出水动力依次减弱、陆源碎屑物质依次减少、水深依次加大的规律;（4）提出了研究区微生物碳酸盐岩的成因模式,认为这3种微生物碳酸盐岩正是以微生物活动为共同基础,在不同的环境条件下形成的。     

Depositional setting and geometric structure of the Beypazari lignite deposits, Central Anatolia, Turkey

The Neogene Beypazari basin is one of the important coal districts of Central Anatolia with approximately 600 million short tons lignite reserves. The coal-bearing Neogene sediments occurring in the Beypazari basin are divided into seven formations, in ascending order; Çoraklar, Hirka, Akpinar, Çayirhan, Bozbelen and Kirmir Formations with Sariyar Limestone and Teke volcanics.The Çoraklar Formation consists of cross-bedded sandstones, channel-fill conglomerates, mudstones, carbonaceous shales and volcanoclastic pebblestones, which are fluvial in origin. The lower lignite seam occurs in the lower part of the Çoraklar Formation.The upper lignite seam occurs in the uppermost part of the Çoraklar Formation and is overlain by the Hirka Formation with a sharp contact. The Hirka Formation consists mainly of alternating shale, mudstone, bituminous shale, claystone, tuffite and silicified limestone, and they all are apparently of lacustrine origin.The lignite deposite occur in the Çayirhan and Koyunaǧili parts of the Beypazari Neogene basin. The Çayirhan coal field consists of lower and upper lignite seams, but the Koyunaǧili field contains only an upper lignite seam.The lower lignite seam, which does not crop out at the surface, indicates a fluvial origin of the lignite deposits, based on the lateral discontinuity and the lower sulphur content of the lower lignite seam, and the sedimentologic and stratigraphic features of the associated sediments. But the uniform stratigraphic and sedimentologic features, high sulphur content and wide-spread distribution of the upper lignite seam indicate that the upper lignites were deposited probably in a mud-flat facies of playa-lake environment. The lower and upper lignites are completely different in relation to the depositional environment, the geometry and degree of rank in lateral directions.The lateral spreading and geometry of the lower lignite deposits were controlled by channel, floodplain and well-drained marshes of a fluvial system. On the basis of recent drillings and field investigations, the lower lignite deposit has been demonstrated to be a linear spreading parallel to the axis of the channel fills and throughcross beds in clastic sediments of fluvial facies. Therefore, the lower lignite deposits trend along a northeastern direction and is not expected to be as widely spread as the upper lignites.     

北京十三陵中元古代1.8Ga和1.6Ga的铁质宇宙球粒研究

北京十三陵中元古代常州沟组底部的粗砂岩（1.8 Ga）和大红峪组硅化碳酸盐岩（1.6 Ga）中都发现了众多铁质宇宙球粒。大多数未喷膜的二次电子像宇宙球粒是圆形的,少数呈长条状,由于在大气层中熔融作用,多数球粒表面具有金相饰纹和“排气”孔洞。使用电子探针分析对30个颗粒中44个测点的检测结果（%）:FeO 80～95,Cr2 O30.78～6.56,NiO 0.06～0.41,CoO 0.02～0.46。相对比较Cr2O3 在常州沟组中较多一些,而FeO在大红峪组中稍多一些。宇宙球粒的氦同位素分析值却截然不同;3He/4He×10-8分别为:57.50±2.16（常州沟组）和1.23±0.43（大红峪组）;4He×10-8 cm3STP/g分别为:55.54（常州沟组）和809.6（大红峪组）;然而宇宙球粒的氦同位测定值都比各自的母岩高出许多;氦同位素的异常为所发现的宇宙球粒的地外来源更加确定。     

Sedimentology,stratigraphy and palynological occurrences of the late Cretaceous Erlian Formation,Erlian Basin,Inner Mongolia,People's Republic of China

The Erlian Basin is one of the non-marine Cretaceous basins of north-east China that developed during the late Mesozoic continental extension in eastern Asia. This basin experienced two major tectonic events: (i) a syn-rift stage that was dominated by a fluvial–lacustrine depositional environment and (ii) a post-rift stage that was dominated by a fluvial environment. A new sedimentological study performed on Erlian Formation drill cores has led to the determination of an architectural model and to the subsequent characterisation of the stratigraphic evolution of this sedimentary unit during the late Cretaceous. The palynological occurrences that were identified in samples provided a possible stratigraphical age for the Erlian Formation.Sediments of the Erlian Formation occur at the top of the Cretaceous stratigraphic column of the Erlian Basin and were deposited during the post-rift stage. Facies architecture and the ideal succession of facies that were identified for this formation exhibit two different members, both dominated by a fluvial depositional environment: (i) the lower member, which is dominated by channels of a braided river system and (ii) the upper member, which is dominated by overbank deposits. The lower member expresses a tectonically induced uplift as indicated by channels clustering under negative accommodation, whereas a period of stratigraphic base-level rise that is associated with an increase of accommodation is identified in the upper member. Therefore the Erlian Formation highlights an alternation of short uplifts that were dominated by braided fluvial channel deposits with periods of stratigraphic base-level rise that were dominated by overbank deposits. This sedimentological architecture has significant metallogenic implications for the origin of confined permeable sandstone layers, which represent adequate host-rocks for roll front-type uranium deposits.The palynological assemblage Exesipollenites, Ulmipollenites/Ulmoideipites, Buttinia and Momipites that were recognised in two samples of the Erlian Formation has revealed a post-late Campanian age therefore more likely indicating a late Cretaceous age of deposition for the sediments of the Erlian Formation.     

山东黄县盆地古近系李家崖组含煤岩系沉积相特征及演化

山东黄县盆地是中国东部一个重要的煤和油页岩共生盆地,古近系李家崖组是盆地主要的含煤岩系发育层段。根据层序地层学理论,建立了古近系层序地层格架;依据钻测井、岩心资料划分了李家崖组的沉积相类型,编制了分体系域的沉积相图。主要结论如下:(1)李家崖组发育湖泊、辫状河三角洲以及扇三角洲3种沉积相类型。(2)层序Ⅰ低水位体系域以辫状河三角洲相为主,湖扩展体系域以扇三角洲相和湖泊相为主,高水位体系域以扇三角洲相为主;层序Ⅱ低水位体系域以辫状河三角洲相为主,湖扩展体系域以扇三角洲相和湖泊相为主,高水位体系域以湖泊相为主。(3)层序Ⅰ发育时期: 低水位期盆地初始形成—湖扩展期盆地扩张—高水位期盆地萎缩;层序Ⅱ发育时期: 低水位期盆地再次缓慢扩张—湖扩展期盆地加速扩张—高水位期盆地萎缩消亡。     

川西前陆盆地上三叠统沉积特征

应用层序地层学方法将川西前陆盆地上三叠统划分为4个三级层序和12个体系域。在层序格架内,研究了不同时期的古地理背景、物源、沉积类型和沉积相展布,明确了上三叠统存在龙门山古陆、米仓山-大巴山古陆、康滇古陆、江南古陆4个物源,识别出上三叠统海湾、冲积扇、曲流河、辫状河、扇三角洲、辫状河三角洲、曲流河三角洲和湖泊8种沉积相类型。层序Ⅰ沉积时期,盆地处于海陆交互相向陆相转变的时期,整体具有填平补齐的沉积特征,发育海湾等沉积;层序Ⅱ沉积时期,川西前陆盆地成为统一的内陆湖盆,其湖侵期为须家河期最大的湖侵期,主要发育三角洲沉积和湖相沉积;层序Ⅲ沉积时期,米仓山-大巴山古陆提供充足的物源,在米仓山-大巴山两逆冲推覆带前缘广泛发育大型冲积扇、辫状河、辫状河三角洲沉积体系;层序Ⅳ沉积时期,主要受江南古陆的影响,发育三角洲沉积和湖泊沉积。整体上,川西前陆盆地沉积相带的展布格局受构造控制,具有平行构造带展布的特点。盆地西北部陡坡带发育粗粒的冲积扇、扇三角洲-湖底扇,西南部陡坡带发育辫状河三角洲、北部-东北部陡坡带发育辫状河三角洲,而在东南部缓坡带则发育远源的曲流河、曲流河三角洲。     

鲁西南地区官庄群沉积特征与沉积环境分析

鲁西南地区上白垩统—始新统主要发育官庄群,前人对该群的研究大多集中于地层归属年代的划分上,而对于沉积环境的分析涉及较少。本文主要运用岩石学、沉积地球化学方法对鲁西南地区平邑盆地广阜庄-挑沟剖面地层沉积特征及沉积环境演化进行了研究。结果表明:官庄群的固城组为陆相河湖碎屑岩沉积,卞桥组为浅湖碳酸盐岩和蒸发岩沉积,常路组以滨浅湖碳酸盐岩沉积为主,朱家沟组为一套山麓洪积扇沉积;卞桥组和常路组碳酸盐岩总体属于高盐度、强蒸发的陆相咸化湖泊环境沉积产物;官庄群沉积旋回的发育主要受蒙山断裂的多期次活动及古气候条件控制。     

Mineralized biota from the neoproterozoic Uluntui Formation

First finds of microfossils from the silicified microphytolitic carbonates of the Uluntui Formation in the southwestern Baikal region are described. They are represented by remains of the cyanobacterial community that formed microphytolites. These microfossils are accompanied by acritarchs probably belonging to green algae. The silicified microfossils are sufficiently well preserved despite complete and repeated recrystallization of host primary carbonate rocks. Main phases of secondary mineralization are related to hydrothermal-metasomatic processes, which were likely provoked by collisional events on the southern flank of the Siberian Craton in the Silurian.     

柴北缘鱼卡地区侏罗纪含煤地层层序地层学研究

运用钻井岩心、测井及层序地层学有关理论、方法,对青海柴北缘鱼卡地区侏罗纪含煤地层进行了层序地层学研究。共识别出4个层序界面,将侏罗系含煤地层划分为3个三级层序,分别对应于中侏罗统大煤沟组、石门沟组下段和石门沟组上段;研究区层序界面主要包括区域不整合面(古风化壳)、三角洲平原分流河道下切谷、河道间古土壤和盆地内基准面下降—暴露—上升旋回的转折点;与海相含煤盆地不同,厚煤层在层序格架内的发育具有多样性。在古隆起和盆地内部,厚煤层常靠近初始湖泛面发育(煤7);在盆地边缘河流—三角洲平原,厚煤层常靠近最大湖泛面发育(煤5)。总体来看,陆相含煤盆地三级层序中,湖侵体系域聚煤最好。