A sequence stratigraphic model for the Lower Coal Measures (Upper Carboniferous) of the Ruhr district, north-west Germany

Upper Carboniferous Coal Measures strata have been interpreted traditionally in terms of cyclothems bounded by marine flooding surfaces (marine bands) and coal seams. Correlation of such cyclothems in an extensive grid of closely spaced coal exploration boreholes provides a robust stratigraphic framework in which to study the Lower Coal Measures (Namurian C–Westphalian A) of the Ruhr district, north-west Germany. Three distinct types of cyclothem are recognized, based on their bounding surfaces and internal facies architecture. (1) Type 1 cyclothems are bounded by marine bands. Each cyclothem comprises a thick (30–80 m), regionally extensive, coarsening-upward delta front succession of interbedded shales, siltstones and sandstones, which may be deeply incised by a major fluvial sandstone complex. The delta front succession is capped by a thin (<1 m), regionally extensive coal seam and an overlying marine band defining the top of the cyclothem. (2) Type 2 cyclothems are bounded by thick (≈1 m), regionally extensive coal seams with few splits. The basal part of a typical cyclothem comprises a thick (15–50 m), widespread, coarsening-upward delta front or lake infill succession consisting of interbedded shales, siltstones and sandstones. Networks of major (>5 km wide, 20–40 m thick), steep-sided, multistorey fluvial sandstone complexes erode deeply into and, in some cases, through these successions and are overlain by the coal seam defining the cyclothem top. (3) Type 3 cyclothems are bounded by regionally extensive coal seam groups, characterized by numerous seam splits on a local (0·1–10 km) scale. Intervening strata vary in thickness (15–60 m) and are characterized by strong local facies variability. Root-penetrated, aggradational floodplain heteroliths pass laterally into single-storey fluvial channel-fill sandstones and coarsening-upward, shallow lake infill successions of interbedded shales, siltstones and sandstones over distances of several hundred metres to a few kilometres. Narrow (<2 km) but thick (20–50 m) multistorey fluvial sandstone complexes are rare, but occur in a few type 3 cyclothems. Several cyclothems are observed to change character from type 1 to type 2 and from type 2 to type 3 up the regional palaeoslope. Consequently, we envisage a model in which each cyclothem type represents a different palaeogeographic belt within the same, idealized delta system, subject to the same allogenic and autogenic controls on facies architecture. Type 1 cyclothems are dominated by deltaic shorelines deposited during a falling stage and lowstand of sea level. Type 2 cyclothems represent the coeval lower delta plain, which was deeply eroded by incised valleys that fed the falling stage and lowstand deltas. Type 3 cyclothems comprise mainly upper delta plain deposits in which the allogenic sea-level control was secondary to autogenic controls on facies architecture. The marine bands, widespread coals and coal seam groups that bound these three cyclothem types record abandonment of the delta system during periods of rapid sea-level rise. The model suggests that the extant cyclothem paradigm does not adequately describe the detailed facies architecture of Lower Coal Measures strata. Instead, these architectures may be better understood within a high-resolution stratigraphic framework incorporating sequence stratigraphic key surfaces, integrated with depositional models derived from analogous Pleistocene–Holocene fluvio-deltaic strata.     

豫西荥巩——新密煤田太原组、山西组的沉积环境和聚煤规律

荥巩和新密煤田是豫西北部的两个相邻煤田。主要含煤地层为晚古生代晚石炭世太原组和早二叠世山西组,总厚100—150m;下石盒子组及晚二叠世的上石盒子组在本区仅偶含薄煤层。太原组位于含煤岩系最底部,为碳酸盐岩和碎屑岩交替沉积,灰岩形成于清澈、温暖、浅水的陆表海潮下环境,碎屑岩则为潮道和潮间带为主的潮道、潮坪沉积。太原组含有6—7层薄煤层,形成于咸水或半咸水的泥炭沼泽中。山西组几乎全由碎屑岩组成,下部发育本区的主要可采煤层二1煤。二1煤以下层位为潮坪和横向与之共生的潮道、潮沟及河口潮汐砂脊沉积,二1煤以上为河流作用为主的三角洲沉积,三角洲由北向南进积到半咸水的海湾中。二1煤形成于海退时期,它们堆积在滨海平原的淡水泥炭沼泽中,其厚度变化及发育程度主要受成煤前沉积环境控制,但在本区西部构造较复杂处,煤层厚度受后期构造影响较大。沉积环境对煤层原生厚度的影响主要表现在潮坪和废弃的潮道、潮沟、河口潮汐砂背沉积物之上,煤层发育好,而在二1煤之下有活动的潮道及河口潮汐砂脊发育时,煤层较薄或不发育。     

Palaeoenvironmental control on coal formation, distribution and quality in the Permian Vryheid Formation, East Witbank Coalfield, South Africa

The No. 1 and No. 2 coal seams from the Permian Vryheid Formation in the east Witbank Coalfield, South Africa are described with respect to their distribution, thickness and quality. These two coal seams accumulated in a postglacial climatic environment and peat accumulation was closely associated with and influenced by deposition in a braided river system. The fluvial channels that were syndepositional with peat accumulation have resulted in thinning of coal below and above channel axes and pinch-out of coal adjacent to channel margins. Low-ash coal originated from peat which accumulated in areas away from the influence of clastic sedimentation. In contrast, higher-ash coals are situated adjacent and parallel to channel margins where interbedded channel sand and silt contaminated the peat.The lower No. 1 seam peat originated under near-optimum conditions in a lacustrine swamp which blanketed an underlying platform of glaciofluvial braided river sediment. This peat swamp was not subjected to syndepositional clastic contamination and as a result is of superior quality (lower ash/higher calorific value and volatile matter) than the overlying No. 2 coal seam. The No. 2 seam is split by a clastic parting produced by a braided fluvial channel which transected the swamp midway through peat accumulation. This fluvial clastic parting deleteriously affected coal thickness and quality.A comparison of the Gondwanan Permian peat-forming conditions with those from Carboniferous northern hemisphere counterparts suggests that the differences in coal characteristics between these two regions are probably related to different palaeoclimatic conditions and basin tectonics. Cool-temperate climatic conditions which prevailed over the Permian peat swamps resulted in less species diversification of vegetation at these high-latitude settings than the diverse floral assemblages of the Carboniferous swamps. A stable intracronic basin platform caused lateral dispersion of sedimentary facies rather than the stacking of vertical facies which occurred in rapidly subsiding depositories. Partial exposure of the Permian peat swamps during peat accumulation may account for the relatively higher inertinite content of the coals.     

Conceptual models for short‐eccentricity‐scale climate control on peat formation in a lower Palaeocene fluvial system,north‐eastern Montana (USA)

Fluvial systems in which peat formation occurs are typified by autogenic processes such as river meandering, crevasse splaying and channel avulsion. Nevertheless, autogenic processes cannot satisfactorily explain the repetitive nature and lateral continuity of many coal seams (compacted peats). The fluvial lower Palaeocene Tullock Member of the Fort Union Formation (Western Interior Williston Basin; Montana, USA ) contains lignite rank coal seams that are traceable over distances of several kilometres. This sequence is used to test the hypothesis that peat formation in the fluvial system was controlled by orbitally forced climate change interacting with autogenic processes. Major successions are documented with an average thickness of 6·8 m consisting of ca 6 m thick intervals of channel and overbank deposits overlain by ca 1 m thick coal seam units. These major coal seams locally split and merge. Time‐stratigraphic correlation, using a Cretaceous–Palaeogene boundary event horizon, several distinctive volcanic ash‐fall layers, and the C29r/C29n magnetic polarity reversal, shows consistent lateral recurrence of seven successive major successions along a 10 km wide fence panel perpendicular to east/south‐east palaeo‐flow. The stratigraphic pattern, complemented by stratigraphic age control and cyclostratigraphic tests, suggests that the major peat‐forming phases, resulting in major coal seams, were driven by 100 kyr eccentricity‐related climate cycles. Two distinct conceptual models were developed, both based on the hypothesis that the major peat‐forming phases ended when enhanced seasonal contrast, at times of minimum precession during increasing eccentricity, intensified mire degradation and flooding. In model 1, orbitally forced climate change controls the timing of peat compaction, leading to enhancement of autogenic channel avulsions. In model 2, orbitally forced climate change controls upstream sediment supply and clastic influx determining the persistence of peat‐forming conditions. At the scale of the major successions, model 2 is supported because interfingering channel sandstones do not interrupt lateral continuity of major coal seams.     

山西阳泉矿区含煤岩系沉积环境及聚煤规律探讨

阳泉矿区位于山西东部,沁水盆地东北部边缘,是我国主要煤炭基地之一。煤炭资源十分丰富。矿区面积约275km2,含煤地层为石炭二叠系。 一、含煤岩系的岩矿特征 本区含煤岩系主要由太原组和山西组组成。     

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.     

平顶山矿区二_1煤层煤相分析

应用煤岩学和煤化学方法,对平顶山矿区二_1煤层的煤相组成、泥炭沼泽类型及其形成条件进行了探讨。将煤相划分为还原相和氧化相。它们具有相应的定性和定量指标。二_1煤层由3～4个周期性相序构成,反映了成煤沼泽由森林沼泽向草本或草本木本混生沼泽的演化过程。这种相序可能代表一种滨海平原环境下的聚煤特征。二_1煤属贫营养的雨成凸起沼泽,基本上为原地堆积成煤。二_1煤层形成于淡水泥炭沼泽,但其顶部曾受过半咸水环境影响。     

Depositional controls on coal distribution and quality in the Eocene Brunner Coal Measures, Buller Coalfield, South Island, New Zealand

The Buller Coalfield on the West Coast of the South Island, New Zealand, contains the Eocene Brunner Coal Measures. The coal measures unconformably overlie Paleozoic-Cretaceous basement rocks and are conformably overlain by, and laterally interfinger with, the Eocene marine Kaiata Formation. This study examines the lithofacies frameworks of the coal measures in order to interpret their depositional environments. The lower part of the coal measures is dominated by conglomeratic lithofacies that rest on a basal erosional surface and thicken in paleovalleys incised into an undulating peneplain surface. These lithofacies are overlain by sandstone, mudstone and organic-rich lithofacies of the upper part of the coal measures. The main coal seam of the organic-rich lithofacies is thick (10–20 m), extensive, locally split, and locally absent. This seam and associated coal seams in the Buller Coalfield are of low- to high-volatile bituminous rank (vitrinite reflectance between 0.65% and 1.75%). The main seam contains a variable percentage of ash and sulphur. These values are related to the thickening and areal distribution of the seam, which in turn, were controlled by the nature of clastic deposition and peat-forming mire systems, marine transgression and local tidal incursion. The conglomeratic lithofacies represent deposits of trunk and tributary braided streams that rapidly aggraded incised paleovalleys during sea-level stillstands. The main seam represents a deposit of raised mires that initially developed as topogenous mires on abandoned margins of inactive braidbelts. Peat accumulated in mires as a response to a rise in the water table, probably initially due to gradual sea-level rise and climate, and the resulting raised topography served as protection from floods.The upper part of the coal measures consists of sandstone lithofacies of fluvial origin and bioturbated sandstone, mudstone and organic-rich lithofacies, which represent deposits of paralic (deltaic, barrier shoreface, tidal and mire) and marine environments. The fluvial sandstone lithofacies accumulated in channels during a sea-level stillstand. The channels were infilled by coeval braided and meandering streams prior to transgression. Continued transgression, ranging from tidal channel-estuarine incursions to widespread but uneven paleoshoreline encroachment, accompanied by moderate basin subsidence, is marked by a stacked, back-stepping geometry of bioturbated sandstone and marine mudstone lithofacies. Final retrogradation (sea-level highstand) is marked by backfilling of estuaries and by rapid landward deposition of the marine Kaiata Formation in the late Eocene.     

Petrography and geochemistry of Carboniferous coal seams in the Donets Basin (Ukraine): implications for paleoecology

The Carboniferous succession in the Donets Basin hosts about 130 seams, each with a thickness over 0.45 m. Nine economically important seams from the (south)western Donets Basin are studied using organic petrographical, inorganic geochemical, and organic geochemical techniques. The main aim of the study is the reconstruction of peat facies of Serpukhovian (Mississippian) and Moscovian (Middle Pennsylvanian) coals.Formation of major coal seams commenced during Serpukhovian times. Early Serpukhovian coal accumulated in a relatively narrow shore-zone and is rich in inertinite and liptinite. Very low ash yields, low to moderate sulphur contents, and upward increasing inertinite contents suggest coal deposition in raised mires.Moscovian coal has a significantly wider lateral extension and is generally rich in vitrinite. Coal properties vary widely in response to different peat facies. Low-sulphur, low-ash k₇ coal was formed in a raised mire or in a low-lying mire without detrital input. l₁ and l₃ seams containing several fluvial partings were formed in low-lying mires. Both seams are more than 2 m thick. Seams m₂ and m₃ contain high-sulphur coal, a consequence of deposition in a peat with marine influence. In contrast, syngenetic sulphur content is low in the m₅^{1 upper} seam, which was formed in a lacustrine setting. The late Moscovian n₁ seam, up to 2.4 m thick, accumulated in a swamp with a vegetation rich in bryophytes and pteridophytes. The properties of the n₁ seam are transitional between those of Serpukhovian and other Moscovian seams. Differences in maceral composition between Serpukhovian and Moscovian coals probably reflect changes in climate and vegetation type.Tuff layers are observed in the l₁, l₃, and m₃ seams. The l₃ and m₃ seams contain abundant authigenic quartz. Trace element contents are high in many seams. As contents are especially high in seams c₁₀², k₇, l₃ and m₃. Ash in the l₃ seam contains up to 8000 ppm As. Co is enriched near the base of several seams. Maxima up to 2400 ppm occur in the ash of the k₇ and l₃ seams. Cd contents in ash are frequently as high as 30 or 40 ppm.     

兴县地区山西组三角洲沉积及聚煤作用

立足于野外露头、钻井资料研究,结合室内薄片分析、微量元素测试等,运用沉积学、沉积地球化学等理论和方法,在鄂尔多斯兴县地区下二叠统山西组中,识别出了三角洲平原和三角洲前缘2种亚相及分流河道、泥炭沼泽、天然堤、决口扇、水下分流河道、分流间湾和河口砂坝7种微相,并发现研究区山一段主要发育三角洲平原亚相,山二段主要发育三角洲前缘亚相,且整体上山西组沉积期区内具有三角洲逐渐向南推进的沉积特征.研究区的聚煤作用研究表明,山西组煤层均形成于短期基准面上升的晚期,8#、7#、6#煤的聚煤作用主要发生在三角洲前缘分流间湾充填淤浅的泥炭沼泽环境,5#煤形成于三角洲平原泥炭沼泽环境;山二沉积段中富煤地带多与砂岩富集带相吻合,山一沉积段中煤层的厚度则与砂砾岩含量呈现负相关性.     

Sequence stratigraphic controls on reservoir characterization and architecture: case study of the Messinian Abu Madi incised-valley fill, Egypt

Understanding sequence stratigraphy architecture in the incised-valley is a crucial step to understanding the effect of relative sea level changes on reservoir characterization and architecture. This paper presents a sequence stratigraphic framework of the incised-valley strata within the late Messinian Abu Madi Formation based on seismic and borehole data. Analysis of sand-body distribution reveals that fluvial channel sandstones in the Abu Madi Formation in the Baltim Fields, offshore Nile Delta, Egypt, are not randomly distributed but are predictable in their spatial and stratigraphic position. Elucidation of the distribution of sandstones in the Abu Madi incised-valley fill within a sequence stratigraphic framework allows a better understanding of their characterization and architecture during burial. Strata of the Abu Madi Formation are interpreted to comprise two sequences, which are the most complex stratigraphically; their deposits comprise a complex incised valley fill. The lower sequence (SQ1) consists of a thick incised valley-fill of a Lowstand Systems Tract (LST1)) overlain by a Transgressive Systems Tract (TST1) and Highstand Systems Tract (HST1). The upper sequence (SQ2) contains channel-fill and is interpreted as a LST2 which has a thin sandstone channel deposits. Above this, channel-fill sandstone and related strata with tidal influence delineates the base of TST2, which is overlain by a HST2. Gas reservoirs of the Abu Madi Formation (present-day depth ～3552 m), the Baltim Fields, Egypt, consist of fluvial lowstand systems tract (LST) sandstones deposited in an incised valley. LST sandstones have a wide range of porosity (15 to 28%) and permeability (1 to 5080mD), which reflect both depositional facies and diagenetic controls. This work demonstrates the value of constraining and evaluating the impact of sequence stratigraphic distribution on reservoir characterization and architecture in incised-valley deposits, and thus has an important impact on reservoir quality evolution in hydrocarbon exploration in such settings.     

京西木城涧矿区窑坡组沉积体系及相关聚煤因素

通过实测剖面、岩矿鉴定、编制沉积断面图、砂体和煤层等厚图等资料分析,从京西木城涧矿区窑坡组中识别出湖泊沉积体系、河流沉积体系和沼泽沉积体系,并详细阐述了其成因相的岩相构成;在此基础上,指出窑坡组沉积早期为湖泊环境,主体沉积期为总体NE流向的网结河环境,其间伴随湖泊或河流周期性消亡而大面积泥炭沼泽化形成了稳定的可采煤层和含煤沉积旋回。富煤带总体呈NE50°～80°展布,与泥炭沼泽沉积期下伏不同沉积相的压实效应有关,后者通过影响地表起伏和积水深度,控制着泥炭的堆积速率和厚度。     

山西平朔井工三矿煤系角砾岩特殊成因探讨

平朔井工三矿煤系角砾岩成因和产状特殊,与煤层关系密切。通过补勘钻孔岩心观测,结合区域地质和以往钻孔资料分析,详细描述研究区角砾岩的成分、结构和构造特征,圈定角砾岩的层位、厚度和分布状况。发现平朔井工三矿角砾岩成分复杂、大小不一,其中泥岩砾径最大可达1.20 m以上,以棱角状为主,分选性极差;角砾岩体顶底界面明显,临近或出现在煤层中,横向连续性差。角砾岩破坏了煤层的连续性,总体北多南少,分布有限,呈透镜状产出,长轴指向西北物源区;垂向上,角砾岩自下而上减少。研究认为,聚煤期植物锚固作用强大,陆源边坡及碎屑受植被禁锢,只能在限定的范围内垂向加积,累积成边坡较陡的碎屑库;泥炭沼泽表层为植被泥炭交织在一起的泥炭网,底部深度降解的膏状泥炭提供了有利的滑移面。突发事件导致物源区边坡和角砾质碎屑库崩塌,冲越到泥炭网上,撕裂成“泥炭筏”,被泥炭筏载运移,断续沉积,并遭受改造。角砾岩成因及分布规律对煤层成因及厚度变化、煤炭资源/储量估算与开采具有重要指导意义。煤系、特别是煤层中沉积角砾岩的成因用泥炭筏载运移模式解释可能更为合理。      

薄互煤层中透射槽波探测断层的正演模拟

为了研究西南地区矿井薄互煤层中透射槽波探测断层的可行性,选择具有代表性的攀枝花煤业集团某矿为研究对象,根据实际地质资料建立不含夹矸、含3层夹矸、含3层夹矸和断层的3个薄互煤层的地质模型,通过三维弹性波正演模拟分析槽波的波场特征和频散特征,总结振幅衰减系数成像在薄互煤层中槽波探测断层发育位置及延展方向的有效性;并结合实际应用,探讨了透射槽波在薄互煤层中的传播速度及频散特征,以及断层、夹矸对槽波传播的影响。结果表明:薄互煤层中透射槽波探测,断层在影响薄互煤层槽波传播中占主导作用;0.5 m以下夹矸对槽波的发育和能量成像影响不大;在煤厚相同的情况下,含夹矸层状模型相比不含夹矸层状模型的槽波主频低,槽波对煤厚2 m、夹矸厚度0.5 m以下的薄互煤层能够进行比较准确的探测。透射槽波可在薄互煤层中探测断距大于1/2煤厚的断层位置、走向及延展长度,可为西南地区薄互煤层中构造探查提供参考。      

Earlier sediment differential compaction in Gibson County, Indiana

A thick wedge of nonmarine gray shale extends from the Galatia Channel and overlies the Springfield Coal Member of the Petersburg Formation (Pennsylvania) in western Gibson Country, but mainly marine black shales overlie the Springfield in the eastern part of the county. The sulfur content of the Springfield coal is lower beneath this wedge of nonmarine gray shale than beneath the marine shales. Fine-grained, compacted bay and overbank deposits form the western delta platform of the coal. Less compacted deposits of fluvial channel sandstone make up the eastern delta platform. Differential compaction of the delta platform of the Springfield coal controlled gray-shale distribution and determined the sulfur content of the coal.     

贵州金沙木孔煤矿可采煤层常量元素特征及沉积环境分析

对金沙木孔煤矿可采煤层的常量元素分析,利用硫分、C/S值、灰成分作为参照指数,讨论金沙木孔煤矿可采煤层的沉积环境.金沙木孔煤矿上煤组2、3和4号煤层形成于陆源物质供给较丰富,盐度低、弱还原的下三角洲泥炭沼泽环境;而5和7号煤层形成于盐度中等,弱还原受到海水影响较大的泻湖相泥炭沼泽环境.     

二连盆地吉尔嘎朗图凹陷下白垩统赛汉塔拉组层序地层及聚煤特征

二连盆地吉尔嘎朗图凹陷是一个陆相断陷聚煤盆地,下白垩统赛汉塔拉组是其主要含煤地层,作者利用岩心、钻孔资料对其岩相类型、沉积相、层序地层及聚煤作用特征进行研究。(1)赛汉塔拉组主要由砂砾岩、砂岩、粉砂岩、泥岩、碳质泥岩及厚层褐煤组成,发育扇三角洲平原相、扇三角洲前缘相、辫状河三角洲平原相、辫状河三角洲前缘相、滨浅湖相,分别属于扇三角洲沉积体系、辫状河三角洲沉积体系和湖泊沉积体系。(2)识别出2种层序界面:不整合面和下切谷冲刷面,将赛汉塔拉组划分为2个三级层序。从层序Ⅰ到层序Ⅱ,煤层厚度逐渐增大,聚煤作用逐渐增强。(3)在滨浅湖环境下厚煤层主要形成于湖侵体系域早期,在扇/辫状河三角洲环境下厚煤层主要形成于湖侵体系域晚期,煤层厚度在凹陷中部最大,向西北和东南方向均变小。聚煤作用明显受基底沉降作用影响,可容空间增加速率与泥炭堆积速率相平衡,从而形成了区内巨厚煤层。     

鄂尔多斯盆地北缘延安组2号煤层稀土元素异常原因及其地质意义

鄂尔多斯盆地北缘延安组2号煤层稀土元素的异常原因一直存在着争议,以2号煤发育较完整的榆林大海则煤矿为例,运用电感耦合等离子质谱（ICP-MS）、扫描电子显微镜（SEM）等方法,分析煤及夹矸中稀土元素（REE）含量及其矿物学特征,并揭示稀土元素异常原因。结果显示:煤中总稀土元素（∑REE）含量为3.71~46.21 μg/g,轻稀土元素（LREE,La-Eu）比重稀土元素（HREE,Gd-Lu）更富集;稀土元素标准化配分模式图显示少数样品为Eu正异常;稀土元素含量较高的样品和拥有Eu正异常的样品主要分布在与夹矸距离较近的煤层中,表明煤中稀土元素分布受到了夹矸的影响;在夹矸中发现很多晶型较好的锆石、磷灰石、透长石及锐钛矿,这些矿物是在聚煤过程中接受火山物质的直接证据。综合认为,鄂尔多斯盆地延安组2号煤沉积期,盆地周缘存在一次火山活动,火山灰降落覆盖在泥炭沼泽之上,影响了聚煤作用,致使煤中稀土元素分布异常。研究结果解释了鄂尔多斯盆地北缘的煤中稀土元素异常原因,为研究区煤的加工利用方式提供参考。      

Sedimentology of Fraser River delta peat deposits: A modern analogue for some deltaic coals

On the Recent lobe of the Fraser River delta peat accumulation has actively occurred on the distal lower dilta plain, the transition between upper and lower delta plains, and the alluvial plain.Distal lower delta plain peats developed from widespread salt and brackish marshes and were not influenced appreciably by fluvial activity. Lateral development of the marsh facies were controlled by compaction and eustatic sea level rise. The resulting thin, discontinuous peat network contains numerous silty clay partings and high concentrations of sulphur. Freshwater marsh facies formed but were later in part eroded and altered by transgressing marine waters. The peats overlie a thin, fluvial, fining-upward sequence which in turn overlies a thick, coarsening-upward, prodelta—delta front succession.Lower delta plain—upper delta plain peats initially developed from interdistributary brackish marshes and were later fluvially influenced as the delta prograded. The thickest peats occur in areas where distributary channels were abandoned earliest. Sphagnum biofacies replace sedge-grass-dominated communities except along active channel margins, where the sedge-grass facies is intercalated with overbank and splay deposits. The peats are underlain by a relatively thin sequence of fluvial deposits which in turn is underlain by a major coarsening-upward delta front and pro-delta sequence.Alluvial plain peats accumulated in back swamp environments of the flood plain. Earliest sedge-clay and gyttjae peats developed over thin fining-upward fluvial cycles or are interlaminated with fine-grained flood deposits. Thickest accumulations occur where peat fills small avulsed flood channels. Overlying sedge-grass and Sphagnum biofacies are horizontally stratified and commonly have sharp boundaries with fine-grained flood sediments. At active channel margins however, sedge-grass peats are intercalated with natural levee deposits consisting of silty clay. These levees reduce both the number and size of crevasse splay deposits.Coal originating from peats of the different environments of the Fraser delta would vary markedly in character. Peats of the lower delta plain will form thin lenticular coal seams with numerous splits and have a high ash and sulphur content. Peats from the lower to upper delta plain will be laterally extensive and of variable thickness and quality. Basal portions of the seams will contain numerous splits and have a high sulphur content whereas upper portions will be of higher quality. Peats from the upper delta plain—alluvial plain will form thick, isolated and laterally restricted coal seams characterized by low ash and sulphur contents.