Investigation of the Petrological and Geochemical Characteristics of Siderite in the Early Cretaceous Sandstone of Lacustrine Sedimentary Sequence in the Erlian Basin from Northeastern China

Siderite is a prevalent authigenic mineral in siliciclastic rocks, which usually occurred in eodiagensis period and could be used as an indicator of sedimentary environment. Some siderite precipitated in burial depth with geochemical information of basin fluid evolution. The crystal morphology, geochemical composition, and isotope values are influenced by physical and geochemical environment of precipitation. In this study, samples from the Early Cretaceous of Erlian basin in the northwestern China were collected, and mineralogy, bulk and in-situ geochemistry, C and O isotopes were analyzed to comprehensively investigate the sedimentary and diagenetic environment that the sediments experienced. Six lithofaices with three types of crystal habits were recognized in the siderite-rich sandstone, bundle crystal in spherical forms, blocky rhombs in intergranular pore and cleavage of muscovite, and micro bundle and mosaic crystals aggregates in nodular. The siderite growth proceeds through micro bundle and mosaic crystals to bundle siderite aggregates and then into blocky rhombs. The crystal evolution is also reflected by geochemical composition. The micro bundle and mosaic crystals are Casiderite. The spheritic shaped bundle aggregates are Ca-Mn-siderite. The blocky rhomb siderite shows gray part and bight part with Ca, Mg and Mn varies. Increase of Ca in block rhomb siderite suggests burial and mesodiagenesis, the high content of Mn may have linkage with eogenetic effects. The relatively positive and slightly negative δ13C value indicates meteoric water domination and influence of organic matter evolution in shallow buried time. The narrow ranges negative δ18O value suggest a small span of temperature of siderite formation.

REE characteristics of the coal in the Erlian Basin, Inner Mongolia, China, and its economic value

The rare earth elements(REE)content of the coal in the Erlian Basin was determined by inductively coupled plasma mass spectrometry(ICP-MS),and it turns out that the REE content from different geological age shows a significant difference:The REE content of the coal in the Jurassic Alatanheli Group is from 152.05×10^(−6) to 1416.21×10^(−6),with an average value of 397.31×10^(−6),and the relative concentration factor shows enriched;the REE content of the coal in Early Cretaceous Baiyanhua Group is from 20.65×10^(−6) to 102.53×10^(−6),the mean value is 49.06×10^(−6),and the relative concentration factor shows normally.The REE distribution patterns samples in Jurassic and Cretaceous shows the difference:The REE pattern in Jurassic coal mainly manifests as H-type distribution,with the Y,Lu positive anomaly,it is speculated that the fluid carried REE ions into the coal-bearing basin,and the heavy REE gather in the coal due to the different chemical properties of each REE.The REE occurrence mode is presumed to be mainly organic.Flat type is the REE main distribution pattern in Cretaceous coal.The REE patterns in clastic rocks of the roof,parting and floor of coal seam are similar to the REE patterns in the coal and the most possible reason is that the REE main source is from the clastic rock.It showed that the coal of the Early Jurassic,especially of Amugulen coalfield has resource value.

Existence and implications of hop-17(21)-enes in the lower Cretaceous of the Saihantala Sag, Erlian Basin, China

C31- to C35-hop-17（21）-enes are identified by gas chromatography-mass spectrometry （GC-MS） analysis to exist as double isomers in most samples of the Aershan Formation and members 1 and 2 of the Tenggeer Formation from well SH3. Comprehensive organic geochemistry and organic petrology study indicates that algae and bacteria are the main biological source of lower Cretaceous sediments in the Saihantala Sag, and this is in accordance with the existence of hop-17（21）-enes. The similar distributions of hop-17（21）-enes and hopanes of these samples indicate that hop-17（21）-enes were transformed into hopanes through hydrogenation during diagenesis processes. The existence of hop-17（21）-enes means that not only the formation of organic matter is related to an anoxic environment and a biological source of algae and bacteria, but also hop-17（21）-enes are direct indicators of hydrocarbon rock at an immature to low-maturity stage. High hydrocarbon conversion ratio, algae and bacteria source and a high abundance of organic matter suggest that the Saihantala Sag has the potential to generate immature to low-maturity oil, which may be of great significance for oil exploration in the Erlian Basin.

Hydrocarbon migration characteristics of the Lower Cretaceous in the Erlian Basin

The paper systematically analyzes the hydrocarbon migration characteristics of the Lower Cretaceous in the Erlian Basin, based on the geochemical data of mudstone and sandstone in the main hydrocarbon-generating sags. (1) The source rocks in K1ba and K1bt1 are estimated to be the mature ones, their hydrocarbon expulsion ratio can reach 32%-72%. The Type-I sags in oil windows possess good hydrocarbon generation and expulsion conditions, where commercial reservoirs can be formed. (2) According to the curves of the mudstone compaction and evolution of clay minerals, the rapid compaction stage of mudstones is the right time of hydrocarbon expulsion, i.e., primary migration. (3) The timing between hydrocarbon generation and expulsion is mainly related to the accordance of the oil window and the rapid compaction stage of mudstones in the hydrocarbon generation sags of Type-I. That forms the most matching relation between hydrocarbon generation and migration. (4) The faults and unconformities are the important paths for the secondary hydrocarbon migration. Especially, the unconformity between K1ba and K1bt1 has a favorable condition for oil accumulation, where the traps of all types are the main exploration targets. (5) Hydrocarbon migration effect, in the Uliastai sag, is most significant; that in the Saihan Tal and Anan sags comes next, and that in the Bayandanan and Jargalangt sags is worst.

Geochemistry and genesis of heavy oil in the Erlian Basin

Heavy oil is commonly distributed in the Erlian Basin, North China. It can be divided into two genetic types: the primary and the secondary. Primary heavy oil is generated directly by Cretaceous immature or low-mature hydrocarbon sources, or is derived from differentiation of crude oil during migration. Oil of this type has viscosity varying in the range of 100-5000 mPa·s. By contrast, secondary heavy oil, which has been thickened to various degrees, is resultant from a combination of biodegradation, water-leaching and oxidation of primary heavy oil. Based upon a large number of determinations on the physical properties of crude oil, GC analyses of saturated and aromatic hydrocarbons, and GC-MS analyses of steranes and terpanes, the characteristics of heavy oil of various types have been described. Differences in inspissation degree have made it possible the grouping of heavy oil of the Erlian Basin into an inspissation series, i.e., low maturity and immature heavy oil with viscosity of 100-2000 mPa·s, weakly biodegradated heavy oil with viscosity of 500-5000 mPa·s, moderately biodegradated heavy oil with viscosity of 1000-50000 mPa·s and highly biodegradated heavy oil with viscosity over 50000 mPa·s. With the progress of inspissation, the products vary from common heavy to over-heavy oil. Slope and uplifted areas inside a reservoir basin are most favorable to the inspissation and formation of heavy oil. Interaction of several mechanisms of inspissation has resulted in a widespread distribution of heavy oil within the Erlian Basin.

Pore structure characteristics of low-rank coal reservoirs with different ash yields and their implications for recoverability of coalbed methane—a case study from the Erlian Basin, northeastern China

Pores are the main accumulation sites and migration pathways for coalbed methane(also referred to as CBM).Pore structure restricts the content and recoverability of CBM from coal reservoirs.In this study,12 representative coal samples with different ash yields that have similar tectonic characteristics and burial depths were collected from different mining areas in the Jiergalangtu and Huolinhe depressions in the Erlian Basin.These samples were used to study the restrictions of ash yield on the characteristics of coal pore structures and the recoverability of CBM through macroscopic and microscopic structure observation,scanning electron microscope observations,vitrinite reflectance tests,low-temperature N2 adsorption,nuclear magnetic resonance(NMR),and micro-computed tomography.The results show that coal reservoirs in the study area vary greatly in ash yield,based on which they can be divided into three types,i.e.,low-ash-content,ash-bearing,and high-ash-content coal reservoirs.In addition,the ash yield has a certain impact on the development of coal pores;coal samples with lower ash yields indicate the presence of well-developed medium-large pores and better connectivity.Ash yield also has a certain impact on the brittleness of coal wherein a lower ash yield implies the development of brittle coal that is more liable to fracture as compared to less brittle samples at the same pressure.Absorbed gas content also varies significantly with ash yield;a low ash yield impacts the gas saturation of coal.Overall,for coal reservoirs in the study area,their porosity,pore diameter,movable fluid porosity,adsorbed gas amount,and recoverability decrease as the ash yield increases.

Sequence Stratigraphic Modeling of Sedimentary Basin: Conceptual Model and Application to Erlian and Yinggehai Basins, China

A quantitative two-dimensional model of sequence stratigraphy is formulated to simulate the development of sequence architecture in sedimentary basins. The model takes into account sea level change, tectonic subsidence, compaction of sediments, flexural isostatic compensation, erosion and sedimentation. It may be used to test sequence stratigraphic model, to analyze the development of sequence architecture and sequence boundaries, and to predict facies distribution in basins. The computer model, combined with backstripping technique, is cali- brated to model the sedimentary filling of the Early Cretaceous Erlian basin and the Tertiary Yinggehai basin. The study shows that the development of high order sequences in the basins was closely related to the multiple stretching and inversion. The development of the progradational sequence set of the Yinghuang Formation in Yinggehai basin formed in synrift period was mainly controlled by a large amount of sediment input high fluctuation of sea level and gradual subsidence of the basin.

Early Paleogene stratigraphic sequences,mammalian evolution and its response to environmental changes in Erlian Basin,Inner Mongolia,China

Paleogene strata in the Huheboerhe area,Erlian Basin,Inner Mongolia,China have been subdivided into three lithological units:the Nomogen Formation,the Arshanto Formation,and the Irdin Manha Formation.At least 12 mammal-bearing horizons have been recognized in these formations,of which 4 in the Nomogen Formation,6 in the Arshanto Formation,and 2 in the Irdin Manha Formation.Recent investigation proved that the "Houldjin Formation" recognized in this area by the Central Asiatic Expeditions(CAE) of the American Museum Natural History in the 1920s is actually the Irdin Manha Formation,while the "Irdin Manha Formation" of CAE is the Arshanto Formation.A recent paleomagnetic study suggests that the upper part of the Nomogen Formation is early Eocene in age and the Arshanto Formation is mainly early Eocene rather than middle Eocene as previously thought.The Gashatan,Bumbanian,and Arshantan land mammal ages are correlated respectively to the Thanetian,the early Ypresian,and the middle Ypresian through earliest Lutetian of the Geological Time Scale.These land mammal ages are also correlated with the late Tiffanian through Clarkforkian,the early Wasatchian,and the middle-late Wasatchian and most of the Bridgerian of the North American Land Mammal Ages.During the early Paleogene,the mammalian history of the Erlian Basin was dominated by the appearance of new mammalian families and the replacement of a variety of genera and species,corresponding to the gradual climatic changes during this time period.The abrupt emergence of several modern mammalian orders at the beginning of the Eocene is probably related to extreme climatic warming in relation to the Paleocene-Eocene Thermal Maximum.

Extensional Tectonic System of Erlian Fault Basin Groupand Its Deep Background

The Erlian fault basin group, a typical Basin and Range type fault basin group, was formed during Late Jurassic to Early Cretaceous, in which there are rich coal, oil and gas resources. In the present paper the abundant geological and petroleum information accumulated in process of industry oil and gas exploration and development of the Erlian basin group is comprehensively analyzed, the structures related to formation of basin are systematically studied, and the complete extensional tectonic system of this basin under conditions of wide rift setting and low extensional ratio is revealed by contrasting study with Basin and Range Province of the western America. Based on the above studies and achievements of the former workers, the deep background of the basin development is treated.

二连盆地赛汉高毕铀矿床渗出成矿作用和模式

通过探讨二连盆地赛汉高毕铀矿成矿作用,构建铀成矿模式,总结成矿特征,提炼关键控矿要素,可指导矿床外围、深部和类似地区铀矿找矿。文章基于赛汉高毕铀矿床构造、建造、油气演化、铀矿化、铀成矿时代等分析,详细阐述了矿床矿石矿物、矿石元素地球化学特征。确认赛汉高毕铀矿床产于赛汉组上段建造间古河道中,受准宝力格深切断陷、贯通性断裂、赛汉晚期深切河道联合控制,形成透镜状或板状铀矿体,铀成矿作用与区域油气逸散活动、挤压构造活动密切相关;铀矿石中CaO+Al_(2)O_(3)和P_(2)O_(5)与铀含量呈正相关,Co、Ni、Zn含量高,Fe^(2+)/Fe^(3+)总体小于0.8;各类砂岩中酸解烃含量均比较高,Th/U均小于2,表明赛汉组上段原生环境主要为红杂色的氧化环境,灰色含矿砂体主要是渗出还原成因;矿石中铀是以多种铀矿物形式存在,主要有黄铁矿-铀矿物型、地沥青包裹铀矿物型和微粒碎屑铀矿物型。赛汉高毕铀矿床主要为渗出成矿作用,赋存于深部的富含有机质和四价铀的流体沿贯通断裂或高角度不整合和下切河道运移至上部赛汉组上段氧化砂体中,流体被分解形成黄铁矿、富含铁铝等杂质的磷钙铀矿、地沥青,粒径大的地沥青将已先结晶的黄铁矿和富含铁铝等杂质的磷钙铀矿包裹其中,大部分铀矿物就位于较小的地沥青的外侧和附近。

二连盆地伊和高勒地区赛汉组砂岩型铀成矿条件

为揭示二连盆地马尼特坳陷伊和高勒地区下白垩统赛汉组砂岩型铀成矿条件,文章通过系统研究伊和高勒地区的构造特征、地层特征、岩性特征、岩石地球化学特征、地层含铀性、沉积相特征、水文地质和放射性水化学特征、氧化特征等,并与巴彦乌拉地区进行对比,分析了砂岩型铀成矿条件。研究区外部铀源条件好,赛汉组含铀性低;具有完善的“补-径-排”体系,放射性水化学异常明显。沙那凹陷具有缓倾的构造斜坡,发育辫状河三角洲,砂体发育,主要为灰色砂岩与泥岩互层;阿北凹陷具有陡倾的构造斜坡,发育扇三角洲,砂体极为发育,岩性为灰色、杂色砾岩夹灰色泥岩;沙那凹陷铀成矿条件较阿北凹陷好,相比巴彦乌拉地区赛汉组铀成矿条件较差。

重力资料在二连盆地构造单元区划及断裂构造识别中的应用

二连盆地是我国重要的产铀盆地,且铀矿多为隐伏盲矿。为了明确研究区内地质构造特征,提供铀矿资源勘探方向,文章利用最新的重力资料,通过布格异常改正、解析延拓和总水平导数计算等处理,得到了与断裂和盆地边界相关的地球物理场信息。研究结果揭示了二连盆地重力异常具有明显的分区性和分带性。根据重力异常特征共推断出48条断裂,断裂构造方向主要呈北东向和北西向,其中以北东向为主,北西向为辅,北西向断裂对北东向断裂进行了改造和错动。结合前人研究、断裂划分和基底埋深,重新划分了马尼特坳陷、乌兰察布坳陷、苏尼特隆起和温都尔庙隆起的构造边界。重力资料显示研究区已知的铀矿化和盆地基底隆坳之间关系密切,铀矿化多分布在构造区的局部斜坡带。综合全区地球物理场特征和推断的断裂分布,乌兰察布坳陷东北部是比较好的砂岩型铀矿床有利区。

二连盆地富气凹陷低阶煤煤层气成因及成藏机制

内蒙古低阶煤煤层气资源丰富,煤层气成因与成藏机制研究对低阶煤煤层气资源选区评价至关重要。以二连盆地重点富气凹陷低阶煤煤层气为研究目标,利用煤层气组分、碳/氢同位素、煤层水水质、氢/氧同位素及放射性同位素^(3)H和^(14)C测试等多种实验手段,分析煤层气、水地球化学特征,揭示低阶煤煤层气成因来源及成藏机制。结果表明,二连盆地煤层气组分以甲烷为主,均为干气,其中甲烷体积分数随埋深增加而增大,CO_(2)体积分数随埋深增加呈先增加后降低趋势,在300~500 m范围出现高值区。甲烷碳、氢同位素普遍偏轻,δ^(13)C(CH_(4))分布在-70.3‰~-48.0‰,δD(CH_(4))分布在-285.5‰~-189.0‰,δ^(13)C(CO_(2))在-37.6‰~1.94‰变化。煤层水化学类型主要为HCO_(3)-Na型和Cl·HCO_(3)-Na型,现今煤层水体环境较为稳定,水动力较弱,煤层水表观年龄在1020~47490 a,主要来源于第四纪大气降水,没有或较少有现今地表水补给。二连盆地煤层气主要为原生生物成因气,混有少量早期热成因气,随着埋深加大,地层环境和产甲烷古菌类型发生变化,生物甲烷生成途径发生转变。其中吉尔嘎朗图凹陷早期以乙酸发酵产气为主,晚期转变为CO_(2)还原产气为主,并混有少量低熟热成因气;巴彦花和霍林河凹陷微生物产气途径均以乙酸发酵为主,其中霍林河凹陷还混有少量甲基发酵型生物气。研究区具有适合生物气生成的低地温、低矿化度和低热演化程度的“三低”煤层条件,其中,吉尔嘎朗图凹陷属于地堑式浅部厚煤层生物气成藏模式,巴彦花和霍林河凹陷属于半地堑式中深部承压区水力封堵生物气成藏模式。寻找适合生物成因气形成和富集的有利目标区,应是二连盆地煤层气未来勘探开发的重点方向,也是二连盆地低阶煤煤层气增储上产的现实保障。

二连盆地脑木更地区黏土矿物特征及其与铀成矿关系研究

本文对二连盆地脑木更地区赛汉组矿层及围岩进行XRD黏土矿物成分分析,以探讨黏土矿物特征与铀成矿作用之间的关系。经电子探针成分分析,该区铀矿物为沥青铀矿,见黄铁矿与沥青铀矿共生。采用X射线粉晶衍射、扫描电镜、电子探针等分析手段,测定黏土矿物相对含量、微观形貌特征,结果显示研究区黏土矿物主要为蒙脱石、高岭石、伊利石,蒙脱石含量在三者中最高,其与高岭石含量呈较明显的负相关性,表明其主要由高岭石转化而来,偏碱性的孔隙流体造成黏土矿物的蚀变和转换。矿层及围岩中黏土矿物的种类及含量差异性不明显,表明黏土矿物与铀成矿及富集作用相关性不明显,在赛汉组砂岩型铀矿成矿过程中黏土矿物可以吸附铀,但不是铀成矿及富集的最主要因素。通过对赛汉组砂岩中黏土矿物含量及特征研究,该区存在两期流体作用,一期是高岭石反映的偏酸性环境,另一期是蒙脱石反映的碱性环境,揭示了由酸性→碱性流体的作用过程。黏土矿物可以作为铀成矿过程中后生流体示踪的重要标志。

二连盆地乌里雅斯太凹陷赛汉组铀矿化特征及找矿前景探讨

针对研究区内前期勘查工作铀矿成矿条件研究尚不深入的问题,为实现区内铀矿找矿突破,本文通过对乌里雅斯太凹陷的构造演化特征、蚀源区铀源条件、含矿目的层特征、水文地质条件、后生蚀变特征、铀矿化特征及白垩系沉积建造特征进行系统分析,结合研究区钻孔、连井剖面等资料,综合探讨了乌里雅斯太凹陷砂岩型铀成矿环境及条件,认为盆缘的富铀花岗岩体为沉积盆地提供了丰富的铀源,中生代后期构造反转形成的剥蚀天窗为含铀含氧水的渗入、渗出提供了通道,凹陷北缘陡坡带扇三角洲平原分流河道及前缘水下分支河道微相发育部位是该区砂岩型铀矿找矿的重点方向,下白垩统赛汉组为主要找矿目标层位,找矿类型以层间氧化带型为主,次为潜水氧化带型。研究区各种成矿要素匹配良好,具备形成中型以上的砂岩型铀成矿潜力。

二连盆地乌尼特坳陷砂岩型铀成矿古水文地质条件分析

本文在分析二连盆地乌尼特坳陷基底、盖层结构特征基础上,对坳陷的古气候古水文地质条件开展研究,包括坳陷中各凹陷的地下水的形成发展史、同生沉积水的形成、分布及演化过程及地静压力系统、水静压力系统对地下水的改造作用。经分析认为,压挤水运动方向与盆缘补给区的含氧含铀水运动方向相反,在其径流过程中,两种不同性质的地下水相遇的混合部位,是水动力条件和水化学环境的变异部位,铀元素在这里富集成矿,并由此提出了铀成矿的有利时期及层位。

重磁井震联合正反演技术在二连盆地深层目标勘探中的应用

二连盆地具有丰富的油气资源,前白垩系作为盆地的主力生油层系,其含油气性早已被证实。但该盆地高力罕凹陷及周缘整体勘探程度较低,早期完成的少量二维地震仅局限在几个独立的凹陷内,无法连片,缺少对该区整体地质结构的认识,油气勘探至今未能取得显著效果。前期研究发现,二连盆地前白垩系地层分布面积广,烃源岩有机质丰度高,成熟度高,处于成熟凝析油湿气阶段。前白垩系地层钻探程度低,探索前白垩系含油气性,实现二连盆地新层系勘探突破,拓展二连盆地战略接替新层系。近年来,高精度重磁勘探通过重磁井震联合正反演等针对性处理解释技术,较好恢复了该盆地前白垩纪盆地原貌,有望开启研究二连盆地深层地质结构的新篇章。

内蒙古额仁淖尔凹陷赛汉组砂(泥)岩地球化学特征及其对铀成矿作用的制约

【研究目的】查明二连盆地额仁淖尔凹陷赛汉组含铀砂(泥)岩的岩石矿物及地球化学特征,探讨铀成矿作用。【研究方法】包括野外地质编录、偏光显微镜、电子探针能谱分析、主微元素、环境地球化学及铀的价态分析等。【研究结果】(1)铀矿物以吸附态和独立铀矿物的形式存在,常与炭屑和黄铁矿共(伴)生并发现闪锌矿。(2)矿石具有高C_(有)、S、CO_(2)的特征,泥岩U^(6+)/U^(4+)平均为1.01,砂岩U^(6+)/U^(4+)平均为0.57。(3)砂(泥)岩的CIA值为50.83~66.34,稀土元素特征与蚀源区花岗岩一致,主微量元素特征均显示存在明显的后期沉积-成岩阶段的水岩作用。【结论】(1)海西期花岗岩是赛汉组砂(泥)岩的主要物源,沉积环境为半干旱—半湿润古气候。(2)吸附作用和氧化还原作用是研究区铀富集的主要机理,泥岩型铀矿以吸附作用为主,砂岩型铀矿以氧化还原作用为主。(3)深部流体可能参与了成矿作用。

二连盆地巴彦乌拉铀矿床氧化带发育样式与岩石地球化学特征

砂岩型铀矿床的形成受氧化带空间展布、规模及强度的影响,对其氧化带发育样式及其岩石地球化学特征的精细解剖,有助于揭示区域铀成矿规律,为下一步勘探提供理论依据。巴彦乌拉铀矿床是二连盆地发现的大型砂岩型铀矿床,文章通过钻孔岩心观察、连井剖面、样品薄片鉴定以及环境指标分析,认为巴彦乌拉铀矿床铀元素的富集程度主要由后生氧化作用的发育程度决定,宏观上,矿体赋存在赛汉组上段古河谷砂体中,受由北向南的潜水-层间氧化作用控制;微观上,铀矿化的富集与矿物组合、岩石地球化学特性及特征元素的分布呈现出明显的规律性。不同的氧化带样式决定了铀矿体的产出部位和形态,而铀含量增高的地方恰好为ΔEh、S_(全)、S^(2-)、C_(有)、CO_(2)、Fe_(2)O_(3)等环境指标的增高部位,表明铀成矿与岩石地球化学障密切相关。