Differences and identification on multi-time hydrocarbon generation of carboniferous-permian coaly source rocks in the Huanghua Depression,Bohai Bay Basin

Coal is a solid combustible mineral,and coal-bearing strata have important hydrocarbon generation potential and contribute to more than 12%of the global hydrocarbon resources.However,the deposition and hydrocarbon evolution process of ancient coal-bearing strata is characterized by multiple geological times,leading to obvious distinctions in their hydrocarbon generation potential,geological processes,and production,which affect the evaluation and exploration of hydrocarbon resources derived from coaly source rocks worldwide.This study aimed to identify the differences on oil-generated parent macerals and the production of oil generated from different coaly source rocks and through different oil generation processes.Integrating with the analysis of previous tectonic burial history and hydrocarbon generation history,high-temperature and high-pressure thermal simulation experiments,organic geochemistry,and organic petrology were performed on the Carboniferous-Permian(C-P)coaly source rocks in the Huanghua Depression,Bohai Bay Basin.The oil-generated parent macerals of coal's secondary oil generation process(SOGP)were mainly hydrogen-rich collotelinite,collodetrinite,sporinite,and cutinite,while the oil-generated parent macerals of tertiary oil generation process(TOGP)were the remaining small amount of hydrogen-rich collotelinite,sporinite,and cutinite,as well as dispersed soluble organic matter and unexhausted residual hydrocarbons.Compared with coal,the oil-generated parent macerals of coaly shale SOGP were mostly sporinite and cutinite.And part of hydrogen-poor vitrinite,lacking hydrocarbon-rich macerals,and macerals of the TOGP,in addition to some remaining cutinite and a small amount of crude oil and bitumen from SOGP contributed to the oil yield.The results indicated that the changes in oil yield had a good junction between SOGP and TOGP,both coal and coaly shale had higher SOGP aborted oil yield than TOGP starting yield,and coaly shale TOGP peak oil yield was lower than SOGP peak oil yield.There were significant differences in saturated hydrocarbon and aromatic parameters in coal and coaly shale.Coal SOGP was characterized by a lower Ts/Tm and C31-homohopane22S/(22S+22R)and a higher Pr/n C17compared to coal TOGP,while the aromatic parameter methyl dibenzothiophene ratio(MDR)exhibited coaly shale TOGP was higher than coaly shale SOGP than coaly TOGP than coaly SOGP,and coal trimethylnaphthalene ratio(TNR)was lower than coaly shale TNR.Thus,we established oil generation processes and discriminative plates.In this way,we distinguished the differences between oil generation parent maceral,oil generation time,and oil production of coaly source rocks,and therefore,we provided important support for the evaluation,prediction,and exploration of oil resources from global ancient coaly source rocks.

Carboniferous-Permian Stratigraphy and Sedimentary Environment of Southeastern Inner Mongolia,China:Constraints on Final Closure of the Paleo-Asian Ocean

In this paper we discuss the timing of final closure of the Paleo-Asian Ocean based on the field investigations of the Carboniferous-Permian stratigraphic sequences and sedimentary environments in southeastern Inner Mongolia combined with the geology of its neighboring areas. Studies show that during the Carboniferous-Permian in the eastern segment of the Tianshan-Hinggan Orogenic System, there was a giant ENE-NE-trending littoral-neritic to continental sedimentary basin, starting in the west from Ejinqi eastwards through southeastern Inner Mongolia into Jilin and Heilongjiang. The distribution of the Lower Carboniferous in the vast area is sparse. The Late Carboniferous or Permian volcanic-sedimentary rocks always unconformably overlie the Devonian or older units. The Upper Carboniferous-Middle Permian is dominated by llttoral-neritic deposits and the Upper Permian, by continental deposits. The Late Carboniferous-Permian has no trace of subduction-collision orogeny, implying the basin gradually disappeared by shrinking and shallowing. In addition, it is of interest to note that the Ondor Sum and Hegenshan ophiolitic melanges were formed in the pre-Late Silurian and pre-Late Devonian respectively, and the Solonker ophiolitic melange formed in the pre-Late Carboniferous. All the evidence indicates that the eastern segment of the Paleo-Asian Ocean had closed before the Late Carboniferous, and most likely before the latest Devonian （Famennian）.

Hydrocarbon generation from Carboniferous-Permian coaly source rocks in the Huanghua depression under different geological processes

Natural gas and condensate derived from Carboniferous-Permian(C-P)coaly source rocks discovered in the Dagang Oilfield in the Bohai Bay Basin(east China)have important implications for the potential exploration of C-P coaly source rocks.This study analyzed the secondary,tertiary,and dynamic characteristics of hydrocarbon generation in order to predict the hydrocarbon potentials of different exploration areas in the Dagang Oilfield.The results indicated that C-P oil and gas were generated from coaly source rocks by secondary or tertiary hydrocarbon generation and characterized by notably different hydrocarbon products and generation dynamics.Secondary hydrocarbon generation was completed when the maturity reached vitrinite reflectance(Ro)of 0.7%-0.9%before uplift prior to the Eocene.Tertiary hydrocarbon generation from the source rocks was limited in deep buried sags in the Oligocene,where the products consisted of light oil and gas.The activation energies for secondary and tertiary hydrocarbon generation were 260-280 kJ/mol and 300-330 kJ/mol,respectively,indicating that each instance of hydrocarbon generation required higher temperature or deeper burial than the previous instance.Locations with secondary or tertiary hydrocarbon generation from C-P coaly source rocks were interpreted as potential oil and gas exploration regions.

Carbonate Diagenesis Controlled by Glacioeustatic Sea-Level Changes: A Case Study from the Carboniferous-Permian Boundary Section at Xikou, China

The platform-facies carbonate rocks of the Carboniferous-Permian boundary strata are well developed and outcropped in Xikou （西口）, Zhen＇an （镇安） County, Shaanxi （ 陕西 ） Province, China. The carbonate diagencsis in the Carboniferous-Permian boundary section at Xikou contains many processes with conspicuous effects, including micritization, cementation, mechanical and chemical compaction, neomorphism, and dissolution. Based on mineralogical composition and microfabrics, the diagenetic environments are distinguished into marine, near surface meteoric and burial environments. Detailed petrographical observation of abundant thin sections integrated with previous studies on sequence stratigraphy reveals that the carbonate diagenesis in the Carboniferous-Permian boundary section is related to the relative stratigraphic position of the rocks in the high-frequency cycles and controlled by the glacioeustatic sea-level changes. There are distinctive differences in diagenetic patterns between the lower transgressive sequence and the upper regressive sequence in a cyclothem. The diagenesis in the lower transgressive sequence is mainly characterized by pressure dissolution and recrystallization of mudstone and wackstone in a burial environment, and the diagenesis in the upper regressive sequence by cementation and leaching of freshwater in a meteoric environment.

Provenance and paleogeography of Carboniferous-Permian strata in the Bayanhot Basin:Constraints from sedimentary records and detrital zircon geochronology

The Bayanhot Basin is a superimposed basin that experienced multiple-staged tectonic movements;it is in the eastern Alxa Block,adjacent to the North China Craton(NCC)and the North Qilian Orogenic Belt(NQOB).There are well-developed Paleozoic-Cenozoic strata in this basin,and these provide a crucial window to a greater understanding of the amalgamation process and source-to-sink relationships between the Alxa Block and surrounding tectonic units.However,due to intensive post-depositional modification,and lack of subsurface data,several fundamental issues-including the distribution and evolution of the depositional systems,provenance supplies and source-to-sink relationships during the Carboniferous-Permian remain unclear and thus hinder hydrocarbon exploration and limit the geological understanding of this basin.Employing integrated outcrop surveys,new drilling data,and detrital zircon dating,this study examines the paleogeographic distribution and evolution,and provenance characteristics of the Carboniferous-Permian strata in the Bayanhot Basin.Our results show that the Bayanhot Basin experienced a long-term depositional evolution process from transgression to retrogression during the Carboniferous-late Permian.The transgression extent could reach the central basin in the early Carboniferous.The maximum regional transgression occurred in the early Permian and might connect the Qilian and North China seas with each other.Subsequently,a gradual regression followed until the end of the Permian.The northwestern NCC appeared as a paleo-uplift area and served as a sediments provenance area for the Alxa Block at that time.The NCC,Bayanwula Mountain,and NQOB jointly served as major provenances during the Carboniferous-Permian.There was no ocean separation,nor was there an orogenic belt between the Alxa Block and the NCC that provided sediments for both sides during the Carboniferous-Permian.The accretion of the Alxa and North China blocks should have been completed before the Carboniferous period.

Megaclasts from the Carboniferous-Permian Rocks in the Langkawi Islands, Malaysia, and Their Implications

The Ninth Regional Congress on Geology, Mineral andEnergy Resources of Southeast Asia was held in KualaLumpur of Malaysia in August of 1998. After the Con-gress, the author participated in the geological fieldexcursion and investigation in the Langkawi Islands,and noted that the Carboniferous-Permian rocks con-tain megaclasts of metamorphic and pegmatitic rocks,which indicate the existence of pre-Carboniferousmetamorphism and magmatism. The observation resultsare as follows:

The species diversity of fusulinaceans and high-frequency sea-level changes in the Carboniferous-Permian boundary section at Xikou, Zhen'an County,Shaanxi Province, China

The study on the interrelation between sea-level changes and biodiversity with its evolu-tion has great significance for understanding the impact of global changes on organic evolution and exploring the inherent laws of life-environment coevolution in geological history. In this paper, the stratigraphic distribution of fusulinacean fauna in the Carboniferous-Permian boundary section at Xikou, Zhen’an County, Shaanxi Province, is analyzed quantitatively, and the relationship between the species diversity of fusulinaceans and relative sea-level changes is discussed. As a whole, the spe-cies numbers of fusulinacean fauna experience a rapid increase and an obvious decline in Xikou, Zhen’an County, from the Late Carboniferous to the Early Permian. There is a significant increase in species diversity around the Carboniferous-Permian boundary, which is one of the biggest bio-events of the fusulinacean fauna, and represents the radiation of Pseudoschwagerininae subfamily in the studied area. Integrated fusulinacean species diversity into sequence stratigraphic framework, de-tailed study suggests that the species diversity of the fusulinaceans is closely related to its relative stratigraphic location, and is essentially controlled by the sea-level changes, especially by the high-frequency sea-level changes. Generally, the species diversity of fusulinaceans is low, and the number of first and last appearance datum is small in the lower unit of high-frequency depositional cycle formed during the quick rise of the sea level; whereas the species diversity of fusulinaceans is high, and the number of first and last appearance datum is large in the upper unit of high-frequency cycle formed during the slow fall of the sea level. Within the third-order depositional sequence, the species diversity of the fusulinaceans at the first flooding surfaces and the maximum flooding surfaces is low, and it increases upward. The fusulinacean species diversity is low within the transgressive systems track, and it is high within the highstand systems track. The second-order rise and fall in sea level coincide with the bloom and decline of high order taxa of fusulinaceans.

Genesis of Kaolinite Deposits in the Jungar Coalfield,North China:Petrological,Mineralogical and Geochemical Evidence

Petrological,mineralogical and geochemical studies carried out on kaolinite deposits in Haerwusu surface mine,Jungar Coalfield,northern Ordos Basin,North China,define their characteristics,ore genesis and economic interest.Based on the crystalline size,two different types of kaolinite rocks,cryptocrystalline and grainy,were identified under the microscope.XRD data show that kaolinite is the predominant mineral,associated with boehmite,magnesite,anatase,pyrite,diaspore and calcite.However,high boehmite content(mean 70%)shows up in the middle layers.Kaolinite minerals present homogeneous shape and a good crystallinity(HI=0.96–1.26).Geochemical studies show that the SiO_(2)/Al_(2)O_(3)molar ratio of kaolinite is close to the theoretical value,and the contents of Na_(2)O,K_(2)O,CaO,Mg O are less,suggesting a strong chemical weathering environment.The REE and Eu anomalies show a close relationship between kaolinite and the Yinshan Oldland granite.A Ce anomaly reflects a continental sedimentary environment with shallow water.A temperature range of 26.7–34℃was calculated on the basis of the isotopic signatures(δ18O,δD)of the kaolinite rocks.All these data indicate that the formation of the kaolinite is caused mainly by the dissolution,coagulation,precipitation and recrystallization of aluminosilicate clastics in acidic conditions.The formation of boehmite in the middle layers indicates that the source rocks have changed.Boehmite is mainly formed by dehydration and compaction of an aluminum-rich colloid which transported into peat swamp during diagenesis.In addition,it formed by desiliconization of kaolinite under acidic conditions.Due to its high kaolinite content(up to 90%)and low iron mineral content(less than 1%),and good crystallinity,kaolinite deposits occurred at Haerwusu surface mine probably have great economical value in the future.

Gravity and magnetic field characteristics and regional ore prospecting of the Yili ancient continent, West Tianshan, Xinjiang Uygur Autonomous Region, China

Gold,iron,copper,lead-zinc and other mineral exploration in West Tianshan,Xinjiang Uygur Autonomous Region,has made remarkable progress in recent years.However,due to the dispute on the tectonic division of West Tianshan,the ore-controlling factors and the regional metallogenic laws are controversial.The authors analyze regional gravity data and notice that the high-value region corresponds to the Yili ancient continent,thus the southeastern boundary of the Yili ancient continent is delineated.Comparative analysis of gravity,aeromagnetic and geologic data reveals that the Tulasu basin,where some medium to large epithermal gold deposits locate,lies above the Yili ancient continent;the Yili Carboniferous-Permian rift extends in E-W direction,numbers of copper deposits have been found in the mid-west section of the rift which lies above the Yili ancient continent,whereas few copper deposits have been discovered in the east section which is outside the Yili ancient continent.Accordingly,the Yili ancient continent may be rich in gold,copper and other metal elements;the metal-bearing hydrothermal solution moves up with the activity of magmatism,and deposits in the favorable places(the Tulasu basin and the Yili Carboniferous-Permian rift),forming numerous small and medium gold,copper deposits,as well as some large and super-large gold deposits.Therefore,the tectonic-magmatic hydrothermal zone above the Yili ancient continent should be the prospective area for epithermal gold and copper polymetallic deposits.

辽东太子河流域石炭—二叠纪岩相古地理及铝土矿成矿地质条件

晚石炭—早二叠世的辽东太子河盆地是一个周边为平移断层的断陷盆地。以东西向垂直运动为主体的构造活动控制了盆地的发展和演化。根据构造特征、沉积相和古地磁与华北腹地石炭一二叠系的差异,太子河地区的石炭一二叠系应是华北型石炭一二叠系的一个分支,作者称“辽东亚型”。古地理演化表现为从晚石炭世早期的扇三角3洲→峡湾海岸→碳酸盐台地的快速海进,直至早二叠世末的三角洲→冲积平原→湖泊体系的缓慢海退,堆积了近陆特征明显的、近尔西展布的各沉积相带。随时代渐新,堆积物中碎屑组分成熟度趋于增高,大地构造背景从部分卷入大陆边缘活动带过渡为大陆板块克拉通内部,均反映本区的断陷活动由次稳定向稳定型转化。铝土矿成矿物质主要来源于北部古陆结晶岩石,系红土(钙红土)—沉积成因。G层铝土矿形成于泻湖边缘环境;B臣则位于近海湖泊的滨—浅湖地带,同受控于北纬41°20′的同沉积断裂,与北东向断裂复合凹地为成矿最佳场所。

A late Carboniferous transition from subduction to collision:Tectonosedimentary evidence from southern Junggar,NW China

The Carboniferous to Permian tectono-sedimentary evolution of the southern Junggar area brings new insights into understanding the subduction-collision processes in the northern Tianshan region.Integrating geophysics,geochemistry,and geochronology approaches,this study investigates the Carboniferous-Permian strata in the southern Junggar Basin.The results have revealed three distinct tectono-stratigraphic evolutionary stages,each marked by a distinctive volcano-sedimentary sequence.The Early Carboniferous strata suggest intense volcanic activities in the southern Junggar area.During the Late Carboniferous,the southern Junggar Basin was controlled by normal faulting in an extensional setting,receiving sedimentary inputs from the Junggar terrane.The Lower Permian,unconformably overlying the Upper Carboniferous,was shaped by an extensional regime and is comprised by volcano-clastic sequences that received detritus from the Yili-Central Tianshan block.These findings indicate that a Late Carboniferous forearc basin developed in the southern Junggar area,and it evolved into a post-collisional rift in the Early Permian.This period marked a dynamic shift from bidirectional subduction(rollback)to the detachment of the North Tianshan oceanic slab.We propose that the collision between the YiliCentral Tianshan block and the Junggar terrane,along with the closure of the North Tianshan Ocean,likely occurred in the Late Carboniferous(ca.306-303 Ma).

Geological characteristics and mineralization setting of the Zhuxi tungsten(copper) polymetallic deposit in the Eastern Jiangnan Orogen

The Zhuxi ore deposit is a super-large scheelite(copper) polymetallic deposit discovered in recent years. It grew above copper/tungsten-rich Neoproterozoic argilloarenaceous basement rocks and was formed in the contact zone between Yanshanian granites and Carboniferous-Permian limestone. Granites related to this mineralization mainly include equigranular, middle- to coarse-grained granites and granitic porphyries. There are two mineralization types: skarn scheelite(copper) and granite scheelite mineralization. The former is large scale and has a high content of scheelite, whereas the latter is small scale and has a low content of scheelite. In the Taqian-Fuchun Basin, its NW boundary is a thrust fault, and the SE boundary is an angular unconformity with Proterozoic basement. In Carboniferous-Permian rock assemblages, the tungsten and copper contents in the limestone are both very high. The contents of major elements in granitoids do not differ largely between the periphery and the inside of the Zhuxi ore deposit. In both areas, the values of the aluminum saturation index are A/CNK>1.1, and the rocks are classified as potassium-rich strongly peraluminous granites. In terms of trace elements, compared to granites on the periphery of the Zhuxi ore deposit, the granites inside the Zhuxi ore deposit have smaller d Eu values, exhibit a significantly more negative Eu anomaly, are richer in Rb, U, Ta, Pb and Hf, and are more depleted in Ba, Ce, Sr, La and Ti, which indicates that they are highly differentiated S-type granites with a high degree of evolution. Under the influence of fluids, mineralization of sulfides is evident within massive rock formations inside the Zhuxi ore deposit, and the mean SO_3 content is 0.2%. Compared to peripheral rocks, the d Eu and total rare earth element(REE) content of granites inside the Zhuxi ore deposit are both lower, indicating a certain evolutionary inheritance relationship between the granites on the periphery and the granites inside the Zhuxi ore deposit. For peripheral and ore district plutons, U-Pb zircon dating shows an age range of 152–148 Ma. In situ Lu-Hf isotope analysis of zircon in the granites reveals that the calculated e_(Hf)(t) values are all negative, and the majority range from -6 to -9. The T_(DM2) values are concentrated in the range of 1.50–1.88 Ga(peak at 1.75 Ga), suggesting that the granitic magmas are derived from partial melting of ancient crust. This paper also discusses the metallogenic conditions and ore-controlling conditions of the ore district from the perspectives of mineral contents, hydrothermal alteration, and ore-controlling structures in the strata and the ore-bearing rocks. It is proposed that the Zhuxi ore deposit went through a multistage evolution, including oblique intrusion of granitic magmas, skarn mineralization, cooling and alteration, and precipitation of metal sulfides. The mineralization pattern can be summarized as "copper in the east and tungsten in the west, copper at shallow-middle depths and tungsten at deep depths, tungsten in the early stage and copper in the late stage".

Sedimentary conditions for good coal reservoir development in the Carboniferous and Permian,Qinshui Basin

In the Carboniferous and Permian of the Qin-shui Basin, coal reservoirs are well developed. But different coal reservoirs are obviously different in distribution, thickness and reservoir performance, etc. This paper studies the factors controlling the development and distribution of good coal reservoirs from the viewpoint of sedimentology and sequence stratigraphy. The study shows that good coal reservoirs are mainly formed in marsh environments on tidal flats and delta plains. The coal reservoirs formed on tidal flats are more continuous laterally than those on delta plains. The fluctuation of sea level shows important control over the vertical and lateral distribution of coal reservoirs. Generally speaking, the coal reservoirs formed in the highstand system tracts are more abundant, thicker and more widespread, and thus the highstand system tracts are more favorable to the formation of good coal reservoirs. The coal reservoirs formed in the transgressive system tracts are lower in abundance, thinner and much less widespread, and thus the transgressive system tracts are not favorable to the formation of good coal reservoirs.

Discriminating hydrocarbon generation potential of coaly source rocks and their contribution:a case study from the Upper Paleozoic of Bohai Bay Basin,China

Although various coaly source rocks widely developed in the Carboniferous-Permian(C-P)of the Bohai Bay Basin,their geochemical characteristics and hydrocarbon generation potential are poorly understood.This study aims to discriminate the contribution of hydrocarbon generation from different C-P coaly source rocks and clarify the differences within generated oils using organic geochemistry,organic petrology,and thermal simulation experiments.The coaly source rocks containt coal clarain and durain,carbonaceous shale,and shale deposited in deltaic and lagoonal environment.The results indicated that clarain,durain,and carbonaceous shale exhibited higher hydrogen index and liquid-gas hydrocarbon yields than lagoonal and deltaic shales,which was mainly associated with the concentrations of sporinite,cutinite,and hydrogen-rich collodetrinite.Aliphatic hydro-carbons originated firom coal and carbonaceous shale presented lower Ts/(Ts+Tm),Ga/17α(H)21β(H)-C_(30)hopane,18α(H)-oleanane/17α(H)21β(H)-C_(30)hopane ratios,and higher 17β3(H)21α(H)-C_(30)Morane/17α(H)21β(H)-C_(30)hopane than deltaic lagoonal shales.Parameters of aromatic hydrocarbons generated from five lithologies of coaly source rocks trended as clear group distribution,e.g.,clarain and durain showing lower MNR,DBT/Fluorene(F)ratios and higher DBF/F ratio than coaly shales.The distinct descending trend of hydrocarbon potential is obtained from clarain,durain,carbonaceous shale to lagoonal and deltaic shales,implying dominated the petroleum and natural gas supplement from coal and carbonaceous shale.The difference between aliphatic and aromatic hydrocarbons provides a significant contribution to analyze the generic relationship between coaly source rock and lacustrine shale.Our results illustrate the importance of coaly source rocks for the in-depth oil-gas exploration of the Bohai Bay Basin and understanding hydrocarbon generation potential of source rocks in coal bearing strata.

Carboniferous and Permian integrative stratigraphy and timescale of North China Block

The Carboniferous-Permian strata in the North China Block(NCB) contain abundant fossils, coals and natural gases.Establishing a high-resolution timescale for the Carboniferous and Permian in the NCB is essential to understand the geologic events and explore the spatial and temporal distributions of the natural resources. The upper Carboniferous and the basal part of Permian are relatively well correlated because they yield marine conodont and fusuline fossils. However, the Permian terrestrial strata mostly rely on poorly constrained palynostratigraphy and phytostratigraphy and are short of the precise geochronologic constraints on the correlation with the marine strata. This study provides a critical review on the state-of-the-art of the latest Carboniferous and Permian chronostratigraphic and biostratigraphic frameworks and stratigraphic correlation in the NCB. The Penchi Formation ranges from lower Bashkirian to lower Gzhelian;the Taiyuan Formation is assigned to the upper Gzhelian to lower Asselian;the Shansi and Lower Shihhotse formations are from middle Asselian to lower Sakmarian;the Upper Shihhotse Formation is assigned to upper Artinskian to lower Kungurian, and the Sunjiagou Formation was assigned to Lopingian, respectively. A long hiatus up to ~20 Myr between the Upper Shihhotse and Sunjiagou formations, mainly marked by a large-scale erosional surface at the base of a coarse conglomeratic sandstone unit and/or multiple paleosol layers as well as significant differences of floras between these two lithostratigraphic units, is present probably due to tectonic uplift in association with the closure of the Paleo Asian Ocean(PAO) during the Cisuralian and Guadalupian. The possible amplitude of sea-level changes from Carboniferous to Permian on the NCB is estimated from 0 to 40 m.The floral succession, depositional records and organic carbon isotope profiles suggest that the latest Carboniferous and earliest Permian was a favorable period for coal accumulation under an ever-wet and warm climate, followed by a prominent shift to dry climate from early-middle Cisuralian. This climatic shift during the Permian was mainly resulted from northward migration of the Pangea and the closure of the PAO, which is comparable with the Carboniferous and Permian trends in central Europe.