Magmatic sulfide deposits are the main global resource of Ni, Cu, and platinum-group elements (PGEs), with significant Co concentrations that enhance their economic importance for the low-carbon transition. Nickel, Cu, and PGEs are enriched via magmatic processes, while Co enrichment typically occurs due to post-magmatic activities. Despite the importance of these post-magmatic processes to the evolution of mineralized systems, their significance to the enrichment of Co remains ambiguous. The Huangshandong (HSD) Ni-Cu sulfide deposit is located in the Huangshan-Jing'erquan belt, Eastern Tianshan, and was modified by regional ductile shearing and later hydrothermal activity. Therefore, this deposit serves as an excellent case study to assess the role of reworking processes on the enrichment of Co in magmatic sulfide systems. Ores within the HSD deposit are classified into three mineralogically and texturally distinct varieties - primary magmatic, metamorphosed-deformed, and hydrothermally altered. Although Co is primarily hosted by pentlandite (18,315-24,776 ppm) and pyrrhotite (44-203 ppm) in all of the ore types, cobaltite-gersdorffite (9.27-26.54 wt% Co) is restricted to the hydrothermally altered ores where it occurs as disseminations (Cob-Gdf-I) and in calcite-chlorite veins (Cob-Gdf-II). The main contributors of Co in the primary magmatic and metamorphosed-deformed ores are pentlandite followed by pyrrhotite. Despite its low abundance, cobaltite-gersdorffite is the major Co contributor in hydrothermally altered ores. Three stages of Co enrichment are identified at HSD based on variations in silicate mineralogy and texture, and trace-element characteristics of base-metal sulfides (BMS) - primary enrichment of Co ( Stage 1 ), mobilization of Co by metamorphism-deformation ( Stage 2 ), and remobilization of Co by hydrothermal fluids ( Stage 3 ). Stage 1 is characterized by elevated concentrations of Co in magmatic pyrrhotite and pentlandite, as well as pyroxene and olivine. Stage 2 is characterized by the replacement of Co-bearing pyroxene and olivine by muskoxite, chlorite, and serpentine, which mobilized Co. Additionally, given that BMS were ductily deformed, it is possible that some Co was mobilized via deformation processes. Based on the FeAsS-CoAsS-NiAsS components of Cob-Gdf-I and Cob-Gdf-II, both formed at similar temperatures of similar to 450-600 degrees C. The restriction of cobaltite-gersdorffite in Stage 3 mineralization implies that Co-Ni-As were remobilized. Cobalt and Ni were likely remobilized from Stage 2 and/or Stage 1 mineralization by hydrothermal fluids given the systematically lower Co and Ni contents of BMS in Stage 3 compared to Stage 2 . Arsenic was likely added to the system from an external source by the hydrothermal fluids given the typically low As contents of sulfide liquids. This contribution demonstrates that Co can be mobilized via deformation, metamorphism, and hydrothermal alteration processes, and highlights the importance of these processes to the overall enrichment of Co in magmatic sulfide systems, which are otherwise valued for their Ni, Cu, and PGE contents. Considering that cobaltite-gersdorffite may significantly contribute to the Co budget of a sulfide deposit, even at low abundances, attention should focus on assessing its occurrence in magmatic sulfide deposits, particularly those that have been reworked by secondary processes.

Lake hydrological change and its driving mechanisms in the Eocene warmhouse climate are important to evaluating environmental and ecological changes induced by global warming. Our limited understanding of lake hydrological changes during the Eocene is in part due to the scarcity of well-dated and continuous terrestrial records. Here we refine the middle-late Eocene cyclostratigraphy and decipher high-resolution lake hydrology changes using sedimentary noise modeling and proxy data at four terrestrial basins (Dongying Depression, Nanxiang Basin, Jianghan Basin, and Fushun Basin) in mid-latitudes of East Asia. Our new astrochronology provides a robust timescale for the period of 48.5-38.5 Ma, and our tuned magnetostratigraphy is at least comparable with other timescales between Chrons C18n.1r and C20n. The new astrochronology reveals synchronous lake-level changes in the four basins in East Asia following 1.2 Myr obliquity and 2.4 Myr eccentricity cycles, indicating astronomical forcing on lake-level changes. The 2.4 Myr cycles of lake-levels are generally in phase with 2.4 Myr cycles of global sea-level changes, suggesting that East Asian lake hydrology was modulated by global sea-level variations in the Eocene warmhouse. Therefore, global sea-level variations may be an important driver of East Asia hydroclimate and freshwater resources.

The Xihu Sag is an important petroliferous area in the East China Sea Basin. Petroleum in this sag was generated from coal-bearing source rocks, i.e., coal, carbonaceous mudstone, and mudstone. The lack of detailed studies on the source rocks restricts petroleum exploration. Hydrocarbon generation potential, geochemical characteristics, and relative contribution were assessed using 38 source rock samples and 13 oil/oil sand samples. Results show that source rocks have different hydrocarbon generation potentials. The total organic carbon (TOC), production yield (S1+S2), extractable organic matter (EOM), and total hydrocarbon content suggest that coal has the highest organic matter abundance, followed by carbonaceous mudstone and mudstone. All source rocks are dominated by Type III-II2 kerogen and are, therefore, gas-prone. Biomarker assemblages indicate that the organic matter of coal is mainly derived from terrigenous higher plants with little contribution from phytoplankton, accompanied by strong bacterial modification, which was deposited in an oxidizing depositional environment with a poorly stratified water column. Mudstones, in contrast, have less terrigenous higher plants but higher phytoplankton contributions and were deposited in a more reducing depositional environment. Almost all biomarker parameters of carbonaceous mudstones are between coal and mudstones, suggesting that the organic matter sources and depositional environments for carbonaceous mudstones are between that of the coals and mudstones. The greater phytoplankton contribution to the mudstones is verified by the higher liptinite content. However, the lower organic matter abundance and the lower hydrogen index indicate that vitrinite rather than liptinite is the major hydrocarbon generation maceral. Although coal and carbonaceous mudstone have significantly higher organic matter abundance, more oil-prone kerogen types, and more gold-tube pyrolysis yields, oil-source correlation employing biomarkers and carbon isotopes suggest that mudstones are the major source rocks in the Xihu Sag. This apparent contradiction may be due to the thin layer thickness and limited distribution of the coal. The fact that more contributions of coal and carbonaceous mudstone for oils are found in the western slope belt where coal and carbonaceous mudstone were deposited seems to support this viewpoint. This contradiction may also be caused by the inability of coal to effectively expel the generated high molecular weight hydrocarbons.

南海南部是我国油气资源调查的前沿,开展南海南部北康盆地构造样式及其形成演化研究对于明确盆地油气远景区带及南部诸盆地构造演化历史具有重要的借鉴意义.利用2D地震资料,在精细构造-地层解释基础上,厘定了北康盆地主要的构造样式;采用平衡剖面技术,对北康盆地的伸展率和伸展量进行定量恢复,重建盆地的构造演化史.结果表明,北康盆地共发育5类主要的构造样式,分别为伸展、反转、挤压、走滑-伸展和底辟构造样式,其中走滑-伸展构造、挤压构造和反转构造为油气最有利富集部位.盆地的形成演化总体上经历了三期六幕,即裂陷期(初始裂陷幕、裂陷鼎盛幕)、断坳转换期(断坳转换1幕、断坳转换2幕)和拗陷期(拗陷1幕、拗陷2幕).

细粒混合沉积是近年来的研究热点,目前对其研究还不够系统和深入.基于持续多年对东部陆相页岩的研究,重新定义了细粒混合沉积概念,综合钻井、录井、测井、岩心、薄片和X射线衍射分析等资料,按照岩相发育特征、砂/灰/泥比值、混积组构方式和沉积微相分带4项分类原则,提出陆相细粒混合沉积扇形分类方案,将细粒混合沉积划分为灰-泥二元混积、砂-泥二元混积和砂-灰-泥三元混积3种类型,并进一步细分为12个亚类.在此基础上,以东营凹陷为例,从点、线、面3个维度分析了陆相细粒混合沉积的发育特征和展布规律,提出细粒混积相带分布模式,认为细粒混积在平面上具有环带分布特征.并进一步分析了细粒沉积中的天文节律特征,认为其可以很好地反映细粒混合沉积中的旋回特征,对于混合沉积精细研究具有借鉴意义.

综合钻井、岩心、薄片和地球化学等资料,详细研究了济阳坳陷沾化凹陷沙三段下亚段细粒混积岩的混积类型、不同类型细粒混积岩的成因、垂向分布以及古湖泊水文演化规律.结果表明,沾化凹陷沙三段下亚段细粒混积岩包括层状-纹层状组构混积型和块状矿物组分混积型等2种混积类型;自下而上主要由层状-纹层状组构混积型夹块状矿物组分混积型发育段,过渡为块状矿物组分混积型夹层状-纹层状组构混积型发育段;表明了由潮湿且受季节性气候影响明显的深水湖泊,演化为水体较浅、盐度均一且受季节性气候影响不明显的湖泊环境,并建立了高水位早期-高水位中-晚期-低水位期的湖泊演化模式.在湖泊高水位早期阶段的早-中期和高水位中-晚期,有机质富集的主控因素主要是氧化还原条件和古生产力;在湖泊高水位早期阶段的晚期,古生产力是有机质富集的主控因素;在湖泊低水位时期,有机质富集的主控因素是氧化还原条件.总体上,适量的陆源供给(粘土矿物和石英含量均小于22％)会促进有机质富集,而过量的陆源碎屑输入以及碳酸盐的快速沉淀都会导致有机质被稀释.

The differences in rare earth elements (REEs) fractionations and abundance of marine carbonates play an important role in the paleoenvironment study. However, it is argued that the primary REE characteristics preserved in dolomites could be complicated by the effect of diagenesis, especially dolomitization. Characterized as the “island of dolomites”, Xisha Islands, South China Sea provide an ideal context to resolve the controversy, therefore, we analyzed the concentrations of trace elements and REEs of 24 Miocene carbonate samples (18 dolostones and 6 limestones) from the XK-1 well in Xisha Islands. The results show that PAAS-normalized REEs exhibit a uniform modern seawater-like pattern, characterized by light rare earth elements (LREEs) depletion, notable negative Ce and positive Y anomalies. The observation indicates that dolomites may preserve REE signatures of seawater, therefore dolomitization does not significantly influence REE compositions of dolomites. Furthermore, Eu/Eu* ranges from 0.80 to 1.23 with an average of 1.06, suggesting that the influences by the post-depositional hydrothermal fluid on REEs are negligible, while the presence of terrigenous input can also be excluded by lacks of correlations between HREE/LREE values and the concentrations of Al and Th. However, we cannot rule out the burial diagenesis alteration since general increasing trends in Y/Ho and HREE/LREE ratios with depth are observed. These findings suggest that dolomitization may not necessarily modify the REE patterns, and dolomites have the potential to record the primary information of past seawater when the carbonate burial history is well constrained.

珠江口盆地白云凹陷是中国南海北部深水区最大的富烃凹陷,近年来在白云凹陷东北部获得了多个商业性轻质油气藏,勘探前景良好,但对其原油运移、聚集成藏的研究还处于探索阶段.基于三维地震资料解释、油气地球化学资料分析以及油气成藏综合研究,探讨白云凹陷东北部油气藏分布特征,研究了原油的输导体系及其运移和聚集特征,建立了原油成藏模式.结果表明:油源断裂是原油垂向运移的主要通道,顺源型油源断裂和向源型油源断裂都具有良好的输导性能,由物性较好的珠江组下段砂体组成的构造脊1和2为原油侧向运移的优势路径;原油主要聚集在反向断裂控制的翘倾半背斜圈闭中,具有"内气外油"的差异聚集特征;原油成藏具有"断-脊输导、断-盖控聚、差异聚集"的特征.白云凹陷东北部展现了以断裂为依托,沿构造脊找油的良好勘探方向,对白云凹陷及其邻区的深水油气勘探具有一定的指导意义.

南海北部深水区白云凹陷油气资源丰富,勘探潜力巨大,白云凹陷东部目前已获得多个商业性油气发现,但是该地区油气分布较复杂,油气聚集规律仍有待深入分析.本文基于三维地震、钻井、测井和岩心分析资料,对白云凹陷东部A井区油气输导体系及其控藏作用进行了综合研究.研究表明:研究区发育断裂、不整合面和砂岩输导层三类输导体.断开层位多,长期活动的Ⅰ类断裂为油源断裂,垂向上深部主要起输导油气作用,而浅部垂向和侧向封闭性较好,主要起封堵油气的作用;断开层位少,活动时期短的Ⅱ类断裂主要起封堵油气的作用.砂岩输导层主要为Z J2段和ZJ3段砂体,输导能力强;而珠海组砂体的区域输导能力较差.T70不整合面主要为削超不整合和平行不整合.靠近洼陷的平行不整合面上、下分别为渗透性的砂岩和灰岩岩层,为油气输导层,东部隆起区的削超不整合则有利于油气聚集.分析得出:沟通白云主洼烃源岩的3号断层系发育的断面脊、ZJ2段和ZJ3段砂岩构造脊以及自西向东发育的不整合构造脊控制了油气优势运移方向,为区域油气运移的优势通道.三种输导体组合形成的复合输导体系类型决定了研究区的油气运移聚集规律:断裂与砂体组成的断-砂复合输导体系表现为断-砂耦合输导、油气近源成藏模式,油气成藏的主要层位为ZJ2段;而断裂与砂体和不整合面复合-网状输导体系则表现为断-砂-不整合-构造脊复合输导、油气远源多层系成藏模式,油气纵向上具有多层系成藏的特征.

Recent studies based on proxy records and paleoclimate simulations have suggested monsoon climate in Asia as early as the Eocene. However, good proxy record of Eocene monsoon is rare in eastern Asia where East Asia summer monsoon prevails. Here we study middle Eocene lacustrine deposits of the Shahejie Formation in the Bohai Bay Basin in eastern China to understand middle Eocene paleoclimate and its stability. Our study integrates new δ13C and δ18O data of authigenic lacustrine carbonates, lake water salinity proxy of Mg/Ca ratio, and published carbonate minerology, chemical weathering proxy data of CIA* and Ln(Al2O3/Na2O), and lithofacies interpretations from two cores to provide new understanding of paleoclimate elements. Our results show that in most part of the record, the authigenic calcite δ18O values in laminated mudstone-dominated lithofacies display frequent variations, up to 2.9‰, while Mg/Ca ratio and dolomite content remain low and nearly stable. These features suggest frequent variations of lake water level driven by changes in runoff amount because of changing intensity of summer monsoonal precipitation during the middle Eocene. The comparison of stable isotope variation with modern precipitation stable isotope record in the study area and seasonal precipitation of the laminated lithofacies both support the interpretation of seasonal climate. We interpret that the lake water and carbonate δ18O values decreased when the East Asia summer monsoon was strong and increased when the monsoon was weak. During two periods of the studied middle Eocene interval, the lake water experienced periodic intense evaporation, causing high Mg/Ca ratios and dolomite content, and high authigenic dolomite δ18O values up to 0‰. These periodic drying events likely reflect millennial-scale droughts that are common today to the East Asia summer monsoon because of warming in the Indo-Pacific Warm Pool. We infer that the frequent droughts in the two periods of the middle Eocene were resulted from very warm climate during the two periods. We conclude that the East Asia summer monsoon existed in eastern China during the middle Eocene, and the climate state was not stable.

It is important to consider the influences of depositional environment on lithofacies characteristics, lithofacies distribution patterns, and organic matter enrichment when defining reservoir properties and predicting "favorable reservoirs" and "sweet spots". In this study, we examined the Niutitang shale of the early Cambrian Niutitang Formation in western Hubei Province, middle Yangtze Block, to understand how depositional environment controlled organic matter accumulation in the Niutitang shale. Through a combination of detailed sedimentologic investigations with geochemical analyses, we identified four primary lithofacies, siliceous shale, siliceous-clay mixed shale, calcareous shale, and argillaceous shale, from the Y1 drill core. The sedimentological analyses, including systematic observations of the color of fresh rocks, grain size, sedimentary textures and structures, biogenic and diagenetic (e.g., veins and pyrite) characteristics in cores and thin sections with mineralogical analyses by X-ray diffraction (XRD), and changes in geochemical proxies, including TOC (wt.%), MOEF, U-EF, Ni/Al and Zn/Al, suggest that siliceous shale and siliceous-clay mixed shale were deposited in euxinic and anoxic deep water with high surficial paleoproductivity which primarily controlled by long term global sea level changes, and that the calcareous shale and argillaceous shale were deposited in shallow and oxygen-rich water conditions with low energy and low paleoproductivity in the surface water. The Niutitang shale changed from the siliceous shale-dominated lithofacies association (LA1), to the argillaceous shale-dominated lithofacies association (LA2), and then back to the siliceous shale-dominated lithofacies association (LA1), suggesting a variation of sedimentary environment from euxinic-anoxic deep-water environment (highstand), to relatively oxic and shallow water environment (lowstand), and then back to euxinic-anoxic deep-water environment (highstand). This may reflect changes in sea level and mechanisms of organic matter enrichment during sea level highstand and lowstand. The low Mo/TOC values of the siliceous shale and siliceous-clay mixed shale lithofacies are similar to the Mo/TOC values of marine sediments in Framvaren Fjord, suggesting that the study area was located in a moderately restricted basin during deposition of the Niutitang shale. The Fe/Ti and Al/(Al + Fe) ratios and the Al-Fe-Mn diagram combined with our detailed petrographic studies and the good correlation between TOC and quartz contents are indicative of a mainly biogenic origin with a minor detrital source for the silica in the Niutitang shale. TOC is well correlated to Mo-EF, U-EF, Ni/Al and Zn/Al values in LA1, but it is only moderately correlated to Mo-EF and U-EF values and weakly correlated to Ni/Al and Zn/Al values in LA2. The correlation relationships suggest that good preservation in euxinic-anoxic water conditions and high primary paleoproductivity were the major controlling factors of organic matter enrichment, whereas organic matter accumulation during sea level lowstand was mainly controlled by water redox conditions because primary paleoproductivity remained persistently low in the more restricted basin with shallow water and limited nutrient upwelling. The correlations between TOC content and clay minerals within the different lithofacies associations suggest that adsorption of carbon components by clay minerals promoted the accumulation of organic matter to various extents in LA2 but probably did not impact organic matter enrichment in LA1.

Hydrocarbon exploration in the deep-water area of the South China Sea is increasingly important. However, the Eocene strata, which are the primary source rock in the deep-water area of the Pearl River Mouth basin (PRMB), are poorly understood. This article studied the geological characteristics and hydrocarbon potential of the Eocene source rocks in the Baiyun Depression, which is the biggest and most important depression in the deep-water area of the PRMB. In the Eocene, the Baiyun Depression was an asymmetric rift basin that was controlled by the north-dipping detachment faults. A big freshwater lake existed in the study area and a huge delta developed in the northern gentle slope. The delta source rocks had higher total organic carbon and were greatly controlled by terrigenous organic matter input. They were type III kerogen and were likely to produce gas during maturation. The lacustrine source rocks were widely distributed in the center and south and had a higher hydrogen index (HI). They had both terrigenous and aquatic organic matter inputs. The kerogen was type II to III. They could produce both oil and gas during maturation. The Eocene source rocks were widely distributed in the Baiyun Depression. They had a huge thickness and high organic matter abundance. The organic matter had enough maturity to generate hydrocarbon from 18.5 Ma to the present. Therefore, the Eocene source rocks can provide sufficient hydrocarbon resources for deep-water petroleum accumulations and gas hydrate formations in the deep-water area of the PRMB.

Ancient deep-marine siliceous-argillaceous-carbonate rock series (SAC) are general name of silicalite, argillite, carbonate rock and their mixed deposit rocks which are all pelagic and hemipelagic sediments.In this paper, it proposes a new mineralogy-based classification scheme of the SAC rock series based on existing classifications.According to quantitative classification standard["pure (＞90％) ", "dominate (50％-90％) ", "rich (50％-25％) ", "bearing (＜25％) "]and using triangular midlines of the ternary plot, the SAC rock series are divided into 4 primary classes and 21 classes.By using the new classification, silicalite, carbonate rock and mixed mudstone primary classes are present in the Lower-Middle Cambrian in the LowerYangtze region and their petrological features are described by optical microscope observation.The SAC rock series of the Lower-Middle Cambrian show the sedimentary evolution trend from siliceous end to carbonate end.The results of classification of three typical SAC rock series indicate that the new classification scheme clearly reflects the mixed sedimentary evolution trend among three terminal minerals.The classification of the SAC rock series may help provide a significant foundation to quantitative description of the ancient pelagic and hemipelagic sedimentation, and also provide an important basis for exploring the evolution of sedimentary environment.

Based on detailed sedimentological observations and geochemical analyses, four geological events have been identified, and a genetic depositional model has been established within a sequence stratigraphic framework. The organic-rich siliceous shale interbedded with dense bentonite layers in the transgressive systems tract 1 (TST 1) is attributed to the first stage of high-frequency volcanism (which started at similar to 447.62 Ma) associated with the collision of the Cathaysia and Yangtze Blocks. The presence of the organic-fair lime mudstone/shelly limestone indicates that Hirnantian Glaciation in the highstand systems tract (HST). The occurrence of organic-rich siliceous shale interbedded with scarce bentonite layers in the transgressive systems tract 2 (TST 2) is attributable to the second stage of low-frequency volcanism (which started at similar to 443.83 Ma) and to postglacial effects. The formation of organic-fair mixed shale with silty laminae is attributed to bottom-current activity in the early highstand systems tract (EHST). The occurrence of organic-poor clay-rich shale is due to terrigenous input in the late highstand systems tract (LHST). Our research also shows that the high marine productivity caused by volcanic ash and a high burial rate in an anoxic depositional setting led to organic matter and siliceous mineral enrichment in the TST 1 and TST 2. The favorable organic matter preservation conditions and the postglacial biotic recovery played significant roles in the formation of the organic-rich shale in the TST 2.

Pore structure has distinct features in different shale lithofacies. This paper presents a case study of the Upper Ordovician Wufeng-Lower Silurian Longmaxi formation in southeast Sichuan Basin to fully describe the characteristics of shale pore structure in different lithofacies. 16 types of shale lithofacies were classified using ternary diagram of siliceous minerals (quartz + feldspar, QF), carbonate minerals (Ca) and clay minerals (Cl). Among all, argillaceous-rich siliceous shale lithofacies (S-3), argillaceous/siliceous mixed shale lithofacies (M-2) and siliceous-rich argillaceous shale lithofacies (CM-1) are the predominant lithofacies. According to scanning electron microscope (SEM) images, combined with focused ion beam-scanning electron microscope (FIB-SEM), mercury intrusion porosimetry (MIP), and gas adsorption (N-2 and CO2), the pore structure characteristics and its influencing factors were systematically analyzed. The results show that Illite + illite/smectite minerals primarily influence the development of the inorganic pores in mixed clay and silica lithofacies (CM-1). Clay minerals are protected from compaction by the rigid minerals, which significantly favors the development of mesopores (2-50 nm) and macropores ( > 50 nm). The abundance of organic matter is an important determinant for the organic pores in the siliceous lithofacies (S-3), and TOC has a positive contribution to the development of micropores ( < 2 nm) in this lithofacies. Shale with high TOC content tends to be easily affected by compaction, which results in reduction of some organic pores. Even though the siliceous S-3 reservoir has slightly lower porosity than CM-1, it is currently the primary reservoir target due to its brittle response to hydraulic fracturing.

The Baiyun Depression is the main hydrocarbon-rich province in the deep-water area of the Pearl River Mouth Basin, South China Sea. Several petroleum samples, well data and 3D-seismic data from the Baiyun Depression were collected, the geochemical features and origins were determined using various methods, and finally, their distribution pattern was analysed. The results are as follows: (1) the natural gases are the thermogenic gases of organic matter belonging to terrestrial organic gas. They are mainly kerogen-cracking gases with high maturities, and their kerogen is the mixed sapropelic-humic type. The carbon isotope of the oil indicates that its source rock may be a continental deposit. Most of the oil in the Baiyun Depression has suffered from gas washing, which substantially affected its light hydrocarbon content. The biomarker features of the oil contain high Pr/Ph (pristane/phytane), high oleanane and medium bicadinane, reflecting that its source rock contains a large amount of terrestrial organic matter. The steranes indicate that the oil is mature and is derived from both higher plant and algae. It can be concluded that natural gas and oil in the Baiyun Depression mainly originated from source rocks of Enping Formation. (2) The distribution pattern of natural gas and oil is mainly controlled by the characteristics of the hydrocarbon source kitchens and the hydrocarbon migration pathways. These results can provide some information for future petroleum exploration in the Baiyun Depression, as well as in other petroliferous basins with similar geological settings.

Based on the corresponding relationship between the paleoproductivity, redox conditions and volcanism within a chronostratigraphic framework, the effects of volcanic events in the Wufeng–Longmaxi period on organic abundance of shale were examined. Bentonite layers were mostly developed in the transgressive systems tract 1 (TST1, Wufeng Formation) and transgressive systems tract 2 (TST2, Longmaxi Formation), and the two systems tracts corresponded to favorite shale lithofacies with high silica and total organic carbon (TOC) contents. According to the stratigraphic characteristics of bentonite rich interval, TST1 is classified as the interval with dense bentonite layers with the frequency of bentonite layer (bentonite layers/time) of more than 1.5 layers/Ma and the cumulative thickness ratio of bentonite layers (thickness of bentonite layers/thickness of shale) of more than 1%; TST2 is classified as the interval with sparse bentonite layers (frequency < 1.5 layers/Ma; cumulative thickness ratio < 1%). TST1 (dense interval) witnessed more intense and high-frequency volcanic activities than TST2 (sparse interval), so the TST1 has generally higher TOC than TST2. The intense and frequent volcanic activities had dual effects on organic-rich shale: on one hand, volcanic ash provided a sufficient supply of nutrients, which triggered high marine productivity; on the other hand, the extremely anoxic environment caused by volcanic activity enhanced the burial amount and preservation rate of organic matter.

The physical mechanisms responsible for hydrocarbon migration in carrier beds are well understood. However, secondary migration is one of poorly understood facets in petroleum system. The Carboniferous Donghe sandstone reservoir in the Tarim Basin's Hudson oilfield is an example of a secondary (or unsteady) reservoir; that is, oil in this reservoir is in the process of remigration, making it a suitable geologic system for studying hydrocarbon remigration in carrier beds. Experimental methods including grains containing oil inclusions (GOI), quantitative grain fluorescence (QGF) and quantitative grain fluorescence on extract (QGF-E) together with the results from drilling, logging and testing data were used to characterize the nature of oil remigration in the Donghe sandstone. The results show that (1) significant differences exist between paleo- and current-oil reservoirs in the Donghe sandstone, which implies that oil has remigrated a significant distance following primary accumulation; (2) due to tectonic inversion, oil remigration is slowly driven by buoyancy force, but the oil has not entered into the trap entirely because of the weak driving force. Oil scarcely enters into the interlayers, where the resistance is relatively large; (3) the oil-remigration pathway, located in the upper part of the Donghe sandstone, is planar in nature and oil moving along this pathway is primarily distributed in those areas of the sandstone having suitable properties. Residual oil is also present in the paleo-oil reservoirs, which results in their abnormal QGF-E. A better understanding of the characteristics of oil remigration in the Donghe sandstone in the Hudson oilfield can contribute to more effective oil exploration and development in the study area. (C) 2017 Published by Elsevier Ltd.

Based on the new all-covering 3D seismic data and the drilling-logging data, we established the sequence stratigraphic framework for Dongying Depression and identified two kinds of structural systems in Palaeogene, i.e. the extensional structural system and the transtensional structural system. The extensional structural system consists of different normal faults that predominantly trend NE, EW, and NW. The attitudes of the normal faults vary in different tectonic settings. However, the transtensional structural system consists of some strike-slip faults and some normal faults. According to the analysis of the relationships between the faults and the sedimentary sequences of Dongying Depression, we considered that the extensional structural system was developed mainly from the Palaeocene to the middle Eocene, whereas the transtensional structural system was mostly developed from the middle Eocene to the Oligocene. In addition, we found that the structural systems had transformed since 43.5Ma, when the subduction direction and activity rates of the Pacific Plate changed and the dextral strike-slip movement of the large-scale Tanlu fault zone started from eastern China. The extensional structural deformation was probably derived from the back-arc extension triggered by subduction rollback of the Pacific Plate under the Eurasian Plate, whereas the transtensional structural deformation was probably related to the regional dextral strike-slip movement induced by the subduction of the Pacific Plate and the continents' collision between the Indian Plate and the Eurasian Plate.