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The metasedimentary Lujiapuzi Formation crops out along the northeastern margin of the North China Craton, close to the Yan‐Liao Rift. The age and tectonic setting of the formation, and its relationship with the Yan‐Liao Rift are currently unclear. Here we present detrital zircon U‐Pb ages, and Hf isotopic and geochemical data for the Lujiapuzi Formation to constrain the timing of deposition, the provenance of the formation, and the regional stratigraphy relationship. Zircon U‐Pb dating constrains the timing of deposition of the Lujiapuzi Formation to younger than 1780 Ma, and indicates that most grains were sourced from the Longgang Block and the Paleoproterozoic Liao‐Ji Belt. Detailed field investigations and a correlation of the regional stratigraphy reveal that much of the Lujiapuzi Formation is equivalent to the Tuanshanzi Formation in the Yan‐Liao Rift; the lower section may represent the earliest sediments deposited within the Fanhe Basin. Based on these results and the findings of previous studies, we suggest that the base of the Changcheng System has an age of 1.80 Ga. Zircon Hf isotopic data indicate that the main period of crustal growth along the northeastern margin of the North China Craton occurred at 3.2–2.5 Ga, with a peak at 2.9–2.7 Ga. [ABSTRACT FROM AUTHOR]

In order to explore the marine redox structure on the earliest Cambrian (ca. 542–529 Ma) Yangtze Platform, South China, new Fe-Mo-C-S geochemical data from the slope Xugongping section for the Liuchapo and the base of Niutitang Formation are reported here. Integrated Fe speciation and Mo abundance data from the Xugongping section, in combination with previously published data from slope-basinal Longbizui section and others, suggest oxic surface waters and ferruginous deep waters coexisting with occasional mid-depth euxinic waters during the Fortunian Stage, and with widespread euxinic waters during the early Stage 2 marine transgression. A compilation of new and published sulfur isotope data of pyrite for the Liuchapo and the base of Niutitang Formations presents high isotopic values (mostly >+10‰) and distinctly different spatiotemporal gradient characteristics during the Fortunian Stage and the beginning of the Stage 2. We propose that redox stratification developed in the earliest Cambrian protected basin, and eustatic change and the connectivity of the protected basin with the open ocean controlled the materials supply from riverine input and open ocean reservoir and thus spatiotemporal variability of ocean chemistry. [ABSTRACT FROM AUTHOR]

The roof, floor and gangue samples of coal seams were collected from a borehole in the Gujiao mining area. The vertical distribution of major elements, trace elements and rare earth elements (REEs) was tested through X-ray fluorescence spectrometry and inductively coupled plasma-mass spectrometry (ICP-MS). The formation environment and material source of the strata were analysed. The results showed that the major elements of the coal seam roof, floor and gangue are Si and Al, followed by Fe, K, and Ti. In the Shanxi Formation, Sn, B, Ta, Bi, Th, U, Li, Be, Nb, In, Cs and Hf are enriched. In the Taiyuan Formation, B, Bi, U, Li, Sr, Mo and Sb are enriched. Sn, B, Th, U, and Be of the Shanxi Formation and B, U, Mo, and Sb of Taiyuan Formation are enriched hazardous elements. The ratios of Sr/Ba, U/Th, Ni/Co and V/Cr could indicate the paleosalinity and redox conditions. The Shanxi Formation was mainly formed in an oxic environment. The roof and floor of the No. 7 coal and the roof of the No. 8 coal are limestone, indicating anoxic and suboxic to dysoxic environments. The lithology of the Shanxi Formation and Taiyuan Formation material source is complex, including sedimentary rocks, granite and alkaline basalt. Most samples are distributed at the intersection of the granite and alkaline basalt, indicating dual sourcing from the granite and alkaline basalt. [ABSTRACT FROM AUTHOR]

The North Qilian orogenic belt is the key in the exploration of the formation and assembly of Asia. The Early–Middle Devonian Xueshan Formation, which is deposited in the north area of North Qilian Orogenic Belt, is the most important for revealing the evolution basin–mountain transition of the North Qilian Belt. In order to reveal the tectonic evolution of the central orogenic belt in China and Paleozoic global plate reconstruction, it is necessary to perform provenance analysis of the Xueshan Formation. Eighteen samples were collected from Yumen and Yongchang profiles in the west of North Qilian Belt (WN), and 16 samples were obtained from Gulang and Jingtai profiles in the east of North Qilian Belt (EN). The compositions of clastic conglomerates and the sandstones suggested that felsic volcanic was the main source of the WN Xueshan Formation deposits and that the sedimentary and metamorphic rocks were the main source of the EN sediments. According to major geochemistry indexes, such as Al2O3/SiO2 ratio ranging from 0.08 to 0.37 and the chemical index of alteration less than 80, the source rocks were moderately weathered and of moderately matured. The samples from the EN were relatively enriched in Cr, Ni, Sc, and V elements and depleted in Hf element. However, those from the WN were enriched in Hf without the enrichment of Cr, Ni, Sc, or V. The samples from WN showed a strong negative Eu anomaly, but the samples from EN showed a weak negative Eu anomaly or a positive Eu anomaly. All the above geochemical characteristics suggested the prominent input of felsic clasts with granitic rocks into the WN. Meanwhile, the discrimination diagrams of trace elements implied that WN rocks were derived from continental island arc and that the EN rocks were derived from orogenic belt and the passive continental margin. The North China Plate subducted southwards and formed subduction‐related arc magmatism along the southern margin of the North Qilian Terrane during the Early–Middle Devonian. In conclusion, the WN is a fore‐arc basin, but EN is a foreland basin. [ABSTRACT FROM AUTHOR]

The South Anhui ophiolite (SAO) and the Northeast Jiangxi ophiolite (NJO) are the only two known Precambrian ophiolite suites within the eastern segment of the Jiangnan Orogen, South China. These ophiolites may provide significant insights into the convergence history of the South China Block during the Rodinia supercontinent cycle. SHRIMP zircon U–Pb dating indicates that the SAO formed at 831 ± 5 Ma whereas the NJO formed at ca. 1000 Ma. Modal mineral assemblages and the preservation of relict primary mineral assemblages indicate that serpentinized peridotites from both ophiolites were mainly harzburgite in protolith. Relict olivine and orthopyroxene fragments within both ophiolite suites yield similarly high Mg# values. The serpentinized peridotite samples yield U-shaped rare earth element patterns and contain high-Cr# spinel, both of which are indicative of supra-subduction zone ophiolites. However, serpentinized peridotites within the SAO contain olivine and clinopyroxene with slightly higher Mg# values, and have lower platinum-group element (PGE) and trace element concentrations than peridotites from the NJO. The SAO peridotites are also depleted in Ir, Pt, and Pd, in contrast to the flat and chondrite-like PGE patterns of the NJO peridotites. These observations indicate that compared with the NJO, SAO peridotites were subjected to a greater degree of melt extraction prior to emplacement. Furthermore, gabbro and basalt from the SAO have N-MORB- or arc-like geochemical characteristics that reflect the incorporation of crustal materials into the mantle source, suggesting that this ophiolite formed in a continental marginal back-arc basin setting. In comparison, the less pronounced depletions in trace elements and PGEs, as well as the restricted 187 Os/ 188 Os isotopic compositions of NJO serpentinized peridotites, suggest that they formed in a fore-arc setting. The contrasting geochemical characteristics of the two ophiolite suites indicate that they were generated during distinct stages of convergence along the southeastern margin of the Yangtze Block. Our results show that ophiolite suites produced within a single orogenic cycle could preserve diverse geochemical characteristics, and may provide insights into the initiation and cessation of continental amalgamation. [ABSTRACT FROM AUTHOR]

An integrated study of zircon U-Pb geochronology and geochemistry, together with Nd-Hf isotopes, have been carried out on the rhyodacite and rhyolitic tuff of the Jingtan Formation in the eastern part of the Jiangnan orogen. SIMS zircon U-Pb dating of two samples yielded weighted mean 206 Pb/ 238 U ages of 784 ± 6 Ma and 788 ± 6 Ma, respectively. Geochemically, they are peraluminous (A/CNK mostly around 1.2) and are characterized by enrichments in Rb, Th, REEs and HFSEs (e.g. Zr and Y) but depletions in Ba, Sr, P, Eu and Ti. The volcanic rocks show a clear A-type granite geochemical signature with high total alkalis (K 2 O + Na 2 O = 5.3–7.64 wt%), FeO t /MgO ratios and low CaO, MgO and TiO 2 contents. They have negative whole-rock ε Nd (t) (−4.2 to −1) and positive zircon ε Hf (t) (+1.26 to +11.6) values, illustrating decoupled Nd-Hf isotopes which may be genetically related to their petrogenesis process. The positive ε Hf (t) values and juvenile T Hf DM1 (0.89–1.3 Ga) of zircons indicate that the volcanic rocks may have been derived from the partial melting of the Neoproterozoic to late Mesoproterozoic crustal materials. Combined with the occurrence of significant volumes of contemporary bimodal volcanic rocks in eastern section of the Jiangnan orogen, it is inferred that the Jingtan felsic volcanic rocks formed during post-collisional extension shortly after the final amalgamation of Yangtze and Cathaysia blocks. [ABSTRACT FROM AUTHOR]

Rare earth element (REE) and Y concentrations, and 87Sr/86Sr ratios were analyzed in 33 carbonate samples from the Paleogene Shahejie Formation in the Qikou depression, eastern China, with the goal of determining depositional environments and post-depositional conditions of carbonates in the region. The REE and Y concentrations were normalized to the post-Archean Australian shale (PAAS) standard. The La*PAAS/Yb*PAAS ratios of 0.35-1.52, where *PAAS indicates values for the PAAS standard, show light REE enrichment and heavy REE depletion in most samples. Values of La*PAAS (0.775-1.284) and Ce*PAAS (0.822-1.224), coupled with a relatively flat REE distribution, indicate that the Shahejie carbonates were deposited in lacustrine environments. Values of Y anomalies (1.009-1.527) and Y/Ho ratios (28.43-45.00) in the Shahejie Formation are greater than those of lacustrine carbonates and closer to those of marine carbonates, indicating that diagenetic fluids were probably influenced by seawater. In the carbonates from Well Kou-42, Eu anomalies (1.171-1.604), 87Sr/86Sr ratios (0.708 001-0.710 893), and high homogenization temperatures (104-151 ºC) suggest that the carbonates were affected by hydrothermal fluids. The REEs and Sr isotope ratios show that the carbonates from the Shahejie Formation in the Qikou depression were deposited in lacustrine environments, and were influenced by seawater and hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Measurements of TOC, Rock-Eval pyrolysis, carbon isotope composition, solvent extract, extract fractionation, and the gas chromatography-mass spectrum (GC-MS) of the saturated fraction were conducted on the Lower Permian Fengcheng Formation carbonate-bearing shales and argillaceous dolomites of Well FN7 in the northwestern Junggar Basin to understand the geochemistry and depositional environmental evolution of the carbonate-bearing lacustrine source rocks. The results indicate that the Fengcheng Formation carbonate-bearing shales are fair to good source rocks with Type II kerogen for generating oil and minor gas, and the argillaceous dolomites are poor source rocks. The thermal mature shales contain more residually generated hydrocarbon, whereas the argillaceous dolomites contain more migrated hydrocarbon. This property is favorable for shale oil or tight oil accumulation in the Fengcheng Formation. Biomarker analyses indicate that the Fengcheng Formation source rocks were formed in the anoxic reducing lacustrine depositional environment with a stratified water column and high salinity. The source rock organic matter has major aquatic phytoplankton and algae input and less terrestrial organic matter input. During the Fengcheng Formation period, oxidation had a weak increasing tendency and salinity had a weak decreasing tendency from the early to late periods under the background of a reducing environment. Except for poor source rocks in upper and lower parts, the good source rocks are primarily in the middle part of the Fengcheng Formation. [ABSTRACT FROM AUTHOR]

We report zircon U-Pb geochronologic and geochemical data for the post-collisional volcanic rocks from the Batamayineishan (BS) Formation in the Shuangjingzi area, northwestern China. The zircon U-Pb ages of seven volcanic samples from the BS Formation show that the magmatic activity in the study area occurred during 342-304Ma in the Carboniferous. The ages also indicate that the Palaeo-KaramailiOcean had already closed by 342Ma. Moreover, the volcanic rocks also contained 10 inherited zirconswith ages ranging from 565 to 2626 Ma, indicating that Precambrian continental crust or microcontinents with accretionary arcs are two possible interpretations for the basement underlying the East Junggar terrane. The sampled mafic-intermediate rocks belong to the medium-K to high-K calc-alkaline and shoshonitic series, and the formation of these rocks involved fractional crystallization with little crustal contamination. These Carboniferous mafic-intermediate rocks show depletions in Nb and Ta and enrichments in large ion lithophile elements (e.g. Rb, Ba, U, and Th) and light rare earth elements. The low initial 87Sr/86Sr values (0.7034-0.7042) and positive εNd(t) values (+2.63 to +6.46) of these rocks suggest that they formed from depleted mantle material. The mafic-intermediate rocks were most likely generated by 5-10% partial melting of a mantle source composed primarily of spinel lherzolite withminor garnet lherzolite that had been metasomatized by slab-derived fluids and minor slab melts. In contrast, the felsic rocks in the BS Formation are A-type rhyolites with positive εNd(t) values and young model ages. These rocks are interpreted to be derived from the partial melting of juvenile basaltic lower crustal material. Taken together, the mafic-intermediate rocks formed in a post-collisional extensional setting generated by slap breakoff in the early Carboniferous (342-330 Ma) and the A-type rhyolites formed in a post-collisional extensional setting triggered by the upwelling asthenosphere in the late Carboniferous (330-304 Ma). [ABSTRACT FROM AUTHOR]

Although Xujiahe Formation source rocks in the central Sichuan Basin, China were determined to have low gas-generation intensity, several large-scale gas fields have been found associated with this formation. Thus origins and formation mechanisms of natural gas in the Xujiahe Formation have attracted attentions of many researchers. In this study, geochemistry techniques were deployed to analyze natural gas and formation water in the Xujiahe Formation tight gas reservoir, central Sichuan Basin. By considering geologic background of the gas reservoir, its formation mechanism was investigated. Research results show that the Xujiahe Formation reservoir contains an independent petroleum system, with its natural gas exclusively originated from coal-measure source rocks in the Xujiahe Formation. The formation water was determined to be CaCl 2 type with high salinity. H and O isotope values are largely deviated from those of meteoric water line, indicating favorable preservation conditions for the formation water. The Xujiahe Formation is composed of multiple coal-measure source rocks and superimposed by tight sandstones. The well-developed formation water provides favorable conditions for generating water-dissolved gas. Structural movements during the Himalayan period induced significant uplifting of the central Sichuan Basin with overlying formations denudated. Consequently, natural gas dissolved in formation water experienced depressurization and exsolution. The released natural gas formed free gas phase in structural highs or provided additional natural gas supplies to existing gas reservoirs. [ABSTRACT FROM AUTHOR]

Organic-rich shale deposited in a marine-continental transitional facies was well developed in the upper Yangtze area during the Late Permian. It is considered to contain a large amount of shale hydrocarbon resources. This paper takes the Upper Permian Longtan shale in the central Guizhou uplift as an example to characterize the transitional shale reservoir. Based on organic geochemistry data, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) observation, the geochemical characteristics of this transitional shale were systematically studied and the shale gas potential was investigated. The results indicate that the Longtan shale has fair to good hydrocarbon potential with high total organic carbon (TOC) and contains type III gas-prone organic matter. Its high thermal maturity favors the generation of gas (Ro, 1.10%–2.74%). XRD analyses show that the mineral components of the transitional shale are dominated by high clay content (58.7 wt%). The clay minerals are dominated by illite (44%) and mixed illite/smectite (43%). SEM observation shows that intra-particle pores, inter-particle pores and microfracture were well developed in the Longtan shale, which can provide reservoir space for the accumulation of shale gas. Organic matter pores appear rare due to its organic type. In summary, the Longtan shale has high organic content, high maturation, and high gas content, all of which demonstrate its great potential as a shale-gas resource. But the high clay content of the Longtan shale may be a challenge to shale-gas production. [ABSTRACT FROM AUTHOR]

The Paleozoic Wufeng-Longmaxi shale is one of the main horizons for shale gas exploration in Sichuan Basin. Outcrop, core and thin section observations, X-ray diffraction analysis, trace element geochemistry and other methods have been used to understand the sedimentary characteristics and identify hydrocarbon source rocks in suitable sedimentary paleoenvironments in the Wufeng-Longmaxi shale in northern Guizhou Province. The thickness of the Wufeng-Longmaxi Formation ranges from 20 to 200 m and it was mainly deposited on a deep-water shelf. The TOC content is high, up to 5.75%. The main non-organic minerals are detrital quartz and clay minerals, with a little plagioclase feldspar, potassium feldspar, calcite, dolomite and pyrite. There is also biogenic microcrystalline quartz. Six lithofacies have been identified: siliceous shale, clay shale, calcareous shale, silty shale, carbonaceous shale, and muddy siltstone. Using biological Ba, V/(V+Ni), TOC, V/Cr, B, Sr/Ba and other indicators, we estimate primary productivity, redox conditions and paleosalinity and show that the early stage of Wufeng-Longmaxi deposition occurred under strong anoxic conditions, high paleosalinity and yielded a high TOC content and an excellent potential shale gas source. The anoxic environment was destroyed at the late stages of Wufeng-Longmaxi deposition, the TOC content decreased, so that it is likely to be a high quality source rock. Organic pores acted as the key reservoir space in the shales, and the pores are mainly mesopose, with most pore diameters less than 20 nm. The siliceous shale has high TOC content and brittle mineral (quartz) content making it an important exploration target for shale oil and gas exploration. [ABSTRACT FROM AUTHOR]

This paper investigated the porosity controlling factors for tight sandstone reservoir in the Daniudi gas field, Ordos Basin based on an integrated petrographic, petrophysical and geostatistical analyses, and proposed a comprehensive prediction model for reservoir porosity. Compaction was found to be a key factor for causing reservoir densification. The degree of sandstone compaction appears to be affected by grain sizes and sorting. Under normal compaction conditions (e.g., cement content less than 6%, and with no dissolution), the variation in reservoir porosity with burial depth can be well correlated with grain compositions, grain sizes, and sorting. Based on qualitative examination of the controlling factors for reservoir porosities, geostatistics were used to quantify the effects of various geological parameters on reservoir porosities. A statistical model for comprehensive prediction of porosity was then established, on the assumption that the present reservoir porosity directly relates to both normal compaction and diagenesis. This model is easy to use, and has been validated with measured porosity data. The porosity controlling factors and the comprehensive porosity prediction can be used to quantify effects of the main controlling factors and their interaction on reservoir property evolution, and may provide a reference model for log interpretation. [ABSTRACT FROM AUTHOR]

Based on the sedimentary and tectonic background of the Termit Basin, this paper focuses on the Upper Cretaceous Yogou Formation and uses organic geochemistry, logging, oil testing and seismic data to analyze the primary control factors of the hydrocarbon accumulation and establish corresponding model in order to predict favorable exploration target zones of hydrocarbon reservoirs. This study demonstrates that the Upper Cretaceous Yogou Formation is a self-generation and self-accumulation type reservoir. The Yogou Formation hydrocarbon reservoirs in the Koulele area are controlled by four factors: (1) the source rock is controlled by a wide range of YS1-YS2 marine shale, (2) the sandstone reservoir is controlled by the YS3 underwater distributary channel and storm dunes, (3) migration of hydrocarbons is controlled by faults and the regional monocline structure, and (4) the accumulation of hydrocarbons is controlled by lateral seal. The structures in the western Koulele area are primarily reverse fault-blocks with large throws, and the structures in the east are dominantly fault-blocks with small throws (co-rotating and reverse) and a fault-nose. In the western Koulele area, where the facies are dominated by storm dunes on a larger scale, it is easier to form lithologic reservoirs of sandstone lens. In the eastern Koulele area, high-quality channel sandstone reservoirs, fault-blocks with small throws, and the monocline structure benefit for the formation of updip pinch out lithologic traps, fault lithologic reservoirs and fault-nose structural reservoirs. Future exploration targets should be focused in the western storm dunes zone and eastern distributary channel sand zone with small fault-blocks. [ABSTRACT FROM AUTHOR]

The conception of special geologic bodies has been applied in this study to define and illustrate economic oil and gas reservoirs in sandbodies, which is helpful for hydrocarbon forecast and exploration. Using the comprehensive analysis of drilling, logging, seismic, seismic attribute extraction, and logging constrained inversion in 3D data volume, the special geologic bodies of the Shahejie Formation (P s ) in northern Qikou sag, which have good hydrocarbon potential, are identified and described under the constraint of sequence stratigraphic framework. The dimensions, geometry, and spatial distribution features of the special geologic bodies, as well as their inner architectures and sequence-structure patterns, are also ascertained. The geologic bodies evolved from relative centralization in the middle part of the lacustrine basin in the early stage of P s Formation, to several dispersive isolated parts in the later stage. This shows a small cycle interval (~2.5 Ma) at the end of the whole transgressive depositional process of P s1 (~7.5 Ma) during the expansion of the lake and relative lake level rise, with the control of sediments supply and fault-related subsidence, which effect the evolution of the sedimentary system. According to the relevance and regularity of the geologic bodies' development, different types of potential profitable reservoir traps, including the lithologic lenticular traps, lithologic updip pinchout traps, and structural-lithologic composite traps, can be preserved in the study area. In addition, the internal architecture models provide scientific basis for further hydrocarbon exploration in the frontier basin without enough data. [ABSTRACT FROM AUTHOR]

A combined investigation of bulk geochemistry and molecular geochemistry was carried out on 31 source rock samples from the Lower Permian Lucaogou Formation, in the Jimsar Sag of the Junggar Basin, northwestern China. Geochemical characterization reveals the depositional environments and other factors favorable for the generation and accumulation of β-carotane, an important hydrocarbon precursor. Many core samples have a total organic carbon content > 1%, and Rock-Eval S 2 values > 2 mg HC/g rock, suggesting relatively high hydrocarbon generation potential. Biomarkers in the Lucaogou source rock extracts are characterized by short- to long-chain n-alkanes, a wide range of Pr/Ph ratios (0.74–1.42) and β-carotane index values (β-carotane/C max , 0.16–1.92), high concentrations of C 29 sterane, relatively low tricyclic terpane content, and moderate gammacerane index values (0.14–0.29). This is consistent with a weakly oxidizing to weakly reducing depositional environment, with fresh to brackish water conditions, rapid input of terrigenous organic matter, and a relatively small contribution of aquatic algal-bacterial organic matter. Cross-plots of biomarker parameters and the β-carotane index show that β-carotane in the Lucaogou source rocks is mainly derived from terrigenous organic matter, and is found predominantly in sediments deposited in weakly reducing, brackish environments. It does not appear to have been affected by thermal maturation. [ABSTRACT FROM AUTHOR]

Hydrothermal sedimentation occurred in the Triassic Yanchang Formation, Ordos Basin, China. However, their macroscopic features at the scale of the stratum and hydrothermal sources still lack correlational research. This paper performed element geochemical study on a large number of core samples collected from the Yanchang Formation of a new drilling well located in the south Ordos Basin. The SiO 2 /(K 2 O + Na 2 O) vs. MnO/TiO 2 crossplot and Fe vs. Mn vs. (Cu + Co + Ni) × 10 ternary diagram demonstrate that the Yanchang stratum in the study area has, in general, hydrothermal components. The Al/(Al + Fe + Mn) and (Fe + Mn)/Ti ratios of the core samples range from 0.34 to 0.84 and 4.81 to 50.54, averaging 0.66 and 10.67, respectively, indicating that the stratum is a set of atypical hydrothermal sedimentation with much terrigenous input. Data analysis shows that the hydrothermal source in the study area was from the deep North Qinling Orogen around the south margin of the basin, where some active tectonic and volcanic activities took place, rather than from the relatively stable internal basin. Early Indosinian movement and volcanic activities activated basement faults around the southern margin of the basin, providing vents for the deep hydrothermal fluid upwelling. The hydrothermal indicators suggest that the study area experienced 4 episodes of relatively stronger hydrothermal activity, namely during the Chang 10, Chang 9–1, Chang 7–3 and Chang 6–2 periods. We also propose a new hydrothermal sedimentation model of hydrothermal fluids overflowing from basin margin faults, for the Yanchang Formation, which is reported here for the first time. [ABSTRACT FROM AUTHOR]

The Ediacaran period was critical in the evolution of the biosphere and ocean in the history of the Earth. Shales rich in organic matter (OM) are well developed for this period in the Yangtze Block, China, and have recently been related to shale gas exploration in South China. To date, detailed characterisation of the Ediacaran shales is not available. The present work sets out a detailed investigation of the composition and pore characteristics of samples from a shallow drill core in the Ediacaran Lantian Formation in the Lower Yangtze area, and the effects of shale composition on the pore growth are discussed. The 90-m-thick Lantian black shales are highly over-mature (equivalent vitrinite reflectance (EVRo) value approximately 4.0%) with a total organic carbon (TOC) content up to 12%. They are dominated by quartz (33–72%), generally with low clay or feldspar content (<20%) and highly varied carbonate content (up to 60%). The Lantian shales are also notable for their high pyrite content (up to 19%), suggesting a depositional environment of an anoxic water body rich in sulphates; greatly enriched OM is facilitated in deep-water environments. Bulk porosities of the shales range from 1.0% to 7.9%, and are positively correlated with TOC content. High-magnification scanning electron microscopy (SEM) images support the crucial importance of OM content on pore development. Generally, pore volume shows excellent, positive correlation with TOC content for micropores, good correlation for mesopores, and relatively poor correlation for macropores. Two samples with mostly high TOC content showed very low macropore volume and medium mesopore volume. These results suggest a close relationship between OM with relatively small pores, and enhanced compaction effect on large pores in highly OM-enriched shales. [ABSTRACT FROM AUTHOR]

Organic-rich black shale of the Upper Yangtze Basin from the Late Ordovician and Early Silurian is considered an excellent source rock in South China. The formation and preservation conditions of this resource are revealed by its geochemical characteristics in this study. Geochemical indices, including redox indices (V/(V + Ni), V/Cr, V/Sc, and Ni/Co) and primary productivity indices (P/Ti and Ba/Al), and paleoclimate, clastic flux and sedimentary rate analyses are presented to investigate the accumulation mechanism of organic matter. Redox indices suggest that a stagnant, anoxic environment predominated in the Upper Yangtze Basin during accumulation of Wufeng and Longmaxi formations. In contrast, ventilated and oxygenated marine conditions pervaded the Upper Yangtze Basin during deposition of Linxiang and Guanyinqiao formations. The concentrations of V and U demonstrate that accumulation of organic matter was mainly controlled by redox conditions. Besides, such factors as clastic fluxes, fresh water inflows or a mixed deposition with a rapid sedimentary rate cannot be ignored due to their influences on organic matter enrichment and preservation. However, weak co-variance relationship of TOC content and productivity proxies, including P/Ti and Ba/Al, demonstrates that the accumulation of organic matter was not controlled by primary productivity. Results of the present study suggest a depositional model that stresses the importance of tectonic movements and glacial events on the accumulation and preservation of organic matter. The model shows that the Upper Yangtze Basin was a semi-restricted basin system influenced by the isolation of Xuefeng, but also it implies that oxygen-depleted bottom water of the basin favored the accumulation and preservation of sedimentary organic matter, resulting in the formation of organic-rich black shale. [ABSTRACT FROM AUTHOR]

Although the annual production of shale gas in China was 13 × 10 8 m 3 in 2014, a systematic study on geochemical and isotopic characteristics of these unconventional gases has not been well addressed. In the present study, almost all shale gas samples available in China, including marine shale gas from the Wufeng-Longmaxi Formation in the Sichuan Basin (O 3 w–S 1 l) and terrestrial shale gas from Chang 7 Member (T 3 y 7 ) in the Ordos Basin, were collected and analyzed for their geochemical and isotopic compositions. The shale gas from the Wufeng-Longmaxi Shale is dry gas with an average methane content of 98.38% and records a highest content of CH 4 in the world (99.59%), which is consistent with the very high thermal maturity levels of the gas shales that have equivalent vitrinite reflectance (EqVRo) values between 2.4 and 3.6%. The δ 13 C 1 values are correspondingly heavy and record a heaviest δ 13 C 1 values (−26.7‰) for the shale gases found in the world as well. The average values of δ 13 C 1 , δ 13 C 2 and δ 13 C 3 for the Wufeng-Longmaxi shale gas are −31.3‰, −35.6‰, and −47.2‰, respectively, displaying a complete carbon isotopic reversal (i.e., δ 13 C 1 > δ 13 C 2 > δ 13 C 3 ). δ 2 H CH4 and δ 2 H C2H6 has an average value of −148‰ and −173‰, respectively, also yielding a hydrogen isotopic reversal (i.e., δ 2 H CH4 > δ 2 H C2H6 ). The Chang 7 shale has an average TOC content of 13.81% with vitrinite reflectance (VRo) values between 0.7 and 1.2%. The Chang 7 shale gas is wet gas with an average methane content of 84.90% and is rich in heavy gaseous hydrocarbons (C 2 –C 5 ). The respective values of δ 13 C 1 , δ 13 C 2 and δ 13 C 3 are −48.7‰, −36.4‰ and −31.3‰, displaying a positive carbon isotopic distribution pattern (i.e., δ 13 C 1 < δ 13 C 2 < δ 13 C 3 ). The average δ 2 H CH4 , δ 2 H C2H6 and δ 2 H C3H8 values are −256‰, −244‰ and −188‰, respectively, and are characterized by a positive distribution pattern (i.e., δ 2 H CH4 < δ 2 H C2H6 < δ 2 H C3H8 ). The differences in gas wetness and carbon and hydrogen isotopic distribution patterns between the shale gases from the Wufeng-Longmaxi and Chang 7 shale are attributed to variations in thermal maturity levels. CO 2 is present in low content in both the Wufeng-Longmaxi and Chang 7 shale gases, mostly less than 1%. δ 13 C values for the CO 2 in the Wufeng-Longmaxi Formation are between 8.9 and −9.2‰, indicating an inorganic origin from the cracking of carbonate mineral in the shales under high temperatures. In contrast, δ 13 C values of the CO 2 in the Chang 7 shale gas range from −8.2 to −22.7‰, indicating an organic origin from the thermal degradation of organic matter. Helium in both the Wufeng-Longmaxi and Chang 7 shale gases is dominantly of curst origin in terms of their R/Ra ratios that vary from 0.01 to 0.08. Positive carbon isotopic distribution pattern is typical of primitive thermogenic gas. However, it can be converted into complete or partial carbon isotopic reversal patterns due to secondary alteration. The causes that yield carbon isotopic reversal include (1) mixing of gases with the same source but different thermal maturity levels; (2) secondary cracking of oil or wet gas; (3) formation water-involved reactions; (4) gas diffusion; and (5) carbon isotope exchange between alkane gases at high temperature. Among them, carbon isotopic exchange between alkane gases at high temperature is a key factor. Nine plots have been drawn based on the shale gases from China, USA and Canada. Among them, the plot of δ 13 C 2 versus wetness demonstrates a “lying-S” shape with two inflection points on the gas wetness axis. The wetness value of 1.4% represents a critical point from pyrolytic gas (primary cracking gas) to cracking gas (secondary cracking gas) and whereas the wetness value of 6% marks the end of oil generation. On the diagram of wetness versus δ 13 C, shale gases with wetness values greater than 1.6% are characterized by positive carbon isotopic distribution pattern, whereas a complete or partial carbon isotopic reversals are observed for shale gases with wetness values less than 1.6%. [ABSTRACT FROM AUTHOR]

Source rock formation influenced by river-delta system, especially in continental margin basins, is still poorly understood. This article aimed to reveal the effect of river-delta system on the formation of the source rock by taking the Baiyun Sag of the Pearl River Mouth Basin for example. Paleo-Pearl River began to develop since the Enping Formation, providing abundant organic matter beneficial for the formation of the source rocks in the Baiyun Sag. The main controlling factor of source rock formation in the Baiyun Sag is terrestrial organic matter supply rather than the paleoproductivity or redox conditions. Low Al/Ti and P/Ti ratios suggest low marine productivity, which may be associated with a large number of terrigenous detritus input, occupying about 43.04%–94.91%. There is a positive correlation between the oleanane/C 30 hopane ratio and the TOC value, showing that terrigenous organic matter controls the source rock formation. The size of the delta below Pearl River estuary determines the extent of terrestrial organic matter supply. Source rocks with high organic matter abundance mainly formed in delta environment, and those in neritic environment in Enping and Zhuhai Formations also have high TOC values as a result of adequate terrestrial organic matter supply. [ABSTRACT FROM AUTHOR]

The carbonates in the Middle Ordovician Ma submember of the Majiagou Formation in the northern Ordos Basin are partially to completely dolomitized. Two types of replacive dolomite are distinguished: (1) type 1 dolomite, which is primarily characterized by microcrystalline (<30 µm), euhedral to subhedral dolomite crystals, and is generally laminated and associated with gypsum-bearing microcrystalline dolomite, and (2) type 2 dolomite, which is composed primarily of finely crystalline (30-100 μm), regular crystal plane, euhedral to subhedral dolomite. The type 2 dolomite crystals are truncated by stylolites, indicating that the type 2 dolomite most likely predated or developed simultaneously with the formation of the stylolites. Stratigraphic, petrographic, and geochemical data indicate that the type 1 dolomite formed from near-surface, low-temperature, and slightly evaporated seawater and that the dolomitizing fluids may have been driven by density differences and elevation-related hydraulic head. The absence of massive depositional evaporites in the dolomitized intervals indicates that dolomitization was driven by the reflux of slightly evaporated seawater. The δO values (−7.5 to −6.1 ‰) of type 1 dolomite are slightly lower than those of seawater-derived dolomite, suggesting that the dolomite may be related to the recrystallization of dolomite at higher temperatures during burial. The type 2 dolomite has lower δO values (−8.5 to −6.7 ‰) and Sr concentration and slightly higher Na, Fe, and Mn concentrations and Sr/Sr ratios (0.709188-0.709485) than type 1 dolomite, suggesting that the type 2 dolomite precipitated from modified seawater and dolomitic fluids in pore water and that it developed at slightly higher temperatures as a result of shallow burial. [ABSTRACT FROM AUTHOR]

The Ediacaran Period witnessed one of the largest phosphogenic events in Earth's history. Coincidently, some phosphorite deposits in South China are associated with the largest-known carbon isotope negative excursion (i.e., Shuram Excursion), suggesting an intimate coupling of the biogeochemical carbon and phosphorous cycles. However, the geomicrobiological linkage between these anomalies remain poorly understood. In this study, we investigated the phosphorite samples from the uppermost Doushantuo Formation in South China. Carbon isotope compositions of authigenic calcite cements and nodules in the phosphorites are as low as –34‰ (VPDB). Petrographic and geochemical investigations indicate that the 13 C-depleted carbonates likely formed as the result of microbial sulfate and iron reduction that released phosphorous from iron oxyhydroxide, concentrating phosphorous in pore waters, and thereby promoting phosphate mineralization. The timing of this event appears to coincide with enhanced sulfate delivery to seawater through continental weathering. The basin-scale distribution of Doushantuo phosphorites suggests a redox control on the availability of iron oxyhydroxide and the recycling of pore water phosphorous. Both inner and outer shelf regions were likely characterized by an oxic water column, and were the main loci for phosphogenesis; on the contrary, intra-shelf and slope regions, which are lean in phosphorite, were subjected to euxinic or ferruginous water column conditions. The intimate coupling between Ediacaran phosphogenesis and the Shuram Excursion suggests strong links among seawater redox conditions, C-S-P-Fe cycling, and fossil phosphatization. Increased microbial sulfate reduction driven by enhanced sulfate reservoir in the Ediacaran ocean may have played an essential role on these biogeochemical events. [ABSTRACT FROM AUTHOR]

The Lower Cambrian organic-rich marine shale, which is a significant source of China’s shale gas, is widely distributed in southern China. An integrated characterization of the Niutitang shale is provided in this study in terms of organic geochemistry, mineralogy, pore characterization, methane sorption capacity, rock mechanical properties, fractures and gas content based on samples from three wells. The results indicate that the Lower Cambrian Niutitang shale is thermally over-mature and has rich shale gas resources, with a total organic carbon content (TOC) between 0.51% and 10.49% and a high quartz content between 35.3% and 78.5%. Compared to the major gas-producing shales in the U.S. and China, most of the organic matter (OM)-hosted pores in the Niutitang shale are generally smaller than 5 nm, significantly affecting the methane sorption capacity. The inter-particle and intra-particle pores and fractures are the primary sources of storage space, especially for free gas. For samples with TOC values less than 6.5%, TOC is positively correlated with the total porosity, total pore volume, brittleness (Young’s modulus), core fracture density, free gas content and Langmuir pressure; however, for samples with TOC values greater than 6.5%, the positive correlations become negative. These characteristics are due to the ductility and low hydrocarbon generation potential of organic matter in high thermal maturity shales that are vulnerable to compaction. Thus, TOC has a significant impact on the macroscopic (e.g., brittleness) and microscopic (e.g., pore structure and sorption capacity) properties of shale reservoirs, potentially controlling the enrichment and productivity of shale gas. These results can be used to optimize drilling and fracturing stimulation intervals during shale gas exploration and development. [ABSTRACT FROM AUTHOR]

The Lower Silurian Longmaxi Formation marine shales are the main shale gas reservoirs in the Sichuan Basin, SW China. The present study analyzes the characteristics of the Longmaxi shales using samples selected from wells N1 and N2 in the Changning block, southern Sichuan Basin. Several methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), helium gas expansion and low pressure nitrogen (N 2 ) adsorption/desorption, were used to investigate the mineralogical composition, geochemical characteristics, pore structure and other characteristics of the shales. The total organic carbon (TOC) contents of the samples range from 0.8 to 6.429%, and the thermal maturity is at the overmature stage. Two wells are rich in quartz and clay, with the average contents of 39.4% and 29.6%, respectively. The Longmaxi shales have the specific surface area and total pore volume around 16.6 m 2 /g and 0.0165 mL/g, respectively. It is suggested that the TOC content contributes significantly to the average pore size, specific surface area and total pore volume, and the thermal maturity strongly influences the development of porosity, as does the mineralogical composition. Based on imagine analysis, we classify shale gas microreservoirs into three types: organic matter with microfractures, organic matter alone and organic matter with mineral pores (interparticle pores (InterP pores) and intraparticle pores (IntraP pores)). The first type is the best for shale gas exploitation. The second type and the type of organic matter with InterP pores are better, while the type of organic matter with IntraP pores is almost useless. The analysis results show that the microreservoirs of well N1 mainly contain the type of organic matter with InterP pores, while the microreservoirs of well N2 are dominated by the type of organic matter with InterP pores and the type of organic matter with microfractures. Combing all the analysis results and their influencing factors, we consider that well N2 is more favorable for gas production than well N1. [ABSTRACT FROM AUTHOR]

The Neoproterozoic successions in the Aksu region, NW China, which lies unconformably on the Precambrian Aksu Group basement, comprises the Qiaoenbrak, Yuermeinak, Sugetbrak, and Chigebrak formations (from bottom to top). The two lowermost units include two distinct glacial diamictites, which indicate distinct episodes of glaciations. We report the major and trace element (including rare earth element) data for the Qiaoenbrak, Yuermeinak, and Sugetbrak formations to identify the paleoclimatic perturbations. The chemical index of alteration (CIA) values show variations from Qiaoenbrak to Yuermeinak, then Sugetbrak formations. The diamictites have relatively lower chemical index of alteration values (45.23-59.64) than inter-, post- and non-glacial sediments (48.28-66.96). This result supported the condition that the diamictites underwent relatively weak chemical weathering from a dry-cold sedimentary environment, which is associated with the sedimentary facies description. The lower Neoproterozoic successions recoded at least two glaciations, one is Qiaoenbrak glaciation and the other is Yuermeinak glaciation. [ABSTRACT FROM AUTHOR]

The Meso-(?) and Neoproterozoic Huaibei Group in the Huaibei region, North China Craton (NCC), is emerging as a target for geobiological and tectonic studies due to its thick unmetamorphosed sediments with well-preserved organic-walled fossils. However, the lack of accurate age constraints for this sedimentary sequence dramatically hampers our ability to take full advantage of the rich geological and paleontological history recorded in the Huaibei Group. Particularly, the depositional age of the uppermost unit of the Huaibei Group, the Gouhou Formation, is a controversial issue. Although it is widely accepted that there is an unconformity between the Gouhou Formation and the overlying early Cambrian Houjiashan Formation, the magnitude of this unconformity and hence the scale of the underlying tectonic event are unconstrained due to the uncertainty of the sedimentary age for the Gouhou Formation which has been variously interpreted as Cambrian, Cryogenian–Ediacaran (∼720 Ma to ∼541 Ma), and Tonian (1000 Ma to ∼720 Ma). To improve our knowledge about this sedimentary gap, we carried out a biostratigraphic study of the Gouhou Formation. Our investigation using a low manipulation maceration technique revealed a diverse organic-walled microfossil assemblage. A total of 22 taxa have been revealed, including a new species— Dictyosphaera tacita n. sp. Importantly, the co-occurrence of Trachyhystrichosphaera , Valeria , and Dictyosphaera in the Gouhou Formation suggests a likely Tonian age. The biostratigraphic data indicate an infra-Cambrian depositional gap of >200 myr between the Tonian Gouhou Formation and Cambrian Houjiashan Formation, perhaps driven by a major tectonostratigraphic event. [ABSTRACT FROM AUTHOR]

The article discusses a research concerning shale distribution and geochemistry of 4th member of Shahejie Formation in Liaohe Western Depression in Bohai Bay Basin, China and examines its shale oil accumulation geological conditions. Details about the shale sedimentary and distribution in the area, shale thickness, and types and abundance of organic matter are noted. Also provided is information on the lacustrine shale oil accumulation of the shales.

In the well-known continental Songliao Basin, the oil shale successions of the Cretaceous Qingshankou Formation are excellent source rocks for oil. The oil shale layers with high TOC (total organic carbon) contents developed at the bottom of the formation. They are divided into the lower oil shale (TOC up to 18.3%) and the upper oil shale layer (TOC up to 14.4%). The oil shale layers and accompanying mudstones are investigated by high resolution analyses of drill cores by pyrolysis, organic petrology, organic and inorganic geochemistry. The results demonstrate the predominance of type-I kerogen derived from algal-microbial mats (i.e. lamalginite). However, increased proportions of plant-derived organic matter are indicated by Rock-Eval parameters and the presence of vitrinite in the upper oil shale. As evidenced from lower concentrations of hopanes, higher sinking rates of organic matter (OM) are suggested to have been responsible for a lower extent of microbial degradation during accumulation of the lower oil shale unit. The environmental conditions are characterized by anoxic saline bottom water overlain by an extended zone of freshwater, favorable for OM production and preservation. Under these preconditions, oil shale thickness and quality are governed by primary productivity, related to accommodation space and nutrient supply. Redox conditions within the water column are the key factor controlling organic matter preservation. [ABSTRACT FROM AUTHOR]

Mt Sanqingshan, a global Geopark and world natural heritage site located in Jiangxi Province, China, is famous for its eroded granite peaks. The uplift and denudation history of the area has been reconstructed using fission track methods for the first time. Apatite fission track ages (AFTAs) cluster into three groups at ca. 25 Ma, 45–55 Ma, and 70 Ma. These ages can be related to ancient multilevel denudation planes at about 900, 1200, and 1500 m above sea level, respectively. The apatite data also reveal four cooling stages for the Mt Sanqingshan region, from ca. 90 to 65–60 Ma, 65–60 to 45 Ma, 45 to 20–15 Ma, and 20–15 Ma to the present, with cooling rates of 1.96°C, 1.18°C, 0.37°C, and 3.78°C per million years, respectively, and an average cooling rate of 1.80°C per million years. Calculated uplift rates are 0.055, 0.034, 0.011, and 0.11 mm year‒1in the four stages, yielding uplifts of 4140, 570, 290, and 1940 m, respectively. The uplift rate of the last stage was significantly faster than that of the other three preceding stages, reflecting rejuvenation of Mt Sanqingshan, as a result of new tectonism. The average uplift rate at Mt Sanqingshan is 0.053 mm year‒1, and the average denudation rate is 0.048 mm year‒1, resulting in 3550 m of uplift and 2540 m of denudation relative to eustatic sea level. The 1010 m difference is very close to the average elevation of about 1000 m at present. A comparison of uplift–denudation histories for Mt Sanqingshan and Mt Huangshan shows that fission track results can be useful for defining geomorphological development stages. [ABSTRACT FROM PUBLISHER]

The article focuses on findings of a study on geochemical characteristics and geological significance of picritic rocks in Permian Tiaohu Formation from Santanghu Basin, Xinjiang of China. Topics include magmatic activity of Permian in Santanghu Basin; characteristics of picritic rocks, such as SiO2 amount of picritic rocks; and voluminous postcollisional granitoids and Armantai and Karamaili suture zone formation age.

The article discusses a research concerning geochemistry and petrography of clastic deposits from the Late Paleozoic Shihezi Formation in Eastern Ordos Basin in China, along with the implications for provenance and tectonic setting. Topics include the significance of provenance studies in reconstructing paleo-drainage systems, mineralogy and petrology of sandstones, and major, trace, and rare earth element compositions of sandstones from the formation.