Paleoenvironmental changes of source rocks from the Carboniferous to Permian sediments of the Mahu Sag, Junggar Basin, China

Feng, Ching Mei; Ma, Mingze; He, Wenjun; Li, Teng; Wu, Qianlin; Zhang, Zexin; Zhao, Hongwei

doi:10.1080/12269328.2020.1802354

Cited by 5 publications

(4 citation statements)

References 21 publications

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“…Thus, the primary microbial gases in the Mahu sag are most likely from the P 2 w coal-bearing source rock. The source rock was deposited under sulfate-poor freshwater to brackish lacustrine environment with mudstone and shale Sr/Ba ratios from 0.36 to 0.57 56 , and are thus favorable for methanogenesis in the Lower Wuerhe Formation to generate primary microbial gas 57 – 59 , followed by its up-migration and accumulation in the overlying Lower Triassic reservoirs. The methanogenesis may have occurred prior to the late Triassic when the Lower Wuerhe Formation has organic matter maturity < 0.5% and the underlying Lower Permian Fengcheng Formation, the main source rock for the petroleum in the Mahu sag 12 experienced temperatures < 70 °C and thus no significant oil and gas has been generated 55 .…”

Section: Discussionmentioning

confidence: 99%

Unrecognized extensive charge of microbial gas in the Junggar basin

Zhang,

Cai,

Mei

et al. 2024

Sci Rep

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Different from the Qaidam basin with about 320 billion m3 microbial gas, only limited microbial gases were found from the Junggar basin with similarly abundant type III kerogen. To determine whether microbial gases have not yet identified, natural gas samples from the Carboniferous to Cretaceous in the Junggar basin have been analyzed for chemical and stable isotope compositions. The results reveal some of the gases from the Mahu sag, Zhongguai, Luliang and Wu-Xia areas in the basin may have mixed with microbial gas leading to straight ethane to butane trends with a “dogleg” light methane in the Chung’s plot. Primary microbial gas from degradation of immature sedimentary organic matter is found to occur in the Mahu sag and secondary microbial gas from biodegradation of oils and propane occurred in the Zhongguai, Luliang and Beisantai areas where the associated oils were biodegraded to produce calcites with δ13C values from + 22.10‰ to + 22.16‰ or propane was biodegraded leading to its 13C enrichment. Microbial CH4 in the Mahu sag is most likely to have migrated up from the Lower Wuerhe Formation coal-bearing strata by the end of the Triassic, and secondary microbial gas in Zhongguai and Beisantan uplifts may have generated after the reservoirs were uplifted during the period of the Middle and Late Jurassic. This study suggests widespread distribution of microbial gas and shows the potential to find large microbial gas accumulation in the basin.

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Section: Discussionmentioning

confidence: 99%

Unrecognized extensive charge of microbial gas in the Junggar basin

Zhang,

Cai,

Mei

et al. 2024

Sci Rep

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“…Therefore, the Sr/Ba value can be used as a marker to judge the paleosalinity. 36 Sr/Ba > 1 means the water is salt, 0.6 ≤ Sr/Ba ≤ 1 means the water is semi-saline, and Sr/Ba < 0.6 indicates that the water is slightly saline. The Sr/Ba values of the fossil matrix ranged from 0.54 to 0.74 with a mean value of 0.62.…”

Section: Paleosalinitymentioning

confidence: 99%

Lycoptera Fossil Elemental Imaging And Paleo-Environment Research Via Laser Ionization Time-Of-Flight Mass Spectrometry

Hang¹

2023

At.Spectrosc.

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Buffer gas-assisted high-irradiance laser ionization time-of-flight mass spectrometry (BGA-LI-TOFMS) was used to determine the elemental distribution of Lycoptera fossils from the Dawangzhangzi Bed of the Yixian Formation in Liaoning Province, China. The Sr, Ba, and Pb images of the Lycoptera fossil highlight the fine structure of the skeleton, and the distribution of Fe and Si provides data regarding the preservation pattern and nature of pyritization in the Jehol Biota. The enrichment of toxic substances such As and H2S may be one of the reasons for the cluster mortality of Lycoptera. Meanwhile, the elemental analysis of the rocks in the fossil preservation shows that the paleoclimate indices MgO/CaO and Sr/Cu indicate dry and hot climatic conditions at that time. Meanwhile, the paleosalinity indicators (m value and Sr/Ba ratio) indicate a semi-saline to slightly saline water body. The paleoredox environment indicators (Th/U and V/(V+Ni) ratio) suggest an anaerobic environment with weak stratification and H2S in the bottom water. Thus, the elemental imaging and analysis of the Lycoptera fossil suggest that the organisms of Jehol Biota were preserved in the anoxic water environment and the toxic effect of hydrogen sulfide. Overall, BGA-LI-TOFMS is an adaptable technique for acquiring comprehensive geochemical information on fossils.

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“…(2019, 2020a). (a)): the C SRs, the P 1 j SRs, the P 1 f SRs and the P 2 w SRs (Chen et al., 2016; Feng et al., 2019, 2020a, 2020b; Tao et al., 2016). Under the tectonic background of continuous compression, Mahu Sag in period C was transformed from ocean to land environment, and its SRs were mainly tuffs and mudstones (Zhou et al., 2019).…”

Section: Geological Settingmentioning

confidence: 99%

“…(2018), Feng et al. (2020a, 2020b) thought that the P 1 f SRs were deposited in the alkali lake environment, with a wide distribution area, good type and large abundance of organic matter. Now they are primarily in the stage of mature evolution and are the best SRs in the region.…”

Section: Geological Settingmentioning

confidence: 99%

Organic geochemical characteristics and comparison of the source rocks and the severely biodegradable oil sands around Karamay, China

Feng

He²,

Cheng

et al. 2020

Energy Exploration & Exploitation

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For the sake of explaining the organic geochemical characteristics of the hydrocarbon source rocks (SRs) around Karamay, such as thermal maturity (TM) (evidences from the temperature of maximum pyrolysis yield (Tmax), the Carbon Preference Index (CPI) and Odd to Even Preference (OEP) values, the C30 M/H versus Tm/Ts, the C29 ββ/(ββ + αα) versus C29 20 S/(20 S + 20 R)), hydrocarbon potential (HP) (evidences from total organic carbon (TOC) and rock pyrolysis (RP)), organic matter (OM) source input (evidences from n-Alkane distribution, the relative quantity of C27-C28-C29 steranes, the (C19 + C20)/C23 tricyclic terpane (TT), and the Terrigenous/aquatic ratio (TAR)) as well as paleoenvironment (evidences from the pristane/phytane (Pr/Ph) and the Gammacerane index), and in order to analyze the biodegradation degree and source of oil sand (OS) oil, 55 core samples of SRs in all were selected to measure TOC and RP. 14 core samples of SRs and 3 OS samples were selected for gas chromatography–mass spectrometry (GC-MS) analysis. 11 core samples of SRs and 3 OS samples were used for organic carbon isotope (OCI) analysis. The results indicate that except the SR from Fengcheng formation (P1 f) which is in the stage of high or over evolution, the other SRs are in mature stage. OM type of Carboniferous (C) SRs are type Ⅱ kerogen, with the largest abundance. OM type of the SRs in Wuerhe formation (P2 w) and Jiamuhe formation (P1 j) are type Ⅲ kerogen with good and medium OM abundances. Almost all SRs were formed in the reduction environment of high salinity, and the main OM source input is the lower aquatic plants. Karamay formation (T2 k) and Badaowan formation (J1 b) oil sands (OSs) around Karamay have undergone serious biodegradation. It is suggested that OS oil are mainly from P1 f SRs (evidences from the tricyclic terpanes (TT), triarysteranes, pregnane, homopregnane and OCI).

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Paleoenvironmental changes of source rocks from the Carboniferous to Permian sediments of the Mahu Sag, Junggar Basin, China

Cited by 5 publications

References 21 publications

Unrecognized extensive charge of microbial gas in the Junggar basin

Unrecognized extensive charge of microbial gas in the Junggar basin

Lycoptera Fossil Elemental Imaging And Paleo-Environment Research Via Laser Ionization Time-Of-Flight Mass Spectrometry

Organic geochemical characteristics and comparison of the source rocks and the severely biodegradable oil sands around Karamay, China

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