Organic Matter Accumulation in the Youganwo Formation (Middle Eocene), Maoming Basin, South China: Constraints from Multiple Geochemical Proxies and Organic Petrology

Xu, Chuan; Hu, Fei; Meng, Qingtao; Liu, Zhaojun; Shan, Xuanlong; Zeng, Wenren; Zhang, Kun; He, Wentong

doi:10.1021/acsearthspacechem.1c00383

Cited by 3 publications

(9 citation statements)

References 52 publications

(145 reference statements)

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“…This indicates that the effect of paleosalinity on OM accumulation is more important for FL shale. This is consistent with a former study on OM in the Eocene Youganwo Formation, Maoming Basin . The redox ( U EF ) proxies exhibit no linear correlation with TOC content in MS and TL source rocks (Figure d) and a medium negative relationship in FL shale samples (Figure d).…”

Section: Discussionsupporting

confidence: 91%

“…This is consistent with a former study on OM in the Eocene Youganwo Formation, Maoming Basin. 94 The redox (U EF ) proxies exhibit no linear correlation with TOC content in MS and TL source rocks (Figure 18d) and a medium negative relationship in FL shale samples (Figure 19d). The variation trends of the the paleoredox condition on TOC are approximately similar to those of paleosalinity (Figure 19c,d).…”

Section: Paleoenvironment On the Accumulation Of Organicmentioning

confidence: 98%

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Differences between Laminated and Massive Shales in the Permian Lucaogou Formation: Insights into the Paleoenvironment, Petrology, Organic Matter, and Microstructure

Yang

Zeng

Qiao

et al. 2022

ACS Earth Space Chem.

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The Permian Lucaogou Formation (LCG Fm.) in the Junggar Basin is an organic-rich source rock interval formed in a salinized paleolake, and organic-rich laminated and massive shales are broadly deposited. However, the paleoenvironment difference between laminated and massive shales is still unclear, and the effect of this difference on petrology, pore structure, and organic matter enrichment is significant to shale oil resource evaluation. In this study, organic and element geochemistry, mineralogy, and nitrogen adsorption are used to analyze key differences between laminated and massive shales. The results show that most shale samples present mature thermal stage and oil-prone type II kerogen. Felsic igneous rocks in the continental island arc are their primary mineral component sources. The differences between laminated and massive shales are mainly from their silica origin, paleoclimate, and salinity. The silica origin in laminated shale is primarily from the terrestrial debris influx, while the massive shale is mixed with terrestrial debris and biogenic origin. The silica origin from hydrothermal activities is negligible. The laminated shale prefers to be deposited in a hot and dry climate with weak weathering and relatively higher salinity. However, the massive shale is mainly deposited in a warm and humid climate with moderate weathering and lower salinity conditions. For both laminated and massive shales from the LCG Fm., the warm and humid climate is beneficial to organic matter (OM) accumulation. Paleoproductivity presents an increasingly positive impact on source rocks when the rock fabric transforms from massive to thick laminae. Overall, lower salinity, humid climate, and strong terrigenous clastic input jointly enhance organic matter (OM) accumulation in both laminated and massive shales. Arid and semiarid climates are beneficial to improving the fractability of both laminated and massive shales. The laminated shale presents a relatively wider average nanopore diameter and lower pore volume than massive samples. These findings provide an important insight into the correlation between organic enrichment, laminae, pore structure, and depositional environment. This study has profound implications for understanding the formation mechanisms of laminated and massive shales in the lacustrine paleoenvironment.

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Section: Discussionsupporting

confidence: 91%

Section: Paleoenvironment On the Accumulation Of Organicmentioning

confidence: 98%

Differences between Laminated and Massive Shales in the Permian Lucaogou Formation: Insights into the Paleoenvironment, Petrology, Organic Matter, and Microstructure

Yang

Zeng

Qiao

et al. 2022

ACS Earth Space Chem.

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“…The carbon isotope values of pristane (δ 13 C Pr , %) and phytane (δ 13 C Ph , %) of biogenic oils are −28.84 and −28.14 for the WC8-2-1 sample and −24.26 and −25.59 for the WC19-1-3 sample, respectively (Table 3 and Figure 5). The δ 13 C Pr and δ 13 C Ph of thermogenic oils synchronously increase with increasing maturity for the two source rock samples, which corresponds well with the changes in the hydrogen isotope composition of pristane and phytane.…”

Section: Carbon Isotope Compositions Of Pristane and Phytanementioning

confidence: 99%

“…The two isoprenoid alkanes, i.e., pristane (2,6,10,14-tetramethylpentadecane) and phytane (2,6,10,14-tetramethylhexadecane), are common biomarkers used in organic geochemical studies because of their high contents and extensive distributions in sedimentary organic matter, as well as convenient and accurate measurements. The pristane/phytane ratio (Pr/Ph ratio) of source rocks and crude oils has been widely used for identifying the redox and salinity of sedimentary environments and for oil–oil and oil–source rock correlations. − It has been reported that anoxic sedimentary environments generally have a low Pr/Ph ratio, while oxic sedimentary environments generally have a high Pr/Ph ratio. For example, the Pr/Ph ratio of marine source rocks is generally smaller than 1, while that of terrestrial source rocks is generally larger than 3. − The Pr/Ph ratio is also diverse for the source rocks in the continental basin of China.…”

Section: Introductionmentioning

confidence: 99%

“…Carbon Isotope Compositions and Isoprenoid Alkane Biomarkers of the Biogenic and Thermogenic Oils for the Original and Artificially Matured Source Rock Samples at Different Maturity Stages a 13 C K , δ13 C Pr , and δ 13 C Ph : carbon isotope values of kerogen, pristane, and phytane, respectively; Pr/nC 17 and Ph/nC 18 : ratios of pristane to C 17 nalkane and phytane to C 18 n-alkane, respectively; and Pr/Ph: pristane/phytane ratio.…”

mentioning

confidence: 99%

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Evolution of the Pristane/Phytane Ratio with Maturity of Lacustrine Source Rocks: Implications of a Thermal Simulation Experiment

Cheng

Gai

Xiao

et al. 2023

ACS Earth Space Chem.

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The pristane/phytane ratio (Pr/Ph) of source rocks has been extensively used for the identification of paleosedimentary environments and oil−source rock correlations. However, the influences of maturity on the Pr/ Ph ratio are not fully understood, which largely limits the applicability of this parameter under geological conditions. Based on a thermal simulation experiment performed on typical lacustrine source rock samples and systematic research on geological source rock samples, the evolution of the Pr/Ph ratio with increasing maturity was investigated in this study. The results indicate that the Pr/Ph ratios of the two source rock extracts progressively decrease with increasing maturity, and the decrease in this parameter is more significant for shallow lacustrine samples than for deep lacustrine samples. The Pr/Ph ratios of the two types of source rocks are different at the oil generation stage with EasyRo less than 1.02% but are similar at the oil cracking stage with EasyRo larger than 1.02%. The Pr and Ph of source rocks are contributed by both biogenic and thermal origins, which are largely determined by the sedimentary environment and maturity, respectively, and the contributions of the two origins are diverse at different maturity stages. The Pr/Ph ratio is mainly controlled by the sedimentary environment at the diagenetic stage, by both sedimentary and thermal maturity at the oil generation stage, and by thermal maturity at the oil cracking stage. The Pr/Ph ratio of source rocks can be used to identify sedimentary environments and oil−source rock correlations at diagenetic and oil generation stages.

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Petrology, Mineralogy, and Geochemical Characterization of Paleogene Oil Shales of the Youganwo Formation in the Maoming Basin, Southern China: Implication for Source Rock Evaluation, Provenance, Paleoweathering and Maturity

Meng

Liu

et al. 2023

Energies

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Oil shale is a crucial unconventional energy source to supplement conventional oil and gas. The oil shale in the Maoming Basin of China has excellent resource potential. In this study, through systematic geochemical testing, the industrial quality and geochemical characteristics of oil shale are revealed, and the hydrocarbon generation potential of oil shale, the parent rock type, and the tectonic setting of the source area are discussed. It is comprehensively assessed that Maoming oil shale has a medium-oil yield (avg. 6.71%) with high ash content (avg. 76.1%), a high calorific value (avg. 7.16 M J/kg), and ultra-low sulfur (avg. 0.54%). The mineralogical compositions primarily consist of clay minerals and quartz, and barely pyrite. Maoming oil shale is in an immature evolution stage, with high TOC and I-II1 kerogen type, and could be considered an excellent hydrocarbon source rock. The chemical index of alteration (CIA), the index of chemical variability (ICV), and the Th/U ratio indicate that the Maoming oil shale parent rock area is strongly weathered. Multitudinous geochemical diagrams also show that the oil shale was mainly derived from Late Cretaceous felsic volcanic rock and the granite zone, and the tectonic setting was a continental island arc environment related to the active continental margin. This is consistent with the tectonic history of southern China in the Late Cretaceous.

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Organic Matter Accumulation in the Youganwo Formation (Middle Eocene), Maoming Basin, South China: Constraints from Multiple Geochemical Proxies and Organic Petrology

Cited by 3 publications

References 52 publications

Differences between Laminated and Massive Shales in the Permian Lucaogou Formation: Insights into the Paleoenvironment, Petrology, Organic Matter, and Microstructure

Differences between Laminated and Massive Shales in the Permian Lucaogou Formation: Insights into the Paleoenvironment, Petrology, Organic Matter, and Microstructure

Evolution of the Pristane/Phytane Ratio with Maturity of Lacustrine Source Rocks: Implications of a Thermal Simulation Experiment

Petrology, Mineralogy, and Geochemical Characterization of Paleogene Oil Shales of the Youganwo Formation in the Maoming Basin, Southern China: Implication for Source Rock Evaluation, Provenance, Paleoweathering and Maturity

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