Organic geochemical characteristics and organic matter enrichment of mudstones in an Eocene saline lake, Qianjiang Depression, Hubei Province, China

Kong, Xiangxin; Jiang, Zaixing; Zheng, Youheng; Xiao, Meng; Chen, Chen; Yuan, Hao; Chen, Fengling; Wu, Shiqiang; Zhang, Jianguo; Han, Chao; Liu, Shengqian

doi:10.1016/j.marpetgeo.2019.104194

Cited by 30 publications

(44 citation statements)

References 71 publications

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“…It implies that their source rocks are derived from the freshwater environment because the ETR is widely used for an effective indicator of salinity. 40 , 41 C 24 tetracyclic terpane/C 23 tricyclic (C 24 Te/C 23 TT) is also an index for terrestrial OM. 42 , 43 The amount of C 24 Te is slightly higher with C 24 Te/C 23 TT varying in a range of 1.25–1.42 (average 1.36) in the A1 oil family compared to that in the A2 oil family (0.48–0.8; average = 0.65; Table 3 ) and A3 oil family (0.30–0.71; average = 0.44; Table 3 ).…”

Section: Resultsmentioning

confidence: 99%

“…The extended tricyclic ratio (ETR) has the ratio of 0.25–0.29 (average = 0.27), 0.26–0.34 (average = 0.31), and 0.34–0.48 (average = 0.43) in the A1, A2, and A3 oil families, respectively. It implies that their source rocks are derived from the freshwater environment because the ETR is widely used for an effective indicator of salinity. , C 24 tetracyclic terpane/C 23 tricyclic (C 24 Te/C 23 TT) is also an index for terrestrial OM. , The amount of C 24 Te is slightly higher with C 24 Te/C 23 TT varying in a range of 1.25–1.42 (average 1.36) in the A1 oil family compared to that in the A2 oil family (0.48–0.8; average = 0.65; Table ) and A3 oil family (0.30–0.71; average = 0.44; Table ). It is consistent with the results from the TAR, suggesting a larger input of terrigenous OM to the source rocks of the A1 oil family than those of A2 and A3 oil families.…”

Section: Resultsmentioning

confidence: 99%

“…ETR) has the ratio of 0.25−0.29 (average = 0.27), 0.26−0.34 (average = 0.31), and 0.34−0.48 (average = 0.43) in the A1, A2, and A3 oil families, respectively. It implies that their source rocks are derived from the freshwater environment because the ETR is widely used for an effective indicator of salinity 40,41. C 24 tetracyclic terpane/C 23 tricyclic (C 24 Te/C 23 TT) is also an index for terrestrial OM 42,43.…”

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confidence: 99%

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Geochemical Characteristics of Three Oil Families and Their Possible Source Rocks in the Sub-Sag A of Weixinan Depression, Beibuwan Basin, Offshore South China Sea

Lin

Hou

et al. 2022

ACS Omega

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Three oil families from the sub-sag A of the Weixinan Depression are identified by integrated analysis of physical properties, stable carbon isotopes, and gas chromatography–mass spectrometry (GC–MS). Their similarities and differences in relative thermal maturities, depositional environments, and biological sources of organic matter (OM) are investigated. A possible oil–source correlation of this area is established. Group A1 oils, defined as low-maturity oils, are characterized by high density and high viscosity. They contain more terrigenous OM deposited in a freshwater environment with unstratified water columns reflected by a relatively high terrestrial/aquatic ratio and Pr/Ph values, low abundance of C 30 4-methlysteranes, and low δ 13 C values. They are derived from the upper hydrocarbon supply combination. Group A2 oils are characterized by moderate density and viscosity and medium stable carbon isotope values. This group of oils has lower terrestrial/aquatic ratios and Pr/Ph values and a medium concentration of C 30 4-methlysteranes and δ 13 C values, suggesting that the oils are derived from the shales which have more contribution from the algal input and are formed in a weakly oxidizing environment. They are a mixture generated from the source rocks in the middle and lower hydrocarbon supply combination. Groups A3 oils, defined as light oils, have low density and viscosity. The geochemical data of the A3 oils, including a less-negative stable carbon isotope, high abundance of C 30 4-methylsteranes, low Pr/Ph values, and highest Ts/(Ts + Tm) ratios (Ts represents C 27 18α(H)-22,29,30-trisnorneohopane and Tm represents C 27 17α(H)-22,29,30-trisnorhopane), suggest that they are generated from the source rocks deposited in a subanoxic environment with the large input of dinoflagellates. The A3 oils are generated from the shales from the lower hydrocarbon supply combination. The oil–source correlation results can be further supported by the distribution of faults and structural ridge as the migration channel of petroleum developed around the sub-sag A.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Geochemical Characteristics of Three Oil Families and Their Possible Source Rocks in the Sub-Sag A of Weixinan Depression, Beibuwan Basin, Offshore South China Sea

Lin

Hou

et al. 2022

ACS Omega

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“…44,56−58 As a result, ratios of C 27 /C 29 regular steranes are a reliable biomarker indicator for evaluating the relative contributions of terrestrial and aquatic organic matter. 38,56 Medium ratios of C 27 /C 29 regular steranes (0.94−1.38, average: 1.08; Table 4) elucidate that Longtan Formation shales were dominated by a mixed source of aquatic and terrestrial organic matter as indicated by the ternary diagram of C 27 −C 28 −C 29 regular steranes (Figure 9). Furthermore, the high abundance of tricyclic terpanes relative to tetracyclic terpanes, represented by relatively low C 24 -tetracyclic/C 23 -tricyclic ratios (C 24 Te/C 23 T; Table 3), is assigned to a high contribution of aquatic organic matter.…”

Section: Organic Matter Sourcesmentioning

confidence: 92%

“…The relative distribution of n-alkanes and their δ 13 C values are commonly used to determine the sources of organic matter. 26,38,44 Typically, the short-chain n-alkanes (<nC 21 ) mainly originated from bacteria and algae, 26,38,47,48 while the long-chain n-alkanes (>nC 25 ) are predominantly derived from higher plants on land. 48,49 The nalkane patterns of the target samples display scattered carbon distributions (e.g., unimodal, bimodal, and multimodal) with the carbon peak in the range of nC 15 −nC 24 (Figure 4).…”

Section: Organic Matter Sourcesmentioning

confidence: 99%

Organic Geochemical Characteristics and Organic Matter Enrichment of the Upper Permian Longtan Formation Black Shale in Southern Anhui Province, South China

et al. 2023

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Although previous studies have yielded valuable insights into shale gas reservoirs, a comprehensive understanding of the organic geochemical characteristics and organic matter enrichment of marine–continental transitional shale has yet to be achieved. The Longtan Formation transitional shales were extensively deposited in Southern Anhui Province, South China, during the Late Permian. Our analysis of twenty-two rock samples from one core (Gangdi-1 well) and two outcrops (Daoshanchong outcrop and Changqiao outcrop) revealed that the Longtan Formation shale extracts exhibit a wide range of C11–C35 n-alkanes and acyclic isoprenoids, with unimodal, bimodal, and multimodal distributions. The carbon peak ranges from nC15 to nC24, with high quantities of medium-chain n-alkanes (nC22–nC25), indicating that the organic matter in Longtan Formation shale originates from a mixed source of higher plant debris and lower aquatic organisms. Our conclusion is supported by the ternary diagram of C27–C28–C29 regular steranes and the variations of the δ13C values of C15–C32 n-alkanes, which is higher than the corresponding value (<1.6‰) of n-alkanes from a single source. Furthermore, thermal maturity proxies based on organic petrography (R o and T max) and biomarkers, such as the ratios of C31 22S/(22S + 22R), C29 20S/(20S + 20R), and C29 ββ/(αα + ββ), suggest that organic matter is in a mature stage of hydrocarbon generation. By analyzing the Pr/Ph ratio and pyrite morphology combined with a plot of total organic carbon (TOC) versus total sulfur (TS) and the Pr/nC17–Ph/nC18 diagram, we speculate that the Longtan Formation shales were chiefly developed in a dysoxic-to-oxic water environment. Finally, we establish depositional models of organic matter enrichment in deltaic and tidal flat-lagoon environments, emphasizing that the abundant mixed-sourced organic matter can significantly enhance primary productivity, and a higher sedimentation rate can distinctly shorten organic matter exposure time in the oxidized water environment, thereby promoting organic matter accumulation in such a setting.

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Application of biomarkers in characterization of organic matter source, maturity and palaeoredox condition of black shales from the upper Permian Dalong Formation in Southern Anhui Province, South China

et al. 2023

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The organic‐rich shale in the upper Permian Dalong Formation in Southern Anhui Province is not only regarded as a high‐quality hydrocarbon source rock, but one of the potential targets for shale oil and gas exploration in Southern China. Organic matter types in such a setting remain a subject of debate. The major point of controversy is whether they are dominated by oil‐prone types or gas‐prone types. A total of 20 rock samples collected from Gangdi‐1 well were conducted for analysis of organic geochemistry. Results show that Dalong Formation shale extracts exhibit a wide range of C12‐C35 n‐alkanes and acyclic isoprenoids. The chromatograms display an unimodal distribution with carbon peak in the range of nC18‐nC22 and low quantities of long‐chain (nC25+) n‐alkanes. Relatively high ratios of nC21‐/nC22+ and C27/C29 regular steranes demonstrate that organic matter is mainly originated from lower aquatic organisms and followed by higher plants in a local area. This is also supported by the variations of the δ13C values of C13‐C26 n‐alkanes for the target samples being in the range of 3.0‰–5.6‰ offset, which is slightly higher than the corresponding value (1.6‰) of n‐alkanes from a single source. All these pieces of information decipher that the organic matter in Dalong Formation shale may be dominated by type I and followed by type II1. Moreover, the maturity proxies according to both organic petrography (Ro and Tmax) and biomarkers such as ratios of C29 20 S/(20 S + 20R) and C29 ββ/(αα + ββ) together indicate that organic matter in Dalong Formation shale is in a mature stage of hydrocarbon generation. Furthermore, a cross‐plot of total organic carbon versus total sulphur as well as Pr/Ph ratio and Pr/nC17‐Ph/nC18 diagram elucidates that Dalong Formation shales were mainly formed in a marine reducing environment. Finally, two depositional models of organic matter enrichment are proposed. The abundant lower aquatic organisms with few terrestrial detrital inputs and the reducing water environment together promote organic matter accumulation.

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Organic geochemical characteristics and organic matter enrichment of mudstones in an Eocene saline lake, Qianjiang Depression, Hubei Province, China

Cited by 30 publications

References 71 publications

Geochemical Characteristics of Three Oil Families and Their Possible Source Rocks in the Sub-Sag A of Weixinan Depression, Beibuwan Basin, Offshore South China Sea

Geochemical Characteristics of Three Oil Families and Their Possible Source Rocks in the Sub-Sag A of Weixinan Depression, Beibuwan Basin, Offshore South China Sea

Organic Geochemical Characteristics and Organic Matter Enrichment of the Upper Permian Longtan Formation Black Shale in Southern Anhui Province, South China

Application of biomarkers in characterization of organic matter source, maturity and palaeoredox condition of black shales from the upper Permian Dalong Formation in Southern Anhui Province, South China

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