Petrologic and geochemical evidence for the formation of organic-rich siliceous rocks of the Late Permian Dalong Formation, Lower Yangtze region, southern China

Liao, Zhiwei; Hu, Wenxuan; Cao, Jian; Wang, Xiaolin; Hu, Zhongya

doi:10.1016/j.marpetgeo.2019.02.005

Cited by 26 publications

(30 citation statements)

References 79 publications

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“…The Southern Anhui Province, with an area of about 1.0 Â 10 4 km 2 , is tectonically located within the Lower Yangtze area and a prospective and target area for shale oil and gas exploration and exploitation in Southern China (Ding et al, 2021;Du et al, 2015;Liao et al, 2019).…”

Section: Geologic Settingmentioning

confidence: 99%

“…Organic‐rich shales are extensively developed in Southern China, particularly in the Yangtze platform (Dang et al, 2022; Nie et al, 2019; Sun et al, 2021; Tan et al, 2014; Zhang et al, 2004; Zou et al, 2019). These black rock strata incorporate various metallic deposits (Liao et al, 2019) and may also act as multiple roles of source, reservoir and cap rock of shale oil and gas reservoirs (Du et al, 2015; Nie et al, 2019; Zhang et al, 2004; Zou et al, 2019). The Southern Anhui Province lies in the core areas of the Yangtze River Economic Belt in Southern China and has a high‐speed economic development, but its energy resources are seriously deficient.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Geologic Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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“…To elucidate the relationship between hydrothermal activity and accumulation of organic matter, we propose the following concept. The process of submarine volcanic hydrothermal activity is associated with abundant nutrients such as Mo, Pb, Ni, Zn, Ba, Sb, and P (Liu et al, 2019b;Liao et al, 2019;Li et al, 2020;Shen et al, 2022). In this case, the solubility of these elements rapidly increases with increasing water temperature.…”

Section: Hydrothermal Influencementioning

confidence: 99%

Characteristics and controlling factors of the Upper Permian Dalong Formation in northwestern Sichuan Basin, China

Wang

Guan²,

Wang³

et al. 2023

Front. Earth Sci.

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It has been generally accepted that the Permian shale is an important target for shale oil and gas exploration. In order to precisely predict the distribution of potential excellent source rocks of shale oil and gas, it is necessary to reveal the forming process and mechanism of high-quality source rocks, such as the Dalong Formation in the Scihuan Basin. In this study, 17 samples were collected from the Dalong Formation in Longfeng Quarry, Northwest Guangyuan City, Sichuan Province. The lithofacies, organic geochemistry, and pyrolysis of these samples were analyzed to evaluate the main factors controllingthe source rock formation. In particular, the influences of hydrothermal and paleoenvironmental conditions on the accumulation of organic matter were analyzed. The total organic carbon (TOC) content of the samples, which ranges from 0.05% to 12.21%, is closely related to the lithology. High TOC has been generally observed in rock intervals developed in a deep-water sedimentary environment, including siliceous rock, dark shale, and siliceous shale. The peak pyrolysis temperature of the samples ranges from 444°C to 462°C, indicating a mature stage. Thin-section observation, combined with the results of previous studies, has confirmed that the source of the organic matter is mainly marine phytoplankton, such as algae and radiolarians, ostracods, and other marine organisms, which consist of these high-quality source rocks. The ratio of trace elements, such as Ni/Co, V/Cr, U/Th, and V/(V + Ni) indicate that high-quality source rocks are mainly formed in anoxic restricted environments. The hydrothermal activity of submarine volcanoes provided many nutrients and compounds, resulting biological prosperity and improving primary productivity. This is simultaneously conducive to the formation of anoxic environments and the preservation of organic matter.

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“…Barium (Ba) is always associated with biological metabolism and can be used to represent organic matter input [105,106]. Aluminium (Al) and titanium (Ti) are primarily of detrital origin, therefore P/Ti and Ba/Al are generally considered effective indicators of productivity by eliminating the impact of terrigenous debris [28,107].…”

Section: Productivitymentioning

confidence: 99%

Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China

et al. 2023

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The Permian Lucaogou Formation in the Junggar Basin, NW China is the target layer for shale oil exploration, but its hydrocarbon precursors have remained the focus of debate. In this study, we investigated the Lucaogou source rocks throughout Well J10025 by conducting detailed petrological, paleontological, and geochemical analyses for the purpose of revealing the occurrence of cyanobacterial blooms as specific hydrocarbon events in the upper Lucaogou Formation. The morphological characteristics of the microfossils and the geochemical signatures of the microfossil-bearing layers support a biological affinity with Microcystis, a kind of cyanobacteria. Microcystis observed as colonial forms embedded in the upper Lucaogou Formation are of great abundance, indicating the presence of cyanobacterial blooms. They were further evidenced by cyanobacteria-derived biomarkers including low terrestrial/aquatic ratio, high 2α-methylhopane index values, and high abundance of 7- and 8-monomethyl heptadecanes. The blooms occurred in a semiarid and brackish paleoenvironment with anoxic to suboxic water conditions and intermittent volcanic eruptions. Permian Microcystis blooms contributed to the enrichment of organic matter in the upper Lucaogou Formation in two main ways: by directly promoting the accumulation of algal biomass and by creating an oxygen-depleted environment for better preservation of organic matter. This study adds a new record to the geological occurrences of cyanobacterial blooms in the Permian, and provides unique insight into the hydrocarbon generation of Jimsar shale oil in the Junggar Basin.

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Petrologic and geochemical evidence for the formation of organic-rich siliceous rocks of the Late Permian Dalong Formation, Lower Yangtze region, southern China

Cited by 26 publications

References 79 publications

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

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

Characteristics and controlling factors of the Upper Permian Dalong Formation in northwestern Sichuan Basin, China

Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China

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