Evaluating source rock organofacies and paleodepositional environments using bulk rock compositional data and pristane/phytane ratios

Evenick, Jonathan C.

doi:10.1016/j.marpetgeo.2016.10.008

Cited by 32 publications

(5 citation statements)

References 25 publications

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“…The Pr/Ph ratio, a potential indicator of redox conditions of sediments, − has been widely utilized to infer oxidation or reduction of depositional environments and OM sources. According to previous studies on Pr/Ph values in China, − the Pr/Ph value <1.0 indicates a reducing environment in lacustrine or carbonate deposition, and a Pr/Ph of 1.0–3.0 indicates a transitional condition in the lacustrine or marine environment, and a Pr/Ph of >3.0 indicates an oxidizing condition in the terrigenous environment (river, swamp, or delta plain).…”

Section: Discussionmentioning

confidence: 99%

Characteristics of Source Rocks and Genetic Origins of Natural Gas in Deep Formations, Gudian Depression, Songliao Basin, NE China

Li³

et al. 2022

ACS Earth Space Chem.

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Numerous large gas fields with large proven reserves occur in the deep formations of Songliao Basin, NE China. However, some challenges remain as follows: (1) the main source rock is poorly studied and (2) the origins and genetic types of the natural gases are controversial. In this study, these problems can be addressed by the research of the paleoenvironments during shale deposition, the organic matter sources, the source rock potential, the gas origin and genetic type, and gas–source correlations. The redox conditions of the water column during the Huoshiling to Yingcheng depositions were transitional (suboxidizing to subreducing) environments, and the Huoshiling deposition corresponded to reducing conditions. The paleosalinity of water was brackish to fresh from Huoshiling to Yingcheng depositions. The organic matters of the Huoshiling–Yingcheng shales mainly originated from terrigenous and/or lacustrine materials. The shales are evaluated as the fair to good source rock potential, and the Huoshiling is the best. The gases in the Huoshiling and Shahezi were mainly organic and thermogenic origins, with some inorganic origins. The gases of organic origins are mainly the mixed sources of coal-derived and oil-associated gases and are predominant products of secondary cracking, suggesting the well gas exploration potential in deep formations of Songliao Basin. The gases in the Shahezi formation are predominantly sourced by the Shahezi shales, indicating an approaching-source accumulation.

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Section: Discussionmentioning

confidence: 99%

Characteristics of Source Rocks and Genetic Origins of Natural Gas in Deep Formations, Gudian Depression, Songliao Basin, NE China

Li³

et al. 2022

ACS Earth Space Chem.

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“…Due to the redox attributes of Pr and Ph shown above (Section ), the ratio of Pr to Ph can be served as an indicator of redox conditions for the sedimentary environment. ,, In general, ratios of <1.0, 1.0–3.0, and >3.0 can be interpreted as anoxic, suboxic, and oxic conditions, respectively . Compared with dark shale samples, Pr/Ph of oil shale samples is relatively low (Figure , Table ), showing more anoxic conditions.…”

Section: Discussionmentioning

confidence: 99%

Factors Controlling the Lower Radioactivity and Its Relation with Higher Organic Matter Content for Middle Jurassic Oil Shale in Yuqia Depression, Northern Qaidam Basin, China: Evidence from Organic and Inorganic Geochemistry

Guo

Chen

et al. 2021

ACS Omega

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Organic-rich oil shale with unusual lower radioactivity (expressed by GR) was found in Member 7 of Dameigou Formation, middle Jurassic (J 2 d 7 ) in Yuqia depression of northern Qaidam Basin, China. In order to systematically and contrastively investigate the factors controlling the lower GR and its relation with higher organic matter (OM) content (expressed by total organic carbon, abbr. TOC), organic and inorganic geochemical analyses were performed on samples consisting of oil shale and the underlying conformable contact dark shale from Well YQ-1Y. Our study shows that GR of J 2 d 7 oil shale is mainly derived from uranium and thorium. Compared with dark shale, oil shale is characterized by higher OY and TOC, lower GR, and clay mineral content. During oil shale deposition, the paleoclimate was relatively arid, indicated by a decreased C value and siderite content as well as an increased carbonate content and Classopollis. Under such paleoclimate conditions, sedimentary water became more anoxic, suggested by higher V/(V + Ni), pyrite content and lower pristane/phytane (Pr/Ph). From oil shale to dark shale deposition, according to analyses of Al 2 O 3 /TiO 2 , TiO 2 versus Zr, La/Sc versus Th/Co, La/Th versus Hf, and La−Th−Sc, the felsic igneous rock could always be deduced as the parent rock of provenance; however, the increasing arid paleoclimate resulted in weakened chemical weathering of provenance, inferred by relatively low chemical index of alteration, chemical index of weathering, and plagioclase index of alteration corresponding to the input degree of radioactive materials and other terrigenous detrital materials (TDMs), evidenced by Ti and Al contents and terrigenous (%). Meanwhile, the relatively high P/Ti and Ba/Al both indicated increased primary paleoproductivity. Together with the maximum flooding stage of oil shale deposition, the relatively low radioactivity tends to be associated with the inhibited input of clay minerals and radioactive materials, largely caused by increasing arid paleoclimate. The accompanying decreased TDM benefited primary paleoproductivity and anoxic conditions; their combined influence could induce sapropelic OM accumulation.

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“…Oil and condensates derived from organic matter rich in lakes, fluvial and deltaic sediments of Pr/Ph ratio is greater than 3 (Connan and Cassou 1980). Evenick (2016) compared the XRD results with the Pr/Ph ratios and suggest that Pr/Ph ratio is greater than 2.5, indicating terrestrial organic facies. Pr/Ph > 1 and high odd-even carbon dominance ratio (CPI > 1) indicate terrestrial components (Peters et al 2000).…”

Section: Gc Analysismentioning

confidence: 98%

Basic geochemical characteristics of lacustrine rocks in the Neogene Kağızman–Tuzluca Basin, Northeastern Turkey

Ayyıldız

Varol

Karakaş

et al. 2018

J Petrol Explor Prod Technol

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The Neogene Kağızman-Tuzluca Basin is located in the NE Anatolia and extends eastward into Armenia Oktemberian Basin. The Halıkışlak (Late Oligocene), Turabi and Tuzluca formations (Lower-Middle Miocene) are time equivalents of the organic-rich Oligo-Miocene Maikop Series in the Caspian region. However, depositional conditions within the KBT are appreciably different and source rocks are not as richer as it. The Halıkışlak Formation has little source rock potentials, with very low values of TOC (0.04-0.25%), HI (14-90 mg HC/TOC) and genetic potential-GP (i.e. Rock-Eval S 1 + S 2 = 0.05 to 0.22 mg HC/g rock). Although a peat facies sample has a relatively high TOC (6.78%), T max of 428 °C, HI values are very low (45 mg HC/TOC). TOC and GP values for the Tuzluca Formation are between 0.06 and 0.39 wt%, and 0.16-1.51 mg HC/g rock, respectively. Some levels of the Turabi Formation have TOC contents up to 6.14 wt%; however, mainly T max values are low 435 °C, and HI range from 25 to 54 mg HC/TOC. The extract of one low-maturity Turabi sample possesses biomarker distributions of an immature rock. Low relative abundance of tricyclic terpane and dominant C29 ααα (20R) are in accordance with the immature source rock. Some samples collected from the outcrops nearby Pliocene/Pleistocene lava series show localized maturation stage. We suggest that the Oligocene to Middle Miocene units could be more studied beneath the volcanic plateau.

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Evaluating source rock organofacies and paleodepositional environments using bulk rock compositional data and pristane/phytane ratios

Cited by 32 publications

References 25 publications

Characteristics of Source Rocks and Genetic Origins of Natural Gas in Deep Formations, Gudian Depression, Songliao Basin, NE China

Characteristics of Source Rocks and Genetic Origins of Natural Gas in Deep Formations, Gudian Depression, Songliao Basin, NE China

Factors Controlling the Lower Radioactivity and Its Relation with Higher Organic Matter Content for Middle Jurassic Oil Shale in Yuqia Depression, Northern Qaidam Basin, China: Evidence from Organic and Inorganic Geochemistry

Basic geochemical characteristics of lacustrine rocks in the Neogene Kağızman–Tuzluca Basin, Northeastern Turkey

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