A re-assessment and calibration of redox thresholds in the Permian Lucaogou Formation of the Malang Sag, Santanghu Basin, Northwest China

Pan, Yongshuai; Huang, Zhilong; Guo, Xingwei; Wang, Rui; Lash, Gary G.; Fan, Tanguang; Liu, Wenhui

doi:10.1016/j.marpetgeo.2021.105406

Cited by 12 publications

(6 citation statements)

References 29 publications

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“…The Corg/P value of the Dongyuemiao shale ranges from 12.5 to 142.7 (average = 54.6), indicating significant fluctuations in the redox conditions and a transition from oxic to anoxic environments. This discrepancy with the results obtained from the ratios and content of redox-sensitive elements suggests that using fixed criteria for evaluating redox conditions based on geochemical proxies may have limitations [49]. Considering multiple geochemical proxies, we conclude that the Dongyuemiao shale in the study area was primarily deposited in an oxic sedimentary environment.…”

Section: Redox Conditionscontrasting

confidence: 78%

“…The differing solubilities of BaSO4 and SrSO4 render the Sr/Ba ratio a valuable indicator of paleo-salinity. Wei and Algeo [49] suggest the Sr/Ba ratios less than 0.2, 0.2 to 0.5, and greater than 0.5 reflect freshwater, brackish water, and marine salinities, respectively. However, it is essential to note that the accuracy of the Sr/Ba ratio as a salinity proxy may be compromised in samples containing over 4% CaO.…”

Section: Salinity Conditionmentioning

confidence: 99%

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Geological Features, Paleosedimentary Environment, and Organic Matter Accumulation Mechanisms of the Lacustrine Shale Oil System: A Case Study of the Jurassic Dongyuemiao Member in the Sichuan Basin

Wang,

Li,

Guo

et al. 2023

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Lacustrine shale has garnered significant attention due to its significant resource potential. The Jurassic shale in the Sichuan Basin is an important target for lacustrine shale exploration in China. However, previous studies have predominantly focused on the Da’anzhai member of the Ziliujing Formation, and little attention has been paid to the shale of other strata. This paper aims to address this gap by investigating the Jurassic Dongyuemiao member in the Sichuan Basin. The study systematically characterizes the geological properties of the Dongyuemiao shale system, reconstructs the paleosedimentary environment, identifies the key factors influencing organic matter (OM) enrichment and physical properties, and assesses its resource potential through comparative analysis. Our results show that the Dongyuemiao shale was deposited in an oxic and semi-humid sedimentary environment characterized by intense weathering conditions. The enrichment of OM in the shale is primarily controlled by redox conditions and salinity, with redox conditions playing the most crucial role in OM accumulation. In terms of pore system characterization, clay mineral-associated pores dominate the pore types in the Dongyuemiao shale, while two types of organic matter-associated pores are also widely observed. The development of framework grain-associated pores is limited and only present in certain siliceous and carbonate minerals. The shales of the Dongyuemiao member and the Da’anzhai member exhibit slight differences in TOC content. However, the kerogen in the Dongyuemiao member displays higher hydrocarbon generation potential, and the Dongyuemiao shale exhibits more favorable pore structure parameters. Overall, the Dongyuemiao shale does not exhibit any significant disadvantages compared to the Da’anzhai shale. Therefore, it deserves greater attention in future exploration endeavors. The research findings presented in this paper provide a solid theoretical foundation for expanding the exploration scope of lacustrine shale in the Sichuan Basin.

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Section: Redox Conditionscontrasting

confidence: 78%

Section: Salinity Conditionmentioning

confidence: 99%

Geological Features, Paleosedimentary Environment, and Organic Matter Accumulation Mechanisms of the Lacustrine Shale Oil System: A Case Study of the Jurassic Dongyuemiao Member in the Sichuan Basin

Wang,

Li,

Guo

et al. 2023

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“…Consequently, the ratios of V/Cr, V/(V + Ni), V/Al, and Mo/Al increase with decreasing water oxidation degree [57][58][59]64]. Previous studies have proposed thresholds for quantitatively classifying redox conditions based on these indicators, although there is no consensus on the applicability of these thresholds in nonmarine environments [22,58,63,65]. In this study, the redox indicators of the samples fall within a range between oxic and anoxic conditions (Figure 6), signifying that the Ha'erjiawu Formation was predominantly deposited in dysoxic environments, which is consistent with reducing depositional settings inferred from thinly laminated black shales and widespread occurrence of framboidal pyrite [26].…”

Section: Paleoenvironmental Conditionsmentioning

confidence: 99%

Paleoenvironmental Conditions and Shale Oil Potential of the Carboniferous Ha’erjiawu Formation in the Santanghu Basin, NW China

Zhang

Liu

Fan³

et al. 2023

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The Carboniferous Ha’erjiawu Formation in the Santanghu Basin represents a significant potential target for shale oil exploration, yet its characteristics remain largely unknown. This study utilizes a combination of elemental and organic geochemical analyses to investigate the paleoenvironmental conditions and shale oil potential of the Carboniferous Ha’erjiawu Formation black shales within the Santanghu Basin. The results suggest that the Ha’erjiawu Formation black shales were deposited in water columns with low salinity and dysoxic conditions, as indicated by paleosalinity and redox proxies such as Rb/K, B/Ga, B content, V/Cr, V/(V + Ni), V/Al, and Mo/Al. Furthermore, the climatic proxies (Ga/Rb, Sr/Cu and K2O/Al2O3) indicate that the Santanghu Basin underwent a warm-humid/cold-dry oscillating climate during the deposition of the Ha’erjiawu Formation black shales, potentially influenced by synsedimentary volcanic activity or the Late Paleozoic glaciation. The organic geochemical analyses have revealed that the Ha’erjiawu Formation black shales are rich in type II kerogen, which is in the early mature to mature stage, indicating a significant potential for oil generation. However, there is considerable variation in the oil content of the analyzed samples, with only a few containing movable oil. Given the high abundance of brittle minerals within the Ha’erjiawu Formation black shales, it will be indispensable to meticulously evaluate and identify intervals exhibiting abundant movable oil for successful shale oil exploration and development within this geological unit.

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“…15 In addition, several redox proxies corresponding to redox thresholds calibrated solely by compound covariance in the correlation diagram do not have accurate values. Although this model has been recently utilized to calibrate the redox thresholds of a few lacustrine systems, 20 the abovementioned problems remain unresolved.…”

Section: Introductionmentioning

confidence: 99%

Threshold Calibration of Redox Conditions in Lacustrine Fine-Grained Sedimentary Rocks Based on the Internal Cross-Calibration of Multiple Redox Proxies: A Case Study of the Upper Triassic Chang 8–Chang 7 Members in the Southern Ordos Basin, China

Zhang

Xia

et al. 2022

ACS Earth Space Chem.

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Redox conditions of lacustrine strata assessed by redox proxies with unified thresholds were conflicted in the Ordos Basin. The internal cross-calibration approach of multiple redox proxies, based on the enrichment sequence model of authigenic redox-sensitive element (RSE) governed by redox potential, has recently been proposed to calibrate redox thresholds in marine depositional systems. However, this assessment model often induces an overlapped threshold between anoxic–ferruginous and anoxic–euxinic conditions. Except for the redox potential, the enrichment of RSE is also controlled by its host phase. Thus, we introduced the enrichment degree and occurrence state model controlled by the host phase content into this approach to identify anoxic–euxinic conditions by an enrichment threshold of Mo (or U). Based on this method including double redox assessment models, we calibrated the thresholds of various redox conditions of the Chang 8–Chang 7 Members in the southern Ordos Basin. Subsequently, the effectiveness of previous bi-element proxies, the evolution of redox conditions, and their influencing factors were analyzed based on the calibrated thresholds. Results show that this method is applicable in the lacustrine strata. The cross plot of DOPT (degree of pyritization based on the total Fe and S content) (or SEF)–MoEF (or UEF) (enrichment factor) is suggested for calibrating thresholds of different redox conditions. Previous bi-element proxies are not suggested to be used again. There is a positive redox evolution sequence from oxic–suboxic (suboxidized) to anoxic–euxinic conditions in Chang 8–Chang 7 Members. Hydrothermal activity and paleoproductivity play different roles in the formation of redox conditions.

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A re-assessment and calibration of redox thresholds in the Permian Lucaogou Formation of the Malang Sag, Santanghu Basin, Northwest China

Cited by 12 publications

References 29 publications

Geological Features, Paleosedimentary Environment, and Organic Matter Accumulation Mechanisms of the Lacustrine Shale Oil System: A Case Study of the Jurassic Dongyuemiao Member in the Sichuan Basin

Geological Features, Paleosedimentary Environment, and Organic Matter Accumulation Mechanisms of the Lacustrine Shale Oil System: A Case Study of the Jurassic Dongyuemiao Member in the Sichuan Basin

Paleoenvironmental Conditions and Shale Oil Potential of the Carboniferous Ha’erjiawu Formation in the Santanghu Basin, NW China

Threshold Calibration of Redox Conditions in Lacustrine Fine-Grained Sedimentary Rocks Based on the Internal Cross-Calibration of Multiple Redox Proxies: A Case Study of the Upper Triassic Chang 8–Chang 7 Members in the Southern Ordos Basin, China

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