Discovery of the lower Cambrian high-quality source rocks and deep oil and gas exploration potential in the Tarim Basin, China

Zhu, Guangyou; Chen, Feiran; Wang, Meng; Zhang, Zhiyao; Ren, Ruizhi; Wu, Lin

doi:10.1306/03141817183

Cited by 76 publications

(45 citation statements)

References 112 publications

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“…The Cambrian-Lower Ordovician strata were interpreted to be the main source rocks using a detailed oilsource correlation [15]. This finding is supported by recent exploration advances of ultradeep Lower-Middle Cambrian reservoirs in the basin [31][32][33].…”

Section: Geological Backgroundmentioning

confidence: 58%

Identification and Implications of Trimethyl-n-Alkylbenzenes in Marine Oils from the Deep Tarim Basin

et al. 2020

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The source of marine oils from the deep Tarim Basin is still in debate due to several alteration processes of source indicators. A series of trimethyl-alkylbenzenes has been detected in marine oils from this old, composite basin, besides the reported aryl isoprenoids with 2,3,6-trimethyl substitution (AIPs). They are characterized by regular gas chromatography elution pattern, which is similar to that of n-alkylbenzenes, and suggest a strong possibility of n-alkyl side chains. C15 trimethyl-n-alkylbenzenes were synthesized by Friedel–Crafts acylation of trimethylbenzene isomers to determine their structures. Based on the chromatography and mass spectra data and the coinjection of synthesized compounds, this series of compounds has been assigned as the 2,4,5-trimethyl-n-alkylbenzenes that coeluted with 2,3,5-trimethyl-n-alkylbenzenes, and other trimethyl-n-alkylbenzene isomers were also detected. This series of trimethyl-n-alkylbenzene (AAs) shows much higher relative abundances in light and waxy oils than in normal and heavy oils, which is opposite to the variation in relative abundances of aryl isoprenoids. The ratios of these trimethyl-n-alkylbenzenes to the aryl isoprenoids (AA/AIP ratio) generally show a good correlation with the maturity indicators for most of studied oils despite of some outliers (mainly condensates). The pyrolysis of asphaltenes has confirmed these trends. These results support an important control of thermal stress on the molecular compositions of marine oils from the deep Tarim Basin, besides other secondary alteration processes (such as oil mixing and migration fractionation, among others). These factors should be given a full consideration for the source determination of deep and ultradeep oils.

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Section: Geological Backgroundmentioning

confidence: 58%

Identification and Implications of Trimethyl-n-Alkylbenzenes in Marine Oils from the Deep Tarim Basin

et al. 2020

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“…The Cambrian strata in the Arksu region, western Tarim Block, consist of, in ascending order, the Yurtus (YF), Xiaoerblak (XF), Wusongger (WF), Shayilike (SF), Awatage (AF), and Qiulitage (QF) formations. The Yurtus Formation unconformably overlies the Ediacaran Qigeblak Formation and conformably underlies the Xiaoerblak Formation (Figure 1) (He et al, 2010(He et al, , 2018Zhu et al, 2018). The basal Yurtus Formation is restricted to the Tommotian (equivalent to Stage 2 of Terreneuvian Series in the Geological Time Scale) by the appearances of Asteridium-Heliosphaeridium-Comasphaeridium acritarch assemblage (Yao et al, 2005;Dong et al, 2009).…”

Section: Geological Backgroundmentioning

confidence: 97%

Quantifying the Seawater Sulfate Concentration in the Cambrian Ocean

Zhu

Huang

et al. 2021

Front. Earth Sci.

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Although the earliest animals might have evolved in certain “sweet spots” in the last 10 million years of Ediacaran (550–541 Ma), the Cambrian explosion requires sufficiently high levels of oxygen (O2) in the atmosphere and diverse habitable niches in the substantively oxygenated seafloor. However, previous studies indicate that the marine redox landscape was temporally oscillatory and spatially heterogeneous, suggesting the decoupling of atmospheric oxygenation and oceanic oxidation. The seawater sulfate concentration is controlled by both the atmospheric O2 level and the marine redox condition, with sulfide oxidation in continents as the major source, and sulfate reduction and pyrite burial as the major sink of seawater sulfate. It is thus important to quantify the sulfate concentration on the eve of the Cambrian explosion. In this study, we measured the pyrite contents and pyrite sulfur isotopes of black shale samples from the Yurtus Formation (Cambrian Series 2) in the Tarim Block, northwestern China. A numerical model is developed to calculate the seawater sulfate concentration using the pyrite content and pyrite sulfur isotope data. We first calibrate some key parameters based on observations from modern marine sediments. Then, the Monte Carlo simulation is applied to reduce the uncertainty raised by loosely confined parameters. Based on the geochemical data from both Tarim and Yangtze blocks, the modeling results indicate the seawater sulfate concentration of 8.9–14 mM, suggesting the seawater sulfate concentration was already 30–50% of the present level (28 mM). High seawater sulfate concentration might be attributed to the enhanced terrestrial sulfate input and widespread ocean oxygenation on the eve of the Cambrian explosion.

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“…It turned into an evaporitic platform during the late stages of the Early Cambrian and the Middle Cambrian. The platform area is positioned in today's western part of the Tarim desert and the basin area in the eastern region of Tarim [21]. There are three large-scale paleouplifts and four paleodepressions separated by them in the Tarim Basin (Figure 1a).…”

Section: Geological Settingmentioning

confidence: 99%

“…The middle part consists of phosphorites with thin layers of micritic dolomites. The upper part is composed of black carbonaceous shales, and thin interbeds of shales and argillaceous dolomites [21,32]. The thickness of the overlying Xiaoerbrak Fm.…”

Section: Geological Settingmentioning

confidence: 99%

Paleoenvironment of the Lower–Middle Cambrian Evaporite Series in the Tarim Basin and Its Impact on the Organic Matter Enrichment of Shallow Water Source Rocks

et al. 2021

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Just as in deep-water sedimentary environments, productive source rocks can be developed in an evaporitic platform, where claystones are interbedded with evaporites and carbonates. However, the impact of the paleoenvironment on the organic matter enrichment of shallow water source rocks in an evaporite series has not been well explored. In this study, two wells in the central uplift of the Tarim Basin were systematically sampled and analyzed for a basic geochemical study, including major elements, trace elements, and total organic carbon (TOC), to understand the relationship between TOC and the paleoenvironmental parameters, such as paleosalinity, redox, paleoclimate, paleo-seawater depth, and paleoproductivity. The results show that the Lower–Middle Cambrian mainly developed in a fluctuating salinity, weak anoxic to anoxic, continuous dry and hot, and proper shallow water environment. The interfingering section of evaporites, carbonates, and claystones of the Awatag Fm. have higher paleoproductivity and higher enrichment of organic matter. Paleosalinity, redox, paleoclimate, paleo-seawater depth, and paleoproductivity jointly control the organic matter enrichment of shallow water source rocks in the evaporite series. The degree of enrichment of organic matter in shallow water source rocks first increases and then decreases with the increase in paleosalinity. All the samples with high content of organic matter come from the shallower environment of the Awatag Fm.

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Discovery of the lower Cambrian high-quality source rocks and deep oil and gas exploration potential in the Tarim Basin, China

Cited by 76 publications

References 112 publications

Identification and Implications of Trimethyl-n-Alkylbenzenes in Marine Oils from the Deep Tarim Basin

Identification and Implications of Trimethyl-n-Alkylbenzenes in Marine Oils from the Deep Tarim Basin

Quantifying the Seawater Sulfate Concentration in the Cambrian Ocean

Paleoenvironment of the Lower–Middle Cambrian Evaporite Series in the Tarim Basin and Its Impact on the Organic Matter Enrichment of Shallow Water Source Rocks

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