Analysing of palaeoenvironment and organic matter enrichment: A case study from the Triassic Yanchang Formation in the southern Ordos Basin, China
Analysing of palaeoenvironment and organic matter enrichment: A case study from the Triassic Yanchang Formation in the southern Ordos Basin, China
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DOI：
10.1002/gj.4889
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发表时间：
2023-09
影响因子：
1.8
通讯作者：
R. Yang;Yang Li;Faqi He;Xuepeng Wu
中科院分区：
文献类型：
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作者：
R. Yang;Yang Li;Faqi He;Xuepeng Wu
鄂尔多斯盆地南缘广泛分布着中晚三叠世延长组长7油段（简称长7段）富有机质页岩。了解长7段沉积时期的古环境条件，对于探索控制优质烃源岩中有机质富集的主要因素至关重要。对鄂尔多斯盆地南部N36井进行了岩相分析，并采集了样品。通过元素地球化学分析恢复了古环境，并通过总有机碳（TOC）测试分析了有机质的富集特征。研究结果表明，长7段沉积时期为相对温暖湿润的古气候和贫氧或亚富氧的微咸水环境，古水深逐渐减小。母岩类型主要为长英质火成岩和中质火成岩，为初级生产者提供的营养元素有限。长7段有机质的富集受到多种因素的影响，主要包括古盐度、古水深、古氧化还原条件、陆地输入和古气候。温暖湿润的古气候、较高的古生产力、相对较高的古盐度、较低的陆源输入、较深的古水深和较好的保存条件有利于长7段优质烃源岩的发育。
The organic‐rich shale of the seventh Oil Member (Chang 7 Member for short) of the Middle‐Late Triassic Yanchang Formation is extensively distributed in the southern margin of the Ordos Basin. Understanding the palaeoenvironmental conditions during the sedimentary period of the Chang 7 Member is crucial to exploring the main factors that control the enrichment of organic matter in high‐quality source rocks. In this study, lithofacies analysis was conducted, and samples were collected from the N36 well located in the southern part of the Ordos Basin. Subsequently, element geochemical analysis was performed to reconstruct the palaeoenvironment, and total organic carbon (TOC) tests were conducted to analyse the characteristics of organic matter enrichment. The findings indicate that the sedimentary period of the Chang 7 Member was characterized by a relatively warm and humid palaeo‐climate and a brackish water environment with oxygen‐poor or sub‐oxygen‐rich conditions, and a gradual decrease in palaeo‐water depth. The parent rock types were mainly felsic igneous rock and intermediate igneous rock, which provide limited nutritional elements for primary producers. The enrichment of organic matter in the Chang 7 Member is influenced by several factors, mainly including palaeo‐salinity, palaeo‐water depth, palaeo‐redox conditions, terrestrial inputs, and palaeo‐climate. The warm and humid palaeo‐climate, higher palaeo‐productivity, relatively higher palaeo‐salinity, lower terrigenous input, deeper palaeo‐water depth, and better preservation conditions are conducive to the development of high‐quality source rock in the Chang 7 Member.