Abstract The Middle Permian Lucaogou Formation in the Santanghu Basin (northwest China) develops one of the thickest salinized lacustrine organic-rich shale (SLORS) in the world. The SLORS has been proven as sources for crude oil and tight oil, as well as sources and reservoirs for shale oil in the basin. A total of 52 SLORS samples were collected from the second member of Lucaogou Formation (P2l2), and analyzed by mineralogy and element geochemistry, in order to reveal the paleoenvironment, provenance, tectonic setting and shale oil potential. The results imply an evolution of paleoenvironment from anoxic, saline to dysoxic-oxic, freshwater lake, which is caused by an increased freshwater influx. Early in the P2l2, volcanic ash and hydrothermal fluids have increased the nutrient level in the lake and therefore elevated the bioproductivity. The P2l2 SLORS is originated from intermediate volcanic rocks, accompanied by minor proportions of basic volcanic rocks. The parent rocks of P2l2 SLORS have experienced weak degree of chemical weathering, and probably derived from a continental island arc setting. Micro-, nano-pores (inter-grain pores, inter-crystalline pores, dissolution pores and organic matter pores) and microfractures are widely observed in the P2l2 SLORS, which provides sufficient storage space for hydrocarbons. The P2l2 SLORS is dominated by carbonate minerals, quartz and feldspar, which are all brittle minerals and favourable for artificial fracturing. Comprehensive study indicates that the upper P2l2 SLORS hosts a better shale oil potential, due to the relatively high TOC, abundant micropores and microfractures, and high brittle mineral contents. In addition, individual element geochemical parameters in the Santanghu Basin should be used with caution, for example, the paleoredox proxy U/Th and paleosalinity proxy Sr/Ba are also influenced by volcanic and hydrothermal activity. This implies that a multi-proxy analysis should be applied during the study of paleoenvironmental conditions.

中文翻译：

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中二叠统三塘湖盆地盐化湖相富有机质页岩矿物学和元素地球化学：对古环境、物源、构造背景和页岩油潜力的启示

摘要 三塘湖盆地中二叠统芦草沟组发育世界上最厚的盐化湖相富有机质页岩（SLORS）之一。SLORS已被证明是盆地内原油和致密油的来源，以及页岩油的来源和储集层。采集芦草沟组二段（P2l2）52个SLORS样品，进行矿物学和元素地球化学分析，揭示古环境、物源、构造背景和页岩油潜力。结果表明古环境从缺氧的咸水湖演变为缺氧的淡水湖，这是由淡水流入增加引起的。在 P2l2 早期，火山灰和热液增加了湖中的营养水平，从而提高了生物生产力。P2l2 SLORS 起源于中度火山岩，伴有少量基性火山岩。P2l2 SLORS 的母岩经历了微弱的化学风化作用，可能来源于大陆岛弧环境。P2l2 SLORS 中广泛观察到微、纳米孔（粒间孔、晶间孔、溶蚀孔和有机质孔）和微裂缝，为油气提供了充足的储存空间。P2l2 SLORS 以碳酸盐矿物、石英和长石为主，均为脆性矿物，有利于人工压裂。综合研究表明，上层P2l2 SLORS具有较好的页岩油潜力，其TOC相对较高，微孔微裂缝丰富，脆性矿物含量高。此外，三塘湖盆地的单个元素地球化学参数应谨慎使用，例如古氧化还原代表U/Th和古盐度代表Sr/Ba也受火山和热液活动的影响。这意味着在研究古环境条件期间应应用多代理分析。