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By optical microscopy and SEM-energy spectrometry, some phenomena that relate to lake-bottom hydrothermal activities, such as the presence of siliceous rocks, ankerite laminar deposits, evidence for marcasite brassil anhydrite symbiosis systems and authigenetic albite filling in early diagenetic fractures, have been discovered in the Chang 7 high-quality source beds of the Yanchang Formation, Ordos Basin. Various geochemical data of the Chang 7 high-quality source rocks testify further to the existence of lake-bottom hydrothermal activities, and they include abnormally abundant S2- content (on average 7.37%), Mo, Cu, U and Mn positive anomalies, high ratios of U to Th, the positive carbon isotope composition of crystalline ankerite (δ13C from 2.88 to 3.03‰), depleted oxygen isotope composition (δ18O PDB from −16.41 to −16.17‰), the enrichment of microelements like Cu and Mn, and isotopically enriched in 34S sulfur isotope compositions of strawberry-shaped pyrite (δ34S CDT from 2.37 to 5.90‰). In the early sedimentary period of the Chang 7, the activation of floor ruptures by violent regional structural activities was a dynamic factor that produced lake-bottom hydrothermal activities. The hydrothermal activities played an important role in accelerating the extensive development of the Chang 7 high-quality source rocks. 摘 要: 光学显微镜和扫描电子显微镜-能谱仪观测在鄂尔多斯盆地延长组长7优质烃源层中发现了硅质岩、铁白云石纹层沉积、白铁矿-黄铁矿-硬石膏共生体系、早期成岩缝中的自生钠长石充填作用等可能与湖底热水活动有关的现象。能进一步佐证同期湖底热水活动存在的证据还有：长7优质烃源岩中异常高的二价硫含量（平均7.37%），Mo、Cu、U、Mn等微量元素的显著正异常特征，高的U/Th值，微晶铁白云石纹层偏重的碳同位素组成（2.88‰～3.03‰)、偏轻的氧同位素组成（－16.41‰～－16.17‰）和富集Cu、Mn等微量元素的特征，莓状黄铁矿偏正的硫同位素组成（2.37‰～5.90‰）特征等。长7段沉积期始，强烈的区域构造活动对基底断裂的激活作用是产生湖底热水活动的动力学因素，湖底热水活动对长7优质烃源岩的大规模发育具有重要的促进作用。图6表1参14 Key words: lake-basin expansion, lake-bottom hydrothermal activity, high-quality source rock, Late Triassic, Ordos Basin