The lacustrine Chang 7 organic‐rich shale of the Upper Triassic Yanchang Formation is a very important hydrocarbon source rock and contains high total organic carbon content (average = 5.54 wt.%). Previous studies suggest that deposits of the Chang 7 accumulated slowly under dominantly oxic–suboxic bottom‐water conditions occasionally interrupted by the establishment of anoxic conditions. However, questions remain regarding the role of palaeoproductivity in accumulation of the Chang 7 organic matter. Palaeoproductivity indicators, including P/Al, Ni/Al, Cu/Al, and Zn/Al, suggest that the deposition of the Chang 7 period was accompanied by high primary productivity level. Furthermore, productivity appears to have been highest in the middle and south‐east region of the lake, diminishing to the north‐east, the north‐west, and the south‐west. Elevated productivity resulted in the flux of large amounts of organic matter to the lake floor. Intermittent anoxic bottom‐water conditions caused by oxygen consumption during organic matter degradation favoured enhanced preservation of organic matter even under oxic–suboxic water column. Low sedimentation rate made the organic matter in sediments avoid dilution of terrigenous clastics, which made it play a positive role in the accumulation of organic matter.

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The Chang 7 black shale in the Upper Triassic Yanchang Formation is the principal source rock of Mesozoic oil-bearing system in the southwest Ordos Basin, containing high abundances of organic matter and hydrocarbon potential. Our study discusses the role of lake-bottom hydrothermal activities in the enrichment of organic matter during the deposition of the Chang 7 black shale. A large number of basement faults developed in the interior and margin of the Ordos Basin, which provided channels for the upwelling of deep hydrothermal fluids. Moreover, the strong tectonic activities during the Chang 7 sedimentary period provided dynamic conditions for the activation of the faults and the upwelling of hydrothermal fluids. The occurrence of hydrothermal activities in the Chang 7 sedimentary period is proved by the evidences of mineralogy petrology, stable isotopes, major, and trace elements in the black shale. Abundant nutrients that were transported from the lake-bottom hydrothermal fluids into lake water promoted the lacustrine surface primary productivity, and then increased the supply of sedimentary organic matter. At the same time, the degradation of a large number of organic matters increased consumption of oxygen in the water column, resulting in the formation of bottom-water anoxic environments. The accumulation of organic matter in sediments was controlled by the lake-bottom hydrothermal activities by the means of increasing the lacustrine surface paleoproductivity and promoting the formation of anoxic environments.