The organic matter-rich mudstones of the Middle Jurassic Dameigou Formation in the northern Qaidam Basin are regarded as the principal petroleum source rocks for unconventional resource exploration in China. In this study, a detailed investigation on the organic petrography, inorganic geochemistry as well as bulk and molecular organic geochemistry is presented. Three different source rock units were identified with TOC contents and VR_r ranging from 1.5–39.2% and 0.35–0.57%, respectively. Carbonaceous mudstone and organic matter-rich mudstone in unit 1 with high Pr/Ph (4.79–7.25) and low Gam index (0.02–0.03) values mainly developed in an oxic freshwater column under warm and humid climatic conditions and strong weathering intensity. Organic matter in unit 1 with high proportions of C₂₉ ααα 20R steranes (61–74%) is interpreted to be derived from terrestrial higher plants. By contrast, units 2 (Pr/Ph: 2.56–4.23; Gam index: 0.03–0.14) and 3 (Pr/Ph: 0.73; Gam index: 0.48) were deposited in sub-oxic to oxic freshwater and anoxic saline environments, respectively. Progressive aridification during the deposition of units 2 and 3 are reflected by decreasing CIA values (59.97–86.68) resulting in weakened weathering intensity and lower terrestrial influx. A mixture of terrestrial higher plants and algal biomass was the main source of organic matter in unit 2 with moderate C₁₉/C₂₃ Tri (0.96–5.44), C₂₀/C₂₃ Tri (1.28–3.87) and C₂₄ Tet/C₂₆ Tri (1.10–2.54) ratios, while unit 3 with the lowest C₁₉/C₂₃ Tri (0.25), C₂₀/C₂₃ Tri (0.95), and C₂₄ Tet/C₂₆ Tri (0.65) ratios and highest proportions of C₂₇ ααα 20R steranes (69%) is characterized by a decrease in terrigenous organic matter content. The dominant source of organic matter is lake plankton, including halophilic algae and cyanobacteria. Organic matter accumulation in unit 1 is associated with a warm and humid climate, weathering intensity, and terrigenous organic matter input. Primary productivity is the most important factor controlling the enrichment of organic matter in units 2 and 3.

柴达木盆地北部中侏罗统大梅沟组富含有机质的泥岩被认为是我国非常规资源勘探的主要石油烃源岩。在这项研究中，对有机岩相学、无机地球化学以及本体和分子有机地球化学进行了详细研究。确定了三个不同的烃源岩单元，其 TOC 含量和 VR _r分别为 1.5-39.2% 和 0.35-0.57%。1单元碳质泥岩和富含有机质泥岩，Pr/Ph值高（4.79~7.25），Gam指数值低（0.02~0.03），主要发育在暖湿气候条件下、风化强度强的好氧淡水柱中。_{单元 1 中含有高比例 C 29}的有机物ααα 20R 甾烷（61-74%）被解释为来源于陆生高等植物。相比之下，单元 2（Pr/Ph：2.56–4.23；Gam 指数：0.03–0.14）和 3（Pr/Ph：0.73；Gam 指数：0.48）分别沉积在低氧到有氧淡水和缺氧盐水环境中. 单元 2 和 3 沉积过程中的渐进干旱化表现为 CIA 值降低（59.97-86.68），导致风化强度减弱和陆地流入量减少。陆地高等植物和藻类生物质的混合物是单元 2 有机质的主要来源，中等 C ₁₉ /C ₂₃ Tri (0.96–5.44)、C ₂₀ /C ₂₃ Tri (1.28–3.87) 和 C ₂₄ Tet/C ₂₆Tri (1.10–2.54) 比率，而单元 3 具有最低的 C ₁₉ /C ₂₃ Tri (0.25)、C ₂₀ /C ₂₃ Tri (0.95) 和 C ₂₄ Tet/C ₂₆ Tri (0.65) 比率和最高的C ₂₇ ααα 20R 甾烷（69%）的特点是陆源有机物含量降低。有机物的主要来源是湖泊浮游生物，包括嗜盐藻类和蓝藻。单元 1 的有机质积累与温暖潮湿的气候、风化强度和陆源有机质输入有关。初级生产力是控制 2 号和 3 号机组有机质富集的最重要因素。