Shiling Shi, Changan Shan, Ze Zhao, Yue Fei, Jiaqi Zhang
The Paleogene-Neogene lacustrine source rocks in the Mangai area of the Qaidam Basin are significant exploration targets. A comprehensive evaluation of four major intervals (E$_3^2$, N$_1$, N$_2^1$, N$_2^2$) was conducted through systematic organic geochemistry, maceral identification, thermal maturity analysis, and burial-thermal history modeling. Results show TOC contents of 0.203~1.28% (avg. 0.74%), chloroform bitumen "A" of 0.0164~0.2495% (avg. 0.132%), and total hydrocarbon contents of 69.29~1637.48 $\mu$g/g (avg. 853.39 $\mu$g/g), indicating fair to good quality. Kerogen elemental analysis (H/C=0.97~1.21), maceral composition (sapropelinite+exinite=70~98%), and saturated hydrocarbon chromatography (dominant peaks at C17, C19, C21, C23) collectively indicate predominantly Type II$_1$ organic matter, with locally developed Type I. Thermal evolution exhibits distinct vertical zonation controlled by Neogene tectonic-thermal events: an immature-low maturity zone (R$_0$<0.7%) dominated by soluble organic matter degradation; a mature zone (R$_0$=0.7~1.0%) with active kerogen cracking (HC/TOC up to 224.95%); and a high maturity zone (R$_0$>1.0%) characterized by gas generation via cracking. The saline to semi-saline reducing environment favored organic matter preservation, while mixed algal-terrestrial inputs (Type II$_1$) determined mainly oil-prone characteristics. The thick succession in the central depression, especially the Kaitemilike-Fenghuangtai region, shows the highest hydrocarbon potential. The mature zone (R$_0$=0.7~1.0%) is optimal for conventional oil exploration, while the high maturity zone (R$_0$>1.0%) holds promise for natural gas. This multi-parameter study deepens the understanding of hydrocarbon generation mechanisms and provides an important case for evaluating Paleogene-Neogene lacustrine source rocks in the northern Tibetan Plateau.