Abstract
The Tarim Basin harbors abundant deep to ultra-deep hydrocarbon resources, yet detailed oil-source correlation remains to be further investigated. As a potential key source rock, the organic geochemical characteristics of the Yuertus Formation (Є(1)y) warrant additional research. This study integrates biomarker, carbon, and sulfur isotope data from Є(1)y source rocks in existing wells and outcrops across the eastern, northern, and northwestern Tarim Basin to better constrain the distribution, hydrocarbon generation potential, biomarker features, and oil-source relations of Є(1)y. Results reveal that Є(1)y exhibits diverse lithofacies, including calcareous mudstones, siliceous shales, and shales as potential source rocks. The calcareous mudstone shows the highest total organic carbon (TOC) content (up to 29.8%), characterized by Type II kerogens and mature to over-mature thermal maturity. Stable biomarkers including triaromatic steroids (TAS), triaromatic dinoflagellate steroids (TDSI), and aryl isoprenoids (1-alkyl-2,3,6-trimethylbenzenes, ATMBs) reveal significant differences among the three lithological types of source rocks: Calcareous mudstones exhibit biomarker distribution patterns similar to those of classical Ordovician source rocks (C(26)R + C(27)S TAS < C(28)S TAS, TDSI < 0.6), while simultaneously containing high abundances of ATMBs characteristic of the Є(1)y. Siliceous rocks display typical Cambrian characteristics with low C(28) TAS, high TDSI, but absence of ATMBs. Shales present typical Cambrian features with low C(28) TAS, high TDSI, and low ATMBs. Oil-source correlation based on n-alkane' carbon and sulfur isotopes suggests that calcareous shales are likely one of the primary sources for currently explored oils. These findings enrich the fundamental understanding of deep and ultra-deep hydrocarbon exploration in the Tarim Basin and provide new insights into the reassessment of oil-source relations.