Abstract: The development mechanism of source rocks of the early Cambrian Yuertusi Formation is one of the key points of deep oil and gas exploration in the Tarim Basin. The completion of ultra-deep drilling of pre-Cambrian strata in the basin in recent years provides an ideal window for the study of the development mechanism of Cambrian source rocks in the basin. In order to investigate the sedimentary environment and paleo-productivity during the deposition of source rocks and clarify the enrichment mechanism of organic matter, a systematic analysis of TOC, major and trace elements and carbon and oxygen isotopes was carried out in a typical well of the Tabei area. The results show that the lower part of the Yuertusi Formation was in anoxic-sulfuration environment with high primary productivity. In comparison, the upper section was formed in the oxygen-poor sedimentary environment, and the productivity was gradually weakened to a low productivity level. Carbon and oxygen isotopes indicate that the lower member of the Yuertusi Formation was deposited under the background of extensive transgression with upwelling. The coupling of upwelling currents and mild hydrothermal activities provides abundant nutrients for the bloom of primary productivity during this period, and the enrichment of organic matter was mainly controlled by high productivity and good preservation conditions. There was basically no hydrothermal activities in the upper member of the Yuertusi Formation when it was deposited, the productivity level gradually decreased, and the reductibility of the water body also began to weaken, which was manifested in the low productivity level and the depositional environment of the upper system domain in the upper member, and eventually resulted in the low abundance of organic matter.

Key words: depositional environment, productivity, hydrothermal activity, Yuertusi Formation, Tarim Basin