Geochemical Evidence of Organic Matter Enrichment and Depositional Dynamics in the Lower Cambrian Yurtus Formation, NW Tarim Basin: Insights into Hydrothermal Influence and Paleoproductivity Mechanisms

The lower Cambrian Yurtus Formation (&#1028:1y) in the Tarim Basin, characterized by its high organic matter content, serves as a critical source rock for oil and gas exploration in the platform basin. This study presents a high-resolution geochemical analysis of a geological section located near the Aksu Cement Plant in the northwest margin of the Tarim Basin. The focus is on elucidating the sedimentary environment, mechanisms of organic matter enrichment, and the depositional history of the &#1028:1y source rock. The &#1028:1y exhibits distinctive geochemical signatures, including elevated concentrations of Mo, Ba, and U, with an average rare earth element (REE) content of 155.75 &mu:g/g. The formation shows significant light REE enrichment (LREE/HREE = 1.74&ndash:5.57), a moderate Ce negative anomaly (&delta:Ce = 0.4&ndash:0.71), and a notable Eu positive anomaly (&delta:Eu = 0.94&ndash:2.14), indicative of a unique depositional environment influenced by hydrothermal processes. Geochemical evidence suggests that the &#1028:1y siliceous shales were deposited in a highly reducing, anoxic, and sulfide-rich environment, promoting organic matter preservation and enhancing sedimentary productivity. The presence of hydrothermal trace elements, likely introduced by hydrothermal fluids from volcanic activity along fractures and faults, played a critical role in enriching the sedimentary system, preserving organic matter, and boosting paleoproductivity. The model of organic matter enrichment proposed in this study underscores the dynamic interplay between hydrothermal influences and high primary productivity. These findings provide important insights into the formation of high-quality source rocks and have significant implications for the exploration of deep and ultra-deep oil and gas reserves in the Tarim Basin.