中—晚三叠世气候变化对鄂尔多斯盆地东南地区延长组7段烃源岩有机质富集的影响机制OA

[Objective]The middle to late Triassic was a period of critical climatic transition in Earth's history.Multiple global humid climate events during this time profoundly impacted both marine and terrestrial depositional environments,facilitating the development of marine and continental source rocks.[Methods]This study focuses on the hydrocarbon source rocks of the seventh member of the Yanchang Formation(Chang 7 Member)in the southeastern Ordos Basin.Based on integrated elemental geochemical and molecular organic geochemical analyses,this study explores the relationship between middle to late Triassic humid climatic events and organic matter enrichment in lacustrine settings.[Results]The lower to middle interval of Submember 3 of Chang 7 Member(695–660 m in depth)is characterized by high total organic carbon content and good hydrocarbon generation potential.Chemical weathering indices indicate that this interval was deposited underwarmer and more humid climatic conditions,while the overlying upper portion of Submember 3 and Submembers 2 and 1 were deposited under cooler and drier conditions.By combining global characteristics of middle to late Triassic humid events with palynostratigraphy,zircon U–Pb geochronology,and carbon isotope stratigraphy,this study links the lower to middle interval of the Submember 3 and the middle to late Triassic Ladinian–Carnian humid climate event.[Conclusions]The findings suggest that,under the influence of humid climate events,enhanced terrestrial nutrient influxes stimulated primary productivity in the lake.Concurrently,intensified water column stratification and bottom-water anoxia created favorable conditions for organic matter preservation,leading to the deposition of high-quality source rocks.Following the event,the climate shifted towards colder and drier conditions.This reduced terrestrial input,decreased primary lake productivity,lowered oxygen depletion in the water,and led to less favorable conditions for organic matter preservation and enrichment.[Significance]This study not only provides new evidence for paleoclimatic and paleoenvironmental reconstruction during the middle to late Triassic but also offers an important reference for understanding organic matter enrichment mechanisms during major climatic transitions in Earth's history.