二连盆地腾格尔坳陷烃源岩类型与热演化及其对油气生成的影响OA

[Objective]The Erlian Basin,located in the eastern segment of the Central Asian Orogenic Belt,occupies a unique tectonic position.Since the Mesozoic,it has undergone multiple phases of tectonic activity with intense later-stage modification.Mesozoic source rocks,as critical targets for oil and gas exploration,exhibit geochemical characteristics and thermal evolution histories that are central to assessing hydrocarbon potential and exploration prospects.However,insufficient research on the development features and thermal evolution of Mesozoic source rocks has led to significant discrepancies in understanding their exploration potential,thereby constraining hydrocarbon exploration progress in these strata.[Methods]This study focuses on the Tengger Depression in the southeastern Erlian Basin,systematically revealing the coupling relationships among source rock geochemical characteristics,thermal evolution history,and hydrocarbon accumulation.[Results]Key findings include:① Distinctive features of major source rock intervals were clarified:The Tengger I Member and the Aershan Formation have mudstone thicknesses of 432~933 m.The Tengger I Member(average TOC:0.98%,type Ⅱ1-Ⅱ2 kerogen)represents immature to mature source rocks(Ro:0.48%~0.93%),while the Aershan Formation(average TOC:0.80%,type Ⅱ2-Ⅲ kerogen)comprises low-maturity to mature source rocks(Ro:0.74%~1.16%).② Effective source rock TOC thresholds(0.55%~1.5%)were determined for key sags,with variations controlled by organic matter type,thermal maturity,and depositional microfacies.③ Post-Late Cretaceous erosion thicknesses(1071–1637.8 m)and paleogeothermal gradients(30.6~71.9℃/km,significantly higher than present-day values of 24.8~50℃/km)were quantified.Four thermal anomaly zones were identified:the Chuanjian Depression,the Tengger Depression–Wenduermiao Uplift transition zone,the southwestern Sunite Uplift,and the northeastern basin.These zones exhibit strong spatial correlation with Cenozoic volcanic rock distributions.④ A"two-phase burial history"(early subsidence with uplift,followed by intense late-stage uplift)was reconstructed.Source rock thermal evolution displays distinct stratigraphic heterogeneity and progressive maturation:The Aershan Formation experienced"early maturation and generation,"peaking in the Late Cretaceous,whereas the Tengger Formation exhibits"layered maturation,"with its base entering the hydrocarbon window earlier.[Conclusions]This thermal regime was governed by the Early Cretaceous high geothermal field.Subsequent regional uplift terminated burial processes,stabilizing source rock maturity.This tectono-thermal evolution exerts dual controls on hydrocarbon accumulation:The Early Cretaceous high heat flow accelerated hydrocarbon generation,while later uplift favored preservation and trap finalization.The study provides critical theoretical support for Mesozoic hydrocarbon exploration in the Erlian Basin and adjacent regions.