Abstract The Amazon Fan provides a natural laboratory to study the generation of overpressure, due to rapid late Cenozoic burial that has resulted in gravitational collapse above shale detachments. Here we examine collapse systems for the first time using the techniques of petroleum systems analysis. We propose an integrated methodology based on numerical modeling constrained by the structural restoration of a seismic profile across the southwestern fan. The results provide information on the evolution of pore pressure and temperature and their implications for the operation of the detachment and overlying extensional and compressional faults during the deposition of up to 6 km of sediment over the last 8 Ma. The modelled thermal history implies that fluid release by smectite-to-illite transformation has taken place within the thickening sedimentary succession, but has not significantly contributed to pore pressures along the detachment. Modeling of hydrocarbon generation and migration from source rocks beneath the fan indicates gas accumulated in successions at depths of 102–103 m beneath the detachment without influencing pore pressures along it. In contrast, model results indicate that overpressures have varied in response to disequilibrium compaction. Fault activity within the collapse system took place during phases of higher sedimentation rates, and ceased from 5.5 to 3.7 Ma when sediment supply to the SE fan decreased. From 2 Ma, renewed sediment flux and shelf-slope progradation led to a basinward migration both of overpressure along the detachment and of fault activity above it. We conclude that gravity tectonics in the Amazon Fan over the last 8 Ma have been mainly controlled by overpressures due to disequilibrium compaction, with secondary contributions from clay mineral transformation. Present-day pressure conditions show that the southeastern Amazon Fan is not at equilibrium and gravity driven deformation could occur at any time.

中文翻译：

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亚马逊深海扇重力坍塌过程中超压演化的控制

摘要 亚马逊扇提供了一个天然实验室来研究超压的产生，这是由于晚新生代快速埋藏导致页岩拆离上方的重力坍塌。在这里，我们首次使用石油系统分析技术检查坍塌系统。我们提出了一种基于数值建模的综合方法，该方法受西南扇地震剖面结构恢复的约束。结果提供了有关孔隙压力和温度演变的信息，以及它们对过去 8 Ma 中长达 6 公里沉积物沉积过程中分离和上覆伸展和挤压断层的作用的影响。模拟的热历史表明，在增厚的沉积层序中发生了由蒙脱石到伊利石转变的流体释放，但并未对沿拆离的孔隙压力产生显着影响。扇下烃源岩生烃和运移的模拟表明，气体在拆离下 102-103 m 深度连续聚集，但不影响沿拆离的孔隙压力。相比之下，模型结果表明超压随着不平衡压实而变化。坍塌系统内的断层活动发生在较高沉积速率阶段，并在 SE 扇的沉积物供应减少时从 5.5 Ma 停止到 3.7 Ma。从 2 马，新的沉积物通量和陆架坡进积导致沿拆离层的超压及其上方的断层活动向盆地迁移。我们得出的结论是，过去 8 Ma 亚马逊扇的重力构造主要受不平衡压实引起的超压控制，次要来自粘土矿物转化。目前的压力条件表明，亚马逊扇东南部处于非平衡状态，重力驱动变形随时可能发生。