Formation and preservation of extremely high-pressure fluid in sedimentary basins is critical to understanding petroleum accumulation and basin evolution; however, this issue remains poorly understood due to a lack of key evidence. We present fluid inclusion evidence from the Paleozoic black shales in the eastern Sichuan Basin (South China block) that suggest that gas generation can form methane-saturated fluids with pressures significantly exceeding the lithostatic pressure. The fluid inclusion internal pressure is so high (e.g., ~77 MPa) that gas hydrate formed at ambient temperature, aqueous-vapor homogenization could not be achieved under ambient pressure, and the homogenization pressure was beyond the scope of the current equation of state for the NaCl-H2O-CH4 system. We infer that the formation of high-pressure (e.g., >230 MPa), methane-saturated fluids induces hydrofracture under weak compressional tectonic regimes, where the excess lithostatic fluids can be accumulated and sustained. Fluid inclusion records with an abnormally high magnitude of overpressure indicate small differential stress and thus can serve as a microscale indicator for tectonic quiescence.

中文翻译：

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沉积盆地中气体生成引起的极端超压的流体包裹体证据

沉积盆地中极高压流体的形成和保存对于理解石油聚集和盆地演化至关重要；然而，由于缺乏关键证据，这个问题仍然知之甚少。我们提出了来自四川盆地东部（华南区块）古生界黑色页岩的流体包裹体证据，表明气体生成可以形成压力显着超过岩石静压的甲烷饱和流体。流体包裹体内压过高（如~77 MPa），常温下形成天然气水合物，常压下无法实现水-汽均质化，均质化压力超出当前状态方程的范围NaCl-H2O-CH4 系统。我们推断高压的形成（例如，>230 MPa），甲烷饱和流体在弱挤压构造状态下诱发水力压裂，其中过量的岩石流体可以积累和维持。具有异常高超压幅度的流体包裹体记录表明应力差很小，因此可以作为构造静止的微观指标。