Fluid inclusion evidence for extreme overpressure induced by gas generation in sedimentary basins

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