Early discordant diagenesis in the Brent Group, Murchison Field, UK North Sea, detected in high values of seismic-derived acoustic impedance

Acoustic impedance inversion of seismic data in the Murchison Field, UK North Sea has revealed a zone of high acoustic impedance within the Rannoch Formation of the Brent Group which is discordant to stratigraphy. The high values of acoustic impedance are caused by the diagenetic growth of siderite and pyrite early in the burial history of the rocks, probably while semi-consolidated at a depth of less than 1000 ft. The zone is approximately parallel to the overlying Base Cretaceous unconformity and its formation may have been controlled by a temperature gradient and/or groundwater chemical boundary that was parallel to ground surface at that time.