Petrographic and isotopic evidence for diagenetic processes in Middle Jurassic sandstones and mudrocks from the Brae Area, North Sea

The diagenetic history of an interbedded sequence of Middle Jurassic Sleipner (or Pentland), Hugin and Heather Formation sandstones and mudrocks from the Brae Area has been investigated using petrographic, stable isotope, fluid inclusion and K-Ar dating techniques. Generally, similar diagenetic processes affected both the mudrocks and sandstones resulting in the formation of carbonate, quartz and clay cements and evidence of dissolution and secondary porosity except for the absence of kaolinite in the Hugin Formation. The mudrocks were possible sources of some components involved in sandstone diagenesis but were not passive exporters of such reactants as similar reactions also occurred in the mudrocks. The stable isotope data indicate that most of the diagenetic processes occurred in the presence of marine or evolved marine pore-waters.