The Main Seam in the Greymouth coalfield (Upper Cretaceous Paparoa Coal Measures) is exceptionally thick (>25m) and occurs in three locally thick pods, termed north, middle, and south. These pods are separated by areas of thin or absent (“barren”) coal. The barren zone between the north and middle coal pods is characterized by a sequence that is 60 m thick comprising relatively thin (1–2.5 m thick) but laterally extensive (up to 500 m) sandstone units. The orientation of both the thin and the barren coal zones is approximately east to west. This is coincident with basement fault systems that occur...