The formation is a sedimentary unit, consisting mainly of fluvial sands and silts.

It was inundated by Phanerozoic seas during the periods of maximum sea level, and subsequent erosion removed these sedimentary units.

The mineralizing fluids are conducted upwards within sedimentary units toward basin-bounding faults.

All the aforementioned sedimentary units can be covered by colluvial gravels of Pleistocene age.

The overall structure of the field is a faulted homocline, with all the sedimentary units dipping in the same direction with little folding.

Many sedimentary units underlie these petroleum-bearing sands, but they either have not produced much oil or have not been completely explored.

The Grafton Formation is the sedimentary unit in the core of the basin.

Under the surface alluvium, a series relatively impermeable sedimentary units cap the petroleum-bearing formation.

It is a sedimentary unit, principally made up of mudstone and siltstone, with calcareous concretions.

It is also a major reason for the thickening of sedimentary units towards the centre of basins.