Extensional basin development and subsequent inversion in Greymouth Coalfield

Abstract

The validity of the history of basin development in the east of Greymouth Coalfield, as broadly accepted for the past 60 years, is examined through reinterpretation of the structure and stratigraphy. Rather than a Late Cretaceous–Paleocene fault-angle basin (extensional half-graben) west from the Mount Davy Fault Zone, a downwarping basin extended across the location of that future fault zone. This basin developed within regionally extensive deposition of Late Cretaceous sediments. Uplift and erosion in the east was followed by the development of an Eocene fault-angle basin extending from the Montgomerie Fault west across the developing Mount Davy Fault Zone. A thick Miocene sequence accumulated in the Grey Valley Trough to the east, and a thinner sequence is inferred to have covered the whole coalfield. Inversion in the coalfield, rather than being intermittent throughout the whole Palaeogene, began c. 4.5 Ma ago with development of the Brunner Anticline and reversal of movement on both the Mount Davy Fault Zone and the Montgomerie Fault.

Keywords:

• basin development
• Brunner Anticline
• Greymouth Coalfield
• inversion
• structure
• Mawhera Basins
• Montgomerie Fault
• Mount Davy Fault Zone

Acknowledgements

Simon Nathan and Steve Edbrooke (GNS Science) provided valuable comments on an early version of the manuscript. The comments of referees are gratefully acknowledged. Carolyn Hume (GNS Science) drew the figures.