Biostratigraphic evidence for the Manganui Fault, near Awakino, southwest Auckland

Abstract

New biostratigraphic evidence confirms the existence of a major fault, the Manganui Fault, within Triassic-Jurassic Murihiku Supergroup rocks in the Manganui Valley, between Awakino and Paparahia (southwest Auckland Province, North Island). The Manganui Fault is interpreted as a steeply dipping fault with a minimum apparent vertical throw of c. 5500 m. There is some indirect evidence to suggest possible strike-slip activity. Timing of the last major fault movement is inferred to be pre-Oligocene.

The Manganui Fault is significant because of its age, magnitude and regional context. It is considered to be a segment of a much more continuous feature, the Taharoa Fault, along which there are significant mid-Cenozoic andesitic volcanics. Several magnetic anomalies along the line of the Manganui Fault may represent buried volcanics of comparable composition and relationship.

Keywords:

• biostratigraphy
• palynology
• macrojlora
• macrofauna
• Upper Triassic
• Lower Jurassic
• Manganui Fault
• Taharoa Fault
• Murihiku Supergroup
• Rangitata Orogeny
• tectonics