Kirks Breccia: a late cretaceous submarine channelised debris flow deposit, Raukumara Peninsula, New Zealand

Abstract

Kirks Breccia constitutes an unusually coarse-grained basal member of the Whangai Formation (late Campanian-Danian: Haumurian-Teurian) at Kirks Clearing, western Raukumara Peninsula. It infills a channel cut into older Cretaceous shelf sediments, and is overlain by mudstone deposited in a shelf to upper slope environment.

Composition, texture, geometry and overall setting of the breccia suggest it is the product of cohesive debris flows generated on the shelf by retrogressive slumping associated with a growing fold. Such deposits indicate local instability at a time when new Zealand as a whole is considered to have been relatively stable tectonically.

Keywords:

• Kirks Breccia
• debris flow
• cross-shelf channel
• breccia
• conglomerate
• Late Cretaceous
• Whangai Formation
• Raukumara Peninsula