A spectacular, dense network of cataclastic faults characterizes the Late Cretaceous Ngatuturi Claystone, a massive and mechanically almost isotropic siliceous mudstone. It is part of a Cretaceous to late Oligocene shelf sequence deposited NE of New Zealand that was translated SW in the late Oligocene with the Northland Allochthon in an obduction event associated with southward propagation of a new convergent plate boundary. The allochthon was reactivated in the Miocene, forming the southward-moving substrate of the Waitemata piggyback basin. The cataclasites are submillimeter- to several centimeters–thick black seams that were formed without contemporaneous open tensile fractures, because any fault asperities...