Clay mineralogy of lithofacies of northland allochthon rocks, north island, new zealand

Northland Allochthon, a bathyal depth sediments, comprises an originally fining-upwards passive margin wedge which accumulated adjacent to northeastern New Zealand between mid-Cretaceous and latest Oligocene. The Northland Allochthon is overlain by Miocene arc and arc-basin deposits. This paper provides clay mineralogy and its transformation of different lithofacies of the Northland Allochthon rocks of North Island, New Zealand to understand the processes of precipitation during deposition and diagenesis of these rocks and possible later effects associated with obduction and re-burial of these rocks. The clay mineral sequence observed in the study area is from smectite to illite through illite/smectite interstratified mixed-layered clays. X-Ray diffractometry and Scanning Electron Microscopy of mixed-layer illite/smectite (I/S) clay from sandstone and shale shows a progressive increase in illite layers with increasing age. (author)