Rocks belonging to a turbidite facies of the Lower Miocene Waitemata Group are exposed extensively about Whangaparaoa Peninsula. Interbedded with this sequence are a number of thick, distinctive, volcaniclastic grits believed to have been emplaced by submarine lahars. These sediments accumulated towards the axial parts of a marine basin within a continental borderland. The turbidites were deposited by predominantly south-east - flowing currents. Directions of weak bottom (traction) currents were more variable. Deformation and contortion of strata occur on a grand scale and are attributed to the penecontemporaneous slumping of poorly consolidated sediments in response to tilting of the sea floor. Injection of clastic dikes accompanied later stages of movement in slumped sequences. Evidence suggests that one great slump sheet extends over a distance of at least 10 miles from near Red Beach in the west to Whangaparaoa Head and possibly Tiritiri Matangi in the east.