The marine, Castlecliffian sedimentation in Central Hawke's Bay is limited to an area between Napier Hill and Black Reef, the fossiliferous sediments having reached a thickness of at least 1,200 ft. The deposition of these sediments has been typically paralic, and indicates that terrestrial and marine conditions alternated in the basin. The downward movement in the basin must have been the result of rather fierce tectonic disturbances, which are now attributed to the southward movements of the New Zealand Overthrust. As the overthrust progressed such stretching developed, that the area between Napier and Cape Kidnappers was literally torn apart. The faulted depression that thus formed was filled with sediments to form the Castlecliffian sequence.