About its late Whaingaroan (about 27 million years ago) creation, it says, “The change from estuarine, shallow brackish water conditions (Mangakotuku Formation), to fully marine, open sea, aerobic conditions (Glen Massey Formation) is evidenced by near shore accumulation of the bioclastic Elgood Limestone, onlap of the succeeding Dunphail Siltstone, and subsequent deposition of Ahirau Sandstone in an inner to mid shelf environment.”