New Zealand limestone purity

This permits, for the first time, a comparative assessment of the purity of onland New Zealand limestones by location and age. The three purest limestone populations have median CaCO 3 contents of 93–97 wt%, and are from: (1) Cambrian to Early Cretaceous basement terranes, (2) Eocene–Pliocene limestones of the Chatham Islands and (3) the Eocene Ototara Limestone.

These have CaCO 3 contents comparable with carbonates found in isolated submarine bank settings that lack appreciable siliciclastic detritus and biogenic silica. By contrast, New Zealand Oligocene–Early Miocene limestones (Whangarei, Te Kuiti, Mahurangi, Nile Group, Otekaike and Forest Hill stratigraphic units) have median CaCO 3 contents of 71–91 wt%, comparable with New Zealand Paleocene–Eocene and Middle Miocene–Pleistocene limestones.