1. Department of Geology, University of Otago, 360 Leith Walk, Post Office Box 56, Dunedin, Otago 9016, New Zealand.
2. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK.
3. Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University, MS 5F1, Fairfax, VA 22030, USA.