Speleothem dates, Quaternary terraces and uplift rates in New Zealand

Abstract

Previous isotopic research on calcite stalagmites, stalactites and flowstones (speleothems) from New Zealand caves has focused on palaeotemperature reconstruction1,2. I report here the use of 230Th/234U and 14C age data from speleothems to investigate the relationships between cave levels, emerged coastal terraces and uplift rates. In the north-west of the South Island of New Zealand, at least seven terraces, provisionally assigned to various stages in the Quaternary, are known to occur to at least 200m above sea level3,4. The terraces sometimes cut across limestones which contain caves formed in association with past sea levels. Uplift, followed by water table lowering and abandonment of cave passages by active streams, permitted speleothem deposition. Dating of these deposits gives a minimum age for the cave level and hence also for any terrace to which it may be related, while successive dates at different levels yield an uplift rate for the area. Data are presented from two localities, which suggest differential emergence rates of 0.27+0.28 −0.09 mm yr−1 and 0.14+0.05 −0.03 mm yr−1. Thus re-evaluation is required of other largely qualitative evidence on the uplift of these parts of the Southern Alps5.