Abstract
Loess is a patchy but widespread constituent of East and Central Otago (South Island, New Zealand), where it attests to extensive aerial mobilisation and deposition of fine-grained sediment. While most Otago loess deposits formed in the Pleistocene, we examine massive, fine-grained but clay-altered, Pliocene beds in Central Otago that may be loess deposits. These Pliocene beds have no obvious mineralogical, elemental abundance or isotopic (O–Sr–Nd–Pb) difference with Pleistocene loess deposits, and both types appear on the basis of REE abundances to be derived from the metamorphosed Otago greywacke terranes. Neodymium and Pb isotope ratios fingerprint the source as the Rakaia Terrane. Deposition is inferred to have resulted from the mobilisation of sediment from braided river systems and other bare ground areas in response to the Pliocene uplift of Otago greywacke and schist ranges and the onset of aridity in Central Otago as a result of the evolving Southern Alps rain shadow.