Luminescence chronology of loess-paleosol sequences from southern South Island, New Zealand

Abstract

The loess-paleosol sequences in New Zealand are among the thickest in the southern hemisphere, and preserve an important terrestrial record of paleoclimatic changes. Unlike loess-paleosol sequences in North Island, most of those in South Island lack discrete chronostratigraphic marker ash beds, excepting perhaps the widespread ∼24 ka Kawakawa Tephra. Therefore, any specific correlation to marine isotope stage (MIS) proxy records or to loess-paleosol sequences in the northern hemisphere has been unknown. Hence, we applied luminescence sediment dating to four key loess-paleosol sequences from southern South Island. Although these pioneering results suggest that further sampling and luminescence dating are needed, they do provide: (1) the first numeric age constraint (44±3 ka on overlying loess) for the end of deposition of the geomorphically and paleoclimatically important Edendale Terrace gravels; (2) the first numeric evidence that the youngest loess-paleosol unit (L1) at the near-coastal Romahapa and inland Stewarts Claim sites began to be preserved much earlier (at ∼60 ka) than at the inland Kingston Crossing site (∼35 ka); (3) the first direct evidence that the 6 m Romahapa sequence extends at least to ∼350 ka, the oldest yet TL-dated such sequence in South Island. Furthermore, the stratigraphically self-consistent (with one exception) luminescence ages between ∼60 and ∼350 ka conflict with a previous indirect chronostratigraphy inferred from trace concentrations of glass shards. This trace-shard chronology implies a major hiatus in loess-paleosol preservation (missing at least MIS 6–7) not recognized by luminescence dating.