Multi-method dating comparison for mid-pleistocene Rangitawa Tephra, New Zealand

Abstract

The Rangitawa Tephra, a widespread mid-Pleistocene marker in the New Zealand region, is dated by fission-track, thermoluminescence (TL), infrared stimulated luminescence (IRSL), K Ar and single crystal laser fusion (SCLF) 40 Ar 39 Ar methods, as well as by matching to the astronomical timescale via oxygen isotope stratigraphy in deep sea cores. Fifty one independent numerical age estimates for Rangitawa Tephra range from 173 to 456 ka. However, only 15 of these results are considered to be reliable: five zircon fission-track results, four isothermal plateau fission-track (ITPFT) age estimates on glass shards, four SCLF 40 Ar 39 Ar results, and two astronomically calibrated age estimates from deep sea cores. The weighted mean of the nine reliable fission-track age determinations is 345 ± 12 ka, in excellent agreement with the weighted mean of 340 ± 7 ka for the two reliable astronomically calibrated age estimates. The weighted mean of the four reliable 40 Ar 39 Ar results (302 ± 8 ka) is significantly younger, and further Ar Ar dating is recommended to investigate this difference. Since the TL and IRSL dating methods are experimental for sediments beyond 200 ka, we have excluded these from the group of reliable age results. TL and IRSL results on dunesand appear to be systematically younger than TL results on loess, and loess results depend upon analytical procedures.