Optical luminescence dating of a loess section containing a critical tephra marker horizon, SW North Island of New Zealand

A new IRSL dataset is presented for the age and setting of a critical Late Glacial Maximum tephra isochron marker. The rhyolitic tephra, known as the Kawakawa Tephra, occurs as a 14 cm thick layer within a 5.9 m thick loess section overlying alluvial gravels in the Rangitikei River valley, SW North Island of New Zealand. Ages range from 21 at the base to 5 ka near the top of the loess and bracket an age of 17.0 ± 2.2 for the tephra. The new IRSL ages are in agreement with published and unpublished luminescence ages from other localities of loess, sand and ash above and below the tephra and of the tephra itself, that indicate an age of ca. 19 ka for the Kawakawa Tephra. This age is considerably younger than the generally accepted 14C 27.1 ka cal yrs BP age of the Kawakawa Tephra and highlights an unresolved discrepancy between the two dating systems.