Moa fossils and chronology of a Pleistocene terrace sequence, Tauweru, Wairarapa, New Zealand

Abstract

The fortuitous preservation of bones of the medium‐sized moa Euryapteryx geranoides (Owen) in Pleistocene colluvial sediments near Tauweru, Wairarapa, has allowed radiocarbon dating of a terrace sequence along the lower Tauweru River. The bones were in a shelly, conglomeratic sandstone on an erosion surface cut into mid‐Pliocene (Waipipian) siltstone, and were overlain by loess and situated immediately adjacent to onlapping fluvial gravels. Most of the bones are from a single skeleton buried articulated and apparently nearly complete, and there is also a single left tibiotarsus from a slightly larger bird. Bone from the right femur gave a radiocarbon age of 14 262 ± 87 yr BP by accelerator mass spectrometry. The material was slightly chalky and had a low collagen yield with a relatively large amount of humic material; contamination which would lower the measured age is thus possible. However, an amino acid profile characteristic of collagen makes it unlikely that high contaminant levels are present. The radiocarbon age for the bone is likely to be 14–18 ka (16–22 000 cal. yr) or possibly older, with the lower limit being set by the radiocarbon age and the upper limit inferred from the amount of humic contamination. This is thus the oldest moa skeleton reported from Wairarapa. Loess overlying the bones contains disseminated shards of clear rhyolitic glass with a composition identical to that of the 22.6 ka (24 500 cal. yr) Kawakawa Tephra, and gave an age by optical dating of 26 ± 2 ka. A thicker tephra deposit within loess on a higher, deeply dissected surface may also be partly reworked; optical dating of a sample of loess from 2 m beneath it gave an age of 22 ± 2 ka. Thermoluminescence dating of two samples of the conglomeratic deposits surrounding the bones gave ages of 52 ± 13.2 and 102 ± 18 ka, respectively, indicating redeposition of these sediments without resetting of the thermoluminescence signal. One of these samples was also dated by optical luminescence at 39 ± 2 ka, and this age may similarly include a component of inherited age. Optical ages and the presence of reworked tephra confirm that all loess overlying the skeleton is Ohakean (deposited between 25 and 9.5 ka BP) and probably Oh2. The radiocarbon age implies that the surface beneath the skeleton is probably equivalent to the Ohakean Oh] terrace defined from the Rangitikei area, with an estimated age of 18 000 yr BP. The most extensive fluvial gravel surface in the area is probably equivalent to the Ratan surface.