Characterisation and paleoclimatic signals within tephric loess deposits aged between c. 33 to 9.5 cal ka in the Rotorua area, northern New Zealand
Lanigan, K. M. (2012). Characterisation and paleoclimatic signals within tephric loess deposits aged between c. 33 to 9.5 cal ka in the Rotorua area, northern New Zealand (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/6513
Permanent Research Commons link: https://hdl.handle.net/10289/6513
I studied tephric loess deposits aged between c. 33 and 9.5 cal ka in the Rotorua region, north-east central North Island. I produced a stratigraphic framework for the loess deposits and characterised them using a range of field and laboratory methods to develop a multi-proxy paleoclimatic reconstruction for the region. A number of key tephra marker layers, including Kawakawa (c. 25.4 cal ka), Te Rere (c. 25.2 cal ka), Okareka (c. 21.9 cal ka), Rerewhakaaitu (c. 17.5 cal ka), Rotorua (c. 15.6 cal ka), Waiohau (c. 13.6 cal ka) and Rotoma (c. 9.5 cal ka) tephras, were used as isochronous tie-points within the loess deposits and to provide ages within the loess. In contrast to those of previous studies, the findings from my study suggest that loess deposition continued at some sites in the Rotorua region until c. 9.5 cal ka. The average rate of loess accumulation was about 2.3 cm per century. The thickest loess sequence deposited between c. 33 and 9.5 cal ka was about 4.3 metres (tephra-free thickness) at Dansey Rd. In general, the tephric loess deposits are largely massive, silty and often yellowish brown, dull yellowish brown or dull yellow orange in colour (Munsell colour codes 10YR 5/4, 5/6, 5/8 or 6/4). Paleoclimate proxy analyses of the loess included grain size, accumulation rates, phytolith analysis, magnetic susceptibility, total carbon content, carbon isotopes and potassium content. The results from my study suggest that the Rotorua region underwent a change from relatively warm, wet and less windy interstadial conditions to relatively cold, dry and more windy stadial conditions (indicative of the beginning of the extended-last glacial maximum) at c. 25.4 cal ka (about the time of deposition of the Kawakawa Tephra). Between c. 25.4 and 18.4 cal ka, stadial conditions likely dominated, although climate was also variable, and results suggest that two short-lived interstadials, centred around c. 23 cal ka and c. 21 cal ka, may have occurred. Stadial conditions appear to have ended at c. 18.4 cal ka when conditions became relatively warmer, wetter and less windy (likely indicative of last glacial – interglacial transition conditions). However, during these warming conditions, between c. 13.8—12.8 cal ka, results suggest that conditions became temporarily relatively cooler and drier (indicative of the late glacial reversal). In general, there is good support from the New Zealand climate event stratigraphy (CES) (D.J. Barrell and others in preparation. “The sequence of climatic events in New Zealand over the past 30 000 years – a composite stratotype for regional correlation and comparison.” Quaternary Science Reviews [Australasian INTIMATE issue]) and other North Island paleoclimate records for these three broad changes in climate from interstadial to stadial and back to interstadial (and possibly interglacial) conditions during this time. However, the exact timing of these broad changes as well as that of the shorter-lived climatic variations are not perfectly synchronised with the timing of similar changes in the CES and other North Island records.
University of Waikato
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