Holocene record of long- and short-term environmental changes in a coastal wetland, New Zealand
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Date
2014-07-07
Journal Title
Journal ISSN
Volume Title
Publisher
Geological Society of Australia
Abstract
Long- and short-term environmental changes in Moawhitu Wetland, D’Urville Island, New Zealand, were reconstructed using a multi-proxy approach. A local Māori oral tradition describes a giant wave destroying a community in the 15th century, however, except for a study in 1962, little geological work had been carried out to investigate this event or to establish a record of paleoenvironmental changes in the area. Three sedimentary sequences sampled across the wetland over a distance of 2 km were analysed for grain size, organic content, geochemistry (ICP-AES, ICP-MS and ITRAX), diatom assemblages and mineralogy, while the chronology was obtained using 14C and 210Pb dating, corroborated with pollen biostratigraphy.
Results of this study indicate that the sand dune barrier at Moawhitu formed ca 7400–7200 years BP at the time when sea levels stabilised following the last deglaciation. This led to the establishment of a freshwater lake in the southern area, which gradually infilled to form a wetland with subsequent peat accumulation. In the central part of Moawhitu, lake and peatland sequences alternated. By ca 1200 years BP, with the exception of the existing lagoon at the northern end of the study area, conditions favourable to peatland formation were found throughout Moawhitu and continued into the 20th century when they were disrupted by drainage activities.
Evidence for a tsunami 3300–3000 years BP was found in the northern part of Moawhitu wetland (based on sedimentological, geochemical and microfossil data). Geochemical signatures and marine diatom assemblages
provide a record of tsunami inundation in the middle part of the wetland, beyond the extent of any sand deposit. No geochemical evidence could be found at the site further inland in the southern part of the wetland. Evidence for a contemporaneous tsunami deposit has also been reported ~100 km N, on Kapiti Island, on the west coast of the North Island of New Zealand, and the event has been attributed to a local fault rupture. So far, no sedimentological, geochemical or micropaleontological evidence for a giant wave in the 15th century has been found in the sedimentary sequence of Moawhitu wetland. However, pebble layers extending across large areas of the dunes have been recorded and these have also been associated with Maori occupation, thus inferring that the sand dune may indeed have acted as an effect barrier to any 15th century tsunami.
This study indicates that more than one tsunami has affected Moawhitu, and further work is planned to document environmental changes in the area. Copyright Geological Society of Australia Inc.
Description
Keywords
Environment, Sediments, Fresh water, Sea level, Geology, Tsunamis
Citation
Chagué-Goff, C., Cope, J., Goff, J., Mooney, S., Kilroy, C., Wong, H., & McFadgen, B. (2014 ). Holocene record of long- and short-term environmental changes in a coastal wetland, New Zealand. Presentation to the Australian Earth Sciences Convention 2014 (AESC 2014), 22nd Geological Convention, Newcastle NSW, 7-10 July 2014, (pp. 179). Retrieved from: http://aesc2014.gsa.org.au/assets/Various-reg-partner-opp-workshop-summ-/AESC-Abstract-Proceedings.pdf