Browsing by Author "Kilroy, C"

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    A 7300 year record of environmental changes in a coastal wetland (Moawhitu), New Zealand, and evidence for catastrophic overwash (tsunami?)
    (Elsevier, 2020-09) Chagué, C; Cope, J; Kilroy, C; Jacobsen, GE; Zawadzki, A; Wong, HKY
    Three sedimentary sequences from a coastal wetland behind a sand barrier, on the west coast of d'Urville Island, New Zealand, were examined using a multi-proxy approach, including sedimentological, geochemical and microfossil (diatom) analyses, with the chronology established using radiocarbon and 210Pb dating. Data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in Moawhitu. This was followed by periods of alternating wetland encroachment and open water, displaying spatial variations, until a peatland was established about 1300 cal. yr BP. The wetland was then partially drained in the early 1900s, leading to compaction of the peat near the surface. A coarse layer containing gravel, sand and shells, with a sharp lower contact, in the northern area of the wetland, is attributed to an overwash about 2500–3000 yr BP, most probably a tsunami generated by the rupture of a local or regional fault. The high-resolution continuous record obtained with XRF core scanning revealed a geochemical signature (Ca and S) for the overwash 600 m inland in the middle area of the wetland, while it was absent from the southern site 1.1 km from the shore. This suggests that, except at the northern end of Moawhitu, the sand dune acted as an effective barrier preventing any sediment from overtopping 2500–3000 yr BP, with only a geochemical evidence marking the extent of seawater inundation. No sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in Moawhitu, as recounted in Māori oral tradition (pūrākau), although pebbles at the surface of the dune are likely to be linked to this event. Thus, the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century. However, our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years. It also shows that a high-resolution continuous XRF record can provide the evidence for short-term changes (catastrophic or not) that did not leave any clear sedimentological signature, thus providing a better insight of environmental changes in any depositional environment. © 2020 Elsevier B.V
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    Holocene record of gradual, catastrophic and human influenced environmental change at Moashitu wetland, D'Urville Island, New Zealand
    (Australian Metrological & Oceanographic Society, 2012-01-31) Cope, J; Chagué-Goff, C; Mooney, SD; Goff, JR; Zawadzki, A; Wong, HKY; Kilroy, C; Jacobsen, GE; Dominey-Howes, D
    Active tectonism, sea level fluctuation and human arrival have moulded the present day physical environment of New Zealand. Coastal wetlands are recognised archives of Holocene environmental changes. By applying sedimentological, geochemical and chronological techniques to coastal wetlands, natural and anthropogenic changes can be observed. Moawhitu Wetland, located on D’Urville Island, New Zealand, is home to a Maori oral tradition that describes a giant wave destroying a community in the 15th century. Little geological work has been carried out to investigate the evidence of the event and no studies have researched the palaeoenvironmental history of the area. This research was therefore aimed at reconstructing the Holocene environmental record at Moawhitu Wetland to determine if there was evidence of severe changes to the landscape as described in Maori oral traditions. Three sedimentary sequences from Moawhitu Wetland were used to reconstruct a 7500 year record that incorporated gradual, catastrophic and human influenced changes. The record was established by using multiple sedimentary proxies (grainsize, organic matter content, geochemistry and mineralogy) at three different sites that were temporally aligned with dating techniques (14C and 210Pb) . Barrier formation, lake and wetland formation, erosion, human influences and a tsunami ~3000-3300 yr BP were identified in the sedimentary record. These changes were applied to a broader spatial context from which inferences of sea level rise, regional faulting and potential climate change were drawn. The central west coast of New Zealand has undergone an array of short and long term environmental changes throughout the Holocene and can be identified as an area susceptible to potential tsunami events.
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    Holocene record of long- and short-term environmental changes in a coastal wetland, New Zealand
    (Geological Society of Australia, 2014-07-07) Chagué-Goff, C; Cope, J; Goff, JR; Mooney, SD; Kilroy, C; Wong, HKY; McFadgen, BG
    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.
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    Return of the Sea Monster – a tale from D’Urville Island, New Zealand
    (International Union for Quaternary Research, 2012-09-04) Chagué-Goff, C; Cope, J; McFadgen, BG; Mooney, SD; Kilroy, C; Zawadzki, A; Wong, HKY; Jacobsen, GE
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