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    Paleoenvironmental analysis of the Mangere Formation, Mangere Island, Chatham Islands, New Zealand : a thesis submitted in Earth Science for the degree of Master of Science at Massey University
    (Massey University, 2006) Davies, George Sydney Fletcher
    Mangere Island consists almost entirely of alkali basalt of the late Miocene early Pliocene Rangiauria Formation (Campbell et al., 1993) with outcrops of the sedimentary Tupuangi Formation on the east coast and the Mangere Formation (Campbell, et al., 1993), a sedimentary remnant, mainly lacustrine but also partly marine, lying between the northeastern and southwestern groups of volcanic vents of Mangere Island: As a result of the present work the sedimentary Mangere Formation of Campbell et al. (1993) has been divided into two formations, Mangere Formation and the overlying Parakeet Formation. Mangere Formation consists of (1) a Basal member (32m of mudstone), and (2) a Cyclic member (12.6m of alternating sandstones and mudstones). Parakeet Formation has (1) a Carbonaceous member (0.6m Of organic rich mudstones), (2) a Skua member (16.8m of tuffaceous siltstone), and (3) a capping rhyolitic tephra. The Basal member of the Mangere Formation is underlain by a breccia that is texturally extremely variable (Bag End breccia). A sedimentary outcrop on the eastern coast of Mangere Island is lithologically and mineralogically identical to Tupuangi Formation on Pitt Island as well as having the same Cretaceous pollen suite. Thus it is inferred that, at the time of Rangiauria volcanism, Tupuangi Formation and its overlying Tertiary strata extended from Pitt Island at least as far as Mangere Island. An arm of the sea between two Mangere Island volcanic centres extended towards Waihere Bay, Pitt Island. At some time in the late Pliocene, volcanic debris avalanches from the northeast and southwest groups of vents formed a debris dam that blocked off the seaward side of the sea arm, resulting in the formation an oligotrophic fresh water lake. As a result of a low energy regime and vegetated slopes, the lake filled to ca. 30m with very fine sediment (the Basal member) from both the volcanics of Mangere Island and the quartzofelspathic Tupuangi Formation of Pitt/Mangere Island. Following this a debris dam, formed by volcanic debris avalanches, was breached by a rising sea. Local marine influence in storms destablised the slopes surrounding the then shallow lake resulting in the influx of coarse sands which alternated with mudstones deposited during quieter periods (the Cyclic Member). At the end of this period there was a eustatic fall of sea level or tectonic uplift or both, probably resulting in subaerial erosion and an unconformity between the Cyclic and Carbonaceous Members. A second shallow fresh water lake (the Carbonaceous member) was established on the top of the Cyclic member. This lake was later overwhelmed by wind-blown material derived from a deposit of Paleocene Red Bluff Tuff exposed probably by a falling sea level or marine erosion. The reworked Red Bluff Tuff was later covered by a layer of rhyolitic tephra probably from the Taupo Volcanic Zone (TVZ), North Island, New Zealand. The distinctive jointing pattern seen in the sandstone units of the Cyclic member resulted from doming with a principal stress directed northwest-southeast. This probably correlates with tectonic uplift in the Castlecliffian. The lack of any positive time markers makes dating the formation rather indeterminate, but the Basal and Cyclic members (Mangere Formation) are probably upper Mangapanian and the Skua member probably Quaternary. The sequence is generally lacking in fossils, except for palynomorphs which occur throughout, and ostracods which occur only in the Cyclic member. Neither proved useful for dating the sequence. The pollen diagrams show a consistent coastal plant association of small trees, shrubs, herbs and ferns throughout the history of the sequence, with the implication that climate during this time did not vary greatly from a mild, moist, equable mean.
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    Palaeoecology by palynology : a palaeoecological study of the vegetation of the Tongariro Volcanic Centre, New Zealand, immediately prior to the c. 232 AD Taupo eruption : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University
    (Massey University, 2001) Banks, Natalie Jane
    The usual source of pollen for analysis has been from within deposits of peat from lakes, bogs and mires. Soils have not generally been considered a potentially useful pollen source. Under some circumstances, however, (such as volcanic eruptions) a soil may be buried so rapidly that the pollen it contains will be more or less completely preserved in the resulting palaeosol. Studies of such volcanically buried palaeosol pollen have been made overseas. The last eruption from the Taupo Volcanic Centre occurred approximately 1800 years ago. The culminating phase of the eruption ejected ca 30 cubic kilometres of ignimbrite as a very hot and fluid pyroclastic flow which covered an area with a radius of 70-90 km centred on Lake Taupo. This deposit is known as the Taupo Tephra. The purpose of the present investigation was to examine peats and palaeosols directly beneath the Taupo Tephra from a variety of sites within the Tongariro area and to analyse any pollen preserved. Samples were taken from a total of 42 sites at various altitudes and distances from the eruptive source, and pollen extracted. Each sample taken, therefore, was from a buried soil or peat directly below the Taupo Tephra. The pollen contained within these samples and contains pollen deposited immediately prior to the eruption. An initial qualitative investigation indicated that the ignimbrite acts as an effective filter in preventing any contemporary pollen and spores from percolating through into underlying layers. The preservation of pollen was reasonably good at most sites allowing some conclusions to be drawn as to the structure and composition of the pre-eruption forests of the Tongariro area. Beech forest was widespread throughout, especially at higher altitudes, although mixed conifer associations were also evident, particularly in the west. At those sites where pollen preservation was poor, some alternative conclusions can be drawn about preservation environments within palaeosols. The pH value is particularly important, and pollen and spores are not well preserved when the soil pH value is in excess of 6.0. The possibility of differential preservation within the New Zealand flora is also examined.