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    Sequence stratigraphy of Plio-Pleistocene sediments in lower Turakina Valley, Wanganui Basin, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Quarternary Science at Massey University
    (Massey University, 1996) van der Neut, Monique
    The Wanganui Basin is a large south westerly facing embayment which contains up to 4000 m of Plio-Pleistocene shallow marine sediment deposited during periodic glacioeustatic sea-level fluctuations. The basin depocentre has shifted progressively southward over time in response to uplift in the north. Ten cycles recorded within the late Pliocene to mid-late Pleistocene sediments exposed along the coast at Castlecliff are correlated to lower Turakina Valley, Whangaehu Valley and Rangitikei Valley. The cyclic basin fill in the study area has been interpreted in terms of sequence stratigraphy. Facies successions of the Transgressive Systems Tract (TST) consist of sediment deposited within shoreface to innermost shelf environments during relative sea-level rise. In the Turakina Valley section, it was found that several depositional sequences show anomalously thick TST's. Where these thick TST's are evident, a relatively thin HST occurs. These anomalously thick TST's occur along the flanks of the Marton Anticline and may represent periods of uplift of the anticline or a significant increase of sediment supply into this part of the basin during relative rises in sea-level. Type A1 Shellbeds in the Turakina Valley section are particularly well represented and tend to be thicker compared to those at Castlecliff. The increase in thickness towards the east of the basin is attributed to increased sedimentation rate with closer proximity to the axial ranges. The faunal assemblage of Type A1 Shellbeds in the Turakina valley section were found to be similar to those at Castlecliff. Condensed Mid-cycle Shellbeds (MCS) (= Type B Shellbed) are rich in well preserved in situ and near situ fauna within a muddy, fine sand or silt matrix. The mid-cycle shellbeds in the Turakina Valley section are thinner than those at the Castlecliff section. This thinning out of the MCS towards the east of the basin is attributed to higher sedimentation rates. Sediment starved conditions necessary for the development of mid-cycle shellbeds are therefore less pronounced. A new kind of Type B shellbed was recognised in the Turakina Valley section (Facies TCS-1) and consists of a basal shell conglomerate followed by a muddy phase with abundant, diverse fauna. This type of shellbed appears to succeed a period of uplift on the Marton Anticline or follows a period of increased sediment supply into this part of the basin. In general, the faunal assemblage of Type B Shellbeds in Turakina Valley was similar to that recorded from the Castlecliff section. The assemblage, however, was more diverse in the Turakina Valley section, perhaps reflecting higher sedimentation and subsidence rates towards the east of the basin. The Highstand Systems Tract (HST) consists of a thick unit of blue-grey siltstone which represents the latter part of a relative sea-level rise and beginning stages of a relative sea-level fall. The siltstone facies that make up the HST were deposited on the inner and inner-middle shelf. The HST's exposed on the onland section of the Wanganui Basin are incompletely preserved. Similarly, the Lowstand Systems Tract (LST), which would be made up of progressively more terrestrial facies as sea-level falls, is only seen at one site in Rangitikei Valley. Both the upper part of the HST and the LST were eroded away and redeposited as the next rise in sea-level occurred, forming the unconformity that represents the sequence boundary. In the depositional sequences where sedimentation wasn't affected by uplift on the Marton Anticline or by a diverted sediment source, HST's are considerably thicker compared to those at Castlecliff. This thickening of siltstone units towards the east of the basin reflects an increasing sedimentation rate due to closer proximity to the axial ranges and increasing subsidence rate with respect to the position of the contemporaneous depocentre.
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    Late Quaternary evolution of Matakana Island, Bay of Plenty, New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Geography at Massey University
    (Massey University, 1996) Betts, Harley David
    Matakana Island consists of two main parts - an area of mainly Pleistocene materials to the southwest and a c.24 km long Holocene barrier to the northeast. Together with the tombolo systems of Bowentown Heads and Mount Maunganui, Matakana Island encloses the c.200 km² Tauranga Harbour. This study establishes the late Quaternary geomorphological history of Matakana Island, focussing primarily on the evolution of the Holocene barrier. The barrier consists largely of relict foredunes, with relict parabolic dunes, lakes/wetland areas, washover deposits and estuarine flats also present. A detailed geomorphological map provides a foundation for palaeoenvironmental reconstructions. The landform information is supplemented with details of the sedimentology, tephrochronology, pedology, archaeology and palynology of the barrier in order to identify and describe past environmental changes. The Pleistocene part of the island contains remnants of at least three late Pleistocene terraces, mantled by thick beds of tephra and ignimbrite. The lowest terrace, which retains some coastal landforms, originated as a relict foredune plain which probably formed during the Last Interglacial maximum (c.125 000 years ago). The older, higher terraces are likely to have originated during earlier interglacial periods. The barrier consists primarily of moderately well sorted to well sorted medium to fine sand. The dominance of quartz, feldspar and hypersthene indicate that much of the sediment was originally derived from the active Taupo Volcanic Zone. Following the end of the Postglacial Marine Transgression c.7 000 cal BP, deposits of these materials on the continental shelf were reworked and transported shoreward to form the Holocene barrier. Barrier formation commenced by around c.6 000 cal BP. The barrier initially formed in at least two separate parts, separated by a tidal inlet at present-day Blue Gum Bay. The entrance migrated southeastward as the barrier prograded and was closed off c.3 750 cal BP. Following the closure of the entrance, foredunes became larger and more irregular, suggesting a major change to the coastal sediment budget. Progradation rates, calculated from shoreline ages determined by airfall tephra deposits, radiocarbon ages and sea-rafted pumice deposits, generally decreased with time, from about 0.46 metres/year initially to about 0.18 metres/year over the last c.650 years. Significant erosion of the southeastern end of the barrier culminated shortly after the Kaharoa eruption (c.650 cal BP), at which time the barrier was approximately 83 percent of its present length. Subsequently, both ends of the barrier extended rapidly. The coarse texture of sand comprising the barrier ends and anomalously old radiocarbon ages of incorporated shells suggests that, as the entrances narrowed, sediment from adjacent ebb-tidal deltas was reworked to form the barrier ends. The barrier also underwent considerable change following the first arrival of humans on Matakana Island sometime after the Kaharoa eruption. Widespread vegetation clearance and soil disturbance are likely to have contributed to dune instability. Matakana Island appears to have developed in a similar fashion to many Holocene barrier systems of southeastern Australia in terms of a predominant shelf sediment source, onshore sediment transport following the end of the Postglacial Marine Transgression and decreasing progradation rates through time.
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    The stratigraphy and environments of deposition of early-mid Pleistocene sediments of the Pohangina Region, Eastern Wanganui Basin, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science with Honours in Quarternary Science at Massey University
    (Massey University, 1999) Brackley, Hannah
    The Pohangina Anticline is one of several growing structures on the northeastern Manawatu Plains. The axis of this asymmetrical anticline lies within the valley of the Pohangina River, with the strata on the western limb dipping gently 2-3° to the west, and those on the eastern limb dipping at up to 70° to the east. The axis of the anticline plunges at 1-2° to the south. The sediments are 1.3-0.6 Ma in age. Age control is provided by several coarse pumiceous tuffs within the sediments. These time planes for regional correlation have been examined using electron microprobe analysis. The Rewa pumice (1.29 ± 0.12 Ma) lies near the base of the studied sequence. Pumice from the Potaka eruption (1.05 ± 0.05 Ma) is well exposed at several sites. The Kaukatea pumice (0.87 ± 0.05 Ma) is exposed as both tuff and airfall deposits, and the Kupe pumice (0.63 ± 0.08 Ma) appears near the top of the studied sequence. Using these tuffs and the dip of the beds, rates of deformation of 7° per 100 ka have been calculated. The Castlecliffian/Nukumaruan sediments accumulated in a gradually shallowing marine environment. Conditions were shallow marine until about the time of the Potaka pumice eruption, above the Potaka the sediments are dominantly fluvial including lignites, overbank deposits and channel gravels, all deposited in a lower coastal plain setting. Sequence stratigraphy and tephrochrononlogy provide correlation of the studied section with age equivalent sections farther west at Castlecliff, Turakina and the Rangitikei River. Cyclothems 33 to 40 are present within the stratigraphy, and are characterised by alternating coarse and fine grained sediments, indicating climatic fluctuations.
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    Late quaternary landscape evolution of western Hawke's Bay, North Island, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1997) Hammond, Andrew Peter
    Western Hawke's Bay, North Island, New Zealand, lies landward of an obliquely convergent offshore plate boundary, the Hikurangi Trough. Landscape elements exhibit classical island arc terrains. From east to west these are: an accretionary wedge, forearc basin, frontal-ridge, and a volcanic backarc basin. The forearc was subdivided into four land systems: ranges, inland basins, hill-country, and plains. Soil patterns and geomorphological processes within each land system are detailed. The architecture and subsequent sculpturing of land systems have been subject to a complex interplay between: tectonic, climatic, fluvial, aeolian and volcanic regimes. These regimes have had a marked bearing upon the stability/instability of the landscape and its evolution. The timing of stability/instability cycles within the district's coverbeds and aggradational/degradational terraces is facilitated by interbedded rhyolitic and andesitic tephra chronohorizons and ignimbrites (Taupo, Oruanui, Rabbit Gully and Potaka) derived from the Taupo Volcanic Zone. The glass chemistries of unknown rhyolitic tephras and ignimbrites were matched with those from the well-dated master sections around the volcanic centres. During this study the geographic distribution of many andesitic and rhyolitic tephra layers have been significantly expanded into a district not previously studied in detail. Andesitic tephras identified include members of the Tufa Trig, Ngauruhoe, Papakai, Mangamate and Bullott Formations. Rhyolitic tephras found, but not previously recorded in Hawke's Bay sequences, include Rerewhakaaitu and Rangitawa Tephras and four previously unidentified rhyolitic tephras termed A, B, C and D within Loess 4 and Loess 5. Major cycles of landscape stability/instability are associated with Quaternary climate changes. During glacial and stadial times intense physical weathering prevailed within the ranges resulting in the transfer of material (aggradation products) through the fluvial and aeolian systems to the downlands and coastal plains. Interglacial and interstadial times were marked by a predominance of chemical weathering (paleosols) and river degradation. The net result was landsurface stabilisation before the next episode of instability. Loess-paleosol layers recognised in Hawke's Bay are correlated to the Rangitikei River Valley sequences. Unlike the Rangitikei sequences, where the best loess-paleosol record overlies terraces, those in Hawke's Bay are found on footslopes. Pre- and early-Ohakean loessial sequences overlying aggradational terraces are absent. Consequently, studies were focussed on colluvial foot- and toe-slopes (depositional sites) within the inland basins and hill-country land systems. Coverbeds from these slope positions have a fuller record and are more useful for stratigraphic studies. Earthquakes, fires (both natural and man-induced), periodic cyclonic storms and ignimbrite sheets punctuate and complicate the climatically induced Quaternary cycles. The record for these non-climatic variables is often local and may mask or even destroy the imprint of older, more poorly preserved climatically-induced Pleistocene stability and instability episodes. Field, morphological, mineralogical and chemical properties of loess and tephra layers were undertaken at four reference sections. These sections are arranged in a west (foothills of the ranges) to east (coast) transect reflecting differences in climate (1800-900mm rainfall/annum, lower rainfalls in the east), soil types (Pumice, Allophanic, Brown and Pallic Soils) and distance from volcanic source areas. The most distant site lies over 100km east of Lake Taupo. Three aggradational terraces associated with the last stadial (Ohakean) are commonly found along Hawke's Bay rivers. Ohakean terraces along the Mohaka River have tread ages of c. 16-14 ka, 14-11 ka and 11-10 ka, respectively. Field and laboratory characterisation of duripan horizons within Pallic Soils were undertaken to elucidate the nature and origin of the cementing medium. Soil chemistry and mineralogy show the cement to be highly siliceous and most likely derived from the weathering products of volcanic ash.
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    A sedimentological and geochemical approach to understanding cycles of stratovolcano growth and collapse at Mt Taranaki, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2008) Zernack, Anke Verena
    The long-term behaviour of andesitic stratovolcanoes is characterised by a repetition of edifice growth and collapse phases. This cyclic pattern may represent a natural frequency at varying timescales in the growth dynamics of stratovolcanoes, but is often difficult to identify because of long cycle-timescales, coupled with incomplete stratigraphic records. The volcaniclastic ring-plain succession surrounding the 2 518 m Mt. Taranaki, New Zealand, comprises a wide variety of distinctive volcanic mass-flow lithofacies with sedimentary and lithology characteristics that can be related to recurring volcanic cycles over >190 ka. Debrisflow and monolithologic hyperconcentrated-flow deposits record edifice growth phases while polylithologic debris-avalanche and associated cohesive debris-flow units were emplaced by collapse. Major edifice failures at Mt. Taranaki occurred on-average every 10 ka, with five events recognised over the last 30 ka, a time interval for which stratigraphic records are more complete. The unstable nature of Mt. Taranaki mainly results from its weak internal composite structure including abundant saturated pyroclastic deposits and breccia layers, along with its growth on a weakly indurated and tectonically fractured basement of Tertiary mudstones and sandstones. As the edifice repeatedly grew beyond a critical stable height or profile, large-scale collapses were triggered by intrusions preceding magmatic activity, major eruptions, or significant regional tectonic fault movements. Clasts within debris-avalanche deposits were used as a series of windows into the composition of previous successive proto-Mt Taranaki edifices in order to examine magmatic controls on their failure. The diversity of lithologies and their geochemical characteristics are similar throughout the history of the volcano, with the oldest sample suites displaying a slightly broader range of compositions including more primitive rock types. The evolution to a narrower range and higher-silica compositions was accompanied by an increase in K2O. This shows that later melts progressively interacted with underplated amphibolitic material at the base of the crust. These gradual changes imply a long-term stability of the magmatic system. The preservation of similar internal conditions during the volcano’s evolution, hence suggests that external processes were the main driving force behind its cyclic growth and collapse behaviour and resulting sedimentation pattern.