7 results for Alloway, B.

  • Environmental change during the last glacial maximum (c. 25 000-c. 16 500 years BP) at Mt Richmond, Auckland Isthmus, New Zealand

    Sandiford, A.; Horrocks, M.; Newnham, R.; Ogden, J.; Alloway, B. (2002)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. A 2 m section at the base of Mt Richmond contains a palynological record of the last glacial maximum (LGM) (c. 25 000-c. 16 500 14C years BP) vegetation of the Auckland Isthmus. Three silicic tephra layers derived from the Taupo Volcanic Centre (Okaia Tephra c. 23 500 14C years BP, Kawakawa Tephra c. 22 500 14C years BP) and the Okataina Volcanic Centre (Okareka Tephra c. 18 000 14C years BP), both centres lying within the Taupo Volcanic Zone, provide the basis of the chronology supported by radiocarbon dates. The pollen diagram is divided into two pollen zones separated by the deposition of a locally derived basaltic ash. From c. 25 000-23 000 14C years BP the site was initially a eutrophic lake fringed by Leptospermum and Typha, which altered to a Cyperaceae/Leptospermum-dominated swamp. The regional vegetation at the time was beech-dominated forest; canopy conifers were present but formed a minor part of the local forest. From c 23 000-16 500 14C years BP regional forest was further restricted to local patches in extensive shrubland/grassland. Temperatures may have been depressed by more than 4-5�C. The eruption of a local volcano dammed the swamp outlet resulting in a return to lacustrine conditions. Local volcanism may have accelerated vegetation change already under way as a result of climate change to cooler conditions. This record provides a view of LGM vegetation of the Auckland Isthmus and a template for earlier cold stages of the Quaternary.

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  • Late Quaternary (post 28 000 year BP) tephrostratigraphy of northeast and central Taranaki, New Zealand

    Alloway, B.; Neall, V.E.; Vucetich, C.G. (1995)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. A comprehensive post-28 ka record of the Egmont volcano's eruptive history is presented, and the relationships of andesitic tephra beds to andic soil material, Egmont-sourced volcaniclastic detritus, and two silicic tephra beds from Taupo Volcano are discussed, along with implications for inter-regional correlation. The post-28 ka tephra succession is recorded in 16 andesitic tephra formations. At least 76 tephra events from Egmont Volcano have been recorded since c28 ka with an average eruptive perodicity of one in every c330 yr. This frequency is considered mininal since more tephras of lesser magnitude may have been erupted but are only represented on the ring plain as intermittent accretion of fine-grained ash that has rapidly weathered to andic soil material.

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  • Stratigraphy and chronology of the Stent tephra, a c. 4000 year old distal silicic tephra from Taupo Volcanic Centre, New Zealand

    Alloway, B.; Lowe, D.J.; Chan, R.P.K.; Eden, D.; Froggatt, P. (1994)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. Tephrostratigraphic and chronologic studies in two areas of the North Island have identified a previously unrecorded, thin, distal silicic tephra derived from the Taupo Volcanic Centre. In Taranaki, three radiocarbon ages of the uncorrelated tephra are consistent with the independent radiocarbon chronology obtained from enveloping Egmont-sourced tephras. In western Bay of Plenty, where the uncorrelated tephra is also directly dated, it is overlain by Whakaipo Tephra (c. 2.7 ka) and underlain by Hinemaiaia Tephra (C. 4.5 ka). From these sites in Taranaki and western Bay of Plenty, seven radiocarbon dates obtained on the uncorrelated silicic tephra yield an error-weighted mean age of 3970 ᄆ 31 conventional radiocarbon years B.P. The ages on the uncorrelated tephra (informally referred to as Stent tephra) from both areas are statistically identical but significantly different from those on both Waimihia and Hinemaiaia Tephras.

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  • A 28 000-6600 cal yr record of local and distal volcanism preserved in a paleolake, Auckland, New Zealand

    Sandiford, A.; Alloway, B.; Shane, P. (2001)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. A 52.5 m core was extracted from Pukaki Crater, an infilled basaltic explosion crater in the Auckland Volcanic Field, for detailed tephra and palynological analysis. The core consists of a lower 6 m of finely laminated lacustrine sediments representing the interval c. 28 000-6600 cal yr overlain by 46.5 m of homogeneous marine silts deposited between c. 7600 and 6600 cal yr. Favourable conditions have preserved at least 40 tephra layers in the sediments. These have been derived from one local and five distal sources and were deposited within the crater lake between c. 28 000 and c. 7600 cal yr. The tephra beds were identified by stratigraphic position, geochemical analyses, and ferromagnesian mineral assemblage. This tephrostratigraphic framework is underpinned by three distinctive tephra beds, namely Tuhua (c. 6950 cal yr), Rotoma (c. 9500 cal yr), and Kawakawa (c. 26 500 cal yr). Of the 40 tephra beds, 7 are sourced from the rhyolitic Okataina Volcanic Centre (Mamaku c. 8200 cal yr; Rotoma c. 9500 cal yr; Waiohau c. 13 800 cal yr; Rotorua c. 15 800 cal yr; Rerewhakaaitu c. 17 700 cal yr; Okareka c. 21 400 cal yr; Te Rere c. 25 000 cal yr), 3 from the rhyolitic Taupo Volcanic Centre (Opepe c. 10 200 cal yr; Kawakawa c. 26 500 cal yr; Poihipi c. 27 500 cal yr), 5 from the andesitic Tongariro Volcanic Centre, 14 from the andesitic Taranaki Volcano, 1 from Mayor Island (Tuhua c. 6950 cal yr), and 8 from the basaltic Auckland Volcanic Field. In addition, two previously unidentified rhyolitic tephra (c. 17 100 cal yr and c. 20 720 cal yr) are recorded. The occurrence of numerous andesitic and rhyolitic tephra beds in the Auckland region extends the known dispersal of the units and has implications for the assessment of volcanic hazards from distal sources. Many of the Taranaki-derived tephra beds do not stratigraphically match those recorded in the Waikato lakes region and this suggests that Taranaki Volcano produced more ash than previously estimated. The distal tephra record preserved at Pukaki provides age constraints for Auckland Volcanic Field basaltic tephra that are otherwise poorly dated. Basaltic fall events are recorded at c. 14 450 cal yr, 15 750 cal yr, 19 380 cal yr, 19 420 cal yr, 23 825 cal yr, 24 175 cal yr, 25 200 cal yr, and 25 700 cal yr. Fresh glass in the basaltic tephra allows them to be chemically fingerprinted and discriminated, and this will open a new avenue to development of a regional basaltic tephrostratigraphy.

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  • Deep-ocean record of major late Cenozoic rhyolitic eruptions from New Zealand

    Carter, L.; Alloway, B.; Shane, P.; Westgate, J. (2004)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. A 12 m.y. record of large rhyolitic eruptions from the Coromandel (CVZ) and Taupo (TVZ) Volcanic Zones of New Zealand is contained in cores retrieved by Leg 181 of the Ocean Drilling Program. Site 1124, located 670 km from the TVZ, has a maximum of 134 macroscopic tephra layers with a total thickness of 13.18 m. These units, along with between 7 and 63 tephras from 3 other sites, were dated by a combination of magnetostratigraphy, biostratigraphy, isothermal plateau fission track determinations, and geochemical correlation with onshore tephra deposits. Additional time control for the last 3 m.y. came from an orbitally tuned, benthic, oxygen isotope profile for Site 1123. Results extend the incomplete terrestrial record of volcanism by placing the first major rhyolitic eruption in the CVZ at c. 12 Ma, c. 1.6-1 m.y. earlier than previously known. Tephras became thicker and more frequent from the late Miocene into the Quaternary-a trend that probably reflected (1) more frequent and intense volcanism and (2) reduced distances between sources and depositional sites on the evolving Australian/Pacific plate system. The passage from CVZ to Quaternary TVZ occurred without a major hiatus in activity, suggesting the transition was gradational. The ensuing TVZ volcanism was more continuous than known previously from the onshore geology. Ash dispersal was primarily eastward, highlighting the dominance of westerly winds since the middle Miocene. Nevertheless, variations in dispersal patterns suggest periodic changes in wind direction/speed and/or ejection of ash beyond the Roaring Forties.

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  • Stratigraphy, age and correlation of middle Pleistocene silicic tephras in the Auckland region, New Zealand: A prolific distal record of Taupo Volcanic Zone volcanism

    Alloway, B.; Westgate, J.; Pillans, B.; Pearce, N.; Newnham, R.; Byrami, M.; Aarburg, S. (2004)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. Coastal sections in the Auckland region reveal highly carbonaceous and/or highly weathered clay-dominated cover-bed successions with numerous discrete distal volcanic ash (tephra) layers, fluvially reworked siliciclastic (tephric) deposits, and two widely distributed pyroclastic density current (PDC deposits generated from explosive silicic volcanism within the Taupo Volcanic Zone (TVZ). The younger of the two PDC deposits (informally named Waiuku tephra) is glass-isothermal plateau fission-track (ITPFT) dated at 1.00 ᄆ 0.03 Ma and occurs in a normal polarity interval interpreted as the Jaramillo Subchron. Waiuku tephra is correlated with Unit E sourced from the Mangakino Volcanic Centre of the TVZ. Waiuku tephra can be subdivided into two distinctive units enabling unequivocal field correlation: a lower stratified unit (dominantly pyroclastic surge with fall component) and an upper massive to weakly stratified unit (pyroclastic flow). At many sites in south Auckland, Waiuku tephra retains basal "surge-like" beds (<1.4 m thickness). This provides clear evidence for primary emplacement and is an exceptional feature considering the c. 200 km this PDC has travelled from its TVZ source area. However, at many other Auckland sites, Waiuku tephra displays transitional sedimentary characteristics indicating lateral transformation from hot, gas-supported flow/surge into water-supported mass flow and hyperconcentrated flow (HCF) deposits. The older PDC deposit is dated at 1.21 ᄆ 0.09 Ma, is enveloped by tephras that are ITPFT-dated at 1.14 ᄆ 0.06 Ma (above) and 1.21 ᄆ 0.06 Ma (below), respectively, and occurs below a short normal polarity interval (Cobb Mountain Subchron) at c. 1.19 Ma. This PDC deposit, correlated with Ongatiti Ignimbrite sourced from the Mangakino Volcanic Centre of TVZ, has laterally transformed from a gas-supported, fine-grained pyroclastic flow deposit at Oruarangi, Port Waikato, into a water-supported volcaniclastic mass flow deposit farther north at Glenbrook Beach. The occurrence of Ongatiti Ignimbrite in Auckland significantly extends its northward distribution. Large numbers of post- and pre-Ongatiti rhyolitic tephra layers, ranging in age from c. 1.31 to 0.53 Ma, are also recognised in the region, with some up to 0.5 m in compacted fallout thickness. Although some tephras can be attributed to known TVZ eruptions (e.g., Ahuroa/Unit D), many have yet to be identified in proximal source areas and remain uncorrelated. However, some can be reliably correlated to tephra layers occurring in marine to nearshore sequences of Wanganui Basin and deep-sea cores retrieved east of North Island. The identification of previously unrecognised mid-Pleistocene TVZ-sourced tephra deposits in the Auckland region, and their correlation to the offshore marine record, represent an advance in the construction of a higher resolution history for the TVZ where, close to eruptive source, the record is fragmentary and obscured by deep burial, or erosion, or both.

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  • Rates of deformation, uplift, and landscape development associated with active folding in the Waipara area of North Canterbury, New Zealand

    Nicol, A.; Alloway, B.; Tonkin, P. J.

    Journal article
    Lincoln University

    Analysis of the geometry and ages of faulted and tilted late Quaternary fluvial terraces and their associated cover beds provide evidence of active folding at three localities in the Waipara area of North Canterbury, New Zealand. Terrace survey data, the occurrence of the approximately 22.6-kyr-old Aokautere Ash, and examination of soil profiles indicate that folding has continued into the late Holocene but that the amounts and rates of deformation are locally variable. Rates of uplift in the Waipara area are compared with those derived from marine terraces preserved at the Pacific coast, east of the study area. Results indicate that rates of measurable deformation reach a maximum along the Waipara range front, where bedrock deformation is most intense and shortening rates of up to 5.57±0.69%/100 kyr occur. Across the coastal ranges the average rate of shortening is 0.8±0.4%/100 kyr, which corresponds with an absolute shortening rate of 1.4±0.6 m/kyr and represents only a small proportion of the predicted plate motion vector in this region. Uplift rates range from 0–1.83 m/kyr for a late last glacial fluvial terrace and from 1.36–2.16 m/kyr for three marine terraces. Fluvial and marine terrace uplift rates vary in accord with the geometries of the folds in bedrock, and the spatial pattern of uplift directly reflects fold growth. The structure contour pattern of folded surfaces provides a first approximation to the spatial pattern of uplift. Differential uplift due to folding accounts for up to approximately 55–75% of the total uplift and has produced folds with structural relief of about 1300 m (i.e., amplitudes of 600–700 m). These folds have formed over the last 0.8±0.4 m.y. since the onset of Quaternary deformation in the Waipara region.

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