4 results for Alloway, B.V.

  • Foraminiferal and molluscan evidence for the Holocene marine history of two breached maar lakes, Auckland, New Zealand

    Hayward, Bruce, W., B.; Grenfell, H.R.; Sandiford, A.; Shane, P.R.; Morley, M.S.; Alloway, B.V. (2002)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. Drillhole records of fossil Foraminifera and Mollusca, together with sparse tephra age control, document similar Holocene marine histories of two of Auckland's breached maars-Pukaki Lagoon, Manukau Harbour, and Onepoto Lagoon, Waitemata Harbour. Following eruption, both maars slowly accumulated carbonaceous mud in freshwater lakes, until they were breached by rising sea level in the early Holocene (c. 8100 cal. yr at Onepoto, c. 7600 cal. yr at Pukaki). Following breaching, both became saltwater tidal lagoons with silled, subtidal basins rapidly accumulating marine mud as the underlying sediment compacted. Onepoto Lagoon may have had deeper water than Pukaki, because it was colonised by a foraminiferal fauna (Bolivina, Bulimina, Buliminella, Spiroloxostoma) that prefers quiet, dysoxic bottom conditions. Both fossil groups identify where the lagoons shallowed from subtidal to low tidal depths. This occurs c. 15 m downhole (6900 cal. yr) in Pukaki and c. 9.5 m downhole in Onepoto, after sea-level rise had levelled off at about its present height (7000 cal. yr). Marine mud sedimentation slowed in the intertidal, accumulating largely in response to 12 m and 5 m compaction of the maar fill, respectively. Subtidal and low tidal fringe foraminiferal faunas of both lagoons are characterised by Ammonia-Haynesina associations, whereas intertidal faunas above mean low water are dominated (>90%) by Ammonia. Pukaki Lagoon foraminiferal faunas differ from Onepoto by their higher subtidal diversity of benthic foraminiferal tests and the presence of planktic tests in the subtidal section. These differences are inferred to relate to the significantly more exposed conditions outside the entrance to Manukau Harbour, where juvenile benthic tests were lifted into suspension and, together with the planktics, carried by the strong tidal currents up the harbour channels into Pukaki Lagoon. These introduced tests settled out of suspension in the quiet subtidal waters and accumulated in the sediment. Once Pukaki Lagoon had been filled with mud to intertidal depths, most introduced tests were apparently flushed away by the outgoing tides and did not accumulate. The presence in the Onepoto sequence (9.8-8.7 m) of the gastropods Micrelenchus huttonii and Notoacmea helmsi f. scapha indicate that Zostera seagrass once grew in the lagoon at around spring low tide level.

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  • Palynology, sedimentology and environmental significance of Holocene swamps at northern Kaitoke, Great Barrier Island, New Zealand

    Horrocks, M.; Ogden, J.; Nichol, S.L.; Alloway, B.V.; Sutton, D.G. (2000)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. Pollen and sediment analyses of two cores from coastal freshwater swamps at northern Kaitoke (Kaitoke Swamp and Police Station Swamp), Great Barrier Island, show that c. 7300 calibrated yr B.P. Kaitoke Swamp was an estuary with tidal flats. Avicennia, now absent from the swamp area, was present in the estuary. By c. 4500 yr B.P. fresh water conditions had developed at the Kaitoke Swamp site as marine influences decreased. Around the same time, fresh water swamp conditions commenced at the Police Station Swamp site on the surface of a low lying area of a Late Pleistocene dune. A sandy layer at Kaitoke may represent rapid infilling followed by a dry soil surface until c. 1000 yr B.P. Conifer-hardwood forest on the hills surrounding the sites c. 7300-c. 1800 yr B.P. was dominated by Dacrydium and Metrosideros. During this period, environmental conditions were relatively stable, with little change in forest composition. Between 1800 yr and 800 yr B.P. Kaitoke Swamp was reflooded, and the Police Station Swamp extended as a shallow lake over the nearby dune flat. These new shallow swamps were invaded by swamp forest (mainly Dacrycarpus with some Laurelia). The presence of charcoal and Pteridium spores above the Kaharoa Tephra suggests that major Polynesian deforestation at northern Kaitoke began c. 600 calibrated yr B.P.

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  • A Late Quaternary palynological and sedimentological record from two coastal swamps at southern Kaitoke, Great Barrier Island, New Zealand

    Horrocks, M.; Ogden, J.; Nichol, S.L.; Alloway, B.V.; Sutton, D.G. (2000)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. Pollen and sediment analyses of two cores from southern Kaitoke (Forsythes' Paddock and Blackwells' Bush), Great Barrier Island, show that at c. 7500 cal. yr B.P., the area was an estuary with tidal flats and Avicennia. By c. 3000 cal. yr B.P., a Restionaceae (Leptocarpus) salt marsh had developed in the estuary as marine influences lessened. By c. cal. 2550 yr B.P., fresh water swamp (Cyperaceae-Gleichenia-Leptospermum) had replaced the salt marsh. Conifer-hardwood forest surrounding the southern Kaitoke sites from c. 7500-c. 2800 cal. yr B.P. was dominated by Dacrydium, Metrosideros and Libocedrus. After c. 2800 cal. yr B.P., Metrosideros was replaced by Agathis, Phyllocladus and Prumnopitys taxifolia, suggesting climatic change to more variable conditions. The presence of the Kaharoa Tephra suggests that major Polynesian deforestation at southern Kaitoke began c. 600 cal. yr B.P. Minor pre-Kaharoa fire disturbance is evident c. 1750 cal. yr B.P. and c. 1290-970 cal. yr B.P.

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  • The palynology and sedimentology of a coastal swamp at Awana, Great Barrier Island, New Zealand, from c. 7000 yr B.P. to present

    Horrocks, M.; Ogden, J.; Nichol, S.L.; Alloway, B.V.; Sutton, D.G. (1999)

    Journal article
    The University of Auckland Library

    An open access copy of this article is available from the publishers website. Pollen and sediment analysis of two Holocene cores from Awana, Great Barrier Island, shows that at 7000 calibrated yr B.P. the local swamp was an estuarine salt marsh dominated by Restionaceae. By c. 6000 yr B.P. the water table was lower, and a fresh water swamp (Gleichenia-Leptospermum) had replaced the salt marsh. Regional conifer-hardwood forest c. 7000 yr B.P. was initially co-dominated by Libocedrus and Dacrydium cupressinum. Libocedrus declined from c. 6000 yr B.P. During the period c. 6000-c. 2500 yr B.P., relatively stable environmental conditions ensued with little change in local or regional vegetation. Around 2500 yr B.P., the swamp surface became drier and was invaded by Dacrycarpus and Laurelia swamp forest. This forest was subsequently repeatedly disturbed (not by fire), indicating climatic change to drier and windier conditions. Ascarina lucida was periodically a major component of swamp forest. Disturbance is also recorded in the clastic (mineral) sediments, where beds of sand within finer-grained sediment and peat are interpreted as wind blown material derived from partly devegetated dunes to seaward. The presence of the Kaharoa Tephra allows the timing of major Polynesian deforestation at Awana to be reliably dated to c. 600 calibrated yr B.P. In contrast, we see no evidence in the clastic sediment record of disturbance at Awana since Kaharoa time. We attribute this to the maintenance of stable dunes by a herb/scrub cover despite nearby fires, or to the presence of scrub or forest buffering the swamp from ablating dunes.

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