New Zealand Journal of Geology and Geophysics

Published by Royal Society of New Zealand
Print ISSN: 0028-8306
Minor and trace elements have been determined in augite, hornblende, and pyrope megacrysts by neutron activation analysis and spark-source mass spectrometry, and the results are compared with published data. The lanthanide patterns are especially significant; relative to chondritic abundances, augite shows a comparatively unfraction- ated pattern, whereas hornblende is progressively depleted and pyrope progressively enriched in the heavier lanthanides. The lava accompanying the megacrysts appears to have been derived from a basaltic magma by the removal of pyrope followed by selective crystallisation.
Radiocarbon ages acquired from the Pukaki core.
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.
The 11 900 yr BP Waiohau eruptive episode is a moderately sized rhyolitic event of the Tarawera Volcanic Complex. Subdivision of the pyroclastic fall deposits previously mapped as Waiohau Tephra has allowed the chronology of the eruption to be deciphered. At least 15 events (units A‐O) with volumes in the range 50 km) poorly preserved in paleosols. Previous volume calculations are considered overestimates because they included tephric loess. Effusive activity represents 3.9 km3, and pyroclastic debris in the northern sector adds another 2.4 km3, but much of the latter is xenolithic.
A 10 mm thick, c. 15 700 calendar yr BP (c. 13 100 14C yr BP) rhyolitic tephra bed in the well-studied montane Kaipo Bog sequence of eastern North Island was previously correlated with Maroa-derived Puketarata Tephra. We revise this correlation to Okataina-derived Rotorua Tephra based on new compositional data from biotite phenocrysts and glass. The new correlation limits the known dispersal of Puketarata Tephra (sensu stricto, c. 16 800 cal yr BP) and eliminates requirements to either reassess its age or to invoke dual Puketarata eruptive events. Our data show that Rotorua Tephra comprises two glass-shard types: an early-erupted low-K2O type that was dispersed mostly to the northwest, and a high-K2O type dispersed mostly to the south and southeast, contemporary with late-stage lava extrusion. Late-stage Rotorua eruptives contain biotite that is enriched in FeO compared with biotite from Puketarata pyroclastics. The occurrence of Rotorua Tephra in Kaipo Bog (100 km from the source) substantially extends its known distribution to the southeast. Our analyses demonstrate that unrecognised syn-eruption compositional and dispersal changes can cause errors in fingerprinting tephra deposits. However, the compositional complexity, once recognised, provides additional fingerprinting criteria, and also documents magmatic and dispersal processes. The final, definitive version of this article has been published in the Journal, New Zealand Journal of Geology and Geophysics, 46(4), (2003), (c) Royal Society of New Zealand at the Royal Society of New Zealand Journals Online webpage.
The 21.9 ka Okareka and 17.6 ka Rerewhakaaitu rhyolite eruption episodes began the construction of Tarawera Volcano in the Okataina Volcanic Centre, Taupo Volcanic Zone. Examination of the proximal and medial stratigraphy of these moderate-size (c. 5 km3 magma) but poorly exposed pyroclastic deposits has increased understanding of their eruption and dispersal processes. The Okareka Tephra consists of at least nine units (A–I), with unit A basaltic scoria at the base, overlain by the rhyolitic units B–I. Unit C is the largest individual plinian fall deposit (c. 0.4 km3), dispersed from an eruption column that reached c. 19 km height in the presence of strong crosswinds. The other pyroclastic units record a variety of phreatomagmatic, sub-plinian, and small ignimbrite eruptions, which were followed by extrusion of voluminous lava flows. The Rerewhakaaitu Tephra consists of 15 rhyolitic fall units A–N. An initial short plinian phase dispersed lapilli-fall unit A, mostly to ENE, from columns c. 15 km in height. Units B–D have high ash contents, indicating phreatomagmatic eruptions with varying magma/water ratios, and were widely dispersed, with lobes to the northeast and southeast. Units E–J were deposited from 20–25 km high plinian eruption columns into strong crosswinds that dispersed tephra to the southeast. The E–J package contains the largest tephra volume of the episode (1.18 km3) and is thought to dominate the deposits widely dispersed in Pacific Ocean sediments to the east of New Zealand. Rerewhakaaitu pyroclastic deposits are interbedded with, and underlie, voluminous lavas.
The 1848 and 1855 earthquakes provide examples of clustered earthquake sequences involving several faults. Historical evidence indicates that fault rupturing and ground deformation on both sides of Cook Strait occurred over periods of several days during the October 1848 earthquakes on the Awatere, Ohariu and possibly the Wellington faults, with shallowing in Lambton Harbour, Wellington. The January–February 1855 earthquakes occurred on the Wairarapa, Wharekauhau, Nicholson Bank, Vernon, Awatere and Needles faults. The pattern of faulting suggests the existence of distinct seismogenic zones across Cook Strait, within which mainshock triggering of aftershock displacement on major faults can occur.
An open access copy of this article is available from the publishers website. Downwasting has altered the morphology of the terminus region of the Tasman Glacier between 1971 and 1993. Rapid melting began in the late 1960s in a few isolated melt ponds in the centre and in a small elongated lakelet at the eastern lateral moraine. These ponds and lakes grew rapidly in size during the 1970s and coalesced to form a large melt lake by about 1990. This melting has led to a disintegration of the entire terminus region, and now occurs as far as 3 km upstream from the old terminus. A poorly understood convection mechanism prevents suspended silt from settling and causes the uniform grey colour of the lake (here called "Tasman Lake'). Surveys demonstrate how the terminus region of the largest New Zealand glacier has disintegrated over the past 22 years.
An open access copy of this article is available from the publishers website. Caves overrun by glaciers are known to accumulate dateable evidence of past glacial and interglacial events. Results are reported from an investigation of Aurora Cave on the slopes above Lake Te Anau in Fiordland. The cave commenced to form before c. 230 ka B.P. Sequences of glacifluvial sediments interbedded with speleothems are evidence of the number and timing of glacial advances and the status of intervals between them. Twenty-six uranium series dates on speleothems underpin a chronology of seven glacial advances in the last 230 ka, with the peak of the late Otira glaciation, Aurora 3 advance, at c. 19 ka B.P. With five advances in the Otiran, the last glaciation is more complex than previously recognised. Comparison of the record with that recorded offshore from DSDP Site 594 reveals little matching, but the correspondence of the Aurora sequence with that interpreted from other onshore deposits is more convincing. Glacial deposits on slopes above the cave for a further 660 m may be evidence of the "missing" glacial events of the mid-early Pleistocene.
There is no obvious distinction in age between the dacites (Upuhue and Kopukairua) and the rhyolites. The Papamoa Ignimbrites are 
Map of northern and central North Island showing the Taupo and Coromandel Volcanic Zones, the Hauraki Rift, and the location of silicic calderas and volcanic centres since 10 Ma. Age data for Coromandel Volcanic Zone are from Skinner (1986), Adams et al. (1994), Takagi (1995), Hoskin et al. (1998), Krippner (2000), and this paper; and for Taupo Volcanic Zone from Houghton et al. (1995), Wilson et al. (1995), and Lowe et al. (2001). Structural data in Bay of Plenty are from Skinner (1986) and Davey et al. (1995).  
Map of the Tauranga area showing the geographical distribution and age of the four groups of silicic domes and flows comprising the Tauranga Volcanic Centre.  
G eo lo g ical map o f Tauranga and southern Kaimai Range showing the distribution of rhyolite and dacite domes and their 40 Ar/ 39 Ar ages. Whole-rock K-Ar ages determined by previous authors are given in brackets: ( ) = Takagi (1995); { } = Brathwaite & Christie (1996); p = K-Ar age from plagioclase. Inset: Location of the Coromandel and Taupo Volcanic Zones in the North Island, New Zealand. The Tauranga-Kaimai area is indicated by the box.  
An open access copy of this article is available from the publishers website. Subduction-related volcanism in the northern part of the North Island of New Zealand shifted abruptly during the late Pliocene. This study focuses on the transition, in time and space, from the NNW-oriented Miocene-Pliocene Coromandel Volcanic Zone to the northeast-oriented active Taupo Volcanic Zone. The volcanic rocks marking this transition are exposed in the Tauranga Basin and adjacent Kaimai Range, and associated here with the recently defined Tauranga and Kaimai Volcanic Centres, respectively. New 40Ar/39Ar age determinations indicate that the transition occurred between 1.90 and 1.55 Ma, that is between the youngest age of silicic volcanism in the Tauranga-Kaimai area, and the age of the oldest silicic volcanism in the Taupo Volcanic Zone. This interpretation is generally consistent with recent plate models and with the initiation of the Kermadec Arc within the last 2 m.y.
Average major element composition of glass shards.
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 ± 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. -from Authors
An open access copy of this article is available from the publishers website. The c. 5600 cal. yr BP Whakatane eruption episode consisted of a sequence of intracaldera rhyolite eruptions from at least five vents spread over 11 km of the Haroharo linear vent zone within Okataina Volcanic Centre. Initial vent-opening eruptions from the Haroharo vent produced coarse lithic clast "blast beds" and pyroclastic density currents (surges). These were immediately followed by eruption of very mobile pumiceous pyroclastic surges from the Makatiti vent 6 km to the southwest. Major plinian eruptions from the Makatiti vent then dispersed Whakatane Tephra pumice fall deposits (bulk volume c. 6 km3) across the northeastern North Island while smaller explosive eruptions produced pyroclastic flows and falls from the Haroharo-Rotokohu vents and at the Pararoa vent on the caldera rim 11 km northeast from Makatiti. The pyroclastic eruptions at all vents were followed by the extrusion of lava flows and domes; extruded lava volumes ranged from 0.03 km3 for the Pararoa dome to 7.5 km3 for the Makatiti-Tapahoro lava flows and domes. Minor variations in whole rock and glass chemistry show that the three main vent areas each tapped a slightly different high-silica rhyolite magma. About 10 km3 of M-type magma was erupted from the Makatiti-Tapahoro vents; c. 1.3 km3 of H-type magma from the Haroharo-Rotokohu vents, and 0.04 km3 of P-type magma from the Pararoa vent. There are no significant weathering or erosional breaks within th e Whakatane eruptive sequence, which suggests that all Whakatane eruptions occurred within a short time interval. However, extrusion of the Haroharo dome within the Makatiti pyroclastic eruption sequence suggests a duration of c. 2 yr for the main pyroclastic eruption phase. Emplacement of the following voluminous (7.5 km3) lavas from the Makatiti-Tapahoro vents would have occurred over >10 yr at the c. 10-20 m3/s inferred extrusion rates.
Changes in Neogene sediment texture in pelagic carbonate-rich oozes on the Challenger Plateau, southern Tasman Sea, are used to infer changes in depositional paleocurrent velocities. The most obvious record of textural change is in the mud:sand ratio. Increases in the sand content are inferred to indicate a general up-core trend towards increasing winnowing of sediments resulting from increasing flow velocity of Southern Component Intermediate Water (SCIW), the forerunner of Antarctic Intermediate Water. In particular, the intervals c. 19-14.5 Ma, c. 9.5-8 Ma, and after 5 Ma are suggested to be times of increased SCIW velocity and strong sediment winnowing. Within the mud fraction, the fine silt to coarse clay sizes from 15.6 to 2 µm make the greatest contribution to the sediments and are composed of nannofossil plates. During extreme winnowing events it is the fine silt to very coarse clay material (13-3 µm) within this range that is preferentially removed, suggesting the 10 µm cohesive silt boundary reported for siliciclastic sediments does not apply to calcitic skeletal grains. The winnowed sediment comprises coccolithophore placoliths and spheres, represented by a mode at 4-7 µm. Further support for seafloor winnowing is gained from the presence in Hole 593 of a condensed sedimentary section from c. 18 to 14 Ma where the sand content increases to c. 20% of the bulk sample. Associated with the condensed section is a 6 m thick orange unit representing sediments subjected to particularly oxygen-rich, late early to early middle Miocene SCIW. Together these are inferred to indicate increased SCIW velocity resulting in winnowed sediment associated with faster arrival of oxygen-rich surface water subducted to form SCIW. Glacial development of Antarctica has been recorded from many deep-sea sites, with extreme glacials providing the mechanism to increase watermass flow. Miocene glacial zones Mi1b-Mi6 are identified in an associated oxygen isotope record from Hole 593, and correspond with times of particularly invigorated paleocirculation, bottom winnowing, and sediment textural changes. The final, definitive version of this article has been published in the Journal, New Zealand Journal of Geology & Geophysics, 47(4), (2004), (c) Royal Society of New Zealand at the Royal Society of New Zealand Journals Online webpage.
747 Mi zones and ages versus the approximate sea- water 8 18 O estimated from the Mg/Ca ratios of benthic foraminifers (after Billups & Schrag 2002). These are used to compare with the values established in Table 6.
Oxygen and carbon isotopic stratigraphies are presented from both benthic and planktic foraminifera for the late early Miocene to earliest Pliocene interval (c. 19–5 Ma) of intermediate water-depth DSDP Site 593 in the southern Tasman Sea. The benthic values are interpreted as recording Miocene Southern Component Intermediate Water, while the planktic species record the Miocene mode and surface water signals. Comparisons are made between temperate Site 593 and the intermediate-depth polar Site 747 in the southern Indian Ocean. Glacial Mi zones Mi1b–Mi6, representing extreme glacial events, are evident in both the Site 593 intermediate and surface water records. Miocene Southern Component Intermediate Water δ18O values are generally lighter than the Holocene equivalent (Antarctic Intermediate Water), indicating slightly warmer intermediate waters and/or less global ice volume. The benthic-planktic gradient is interpreted as indicating a less stratified Tasman Sea during the Miocene. The benthic δ13C record contains most of the global carbon maxima (CM) events, CM1–7 (CM1–6 = the Monterey Excursion). Like global deep-water records, the Tasman Sea intermediate water δ13C values indicate that most CM events correspond with Mi glacials, including Mi4 at Site 593, not reported previously. Intermediate waters play an important role in propagating climatic changes from the polar regions to the tropics, and the Site 593 dataset provides a full water column record of the structure of Miocene intermediate to surface watermasses prior to the modern situation.
An open access copy of this article is available from the publishers website. In the late Mesozoic Waioeka petrofacies in northeastern North Island, New Zealand, sandstone pebbles differ significantly in petrography from their enclosing sandy conglomerate matrix, and yield contrasting provenance signatures. The compositional contrast demonstrates the extrabasinal origin of most of the analysed clasts. Differences in clast provenance have been used to review boundaries and the terrane affiliation to the neighbouring Torlesse and Waipapa composite terranes. A previously postulated Cretaceous large-scale dextral strike-slip displacement of eastern North Island along the Wellington-Mohaka-Whakatane Fault is supported by these data. The timing for this movement can be further bracketed between c. 98 and 85 Ma. The Waioeka and Omaio petrofacies, formerly attributed to the Torlesse terranes as the Waioeka Subterrane, are reinterpreted to constitute a separate terrane (Waioeka-Mata River Terrane). However, the westernmost portion of the former Waioeka Subterrane, west of the Wellington-Mohaka-Whakatane Fault, is considered to be part of the Waipapa composite terrane.
A small partial actinopterygian (ray-finned) fish from the Lower Triassic Greville Formation of D'Urville Island is reported as the first formally noted and described Triassic actinopterygian from New Zealand. The specimen includes the upper lobe of a slender heterocercal caudal fin, with fringing fulcra and a series of dorsal caudal fulcra and epaxial basal fulcra. The fossil also preserves additional fin rays and a series of probable neural and haemal arch elements. The fossil is too incomplete to be precisely identified, but the heterocercal caudal fin with associated fringing and dorsal caudal fulcra are sufficient to diagnose the specimen as a phylogenetically basal ‘palaeoniscoid’-grade actinopterygian, the first to be reported from New Zealand.
The observed Bouguer gravity anomalies on Atiu, Manuae, and Nassau Islands in the Cook Group are consistent with the calculated gravity effects of uncompensated island platforms of average density 2·38 g/cm containing volcanic cores of average density 2·85 g/cm. Although insufficient gravity data are available for Aitutaki, Penrhyn, and Pukapuka, these islands also appear to have high density cores.
Summary of AFT population ages and statistical data.
Apatite fission track (AFT) and vitrinite reflectance (VR) data for early Miocene outcrops from the Waitemata Basin reveal that the basin sequence was subjected to shallow burial before denudation. AFT results suggest that the total sediment thickness within the basin was <=1 km and maximum paleotemperatures during burial never exceeded c. 60deg.C. Statistical analyses of the detrital AFT ages distinguish four dominant sources of sediment supply: contemporaneous volcanism; metagreywacke rocks of the Waipapa Group; the Northland Allochthon; and an unidentified source south of the basin. The apatite and zircon fission track results from the Waipapa Group rocks (Gondwana Terrane) adjacent to the basin suggest two discrete phases of accelerated cooling: the first during the early Cretaceous (c. 117 Ma) and the second during the mid Cretaceous (c. 84 Ma). These events probably reflect key stages in the tectonic development of the New Zealand microcontinent during the Cretaceous period, the earlier event being related to the climax of compressional deformation (Rangitata Orogeny) and the latter to extensional tectonism associated with the opening of the Tasman Sea. Waipapa Group rocks now exposed at the surface cooled from maximum paleotemperatures of c. 250deg.C at an estimated rate of c. 180-36deg.C/m.y., involving substantial denudation. This article has been published in the journal: New Zealand Journal of Geology and Geophysics. ©1999 The Royal Society of New Zealand.
Structures and microstructures within flanking lithologies of the Buller and Takaka Terrane boundary, the Anatoki Fault, record three pre‐Cenozoic deformation events in northwest Nelson. Each deformation event recognised in the Buller Terrane has structures that can be matched in style, orientation, and timing of development with that in the adjacent Takaka Terrane. D 1 is represented by north‐trending, upright or overturned to the west, large‐scale folds with an axial planar slaty cleavage. D 1 is mid Devonian in age and relates to amalgamation of the Buller and Takaka Terrane. D 2foliation occurs in a zone of ductile deformation adjacent to the Anatoki Fault near Boulder Lake. Rb‐Sr geochronology, and the relationship between the foliation and metamorphism associated with the adjacent c. 111 Ma Mt Olympus Pluton, suggests D 2 formed in the Early Cretaceous following pluton emplacement. D 3 is represented mainly by mesoscopic folds with an axial planar crenulation cleavage. D 3 structures crenulate and refold both D 1 and D 2 structures and are mid Cretaceous in age. Both D 2 and D 3 relate to an extremely active and changing tectonic period of New Zealand in the Early to mid Cretaceous. The east‐dipping Anatoki Fault in northwest Nelson records a complex history of ductile and brittle movement. Tectonites from central segments record ductile/brittle east‐over‐west reverse‐slip associated with D 1. To the north, D 2 tectonites from the Boulder Lake area record Early Cretaceous ductile dextral‐slip reactivation. To the south, tectonites from the Crow River and Mt Benson area record ductile/brittle dextral‐normal slip which, in the Crow River area, represents reactivation that postdates the intrusion of the c. 137 Ma Crow Granite. From the Crow River southwards, the Anatoki Fault has also undergone late Cenozoic brittle reactivation.
An open access copy of this article is available from the publishers website. Understanding the temporal and spatial development of the early Miocene Northland Volcanic Arc is critical to interpreting the patterns of volcanic activity in northern New Zealand through the late Cenozoic. The northwesterly trending arc is considered to have developed above a south west-dipping subduction system. The distribution of its constituent eruptive centres is described in terms of an eastern belt that extends along the eastern side of Northland and a complementary broad western belt which includes subaerial and submarine volcanic edifices. Critical examination of all 216 K-Ar ages available, including 180 previously unpublished ages, and their assessment against tectonic, lithostratigraphic, seismic stratigraphic, and biostratigraphic constraints, leads us to deduce a detailed chronology of periods of activity for the various early (and middle) Miocene arc-type volcanic complexes and centres of northern New Zealand: Waipoua Shield Volcano Complex (19-18 Ma, Altonian): Kaipara Volcanic Complex (23-16 Ma, Waitakian-Altonian); Manukau Volcanic Complex (c. 23-15.5 Ma, Waitakian-Clifdenian); North Cape Volcanic Centre (23-18 Ma, Waitakian-Altonian); Whangaroa Volcanic Complex (22.5-17.5 Ma, Waitakian-Altonian); Taurikura Volcanic Complex (22-15.5 Ma, Otaian-Clifdenian); Parahaki Dacites (22.5-18 Ma, Waitakian-Altonian); Kuaotunu Volcanic Complex (18.5-11 Ma, Altonian-Waiauan). In general, volcanic activity does not show geographic migration with time, and the western (25-15.5 Ma) and eastern (23-11 Ma) belts appear to have developed concurrently.
The middle Pliocene–Pleistocene progradation of the Giant Foresets Formation in Taranaki Basin built up the modern continental margin offshore from western North Island. The late Miocene to early Pliocene interval preceding this progradation was characterised in northern Taranaki Basin by the accumulation of hemipelagic mudstone (Manganui Formation), volcaniclastic sediments (Mohakatino Formation), and marl (Ariki Formation), all at bathyal depths. The Manganui Formation has generally featureless wireline log signatures and moderate to low amplitude seismic reflection characteristics. Mohakatino Formation is characterised by a sharp decrease in the GR log value at its base, a blocky GR log motif reflecting sandstone packets, and erratic resistivity logs. Seismic profiles show bold laterally continuous reflectors. The Ariki Formation has a distinctive barrel-shaped to blocky GR log motif. This signature is mirrored by the SP log and often by an increase in resistivity values through this interval. The Ariki Formation comprises (calcareous) marl made up of abundant planktic foraminifera, is 109 m thick in Ariki-1, and accumulated over parts of the Western Stable Platform and beneath the fill of the Northern Graben. It indicates condensed sedimentation reflecting the distance of the northern region from the contemporary continental margin to the south. This article has been published in the journal: New Zealand Journal of Geology and Geophysics. © 2004 The Royal Society of New Zealand.
An open access copy of this article is available from the publishers website. Permian-Triassic Beacon Supergroup (dominantly quartz-rich sandstones with coal) and Jurassic Ferrar Supergroup (mafic intrusives, extrusives, and phreatomagmatic clastic rocks), in the region studied, are separated by 20 m.y. of uplift, erosion, and nondeposition. Probable pre-Ferrar secondary minerals in Beacon rocks comprise overgrowths of quartz and K-feldspar followed by a cement of fine-grained sericitic mica and quartz. In Ferrar clastic rocks, some intrastratal dissolution of quartz and feldspar was followed by a cement of hydrothermal zeolite (heulandite/clinoptilolite-stilbite) which fills pores and replaces fine matrix and detrital mineral grains. Later overgrowths of plagioclase, quartz, and potash feldspar all replace zeolite. Finally, calcite replaces all previous mineral phases. This paragenesis occurs in Carapace Sandstone (Ferrar Supergroup), but Mawson Formation breccias (Ferrar) and some Beacon sandstones probably follow the same sequence, though less completely. Silica needed to form the late phases may have been derived from mineral conversions deeper in the stratigraphic pile or in underlying basement rocks (e.g., sodic plagioclase to laumontite), whereas silica released by conversion of heulandite to late calcite may have provided the quartz-chalcedony filling of vugs in Kirkpatrick Basalt. Pore-filling calcite cement in some Beacon sandstones may be pre-Ferrar, but a suitable Ca source is not known. Late replacement calcite may have utilised methane and CO2 from Beacon coals, and Ca from plagioclase and calcium zeolites in Ferrar rocks. Zeolite-facies burial metamorphism is indicated by laumontite, but its rarity constrains temperatures to around or below 210ᄚC, and there is no indication of a vertical temperature zonation. Thermal metamorphism adjacent to dikes and sills is generally minor, involving recrystallisation of matrix and loss of original fabric. Sandstone blocks within large dolerite intrusions have locally melted; tridymite and cristobalite probably formed at this time but inverted to quartz during cooling. Slow cooling of partial fusion melt produced spherulitic structures. Zeolite and calcite cements postdate thermal metamorphism. The main zeolite minerals are heulandite/clinoptilolite and stilbite, accompanied locally by one or more of laumontite, chabazite, analcime, and epistilbite.
An open access copy of this article is available from the publishers website. Northland Allochthon at Parua Bay and north Ocean Beach, east of Whangarei, consists of Late Cretaceous-Oligocene Mangakahia and Motatau Complex units. At both localities, deformed allochthon was emplaced onto autochthonous early Miocene basal Waitemata Group (which rests unconformably on Mesozoic Waipapa Terrane rocks) along a shear zone indicating westward or southwestward transport. This contact was subsequently deformed by eastwest-trending folds, causing northward overturning of units at Parua Bay and tight infolding between two blocks of autochthon at north Ocean Beach. At north Ocean Beach, intrusion of a dike/sill related to the Miocene Kauri Mountain Pluton predated the infolding. Other folds with similarly oriented axes and the same northward vergence have been found south of Whangarei Harbour. These north-verging, east-west-trending structures represent a north-south shortening after the emplacement of the Northland Allochthon not previously recognised. They indicate that the "autochthonous" blocks in the region were unusually mobile and may in fact be parautochthonous. The significance of the northward vergence of these late folds in the Whangarei area is not yet clear. Possibly equivalent structures indicating similar late north-south shortening are distributed throughout the northern North Island, but most commonly verge south.
Geometry of the Top Basement Unconformity (TBU) west of the Alpine Fault has been reconstructed through a set of cross-sections linking surface and subsurface geology. Onshore, the TBU shows tectonic relief of several kilometres between antiformal pop-ups and synformal depressions in contrast with a smoother topography offshore. This geometry arises from reverse slip on sets of north–south to NNE–SSW faults, mostly dipping 50–66° both west and east, that control folding of the TBU and overlying cover sequence. Some of these faults are inherited Upper Cretaceous–Palaeogene normal faults that displaced the TBU during the extensional phases and were later reactivated as reverse faults under compression, whereas others appear to be newly propagated Neogene reverse faults. The faults that deform the TBU have vertical displacements of 3–5 km and lengths of >150 km, and have the potential of being reactivated in the present stress field. Currently active faults comprise a set of blind reverse faults that propagate upsection from pre-existing extensional fault fabric in the basement, imposing a short-wavelength undulation on the TBU.
An open access copy of this article is available from the publishers website. The efficacy of low-resolution infrared (IR) satellite data for the estimation of the spatial variation of rainfall is examined. Three analysis techniques were applied to 41 NOAA satellite images of the Southern Alps of New Zealand. Estimated rainfall is compared with surface measurements from 35 sites. Single-channel histograms of cloud-top temperature are shown to have limited application but demonstrate the diurnal variation of cloud cover. Plots of the fraction of cloud amount below four selected temperatures in each of 14 areas across the Alps showed strong orographic dependence for low and middle cloud. Three simple regression models of rainfall dependence on cloudiness and position along a transect crossing the Main Divide show stronger correlation with location than with cloudiness.
At the central Maratoto valley prospect, southern Coromandel Peninsula, New Zealand, andesite flows and dacite breccias host rare porphyry‐style quartz veins that are telescoped by widespread epithermal veins and alteration. Early porphyry‐style quartz veins, which lack selvages of porphyry‐style alteration, host hypersaline fluid inclusions that contain several translucent daughter crystals, including halite and sylvite. Overprinting epithermal veins and alteration are divided into two stages. Main‐stage epithermal alteration and veins are characterised by the successive deposition of pyrite, quartz, and ankerite‐dolomite veinlets coupled with intense alteration of the wall rock to quartz, illite, interlayer illite‐smectite (≤10% smectite), chlorite, pyrite, ankerite, and dolomite. Late‐stage epithermal veins and alteration are characterised by the formation of calcite and siderite veinlets, coupled with overprinting of the wall rocks by both these minerals. Multiphase fluid inclusions in a porphyry‐style quartz vein formed at temperatures >400°C and trapped hypersaline magmatic fluid. Lower temperature secondary liquid‐rich inclusions in the porphyry‐style quartz vein homogenise between 283 and 329°C and trapped a dilute fluid with <1.8wt% NaCl equivalent. Inclusions in later epithermal quartz and calcite veins homogenise between 240 and 280°C (av. 260°C) and trapped a dilute fluid with apparent salinities of <2.9 wt% NaCl equivalent. Based on homogenisation and salinity data, secondary inclusions in porphyry‐style quartz veins may have formed 700–950 m deeper than telescoping epithermal veins. Main‐stage epithermal ankerite and dolomite have δ¹⁸O(VSMOW) values of 13.5–18.1‰, whereas late‐stage epithermal calcite has δ¹⁸O(VSMOW) values of 3.1–5.1‰. Calculated isotopic compositions for the fluid in equilibrium with ankerite‐dolomite and calcite at 260°C, averages 6 and ‐3‰, respectively. The enriched value for main‐stage ankerite‐dolomite suggests formation from waters that underwent significant water‐rock exchange, whereas isotopically lighter water that formed late‐stage calcite underwent little water‐rock interaction. We propose a three‐stage model to explain telescoped veins and alteration styles at the central Maratoto valley prospect area. Porphyry‐style quartz veins were the first to form from hot hypersaline multi‐cation magmatic fluids. These are telescoped by later widespread epithermal veins and alteration following descent of the paleowater table possibly due to rapid erosion or sector collapse of a volcanic edifice. Main‐stage epithermal alteration and deposition produced quartz, chlorite, illite, interlayered illite‐smectite, pyrite, and isotopically heavy ankerite‐dolomite from deeply circulating upwelling alkali chloride waters. Late‐stage collapse of the hydrothermal system resulted in the formation of overprinting calcite and siderite from isotopically lighter descending marginal steam‐heated CO2‐rich waters.
High‐alumina basalts (HABs) that occur throughout the central part of the Taupo Volcanic Zone (TVZ) are associated particularly with faulting, and many occur where faults intersect caldera margins. For convenience, the basalts are described in terms of three geographic‐tectonic segments: Okataina in the north, Kapenga in the middle, and Taupo in the south. Evidence for mixing and mingling between rising basaltic magmas and rhyolitic rocks and magmas is common, including the frequent occurrence of xenocrysts and xenoliths, quench textures, and melting around the rims of inclusions. Chemically, the basalts are similar in terms of major element compositions, suggesting relatively homogeneous PT conditions in the mantle source, but variation between some trace elements suggests different processes are operating in the crust with variable degrees of contamination. The model presented for HAB generation in the TVZ is for partial melting of mantle peridotite in the upper mantle, with the melt rising into the lower crust via dike swarms. In the upper crust, the distribution of HAB is strongly influenced by location and structure. In the Kapenga segment, there is little evidence for interaction between basaltic and rhyolitic magma, other than at very shallow levels, perhaps because the rhyolitic magma chambers (or pods) were solid, allowing brittle deformation and rapid intrusion of basalt dikes. At Okataina there is much greater mixing and mingling, suggesting there was still partially molten rhyolitic magma chambers beneath this area during basalt intrusion. Basalt in the Taupo segment occurs outside the Taupo caldera complex and may be related to the earlier Whakamaru caldera complex. The basalt is thought to rise through the crust as a network of unrelated melt batches into a plexus of discrete magma chambers and conduits, many of which are sited along fault zones causing fissure eruptions at the surface.
An open access copy of this article is available from the publishers website. Several new ammonite assemblages are described from the uppermost Temaikan and basal Heterian regional stages of New Zealand, Auckland Province, consisting mainly of the east Pacific Eurycephalitinae (Family Sphaeroceratidae). Four successive faunas are distinguished in the upper Awakino valley: All include the Andean genus Araucanites, here occurring with both sex-morphs. Fauna 1 includes Araucanites awakino n. sp., Iniskinites cf. crassus Riccardi and Westermann, and Xenocephalites grantmackiei Westermann and Hudson ?/m x Lilloettia aff. steinmanni (Spath) ?/M-latest Bathonian; Fauna 2 includes Araucanites postawakino n. sp. and Xenocephalites cf. stipanicici Riccardi et al.-Early/earliest Callovian; Fauna 3 with Araucanites ponganui n. sp., Iniskinites gr. cepoides (Whiteaves), and Choffatia gr. furcula (Neumayr)-Early Callovian; Fauna 4 with Araucanites spellmani n. sp.-? Middle Callovian. The Oraka Sandstone at Kawhia Harbour is now placed entirely in the uppermost Bathonian and Lower Callovian (i.e., with Faunas 1 and 2). Ammonities previously identified with Kimmeridgian taxa-that is, "Epimayaites", "Epicephalites", and "Subneumayria"-are now classified as microconchs of Araucanites and with macroconchs of Lilloettia and Iniskinites. The superjacent Ohineruru Formation contains a typically Indo-Pacific fauna of Late Oxfordian to Early Kimmeridgian age, based on Sulaites heteriensis (Stevens) [ex Idoceras], a close relative of S. gerthi Oloriz and Westermann from New Guinea, and, above, Paraboliceras macnaughti (Stevens) [ex Kossmatia]. The interval Upper Callovian to Middle Oxfordian cannot be documented by ammonites in New Zealand, suggesting a hiatus between Oraka and Ohineruru Formations, marked by the Captain King's Shellbed. Other useful index fossils are forms of the bivalve Retroceramus. The first occurrence of R. galoi (Boehm) defines the base of the Heterian regional stage, but its New Zealand occurrence is much earlier than in Indonesia (Middle Oxfordian). Furthermore, first occurrence is diachronous according to ammonite biostratigraphy even in Auckland Province, that is, between Faunas 3 and 4 in Awakino valley and in Fauna 2 at Kawhia Harbour. Regional and local facies control is indicated. On the other hand, Fauna 2 includes R. stehni Damborenea known from the Early/earliest Callovian of the Andes.
High?resolution seismic reflection data from the east Coromandel coast, New Zealand, provide details of the sequence stratigraphy beneath an autochthonous, wave dominated inner shelf margin during the late Quaternary (0?140 ka). Since c. 1 Ma, the shelf has experienced limited subsidence and fluvial sediment input, producing a depositional regime characterised by extensive reworking of coastal and shelf sediments during glacio?eustatic sea?level fluctuations. It appears that only one complete fifth?order (c. 100 000 yr) depositional sequence is preserved beneath the inner shelf, the late Pleistocene Waihi Sequence, suggesting any earlier Quaternary sequences were mainly cannibalised into successively younger sequences. The predominantly Holocene?age Whangamata Sequence is also evident in seismic data and modern coastal deposits, and represents an incomplete depositional sequence in its early stages of formation. A prominent aspect of the sequence stratigraphy off parts of the east Coromandel coast is the presence of forced regressive deposits (FRDs) within the regressive systems tract (RST) of the late Pleistocene Waihi Sequence. The FRDs are interpreted to represent regressive barrier?shoreface sands that were sourced from erosion and onshore reworking of underlying Pleistocene sediments during the period of slow falling sea level from isotope stages 5 to 2 (c. 112?18 ka). The RST is volumetrically the most significant depositional component of the Waihi Sequence; the regressive deposits form a 15?20 m thick, sharp?based, tabular seismic unit that downsteps and progrades continuously across the inner shelf. The sequence boundary for the Waihi Sequence is placed at the most prominent, regionally correlative, and chronostratigraphically significant surface, namely an erosional unconformity characterised in many areas by large incised valleys that was generated above the RST. This unconformity is interpreted as a surface of maximum subaerial erosion generated during the last glacial lowstand (c. 18 ka). Although the base of the RST is associated with a prominent regressive surface of erosion, this is not used as the sequence boundary as it is highly diachronous and difficult to identify and correlate where FRDs are not developed. The previous highstand deposits are limited to subaerial barrier deposits preserved behind several modern Holocene barriers along the coast, while the transgressive systems tract is preserved locally as incised?valley fill deposits beneath the regressive surface of erosion at the base of the RST. Many documented late Pleistocene RSTs have been actively sourced from fluvial systems feeding the shelf and building basinward?thickening, often stacked wedges of FRDs, for which the name allochthonous FRDs is suggested. The Waihi Sequence RST is unusual in that it appears to have been sourced predominantly from reworking of underlying shelf sediments, and thus represents an autochthonous FRD. Autochthonous FRDs are also present on the Forster?Tuncurry shelf in southeast Australia, and may be a common feature in other shelf settings with low subsidence and low sediment supply rates, provided shelf gradients are not too steep, and an underlying source of unconsolidated shelf sediments is available to source FRDs. The preservation potential of such autochthonous FRDs in ancient deposits is probably low given that they are likely to be cannibalised during subsequent sea?level falls.
An open access copy of this article is available from the publishers website. Detailed mapping and sampling on Turoa skifield and surrounding areas on Mt Ruapehu has enabled identification of individual flow packets that represent small scale eruptive events during the major cone-building episodes previously identified on Ruapehu by Graham and Hackett. The area is dominated by plagioclase-pyroxene-phyric andesitic lavas of Mangawhero Formation, which are petrographically and geochemically typical of post-120 ka Ruapehu lavas. Although the lavas are from a relatively small area of the volcano, geochemical and isotopic compositions show a range in variation similar to that observed for the entire volcano. Examination of geochemical variations between individual flow packets and also between sequential lava flows indicates complex processes of assimilation and influx of 'new', variably evolved and fractionated magmas into high level magma chambers. These chambers are most likely heterogeneous, and individual eruptions may also sample compositionally distinct regions of the same chamber. It is probable that a complex plumbing system exists beneath Ruapehu with at least two levels of magma storage, evolution, and crustal interaction. Consequently, attempts to numerically quantify such a complex system using models such as assimilation-fractional crystallisation processes are inherently oversimplifications.
Recent eruptions from Tongariro volcano, particularly from Ngauruhoe, have been small (Volcanic Explosivity Index or VEI ≤ 3), but between 11,000-12,000 calendar years BP there was a series of larger subplinian eruptions (VEI 4) from Tongariro volcano (Mangamate Formation), the last of which formed the Poutu Lapilli. This unit is considered to have had a volume of 1.1 km³, distributed in three main lobes (NW, NE, E) around a possible source or sources close to the present site of Ngauruhoe. Column height during the eruption ranged from 16 to 23 km. If such an eruption occurred today it would have a significant impact on the surrounding area. In the proximal zone (<25 km from source) >20 cm of ash/lapilli would be deposited, sufficient to cause collapse of some buildings in Tokaanu and the surrounding communities and damage to the Tokaanu Power Station. Much of the other infrastructure in the area (e.g electricity transmission lines, water supply and distribution, roads) would also be affected, as would the tourist industry. Evacuation may be necessary from this proximal area, and plans for this should be drawn up well before the event. Adequate provision also has to be made for disposal of ash from towns/communities and from key roads. Medial and distal areas (up to 100 km from source) would be affected, but to a decreasing extent with distance from source. An eruption like that forming the Poutu Lapilli is possible at any time in the future from Tongariro, and it is important that an effective management system is put in place to deal with such an event.
A-E Locality maps of the Antarctic Peninsula, Ellsworth Land, and the Behrendt and Hauberg Mountains, showing collection sites of crinoid specimens described herein. F, Stratigraphic columns of part of the Latady Formation showing levels at which crinoid specimens were found (a, 8 km northeast of the summit of Mt Hirman (early Bajocian); b, 4 km northeast of the summit of Mt Hirman (Callovian) (modified from Laudon et al. 1983). 
An open access copy of this article is available from the publishers website. Specimens of a late Bajocian to early Callovian isocrinid assigned to Pentacrinites cf. P. californicus (Clark), and specimens collected by Hikuroa in 1999-2000, are described as a new species of Chariocrinus. All specimens were collected from rock exposures of the Latady Formation at eight localities in the Behrendt and Hauberg Mountains, Ellsworth Land, Antarctica. The fauna, preserved in situ at all localities, is essentially complete, but due to tectonism, localities may have been moved many kilometres from their original position. Chariocrinus latadiensis n. sp. is compared with congeneric species and those of Hispidocrinus. It is the first record of the genus in the Southern Hemisphere, which has European Tethyan affinities. Columnals are pentastellate to pentalobate, and the symplectial articula appear diagnostic of Hispidocrinus but are included in Chariocrinus on the basis of spineless axillaries and fused adjacent crenulae; those of Hispidocrinus are spined and separated by a furrow or smooth band, respectively. A single pluricolumnal (?Apiocrinus) is the only associated crinoid found at any of the localities. Chariocrinus latadiensis lived a semi-sessile existence on a volcarenite substrate in association with vagrant ammonites, epifaunal and infaunal bivalves, and epifaunal brachiopods. The benthic taxa lived in shallow, low energy marine environments in the Middle Jurassic, part of a submarine back-arc basin near the shore off southeastern Gondwana.
Dicyclopsodites leei gen. et sp. nov. is described from New Zealand sediments close to the Oligocene–Miocene boundary. Its botanical affinity is deemed to be within the family Apocynaceae with links to southeast Asia where taxa with pollen of similar morphology exist today.
An open access copy of this article is available from the publishers website. Marine volcaniclastic gravity flow deposits of Miocene age are described from island exposures on the Tongan frontal arc platform (southwest Pacific Ocean). Background sedimentary rocks between gravity flow beds include non-calcareous brown mudstone, calcareous pebbly sandstone, and chalk. Depositional environments inferred from microfaunas, macrofaunas, trace fossils, and sedimentary structures range from shallow (shelf) to deep water (c. 1500 m). The depth range of the deposits is considered deeper than continental shelf, and shallower than typical non-volcanic large-scale depositional gravity flow environments such as submarine fans. Six lithofacies are distinguished. They embrace a wide range of gravity flow deposits, but within each lithofacies/environment there is one dominant association. The lithofacies contain varying proportions of mafic and silicic volcanic clasts. Some are solely mafic, some contain interleaved mafic and silicic intervals, and some contain mixed mafic and silicic clasts in the same beds. Clast size ranges from silt (<1/16 mm) to boulders (>64 cm). Accretionary lapilli are present in three lithofacies. The dominant gravity flow mechanisms were turbidity currents and debris flows. Derivation from underwater eruptions is likely in some lithofacies, while others are likely to be from subaerial eruptions. It is rarely possible to make the distinction from the clasts themselves. On Mango Island, bouldery debris flow material was transferred directly from a probable subaerial volcano to the basin. In all other cases a marked upper limit of clast size suggests that eruption process(es), or processes in the transfer of sediment before generation of gravity flows, effectively removed the largest clasts (>5 cm). The overall control on deposition is considered to be eruption-controlled sediment supply.
Geological map of northern part of Arrow rocks (modified after Aita & Spörli 2007; Suzuki et al. 2007) showing locality PO4/f139 (solid star) from which the fossil cast was collected. Unit 1: meta-basalts associated with meta-limestone and red shale. Unit 2A: Middle-Upper Permian red and green argillites. Units 2B-5: Lower-Middle Triassic black, green and red bedded chert intercalated with argilliceous beds (in particular, Unit 3 includes carbonaceous black chert). Unit 6: Middle Triassic maroon bedded chert and siliceous argillites. Unit 7: Middle Triassic alternating maroon and pale green siliceous bedded argillite. Unit 8: Middle Triassic green argillite. Solid lines: major logs, ARB and ARBN. 
Stratigraphic columns of the ARB and ARBN sections showing the horizon from which fossil fragment V447 was collected (modified from Yamakita et al. 2007). 
External casts of bone fragment V447 from Unit 4 of Oruatemanu Formation, Lower Triassic, Arrow Rocks, PO4/f139. A, Complete specimen, scale bar 10 mm. B, Area near right-hand end of specimen in 3A magnified ×11.4 to show longitudinal ornament between tubercles. 
Left lateral view of the anterior dorsal fin spine of Pyknotylacanthus spathianus Mutter & Rieber from the Early Triassic of Idaho, reversed to appear as the right lateral view, showing crown and root surface texture. A box indicates the approximate likely position of the Arrow Rocks fragment (V447), superimposed upon an outline of the Triassic ctenacanthoid Acronemus tuberculatus (Bassani). Modified from Mutter & Rieber (2005, fig. 2A); their fig. 2B illustrates the right side of A. tuberculatus but has been damaged in the relevant area. The diagonally hatched area in the figure marks a portion of the spine that is missing in the Pyknotylacanthus specimen; the outline of Acronemus is reversed from fig. 36L of Cappetta (1987) to show the location of the fin spine in right lateral view. The 10 mm scale bar refers to the fin spine; the original of the shark outline is c. 0.53 m long. 
The ornament on a small external cast in pink chert shows considerable similarity with that of various Middle Palaeozoic and Triassic fish genera. It comes from the Permian–Triassic Oruatemanu Formation of Arrow Rocks, Whangaroa area, eastern Northland. Conodont faunas from a few metres above and below the sample allow correlation with the Neospathodus pakistanensis zone of the Early Triassic, which is assigned to the late Dienerian (late Induan), with adjacent conodont zone faunas in their correct stratigraphic association. The cast is assumed to be that of a small fragment of fin spine, most likely from the junction area of the crown and root on the right-hand side of a dorsal fin spine, possibly anterior, of a marine ctenacanthoid shark, a basal shark order not previously recorded from New Zealand.
Suggests that the article by Whitehead & Ditchburn (1994), although presenting useful new data on 230Th/232Th analyses, is flawed and misleading in suggesting that the Rotoiti Tephra is considerably younger than c. 50 ka. The final, definitive version of this article has been published in the New Zealand Journal of Geology and Geophysics, 37(1), 1994, (c) The Royal Society of New Zealand at The Royal Society of New Zealand Journals Online webpage.
In their note, Whitehead & Ditchburn (1994) considered some U-Th, ESR, and ¹⁴C dates that relate to the age of the Rotoehu Ash and Rotoiti Ignimbrite members of the Rotoiti Tephra Formation (Froggatt & Lowe 1990). They suggested that the U-Th disequilibrium age (71 ± 6 ka) of Ota et al. (1989) is almost certainly incorrect, the true age being much younger, and hence, by implication, that the K-Ar age (64 ±4 ka) of Wilson et al. (1992) is likely to be too old. To support this contention, Whitehead & Ditchburn (1994) pointed firstly to problems with the ESR age (45.2 ± 8.2 ka) of Buhay et al. (1992), making it younger by 5% (42.9 ± 7.8 ka). Secondly, they presented and discussed four I4C ages said to be "surprisingly closely clustered and form[ing] a coherent set with no outliers", and with a mean of 35.1 + 2.8 ka*. The four ages comprise NZ877 and NZ1126 (both published previously), revised according to current IGNS procedures to give 37.7 ± 8.3 and 36.6 ± 5.3 ka, respectively; and NZ1357 and NZ1366 (purportedly not cited previously), similarly revised to give 31.4 ± 4.4 and 34.6 ± 7.9 ka, respectively. Whitehead & Ditchburn (1994) thus concluded that the age for Rotoehu Ash is likely to be <50 ka and that more work is required to explain why this result differs from the K-Ar age of 64 ± 4 ka. We comment briefly here on the findings of Whitehead & Ditchburn (1994) and present an alternative interpretation for the age of Rotoiti Tephra.
An extraordinarily diverse assemblage of cirripedes is described from a shallow-water deposit of late Oligocene age from Cosy Dell farm, near Waimumu, Southland, New Zealand. It is unusual not only because it represents a rarely preserved intertidal to shallow subtidal fauna, but also because it contains at least nine species, five of which are new to science. The deposit contains the earliest known representatives of the genera Chamaesipho and Notobalanus and these are associated with abundant Verruca, an association that no longer occurs in present-day New Zealand waters. Although the remains are intimately associated with each other, the deposit is interpreted as a condensed heterogeneous taphocoenosis, with intertidal zone taxa (Verruca, Chamaesipho, Tetraclitella, Austrobalanus, Protelminius) mixing with upper subtidal species (Eolasma, Notobalanus, Tasmanobalanus) and pelagic cirripedes (Lepas)
Upper depth limits of key benthic foraminiferal species from throughout the study area, and separately from north, east and south of Chatham Rise, compared with upper paleodepth limits determined from Lewis's (1979) Recent distribution data off southern Hawke's Bay, and upper depth limits determined for identical or similar species in the late Neogene of Taranaki Basin, west New Zealand (from Hayward et al. 1999).
An open access copy of this article is available from the publishers website. Paleobathymetric assessments of fossil foraminiferal faunas play a significant role in the analysis of the paleogeographic, sedimentary, and tectonic histories of New Zealand's Neogene marine sedimentary basins. At depths >100 m, these assessments often have large uncertainties. This study, aimed at improving the precision of paleodepth assessments, documents the present-day distribution of deep-sea foraminifera (>63 ?m) in 66 samples of seafloor sediment at 90-4700 m water depth (outer shelf to mid-abyssal), east of New Zealand. One hundred and thirty-nine of the 465 recorded species of benthic foraminifera are new records for the New Zealand region. Characters of the foraminiferal faunas which appear to provide the most useful information for estimating paleobathymetry are, in decreasing order of reliability: relative abundance of common benthic species; benthic species associations; upper depth limits of key benthic species; and relative abundance of planktic foraminifera. R-mode cluster analysis on the quantitative census data of the 58 most abundant species of benthic foraminifera produced six species associations within three higher level clusters: (1) calcareous species most abundant at mid-bathyal to outer shelf depths (<1000 m); (2) calcareous species most abundant at mid-bathyal and greater depths (>600 m); (3) agglutinated species mostly occuring at deep abyssal depths (>3000 m). A detrended correspondence analysis ordination plot exhibits a strong relationship between these species associations and bathymetry. This is manifest in the bathymetric ranges of the relative abundance peaks of many of the common benthic species (e.g., Abditodentrix pseudothalmanni 500-2800 m, Bolivina robusta 200-650 m, Bulimina marginata f.marginata 20-600 m. B. marginata f. aculeata 400-3000 m, Cassidulina norvangi 1000-4500 m, Epistominella exigua 1000-4700 m, and Trifarina angulosa 10-650 m), which should prove useful in paleobathymetric estimates. The upper depth limits of 28 benthic foraminiferal species (e.g., Fursenkoina complanata 200 m, Bulimina truncana 450 m, Melonis affinis 550 m, Eggerella bradyi 750 m, and Cassidulina norvangi 1000 m) have potential to improve the precision of paleobathymetric estimates based initially on the total faunal composition. The planktic percentage of foraminiferal tests increases from outer shelf to upper abyssal depths followed by a rapid decline within the foraminiferal lysocline (below c. 3600 m). A planktic percentage <50% is suggestive of shelf depths, and >50% is suggestive of bathyal or abyssal depths above the CCD. In the abyssal zone there is dramatic taphonomic loss of most agglutinated tests (except some textulariids) at burial depths of 0.1-0.2 m, which negates the potential usefulness of these taxa in paleobathymetric assessments.
An open access copy of this article is available from the publishers website. Small volume (<2 km3) basaltic volcanoes have been active throughout the late Quaternary in the Auckland Volcanic Field (AVF) in northern New Zealand. The main pyroclastic products of these centres are phreatomagmatic surges containing abundant accidental ejecta and magmatic fall deposits of limited aerial extent. Previously they had received no attention from a tephrostratigraphic perspective. Despite extensive weathering, many of these deposits contain basaltic glass that can be used to geochemically fingerprint the volcanic source and individual eruptive events. The glasses are predominantly basanites with SiO2 contents in the range 42-50 wt%. Many individual emplacement units are compositionally homogeneous on the basis of electron microprobe analysis (SiO2 ᄆ 0.5 wt%), and can be distinguished on the basis of TiO2, CaO, K2O, and P2O5 contents. Individual tephra beds can easily be characterised, however volcanoes are more compositionally diverse. Although the volcanoes are considered monogenetic, they display a wide range of different eruptive styles, and their pyroclastic deposits can display a compositional range (SiO2 45-50 wt%) within short stratigraphic sequences that show no evidence of hiatus. This increases the difficulty in matching distal tephra deposits to their source. Glass compositional data from 18 volcanoes show no evidence of spatial or temporal trends within the AVF.
An open access copy of this article is available from the publishers website. The Late Triassic and Jurassic rocks of the Marokopa area, southwest Auckland, form part of the western limb of the Kawhia Syncline. Within the area mapped, the Late Triassic - Early Jurassic Newcastle Group consists of 3100 m of generally fine to very fine sandstone and siltstone with common tuff beds, and occasional coarser sandstones and shellbeds. Faunas are marine, generally sparse to moderate, and dominated by bivalves and brachiopods. The Arawi Shellbed, Ngutunui Formation, Tewharau Formation, Ururoa Shellbed, and Ururoa Formation are recognised. The Middle Jurassic Rengarenga Group marks a change to shallow water, marginal marine, and nonmarine conditions. Lithologies are generally coarse to medium sandstone with abundant fine plant fragments, with occasional pebble-granule conglomerates, tuffs, and shellbeds. Thin coal and plant beds mark the southern limit of nonmarine conditions in the Rengarenga Group. Fully marine conditions return with the Late Jurassic Kirikiri Group. Oraka Sandstone and Ohineruru Formation consist mainly of slightly calcareous, concretionary fine sandstone and sandy siltstone, with a rich molluscan fauna dominated by bivalves. These formations are separated by the 1 m thick Captain King's Shellbed, with a glauconitic sandstone matrix and a distinctive molluscan and brachiopod fauna. The uppermost part of the sequence in the mapped area is the interfingering Kiwi Sandstone and Waikutakuta Formation. Strata generally dip regularly to the east-northeast at between 20 and 45ᄚ. Minor folding may be present in the Kairimu valley. The north-south trending Whareorino Fault is part of the Taharoa Fault Zone. A NE-ENE trend is shown by two faults in the Marokopa valley and two in the eastern part of the area. A fault in the Paraohanga valley shows a northwest trend.
An open access copy of this article is available from the publishers website. New aeromagnetic data from the Auckland Volcanic Field reveal negative magnetic anomalies over Taylor Hill and Mt St John volcanoes which are interpreted as resulting from anomalous remanent magnetisation directions. These anomalies are comparable in character to those occurring over three volcanoes in the southern part of the field that record coincident anomalous directions associated with a geomagnetic excursion. Since rates of change of the geomagnetic field may be rapid during such excursions, and their duration short, a strong temporal link is implied between these five separate volcanic centres, which are geographically spread throughout the Auckland field. Even assuming normal rates of secular variation, the total time period for these eruptions might be only several hundred years, which suggests a recurrence interval for these volcanoes that is much less than any currently estimated for the field.
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.
Belemnopsis stevensi, Belemnopsis maccrawi, and Belemnopsis sp. A (Challinor 1979a) are synonymous; B. stevensi has priority. New belemnite material from Kawhia Harbour and Port Waikato, together with graphical study methods, indicates that many small fragmentary specimens associated with B. stevensi in the lower part of its stratigraphic range are probably the same taxon. B. stevensi has been found only in the Middle and Upper Heterian Stage (Lower Kimmeridgian) at Kawhia and only in the Lower Ohauan Stage (Upper Kimmeridgian) at Port Waikato. This apparently disjunct distribution is attributed to poor exposure in the relevant sections. Belemnopsis kiwiensis n.sp., Belemnopsis cf. sp. B, Belemnopsis sp. B, Belemnopsis sp. D, and Belemnopsis spp. are associated with B. stevensi near the lowest known point in its stratigraphic range. The distribution of stratigraphically useful belemnites within the Heterian and Ohauan Stages is: Conodicoelites spp. (Lower Heterian; correlated with Lower Callovian); Belemnopsis annae (Lower and Middle Heterian; Lower Callovian/Lower Kimmeridgian); Belemnopsis stevensi (Middle Heterian/Lower Ohauan; Kimmeridgian); Belemnopsis keari (Upper Heterian; Kimmeridgian); Belemnopsis trechmanni (Upper Ohauan; Upper Kimmeridgian/Middle Tithonian). The apparently extreme range of Belemnopsis annae remains unexplained. Klondyke Sandstone (new) is recognised as the basal member of Moewaka Formation (Port Waikato area). The final, definitive version of this article has been published in the Journal, New Zealand Journal of Geology and Geophysics 46(1), 2003. (c) The Royal Society of New Zealand at the The Royal Society of New Zealand webpage.
An open access copy of this article is available from the publishers website. Te Pouhawaiki Volcano in the Auckland Volcanic Field was identified on the basis of a small scoria cone, but whether this come marked the location of a significant eruption centre has been unknown. Volcanic stratigraphy in the central Auckland isthmus is complex, with older deposits (possibly entire volcanic centres) obscured by younger deposits. The distribution of lava flows in the central Auckland isthmus was strongly influenced by the pre-volcanic topography, and is a major control on present-day groundwater flow regimes. Detailed gravity data from the central Auckland isthmus are used here to model the thicknesses of volcanic deposits and hence determine the pre-volcanic topography. The site of the former Te Pouhawaiki scoria cone is shown to correlate with a distinct positive gravity anomaly (c. 6 ? interpreted in terms of a lava-filled depression in the Waitemata surface, surrounded by a tuff ring. This inferred explosive eruption centre is similar in both size and eruption style to a number of others in the Auckland Volcanic Field and suggests that the Te Pouhawaiki scoria cone may have been the surface manifestation of a substantial eruption centre which also produced phreatomagmatic deposits and lavas. The gravity model also defines the location and geometry of the paleotopographic divide between the ancestral Waitemata and Manukau River systems, showing it to be a complex ridge system. These buried ridges peak at c. 10-20 m depth (60-70 m a.s.l.) with a saddle in an eastern limb of the ridge which may have allowed lava from One Tree Hill Volcano to flow north of this divide. The configuration of the pre-volcanic Waitemata surface indicates that the present-day groundwater flow regime is likely to be complex and divergent away from the ridge system, controlled in some areas by narrow paleovalleys. Within the ridge complex, an area in which groundwater flow is likely to be convergent has been defined which correlates with the location of occasional surface flooding.
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.
An open access copy of this article is available from the publishers website. Lake Pupuke provides a near-complete, high-resolution environmental record of the Holocene from northern New Zealand. Tephra beds constrain the timing of a range of proxy indicators of environmental change, and demonstrate errors in a radiocarbon chronology. Agathis australis forest progressively increases from c. 7000 yr BP and, in conjunction with indicators of reduced biomass productivity, support a model of long-term climate change to drier conditions over the Holocene. However, except for Agathis, conifer-hardwood forest dominated mainly by Dacrydium cupressinum shows little change throughout the pre-human Holocene, suggesting environmental stability. Dramatic vegetation change occurred only within the last millennium as a result of large-scale Polynesian deforestation by fire. This happened a short time before the local eruption of c. 638 cal. yr BP Rangitoto Tephra. The identification of two eruptions of tephra from Rangitoto volcano has implications for future hazard planning in the Auckland region, because the volcanoes were previously considered single event centres. Changes in atmospheric circulation since the Late Glacial, possibly causing lower frequency of distal ashfall in Auckland during the Holocene, complicates the use of long-term records in hazard frequency assessment.
Some 1500 m of marine Ohauan and Puaroan strata in the Port Waikato region of New Zealand are restudied in an attempt to resolve lithostratigraphic and biostratigraphic anomalies in published works. New correlations are proposed for some units of the Apotu Group. A lower 650 m siltstone, previously correlated entirely with Kinohaku Siltstone, is here regarded as including the interval Kinohaku Siltstone to Lower Puti Siltstone (new member), The Waiharakeke Conglomerate is not represented in the area by coarse sediments. A thin sandstone unit overlying the Lower Puti Siltstone and previously correlated with Waiharakeke Conglomerate is here correlated with the Ruakiwi Sandstone. The overlying 400 m siltstone, regarded previously as the entire Puti Siltstone, is here recognised as a new member, the Upper Puti Siltstone. The Coleman Conglomerate is much thicker in the region than mapped, and located higher in the sequence. Biostratigraphy is a key element in correlating the sequence with named units to the south. The sequence is mostly siltstone, but sandstone units provide some lithostratigraphic control. Belemnites are almost the only fossils found in the Late Ohauan and Early Puaroan part of the sequence and are important in the Late Puaroan. Formal belemnite zones, based in part on their stratigraphic distributions in other parts of southwest Auckland, are erected. Occasional ammonites provide tie points that correlate the succession with the standard stratigraphic column for the Tethyan realm. Belemnopsis aucklandica (Hochstetter) is redescribed and considered to be of full specific status as is its former subspecies, Belemnopsis trechmanni Stevens. Many pre-adult Belemnopsis aucklandica differ in form from adults; some have been previously identified in the field as Hibolithes. Some earlier identifications of belemnites from the Late Puaroan of Port Waikato are incorrect; most are now included in Belemnopsis aucklandica.
Samples used for testing.
Summary of TG methods used for proximate analysis.
Initial proximate analysis results for New Zealand coals.
Proximate analysis results obtained by TG.
analysis results for Ohai subbituminous coal (52/057) by TG using different sample weights.
An open access copy of this article is available from the publishers website. A technique has been developed at The University of Auckland for proximate analysis of coals by thermogravimetry using sample weights of <20 mg. Samples from three New Zealand coalfields and the Bowen Basin of Queensland, Australia, have been analysed. Coals tested range in rank from subbituminous to semianthracite, and have ash contents from 3.1 to 21.4% on a dry basis. Results obtained using the technique are within acceptable precision limits of the standard procedure. Volatile matter content of the coal shows a logarithmic increase with decreasing sample weight. The technique is ideally suited to: 1) analysing samples where insufficient material is available for standard proximate analysis, and 2) correlation with microstudies of coal. -from Author
Pliocene cool-water, bioclastic Te Aute limestones in East Coast Basin, New Zealand, accumulated either in shelfal shoal areas or about structurally shallow growth fold structures in the tectonically active accretionary forearc prism. Up to five stages of carbonate cementation are recognised, based on cement sequence-stratigraphic concepts, that formed on the seafloor during exposure of the limestones before burial, during burial, uplift, and deformation. Two principal fluid types are identified--topography-driven meteoric fluids and compaction-driven fluids. We have developed conceptual and quantitative models that attempt to relate the physical characteristics of fluid flow to the cement paragenesis. In particular, we have simulated the effects of uplift of the axial ranges bordering East Coast Basin in terms of the degree of penetration of a meteoric wedge into the basin. The dynamics of meteoric flow changed dramatically during uplift over the last 2 m.y. such that the modelled extent of the meteoric wedge is at least 40 km across the basin, and the penetration depth 1500 m or more corresponding with measured freshwater intersections in some oil wells. Cement-fluid relationships include: (1) true marine cements that precipitated in areas remote from shallow freshwater lenses; (2) pre-compaction cements that formed in shallow freshwater lenses beneath limestone "islands"; (3) post-compaction cements derived from compaction-driven flow during burial; (4) early uplift-related fracture-fill cements formed during deformation of the accretionary prism and uplift of the axial ranges; and (5) late uplift-related cements associated with uplift into a shallow meteoric regime. The final, definitive version of this article has been published in the Journal, New Zealand Journal of Geology & Geophysics, 47(4), (2004), (c) Royal Society of New Zealand at the Royal Society of New Zealand Journals Online webpage.
Top-cited authors
Kelvin Berryman
  • GNS Science
David J. Lowe
  • The University of Waikato
Alan Cooper
  • University of Otago
I.A. Nairn
Hamish J. Campbell