Showing papers in "New Zealand Journal of Geology and Geophysics in 1980"

Geology of the granulite and amphibolite facies gneisses of Doubtful Sound, Fiordland, New Zealand

Abstract: The geology of 700 km2 of high-grade metamorphic rocks from Doubtful Sound, New Zealand, is described Malaspina, Turn Point, and Waipero Cove Gneiss Zones, constituting the granulite, transition, and amphibolite zones of the basement, are separated by Doubtful Sound Thrust from the amphibolite facies cover, consisting of Kellard Point Gneisses, Deep Cove Gneisses, and Straight River Granite The last was intruded into the cover during the Tuhuan metamorphism and has a whole rock Rb-Sr isochron age of 372 ± 12 my BP Regionally important syn-metamorphic faults cut the cover and may link up to form another thrust It is suggested that Tuhuan retrogressive metamorphism of granulite facies basement, which gave rise to the transition and amphibolite zones, occurred during progressive amphibolite facies metamorphism of the cover sequence Synmetamorphic migmatites from the cover give a whole rock Rb-Sr isochron age of 388 ± 23 my bp The unaffected granulite basement is thought to be Precambrian

Distribution of landslips in the Wairarapa hill country

Abstract: Data gathered from airphoto and field surveys are statistically analysed to establish the distribution of landslips which occurred in the Wairarapa area, North Island, New Zealand, during the winter of 1977. The pattern of landslip occurrence is closely related to slope aspect and position on the hillslope. Slipping was concentrated on the upper parts of northerly facing slopes. The preference for northerly aspects is evident in each of the distributions of slips drawn separately from the upper, middle, and lower parts of the hillslopes. The 1350 km2 area studied yielded a mean density of 0.98 slips/ha. For 1 catchment field measurements of 4.78 slips/ha and a surface lowering of 69 mm were recorded. In comparison with other recorded events the degree of erosion experienced was severe. Slope angle, slope hydrology, and rainfall distribution appear to have little influence on the distribution of landslips. However, much of the hillslope regolith had been affected by mass movement in the past and i...

K—Ar age, composition, and origin of Mesozoic mafic rocks related to Ferrar Group, Pensacola Mountains, Antarctica

Abstract: A variety of mafic igneous bodies, including the unusually large, differentiated, layered gabbroic Dufek intrusion, and basalt and dolerite dikes and sills, intrude a Permian and older sequence in the Pensacola Mountains, near Weddell Sea, Antarctica. K-Ar age determinations show that the sills (179 ± 5 m.y.), the Dufek intrusion (172 ± 4 m.y.), and probably the dikes (minimum age 169 ± 4 m.y.) were emplaced over a narrow time interval in the Early to Middle Jurassic and are about coeval with the Ferrar Group of the Transantarctic Mountains and tholeiite elsewhere near Weddell Sea. Minerals of the sills and dikes seem to contain variable, generally minor amounts of extraneous 40Ar. Pyroxene of the Dufek intrusion lost much 40Ar, probably resulting from subsolidus phase-change activity. Inferred dike and sill magmas in Pensacola Mountains were Si02-rich tholeiites chemically like the Ross Sea area Ferrar hypersthene tholeiite, and have comparable anomalously high initial 87Sr/86Sr ratios (0.7104-0...

Patterns of Quaternary basaltic volcanism in the northern North Island, New Zealand

Abstract: North of Taupo Volcanic Zone (TVZ) are 4 major Quaternary volcanic fields; South Auckland, Auckland, Whangarei, and Kaikohe-Bay of Islands. Volcanoes in these fields are monogenetic and include maars and scoria cones atop lava pedestals. Volumes are small (<1 km3) although a few centres erupted approximately 5 km3 of lava and scoria. Early,, often explosive, undersaturated volcanism is followed by eruption of more voluminous saturated basalts. Differences in chemistry and volcanic style between earlier and later volcanism are matched by differences in texture and mineralogy of the lavas. A similar style of basaltic volcanism occurred throughout the Pliocene and Miocene. The basalts are explained as products of progressive melting of mantle diapirs formed by convection in the mantle wedge to the rear of the TVZ. Melting probably occurs between 70 and 120 km, which is a zone of low Q beneath the northern North Island. Ascent rates of mantle diapirs of the order of 102 cm/year are suggested by the r...

Moanasaurus, a new genus of marine reptile (Family Mosasauridae) from the Upper Cretaceous of North Island, New Zealand

Abstract: A new genus and species of mosasaur, Moanasaurus mangahouangae of Piripauan-Haumurian age (Campanian-Maastrichtian) is described from the North Island, New Zealand. The remains upon which the new genus and species is based (disarticulated skull, teeth, vertebrae, paddle elements, and rib fragments) are sufficiently distinct to enable it to be distinguished from previously described taxa.

Late Quaternary movement on White Creek Fault, South Island, New Zealand

Abstract: The faulted Buller River terrace sequence at White Creek Fault is the best locality to document the faulting that occurred during the Murchison earthquake of 17 June 1929. The upper faulted tread at White Creek is correlated with the later Otiran aggradation surface of the Buller valley. Riser height consistency and constant scarp height on all terrace treads, and a planar granite platform, are consistent with one single fault movement since the aggradation surface formed c. 18 000 y. ago. Tree-ring dating of Nothofagus fusca trees that were growing on the fault scarp indicates a significant event in 1929 and is attributed to the faulting during the Murchison earthquake. Periodicity of faulting at two Buller-NW Nelson reverse faults—Inangahua Fault and White Creek Fault—is found to be longer than 6000 y., about one order of magnitude longer than for faults within the shear belt of New Zealand.

Stratigraphy and chronology of late Quaternary tephras in Lake Maratoto, Hamilton, New Zealand

Abstract: A 3 m piston core from Lake Maratoto (37°53'S 175°18'E) near Hamilton shows at least 12 thin, well-preserved distal airfall tephras intercalated with humic copropel (dy) deposits. Most of the tephras have been identified by their dominant ferromagnesian mineralogy, their stratigraphic position, and 5 radiocarbon dates. The majority of the tephras are derived from the Taupo and Okataina Volcanic Centres, while others originate from Mayor Island, Tongariro, and possibly Mount Egmont sources. The tephras dated (Libby ages) are: Taupo Pumice (Wk215) 1730 ± 60 years B.P., Tuhua Tephra (Wk214) 6210 ± 70 years B.P., Mangamate Tephra (Wk213) 10 120 ± 100 years B.P., and Rerewhakaaitu Ash (2 dates) (Wk237) 14 700 ± 220 years B.P. and (Wk238) 14 700 ± 180 years B.P. The identification of the tephras in Lake Maratoto extends the previously mapped distribution of North Island post-glacial (Holocene) tephras, and complements studies of soil genesis and weathering in the Waikato region. The core also provides ...

Late Quaternary volcanic ash stratigraphy of the Poukawa area, Central Hawke's Bay, New Zealand

Abstract: 7 Holocene and 3 Late Pleistocene volcanic ashes (=tephras) are interbedded with peat, lake sediment, loess, and alluvial fan debris in the Poukawa Basin, Central Hawke's Bay. Identification is based on field appearance and stratigraphy, and where possible, is supported by mineralogy. These tephras are from youngest to oldest: Kaharoa, Taupo, Mapara, Whakaipo, Waimihia, Whakatane, Hinemaiaia, Okareka, Kawakawa, and Tahuna. new radiocarbon dates (new 1/2 life) were obtained: Waimihia 3380 ± 110 years B.P.; Whakatane 4740 ± 90 and 4770 ± 70 years B.P.; Hinemaiaia 5840 ± 140 and 5530 ± 100 years B.P. Assuming constant peat accumulation rates, estimated ages for the Mapara and Whakaipo Tephras are 2280 ± 20 and 2730 years B.P. respectively.

Upper Cretaceous and Tertiary geology of Mangatu State Forest, Raukumara Peninsula, New Zealand

Abstract: In the upper Waipaoa catchment, Raukumara Range, the oldest unit is Tikihore Formation (Arowhanan-lower Haumurian, upper Cenomanian-Maastrictian), a 400-m-thick unit of shallow, shelf deposited, alternating sandstone and siltstone beds. This is conformably overlain by Mangatu Formation (upper Haumurian-Runangan, Maastrictian-Eocene), 1100 m thick, which consists characteristically of fine-grained calcareous and quartzose siltstone, minor greensand, chert, carbonaceous siltstone, and fine-grained limestone. Unconformably overlying the Mangatu Formation is 2200 m of Miocene sediments subdivided into the Te Arai and Tokomaru Formations. Te Arai Formation (Altonian-Waiauan, Middle Miocene) comprises a coarse basal igneous conglomerate and alternating blue-grey mudstone and fine sandstone, with minor coquina limestone. This sequence is unconformably overlain by the youngest sedimentary unit, Tokomaru Formation (Tongaporutuan-Kapitean, Upper Miocene), consisting of massive, fine-medium-grained quartzol...

Little Ben Sandstone, Maitai Group (Permian): nature and extent in the Hollyford-Eglinton region, South Island, New Zealand

Abstract: The Upper Permian Matai Group and its constituent formations of the Nelson Regional Syncline may be extended across the Alpine Fault into the Key Summit Regional Syncline, southern South Island. The Bryneira Group and its constituent formations are in most respects indistinguishable from the Maitai, and their usage should be discontinued in favour of the senior synonym. Little Ben Sandstone (previously mapped in Southland and Otago as Key Summit Sandstone) comprises distinctive green, quartz-deficient, vol-canogenic strata which are exposed extensively in the Eglinton-Hollyford region. Stratigraphy, field sedimentology, petrography (sedimentary and metamorphic), and chemistry of Little Ben rocks are described. It is suggested that Little Ben sediments were derived from a basaltic-andesitic volcanic arc and were deposited by mass flow processes in coalescing submarine fans flanking the arc.

Source, age, and eruptive mechanisms of Rotorua Ash

Abstract: Rotorua Ash is a widespread (>10 000km2) pyroclastic fall deposit erupted during extrusion of a rhyolite lava complex sited adjacent to the Lake Tikitapu basin, 10 km south-east of Rotorua City, North Island, New Zealand The eruption was plinian in character, with maximum rate of emission occurring early in the eruption sequence to produce a high (c 20 km) eruption column Later explosions accompanied extrusion of lavas Local, near-vent, pyroclastic flow and surge deposits may have resulted from periods of column collapse Extrusion of a lava flow from the main pyroclastic vent appears to have terminated the eruption A 14C age of 13 800 ± 250 years BP (new T 1/2) has been obtained for Rotorua Ash close to the source

Ironsand in continental shelf sediments off western New Zealand—a synopsis

Abstract: The ironsand component (ilmenite, titanomagnetite, and/or magnetite) of surficial sediments on New Zealand's western continental shelf is highest on the inner-middle shelf between Auckland and Taranaki where the mean concentration is x 0304; = 3.85% by weight. Sediments off Westland and Nelson contain only x 0304; = 0.17% ironsand. The subsurface distribution of ironsand, as revealed in piston cores, resembles that at the surface except that subsurface concentrations are markedly lower (e.g., x 0304; = 0.77% for Auckland-Taranaki) Textural and compositional data from the Auckland-Taranaki shelf suggest ironsand was originally concentrated under littoral conditions during the Holocene transgression and was dispersed north and southeast of the main primary source, the Egmont volcanics. The ironsand and host sediment are now approaching equilibrium with the modern hydraulic regime of waves and storm-induced currents and, therefore, are regarded as palimpsest. Any ironsand concentrated on the Westlan...

Basement structure of the Wanganui Basin, onshore, interpreted from gravity data

Abstract: The Wanganui Basin, western North Island, New Zealand, contains a thick (up to 5 km) sequence of Cenozoic sediments unconformably overlying Mesozoic and Paleozoic greywacke basement rocks. Gravity anomalies suggest that along the western edge of the basin, north of Moeroa, a trough in the basement extends northwards as far as Waitaanga where it splits into two branches; one continuing NNE to Aria, the other NE to Waimiha. Between the Te Ahi-Ohura Fault and the Nukumaru-Hauhungaroa Fault, the basement forms a broad, gently sloping shelf. On the eastern side of the basin, a smaller trough extends NE from Taihape to Erewhon. Known basement uplifts at Mt Stewart, Marton, and Santoft do not have any significant gravity expression. The anomalies do not support the idea that the basin contains two sub-basins separated by a basement high. Magnetic measurements indicate that no large amounts of strongly magnetised volcanic rock are likely within the Cenozoic sediments.

Structure and interpretation of the Caples terrane of the Thomson Mountains, northern Southland, New Zealand

Abstract: In the Thomson Mountains, vokaniclastic submarine fan and trench sediments of the Caples terrane have been deformed and metamorphosed and subsequently extensively faulted. The first of two phases of folding was dominated by large open to tight folds in bedding with subhorizontal axes and vertical axial planes. Few mesoscopic structures were developed in this phase. Metamorphism was coincident with, and may have outlasted, Phase 1 deformation; schistosity is developed in the east of the area and is axial plane to Phase 1 folds in bedding. Phase 2 deformation was limited to warping of metamorphic foliation. Phase 1 folding was accompanied by tectonic sliding. Tectonic slides are manifested as discrete fractures or as wide zones of deformation akin to melanges, intimately associated with major folds. Characteristic mesoscopic structures were developed within tectonic slide zones. Most of the area is within pumpellyite-actinolite metamorphic facies; prehnite occurs in veins and in one small area of p...

Radiocarbon dates for post-Otiran glacial activity in the Mount Cook region, New Zealand

Abstract: Radiocarbon dates of organic deposits in the glacial moraines near Mount Cook show that there were episodes of glacier expansion about 8000, 1800, and 1000 years B.P. Correlations between the dated moraines and those in nearby areas are suggested

The Monowai seamount : an active submarine volcanic centre on the Tonga-Kermadec ridge (Note)

Abstract: An active submarine volcanic centre has been detected on the western flank of the Tonga-Kermadec ridge midway between the Tonga and Kermadec islands group. It has the form of an isolated cone about 1000 m high reaching to within 200 m of the sea surface. Activity of the volcanic centre was observed acoustically and visually (upwelling and discolouration of sea water over the seamount) several times during 1977–79.

Seismic refraction measurements in Fiordland southwest New Zealand

Abstract: Seismic refraction measurements have demonstrated the existence of rocks with lower crustal velocities at shallow depth under central Fiordland. Rocks with compressional wave velocities of 7.3, 6.8, 6.5, 5.7–5.3, and 5.1 km/s have been detected. The rocks with a velocity of 6.8 km/s occur within 3.5 km of the surface, while those with a velocity of 7.3 km/s lie at a depth of about 8 km. No rocks with velocities normally associated with the mantle (>8 km/s) were detected, indicating that they probably lie at depths greater than 15 km. It is suggested that the Fiordland crustal block has been uplifted by at least 10 km in the west and tilted to the east.

Varieties of glauconite in late Cretaceous and early Tertiary rocks of the South Island of New Zealand, and new proposals for classification

Abstract: Glauconites from 142 samples of Upper Cretaceous and lowermost Tertiary rocks in the South Island of New Zealand, and Chatham and Campbell Islands, were analysed comprehensively to provide data for paleoenvironmental, paleogeographic, and stratigraphic studies. All morphological varieties and all internal textures of glauconite that have been previously distinguished by Triplehorn and Konta were found in the suite of samples. Two new morphological classes are defined: (1) fragmentary glauconite, comprising angular (Subclass A) or rounded (Subclass B) fragments of once larger grains; (2) spongy glauconite, comprising grains with a porous surface morphology which is subdividable with scanning electron microscopy into “cauliflower” and “serrulate” varieties. Fragmentary grains reflect transportation and abrasion; spongy grains probably reflect diagenetic alteration. Neither glauconite type is suitable for radiometric determination of the time of sediment accumulation. One new class of internal textu...

Globorotalia inflata lineage and G. crassaformis from Blind River, New Zealand: recognition, relationship, and use in uppermost Miocene-lower Pliocene biostratigraphy

Abstract: The biostratigraphic use of variations in shell form in the Globorotalia inflata lineage and in G. crassaformis from an upper Miocene-Pliocene sequence in central New Zealand is studied. In the G. inflata lineage compressed, angular shells in early populations of G. puncticulata sphericomiozea are succeeded by progressively more globose forms (G. puncticulata puncticulata, G. inflata). The gradual changes in morphology are a problem in biostratigraphic applications. A keel, which is developed at the periphery of angular shells, is absent in more inflated shells and its existence is suggested as a biostratigraphic criterion that is simpler to apply than estimates (qualitative or quantitative) of chamber shape. For biostratigraphy, it is suggested that the appearance of G. puncticulata sphericomiozea occurs when shells without a keel comprise at least 5% of a sample and that the appearance of G. puncticulata puncticulata occurs when a keel is absent from all shells. No simple rule, potentially suit...

Morphology of the Onyx River system, McMurdo Sound region, Antarctica

Abstract: Onyx River has three characteristic reaches, bedrock incision, moraine breaches, and alluvial. Antecedent geomorphological events control the slope of these reaches and to some extent the bed material. Coarse bed materials occur in the steep reaches of the bedrock and moraine breach channels. Discharge hydrographs and flow-duration curves reveal a division into two flow regimes with a hiatus at about 1 m3/s. The modern channel form and pattern and distribution of bed materials may be related to these flow regimes. Channel-in-channel features, berms, overspill channels, and longitudinal bars are related to flow characteristics. The evolution of the river and its terraces is discussed in terms of changes in discharge and sediment supply. Prominent terraces are explained in terms of relative contributions of water and sediment from Wright Lower Glacier and from other glaciers. The terraces reflect climatic changes and their chronology is related to recent glacier activity and changes in level of Lak...

Microseismicity in the Tararua—Wairarapa area: depth-varying stresses and shallow seismicity in the southern North Island, New Zealand

Abstract: Results from previously unpublished microearthquake field studies in the Tararua-Wairarapa area during 1971–72 demonstrate important differences between crustal seismicity shallower than 20 km and intense, regionally extensive, underlying seismicity in the 20–40 km depth range. As earlier observed in the Marlborough region, and more recently in the southernmost North Island, composite focal mechanisms in the Tararua-Wairarapa area indicate markedly different stress orientations above and below 20 km. Compressional transcurrerit faulting in the upper crust contrasts with extensional normal faulting at depths of 20–40 km. The layer 20–40 km deep appears to be far more seismically active than the upper crust and is interpreted to mark the uppermost part of the subducted Pacific plate. Accordingly, the data here provide valuable control for locating the plate interface, for modelling elastic deformation at a convergent plate boundary, and for assessing fault activity and shallow seismicity in the sou...

Uniformity of vertical faulting for the last 7000 years at Lake Poukawa, Hawke's Bay, New Zealand

Abstract: Rates of fault movement are commonly assumed to be uniform. Analysis of the progressive increase in offset, by the Wairarapa Fault, of dated tephras within peat at Lake Poukawa, shows this to be true. A uniform vertical faulting rate of 0.2 mm/year is determined. Age of each offset of the fault is estimated giving a recurrence time of 800-900 years. The constant rate of faulting indicates that the next major earthquake affecting the fault at Poukawa will be in no more than 500 years time. This does not, however, exclude the possibility of other earthquakes in this region.

Observations of beach gravel transport, Wellington Harbour entrance, New Zealand

Abstract: Two small embayments at the entrance to Wellington Harbour, New Zealand, which are thought to have been depleted of sediment by regional tectonic uplift in 1855, have shown a sudden and rapid accumulation of gravel since 1941. A tracer experiment in this locality revealed that pebble-sized sediment moves northwards into the harbour at an average rate of 1.66 km y-1. Further north, inside the harbour, there is a sudden change in the nature of the beach. Towards the entrance, plentiful gravel of fresh appearance occurs, while to the north scarce weathered gravel is present. This sudden change in the nature of the beach is here named a gravel front and it is moving northwards at a rate of approximately 0.42 km y-1. Pebbles are transported during high wave energy events in a zone near low water level. Loss of pebbles offshore and by abrasion is probably small. It appears that gravel is moved alongshore during storms in discrete packages that subsequently coalesce and move landwards to form a berm dur...

A reconstruction of late Quaternary erosional events in the West Tamaki River catchment, southern Ruahine Range, North Island, New Zealand

Abstract: Evidence is presented for the sequential nature of erosional events within a selected catchment of the southern Ruahine Range during late Quaternary time. The mapping of depositional surfaces, together with description of soil profiles and vegetation maturity on these surfaces, has enabled a chronology of erosional events to be established within the main channel of the West Tamaki River catchment. This chronology is aided by ages determined by: (1) radiocarbon dating of wood, and (2) a tephra, the Aokautere Ash, which has been identified on the main channel valley-side. An examination of the Takapari peaty loam, a Histosol which occurs at the head of the selected catchment, and the recognition of Taupo Pumice and Waimihia Formation tephras within it enable an interpretation of the erosional history of this soil site to be made.

Evaporite encrustations and sulphide oxidation products from the southern Antarctic peninsula.

Abstract: White evaporite encrustations collected from 66 sites scattered over 30 000 km2 of southern Antarctic Peninsula are dominantly gypsum and calcite, and subordinate aragonite and thenardite. Natrojarosite occurs as locally developed yellow surface stains on approximately 30% of the white encrustations examined. Water, which forms by the melting of snow blown into cracks in highly fractured rocks by ground blizzards, dissolves soluble ions from minerals in these rocks as it percolates into them. The white encrustations appear to be deposited when this water later rises to the surface by capillary action and evaporates. Yellow surficial salts (alunite, fibroferrite, natrojarosite) collected at 5 sites form in place by the near-surface oxidation of pyrite disseminated in the sedimentary and plutonic rocks. Green surficial salts (atacamite, antlerite, brochantite, plancheite) collected at 4 sites form in place by the near-surface oxidation of copper sulphides under conditions of low acidity. This is th...

The Marshall Paraconformity (Note)

Abstract: The Whaingaroan-Duntroonian “Marshall Paraconformity”, promoted as an unconformity of international extent, is but one of many extensive unconformities within the preserved Tertiary record of the Canterbury region, New Zealand. Forty-six measured sections in Canterbury contain paleontological control adequate to date features indicating intra-Tertiary and Late Cretaceous erosion, non-deposition, and condensed sequences at many stratigraphic levels. These data indicate that Oligocene rocks have been the most studied of the Tertiary rocks in Canterbury, and that it may be premature to elect, as the principal of New Zealand's Tertiary unconformities, the “Marshall Paraconformity”.

Storm-generated graded beds and debris flow deposits with Ophiomorpha in a shallow offshore Oligocene sequence at Nelson, South Island, New Zealand

Abstract: An Oligocene (Whaingaroan) succession of sandstones with rare perigenic breccias and fossiliferous detrital conglomerates is well exposed for 1 km along strike and for a stratigraphic thickness of 140 m on a wave-cut platform at Magazine Point, Nelson. Regional tectonic and stratigraphic relationships are uncertain. All lithologies are lensoidal; virtually no bed extends for more than 200 m. Planar-laminated to hummocky cross-stratified, normally graded, mud-free sandstones 10-80 cm thick alternate with bioturbated muddy finer sandstones and sandy mudstones 10-35 cm thick. Ophiomorpha nodosa is the only common trace within the clean sandstones; it is locally abundant in the lower 60 m of the succession and exceedingly rare in the upper 80 m. Thallassinoides, formed by the same progenitor as Ophiomorpha, occurs with more common other indeterminate traces within the muddy units. Benthic microfauna from the muddy intervals indicate “shelf” settings ranging from inner, at the base of the sequence, to...

An Early Jurassic age for chert within the Early Cretaceous Oponae Melange (Torlesse Supergroup), Raukumara Peninsula, New Zealand

Abstract: Re-examination of a radiolarian fauna from an allochthonous chert block within the Oponae Melange shows the chert to be of Ururoan (Pliensbachian-Toarcian) age. The Oponae Melange occurs near the top of a thick sequence of Torlesse Supergroup flysch-type sedimentary rocks. Macrofossils indicate a Motuan (Albian) age of emplacement for the melange, and for the uppermost Torlesse Supergroup strata. This radiolarian fauna provides an opportunity to demonstrate clearly the considerable age difference (c. 80 m.y.) between older probable oceanic basement cover rocks characteristically occurring in Torlesse Supergroup melange zones and the enclosing younger clastic submarine fan-type strata.

Akatarawa Conglomerate (Permian), Lake Aviemore South Canterbury

Abstract: The Akatarawa Conglomerate occurs with sandstone, siltstone, volcanics, and fusilinid limestone in a fault-bounded block 2 km northwest of Lake Aviemore. The conglomerate is underlain by massive sandstones, is about 100 m thick, steeply dipping, massive, and very indurated. It is fine grained (the clast size averaging 4 mm), polymodal, has little matrix, and contains large (up to 1-m-long) mudstone rafts. A grid count of 300 clasts indicated that most are cherty quartzite and coarse quartz, with fewer sandstone, microgranite, volcanic, mudstone, and black phosphate clasts. Some cherty quartzites contain possible radiolarian remains, but diagenesis has obscured them. Cherry clasts are more abundant in the conglomerate (and sandstone lenses within it) than in its enclosing sandstones, and indicate the influence of a different source for the time of its deposition. The siliceous clasts may partly be products of more than one erosion cycle. Their dominance does not necessarily indicate dominance in t...

Subseafloor mineralisation in rocks of the Matakaoa Volcanics around Lottin Point, East Cape, New Zealand

Abstract: Matakaoa Volcanics include basalts, dolerite, gabbro, and minor undersaturated alkaline plutonics; sedimentary bands or lenses are intercalated within the igneous rocks Mineralisation occurs at 4 localities in the Lottin Point area, always associated with sediments, and distributed along eastnortheast trends The mineral associations are manganese oxides, pyrite-sphalerite-galena-chalcopyrite with traces of gold and silver in barite gangue, andpyrite-chalcopyrite The mineralisation is the result of exhalative precipitates from submarine hot springs, in places accompanied by biological activity and deposited with sediments between lava flows in a subseafloor environment The economic potential is insignificant because of very limited strike extent