three dimensional architecture of shelf building sediment drifts in the offshore canterbury basin new zealand abstract a grid of high resolution multichannel seismic profiles from the offshore canterbury basin new zealand reveals that at least 11 large up to 1000 m thick 50 km long along strike and 20 km wide down dip elongate sediment drifts developed within the lower miocene to recent shelf slope sediment prism the drifts overlie a condensed section of late eocene to late oligocene limestone and cover an area of 5000 km2 the drifts were deposited in water depths of 300 750 m probably by a northward flowing contour current and aggraded to shelf depths the drifts exhibit mounded morphologies with channel like moats along their landward flanks erosion of the landward flanks creates prominent unconformities these unconformities are diachronous and therefore not sequence boundaries the internal architecture of the drifts defines two end members of elongate drift which we describe as simple and complex early early to middle miocene simple drifts are small 50 km long and up to 20 km wide and occur in the northeastern part of the survey area these late simple elongate drifts are subdivided into three parts base core and crest based on seismic facies these facies form in response to progressive confinement of current flow within the moat complex drifts may be multi crested or multistage multi crested drifts form in response to rapid lateral shifts in position of the moat perhaps associated with relative sea level change modulated by paleoslope inclination and orientation such drifts together with the observation that several drifts were often active simultaneously indicate that flow patterns were complex and involved multiple pathways multistage drifts comprise superimposed subdrifts whose retrogradational and progradational stacking patterns indicate fluctuations in the rate of sediment supply complex drift formation may require intermediate shelf relief high enough to sustain drift development during changes in sea level and rate of sediment supply but low enough so that such changes are still able to influence moat position in addition coeval climatic cooling may amplify changes in sea level current intensity and sediment supply thereby contributing to complex drift formation

evolution of faulting and plate boundary deformation in the southern taranaki basin new zealand abstract faulting and folding in the southern taranaki basin constrain the evolution of the new zealand plate boundary since 80 ma sedimentary rocks up to 8 km thick record multiple phases of deformation which have been examined using 2d and 3d seismic reflection data resulting in fault displacement time curves and basin wide isopach maps with temporal resolutions of 5 10 myr and 1 4 myr pre and post 23 ma respectively three main phases of tectonic activity have been recognised late cretaceous and palaeocene extension 80 55 ma mainly oligocene and younger contraction and plio pleistocene 3 7 0 ma extension most of the largest faults e g cape egmont fault accrued displacement during the late cretaceous and were reactivated one or more times during subsequent episodes of deformation the oldest phase of extension occurred during gondwana break up and was ubiquitous throughout the basin contraction along the eastern boundary of the basin associated with the onset of hikurangi margin subduction commenced as early as late eocene the zone of contraction widened and migrated westward during the miocene with reverse faults and folds in westernmost parts of the basin formed in the late miocene 7 5 ma initiation and episodic widening of this zone of contraction may have been partly triggered by changes in the rate of plate convergence contraction is now mainly confined to the northern south island and has been succeeded to the north by plio pleistocene extension the present day transition zone between extension in the north and contraction in the south is defined by a wnw trending line across the basin the extension contraction transition migrated southward during the late miocene and pliocene consistent with steepening of the subducting plate and associated southward movement of the southern termination of the hikurangi subduction system

petrology and stratigraphy of some texturally well preserved thin komatiites from kambalda western australia archaean komatiite volcanics at kambalda western australia have been metamorphosed to upper greenschist lower amphibolite grade and have experienced intense though heterogeneously developed polyphase deformation despite this preservation of igneous textural features is often good particularly in areas which underwent only static style metamorphism thin lavas from the tripod hill member of the kambalda komatiite formation over the western margin of the hunt nickel shoot display textural elements and facies variations which are virtually identical to those found in fresher thin komatiite sequences in other archaean greenstone belts four principal flow profile facies types are defined comprising nine subtypes these represent stages in a facies continuum ranging from mature profiles which comprise thick spinifex textured tops and close packed cumulate bases through to massive jointed immature profiles devoid of mesoscopic spinifex texture the causes of textural diversity within and between profiles are many and complex however facies variations can be attributed mainly to the effects of lava velocity at the time of major heat loss combined with relative lateral position within any flow the most mature textural and geochemical profiles developed in parts of lavas which had become ponded prior to major heat loss whereas the least evolved profiles developed along the lateral margins levees of moving lavas the study area komatiites occur as alternating stacks of flows of similar type this stratigraphy records temporal and spatial shifts in the locus of lava ponding over the western margin of the hunt nickel shoot such shifts may have been caused by irregularities in the underlying volcanic topography and or by synvolcanic faulting and subsidence

the transformation of sediment into rock insights from iodp site u1352 canterbury basin new zealand abstract at integrated ocean drilling program iodp expedition 317 site u1352 east of the south island new zealand we continuously cored a 1927 m thick holocene to eocene section where we can uniquely document downhole changes in induration and lithification in siliciclastic to calcareous fine grained sediment using a wide range of petrological physical property and geochemical data sets porosity decreases from around 50 at the surface to 5 10 at the base of the deepest hole with a corresponding increase in density from 2 to 2 5 g cm 3 there are progressive bulk mineral changes with depth including an increase in carbonate and decrease in quartz and clay content grain compaction is first seen in thin section at 347 m below sea floor and intensifies downhole pressure solution chemical compaction begins at 380 m and is common below 1440 m with stylolite development below 1600 m and sediment injection features below 1680 m porewater geochemistry and petrographic observations document two active zones of cementation one shallow eogenetic down to 50 m as evidenced by micritic nodules and pore water geochemistry driven by methane oxidation by sulfate and another burial related cementation zone mesogenetic starting at 300 m a transitional zone occurs between 50 and 300 m our results quantify downhole diagenetic changes and verify depth estimates for these processes inferred from outcrop studies and provide an actualistic example of cementation and compaction trends in a slope setting

impact of antarctic circumpolar current development on late paleogene ocean structure global cooling and the development of continental scale antarctic glaciation occurred in the late middle eocene to early oligocene 38 to 28 million years ago accompanied by deep ocean reorganization attributed to gradual antarctic circumpolar current acc development our benthic foraminiferal stable isotope comparisons show that a large 13c offset developed between mid depth 600 meters and deep 1000 meters western north atlantic waters in the early oligocene indicating the development of intermediate depth 13c and o2 minima closely linked in the modern ocean to northward incursion of antarctic intermediate water at the same time the ocean s coldest waters became restricted to south of the acc probably forming a bottom ocean layer as in the modern ocean we show that the modern four layer ocean structure surface intermediate deep and bottom waters developed during the early oligocene as a consequence of the acc

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

fission track analysis of the late cenozoic vertical kinematics of continental pacific crust south island new zealand during the late cenozoic the pacific plate has been converging obliquely with the australia plate in south island new zealand a result of this convergence has been the growth of a major mountain range the southern alps at the leading edge of the pacific plate the results of fission track analysis of 140 samples from 13 transects across the alps reported here establish the late cenozoic vertical kinematics amount age and rate of rock uplift of the pacific crust underlying the alps the late cenozoic rock uplift of the pacific crust is asymmetrical with respect to the alpine fault being a maximum 19 km immediately east of the central part of the fault with lesser values at the eastern 3 km northern 10 km and southern 8 km extremities of the alps the age of the start of rock uplift varies spatially across the southern alps the earliest indications from fission track analysis being at 8 ma at the southern end of the alps decreasing to 5 ma at the northern end and 3 ma along the southeastern margin this age variation reflects the longer time over which the southern parts of the alps have been in collision the rate of propagation of rock uplift southeastward into the pacific plate has been 30 mm yr nearly 4 times the late cenozoic average rate of convergence normal to the plate boundary late cenozoic mean rock uplift rates range from a maximum of 2 8 mm yr at the alpine fault to a minimum of 1 0 mm yr in the east and have been sustained for periods of 3 8 m y accompanying denudation has exhumed amphibolite grade rocks immediately east of the alpine fault the rock uplift has been controlled by oblique slip displacement on the alpine fault a continental crustal section at least 19 km thick has been uplifted on the alpine fault comparison of the late cenozoic mean rock uplift rates with uplift rates derived from reset zircon data 2 10 mm yr near the alpine fault shows that uplift has accelerated over time but only significantly since 1 3 0 3 ma the amount of mesozoic uplift ranged from minimal amounts north of arthur s pass to 3 km near mount cook to 10 km in the south at lake wanaka

linking late pleistocene alpine glacial erosion and continental margin sedimentation insights from 40ar 39ar dating of silt sized sediment canterbury basin new zealand abstract quaternary climatic and eustatic cycles in mid latitude regions have led to more extensive alpine glaciations and continental shelf progradation respectively however the glacial influence on sediment fluxes to the ocean creating continental margin strata is poorly documented this contribution analyzes the provenance of fine sediment accumulating on the continental shelf during the late pleistocene to evaluate the influence of glacial cycles on sediment erosion and routing to the continental shelf taking advantage of the contrasting bedrock ages exposed across the southern alps new zealand we perform 40 ar 39 ar incremental heating on the bulk silt size sediment from three drill sites of iodp expedition 317 canterbury basin new zealand the results suggest that a large proportion of sediment accumulating on the continental shelf results from erosion within the main divide fault zone of the southern alps sediment 40 ar 39 ar age fluctuations over this time period suggest that bedrock with various 40 ar 39 ar cooling ages has been differentially eroded in the upper waitaki river catchment and mixed in the waitaki canterbury sediment routing system across shelf variations in sediment 40 ar 39 ar age reflect changing modes of sediment dispersal on the continental shelf fluvial material likely derived from the main drainage divide zone preferentially accumulates in the middle continental shelf whereas material representing erosion of older bedrock torlesse terrane located lower in the drainage basin is dispersed uniformly across the shelf the age signature of the muddy sediment accumulating on the continental shelf reflects late pleistocene landscape evolution of the southern alps and its influence on sediment dispersal to the continental shelf

the nature of sulfidic metasediments at kambalda and their broad relationships with associated ultramafic rocks and nickel ores sedimentary horizons at kambalda occur at the base of and at interflow boundaries within the same lower one third of the ultramafic sequence as do the major ni cu orebodies although sediments occur on all the same stratigraphic horizons as the ores they are almost entirely absent from within the volume containing the ores being separated by zones free of both sediments and ni cu sulfides generally they are broadly lenticular are not very extensive in area and correlate poorly laterally mineralogically and chemically the sediments are very variable but much of this is attributable simply to a variable iron sulfide content geographic and stratigraphic location and lithology are other significant causes of these variations proximity to the ni cu ores has at best an exceedingly subtle control on chemistry or mineralogy the kambalda sediments are not compositionally very different from other archean sediments in broadly similar environments however their sulfur and chalcophile element levels are high and au is especially enriched sulfur isotopes have a narrow spread near zero range 1 5 5 and the s se is around 15 000 to 20 000 indicating a little modified magmatic source for the sulfur apart from transfer of sulfur due to pyrite breakdown at peak metamorphism to the ultramafics there was negligible chemical exchange across sediment ultramafic interfaces virtually no ni was extracted from the ultramafic silicates during this sulfurization and migration of ni into the sediments was negligible nickel sulfide ore formation by sulfurization or sedimentary replacement is rejected ores intimately involved with sediments make up only 3 to 5 percent of the total ni reserve there is a strong inverse relationship between the quality of ore environments and the amount of their ore which is in contact with sediments the four largest ore locations accounting for about 70 of the reserve each has considerably less than 1 percent of ore with sediments extensive ore sediment contact occurs locally and can result from either 1 physical injection of preexisting ni cu ore into previously barren sediments 2 a synsedimentary intermixing of ores and sediments or 3 a passive and largely coincidental relationship the volcanic exhalative model of lusk 1976 for the ni ores is rejected the sediments are interpreted to be a mixture of local mafic ultramafic and distant felsic granitic detritus s pb zn fe and cu from ultramafic exhalations s co ni and cu from local sea floor leaching of ultramafics a biological carbonaceous component and probably minor chemical silica sea floor alteration affecting na k and mn diagenesis and metasomatic k rb ba sr and co 2 introductions are evident

new insights into the tectonic inversion of north canterbury and the regional structural context of the 2010 2011 canterbury earthquake sequence new zealand the 2010 2011 canterbury earthquake sequence highlighted the existence of previously unknown active faults beneath the north canterbury plains and pegasus bay south island new zealand we provide new insights into the geometry and kinematics of ongoing deformation by analyzing marine seismic data to produce new maps of regional faults and cross sectional reconstructions of deformation history active faulting and folding extends up to 30 km offshore and involves reactivation of sets of late cretaceous paleogene normal faults under nw se tectonic compression the active faults consist predominantly of ne sw striking se dipping reverse faults and less commonly e w to nw se faults suitably oriented for strike slip reactivation additionally newly developing reverse faults obliquely segment and overprint the inherited basement fabric and impose geometric and kinematic complexities revealed by mapping and reverse displacement profiles of markers the quaternary reverse slip rates decrease from 0 1 0 3 mm yr beneath northern pegasus bay to 0 05 mm yr approaching banks peninsula fault growth modeling involving trishear fault propagation folding mechanisms successfully restores an evolutionary sequence of progressive fault inversion revealing a history of reactivated individual faults tectonic inversion and overprinting processes beneath pegasus bay are immature and 1 2 0 4 ma old with no evidence of systematic spatial migration of deformation our marine data analyses give insights into the structural context of the 2010 2011 canterbury earthquake sequence while the combined onshore to offshore data provide an excellent illustration of fault growth associated with immature inversion tectonics in which selective fault reactivation results from compressive stress imposed across a complex network of inherited faults

the komatiite nickel sulfide association at scotia a petrochemical investigation of the ore environment the scotia nickel deposit is typical of the volcanic peridotite associated type of archean sulfide deposit it occurs at the basal contact of a massive dunitic unit which is itself the basal unit of a thick extrusive komatiitic sequence the ore zone is marked by a thickening of the overall ultramafic sequence and is located in a depression at the footwall contact sulfide textures in the massive ore indicate that it has been strongly deformed which is in marked contrast to the overlying matrix ore and komatiitic sequence textural and mineralogical preservation of olivine in the ultramafic sequence shows that the sequence is made up of a series of thin flow units with gravity or flow differentiated olivine rich zones between these flows are thicker flows characterized by massive olivine harrisites commonly with ocelli structures throughout the sequence there are spinifex textured olivine zones and well preserved ultramafic volcanic breccias major element data indicate that the primary komatiitic magma had 30 wt percent mgo anhydrous and this gave rise to all the flow types microprobe data on relic brown olivines show that the spinilex textured olivines are strongly zoned fo sub 75 93 while the harrisitic olivines are remarkably constant at about fo 92 olivine chemistry within the ore zone reflects the position of the olivine with respect to the massive sulfides and also subsolidus reequilibration a particular feature of the ore zone is the occurrence of colorless olivine which appears to be degraded after brown igneous olivine the colorless olivine has abnormally low ni concentrations associated with fo and mn rich cores rims to these grains are mn depleted ni enriched and more fayalitic than the cores various possible models are discussed for the origin of the orebody and it is proposed that the sulfide was erupted as a dispersed liquid phase within an intratelluric mush of olivine and komatiitic liquid the sulfides are thought to fill topographic lows or rifts on the sea floor in which the supernatant komatiite liquid is decanted off as the trough fills with later erupted olivine grains within the ore bearing ultramafic unit there is little evidence for in situ olivine crystallization

facies architecture of an archean komatiite hosted ni sulphide ore deposit victor kambalda western australia implications for komatiite lava emplacement nickel sulphide mineralisation is located in structural embayments or troughs at the base of thick basal komatiite lava flows at the victor ore body kambalda western australia primary contact relations and textural and vesicle distribution of the host komatiite lavas particularly the development of coherent or quench fragmented margins is consistent with emplacement of komatiites under laminar flow conditions however the absence of sedimentary units beneath komatiites with coherent flow tops in the ore environment seems contradictory and suggests both turbulent and passive laminar emplacement respectively the presence of erosive basal contacts in the ore environment suggests the komatiite lava was initially turbulent and probably open channel fed it is during this initial stage that both erosion and deposition of the nis deposits occurred as the flow evolved widened and thickened laminar flow conditions prevailed the komatiites are inferred to have flowed in a laminar state through the development of interior magma tubes beneath surface crusts and to have grown endogenously

early to middle pleistocene tephrochronology of north island new zealand implications for volcanism tectonism and paleoenvironments thick volcaniclastic sequences of early to middle pleistocene age in southern north island new zealand contain rhyolitic tephra beds that record the early history of the taupo volcanic zone tvz at least 54 different tephra beds are recorded and their chronology is defined by glass fission track ages and paleomagnetism the tephra beds span the interval ca 2 0 0 6 ma and provide an event frequency of 1 19 k y significantly higher than the frequency of sheet forming ignimbrites preserved in the tvz at this time 1 100 k y the distal tephra beds thus provide a record of volcanism not revealed in the proximal volcanic region and suggest a major period of explosive activity at ca 1 79 1 60 ma several important marker horizons are identified pakihikura tephra 1 63 ma mangatewaiiti tephra 1 24 ma potaka tephra 1 00 ma kidnappers b tephra 1 00 ma and kaukatea tephra 0 88 ma these tephra beds allow direct correlation between 1 marine and nonmarine facies and 2 the fore arc and back arc regions of new zealand the tephra beds provide a framework for a paleoenvironmental reconstruction of the southern north island volcaniclastic transport routes from the tvz to basins in the south and southeast and through the site of present mountain ranges supplied material to a terrestrial lowland fore arc area in the interval 1 64 0 7 ma uplift and deformation since 0 7 ma have disrupted paleodrainage routes diverting them to the north and southwest

rotation and offset of the gondwana convergent margin in the new zealand region following cretaceous jamming of hikurangi plateau large igneous province subduction jamming of the hikurangi plateau large igneous province subduction within the chatham rise convergent margin of gondwana at circa 105 ma led to offset and rotation of the convergent margin before subduction ceased in the new zealand region at circa 100 ma the southern limit of the plateau following leading slab break off is highlighted by a lineament of prominent horst blocks in the southern bounty trough subduction jamming of the gondwana margin and accompanying compression of the onshore margin and or extension of the offshore margin has led to two 60 km left lateral sse offsets of the chatham rise convergent margin at the coast and in inland canterbury recognition of the onshore chatham rise using the gravity data also highlights the correlation of the inland chatham rise and central south island seismicity in a similar manner to the rotation of cretaceous spreading ridge and transform fault fabric adjacent to the osbourn trough spreading ridge the convergence direction at the gondwana margin was rotated anticlockwise to n s between 105 and 100 ma most of this rotation has been accommodated by offshore extension and margin offset the divergence between the anticlockwise rotation of offshore crustal structure and the jammed onshore margin led to the development of the great south basin at 105 100 ma further offshore in the bounty trough extensional zones formed between crustal blocks rotated to adjust to a changed cretaceous direction of subduction are evident in gravity and seismic profiles

drake passage and cenozoic climate an open and shut case drake passage opening has often been viewed as a single discrete event possibly associated with abrupt changes in global circulation and climate at or near the eocene oligocene boundary a new plate tectonic model based on recent reinterpretations of the opening history of basins in the scotia sea suggests that an effective ocean gateway may have developed even earlier during the middle eocene this is consistent with a growing body of evidence from sediment core proxy data for eocene changes in southern ocean circulation and biological productivity the period between earliest opening after 50 ma and the latest eocene was characterized by the evolution of various current pathways across the subsiding continental shelves and intervening deep basins this shallow opening may have caused important changes in southern ocean circulation contributing to eocene cooling and the growth of antarctic ice sheets

late cretaceous coeval multi directional extension in south zealandia implications for eastern gondwana breakup abstract gondwana continental crust in south zealandia was deformed by cretaceous rift faults with multiple orientations our interpretation of 2d and 3d seismic reflection lines tied to wells in the canterbury basin of south zealandia shows three coeval sets of faults with trends of ne sw e w and nw se geometric and displacement analyses of segmented faults from each set suggests that they mainly accommodated normal dip slip producing multi directional stretching growth strata indicate that the three fault sets were active synchronously over 20 myr from 105 to 85 ma the fault sets are present throughout zealandia and roughly parallel to spreading centres produced during gondwana breakup primarily defining the present day margins of zealandia faults trending ne sw and e w are parallel to the mid ocean ridge separating south zealandia and western antarctica 800 1000 km from the canterbury basin while nw se rift faults are sub parallel to the spreading centre between australia and north zealandia sub parallelism between spreading centres and rift faulting is consistent with a model in which the multiple directions of extension produced mild 500 km from these centres ceased or continued at much diminished rates

vesicles in thick komatiite lava flows kambalda western australia traditionally vesicles have been considered to be rare in komatiites however field studies at kambalda western australia and critical literature examination suggest that vesicle presence and content in komatiites are grossly underestimated at kambalda vesicles are observed in significant amounts up to 30 in internal horizons within komatiite lavas the vesicular horizons are inferred to represent bubbles frozen in place below the upper crust during multiple episodes of flow through of bubble rich lava we conclude that vesicle and crystal distribution are compatible with many komatiites being emplaced under laminar flow conditions analogous to models for basalt lava emplacement

continental shelf progradation by sediment drift accretion multi channel seismic profiles from the canterbury basin on the eastern margin of the south island of new zealand reveal the importance of current activity in shaping a neogene shelf sediment prism the shelf prism prograded across a broad near horizontal platform in water depths of 1 000 to 1 750 m the platform was formed above a condensed section of late eocene to late oligocene limestones which overlie cretaceous to paleogene rift fill and transgressive sediments the neogene sediment prism contains sediment drifts which are as much as 25 km long and 15 km wide and extend up to 1 600 m uncompacted vertically individual drifts migrated westward and can be traced between dip profiles revealing that the long axes of most are subparallel to the present coastline and shelf edge channel like features at the landward edges of the drifts correspond to residual space left between the landward prograding off shelf sediment drift and the adjacent shelf foreslope erosion or slow deposition characterized the foreslope progradation of the shelf was by the accretion of successive sediment drifts before ca 11 5 ma pink horizon the shelf edge parallel drifts were distributed across the central part of the basin whereas subsequently they were concentrated to the northeast the seismic architecture of the neogene sediment prism results from the interplay of an abundant western sediment source and an offshore boundary current system present day ocean circulation involves northward flow along the east coast of the south island the basin may have been subjected to a middle miocene to late pliocene phase of intensified flow caused by local topographic enhancement and or global paleoceanographic events current activity has played a crucial role in the sedimentary evolution of the canterbury basin neogene shelf prism

new zealand and australian cenozoic sedimentary cycles and global sea level changes a global sea level history determined by vail et al consists of 23 sea level cycles between the base of the cenozoic and the pliocene pleistocene boundary 65 to 1 8 ma we have examined the relation between this global sea level history and the new zealand and australian continental margin shallow marine sedimentary record sedimentary cycles in the australian cenozoic marginal marine sequences are bounded by unconformities of various durations the tectonic stability and aridity of the western and southwestern margin of australia during the cenozoic produced a sedimentary record dominated by hiatuses this contrasts with the relatively complete sequences of the tectonically more active southeastern marginal basins the four major sedimentary cycles in the australian cenozoic paleocene to early eocene middle to late eocene latest oligocene to late middle miocene and latest miocene to quaternary correlate with the supercycles ta tb tc td and te of vail et al in new zealand most of the cenozoic stages represent classic sedimentary cycles bounded by unconformities or correlative conformities formed as a result of large rapid eustatic sea level changes the marine tertiary sequence in new zealand consists of 23 stages of the 18 stage boundaries between the end of the paleocene 53 ma and the end of the miocene 5 ma 16 appear to correlate with the boundaries of eustatic sea level cycles eustatic sea level lowstands are well recorded as unconformities in new zealand as a result of its unique tectonic setting during the cenozoic for most of the early cenozoic until the middle oligocene 30 ma new zealand was generally subsiding after the middle oligocene this region began to be uplifted as the pacific australian plate boundary migrated onto new zealand climaxing in the latest cenozoic late pliocene quaternary thus exposing a nearly complete sequence of marine cenozoic strata well suited for the study of sedimentary cycles unconformities which form as a result of eustatic sea level changes represent a very useful correlation tool especially on continental margins with a sufficiently high terrigenous sediment supply and can be used to supplement paleontologic correlations their ultimate usefulness for correlation depends on the rapidity of the sea level changes or the speed at which sedimentary facies change in response to sea level changes if sea level changes rapidly 10 m 1 000 years stratigraphic resolution will be high 105 years but resolution decreases as the speed of sea level change decreases unconformities may well prove to be a vital tool linking the classic land based sections around the world with deep sea sections

sandstone provenance and sediment dispersal in a complex tectonic setting taranaki basin new zealand abstract mineralogical geochemical and detrital zircon data from key reservoir intervals in taranaki basin are integrated with paleogeography and basement maps to provide a synthesis of changes in sediment provenance and sandstone composition through time results show that sandstone composition and quality in taranaki is strongly related to sediment provenance and basin history late cretaceous syn rift deposits display clear evidence for first cycle erosion from local basement rocks dominated by granites of the median batholith a ne sw trending shoreline belt developed through the paleocene which was associated with a gradual increase in sandstone maturity that peaked during the eocene passive margin phase sediment provenance continued to be primarily from granitoids with transport directions from the s sw to n ne progressive quartz enrichment is interpreted to be a result of cleaning through longshore drift longer transport distances and enhanced chemical weathering due to warmer paleoclimates we also invoke a component of eroded and recycled cretaceous paleocene sediment linked to an episode of uplift in the south a transition period ensued from the late eocene to early miocene associated with a change in basin tectonics from passive margin to active margin compositional and detrital zircon u pb data indicate that rocks to the east of taranaki basin became emergent with progressive erosion of cretaceous eocene cover rocks and underlying basement terranes minor southward propagating uplift of the eastern basin margin was initiated in the latest eocene and by the late oligocene provenance and sedimentation patterns had clearly changed with the earliest miocene strata sourced from eastern metasedimentary basement rocks the eastern province continued to be a major sediment source through the active margin phase but mixed with the re appearance of granite reworked sources and miocene volcaniclastic detritus these changes in sediment provenance through time are displayed on a set of eight sediment dispersal maps which can be used to help predict composition and hence reservoir quality in undrilled parts of the basin

the behaviour of the fronts of komatiite lavas in medial to distal settings abstract field characteristics of komatiites and observations of flow behaviour and propagation processes for subaerial basalt lavas are used to reconsider the flow behaviour of archean komatiite lavas planar conformable bases at contacts with pelitic sedimentary strata the existence of coherent to quench fragmented tops but the absence of autobreccias indicate that many komatiite lavas were emplaced passively under laminar flow conditions to determine how widely this may apply to active komatiite lavas we model flow front thicknesses noting that the preserved flow thickness is thus significantly greater than the thickness of the propagating flow front we apply the concept of inflation of basalt lava flows to komatiites application of the jeffreys equation allows lava thickness to be determined as a function of flow velocity viscosity density and slope of the terrain using the results together with estimates of flow front velocities and viscosity in the reynolds number equation indicates that at expected low flow front velocities in medial to distal settings most komatiites would have propagated in a laminar flow state we therefore envisage that komatiites were turbulent in near vent settings and capable of physical erosion and at times as previously proposed channel forming thermal erosion as flow area increased downstream and magma supply rate to the flow front and the flow front velocity decreased significantly the flow state would have transformed to laminar flow preserved flow thicknesses are often considerably greater than the calculated flow front thicknesses for such low viscosity lavas indicating that the final preserved thicknesses are either due to flow inflation ponding in topography or that some komatiites were intrusions

subduction platform subsidence and foreland thrust loading the late tertiary development of taranaki basin new zealand borehole seismic and gravity data are used to investigate deformation of continental lithosphere at a miocene collisional zone deformation is manifested in the three following principal forms a long wavelength 500 km platform subsidence ascribed to mantle convection flexural deformation on a scale of 100 200 km due to crustal thrusting at the eastern boundary of the taranaki basin and a ductile thickening evident on the deep seismic section of taranaki basin that occurs on a scale of 10 km evidence for flexural deformation principally comes from the deep seismic section that shows a 150 km wavelength bending of the moho down toward the major zone of thrusting within the taranaki fault zone paleowater depths however provide evidence for an initial early miocene regional subsidence that is too long in wavelength to be explained by flexure induced from thrust sheet loading instead we propose that this broad platform subsidence was driven by loading from a deep source probably subduction induced flow in the mantle by 22 19 ma 1 2 km of water existed over most of the area now occupied by south taranaki basin by 19 17 ma the water depth in the zone east of the taranaki basin the taranaki fault zone had been replaced by rock due to submarine thrusting and crustal thickening this build up of submarine topography in the taranaki fault zone constitutes part of the load 25 8 mpa that created and maintains south taranaki basin gravity data place further constraints on loading at the thrust front and point to an additional intracrustal loading equivalent to 15 7 mpa over a 50 km wide zone this intracrustal load is explained as being due to thick skinned thrusting bringing denser lower crustal rocks nearer to the surface in the thrust zone the complete load on the taranaki foreland is therefore in three parts the submarine topographic load the intracrustal load and the loading of infilling sediments

stratigraphy of the southern norfolk ridge and the reinga basin a record of initiation of tonga kermadec northland subduction in the southwest pacific abstract seismic stratigraphic interpretations of a large new 2d seismic reflection dataset from the reinga basin region northwest of new zealand constrain the history of cretaceous fragmentation of gondwana and cenozoic initiation of tonga kermadec northland subduction the southern norfolk ridge system lay in a proximal location to plate boundaries that were active during both cretaceous and cenozoic events and persistent marine conditions led to a relatively complete record of sedimentation cretaceous extension was followed by regional subsidence and transgression two cenozoic contractional events are separated by substantial 1 km subsidence late eocene contraction led to reverse faulting and folding between new caledonia and the southern norfolk ridge system and topographic highs created in the north western sector were locally eroded by wave abrasion reinga basin was located at the southern tip of this event which had only limited impact in adjacent northern new zealand regional oligocene and miocene subsidence was contemporaneous with late oligocene and early miocene emplacement of nappes in northern new zealand and the onset of arc volcanism early miocene contraction in the reinga basin led to formation of the wanganella ridge these events can be related to calculated plate motions and are shown to be consistent with models of induced subduction nucleation that require c 150 km of convergence the first contraction is associated with regional inception of tonga kermadec subduction whereas oligocene to miocene events and the onset of hikurangi northland subduction were in response to a local change in plate boundary displacement rate and consequent linkage between subduction north of new zealand with alpine fault formation farther south

interspinifex ni sulfide ore from the coronet shoot kambalda characterization using microbeam x ray fluorescence mapping and 3 d x ray computed tomography interspinifex ores are developed where pools of sulfide liquid overlie thermally eroded komatiite flows such that sulfide occupies the space between spinifex olivine plates microbeam x ray fluorescence mapping and 3 d x ray computed tomography have been used to investigate microstructures and chemical zonation within interspinifex ores from coronet shoot kambalda sulfide compositions in the interspinifex space match the composition of the overlying sulfide pool aluminous silicate interpreted as displaced silicate melt forms a film at the silicate sulfide interface locally developing dome like plumes the film and plumes are characterized by fine skeletal chromite that diminishes in abundance over about a decimeter downward into the interspinifex zone these relationships are strong evidence for a primary magmatic origin for this ore type driven by the strong tendency of dense inviscid sulfide liquid to infiltrate and melt underlying rocks such infiltration melting interfaces may be a common feature at the base of massive sulfide ores taking different forms depending on the lithological and fracturing characteristics of the footwall rocks

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

the age of the kambalda greenstones resolved by ion microprobe implications for archaean dating methods abstract a chert horizon within the archaean basalt pile at kambalda western australia contains zircons from air fall tuffs erupted as the sediment was laid down ion microprobe analyses of these magmatic zircons constrain the long sought age of the kambalda lavas to 2692 4ma 2 and show that regional metamorphism and deformation of the greenstone pile occurred within 30 ma of deposition rare zircon xenocrysts are evidence of pre greenstone crust as old as 3450 ma exposed remnants of which are yet to be identified subsets of both the magmatic and xenocryst zircons show evidence of hitherto unsuspected low temperature u and or pb mobility in the proterozoic long after stabilisation of the craton the ion microprobe data unravel complexities of isotopic inheritance and alteration illustrating the hazards of using bulk or whole rock samples in archaean isotopic investigations identification of interflow cherts as a precisely dateable rock type opens the way to direct ion probe dating of mafic ultramafic piles and close numerical age control of the complex but ill exposed stratigraphic and structural relations in this richly mineralised greenstone belt

emplacement and cooling of komatiite lavas we propose that komatiite lavas were emplaced as turbulent flows accompanied by vigorous forced convection with cooling rates often in excess of hundreds of c h 1 they melted and assimilated up to 10 of the ground over which they flowed forming deep channels nickel sulphide mineralization may have resulted from incorporation of sulphur rich sediment after emplacement high cooling rates persisted resulting in spinifex textures due to compositional convection

the volcanology of komatiites as deduced from field relationships in the norseman wiluna greenstone belt western australia abstract komatiites in the western part of the norseman wiluna greenstone belt in the yilgarn block of western australia display a wide variety of volcanic facies ranging from very thin differentiated munro township type flow units through to very thick olivine rich cumulate flow units containing high proportions of adcumulate dunite cumulate flow units have been mapped in detail in the agnew wiluna segment of the norseman wiluna greenstone belt in the yakabindie and mt keith areas thick lenticular bodies of olivine adcumulate are flanked and overlain by thinner sheet like sequences of finer grained olivine orthocumulates they show fine scale internal layering broad scale cryptic layering and upper fractionated sequences containing harrisites pyroxene bearing cumulates and in some cases gabbroic derivatives low grade disseminated sulphide mineralisation occurs within the dunite lenses in the stratigraphically equivalent kathleen east area adcumulate dunite grades laterally into olivine orthocumulates and spinifex textured flows a similar relationship is also seen further south where the perseverance ultramafic complex consists of a thick central dunite lens flanked on one side by thin fine grained orthocumulate sequences and on the other by intercalated orthocumulates and spinifex textured flows these field relationships indicate an extrusive origin for the adcumulate dunite bodies the walter williams formation in the west central part of the norseman wiluna belt is a very large cumulate flow unit 150 km long and 30 km wide in presently exposed extent it consists of a central sheet like body of adcumulate dunite underlain and overlain by olivine orthocumulates the adcumulate sheet is everywhere capped by a distinctive thin layer of olivine harrisite at its northernmost extent the flow unit consists of cyclically layered olivine and pyroxene bearing cumulates capped by gabbros dolerites and pyroxene spinifex textured material interpreted as a periodically replenished lava lake sequence both the lenticular dunite bodies of the agnew wiluna belt and the sheet like dunite body of the walter williams formation are interpreted as crystallisation products of very large submarine komatiite lava flows which erupted and flowed at very high rates the adcumulate dunites are interpreted as the products of in situ crystallisation at low degrees of supercooling at the top of upward and inward accreting crystal piles at the bases of the flows flanking and overlying olivine orthocumulates reflect higher rates of heat loss at the site of crystallisation due to lower lava flow rates field evidence from perseverance and the general geometry of the dunite lenses suggest that the lenses formed within large thermal erosion channels developed by turbulent lava rivers flowing over low melting felsic volcanic substrates the textural range exhibited by komatiites can be integrated into a comprehensive model for the geometry of large komatiite flow fields formed by rapid extrusion dunite sheets form close to the eruption sites and dunite lenses as a result of channellisation further away from the vent or close to the vent in the situation where the substrate is non refractory and thermal erosion can take place readily kambalda type volcanic facies develop in more distal environments where lava emplacement is channellised and episodic and munro type flow units represent small scale lava tubes formed at low flow rates on the distal flanks of major eruptions or close to the vent of very small ones waning eruption rates leads to proximal facies being overridden by distal ones a common observation in komatiite sequences the size of thermal erosion channels requires very rapid eruption rates comparable to those in phanerozoic flood basalt terrains

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

late eocene early miocene facies and stratigraphic development taranaki basin new zealand the transition to plate boundary tectonics during regional transgression eight latest eocene to earliest miocene stratigraphic surfaces have been identified in petroleum well data from the taranaki basin new zealand these surfaces define seven regional sedimentary packages of variable thickness and lithofacies forming a mixed siliciclastic carbonate system the evolving tectonic setting particularly the initial development of the australian pacific convergent margin controlled geographic stratigraphic and facies variability this tectonic signal overprinted a regional transgressive trend that culminated in latest oligocene times the earliest influence of active compressional tectonics is reflected in the preservation of latest eocene early oligocene deepwater sediments in the northern taranaki basin thickness patterns for all mid oligocene units onwards show a shift in sedimentation to the eastern taranaki basin controlled by reverse movement on the taranaki fault system this resulted in the deposition of a thick sedimentary wedge initially of coarse clastic sediments later carbonate dominated in the foredeep close to the fault in contrast oligocene active normal faulting in a small sub basin in the south may represent the most northerly evidence for rifting in southern zealandia related to emerald basin formation the early miocene period saw a return to clastic dominated deposition the onset of regional regression and the southward propagation of compressional tectonics

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

reconstruction of an extensive archaean dacitic submarine volcanic complex associated with the komatiite hosted mt keith nickel deposit agnew wiluna greenstone belt yilgarn craton western australia abstract felsic volcanic rock units characterise a large portion of the 2 7 ga agnew wiluna greenstone belt western australia stratigraphy and form the hangingwall and footwall sequences to several komatiite hosted nickel sulphide deposits in the region the mt keith region of the agnew wiluna greenstone belt awb comprises a sequence of felsic mafic and ultramafic extrusive and intrusive units the felsic volcanic dominated footwall and hangingwall sequences to the mt keith nickel deposit comprise cyclical packages of coherent dacite lavas with associated monomictic in situ to resedimented breccias clasts in the monomictic breccia facies are identical to the coherent dacite and the two facies are often in gradational contact the dacites are interpreted as submarine lavas and the breccias as associated autoclastic facies hyaloclastite autobreccia these dacite lavas are inferred to have been emplaced into a deep water environment which retarded volatile exsolution suppressing explosive fragmentation and increasing lava mobility resulting in large tabular flow units the awb sequence has undergone multiple periods of deformation and metamorphism subsequent to emplacement resulting in strain and alteration in large sections of the coherent lava facies a notable textural variant within the lavas is a set of pseudo textures structures resembling tuffaceous and brecciated dacitic units the process of pseudo clastic texture structure generation is related to a combination of polyphase alteration brecciation and development of a secondary structural metamorphic layering understanding the origin of these pseudo clastic textures structures has allowed recognition of the lateral and vertical facies variation of the felsic sequence and reconstruction of the original volcanic architecture

reconstructing the migration patterns of late pleistocene mammals from northern florida usa abstract we used analyses of the strontium isotope 87sr 86sr ratios of tooth enamel to reconstruct the migration patterns of fossil mammals collected along the aucilla river in northern florida specimens date to the late glacial period and before the last glacial maximum pre lgm deer and tapir displayed low 87sr 86sr ratios that were similar to the ratios of florida environments which suggest that these taxa did not migrate long distance outside of the florida region mastodons mammoths and equids all displayed a wide range of 87sr 86sr ratios some individuals in each taxon displayed low 87sr 86sr ratios that suggest they ranged locally while other animals had high 87sr 86sr ratios that suggest they migrated long distances 150 km outside of the florida region mastodons were the only taxa from this region that provided enough well dated specimens to compare changes in migration patterns over time pre lgm mastodons displayed significantly lower 87sr 86sr ratios than late glacial mastodons which suggests that late glacial mastodons from florida migrated longer distances than their earlier counterparts this change in movement patterns reflects temporal changes in regional vegetation patterns

emplacement and erosion by archean komatiite lava flows at kambalda revisited we have developed a mathematical model to evaluate the flow and erosional potential of submarine channelized komatiite lavas at kambalda western australia field data from kambalda were used to constrain the choice of important input parameters and model results were compared with data from field studies and geochemical analyses our results suggest that thermal erosion is strongly dependent upon the nature and behavior of the substrate if the substrate is treated as an unconsolidated hydrous sediment that can be fluidized by vaporized seawater then our model predicts that an initially 10 m thick basal kambalda komatiite lava could have produced very high thermo mechanical erosion rates 23 10 m day crustal thicknesses of 5 20 cm at distances of 5 35 km from the source and a high degree of lava contamination 3 12 in contrast if the substrate is treated as a more consolidated anhydrous sediment that could not be fluidized then our model predicts that a kambalda komatiite flow would have had much lower thermal erosion rates 1 2 0 4 m day and degrees of contamination 1 3 and would have had crustal thicknesses of 5 20 cm at longer flow distances of 30 165 km field constraints are generally consistent with our predictions for a non fluidized substrate the reentrant embayments at kambalda are thought to form from either erosion of deep channels in a flat basaltic seafioor huppert et al 1984 or erosion of a thin 5 m sediment with minor undercutting of basalt in pre existing topography lesher et al 1984 our modeling indicates that the former was possible for long eruption durations months whereas the latter was possible for short eruption durations 2 weeks as the latter hypothesis is more consistent with the existing field evidence for thermal erosion at kambalda we believe it is the preferred interpretation

the mid oligocene marshall paraconformity new zealand coincidence with global eustatic sea level fall or rise the marshall paraconformity is a regional mid oligocene unconformity that occurs widely in shelf sequences from the eastern new zealand passive continental margin the paraconformity represents a break in sedimentation of at least 3 m y and coincided with a regional sea level highstand in contrast to the prediction of global lowstand at 29 m y b p similar paraconformities are widespread on other southern continents deep sea hiatuses of similar age occurred in the adjacent southwest pacific ocean basins they may or may not have a common origin with the hiatus associated with the marshall paraconformity possible causes for the paraconformity and its associated glauconitic and bioclastic sediments are sea level fluctuations including those related to local geoidal effects or erosive bottom waters stemming from the development of antarctic glaciation or from splitting of the southern continents

early oligocene marine canyon channel systems implications for regional paleogeography in the canterbury basin new zealand abstract the oligocene is a time of maximum submersion of the zealandia landmass it coincides with changes in oceanographic currents as well as with the inception of the cenozoic plate boundary through new zealand our analysis of offshore wells and seismic reflection lines in the canterbury basin reveals condensed oligocene strata

marshall paraconformity a mid oligocene record of inception of the antarctic circumpolar current and coeval glacio eustatic lowstand abstract the sedimentary fill of the canterbury basin new zealand is the product of a long term 80 ma tectonically controlled relative sea level cycle with a megasequence geometry analogous to the sequence stratigraphic model of vail am assoc petrol geol stud geol no 27 1 1 10 1987 the condensed section of the megasequence resolvable in detail in outcrop and on seismic profiles comprises a basin wide pelagic to hemipelagic limestone interval a regional mid oligocene unconformity the marshall paraconformity lies within the limestone interval onshore and correlates with hiatuses in at least two and possibly three offshore exploration wells and with a temporary lithological change from limestone to quartz sand at a fourth strontium isotopic age estimates confirm that a 2 4 ma hiatus is associated with onshore outcrops of the marshall paraconformity between 32 and 29 ma which correlates with the opening of the pacific sector of the southern ocean and the postulated mid oligocene sea level fall of haq et al science235 1156 1167 1987 spec publ soc econ paleonotol mineral no 42 71 108 1988 lowering of base level coupled with cooling and enhancement of current activity may have caused the temporary cessation of limestone deposition and a regional hiatus this hypothesis reconciles the apparently contradictory palaeogeographical evidence for a regional highstand the marshall paraconformity may exemplify the signature by which similar glacio eustatic events can be recognized in offshore platform facies

the geology of the kambalda nickel field western australia the kambalda nickel field contains the major concentration of volcanic peridotitc associated nickel ores in the archean of australia it occupies an area of 400 km 2 underlain by two sequences of ultramafic mafic and felsic volcanics and sedimentary rocks which can be broadly correlated with previously erected regional stratigraphic sections most ores occur in the lower kambalda sequence at the base of the kambalda ultramafic rocks the ultramafic rocks of the upper bluebush sequence contain only minor mineralization four phases of deformation occurred over an interval of more than 300 m y resulting in a dominant north northwest structural trend faulting was active during original volcanism and continued intermittently until after mafic felsic dike intrusion the ultramafic rocks have been serpentinized and all rocks have exerienced low strain upper greenschist to lower amphibolite facies metamorphism and variable carbonation and potash metasomatism the kambalda ultramafic rocks are of variable thickness and in places exceed 1 000 m the lower member of the ultramafic rocks occupying approximately one third of the sequence comprises thicker high magnesium flows i e generally 36 volatile free mgo commonly separated by sulfidic quartz albite sediments thinner lower magnesium flow units characterize much of the upper member the ores occur in 24 shoot complexes each containing multiple ore surfaces caused by structural dislocation of a few grouped ribbonlike original orebodies eighty percent is contact ore occurring at the base of the lowermost ultramafic flow and generally occupying elongate troughs in the footwall basalt ultramafic contact these troughs are thought to be original volcanic depressions which focused later deformation the remainder is hanging wall ore usually occurring directly above contact ore at the base of the second or third ultramafic flow hanging wall orebodies occasionally grade into stratigraphically equivalent interflow sediments the ores contain varying proportions of massive matrix and disseminated sulfides the hypogene mineral assemblage is pyrrhotite pentlandite pyrite chalcopyrite but millerite is locally significant the massive ores in particular are commonly severely deformed and some have been remobilized tens of meters from their original contact position metamorphism has caused recrystallization of the ores and some redistribution of elements there is commonly marked variation of mineralogy and s ni ratios between contact and overlying hanging wall ores and within and between original ore surfaces within shoots but the relative contributions of primary composition and metamorphism to this variation are uncertain in ore environments the footwall basalt ultramafic contact is more deformed than in non ore environments the basal ultramafic flows are thicker and richer in magnesium the trend toward lower magnesium flows upward through the ultramafic formation is less well developed and there is better textural development and compositional differentiation within flows non ore environments usually contain interflow sediments whereas there is generally a sediment free prism of ultramafic rocks above ore environments most ores are interpreted to have originated by either simultaneous or sequential extrusion of sulfide melts and ultramafic lavas rich in olivine phenocrysts along active linear fissures in a basaltic ocean floor volcanic exhalations probably contributed to minor ore in sulfidic sediments

rapid biological speciation driven by tectonic evolution in new zealand plate tectonic motions can influence biological systems numerical modelling of the topographic evolution of new zealand combined with fish phylogenetic analyses suggest mountain growth directly influenced biological diversification collisions between tectonic plates lead to the rise of new mountain ranges that can separate biological populations and ultimately result in new species1 however the identification of links between tectonic mountain building and biological speciation is confounded by environmental and ecological factors2 3 4 thus there are surprisingly few well documented examples of direct tectonic controls on terrestrial biological speciation here we present examples from new zealand where the rapid evolution of 18 species of freshwater fishes has resulted from parallel tectonic landscape evolution we use numerical models to reconstruct changes in the deep crustal structure and surface drainage catchments of the southern island of new zealand over the past 25 million years we show that the island and mountain topography evolved in six principal tectonic zones which have distinct drainage catchments that separated fish populations we use new and existing5 6 phylogenetic analyses of freshwater fish populations based on over 1 000 specimens from more than 400 localities to show that fish genomes can retain evidence of this tectonic landscape development with a clear correlation between geologic age and extent of dna sequence divergence we conclude that landscape evolution has controlled on going biological diversification over the past 25 million years