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

gold in porphyry copper deposits its abundance and fate abstract porphyry copper deposits are among the largest reservoirs of gold in the upper crust and are important potential sources for gold in lower temperature epithermal deposits whether gold remains in porphyry copper deposits is important both to their economic attractiveness and to the distribution of gold in the upper crust cu au atomic ratios of porphyry copper ore deposits form a continuous range from about 5000 to 5 000 000 with a median near 40 000 which separates gold rich and gold poor deposits gold is found in porphyry copper deposits in solid solution in cu fe and cu sulfides and as small grains of native gold usually along boundaries of bornite sims ion probe analyses of ore minerals from the gold rich batu hijau kingking and skouries porphyry copper deposits show that bornite contains about 1 ppm au whereas chalcopyrite contains about an order of magnitude less chalcocite and covellite contain 10 20 ppm au but are not abundant enough to account for a significant part of the gold endowment in many porphyry copper deposits the amount of gold presently in solid solution in cu fe sulfides is not adequate to account for all the gold in porphyry copper deposits and the remainder is present as micron scale grains of native gold experiments in the cu fe s au system show that bornite and chalcopyrite can contain about 1000 ppm gold at typical porphyry copper formation temperatures of 600 700 c and indicate that bornite and chalcopyrite in porphyry copper deposits were saturated with respect to gold at temperatures of only 200 300 c in contrast cu au ratios of bulk ore in porphyry copper deposits would require bornite and chalcopyrite to be saturated with respect to gold at temperatures similar to those at which primary potassic ore and alteration are thought to form this indicates that the maximum gold endowment of porphyry copper deposits is probably fixed by the amount of gold that will go into solid solution in cu fe sulfides when the deposit forms at high temperature and that gold is not commonly added later from other sources although it can be redistributed during cooling or later events the experimental data also suggest that high temperature 600 700 c vapors can extract considerably more gold from porphyry copper systems than can low temperature 300 c alteration comparison to cu au ratios of volcanic emissions suggests further that high temperature processes remove copper relative to gold from porphyry copper systems whereas low temperature processes remove gold preferentially and that this can account for deposits with extremely low and high cu au ratios respectively deposits with cu au ratios between about 20 000 and 100 000 however probably reflect different degrees of removal of gold or copper by immiscible sulfides

pacific ocean and cenozoic evolution of climate 1 the pacific ocean has played a major role in climate evolution throughout the cenozoic 65 0 ma it is a fundamental component of global heat transport and circulation the dominant locus of primary productivity and consequently the largest reservoir for carbon exchange between the oceans and the atmosphere a satisfactory understanding of the cenozoic evolutionary history of the pacific and its impact on global climate is currently data limited nevertheless the large dynamic range of cenozoic conditions sets the stage to greatly expand our understanding of global climate and biogeochemical cycles past earth experiments are particularly useful to understand interactions between climate and geosystems under different greenhouse gas loads we highlight in this review four important problems in which the pacific played a major role the effect of changing geographic boundary conditions on ocean circulation interactions between the carbon cycle and climate the pacific ocean s influence on north american climate and its water cycle and the gradual evolution of climate systems

chronostratigraphy of odp 181 site 1121 sediment core southwest pacific ocean using 10be 9be dating of entrapped ferromanganese nodules a 10be 9be based chronostratigraphy has been determined for odp 181 site 1121 sediment core recovered from the foot of the campbell plateau southwest pacific ocean this core was drilled through the campbell skin drift in ca 4500 m water depth on the mid western margin of the extensive campbell nodule field beneath the flow of the major cold water deep western boundary current dwbc in the absence of detailed biostratigraphy beryllium isotopes have provided essential time information to allow palaeo environmental interpretation to be undertaken on the upper 7 m of the core measured 10be 9be ratios of sediment and of ferromanganese nodules entrapped in the sediment decrease systematically with depth in the core in accordance with radioactive decay however the 10be 9be data diverge from ca 3 m below the seafloor mbsf to the top of the core giving rise to several possible geochronological models the preferred model assumes that the measured 10be 9be ratios of the nodule rims reflect initial 10be 9be ratios equivalent to contemporary seawater and that these can be used to derive the true age of the sediment where the nodules occur the nodule rim ages can be then used to interpret the sediment 10be 9be data which indicate an overall age to ca 7 mbsf of ca 17 5 ma the derived chronology is consistent with diatom biostratigraphy which indicates an age of 2 2 3 6 ma at 1 mbsf calculated sedimentation rates range from 8 to 95 cm m y 1 with an overall rate to 7 mbsf of ca 39 cm m y 1 the lowest rates generally coincide with the occurrence of entrapped nodules and reflect periods of increased bottom current flow causing net sediment loss growth rates of individual nodules decrease towards the top of the sediment core similar to the observed decrease in growth rate from core to rim of seafloor nodules from the campbell nodule field this may be related to an overall increase in the vigour of the dwbc from ca 10 ma to the present

platinum group elements in ores from the kalmakyr porphyry cu au mo deposit uzbekistan bulk geochemical and laser ablation icp ms data we studied primary ore samples from kalmakyr a giant cu au mo porphyry deposit in eastern uzbekistan disseminated and stockwork type high grade cu au mo mineralization showed average concentrations of 55 ppb pd 5 5 ppb pt 0 95 ppb rh 0 49 ppb ir and 4 1 ppm au n 8 this type of mineralization is characterized by the presence of pyrite chalcopyrite molybdenite and gold a peak pd content of 292 ppb was determined in a base metal rich quartz vein in granodiorite porphyry which contains galena sphalerite chalcopyrite tetrahedrite and gold palladium correlates with cu ag se and s mineralogical and laser ablation icp ms study confirmed that pd is homogeneously distributed in chalcopyrite which contains up to 110 ppm pd and tetrahedrite containing up to 20 ppm pd an assessment of the pd and pt budget at kalmakyr showed the potential of approximately 17 t of pd and 1 7 t of pt

geochemistry of oils in the northern viking graben the composition of crude oils in the northern viking graben area reflects the influence of both the type of organic matter and the thermal maturity of jurassic source rocks in the major basin depocenters referred to as the oseberg and troll kitchens forty four oil samples were analyzed and classified primarily based on chemical composition but with recognition of constraints on origins imposed by geographic and stratigraphic locations five groups are recognized 1 snorre oils 2 stratfjord gullfaks oils 3 brent oseberg beta veslefrikk oils 4 oseberg alpha troll oils and 5 agat and blocks 35 8 and 35 11 oils the composition of oils in the first three groups reflects the large relative proportions of marine organic matter and the lower expulsion temperatures characteristic of oils derived from the draupne formation the composition of oils in the last two groups reflects source rocks having more terrestrial organic matter and higher expulsion temperatures the initial phase of hydrocarbon expulsion and migration from the draupne formation in the northern viking graben began about 56 ma in the troll kitchen and about 45 ma in the oseberg kitchen with continued subsidence and heating of jurassic source rocks gases and condensates were expelled beginning about 40 ma in the trollmore kitchen d about 30 ma in the oseberg kitchen this secondary phase of hydrocarbon generation has mixed with and displaced some of the earlier accumulations less

new style of honeycomb structures revealed on 3d seismic data indicate widespread diagenesis offshore great south basin new zealand abstract in the great south basin within the eocene section at time depths around 700 900 ms two way time below the seafloor unusual features are observed on 3d seismic data closely associated with polygonal faults the features referred to as honeycomb structures hs cover an area of 600 km 2 are packed circular oval to polygonal depressions 150 400 m across in plan view and several to 10 m in amplitude polygonal faults rapidly die out at the marshall paraconformity which is overlain by the oligocene penrod formation hence the polygonal faults are inferred to have formed prior to the marshall paraconformity and they cross cut hs features consequently the top of the hs probably formed at burial depths of around 375 500 m which is their decompacted depth below the paraconformity the interval containing hs is about 125 m vertical thick there are several possible origins for the hs the most probable is related to bulk contraction of the sediment volume accompanied by fluid expulsion which suggests a diagenetic origin in particular the opal a ct transition there are actually two polygonal fault systems pfs present in the area the southern tier 1 pfs lies laterally to the hs and overlaps with it the northern pfs tier 2 lies above the hs appears to be independent of the hs and formed in the upper 200 300 m of the sediment column the tier 1 pfs probably formed by shear failure related to the same diagenetic effects that caused the hs

geostatistical analysis of seafloor depressions on the southeast margin of new zealand s south island investigating the impact of dynamic near seafloor processes on geomorphology abstract seafloor depressions are widespread on the present day continental slope along the southeast coast of new zealand s south island the depressions appear to be bathymetrically constrained to depths below 500 m correlating to the top of the gas hydrate stability zone and above 1100 m similar depressions observed on the chatham rise are interpreted to have formed as a result of gas hydrate dissociation leading to the hypothesis that a similar origin can be applied for the depressions investigated in this study our investigation however has found limited geophysical or geochemical evidence to support this hypothesis the objective of this paper is to examine whether a causal relationship can be established between potential mechanisms of depression formation and the present day seafloor geomorphology geostatistical analysis methods applied to multibeam bathymetry and interpretation of 3d seismic data have been used to empirically describe the geomorphology of the seafloor depressions and investigate potential correlations between geomorphology and other processes such as current flow along the shelf and slope in this region and underlying polygonal fault systems although the results of our analysis do not preclude that the seafloor depressions formed as a result of gas hydrate dissociation neither does our geophysical or geochemical evidence support the theory therefore we propose an alternative mechanism that may have been responsible for the formation of these structures based on the evidence presented in this study the most likely mechanism responsible for the formation of these seafloor depressions is groundwater flux related to the interaction of current systems and the complex geomorphology of submarine canyons on the southeast coast of the south island

thermal evolution of the new zealand hikurangi subduction margin impact on natural gas generation and methane hydrate formation a model study abstract we present an integrated 2d model of thermal and microbial generation of methane migration into the gas hydrate stability zone hsz and formation of methane hydrates the model reconstructs the shallow 0 20 km thermal structure of the subduction interface between the australian plate and the subducting pacific plate and the trench basin pegasus basin modelled temperatures of less than 110 c within pegasus basin constrain the generation of oil and gas whilst a cool thermal regime is predicted to limit thermogenic generation of gas to a burial depth of 10 km it extends the interval where prolific microbial gas generation occurs the modelled rate of microbial generation of methane increases beneath the hsz and peaks at 1600 m below seafloor diffusive upward migration of microbially generated methane is interpreted to lead to widespread methane hydrate formation and the presence of a semi continuous bottom simulating reflector bsr predicted average hydrate saturation within the hsz is 0 9 for a modelled sedimentary organic matter content of 0 5 and 1 6 for 1 organic matter in fine grained pegasus basin sediments considerably higher concentrations of methane hydrate of up to 20 70 are predicted to occur where gas migration is focussed within the frontal anticline and proto thrust zone southeast of the modern accretionary wedge and in channel and basin floor sandstones related to the hikurangi channel the hikurangi channel sedimentary system transported coarse clastic sediments eroded from the rising southern alps along the eastern margin of the pegasus basin since the miocene it provides carrier beds specifically for transport of thermogenic gas generated close to the subduction interface a buried mesozoic accretionary wedge originating from subduction of the pacific plate beneath gondwana further focusses the migration of gas focussed migration of thermogenic gas leads to the highest predicted hydrate concentrations in potential channel sand reservoirs

hydrothermal alteration and mineralization of the galore creek alkalic cu au porphyry deposit northwestern british columbia canada the late triassic galore creek porphyry district is the largest accumulation of cu au prospects in british columbia canada in terms of contained metal the principal economic resource is the central zone deposit it comprises three high grade centers the au rich north and south gold lenses and the cu dominated central replacement zone alteration footprints ore shells and porphyry intrusions in these centers dip 45 to 60 to the west in the north gold lens and southwest in the south gold lens and central replacement zone indicative of significant postmineral tilting this inclination created an oblique vertical expression of the central zone at surface and at depth providing a 700 m depth profile through the deposit galore creek is considered to be the end member of the silica undersaturated class of alkalic porphyry cu au deposits it displays a unique hydrothermal alteration footprint generally devoid of quartz veining despite the lack of crosscutting veins a paragenetic sequence of several discrete potassic and calcic alteration events has been established during main stage alteration two mineralization events occurred that formed the economic resource in the central zone highly oxidizing fluids derived from porphyritic syenite to monzonite intrusions produced initial potassic alteration and sulfide mineralization in the north gold lens and south gold lens cu au ore shells are characterized by a gold rich core dominated by bornite associated with hematite dusted orthoclase specular hematite and anhydrite the second period of hydrothermal activity caused brecciation and calcic alteration in the central replacement zone the calcic fluids formed hydrothermal cement grading from ti rich andraditic to grossularitic garnet in the core of the breccia to a diopside and magnetite dominated assemblage at the margins calcic alteration also formed in the surrounding host rock this alteration event was followed by potassic alteration and mineralization characterized by biotite anhydrite and chalcopyrite in the cu rich ore shell of the central replacement zone most of the au is hosted in bornite that is spatially associated with oxidized reddened rock units dominated by an alteration assemblage of orthoclase hematite specular hematite garnet anhydrite high grade cu in the central zone is related to abundant chalcopyrite that has commonly replaced an assemblage of biotite magnetite diopside this distinct spatial separation strongly suggests that the local redox environment within the wall rocks governed sulfide and gold distributions the switch from early au rich mineralization to late stage cu dominated mineralization appears to have been controlled by varying redox conditions within the magma the change from more oxidized alteration assemblages fe3 fe2 to more reduced assemblages fe3 fe2 is indicative of a change in oxidation potential that may have propelled sulfide saturation in the magma and thus the subsequent depletion of most of the au

neogene changes in southern ocean sedimentation based on mass accumulation rates at four continental margins 1 high resolution mass accumulation rates mar were determined from lithologic logs based on downhole log and continuous core data for six sites at four continental margins around the southern ocean total mar was calculated at ocean drilling program odp site 1095 on the margin of the antarctic peninsula and odp site 1165 on the margin of prydz bay antarctica carbonate and noncarbonate terrigenous mar were calculated for odp sites 1123 and 1124 east of new zealand and sites 1168 and 1172 west and southeast of tasmania shifts in carbonate mar are seen around tasmania and new zealand at 23 and 14 ma suggesting changes in deep water circulation and surface carbonate productivity at these times carbonate mar dropped at sites 1124 and 1168 at 23 ma and increased at 14 ma at sites 1123 1168 and 1172 the overall character of total mar at antarctic sites 1095 and 1165 is a continual and relatively constant decrease in total mar during the neogene with periods of stepwise decrease one such decrease is seen at 14 ma at site 1165 coincident with increased carbonate mar in new zealand and tasmania sites 1123 1124 1168 and 1172 and likely related to mid miocene expansion of the east antarctic ice sheet another step drop in total mar is seen at 9 ma at site 1165 possibly reflecting diversion of sediment to a newly formed prydz channel fan

test of seismic sequence methodology on a southern hemisphere passive margin the canterbury basin new zealand abstract analysis of a detailed grid of multichannel seismic reflection profiles from the central canterbury basin demonstrates the presence of nine unconformity bound seismic sequences within a miocene recent prograding clinoform shelf sediment prism two different sets of seismic lines are available they show that the pattern of sequences inferred depends at least partly upon the way in which the profiles are processed significant differences exist between the sequence pattern seen on parallel dip lines even when they are only a few kilometres apart nonetheless truncation and onlap criteria indicate that an apparently consistent set of sequences can be traced for 90 120 km along depositional strike correlation with the nearby clipper 1 exploration well indicates the sequences are middle to late miocene ranging in age from 11 5 7 0 ma and of average duration 0 3 1 0 ma the equivalent part of the haq et al 1987 global sea level chart only contains two to three cycles either the canterbury basin contains a particularly high resolution record of middle to late miocene sea level fluctuations better than that so far summarized on the global chart or the extra sequences were produced by other mechanisms for example fluctuations in sediment supply if the latter explanation is true we are unable to delineate objective ways to discriminate between sequences defined by sediment depositional pulses and sequences produced by global sea level cycles our results suggest that extreme caution is required in applying the so called global sea level curve to the interpretation of far flung sedimentary sequences at least in the southern hemisphere

oligocene glacio eustasy and erosion on the margins of the north atlantic oligocene foraminiferal 18 o records suggest the development of ice caps inferred glacio eustatic falls at ca 36 31 and 25 ma biostratigraphic analyses of wells from the united states east coast and irish continental margins consistently show that upper oligocene sediments overlie a diachronous erosional surface underlain by lower oligocene to eocene strata at the minimum the hiatus extends between ca 34 and 30 ma we speculate that erosion during a glacio eustatic fall near the early late oligocene boundary ca 32 31 ma developed 1 an unconformity on the margins 2 numerous canyons noted in seismic profiles from the margins of the north atlantic and 3 a coastal offlap event using 18 o data we apply a model for eustatic changes and margin response that explains the relationships of sea level unconformities and coastal onlap offlap events

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

late quaternary marine isotope stages 6 1 seismic sequence stratigraphic evolution of the otago continental shelf new zealand abstract a proposed chronostratigraphic model for the late quaternary evolution of the otago continental shelf new zealand includes fluvially incised sequence boundaries eroded during marine isotope stages 2 4 and 6 bounding three sequences subdivided into lowstand transgressive and highstand regressive systems tracts datable material is limited to the uppermost 1 m of the sequence and consequently the model is based on correlation of new high resolution seismic reflection data geopulse to a compilation of independent global sea level curves a second chronostratigraphic model that lacks a stage 4 sequence boundary and distinct stage 3 highstand forced regressive deposit is discounted because its subsidence corrected paleoshoreline depths do not match lowstands in the eustatic curves or temporally constrained sequences at other far field locations in the preferred chronostratigraphic model sea level lowstands during stages 2 4 and 6 reached maximum depths of 126 131 m 101 111 m and 116 135 m respectively producing sequence boundaries landward pinching deltaic wedges on the outer otago shelf and submarine canyon incision lowstand paleoshoreline depths have been corrected for subsidence from thermal cooling sediment compaction and loading but may be erroneously deep owing to erosion of paleoshoreline indicators clastic shallow marine wedges and back barrier valley fill deposits accumulated during the stage 6 5 4 3 and 2 1 marine transgressions contrary to the traditional sequence stratigraphic model deltaic and strandline units deposited during highstand through falling sea level stages 5 4 3 2 1 volumetrically dominate otago late quaternary sequences discrete units and minor marine erosion surfaces within the transgressive and regressive systems tract deposits are interpreted as strong evidence for seventh 20 ka or higher order sea level fluctuations influencing sedimentation on the otago shelf

precious metal mineralogy in porphyry skarn and replacement type ore deposits of the ertsberg gunung bijih district irian jaya indonesia petrographic and electron microprobe analyses of native au and a variety of sulfide minerals indicate a generally high but widely varying native au fineness and a cu fe sulfide host for most ag in the gunung bijih timur complex of cu au skarn deposits the big gossan and dom cu skarn deposits and the grasberg porphyry cu au deposit native au rims bornite in veins and forms inclusions in bornite and chalcopyrite in samples from grasberg and from the gunung bijih timur complex as well as filling open space in quartz veins in the complex skarn and quartz veins in the big gossan area host native au in association with pyrite pyrrhotite galena chalcopyrite sphalerite and arsenopyrite native au from the gunung bijih timur complex has a wide but bimodal range of fineness 920 to 990 and 340 to 820 avg 860 native au from grasberg samples is or 930 fine avg 960 fineness of big gossan au ranges from 540 to 960 avg 830 although compositional ranges are small within most individual samples native au from grasberg falls into two groups with respect to pd pd bearing or 3 500 ppm avg 1 800 ppm and with no detectable pd fire assay of grasberg ore reveals trace but detectable 10 ppb pd 500 ppb avg or 50 ppb concentrations of pd and no detectable pt native au from the gunung bijih timur complex averages twice as much cu as that from grasberg 1 7 vs 0 8 wt cu native au from big gossan has uniformly low cu contents or 1 200 ppm cu avg 300 ppm mass balance calculations and analytical data indicate that the bulk of the ag in the gunung bijih timur complex is contained by bornite indicating a partitioning of ag into bornite relative to native au or a discrete ag mineral this is supported by the consistent positive correlation of cu and ag throughout the gunung bijih timur complex as well as in grasberg and dom ag bearing galena occurs in the big gossan area but is rare in the grasberg the gunung bijih timur complex and the dom orebodies the high fineness of native au from the gunung bijih district represents the upper end of the reported range for porphyry and skarn type cu au deposits but is similar to values reported elsewhere in indonesia the fineness of native au in the gunung bijih timur complex does not appear to be controlled by depth or distance from the local intrusive contact mineral assemblage or paragenetic relationship the fineness of native au from the big gossan area shows a positive correlation with elevation suggestive of a lower temperature more distal character than in the other skarns of the district differences in pd contents may be related to acidity and redox conditions during native au deposition high cu high pd and low ag compositions of au grains in pan concentrates suggest a porphyry or cu skarn source relative to a more distal source compositional characteristics identified in this study may have applications to exploration within the ertsberg district and elsewhere

geological controls on seismic sequence resolution a seismic sequence analysis of the canterbury basin eastern south island of new zealand has illustrated the roles of subsidence sediment supply and current activity as controls on sequence resolution and architecture during basin evolution the rates of sediment supply and subsidence determine the background depositional regime transgressive or regressive and effectively determine the frequency response of the continental margin sedimentary section to input signals with a broad range of frequencies including eustasy a regressive progradational depositional regime and minimal current erosion favor the preservation of high frequency sequences particularly at fourth order level under less favorable conditions the record of sequences is incomplete or ambiguous such frequency response characteristics must be considered when inverting sequence records to derive the frequency of the input cyclicity and when making global comparisons of regional sequence stratigraphic studies clastic basins with simple subsidence histories and uniform or increasing rates of sediment supply develop from a transgressive phase characterized by ramplike major sequence boundaries to a mature progradational shelf phase with clinoform sequences and optimum sequence resolution the mature phase constitutes the preferred setting for sequence stratigraphic analyses

cenozoic tectonics of new guinea major hydrocarbon discoveries have been made in eastern and westernmost new guinea and there is great potential for additional discoveries although the island is a type locality for arc continent collision during the cenozoic the age number and plate kinematics of the events that formed the island are vigorously argued the northern part of the island is underlain by rocks with oceanic island arc affinities and the southern part is underlain by the australian continental crust based on regional sedimentation patterns it is argued herein that the cenozoic tectonic history of the island involves two distinct collisional orogenic events the first cenozoic event the peninsular orogeny of oligocene age 35 30 ma was restricted to easternmost new guinea emergent uplifts that shed abundant detritus resulted from the subduction of the northeastern corner of the australian continent beneath part of the inner melanesian arc this collision uplifted the papuan ophiolite and formed the associated mountainous uplift that was the primary source of siliciclastic sediments that largely filled the aure trough between the oligocene and miocene the paleogeography of the region was similar to present day new caledonia the continental crust under central and western new guinea remained a passive margin the second event the central range orogeny began in the latest middle miocene when the bulldozing of australian passive margin strata first created emergent uplifts above a north dipping subduction zone beneath the western part of the outer melanesian arc the cessation of carbonate shelf sedimentation and widespread initiation of siliciclastic sedimentation on top of the australian continental basement is dated at about 12 ma this collision emplaced the irian ophiolite and created the present mountainous topography forming the spine of the island

platinum group minerals in the santo tomas ii philex porphyry copper gold deposit luzon island philippines mineralized quartz diorites of the santo tomas ii porphyry copper gold deposit carry high au contents average 1 8 ppm as well as 160 ppb pd and 38 ppb pt values of other platinum group elements pge and rhenium are below the analytical detection limits there is a significant positive correlation between au and cu the highest pd values were detected in the most au and cu rich rocks platinum group minerals pgm occur exclusively as inclusions in chalcopyrite and bornite potential pd and pt contents in sulphide concentrates are estimated at 1 5 g t and 0 4 g t respectively the precious metal assemblages consist of merenskyite main pgm kotulskite moncheite native gold electrum hessite and petzite polyphase fluid inclusions in quartz veinlets associated with a pgm bearing bornite chalcopyrite magnetite assemblage are characterized by high salinity 35 to 60 eq wt nacl and high trapping temperatures between 380 and 520 c they may represent primary magmatic hydrothermal fluids which have been responsible for the transport of pd pt and au as chloride complexes

contrasting watermass conditions during deposition of the whitby mudstone lower jurassic and kimmeridge clay upper jurassic formations uk abstract the whitby mudstone formation wmf and kimmeridge clay formation kcf are both jurassic organic rich black shale units containing well preserved marine organic matter despite such gross similarities they exhibit opposite trends in 13 c toc versus wt decarbonated total organic carbon toc r 0 76 for wmf and 0 71 for kcf the 13 c toc versus toc trend also varies geographically within both units only the kcf data exhibit a positive correlation between 13 c toc and 15 n org r 0 76 and the presence of aryl isoprenoids probable indicators of photic zone anoxia maturity differences are insufficient to explain such contrasts bulk and compound specific isotopic variations in the kcf are interpreted largely as a reflection of primary productivity during deposition rather than a dominantly diagenetic signal due to incorporation of sulphurised carbohydrate the contrasts between the formations and the geographic variation in coeval shelf sediments are explained by a model stressing the relative positions and stabilities of the chemocline pycnocline nutricline and euphotic zone and the effect these have on productivity co 2 recycling and bacterial floras

subaqueous eruption and shallow water reworking of a small volume surtseyan edifice at kakanui new zealand kakanui volcaniclastic deposits on the south island of new zealand are the remnants of two late eocene to early oligocene surtseyan type cones eruptive dominated material of the i stratified tuff and lapilli tuff and ii lapilli tuff breccia lithofacies and post eruptive debris of the iii shell rich tuff and lapilli tuff and iv chaotic and cross bedded tuff and lapilli tuff lithofacies compose the deposits the 9 250 m thick stratified tuff and lapilli tuff contains grain flow deposits originating from low volume tephra jets and local thinning and fining upward sequences that formed from density currents during sustained uprush the lapilli tuff breccia up to 4 5 m thick contains inward dipping beds deposited via debris flows along inner cone walls burrows and articulated shells in the 2 4 m thick shell rich tuff and lapilli tuff indicate volcanic quiescence and low sedimentation rates whereas shell fragments upsection signal increased wave and current activity burrows pyrite concretions and mudstone in the lower part of the 26 m thick chaotic tuff and lapilli tuff indicate suspension deposition and cessation in pyroclastic volcanism high angle trough cross beds and limestone rip up fragments upsection are consistent with wave induced current reworking the depositional model involves a surtseyan type eruption on a continental shelf followed by colonization of organisms on the tops of planed off cones the kakanui deposits comprise a cluster of cones constituting part of a late eocene early oligocene monogenetic volcanic field the kakanui succession provides an opportunity to study deposits that form from explosive subaqueous pyroclastic eruptions and wave dominated deposition and erosion

current controlled sediment deposition from the shelf to the deep ocean the cenozoic evolution of circulation through the sw pacific gateway the circulation of cold deep water is one of the controlling factors of the earth s climate forty percent of this water enters the world ocean through the southwest pacific as a deep western boundary current dwbc flowing northwards at bathyal to abyssal depths east of the new zealand microcontinent south of latitude 50 s the dwbc is intimately linked with the antarctic circumpolar current acc which is the prominent force for the shallow water circulation the pacific dwbc is presently the largest single contributor of deep ocean water and deciphering its evolution is of fundamental importance to understanding ocean and climate history and global ocean hydrography the evolution of the dwbc system and of related circum antarctic currents has taken place since 30 25 ma when plate movements created the first oceanic gaps south of australia and south america the stratigraphic record preserved in sediment drifts of the southwest pacific in eastern new zealand is the best available for deciphering the neogene history of southern ocean water masses and of the circulation of the acc dwbc and their precursor systems major current activity commenced on the new zealand margin in the late eocene or early oligocene hoiho drift early acc and was widespread by the mid late oligocene marshall paraconformity and weka pass limestone drift acc during the neogene the eastern south island continental shelf built seawards by accretion at its outer edge of large miocene current drifts up to tens of kilometres long and hundreds of metres thick canterbury drifts also commencing in the mid cenozoic but in depths 2000 m the dwbc emplaced large deep water sediment drifts rates of drift deposition accelerated considerably in the late neogene when climatic change and particularly glacial sea level falls caused the delivery of large volumes of turbiditic sediment into the path of the dwbc via the bounty and hikurangi channels

microchemical studies of placer and lode gold in the klondike district yukon canada 2 constraints on the nature and location of regional lode sources alloy compositions and associated suites of opaque mineral inclusions have been used to define the micro chemical signature of 3 050 placer gold grains from 34 localities and 561 gold grains from six lode localities from the northeastern central and southern klondike gold district yukon canada these data augment those from a detailed parallel study of placer lode gold relationships in the western part of the klondike goldfield see chapman et al 2010 gold compositions have been considered in association with chemical controls on alloy compositions to establish whether variation between signatures represents zonation within a single mineralizing event or discrete episodes of mineralization three main gold types have been identified each of which exhibits subtypes type 1 gold is generally a simple au ag alloy with low ag 12 25 and an inclusion suite dominated by pyrite and simple base metal sulfides type 2 gold is generally ag rich 18 55 and contains hg 9 type 3 gold 10 40 ag hg 4 is prevalent in the south of the region analysis of large sample sets has allowed us to delineate the geographic extent of each gold type and their relative importance within the placer populations type 1 gold is the major component of placer deposits in bonanza hunker dominion and upper sulphur creeks type 2 gold is relatively trivial but contributes to placer gold in bear creek and some of the paleoplacers in white channel gravel in the north of the study area type 3 gold is actively augmenting the placer inventory in the south of the region this study builds upon a detailed parallel study in the western klondike which concluded that types 1 and 2 gold were emplaced by a single hydrothermal system of limited geographic extent centered on the lone star ridge here we propose that small rich hydrothermal systems were also present in the upper reaches of bear and last chance creeks and hunker dome if correct this model shows that economically important orogenic gold mineralization can be formed in smaller hydrothermal systems than previously recognized in addition type 3 gold is widespread in the south of the study area where it appears to be present at the surface consideration of the abundance of the various gold types contributing to the placers has established type 1 gold to be the most important and originally present in geographically constrained vertically persistent mineralization we propose that this type offers the best target for exploration in the northern and central klondike in the southern klondike the large placers containing only type 3b gold suggest a potentially important undiscovered source in the catchment of gold run creek

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

giant depressions on the chatham rise offshore new zealand morphology structure and possible relation to fluid expulsion and bottom currents abstract several giant seafloor depressions were investigated on the chatham rise offshore new zealand using mainly bathymetric and seismic data supplemented by sediment cores and reported porewater geochemistry data the depressions have diameters of up to 11 km and occur on the southern flank of the chatham rise in water depths between 600 and 900 m i e roughly underneath the location of the strongest thermal gradients of the subtropical front stf and characterized by eastward flowing currents with up to 150 m of relief the depressions cut into post miocene deposits some of the depressions are partially filled with drift deposits that have similar seismic characteristics as the surrounding sediments and consist of alternations of silty muds and silts seismic profiles also show completely filled depressions that no longer have a bathymetric expression despite several pipe structures indicating vertical fluid flow neither active fluid seepage nor indications for past fluid seepage are present at the seafloor of the chatham rise also both pore water geochemistry and geophysical data do not show indications for an existing or past gas hydrate system in the area instead seismic data suggest widespread polygonal faulting and the presence of silica diagenetic fronts the release of mineral bound water during silica diagenesis or fluid expulsion during sediment compaction can explain the presence of vertical fluid flow features but not the giant depressions themselves instead the depressions are interpreted as the result of scouring by strong bottom currents for which fluid venting may have created the nucleation points

organic rich sedimentation in the south pacific ocean associated with late paleocene climatic cooling abstract a distinctive organic rich marine mudstone of late paleocene age occurs in most of new zealand s sedimentary basins and has been identified as a potential source rock for oil and gas identified as the waipawa formation in the east coast basin and the tartan formation in the great south and canterbury basins the unit is a relatively uniform massive mudstone that varies greatly in thickness 2 70 m and grades laterally into distinctive facies equivalents notably greensand and a thin bedded siliceous mudstone all these facies are characterised by relatively high toc 0 5 10 wt and 13 c enrichment 13 c toc 24 and we refer to them collectively as waipawa organofacies our detailed stratigraphic and geochemical studies refine the age 58 7 to 59 4 ma distribution and nature of the waipawa organofacies we have determined that deposition occurred in continental margin settings throughout much of the southwest pacific under cool dysoxic conditions associated with a significant influx of terrestrial organic matter high marine productivity a global fall in sea level and a regional unconformity across shallow and deep marine settings the combination of cool temperatures lowered sea level and bathyal erosion suggests that deposition was linked to short lived growth of an antarctic ice sheet in the earliest late paleocene 59 ma

the role of tectonism in sequence development and facies distribution of upper oligocene cool water carbonates coromandel peninsula new zealand the torehina formation is part of a cool water carbonate succession of oligocene age in new zealand that crops out on the coromandel peninsula north island it contains two major transgressive sequences that record successive onlap of a once emergent landmass the first sequence records marine flooding of non marine to marginal marine fan delta estuarine facies followed by deepening upward and formation of a low energy deep 100 m muddy carbonate ramp the capping sequence boundary is characterized by differential uplift and varies considerably in its character over a small 9 km2 area varying from a burrowed glauconitic firmground to an erosional hardground to an undulatory marine contact to a palaeokarst with planktic echinoderm and bivalve limestones in another this variation disappears upsection which suggests that initial bathymetric differences were eliminated with renewed rise in sea level yielding deeper water inner shelf sediment facies followed by the accumulation of still deeper but higher energy outer shelf bivalve and bryozoan facies the sequence architecture of the torehina formation is controlled by tectonism both long term subsidence and short term differential uplift this arose as a result of increasing tectonic activity throughout proto new zealand during the late oligocene in such a system local and regional variation in tectonism among adjacent basins can impose subtle to marked differences in the timing of sequence boundaries and the character of basin fill patterns

evolution of the sedimentary system beneath the deep pacific inflow off eastern new zealand results from ocean drilling program sites 1121 1124 show the eastern new zealand oceanic sedimentary system enzoss evolved in response to 1 the inception of the circum antarctic circulation 2 orbital and non orbital regulation of the global thermohaline flow and 3 development of the new zealand plate boundary enzoss began in the early oligocene following opening of the tasmanian gateway and inception of the ancestral antarctic circumpolar current acc and sw pacific deep western boundary current dwbc widespread erosion marked by the marshall paraconformity was followed by extensive drift formation in the late oligocene early miocene alternating nannofossil chalk and nannofossil rich mud deposited in response to 41 kyr orbital regulation of the abyssal circulation with the mudstones representing times of increased inflow of corrosive southern source waters drift deposition at the deepest sites was interrupted by bouts of erosion coincident with mi1 5 isotopic events signifying expansions of the east antarctic ice sheet and enhanced bottom water formation by late miocene times the basic enzoss was established south of bounty trough the energetic acc instigated an erosional low depositional regime to the north where the dwbc prevailed orbitally regulated drift deposition continued increased convergence at the new zealand plate boundary enhanced the terrigenous supply but little of this sediment reached the deep enzoss as the three main sediment conduits solander bounty and hikurangi channels had not fully developed the plio pleistocene heralded a change from a carbonate to terrigenous dominant supply caused by interception of the dwbc by the three channels 1 6 ma for bounty and hikurangi time of solander interception unknown the solander and bounty fans and hikurangi fan drift systems formed and drifts downstream of those systems received terrigenous detritus supply increased with accelerating uplift along the plate boundary but delivery to the dwbc was regulated by eustatic fluctuations of sea level times of maximum supply to all three channels was during glacial lowstands whereas the supply either ceased bounty solander or reduced hikurangi in highstands in glacial times sediment was entrained by a dwbc invigorated by an increased input of antarctic bottom water the acc also accelerated under strengthened glacial winds thus glacials were times of optimum sediment supply to enzoss depocentres where depositional rates were 2 3 times more than interglacial rates

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

benthic foraminiferal proxy evidence for the neogene palaeoceanographic history of the southwest pacific east of new zealand abstract canonical correspondence analysis indicates that the distribution of neogene benthic foraminiferal faunas 63 m in seven dsdp and odp sites 500 4500 m water depth east of new zealand 38 51 s 170 e 170 w is most strongly influenced by depth water mass stratification and secondly by age palaeoceanographic changes influencing faunal composition and biotic evolution stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern and later northern polar glaciation and consequent cooling of bottom waters increased vertical and lateral stratification of ocean water masses and increased overall and seasonal surface water productivity oligocene initiation of the antarctic circumpolar current and deep western boundary current dwbc flowing northwards past new zealand resulted in extensive hiatuses throughout the southwest pacific some extending through into the miocene planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the neogene peaking at upper abyssal depths in the late miocene 11 7 ma with the lysocline progressively deepened thereafter miocene abyssal faunas are dominated by globocassidulina subglobosa and oridorsalis umbonatus with increasing epistominella exigua after 16 ma at upper abyssal depths peak abundances of epistominella umbonifera indicate increased input of cold southern component water to the dwbc at 7 6 ma faunal association changes imply establishment of the modern oxygen minimum zone upper circumpolar deep water in the latest miocene significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the chatham rise location of present subtropical front since the early late miocene at least with more pulsed productivity higher e exigua along the south side modern antarctic intermediate water faunal associations were established north of the chatham rise at 10 9 ma and south of it at 3 1 5 ma middle upper bathyal faunas on the campbell plateau are dominated by reticulate bolivinids during the early and middle miocene indicative of sustained productivity above relatively sluggish suboxic bottom waters faunal changes and hiatuses indicate increased current vigour over the campbell plateau from the latest miocene on surface water productivity food supply appears to have increased in three steps at times of enhanced global cooling marked by substantially increased relative abundance of 1 abditodentrix pseudothalmanni alabaminella weddellensis cassidulina norvangi 16 15 ma increased pulsed productivity 2 bulimina marginata f aculeata nonionella auris trifarina angulosa uvigerina peregrina 3 1 5 ma increased overall productivity and 3 cassidulina carinata 1 0 5 ma increased overall productivity three intervals of deep sea benthic foraminiferal taxonomic turnover are recognised 16 15 11 5 10 2 0 5 ma corresponding to intervals of enhanced global cooling and possible productivity changes the late pliocene middle pleistocene extinction associated with increasing northern hemisphere glaciation culminating in the middle pleistocene climatic transition was more significant in the study area than the earlier neogene turnovers

the evolution of a porphyry cu au deposit based on la icp ms analysis of fluid inclusions bajo de la alumbrera argentina the chemical and physical evolution of magmatic to hydrothermal processes in the porphyry cu au deposit of bajo de la alumbrera northwestern argentina has been reconstructed with a quantitative fluid inclusion study fluid inclusion petrography microthermometry and single inclusion microanalysis by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms are combined to determine the evolution of pressure temperature and ore metal concentrations including cu and au in the fluids complementary hydrogen and oxygen isotope analyses are used to further constrain the water sources in the evolving system the combined data provide a new level of insight into the mechanisms of metal sourcing and ore mineral precipitation in a porphyry style magmatic hydrothermal system based on previously reported observations of the igneous geology alteration geochemistry and veining history of the subvolcanic porphyries at alumbrera the distribution of fluid inclusion types in space and time is documented six major inclusion types are distinguished the highest temperature brine inclusions up to 750 c p 1 kbar are mainly recorded in barren quartz magnetite veins in the core of the alteration system these polyphase brine inclusions halite sylvite multiple opaque and transparent daughter crystals are interpreted as the most primitive magmatic fluid recorded at the level of the deposit they are of moderately high salinity 50 60 wt nacl equiv dominated by nacl kcl and fecl 2 and contain on average 0 33 wt percent cu and 0 55 ppm au upon cooling and decompression these saline liquids exsolve a vapor phase which is preferentially enriched in cu relative to its main salt components but probably plays a minor role in the formation of this particular deposit because of the inferred small mass fraction of vapor cooling and decompression from the highest initial p t conditions down to about 450 c causes magnetite k silicate alteration but no saturation in au or cu sulfides as recorded by continually high ore metal concentrations in the fluid inclusions coprecipitation of cu and au as chalcopyrite and native gold some early bornite occurs over a narrow range of decreasing fluid temperature with cooling from 400 to 305 c the cu concentration in the brine drops by about one order of magnitude to less than 0 07 wt percent without a proportional decrease in major salt components ore mineral precipitation extracts 85 percent of the cu and au from the fluid it is associated with potassic alteration as shown by a concomitant decrease in the k na ratio of the cooling magmatic brine and by an increase in its ba and sr concentrations elements which are probably liberated in the destruction of calcic igneous minerals the fluid chemical data demonstrate that the metal ratios in this and probably many other porphyry style ore deposits are primarily controlled by the magmatic source of the ore brines on the other hand the final hypogene ore grade of the deposit is controlled by the efficiency of ore mineral precipitation at alumbrera metal extraction is governed by the efficiency of cooling a high flux of magmatic fluid within a small rock volume dilution of residual magmatic fluids as recorded by aqueous fluid inclusions of decreasing salinities and temperatures below 295 c follows after the main stage of copper introduction and is associated with feldspar destructive phyllic alteration geometric relationships fluid analyses and stable isotope data together indicate that phyllic alteration results from postmineralization hydrothermal activity involving minor mixing between meteoric water residual brine and a waning input of magmatic vapor

variation in the isotopic composition of single components in the c4 c20 fraction of oils and condensates abstract determination of the isotopic composition of individual compounds in the c4 c15 range has been difficult due to the lack of suitable instrumentation it has also been suggested that isotopic fractionation during storage might occur with the introduction of online gc irms an instrument is now available to test whether or not isotopic fractionation occurs during storage to test this two condensates were analysed using the gc irms method samples were taken for analysis at regular intervals during storage at elevated temperatures only small changes in isotopic composition were observed during evaporation with a slight enrichment in 13c in some compounds however the changes are so small that even prolonged storage times do not significantly affect the carbon isotopic composition of the compounds as long as there is enough material left for analysis two separate suites of samples one from the central graben the other from the viking graben were used to demonstrate the use of the technique in correlating oils and condensates this study shows that the oil condensates in the central graben are not sourced from a single source rock differing only in maturity as reported earlier but are sourced from various source facies where especially edda differs significantly from the others i e the compounds in edda are 1 2 0 heavier than the rest of the analysed samples in the central graben the analysed viking graben oils and condensates were divided into three groups based on this study

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

magnetostratigraphic calibration of southern ocean diatom datums from the eocene oligocene of kerguelen plateau ocean drilling program sites 744 and 748 ocean drilling program holes 744a and 748b represent key sections for calibration of southern ocean eocene oligocene biostratigraphic zonations sites 744 and 748 were above the carbonate compensation depth throughout this time interval and contain good planktonic foraminiferal calcareous nannofossil and diatom biostratigraphic records in particular the southern ocean diatom biostratigraphic zonation for the oligocene critically hinges on calibration of these two holes previous low resolution magnetostratigraphic studies at these sites were hampered by limited sampling and technical difficulties which prompted our high resolution reinvestigation of the magnetostratigraphy magnetic polarity zonations for holes 744a and 748b were constructed after inspection of vector component plots at 1 cm stratigraphic intervals from continuous u channel measurements the magnetizations are generally stable and a robust polarity stratigraphy has been obtained for both holes the increased resolution of our study and identification of persistent secondary overprints which were not recognised in previous studies suggests that the previously published interpretations need to be revised our magnetostratigraphic interpretations for both holes are constrained by foraminiferal and calcareous nannofossil datums as well as by sr isotope ages we have calibrated four diatom datums which are synchronous at the two studied sites to the geomagnetic polarity timescale including the first occurrence fo of lisitzinia ornata 27 8 ma the fo of rocella vigilans var b 27 8 ma the fo of cavitatus jouseanus 30 9 ma and the fo of rhizosolenia oligocaenica 33 8 ma the synchroneity of these datums suggests that diatom biostratigraphy has considerable potential for palaeogene biostratigraphic correlation in the southern ocean although the ages of some datums are obscured by an unconformity in hole 744a our age model from hole 748b suggests age estimates for the last common occurrence of rocella vigilans var a 29 0 ma the fo of rocella vigilans var a 30 0 ma and the fo of rhizosolenia antarctica 33 2 ma it should also be noted that the last occurrence of the calcareous nannofossil chiasmolithus altus occurs in chron c8r rather than c8n in our revised magnetostratigraphic interpretation which indicates that this datum is not diachronous between low and mid latitudes as had previously been suggested significant unconformities are documented in both holes in the middle oligocene and in the middle late oligocene respectively which probably resulted from periods of enhanced circumpolar deep water circulation

a distinctive pd hg signature in detrital gold derived from alkalic cu au porphyry systems abstract this study comprises the first systematic classification of native gold geochemistry within alkalic porphyry cu au systems and the placer expression of such systems the geochemistry and mineral associations of gold from four alkalic porphyry deposits in british columbia canada afton mount milligan mount polley and copper mountain have been compared to comment on the likely detrital gold expression of similar systems globally populations of gold grains collected from in situ hypogene mineralization as well as fluvial deposits downstream of these deposits have been characterized in terms of their alloy composition au ag cu hg and pd and associated mineral inclusions these data are combined to generate a microchemical signature gold compositions vary according to the alteration zone within a porphyry system previous compositional studies of gold in porphyry systems have focused on the most economically important ore associated with potassic alteration wherein native gold hosted either by bornite or chalcopyrite comprises tiny blebs typically 5 20 m containing detectable cu in the gold alloy to a maximum of around 5 but quite variable 2 30 wt ag the presence of such grains have been confirmed in hypogene ore from the four systems studied but they have been shown to be compositionally distinct from detrital gold collected from nearby fluvial placers which exhibit a strong pd and hg signature both in the alloy and as mineral inclusions several workers have described late stage veins associated with alkalic porphyries which contain distinctive pd hg bearing minerals in association with other sulphides and sulphosalts this unusual mineralogy has been observed in the mineral inclusion suites of populations of detrital gold grains collected in the environs of the porphyry systems we conclude that whilst the micron scale cu rich gold grains formed in potassically altered rocks are in general too small to be recovered during routine sediment sampling those formed in later stage hydrothermal systems are larger and exhibit a distinctive microchemical signature which may be differentiated from those of gold formed in other mineralizing systems consequently compositional studies of detrital gold could underpin a mineral indicator methodology in the exploration for alkalic porphyry cu au deposits

opening of drake passage gateway and late miocene to pleistocene cooling reflected in southern ocean molluscan dispersal evidence from new zealand and argentina thirty two benthic marine molluscan genus group taxa are newly recognised as common to new zealand and argentina previously suggested examples including panis athlopecten austrovenus large cirsotrema lucinoma aulacomya and zygochlamys are confirmed from new collections the total of 46 cenozoic dispersed taxa now recognised falls into four main groups a oligocene early miocene dispersals from south america to new zealand 8 taxa b oligocene early miocene dispersals from new zealand to south america 22 c latest miocene pliocene dispersals from south america to new zealand 9 and d pleistocene holocene dispersals from south america to new zealand at least 7 taxa dispersal seems to have occurred in bursts both to and from south america when the antarctic circumpolar current acc initiated i e when drake passage opened late in the oligocene while dispersal from south america to new zealand only seems to have occurred again at two later times 1 during the latest miocene pliocene enhancement of acc circulation caused by the initiation of west antarctic glaciation and 2 during pleistocene glaciations however the incompleteness of the argentinian record exaggerates the size of the initial burst and allows no assessment of post middle miocene dispersal to south america formation of the acc through the opening of a passage south of australia at ca 43 40 ma and of drake passage at ca 23 ma not only led to the glaciation of antarctica but also greatly altered southern ocean biogeography

middle eocene to early oligocene calcareous nannofossil stratigraphy at leg 177 site 1090 semi quantitative and quantitative analyses on nannofossil assemblages were carried out on the middle eocene to early oligocene interval of site 1090 hole b several biozones were recognized according to the schemes of martini 1971 okada and bukry 1980 and wei and wise 1990a between the fo of reticulofenestra reticulata and the lo of reticulofenestra umbilica based on nannofossil biostratigraphy our proposed interpretation of shipboard magnetic inclination data recognizes magnetic chrons from c12 to c19 according to the geomagnetic polarity time scale of berggren et al 1995 the eocene oligocene boundary is placed between the last occurrences of reticulofenestra oamaruensis and discoaster saipanensis within chron c13r on the basis of the correlation between magnetostratigraphy and biostratigraphy a new biochronology is proposed for some nannofossil events the age of fo of reticulofenestra circus was estimated at 33 39 ma no previous biochronology is available in the literature for this event an age depth curve is constructed on the basis of the correlation between nannofossil biostratigraphy and the gpts of berggren et al 1995 a very low value of sedimentation rate 0 5 m ma characterizes the upper part of the study site from the last occurrence of ericsonia formosa to the last occurrence of r umbilica the presence of a hiatus or a condensed interval may occur at this level it may be related to the mid oligocene marshall paraconformity and the inception of the antarctic circumpolar current which contributed to the modification of the nannoflora composition and sedimentation in this sector of the south ocean 9 2002 elsevier science b v all rights reserved

evidence for late oligocene establishment of the antarctic circumpolar current removal of the last impediment to circum antarctic flow opening of the drake passage between antarctica and south america is essential to establishment of the acc and has been placed in both the earliest oligocene and earliest miocene on the basis of paleomagnetic reconstructions the tasman gateway between antarctica and tasmania notably deepened following 33 5 ma completion of the acc circuit has been seen as the key to major growth of the east antarctic ice sheet by thermal isolation of the continent an alternative argument attributes ice sheet growth to changes in atmospheric pco2 we present evidence on current strength and water mass properties suggesting a clear increase in flow speed and homogeneity of southern ocean water masses in the latest oligocene after about 23 95 ma marking establishment of the acc attributable to deep opening of drake passage the mi 1 glaciation may be a consequence establishment of a permanent low altitude ice sheet does not appear to take place prior to mid miocene cooling

late oligocene initiation of the antarctic circumpolar current evidence from the south pacific the antarctic circumpolar current acc is a key feature of the southern ocean its development may have helped cool antarctica and initiate southern hemisphere glaciation the deep circulation of the acc must have been established after both the tasman gateway between antarctica and australia and the drake passage between south america and antarctica opened however estimates for acc initiation range over 20 m y from the middle eocene to early miocene a new piston core of upper oligocene to holocene sediments from the south pacific has allowed us to delimit the formation of the acc to the late oligocene ca 25 23 ma upper oligocene current worked sediments and a hiatus to the upper miocene result from the beginning of the modern acc flow i e when strong currents and mixing throughout the water column were established previously published nd isotope data date the first intrusion of pacific water into the atlantic much earlier the discrepancy with our results can be reconciled by the different methods measuring different flow regimes tracer methods such as nd are sensitive to relatively small and shallow incursions of water whereas pelagic erosional regimes require vigorous deep flow

diagenetic implications of stylolitization in pelagic carbonates canterbury basin offshore new zealand abstract stylolites are irregular discontinuity surfaces that are thought to result from localized stress induced dissolution during burial or tectonic compression the genesis of stylolites and the controls on stylolitization are still debated and the interplay between stylolitization generation of carbonate rich fluids diagenetic fluid flow within fractures and matrix cementation and porosity modifications is complex all of these processes have important diagenetic effects potentially altering the intrinsic properties of the host rock with implications for hydrocarbon exploration and water resources in aquifers we investigate the process of stylolitization by a macroscopic petrographic and geochemical study of pressure solution features in eocene to early oligocene limestones in cores from the integrated ocean drilling program iodp hole 317 u1352c canterbury basin the results indicate correlations among stylolite amplitude stylolite density and siliciclastic content of the host rock these relationships are interpreted to suggest that siliciclastic content in carbonate rocks increases heterogeneity which in turn impacts stylolite nucleation moreover the geochemical data support that clay along the stylolite is not authigenic but a relict from impurities in the limestone host rock the statistical approach of stylolite spacing used in this study which is different than previous studies reinforces the model of random occurrence of stylolites in carbonate lithologic units this study shows that local stresses in tectonically passive areas may allow the formation of rare oblique stylolites with peaks perpendicular to the stylolite plane estimation of the amount of limestone dissolved during stylolitization minimum 7 to 12 of the depositional limestone and the volume of sparite in the host rock up to 1 6 of the compacted limestone suggests that the pressure solution fluids cemented the micropores reducing porosity to about 10 from a common porosity of about 40 in mechanically compacted chalk this study thus highlights the importance of microporosity as a sink for burial cements an observation difficult to make in thin section analysis of stylolite infills at site u1352 shows no evidence that the stylolites acted as conduits for diagenetic fluids unless if the fluid was host rock buffered and thus its chemistry indistinguishable from that of the host rock the link between siliciclastic content in carbonate rocks and the spacing and amplitude of stylolites improves understanding of burial compaction processes predicting the morphology and spacing of stylolites in the subsurface can be used to identify baffles to cross stylolite fluid flow or cementation of microporosity influencing heterogeneity of petrophysical properties in subsurface reservoir host rocks

geochemically driven exploration models in uplifted areas examples from the norwegian barents sea the norwegian barents sea with multiple source rock intervals represents a prime example of an overfilled petroleum system however several episodes of uplift and erosion from the paleocene until the pliocene pleistocene have caused the depletion of hydrocarbon accumulations in the region these uplift events were not only potentially catastrophic but have also caused the redistribution of the remaining oil and gas over laterally large distances in the barents sea region this redistribution directed petroleum to distal parts of the various hydrocarbon generating basins thus charging traps which otherwise would not have been reached therefore we expect that discoveries will be made in distal basin settings particularly in traps with partly leaking cap rocks which can bleed off gas and thereby retain oil many oil accumulations in the region represent various mixtures of oils from several different stratigraphic source intervals this suggests that triassic and paleozoic oils may be trapped below the presently drilled targets which are mostly jurassic in the hammerfest basin and older to the north and east deeper exploration targets also stand a higher chance of containing oil because the amount of gas being released from oil during uplift erosion and subsequent pressure release is lower uplift and erosion are followed by a reduction in temperature this is why hydrocarbon generation is believed to have ended in uplifted areas some discoveries in this data set suggest however a significant fresh gas charge

upper eocene to oligocene isotope 87sr 86sr δ18o δ13c standard section deep sea drilling project site 522 we improved upper eocene to oligocene deep sea chronostratigraphic control by integrating isotope 87sr 86sr 18o 13c stratigraphy and magnetostratigraphy most previous attempts to establish the timing of isotope fluctuations have relied upon biostratigraphic age estimates which have uncertainties of 0 5 to over 4 0 m y deep sea drilling project dsdp site 522 contains the best available upper eocene to oligocene magnetostratigraphic record which allows first order correlations of isotope records 87sr 86sr 18o 13c to the geomagnetic polarity time scale gpts empirical calibrations between the 87sr 86sr of foraminifera and magnetochronology at site 522 allow more precise correlation of unknown samples with the gpts for example shallow water and high latitude sections may be tied into the deep sea record sr isotope stratigraphic resolution for the latest eocene to oligocene is approximately 2 m y

the motunau fault and other structures at the southern edge of the australian pacific plate boundary offshore marlborough new zealand abstract the boundary between the indo australian and pacific plates passes through new zealand as the alpine fault then links northeastwards with the hikurangi subduction margin through the marlborough shear zone a group of five major subparallel transcurrent faults the southern limit of the marlborough shear zone is situated at the motunau fault a previously unrecognized offshore extension of the active porters pass fault and lineation system to the south of the motunau fault the kaikoura sequence cretaceous cainozoic sediments that underlie the canterbury continental shelf are effectively undeformed and lie outside of the plate boundary zone 3 5 khz profiler records and other marine geologic data collected on g r v tangaroa cruises 1097 and 1116 show that the shelf north of the motunau fault is underlain by complexly deformed sediments faulting and folding continue in this area today as evidenced by the presence of deformed late pleistocene strata and by the distribution of earthquake epicentres within the marlborough plate boundary zone the five major strike slip faults delimit four substantial blocks or microplates 20 60 km wide and up to 220 km long from north to south these are the spenser inland kaikoura seaward kaikoura and conway blocks respectively kaikoura sequence sediments are most strongly deformed near the margins of the blocks and their subsidiary fault systems within each microplate deformation is restricted to moderate folding and faulting the overall structural pattern being consistent with dextral movement on the boundary faults the available marine geologic and geophysical data suggest that subduction of the pacific plate may have propagated southwards during the late neogene causing successive activation of the marlborough faults today subduction is occurring right to the southern head of the hikurangi trough where the motion is transferred to the motunau fault system since earthquake epicentres only reach to intermediate depths beneath the southern part of the conway microplate and since the motunau fault system is not such a continuous physiographic features as faults further north it is likely that this southern margin to the plate boundary zone is still actively developing

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

gold in porphyry copper deposits experimental determination of the distribution of gold in the cu fe s system at 400 to 700 c experiments in the system au cu fe s were carried out at temperatures of 400 to 700 c to determine how much gold could be accommodated by bornite and chalcopyrite the two most common ore minerals in porphyry copper gold deposits our results show that for all temperatures bornite contains one order of magnitude more gold than chalcopyrite or intermediate solid solution iss its high temperature equivalent the range of gold concentrations in bornite and chalcopyrite or iss decreases with decreasing temperature from 1 280 to 8 200 ppm au in bornite and 100 to 125 ppm au in iss at 600 c to 235 to 364 ppm au in bornite and 5 to 16 ppm au in chalcopyrite or iss at 500 c and to 13 to 80 ppm au in bornite and 2 to 4 ppm au in chalcopyrite or iss at 400 c the amount of gold in bornite is also strongly dependent on the composition of bornite being highest in stoichiometric bornite compositions cu5fes4 and decreasing toward cu rich and cu poor compositions phase equilibrium constraints for solutions with geologically reasonable reduced sulfur contents indicate that high temperature porphyry copper gold deposits will contain bornite and magnetite whereas lower temperature deposits whether primary or overprinted by phyllic alteration will contain chalcopyrite and pyrite if gold is present in the ore forming solutions more of it will be deposited in high temperature porphyry copper gold deposits where it will be closely associated with bornite coexisting magnetite in these deposits should generate magnetic anomalies lower temperature deposits will contain less gold which is hosted by pyrite as well as chalcopyrite and will lack magnetic anomalies comparison of the amount of gold hosted by natural porphyry copper gold ores to that hosted by bornite and chalcopyrite in our experiments suggests that significant amounts of gold can be lost from these deposits into surrounding hydrothermal systems

vertical and lateral variation of mineralogy and chemistry in the early jurassic mt milligan alkalic porphyry au cu deposit british columbia canada the moderately tilted and faulted early jurassic mt milligan au cu deposit provides a cross section view of the hydrothermal alteration sulfide mineralogy and geochemical zonation of a silica saturated alkalic porphyry system over a vertical distance approaching 700 m magnetite bearing potassic alteration and associated au cu form a core to the system in the central monzonitic stock and adjacent basaltic trachyandesite host rock lateral to the high temperature core are sodic calcic and inner and outer propylitic alteration assemblages chalcopyrite dominates the high temperature potassic core whereas pyrite is the predominant sulfide within and outboard from the sodic calcic assemblage a funnel shaped remnant of carbonate rich phyllic alteration of the host supracrustal rocks in the fault bounded 66 zone represents the upper auriferous alteration in the alkalic porphyry au cu system alteration mineral assemblage s isotope ranging from 34s 5 relative to canon diablo troilite in the core to 34s 0 5 in the periphery and limited fluid inclusion data suggest mineralization at the au cu alkalic porphyry system was derived from an oxidized co2 bearing magmatic fluid that rose upward along the margins and through the magnetite breccia stock laterally from the au cu mineralized potassic core magmatic fluid evolved through water rock interaction mixing with an external fluid as shown by a shift in calculated 87sr 86sr for alteration minerals to values higher than magmatic values declining temperature or some combination of all variations in trace element concentrations of epidote v mn sb zr as and bi and pyrite mn as zr pb and bi across the deposit show a local high degree of variability but general increases or decreases in overall trends in their median values are inferred to reflect the hydrothermal evolution of the system pistachite ratios of epidote show an outward decrease in ferric iron as recorded in the pistachite ratio changing from ps36 to ps25 suggesting less oxidizing conditions on the system periphery additionally light rare earth elements in epidote fractionate toward the core of the deposit and the height of positive eu anomalies also appears to have a similar spatial trend in pyrite there is a general increase in trace element concentration toward the epidote pyrite rich outer propylitic assemblage forming the system periphery alteration mineralogy and trace element signatures indicate the southeastern portion of the deposit the 66 zone is a down dropped segment from higher in the paleohydrothermal system s isotope signatures of sulfides within and surrounding the stratiform upper trachyte unit in the 66 zone indicate structural channeling of oxidizing fluids that likely were the distal and cooler expression of more oxidizing magmatic derived hydrothermal fluids responsible for potassic alteration and au cu in the subjacent magnetite breccia zone the main orebody

seismic models of a carbonate foreslope to basin transition picco di vallandro dolomite alps northern italy detailed geologic cross sections augmented by laboratory calibration of lithology and acoustic impedance have been used to produce synthetic reflection seismic sections of a carbonate foreslope to basin transition two areas from the picco di vallandro region of the dolomite alps were modeled a progradational section and a retrogradational backstepping section the resulting models show how these complex areas of strata interfingering might be displayed on conventional reflection seismic lines in the area of progradation rapid stratigraphic thinning below seismic detectibility coupled with abrupt impedance changes produces a reflection discontinuity between steeply dipping reflections of the foreslope and gently dipping parallel reflections of the basin section this apparent downlap surface marks the toe of slope for successive clinoforms but does not correspond to a discrete stratigraphic surface in the backstepping example similar stratigraphic thinning and impedance changes create an apparent onlap surface wavelet interference causes complications in both examples these models indicate how stratigraphic complexity can be simplified by the seismic reflection process and suggest that caution should be exercised when using seismic data to construct general models in areas of complex depositional geometries and rapidly changing facies

oligocene miocene strontium isotopes stratigraphic revisions and correlations to an inferred glacioeustatic record this study tests and improves on previously published early and middle miocene 87sr 86sr marine correlations presents sr isotopic age correlations for this interval using the new timescale of cande and kent 1992 and evaluates sr isotopic changes against an inferred glacioeustatic proxy we generated a latest oligocene to early late miocene 87sr 86sr isotope record from ocean drilling program odp hole 747a this site provides an excellent magnetostratigraphic record during most of this interval for independent age estimates very good foraminiferal preservation and excellent core recovery comparisons of new 87sr 86sr data from hole 747a with previously published data from deep sea drilling project dsdp sites 608 miller et al 1991a and 588 hodell et al 1991 yield the following results 1 confirmation and refinement of the early miocene sr isotope changes 2 improved definition of the timing of the changes in slope of 87sr 86sr near 15 4 ma and 22 8 ma 3 improved sr isotopic age resolution for the middle miocene with resolution as good as 0 7 m y and 4 identification of an inflection in the sr isotope record at 28 0 ma based on the combined records from dsdp site 522 miller et al 1988 and odp hole 747a we have been unable to determine the cause of middle miocene offset between site 588 and hole 747a data although we believe it may be attributed to problems in the age assignments for hole 588a for the interval 14 11 ma and site 747 for the interval 11 8 ma because hole 747a results provide a better chronology than site 588 for most of the miocene and a better middle miocene sr isotope record than site 608 we propose that hole 747a serves as the best reference section for miocene 87sr 86sr variations from ca 23 to 11 ma using 87sr 86sr data from sites 522 608 and 747a we relate late eocene to early miocene inflections in the 87sr 86sr isotope record to oxygen isotope increases and decreases inferred to represent glacioeustatic events the decreases deglaciations observed in the 18o record apparently lead the 87sr 86sr inflections by 1 to 1 5 m y

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

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

integrated late eocene oligocene stratigraphy of the alabama coastal plain correlation of hiatuses and stratal surfaces to glacioeustatic lowerings we integrated strontium and oxygen isotopic biostratigraphic and magnetostratigraphic studies of two upper eocene oligocene boreholes drilled near bay minette and st stephens quarry ssq alabama continuous coring provided fresh unweathered material for magnetostratigraphic studies minimizing problems reported from nearby outcrops difficulties with each technique were encountered because of diagenesis absence of marker fossils and the presence of unconformities however by integrating results from isotopic stratigraphy biostratigraphy and magnetostratigraphy we correlated these relatively shallow water deposits to the geomagnetic polarity time scale gpts at the ssq borehole the upper eocene to lower oligocene section is apparently complete within our stratigraphic resolution 0 2 0 5 m y allowing us to estimate the ages of several stratal surfaces late eocene sr isotope age estimates are as expected at the ssq borehole but oligocene ages are 1 m y older than expected due to diagenesis at the bay minette borehole a latest eocene earliest oligocene and a late early oligocene hiatus were detected we correlate these two hiatuses and stratal surfaces at ssq with global 18o increases inferred to represent glacioeustatic lowerings and with evidence for hiatuses on other continental margins 1 a distinct disconformity at the base of the chickasawhay limestone at both boreholes and a hiatus at bay minette correlates with a global 18o increase we revise the age of this surface equivalent to the tb 1 1 sequence boundary making it 2 m y older than previously reported and 2 a surface at the top of the shubuta member lowermost oligocene has been interpreted both as a condensed section and a disconformity this surface at ssq and a hiatus at bay minette correlate with a sharp global 18o increase and with hiatuses on the new jersey and irish margins the timing of the hiatuses and stratal surfaces correlates with the inflection of the 18o increases and not with the maximum values supporting models that indicate that unconformities form during the maximum rates of sea level fall

neogene history of the deep western boundary current at rekohu sediment drift southwest pacific odp site 1124 abstract odp site 1124 located 600 km east of the north island of new zealand records post middle oligocene variations in the pacific deep western boundary current dwbc and new zealand s climatic and tectonic evolution sediment parameters such as terrigenous grain size flux magnetic fabric and non depositional episodes are used to interpret dwbc intensity and antarctic climate interpretations of dwbc velocities indicate that the antarctic circumpolar current reached modern intensities at 23 ma as the tectonic seaways expanded completing the thermal isolation of antarctica periods of more intense bottom water formation are suggested by the presence of hiatuses formed under the dwbc at 22 5 17 6 16 5 15 and 14 11 ma the oldest interval of high current intensity occurs within a climatically warm period during which the intensity of thermohaline circulation around antarctica increased as a result of recent opening of circum antarctic gateways the younger hiatuses represent glacial periods on antarctica and major fluctuations in the east antarctic ice sheet whereas intervals around the hiatuses represent times of relative warmth but with continued current activity the period between 11 to 9 ma is characterized by conditions surrounding a high velocity dwbc around the time of the formation and stabilization of the west antarctic ice sheet the increased terrigenous input may result from either changing antarctic conditions or more direct sediment transport from new zealand the pacific dwbc did not exert a major influence on sedimentation at site 1124 from 9 ma to the present the late miocene to pleistocene sequence is more influenced by the climatic and tectonic history of new zealand despite the apparent potential for increased sediment supply to this site from changes in sediment channeling increasing rates of mountain uplift and volcanic activity terrigenous fluxes remain low and constant throughout this younger period

geological and geochemical controls on the silver content fineness of gold in gold silver deposits abstract a compilation of microprobe fineness data and a re evaluation of bullion production fineness data suggest that the gold fineness model of fisher 1945 can be updated and applied to a wide range of gold mineralised environments the major deposit classes are characterised by the overall average or range of deposits averages and total range of gold fineness values as follows archaean 940 780 1000 slate belt 920 800 1000 plutonic 825 650 970 porphyry 700 1000 650 1000 volcanogenic 650 850 520 870 epithermal 440 1000 0 1000 the archaean including witwatersrand slate belt and plutonic classes are characterised by a high and consistent average fineness and a narrow fineness range there is no clear subdivision within these classes according to deposit style or inferred genesis the porphyry volcanogenic and epithermal classes have a variable average deposit fineness and a wide total range of fineness values within these three classes higher fineness is typical of deposits in andesitic rather than rhyolitic volcanic settings deposits with cu au rather than cu mo or pb zn element associations and deposits with telluride or selenide minerals solubility calculations indicate that in all these environments gold and silver form the same aqueous species with agcl 2 dominating for silver and au hs 2 dominating for gold in all the environments the fluids transport an equal amount of gold and silver in the form of their bisulphide complexes therefore the observed gold fineness values can not be explained by the transporting mechanism only low silver in the ores and higher gold fineness values observed in the archaean plutonic and slate belt environments can be attributed to sulphidation as the dominant mechanism of ore deposition sulphidation of wall rocks destabilises only the bisulphide complexes of gold and silver in contrast epithermal volcanogenic and porphyry environments are characterised by a diversity of ore depositing mechanisms cooling boiling mixing which act alone or in combination and destabilise chloro and bisulphide complexes of gold and silver the high silver concentration in the ores low fineness values and large variation in the fineness values in these environments can be attributed to the complexities in the ore depositing mechanisms

the deep western boundary current at the bounty trough east of new zealand indications for its activity already before the opening of the tasmanian gateway abstract the eastern new zealand oceanic sedimentary system is influenced by the main deep cold water inflow to the pacific ocean the deep western boundary current dwbc odp leg 181 targeted this region the two northern sites odp 1123 and 1124 are mainly used for interpretation of dwbc flow newly acquired high resolution seismic reflection profiles directly cross odp site 1122 in the outer bounty trough area we can decipher the first appearance of a branch of the dwbc meandering into the bounty trough as early as 20 to 16 7 ma we identified four different drift deposits of the dwbc in the outer bounty trough area the deepest two drifts were formed before the opening of the tasmanian gateway and thus provide the first evidence of a pre oligocene deep circulation at the eastern new zealand margin additionally migration of the drift crests to the west and to the east is interpreted to indicate modifications in core flow pathway of the dwbc due to response to climate changes eocene cooling cooling due to west antarctic ice shield build up tectonic influence opening of tasmanian gateway and enhanced sediment input first turbiditic deposits of bounty channel

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

sequence concepts at seismic and outcrop scale the distinction between physical and conceptual stratigraphic surfaces abstract the sequence stratigraphic terms maximum flooding surface and downlap surface as currently applied are ambiguous examples of these intra sequence surfaces are summarised from high frequency mid pleistocene sequences and from a cretaceous recent seismic megasequence both from new zealand at any one locality a mid pleistocene sequence contains up to four stratal discontinuities in ascending order the sequence boundary ravinement surface local flooding surface and downlap surface these physical surfaces which occur in outcrop are regionally diachronous and should be differentiated from theoretical isochronous horizons such as the time of maximum flooding horizon corresponding to maximum shoreline transgression and the time of peak eustatic or local relative sea level horizons corresponding to the highpoint of the eustatic and relative sea level cycles respectively in seismic studies the boundary between the transgressive and highstand systems tracts is usually located at the downlap surface on the basis of a major thermo tectonic sea level cycle in the canterbury basin it is shown that the downlap surface is not a single regional surface and that the change in slope associated with toes of successive prograding clinoforms rises in stratigraphic height basinwards the downlap surface therefore does not usually coincide with the maximum flooding horizon in plio pleistocene cyclothems a discrete unit the mid cycle shellbed straddles the contact between the transgressive and highstand systems tracts this unit might be classified within its own systems tract the condensed section systems tract csst alternatively the position of the boundary between the transgressive and highstand systems tracts can remain unspecified or unknowable

petroleum migration alteration and remigration within troll field norwegian north sea troll field represents the largest petroleum discovery within the entire north sea area in oil equivalents with 74 of the accumulated petroleum present as dry gas and 26 as a heavy biodegraded oil leg the field is divided into several provinces based on the distribution of gas and oil and the gas and oil have been suggested to be cogenetic the migration and filling model presented in this paper suggests that the oil and gas represent two different migration phases and that gas migration and filling predate oil emplacement two different oil populations have been characterized and mapped in troll field applying conventional geochemical techniques we suggest that the two oil populations migrated into the structure through two different migration systems oil and gas were subsequently biodegraded within the reservoir the two oil populations have been found in neighboring oil and gas discoveries and an oil oil correlation with these discoveries has been used to determine the location of field filling points and regional migration routes when oil biodegradation terminated fresh oil continued to migrate into the reservoir and mixed with the residue of the biodegraded oil the field was tilted downward to the west in the neogene and oil and gas remigrated within the field with a possible spillage of gas tilting resulted in a dominantly upward movement of the oil phase whereas gas migrated laterally residual oils in the water zone copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received july 18 1995 revised manuscript received march 14 1996 final acceptance august 16 1996 2saga petroleum a s kjorboveien 16 p o box 490 n 1301 sandvika norway 3newcastle research group drummond building university of newcastle upon tyne newcastle upon tyne ne1 7ru united kingdom we would like to thank the partners in the troll license who allowed us to publish these results per erling johansen and tone molvik are acknowledged for the analytical work and snorre olaussen nigel mills and terje hellem are thanked for helpful discussions and for assistance with the back tilting of the irap reservoir field model jill sonrier is acknowledged for typing we acknowledge k m wolgemuth john f brint and two anonymous reviewers for helpful comments that improved the paper significantly

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

cenozoic bottom current sedimentation in the cape basin south atlantic the cape basin is located at a central location with respect to variouswater masses the coldest and densest of these water masses is thelower circumpolar deep water the location and topography of the agulhas ridge effectively blocks itsnorthward flowing branches and deflects them into a south westerndirection to follow the bathymetric contours of the agulhas ridge wheresuspended sediments accumulate in contourite drifts several hundred metres of sediments have accumulated since the onsetof antarctic bottom water intrusion into the basins of the south atlantic a present day like bottom current following agulhas ridge contours existssince an erosional event in the early oligocene took place which markeda prominent change in sedimentation strong and varying currents in the early oligocene formed a sheet likedeposition at high sedimentation rates the fluctuating types of sediments produce strong seismic reflections it was followed by a very stable unidirectional bottom current with mainlymuddy sediments this resulted in the formation of a more than 200 kmlong approx 30 km wide elongate contourite drift which shows fewinternal reflections on the seismic data an increase of well defined unitsis found after a period of non deposition in the middle miocene still the build up of the drift structure continued but at places erosion isfound especially in quaternary sediments and probably in relation toglaciation cycles

introduction to the special issue devoted to alkalic porphyry cu au and epithermal au deposits this special issue is devoted to alkalic porphyry cu au and epithermal au deposits and focuses on two regions british columbia canada fig 1 and the southwest pacific region australia and papua new guinea fig 2 the special issue commences with a review of triassic to jurassic metallogeny of british columbia logan and mihalynuk 2014 then documents ore zones from several alkalic deposits central zone galore creek micko et al 2014 southwest zone galore creek byrne and tosdal 2014 northeast zone mt polley pass et al 2014 lower main zone lorraine bath et al 2014 mt milligan jago et al 2014 and provides a comprehensive overview of mineralization in the lorraine district devine et al 2014 four contributions document alkalic porphyry and epithermal deposits in new south wales northparkes harris and holcombe 2014 endeavour 41 zukowski et al 2014 endeavour 42 henry et al 2014 cadia harris et al 2014 the final contribution uses the results of mapping and core logging in order to resolve the physical volcanology and hydrothermal evolution of the giant ladolam alkalic epithermal gold deposit papua new guinea blackwell et al 2014 eight of these papers are the outcome of a collaborative project between the mineral deposit research unit mdru at the university of british columbia the australian research council s centre for excellence in ore deposits codes at the university of tasmania and industry partners the remaining are based on work by the british columbia geological survey logan and mihalynuk 2014 teck resources ltd devine et al 2014 a research collaboration between codes and newcrest mining ltd harris et al 2014 and the university of queensland harris and holcombe 2014 fig 1 terrane map and location of selected alkalic porphyry cu au deposits of british columbia deposits that are the subject of

mixed signals of the source and thermal maturity for petroleum accumulations from light hydrocarbons an example of the beryl field abstract we have investigated compositional variations of light hydrocarbons in crude oils from the beryl and adjacent fields of the north sea in combination with carbon isotopic ratios of light hydrocarbons and biomarker properties of oils although there appears to be a strong source influence on various light hydrocarbon maturity parameters this is a consequence of the mixing of hydrocarbons derived from the kimmeridge clay formation as well as from the heather formation and brent coal at varying thermal maturity levels light hydrocarbon parameters based on mango s reaction scheme involving 3 ring and 5 ring intermediates are supported by carbon isotopic ratios of light hydrocarbons however there also is evidence that iso and cyclo heptane precursors exist that contribute c 7 light hydrocarbons independent of mango s model the ratio of 2 4 dimethylpentane to 2 3 dimethylpentane 2 4 dmp 2 3 dmp and other related parameters appear to be reliable indicators of thermal stress but must be interpreted within a complete understanding of the petroleum system under study