good neighbours shaped by vigorous currents cold water coral mounds and contourites in the north atlantic abstract over the recent years two research fields addressing continental slope sedimentary systems have gained significant momentum contourites and cold water coral mounds being both related to intense bottom currents and being both dependent on sediment supply they share some commonalities resulting in their widespread co occurrence however as cold water coral mounds predominantly occur in shallow to intermediate water depths this co occurrence is restricted to these depth levels for both systems the available knowledge is derived basically from north atlantic ocean settings indicating the potential to discover such systems hidden in the other ocean basins as well as still hidden in the atlantic contourites and cold water coral mounds have the capability of providing high resolution palaeo environmental records although with often differing temporal ranges and or temporal resolutions applying the concept of a joint exploitation of sedimentary records obtained from mounds and contourites offers the unique possibility of analysing contourite and mound development as well as the related palaeo environmental settings much more comprehensively than done when only considering one of these archives thus after two decades of intense research providing significant knowledge about contourites and cold water coral mounds from the north atlantic new ideas and concepts may arise from a close collaboration of scientists working in these two fields

multistage intrusion brecciation and veining at el teniente chile evolution of a nested porphyry system the el teniente copper molybdenum deposit is hosted by the late miocene teniente mafic complex a largely subvolcanic package of primarily basaltic andesite porphyry sills and stocks that were emplaced within the mid late miocene farellones formation in the late miocene pliocene a series of intermediate felsic plutons were intruded into the teniente mafic complex these are spatially associated with magmatic hydrothermal breccias and multiple vein types that form individual mineralized complexes here we present detailed observations on mineralogy textures and intrusion breccias and vein crosscutting relationships to constrain the nature and relative timing of magmatic and hydrothermal events our revised classification defines 13 vein types divided lilt three main stages 1 premineralization biotite and or k feldspar quartz anhydrite albite magnetite actinolite epidote veins that formed prior to emplacement of mineralized intrusions and breccias 2 main mineralization stage veins that grade from gangue dominated quartz anhydrite veins potassic alteration halos into sulfide dominated veins with phyllic alteration halos and 3 late mineralization veins containing sulfosalts five breccia types have been observed in the deposit typically forming individual vertically zoned complexes spatially associated with individual intrusions and overlapping in time i igneous cemented breccias 2 k feldspar cemented breccias 3 biotite cemented breccias 4 anhydrite cemented breccias and 5 tourmaline cemented breccias breccia cements display 1 similar paragenetic evolution to main mineralization stage veins indicating a close genetic link between them a distinction can be made between early premineralization vein types types 1 2 that represent veins formed possibly deposit wide prior to emplacement of intrusion breccia complexes late pre and main mineralization vent types types 3 8 which are interpreted to reflect the repeated cycle of fluid release associated with each mineralized intrusive complex and late mineralization vein types types 9 10 that represent it single event linked to the emplacement of the braden breccia pipe the geologic evidence indicates a close spatial and temporal relationship between emplacement of shallow felsic intermediate pipelike intrusions and the development of igneous mid mineralized magmatic hydrothermal breccias and vein halos the magmatic hydrothermal transitions observed in these complexes indicate that the deposit formed from a series of localized pulses of magmatic hydrothermal activity which followed rather similar evolution paths single deposit wide models of fluid evolution and mineralization are therefore inappropriate we conclude that el teniente represents a nested but otherwise rather typical porphyry cu mo system unusual only in thia the teniente mafic complex pi is it particularly efficient physical trap in terms of pervasive fracturing during intrusion of magmatic hydrothermal breccia complexes and its an effective chemical trap for deposition of sulfides the overlapping of mineralized envelopes from successive fertile intrusions and the absence of barren intermineral porphyries resulted in its unusual size and high hypogene grades

mesozoic and cenozoic stratigraphy eastern scotian shelf new interpretations a 320 km long deep seismic reflection line across the central part of the scotian basin provides new insight on the deep stratigraphy of the basin confirms the existence of up to 18 km of mesozoic and cenozoic sedimentary strata and provides additional control on the relationship of proximal and distal stratigraphic units within the basin detailed biostratigraphic and seismic correlation from three outer shelf upper slope wells yields important new information on late cretaceous and tertiary unconformities and identifies a number of third order sequence boundaries the dating of prominent unconformities and correlation with the oceanic seismic markers ac and au results in the reidentification of these horizons in the sohm abyssal plain

in situ elemental and sr isotope characteristics of magmatic to hydrothermal minerals from the black mountain porphyry deposit baguio district philippines at the black mountain porphyry cu au deposit in the baguio district northern luzon philippines pre and synmineralized rocks preserve magmatic and hydrothermal minerals e g plagioclase amphibole titanite and epidote spanning the complete paragenesis of the deposit strontium isotope values in early crystallized plagioclase phenocrysts from all felsic porphyries can be divided into two types the type i plagioclase crystals show relatively homogeneous sr isotope values 0 7035 0 7038 1 0 0001 indicating crystallization from a relatively stable and long lived felsic magma chamber the type ii plagioclase grains have a wider range of sr isotope compositions 0 7032 0 7039 1 0 0001 indicating mafic and or felsic magma recharge in magmatic titanite nb ta values are higher than those in the whole rock while zr hf and y ho values are lower in hydrothermal titanite and epidote the ratios are similar to those in the whole rock these patterns reflect crystallization effects imposed during the magmatic stage but an absence of differentiation during the hydrothermal stage the consistent gradual decrease in total rare earth element y zr and u contents in both hydrothermal titanite and epidote from early to late stages indicates the effect of hydrothermal fluid evolution with decreasing temperature the variation of 87sr 86sr values in magmatic amphibole plagioclase and hydrothermal epidote in felsic and mafic rocks indicates the addition of mafic magma derived fluid into the felsic magma derived fluid one extra source of fluid probably derived from wall rock limestone was required to generate the highly radiogenic 87sr 86sr values of some epidote 0 7038 0 7053 thus in situ elemental and sr isotope variation in minerals from different paragenetic stages can be used to interpret formation process and source for both magmas and hydrothermal fluids

seismic stratigraphic framework and depositional history for cretaceous and cenozoic contourite depositional systems of the mozambique channel sw indian ocean this study describes previously unrecognized contourite depositional systems cdss in the mozambique channel which constrain palaeoceanographic models for this area the stratigraphic stacking patterns record nine seismic units su1 to su9 separated by eight major discontinuities a to h oldest to youngest key seismic markers in cds evolutionary history occur during aptian albian 122 ma late cenomanian 94 ma early 38 2 36 2 ma and late 25 23 ma oligocene and early middle miocene 17 15 ma epochs these record onset 122 to 94 ma growth 94 to 25 23 ma maintenance 25 23 to 17 15 ma and burial 17 15 ma to the actual time stages for cdss cdss first develop during the onset stage which coincides with the opening and deepening of the african southern ocean gateway at 122 and 100 ma respectively the growth stage beginning in the late cenomanian 94 ma correlates with the opening and deepening of the equatorial atlantic gateway during the growth stage two major shifts in sedimentary stacking pattern occur which coincide with palaeoceanographic changes during the early 38 2 36 2 ma and late 25 23 ma oligocene these in turn coincide with the onset and local enhancement of antarctic water masses cds growth continued until the early middle miocene during the maintenance stage 17 15 ma most cds growth ceased at the end of the maintenance stage circulation of the north atlantic water mass into the southern hemisphere led to a deepening of antarctic water masses in the area

exploration targeting in porphyry cu systems using propylitic mineral chemistry a case study of the el teniente deposit chile the mineral chemistry of epidote and chlorite from the propylitic halo at el teniente in samples collected at distances up to 6 6 km from the deposit center was determined by microprobe and laser ablation inductively coupled plasma mass spectrometry results show that both minerals systematically incorporated a range of trace elements that define a much larger footprint to the system than is easily recognized using conventional means such as whole rock geochemistry apart from fe and mg in chlorite there is no significant control of mineral chemistry by bulk rock composition for chlorite geothermometry temperatures and ti and v concentrations are high proximal whereas li as co sr ca and y are low proximal and elevated in distal positions ratios of these elements define gradients toward ore varying over three to five orders of magnitude the proximal high ti content is thought to reflect crystallization temperature whereas proximal low signatures are believed to characterize elements that are relatively fluid mobile in the inner parts of the propylitic halo in the presence of mildly alkaline to mildly acidic and oxidized fluids so that they are not incorporated into crystallizing chlorite despite being generally compatible within the mineral structure these elements begin to substitute into chlorite in the distal parts of the propylitic halo where fluids are largely rock buffered in terms of major element chemistry in epidote as defines a broad proximal low and is generally elevated at distances of at least 3 km from the edge of the ore shell zinc la yb y and zr in epidote among others appear to define a geochemical shoulder that surrounds the deposit these patterns are broadly similar to those observed in previous work at batu hijau and in the baguio district suggesting that these minerals behave consistently in porphyry systems and can therefore provide useful exploration tools within propylitic green rocks

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

seismic stratigraphic framework and depositional history of a large upper cretaceous and cenozoic depocenter off southwest nova scotia canada abstract interpretations of the late cretaceous to quaternary geological history of the north american basin rely on a seismic and lithostratigraphic framework developed predominantly from data along the northeastern united states margin prior to this study attempts to extend this framework northward to the nova scotia margin were hindered by correlation issues across seamounts limitations in data coverage and significant complications caused by widespread canyon erosion and shallow salt structures these challenges are overcome using modern seismic reflection data along the southwestern nova scotia margin in the shelburne sub basin where upper cretaceous through quaternary sequences manifest four distinct phases in the interplay between down slope and along slope depositional and erosional processes the first phase spanning the late cretaceous to late eocene is characterized by widespread periods of gully erosion interspersed with periods of pelagic and hemipelagic carbonate rich sedimentation extensive failure of upper slope regions related to the montagnais meteorite impact also occurred during this time the second phase spanning the oligocene to late miocene is dominated by widespread erosion deposition by gravity flow processes and sediment re working by bottom currents marked erosion and or non deposition along the mid to lower slope is attributed both to down slope and along slope processes the third phase spanning the late miocene to late pliocene is dominated by bottom current deposition including stacked sequences of giant sediment waves and large contourite drifts along the slope the final phase from the late pliocene to present exhibits a return to predominance of down slope gravity flows with deposition focused below the upper slope this four phase history of depositional and erosional processes is similar to that documented south of the study area along the u s margin

low frequency circulation at the edge of the scotian shelf abstract records of current temperature and salinity from a two year mooring program at the shelf break off nova scotia are examined to determine the low frequency oceanic responses to the driving surface wind field and fluctuating offshore currents associated with the gulf stream the seasonal mean and subtidal variance at periods of 2 10 days of the cross shelf currents reflect the strong annual cycle in the wind field measured at sable island the mean vertical shear suggests a simple ekman response to winter increases in the longshore wind component but this model fails quantitatively because 1 the inferred surface layer 20 m transport is much too large and 2 the deep 150 m return flow shows no annual signal the excessive offshore near surface transport in winter must be reconciled with the relatively stationary position of the shelf slope water boundary ssb by invoking intense cross frontal mixing and or a seasonal mean alongshore pressure gradient the seasonal mean longshore currents

using mineral chemistry to aid exploration a case study from the resolution porphyry cu mo deposit arizona the giant high grade resolution porphyry cu mo deposit in the superior district of arizona is hosted in proterozoic and paleozoic basement and in an overlying cretaceous volcaniclastic breccia and sandstone package resolution has a central domain of potassic alteration that extends more than 1 km outboard of the ore zone overlapping with a propylitic halo characterized by epidote chlorite and pyrite that is particularly well developed in the laramide volcaniclastic rocks and proterozoic dolerite sills the potassic and propylitic assemblages were overprinted in the upper parts of the deposit by intense phyllic and advanced argillic alteration the district was disrupted by tertiary basin and range extension and the fault block containing resolution and its cretaceous host succession was buried under thick mid miocene dacitic volcanic cover obscuring the geologic geophysical and geochemical footprint of the deposit to test the potential of propylitic mineral chemistry analyses to aid in the detection of concealed porphyry deposits a blind test was conducted using a suite of epidote chlorite pyrite altered laramide volcaniclastic rocks and proterozoic dolerites collected from the propylitic halo with samples taken from two domains located to the north and south and above the resolution ore zone laser ablation inductively coupled plasma mass spectrometry la icp ms data of epidote provided indications of deposit fertility and proximity competition for chalcophile elements as sb pb between coexisting pyrite and epidote grains led to a subdued as sb fertility response in epidote consistent with epidote collected between 0 7 and 1 5 km from the center of a large porphyry deposit temperature sensitive trace elements in chlorite provided coherent spatial zonation patterns implying a heat source centered at depth between the two sample clusters and application of chlorite proximitor calculations based on la icp ms analyses provided a precisely defined drill target in this location in three dimensions drilling of this target would have resulted in the discovery of resolution confirming that epidote and chlorite mineral chemistry can potentially add value to porphyry exploration under cover

sand wave fields beneath the loop current gulf of mexico reworking of fan sands extensive fields of large barchan like sand waves and longitudinal sand ribbons have been mapped by deep towed seamarc ia sidescan sonar on part of the middle and lower mississippi fan that lies in about 3200 m of water the area is beneath the strongly flowing loop current the bedforms have not been adequately sampled but probably consist of winnowed siliciclastic foraminiferal sands the size about 200 m from wingtip to wingtip and shape of the large barchans is consistent with a previously observed peak current speed of 30 cm s measured 25 m above the seabed the types of small scale bedforms and the scoured surfaces of chemical crusts seen on nearby bottom photographs indicate that near bed currents in excess of 30 cm s may sometimes occur at the time of the survey the sand transport direction was to the northwest in the opposite direction to the loop current but consistent with there being a deep boundary current along the foot of the florida escarpment some reworking of the underlying sandy turbidites and debris flow deposits is apparent on the sidescan sonar records reworking by deep sea currents resulting in erosion and in deposits characterised by coarsening upwards structures and cross bedding is a process that has been proposed for sand found in cores in shallower parts of the gulf of mexico this process is more widespread than hitherto supposed

the morphology of barchan shaped sand banks from western torres strait northern australia abstract large barchan shaped sand deposits have been observed in the north west of torres strait these deposits share characteristics of both subaerial barchan dunes and subaqueous sand banks a study of satellite imagery indicate that the deposits migrate in the direction indicated by their horns 10 15 m west per year and that sediment is shed from their horns features that are characteristic of barchan dunes however the orientations of sand dunes superimposed upon the sand banks indicate the presence of mutually evasive channels and circulation of sediment around the sand bank a characteristic of subaqueous sand banks the presence of mutually evasive channels is the criteria used to categorise the deposits as sand banks barchan forms are known to exist in regions with limited sediment supply and unidirectional current or wind regimes in the torres strait both these criteria are met previous work has demonstrated the presence of a net westward current through the torres strait that is driven by the southeast trade winds the relatively high displacement of the wind driven currents during the trade wind season relative to the monsoon appears to provide the necessary unidirectional regime to form barchans the low and typically eastwards displacement of the residual monsoon season current appears to have a negligible affect on the barchan form while seasonal wind driven currents appear to maintain the barchan shape of the sand banks tidal currents actively maintain mutually evasive channels observed by variations in dune orientation on the sand banks a sediment starved environment combined with bedload transport attributed to both wind driven and tidal currents is concluded to create a unique hydrodynamic environment where sand banks can attain a barchan form

magmatic evolution of the giant el teniente cu mo deposit central chile elteniente the world s largest cu deposit is hosted in late miocene and pliocene plutons that intrude the older teniente volcanic complex or farellones fm 14 2 6 5 ma the late miocene and pliocene plutonic host rocks of the deposit include sequentially the relatively large 450 km teniente mafic complex laccolith 8 9 1 4 ma the smaller 30 km sewell equigranular tonalite complex 7 05 0 14 ma and associated andesitic sills 8 2 0 5 to 6 6 0 4 ma small dacitic porphyry stocks 51km 6 09 0 18 ma the unusual cuand s rich porphyry a anhydrite bearing granitoid stock 51km 5 67 0 19 ma the teniente dacite porphyry dike 51km 5 28 0 10 ma minor latite dikes 4 82 0 09 ma and finally a small dacite intrusion 4 58 0 10 ma these plutonic rocks are all isotopically similar to each other sr sr1 4 0 7039 0 7042 end1 4 2 5 to 3 5 and also to the teniente volcanic complex extrusive rocks but distinct from both older late oligocene to early miocene volcanic rocks sr sr1 4 0 7033 0 7039 end1 4 3 8 to 6 2 and younger pliocene post mineralization mafic dikes and lavas sr sr1 4 0 7041 0 7049 end1 4 1 1 to 1 1 multiple cu mineralized magmatic hydrothermal breccia pipes were emplaced into these plutonic rocks during the same time period as the felsic porphyry intrusions between at least 6 31 0 03 and 4 42 0 02 ma these mineralized breccia pipes which formed by exsolution of magmatic fluids from cooling plutons have their roots below the deepest level of mining and exploration drilling and were derived from the same magma chamber as the felsic porphyries 44 km below the paleosurface to produce the 100 10 tonnes of cu in the deposit requires a batholith size 4600 km amount of magma with 100 ppm cu we suggest that both the mineralized magmatic hydrothermal breccias and the progressively smaller volumes of more fractionated but isotopically equivalent late miocene and pliocene felsic plutonic rocks that host the deposit were derived from the roof of a large long lived thermally and chemically stratified open system magma chamber or magmatic plumbing system recharged from below by mantle derived magmas only when this system fully solidified did post mineralization mafic olivine hornblende lamprophyre dikes 3 85 0 18 to 2 9 0 6 ma pass through the system from the mantle to the surface the significant progressive temporal isotopic evolution to higher sr sr from 0 7033 to 0 7049 and lower end from 6 2 to 1 1 that occurred between the late oligocene and pliocene in the vicinity of el teniente for mafic mantle derived magmas and by implication their sub arc mantle source region was due in part to increased mantle source region contamination by subducted crust tectonically eroded off the continental margin the post mineralization olivine hornblende lamprophyres also imply extensive hydration of the mantle below this portion of the andean arc by the pliocene which may have played a role in producing oxidized volatile rich magmas and mineralization at elteniente

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

seismic and geologic evidence for early paleogene deepwater circulation in the western north atlantic previous studies of paleogeography global climate and foraminiferal stable isotopes have suggested that paleogene deepwater circulation was significantly different from that of today extracting details of deepwater history from the western north atlantic has been hampered by oligocene erosion and the lack of ideally located drill holes we report the discovery of a seismic disconformity on the sw bermuda rise that we have tied to a late paleocene erosional event in deep sea drilling project dsdp boreholes from this region distribution of this new seismic marker reflector ab indicates that it was formed by cyclonically circulating bottom water entering the western north atlantic from the south we attribute this vigorous deep circulation to a southern ocean source analogous to the effects of modern antarctic bottom water this interpretation is supported by isotopic comparisons that show the paleocene southern ocean was enriched in 13c relative to the pacific we distinguish reflector ab from the overlying reflector au on the basis of superposition and ages obtained at dsdp sites and piston cores using one of the cores we have estimated that the youngest age for reflector au is earliest oligocene 36 6 34 0 ma while its oldest age has been previously established as late eocene laminated sediments beneath reflector ab are enriched in organic carbon indicating that the early paleocene deep western north atlantic was occasionally anoxic these low oxygen levels may have been the result of sluggish deep circulation and or low latitude production of warm saline deep water wsdw sediments immediately above reflector ab show that deposition resumed on the western bermuda rise site 387 by the latest paleocene to earliest eocene biochron np10 57 2 0 6 ma while deposition resumed on the central bermuda rise site 386 during the late paleocene erosion nondeposition continued across much of the bermuda rise widespread resumption of pelagic deposition in the early eocene is consistent with 13c evidence for reduced southern ocean influence at this time however lower eocene sediments record well oxygenated conditions and 13c and 18o comparisons indicate that there were two early eocene deepwater sources the southern ocean and wsdw pak and miller this issue

morphology and composition of submarine barchan dunes on the scotian shelf canadian atlantic margin abstract submarine barchan dunes have been mapped on browns bank scotian shelf using multibeam sonar bathymetry and backscatter strength the morphology of subaerial barchans has been studied for almost a century but the advent of multibeam sonar technology now enables a quantitative investigation of their submarine counterparts the browns bank submarine barchans occur at a depth of 60 70 m and are crescentic in planform reaching almost 700 m in horn width and 5 m in height the barchans are convex to the se with steep lee faces to the nw indicating a dominant nw flowing current the barchans overlie a widespread gravel lag covered elsewhere with little or no sand obstacle marks emanate from the lee faces of the barchans and represent a lack of sand deposition and exposure of gravel lag on the sea floor the browns bank submarine barchan sediment texture is gravelly sand or sandy gravel and is primarily composed of subrounded to well rounded quartz grains the allometric relationship between submarine barchan slip face height and distance between horns is markedly different from that of subaerial barchans for the same dune height barchan horn width is about ten times greater in the marine environment the superimposition of megaripples on the stoss slopes of the submarine barchans suggests that the barchans are active and therefore represent an engineering risk to sea floor infrastructure current observations and models indicate that seasonal mean current strength is less than the critical velocity required for barchan migration however the barchans may be active under higher velocity storm induced currents repetitive multibeam sonar mapping is required to detect if barchan migration is occurring over longer time scales

cenozoic alongslope processes and sedimentation on the nw european atlantic margin based on studies of sediment accumulations deposited from and erode by alongslope flowing ocean currents on the european continental margin from porcupine ireland to lofoten norway the evolution of the cenozoic paleocirculation was reconstructed as part of the stratagem project there is evidence of ocean current controlled erosion and deposition in the rockall trough in the faeroe shetland channel and on the voring plateau since the late eocene although the circulation pattern remains ambiguous the late palaeogene flow in the rockall trough was almost probably driven by southerly derived tethyan outflow water the extent and strength of any northerly derived flow is uncertain from the early neogene early mid miocene there was a massive regional expansion of contourite drift development both in the north atlantic and in the norwegian greenland sea this was most probably related to the development of the faroe conduit the opening of the fram strait and the general subsidence of the greenland scotland ridge these may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the arctic and atlantic oceans an early late neogene late early pliocene regional erosional event has been ascribed to a vigorous pulse of bottom current activity most probably the result of a global reorganisation of ocean currents associated with the closure of the central american seaway during the late neogene contourites and sediment drifts developed in deep water basins between units of glacigenic sediments as well as infill of several paleo slide scars these sediments were derived from areas of bottom current erosion as well as from the development of plio pleistocene prograding sediment wedges incorporating the extensive sediment supply derived from shelf wide ice sheets presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of atlantic water depocentres of sediments derived from the winnowing are located locally in lower slope embayments and in slide scars

a model for the growth of mudwaves in the presence of time varying currents abstract mudwaves are produced in a model when a periodic current produces lee waves that alter the deposition erosion rates of sediment at the bottom of an ocean a technique analogous to using a lagrangian representation for calculating the velocity perturbations associated with these lee waves is determined and then applied to a situation typical of one observed in the argentine basin the fact that the imposed current is variable results in the perturbation velocities also being time dependent with two major time scales one of these time scales is the period of the variable current which is taken to be on the order of weeks this is consistent with the dominant periods indicated in the data the other time scale is on the order of a day or two and is associated with the time required for the time dependent part of the imposed current total current minus its time averaged part to cross a ridge waves on this time scale are excited when the imposed current passes through a value that changes the character of the lee waves from vertically propagating to bottom trapped or vice versa the long term erosion deposition and mudwave growth rates are insensitive to the details of these shorter time scale variations

cenozoic north atlantic deep circulation history recorded in contourite drifts offshore newfoundland canada abstract in the north atlantic ocean contour following deep currents have created regional erosional unconformities and deposited contourite drifts that exceed 2 km in thickness and extend for 100 s of km the stratigraphic records in the drifts have been used to reconstruct variations in north atlantic deep water circulation throughout the cenozoic however uncertainties remain about certain aspects of the timing intensity depth distribution and regional impact of these currents here we use an integrated dataset of seismic reflection profiles and iodp core data lithology biostratigraphy and magnetostratigraphy to document sedimentation history and the development of current effects in the cretaceous to present sedimentary record on the j anomaly ridge and southeast newfoundland ridge offshore newfoundland canada the newfoundland ridges are in a key location lying between well studied areas in the northern and western north atlantic and under the path of both the modern deep western boundary current and the gulf stream late cretaceous through early eocene sedimentation on the ridges was dominated by biogenic pelagic sedimentation but at 47 ma near the early middle eocene boundary well developed contourite drifts began to accrete in paleo water depths of 4000 4500 m accompanied by an order of magnitude increase in terrigenous sediment mass accumulation rates from this time forward drift deposition interrupted by brief episodes of erosion continued unabated this timing for the onset of persistent deep currents is coincident with reorganization of atlantic circulation inferred from a change from biosiliceous to non biosiliceous sedimentation in the western north atlantic horizon a c and with the current eroded intra eocene unconformity ieu in the northern north atlantic a change in sedimentation style occurred within the middle eocene to upper oligocene drift sequence and it likely was related to a shift to deeper more intense currents that eroded the widespread horizon a u along the margin of eastern north america about early oligocene time beginning in the late oligocene 25 ma a thick drift exhibiting seismically laminated mudwaves was deposited in a distinct belt at 3500 4500 m paleodepth on the southeast newfoundland ridge this development correlates with widespread late oligocene through miocene pliocene drift accumulation throughout the north atlantic the most recent phase of drift deposition since late pliocene time 3 ma occurred after a shift to the modern circulation system of deeper swifter currents and it includes mixed pelagic hemipelagic sediments and ice rafted debris that reflect glacial interglacial influences on sedimentation

global miocene tectonics and the modern world abstract an amazing congruence of seemingly unrelated diverse global events began in the middle and upper miocene and established our modern world two global orogenic belts were active mostly in the middle and upper miocene while backarc basins formed along the eastern margin of asia coincident with these events global temperatures cooled in both the ocean and atmosphere desertification occurred from central asia into and across most of northern africa and also in australia and in southern south america coincident with the expansion of the antarctic ice cap at 14 ma there was initial widespread deep sea erosion and changes in patterns of deep sea sedimentation muddy pelagic sedimentation increased six fold in the north and central atlantic and pacific oceans and global changes in circulation lead to more diatomites in the pacific and fewer in the atlantic by the end of the miocene most of the mediterranean sea had evaporated broadly coincident with these events many old large river systems were destroyed and new ones formed as much of the world s landscape changed collectively these global on shore tectonic and ocean atmospheric events provide the foundation for our modern world a mixture of new and rejuvenated orogenic belts and their far field effects distant epiorogenic uplift rain shadow deserts large alluvial aprons and distant deltas as inherited gondwanan landscapes persisted remote from plate boundaries thus at the end of the miocene much of the world s landscape except for that changed by pleistocene continental glaciation would be recognizable to us today we argue that all of these events had the same ultimate common cause an internal earth engine that drove plate motions in two broad ways first the opening and closing of seven key gateways to deep water oceanic currents radically altered global heat transfer and changed a lingering greenhouse to an icehouse world secondly these events were in part coincident with renewed heat flow in the african and pacific superplumes that energized global plate motions in the middle and upper miocene we hope this global synthesis will stimulate more research on the many global events of the miocene to understand better both our modern world and earlier global orogenies

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

epidote trace element chemistry as an exploration tool in the collahuasi district northern chile the collahuasi district of northern chile hosts several late eocene early oligocene world class porphyry cu mo deposits including rosario ujina and quebrada blanca deposits and associated high sulfidation epithermal mineralization at la grande mineralization is hosted by intermediate to felsic intrusive and volcanic rocks of the upper paleozoic to lower triassic collahuasi group which experienced lower greenschist facies regional metamorphism prior to mineralization extensive hydrothermal alteration zones surround the porphyry and epithermal deposits associated with hypogene ore forming processes however outside of the observed sulfide halo the limits of geochemical anomalism associated with mineralization are difficult to define due to mineralogical similarities between weak distal propylitic alteration and regional metamorphism affecting the host rocks recent advancements in laser ablation inductively coupled plasma mass spectrometry analysis of epidote from hydrothermal alteration zones around porphyry and skarn deposits have shown that low level hypogene geochemical anomalies can be detected at distances farther from the center of mineralization than by conventional rock chip sampling selective analysis of propylitic epidote from the collahuasi district indicates that anomalous concentrations of distal pathfinder elements in epidote including as 50 ppm sb 25 ppm pb 100 ppm and mn 5 000 ppm were detectable 1 5 to 4 0 km from deposit centers significantly the concentrations of these trace elements in epidote were obtained from samples that contained whole rock concentrations of

morphology of abyssal mudwaves at project mudwaves sites in the argentine basin abstract extensive fields of mudwaves are present in the argentine basin mudwaves and water parameters at three sites were studied to provide detailed information on bathymetry mudwave structure sediment parameters and bottom water flow characteristics two sites 5 and 6 are discussed in this paper crests of mudwaves at site 5 on the north flank of the zapiola drift are oriented 45 anti clockwise from the measured westward flow direction and migrate to the left of the flow direction mudwaves at site 6 on the south flank of the zapiola drift are oriented 20 anti clockwise from the inferred southeast bottom flow direction and also migrate to the left of direction evidence from current meters and surface sediments suggests that the mudwaves at site 5 are active today while those at site 6 have been active in the holocene but perhaps not within the last 100 years mudwave orientation anti clockwise to mean flow preferential sediment accumulation on the left wave flank and apparent sediment accumulation on the wave crest agree with a model for mudwave growth presented by blumsack and weatherly 1989 deep sea research 36 1327 1339 cross wave asymmetry in sediment accumulation pattern is sufficient to cause a 10 change in surface sediment bulk density over the wave profile the record of mudwave migration obtained from sites 5 and 6 in the southern argentine basin and from site 7 in the northern argentine basin suggests that bottom water flow has changed over a number of time scales during the last 200 000 years thus the analysis of abyssal bed forms can provide independent evidence about past changes in bottom flow

the role of deep water sedimentary processes in shaping a continental margin the northwest atlantic abstract the tectonic history of a margin dictates its general shape however its geomorphology is generally transformed by deep sea sedimentary processes the objective of this study is to show the influences of turbidity currents contour currents and sediment mass failures on the geomorphology of the deep water northwestern atlantic margin nwam between blake ridge and hudson trough spanning about 32 of latitude and the shelf edge to the abyssal plain this assessment is based on new multibeam echosounder data global bathymetric models and sub surface geophysical information the deep water nwam is divided into four broad geomorphologic classifications based on their bathymetric shape graded above grade stepped and out of grade these shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope accommodation this descriptive method of classifying continental margins while being non interpretative is more informative than the conventional continental shelf slope and rise classification and better facilitates interpretation concerning dominant sedimentary processes areas of the margin dominated by turbidity currents and slope by pass developed graded slopes if sediments did not by pass the slope due to accommodation then an above grade or stepped slope resulted geostrophic currents created sedimentary bodies of a variety of forms and positions along the nwam detached drifts form linear above grade slopes along their crests from the shelf edge to the deep basin plastered drifts formed stepped slope profiles sediment mass failure has had a variety of consequences on the margin morphology large mass failures created out of grade profiles whereas smaller mass failures tended to remain on the slope and formed above grade profiles at trough mouth fans or nearly graded profiles such as offshore cape fear

sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the laurentian channel ice stream abstract eastern canadian margin sediments bear testimony to several catastrophic deglacial meltwater discharges from the retreating laurentide ice sheet the reddish brown plumite layers deposited on the levees of the laurentian fan valleys have been recognized as indications of multiple outburst floods between heinrich events 2 and 1 five event layers have been consistently recorded in three new gravity cores retrieved on the sw grand banks slope and comply with the previously published laurentian fan core md95 2029 the apparently huge extent of these outburst plumes around the laurentian fan as well as their causes and consequences are investigated in this study using physical properties rock magnetic and grain size analyses together with seismoacoustic profiling we provide the first detailed 14c ages of the outburst event sequence and discuss their recurrence intervals in the context of regional ice retreat compared to the hemipelagic interlayers event layers have overall uniform and systematic changes of rock magnetic properties hematite contents increase over time and proximally while magnetite grain sizes fine upwards and spatially away from the fan based on the sediment composition and load we argue that these plumites were formed by recurrent erosion of glacial mud deposits in the laurentian channel by meltwater outbursts three alternative glaciological scenarios are evaluated in each case the provenance of the transported sediment is not an indicator of the precise source of the meltwater

a microscale analysis of hydrothermal epidote implications for the use of laser ablation inductively coupled plasma mass spectrometry mineral chemistry in complex alteration environments high resolution quantitative imaging of epidote from the ann mason fault block yerington district nevada using scanning electron microscopy sem x ray fluorescence xrf and laser ablation inductively coupled plasma mass spectrometry la icp ms has revealed at least two types of epidote type 1 and type 2 each with different major and trace element chemistry type 1 epidote is coarser grained typically greater than 50 m in diameter and forms euhedral crystals that display twins and sector zones enriched in fe sr and mn type 2 epidote is finer grained typically less than 30 m in diameter irregularly zoned with respect to fe and al and forms polycrystalline aggregates that include void space two sources of intragranular compositional variability are defined in this study one related to different generations of epidote only visible on the microscale and the other related to crystallographic features such as sector zones and twins intragranular compositional variations within yerington epidotes highlight the potential importance of detailed sample characterization in complex alteration environments prior to undertaking mineral chemistry studies in the context of resource exploration based on statistical analysis of la icp ms spot data from one sample the optimal number of spot analyses to adequately represent the range in element concentrations within zoned or twinned crystals is determined to be at least 40

giant mounded drifts in the argentine continental margin origins and global implications for the history of thermohaline circulation abstract partially buried giant drifts are located in the southern most sector of the argentine continental margin generating a bathymetric jump at the base of the slope they are characterised as giant asymmetrical elongated mounded contourite drifts and are described in detail here for the first time this description is mainly based on the bathymetric and multichannel seismic reflection profiles data their origin and evolution in the argentine basin are decoded and their implications in an area crucial for geologic and palaeoceanographic reconstruction between the atlantic and antarctica are discussed the buried giant drifts are divided into two zones by a large seamount the major giant drift 50 km wide 300 km long and having a sedimentary thickness of nearly 1 km is located to the south of this seamount and oriented to the north where its summit outcrops at present seafloor here its asymmetric external shape is characterised by a steep western side and a gently dipping smooth eastern side with internal reflections prograding eastward based on its position morphology and internal characteristics it has been deduced that this giant drift was generated in the argentine basin by the southward branch of a confined large loop of the antarctic bottom deep water from the eocene oligocene boundary coevally with the drake passage opening until the middle miocene however after a major palaeoceanographic change in the mid to late miocene a new oceanographic scenario was established that fossilised these giant drifts these changes produced a new depositional style in the margin resulting in initiation of the present contourite depositional system and morphologic features over the slope extension of north atlantic deep water circulation into the southern hemisphere and deepening of antarctic bottom water circulation in the argentine basin are herein postulated as the factors that controlled said changes these giant drifts show strong seismic evidence of hydrates and free gas that are ripe for energy resources exploration thus demonstrating the economic potential of contourite deposits in deep marine environments

paleogene neogene depositional history of the middle u s atlantic continental rise mixed turbidite and contourite depositional systems abstract the construction of the middle u s atlantic continental rise from late paleogene to late pliocene time included downslope sediment gravity flows and alongslope contourite deposition some previous studies have suggested that contour following bottom currents were the dominant control on depositional patterns depositional relief from two large contourite drifts largely built in late miocene to late pliocene time continue to dominate present day lower rise morphology detailed seismic sequence mapping presented here suggests that significant turbidite fan systems also were active and are preserved in the stratigraphic section a single thick depositional sequence is mapped for oligocene to middle miocene sediments deposited when inferred fan systems off the norfolk washington canyons were reworked by bottom currents along the lower rise to form the proto hatteras outer ridge detailed mapping of three late miocene to late pliocene depositional sequences indicates that fan channel systems were active at the same time large contourite drifts were being constructed sediment delivered to the lower rise by these elongate turbidite systems undoubtedly was an important local source for construction of the hatteras outer ridge and through entrainment and resuspension was an important source for regional contourite deposition controlled by the deep western boundary undercurrent we suggest that submarine fans and current controlled sediment drifts may develop simultaneously as companion systems types of fan drift interaction include current only modification of fans transitional fan to drift and adjacent or overlapping submarine fan and sediment drift deposition

late cretaceous cenozoic development of outer continental margin southwestern nova scotia the growth pattern for the outer continental margin of nova scotia during the late cretaceous and cenozoic was studied using seismic stratigraphy and well data sediment accumulation was broadly controlled by temporal changes in relative sea level but significant spatial and temporal changes in accumulation patterns were caused by changes in sediment supply rate morphology erosion by abyssal currents and salt tectonics a jurassic early cretaceous carbonate platform remained exposed until the late cretaceous and controlled the location and steepness of the paleoslope until the late miocene local erosion of the outer shelf and slope in the late paleocene early eocene produced chalky fans on the upper rise the relationship between erosion of the shelf in the late eoce e and early oligocene and abyssal current erosion of the upper rise in the oligocene is unclear seaward extensions of tertiary shelf edge canyons are poorly defined except for the eocene fans in the miocene abyssal currents eroded a bench on the upper continental rise subsequently sediments lapped onto and buried the paleoslope the lower rise above horizon au oligocene is composed of fans and olistostromes shed from halo kinetic uplift of the upper rise current eroded unconformities are common in the rise sequence but the only current deposit is a pliocene interval 300 m restricted to the lowermost rise pleistocene turbidity currents eroded the present canyon morphology

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

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

hydrodynamic significance of variable ripple morphology across deep water barchan dunes in the faroe shetland channel a combination of high resolution 30 khz sidescan sonar and seafloor photography has been used to image barchan dunes and sand ripples in the faroe shetland channel the barchan dunes display body lengths and horn to horn widths of up to 120 m and the horns point downcurrent to the southwest the seafloor surrounding the dunes is variable with gravel patches sand with gravel streaks and uniform rippled sand all observed the pattern of sand ripples across the dune surface is strongly controlled by the dune morphology on the lower stoss slopes of the dunes straight crested transverse ripples gradually merge upslope into sinuous crested transverse ripples most of the upper dune surface is dominated by short crested linguoid ripples this sequence represents an increase in height above seafloor and increasing flow velocity the overall pattern of ripples across the dune surface indicates that the bottom current flow is modified by the dune morphology with flow concentrated over the dune crest and along the inner edge of the horns it is also possible to estimate flow velocity across the dune field using published analogues and short term current meter observations generally published examples of submarine barchans suggest a flow velocity of 40 80 cm s this range of values is in agreement with near bed current meter measurements in the study area which indicate peak flow velocities of 50 60 cm s however in the longer term higher flow speeds may be possible especially considering the presence of erosional furrows adjacent to the dune field

slope instability on a shallow contourite dominated continental margin southeastern grand banks eastern canada abstract submarine sediment failures and related mass transport deposits mtds are widespread on the eastern canadian continental slope settings and in general have been related to ice sheets crossing the outer shelf the southeastern grand banks margin was not glaciated in the last 10 5 years and has a deep shelf break as a result the upper continental slope consists principally of sediment transported from the north by the labrador current high resolution seismic profiles and 10 m long piston cores show widespread sediment failure and mtds in a plastered contourite drift from 500 to 1000 m water depth this study documents the stratigraphy of the past 48 000 years and the record of sediment failure events heinrich layers h1 to h5 have been recognized from distinctive petrology physical properties and bulk geochemistry and are constrained by numerous 14 c ams dates the geotechnical analysis shows that the latest quaternary sediment section is mildly underconsolidated perhaps related to high sedimentation rates up to 0 5 m ka enhanced by some leakage of deep fluids nevertheless factor of safety calculations using su p 0 and friction angles from triaxial testing suggest the slope is statically stable up to gradients of 9 atterberg limit measurements of silty contourite sediments indicate susceptibility to liquefaction under cyclic loading there is evidence that apparently synchronous failure occurred over many tens of kilometres of the slope probably as a result of rare passive margin earthquakes these shallow water contourite deposits have a higher sand and coarse silt content much less biogenic material and more rapid variations in sediment and geotechnical properties than those of the deep water equivalents all of which make them more susceptible to sediment failure

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

a margin wide bsr gas hydrate assessment canada s atlantic margin abstract it is the intent of this paper to explore a significant extent of an entire passive continental margin for hydrate occurrence to understand hydrate modes of occurrence preferred geologic settings and estimate potential volumes of methane the presence of gas hydrates offshore of eastern canada has long been inferred from estimated stability zone calculations but little physical evidence has been offered an extensive set of 2 d and 3 d single and multi channel seismic reflection data comprising in excess of 140 000 line km was analyzed bottom simulating reflections bsr were unequivocally identified at seven sites ranging between 250 and 445 m below the seafloor and in water depths of 620 2850 m the combined area of the bsrs is 9311 km 2 which comprises a small proportion of the entire theoretical stability zone along the canadian atlantic margin 715 165 km 2 the bsr within at least six of these sites lies in a sedimentary drift deposit or sediment wave field indicating the likelihood of grain sorting and potential porosity and permeability reservoir development although there are a variety of conditions required to generate and recognize a bsr one might assume that these sites offer the most potential for highest hydrate concentration and exploitation total hydrate in formation at the sites of recognized bsr s is estimated at 17 to 190 10 9 m 3 or 0 28 to 3 12 10 13 m 3 of methane gas at stp although it has been shown that hydrate can exist without a bsr the results from this regional study argue that conservative estimates of the global reserve of hydrate along continental margins are necessary

geology mineralization alteration and structural evolution of the el teniente porphyry cu mo deposit sir the el teniente cu mo deposit in central chile is an extraordinary accumulation of cu mo ore fig 1 and we welcome the opportunity provided by skewes and stern 2007 to discuss and clarify several important issues regarding its classification and interpretation and to address several incorrect assertions that they make regarding our manuscript cannell et al 2005 we have interpreted el teniente to be a typical porphyry deposit in terms of its alteration assemblages vein and breccia styles and spatial and temporal relationships between cu mo mineralization and felsic porphyries skewes and stern 2007 dispute our claims that mineralization occurred primarily in veins and was related to felsic intrusive activity they also take issue with our interpretations of the various geochronological datasets from el teniente and our classification of el teniente as a porphyry cu mo deposit we address each of these in turn below in order to facilitate the following discussion table 1 correlates the geologic nomenclature of skewes and stern 2007 with that of cannell et al 2005 figures 1 and 2 illustrate the location of the main geologic units on underground mine level 6 at el teniente also shown on figure 1 are the approximate locations of the hypogene sulfide mineral zones figure 2 shows the block model of mo grades in the mine for more details of geologic relationships at el teniente refer to figure 4 of cannell et al 2005 and figures 4 and 5 of skewes et al 2002 although the dacite porphyry dike is shown as a single unit on figure 1 note that rojas 2002 2003 mapped multiple phases within this composite intrusive body skewes and stern 2007 criticized our use of what they assert to be an outdated map of hypogene mineralization

a late cretaceous mixed turbidite contourite system along the uruguayan margin sedimentary and palaeoceanographic implications abstract the late cretaceous is a critical period in the evolution of the south atlantic significant changes in the tectonic configuration of continental landmasses and marine basins during this time lead to major shifts in the sedimentary and oceanographic regimes using a combination of 2d and 3d seismic data with well data from the uruguayan margin this work provides a new highly detailed description of the late cretaceous sedimentary evolution of the margin and its regional and global palaeoceanographic implications the polonio drift system pds occupies the middle to lower slope of the uruguayan margin the pds is characterised by four channel drifts which propagate obliquely 120 170 from the palaeoslope and exhibit over 800 m of local relief relative to the surrounding seafloor seismic interpretation identified four seismic units su 1 su 4 separated by five major discontinuities r 1 r 5 these record the onset albian upper turonian 113 89 8 ma growth coniacian upper maastrichtian 89 8 66 ma and burial paleocene 66 56 ma phases for the pds during the onset stage down slope processes dominate but three major shifts in the sedimentary stacking pattern occur these coincide with palaeoceanographic changes in the south atlantic during the cenomanian turonian 100 5 89 9 ma campanian maastrichtian 83 6 66 ma and paleocene 66 56 ma following the opening of the falkland malvinas agulhas seaway fas the subsidence of the walvis ridge and the opening of the vema channel bottom current influence first occurs during the growth stage coniacian campanian when mounded deposits shift from aggradational and slightly progradational towards the n su 2 to clear lateral migration towards the s su 3 this sedimentary pattern indicates a regional palaeoceanographic shift in bottom current flow from northerly to a subsequent southerly direction bottom currents do not appear to have actively eroded sediment although they apparently had the potential to pirate and entrain fine grained material from turbidity plumes which build on underlying bathymetric features such as basement horsts and channel levees these produce large mounded morphologies adjacent to channels drift growth ceases following the termination of shelf progradation r 4 enabling sluggish bottom currents contributed to a homogeneous sedimentary drape bottom currents intensify in the beginning of the paleocene forming contourite depositional systems with well developed contourite terrace along the middle slope further research can elucidate the nature and mechanics of turbidite contourites interactions along continental margins this work offers new insights for the implications and consequences of the interaction of turbidites and contourites which can improve the characterisation of deep water deposits and understanding palaeoceanographic interpretations

the distribution and timing of molybdenite mineralization at the el teniente cu mo porphyry deposit chile this journal is published under the terms of green open access authors may post a copy of the accepted i e post peer review version of their paper https doi org 10 2113 econgeo 110 2 387 in a repository of their choice or to their personal website after the relevant embargo period has passed the embargo period will be 12 months from formal online publication

magnetic polarity zonation within the el teniente copper molybdenum porphyry deposit central chile el teniente porphyry copper deposit the world s greatest intrusion related cu mo ore body is hosted within basaltic andesitic volcanic and gabbroic rocks mafic complex this ore body is strongly affected by multiple events of alteration mineralization with pervasive potassic and chloritic alteration and coetaneous with associated copper mineralization we present paleomagnetic results obtained from oriented samples at four locations within the mine and from two drill cores 200 and 400 m long respectively samples are representative of all the main hydrothermally altered rock units with emphasis on the mafic host rock and dacitic teniente dacite porphyry and dioritic porphyry intrusions magnetic experiments hysteresis loop isothermal remanent magnetization irm k t curves thermal and alternating field demagnetization show the presence of prevailing magnetite microscope and sem observations show two families of magnetite a large multidomain magnetite grains associated with biotite and chlorite of various different hydrothermal alteration events and b abundant small to medium grain size magnetite 0 01 and up to 0 2 si with nrm in the range 0 1 2 am 1 most mafic complex rock samples have univectorial magnetizations during alternating field or thermal demagnetization within the mine the magnetic polarity is spatially distributed in the northern part of the deposit the teniente dacite porphyry the associated hydrothermal breccias and the hosting mafic complex record a reverse polarity magnetization also observed in the el teniente sub 6 mine sector immediately to the east and southeast in the eastern part of the deposit a normal polarity is observed for samples of the mafic complex from the two long drill cores there is no evidence for superimposed magnetizations of opposite polarities in samples of the mafic complex anhysteretic remanent magnetization arm in a dc field of 40 t and nrm have similar magnitude and comparable behavior upon alternating field demagnetization the well defined strong remanent magnetizations associated with high unblocking temperatures 500 c indicate an acquisition of remanent magnetization during mineralization by circulating high temperature fluids related with ore deposition paleomagnetic results and the recorded polarity zonation suggest multiple mineralization events occurred at el teniente each one with its own evolution stages superimposed within the district these results indicate that a simplified broad four stage model for el teniente as presented and overly employed by many authors divided in 1 late magmatic 2 main hydrothermal 3 late hydrothermal and 4 posthumous stage does not recognize various short lived single mineralization events some superimposed and some distinctly separated in time and space there is no paleomagnetic evidence for post mineralization deformation

geophysical evidence for widespread cenozoic bottom current activity from the continental margin of nova scotia canada abstract two dimensional and three dimensional multichannel seismic reflection data are utilized to examine previously unrecognized contourite depositional systems along the continental margin of nova scotia canada prior to this study these features were thought to be of limited extent in the study area the new data show that contourite drifts are widespread with greatest drift development during the late miocene to pliocene giant sediment waves form stacked aggrading sequences of bedforms and their development is linked to pre existing seafloor morphology small sediment drifts developed locally throughout the late paleogene and neogene either southwest and down current of seafloor obstacles or form channel fills major erosional pulses form regional seismic markers first along the continental rise in the early oligocene then along the continental slope during the late miocene and pliocene three dimensional seismic data show that erosion surfaces preserve along slope amplitude anomalies two dimensional low relief sediment waves and barchanoid bedforms the geophysical evidence implies that a northeast to southwest along slope bottom current influenced cenozoic depositional patterns throughout the study area

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period 1 we perform a monte carlo pattern recognition analysis of the coincidence between three regional volcanic histories from ice coring of greenland and antarctica over the period 2 to 45 ka using so4 anomalies in greenland and east antarctica determined by continuous core chemistry together with west antarctic volcanic ash layers determined by remote optical borehole logging and core assays we find that the antarctic record of volcanism correlates with glacial abrupt climate change at a 95 to 99 8 3s significance level and that volcanic depositions at the three locations match at levels exceeding 3s likely indicating that many common horizons represent single eruptive events which dispersed material world wide these globally coincident volcanics were associated with abrupt cooling often simultaneous with onsets or sudden intensifications of millennial cold periods the striking agreement between sites implies that the consistency of current timescales obtained by isotopic and glaciological dating methods is better than estimated

the early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

contourite drift types and their distribution in the north and south atlantic ocean basins abstract patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors intensity of the regional deep circulation morphology of the sea floor coriolis effects abundance of terrigenous and biogenic supplies subsequent turbidity of deep nepheloid layers and depth of the ccd based on many examples of bottom current deposits from the atlantic and from other oceans we recognise three major types of contourite accumulation 1 giant elongate drifts 2 contourite sheets and 3 channel related drifts they generally occur in distinct topographic settings and show different geometries facies and rates of deposition in the north atlantic strong bottom circulation an open basin system and high sediment supply have led to the construction of large elongate contourite drifts which have striking relief 200 1000 m above the surrounding sea floor and are composed of muddy contourites rich in calcareous pelagic material in the south atlantic strong bottom currents are often trapped in gyre like circulation patterns around topographically closed basins or are accelerated through deep narrow connecting passages the resulting deposits are mainly extensive contourite sheets covered by fields of large sediment waves and channel related drifts including contourite fans constructed at the downstream exit of deep passages

widespread erosion and mass failure from the 51 ma montagnais marine bolide impact off southwestern nova scotia canada12 1this article is one of a series of papers published in this cjes special issue on the theme of mesozoic cenozoic geology of the scotian basin 2earth sciences sector contribution 20120241 the 51 ma montagnais impact crater on the outer scotian shelf is well known but the potential effects from the impact event on the slope and rise seaward of the crater have until now remained poorly understood through detailed seismic stratigraphic correlation and ties to available wells we define a threefold seismic stratigraphic subdivision for upper cretaceous to eocene strata on the shelf and slope calibrated to the most recent biostratigraphic results using this framework we identify a number of depositional and erosional products that are temporally consistent with a late ypresian impact event within the limits of seismic and biostratigraphic resolution we link a series of prominent failure scarps on the outer shelf and upper slope to a single widespread mass transport deposit mtd on the lower continental slope rise and abyssal plain failed material amassed in a large debris field referred to here as the montagnais mtd it covers an area of 93 000 km2 and travelled up to 580 km f

storms and flow reversals at the hebble site abstract we examine a 20 month long abyssal current meter record obtained from the hebble site about 40 27 n 62 22 w as expected the westward flowing abyssal western boundary current described by richardson et al 1981 and weatherly and kelley 1982 generally passes over this site we call this current the cold filament current cfc and conclude that it is appreciably stronger than suggested by weatherly and kelley 1984 15 cm s 1 as compared to 10 cm s 1 after comparing the abyssal current record with charts showing the surface location of the gulf stream and rings we conclude that the majority of abyssal storms at the hebble site are due to the presence of the cfc passing by and the absence of a meander or ring overhead the presence of a ring or meander overhead apparently results in the cfc being displaced out of the hebble site as suggested by kelley 1984 at such times the near bottom flow appears to respond to the barotropic component of the overlying ring or meander

the cenozoic ocean circulation based on ocean general circulation model results abstract a series of ocean general circulation model gcm experiments for paleocene eocene miocene and present day continental geography with atmospheric forcing prescribed from atmospheric gcm experiments is utilized to investigate the changes in surface and deep water ocean circulation through the cenozoic the experiments illustrate a number of similarities with previous observation based reconstructions although the timing of the development of particular gyre systems and the nature of the high southern latitude circulation are generally different than previous interpretations in addition the model results suggest substantial changes in the sites of deep water formation including a middle eocene subtropical source because of a number of experimental limitations the experiments should be considered largely as a sensitivity analysis of the role of changing geography in modifying the ocean circulation

channel levee evolution in combined contour current turbidity current flows from flume tank experiments turbidity currents and contour currents are common sedimentary and oceanographic processes in deep marine settings that affect continental margins worldwide their simultaneous interaction can form asymmetric and unidirectionally migrating channels which can lead to opposite interpretations of paleocontour current direction channels migrating against the contour current or in the direction of the contour current in this study we performed three dimensional flume tank experiments of the synchronous interaction between contour currents and turbidity currents to understand the effect of these combined currents on channel architecture and evolution our results show that contour currents with a velocity of 10 19 cm s 1 can substantially deflect the direction of turbidity currents with a maximum velocity of 76 96 cm s 1 and modify the channel levee system architecture a lateral and nearly stationary front formed on the levee located upstream of the contour current reduced overspill and thus restrained the development of a levee on this side of the channel sediment was preferentially carried out of the channel at the flank located downstream of the contour current an increase in contour current velocity resulted in an increase in channel levee asymmetry with the development of a wider levee and more abundant bedforms downstream of the contour current this asymmetric deposition along the channel suggests that the direction of long term migration of the channel form should go against the direction of the contour current due to levee growth downstream of the contour current in agreement with one of the previously proposed conceptual models

geological effects of the gulf stream system on the northern bermuda rise abstract the gulf stream system contains a clockwise rotating set of bottom currents which influence the sea bed in the northern north american basin it is possible to interpret the present day and historical record of current activity in this basin in terms of the deep flow of the gulf stream this interpretation provides a much more satisfactory and consistent explanation of the geologic record than previous interpretations based strictly on the influence of the classic abyssal circulation the present day circulation of the gulf stream actively resuspends large quantities of sediment on and near the northern bermuda rise and it is suggested that this resuspension may be due to the eddy field which is embedded in the westward flowing return flow during the late cenozoic the gulf stream system was responsible for depositing and shaping the major acoustic sedimentological units on the relatively smooth surface of the horizon a complex fine grained mont morillionite rich sediments derived from the chemically weathered saprolites of the hudson and st lawrence drainage basins were injected into the deep ocean basins by turbidity currents during the late paleogene and the neogene fine grained turbidites from the st lawrence spread southward down the southeastern sohm abyssal plain across the eastward flowing gulf stream and its westward flowing return flows portions of these fine grained sediments were entrained by the main and return flows and deposited downstream as acoustically non laminated accumulations on the corner and bermuda rises respectively the hudson river input was injected into the deep basin through the hudson canyon system the interaction of these fine grained turbidites with the northward flowing deep flow of the gulf stream system led to the formation of the gulf stream outer ridge here defined for the first time during the late neogene or early pleistocene the gulf stream outer ridge was partially eroded by the gulf stream system and portions subsequently covered by coarse grained pleistocene turbidites the coarse grained illite rich turbidites that flowed across the southeastern sohm abyssal plain also crossed the main and return flows of the gulf stream system the finer portions of these sediments were entrained and deposited as pleistocene acoustically laminated sediments on the plateaus of the bermuda and corner rises

bedform velocity matrix the estimation of bottom current velocity from bedform observations a wide variety of bedforms both depositional and erosional in origin has been recognized on the deep seafloor and attributed to the influence of bottom currents these range in scale from those visible in bottom photographs centimeter to decimeter to those recorded with seafloor bathymetric imaging meter to kilometer in many cases it has been possible to provide some quantification of substrate grain size and flow velocity responsible for each bedform type we have synthesized both our own and published data in order to present a bedform velocity matrix which facilitates the estimation of bottom current velocity based on bedform type despite imperfections we believe this to be a valuable model for assessing strength and variability of bottom currents that can have a significant influence on the siting of submarine cables pipelines and other seafloor installations

chlorite and epidote mineral chemistry in porphyry ore systems a case study of the northparkes district new south wales australia propylitic alteration characterized by the occurrence of chlorite and epidote is typically the most extensive and peripheral alteration facies developed around porphyry ore deposits however exploration within this alteration domain is particularly challenging commonly owing to weak or nonexistent whole rock geochemical gradients and the fact that similar assemblages can be developed in other geologic settings particularly during low grade metamorphism we document and interpret systematic spatial trends in the chemistry of chlorite and epidote from propylitic alteration around the e48 and e26 porphyry cu au deposits of the northparkes district new south wales australia these trends vary as a function of both distance from hydrothermal centers and alteration paragenesis the spatial trends identified in porphyry related chlorite and epidote at northparkes include 1 a deposit proximal increase in ti as sb and v in epidote and ti in chlorite 2 a deposit distal increase in co and li in chlorite and ba in epidote and 3 a pronounced halo around deposits in which mn and zn in chlorite as well as mn zn pb and mg in epidote are elevated chlorite al si ratios and epidote al fe ratios may show behavior similar to that of mn zn or may simply decrease outward and v and ni concentrations in chlorite are lowest in the peak mn zn zone in comparison to porphyry related samples chlorite from the regional metamorphic assemblage in the district contains far higher concentrations of li ca ba pb and cu but much less ti similarly metamorphic epidote contains higher concentrations of sr pb as and sb but less bi and ti these chlorite and epidote compositional trends are the net result of fluid mineral partitioning under variable physicochemical conditions within a porphyry magmatic hydrothermal system they are most easily explained by the contribution of spent magmatic derived ore fluid s into the propylitic domain it is envisaged that such fluids experience progressive cooling and reduction in 119891 s2 during outward infiltration into surrounding country rocks with their ph controlled by the extent of rock buffering experienced along the fluid pathway

a synthesis of the sedimentary evolution of the demerara plateau central atlantic ocean from the late albian to the holocene abstract the demerara plateau off the french guiana and surinam margin corresponds to a prominent sub horizontal marginal plateau the interpretation of a large set of seismic data acquired along the demerara plateau and integration with previous seismic stratigraphy and drill studies enables a better understanding of the sedimentary evolution of the outer demerara marginal plateau since the end of the transform activity late albian three sedimentary evolutionary stages have been identified 1 the pre contourite stage late albian to early miocene is strongly controlled by the structure of the margin that influences the distribution pattern of post transform deposits through differential thermal subsidence between transform and divergent segments 2 the transitional stage middle miocene to early pliocene is expressed as a current controlled erosive surface resulting from the onset of bottom current interactions due to the establishment and strengthening of the modern thermohaline circulation that is coeval with the progressive closure of the isthmus of panama 3 the contourite stage middle pliocene to holocene is characterized by the development of a contourite depositional system that is linked to the activity of the north atlantic deep water circulation and by a complex interaction between alongslope and downslope processes our study highlights that marginal plateaus might be particularly prone to develop contourite features since they regionally influence ocean current dynamics in guiding and accelerating bottom contour currents marginal plateaus should thus be considered as a key target to study bottom current dynamics and paleocirculation patterns