the closing of tethys and the tectonics of the himalaya recent geological and geophysical data from southern tibet allow refinement of models for the closing of southern neo tethys and formation of the himalaya shelf sediments of the indian passive continental margin which pass northward into deep sea tethyan sediments of the indus tsangpo suture zone were deposited in the late cretaceous an andean type margin with a 2 500 km long trans himalayan kohistan ladakh gangdese granitoid batholith formed parallel to the southern margin of the lhasa block together with extensive andesites rhyolites and ignimbrites lingzizong formation the southern part of the lhasa block was uplifted deformed and eroded between the cenomanian and the eocene in the western himalaya the kohistan island arc became accreted to the northern plate at this time the northern part of the lhasa block was affected by jurassic metamorphism and plutonism associated with the mid jurassic closure of the bangong nujiang suture zone to the north the timing of collision between the two continental plates ca 50 40 ma marking the closing of tethys is shown by 1 the change from marine flysch like to continental molasse like sedimentation in the indus tsangpo suture zone 2 the end of gangdese i type granitoid injection 3 eocene s type anatectic granites and migmatites in the lhasa block and 4 the start of compressional tectonics in the tibetan tethys and indus tsangpo suture zone south facing folds south directed thrusts after the eocene closure of tethys deformation spread southward across the tibetan tethys zone to the high himalaya deep crustal thrusting barrovian metamorphism migmatization and generation of oligocene miocene leucogranites were accompanied by south verging recumbent nappes inverting metamorphic isograds and by south directed intracontinental shear zones associated with the main central thrust continued convergence in the late tertiary resulted in large scale north directed backthrusting along the indus tsangpo suture zone more than 500 km shortening is recorded in the foreland thrust zones of the indian plate south of the suture and 150 km shortening is recorded across the indian shelf zanskar range and the indus suture in ladakh there was also large scale shortening of the karakoram and tibetan microplates north of the suture as much as 1 000 km shortening occurred in tibet the more recent deformation however involved the spreading of this thickened crust and the lateral motion of the tibetan block along major approximately east west trending strike slip fault zones

yvonaspis nouveau genre d osteostraci vertebrata agnatha du devonien emsien eifelien des gres de gaspe quebec canada all osteostracan species of the gaspe sandstones devonian of canada formerly attributed to the genus cephalaspis are referred here to the new genus yvonaspis the latter is characterized by the very elongated shape of the naso hypophysal opening this monophyletic genus may be the sister group of parameteoraspis among cephalaspidians

mesozoic neo tethyan pre orogenic deep marine sediments along the indus yarlung suture himalaya shelf forereef and basin margin slope olistoliths exotic blocks of limestone of permian jurassic age are tectonically juxtaposed within the triassic to eocene age pre orogenic deep abyssal plain turbidites of the lamayuru the pre collision tectonic setting and depositional environment of the limestone olistoliths can be reconstructed from within the neighbouring zanskar range the disorganized ophiolitic melange zone an association of different tectonic rock slivers of jurassic eocene age is tectonically underlain by the overthrusted lamayuru formation and tectonically overlain by the nindam formation tectonic slivers of late jurassic early cretaceous age red radiolarian cherts represent a characteristic lithotectonic unit of the ophiolitic melange zone those occurring near the contact zone with the lamayuru formation were deposited within the neo tethyan deep ocean floor of the indian passive margin below the carbonate compensation depth these tectonic slivers accumulated along the northern margin of the indus yarlung suture zone of the ladakh indian himalaya during subduction accretion associated with the initial convergence of the indian plate beneath the eurasian plate

earthquake induced soft sediment deformation in the lower shyok river valley northern ladakh india abstract soft sediment deformation structures occur in the 150 m thick pliocene quaternary fluvio lacustrine sediments exposed around the khalsar and tirit areas in the lower shyok river valley northern ladakh and eastern karakoram india these structures vary in morphology and pattern and occur at different stratigraphic horizons they satisfy the criteria for attributing them to seismic events and it is proposed that these structures were formed as a result of earthquake induced liquefaction the deformation structures are thus interpreted to represent pre historic seismic events which occurred up to 5 ma ago and were associated with tectonic activity along the karakoram fault

marine os isotopic fluctuations in the early eocene greenhouse interval as recorded by metalliferous umbers from a tertiary ophiolite in japan abstract the mineoka umbers occur within the tertiary accretionary complex of central japan immediately overlying 53 7 ma tholeiitic basalts the associated tholeiitic basalts exhibit typical normal mid ocean ridge basalt n morb type geochemical signatures and are interpreted to be a remnant of tertiary oceanic crust centimeter resolution bulk rock chemical analyses were performed to cover the entire section of the 35 cm thick umber deposit there are striking similarities in major element trace element re and os contents between the umbers and modern metalliferous sediments along the east pacific rise these results demonstrate that the mineoka umbers are ancient counterparts of mor metalliferous sediments that are plume fall out ferromanganese precipitates scavenging various seawater derived elements including p v y rees and os and confirm that the umbers subaerially exposed in the accretionary complex generally preserve their primary geochemical signatures at the time of deposition the marine 187 os 188 os ratios inferred from the mineoka umbers gradually increase up section with moderate fluctuations the 187 os 188 os composition ranging from 0 47 to 0 54 is significantly higher than that of the prior period post paleocene eocene thermal maximum petm 187 os 188 os 0 38 this was probably the result of an increase in the chemical weathering rate of continental crust caused by the long duration of noticeably warm climate during the early eocene greenhouse interval several fluctuations observed in the marine 187 os 188 os record during this interval are most likely related to petm like brief hyperthermals supporting the suggestion that the intensity of continental crustal weathering controlled by climatic changes can fluctuate on timescales of 10 5 yr

sedimentology petrography and tectonic significance of the shelf flysch and molasse clastic deposits across the indus suture zone ladakh nw india abstract in the ladakh area of india a passive triassic to lower cretaceous continental margin is indicated by indian shield derived clastics on the shelf and atlantic type turbidites off the continental margin mid cretaceous initiation of ocean closing is reflected in pacific type flysch and associated island are volcanics which were initially emplaced over the northern indian continental margin in late cretaceous times resulting in the formation of a fore deep in which flysch and minor continental molasse accumulated briefly during the late cretaceous these transient uplifts were however rapidly destroyed for by the latest cretaceous to latest palaeocene uniform carbonate sediments were being laid down over the area with the early eocene the development of a second fore deep this time filled with very thick flysch and molasse sediment indicates a major uplift of the northern indian margin which we attribute to the development of an andean type magmatic arc on the northern edge of the indian plate uplift and molasse sedimentation in this fore deep continued through the oligocene and miocene when the collision of india and asia caused extensive deformation of all the sequences and the shift of molasse sedimentation southwards to the himalaya foothills and indo gangetic plain

the xigaze forearc basin evolution and facies architecture cretaceous tibet abstract the mid cretaceous to eocene flysch deposits of the xigaze forearc basin in southern tibet were investigated in a 120 km segment along the indus yarlung suture zone the basin evolved south of the magmatic arc gangdise belt of the lhasa block on top of trapped oceanic or transitional crust remnants of shelf carbonates are preserved along the northern edge of the basin the mapped segment was shortened by about 65 metamorphism reached low grade conditions along the northern margin of the basin the flysch sequence reaches a thickness of at least 5 km and consists to a large degree of volcaniclastic andesitic to dacitic material shed from the magmatic arc gangdise belt particularly in the western part of the study area plutonic and sedimentary rocks from deep erosion levels and or more distal sources contributed to the basin fill rivers from the lhasa block acted as point sources and fed five major deep sea channel systems turbidity currents in the channels were directed towards the growing accretionary wedge of the subduction zone thus indicating that the basin was continuously filled up to outer ridge level and gradually shallowing the forearc flysch is subdivided into at least three megasequences which begin with wide up to several km incised 10 to 50 m coarse grained channel fills and their associated fan deposits the upper parts of the megasequences contain hemipelagic dark shales and marls deposited above the calcite compensation depth lateral channel migration channel lobe switching but also volcanic pulses generated a predominantly fining upward high frequency cyclicity after continental collision the marine sedimentation in the forearc basin was replaced by fluvial deposits of the eocene oligocene qiuwu formation which is time equivalent to the kailas and indus molasses farther west and rich in coarse gravel derived from the gangdise belt both forearc flysch and qiuwu formation were deformed simultaneously during the miocene we assume that the molasse type qiuwu formation represents the final continental facies of the forearc basin filling

influence of shimada seamount on sediment composition in the eastern tropical north pacific abstract shimada seamount is a large young volcanic edifice in the east central pacific that is not associated with any active spreading center or known hot spot the sediments on the abyssal plain surrounding shimada seamount consist of pelagic clay with ferromanganese micronodules and zeolites the pelagic clay is mostly barren of microfossils except for a few occurrences of highly corroded specimens of radiolaria and diatoms eolian terrigenous material is the dominant component of the pelagic clay to a depth of at least 8 m below sea floor with minor contributions from volcanic debris and hydrothermal and hydrogenous sources the average amount of basaltic debris is only 0 25 but concentrations are as high as 10 in some samples the average hydrothermal component metalliferous sediment is 8 8 with a maximum of about 13 at 7 5 m below sea floor in one core the hydrogenous component mostly as ferromanganese micronodules averages 4 1 with a maximum of 5 6 there is no calcareous biogenic debris and essentially no siliceous biogenic debris in the past a decrease in hydrothermal components through time may have been the result of a decrease in relative importance of hydrothermal influences or an increase in the flux of terrigenous debris transported by the northeast trade winds because volcanic activity is still active on shimada seamount or has been in the recent past the observed increase in relative abundance of terrigenous components probably was the result of increased wind transport and not decreased hydrothermal activity shimada seamount may be an important local source of metalliferous sediment in the eastern equatorial north pacific and may have been an even more important source in the past

sedimentology and tectonic implications of the lamayuru complex deep water facies of the indian passive margin indus suture zone ladakh himalaya

zircon u pb and hf isotopic constraints on the onset time of india asia collision the time of initial collision between india and asia has been extremely controversial despite the fact that it is vital to constraining the orogenesis and subsequent evolution of the himalayas and tibetan plateau here we report u pb and hf isotope analysis of detrital zircons from two principal foreland basins that is the sangdanlin and gyangze basins respectively in the western and central parts of southern tibet our data suggest that asian derived clastic sediments started contributing to sedimentation on the indian continental margin earlier than generally thought at 60 ma in both basins near the yarlung zangbo suture zone in southern tibet no evidence for the existence of an intra oceanic arc within the neotethys is observed we conclude that 60 ma can be used to constrain the onset time of the india asia collision at least in central tibet after this initial collision closure of the neotethys propagated both westward and eastward with the final closure occurring at 50 and 45 ma in northwestern and eastern himalayas respectively our conclusion differs significantly from the previous view that the india asia collision may have started in northwestern himalaya and propagated eastward with diachronous suturing

hydrothermal activity associated with off axis volcanism in the peru basin abstract products of low temperature hydrothermal activity are widespread in the peru basin and are associated with late tertiary oceanic island type intraplate volcanics hydrothermal activity is still taking place as indicated by a series of sharp high and narrow temperature anomalies over one of the volcanic cones submarine hydrothermal activity associated with off axis volcanism has been frequently observed elsewhere but was usually found to be limited to seamounts in the peru basin a hydrothermal halo was found in sediments surrounding hydrothermally active seamounts in addition to hydrothermal precipitates on the tops of the seamounts todorokite birnessite fe nontronite goethite and silica were found on top of young volcanic edifices and occur as coatings on volcanic rocks and in nuclei of manganese nodules the hydrothermal precipitates in the sediments are mg fe silicates as is the case in the adjacent bauer basin the proportion of hydrothermal precipitates in the sediments increases with depth in the cores down to the appearance of the basalt that indicates the beginning of intraplate volcanism 5 million years ago sediments overlying late tertiary volcanic rocks are locally enriched in hydrothermal material by solutions percolating upwards directly into the sediment in these sediments apatite and phillipsite appear to have been precipitated directly from these ascending hydrothermal solutions

the holocene sedimentary regime in the northern mid atlantic ridge region the holocene 10 000 yr b p mid atlantic ridge sedimentary regime between 45 n and 65 n has been investigated by examination of sediments from 70 cores smectite chlorite and quartz 87sr 86sr isotopes and ree have been used as conservative tracers to provide source identification and to calculate accumulation rates the entire holocene sedimentary regime in this part of the atlantic can be attributed to particle fluxes from two sources the icelandic and north american systems two main transport mechanisms are identified 1 particles derived from the icelandic system have been transported southwards as far as 45 n by bottom currents 2 material coming from north america is mainly transported by the aeolian regime at 45 n the windborn accumulation rate is estimated to be 0 5 g cm 2 kyr 1 which is identical to the accumulation rate of bottom advected material from iceland finally a diagnostic model for the north atlantic sedimentary regime is proposed

remobilization of transition metals in surficial pelagic sediments from the eastern pacific abstract the top thirty centimeters of sediment at two sites in the eastern equatorial pacific contain evidence of post depositional remobilization of mn fe co ni cu and zn remobilization takes place as mn and fe oxyhydroxides are released to the pore water during the microbially mediated decomposition of organic matter precipitation of the dissolved metals in near surface more oxic strata controls the solid phase distribution of mn fe and zn the solid phase redistribution of co and ni requires only suitable material for readsorption comparison of pore water fluxes with solid phase metal distributions in the solid sediment indicates no loss of dissolved metal to the overlying water column at the present time loss of mn during the quaternary is indicated by the composition of the sediments however leaching experiments suggest that portions of the mobile mn fe co ni and cu are fixed by incorporation in authigenic smectite in the surficial sediments

mesozoic deep water slope rise sedimentation and volcanism along the north indian passive margin evidence from the karamba complex indus suture zone western ladakh himalaya abstract mesozoic deep water sedimentary and basic volcanogenic rocks defined as the karamba complex are exposed within the indus suture zone of western ladakh n india the karamba complex originated as part of the north indian passive margin in its entirety and does not include exotic melange or accreted oceanic units as recently suggested the complex preserves younger more distal equivalents relative to more proximal deep water slope lamayuru complex and shelf zanskar successions of the north indian passive margin the karamba complex is mainly inverted youngs to the nnw and includes many outcrop scale folds that face nnw the complex was initially emplaced onto the zanskar shelf as three main thrust slices probably in the latest cretaceous and later inverted faulted and sheared during mid late tertiary nw backthrusting that accompanied uplift of the high himalaya sedimentation in the karamba complex began in the mid late triassic with mainly siliciclastic turbidites derived from the indian basement together with redeposited limestones and minor basic volcanics mixed radiolarian sediments siliciclastic turbidites and redeposited shelf derived calciturbidites accumulated in early mid jurassic accompanied by eruption of alkaline volcanic rocks mainly in the mid jurassic the probable cause of the jurassic volcanism was a pulse of crustal extension along the continent ocean transition zone triggered by late stage rifting of india from gondwana as a precursor to its northward drift quartzose sandstone turbidites accumulated on the upper slope in the early cretaceous whereas sedimentation on the lower slope rise was pelagic marked by depositional hiatuses and sediment redeposition during the late cretaceous a switch to mainly calcareous pelagic deposition took place interspersed with radiolarian accumulation on the lower slope rise initial thrust emplacement onto the zanskar shelf in the latest cretaceous is suggested by the absence of post upper cretaceous sediments within the karamba complex

palaeoenvironments of early devonian fish and other aquatic fauna of the campbellton formation new brunswick canada abstract the palaeoecology and palaeoenvironments of the classic fish bearing strata of the campbellton formation are here described a well documented fossil assemblage includes acanthodian placoderm chondrichthyan and cephalaspid fishes tracheophyte remains eurypterids ostracods and molluscs as part of the old red sandstone continent the emsian campbellton formation occupied a small basin within the mountainous terrain of the acadian orogen and may have connected through a narrow seaway to a closing foreland basin the highest diversity of vertebrate fossils was found above a basal unconformity with val d amour formation volcanics marked by fissure fills and unstratified breccia representing a craggy irregular palaeosurface that provided shelter for some fauna and sediment for rapid burial of skeletal remains overlying prodeltaic calcareous siltstones are also highly fossiliferous and represent a low energy habitat occurrences of pterygotid eurypterids cephalaspids and chondrichthyans in deltaic sandstones place these taxa in a habitat that may have been variably fresh or brackish the surrounding landscape was vegetated with primitive tracheophytes and abundant plant debris is preserved throughout the basin the diverse assemblage of fish arthropods gastropods plants and microbial growths suggests that a trophically complex ecosystem was in existence

shyok suture zone n pakistan late mesozoic tertiary evolution of a critical suture separating the oceanic ladakh arc from the asian continental margin abstract the shyok suture zone northern suture of north pakistan is an important cretaceous tertiary suture separating the asian continent karakoram from the cretaceous kohistan ladakh oceanic arc to the south in previously published interpretations the shyok suture zone marks either the site of subduction of a wide tethyan ocean or represents an early cretaceous intra continental marginal basin along the southern margin of asia to shed light on alternative hypotheses a sedimentological structural and igneous geochemical study was made of a well exposed traverse in north pakistan in the skardu area baltistan to the south of the shyok suture zone in this area is the ladakh arc and its late cretaceous mainly volcanogenic sedimentary cover burje la formation the shyok suture zone extends northwards ca 30 km to the late tertiary main karakoram thrust that transported asian mainly high grade metamorphic rocks southwards over the suture zone the shyok suture zone is dominated by four contrasting units separated by thrusts as follows 1 the lowermost askore amphibolite is mainly amphibolite facies meta basites and turbiditic meta sediments interpreted as early marginal basin rift products or trapped tethyan oceanic crust metamorphosed during later arc rifting 2 the overlying pakora formation is a very thick ca 7 km in outcrop succession of greenschist facies volcaniclastic sandstones redeposited limestones and subordinate basaltic andesitic extrusives and flow breccias of at least partly early cretaceous age the pakora formation lacks terrigenous continental detritus and is interpreted as a proximal base of slope apron related to rifting of the oceanic ladakh arc 3 the tectonic melange reconnaissance further east north of the shyok river indicates the presence of redeposited volcaniclastic sediments and thick acid tuffs derived from nearby volcanic centres presumed to lie within the ladakh arc in addition comparison with lower cretaceous clastic sediments maium unit within the northern suture zone west of the nanga parbat syntaxis hunza river reveals notable differences including the presence of terrigenous quartz rich conglomerates serpentinite debris flow deposits and a contrasting structural history the shyok suture zone in the skardu area is interpreted to preserve the remnants of a rifted oceanic back arc basin and components of the asian continental margin in the west hunza river a mixed volcanogenic and terrigenous succession maium unit is interpreted to record syn deformational infilling of a remnant back arc basin foreland basin prior to suturing of the kohistan arc with asia 75 90 ma

diagenesis of oxyanions v u re and mo in pore waters and sediments from a continental margin this research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way we describe pore water and sediment measurements of iron fe manganese mn vanadium v uranium u rhenium re and molybdenum mo along a transect off washington state usa sediments become less reducing away from the continent and the stations have a range of oxygen penetration depths depth to unmeasurable o2 concentration varying from a few millimeters to five centi meters when oxygen penetrates 1 cm or less fe is reduced in the pore waters but reoxidized near the sediment water interface preventing a flux of fe 2 to overlying waters whereas mn oxides are reduced and mn 2 diffuses to overlying waters both re and u authigenically accumulate in sediments only at the most reducing location where the oxygen penetrates 0 3 cm below the sediment water interface does the surface 30 cm of sediments become reducing enough to authigenically accumulate mo stations in close proximity to the juan de fuca ridge crest are enriched in mn and fe from hydrothermal plume processes both v and mo clearly associate with mn cycling whereas u may be associating with either mn oxides and or fe oxyhydroxides rhenium is uncomplicated by adsorption to mn oxides and or fe oxyhydroxides and re accumulation in sediments appears to be due solely to the extent of reducing conditions therefore authigenic sediment re enrichment appears to be the best indicator for intermediate reducing conditions where oxygen penetrates less than 1 cm below the sediment water interface when coupled with negligible authigenic mo enrichment copyright 2005 elsevier ltd 1 introduction oceanic and atmospheric carbon cycles are strongly coupled with the ocean reservoir of dissolved inorganic carbon being 60 times larger than that of the atmosphere broecker and peng 1987 models that couple both ocean and atmosphere have been used to investigate why atmospheric carbon dioxide pco2 atm was reduced during the last glacial age and thus may be useful in predicting the environmental impact of future changes in pco2 atm some of these models require a large increase in organic carbon export through the more efficient use of nutrients to predict the lower pco2 atm observed during

a large arthropod trackway from the gaspe sandstone group middle devonian of eastern canada a large arthropod trackway from the cap aux os member of the battery point formation gaspe sandstone group middle devonian from the baie de gaspe eastern canada is described and assigned to the ichnotaxon palmichnium paleohelcura antarcticum gevers et al 1971 a large stylonurid eurypterid or scorpion is considered the most likely producer a shallow water marginal fluvial environment is inferred as the setting the animal making a transition from walking to swimming along the course of the trackway resume la trace d une piste d un grand arthropode dans le membre de cap aux os de la formation de battery point groupe gres de gaspe devonien moyen dans la baie de gaspe dans l est du canada est decrite et assignee a l ichnotaxon palmichnium paleohelcura antarcticum gevers et al 1971 il semble que la trace ait ete produite par un grand eurypteride stylonuride ou un scorpion on presume que c est dans un environnement fluviatile marginal sous une mince tranche d eau que l animal a creuse cette empreinte en marchant vers un lieu de nage traduit par la redaction braddy and milner 1122 a large arthropod trackway was discovered in 1988 milner 1992 along the northern shore of the baie de gaspe grid reference 20u lk 993112 approximately 5 km east of the town of gaspe near the village of cap aux os on the forillon peninsula in the province of quebec eastern can ada fig 1 the locality is within the cap aux os member of the battery point formation gaspe sandstone group approximately 750 m above the base of the formation in the lower part of unit 4 lawrence and rust 1988 fig 7 the battery point formation comprises a coarsening upwards clastic sequence ranging in age from early emsian to early eifelian middle devonian based on abundant spores oc curring throughout the formation mcgregor 1977 the cap aux os member approximately 640 m thick consists mainly of interbedded sandstones and mudstones which were deposited in a meandering fluvial system the prevail ing palaeocurrent direction varied from the north northwest to the west northwest lawrence and rust 1988 sand was deposited in the river channels and finer grained silts and muds on the extensive vegetated floodplain lawrence 1986

palynological evidence for the palaeocene evolution of the forearc basin indus suture zone ladakh india the discovery of permian mesozoic and palaeocene palynomorphs from the nindam forearc basin exposed along the indus suture zone in ladakh is reported the palynomorphs are from volcanogenic sandstones and are poorly preserved distorted and show the effects of abrasion striation marks the frequent occurrence of proxapertites indicates the assemblage is at least palaeocene in age the palaeocene palynomorphs and sediments were transported to the nindam trough from nearby elevated landward regions islands these palaeocene provenance areas were characterized by an estuarine nearshore tropical warm humid environment and were situated at equatorial palaeolatitudes however the occurrence of permian and mesozoic palynomorphs in the assemblage indicates that the late palaeozoic and mesozoic tethyan sedimentary rocks exposed along the northern margin of the indian plate were redeposited into the tectonically active cretaceous palaeocene trench subduction complex that existed between the indian and the asian plates until the collision took place at 50 60 ma

the dras arc complex lithofacies and reconstruction of a late cretaceous oceanic volcanic arc in the indus suture zone ladakh himalaya abstract the purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the ladakh himalayas the mainly late cretaceous aptian paleocene dras arc complex in the indus suture zone n india is reconstructed as an oceanic arc passing southwards into a proximal to distal forearc apron the arc complex comprises three structural units from west to east these are the suru unit the naktul unit and the nindam formation the suru unit and the naktul unit are unconformably underlain by dissected late jurassic oceanic crust and mantle the suru unit preserves the interior of the arc and is divided into dras 1 and dras 2 sub units the dras 1 sub unit of mid late cretaceous age was intruded by arc plutonics deformed then unconformably overlain by the poorly dated dras 2 sub unit lower tertiary the dras 1 sub unit comprises arc extrusives volcaniclastic and tuffaceous sedimentary rocks and mainly redeposited shallow water limestones the dras 2 sub unit is dominated by coarse volcaniclastics and lava flows passing up into rhythmically layered acidic extrusives with interbedded turbiditic siltstones and siliceous pelagic limestones further east the naktul unit is mainly clastic with large volumes of massive volcaniclastic talus thick bedded debris flows volcaniclastic turbidites and reworked shallow water carbonates pillowed extrusives and ribbon radiolarites are present mainly low in the succession in some areas while pelagic carbonates are abundant near the top the naktul unit is interpreted as a proximal forearc apron the nindam formation in the east is dominated by deep water volcaniclastic turbidites tuffaceous sediments and pelagic carbonates with subordinate debris flows and is interpreted as a distal deep water forearc succession cyclical alternations of mainly volcaniclastics and pelagic carbonates in the nindam formation are thought to reflect relative sea level changes of tectono magmatic and or global eustatic origin the oceanic dras arc complex formed within neotethys in the mid late cretaceous above an assumed northward dipping subduction zone around 79 ma campanian the oceanic arc underwent collisional deformation possibly related to accretion to the trans himalaya ladakh block and or the southern margin of eurasia to form an andean type active continental margin the suru unit in the west dras 1 sub unit was deformed then overlain by the mainly acidic dras 2 sub unit however there is no direct evidence that the nindam formation in the east was deformed until the early eocene when final collision of india and eurasia took place with southward thrusting of the dras arc complex this was followed by partial erosion during deposition of the indus molasse and then back thrusting and folding related to uplift of the high himalayas in the later tertiary

composition oxygen isotope geochemistry and origin of smectite in the metalliferous sediments of the bauer deep southeast pacific the sediments of the bauer deep an open ocean basin situated on the northwest nazca plate in the southeast pacific constitute a regional metalliferous deposit dominated by authigenic smectite two 2 metre long cores from the bauer deep were examined to investigate the nature and origin of the smectite infra red and mossbauer spectroscopy and wet chemical analysis libo2 fusion of isolated smectite indicate the mineral is a mg rich al rich nontronite oxygen isotopic compositions for isolated smectite are uniform and translate to a non hydrothermal temperature of formation of about 3 c sem observations show an abundance of well preserved biogenic opal in surface and near surface sediment but postburial dissolution and transformation of this phase to smectite is evident at depth smectite formation is the result of interaction between iron oxyhydroxide ponded in the bauer deep following a hydrothermal origin at the adjacent east pacific rise and biogenic opal a reaction mechanism is proposed regional factors control smectite formation in particular formation is inhibited in areas of caco3 accumulation topographic elevations but favoured in areas of oxyhydroxide and opal ponding topographic depressions

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

fe and mn enrichment in middle ordovician hematitic argillites preceding black shale and flysch deposition the shoal arm formation north central newfoundland the middle ordovician shoal arm formation in the central volcanic belt of north central newfoundland consists of hematitic argillites overlain by grey cherts then black shales directly underneath a late ordovician early silurian flysch sequence using principal component analysis geochemically definable components within related lithologie groups are 1 biogenic 2 mixed detrital 3 hydrothermal and 4 mn ca carbonate close sampling of the whole 350 m thick sequence provides reconstruction of variations among the sediment components through time at the base of the hematitic section a sharp increase in the hydrothermal component enrichment in mn fe ni pb and zn decreases stratigraphically upward and disappears in the upper red shoal arm formation the mn ca carbonate component also decreases upward but persists into the grey cherts indicating an additional source of mn the clastic component is largely mixed mafic pelagic clay like detritus with a strong pulse of zr nb and y rich

physicochemical conditions of sedimentation of the fish clay from stevns klint denmark and its detrital nature vanadium and other supportive evidence cretaceous tertiary k t boundary samples of the fish clay in denmark from three sites stevns klint nye klov and dania have been analyzed mineralogically and chemically all samples contain major amounts of biogenic calcite and smectite in some samples minor amounts of authigenic pyrite and siderite stevns klint and lepidocrocite dania are also present to obtain an indication of the chemical nature of the v present in the danish boundaries the samples were analysed for v and vanadyl vo2 at various stages of selective leaching the results obtained indicate that the bulk of v is associated with the smectite fractions 47 of total v all vo2 resides in the smectite portions from the chemistry of vo2 pyrite and carbonates it is deduced that the oxidation potential and ph of the interstitial seawater of the stevns klint boundary was approximately 0 0 to 0 2 v and 6 to 7 respectively during the accumulation of the lower black basal part but rose during the accumulation of the upper grey part the geochemical data do support the hypothesis that the danish boundary smectite represents weathered clay along with some asteroid and local material that was redeposited to the danish boundary sites after the k t event substantial proportions of the vo2 contents of the nye klov and dania smectite were probably already contained in the detrital clay arriving at the site of boundary sedimentation but at the stevns klint site they have been significantly augmented by uptake from the interfacial and interstitial seawaters through the humic substances involvement abundances and major mineralogical residences have been determined for trace metals cr ni co and ga and minor fe much of these elements is located in the boundary smectite structure as the corresponding ionic forms croh2 ni2 co2 ga3 and fe3 and is strictly detrital in character i e having been transported to the danish boundary sites already contained in smectite all these metals in the danish boundary smectite are well above normal abundances in clays

reply to comments on palynological evidence for the palaeocene evolution of the forearc basin indus suture zone ladakh india by peter clift

osmium isotopic variations in metalliferous sediments from the east pacific rise and the bauer basin the osmium concentration and isotopic composition of metalliferous sediments from the east pacific rise epr and bauer basin have been determined 187os186os ratios range from 7 9 to 8 6 with epr samples between 8 4 and 8 6 and bauer basin samples between 7 9 and 8 2 the osmium isotopic composition of epr samples is indistinguishable from the inferred osmium isotopic composition of seawater requiring that nearly all the osmium in these sediments is hydrogenous in origin this result is used to place broad constraints on the behavior of osmium in ridge crest hydrothermal systems while bauer basin samples also contain predominantly hydrogenous osmium an additional source of osmium with low 187os186os is required to account for the lower measured ratios calculation of total osmium burial fluxes in the bauer basin show that the background flux of cosmic osmium is adequate to produce the observed depression in bauer basin 187os186os ratios burial flux calculations also suggest that metalliferous sediment deposition is a significant sink in the marine osmium cycle

atypical ferromanganese nodules from pelagic areas of the central indian basin equatorial indian ocean abstract two box core samples one each from red clay and siliceous ooze sediment provinces from the central indian basin indian ocean were studied both cores contained ferromanganese nodules at their tops the red clay sediment also hosts buried nodules at a depth of 82 cm chemical characterization of the sediments indicates that early diagenetic remobilization of transitional metals is pronounced in the siliceous ooze sediment while in the red clay no such effect is discernible this is further corroborated by the abundance and dissolution patterns of microorganisms and ferromanganese micronodules occurring in the two sediment columns bulk chemical analyses indicate that all the nodules are of the hydrogenetic b type vernadite and todorokite are the major minerals both of which constitute laminated nondirectional colloform and cuspate microstructures petrographic studies yield evidence of recrystallization of todorokite and partial transformation of vernadite to todorokite the former process being more advanced in buried nodules microprobe analyses revealed that primary todorokite has a lower mn fe ratio and higher ni content than recrystallized todorokite in the same sample the mineralogical reconstitution in the nodules is attributed to postdepositional intranodule diagenesis the present study does not reveal the correlation between mineralogy and microstructure in the nodules which has been suggested for the nodules from the pacific neither can any mineral or microstructure be considered specific for any particular genetic model the studied nodules are therefore atypical the mineralogical and chemical reordering in these ferromanganese nodules raises the question of the viability of radiometric methods in determining growth rates of such nodules

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

sedimentary and geochemical evolution of the dras forearc basin indus suture ladakh himalaya india the nindam formation of the indus suture zone represents the forearc basin to the dras kohistan volcanic arc which was generated in an intraoceanic setting during mid cretaceous time and accreted to the margin of eurasia during late cretaceous time the nindam formation comprises volcaniclastic sediment and pelagic carbonate deposited in cyclic influxes of high density sheet like turbidites with locally well defined channel morphologies debris flow deposits as much as 5 m thick that rework older material are volumetrically 5 of the sequence a fine grained basal section is succeeded by several hundred meters of cyclic sandy turbidites and finally a more shaley top this large scale variation may be linked to tectonic controls on arc activity while individual sandy packages 50 100 m thick are inferred to have a glacioeustatic origin sedimentation mirrors similar patterns observed in the modern mariana and tonga forearcs the lack of major unconformities and large scale reworking suggests that the volcaniclastic sedimentary rocks should form a relatively complete record of geochemical change in the arc source the sediment trace and rare earth element ree signature is similar to that of the dras and chalt volcanic rocks erupted at the volcanic front during the intraoceanic phase of activity and is distinct from the kardung volcanic group erupted during the continental arc phase following collision with the eurasian margin nd isotopes also support an intraoceanic origin the sedimentary rocks show either no or slight light ree enrichment similar to modern sediments from the mariana arc as well as the volcanic and intrusive core of the dras kohistan arc the overall chemistry of the dras kohistan arc is thus more depleted in light ree than continental crust our data do not support models that propose continental crust being formed along intraoceanic active margins

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

zircon u pb geochronology and hf isotopic constraints on petrogenesis of the gangdese batholith southern tibet abstract during the mesozoic cenozoic northward neotethyan subduction and subsequent india asia collision gave rise to the extensive transhimalayan magmatism that stretches from burma and western yunnan through southern tibet to the ladakh and kohistan complexes to understand the age distribution and petrogenesis of the gangdese batholith the largest intrusive exposure along the transhimalayan magmatic belt fifty granitic samples were selected for in situ zircon u pb and hf isotopic analyses the u pb data suggest four discrete stages of magmatic activity i e 205 152 109 80 65 41 and 33 13 ma respectively with the 65 41 ma stage being the most prominent the hf isotopic data indicate that the gangdese batholith is overwhelmed by positive e hf t values which are comparable to those of the kohistan ladakh batholiths in the west but differ markedly from those of the chayu burma batholiths in the east most of the gangdese granites show similar and young hf model ages 1000 300 ma indicating their derivation from juvenile crust however those formed in the 65 41 ma stage exhibit more heterogeneous hf isotopic ratios with negative e hf t values being observed in some granites younger than 50 ma suggesting the involvement of old indian continental crust in their petrogenesis this age may thus mark the onset of the india asia collision the newly established zircon u pb age and hf isotope database of the gangdese batholith can be used as a powerful tracer or fingerprint when studying the source to sink relation of the sediments eroded from the southern tibetan plateau

formation of melanges in the indus suture zone ladakh himalaya by successive subduction related collisional and post collisional processes during late mesozoic late tertiary time

emplacement of the resurrection peninsula ophiolite in the southern alaska forearc during a ridge trench encounter the 57 1 ma resurrection peninsula ophiolite of southern alaska s chugach terrane formed in a near trench environment as the kula farallon ridge was being subducted beneath north america the magmatic sequence includes pillow lavas sheeted dikes gabbros trondhjemites and a poorly exposed ultramafic section the lavas show mid ocean ridge basalt and arc like geochemical signatures interpreted to reflect compositionally diverse melts derived from near fractional melting of a variably depleted mantle source mixed with variable amounts of assimilated continentally derived flysch a sedimentary sequence overlying the ophiolite here named the humpy cove formation of the orca group preserves a continuous 3 6 plusmn 1 4 ma record of turbidite sediments that were deposited on the ophiolite as it was transported to north america and emplaced in the chugach accretionary prism a transition from thinly bedded turbidites at the base of the section to thickly bedded turbidites is interpreted as a distal to proximal facies change recording the migration of the ophiolite toward the continent chemical trends vertically through the sedimentary sequence show an increasing biogenic component diluting terrigenous matter 950 m above ophiolitic basalt signaling a change to more favorable biologic conditions or increased preservation of biogenic matter with proximity to the continent hydrothermal metals are not resolvable in sediments interbedded with pillow lavas or in sediments above the ophiolite suggesting that they were diluted by turbidite sedimentation the top of the section is truncated by the fox island shear zone a 1 km thick greenschist facies west over east thrust related to the emplacement of the ophiolite into the accretionary wedge the fox island shear zone is intruded by a 53 4 0 9 ma granite showing that the ophiolite formed was transported to the north american continent overthrust by a major accretionary prism related thrust and intruded by granite all within 3 6 1 4 ma using these estimates for the timing of formation and emplacement of the ophiolite with palinspastic reconstructions and plate motion vector triangles we suggest that the resurrection peninsula ophiolite was transported up to 500 km 461 79 km relative to north america from the place of its formation at the kula farallon ridge prior to its emplacement into the north american margin since the best estimates of the amount of translation of the chugach terrane come from paleomagnetism of the resurrection peninsula ophiolite current estimates of margin parallel strike slip need to be reduced considerably

the scavenging of u 230th and 231pa during pulsed hydrothermal activity at 20 s east pacific rise abstract uranium th and pa isotopes were measured in eight box cores from two transects to the west of the east pacific rise at 10 s and 20 s sediment geochemistry al ca fe mn and water column paniculates mn suggest that highly metalliferous plumes rich in fe and mn are emanating from the rise crest at 19 s measurements of 230thxs and 231paxs indicate decreasing sediment accumulation rates from the rise flank 0 4 cm ky 1 to the tiki basin 0 23 cm ky 1 over this geographical area al is found to have a constant flux of 3 6 10 4 g cm 2 ky 1 application of an al constant flux model to ridge crest metalliferous sediment reveals two 1 000 year pulses of hydrothermal activity during the holoccne since 11 000 y bp these hydrothermal pulses are characterised by hydrothermal fe mn ratios 3 5 1 enhanced 230th and 231pa scavenging and low 230thxs 231paxs ratios 3 4 the similarity of the 230thxs and 231paxs ratio to the dissolved seawaterrauo suggests that in fracuonation of the isotopes occurs during scavenging supplementary supply of dissolved 230th and 231pa in a westwards moving water mass is suggested

sediments and micronodules in the northern and central peru basin the mineralogy and composition of sediments and manganese micronodules from the northern and central sectors of the peru basin are discussed because of the proximity of the basin to the carbonate compensation depth c c d surface sediments vary between calcareous oozes and siliceous muds besides biogenic components clay minerals are important by far the most abundant clay mineral is smectite which is thought to be of diagenetic origin on a carbonate free basis the surface sediments are rather uniform in composition throughout the basin and are similar in composition to those of the equatorial pacific sedimentation rates for the uppermost core sections are in the range of 3 to 5 mm 1000 yr

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

hydrothermal sediments record changes in deep water oxygen content in the se pacific the distribution of redox sensitive metals in sediments is potentially a proxy for past ocean ventilation and productivity but deconvolving these two major controls has proved difficult to date here we present a 740 kyr long record of trace element concentrations from an archived sediment core collected at 15 s on the western flank of the east pacific rise epr on 1 1 myr old crust and underlying the largest known hydrothermal plume in the world ocean the downcore trace element distribution is controlled by a variable diagenetic overprint of the inferred primary hydrothermal plume input two main diagenetic processes are operating at this site redox cycling of transition metals and ferrihydrite to goethite transition during aging the depth of oxidation in these sediments is controlled by fluctuations in the relative balance of bottom water oxygen and electron donor input organic matter and hydrothermal sulfides these fluctuations induce apparent variations in the accumulation of redox sensitive species with time subsurface u and p peaks in glacial age sediments in this and other published data sets along the southern epr indicate that basin wide changes in deep ocean ventilation in particular at glacial interglacial terminations ii iii iv and v alter the depth of the oxidation front in the sediments these basin wide changes in the deep pacific have significant implications for carbon partitioning in the ocean atmosphere system and the distribution of redox sensitive metals in ridge crest sediment can be used to reconstruct past ocean conditions at abyssal depths in the absence of alternative proxy records

the hydrothermal component in ferromanganese nodules from the southeast pacific ocean abstract statistical analyses of geochemical data from ferromanganese nodule samples representing a broad area of the southeast pacific ocean indicate nodule compositions are controlled by four factors 1 suboxic diagenesis 2 oxic diagenesis 3 hydrogenous precipitation and 4 hydrothermal precipitation the first three are identical to those identified in studies of nodules from the north pacific the fourth factor represents the first quantitative determination of a significant hydrothermal end member in ferromanganese nodules nodules apparently acquire a hydrothermal component through the accretion of colloidal sized hydrothermal precipitates which are widely dispersed from their origin at vents along the east pacific rise epr nodules recovered from beneath the shadow of the present day hydrothermal plumes emanating from the epr contain significantly higher amounts of hydrothermal material relative to nodules from other areas

mineral chemistry and k ar ages of plutons across the karakoram fault in the shyok nubra confluence of northern ladakh himalaya india abstract petrographic analyses of plutons across the karakoram fault in the shyok nubra confluence of northern ladakh area revealed that the rocks consist of diorite granodiorite granite and leucogranite pyroxene and biotite chemistries by epma indicate that most of the diorite granodiorite and granite are calc alkaline and formed in an arc related tectonic setting these calc alkaline plutons yield k ar biotite ages from 49 3 1 1 to 51 2 1 1 for ladakh batholith in khardung la and from 60 8 1 3 to 65 8 1 4 ma for granites and diorites in hundar area the k ar ages of the hundar igneous complex are within the age range of 46 70 ma of the ladakh batholith near leh town and the neighbor sites indicating the hundar igneous complex as a part of the ladakh arc their ages are also coincident with the khardung volcanics 67 4 and 60 5 ma the calc alkaline granites from panamik of karakoram block yield k ar biotite ages of 95 7 2 1 and 96 7 2 1 ma suggesting that the granites are member of the plutons 90 120 ma occurring in northern pakistan tangtse in ladakh and western tibet that emplaced during subduction of the neo tethyan oceanic plate under the karakoram block the leucogranite and granodiorite in the panamik region yield k ar biotite and muscovite ages ranging from 9 18 0 21 to 9 45 0 21 ma the leucogranites are the s type related to post collision tectonic setting and are considered to have emplaced in relating to activation of the karakoram fault

volcanic and hydrothermal history of ridge segments near the rodrigues triple junction central indian ocean deduced from sediment geochemistry abstract sediments from the central indian ridge cir and southeast indian ridge seir near the rodrigues triple junction rtj were investigated in order to relate the accumulation rates of sediment components to the volcanic and hydrothermal history of the respective ridge segments the sediments contain 50 90 biogenic carbonates and have been deposited over at least the last 2 5 myr without large hiatuses since there is no early diagenetic element mobilization the main primary geochemical signals are preserved in the sediments a three step multivariate analysis of carbonate free geochemical data showed that the sediments consist of two main endmembers with respect to si ti al fe mg k mn cu ni and zn which are mixed in different ratios in the samples the first endmember comprises volcanic detrital components mainly basalt fragments basaltic glass and their weathering products smectites the second endmember is made up of hydrothermal fe mn oxides the volcanic detritus is distributed via bottom currents the fe mn oxides are formed as particle fallout from hydrothermal plumes the first component dominates in the rift valley the second on the ridge flanks along the seir varying accumulation rates were found to reflect the cyclic magmatic volcanic activity of the intermediate spreading rift axis in cores from the cir the accumulation of both endmembers reflects the evolution of a non transform fault separating the first and second cir segments rather than the spreading axis history