remobilization events involving cd and zn from intertidal flat sediments in the elbe estuary during the tidal cycle in laboratory experiments the effect of periodic alternations between aerobic and anaerobic conditions on the mobilization of zn and cd from the surface layers of an intertidal sand and mud flat sediment was studied a percolation technique was used to simulate submersion and exposure to the air by controlling the concentrations of oxygen and nitrate within undisturbed 2 cm sediment layers zn and cd released from the sediment were removed from the pore water under anerobic conditions and maintained in the percolating water when aerobic conditions were established zn was mobilized immediately after re oxidation whereas cd mobilization was observed after a retention time of 53 to 180 min and 25 72 h in sand and mud flat sediments respectively from 0 3 to 1 8 of the total cd was then lost from these sediments the rates of particulate organic matter degradation calculated from the production of co 2 under aerobic and anaerobic conditions were similar the ph values in sand flat sediments used in the experiments were significantly higher than in mud flat sediments neither the rates of organic matter mineralization nor the variations in ph controlled the observed trace metal mobility the results strongly indicate that trace metals were precipitated as sulphides under anaerobic conditions the release of trace metals under aerobic conditions was attributed to the oxidation of sulphides and the mineralization of organic matter in the surface layer of the mud flat the rate of zn mobilization reached 8 79 10 7 mol g 1 s 1 in summer but was only 1 82 10 7 mol g 1 s 1 in winter cd was released from the same layer during the whole year at a constant rate of 5 89 10 9 mol g 1 s 1 calculations based on the percolation experiments indicate that in mud flat sediments from the elbe estuary a loss of up to 50 of the total cd occurs within one month

omission surface incipient phosphate crusts on early diagenetic calcareous concretions and their possible origin upper campanian southern israel abstract flattened calcareous concretions enveloped by a 2 4 mm thick phosphate bearing crust occur in a single level in the lower part of the phosphorite unit upper part of mishash formation in nahal zinim southern israel negev the crust is associated with various ichnofossils penetrating an originally incompletely lithified surficial zone at the periphery of the hardened part of the concretions in thin section the phosphate fraction appears structureless scanning and backscattered electron microscopy shows that this fraction occurs as walls and envelopes of polyhedral cell like units of about 5 m in diameter these structures are interpreted as synsedimentary phosphate coated possible remnants of chasmolithic and epilithic colonial unicells which colonized the pre hardened surficial zone around the concretions during exposure on the sea floor this thin microbially constructed phosphate coat is believed to be an incipient equivalent of more intensely developed phosphate crusts on many omission surfaces in the geological record

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

development of forearcs of intraoceanic subduction zones the uplifted costa rican forearc landward of the middle america trench and the mariana forearc drilled on ipod leg 60 both lack the thick clastic sequences complex deformation and abundant evidence of accretion which characterize more widely known forearcs that border continents both regions contain significant in situ accumulations of pelagic and hemipelagic sediments in place of thick trench and trench slope basin sequences composed of terrigenous turbidites the nicoya peninsula of costa rica contains no significant melange terranes deformation of the mafic igneous basement and its thin cover of pelagic hemipelagic and first cycle volcanogenic material is mild overall with discrete zones of intense deformation disrupting otherwise well preserved stratigraphic sections intraoceanic subduction zones lacking longitudinal trench feed are sites of little or no accretion of sediments and recently suggested experimental and theoretical models of subduction zone processes involving flow melanges are inappropriate for intraoceanic forearcs intraoceanic forearcs generally lack high grade exotic components such as blueschist and eclogite tectonically incorporated as blocks in lower grade matrix although uplift and erosion of the forearc basement may provide detritus of amphibolite and ultramafic rock to the trench and trench slope

the niujiaotang cd rich zinc deposit duyun guizhou province southwest china ore genesis and mechanisms of cadmium concentration the niujiaotang zinc deposit in southeastern guizhou china is a mississippi valley type zn deposit within early cambrian carbonate rocks sphalerite is enriched in cadmium average 1 4 wt cd which occurs mostly as isomorphous impurities in the sphalerite lattice discrete cadmium minerals greenockite and otavite are rare and are found almost exclusively in the oxidation zone of the deposit probably formed as secondary minerals during weathering leaching processes geochemical data show that the sulfides are enriched in heavy sulfur with 34s ranging from 10 0 to 32 8 mean 22 5 the consistent pb isotopic compositions in different sulfide minerals are similar to that of cambrian strata the ore lead probably came from u and th rich upper crustal rocks such as the lower cambrian wuxun formation the ore fluid is of low temperature 101 c to 142 c type with a na ca mg cl dominant composition and is interpreted as oil field brine the data indicate that the metals were mainly derived from the early cambrian strata qingxudong and wuxun formations whereas sulfur is sourced from sulfate in cambrian strata or oil field brines of the majiang petroleum paleoreservoir the genetic model for the deposit invokes an early cambrian shallow sea environment on the yangtze platform zinc and cd in seawater were concentrated in abundant algae via unknown biological mechanisms resulting in large amounts of zn and cd rich algal ooliths during the ordovician concurrent with destruction of the majiang petroleum paleoreservoir oil field brines migrated from the center of the basin to the margin leaching metals from the cambrian strata in the niujiaotang area preexisting zn and cd particularly in the qingxudong and wuxun formation were further mobilized by hot brines rising along the zaolou fault system forming stratiform and generally conformable zn cd orebodies in reactive carbonate lithologies

volcanic shards from santorini upper minoan ash in the nile delta egypt one of the largest volcanic outbursts recorded in early human history is the cataclysmic eruption of santorini thera which occurred about 35 centuries ago in the southern aegean sea this explosive event termed upper minoan or upper thera produced a tephra fall believed by archaeologists and volcanologists to have been widespread in the eastern mediterranean1 4 upper minoan ash has been found on land in the aegean and hellenic arc regions including crete5 6 and rhodes7 to date however there has been no confirmed observation of this ash on land across the mediterranean in north africa we now report evidence for the presence of ash ejected from this explosion in sediment cores recovered in the eastern nile delta of egypt this discovery of upper minoan glass shards extends considerably the zone of confirmed ash fall to the southeast of santorini and serves as evidence of a major natural phenomenon affecting egypt during the reign of pharaohs in the eighteenth dynasty it is quite possible that this ash fall event may have given rise to texts pertaining to darkening of the sky and veiling of the sun in early historic records

anoxic vs dysoxic events reflected in sediment geochemistry during the cenomanian turonian boundary event cretaceous in the umbria marche basin of central italy abstract one of the most spectacular expressions of global oceanic anoxic events oaes of the cretaceous is the livello bonarelli of central italy deposited during the cenomanian turonian boundary event ctbe or oae2 at around 93 5 ma at furlo in the umbria marche basin in italy the bonarelli consists of approximately 1 m of c org rich shales interbedded with radiolarian rich layers and contrasts sharply with the extensive over and underlying siliceous limestones several minor c org rich intervals herein termed black levels average thickness 4 5 cm are interbedded within the scaglia bianca beneath the bonarelli x ray fluorescence and icp ms analyses show that these sediments consist of different mixing systems with three end members 1 sio 2 caco 3 scaglia bianca 2 average shale caco 3 black levels and 3 average shale sio 2 bonarelli given the sharp lithologic contacts and the little geochemical mixing between the groups these are thought to represent rapid switching events between sedimentary modes major element concentrations are generally low except for si and p owing to dilution by silica up to 96 and carbonates as al normalised ratios for elements such as ti or zr taken as proxies for higher energy environments are close to average shale values excess sio 2 is most likely linked to biogenic processes rather than quartz element al ratios of ti mg k rb and zr are fairly constant pointing to a mostly homogeneous source area the black levels and bonarelli are characterised by lower mg al ratios compared to the scaglia bianca sediments suggesting variability in chlorite input which could be linked with short term sea level drops indicated by ti al ratios the bonarelli sediments are severely depleted in mn which is indicative of oxygen depleted bottom water conditions and an open marine environment while the black levels appear to have been deposited in a much more restricted setting a model involving partial physical isolation of the furlo site by a sill coupled to omz variations by extra basinal forcing mechanisms is proposed to account for these conflicting data based on re mo ratios the bonarelli sediments were deposited under varying oxygen depletion levels from suboxic to anoxic while re mo ratios in the black levels show deposition under less oxygen deficient conditions most minor elements many of them redox sensitive or sulphide residing are strongly enriched in the c org rich sediments further documenting the absence of oxygen and potential availability of hydrogen sulphide in the water column at times while high zn concentrations suggest elevated submarine hydrothermal activity during this time interval ba is also present in very high concentrations up to 1 4 with an average weighed concentration of 0 6 for the entire bonarelli and is probably indicative of high paleoproductivity in this area this is further supported by high p concentrations hinting at nutrient availability at this site

intermediate members of the lime monteponite solid solutions ca1 xcdxo x 0 36 0 55 discovery in natural occurrence lime monteponite solid solutions ca cd o ss with 58 5 73 3 wt cdo were discovered as an accessory phase in medium temperature combustion metamorphic cm spurrite fluorellestadite fluorapatite marbles from central jordan the type locality is situated in the northern part of the siwaqa complex tulul al hammam area the largest area of the mottled zone formation in the dead sea region the marbles were derived from bitumen rich calcareous marine sediments of the muwaqqar chalk marl formation which have high cd zn u and ni enrichments and contain cd rich wurtzite and sphalerite oxidative sintering of these sediments at 800 850 c gave rise to unusual oxide accessories lime monteponite solid solutions cd bearing ca and zn aluminate tululite zincite and zn ni and cu rich periclase cadmium incorporation into different oxides was controlled by steric factors while cd 6 ca 6 was the principal isomorphic substitution the intermediate members ca 0 645 cd 0 355 o ca 0 453 cd 0 547 o with a halite type structure have a cadmium incorporation ratio k cd cd mineral cd rock of about 843 and are the main sites for cadmium in cm marbles in supergene environments at low water rock ratios ca 1 x cd x oh 2 ss x 0 5 constitute the main secondary phase after ca cd o ss at higher water rock ratios and in the presence of cl and f in the solutions calcium and cadmium precipitated as separate phases fluorite caf 2 and basic cadmium chloride cd oh 2 x cl x a part of cadmium becomes retained in calcium silicate hydrates the common occurrence of anhydrous ca cd o grains in natural rocks only partly altered to ca cd hydroxide after at least 100 ka exposure to weather and climate proves that both phases are effective long term cd immobilizers

depositional sequences of the duwi sibâiya and phosphate formations egypt phosphogenesis and glauconitization in a late cretaceous epeiric sea

the inorganic geochemistry of cretaceous black shales dsdp leg 41 in comparison to modern upwelling sediments from the gulf of california

global tectonic significance of the solomon islands and ontong java plateau convergent zone abstract oceanic plateaus areas of anomalously thick oceanic crust cover about 3 of the earth s seafloor and are thought to mark the surface location of mantle plume heads hotspot tracks represent continuing magmatism associated with the remaining plume conduit or tail it is presently controversial whether voluminous and mafic oceanic plateau lithosphere is eventually accreted at subduction zones and therefore 1 influences the eventual composition of continental crust and 2 is responsible for significantly higher rates of continental growth than growth only by accretion of island arcs the ontong java plateau ojp of the southwestern pacific ocean is the largest and thickest oceanic plateau on earth and the largest plateau currently converging on an island arc solomon islands for this reason this convergent zone is a key area for understanding the fate of large and thick plateaus on reaching subduction zones this volume consists of a series of four papers that summarize the results of joint us japan marine geophysical studies in 1995 and 1998 of the solomon islands ontong java plateau convergent zone marine geophysical data include single and multi channel seismic reflection ocean bottom seismometer obs refraction gravity magnetic sidescan sonar and earthquake studies objectives of this introductory paper include 1 review of the significance of oceanic plateaus as potential contributors to continental crust 2 review of the current theories on the fate of oceanic plateaus at subduction zones 3 establish the present day and neogene tectonic setting of the solomon islands ontong java plateau convergent zone 4 discuss the controversial sequence and timing of tectonic events surrounding ontong java plateau solomon arc convergence 5 present a series of tectonic reconstructions for the period 20 ma early miocene to the present day in support of our proposed timing of major tectonic events affecting the ontong java plateau solomon islands convergent zone and 6 compare the structural and deformational pattern observed in the solomon islands to ancient oceanic plateaus preserved in precambrian and phanerozoic orogenic belts our main conclusion of this study is that 80 of the crustal thickness of the ontong java plateau is subducted beneath the solomon island arc only the uppermost basaltic and sedimentary part of the crust 7 km is preserved on the overriding plate by subduction accretion processes this observation is consistent with the observed imbricate structural style of plateaus and seamount chains preserved in both precambrian and phanerozoic orogenic belts

crustal strain phenomena in the solomon islands constraints from field evidence and relationship to the india pacific plates boundary abstract the solomon islands lie along the india pacific plates margin and have recorded a history of deformation resulting from the interaction of these two plates various kinematic models have been proposed for the solomons and these have involved a variety of plate tectonic processes it is pointed out that almost without exception these models have been based on a provincial geological classification of the island group in which it is assumed that two of these provinces pacific and central provinces commenced their geological development in regions distant from one another invariably such models require that santa isabel represents part of a collision zone between these two provinces though field evidence from santa isabel for such a collision has in the past been largely lacking these various kinematic models are examined in the light of more recent field evidence and a premise on which they have been based initial separate development for two of the provinces is questioned rather it is here suggested that the central and pacific provinces developed in roughly similar positions one with the other as they occur today and that they were at least in part separated from oligocene time onward by a linear peridotite gabbro ridge korighole florida high which acted as a sediment barrier to much of the coarser clastic and volcanogenic sedimentation the initial development of the solomon islands began in an oceanic environment with the extrusion of extensive submarine tholeiitic flood basalts and intrusion of associated gabbroic and ultramafic rocks at depth during the late mesozoic to early tertiary this igneous phase occurred with the whole of the island group representing the western margin of the ontong java plateau subsequent asymmetric development of the solomons during the eocene and oligocene resulted in uplift shearing and the initiation of arc volcanism plutonism and arc related sedimentation in the central province to the west in contrast through much of the tertiary the pacific province to the east continued to receive dominantly pelagic sediments before undergoing uplift and renewed deformation in the pliocene the recognition that the ophiolite crust in the solomon islands represents an autochthonous entity which has acted as basement to subsequent arc volcanism has significant implications on geochemical studies of these islands now being undertaken

polarity reversal in the solomon islands arc mckenzie1 proposed that the direction of subduction beneath an island arc will reverse following arc continent collision dewey and bird2 suggested that such an arc polarity reversal occurred in northern new guinea johnson and molnar3 however proposed two alternative models of plate convergence that could explain the observed seismicity we present here a spatial seismicity study of the solomon islands region which has revealed the existence of two juxtaposed wadati benioff w b zones of opposite polarity shallow and intermediate foci define a north east dipping w b zone associated with active subduction along the new britain and san cristobal trenches and a south west dipping w b zone associated with the inactive north solomon trench nst these data provide the first direct seismic evidence of a reversal in subduction polarity at an island arc

geochemical changes in the early cambrian interval of the yangtze platform south china implications for hydrothermal influences and paleocean redox conditions abstract the possible triggering mechanisms of the ediacaran cambrian transition in south china have been debated for many years in this study 80 samples from liuchapo niutitang and mingxinsi formations were collected from well yk 1 located in southeastern chongqing a high resolution chemostratigraphic study including evaluation of rare earth elements rees and trace elements was used to elucidate the paleoenvironments of the upper yangtze platform margin the mingxinsi gray shale and the liuchapo formation exhibit flat post archean australian normalized ree patterns with weakly negative ce anomalies which is typical of detritus obvious positive eu anomalies in chert samples of the basal niutitang formation imply a short term influence of hydrothermal fluid the ree patterns of the basal niutitang phosphatic rocks show significant enrichment of heavy rees significantly negative ce anomalies and positive y anomalies similar to the ree distribution pattern in seawater demonstrating that these sediments were produced under oxic seawater conditions moderately positive eu anomalies and positive y anomalies of the lower niutitang shales may indicate mixing of hydrothermal fluids and seawater the flat ree patterns with weak eu anomalies of the upper niutitang shale may have been generated by hydrothermal inputs diluted by detrital materials dramatic increases of ce anomalies in the basal niutitang formation reveal a significant decrease of the oxygen level in seawater trace elements such as ba u v u cu cr zn ni and sr are commonly enriched in these formations compared to the upper continental crust authigenic abundances of al normalized u and al normalized v as well as ratios of th u and v sc are used as indicators of redox conditions these distributions demonstrate that the redox conditions of the bottom water during the ediacaran cambrian transition abruptly changed from oxic in the nemakit daldynian age to anoxic in the early tommotian age and gradually became less reducing in the late tommotian age and the atdabanian age a strong correlation between total organic carbon toc concentrations and ratios of u al and v al in the entire section except in the phosphatic rocks implies non sulfidic conditions most trace elements cannot be used as proxies for redox conditions associated with the phosphatic rocks in the basal niutitang formation because abundant trace elements were especially absorbed in apatite the toc concentrations correlated well with the redox conditions of bottom water we infer that the section deposited in the platform margin was influenced by episodic hydrothermal activities that began at the beginning of the tommotian age and these activities may have terminated at the beginning of the atdabanian age enrichments of organic matter that were mainly derived from the photic zone were controlled by the redox conditions of the bottom water

widespread coastal upwelling along the eastern paleo tethys margin south china during the middle permian guadalupian implications for organic matter accumulation abstract guadalupian organic rich depositions within the eastern paleo tethys margin have been attributed to coastal upwelling but the idea has not been tested here a suite of geochemical proxies from the gufeng formation of the lower yangtze region south china are used to investigate the formation mechanisms of organic matter accumulation a high organic carbon content and similar enrichments of bio redox sensitive trace metals show strong similarities to the geochemical characteristics of modern upwelling sediments the use of high cd mo ratios and low co x mn values characteristic of modern upwelling settings sweere et al 2016 is replicated in the gufeng strata implying that lower yangtze area was dominated by persistent upwelling that become less intense seasonal later in the guadalupian application of these new geochemical proxies shows that the characteristics of modern upwelling systems such as the formation of an intense oxygen minimum zone omz can be confirmed in the ancient calculation estimates show that primary productivity was sustained at moderate to high levels and was at comparable levels to those of the modern peru upwelling system omz related anoxic conditions with transient euxinic episodes dominated permanently during the deposition of the gufeng formation and then became more intense conditions euxinia later in the guadalupian the radiolarian chert siliceous mudstone rhythms that coincide with fluctuations in major elements organic carbon total sulfur and trace metal concentrations may reflect dilution by biogenic silica chert zr al ratios are also higher than in mudstone suggesting the cherts may record more winnowed deposition at the margin of an ancient omz compared with a location within the omz for the mudstone the organic matter accumulation of the middle permian gufeng formation may be mainly controlled by the upwelling driven primary productivity and also influenced by the changes of anoxic euxinic conditions and the dilution of biogenic silica

breakup of young oceanic lithosphere in the upper part of a subduction zone implications for the emplacement of ophiolites it is investigated by means of numerical modelling whether the interaction between young oceanic lithosphere and a subduction zone can lead to the breakup of a young and thin oceanic plate first a thermal model of the upper part of a subduction zone the region between the trench and the volcanic arc is presented temperatures are modelled for situations in which the age of the subducting oceanic lithosphere gradually decreases culminating in the arrival of a spreading ridge at the trench temperatures are used to infer the strength of material within the subducting plate from a pressure and temperature dependent rheology next it is investigated by means of finite element modelling whether the forces acting upon young subducting oceanic lithosphere recently created at a spreading center in the vicinity of a subduction zone can lead to its breakup our modelling results show that very young oceanic lithosphere may indeed break up during the early phase of its subduction whether breakup occurs depends upon the spreading velocity and the length of the ridge segment that interacts with the trench if breakup occurs some young oceanic lithosphere situated in the upper part of the subduction zone and in the region between the ridge and the trench will be detached from the other parts of the subducting plate the detached sheet of thin oceanic lithosphere will not be subducted to mantle depths instead subduction of the trailing plate at the opposite side of the ridge can lead to the incorporation of this sheet into the forearc region our modelling provides a mechanism to incorporate thin oceanic lithosphere into an arc trench region and eventually upon closure of the ocean basin into an orogenic belt it is shown that a large subset of ophiolites those with a harzburgite dominated mantle section has properties in good agreement with an emplacement history in which the breakup of young oceanic lithosphere in the upper part of a subduction zone is the first phase

immobility of 210pb in black sea sediments we measured 210pb in a core from the deep black sea which contained a turbidite of low 210pb activity surrounded above and below by pelagic sediments of much higher activity to evaluate in situ210pb mobility under the anoxic moderately sulfidic conditions by measuring at millimeter scales across the distinct laminae turbidite contacts and modeling the observed profile we estimated a lower limit of the kd of 107 deff 5 10 13 this result increases confidence in sediment chronologies from the black sea based on 210pb because it implies that profiles will not be altered significantly by diffusive transport of 210pb below the turbidite the 210pb inferred accumulation rate was 50 g m2 a which is lower than laminae based estimates by a factor of 3 4

primary bedded phosphorites in the campanian mishash formation negev southern israel abstract thin lentiform beds up to 1 cm thick of primary non pelletal phosphate have been found sporadically in the highly condensed anticlinal sections of the late campanian mishash formation of the central negev southern israel these primary phosphate beds are typically associated with iron rich montmorillonites of probable authigenic origin and occur at the top of upward fining phosphate dominated sequences the clay rich and primary phosphate levels are commonly truncated by amalgamated beds of high energy coarse grained phosphorites which form the basal part of these sequences with ripped up clasts of the primary phosphate commonly re incorporated in these rocks sem eds study of both the primary phosphate levels and the reworked phosphate clasts shows that they are built by a crudely stratified network of closely packed and gently compressed capsule like phosphate cells 2 5 m in external diameter and with walls of 0 5 m thick these structures are interpreted as being the synsedimentarily phosphatized remnants of former mat forming coccoid prokaryotes now represented as extracellular envelopes which intermittently colonized the mishash sea bottoms at the end of the high energy episodes differential degradation of the periphytic mat community possibly coupled with fe p redox cycling across the surficial mat iron was trapped as iron rich montmorillonites in the anoxic zone below the living mat probably resulted in an excess of dissolved phosphate immobilized as solid phases on decay resistant microbial remains which escaped total degradation development of the mat forming microbes on the mishash bottoms and their mineralization to form primary phosphorite beds occurred during periods of halted deposition which resulted in a high residence time of the mat on the seafloor and hence in intensified interface linked biogeochemical reactions ending in phosphate precipitation the restriction of primary phosphate occurrences to the condensed mishash sections of marginal palaeohigh positions strengthens previous assumptions that these zones were probably the main locus of mishash phosphate production it also points to a phosphate grain supply from marginal to basinal sites leading to the accumulation of pelletal phosphorites in the latter areas

geochemical diagenetic trends during phosphorite formation economic implications the case of the negev campanian phosphorites southern israel research on the upper campanian upper cretaceous negev phosphorites mishash formation based on microprobe analyses fourier transform infrared spectroscopy wet chemistry microtextural scanning electron microscopy studies and mineralogical analyses together with quantified rates of sedimentation and p accumulation enables the chemistry of these rocks to be better constrained across the negev area and allows their suitability for the manufacture of p fertilizers to be better determined two phosphorite facies are differentiated i a pristine phosphorite facies of low p content more typical of basinal sections and ii a reworked granular phosphorite facies commonly enriched in p found predominantly near palaeo highs and forming most of the economic phosphates the distribution of f p2o5 co2 f u iv cd zn and other trace metals mo ni cr cu v and y rare earth elements concentration ce and eu anomalies and heavy rare earth elements enrichment are controlled by these two facies f p2o5 in carbonate fluorapatite is much lower 0 090 to 0 107 in the pristine than in the reworked facies 0 107 to 0 120 in addition the lower f p2o5 in the pristine facies is coupled with i higher cd zn mo ni cr cu and v concentrations ii a considerably reduced 10 u iv fraction of total u iii lower rare earth elements p2o5 and y p2o5 ratios iv less negative ce and eu anomalies and lower heavy rare earth elements lu la enrichment v an increase in fe rich smectites in the clay fraction and vi presence of oh in the carbonate fluorapatite structure sedimentary reworking of previously formed pristine phosphate together with its redeposition near structural highs in more oxic bottom conditions results in considerable diagenetic changes in the chemistry of the phosphorites making them more suitable for economic exploitation the results presented here provide geochemical criteria for identifying pristine phosphate in other phosphorite sequences and may help to better locate phosphate strata chemically suitable for the phosphate industry elsewhere

arc segmentation and seismicity in the solomon islands arc sw pacific abstract this paper evaluates neotectonic segmentation in the solomon islands forearc and considers how it relates to regional tectonic evolution and the extent of ruptures of large megathrust earthquakes we first consider regional geomorphology and quaternary vertical displacements especially uplifted coral reef terraces then we consider geographic seismicity patterns aftershock areas and vertical displacements for large earthquakes focal mechanisms and along arc variations in seismic moment release to evaluate the relationship between neotectonically defined segments and seismicity notably one major limitation of using seismicity to evaluate arc segmentation is the matter of accurately defining earthquake rupture zones for example shoreline uplifts associated with the 1 april 2007 mw 8 1 western solomons earthquake indicate that the along arc extent of rupture was about 50 km smaller than the aftershock area thus if we had relied on aftershocks alone to identify the 2007 rupture zone as we do for most historical earthquakes we would have missed the rupture s relationship to a major morphologic feature in many cases the imprecision of defining rupture zones without surface deformation data may be largely responsible for the poor mismatches to neotectonic boundaries however when a precise paleoseismic vertical deformation history is absent aftershocks are often the best available tool for inferring rupture geometries altogether we identify 16 segments in the solomon islands these comprise three major tectonic regimes or supersegments that correspond respectively to the forearc areas of guadalcanal makira the new georgia island group and bougainville islands subduction of the young and relatively shallow and buoyant woodlark basin and spreading system distinguishes the central new georgia supersegment from the two neighboring supersegments the physiographic expression of the san cristobal trench is largely absent but bathymetric mapping of the surface trace of the interplate thrust zone defines it adequately the new georgia supersegment has smaller arc segments and more islands due to general late quaternary forearc uplift very close to the trench where vertical displacement rates tend to be faster prior to the 2007 earthquake it had much lower rates of seismic activity than the neighboring supersegments generally the mean along arc lateral extent of solomon arc segments is about 75 km somewhat smaller than the segments reported in some other island arcs such as japan 100 260 km but larger than those of the tonga 30 80 km and central new hebrides arcs 30 110 km these differences may be real but it may occur simply because the coral friendly tropical environment of the south pacific arcs numerous emerged forearc islands and high seismicity rates provide an unusually favorable situation for observing variations in vertical tectonic activity and thus for identifying segment boundaries over the past century seismic slip in the solomons as indicated by seismic moment release has corresponded to about half the plate convergence rate however there are notable variations along the arc even with the 2007 earthquake the long term moment release rate in the new georgia supersegment is relatively low and this may indicate that large earthquakes are imminent

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

submarine evidence of a debris avalanche deposit on the eastern slope of santorini volcano greece abstract hummocky seafloor features were discovered on the eastern flank of santorini volcano greece multibeam bathymetric mapping airgun seismic profiling side scan sonar survey and remotely operated vehicle rov dives have been carried out to characterize the nature of the hummocks these hummocks appear to be composed of several tens of blocks that are up to several hundred meters in diameter and are the surface expression of a much larger deposit than is observed in the bathymetry the sidescan and airgun data show that the deposit covers an area of approximately 6 km wide by 20 km long and is up to 75 m thick we estimate the total volume of the deposit to be approximately 4 4 10 9 m 3 sampling of these blocks show they are composed of pyroclastic flow deposits produced during the minoan eruption of santorini ca 3600 bp we propose that the deposit is the result of a multi stage landslide event that was caused by one of the several large earthquakes or volcanic eruptions that have occurred in the vicinity of santorini since the minoan eruption one or more of these events likely triggered the destabilization of a part of the eastern flank of santorini which led to a debris avalanche depositing blocks and forming a hummocky terrain at the base of the island s slope the mass movement later evolved into a turbulent suspension flow that traveled 20 km or more from the presumed initial failure given the size of the landslide deposit it might have a tsunami potentially affecting the islands across the southern aegean sea the understanding of earthquake landslide dynamics has important implications for hazard assessment in this seismically active historical and highly populated region of the world

tephra from the minoan eruption of santorini in sediments of the black sea the explosive eruption of santorini volcano in the aegean sea about 3 300 years ago is of considerable archaeological and volcanological significance1 5 here we report the discovery of tephra from this minoan event in laminated sediments of the black sea this finding provides constraints on the distribution of debris from the eruption we estimate a minimum fallout area of 2 l06 km2 extending from the black sea in the north to the southeastern mediterranean sea the main dispersal axis trends through southern turkey in agreement with other studies of minoan tephra6 7 the tephra deposits should provide a useful reference horizon for assessing the chronology of black sea sediments which has been much debated8 15

iunconsistencies in accumulation rates of black sea sediments inferred from records of laminae and 210pb recently published estimates for the age of the unit 1 unit 2 contact in black sea sediments based on accelerator mass spectrometry ams 14c measurements jones 1990 calvert et al 1991 appear to be older than those based on the previously published chronology based on lamina couplets degens et al 1980 hay 1988 by a factor of 2 to 3 to help reconcile the differences we compare sediment accumulation rates based on the 210pb method with estimates based on lamina counts for two cores from the black sea abyssal plain accumulation rates estimated using the 210pb technique have varied little over the last 150 years from the averages of 55 and 50 g m 2 yr 1 at stations in the western and eastern basins respectively these values are about a factor of 2 lower than accumulation rates derived by counting lamina couplets over the dated intervals close examination of the laminae suggests that the discrepancy exists both because it is difficult to count the very fine laminae and because a complete couplet is not deposited every year in order to provide a useful stratigraphic horizon for future investigators studying sedimentary records of the black sea we estimate the age of a distinct black marker horizon which can be easily identified across the entire abyssal plain to be 150 8 years deposited in 1838 8 a d

antarctic bottom water formation and the global cadmium to phosphorus relationship near surface waters close to the antarctic continent are found to have high cadmium concentrations with respect to phosphorus these waters have been shown to be the major component in the local formation of antarctic bottom water in this region it is demonstrated that antarctic bottom water so formed would have a high preformed cadmium to phosphorus ratio the ventilation of the abyssal ocean with this water would contribute to the observed kink in the global cadmium to phosphorus relationship this is an important conclusion for paleochemical studies and may account for part of the discrepancy between cadmium and carbon 13 paleochemical tracers observed in the southern ocean

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

early cambrian ocean mixing recorded by phosphorite successions in the nanhua basin south china abstract phosphorite successions in the nearshore meishucun section and the offshore gezhongwu section of the nanhua basin south china were investigated to decipher the circulation pattern of the early cambrian ocean the 539 535 ma phosphorites from the meishucun section contain authigenic phosphorus rich mineral aggregates collophanite grains with much lower bio limiting elements zn cd and ni than those from the gezhongwu section in contrast collophanite grains in the 535 526 ma phosphorites from both sections have similar concentrations of these elements this change indicates that the ocean likely transformed from a chemically stratified state to a homogeneous state at 535 ma phosphorites from both sections have constant 87sr 86sr ratios and end t values supporting the interpretation of a relatively constant terrestrial input into the nanhua basin between 539 ma and 526 ma instead negative 13c excursions and similar 208pb 204pb ratios of the 535 526 ma phosphorites are indicative of an extensive upwelling of the deep oceanic water in combination with previous studies of deep ocean oxygenation our work provides evidence for the vertical mixing of the ocean between 535 ma and 526 ma which introduced o2 rich water at the ocean bottom to promote early cambrian biodiversity

a simple evolutionary model for water and salt in the black sea this paper presents a time dependent variable size box model for the total fluid and salinity balances of the black sea in addition to the advective flows due to riverine and mediterranean inputs of water the model accounts for entrainment flows which are parameterized using the theory of ellison and turner 1959 and employs a modified version of the gargett 1984 formulation for eddy diffusivity in describing cross pycnocline mixing flows the variable volume of the boxes permits explicit simulation of the replacement of the preexisting late pleistocene lake water by the inflow of denser mediterranean water our results indicate that the time needed to displace the old deep water with new saltier water is 2000 years or less because of the effects of mixing the salinity of both the surface and deep waters requires a greater time interval to obtain present day values i e 4000 years if the inflow of mediterranean water is constant in time at its present value and 6000 years if this input changes with time in approximation to the rate of sea level rise the occurrence of the marine coccolithophorid emiliania huxleyi in the holocene sapropel layer requires a minimum surface salinity of 11 which takes some 1600 to 3100 years to develop this range is a result of the uncertainty in the history of the mediterranean water input the model is also employed to investigate the freshening of the black sea after cutoff of mediterranean input the salinity of both surface and deep waters is found to fall below 11 in less than 3000 years and the freshening process is complete in 9000 years

distribution and tectonic implications of cretaceous quaternary sedimentary facies in solomon islands abstract sedimentary rocks of the solomon islands bougainville arc are described in terms of nine widespread facies four facies associations are recognised by grouping facies which developed in broadly similar sedimentary environments a marine pelagic association of early cretaceous to miocene rocks comprises three facies facies al early cretaceous siliceous mudstone found only on malaita is interpreted as deep marine siliceous ooze facies a2 early cretaceous to eocene limestone with chert overlies the siliceous mudstone facies and is widespread in the central and eastern solomons it represents lithified calcareous ooze facies a3 oligocene to miocene calcisiltite with thin tuffaceous beds overlies facies a2 in most areas and also occurs in the western solomons this represents similar but less lithified calcareous ooze and the deposits of periodic andesitic volcanism an open marine detrital association of oligocene to recent age occurs throughout the solomons this comprises two facies facies b1 is variably calcareous siltstone of hemipelagic origin and facies b2 consists of volcanogenic clastic deposits laid down from submarine mass flows a third association of shallow marine carbonates ranges in age from late oligocene to recent facies c1 is biohermal limestone and facies c2 is biostromal calcarenite the fourth association comprises areally restricted pliocene to recent paralic detrital deposits facies d1 includes nearshore clastic sediments and facies d2 comprises alluvial sands and gravels pre oligocene pelagic sediments were deposited contemporaneously with and subsequent to the extrusion of oceanic tholeiite island arc volcanism commenced along the length of the solomons during the oligocene and greatly influenced sedimentation thick volcaniclastic sequences were deposited from submarine mass flows and shallow marine carbonates accumulated locally fine grained graded tuffaceous beds within the marine pelagic association are interpreted as products of this volcanism suggesting that the santa isabel malaita ulawa area where these beds are prevalent was relatively close to the main solomons chain at this time a subduction zone may have dipped towards the northeast beneath this volcanic chain pliocene to pleistocene calcalkaline volcanism and tectonism resulted in the emergence of all large islands and led to deposition of clastic and carbonate facies in paralic shallow and deep marine environments

the opening of the woodlark basin subduction of the woodlark spreading system and the evolution of northern melanesia since mid pliocene time abstract magnetic anomaly and seismological data define segments of active seafloor spreading and associated magnetic lineations trending ene in the woodlark basin the total opening rate has been approximately 6 cm yr for the last 1 m y spreading rates diminish by over 10 from east to west along the woodlark spreading system implying a pole of current opening 15 20 to the west commencement of seafloor spreading in the basin has apparently been time transgressive beginning prior to 3 5 m y in the east and at successively later times to the west earthquake focal mechanisms and geological evidence suggest that the land areas bounding the western end of the woodlark basin are undergoing tensional deformation we believe that eventually the woodlark basin plate boundary will propagate westward through the d entrecasteaux islands into the papuan peninsula hitherto unreported shallow seismicity associated with the northern margin of the ne trending section of the woodlark rise probably reflects partial decoupling of the woodlark and solomon basins possibly due to mechanical difficulties in subducting the young woodlark lithosphere analysis of the relative motions between the solomon indo australian and pacific plates shows that the woodlark spreading system has been subducted at high rates 10 cm yr beneath the solomon islands during the opening of the woodlark basin several tectonic and geological features limited to the region of interaction of the woodlark basin with the solomon trench and arc may be symptomatic of ridge subduction these features include high heat flow in the solomon trench which shoals to 4 km low levels of seismicity and only shallow hypocenters and voluminous eruptions of high k 2 o tio 2 olivine basalts and basaltic andesites extremely close to the trench axis this close association in space and time of an unusual volcanic suite with ridge subduction implies a strong dependence of the petrogenesis on the tectonic regime a combination of this study of the woodlark basin and the previous study of the bismarck basin taylor 1979 provides a reconstruction of the positions of the continents ocean basins and island chains in northern melanesia for mid pliocene time in accepting the existence of a solomon plate we can explain the trench like structure off the trobriand margin of new guinea the occurrence of late cenozoic calc alkaline volcanism along the papuan peninsula and the presence of intermediate depth seismicity beneath the north papuan peninsula the rapid changes in relative motions along or across the new ireland solomons chain over the past 3 5 m y may explain the spatial and temporal changes in igneous activity observed on these islands

carbon accumulation rates and the origin of the holocene sapropel in the black sea a detailed radiocarbon chronology obtained by accelerator mass spectrometry together with organic carbon and carbonate measurements on two black sea cores has been used to compare and contrast the burial fluxes of organic carbon in the holocene sapropel and the modern sediment at both deep water and eastern slope sites the sapropel is separated from the modern facies by a variable thickness of compositionally homogeneous sediment with low levels of organic carbon and anomalously old radiocarbon ages this homogeneous unit probably represents deposition by slumping or mudflow the age limits of the sapropel are 1600 6600 b p at the deep water site and 4000 6000 b p radiocarbon years before 1950 a d at the shallow water site the carbon accumulation rate in the deep water sapropel is higher than that in the modern deep water facies by a factor of 2 and is approximately the same as that in the modern sediment in shallow water the revised chronology of sapropel formation and the differences in the carbon accumulation rates probably indicate that the sapropel was formed by increased production during the transition from the premodern lake to the modern marine phases of the black sea this conclusion is consistent with the clear marine carbon isotope signal in the organic mattermore in the sapropel in both cores results to be reported elsewhere in contrast to the mixed source of carbon in the other facies less

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

uranium oxidation state and related variations in geochemistry of phosphorites from the negev southern israel abstract study of the u iv fraction in mishash phosphorites of the negev reveals an apparently paradoxical trend the u iv fraction is very low less than 10 in the pristine organic rich laminated phosphorites while this proportion considerably increases up to 60 in the recycled mechanically reworked granular phosphorites which deposited under more oxidizing conditions this u iv trend seems to differ from that reported in other phosphate sequences elsewhere and is also quite unexpected in view of the sediment patterns and the specific formational conditions of the two phosphorite facies in addition a lower u iv in the analyzed granular phosphorites is coupled with a lower rare earth elements ree p 2 o 5 and y p 2 o 5 ratio a higher cd and zn concentration less negative ce ce ce and eu eu eu anomalies a lower hree dy er enrichment and a lower f p 2 o 5 and higher co 2 f ratio in francolites this u iv trend in the two negev phosphorite facies may be explained by varying time spans of apatite growth changes in sediment burial rates and principally different residence times of the phosphate fraction in the suboxic apatite forming diagenetic zone near the sediment water interface the associated varying concentrations of rees y cd and zn in phosphorites and of f and co 2 in francolites in the two granular phosphorite facies are apparently collectively regulated by the same sedimentary dynamics during phosphate deposition it is presumed that the u iv trend observed in the negev phosphorites could be detected in other phosphate sequences as well if pristine phosphorites are carefully identified and selectively analyzed

ultra fine structures and genesis of the campanian negev high grade phosphorites southern israel ultra fine structures of the negev high grade phosphorites provide valuable clues to unravelling the genesis of these rocks the question of their differential areal distribution and the biosedimentary mechanisms involved in their considerable enrichment peculiar to these phosphorites is an intergranular phosphate matrix for the most part constituted by a variety of phosphatic microbial tubules displaying a range of spatial micro organizations the phosphate particles fixed by this filamentous meshwork also consists of internally organized and non organized packed microbial remains of different types analogies between the fabrics of the matrix and the corpuscles lead to conception of a two stage depositional scheme for these phosphorites based on rhythmical repetition of two sedimentary mini events in a slightly oscillating very shallow marine system 1 a low energy event of microbial colonization of the mishash bottoms followed by early phosphatization of the organic structures mainly in marginal situations and 2 a higher energy event which broke up the phosphatic mats into debris redepositing them as clastic layers in nearby basinward sites while becoming bound by a new meshwork of filamentous microphytes the differential phosphatization of the intergranular microbial binder again occurring mostly in marginal localities produced highly enriched phosphorites minor truncations and redepositions leading to amalgamation of the successive layers account for the massive fabric now displayed by most of these rocks examining the structural and textural features the validity of the sedimentary mechanisms of recent phosphorite formation for the campanian negev rocks is discussed

the discovery of santorini minoan tephra in western turkey dispersal of volcanic ash from the violent bronze age minoan eruption of the santorini volcano in the southern aegean has been the subject of much research1 6 a sediment core taken from a small mountain lake in western turkey contains a layer of tephra from the minoan eruption the santorini origin is established by refractive index major glass chemistry and stratigraphic position the lake is located north of the recognized dispersal area for the tephra this deposit provides evidence for dispersal of the minoan tephra well to the northeast of santorini and implies that the west coast of asia minor must have experienced heavy tephra fallout from the bronze age eruption the minoan tephra has not previously been identified from sites in turkey

neogene displacements in the solomon islands arc abstract the geology and present configuration of the solomon island arc can be explained in terms of the neogene displacement of a single linear chain of islands the central part of an original arc consisting of bougainville choiseul santa ysabel guadalcanal and san cristobal was displaced to the northeast as a consequence of the attempted subduction of the woodlark spreading system malaita arose on the northeastern side of the arc as a result of interaction between the arc and the pacific ocean floor and the volcanic islands of the new georgia group formed to the southwest in response to the subduction of a spreading ridge thus giving rise to the present double chain structure of the arc

implications of paleomagnetic data on the collision related bending of island arcs paleomagnetic studies from the marianas central philippines ryukyus sulawesi fiji new hebrides all show major differences in the declination values observed from individual islands within the same arc comparable differences are not observed in the inclination values a simple plate tectonic model would predict that each island arc should experience the same rotation along its entire length as the plate moves around its rotation axis bathymetry from each of these arcs show that the differentially rotated segments of the upper plate occur in areas where the downgoing plate carries a feature such as a seamount chain rifted continental fragment or an island arc the coincidence of the bathymetric feature and the discordant paleomagnetic declination data support an earlier hypothesis of vogt 1973 that these features are buoyant zones on the downgoing plate which interact with the margin of the upper plate as a result of this interaction the upper plate boundary is locally deformed in addition to the paleomagnetic evidence other geologic and geophysical data from these areas suggest such interactions for example there appears to be a good correlation between the deflections in major structures around the collision zone and the paleomagnetic directions that are reported as this deformation proceeds eventually the stresses resulting from the collision may result in any of the following tectonic processes 1 slip line style strike slip faults allowing for the sideward extrusion of portions of the upper plate tapponnier et al 1983 2 changes in the polarity of the subduction zone 3 development of strike slip faults around the margin of the indenter or 4 reorganization of the entire plate margin in addition data from the marianas southern end of the ryukyu arc and the lau basin suggest that back arc basin development may result from the collision related deformation

continental margin tectonics forearc processes recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of u s research from the period 1987 1990 topics addressed include the geometry of accretionary prisms coulomb wedge taper and vertical motion in response to tectonic processes offscraping vs underplating or subduction the response to oblique convergence fluids in forearc settings the thermal framework and the effects of fluid advection and serpentinite seamounts also included is a comprehensive bibliography for the period

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

tholeiitic calc alkaline and alkaline igneous rocks of the shortland islands solomon islands abstract the shortland islands lie in a northeast southwest line across the western end of solomon islands immediately adjacent to bougainville three major islands dominate the group fauro and surrounding islands in the northeast have an altered basement suite comprising tholeiite icelandite and tholeiitic dacite this is intruded by a high level calc alkaline assemblage of microdiorite hornblende andesite and rhyodacite and overlain by volcanogenic sandstones derived from an andesitic to dacitic volcano pyroclastics comprising high alumina basalt and pyroxene andesite overlie the volcanogenic sandstones the tholeiitic basement lavas may be of late oligocene to early miocene age and the calc alkaline rocks are probably also pre pliocene in age alu in the centre of the group also has an altered tholeiitic lava basement which is intruded by a quartz diorite body and overlain by hypersthene augite basaltic andesite pliocene siltstone and quaternary shallow marine carbonates cover these igneous rocks over much of the island mono in the southwest has a small basement exposure of altered pillowed hawaiite overlain by miocene pelagic limestone pliocene siltstone and quaternary reef limestone isolated clasts of pyroxene andesite and benmoreite occur in streams and on beaches the younger calc alkaline suites on all islands were formed in an island arc environment possibly related to subduction from the southwest beneath the new britain trench the basement lavas on alu are probably early island arc tholeiites and both these lavas and the calc alkaline rocks of alu share a common trend on variation diagrams the two igneous suites of fauro however have distinctly different trends the basement lavas have some chemical similarities with oceanic tholeiites but an early island arc origin for these lavas cannot be ruled out the altered hawaiite and benmoreite on mono probably originated in an oceanic island environment

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

accelerating late quaternary uplift of the new georgia island group solomon island arc in response to subduction of the recently active woodlark spreading center and coleman seamount abstract the new georgia island group of the solomon islands is one of four places where an active or recently active spreading ridge has subducted beneath an island arc we have used coral reef terraces paleobathymetry of neogene sedimentary rocks and existing marine geophysical data to constrain patterns of regional quaternary deformation related to subduction of the recently active woodlark spreading center and its overlying coleman seamount these combined data indicate the following vertical tectonic history for the central part of the new georgia island group 1 subsidence of the forearc region tetepare and rendova islands to water depths of 1500 m and deposition of marine turbidites until after 270 ka 2 late quaternary uplift of the forearc to sea level and erosion of an unconformity 3 subsidence of the forearc to 500 m bsl and deposition of bathyal sediments and 4 uplift of the forearc above sea level with holocene uplift rates up to at least 7 5 mm yr on tetepare and 5 mm yr on rendova in the northeastern part of the new georgia island group our combined data indicate a slightly different tectonic history characterized by lower amplitude vertical motions and a more recent change from subsidence to uplift barrier reefs formed around new georgia and vangunu islands as they subsided 300 m by 50 100 ka subsidence was replaced by uplift that accelerated to holocene rates of 1 mm yr on the volcanic arc compared with rates up to 7 5 mm yr in the forearc area of tetepare and rendova uplift mechanisms such as thermal effects due to subduction of spreading ridges tectonic erosion or underplating of deeply subducted bathymetric features are not likely to function on the 270 ka period that these uplift events have occurred in the new georgia island group a more likely uplift mechanism for the post 270 ka accelerating uplift of the forearc and volcanic arc of the new georgia island group is progressive impingement of the coleman seamount or other topographically prominent features on the subducting plate regional effects we relate to this ongoing subduction related process include 1 late quaternary post 270 ka accelerating uplift of the rendova tetepare forearc area in response to initial impingement of the coleman seamount followed by exponentially increasing collisional contact between the forearc and seamount 2 later quaternary propagation of uplift arcward to include the volcanic arc as the area of collisional contact between the forearc and seamount increased and 3 large wavelength folding that has produced regional variations in late holocene uplift rates observed in both forearc southern rendova tetepare and volcanic arc new georgia island areas we propose that the dominant tectonic effect of coleman seamount impingement is horizontal shortening of the forearc and arc crust that is produced by strong coupling between the subducting seamount and the unsedimented crystalline forearc of the new georgia island group the horizontal forces due to mechanical resistance to subducting rugged ridge and seamount topography may have terminated spreading of the woodlark spreading center entering the trench ghizo ridge and converted it to a presently active strike slip fault zone

tectonic setting of western pacific marginal basins abstract global kinematics as well as magnetic anomalies of marginal basins with continental geology and paleomagnetic data as additional constraints are used to present a set of reconstructions of the western pacific marginal basins between 56 ma and the present at key periods 56 43 32 20 12 and 3 ma our model accounts for the rapid motion of exotic terranes along the whole of the western pacific convergent zone marginal basins appear to open in a great variety of tectonic settings the two extreme examples being the mariana trough where trench suction may be the predominant driving force and the south china sea where intracontinental deformation appears to be the major mechanism the study of marginal basins is a 3 d problem which must take into account the whole tectonic context subduction related tectonics in cross section and upper plate deformation in map view and not only a 2 d problem the classical trench arc back arc problem

dimensions and dynamics of co ignimbrite eruption columns very powerful volcanic eruptions cannot always form classical plinian eruption columns1 4 instead collapsing fountains may develop above the vent and shed pyroclastic flows which spread laterally along the ground5 the upper part of these hot dense pyroclastic flows may become buoyant through the entrainment heating and expansion of ambient air coupled with the sedimentation of larger clasts suspended in the flow the buoyant material may rise in a co ignimbrite eruption column carrying massive quantities of fine dust and volatiles into the stratosphere6 7 here we present a model of this process and show that the co ignimbrite columns associated with the eruptions of toba8 9 75 000 years ago and tambora10 in 1815 may have ascended only about 32 and 23 km the latter is comparable with the less powerful 1982 plinian eruption column of el chichon11 this corroborates arguments that the mass of sulphuric acid aerosols injected into the stratosphere and not the eruptive power determines the climatic impact of an eruption12 13

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine

geochemical mineralogical and isotopic signatures of the semikan west kasrik turkish phosphorites from the derik mazidagi mardin area se anatolia the geochemistry and mineralogy of a condensed section 6 m thick of the west kasrik member coniacian santonian near the uplifted northern flank of the mardin derik anticline south eastern turkey was studied the only deposit exploited in turkey is found in this area the sediment textures as well as the mineralogical and the geochemical results collectively suggest that these recycled phosphorites accumulated in areas of intensive very early diagenesis of the sediments in highly oxic bottom waters and almost no detrital apport the total concentration of redox sensitive trace metals is very low 600 g g in addition the structural co2 and f p2o5 are unusually high 5 wt and 0 14 respectively ree distribution shows a clear seawater pattern with a strongly negative ce anomaly 0 20 0 02 and heavy ree enrichment lun lan 1 50 0 12 however their total concentration is very low the low ree contents quite unexpected in recycled phosphorites are explained by the scarcity of terrigenous components which leads to minimal incorporation of rees from detrital clastic phases in the cfa fraction weathering previously suggested as responsible for the high p enrichment of the mazidagi phosphorites is rather improbable in the samples we studied in view of their high structural co2 high f p2o5 high la nd n and la sm n ratios and high sr p and ca p of separated cfa fractions that all negate post depositional weathering more likely the high p enrichment of some rocks p2o5 content reaches 34 was produced by sedimentary and early diagenetic processes acting in oxygenated areas of starved sedimentation on and around tectonic highs

diagenetic trends of fluorine concentration in negev phosphorites israel implications for carbonate fluorapatite composition during phosphogenesis an electron probe and chemical study of bulk phosphorite samples and separated constituents from various negev deposits was carried out together with xrd ftir spectroscopy and textural analysis the results allow a better understanding of the distribution of fluorine in these upper cretaceous phosphorite sequences and shed light on variations in the composition of the carbonate fluorapatite cfa phase during phosphogenesis two facies are recognized 1 a pristine microbially generated phosphorite facies 2 a recycled peloidal and biodetrital facies fluorine distribution in the negev phosphorites is facies controlled f p2o5 is much lower in the pristine facies 0 090 0 107 than in the recycled facies 0 107 0 120 in addition f p2o5 varies considerably between the various constituents of the phosphate fraction f poor francolites f p2o5 as low as 0 080 co exist with f rich francolites f p2o5 as high as 0 135 in the same phosphorite bulk sample a lower f p2o5 in francolite is associated with higher cd and zn concentrations in the phosphorite an increase in fe rich smectites in the clay fraction and the presence of structural oh in the francolite the lower f p2o5 ratios in the pristine facies are attributed to high organic deposition rates during the formation of these matted sediments leading to rapid burial of the in situ forming cfa this is possibly coupled with diffusion of f from sea water into bottom sediments being hampered by microbial mat coatings these conditions resulted in o2 depleted porefluids inducing the precipitation of cd rich zn sulphides and the formation of fe rich smectites f enrichment probably takes place when the earlier formed f poor primary cfa is relocated close to the sea floor and bathed with interstitial sea water solutions of higher f concentrations oxidation and removal of the sulphide bound cd and zn apparently occurred together with enrichment in f of the francolite combining chemical data with xrd and ftir results suggests a multistage growth for the negev phosphate constituents in shifting formational sites and porefluids of varying f concentrations this multiphase growth is reflected in the patchy distribution of f in the negev constituents and might explain the inverse correlation between mean co2 f and f p2o5 ratios of the analysed phosphorites in the two facies it also suggests that cfa or an amorphous precursor initially formed with some oh groups in the apatite structure which were subsequently substituted by f ions in recycled francolite through re equilibration with porefluids of higher f concentrations

geochemistry of cadmium in the negev phosphorites cadmium cd in the negev phosphorites as in many other phosphorites is the most enriched trace element relative to average shale nevertheless similar to many other phosphorites cd is either not correlated to p2o5 or has a slightly negative correlation with it there is a clear correlation between the cd content the textural and the compositional characteristics of the phosphorites and the structural position of the phosphate deposits well developed synclinal sections comprised of many thin strata of laminated non disturbed pelletal phosphorites have much higher cd concentrations than the condensed anticlinal sections which consist of a few amalgamated thick beds of massive reworked phosphorites cd is in general poorly related to the present organic matter content but has a good correlation with organic matter in unoxidized beds of the synclinal sections cd is strongly correlated to zn in the relatively undisturbed beds of the synclinal sections but shows no correlation in the highly reworked beds of anticlinal sections the source of cd is upwelled seawater that is enriched in both p and cd this is the basis of the relationship between phosphogenesis and cd concentration reducing conditions during decomposition of organic matter immobilize cd in the pore fluids of the bottom sediments precipitation of cd rich sphalerite and adsorption on organic matter appear to be the main processes for its initial speciation and concentration in the negev phosphorites cd is concentrated mainly in laminated non disturbed microbially generated phosphorites where authigenic apatites are also found cd does not as a rule replace ca in the structure of authigenic primary sedimentary apatites this finding has practical applications since it makes possible the production of a phosphate concentrate with a much lower cd concentration than the original phosphorite exposure to oxic conditions leads to mobilization of the sulfide bound cd scouring activity bioturbation and recycling and transportation of stirred up phosphate corpuscles in an oxidizing environment appear to be effectual for removing cd oxidation alone without fabric disruption and mobilization of the phosphate grains does not significantly lower cd concentrations since the released cd may be almost immediately readsorbed on the various components of the phosphorite such as iron oxyhydroxides organo clay fractions and apatites the cadmium concentration and the cdzn ratio of a phosphorite may help to determine whether a phosphorite is pristine or not and to unravel its diagenetic history

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

early diagenesis of trace metals used as an indicator of past productivity changes in coastal sediments in sediments of kiel bight which differ significantly in their redox states and the rates of corg degradation depth profiles of both dissolved and solid phase fe mn cd cu ni and co were measured porewater fluxes of cd cu and ni were significantly higher at shallower more oxic stations as compared to highly reducing deeper subthermocline sediments while mn fluxes behaved the opposite way when normalized to fe for grain size correction the measured solid phase metal contents revealed that the high porewater flux has led to a near surface depletion of mn from more anoxic sediments and to a reduced rate of accumulation of anthropogenic cd in more oxic sediments this difference in early diagenetic behaviour suggests the use of these metals as a proxy for the redox state and the intensity of carbon recycling contrary to the recent sediment layers the normalized metal contents of preindustrially deposited sediment layers were similar for both metals at all stations thus at stations having highly anoxic sediments today the preindustrial benthic flux must have been lower for mn and higher for cd reflecting a shift from more oxic to more reducing conditions in subthermocline sediments during the last 100 years this change of the redox state in subthermocline sediments reflects an increase of primary production and of subsequent corg input to the sediment due to eutrophication which accompanied industrialization