silurian graptolite biostratigraphy in the welsh basin silurian graptolite zones are of markedly shorter duration than those of the ordovician averaging 0 8 ma several can be sub divided and further refinement will undoubtedly follow a revision of many of the graptolite species and their stratigraphic range locally integration of palaeontological and sedimentological studies facilitates correlation a premilinary subdivision of the crispus and griestoniensis zones in central wales is made

trace element characteristics ree patterns and partition coefficients of zircons from different geological environments a case study on indian zircons abstract twelve zircon separates from diverse geological settings in peninsular india have been analyzed for their zr hf sc ree th and u contents employing neutron activation techniques the whole rock samples of acid charnockite and a related rock of syenitic composition were also analyzed for these elements after separation of zircons the study reveals that 1 a the zircons exhibit a wide range of variation in elemental abudances and their ratios 2 b their chondritic normalised ree patterns exhibit negative or positive ce and negative eu anomalies in addition to smooth hree enriched patterns without anomalies and 3 c there are significant differences in the ree partition coefficients of zircons from the charnockite and the associated syenite the overall elemental abundances and ree patterns of the zircons could be explained in terms of crystallochemical factors bulk compositional differences of parent melts and paragenetic histories

nd and sr isotopic variations in acidic rocks from japan significance of upper mantle heterogeneity initial nd and sr isotopic ratios have been measured for cretaceous acidic and related intermediate rocks 24 volcanic and two plutonic rocks from the inner zone of southwest japan izswj to investigate the genesis of acidic magmas the initial nd and sr isotopic ratios for these rocks show three interesting features 1 end values for acidic rocks 2 to 9 are negatively correlated with esr values 10 to 90 together with those for intermediate rocks end 3 to 8 esr 0 to 65 2 the end values for silica rich rocks 60 sio2 correlate with the longitude of the sample locality decreasing from west to east in a stepwise fashion four areas characterized by uniform end values are discriminated 3 low silica rocks 60 sio2 in a certain area have distinctly different end values from those of the high silica rocks in the same area

pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

discriminating hydrothermal and terrigenous clays in the okinawa trough east china sea evidences from mineralogy and geochemistry abstract the okinawa trough ot in the east asian continental margin is characterized by thick terrigenous sediment and ubiquitous volcanic hydrothermal activities in this study the clays collected during iodp expedition 331 to the middle ot iheya north knoll were analyzed for mineralogical and geochemical compositions by comparing with the clays from the east china sea shelf and surrounding rivers we examine different clay origins the hydrothermal field in the mid ot is dominated by mg rich chlorite while the recharge zone has clay mineral assemblages similar to the shelf and rivers showing high content of illite subordinate chlorite and kaolinite and scarce smectite compared to the terrigenous clays the hydrothermal clays in the ot have high concentrations of mg mn and zr but low fe na k ca ba sr p sc and ti while the hydrothermal clays in the mid ocean ridge are relatively enriched in fe and v and depleted in al mg zr sc and ti different fractionation patterns of rare earth elements also register in the terrigenous and hydrothermal clays diagnostic of variable clay origins we infer that the ot hydrothermal clay was primarily formed by the chemical alteration of detrital sediments subject to the hydrothermal fluids the remarkably different compositions of hydrothermal clays between the sediment rich back arc basin like ot and the sediment starved ocean ridge suggest different physical and chemical processes of hydrothermal fluids and fluid rock sediment reactions under various geologic settings

mobility of arsenic and trace element inventories in sediment cores from masuda city southwestern japan the vertical distribution of arsenic and other trace and major elements has been studied in four sediment cores from masuda city nagashima and okite in the shimane prefecture of southwestern japan the sediment cores were also subjected to leaching techniques and 14c dating the stratigraphic sequences in the cores consist of silt and sandy silt at top passing downward into gray to black clays elevated values of as pb zn cu ni cr and v are present in several horizons while abundances of these elements tend to be higher in the black and gray clays probably due to adsorption onto clay sediments higher concentrations of fe and total sulfur ts occur in black clays the correlations of the trace metals with iron suggest their adsorption onto fe oxy hydroxides whereas correlations with sulfur in some cores indicate that they were precipitated as fe sulfides age determinations suggest that clay horizons at 5 m depth were deposited at around 5 000 and 6 000 years bp 14c ages during the transgressive phase of sea level change the results of the leaching techniques in the core samples show that higher amounts of as were extracted with deionized water even at neutral ph as can be released from sediments to groundwater and therefore groundwater pollution is a concern in masuda city and the surrounding area

trace element mobility in dolomitic argillites of the mesoproterozoic belt purcell supergroup western north america the belt purcell supergroup comprises dolomite rich stratigraphic units in a dominantly siliciclastic succession where sedimentation spans 1400 1470 ma dolomitic units are variable mixtures of co sedimented argillite and primary carbonate post depositionally converted to secondary dolomite based on rare earth element ree relationships three distinct ree patterns are identified in the dolomite rich units type 1 t1d d dolomitic sample with ree patterns parallel to post archean upper continental crust pa ucc albeit at lower absolute abundances due to dilution by carbonate content type 2 t2d with heavy ree hree enrichment but light ree lree depletion relative to t1d and type 3 t3d with enrichment in lree and hree relative to t1d but erratic middle ree mree patterns there is a progressive increase of ree from t1d through t2d to t3d whereas for lree hree t2d t1d t3d t1d t2d and t3d represent three different snapshots of a continuous process in terms of timing dolomitization of calcite primary sediment in all samples likely took place broadly during burial diagenesis as inferred for most proterozoic dolomites t1d is easily explained by provenance however t2d and t3d cannot be related to provenance weathering or sedimentary sorting processes to explain higher concentrations of hree referenced to pa ucc and consequently developed in the sediment from a t1d precursor the same three ree signatures have been described in previous studies in counterpart siliciclastic counterparts throughout the belt purcell supergroup at three different locations mobility of normally stable ree is accompanied by mobility of normally isochemical high field strength elements hfse in t2d and t3d to give ree ree hfse hfse ree hfse and y hree fractionations no specific ree hfse signatures are apparent in the carbonate rich units as compared to their non dolomitic siliciclastic counterparts this unusual mobility of ree and hfse reflected in t2d and t3d is attributed to alkaline oxidizing post depositional brines salinity was derived from seawater sediment reactions dissolution of evaporite minerals and the smectite illite transformation whereas alkaline oxidizing conditions were promoted by groundwater interaction with mafic units in the basin co2 introduced into the system during episodic rifting with mantle degassing and interaction of syn sedimentary mafic intrusions with carbonate units at early stages of bps deposition intermittent brine activity inducing t2d and t3d patterns spanned 1 ga as recorded by secondary monazite grains with age distributions that correspond to large scale tectono thermal events in laurentia post depositional processes and redistribution of carbonate can have an impact on transitional stratigraphic contacts between dolomitic and siliciclastic units which may have been incorrectly described as primary due to sedimentary environment changes

experimental studies on the mobility of lanthanides accompanying alteration of andesite by acidic hot spring water abstract the mobility of lanthanides lns accompanying interactions of powdered andesitic rocks with acidic hot spring water and acidic hot spring water vapor steam was studied in the experiments set up in the field at the early stage of rock alteration light lns were slightly easier to be leached out by acidic hot spring waters from andesitic rocks than heavy lns this result qualitatively agreed with the result obtained in the previous experiments carried out in the laboratory it was also found that the ln abundance patterns ln patterns obtained by normalization with ln contents of the original rock showed slightly positive eu anomalies at the early stage of rock alteration and turned to show negative eu anomalies and the extent of negative anomaly monotonously increased as rock alteration proceeded this trend in the direction of eu anomaly was correlated to the degrees of decompositions of major rock forming minerals and interstitial materials in the rock at the earliest stage of rock alteration in acidic environments the interstitial materials with relatively low eu contents were decomposed which resulted in the positive eu anomaly in the following stage feldspar that had a relatively high eu content was decomposed which led to the negative eu anomaly

along strike variation in the stratigraphical and structural profile of the southern uplands central belt in galloway and down the modern interpretation of the southern uplands depends on the recognition of laterally extensive linear fault bounded tracts of northward younging lower palaeozoic sediments with rare volcanics the tracts become progressively younger southwards and are thought to have been sequentially accreted by northward underthrusting above a subduction zone detailed mapping and tentative correlation of three well exposed coastal profiles through the central belt in sw scotland and ne ireland offers a new test of the southern uplands model comparison of the northern parts of each section indicates the presence of strike parallel tracts with model structure moffat shale outcrops associated with the tract defining faults demonstrate a diachronous incremental southerly decrease in the age of the base of the overlying turbidites essentially as in the northern belt southward this becomes markedly less pronounced particularly in down where the central belt is much wider than in galloway distinctive hawick group lithologies permit the correlation of the southern parts of the sections large areas of predominantly southward younging occur in each section especially in galloway where the southward younging area is 12 km across here northerly verging d 1 fold pairs are consistent with observed fault movement opposite in sense to the northerly underthrusting of the model back thrusting in the style of the pleistocene cascadia basin is invoked to account for the landward verging structure of these areas and to explain the narrowing of the central belt in galloway the structure of the central belt thus differs significantly from that of the northern belt and the accretionary prism model

rare earth element mobility in the roffna gneiss switzerland the roffna gneiss a deformed hercynian granite porphyry within the penninic nappes of eastern switzerland underwent extreme cataclasis with the progressive development of phengite towards the margins of the nappe under conditions of the glaucophane schist to greenschist facies this resulted in the selective mobilization of major and trace elements over distances of 10 s to 100 s of meters and the resetting of the rb sr whole rock isotopic systems some 100 my ago the component ratios and compositionvolume relationships of progressively deformed gneiss samples studied here suggest that this process was essentially isovolumetric the mineralogy of the deformation sequence appears to have been controlled by a reaction involving the breakdown of microcline albite and biotite and the formation of phengite and quartz the fluids introduced mg and h2o promoting the development of phengite and removed the na being released by the breakdown of albite the fluids were most probably derived from the surrounding triassic carbonates and quartzites these relatively high fo2 and carbonate rich fluids also introduced rare earth elements ree into the gneiss the gneiss was progressively enriched in eu up to 60 y up to 40 and yb up to 100 these enrichments are associated with the development of epitaxial xenotime around zircon in the most phengite rich sample while the ree were mobile uranium and thorium were essentially immobile the formation of xenotime was suggested to explain the observed heavy ree enrichment when large differences in the ree contents were found for replicate analyses using hf and then lithium metaborate for dissolution these differences arose because xenotime like monazite can be difficult if not impossible to dissolve in hydrofluoric acid due to the possibility of incomplete sample dissolution we now recommend fusion with lithium metaborate for all ree lu hf or sm nd studies

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

rare earth element mobility around the volcanogenic polymentallic massive sulfide deposit at que river tasmania australia abstract the que river volcanogenic base and precious metal deposit is located in the cambrian mt read volcanics of western tasmania the host andesites and dacites adjacent to mineralization have been hydrothermally altered during mineralization and the entire sequence has undergone devonian regional prehnite pumpellyite facies metamorphism rocks petrographically recognizable as andesites exhibit chondrite normalized ree patterns similar to modern orogenic high k andesitic rocks with ce yb n ratios ranging from 6 4 to 8 6 dacites are more fractionated with ce yb n ranging from 10 6 to 16 0 like the andesites the dacites are characterized by negative eu anomalies eu eu 0 73 0 85 except for a more extreme eu anomaly in one sample eu eu 0 57 polymict volcaniclastic rocks have patterns very similar to those of the andesites the chondrite normalized ree patterns for the hydrothermally altered volcanics fall into three groups that can also be distinguished petrographically a single chloriterich sample has a substantial eu anomaly and shows less relative depletion in the middle ree than do either the andesites or the dacites highly silicified samples are all characterized by large negative eu anomalies eu eu 0 37 0 46 and many are relatively unfractionated with ce yb n ratios ranging from 3 5 to 7 7 a third group of samples characterized by the development of phengitic mica and carbonate show ree patterns similar to the andesites although their eu anomalies are generally smaller a sample of massive zn 1bpb ore has very low ree abundances showing light ree enrichment and a small negative eu anomaly eu eu 0 82 massive pyrite has a similar pattern except for higher overall abundances and a small positive eu anomaly eu eu 1 10 except for the eu anomalies the andesites and dacites show no evidence for ree mobility eu anomalies in the andesites are probably due to alteration of phenocrystic plagioclase and subsequent removal of divalent eu substantial ree mobility has occurred in the hydrothermally altered volcanic rocks the degree of mobility correlating with alteration style and intensity eu has been leached from both former plagioclase phenocrysts and the groundmass some of the eu leached from zones of the most intense alteration may have been redeposited in lower temperature more distal alteration zones

behaviour of rare earth elements during hydrothermal alteration at the buena esperanza copper silver deposit northern chile abstract a study of the ree behaviour in alteration zones of the buena esperanza subvolcanic cu ag deposit located in the coastal range of northern chile reveals that the elements are mobile in the rocks during alteration the ore forming process developed in three different stages of alteration mineralization the hydrothermal alteration of the early and middle stages affected basaltic fragments of a breccia pipe la and ce were leached from the rock fragments located at the bottom and at the middle part of the breccia pipe and partly redeposited at the top during alteration sm eu and tb were released selectively and the heavy ree behaved as relatively immobile elements sericite is the most important alteration mineral for fixing the ree during this stage the incoming fluids had low ree contents the late stage of hydrothermal alteration happened simultaneously with the intrusion of a gabbroic volcanic neck affecting mainly these subvolcanic rocks ree patterns of samples from the top and bottom of the alteration zone exhibit roughly parallel trends but are systematically enriched in ree in comparison to unaltered samples this enrichment seems to be more intensive at the top of the altered area coinciding with the enrichment of rb k and cu in these rocks epidote plays the most important role for fixing this hydrothermal input of ree during the latest stage of alteration

early silurian sea level changes global sea level fluctuated markedly during the early silurian probably as a result of the waxing and waning of ice sheets in the south american portion of gondwana the highest sea levels of the silurian are recorded by the telychian upper crispus lower griestoniensis and spiralis lower lapworthi biozones other highstands occurred in the early aeronian during the convolutus zone mid aeronian guerichi zone and late turriculatus zone early telychian and early sheinwoodian low sea levels characterized much of the argenteus and sedgwickii zones aeronian the utilis subzone late guerichi early turriculatus zones early telychian the late telychian commencing in the mid lapworthi zone and after a period of apparently only small amplitude sea level fluctuations in the late sheinwoodian and earliest homerian the mid late homerian in particular the early nassa zone facies and faunal changes in the lower silurian do not support the p and s model of jeppsson and others but are consistent with the sea level changes proposed herein mid telychian marine red beds appear to have been deposited during a minor sea level fall immediately after a period of very high sea levels rather than during a transgressive episode as previously suggested comparison of the sea level curve presented herein with those constructed in the past is hampered by the lack of precision currently possible in the correlation of early silurian deep water graptolitic and shallow water shelly sequences improving the precision of this correlation should be a priority for future research

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

mineralogy and geochemical behavior of trace elements of hydrothermal alteration types in the volcanogenic massive sulfide deposits ne turkey abstract volcanogenic massive sulfide vms deposits of the eastern pontides turkey are hosted by the maastrichtian eocene dacite and rhyodacite series accompanied by lesser andesite and basalts as well as their pyroclastic equivalents with tholeiitic to calc alkaline affinity the ore mineral assemblages are chalcopyrite sphalerite galena chalcocite covellite bornite and tetrahedrite potassic phyllitic sericitic argillic kaolinitic and smectitic silicic propylitic and hematitic alteration is commonly associated with these deposits hfse lile trte and ree contents show strong variability in different alteration types resulting from interaction with acid or alkaline fluids sample groups showed chondrite normalized enrichment of lree relative to hree and sub parallel trends except for the hematitic and phyllitic alteration types mree are strongly depleted in the zones of most intense silicification and kaolinization most sample groups have strongly to slightly negative eu anomalies ranging from 0 35 to 0 88 mean hematitic 1 45 and propylitic altered rocks 1 11 have slightly to moderately positive anomalies the negative eu anomalies indicate the low temperatures of fluids 200 c no ce anomaly was observed except for phyllitic alteration where a slight positive anomaly was noted the chondrite normalized trace and ree patterns of the altered rocks are similar to each other suggesting that they were derived from a common felsic source the alteration groups formed from acid intermediate and alkaline hydrothermal solutions some transition base and precious metals and volatile elements were clearly enriched especially in the hematitic silicic kaolinitic and phyllitic altered samples the other elements exhibit different behaviors in different sample groups ree behavior is relatively immobile in the silicic hematitic kaolinitic and partially in moderately and propylitic altered rocks based on mass balance calculations lile and hfse appear mobile in the altered sample groups except in the propylitic altered rocks trte behave as relatively immobile in most of samples except in some of the silicic and phyllitic altered rocks and especially in the hematitic altered samples hfse most of the transition w mo cu and sb and some other trace elements pb as hg bi se and tl are enriched in the hematitic altered samples and in the some silicic altered samples the highest as bi mo se and hg concentrations in the hematite altered samples can be used to distinguish other alteration types and may be a useful indicator in a prospect scale base metal exploration

behavior of the rare earth elements and other trace elements during interactions between acidic hydrothermal solutions and silicic volcanic rocks southwestern japan abstract rare earth elements and other trace elements in some roseki deposits mostly pyrophyllite and sericite silicastones alunites and related rocks were determined in order to examine behavior of the trace elements in the acidic hydrothermal alteration of silicic volcanic rocks the analyzed concentrations were normalized to the probable unaltered original rock values inferred from the averaged data of some silicic volcanic rocks the trace element characteristics for those materials are as follows 1 most of the elements such as na fe ba and light ree were leached from the silicastones while heavy ree th hf and zr were retained in them 2 alunite samples have light ree enriched and heavy ree depleted features 3 the typical roseki deposits are characterized by middle ree depletions and have v shaped ree patterns on the normalized concentrations vs atomic number diagram such characteristic patterns of the roseki deposits can be explained by superimposition of the light ree enriched and heavy ree enriched materials such as alunite and silica it is important that trace element behaviors are highly selective and some elements e g yb lu hf and zr were strongly retained in the rocks even under strongly acidic hydrothermal processes

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

partition coefficients of hf zr and ree between zircon apatite and liquid concentration ratios of hf zr and ree between zircon apatite and liquid were determined for three igneous compositions two andesites and a diorite the concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients those for the apatite in the diorite may deviate from the partition coefficients the hree partition coefficients between zircon and liquid are very large 100 for er to 500 for lu and the hf partition coefficient is even larger the ree partition coefficients between apatite and liquid are convex upward and large d 10 100 whereas the hf and zr partition coefficients are less than 1 the large differences between partition coefficients of lu and hf for zircon liquid and for apatite liquid are confirmed these partition coefficients are useful for petrogenetic models involving zircon and apatite

the durations of silurian graptolite zones recently published radiometric data show the duration of the silurian period to be approximately 32 ma significantly longer than previous estimates radiometric and graphic correlation studies demonstrate considerable variation in the durations of the four silurian epochs approximately 13 ma for the llandovery 4 ma for the wenlock 5 ma for the ludlow and 10 ma for the p idoli using this new geochronological data figures for average graptolite zone duration are presented for each epoch ranging from as little as 0 44 ma in the wenlock to 1 43 ma in the p idoli the figures provide a refined subdivision of the silurian timescale of value to studies which use silurian graptolite zones to calibrate geological processes

a basin model for the silurian of the midland valley of scotland and ireland identification of terranes is frequently based on the apparent disparity of source area for sediment supply palaeontological evidence and the presence of faults whose sense and amount of displacement is sometimes conjectural as an example of such superficially unrelated stratigraphies the silurian successions of the midland valley of scotland and the northern part of ireland are compared a diachronous late llandovery early middle telychian transgressive episode which is earlier in the midland valley inliers is common to many of the successions the transgression resulted in the development of comparable sedimentary facies and fossil assemblages the clast compositions of llandovery and wenlock conglomerates suggest erosion of a common provenance of volcanic rocks founded on a metaquartzite basement areas of active volcanism appear to have migrated in a north westerly direction with time a similar sequence is evident in canada it is suggested that the common features of the scottish irish successions may be accommodated in a unified basin model for silurian sedimentation and volcanism such a basin may have formed in an intra arc environment and been controlled by oblique slip fault mechanisms although evidence for the presence of a silurian arc is equivocal

graptolite biozonation of the wenlock series silurian of the builth wells district central wales the graptolite biozonation of the wenlock series in the builth wells district is reassessed the graptolite fauna is dominated by relatively few but variable species of monograptus s s pristiograptus and monoclimacis these species are mostly long ranging and are of limited biostratigraphical use biozonation is based largely on the relatively rare cyrtograptids the lower wenlock series of the district comprises the widely recognized centrifugus murchisoni and riccartonensis biozones the middle to upper wenlock biostratigraphy differs from that previously recognized in the uk above the riccartonensis biozone dubius rigidus and lundgreni biozones are distinguished separate flexilis and ellesae biozones are not recognized monograptus flexilis appears earlier than then largely co exists with cyrtograptus rigidus s l while cyrtograptus ellesae appears later than cyrtograptus lundgreni the uppermost wenlock nassa ludensis biozone is sparsely fossiliferous its subdivision has not proved possible this revised biostratigraphical scheme for the wenlock series of the builth wells district suggests that the sheinwoodian homerian boundary as defined in the welsh borderland might occur within rather than at the base of the lundgreni biozone however difficulties in correlation with other wenlock sequences particularly overseas suggest significant biofacies control with the wenlock seas of the builth wells district appearing to have been periodically inhospitable to graptolites

late holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from lake hamana central japan abstract late holocene environmental changes in lake hamana a coastal lagoon in central japan were reconstructed by a diatom fossil analysis and tephra and radiocarbon dating of a lakebed sediment core hmn08 7 with high temporal resolution on the basis of major species composition changes in diatom assemblages we divided the core into six zones i to vi and subdivided zones v and vi into 3 subzones the environment of lake hamana developed in six stages that corresponded to the diatom zones stage i 4700 4600 cal bp was characterized by vigorous seawater inflow in an inner bay environment during stage ii 4600 4500 cal bp a closed inner bay environment with laminated sediments formed as a result of the formation of sand barriers stage iii 4500 2650 cal bp was characterized by a well mixed brackish water environment caused by active mixing with riverine fresh water and after 3500 cal bp an enhanced inflow of seawater during stage iv 2650 2250 cal bp the salinity of the lake water gradually decreased owing to reduced seawater inflow during stage v 2250 cal bp to 480 cal bp the lake water changed from brackish to fresh although salinity increased temporarily during the middle of the period and the depth of the lake increased and during stage vi 480 cal bp to the present an inner bay environment developed again following the ad 1498 meio earthquake although salinity increased temporarily from ad 1600 1750 we also identified two event deposits ea and eb on the basis of spikes in the abundance of minor diatom species in ea layer 4600 4500 cal bp glyphodesmis williamsonii a marine or brackish water species was temporarily dominant and lamination disappeared therefore this layer was interpreted to represent a brief episode of sediment supply from seaward such as by a tsunami or storm surge the eb layer ca 4200 cal bp in contrast was characterized by an increase in fresh and fresh to brackish water species suggesting a temporary supply of allotopic riverine or lake shore sediments during a large flood event

ree fractionation and ce anomalies in weathered karoo dolerite abstract analyses of samples from a weathering profile on karoo dolerite allow elements to be divided into three groups depending on their behaviour si k na mg ca sr ba and v are mobilized and removed from weathered products fe al ti zr hf zn cu sc co and ni are immobile ree y and to a lesser extent cr are mobile and redistributed within the profile without a net loss of these elements from the profile large positive ce anomalies are developed in oxidized weathered products by preferential leaching of the other ree s negative ce anomalies and ree enrichment is a feature of less altered dolerite

redistribution of rare earth elements during diagenesis of carbonate rocks from the mid proterozoic newland formation montana u s a abstract ree data for carbonate rocks from the mid proterozoic newland formation belt supergroup show variable degrees of relative ree enrichment when normalized to a composite shale of the newland formation most conspicuous are relative enrichments in lree s and positive eu anomalies possible coprecipitation of ree s in carbonates from seawater is much too small to account for the ree enrichment thus only diagenetic ree enrichment has to be considered by far the strongest lree enrichment is observed in carbonates with interbedded shales during diagenesis ree apparently moved from the shale partings to the adjacent limestone beds massive limestone units have considerably smaller ree enrichments except in proximity to shales suggesting that ree addition from formation waters is less efficient for supplying ree s than is local redistribution between shale and limestone beds early precipitation of diagenetic silica in pore spaces reduces ree enrichment in limestone beds by reducing their permeability dolostones are cemented by pervasive early diagenetic silica and lack significant ree enrichment except for eu probably because silica cement prohibited access of ree bearing pore waters positive eu anomalies indicate reduction of eu to the divalent state during diagenesis and relatively large mobility of divalent eu

trace element mobility during spheroidal weathering of basalts and andesites in hawaii and guatemala abstract trace element mobility has been studied in spheroidally weathered corestone shell complexes developed on late tertiary and quaternary volcanic rocks the parent materials are basalts and andesites related to 1 a subduction zone tecuamburro and moyuta volcanoes guatemala and 2 a hot spot hawaiian islands of oahu maui and hawai i the initial major element compositions are largely preserved in the corestones each corestone sample shows major element abundances characteristic of the different magmatic processes through which the lavas were generated however the changes in trace element compositions due to weathering show similar patterns in the corestone shell complexes independent of the tectonic setting and age element mobility within the different corestone shell complex was determined using an isovolumetric reference frame in this method bulk density is chosen as an independent measure of the extent of weathering based on volumetric concentrations the notion of element immobility cannot be applied to all the corestone shell complexes elements commonly assumed to be immobile e g zr ti and al vary in volumetric concentration for some corestone shell complex despite petrographic evidence of only minor weathering two corestones oahu and tecuamburro have become enriched in ree 3 relative to other lava flows from the same volcanoes and display negative ce anomalies the exfoliated shells from these complexes tend to have lower concentrations of ree 3 and have positive ce anomalies the fractionation of ce from the other rare earth elements ree is inferred to be a manifestation of changes in the valence state of ce from trivalent to tetravalent under oxidizing conditions in settings where the development of corestone shell complex is advanced an acidic solution can mobilize trivalent ree leach them out of more extensively weathered materials and transport them to less acidic portions of the regolith undergoing incipient weathering the precipitation of the ree 3 in the rinds and centers of the corestones are likely due to increases of the ph of the weathering solution systematic weathering induced ree behavior enrichment of most ree with lesser ce enrichment resulting in a negative ce anomaly can be discerned even in corestone samples that exhibit major element abundances and petrographic features otherwise similar to unweathered basalts and andesites

eolian contribution to soils on mount cameroon isotopic and trace element records abstract we determined sr nd and pb isotopic compositions and major and trace element compositions of soil samples recovered from three soil profiles developed on relatively young pyroclastic deposits less than 10 000 years old of the mount cameroon volcano the time elapsed since then is short compared with the half lives of rb sm u and th suggesting that radioactive decay can be neglected we therefore assumed that i these polyphase soils developed on isotopically homogenous substrates and ii any isotopic variation within such profiles cannot be due to selective dissolution of primary minerals with isotopic compositions different from that of bulk bedrock any sr nd or pb isotopic variation would therefore record an allochtonous input occurring either in a solid or dissolved state sr and nd isotope compositions change systematically with depth in the soil profile in particular 87 sr 86 sr ratios are far greater in the humic horizons than in the underlying horizons except in the ca9h soil profile although smaller than for sr isotope compositions 143 nd 144 nd ratios displayed an inverse relationship with a decrease towards the uppermost organic rich horizons these isotope shifts correlate with changes in sr and nd contents suggesting an allochtonous input characterized by significantly different isotope compositions and slightly lower sr contents but higher nd contents pb isotopic compositions and pb concentrations in the uppermost horizons were distinct from those of underlying horizons in the soil sequences since an anthropogenic contamination such as from leaded petrol cannot explain the pb shifts a natural source has to be invoked for pb as well as for sr and nd considering both the wind paths in west africa and the isotopic shifts registered in the uppermost horizons saharan dust appears to be the best candidate to explain such variations these inputs probably happened in winter when dry warm harmattan wind blows from the northeast a maximum of 8 of saharan dust accretion was calculated for the mount cameroon soils this corresponds to average dust deposition rates between 1 3 and 0 8 g cm 2 ka 1 values that are much higher than those found in hawaiian soils by kurtz et al kurtz a c derry l a chadwick o a 2001 accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances geochim cosmochim acta 65 1971 1983 and are probably related to shorter distance between dust source and deposit any elemental mass balance calculated in the upper organic rich horizons should be then corrected from allochtonous wind borne saharan dust before evaluating weathering linked chemical mobilities

the behaviour of trace and rare earth elements ree during hydrothermal alteration in the rangan area central iran the rhyolitic dome in the rangan area has been subjected to hydrothermal alterations by two different systems 1 a fossil magmatic hydrothermal system with a powerful thermal engine of a deep monzodioritic magma 2 an active hydrothermal system dominated by meteoric water based on mineralogical and geochemical studies three different alteration facies have been identified phyllic advanced argillic and silicic with notable differences in ree and other trace elements behaviour in the phyllic alteration zone with assemblage minerals such as sericite pyrite quartz kaolinite lree are relatively depleted whereas hree are enriched the advanced argillic zone is identified by the presence of alunite jarosite and pyrophyllite as well as immobility of lree and depletion in hree in the silicic zone most of lree are depleted but hree patterns are unchanged compared to their fresh rock equivalents all the ree fractionation ratios la yb cn la sm cn tb yb cn ce ce cn and eu eu cn are low in the phyllic altered facies eu eu cn in both advanced and silicic facies is low too in all alteration zones high field strength elements hfse e g ti zr nb are depleted whereas transition elements e g v cr co ni fe are enriched geochemically speaking trace and rare earth elements behave highly selective in different facies

a conodont based silurian chronostratigraphy ranges of 79 conodont species are used to effect a graphic correlation of upper llandoverian pridolian silurian rocks in 30 stratigraphic sections in europe and north america a silurian composite standard section css developed by this method provides the total stratigraphic ranges for all species for which there is information in the system these ranges are stated in terms of the sequence of silurian rocks at cellon austria which is the standard reference section srs the llandoverian wenlockian and ludlovian pridolian boundaries are recognized based on the position of the golden spike in the boundary stratotypes the leasows hughley brook and pozary sections which form parts of the css range data for graptolite species in ten of the stratigraphic sections are used to approximate positions of all other boundaries between silurian series and stages that have been designated in boundary stratotypes that are not parts of the composite standard section the pridolian is shown to have had a longer duration than either the ludlovian or wenlockian and the llandoverian possibly approximated the pridolian in duration the css is divisible into 48 standard time units stu9s of conceptually equal length hence the chrono stratigraphy based on it resolves at a level two to four times higher than any previously proposed for the silurian the css is also divided into a succession of conodont chronozones that are based on zones proposed by walliser 1964 aldridge 1972 and barrick and klapper 1976 conodont chronozones can be recognized with confidence only in sections that are parts of the css framework

holocene uplift derived from relative sea level records along the coast of western kobe japan abstract mid to late holocene sea level observations have been obtained from tamatsu and tarumi in western kobe japan in this tectonically active area we evaluate the local tectonic effect during the holocene by comparison between observations and predictions of sea level variations for the purpose of this study we analysed the diatom assemblages and carried out sulphur analysis of sediments these were used along with radiocarbon dates to derive relative sea level variations for the sites a rate of tectonic uplift of between 0 1 and 0 3 mm per year corrected for the prediction fits well with relative sea level rsl index points of tamatsu at 6415 5320 cal bp depending on the altitude of the rsl index point at about 5700 cal bp the best estimate of the rate of tectonic uplift for tamatsu is calculated as 0 11 0 25 mm yr over the period concerned a rate of tectonic uplift between 0 3 and 0 5 mm per year is derived for tarumi at about 7300 and 3835 3365 cal bp these values may explain the height distributions of the late pleistocene marine terraces along the coast of the western kobe providing a first approximation for rates of local crustal movements during the late quarternary

rbsr dating of acidic rocks from the middle part of the inner zone of southwest japan tectonic implications for the migration of the cretaceous to paleogene igneous activity abstract rb sr age determinations by mineral and whole rock isochron methods have been performed on cretaceous to paleogene granitic and rhyolitic rocks from the middle part of the inner zone of southwest japan in order to examine some chronological problems and tectonic models for the migration of igneous activity our chronological results include 1 isotopic homogenization of granitic and rhyolitic rocks in the miyazu izushi area was disturbed by mixing of acidic and basic magmas 2 the rokko granite was emplaced at 77 8 ma and reheated at 72 ma 3 mineral isochron ages obtained for the acidic volcanic rocks range from 62 6 to 85 8 ma and are considered to date the time of eruption igneous activity migrated eastward from 95 ma to 70 ma which may be related to a similar eastward migration of the development of sedimentary basins in fore arc regions the observed eastward migration has been discussed with relevance to a ridge subduction model in which the heated position by subducted ridge moved from west to east although the cause for the migration of the igneous activity is poorly understood several difficulties with the simple ridge subduction model are pointed out

chronometric calibration of mid ordovician to tournaisian conodont zones a compilation from recent graphic correlation and isotope studies three available graphic correlation analyses are used to calibrate mid palaeozoic conodont zonations sweet s scheme for the mid to upper ordovician kleffner s for the mid to upper silurian and murphy berry s for the lower and middle lower devonian the scheme of sweet is scaled by applying the high precision u pb zircon date of tucker and others for the rocklandian and linked with that of kleffner by scaling the graptolite sequence of the ordovician silurian global stratotype section to fit two similarly derived dates from this sequence the top of kleffner s scheme all of murphy berry s as well as standard zones to the frasnian are calibrated by using tie points of the latest cambridge bp time scale gts 89 however the recent microbeam zircon date by claoue long and others for the hasselbachtal devonian carboniferous auxiliary stratotype is used to calibrate the standard famennian zones also the similarly derived but preliminary determination reported by roberts and others from the isismurra formation of new south wales is tentatively taken as the top of the tournaisian and so used to calibrate tournaisian zones despite the considerable extrapolation required to compile these schemes and their inherent errors the resultant time scale closely agrees with other dates of tucker and others from the llanvirn as well as the gts 89 homerian gorstian tie point this suggests that stratigraphic methods can be usefully applied to geochronometry the llandovery appears to have lasted longer 16 m y than usually envisaged and the ordovician silurian boundary may need to be lowered to approximately 443 5 ma certainly chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high resolution dating for their calibration will be crucial to more accurate biochronometries

u pb chronology of the ennerdale and eskdale intrusions supports sub volcanic relationships with the borrowdale volcanic group ordovician english lake district u pb analyses of zircons from the ennerdale granitic intrusion and eskdale granite english lake district give ages of 452 4 ma and 450 3 ma respectively these data confirm the sub volcanic association of these intrusions and show that previously published rb sr whole rock and k ar mineral ages do not correspond to the emplacement and cooling of these igneous bodies the new ages show that only two phases of acid magmatism can now be linked to the exposed parts of the lake district batholith the caradoc late ordovician phase was caused by the subductionrelated processes which gave rise to volcanism and was followed by a separate early devonian phase of granite emplacement

vila maria formation silurian parana basin brazil integrated radiometric and palynological age determinations fresh shale samples taken from a well known outcrop section of the silurian vila maria formation located on the northeastern margin of the parana basin tres barras farm goias state central western brazil have been analysed for both palynological and radiometric age determi nations the rocks yielded a fairly diverse age definitive cryptospore assemblage and the same samples proved suitable for rb sr analysis despite silurian sedimentary rocks being rarely suited to radiometric dating techniques this study thus introduces an alternative independent method for estimating the minimum depositional age of the vila maria formation the rb sr age value has been calculated via an isochron diagram that yields 435 9 7 8 ma accordingly the latter value is inter preted as the minimum depositional age of the analysed vila maria strata implying their deposition during llandovery times this concurs with the palynological results which indicate an age no older than early silurian and more particularly favour an early to middle llandovery rhuddanian early aeronian attribution

late holocene depositional environments and coastal evolution of the mekong river delta southern vietnam abstract the mekong river delta in southern vietnam is a tide dominated delta and has been formed by the mekong river system the sediments are dominantly fine grained and were deposited in the receiving basin with slight inclination of pre existing deposits in the south china sea and gulf of thailand around 6000 to 5000 yr bp maximum holocene transgression occurred and seawaves surrounded uplands of the late pleistocene terrace basement rock and weathered land in the northern parts of the delta double notches were undercut by seawaves on the limestone hill in hatien at about 4 5 and 2 5 m above present sea level marine deposits prevailed throughout the delta during the highstand and regressions of relative sea level over the last 4550 yr bp delta progradation has produced a great flat plain of 62 520 km 2 this extremely fast progradation could be due to a very high sediment supply depositing in the slight inclination of the receiving basin b neotectonic movements and relative sea level changes c widespread mangrove forests playing an important role to enhance sediment accumulation former mangrove marshy deposits were significantly developed in the plain of reeds and longxuyen quadrangle mangrove marshes have also been developing well in the camau peninsula and present coastlines moreover regressions over the last 4550 yr bp have produced many distinct sets of relict beach ridges which are useful in distinguishing the former coastlines and evolutionary history of the delta

completeness of the known graptoloid palaeontological record using a high resolution chronology of graptoloid first and last appearances we apply mathematical models that allow the simultaneous inference of the probability distribution of species durations and the effective sampling rate relating those durations to the observed stratigraphic ranges this approach allows the completeness of the documented palaeontological record of graptoloids to be assessed we estimate that c 75 of species in the geographical regions that contribute to the stratigraphic data have been sampled and that of those species known from more than a single stratigraphic horizon c 85 of their original durations on average are represented by their global composite stratigraphic ranges as expected in light of their biostratigraphic importance graptoloids have one of the most completely documented records among groups of fossil organisms we expect that application of the methods used herein will show comparably complete records for other biostratigraphically relevant groups supplementary material the r code and data are available at https doi org 10 6084 m9 figshare c 4547174

significance of iron and cobalt partitioning between plagioclase and biotite for problems concerning the eu2 eu3 ratio europium anomaly and magnetite ilmenite series designation for granitic rocks from the inner zone of southwestern japan abundances of rees and other trace elements were determined for granitic rocks and their mineral separates from the sanin sanyo and ryoke belts in the inner zone of southwest japan among those data obtained the fe and co partition coefficients between plagioclase and biotite were found to be specially important the partition coefficients for fe are negatively correlated with those for co and values for the magnetite series granites from sanin belt are clearly separated from those for the ilmenite series granites of ryoke belt the sanyo belt samples which include both types of granites fall within the range of the ryoke ilmenite series granites the variation of fe and co partition coefficients can be interpreted by the difference in redox states crystal chemistry of these minerals and kinetic disequilibrium effect the sanyo belt data suggest that the ilmenite series granites were converted from a magma with magnetite series affinity during later solidification stages moreover the eu2 eu3 ratios in minerals were calculated by the philpotts method in which the equivalence of eu2 and sr2 partitioning is assumed the eu2 eu3 ratio in plagioclase from the sanyo and ryoke belt granites seems to be correlated with the whole rock fe2 fe3 though the sanin belt granites tend to show high plagioclase eu2 eu3 ratios probably due to a disequilibration caused by rapid solidification furthermore effect of redox states on the size of the eu anomaly in plagioclase melt partition coefficient was examined from the plagioclase eu2 eu3 data of the granites

graptolites in british stratigraphy 697 taxa of planktonic graptolites are recorded and their stratigraphical ranges are given through 60 biozones and subzones in the ordovician and silurian strata of england wales and scotland in the first such stratigraphical compilation for great britain since the synthesis of elles wood 1901 1918