the composition of the subsurface neogene shales of the surma group from the sylhet trough bengal basin bangladesh abstract nineteen shale samples from six wells penetrating the neogene surma group in the sylhet trough in northeastern bangladesh were analyzed by x ray diffraction x ray fluorescence spectrometry and direct current plasma optical emission spectrometry mineralogically the subsurface neogene shales of the surma group comprise predominantly quartz plagioclase illite chlorite kaolinite with lower amounts of k feldspar dolomite and smectite and minor to trace amounts of calcite and siderite significant variation in the content of k feldspar smectite and illite smectite mixed layer clays with depth has been observed k feldspar has not been noted below the depth of about 3200 m and smectite has not been observed deeper than 3000 m it is inferred that illite chlorite quartz and feldspar are predominantly detrital in origin reflecting a fast rising source terrain with no intense weathering activity geochemically the mean major element composition of the shales is similar to that of the average shale with the exception of the cao content which is lower here the low cao content could be due to lower carbonate and total organic content the samples are enriched in sc and cu and are depleted in be sr and la other trace elements have values close to the average shale the geochemical characteristics suggest that the neogene shales of the surma group were derived from an active margin setting related to a recycled source

silurian turbidite provenance on the northern avalonian margin the windermere supergroup of nw england was deposited in a foreland basin on the northern margin of eastern avalonia and preserves an almost complete ashgill to poidoli sequence it was ideally positioned to record provenance changes associated with the closure of the iapetus ocean petrographic geochemical and nd isotopic parameters show distinct and concordant temporal trends the late ashgill to early llandovery is characterized by progressive hemipelagic dilution of material derived from the underlying borrowdale volcanic group from the llandovery onward petrographic and geochemical data indicate supply from a recycled orogen source input from the scandian orogen may be inferred no conclusive evidence is recorded of laurentian input into the basin by the late wenlock a unified sedimentary system probably spanned the iapetus ocean an abrupt reversal in provenance trends towards the end of the ludlow records basin inversion the occlusion of the iapetus seaway and concomitant cannibalization of older foreland basin sediments provenance data derived from upper wenlock to poidoli sediments aid the characterization of marine foreland basins

evidence for the formation of illite from smectite during burial metamorphism in the belt supergroup clark fork idaho abstract mineralogic and chemical data have been obtained for 26 argillite samples collected from an 8500 meter section of the precambrian belt supergroup clark fork idaho minerals present are quartz feldspar illite and calcite calcite and or dolomite illite quartz and chlorite quartz ratios decrease up section supporting the conclusion of boyce 1973 that the belt section represents an ancient prograding delta the ratio of k feldspar to total feldspar decreases from 20 80 percent in the upper two thirds of the section to 0 10 percent in the lower one third the mechanism proposed for the decrease in k spar down section is the conversion of k poor smectite into k rich 1md illite a later higher temperature reaction converted much of the 1md illite into 2m illite muscovite e suggest that a low k spar plagioclase ratio in an illite containing shale suite indicates that the illite formed from smectite during metamorphism rather than from the direct weathering of some high temperature phase such as feldspar most continental volcanic material is produced during orogenic episodes most smectite forms from volcanic material and smectites will be converted into illites if enough time has elapsed for them to have been involved in one or more geosynclinal cycles therefore the proportion of smectite in sediments through time can be related to the timing of orogenic episodes this model works fairly well in north america where smectite maxima coincide with orogenic episodes becoming smaller with increasing antiquity of the orogeny

water and sediment chemistry of higher himalayan lakes in the spiti valley control on weathering provenance and tectonic setting of the basin the geochemical study of the dankar thinam and gete lakes of the spiti valley has revealed that these lakes are characterized by varying contents of major ions i e ca mg hco3 na k cl so4 sio2 and sr as trace element the concentration of these elements is significant as they indicate the nature of the lithology and the type of weathering at the source the sediment chemistry data have also been employed to quantify weathering intensity and to elucidate the provenance and basin tectonic setting where terrigenous sediment is deposited

plate tectonics and geochemical composition of sandstones a reply the comments of roser and korsch 1984 are related to two aspects 1 their apparent inability to reproduce the results of the discriminant scores as given in table 9 of my paper bhatia 1983 and 2 the effect of grain size on the composition of clastic sedimentary rocks the apparent discrepancy in the discriminant scores is due to their error in calculation roser and korsch 1984 calculated the discriminant scores using the volatile free averages of the published sandstone suites tabulated in tables 5 8 of my paper however the discriminant functions that i developed are based on the actual non volatilefree analyses of the sandstone suites of eastern australia thus the discriminant scores on the published averages given in table 9 of my paper were also calculated using the actual analyses and not the volatile free analyses this is mentioned in the text of my paper bhatia 1983 p 620 discriminant scores for averages of the published analyses were calculated using the unstandardized function coefficients of table 3 and the actual abundance of element oxide in the average italics added the actual average chemical analyses and the calculation of the discriminant scores for three of the suites on which significant apparent discrepancies exist are presented in table 1 as examples in the three cases presented aure trough santa ynez and the rhyolitic sand suites all the scores agree with those given in bhatia 1983 and differ significantly from those calculated by roser and korsch 1984 the incomplete published analyses certainly posed some problem due to the im

composition of modern deep sea sands from arc related basins summary petrographic and chemical examination of modern deep sea sands shows a clear distinction between active and passive plate tectonic settings among active settings sands from forearc basins of island arcs and basins from strike slip continental margins can be distinguished but those from other arc related settings overlap considerably in composition in particular sands from continental margin subduction zones and those from the backarc of island arcs appear to be indistinguishable chemically arc related sands are very close in composition to ancient greywacke sandstones for instance sodium almost always exceeds potassium thus it is not necessary for sodium to be added to sands diagenetically to make greywackes as has been suggested the influence of tectonics on the composition of sandstones has long been a central feature of sandstone petrology the geosynclinal model of global tectonics stimulated much thought on this subject probably the best known ideas are those of krynine e g 1942 subsequently such research declined but the plate model for global tectonics has produced a new wave of interest e g crook 1974 schwab 1975 potter 1978 dickinson suczek 1979 much of this work has relied on data from ancient sediments where diagenetic changes and difficulty in de ciphering the tectonic setting limit the useful ness of the conclusions much more work is needed on recent sediments to establish a base line against which ancient sediments can be compared we have previously reported valloni maynard 1981 the results of our work on the petrography of a set of recent deep sea sands from piston cores in this paper we shall com pare this petrographic information with bulk chemistry and attempt to relate these to tecto nics in arc related settings

evolution of geochemistry and depositional settings of early palaeozoic siliciclastics of the barrandian tepla barrandian unit bohemian massif czech republic cambrian and ordovician middle devonian sequences of two successive early palaeozoic basins of the barrandian unconformably overlie cadomian basement in the bohemian massif nw interior tepla barrandian unit which is the easternmost peri gondwanan remnant within the variscides correlation of stratigraphy and geochemistry of the early palaeozoic siliciclastic rocks elucidated sediment provenances sandstones of the middle cambrian p ibram jince basin were derived from a cadomian neoproterozoic island arc the source area of the ordovician shallow marine siliciclastics of the successor prague basin is a dissected cadomian orogen late cambrian acid volcanics of the barrandian and cambrian meta granitoids emplaced in the w part of the tepla barrandian cadomian basement are also discernible in these sediments old sedimentary component increased during the ordovician early llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of silurian transgression emsian siliciclastics intercalated in the late silurian to early devonian limestone suite presumably comprise an addition of coeval basic ultrabasic volcaniclastics middle devonian flysch like siliciclastics indicate reappearance of cadomian source near the barrandian during early variscan convergences of armorican microplates that preceeded accretion of the tepla barrandian unit within the bohemian massif terrane mosaic

high latitude e and f region coupling signature a case study results from rapid run ionosonde rapid run ionosonde installed in the high latitude sodankyla geophysical observatory enables us to observe for the first time extraordinary details of e f region coupling process in high latitude ionosphere during geomagnetically quiet period we present an example on 15 august 2009 when a dense patchy sporadic e layer was detected associated with this unstable sporadic e layer exhibiting in addition an unusual enhancement with a vertical extent of about 10 km the highly structured f layer plasma was observed with apparent plasma depletions we examine this event taking into account the presence of mesoscale traveling ionospheric disturbances which can initiate coupling between these two regions and compare the data with current theories

provenance and tectonic setting of the proterozoic turbidites in hunan south china geochemical evidence the geochemical composition of the middle upper proterozoic turbidites in hunan south china is related to provenance and tectonic setting of the sedimentary basin the turbidites are characterized by moderate sio 2 contents al 2 o 3 sio 2 typically 0 1 0 3 and moderate k 2 o na 2 o ratios generally 0 1 0 3 but relatively high fe 2 o 3 mgo contents 5 10 wt and unusually low contents of cao typically 1 wt abundances of ferromagnesian trace elements and incompatible elements are moderate the ree patterns are uniform and similar to the upper continental crust and typical post archean shales with lree enrichment flat hree and significant negative eu anomalies in general the slates show higher contents of fe 2 o 3 mgo and ferromagnesian trace elements and lower ratios of la sc and th sc than the associated graywackes suggesting that more mafic materials were incorporated into the clay size fraction compared to the upper proterozoic banxi group the middle proterozoic lengjiaxi group has higher concentrations for most ferromagnesian trace elements and lower la sc ratios implying more mafic components in the provenance of the latter the relationship among alkali and alkaline earth elements the chemical index of alteration cia and the th u ratios indicate that the source area was affected by a moderate weathering history the main source was old continental crust the yangtze craton dominated by felsic rocks of magmatic origin with a variable admixture of mafic components from continental island arcs e g the fangjingshan dayong and the sibao yiyang island arc chains the flysch deposition took place in a back arc basin rather than a failed intracontinental rift as proposed by some workers we suggest that suturing between the yangtze and cathaysia blocks did not occur until late proterozoic time and that the final assembly of the supercontinent rodinia in south china was probably marked by the jingning orogeny at 0 8 ga

geochemistry and tectonic setting of lewisian clastic metasediments from the early proterozoic loch maree group of gairloch nw scotland abstract the early proterozoic 2 0 ga loch maree group lmg of the lewisian complex consists of a supracrustal sequence of metasedimentary schists and associated tholeiitic metavolcanic amphibolites within the archaean basement the metasediments comprise three main mapped units the flowerdale schists kerrysdale schists and charlestown schists together with numerous narrower bands the dominant clastic metasediments within the schist units semipelites and psammites are chemically distinguished as a series of greywackes and lithic sandstones with variable lil and transition element abundances fractionated ree patterns and overall compositions similar to paas three chemical groups are recognized whose range of composition largely reflects the mixing between two main source components lewisian gneissose basement with an intermediate acid continental crust composition and local rift related amphibolites with a primitive tholeiitic composition which also incorporates components not preserved within the lmg the geochemistry of the clastic metasediments confirms a previous tectonic model for the lmg as an intracontinental extensional rift receiving clastic detritus from the adjacent uplifted basement as well as from internal volcanogenic sources

meteor induced transient sporadic e as inferred from rapid run ionosonde observations at midlatitudes 1 observations were made with a rapid run ionosonde during a 1 month period from the end of july to the end of august 2002 that included the perseid meteor shower ionograms were obtained at 1 minute intervals all the echo traces below a virtual height of 200 km were hand scaled for detecting weak and broken traces as well as well determined sporadic e among the scaled e region traces a distinct meteor echo persisting for 40 min was observed this long duration meteor event was similar to that observed during the leonid meteor shower in 2001 however the apparent height of the echo traces in the current event first decreased and then increased after equaling the height of a persistent sporadic e layer while the apparent height of the long duration meteor echo trace observed in leonids 2001 remained nearly constant the descending rate of the meteor echo was approximately 22 m s which was considerably greater than that of the tidal ion layer trapped in a downward moving wind shear node we ascribe the long duration meteor echo to a transient and horizontally drifting sporadic e patch generated from meteor trail plasma

ionospheric effects of the missile destruction on 9 december 2009 we report on ionosonde and meteor radar observations made in sodankyla geophysical observatory sgo 67 22 n 26 38 e finland on 9 december 2009 during a test launch of the russian solid propellant military missile due to a technical problem the missile was self destroyed around 07 ut at an ionospheric height near 200 km altitude over the kola peninsula russia at a distance about 500 km to east from the observatory products of the explosion were spread into a large area and reached the region of sgo meteor radar observations in about 2 h around 09 ut after about 3 h around 10 ut a sporadic e layer presumably composed of the remains including long lived metallic aluminum and its oxides ions was observed near the zenith of the sgo ionosonde we discuss possible mechanisms accounting for transport of the remains 1 since the event occurred during a long lasting period of extremely low solar and magnetic activity the ionospheric electric field was unlikely to play a substantial role in the transport of the remains and sporadic e layer formation 2 the horizontal transport of the remains cannot be explained by the neutral winds based on empirical models 3 theoretical estimations suggest that the observed transport could be due to thermospheric turbulence

geochemistry of renuka lake and wetland sediments lesser himalaya india implications for source area weathering provenance and tectonic setting the geochemical investigation of sediments deposited in the renuka lake basin and its adjoining wetland has shown variation in the distribution and concentration of major trace and rees the major elements are depleted in the lake in relation to wetland and that of post archaean australian shale paas except for cao which is strikingly in excess and has a dilution effect on sio2 and other oxides and trace elements the wetland sediments on the other hand are enriched in al2o3 fe2o3 k2o and tio2 and the latter three show a positive correlation with al2o3 in both wetland and lake sediments suggesting their association with phyllosilicates and similar source rocks the enrichment of y zr ni th u and nb in wetland compared to lake and their similarity with paas in the former suggests more clay fractions in the wetland a high zr hf ratio in wetland and lake sediments and a positive correlation of zr with y and hree indicate zr control on hrees however higher zr yb and zr th ratios in wetland compared to lake indicate mineral sorting during the process of lighter particles clays being trapped in wetland soil this is also reflected from negative correlation of gdn ybn with al2o3 and a strong positive correlation with sio2 in wetland sediments the wetland in this context has a control on lake sediment chemistry the chondrite normalized ree patterns are essentially the same for lake as well as wetland sediments but abundance decreases in the former the similarity of pattern with that of paas and negative eu anomaly indicates a cratonic source of sediments in a plot of the individual samples wetland samples cluster while lake samples are separated indicating fractionation of lake sediments a strong positive correlation of lan ybn with al2o3 and a positive correlation of zr lree and zr lan ybn suggest that lrees are controlled by both phyllosilicates and zircon the chemical index of alteration cia indices in lake sediments and in wetland are higher than paas indicating moderate chemical weathering in the source area the petrography lack of felsic magmatic rock fragments and negative correlation between zr gd yb c indicate sedimentary source rocks for the detritus this is in conformity with the lesser himalayan sedimentary sequence belonging to neo proterozoic proterozoic age and constituting lake catchment of renuka the tectonic delineation and discriminant function plots of lake and wetland sediments indicate their cratonic and or quartzose sedimentary orogenic terrain source that has been deposited in a passive margin setting

geochemical characteristics of the triassic tethys turbidites in northwestern sichuan china implications for provenance and interpretation of the tectonic setting the triassic tethys graywacke slate turbidites in the northwestern sichuan china have been analysed for major and trace elements and petrographically studied compared to phanerozoic turbidites the turbidites in this study are quartz intermediate average 55 in composition and are characterized geochemically by their moderate fe2o 3 mgo 9 28 2 84 tio2 0 72 0 17 contents and al2o3 sio2 0 25 0 10 ratios moderate abundances of ferromagnesian trace elements co 15 8 ppm cr 113 72 ppm ni 14 9 ppm sc 12 4 ppm etc and moderate contents of incompatible elements such as th 11 3 ppm u 3 0 7 ppm zr 170 64 ppm hf 4 1 ppm and total rees 159 33 ppm in general the slates show systematically higher fe2o 3 mgo sc co and eueu but lower sollasc and thsc than the associated graywackes suggesting that various provenance components may separate into different grain size fractions during sedimentary sorting processes that is the more mafic materials tended to incorporate into the sedimentary record for the clay size fraction framework modes and geochemical data indicate that the turbidites were mainly derived from a recycled orogenic provenance characterized chiefly by sedimentary metasedimentary rocks and granite gneisses similar to the upper continental crust but with a variable admixture of continental island arc volcanic components flysch deposition took place in a back arc basin situated between an active continental margin the kunlun qinling fold belt and a continental island arc the yidun island arc weathering conditions in the source area significantly influenced the composition and distribution of elements in the sediments with the elapse of time during sedimentation the degree of chemical weathering in the provenance became intense while the tectonic activity decreased gradually

ionospheric effects of the leonid meteor shower in november 2001 as observed by rapid run ionosondes 1 we operated ionosondes at four stations in a rapid run mode to obtain ionograms every minute for 102 hours during the period of the leonid meteor shower in november 2001 plenty of radio echoes that looked like echo traces produced by sporadic e reflection were seen in the ionograms and this allowed statistical analysis in a single meteor shower event including discrimination of the backscattering by meteor trails from reflection by a horizontally stratified sporadic e layer the radio echoes seen in the ionograms were categorized into three types the first were spontaneous echoes which were distributed across a wide range of virtual heights at times during the period of maximum meteor activity there was a statistically good correlation among the echoes seen at the four stations the echoes of this type appear to be produced by fresnel backscattering from meteor trails the second were also spontaneous echoes observed during the shower period but persisted for several tens of minutes at the same virtual height as the typical sporadic e layer and the top frequency of these echoes decayed with time echoes of this type are thus attributed to the reflection from a meteor induced sporadic e patch echoes of the last type appeared outside the period of maximum activity of the meteor shower in the same range of virtual heights as the conventional sporadic e layer and there was no time correlation between the events observed at the four stations these events are attributed to a periodical increase in foes which is modulated by planetary wave activity and have no relation with the meteor shower

radar interferometric imaging studies of long duration meteor echoes observed at jicamarca a large number of long duration 15 s meteor echoes were detected at the jicamarca radio observatory on two nights in early august 1990 during an evening electrojet experiment using an interferometric imaging technique we were able to measure a zonal velocity profile for each meteor trail our analysis procedure differs from conventional meteor wind methods in that it provides instantaneous profiles rather than long term average information significant altitudinal and temporal variabilities of the horizontal velocities were noted zonal speeds of up to 100 m s 1 large vertical shears of up to 20 m s 1 km and rapid temporal variations of up to 50 m s 1 over an hour interval were observed spectral analysis indicates the presence and decay of asymmetrical high frequency signal components possible explanations for the observed high frequency components are discussed as are the angle of arrival of and the scattering mechanism responsible for the meteor echoes

neoproterozoic nb ta w sn bearing tourmaline leucogranite in the western part of jiangnan orogen implications for episodic mineralization in south china abstract there are four episodes neoproterozoic early paleozoic early and late mesozoic of sn w nb ta mineralization in south china accounting for more than 50 w and 20 sn reserves of the world and hosting considerable nb and ta resources the genesis for such large scale mineralization that may have seen multiple phases of recycling of ore elements is not well unterstood the study of the earliest mineralized granites in south china however may be helpful to better understand the mechanism of mineralization we present detailed mineralogical geochemical and isotopic data from two typical neoproterozoic mineralized intrusions i e the fanjingshan and yuanbaoshan tourmaline leucogranites there is a characteritstic mineral succession of diverse magmatic columbite group minerals cgms nb ta bearing cassiterite and hydrothermal wolframite wolframoixiolite nb ta poor cassiterite sn w nb ta oxides hydrothermal cassiterite and w bearing oxides wolframite wolframoixiolite in the yuanbaoshan intrusion were deposited separately by two types i e sn rich and nb w rich fluids in situ u pb dating of zircon columbite and wolframoixiolite yields ages of 830 5 832 5 and 821 5 ma respectively whole rock end t values of 2 5 to 6 4 correspond to crustal nd model ages of 1 6 1 9 ga paleoproterozoic model ages 1 6 2 2 ga for most episodes of w nb ta mineralization in south china indicate that i paleoproterozoic or older sediments may have been involved in the formation of w nb ta bearing granites and ii contributions of juvenile material was not important for these w nb ta mineralization neoproterozoic peraluminous granites along the jiangnan orogen formed in post collision environments but only those in the western part show sn w nb ta mineralization the mineralized neoproterozoic granites of the western part have experienced more extensive fractional crystallization lower nb ta zr hf ratios and more depleted in fe mg ca sr ba eu ti and are richer in volatiles h2o b than the barren peraluminous intrusions of the eastern part as similarly evolved mesozoic metaluminous granites of the nanling area have considerably more important tin mineralization than the mineralized neoproterozoic granites fractionation is not the only factor controlling mineralization instead other factors such as protolith and conditions of partial melting may account for the more important mesozoic tin mineralization

on the vhf radar echoes in the region of midnight aurora signs of ground echoes modulated by the ionosphere we present all sky interferometric meteor radar mr vhf 36 9 mhz observations from sodankyla geophysical observatory and report on the unusual echoes which were detected at low elevation on the northern horizon typically during substorms these echoes have a near zero doppler shift relatively low power but with a sharp rise to the power peak short lifetime less than 2 s and nonexponential decay ned we suggest that such auroral ned echoes are in fact ground backscatter of the mr waves which have been refracted in the ionosphere passing through the ionosphere in the substorm region where pulsating aurora at a frequency higher than 1 7 hz occurs and causes quasiperiodic modulation of the wave propagation conditions which leads to corresponding modulation of the amplitude of return the mr treats such oscillating signal as meteor trails

the metamorphic characteristics of metapelites of the mashan group in mashan area eastern heilongjiang province china constraint on the crustal evolution of the jiamusi massif abstract mashan complex in the southeastern margin of the jiamusi massif has traditionally been interpreted to be the oldest stratigraphic sequence in eastern ne china here we investigated the mashan complex in the ximashan area and present lots of new la icp ms zircon u pb petrological and mineralogical chemical data in addition with phase equilibria modeling to constrain the timing of metamorphism p t conditions and the p t path of the mashan complex and furthermore to deduce the crustal evolution of the jiamusi massif the protoliths of the metapelites from the mashan complex in the ximashan area are clay rocks and sandstones whose provenance is dominantly felsic rocks which formed from a continental island arc three metamorphic generation assemblages m2 m4 are recognized in the studied samples a peak granulite facies stage a post peak near isothermal decompression stage and a late near isobaric cooling stage which together define a clockwise p t path it reveals important information related to the collision orogeny subsequent uplift and post collision process zircon u pb dating of two metapelitic samples yielded metamorphic ages of the older group varying from 535 6 to 480 5 ma which can be perfectly correlated with the age range 501 6 to 498 6 ma of magmatic activities recorded by the gneissic granite sample the data presented here together with those published allow us to preliminarily infer that the peak of the granulite facies metamorphism in the ximashan area of the jiamusi massif might have occurred at 530 500 ma the younger of the metamorphic ages 476 453 ma should be regarded as the age of late stage therefore a collision orogeny regime is favored to interpret the metamorphic evolution of metapelites of the mashan group in the mashan area

geochemistry of the miocene oil shale hancili formation in the cankiri corum basin central turkey implications for paleoclimate conditions source area weathering provenance and tectonic setting abstract the geochemistry of oil shale units of hancili formation in the cankiri corum basin central turkey was studied using various chemical analyses the mineralogical composition of the samples were preliminarily investigated using pearson s correlation coefficients of selected elements indicating that the samples contain abundant clay minerals as well as k feldspar and carbonate the k 2 o al 2 o 3 and sio 2 al 2 o 3 ratios indicate that the major proportion of clay minerals is composed of smectite si al ti k na and fe reside in clay minerals while ca mg and mn are mostly associated with carbonates e g calcite and dolomite and phosphorous p is present as apatite the total ree content of the oil shale range from 19 to 113 ppm the chondrite normalized patterns of the oil shale show lree enrichments hree deficits negative eu anomalies and negligible ce anomalies in general major trace and rare earth element abundances suggest that the studied oil shale in the cankiri corum basin are mainly from the intermediate rocks mixed with small amounts of basic rocks and that their source rocks are mostly deposited in the continental collision setting the ree geochemistry of the oil shale suggests that these samples were derived from a consistent terrigenous source and the eu anomaly was inherited from the source rocks the paleoclimate index c value varies between 0 07 and 1 22 reflecting a generally semi arid to humid conditions in addition rb sr 0 22 and sr cu 9 09 ratios support the idea that warm and humid conditions prevailed during deposition of the hancili formation sr ba ratios 0 54 3 7 of the studied samples suggest a paleoenvironment with variable salinity the co variation among this factor and paleoclimate indicators suggest that variations in climatic conditions exerted a primary control on salinity the substantially low c value and rb sr ratio and significantly high ratios of sr cu and sr ba and also elevated carbonate content of four samples indicate that these samples were deposited during hot and arid periods and that the paleoclimate controlled the terrigenous sediment flux to the lake basin the chemical index of alteration cia a cn k ternary diagram and high th u ratios indicate that the parent rocks of the oil shale experienced moderate chemical weathering steady state

the geochemistry of the sedimentary rocks from the huadi no 1 well in the wufeng longmaxi formations upper ordovician lower silurian south china with implications for paleoweathering provenance tectonic setting and paleoclimate abstract the late ordovician early silurian transition was a critical interval in earth s history marked by mass extinction the gondwana glaciation and volcanic events here we present mineralogical and geochemical characteristics across the ordovician silurian boundary wufeng guanyinqiao and longmaxi formations from the huadi no 1 well in the sichuan basin in order to explore the paleoweathering provenance tectonic setting and paleoclimatic conditions of the source area thin sections xrd x ray diffraction data and major element results reveal that the rocks were abundant in clay minerals quartz minor feldspar pyrite and carbonate minerals the samples have similar chondrite normalized ree patterns to those of paas which are characterized by slight lree enrichments and accompanied by flat hree trends with weakly negative eu anomalies paleoweathering indices cia and pia suggest that the sediments experienced weak to moderate chemical weathering in the source area cia values in the lower wufeng formation range from 67 11 to 72 17 indicating a warm and humid climate the cia values in the upper wufeng formation decrease from 70 35 to 66 15 and the cia values in the guanyinqiao and lower longmaxi formation are persistently low 56 64 62 87 suggesting a cold and dry climate which is consistent with the widespread presence of glaciation in the hirnantian period further upward in the upper longmaxi formation the cia returns to a high value 65 59 which may reflect that the climate started getting warm and glaciation had finished fluctuations in cia values reflect that the climate shifted from warm to cold and then to warm again during the end ordovician early silurian time period the a cn k triangular diagram and sio2 al2o3 tio2 tio2 zr and la th hf bivariate diagrams indicate that the provenance of the rocks from the three formations was primarily felsic igneous rocks discriminant function diagrams and la th sc th co zr 10 and th sc zr 10 triangular diagrams show that the clastic sediments of the wufeng longmaxi formations were derived most likely from an active continental margin finally across the late ordovician early silurian tectonic activity and the end of the ordovician glaciation dominantly controlled the deposition of black shales and siltstones in the wufeng longmaxi formations of south china

trace element geochemistry and sedimentary provinces a study from the tasman geosyncline australia abstract the abundances of la th u and hf have been determined in flysch sequences of the tasman geosyncline australia the arc derived graywackes differ from those of rifted continental margins and marginal basins in containing low abundances of la th u and hf la 9 2 1 7 ppm th 1 4 0 6 ppm u 0 52 0 2 ppm hf 2 1 0 6 ppm reflecting similar low abundances in the andesitic source rocks graywackes of rifted continental margins and marginal basins in contrast are mature and characterised by high abundances of la th u and hf la 39 9 9 ppm th 16 0 6 ppm u 3 40 0 5 ppm hf 7 9 ppm mirroring increased abundances in the granitic and sedimentary source rocks sedimentary rocks deposited in inter arc basins show wide dispersion but have characteristics intermediate between these two types the th u ratio for magmatic arc sediments is 2 7 for most other sedimentary rocks it remains uniform at 4 5 0 3 for sediments having andesitic and dacitic rocks as provenance the la th ratios are 6 7 and 4 5 respectively this ratio remains constant at 2 6 for most quartzose sedimentary rocks

tectonic environment of the devonian gramscatho basin south cornwall framework mode and geochemical evidence from turbiditic sandstones the portscatho formation within the allochthonous unit of the middle and upper devonian gramscatho group is a thick sequence of deep water sandstones and interbedded slates deposited by southerly derived turbidity currents into the gramscatho basin of south cornwall throughout an approximately 3 5 km thick sequence the portscatho formation is petrographically and chemically coherent except that the upper section shows a higher proportion of metamorphic clasts high but variable cr and low uniform zr abundances complementary framework mode and bulk geochemistry indicate that the sandstones were derived from a dissected continental magmatic arc of predominantly acidic composition similar to average upper continental crust but with an admixture of minor intermediate basic material flysch deposition took place in a fore arc setting the presence of an arc to the south of cornwall during the devonian implies that there was subduction at the margin of the gramscatho basin whose ultimate closure was accommodated by the northward stacking of flysch ophiolite nappes

geochemistry of the shitoumei oil shale in the santanghu basin northwest china implications for paleoclimate conditions weathering provenance and tectonic setting abstract thick sequences of organic rich lacustrine oil shale were deposited in the middle permian lucaogou formation of the junggar basin and the santanghu basin the mineralogy and major trace and rare earth element geochemistry of the oil shales and mudstones collected from the lucaogou formation are discussed the chondrite normalized patterns of the studied samples show lree enrichments hree deficits and generally negative eu anomalies and positive ce anomalies the paleoclimate indictor c value varies between 0 08 and 0 62 reflecting generally arid to subhumid conditions in addition low rb sr with a mean value of 0 14 and high sr cu with a mean value of 33 22 values indicate that arid conditions prevailed during the deposition of the lucaogou formation sr ba ratios 0 31 7 73 of the studied samples suggest a paleoenvironment with variable salinity the salinity of the lake is controlled by climate variations freshwater replenishment seawater intrusion and redox conditions the studied oil shales in the lucaogou formation are mainly derived from a felsic dacite and rhyolite to intermediate andesite source that formed in the early permian and mixed with small amounts of basic rocks basalt volcanic eruptions provided the source rocks for the lucaogou formation the chemical index of alteration cia the plagioclase index of alternation pia and an a cn k ternary diagram indicate that the parent rocks of the oil shale experienced weak to moderate chemical weathering

composition and classification of paleozoic flysch mudrocks of eastern australia implications in provenance and tectonic setting interpretation abstract the mudrock suites of paleozoic flysch sequences of eastern australia can be characterised on the basis of the relative abundances of phyllosilicates and tectosilicates mainly feldspar and quartz a mudrock maturity index is defined as the ratio of total phyllosilicates to phyllosilicates feldspar quartz mudrocks are classified into tectic phyllo tectic and phyllic types on the basis of increasing maturity based on studied examples of eastern australia preliminary characteristics of mudrocks of various tectonic settings are identified oceanic island arc mudrocks are of the tectic type characterised by high feldspar and low phyllosilicate content they are derived from calc alkaline andesitic rocks of the magmatic arc mudrocks of the continental island arc and active continental margins andean type and strike slip basins are characterised by a higher phyllosilicate content and are mainly phyllo tectic in type passive margin mudrocks are of the phyllic type characterised by extremely high phyllosilicate and low feldspar contents suggesting their recycled nature mudrock maturity is accompanied by an increase in the k2o na2o ratio from oceanic island arc to continental island arc and active continental margin to passive margin type mudrocks

the origin of early archean banded iron formations and of continental crust isua southern west greenland abstract a long standing geological debate is whether the fe component of precambrian banded iron formations bifs was derived from continental sources or had its origin in hydrothermal alteration of the oceanic crust recent ree and nd and fe isotope studies of iron rich layers in bifs have provided strong supporting evidence for the hydrothermal origin of the fe component pillow basalts from the 3800 3700 ma isua greenstone belt west greenland underwent significant enrichment of fe up to 21 wt fe2o3 and some chalcophile elements e g pb 5 4 7 2 ppm prior to a late archean tectonothermal metamorphic event recorded in the region published and new pb pb isotopic data from the isua pillow basalts and the spatially associated bifs suggest that the enrichment of fe and pb and deposition of the bifs took place between 3800 and 3600 ma similar pb isotopic compositions in pillow basalts and bifs are consistent with a common source of pb for both supracrustal rocks iron and pb were probably scavenged from the oceanic crust and were re deposited on the ocean floor by hydrothermal fluids suggesting that high temperature hydrothermal alteration of early archean oceanic crust played an important role in the deposition of the isua bifs geochemical lithological and structural data from the isua greenstone belt are all collectively consistent with a convergent margin geodynamic setting the isua bifs are spatially and temporally associated with boninitic and island arc picritic pillow basalts given the observations that cenozoic boninites and picrites tend to form in an intra oceanic arc forearc setting we suggest that the isua bif boninite and bif picrite associations were also deposited in a similar geodynamic setting the original pillow basalt bif stratigraphy was dismembered and transposed throughout the belt during early to late archean tectonothermal events the high temperature hydrothermal alteration of the oceanic crust produced significant hydrothermal discharge with large quantities of fe necessary to contribute to the deposition of the isua bifs the hydrothermal alteration may have resulted from the opening of an asthenospheric window developed as a consequence of ridge subduction beneath an early archean arc forearc region the ridge subduction model can also explain the origin of the contemporaneous tonalite trondhjemite granodiorite ttg intrusions in the isua region partial melting of laterally accreted and thickened oceanic crust under amphibolite to eclogite metamorphic conditions by upwelling of asthenospheric windows may have produced ttg melts the diapirically upwelling ttg melts formed the early archean continental crust and the complementary eclogitic residues contributed to the sub continental lithospheric mantle

geochemistry of mansar lake sediments jammu india implication for source area weathering provenance and tectonic setting abstract the sediment geochemistry including ree of surface and core samples from mansar lake along with mineralogical investigations have been carried out in order to understand the provenance source area weathering hydrolic sorting and tectonic setting of the basin the geochemical signatures preserved in these sediments have been exploited as proxies in order to delineate these different parameters the major element log values fe 2 o 3 k 2 o vs sio 2 al 2 o 3 and na 2 o k 2 o vs sio 2 al 2 o 3 demarcate a lithology remarkably similar to that exposed in the catchment area the chondrite normalized ree patterns of lake samples are similar to post archaean australian shale paas with lree enrichment a negative eu anomaly and almost flat hree pattern similar to a felsic and or cratonic sedimentary source however the la th sc plot of samples fall in a mixed sedimentary domain close to upper continental crust ucc and paas suggesting sedimentary source rocks for the mansar detritus it also indicates that these elements remained immobile during weathering and transportation the mineralogical characteristic rees and high field strength elements hfse together with the high percentage of metamorphic rock fragments in the siwalik sandstone support a metamorphic source for lower siwalik sediments a very weak positive correlation between zr and sio 2 poor negative correlation with al 2 o 3 negative correlation of la yb n and gd yb n ratios with sio 2 and positive correlation with al 2 o 3 suggest that zr does not dominantly control the ree distribution in mansar sediments the petrographic character and textural immaturity indicate a short distance transport for the detritus the distribution of elements in core samples reflect fractionation the higher zr th and zr yb ratios in coarse sediments and paas compared to finer grained detritus indicate sedimentary sorting plots of the geochemical data on tectonic discrimination diagrams suggest that the sediments derived from the lower siwalik were originated within a cratonic interior and later deposited along a passive margin basinal setting it therefore reveals lower siwalik depositional history

petrography and geochemistry of the carboniferous triassic trinity peninsula group west antarctica implications for provenance and tectonic setting the carboniferous triassic trinity peninsula group is a metasedimentary sequence that crops out widely in the northern antarctic peninsula these are some of the most extensive outcrops in the area and hold the key to evaluating the connections of the antarctic peninsula in gondwana however they are still poorly understood here we present our provenance study of the trinity peninsula group using petrographic and geochemical approaches in combination with cathodoluminescence of detrital quartz in order to constrain its source characteristics and tectonic setting using differences in modal composition and quartz cathodoluminescence characteristics we define three petrofacies derived from the progressive uplift and erosion of a volcano plutonic continental arc which exposed the plutonic metamorphic roots as indicated by major and trace elements the source is felsic with a composition ranging from tonalitic to granodioritic the relatively unweathered condition of the source area points to a dry and cold climate at the time of deposition but this does not necessarily mean that it was glaciated deposition of the sediments occurred within an active continental margin relatively close to the source area probably along the south patagonia antarctic peninsula sector of gondwana strong chronological petrological and chemical similarities with the sediments of the duque the york complex in patagonia suggest that they were derived from the same source

mid latitude e region field aligned irregularities observed with the mu radar fine structures e region field aligned irregularities were observed on june 24 25 1989 with the mu radar at shigaraki japan 34 9 n 136 1 e geomagnetic latitude 25 0 n the 3 2 m scale irregularities were observed with the mu radar in five main beam directions each of which was nearly perpendicular to the geomagnetic field at 100 km altitude doppler spectra were obtained every 20 s with a range resolution of 600 m field perpendicular echoes appeared from 2130 to 2330 lt and from 0400 to 1100 lt times that correspond to postsunset and postsunrise period in the e region a preliminary examination of the doppler spectra indicates spectral widths of 50 120 m s 1 and the mean doppler velocities are well below the ion acoustic speed these spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets and have been attributed to the gradient drift instability the echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time height distribution for this reason they are classified into two types continuous and quasi periodic the appearance of the continuous echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period the appearance of the quasi periodic echoes was intermittent with periods of 5 10 min and situated above 100 km altitude during the postsunset period the quasi periodic echoes showed phase propagation toward the radar while the averaged mean doppler velocity was away from the radar by measuring the time delays in echo regions from five directions an apparent westward motion approximately 120 m s 1 of the irregularity regions was estimated

the seek chemical release experiment observed neutral wind profile in a region of sporadic e wind measurements made with the chemical release technique during a sporadic e layer event are presented the data were obtained as part of the sporadic e experiment over kyushu seek sounding rocket campaign the winds show a strong maximum in the lower e region approaching 150 m s 1 near 105 km altitude and a large shear below the maximum the large shear was within a few kilometers altitude of the peak in the electron densities measured on the downleg of the rocket trajectory calculations of the richardson numbers for the wind profile show that the altitude range near the layer was highly unstable