palaeoclimate perturbations before the sheinwoodian glaciation a trigger for extinctiond during the ireviken event telychian to sheinwoodian conodonts pterospathodus eopennatus ssp n 1 zone through the ozarkodina sagitta rhenana superzone were studied in detail for their oxygen isotope composition the upper kockelella ranuliformis and ozarkodina sagitta rhenana zones represent the peak interval of the sheinwoodian positive 18oapatite excursion reflecting the coolest conditions with marine sea water temperatures decreased by more than 6 c in the subtropics the 18oapatite data cover pre through post ireviken event strata the study includes also material from younger levels up to the late wenlock ctenognathodus murchisoni zone however this record is incomplete with one major hiatus reflecting the regression associated with the middle silurian mulde event the stratigraphic levels of the analyzed conodont samples from estonia can be correlated with high precision to the datum points of the ireviken event strata in the lower and upper visby formations on gotland sweden inferred short term climatic changes in the upper telychian part of the studied interval may have been caused by phases of major volcanic activity along the caledonian front across the ireviken event we observe variations in oxygen isotope ratios which allow a direct comparison to the stepwise extinctions and faunal reorganisations in different groups our data suggest that faunal extinctions are connected to time intervals of warming before the establishment of more stable and cooler conditions during the main sheinwoodian glacial the most severe extinctions and faunal turnovers at datum points 2 and 4 occurred during the early warmer interval of the event after the shift into the sheinwoodian icehouse in the lower kockelella ranuliformis zone reflected by rapidly decreasing sea water temperatures faunas restabilized and reefal communities started to flourish sedimentary evidence for the glaciation is discussed for different palaeolatitudes less

provenance of jurassic accretionary complex mino terrane inner zone of south west japan implications for palaeogeography of eastern asia provenance and tectonic history of the jurassic accretionary complex mino terrane located in the inner zone of south west japan were studied using sandstone framework composition and mudrock geochemistry modal analysis of sandstones shows that the tectonic setting of the source area for the studied mino terrane clastic rocks was uplifted basement largely dominated by high grade metamorphic terrain composed of quartz and feldspar especially plagioclase the textural and mineralogical immaturity extent of alkali and alkaline earth element leaching low chemical index of alteration values and depleted rare earth element ree contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity factor analysis revealed that grain size effects governed compositional heterogeneity in the studied sediments provenance of the sediments is interpreted as being plagioclase enriched felsic basement rock such as granodiorite within a continental margin and evolved arc tectonic setting rather than active volcanic arc lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and or erosion of arc volcanics and exposure of basement considering the previous studies on palaeogeography and palaeocurrent reconstruction the north eastern part of the yeongnam massif in the korean peninsula is interpreted as the most probable source area for the studied turbidites the results of mixing calculation for mino terrane sediments suggest that precambrian leucocratic granite and the basement rock of the cretaceous gyeongsang basin shed large amounts of sediments to the mino trench whilst precambrian granitic gneiss and the triassic pluton supplied lesser amounts the results of this study reveal that although active subduction accretion processes were occurring the mino trench was bordered by continental basement rocks this knowledge contributes to enhanced understanding of the jurassic palaeogeography of the east asia continental margin

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

offscraping accretion of jurassic chert clastic complexes in the mino tamba belt central japan abstract detailed structural and biostratigraphical analysis of the jurassic inuyama sequence a coherent chert clastic complex in the mino tamba belt central japan clarifies the evolution of accretionary processes at shallow structural levels the inuyama sequence is characterized by a series of stacked thrust sheets each sheet consists of an early triassic to middle jurassic oceanic plate stratigraphy composed of four lithologic units which are in ascending order siliceous claystone ribbon chert siliceous mudstone and clastic rocks the structural features of the inuyama sequence demonstrate a four stage progressive deformation 1 a decollement was initiated within the siliceous mudstone when this sequence was just seaward of the deformation front clastic dikes and sills formed at the horizon just above the decollement at this time 2 the stratigraphic section above the decollement was imbricated by in sequence thrusting in the frontal part of the wedge this initial stage of thrusting and imbrication was followed by 3 the formation of duplex structures with fault related folds within the lower stratigraphic section as the decollement stepped down section to the lowest siliceous claystone interval finally 4 these thrust packages were overprinted by secondary prism thickening in the form of out of sequence thrust faulting

paleomagnetic evidence for the miocene counter clockwise rotation of northeast japan rifting process of the japan arc paleomagnetic results have been obtained from more than 700 oriented samples in igneous rocks of cretaceous to miocene age from northeast japan the remanent magnetizations of welded tuffs with age between 32 ma and 21 ma old from 17 widely distributed sampling sites in northeast japan are fairly well grouped with a mean ofd 41 2 i 56 5 95 7 2 the remanent magnetization of welded tuffs of 14 ma and 11 ma from 4 sites shows a northerly direction d 11 7 i 60 5 95 15 3 these data imply that northeast japan was apparently subjected to a counter clockwise rotation through 47 14 about a vertical axis on the representative point of northeast japan 141 e 39 n during the past 21 ma comparing with the period of the clockwise rotation of southwest japan the differential rotation between northeast japan and southwest japan is concluded to have occurred concurrently during the period between 21 ma and 12 ma a rifting model of the japan arc is proposed northeast japan rotated counter clockwise through 50 about a northern pivot at 146 e 44 n while southwest japan rotated clockwise through 54 about a southern pivot at 129 e 34 n the differential rotation about different rotation pivots gives rise to the opening of a diamond shaped back arc basin the japan sea

an oceanic model for lithological and faunal changes tested on the silurian record a model for oceanic cycles is presented the cycles are expressed as changes between more humid low latitude and cooler high latitude climates p episodes and dryer low latitude and warmer high latitude climates s episodes the cyclicity may be self regulating through changes in the co 2 storage capacity of the deep ocean due to temperature changes and through changes in the oceanic input and output of dissolved carbonate the model permits over 30 predictions regarding observable changes in both deep water and shelf lithologies and variations in the abundance diversity and extinction rate of planktic and benthic faunas sedimentary changes involve fluctuations in the rate of clay deposition and carbonate production the advance and retreat of carbonate deposition on the shelf edge the timing of oolite reef and black shale formation and changes between oxic and anoxic deep water faunal effects include both iterative evolution and intermittently widespread taxa lazarus taxa these predictions agree well with changes observed in well known sequence of wenlock and ludlow age as well as changes seen in selected older and younger sequences

scanning electron micrographs of quartz sand grains from cold environments examined using fourier shape analysis abstract the use of grain shape to identify sedimentary environments assumes that grain morphology reflects environmental history scanning electron microscopy permits detailed examination of quartz sand grain surface morphology particle shape from gross form to surface texture is quantified using closed form fourier analysis of whole grain outlines from micrographs of 158 quartz sand grains representing subglacial transport and subaerial weathering in cold environments mean harmonic amplitude spectra and roughness coefficients are calculated and three problems are investigated yielding the following results findings are preliminary due to the relatively small number of grains analyzed 1 two dimensional particle micrographs are a suitable surrogate for three dimensional grain roundness a d texture 2 the particle size of a sand grain sample affects its roundness and texture and only samples of similar size range should be compared 3 fourier shape analysis distinguishes significant differences between basal and englacial grains the latter being more angular and rough in texture this finding is relevant to the definition of debris transport paths through glaciers the technique may also prove useful in the interpretation of marine sediments from cold regions and pre quaternary diamictites of controversial or unknown origin

mesozoic radiolarian biostratigraphy of japan and collage tectonics along the eastern continental margin of asia abstract jurassic accretionary complexes mainly composed of carboniferous to permian limestone associated with greenstone triassic bedded chert jurassic siliceous shale and clastic rocks form the basement rocks of japan the stratigraphy of these complexes has recently been analysed utilizing radiolarian fossils resulting in the discovery that japan comprises a collage of disrupted terranes international co operative works reveal that lithologically and biostratigraphically similar terranes are distributed in northeast china nadanhada terrane and sikhote alin ussr khabarovsk terrane paleomagnetic studies demonstrate that prior to opening of the sea of japan the japanese islands were located much closer to the eastern margin of the asian continent where the nadanhada and khaborovsk terranes are now exposed features of the mino terrane in central japan are characteristic of these terranes which originally formed along the continental margin of east asia seamounts covered by fossiliferous limestone formed during the carboniferous to permian at low latitudes the seamounts drifted towards a continental margin together with upper paleozoic sediments triassic bedded chert and lower jurassic siliceous shale which accumulated around them upper paleozoic triassic and lower jurassic formations were accreted to the eastern continental margin which was a large tectonic collage developed as the chinese mainland during the late triassic enormous amounts of clastic detritus were deposited in sedimentary basins where jumbling and telescoping of pelagic sediments took place in a complicated fashion producing a melange the provenance of clastic detritus within the mino terrane is interpreted as a platform on which permian and carboniferous calcareous sediments containing diagenetic lutecite and orthoquartzite formations were widespread these formations covered a precambrian metamorphic and granodioritic basement similar to that seen in the south china region accretion culminated in the earliest cretaceous and the large disrupted terrane which had developed was transpressed northwards along the eastern margin of the continent during this period of dispersal the original terrane was sheared fragmented and separated into many smaller terranes some of which were transported to the sikhote alin region by the late cretaceous the most recent dispersal occurred during the opening of the sea of japan which is closely related to the latest movement of the pacific plate studies of radiolarian micropaleontology and the significance of these fossils to the resolution of the biostratigraphy and the tectonic history of japan are reviewed the results of biostratigraphic analyses are discussed in relation to the mesozoic tectonics of east asia

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

paleomagnetic constraints on the late cretaceous and cenozoic tectonics of southeastern asia abstract many features of the cenozoic tectonic history of central and southeastern asia can be understood as direct consequences of the thrust and penetration of india into asia recent indentation experiments with plasticine tapponnier et al 7 have extended this idea and have led to the prediction of a pattern of large rotations and displacements of continental blocks that can be tested by paleomagnetism the available cretaceous and cenozoic paleomagnetic data from this part of the world have been reviewed and a new apwp for eurasia has been constructed for reference the negligible rotation of south china and large clockwise rotation of indochina are consistent with the model i e with an history of large scale left lateral strike slip motion along the altyn tagh and red river faults data from malaya and borneo can be reconciled with the model although in a less straightforward fashion the large counter clockwise rotation of south tibet implies that it rotated in sympathy with india during the collision and suggests that future indentation experiments should include this feature finally a middle cretaceous reconstruction of the south margin of asia is proposed one interesting result is the restored continuity of geological features in tibet and indochina with active subduction of oceanic indian plate crust taking place to the south at subtropical latitudes

integrated biostratigraphy of the lower silurian of the kolka 54 core latvia integrated graptolite conodont and chitinozoan biostratigraphical data are presented from the llandovery and wenlock of the kolka 54 core latvia correlations between graptolite and chitinozoan biozones are consistent with those published from other east baltic sections and the welsh basin while most correlations between graptolite and conodont biozones agree with those presented in previous studies there are important exceptions significantly we report here the discovery of distomodus staurognathoides biozone conodonts in the lowest aeronian demirastrites triangulatus graptolite biozone the base of the d staurognathoides biozone was previously considered to lie much higher in the aeronian also it is shown that walliserodus survived the late wenlock mulde event during which it was considered previously to have become extinct

arkose subarkose quartz sand and associated muds derived from felsic plutonic rocks in glacial to tropical humid climates abstract in the range of climates from high latitude glacial to equatorial tropical the mineral and chemical compositions of over 600 modern nonmarine first cycle sands and muds produced from felsic crystalline basement provenance in various tectonic settings were studied under glacial conditions sediments are developed by mostly mechanical weathering and thus are mineralogically and chemically similar to their source rocks humid tropical climates yield quartz rich sands kaolinite rich muds along with si mg ca na and k in solution between these extremes a wide range of detrital sediment compositions are developed in arid to wet climates in arid climate and semi arid climate sands feldspar is commonly more abundant than quartz and plagioclase k feldspar except in the cases of granite source rocks the muds are feldspathic with smectite dominant in the clays with increasing temperature and moisture in temperate to subtropical climates mafic silicates and feldspars are destroyed so that the sands range from arkoses with plagioclase as the major feldspar to subarkoses with dominant k feldspar through this range of climate muds become more kaolinitic and thus more aluminous with increasingly severe weathering typically feldspathic sands are associated with feldspathic muds with decreasing feldspar in sands there is less feldspar in muds with increasingly intense chemical weathering rare earth elements ree are more fractionated into muds typically sands contain 150 ppm ree with much of the ree in heavy minerals abundance differences are greatest between humid tropical sands and muds in many samples the ree are mostly in monazite allanite sphene and apatite more intensely weathered samples contain more xenotime and zircon evidenced by yb enrichment

influence of the changing lunar orbit on the astronomical frequencies of pre quaternary insolation patterns the sensitivity of the frequencies of the earth s orbital elements involved in the astronomical theory of paleoclimates obliquity and climatic precession to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth is investigated for the last billions of years but the new frequencies have been computed for the last 440 million years only a time interval over which data and a model of the earth were available moreover we consider only the impact of the changing precessional parameter assuming that the fundamental frequencies of the planetary motion are steady at the geological time scale under such hypotheses the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for obliquity and precession a shortening that is larger for longer periods

radiolarian bearing conglomerate from the hayang group the kyongsang supergroup southeastern korea abstract the non marine cretaceous kyongsang supergroup which is divided into the sindong the hayang and the yuchon groups is widely distributed in southeastern korea radiolarian bearing pebbles are collected from the conglomerates of the kumidong and the kisadong formations of the hayang group the age of radiolarian fossils range from late permian to middle jurassic in korea permian to middle jurassic marine chert beds are not exposed the directions of paleocurrents of the kumidong and the kisadong formations are mainly from the northeast to southwest during cretaceous time the mino tamba belt within which permian to middle jurassic chert beds are exposed is suggested to have been located northeast of the kyongsang basin the radiolarian faunas of the hayang group are similar to those of the mino tamba belt and other associated mesozoic accretionary belts in japan e g the ashio belt the provenance of the radiolarian bearing pebbles collected from the kumidong and the kisadong formations is interpreted to be the mino tamba belt and other associated mesozoic accretionary belts in japan

nature and development of late mesozoic and early cenozoic sedimentary basins in southwest japan abstract the southwestern part of the japanese islands is a typical example of an active continental margin characterized by backarc intra arc and forearc sedimentary basins the back arc basins provide evidence of tectonic continuity with the asian continent the basins are genetically classified as half graben ridge and forearc basins the half graben and ridge basins are controlled by strike slip faulting although the half graben basins are pull apart basins on a much larger scale than the ridge basins and are in many instances closely associated with igneous activity forearc basins occupy the area from the deep sea terrace to the trench floor forearc basin fill sediments form accretionary prisms as a result of subduction processes good examples of these basins are well developed in the cretaceous and paleogene sediments of southwest japan

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

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

integrated biostratigraphy of the lower silurian of the aizpute 41 core latvia integrated graptolite conodont and chitinozoan biostratigraphical data is presented from the rhuddanian through to lower sheinwoodian of the aizpute 41 core latvia correlation of the biozonation schemes based upon the three groups is achieved from the cyphus through to lowermost riccartonensis graptolite biozones except for the upper aeronian and lower telychian which lack both chitinozoans and graptolites and upper lapworthi through to approximately base murchisoni graptolite biozone where there is interpreted to be an unconformity datum 2 of the ireviken event is correlated with a level at the base of or within the murchisoni biozone it is possible that the changes in conodont assemblages at datum 2 on gotland are the result of an unconformity here streptograptus kaljoi sp nov from the lower spiralis graptolite biozone is described

insights on why graphic correlation shaw s method works in 1964 a b shaw presented a method of correlating fossiliferous sedimentary rocks based on interpretation of graphic plots of first and last occurrences of taxa because there is no way to determine the true total ranges of fossil taxa it is instructive to test the accuracy of the method using hypothetical datasets the dataset used here consists of 16 taxa in six sections with differing known rates of rock accumulation in all graphs a single straight line correlation was a reasonable interpretation the resulting ranges after the first and third rounds of compositing reproduce the true ranges but with small errors slight errors in the positioning of individual correlation lines are more likely to lengthen ranges artificially than to shorten them shaw s method works well because whereas actually sampled ranges will be shorter than true ranges errors in correlation will be likely to extend some ranges this or any exercise using simulated data is useful only if the hypothetical situation resem

radiolarian and u pb zircon dating of late cretaceous and paleogene shimanto accretionary complexes southwest japan temporal variations in provenance and offset across an out of sequence thrust abstract in this study we describe radiolarian fossils analyze sandstone petrography and geochemistry and perform detrital zircon u pb dating on the late cretaceous and paleogene shimanto accretionary complexes these data are used to constrain temporal variations in provenance which are related to volcanic arc activity we also determine the behavior of the aki tectonic line which represents an out of sequence thrust based on lithology and radiolarian assemblages we subdivide the late cretaceous to early paleocene mugi unit into the mg1 mg2 and mg 3 subunits and the eocene naharigawa unit into the nh1 and nh2 subunits detrital zircon u pb ages indicate that sandstones of the mugi unit were sourced mainly from late cretaceous to paleocene igneous rocks nh1 sandstone records a single peak age in the late cretaceous whereas nh2 sandstone preserves multiple peaks from the pre jurassic to early paleocene the naharigawa unit lacks syn depositional detrital zircons however felsic tuff within nh1 records an age of 48 7 ma which is consistent with radiolarian ages the nh1 and nh2 sandstones contain slightly higher ba and rb concentrations than those of the mugi unit suggesting that basement had been uplifted and eroded in the source region prior to deposition we conclude that temporal variations in sandstone composition within the late cretaceous to early paleocene shimanto accretionary complex resulted from tectonic events that occurred in response to syn depositional igneous activity we infer that the evolution of the eocene shimanto accretionary complex was influenced by uplift and erosion of pre jurassic basement late cretaceous radiolarians were identified in subunit mg3 that forms the footwall of the aki tectonic line which was previously interpreted as a boundary fault between the late cretaceous and paleogene shimanto accretionary complexes the aki tectonic line is re interpreted as an out of sequence thrust ost that was active under low grade metamorphic conditions we classify several osts close to the late cretaceous and paleogene shimanto accretionary complexes based on contrasts in metamorphic grades across the faults within the study area the aki tectonic line is classified as a type 2 ost indicating that it developed within the cretaceous shimanto accretionary complex at temperatures of 250 270 c

surface textural analysis of quartz sand grains from odp site 918 off the southeast coast of greenland suggests glaciation of southern greenland at 11 ma shipboard analysis of the 1 183 m sedimentary section recovered at site 918 in the irminger basin during ocean drilling program leg 152 revealed material of glacial origin diamictons ice rafted debris ird and dropstones as deep as 543 m below sea floor bsf the sediment containing the deepest dropstone was biostratigraphically dated shipboard as approximately 7 ma pushing back the date for the onset of glaciation on southern greenland by 5 ma thin layers of fine sand were found as much as 60 m deeper in the core raising the possibility of an even earlier date for glaciation to determine the sedimentary history of these deeper sand layers the surface textures on quartz grains from eleven cores bracketing the interval of interest were analyzed by scanning electron microscope the results suggest that the grains in the 60 m interval below the deepest dropstone have a glacial history at that level an 11 ma sr isotope date was obtained from planktonic foraminifers this late miocene timing is supported biostratigraphically by both nanofossil and foraminifer assemblages indicating a new minimum age for the onset of glaciation on southern greenland and in the north atlantic

geochemistry of jurassic to earliest cretaceous deposits in the nagato basin sw japan implication of factor analysis to sorting effects and provenance signatures abstract one of the intractable problems in provenance analysis is the hydraulic sorting effect and resultant mineralogical heterogeneity in coarse and fine grained sediments which conceals provenance characteristics the present study uses factor analysis to address geochemical responses to the sorting effect and provenance of late mesozoic sediments in the nagato basin sw japan factor analysis has proven useful for comprehending geochemical gradients between coarse and fine grained sediments in the present example compositional differences are based on varying proportions of quartz plagioclase chrome spinel authigenic minerals and phyllosilicates the contrasting behaviors of these minerals during the depositional stage resulted in the systematic fractionation of sio2 al2o3 na2o k2o and cr ba sandstones and mudstones exhibit an array of compositions in sio2 al2o3 na2o k2o and sio2 al2o3 cr ba diagrams the ranges of which reflect compositional variations due to the sorting effect sediments of different provenance exhibit distinctive mineral arrays and can be discriminated simply by reading the gradients of the continua therefore this kind of data management concurrently quantifies the sorting effect and allows an estimation of the original source material the sio2 al2o3 na2o k2o diagram is particularly useful for scrutinizing igneous and mature continental provenances while the sio2 al2o3 cr ba diagram ascertains contributions from mafic sources this investigative approach delineates a systematic provenance transition within the nagato basin a serpentinite melange provenance in the early early jurassic a magmatic arc in the late early to middle middle jurassic and a continental interior in the latest jurassic to earliest cretaceous the provenance changed by the direct input of mature continental material into the nagato basin which resulted from dissection of the volcanic arc

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

paleoclimatic control on the composition of the paleoproterozoic serpent formation huronian supergroup canada a greenhouse to icehouse transition unlike other feldspathic arenites in the 12 km thick huronian supergroup strata of the 250 350 m thick serpent formation contain abundant plagioclase deposited in a distal alluvial setting the serpent formation consists of arenites with minor shale and siltstone the plagioclase abundance could reflect unroofing of a unique source relative to other huronian units or could be due to less intense chemical weathering major trace and rare earth element ree geochemistry of the serpent formation are used to evaluate these two possibilities serpent formation source rocks form part of the archean superior province which mainly consists of tonalitic granitic and supracrustal assemblages and their metamorphosed equivalents in al2o3cao na2ok2o acnk space shales define a linear array which indicates that the unweathered source contained plagioclase and k feldspar in the ratio of 5 1 this particular array indicates that serpent fluvial systems tapped a variably weathered carapace developed on the superior province rather than purely fresh bedrock a modelled mixture of 80 tonalite and 20 granite group rocks reproduces ree and trace element characteristics of the serpent formation sandstones and shales average eu eu 0 87 lan smn 4 4 gdnybn 1 8 and th sc 1 65 mass balance considerations indicate that less than 5 supracrustal group rocks can be added at the expense of the granite group a unique source for serpent detritus is rejected because underlying and overlying units have approximately the same provenance composition plagioclase k feldspar ratios in serpent sandstones range from 2 1 to 1 2 which achieves mass balance among source mudstone and sandstone compositions when plotted in acnk space achievement of mass balance implies that sandstones and mudstones were derived from the same weathering profiles these findings indicate that plagioclase preservation in the serpent formation is related to less intense compared with other huronian arenites paleoweathering conditions probably a harbinger of the widespread continental glaciation recorded in the overlying gowganda formation

high resolution correlations between gotland and estonia near the base of the wenlock the strata of the ireviken event can be correlated between gotland sweden and the viki core on saaremaa estonia with a high degree of precision most of the ten datum planes are found with a precision of better than 0 1 m in the lower and upper visby beds on gotland and high in the mustjala member of the jaani formation on saaremaa five of the latest llandovery early wenlock units defined by these datum planes are between c 0 12 and 1 77 m thick on gotland and 0 12 and 0 67 m in estonia the duration of each was between a few thousand and c 31 000 years the stratigraphic resolution achieved in the interval of the ireviken event is 10 000 years ultimate range ends are lacking within a preceding slightly longer interval but the pattern of intermittent presence of some taxa agrees well with an unchanged relative rate of sedimentation their coeval presence in different places indicates ecological regional or more widespread changes

geochemistry of shales of the upper cretaceous hayang group se korea implications for provenance and source weathering at an active continental margin abstract shales of the upper cretaceous hayang group in the yeongyang subbasin southeastern korea were deposited in fluvio lacustrine environments as the paleo pacific izanagi plate obliquely subducted beneath the asian continent major and trace element compositions derived from shales analyzed from the hayang group reveal geochemical signatures that are different from post archean average australian shale paas but are typical of igneous rocks found in the continental margin island arc settings for example most major element concentrations are depleted relative to paas among them mgo and mno depletions are most pronounced in all shales cao enrichment is notable in some formations due to the presence of secondary calcite as dispersed micro calcite nodules sc y and th concentrations are also slightly depleted relative to paas while chondrite normalized ree data for shales from the hayang group show moderate to large uniform lree enrichment but variable hree depletions in addition they are more fractionated than paas and have significant negative eu anomalies moreover the chemical index of alteration and a cn k relations comply that the source area was dominated by non steady state weathering regimes indicative of active uplift along an active continental margin these regions were punctuated by two periods of steady state weathering or alternatively by enhanced recycling of sediments the latter interpretation is in accord with the timing of exposure of a cherty sequence in the source area mixing calculations based on ree data suggest that the average shale in the hayang group was derived from sources composed of precambrian granitic gneiss arc basaltic rocks triassic yeongdeok granite in the subbasin and the mino accretionary complex of sw japan with ratios around 43 7 31 8 73 2 26 4 15 8 36 7 15 4 2 8 33 9 14 5 0 0 33 8 however these proportions change up sequence

a global chitinozoa biozonation for the silurian a global chitinozoan biozonation for the silurian period is proposed each biozone is an interval range defined by the first occurrence of an index species selected from well defined species with a relatively short biostratigraphic range to be included in the scheme index species must have been recorded from at least two major silurian palaeocontinents where usable chitinozoa assemblages have been studied that is avalonia baltica which had already undergone collision by the silurian laurentia gondwana and southern china seventeen biozones are identified with seven in the llandovery the fragilis postrobusta electa maennili alargada dolioliformis and longicollis biozones four in the wenlock the margaritana cingulata pachycephala and lycoperdoides biozones three in the ludlow the elongata philipi and barrandei biozones and three in the p idoli the kosovensis elegans and superba biozones chronostratigraphic calibration is partly provided by reference to the range of the appropriate chitinozoa index species in the global stratotype sections and points gssp of the silurian series e g in bohemia czech republic for the p idoli and the welsh borderland in england for the ludlow and part of the wenlock when this information was not available independent biostratigraphic control was provided by calibration with graptolite biozones or in a few cases conodont or trilobite biozonal schemes the index and most characteristic species of each biozone are illustrated and their total stratigraphie range provided

how complete are cretaceous tertiary boundary sections a chronostratigraphic estimate based on graphic correlation cogent interpretations of data bearing on the cretaceous tertiary k t extinction controversy depend on the existence of accurate chronostratigraphic models for the various k t boundary sections we have employed the graphic correlation technique to summarize biostratigraphic and lithostratigraphic data from 15 intensively sampled k t boundary sections within a common chronostratigraphic model our results indicate that almost all of these sections along with 13 additional boundary sections not used to construct the model contain prolonged and in many cases multiple hiatuses of these 28 boundary sections only six were found to contain a continuous record of sediment accumulation across the k t boundary itself these six k t complete sections are el kef tunisia agost spain caravaca spain and three sections along the brazos river texas a comparative analysis of hiatus distributions among these 28 k t boundary sections also reveals the presence of systematic differences between continental shelf and deep sea depositional environments the lower danian interval immediately following the k t boundary and extending into biochronozones p0 and p1a is typically missing from the deep sea whereas boundary sections deposited in shallower middle neritic to upper slope environments are in most cases complete across the k t boundary these shallow neritic boundary sections however are in many instances disrupted by hiatuses at the p0 p1a boundary and again in the upper part of zone p1a these differential patterns of hiatus distribution between deep sea and continental shelf depositional settings appear to be linked to sea level fluctuations our data suggest that the apparently sudden mass extinction of planktonic foraminifera and anomalies in the occurrence of geochemical tracers that are characteristic of the k t boundary in deep sea sections may be artifacts of a temporally incomplete deep sea stratigraphic record

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

chemistry and mineralogy of precambrian paleosols at the base of the dominion and pongola groups transvaal south africa abstract we have studied alteration zones found between sedimentary rocks of the lowest proterozoic dominion and archean pongola groups and underlying granitic rocks transvaal south africa the alteration zones have a transitional lower boundary primary igneous minerals are gradually destroyed upward toward the contact with overlying sedimentary rocks ca mg na p and mn are progressively lost upwards in the zone the chemical and mineralogical variations and available stratigraphic evidence are all consistent with the interpretation that these zones are paleosols formed by precambrian weathering 2 8 3 0 ga ago after formation the paleosols underwent metasomatism and metamorphism sericite now present in the paleosols was probably formed by low temperature potassium metasomatism of original clays andalusite in the pre pongola paleosol was probably formed by metamorphism of original clays in impermeable zones which prevented groundwater flow and potassium metasomatism the dominion paleosol was investigated at three localities the effects of weathering were similar at the three sites except for the behavior of iron one site lost about 20 of iron whereas the other sites lost 75 and 80 of initial iron content the differences in iron loss may be due to variation in soil ventilation and diffusion of atmospheric gases as a function of grain size and topography variations in iron loss may be used to place some constraints on the composition of the precambrian atmosphere given constraints imposed by dominion paleosols overlying uraniferous conglomerates requirements for chemical weathering and the greenhouse effect and possible presence of non diffusing photochemical oxidants the partial pressures of oxygen and carbon dioxide gases probably are in the ranges po1 0 02 to 0 5 pal present atmospheric level and pco2 5 to 30 pal

middle precambrian provenance of jurassic sandstone in the mino terrane central japan th u total pb evidence from an electron microprobe monazite study precise electron microprobe analyses have been made on detrital monazites in jurassic sandstones of the mino terrane central japan and their th u pb relations are examined in terms of pbo and tho2 tho2 tho2 plus the equivalent of uo2 the pbo tho2 ratios of most detrital monazites 403 of 581 grains cluster in the range from 0 0763 to 0 0618 other grains show the ratio of about 0 0541 46 grains 0 0364 29 grains 0 0170 24 grains and 0 0116 79 grains the pbo tho2 ratio of 0 0763 0 0618 is nearly identical with that of monazites in a middle precambrian 1740 ma gneiss clast from the kamiaso conglomerate of the mino terrane this strongly suggests that the detrital monazites were derived from gneisses and or granitoids of middle precambrian age the ratio of 0 0116 is nearly the same as that of monazites in a permian 274 ma paragneiss of the hida terrane north to the mino terrane the pbo tho2 monazite data coupled with palaeocurrent analyses and petrological characteristics of sandstones show that middle precambrian high grade metamorphic rocks and granitoids were widespread both in the northern and southern source regions of the e w trending jurassic basin of the mino terrane the pbo tho2 ratio of detrial monazites is a useful new measure for the provenance analysis of clastic rocks

geochemistry of soils of king george island south shetland islands west antarctica implications for pedogenesis in cold polar regions fine fractions of soils on the barton peninsula king george island west antarctica have been forming during the last 6000 yr since the last deglaciation texturally they are mostly composed of mineral and rock fragments with some volcanic ashes which are also indicated by geochemical compositions representing for the nonclay silicate minerals and low values of chemical index of alteration no significant changes are observed in major and trace element abundances such geochemical characteristics suggest that chemical weathering of bedrocks on the barton peninsula seems insignificant and that the soils are composed of physically weathered mineral and rock fragments which are mixed with eolian additions of volcanic ashes and patagonian dusts chondrite normalized rare earth element ree distribution patterns of the barton peninsula soils are slightly different from those of bedrocks indicating that the ree abundances and characteristics were influenced by eolian additions mixing calculations which mass balance the rees suggest that volcanic ashes blown from deception island were the major eolian contributor followed by atmospheric dusts sourced from patagonia south america even in the warmer and humid climatic conditions in the maritime antarctic region the chemical weathering of bedrocks appears to be insignificant probably due to the relatively short duration of weathering since the last deglaciation

low pressure metamorphism and leucogranite magmatism northeastern yeongnam massif korea implication for paleoproterozoic crustal evolution abstract the northeastern yeongnam massif consists primarily of pelitic to psammopelitic metasedimentary rocks together with garnet bearing leucogranites and granitic gneisses metapelitic mineral assemblages define three progressive metamorphic zones of the low pressure facies series cordierite sillimanite and garnet zones with increasing temperature metamorphic grade ranges from lower amphibolite to lower granulite facies reaching 750 800 c and 4 6 kbar in migmatitic gneisses geochemical characteristics such as the enrichments of rb and ba relative to sr high k contents and negative e nd 1 9 ga values indicate that peraluminous leucogranites were produced primarily by the fluid absent melting of supracrustal rocks trace element characteristics of leucogranites are generally compatible with those of volcanic arc granites and the widespread crustal melting may be attributed largely to magmatic heat flux in an arc environment whole rock pb pb ages suggest that leucogranite intruded at ca 1 93 1 86 ga into the granitic gneiss formed by an earlier magmatic episode at ca 1 95 ga these ages are compatible with those of felsic magmatism reported from other parts of the yeongnam massif our results in conjunction with the available geochronologic data suggest that four stages of precambrian crustal evolution are represented in the yeongnam massif 1 the formation of proto crust at ca 2 9 2 5 ga and felsic magmatic episodes primarily at 2 ca 2 1 ga 3 1 95 ga and 4 1 9 ga in particular the last tectonothermal event produced widespread low pressure type metamorphism in association with the emplacement of leucogranite and is correlative with the luliangian orogeny in north china

mesozoic terrane accretion in northeast china sikhote alin and japan regions abstract the nadanhada range in northeast china is composed of upper paleozoic limestone greenstone middle to late triassic bedded chert and middle jurassic siliceous shale these rocks are enclosed in post middle jurassic clastic rocks the lithologic association ages radiolarian assemblages and geologic structure of the nadanhada range are very similar to those of the tamba mino ashio terrane in southwest japan this indicates that the nadanhada range is the northern extension of the tamba mino ashio terrane mesozoic tectonostratigraphic terranes identified in northeast china sikhote alin and southwest japan are the khanka terrane a micro continent composed of precambrian metamorhic rocks and paleozoic to mesozoic sedimentary and volcanic covers the nadanhada western sikhote alin terrane a disrupted terrane composed of upper paleozoic to jurassic sedimentary rocks the eastern sikhote alin terrane a terrane composed mainly of early cretaceous clastics the tetyukhe terrane a disrupted terrane composed of upper paleozoic to early cretaceous sedimentary rocks the hida terrane a continent type stratigraphic terrane composed of precambrian and upper paleozoic basement covered with jurassic to cretaceous coarse clastics and the tamba mino ashio terrane a disrupted terrane composed of upper paleozoic to earliest cretaceous sedimentary rocks accretionary history of these terranes is discussed on the basis of paleomagnetic and paleobiogeographic data

distribution of major trace and rare earth elements in surface sediments of the wharton basin indian ocean bulk chemical analyses of eighteen surface sediments taken on an east west transect lat 15 40 s in the wharton basin indian ocean were analysed for major trace and rare earth elements ree by inductively coupled plasma atomic emission spectrometry icp aes the relationship between al and k suggests in situ formation of authigenic phillipsite the relationship between p and ca suggests accumulation of biogenic apatite fish bone debris from high biological productivity waters which is confirmed by the linear relationship with p and cu a strong positive correlation among redox sensitive metals mn fe cu ni and zn suggests that they are incorporated into a ferromanganese oxide phase probably micronodules calcareous oozes from the transect have low ree abundance la 8 ppm with a very strong negative cece value 0 41 siliceous oozes have high ree abundance la 28 ppm with moderate positive cece 1 24 and red clays have highest ree abundance la 66 ppm with a weak positive 1 05 to moderate negative cece 0 73 shale normalized ree patterns and layb n ratios record similar enrichment of heavy ree hree relative to light ree lree in all sediment types this might be due to retention of the bottom water ree pattern and the presence of fish bone debris correlation coefficient and r mode factor analyses suggest a very strong positive association r2 0 9 of ree with p and thus most likely with biogenic apatite fish bone debris as p is directly associated with biological activity it is thus related to surface primary productivity ree in the wharton basin sediments appear to reflect a combination of surface water effects and diagenetic processes

u pb geochronology and ree geochemistry of zircons from palaeoproterozoic paragneiss clasts in the mesozoic kamiaso conglomerate central japan evidence for an archean provenance abstract sensitive high resolution ion microprobe shrimp u pb analyses of zircons from a pelitic gneiss clast from the jurassic kamiaso conglomerate in central japan show that most grains are 1850 1950 ma but six are 2400 ma including a very old one 3254 14 ma the shrimp data give chronological evidence for previously unrecognized igneous activity from 1850 to 1950 ma the existence of archean zircons allows us to consider the evolutionary history of the archean crust in eastern asia chondrite normalized ree patterns of the individual zircons determined by shrimp show that the 2400 3250 ma zircons have large positive ce and small negative eu anomalies whereas the 1850 1950 ma zircons have small positive ce and significantly negative eu anomalies these differences in the ree abundances for the 2400 3250 and 1850 1950 ma zircons may reflect the composition of the melt that produced the zircons and reveal the possibility of a geological constraint on the origin of kamiaso zircons

tectonostratigraphy of mino terrane jurassic accretionary complex of southwest japan abstract the mino terrane a disrupted accretionary terrane in central japan consists of four fault bounded mappable units of mesozoic and paleozoic unmetamorphosed sedimentary rocks the four units are described as 1 permian greenstone carbonate chert unit 2 lower triassic to lowest cretaceous siliceous pelagite distal turbidite unit 3 middle jurassic proximal turbidite unit and 4 upper lower jurassic to lowest cretaceous olistostrome slump unit the first unit is interpreted as a sedimentary cover which was formed on and around a seamount in an open ocean setting the second unit records the accumulation of deep water radiolarian rich sediments in a pelagic realm and a tapering wedge of trench turbidites the third unit contains submarine fan sediments deposited in a possible trench slope basin the forth unit labeled as sedimentary melange containing blocks derived from accretionary prisms is considered to be submarine deposits which accumulated in a lower trench slope basin to trench floor setting an originally southward vergent imbricate stacking of structural wedges of these four units characterizes the highly complicated structure of the mino terrane rocks collision and subsequent offscraping accretion of permian to middle jurassic oceanic rocks and lower jurassic to lowest cretaceous clastic rocks provide the most satisfactory explanation for juxtaposition of the structural wedges of the four units which were originally laid down in largely different depositional sites these tectonic events most probably took place during early jurassic to early cretaceous time along an active continental margin of east asia

correlation of silurian bentonites from gotland and the eastern baltic using sanidine phenocryst composition and biostratigraphical consequences silurian bentonites from sweden and the eastern baltic are correlated using xrd analysis of sanidine composition identifying the same bentonite in different sections has constrained correlations between the conodont graptolite and chitinozoan zonations three bentonites correlate the cyrtograptus murchisoni zone with the upper part of the pterospathodus amorphognathoides zone and both the lower and the upper pseudooneotodus bicornis conodont biozones at their type locality thus the base of the llandovery wenlock boundary stratotype can be correlated with a level in the upper part of the cyrtograptus murchisoni graptolite biozone identifying the y bentonite gotland sweden in eastern baltic drill cores shows that the base of the eisenackitina lagena chitinozoan biozone is close to the base of the k patula conodont biozone which is coeval with an upper part of the c rigidus graptolite zone sanidine data from the grotlingbo bentonite fit well with previous correlations some bentonites from gotland with distinct sanidine compositions and bulk geochemistries have not yet been identified elsewhere

variscan syncollisional extension in the iberian massif structural metamorphic and geochronological evidence from the somosierra sector of the sierra de guadarrama central iberian zone spain abstract the rocks affected by the variscan orogeny in the sierra de guadarrama central iberian zone can be separated into two domains a high grade western domain and a medium to low grade eastern domain these domains are separated by the berzosa riaza shear zone a new integrated analysis of structural metamorphic and u pb monazite age data indicates that the berzosa riaza shear zone is a major d2 extensional structure associated with oblique crustal scale extensional shearing and important decompression low p high t metamorphism associated with the d2 event overprints earlier barrovian metamorphic assemblages formed during the variscan d1 compressional event the kilometre scale berzosa riaza shear zone exhibits a s c mylonitic front at its base and a crenulation front at its top with successive fabric development under different p t conditions indicating crustal thinning textural relationships and u pb dating of monazite indicate that the main d2 extensional event took place between 337 2 and 326 3 ma early mid carboniferous a late d2 extensional episode overprinted the major d2 ductile shear zone along narrow low grade oblique normal detachment zones kinematic indicators in both d2 and late d2 fabrics indicate a displacement of the upper structural levels to the southeast field relationships microstructures and qualitatively derived p t t d paths suggest that the early mid carboniferous syncollisional extension in the sierra de guadarrama was associated with the major extensional collapse of the variscan hinterland central iberian zone and was contemporaneous with the earliest thrusting in the foreland

carbon and oxygen isotopic composition of silurian brachiopods gotland sweden palaeoceanographic implications abstract one hundred and seventy two non luminescent brachiopod shells from the silurian sequence of gotland were investigated for their carbon and oxygen isotopic composition diagenetic alteration of the shell calcite was excluded by means of petrographic trace element and cathodoluminescence analysis oxygen and carbon isotopic signals vary considerably within the uppermost llandovery to the ludlow average 18o and 13c values of well defined stratigraphic units range from 2 4 to 5 9 and 1 to 8 respectively we observed parallel trends in the carbon and oxygen isotope curves with the most prominent shifts occurring in the lower wenlock upper wenlock and middle ludlow average 18o values 2 4 to 2 9 recorded in the middle ludlow are among the highest 18o values reported for the early palaeozoic the recorded 18o variations cannot solely be explained by changes in sea surface temperature and salinity the variations in the isotopic signals correlate negatively with changes in sea level heavy carbon and oxygen signals coincide with sea level lowstands whereas light signals are recorded during sea level highstands sea level highstands were probably characterized by the formation of warm saline waters on subtropical epicontinental shelves inducing oxygen deficiency in the basins alumshale facies the low 18o values are attributed to 18o depletion in surface waters owing to the storage of 18o enriched saline waters in the basins low 13c values are explained by a low surface water productivity since nutrients were not supplied to the photic zone but rather stored in the deeper ocean during sea level lowstands colder waters that formed in higher latitudes may have represented the main intermediate water source a better ventilation of the basins is documented by the deposition of well aerated sediments whereas the high 18o values are explained by the change in oceanic circulation the high 13c values are attributed to an enhanced primary productivity and possibly to an enhanced burial of corg the model discussed here may provide an attractive scenario for accounting for the recorded short term variations in the isotopic signals without the necessity of introducing an isotopic correction factor for silurian sea water

processes of debris comminution in the glacial environment and implications for quarts sand grain micromorphology abstract studies of till composition rock crushing and abrasion experiments and detailed consideration of the mechanics of the comminution processes which occur in the subglacial environment suggest that monomineral quartz sand grains are mostly produced by the brittle fracture of larger particles abrasive wear is an inefficient mechanism for producing and modifying quartz sand grains because of the relatively great hardness of quartz viewed under the scanning electron microscope surface textures of subglacially derived quartz sand grains are typically those associated with brittle fracture of quartz since the release of quartz sand grains from bedrock by mechanical weathering may also involve brittle fracture grains which have been passively transported through a glacier may exhibit similar textures to those actively produced in the glacial environment hence the examination of the surface textures of quartz sand grains under the scanning electron microscope is unlikely to be a satisfactory technique for the discrimination of active and passive transport paths through glaciers

submarine fan development in the southern chile trench a dynamic interplay of tectonics and sedimentation submarine fans are well developed in the southern chile trench from 33 s to 41 s latitude seamarc ii side scan sonar and seismic reflection records image steep erosional escarpments as much as 400 m in relief extending seaward across the trench basin from the mouths of submarine canyons the scarps bisect trench fans into paired lobes of contrasting morphology where gravity flows either follow or oppose the gradient of the axial trough fanlobes are depositional and constructional up gradient south from the canyon mouths they are composed of aggraded channel levee complexes smooth and conformable sediment drapes and crescentic levees rimming the headwalls of erosional scarps fanlobes are carved and dissected by erosional processes down gradient north from the canyon mouths they exhibit amalgamated lag pavements composite sediment lobes longitudinal furrows braided channels and canyon mouth bars thick massive to laminated sand and gravel with abundant scour surfaces were sampled from the erosional fanlobes whereas fine grained turbidites with expanded hemipelagic intervals typify the depositional fanlobes the texture and composition of the sediment supply the onshore climate and the tectonic perturbations of the axial gradient affect the morphologic development of trench fans stratigraphic intervals recording periods of intensified fan erosion and progradation of the axial channel are manifested by channeled high amplitude seismic facies reflective lenticular bodies truncation and scour surfaces planar amalgamation and sigmoidaccretion structures the severe erosional dissection of down gradient fanlobes and the northerly encroachment of the axial channel are best developed in the surficial strata of the trench basin extensive sediment remobilization and efficient longitudinal transport sculpted the present fan surface and are correlated with the last glacial maximum the trench fans may have been deposited on progressively steeper trench gradients because the buoyant chile rise migrates northward as it subducts beneath the andean continental margin fan distributary channels axial channels slump scars and erosional gullies are largely localized along structural features normal faults propagate through the sedimentary cover and create elongate depressions on the sea floor that capture the high velocity mainstreams of turbidity currents orthogonal fault sets within the deposits of the trench basin which parallel the spreading and transform structures of the extinct pacific farallon rise and the chile rise are evidently reactivated during subduction by flexure of the oceanic basement along the outer wall of the trench basin uplifted thrust ridges generally restricted to a narrow zone along the base of the deformation front are dissected by distributary channels and channel courses are locally deflected seaward of these propagating structures transform oriented basement ridges associated with strike displacements of the axial channel and vertical faults in the trench basin may accommodate renewed strike slip motion as they enter the subduction zone and thereby influence the debouchment points of submarine canyons to the trench basin

petrography and geochemistry of holocene sands in the western gulf of mexico implications for provenance and tectonic setting abstract petrographic and geochemical analysis of recent fluvial beach and dune sediments derived from the same source terrane was carried out in the western gulf of mexico to show the usefulness of the these three environments in determining the tectonic setting of the source petrographic analysis showed that dunes concentrate the less heavy minerals and quartz grains by means of the selectiveness of the wind as a transport agent in contrast the heavier grains such as the rock fragments remain in the beach and fluvial environments because of the high transport energy beach and dune sands do not define a particular tectonic setting because of the selective wind action of the backshore of the beach and the dune environments and the less intense chemical weathering the fluvial sands are the most representative in terms of interpretation of tectonic setting because they reflect the volcanic domain of the source rocks of the trans mexican volcanic belt the geochemical results of all three sedimentary environments reflect the calcalkaline character of the igneous source rocks of the trans mexican volcanic belt the samples fall in a continental island arc margin field with basaltic and andesitic source rocks a correlation and factor analysis indicates an alkali basalt source that contributes to the composition of the beach dune and fluvial sediments the geochemical analysis of the sediments more accurately reflects the tectonic setting regardless of the depositional setting of the sediments

reconstruction of eastern gondwanaland substantial additions of large continental blocks to the smith et al 1 model of eastern gondwanaland are proposed here largely on the basis of the distribution of key land floras tropical and subtropical marine faunas lithofacies patterns and the identification of a triassic magmatic arc that characterized all the eastern margin of gondwanaland the continental fragments that must have been rifted from northern australia new guinea in the jurassic are identified as south tibet burma thailand malaya and sumatra the original site of deposition of the subtropical permian limestones and tropical late triassic limestones overthrust onto the northern margin of australia by the late cenozoic collision2 is located in this greater gondwanaland palaeomagnetic data except those from malaya3 support this reconstruction

geochemistry of precambrian and paleozoic siliciclastic rocks from the iberian range ne spain implications for source area weathering sorting provenance and tectonic setting abstract the major and trace element chemical composition of precambrian and paleozoic shales and sandstones from the iberian range spain has been investigated to determine the provenance and tectonic setting of these rocks as well as to appraise the influence of the weathering hydraulic sorting and recycling processes upon source rock signature the samples studied belong to a prograde sequence from diagenesis to anchizonal grade and are mainly composed of quartz illite mica phases and or kaolinite with chlorite feldspars and carbonates as minor components the major element distribution chemical index of alteration cia indices reflects that recycling processes have been important in homogenizing the composition of shales and sandstones the higher cia indices observed in the silurian and devonian shales 80 and 85 respectively compared with those of precambrian to ordovician and the carboniferous age about 70 indicate that their source area underwent more intense chemical weathering processes possibly due to climatic and or tectonic variations alternatively the source area of the silurian and devonian shales may have been composed of recycled sedimentary materials mineral fractionation is mainly observed in coarser rocks through zircon apatite and xenotime accumulation although the shales are not free of these phases the zircon content of the fine grained rocks is not high enough to affect rare earth element ree contents but phosphate minerals apatite and xenotime at least partially control the ree distribution the influence of apatite and xenotime are slightly higher in the precambrian shales as the phosphate concentration produces a decrease in the la sm ratios chondrite normalized ree patterns and negative eu anomaly size of the studied rocks are similar to that of post archean australian shales paas indicating that they originally come from a differentiated silicic source the higher ree contents in the studied shales in relation to paas indicate that recycling processes in the iberian range sources were probably more intense than that of paas the slight differences among the ree patterns of the different groups of shales probably do not reflect changes in source area composition but instead suggest variations in mineral sorting chemical weathering and or sediment recycling the th sc co th cr th cr v v ni ratios support a primitive silicic source for these rocks with the higher th sc and lower co th in cambrian and ordovician shales indicating a higher proportion of felsic material in their primitive source area the compositional maturity of analyzed sandstones is typical of cratonic environments and their la sc th and zr contents reflect their passive continental margin setting

silurian records of carbon and sulfur cycling from estonia the importance of depositional environment on isotopic trends abstract the llandovery wenlock carbonate marl succession of the baltoscandian basin has been analyzed in the viki drill core western estonia for carbonate carbon 13 c carb organic carbon 13 c org carbonate associated sulfate 34 s cas and pyrite 34 s pyr isotopes along with trace element concentrations following the end ordovician glaciation and the hirnantian carbon isotope excursion 13 c carb values rise to an early llandovery carbon isotope maximum 2 subsequently 13 c carb and coeval 13 c org record a large 4 5 excursion in the early wenlock associated with a regression and biotic turnover known as the ireviken bioevent ibe overall 34 s cas values generally fall within a range 25 to 35 similar to that reported in other sections of comparable age two distinct trends are observed low and stable 34 s cas values are associated with deep water facies while 34 s cas becomes higher and more variable in the shallow water facies similarly 34 s pyr values are low and invariant 15 in deep water facies but become higher and more variable ranging between 35 and 16 in shallow water deposits despite abundant recrystallization no obvious evidence for large scale alteration of proxies is apparent in concentrations of fe sr mn and mg or in isotopic correlations although increased variability and lower values of 34 s cas are observed where cas abundance is low a large well resolved positive excursion in 34 s cas observed during the ibe from a time correlative section on gotland sweden is absent in the data presented here this difference demonstrates that counter to general understanding local environmental variations can give rise to divergent 34 s cas profiles in coeval sections the s isotope fluctuations in cas and pyrite in the viki drill core can be explained by local processes involving facies changes early diagenetic processes and associated open vs closed system behavior that can overprint and potentially mask basin or global signals

provenance of the hayang group early cretaceous in the yeongyang subbasin se korea and its bearing on the cretaceous palaeogeography of sw japan abstract the lower cretaceous hayang group in the yeongyang subbasin se korea was deposited in a forearc basin formed by the subduction of the palaeo pacific izanagi plate underneath the east asian continent it is characterized by an alternating sequence of reddish sandstones and mudstones deposited in fluvial plain environments sandstone compositions upsequence reveal that the tectonic regimes of source terrains evolved successively from basement uplift to recycled orogen to magmatic arc and back to recycled orogen characteristically sandstones contain abundant plagioclases but rare k feldspars except for sandstones derived from basement sources sandstones derived from recycled orogens are rich in sedimentary rock fragments especially chert fragments which contain radiolarian faunas similar to those of the jurassic accretionary complex located in southwest japan minor continental arc volcanism contributed volcanic materials to the basin during the middle stage of the basin filling during the deposition of the hayang group strike slip fault movements were active due to the oblique subduction of the izanagi plate and caused strong pulsed uplift of the trench slope break areas resulting in supply of accretionary complex derived sediments considering a direct drainage connection between the uplifted accretionary complex in southwest japan and the yeongyang subbasin current cretaceous palaeogeographic reconstructions of the east asian continental margin need to be reconsidered and it is suggested that the collage of tectonic blocks in southwest japan assembled in post early cretaceous time

gravel bearing radiolaria as tracers for erosional events a review of the status of recent research in sw japan and korea abstract the authors introduce a case study of research on the provenance of radiolaria bearing gravels and clasts of the monomictic chert pebble conglomerates in the lower cretaceous monobegawa group a paralic molasse in the outer zone of southwest japan reconstruction of oceanic plate stratigraphy from gravels and clasts in monomictic chert pebble conglomerates based on their lithology and radiolarian ages is possible and effective for the provenance research in the case of the monobegawa group a review of provenance studies of radiolaria bearing gravels in mesozoic orogenic sediments in sw japan and korea is included the paper concludes with the discussion of the erosional events of the jurassic and pre jurassic accretionary complexes in sw japan with reference to the late mesozoic geological history in the eastern margin of asian continent

paleomagnetic evidence for the clockwise rotation of southwest japan abstract over 500 oriented samples of felsic rocks of cretaceous to middle miocene age were collected along the go river in the central part of southwest japan in an attempt to detect the process of tectonic rotation of southwest japan from the paleomagnetic view point thermal demagnetization was successful in isolating characteristic directions from the remanent magnetization of samples reliability of the paleomagnetic direction is ascertained through the agreement of directions from different kinds of rocks as well as the presence of both normal and reversed polarities the paleomagnetic results establish that southwest japan began to rotate clockwise through58 14 later than 28 ma and ceased its motion by about 12 ma southwest japan has undergone no detectable north south translation since 28 ma these results imply that southwest japan was rotated about the pivot around 34 n 129 e between 28 ma and 12 ma in association with the opening of the japan sea

743 17 ma granite clast from jurassic conglomerate kamiaso mino terrane japan the case for south china craton provenance korean gyeonggi block abstract the polymict kamiaso conglomerate mino terrane japan contains jurassic to palaeoproterozoic clasts probably derived from korean basement that lay nearby to the northwest at time of deposition clast k2 broke cleanly into two halves during sampling but the halves were recombined for zircon separation a third of the k2 zircons are colourless euhedral prisms with oscillatory zoning with no inheritance and yielded a shrimp u pb date of 743 17 ma two thirds of k2 zircons are brown oscillatory zoned corroded prisms with a date of 1860 8 ma with inherited cores up to 2460 ma a likely explanation for this could be that clast k2 might have been composite and contained undistinguished 743 ma and 1860 ma granites kamiaso granitic clast k3 igneous zircons gave a date of 179 3 2 1 ma toarcian early jurassic with 2100 2300 ma and 1860 ma inherited cores 740 ma a type magmatism related to the extension and break up of rodinia occurs in both korea gyeonggi block and the main part of the south china craton but is unknown in the sino korean craton thus from recognition of a 743 ma clast the kamiaso detritus was probably derived from the northernmost part of the south china craton in korea

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

granulite facies metamorphism in the punggi area northeastern yeongnam massif korea and its tectonic implications for east asia abstract in the punggi area of the northeastern part of the yeongnam massif one of precambrian basement terrains in korean peninsular the metamorphic grade increases from the amphibolite to the granulite facies zones towards the southeast the boundary of the granulite facies zone is defined by the orthopyroxene opx in reaction in metabasites as metamorphic grade increases across the opx in isograd the mineral assemblage in calcic metabasites is changed from clinopyroxene amphibole plagioclase to orthopyroxene clinopyroxene amphibole plagioclase and that in alkali metabasites from garnet orthoamphibole plagioclase to garnet orthopyroxene plagioclase the metamorphic rocks in the granulite facies zone were overprinted by upper amphibolite facies retrograde metamorphism during retrograde metamorphism cordierite and spinel formed in the migmatitic gneiss the p t conditions of granulite facies metamorphism are 767 815 c and 6 0 8 4 kb and the p t conditions for the retrograde stage are 595 707 c 4 7 6 4 kb a u pb zircon age of 1904 9 ma has been obtained from a garnet granitic gneiss and is inferred to date the emplacement of its precursor this is consistent with the intrusion age of precursors to most orthogneisses in other parts of the yeongnam massif the same sample has yielded a sm nd whole rock garnet age of 617 38 ma which is inferred to represent a late proterozoic metamorphic event of upper amphibolite facies

silurian conodont based correlations between gotland sweden and saaremaa estonia correlations between the silurian successions of gotland and the east baltic are based on the narrowest stratigraphic units that can be distinguished in both areas in order further to increase precision true ends of ranges in measured sections have been used instead of pooled formational faunas where outcrops and collections permit some previous correlations are confirmed in other cases there are considerable changes both in levels of correlation and in precision the major differences are found mostly when one or more of the major gaps have remained unrecognized and stratigraphic units therefore have been extended and translated upwards or downwards at least some of these gaps decrease in magnitude southwards in estonia gaps at these levels are also noted on gotland although they are small and probably do not extend across the island the patterns through time of deposition during secundo episodes and gaps during primo episodes agree very well with what can be predicted from a model of oceanic and climatic cyclicity