paleoclimatic and paleomagnetic constraints on the paleozoic reconstructions of south china north china and tarim abstract paleomagnetic and paleoclimatic data provide the most useful latitudinal constraints for plate reconstructions distributions through the paleozoic of five types of climatically sensitive sediments coals evaporites reefs dolomites and limestones for south china north china and tarim are shown on 15 maps that include 1578 reliable data points these paleoclimatic data agree reasonably well with available paleomagnetic directions although significant divergence between the two exists for the early paleozoic these data indicate the following 1 1 south china was in low latitudes during the entire paleozoic with a subtropical position in the cambrian 2 2 north china also remained near the equator in the early and late paleozoic except for the ordovian and the late permian when extensive evaporites suggest slightly higher latitudinal positions while its middle paleozoic position is uncertain due to the missing stratigraphie record 3 3 in south china local tectonics appears to have played a dominant role in determining paleogeography and therefore marine sedimentation especially after the late ordovician early silurian because the areal coverage of marine sediments through time is distinctly different from what would be expected from published global sea level curves 4 4 paleoclimatic and paleomagnetic data are compatible with biogeographic data which suggest that south china was part of eastern gondwana in the early paleozoic but was widely separated from gondwana in the late paleozoic and the split between the two probably happened in the devonian giving rise to a major break up unconformity in central south china

early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

sea level driven changes in ocean chemistry at an upper cambrian extinction horizon a combined stratigraphic and isotopic study across a late cambrian mass extinction horizon pterocephaliid ptychaspid biomere boundary in cratonal and miogeoclinal sections of the western united states reveals evidence for a pattern of sea level rise decreasing 87 sr 86 sr ratios and increasing 13 c the positive shift in 13 c reaching maximum values a few metres above the extinction interval is interpreted to reflect elevated primary productivity and an increase in the rate of burial of organic matter during expansion of the oxygen minimum zone the 87 sr 86 sr decrease is interpreted to reflect some combination of increased sea floor spreading rates and decreased continental weathering rates the 13 c and 87 sr 86 sr trends independently support the field based hypothesis that a sea level rise led to catastrophic oceanic overturn possibly culminating in anoxic conditions that ultimately proved lethal to a large fraction of the existing shelf fauna

geodynamics of the ogcheon belt south korea abstract the ogcheon belt is a stack of synmetamorphic southeastward verging nappes resulting from the deformation of a volcanosedimentary sequence deposited in an early palaeozoic rift which was affected by polyphase tectonics its pre cretaceous structure results from three main orogenic events the ogcheon late silurian devonian indosinian late permian triassic and yenshanian middle jurassic early cretaceous tectonic phases the external autochthonous or para autochthonous units represent platform zones with shallow water deposits whereas rift facies characterize the internal domain the yeongweol sequence forming an outer shelf on the southeastern margin of the rift displays affinities with the jiangnan basin of south china it is in wrench fault contact with the easternmost duwibong sequence correlated with the north china north korea platform in the internal metamorphic units post cambrian early ordovician pelitic and turbiditic rift metasediments overlie a thin cambrian or cambrian ordovician early platform sequence two subdomains are distinguished the upper units chung ju and pibaryeong units representing the deep axial part of the basin contain distal flyshoids and large olistoliths derived from the northwestern narrow margin the lower units turung san poeun and iwharyeong are related to the wide margin located between the deep rift domain and the stable southeastern platform the latter transitional domain is characterized by thick submarine debris flows and volcanics of alkali or transitional tholeiitic affinity the volcanic activity and mass gravity flow sedimentation are closely related to the crustal thinning and subsequent rifting and tilting lithostratigraphic evidence allows the correlation of the unfossiliferous rift metasediments with the cambrian ordovician platform sequence in one single basin the post middle silurian pre mid carboniferous ogcheon ensialic orogeny resulted in the closure of the rift with relatively minor effects in the platform area it gave rise to an intracontinental fold thrust belt without ophiolites this tectonic event may have been contemporaneous with early palaeozoic tectonism in the quinling belt in central china and in the southeast china fold belt the definitive constitution of the sino korean craton took place before the mid carboniferous and molasse sedimentation was initiated on a single platform located on the western edge of the yakuno oceanic basin of southwest japan in late permian and early triassic times the closure of the oceanic area and the subsequent westward collision of the honshu block are marked in korea by the intracratonic indosinian tectonism since late triassic times predominantly transcurrent movements have occurred along nne ssw faults associated with syntectonic intermontane troughs and important granitization

analysis techniques for coherent airborne radar sounding application to west antarctic ice streams 1 analysis of coherent radar sounding echoes from polar ice sheets can provide information suitable for classifying the subglacial environment echoes from a general interface consist of both specularly reflected and diffusely scattered contributions specular reflection results from smooth uniform interfaces whereas diffuse scattering results from rough nonuniform interfaces and inhomogeneous media this article discusses how these phenomena are important to the acquisition and analysis of coherent radar sounding data reflection results are presented from airborne surveys conducted in 1987 over the downstream portions of whillans ice stream and ice stream c west antarctica additionally reflection and scattering analyses along with new results are presented for repeat profiles flown in 2001 over ice stream c analysis methods include using echo amplitudes to compute reflection coefficients which are used for inferring the dielectric properties of the subglacial material echo phase analysis provides the locations of dominant scattering centers which relate to reflection or scattering from the interface as well as provide interface roughness estimates comparison of low and high resolution imaging obtained from synthetic aperture radar techniques indicates a reflecting and or scattering interface combining the results from these independent analyses provides classification of the subglacial environment classified regions include smooth seawater smooth saturated sediments accreted marine ice rough bottom crevasses mixed conditions with partial subglacial water and dry frozen conditions

indosinian dextral ductile fault system and synkinematic plutonism in the southwest of the ogcheon belt south korea reply abstract the structure of the mylonite belt in the southwestern part of the ogcheon belt has been investigated and interpreted in the light of recent radiometric data the shear belt is composed of several en echelon dextral shear zones relayed by compressional or extensional tectonic bridges the dextral displacement along the fault system which may be extended to the hida zone of japan is of the order of 200 km it has brought into contact the ryeongnam block and its cambrian middle ordovician cover of north china affinity with the southwestern margin of the ogcheon belt characterized by cambrian middle silurian rift facies and shelf deposits of south china affinity synkinematic plutons are emplaced within the shear belt which is postdated by uppermost triassic unfoliated granitoids at the surface the shear belt generated elongated intermontane coal basins initiated as transtensional half grabens because of its post permian pre early jurassic age and its dextral kinematics we correlate the shear belt with the late stages of the akyioshi indosinian collisional orogeny of the east asian margin the synkinematic plutonism that accompanied the shear zone may be due to post collisional crustal stretching and subsequent anatexis at the mantle crust interface

late cambrian missing link in macroborer evolution preserved in intraclasts abstract macroborings are known to be rare to absent in middle to late cambrian successions the time interval between the end early cambrian archaeocyath extinction and the advent of new boring organisms during the mid late ordovician the ordovician bioerosion revolution the occurrence of macroborings was controlled mainly by hard substrate availability archaeocyath reefs and hardgrounds provided synsedimentarily lithified substrates during the early cambrian and ordovician respectively in this study we report bioerosion structures from micritic intraclasts of flat pebble conglomerates in the hwajeol formation furongian taebaeksan basin korea two types of macroborings trypanites and cf gastrochaenolites are recognized both of which penetrate micritic clasts and are filled with bioclastic grainstone matrix several lines of evidence including the sharp boundaries and unaltered shapes of macroborings as well as the occurrence of macroborings penetrating the coating of iron and or manganese oxide coated micritic clasts indicate that these macroborings formed after the cementation of micritic substrates the hwajeol macroborings would have formed on micritic clasts and or hardgrounds that were eroded and formed flat pebbles the presence of bioerosion structures within clasts of the hwajeol flat pebble conglomerates supports a previous hypothesis that macroborers survived in hardgrounds during the middle to late cambrian after the extinction of archaeocyath reefs in addition the hwajeol cf gastrochaenolites is the earliest of its kind implying that there could be more kinds of macroborings hidden within cambrian flat pebble conglomerates

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

silurian and devonian paleomagnetic poles from north china and implications for gondwana abstract we have obtained paleomagnetic results from silurian and devonian rocks on the western margin of the north china block ncb ages which previously were thought to be unrepresented throughout north china high unblocking temperature components of magnetization isolated from both the silurian and devonian strata pass fold and reversal tests suggesting that they are primary remanence the corresponding paleopoles at 228 4 e 26 2 n silurian and 228 7 e 34 2 n devonian imply low paleolatitude positions of north china during the middle paleozoic probably adjacent to east gondwana

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

radar absorption basal reflection thickness and polarization measurements from the ross ice shelf antarctica author s hanson jc barwick sw berg ec besson dz duffin tj klein sr kleinfelder sa reed c roumi m stezelberger t tatar j walker ja zou l abstract radio glaciological parameters from the moore s bay region of the ross ice shelf antarctica have been measured the thickness of the ice shelf in moore s bay was measured from reflection times of radio frequency pulses propagating vertically through the shelf and reflecting from the ocean and is found to be 576 8m introducing a baseline of 543 7m between radio transmitter and receiver allowed the computation of the basal reflection coefficient r separately from englacial loss the depth averaged attenuation length of the ice column l is shown to depend linearly on frequency the best fit 95 confidence level is l v 460 20 180 40 vm 20 db km 1 for the frequencies v 0 100 0 850 ghz assuming no reflection loss the mean electric field reflection coefficient is r 0 82 0 07 1 7db reflection loss across 0 100 0 850 ghz and is used to correct the attenuation length finally the reflected power rotated into the orthogonal antenna polarization is l5 below 0 400 ghz compatible with air propagation the results imply that moore s bay serves as an appropriate medium for the arianna high energy neutrino detector

early to mid holocene rapid sea level rise and coastal response on the southern yangtze delta plain china we used accelerator mass spectrometry ams 14 c dated sediments of the holocene basal supratidal flat to upper tidal flat facies in 11 cores on the southern yangtze delta plain to reconstruct relative sea levels of 8 5 8 0 cal ka bp three cores were further ams 14 c dated and used to examine the evolution of sedimentary geomorphological environments in response to the rapid sea level rise during the early to mid holocene results demonstrate relative sea level rise of around 30mm a 1 from 8 5 to 8 3 cal ka bp and around 10mm a 1 from 8 3 to 8 0 cal ka bp retrogradation from supratidal to lower tidal flat environments occurred in response to the rapid sea level rise at 8 5 8 3 cal ka bp and aggradation from middle to upper tidal flat occurred at 8 3 7 9 cal ka bp further retreat of the tidal flat at 7 9 7 2 cal ka bp implies a mean sea level rise rate exceeding 5mm a 1 at this time we suggest that the rapid relative sea level rise during 8 3 8 5 cal ka bp and subsequent slower rise caused drastic changes in the coastal zone and that these changes are key phenomena for understanding the coastal response to future sea level rise copyright 2013 john wiley sons ltd

predicting radar attenuation within the antarctic ice sheet abstract to better understand the ability of ice penetrating radar to diagnose the subglacial environment from bed returned power we model the englacial radar attenuation of antarctic ice first we use a one dimensional thermo mechanical model to evaluate the sensitivity of the depth averaged attenuation rates to ice temperature as a function of surface accumulation rate geothermal flux and ice thickness we find that attenuation is most sensitive to variations in geothermal flux and accumulation rate when the bed temperature is close to the pressure melting point but even if geothermal flux and accumulation rate remain fixed attenuation can easily vary with ice thickness such high sensitivities show that one should not assume a uniform attenuation rate in the radar data analysis then using ensembles of modeled ice temperatures with different boundary conditions we generate multiple attenuation predictions for the antarctic ice sheet and evaluate the resulting uncertainties the largest contributor to uncertainty in these predictions is the geothermal flux this uncertainty is localized within the deeper half of the ice sheet by combining these temperature ensembles with ice core chemistry data we show that the sea salt adds little to the attenuation but the contribution from acids accounts for 29 inland to 53 coast of the total attenuation we conclude that improving radar diagnosis of the subglacial environment using bed returned power requires both 1 better data interpretation algorithms that account for attenuation variations and 2 better constraints of geothermal flux and bulk chemistry

south east asia as a part of an ordovician gondwanaland a palaeobiogeographic test of a tectonic hypothesis the hypothesis that thailand and malaysia the sibumasu block were adjacent to australia in the early palaeozoic has been tested by an examination of the ordovician sequences and faunas of sibumasu and australia the relatively stenogeographic nautiloids of the two areas are remarkably similar and have a simpson index of 0 92 at the generic level two new genera of discosorids are restricted to the two blocks andgeorgina andmesaktoceras are found elsewhere only in tibet very close affinities are also evident between the gastropod polyplacophoran and rostroconch molluscs the ordovician brachiopod faunas are also very close including the genusspanodonta other very close similarities are found between the upper cambrian trilobite faunas and the ordovician conodonts and stromatoporoids no ordovician faunas younger than upper whiterockian were found during this study in either northern australia or sibumasu and a stratigraphic gap probably exists from the upper whiterockian to the upper ordovician over most of the two blocks these remarkably close faunal similarities are good evidence in favour of the hypothesis that sibumasu was adjacent to australia during the early palaeozoic similarly close faunal relationships between north china south east asia tibet and australia may also suggest close proximity of those blocks during the early palaeozoic

ironstones and green marine clays in the dongjeom formation early ordovician of korea abstract in the sino korean north china block the occurrence of ironstone is reported for the first time from the lower ordovician dongjeom formation korea the dongjeom formation comprises much quartzose sediment deposited on the extensive carbonate platform and is composed of three coarsening upward sequences ironstone beds are distributed on the tops of the lower two sequences suggesting that they mark approximately maximum flooding events during the relative lowstand of sea level when the dongjeom formation was deposited extensive weathering in the source areas coupled with higher order sea level rises resulted in the formation of the dongjeom ironstones the dongjeom ironstones include much green marine clays ironstones of the lowest sequence are characterized by glaucony facies and those of the middle sequence by chamosite facies chemical compositions of dongjeom glauconies reveal that they were originally nascent to slightly evolved 3 to 5 k 2 o wt and that they were affected by illitization after burial their immature compositions suggest that glauconies were formed in about 10 3 to 10 4 years or less on the seafloor the substrates for glauconitization are interpreted as detrital mineral grains regressions after glauconitization introduced iron oxides to the green grains eventually forming the iron oxide rich band under the most oxidizing conditions the distribution of glauconies in limited horizons suggests that the dongjeom glauconies are autochthonous in origin chamosites have granular shapes and are mixed with quartzose sand grains suggestive of reworking during storms the dongjeom chamosites were transformed from the precursor berthierines the occurrence of glauconies in correlative horizons in korea and north china may indicate that glauconitization in the host sediments which were deposited in far northern gondwana occurred under the influence of a coeval transgressive event

the dynamic evolution of the palaeozoic geography of eastern asia abstract new palaeogeographical reconstructions are presented for eleven time intervals through the palaeozoic of the eastern asia region from the middle cambrian at 510 ma to the end of the permian at 250 ma they centre on the continental blocks of north china south china and annamia indochina and their relationships with northeastern gondwana which was united to form part of pangea from the late carboniferous onwards also shown is the continent of tarim during the lower palaeozoic as well as the hutag uul songliao and khanka jiamasu bureya terranes both of which straddle the russian mongolian and chinese borders today from silurian times onwards we conclude that annamia and south china were united as a single continent throughout the lower palaeozoic and early devonian and were translocated by major strike slip faulting along the northeastern gondwana margin during that period from off afghanistan to outboard of the sibumasu and australian sectors of the superterrane they left the gondwana marginal area together during the lower devonian opening of the palaeotethys ocean but very shortly afterwards they themselves divided into the two separate continental blocks that we recognise today not to reunite until the triassic the various cambrian to permian rocks found in japan largely represent active volcanic arcs which originally lay to the southeast of south china although the carboniferous was more quiescent there the neotethys ocean opened during the permian dividing sibumasu and the tibetan terranes from gondwana and the palaeotethys ocean started to close progressively in the upper palaeozoic as most of the east asian continents and smaller terranes moved towards siberia the positions of the various continents and terranes have been deduced from a mixture of palaeomagnetic and faunal data the positions of large igneous provinces and kimberlites and the need to provide kinematic continuity between maps of successive ages however many uncertainties remain

the recommended cambrian ordovician global boundary stratotype of the xiaoyangqiao section dayangcha jilin province china this paper provides a brief outline of the current detailed inter disciplinary work on the xiaoyangquiao section trying to expose all the aspects for reference tied to the global single stratigraphic point gssp concept for defining the cambrian ordovician boundary the 45 m critical interval of this section outcrops very well along the steep bank of a stream and is free from folding faulting intrusions and has not been affected by weathering colour alternation of conodonts and acritarchs and crystallinity indices of illite all indicate a maximum thermal grade of 100 c the lithofacies being of great lateral persistence for a hundred kilometres consists mainly of a rhythmical sequence of lime mudstone and shales deposited in a moderately deep outer shelf environment of quiet water well below the normal storm wave base chemical investigation of the rocks demonstrates strong positive correlation between a12o3 content and those of k2o mgo fe2o3 tio2 be cr co ni zn and ba indicating these components are tied to the clay fractions a stable depositional environment is demonstrated by the uniform chemistries through the boundary interval close to the boundary itself p2o5 contents are low indicating continuous sedimentation at fairly substantial rates the major biological events the biostratigraphic framework and the stratigraphic range of conodont graptolite trilobite and acritarch taxa are illustrated briefly with diagrams following the majority views of the calgary plenary session the boundary level is to be chosen at a point marked by the first appearance datum fad of the selected conodont taxon or taxa in the vicinity of the level close to but below the first influx of nematophorous graptolites the following four points marked by the incoming of conodont taxon or taxa are recommended for consideration of the golden spike 1 fad of cordylodus intermedius at 5 28 m below the first influx of nematophorous graptolites 2 fad of hirsutodontus simpler cordylodus drucei albiconus postcostatus at 5 23 m 3 fad of semiacontiodus lavadamensis utahconus utahensis monocostodus sevierensis at 3 85 m 4 fad of cordylodus lindstromi at 2 23 m for the following reasons the fad of h simplex c drucei a postcostatus is favoured 1 the taxa are all distinct and widely dispersed 2 intensive evolutionary change took place in conodonts graptolites trilobites and acritarchs prior to or after this point all the fossil groups occur together providing correlation with many regions throughout the world 3 the point is in a position between the previously widely accepted boundary levels based on graptolites and trilobites 4 the proposed point lies within a thin laterally persistent rhythmical sequence the fad of cordylodus lindstromi is also a favourable point sharing many advantages mentioned above but this point is less satisfactory in being defined by the fad of a single taxon c lindstromi which also has an extremely small population size an isochron age of 500 7 7 4 ma is determined from clay fractions of mudstones 8 5 m below the proposed point by means of the rubidium strontium method the nd signature determined from conodonts trilobites hyolithids and acrotretid brachiopods has a mean value of 6 7 comparable with that of the coeval oceanic water mass occupying southeastern north america and europe and indicating that northeastern china bordered the same ocean the mean tdm model age determined was 1 26 ga at the time of sedimentation compatible with the mean tdm model age of approximately 1 1 ga for the pacific ocean today the relatively low value of the tdm model age indicates a substantial input from young orogenic volcanic island arcs and terranes

tectonic elements with south china affinity in the korean peninsula new early jurassic palaeomagnetic data summary early jurassic sandstones and shales were collected at 14 sites from the kimpo area in the western part of the korean peninsula for a palaeomagnetic study a characteristic remanent magnetization component which passes the fold test was isolated from seven sites this characteristic component is interpreted to be of primary early jurassic origin because the folding age is middle late jurassic the primary directions together with previously reported ones provide a mean direction d 38 1 i 39 7 95 3 8 11 sites and a palaeomagnetic pole 54 1 n 230 2 e a95 4 1 for the kimpo area this palaeomagnetic pole shows good agreement with the coeval poles for the south china block and is significantly removed from that for the north china block suggesting that the kimpo area has been part of the south china block since at least early jurassic times the kimpo area constitutes a part of the imjingang belt which is palaeontologically allocated to the south china block in its origin while all precambrian tectonic blocks that compose the basement of the korean peninsula are interpreted to be of north china origin we conclude that the imjingang belt including the kimpo area is a tectonic extension of the south china block on the korean peninsula the south china elements were obducted onto the north china block at the site of the present korean peninsula during the collision event of the north and south china blocks and hence the korean peninsula is composed of areas with both north and south china affinities

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

radiaxial fibrous calcites as low magnesian calcite cement precipitated in a marine meteoric mixing zone radiaxial fibrous calcite rfc has previously been interpreted as a marine or replacive cement study of the dongjeom formation early ordovician korea shows that rfc can form in marine meteoric mixing zones as a low magnesian calcite lmc cement rfc in the shallow marine dongjeom formation occurs in arenaceous limestones at the top of a transgressive facies overlying a regressive facies it shows well developed growth zonation and lighter oxygen isotope values and more radiogenic strontium isotope ratios than those of early ordovician marine calcite such petrographic and chemical evidence indicates that the rfc was precipitated as a primary lmc cement in a marine and meteoric mixing zone owing to the unique environment of formation the dongjeom rfc is characterized by growth zonal fabric comprising alternating subzones which may indicate precipitation from varying fluids in addition this study documents the importance of substrate for development of rfc early nucleation for rfc occurred mainly on microcrystalline skeletal grains and internal sediments whereas on homogeneously altered substrates thin coated banding structure developed ultimately forming coarse crystalline spar this suggests that microcrystalline substrates are preferred sites for nucleation of rfc

ross ice shelf antarctica in situ radio frequency attenuation we have measured the in situ average electric field attenuation length hli for radio frequency signals broadcast vertically through the ross ice shelf antarctica we chose a location moore embayment south of minna bluff known for its high reflectivity at the ice sea interface we confirmed specular reflection and used the return pulses to measure the average attenuation length from 75 1250 mhz over the round trip distance of 1155 m we find hl i to vary from 500 m at 75 mhz to 300 m at 1250 mhz with an experimental uncertainty of 55 15 m

radar attenuation and temperature within the greenland ice sheet 2015 american geophysical union all rights reserved the flow of ice is temperature dependent but direct measurements of englacial temperature are sparse the dielectric attenuation of radio waves through ice is also temperature dependent and radar sounding of ice sheets is sensitive to this attenuation here we estimate depth averaged radar attenuation rates within the greenland ice sheet from airborne radar sounding data and its associated radiostratigraphy using existing empirical relationships between temperature chemistry and radar attenuation we then infer the depth averaged englacial temperature the dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry where radar transects intersect boreholes radar inferred temperature is consistently higher than that measured directly we attribute this discrepancy to the poorly recognized frequency dependence of the radar attenuation rate and correct for this effect empirically resulting in a robust relationship between radar inferred and borehole measured depth averaged temperature radar inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice sheet model particularly in southern greenland this pattern suggests that past changes in surface boundary conditions temperature and accumulation rate affect the ice sheet s present temperature structure over a much larger area than previously recognized this radar inferred temperature structure provides a new constraint for thermomechanical models of the greenland ice sheet

phanerozoic polyphase orogenies recorded in the northeastern okcheon belt korea from shrimp u pb detrital zircon and k ar illite geochronologies abstract we present the shrimp u pb detrital zircon and k ar illite 1m d 1m and 2m 1 ages suggesting new insight into the phanerozoic polyphase orogenies preserved in the northeastern okcheon belt korea since the initial basin formation during neoproterozoic rifting through several successive contractional orogens the u pb detrital zircon ages from the early paleozoic strata of the taebaeksan zone suggest a cambrian maximum deposition age and are supported by trilobite and conodont biostratigraphy although the age spectra from two sedimentary groups the yeongwol and taebaek groups show similar continuous distributions from the late paleoproterozoic to early paleozoic ages a grenville age hiatus 1 3 0 9 ga in the continuous stratigraphic sequence from the taebaek group suggests the existence of different peripheral clastic sources along rifted continental margin s in addition we present the k ar illite 1m d 1m ages of the fault gouges which confirm fault formation reactivation during the late cretaceous to early paleogene ca 82 62 ma and the early miocene ca 20 18 ma the 2m 1 illite ages at least those younger than the host rock ages provide episodes of deformation metamorphism and hydrothermal effects related to the tectonic events during the devonian ca 410 ma and permo triassic ca 285 240 ma these results indicate that the northeastern okcheon belt experienced polyphase orogenic events namely the okcheon middle paleozoic songrim late paleozoic to early mesozoic daebo middle mesozoic and bulguksa late mesozoic to early cenozoic orogenies reflecting the phanerozoic tectonic evolution of the korean peninsula along the east asian continental margin

origin of quartz cement in the lower ordovician dongjeom formation korea abstract this study deals with the origin of quartz cement developed in deeply buried mature sandstones intercalated in a thick carbonate sequence the dongjeom formation early ordovician korea is composed of three coarsening upward sequences and is divided into two facies according to depositional conditions with respect to changes in relative sea level transgressive facies and regressive facies the transgressive facies are characterized by calcite cemented allochem bearing sandstones whereas the regressive facies is characterized by non calcareous quartzose to arkosic sandstones quartz overgrowths occupy significant amounts of pore space average 16 in the regressive facies sandstones fluid inclusions reveal that quartz overgrowths precipitated between 110 and 165 c petrographical study and homogenization temperatures indicate that quartz overgrowths precipitated mostly during and after chemical compaction during the late diagenetic stage considering the 18 o values of detrital quartz grains and the volumes of quartz overgrowth the 18 o values of quartz overgrowth are estimated to range from 14 4 to 19 0 smow on the basis of mass balance silica for quartz overgrowths was principally derived from chemical compaction pressure solution of detrital quartz quartz overgrowths in the dongjeom sandstones precipitated from formation waters 2 1 to 2 5 smow that evolved from contemporary meteoric waters by diffusion

nd isotopic study of upper cambrian conodonts from korea and implications for early paleozoic paleogeography abstract correlation of the korean peninsula with the neighboring south and north china blocks has been one of the most important and long debated issues in east asian tectonics the eastward extension of the chinese collisional belt between the south and north china blocks into the korean peninsula is still in dispute the lower paleozoic sedimentary rocks in south korea the joseon supergroup accumulated in the okcheon belt which has been proposed as the suture zone or the block boundary between the south and north china blocks in korea the joseon supergroup comprises five different lithostratigraphic units and has been proposed to represent two tectonostratigraphic blocks bounded by the honam shear zone hsz in the okcheon belt among them the yeongweol unit in the western part of the hsz is correlated with south china and the duwibong unit in the eastern part of the hsz with north china to test the above geodynamic interpretation this study analyzed the nd isotopic composition of upper cambrian conodonts from the duwibong and yeongweol units the difference of the nd t values between the upper cambrian duwibong and yeongweol units is about 3 units compared to a wide range of the nd 0 values in the modern oceanic basins this slight difference can be regarded as a variation in a same paleo watermass the nd t values of the two units are consistent with coeval values from north china and this suggests that the duwibong and yeongweol units shared the same oceanic watermass with the north china considering current early paleozoic paleogeographic reconstructions the nd isotopic signatures of north china duwibong and yeongweol units may be independent of laurentia and baltica and thus can be indicative of another unique oceanic watermass in contrast to the previous tectonic interpretations the same paleoceanographic signatures shown by the duwibong and yeongweol units and north china and recent developments suggest that the yeongweol unit in the early paleozoic joseon supergroup is not correlated with south china but correlated with north china and the korean peninsula and north china block may have been included in a larger continental block the sino korean block the collisional belt between the south and north china blocks may not extend into the korean peninsula

a millennium of variable ice flow recorded by the ross ice shelf antarctica an enhanced composite advanced very high resolution radiometer avhrr image is used to map flow stripes and rifts across the ross ice shelf antarctica the patterns of these flow related features reveal a history of discharge variations from the ice streams feeding the eastern part of the shelf the most profound variations are visible in the track of rifts downstream of crary ice rise flow stripe bends to the west of this ice rise and adjacent to steershead ice rise and changes in the northern margin of ice stream b the track of rifts downstream of crary ice rise indicates that the ice rise has existed for at least 700 years the character of this track changes about 350 km downstream indicating a rearrangement of flow patterns about 550 years ago the large bulge in the flow stripes to the west of crary ice rise is shown in detail with bent flow stripes extending for several hundred kilometers along flow this feature formed from the south possibly due to a change in the discharge of ice stream a the avhrr image documents a complex history associated with the shutdown of ice stream c with changes in the margins of ice stream c and the northern margin of ice stream b and the grounding of steershead ice rise with an associated bending and truncation of flow stripes landsat imagery shows a region that appears to be actively extending just downstream of the ice rise as the shelf continues to respond to recent changes in ice stream discharge we present a four stage flow history which accounts for the features preserved in the ice shelf

the tectonic setting of the eastern margin of the sino korean block inferred from detrital zircon u pb age and nd isotope composition of the pyeongan supergroup upper palaeozoic lower triassic korea the upper palaeozoic succession pyeongan supergroup in central eastern korea is well correlated with the equivalent successions distributed in north china suggestive of the korean upper palaeozoic being part of the sino korean block detrital zircon u pb ages and sm nd isotope compositions of the pyeongan supergroup in the samcheok coalfield of the taebaeksan basin were analysed a single predominant zircon age peak at c 1 9 ga 70 is marked in all sedimentary units followed by varying amounts of minor late palaeozoic grains up to 30 the rarity of meso to neoproterozoic and silurian aged zircons confirms that sediment influx from the south china and qinling blocks was insignificant the 2 0 1 8 ga dominated zircon age pattern and the nd isotope composition average end 0 15 5 4 0 of the pyeongan supergroup most closely reflect the signature of the yeongnam massif basements which supports a previous hypothesis that the pyeongan supergroup was mostly derived from a palaeo orogen located to the east southeast relatively higher end 0 values 10 1 in the lowermost and the upper parts of the succession are closely matched by the increased occurrence of syn depositional aged zircons which indicates considerable mixing of juvenile materials at c 320 ma and 260 ma both arc related magmatic events are interpreted to have been related to oceanic subduction suggesting that the eastern margin of the sino korean block was an active continental margin during late palaeozoic times

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

darriwilian carbon isotope stratigraphy in the taebaeksan basin korea and its implications for middle ordovician paleoceanography abstract the middle darriwilian carbon isotope excursion mdice event is first documented from central eastern korea taebaeksan basin the eastern part of the sino korean block and is well correlated with global carbon isotope chemostratigraphy the korean mdice record shows three broad positive peaks and complements records from the middle ordovician peri gondwanan epeiric seas showing incomplete records due to disconformity this study reconstructed paleoceanographic conditions with nitrogen isotopic compositions and clay mineral compositions to understand the causes of carbon isotope excursions the heavier excursion in nitrogen isotopic curve and abrupt increase of kaolinite in the early mdice interval are interpreted as a result of epeiric sea denitrification associated with strong seawater stratification and the main cause of those conditions was likely increased precipitation in the adjacent land subsequent sea level rise caused an anti estuarine circulation in the taebaeksan sea and increased the organic carbon burial in the adjacent basin setting which might have sustained the mdice the documentation of the mdice event in this study supports the view that the mdice occurred globally this study provides not only information on the regional paleoceanographic conditions that occurred in the middle ordovician epeiric seas during the course of mdice but also reports that the mdice event occurred as a response to seawater circulation associated with global sea level rising in the middle ordovician

comparison of the ordovician carboniferous boundary between korea and ne china implications for correlation and tectonic evolution abstract there is a great hiatus between ordovician and carboniferous strata in the northeast china and korean peninsula in order to understand geology and tectonic evolution and to find out the similarities and differences in both regions two sections in the western hill near beijing in ne china and several sections in the korean peninsula were selected to examine their geologic boundaries between lower and upper paleozoic strata to compare their characteristic features at four sites in the two sections in the western hill near beijing were examined their contact relations the hui yu section is the same horizon where one site is top of a quarry hill and the other of down hill mid carboniferous qingshuijian formation rests on the ordovician majiagou formation limestone beds are more commonly intercalated with shale and sandstone at site 2 of the hui yu section while at site 1 conglomerate beds are dominant site 1 of the se shu fen section shows eroded and concealed karst topography and conglomerate beds are intercalated within shale beds silurian and devonian strata are absent in these areas in the korean peninsula most o c contacts occur between ordovician limestone formation and carboniferous strata although silurian strata occur beneath the carboniferous strata in the jeongseon area and pyeongnam basin most contact relations are parallel unconformity and angular unconformity is rarely seen the o c relations in both regions are similar to each other and these indicate that the korean peninsula was located near or belonged to the sino korean paraplatform during paleozoic time

late cambrian biogeography conodont bioprovinces from korea abstract although the collisional belt between the north and south china blocks has been well defined in china the location of its eastward extension in the korean peninsula is highly controversial the cambro ordovician sedimentary rocks in south korea the joseon supergroup accumulated in the ogcheon belt which has been proposed as the suture zone between the north and south china blocks or the block boundary the joseon supergroup comprises five different lithostratigraphic units and may be divided into two tectonic blocks by the honam shear zone hsz in the ogcheon belt based on the affinities of the cambrian trilobite faunas previous studies correlated the yeongweol unit in the western part of the hsz with south china and the duwibong unit in the eastern part of the hsz with north china to test the above geodynamic interpretation this study analyzed and compared the degree of the provinciality of upper cambrian conodonts from the yeongweol and duwibong units and north and south china the quantitative test for the upper cambrian provincialism shows high bioprovincial affinities between the yeongweol and duwibong units and both conodont faunas from the two units display higher bioprovincial affinities with that of north china rather than with that of south china their high conodont faunal similarity suggests that the korean peninsula might have been included in a larger continental block including the north china and the korean peninsula the sino korean block in early paleozoic time this result is supported by recent studies on lower paleozoic biogeography stratigraphy and sedimentology that suggest that the yeongweol unit of the joseon supergroup is more closely correlated with north china than with south china

cambrian ordovician conodonts from slump deposits of the argentine precordillera new insights into its passive margin development fil voldman gustavo gabriel consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet cordoba centro de investigaciones en ciencias de la tierra universidad nacional de cordoba facultad de ciencias exactas fisicas y naturales centro de investigaciones en ciencias de la tierra argentina

initial constraints on the timing of granitic magmatism in north korea using u pb zircon geochronology abstract the geology of north korea is very poorly known in this paper twenty seven granitic samples from the tumangang belt and the rangnim massif including diorite granodiorite and monzogranite were selected for in situ zircon u pb isotopic dating in the tumangang belt granites formed mainly in the jurassic with one sample giving a triassic age this is contrary to previous views that considered the granites to be permian to triassic in age in the rangnim massif precambrian granitic magmatism mainly took place at 2 1 and 1 9 1 8 ga no archean emplacement ages have been documented in this study although some inherited discordant zircon may be of this age mesozoic magmatism in this area can be divided into three stages with ages of 234 213 173 and 114 109 ma the triassic granites are mostly exposed in the north and the early cretaceous ones in the west the distribution of jurassic granites is less well documented and only one sample was identified in this study however previous data indicate they are more widely distributed in the area the 2 1 and 1 9 1 8 ga precambrian ages are comparable to paleoproterozoic magmatism in northeastern china indicating that the rangnim massif was most likely part of the north china craton during that time however the absence of 2 5 ga granites and the occurrence of 1 2 ga granites indicate that the rangnim massif was probably at the margin of the north china craton and affected by mesoproterozoic magmatism the similarity in age patterns of the mesozoic granites in north korea to surrounding areas of south korea and the liaodong peninsula of northeastern china indicate that they were controlled by subduction of the pacific ocean under eastern asia however roll back or retreat of the subduction zone resulted in a younging trend from northwest to southeast during the cretaceous

palaeomagnetism of the upper palaeozoic lower mesozoic pyongan supergroup korea a phanerozoic link with the north china block summary the upper carboniferous lower triassic pyongan supergroup is exposed in an e w trending syncline comprising the samcheok coalfield in eastern south korea it borders the southern margin of a ne sw trending okcheon zone of upper jurassic lower cretaceous deformation daebo orogeny although a recent field overprint widely recorded in korean rocks is represented here an ancient field component structure is recovered from the red bed facies in this supergroup by detailed thermal demagnetization a prominent upper jurassic cretaceous overprint is widespread diz 56 1 54 8 ags 9 6 palaeopole at 200 4 e 46 7 n and records the magnetic effect of the daebo orogeny within the okcheon belt it is post deformational in origin and appears to have been confined mainly to the cretaceous normal superchron it has been rotated clockwise since these times in common with the main synclinal axis as a consequence of dextral movements along the tan lu fault system components predating this deformation are recovered from the lower triassic diz 1 1 19 4 ags 18 2 palaeopole at 306 1 e 63 2 n permian diz 358 3 11 5 c 6 3 palaeopole at 311 9 e 58 7 n and upper carboniferous diz 34l u 9 2 mgs 7 2 palaeopole at 335 7 e 44 6 n sediments second order small circle dispersions of site palaeopoles record unaccommodated tectonic rotations and are largest in the oldest beds below an upper carboniferouslower permian unconformity however the presence of reversals probably acquired before and after the carboniferous permian reversed superchron defines ancient field axes and identifies an upper carboniferous lower triassic apw path this path correlates with the contemporaneous path from the north china block and is removed from the path from the south china block agreement with north china is enhanced when these results are corrected for the rotation indicated by the cretaceous overprint we therefore identify a first order correlation between the korean peninsula and north china at least since upper palaeozoic times establishment of and movements along the tan lu fault system since mesozoic times have not obscured this palaeomagnetic correlation

detrital zircon u pb ages of the jangsan formation in the northeastern okcheon belt korea and its implications for material source provenance and tectonic setting abstract the jangsan formation distributed in the taebaeksan basin central eastern korea is unfossiliferous and is composed of quartz arenite this formation is conventionally believed to be the lowermost stratigraphic unit of the lower paleozoic sequence deposited on the yeongnam massif in south korea corresponding to early cambrian in age u pb dating of detrital zircon grains using a laser ablation inductively coupled mass spectrometer yields ages ranging from archean to middle proterozoic 1738 67 ma to 3058 53 ma detrital zircons show no ages younger than 1 8 ga suggesting that the jangsan formation was deposited at some time after this age but much prior to ca 520 ma the depositional age of the immediately overlying myobong formation this interpretation is supported by the recent report on the presence of the unconformity between the jangsan and the myobong formations kim and lee 2006 zircon ages from jangsan sandstones define two major groups archean age grains with a maximum frequency at about 2 5 ga and paleoproterozoic age grains with maximum frequencies at about 2 1 and 1 8 ga the observed zircon age distribution in the jangsan sandstones may represent that of the yeongnam massif on which the jangsan formation was deposited such an age distribution of the yeongnam massif matches well with that the north china block suggestive of the yeongnam massif being a part of the sino korean craton during the precambrian

diagenesis of shallow marine sandstones the lower ordovician dongjeom formation korea response to relative sea level changes abstract this study deals with the diagenesis of shallow marine mature sandstones in the view of relationship between depositional conditions and diagenesis the dongjeom formation early ordovician korea is composed of three coarsening upward siliciclastic sequences deposited on an extensive carbonate platform dongjeom sandstones are divided into two facies according to depositional conditions with respect to changes in relative sea level transgressive facies and regressive facies the transgressive facies are characterized by calcareous sandstones and regressive facies by quartzose to feldspathic non calcareous sandstones dongjeom sandstones in the different facies experienced different pathways of diagenesis in the regressive facies siliciclastic deposition was dominant and feldspar grains were broken by active reworking and concentrated in the finer fraction with deep burial the regressive facies sandstones experienced significantly chemical compaction and quartz cementation in the transgressive facies carbonate grains were concentrated which was successively followed by extensive early calcite cementation such early calcite cementation prevented the transgressive facies sandstones from further significant diagenetic changes during deep burial the results of this study indicate that the composition early diagenesis and late diagenesis are intimately related to each other and that diagenesis of dongjeom sandstones was mainly controlled by depositional facies formed in response to relative sea level changes