sequence model and its application to a miocene shelf slope system in the tectonically active ulleung basin margin east sea sea of japan abstract in a broader application of sequence stratigraphic concept to a tectonically active margin setting this study presents a sequence model that considers all three controls on sequence development i e eustasy tectonic movement and sediment supply as independent variables the model introduces six sequence types a to f including type 1 and type 2 sequences defined in the original exxon scheme each sequence shows a variety in number and stacking pattern of its constituent parasequence sets reflecting combined effects of accommodation change and sediment supply this model is applied to a seismic sequence analysis of the shelf slope system middle to upper miocene in the southwestern margin of ulleung basin which has experienced significant crustal deformation during the tertiary back arc opening and subsequent closing of the east sea sea of japan the model application delineates four sequence types whose development is closely associated with the tectonic evolution of the ulleung basin margin during the back arc opening early to middle miocene type a and b sequences were emplaced as a result of steady creation of accommodation space due to a rapid subsidence combined with a tectonic controlled high to moderate rate of sediment supply the sequences associated with the extensional tectonism are characterized by active progradation and aggradation without forced regressive phases in the initiation stage of back arc closure middle to late miocene subsidence rates were significantly reduced because of a widespread contractional deformation while subaerial erosion of the uplifted thrust belt resulted in an increase in sedimentation rate as a result steady prograding type e sequences were formed by alternating normal and forced regressions during the quiescent phase of back arc closure in the late miocene rise dominant fluctuating relative sea level change and moderate to low sediment supply gave rise to type f sequences similar to type 1 sequences of the exxon group reflecting a major control of eustatic sea level change

heterogeneity of initial 87sr 86sr ratios within a single pluton evidence from apatite strontium isotopic study abstract magmatic apatite in samples of the unmetamorphosed undeformed cretaceous pluton of the habu granodiorite southwestern japan was examined to determine its viability as an indicator of initial 87sr 86sr heterogeneity in magmatic bodies the habu granodiorite is a zoned pluton in the ryoke metamorphic belt of southwestern japan a published rb sr whole rock isochron age of 124 2 10 8 ma is significantly older than th u total pb monazite ages of ca 86 ma a rb sr mineral isochron of 90 0 2 5 ma for a sample of granodiorite from the margin of the pluton has an initial 87sr 86sr sri of 0 7056 0 0001 similar to a 87sr 86sr of 0 70539 for coexisting euhedral apatite similarly a rb sr mineral isochron of 91 4 2 5 ma for a sample of adamellite from the center of the pluton has an sri of 0 7068 0 0001 corresponding to a 87sr 86sr ratio of 0 70673 0 70684 for three fractions of coexisting euhedral apatite the uniformity of 87sr 86sr values of apatite in individual samples and accordance of 87sr 86sr values of apatite and sri from the mineral isochron suggest that magmatic apatite can be considered as a reliable indicator of sri in granitic rocks the sr isotopic compositions of euhedral apatite coupled with those determined through the mineral isochrons and whole rock data indicate that sri varies between samples from 0 7054 to 0 7074 this provides direct evidence of sri heterogeneity within a compositionally zoned pluton such heterogeneity can produce spurious whole rock age estimates in granitic plutons even where the true age of a pluton is uniform within measurable error assimilation cannot account for chemical differences between granodiorite and adamellite as well as sr isotopic heterogeneity it is likely that the heterogeneity of sri is caused by magma source materials

reconstruction of northeast asian deformation integrated with western pacific plate subduction since 200 ma abstract the configuration and kinematics of continental deformation and its marginal plate tectonics on the earth s surface are intrinsic manifestations of plate mantle coupling the complex interactions of plate boundary forces result in plate motions that are dominated by slab pull and ridge push forces and the effects of mantle drag these interactions also result in continental deformation with a complex basin mountain architecture and evolution the kinematics and evolution of the western pacific subduction and northeast asian continental margin deformation represent a first order tectonic process whose nature and chronology remains controversial this paper implements a deep time reconstruction of the western pacific subduction continental accretion or collision and basin mountain deformation in northeast asia since 200 ma based on a newly revised global plate model we use gplates software to examine strain recovery geological and seismic tomography constraints for the western pacific plate subduction and sequentially backward rotations of deforming features the results indicate a nw se oriented shortening from 200 to 137 ma a nww see oriented extension from 136 to 101 ma a nearly n s oriented extension and uplift with a short term nww see oriented compressional inversion in northeast china from 100 to 67 ma and a nw se and nearly n s oriented extension from 66 ma to the present day the western pacific oceanic plate subducted forward under east asia along mudanjiang honshu island during the jurassic and the trenches retreated to the sikhote alin north shimanto and south shimanto zones from ca 137 128 ma ca 130 90 ma and in ca 60 ma respectively our time dependent analysis of plate motion and continental deformation coupling suggests that the multi plate convergent motion and ocean continent convergent orogeny were induced by advance subduction during the jurassic and earliest cretaceous our analysis also indicates that intra continent rifting and back arc extension were triggered by trench retreat during the cretaceous and that the subduction of the oceanic ridge and arc were triggered by trench retreat during the cenozoic therefore reconstructing the history of plate motion and subduction and tracing the geological and deformation records in continents play a significant role in revealing the effects of complex plate motions and the interactions of plate boundary forces on plate mantle coupling and plate motion intracontinental deformation coupling

evolution of the sanbagawa and shimanto high pressure belts in sw japan insights from k ar ar ar geochronology abstract the sanbagawa belt sensu lato in japan is one of the world s classical high pressure hp metamorphic belts and has long been considered to be a coherent hp belt of the cretaceous age however recent progress in detrital zircon geochronology together with the accumulation of abundant phengites k ar ar ar ages revealed that the belt is comprised of two petrotectonic belts sanbagawa sensu stricto hp belt and shimanto hp belt these two belts have distinctly different ages of peak metamorphism and different p t conditions of metamorphism the sanbagawa schists sensu stricto were metamorphosed in the conditions of the pumpellyite actinolite facies through the epidote blueschist to epidote amphibolite facies and up to the eclogite facies during a prograde stage in a subduction zone at 120 115 ma phengite k ar geochronology revealed that the subsequent exhumation after the peak metamorphism took placed in a manner that the higher grade rocks exhumed more rapidly in comparison with the lower grade rocks this is supported by a positive correlation between age and apparent metamorphic gradient that have formed during the post metamorphic peak hydration recrystallization moreover the schists have experienced intense ductile deformation and long term exhumation it took longer than 31 m y to reset the phengite k ar system in contrast the shimanto hp schists were metamorphosed in the epidote blueschist greenschist transitional facies to the epidote amphibolite facies and have experienced a short term deformation for less than 13 m y this short deformation formed a negative correlation between k ar age and apparent metamorphic gradient these two contrasting age temperature relationships suggest different exhumation processes between the two hp belts most likely due to a change in subducting oceanic plates in the cretaceous along the paleo japanese convergent margin

plio quaternary seismic stratigraphy and depositional history of the ulleung basin east sea association with debris flow activity abstract we analyzed multi channel seismic reflection profiles to decipher the plio quaternary stratigraphic architecture and resolve the depositional history of the ulleung basin a detailed seismic stratigraphic interpretation revealed nine seismic units units 1 9 separated by unit boundaries in the plio quaternary deposits of the ulleung basin unit 1 pliocene is dominated by debris flow deposits dfds throughout the basin units 2 9 quaternary are characterized by stacked dfds interbedded with thin hemipelagic sediments along the southern slope whereas the northern basin floor is filled with hemipelagic and pelagic sediments the areal distribution and dimensional characteristics of the dfds indicate that sedimentation in the ulleung basin has been controlled by a combination of tectonic movement eustatic changes in sea level and gas hydrates dissolution and dissociation during the pliocene unit 1 sedimentation was mainly controlled by tectonic movements causing margin wide slope failures under the compressional regime large sediment deposits were supplied to the basin through mass transport processes resulting in an abundance of dfds throughout the basin during the quaternary units 2 9 compressive stress decreased sharply causing the dfds to retreat landward at that time sedimentation was mainly influenced by eustatic changes in sea level and gas hydrates dissolution and dissociation as the sea fell to the lowstand slope failures were activated by the generation of high pore water overpressure and the generation of weak layers in the sediments resulting in stacked dfds however as the sea level rose to the highstand sediment was primarily deposited via hemipelagic and pelagic processes due to increased hydrostatic pressure and slope stability

active tectonics of an apparently aseismic region distributed active strike slip faulting in the hangay mountains of central mongolia summary we identify and describe a series of east west left lateral strike slip faults named the songinomargats the hag nuur the uliastay and the south hangay fault systems in the hangay mountains of central mongolia an area that has little in the way of recorded seismicity and which is often considered as a rigid block within the india eurasia collision zone the strikeslip faults of central mongolia constitute a previously unrecognized hazard in this part of mongolia each of the strike slip faults show indications of late quaternary activity in the form of aligned sequences of sag ponds and pressure ridges developed in alluvial deposits total bed rock displacements of 3 km are measured on both the songino margats and south hangay fault systems bed rock displacements of 11 km are observed across the hag nuur fault cumulative offset across the uliastay fault systems are unknown but are unlikely to be large we have no quantitative constraint on the age of faulting in the hangay the 20 km of cumulative slip on the hangay faults might at least in part be inherited from earlier tectonic movements our observations show that despite the almost complete absence of instrumentally recorded seismicity in the hangay this part of mongolia is cut through by numerous distributed strike slip faults that accommodate regional left lateral shear between siberia and china central mongolia is thus an important component of the india eurasia collision that would be overlooked in models of the active tectonics based on the distribution of seismicity we suggest that active faults such as those identified in the hangay of mongolia might exist in other apparently aseismic regions within continental collision zones

intra tooth isotope variations in late miocene bovid enamel from afghanistan paleobiological taphonomic and climatic implications abstract the rich mid turolian site of molayan afghanistan has yielded more than 100 mandibles from the bovid tragoportax afghanicus in this study we document different aspects of the paleobiology and paleoecology of this fossil bovid by examining patterns of inter and intra tooth carbon and oxygen isotopic analyses in m1 to m3 molars from five specimens accurate paleoecological and paleoclimatic inferences based on carbon and oxygen isotope analyses in fossil enamel are directly dependent upon the way in which teeth are sampled as well as taphonomic processes which are responsible for fossil accumulation because this sampling methodology provides a unique opportunity to detect seasonal changes in diet and environment during tooth formation it also offers the possibility of testing between catastrophic and progressive deposition at this site preservation of 13c and 18o values is shown to be good and permits inter individual comparisons of isotopic trends to be made timing of molar crown formation and enamel growth rate were deduced from the pattern of intra tooth carbon and oxygen isotope variation the pattern of 18o variation found in the first and second molars is similar in all the individuals which suggests that a single birth season occurred probably before the hot dry season large differences in average 18o values 2 5 are found within a single cohort and indicate that fossil accumulation was progressive rather than catastrophic the hypothesis that t afghanicus evolved in an open environment is supported by high 13c values in a c3 context increasing temperature and or aridity eastward along the greco irano afghan biogeographic province is strongly suggested by increasing 18o values between greece and afghanistan

gas origin and migration in the ulleung basin east sea results from the second ulleung basin gas hydrate drilling expedition ubgh2 abstract we have investigated the gas chemistry of marine sediments up to 250 m below seafloor m bsf recovered during the second ulleung basin gas hydrate drilling expedition ubgh2 to identify and compare the gas origin and its migration at seismically non chimney truncated chimney and chimney sites in this basin the molecular and isotopic data c1 c2 ratios 300 13 c ch 4 d ch 4 kim et al 2012 and thought to reflect two phase methane transport processes in chimney sites deep sourced methane migrates independently of the carbon dioxide which remains dissolved in the aqueous phase leading to the extremely low c values observed in the upper 30 m bsf upward methane diffusion at non chimney sites may also add a transport induced fractionation as evidenced in mixing diagrams but this process does not significantly affect the c values 13 c co 2 shows usually minimum values at the sulfate methane transition zone smtz at all sites however in chimney sites these values have a much more depleted signature indicating faster rates of methane consumption by anaerobic oxidation of methane aom supported by the higher methane flux moreover here the massive hydrate that forms in shallow sediments incorporates gases with a lower c1 c2 ratio higher c2 c1 than the surrounding sediment as documented in hydrate bound gas bg and void gas vg samples gas hydrate dissociation during the core recovery is released enriched ethane c2h6 trapped in gas cage which leads to have high c2h6 in vg samples

occurrence and seismic characteristics of gas hydrate in the ulleung basin east sea abstract multi channel seismic reflection and well log data from the ulleung basin east sea reveal several seismic signatures indicative of gas hydrate occurrence in the ulleung basin that are associated with vertically and or laterally stacked mass transport complexes the seismic indicators include a a bottom simulating reflector bsr b a seismic chimney c high amplitude reflections within the gas hydrate stability zone ghsz d acoustic blanking e enhanced reflections below the bsr and f seafloor gas escape features the bsr associated with enhanced reflections below is most commonly found over much of the basin indicating a physiochemical boundary of gas hydrates overlying free gas seismic chimneys are characterized by velocity pull up and reduced reflectivity on the seismic sections which appear to be caused by active migration of fluid gas vertically into the ghsz the logging data retrieved from the seismic chimneys showed elevated electrical resistivity 80 ohm m and p wave velocity 2000 m s indicating the presence of gas hydrate another seismic characteristic observed in gas hydrate bearing sediments is the strong amplitude reflections defined by the relatively high reflectivity within the ghsz acoustic blanking is likely to be the result of hydrate accumulation in the sediments causing a significant reduction of acoustic impedance contrast between sedimentary layers where the upward migrating gas seeps into the deep water column seafloor pockmarks and mud mounds may be formed gas hydrate was recovered from the ulleung basin east sea in 2010 during the second ulleung basin gas hydrate drilling expedition ubgh2 under the korean national gas hydrate program based on the results gas fluids migrate into the ghsz through two distinct pathways 1 structural conduits which include fault and fracture systems associated with seismic chimneys and 2 stratigraphic conduits associated with inclined turbidite hemipelagic layers two types of gas hydrate occurrence were identified in the basin 1 a stratally bound type pore filling within turbidite sand layers and 2 a locally concentrated type massive nodule or fracture filling within upward growing chimneys associated with near vertical faults relatively high concentrations of gas hydrate however tend to occur in localized seismic chimneys rather than in the strata related features the successful recovery indicates that the ulleung basin provides favorable conditions for gas hydrate formation

the hunghae formation se korea miocene debris aprons in a back arc intraslope basin during early to middle miocene times a sudden opening of the ulleung tsushima back arc basin in the east sea sea of japan led to the development of intraslope basins along the rifted southwestern margin southeast korea abrupt subsidence resulted in the deposition of the 200 m thick hunghae formation middle miocene a sand mudstone sequence that can be divided into five facies facies i sand and mudstone couplet and ii coarse sand are turbiditic in origin as evidenced by massive graded crudely layered and parallel laminated sand beds facies iii homogeneous mudstone is characterized by various lignite and plant fragments clastic and biogenic grains that are randomly oriented suggestive of hemipelagic deposition facies iv chaotic deposit is characterized by the disruption of beds the presence of isolated siltstone blocks or balls and large clasts in the muddy matrix indicative of retrogressive rockfall and slide slump facies v conglomerate is of debris flow origin as evidenced by clast and matrix supported features floating large clasts and absence of traction structures individual facies are organized into two types of facies association 1 homogeneous mudstone facies iii associated randomly with the rest facies i ii iv and v indicative of hemipelagic and episodic sediment gravity flow processes respectively 2 conglomerate facies v coarse sand facies ii and sand mudstone couplet facies i representing the flow transformation from debris flow to high and low concentration turbidity currents these facies associations are similar in many respects to modern and ancient debris or slope aprons found elsewhere numerous isolated slide slump blocks wedged conglomerates with armoured mudstone balls discontinuous lignite containing sand mudstone beds chaotic structure and growth faults suggest that the deposition occurred on a steep slope intraslope basin off coalescing fan deltas mainly by unchannellized sediment gravity flows ancient deposits with irregular facies sequences can be viewed as debris apron systems which provide alternatives to submarine fan models in many clastic basins with a line rather than point source

seismic stratigraphy and structural analysis of the western south korea plateau wskp east sea abstract the western south korea plateau wskp situated on the southwestern part of east sea is characterized by rifted continental fragments that were formed in the early phase of back arc opening in this work we analyze multi channel seismic reflection profiles from the wskp to document the structural and stratigraphic framework of the area we also present fault derived stretching beta factors related to the continental rifting along two regional seismic profiles our data reveal several graben and half graben subbasins up to 1300 m thick bound by n s trending normal faults we show that on the basis of constructed isopach maps tectonic activity was the main controlling factor on the sedimentation through much of the plateau history the seismic data reveal that the sedimentation history of the wskp is characterized by four main phases phase 1 to phase 4 p1 p4 separated by regional unconformities rapid extension and subsidence took place at an early stage of p1 leading to the graben and half graben openings volcanic activity was widespread at early times and 700 m thick succession of lacustrine and fluvial sediments was deposited following p2 early mid miocene latest miocene dramatic extension and subsidence changed the lacustrine environment into marine enabling to the deposition of thick marine sediments 750 m over the subbasins extension ceased during p3 latest miocene early pliocene and less pronounced subsidence continued at this time the sedimentation was uniform over the area and included the cyclic succession of hemipelagic deposits and turbidites which were probably expressed by climatic forcing p3 was interrupted by regional compression when normal fault movement was reversed and gentle anticlines formed as a result of inversion the latter was accompanied by widespread uplift and erosion along the western margin of the plateau and substantial erosion took place on the crests of the folds the uplift also shifted the main depocenters of the plateau which were ultimately filled by thick mass transport deposits during the following phase of p4 early pliocene holocene subsidence has been dominant in the area since the beginning of p4 which was locally interspersed by inversion along the reactivated normal faults total upper crust f and whole crust extension c estimates in the wskp show similarities suggesting that the observed rift structure in wskp has resulted from uniform pure shear stretching

an insight into asymmetric back arc extension tecto magmatic evidences from the ulleung basin the east sea sea of japan abstract this paper presents an ancient example of asymmetric back arc extension found in the ulleung basin the southwestern east sea sea of japan the paper focuses on the formative processes of variable asymmetric features of the basin and on their relationship to the style of lithospheric stretching in the ulleung basin features resulting from asymmetric back arc extension include 1 the syn extensional volcanism concentrated to the northern flank of the basin 2 the overwhelming number of north dipping syn extensional normal faults 3 the style of boundary faults different between the northern and southern conjugate margins and 4 the thickness of the crust and the depth to the moho discontinuity that together decrease toward north we argue that the fundamental control of such asymmetric features was the simple shear style lithospheric extension which presumably involved a crustal detachment the mid crustal extension of north dipping syn extensional listric normal faults by the simple shear style extension syn extensional faults evolved to dip toward north and at the same time volcanic activities that had been initially widespread throughout the basin became to concentrate to the north of the basin the northward deviantion of volcanic centers and the zone underlain by maximally attenuated crust possibly the extinct spreading center might be the result of separation between the loci of basin subsidence and asthenospheric upwelling that is common in simple shear cases

changes in depositional systems and sequences in response to basin evolution in a rifted and inverted basin an example from the neogene niigata shin etsu basin northern fossa magna central japan abstract the niigata shin etsu basin which occurs along the eastern margin of the sea of japan was generated in middle miocene time as a failed rift basin in relation to the backarc opening of the japan arc and was converted to a compressional basin in late miocene time the basin filling succession can be divided into four tectonostratigraphic units stages based on characteristics of depositional systems depositional sequences tectonic subsidence rate and sediment supply these units coincide in time with major tectonic events during backarc rifting and subsequent basin inversion unit i 16 13 5 ma represents a syn rift stage characterized by rapid basin subsidence the rate of accommodation exceeded the rate of accumulation resulting in a retrogradational stacking pattern of muddy slope to basin floor systems unit ii 13 5 6 5 ma represents a post rift thermal subsidence stage the rate of accommodation nearly equaled the rate of accumulation resulting in an aggradational stacking pattern of five third order depositional sequences mainly comprising submarine fan turbidite systems affected by supply of coarse clastics unit iii 6 5 1 ma represents the basin inversion stage showing no subsidence or uplift the accumulation rate exceeded the rate of accommodation resulting in rapid progradation of depositional sequences composed of slope shelf shallow marine delta and fluvial systems unit iv 1 ma present represents an intense compressional stress field sedimentation has been restricted to a synclinal area due to syndepositional folding and uplift changes in basin subsidence rate and sediment supply resulting from tectonics and climate change in the basin and the provenance strongly affected characteristics of the depositional systems and sequences the change in basin subsidence also created a basinwide depositional cycle whereas eustasy affected relative sea level changes created higher order depositional sequences during relatively stable phases of tectonics

uplift of the ou backbone range in northeast japan at around 10 ma and its implication for the tectonic evolution of the eastern margin of asia abstract the late cenozoic uplift history of a sedimentary basin located in the axial part of the ou backbone range northeast japan was studied using detailed mapping fission track dating and basin analysis the subsidence analysis of the basin clarified the more complex stepwise uplift of the ou backbone range three stages of uplift have been recognized and are interpreted to be the result of compressional stress possibly accompanied by basin inversion the three stages are identified as 1 a phase of surface uplift and regional unconformity 12 9 ma 2 a stage of differential uplift and compression 6 5 3 ma and 3 an intense compression stage 3 ma in the first stage the eastern sector of the backbone range uplifted and a notable unconformity was formed at 10 ma the western sector remained submerged suggesting that the eastern sector uplifted earlier than the western sector although the first uplift stage has been regarded as a tectonically quiet period in northeast japan this tectonic event at 10 ma is supposed to have a regional origin because coeval tectonic events took place across all northeast japan as well as on the eastern margin of asia this study thus provides new insights into the neogene tectonic evolution in the eastern margin of asia

late paleozoic mesozoic tectonic evolution of sw japan a review reappraisal of the accretionary orogeny and revalidation of the collisional model abstract this paper makes a review of the interpretations of the tectonic evolution of sw japan during the last three decades in the late 1970s the dominant model was the so called pacific type orogeny emphasizing the purported absence of nappes and the contrast with the alpine chains and interpreting the evolution as due to a steady oceanic subduction since the paleozoic time in the 80s the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models involving the intermittent underthrusting of buoyant blocks like micro continents at the same time the use of high resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges with a reconstructed ocean plate stratigraphy of individual accreted units especially in the tanba and shimanto zones also precise radiometric dating permitted the distinction of metamorphosed units especially in sanbagawa and shimanto belts as a result of these new data since the 1990s the plate tectonic interpretation of the history of the japanese islands was revised by japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction with an episodic ridge subduction the so called miyashiro type orogeny the review of different data leads to the following conclusions the structure of sw japan is made of a pile of sub horizontal nappes polydeformed with a geometry similar to the one encountered in collisional orogens the geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept miyashiro type orogeny are inappropriate a permanent oceanic subduction with the intermittent collision actually subduction of an active ridge or seamount chain is unable to build such structures as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate the underthrusting of a micro continent or mature arc is likely needed the exhumation story of sanbagawa hp schists suggests the setting of a continental subduction the petrological and new geochemical data from the literature strongly support the existence beneath the nappes of accretionary complexes of continental bodies showing affinities with south china from which they were once separated the episodic collision underthrusting of such blocks was responsible for the tectonic piling tectonic erosion plaid likely a major role in removing material during the intervening subduction stages a revised geodynamic model implying the collision of the honshu south kitakami kurosegawa and shimanto blocks is proposed for explaining the three orogenic crises which took place respectively at around 240 130 and 80 60 ma ago in sw japan the paleogeographic position and affinity of the hida block with surrounding units in the hinterland are still unclear more work is needed to solve this question

stratigraphic review of eocene to oligocene successions along the eastern japan sea implication for early opening of the japan sea abstract stratigraphic review of the on land successions exposed on the back arc side of japan and sakhalin combined with supplemental radiometric dating reveals the existence of late eocene or oligocene marine sediments along the eastern coast of the japan sea this finding implies that the origin of the japan sea dates back to the oligocene or earlier time much older than ever supposed the host eocene to oligocene subaerial to shallow water successions distribute immediate west of the volcanic front of that time and contain volcanic rocks the chemistry of which is characteristic of continental rift or volcanic arc they are associated with parallel dike swarms or normal faults and could be infillings of an incipient back arc rift collective evidence suggests that the rift was rapidly subsided and spread during the following early to middle miocene time however a back arc wide unconformity was produced during a short period from the latest oligocene to the earliest miocene and was succeeded by extensive bimodal volcanism with rapid migration of the volcanic front to the fore arc side these short term events could have been induced by upwelling or inflow of hot asthenosphere beneath the arc rift system followed by rapid subsidence and spreading of the japan sea

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

stable isotopes in large herbivore tooth enamel capture a mid miocene precipitation spike in the interior pacific northwest abstract stable carbon and oxygen isotopes of fossil ungulate tooth enamel were used to investigate the paleoclimate of the pacific northwest from the mid oligocene through pleistocene particularly targeting the mid miocene climatic optimum mmco we specifically test whether precipitation as inferred from tooth enamel 13c values relative to the 13c values of atmospheric co2 13c increased with increasing partial pressure of atmospheric co2 pco2 analysis emphasized water dependent equids rhinos and proboscideans but several artiodactyls and castor were also analyzed as available values of 13c 19 5 in the lower john day 27 and 18 ma and mascall 15 16 ma localities imply relatively high mean annual precipitation map ca 550 800 mm yr values of 13c

potential freshening impacts on fines migration and pore throat clogging during gas hydrate production 2 d micromodel study with diatomaceous ubgh2 sediments abstract the methane gas hydrate stored in natural sediments is considered a potential gas resource countries such as china india japan and korea are interested in commercializing this resource and offshore field pilot tests for gas production have been conducted using depressurization methods to destabilize gas hydrate and facilitate the migration of methane to the production well however fine grained sediments fines which are present even in coarse grained gas hydrate bearing sediments can be resuspended in the production fluid subsequently clogging pore throats in the formation and reducing the overall production efficiency we conducted laboratory tests to evaluate the suspension and clogging potential of fines collected from the ulleung basin east sea korea during the 2010 ulleung basin gas hydrate expedition 2 ubgh2 experimental results reveal that diatoms are prevalent in the sediment and largely control the suspension and clogging behavior fluid flow experiments in 2d micromodels show clogging occurs even when injecting the minimum sediment concentration 0 1 wt in the fluid through micromodels with pore throat widths at the high end of the anticipated range for ubgh2 gas hydrate bearing sands 100 m mobile gas fluid interfaces forming during gas hydrate dissociation accentuate clogging by concentrating and mobilizing fines sedimentation tests show pore water freshening during dissociation is not anticipated to change the potential for diatoms to become entrained in the pore water flow even for the observed gas hydrate saturations of 80 muscovite and illite are also significant components of the tested sediment however and pore water freshening increases their potential for resuspension and clogging overall the resuspension and clogging potential of these fine sediments should increase as gas hydrate dissociation progresses in the thin gas hydrate bearing sands investigated in the ulleung basin

double saloon door tectonics in the japan sea fossa magna and the japanese island arc abstract a number of criteria considered diagnostic of double saloon door rifting and seafloor spreading are matched by data from the japanese arc these include i a pair of terranes sw and ne honshu which rotated in opposite directions from 22 21 ma to 14 11 ma ii rotated terranes which comprise a retro arc fold thrust belt attached to an accretionary wedge intruded by a magmatic arc iii contemporaneous backarc extension from 24 to 21 ma which is brought to a halt by progressive collision of the izu bonin and japan arcs from 15 to 5 ma iv isolation of blocks of thicker continental crust by areas of thin continental or oceanic crust during backarc rifting v such isolation may be due to simultaneous rifting or to progressively seaward rifts associated with ridge jumps towards the subduction zone vi opposite rotations are accommodated by subduction rollback demonstrated by seaward migration of the volcanic front from 30 26 ma to 16 15 ma vii concurrent development of a major arc orthogonal rift the fossa magna from 23 18 ma to 14 ma which was thereafter inverted from 15 ma to the recent viii a northeast propagating rift in the northern japan basin demonstrated by the relationship of linear magnetic anomalies to the mapped continent ocean boundary driving mechanisms for double saloon door tectonics are discussed in relation to various reconstructions of the northwest pacific opposite rotational torques leading to opposite terrane rotations may be caused by rollback of a curved trench hingeline or by the divergent slab sinking forces of the pacific and philippine sea plates

distribution and origin of seismic chimneys associated with gas hydrate using 2d multi channel seismic reflection and well log data in the ulleung basin east sea abstract analysis of multi channel seismic reflection and well log data from the ulleung basin east sea reveals that two distinct types of seismic chimneys have been identified in the basin based on their geometries seismic reflection patterns well log response and lithology type i is a mound like feature with a transparent or chaotic reflection pattern well log interpretation and lithology of this type indicate that type i consists of mobilized homogeneous mud including fracture filling gas hydrate this type is mainly located on the structural highs and is mostly restricted to the pliocene sedimentary succession in contrast type ii is a pipe like feature with vertically stacked distorted reflectors based on well log data and lithology type ii filled with fracture filling gas hydrate without breaking up primary sedimentary structure this type appears along the deep seated fault and mainly developed within the quaternary deposit our primary conclusion is that type i resulted from the subsurface sedimentary remobilization in response to regional uplift in the pliocene whereas type ii resulted from the focused vertical fluid flow through fractures triggered by reactivation of deep seated fault during the quaternary

volcanism and paleoenvironment of the pula maar complex a pliocene terrestrial fossil site in central europe hungary abstract we describe the late pliocene paleoenvironment and paleoclimate of the pula fossil site of the western pannonian basin hungary which occurs within a lacustrine succession deposited in a volcanic crater maar radiometric dating of adjacent volcanic bodies hosting the fossil bearing sedimentary assemblages gives an age of 4 25 0 17 ma k ar to date five articulated rhinoceros skeletons dihoplus sp have been recovered and a few fragmentary remains of artiodactyls and freshwater fishes perca sp leuciscus sp and gobius sp are also present an insect taphocoenosis comprises terrestrial groups that inhabited the former lake margins syrphidae heteroptera chalcidoidea tenebrionidae as well as aquatic insects dytiscidae baetidae and chironomidae deciduous broad leaved woody plants prevailed in and around the pula locality quercus ulmus zelkova acer salicaceae and are associated with some rare floral elements ginkgo sassafras and buxus deposition at the lake bottom seems to have taken place in oxygen depleted layers and taphonomic evidence indicates that fossil material underwent minimal if any weathering 13c values of one rhinoceros tooth suggest that this mammal consumed mixed c3 plants in a wooded environment the climatic conditions inferred from the reconstructed vegetation and stable oxygen isotope data from the tooth enamel support a cf type climate koppen classification with a mean annual temperature of 10 13 c with some dry periods during the year pula is comparable to other maar fossil sites of pliocene age such as camp dels ninots spain and hajnacka i slovakia

characterization of gas hydrate reservoirs by integration of core and log data in the ulleung basin east sea abstract examinations of core and well log data from the second ulleung basin gas hydrate drilling expedition ubgh2 drill sites suggest that sites ubgh2 2 2 and ubgh2 6 have relatively good gas hydrate reservoir quality in terms of individual and total cumulative thicknesses of gas hydrate bearing sand hybs beds in both of the sites core sediments are generally dominated by hemipelagic muds which are intercalated with turbidite sands the turbidite sands are usually thin to medium bedded and mainly consist of well sorted coarse silt to fine sand anomalies in infrared core temperatures and porewater chlorinity data and pressure core measurements indicate that gas hydrate occurrence zones ghoz are present about 68 155 mbsf at site ubgh2 2 2 and 110 155 mbsf at site ubgh2 6 in both the ghoz gas hydrates are preferentially associated with many of the turbidite sands as pore filling type hydrates the hybs identified in the cores from site ubgh2 6 are medium to thick bedded particularly in the lower part of the ghoz and well coincident with significant high excursions in all of the resistivity density and velocity logs gas hydrate saturations in the hybs range from 12 to 79 with an average of 52 based on pore water chlorinity in contrast the hybs from site ubgh2 2 2 are usually thin bedded and show poor correlations with both of the resistivity and velocity logs owing to volume averaging effects of the logging tools on the thin hybs beds gas hydrate saturations in the hybs range from 15 to 65 with an average of 37 based on pore water chlorinity in both of the sites large fluctuations in biogenic opal contents have significant effects on the sediment physical properties resulting in limited usage of gamma ray and density logs in discriminating sand reservoirs

spatial and temporal variations in the isotopic composition of bison tooth enamel from the early holocene hudson meng bone bed nebraska the hudson meng bone bed in northwestern nebraska is an early holocene deposit of hundreds of bison of divering ages that were killed in a catastrophic event of unknown origin the m 1 m 2 and m 3 molars of individuals ranging from ca 1 to 7 years of age at the time of their death were examined to determine inter and intra tooth isotopic variability and to link this variability to time in order to better understand the environments that existed prior to the mass death event the d13c value of molar structural carbonate increases by 2 3 from the m 1 to m 3 molars reflecting increasing direct forage signals and decreasing maternal influences the d18o value of molar structural carbonate in a given individual shows no consistent trend with time from birth indicating a fairly direct linkage to dietary water regardless of tooth ontogeny detailed down tooth isotopic measurements indicate a small seasonal signal in the d13c value of forage maternal milk which appeared to have been largely dominated by c 4 flora in contrast there was almost a 10 range in the isotopic composition of dietary water a range that is within present day summer versus winter precipitation in the region the d18o value of bulk tooth enamel arranged by approximate time prior to the death event indicate a consistent increase in the d18o value of body water 2 3 suggesting a long term decrease in winter spring precipitation and or drought the d18o trend with time coupled with the high c 4 grass abundance suggest environmental stresses on the herd preceding the catastrophic death event 2000 elsevier science b v all rights reserved

late cretaceous age of eclogite facies metamorphism of the sanbagawa belt in the asemi river area shikoku sw japan evidence from detrital zircon abstract within the sanbagawa metamorphic belt the timing of high pressure and retrograde metamorphism is controversial recently an area in the asemi river region central shikoku japan was delineated that had been subjected to ecologite facies metamorphism prior to retrograde metamorphism in the epidote amphibolite facies which provides a new opportunity to constrain the age of high pressure metamorphism detrital zircon from this area yields ages as young as 84 4 ma hence the protoliths were deposited not earlier than ca 88 ma and thus eclogite facies and retrograde metamorphism occurred after 88 ma probably at 86 82 ma as indicated by the age of metamorphic zircon and k ar and ar ar ages for white mica

multiproxy approaches to investigating palaeoecology and palaeohydrology in the upper cretaceous kaiparowits formation usa

gas hydrate occurrences and their relation to host sediment properties results from second ulleung basin gas hydrate drilling expedition east sea the second ulleung basin gas hydrate drilling expedition ubgh2 recovered various forms of gas hydrate bearing sediments from 10 drill sites in the lower slope and basin floor of the ulleung basin to characterize the gas hydrate occurrences and the properties of the host sediments whole round core samples were taken from portions of recovered cores determined to be hydrate bearing based on infrared ir scanning these samples were further characterized by a variety of shipboard experiments such as imaging of the sediments with hand held ir and visual cameras measurements of pore water chlorinity within and around ir inferred cold regions in the core and grain size analysis of pore water squeeze cakes sediment compositions of selected samples were further characterized by x ray diffraction and scanning electron microscopes during post cruise analysis the shipboard and post cruise analysis results collectively indicate that the recovered gas hydrates mainly occur as 1 pore filling type bounded by discrete silty sand to sandy silt layers 2 fracture filling veins and nodules or 3 disseminated type in silt in addition minor but significant variation in gas hydrate concentrations were observed in diatomaceous silt where gas hydrates occur as pore filling material in layers dominated by intact diatom frustules gas hydrate accumulations of fracture filling type occur predominantly in regions where acoustic blanking features in the seismic record suggest gas migration from below the gas hydrate stability zone results from the ubgh2 core studies along with the analysis of similar samples from other expeditions including those executed by the ocean drilling program the integrated ocean drilling program and the first ulleung basin gas hydrate drilling expedition greatly improved our understanding of lithologic controls on marine gas hydrate occurrences

structural evolution of the southwestern margin of the ulleung basin east sea japan sea and tectonic implications abstract structural mapping and restoration of depth converted seismic profiles from the southwestern ulleung basin in the east sea japan sea back arc basin reveal the structural evolution of the area since the middle miocene the back arc closure began in the earliest middle miocene ca 15 ma and caused compressional deformation that has propagated southwestward from the dolgorae to the gorae structures and further to the unnamed inversion structure immediately adjacent to se korea the accelerated convergence of the young

paleomagnetism of tertiary rocks on the korean peninsula tectonic implications for the opening of the east sea sea of japan abstract two different distributions of declinations with dual polarities are found in the tertiary rocks of the yeonil basin and yangnam basin along the yangsan fault in the southeastern part of the korean peninsula these are northward declinations in the middle miocene yeonil group and strong eastward declinations in the early miocene yangbuk group and in the eocene volcanic rocks this is interpreted by invoking 1 the yangsan fault as a dextral wrench fault system by spreading in the uleung basin of the east sea sea of japan and 2 a clockwise vertical rotation caused by the movement of the fault at around 17 3 ma just prior to the sedimentation of the yeonil group the timing of the deflection found in korea is distinguished from that in southeastern and northwestern japan at around 15 ma two stages of spreading are thus constrained in the east sea area parallel at 23 15 ma and pivotal at around 15 ma crustal thinning also occurred a reliable pole position 84 9 n 292 6 e d p d m 3 3 4 8 for the miocene about 15 ma in korea is obtained from the yeonil group

early neogene biochemostratigraphy of pohang basin a paleoceanographic response to the early opening of the sea of japan east sea abstract the location of the pohang basin near the korea strait in the southwest of the sea of japan east sea makes this area appropriate for providing a record of paleoenvironmental biotic changes associated with the early neogene 16 5 ma opening of this gateway to the pacific ocean stable isotopic and planktonic foraminiferal records are presented that assist with the understanding of paleoenvironmental changes in the sea of japan resulting from the opening of the korea strait the oldest sediments of early neogene age of the pohang basin overlie cretaceous basement and are early miocene 16 5 ma shallow estuarine facies containing a benthic foraminiferal assemblage dominated by ammonia beccarii l the oldest early neogene planktonic foraminiferal assemblages in the basin are 16 5 ma in age latest early miocene foraminiferal zone n8 the migration of these planktonic assemblages to the sea of japan at that time appears to have resulted from the initial opening of the korea strait the overlying early neogene marine sequence of the pohang basin extends from 16 5 ma zone n8 through 14 ma zone n10 change in the oxygen isotopic record of the pohang basin sequence suggests strong local paleoenvironmental control related to the early opening of the korea strait early middle miocene isotopic temperatures of planktonic foraminifera are relatively cool at 15 ma at a time when global temperatures were high in the middle low latitude regions it was not until 14 8 ma that isotopic temperatures of planktonic foraminifera increased markedly this distinct warming is inferred to reflect the major intrusion of the kuroshio current into the sea of japan probably as a result of further critical opening and deepening of the korea strait at this time planktonic foraminifera increased in abundance reflecting expanding oceanic influence a cooling that followed at 14 5 ma when the strait was well open is unlikely to reflect local tectonic control on the paleoceanography but global cooling during the early middle miocene associated with the expansion of the east antarctic ice sheet

kinematic interpretation of remnant en echelon rift segments of the southwestern japan sea abstract the southwestern japan sea and the margin of southwestern japan feature parallel elongate extensional sub basins and grabens these structures are oblique to the trend of southwestern japan and are interpreted as the remnant of an en echelon array such a right stepping remnant en echelon pattern indicates sinistral rifting of the southwestern japan block from asia the major extensional fault trends are parallel over a distance of 600 km infinitesimal kinematic relations show that it is unlikely that these faults initiated in response to rotation about the nearby pole determined from paleomagnetic studies rather an earlier stage of rifting about a distant pole is indicated the rotational pole of this early rifting was probably located at least 6000 km away from the rift and the pole of rotation was offset from the rift trend by a similar distance rifting about this distant rotational pole loosened the southwestern japan continental block from the asian mainland making it susceptible to a large rotation about a nearby pole

physical properties of sediments from the ulleung basin east sea results from second ulleung basin gas hydrate drilling expedition east sea korea abstract physical properties including basic index properties undrained shear strength and thermal conductivities were measured on conventional cores retrieved from the ulleung basin during the second ulleung basin gas hydrate expedition ubgh2 the ubgh2 logged 13 sites and cored 10 sites to locate potential sites for an offshore test production a total of 211 conventional cores were recovered undrained shear strength thermal conductivity and index properties including porosity and grain density were measured onboard mineral composition analyses and grain size analyses were completed onshore after the expedition the averaged porosity at each site ranges from 65 to 71 the averaged grain density at each site ranges from 2 57 to 2 66 g cm3 and the mean grain size mostly lies between 4 m and 25 m with sparsely scattered coarse grained intervals the relatively high porosity and low grain density are due to the large portion of diatomaceous sediments the thermal conductivities average around 0 8 w mk and the low porosity and the abundance of clay mineral and oapl a may have caused the relatively low thermal conductivity in the ulleung basin the geomechanical analyses revealed a few relevant findings important for sediment physical behaviors during gas hydrate production the particle migration in coarse grained layers during production necessitates proper measure for sand productions while fine grained layers are mostly self filtering the vertical deformation estimated from the compression index suggested that the subsidence induced by the pore pressure change from the depressurization is much higher than those induced by the lost of gas hydrate particles from dissociation massive vertical deformation in fine grained layers has been predicted to occur due to the pore pressure change from depressurization induced gas hydrate production the drilling mud weight induced pressure window is mostly determined by the water depth in deep sea drilling but caution should be taken in determination of fracture pressures in hydrate bearing sediments because gas hydrate saturations alter poisson s ratio

stress dependent and strength properties of gas hydrate bearing marine sediments from the ulleung basin east sea korea abstract this paper presents a comprehensive laboratory experimental characterization of the host sediment from natural hydrate bearing sediments recovered during the ulleung basin gas hydrate expedition 2 ubgh2 in 2010 the basic geotechnical properties are characterized and compared with previously reported data the mineralogy and microstructure analyses confirm that the sediments mainly consist of illite kaolinite chlorite calcite and montmorillonite with a high concentration of microfossils diatoms the presence of microfossils may affect many of the geotechnical properties including plasticity activity specific surface and grain size the tested specimens have a relatively high initial void ratio with a high compression index e g cc ranging from 0 6 to 1 0 and swelling index e g cs ranging from 0 1 to 0 25 the shear wave velocities measured during loading indicate a high sensitivity to the stress state which demonstrates the critical role of effective stress in controlling the stiffness of the sediments the peak friction angles are determined to be 17 6 24 6 for clay and silt sediments and 27 1 for high sand fraction specimens the stress dependent and strength parameters obtained in this study may be very useful for performing stability analyses during hydrate dissociation and production

mass transport deposits and gas hydrate occurrences in the ulleung basin east sea part 1 mapping sedimentation patterns using seismic coherency abstract seismic coherency measures such as similarity and dip of maximum similarity were used to characterize mass transport deposits mtds in the ulleung basin east sea offshore korea using 2 d and 3 d seismic data several slope failure masses have been identified near drill site ubgh1 4 the mtds have a distinct seismic character and exhibit physical properties similar to gas hydrate bearing sediment elevated electrical resistivity and p wave velocity sediments recovered from within the mtds show a reworked nature with chaotic assemblage of mud clasts additionally the reflection at the base of mtds is polarity reversed relative to the seafloor similarly to the bottom simulating reflector commonly used to infer the presence of gas hydrates the mtds further show regional seismic blanking absence of internal reflectivity which is yet another signature often attributed to gas hydrate bearing sediments at the drill site ubgh1 4 no gas hydrate was recovered in sediment cores from inside a prominent mtd unit instead pore filling gas hydrate was recovered only within thin turbidite sand layers near the base of the gas hydrate stability zone with the analysis of seismic attributes the seismic character of the prominent mtd unit 3 was investigated the base of the mtd unit exhibits deep grooves interpreted as gliding tracks from either outrunner blocks or large clasts that were dragged along the paleo seafloor similar seismic features were identified on the seafloor although the length of the gliding tracks on the seafloor is much shorter a few hundred meters to 1 km compared to over 10 km long tracks at the base of the mtd the seismic coherency attributes allowed to estimate the volume of the failed sediment as well as the direction of the flow of sediment tracking the mtd and extrapolating its spatial extent from the 3 d seismic volume to adjacent 2 d seismic profiles a possible source region of this mass failure was defined 50 km upslope of site ubgh1 4

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

oxygen isotope evidence for progressive uplift of the cascade range oregon oxygen isotope compositions of fossil equid teeth in the cascade rainshadow reveal a v5x decrease in mean n 18 o since 27 ma isotopic changes are inconsistent with expected effects from global climate change because a the expected isotopic shift to tooth n 18 o values due to global climate change v1x is much smaller than the observed shift b predicted and observed isotopic trends are opposite for oligocene vs miocene samples and c average compositions and ranges in compositions remained unchanged for samples from before and after major global cooling in the mid miocene accounting for a decrease in relative humidity of at least 15 we infer a topographically driven secular shift in the n 18 o value of rainwater of 6 8x since the late oligocene which is approximately equivalent to the modern day difference in n 18 o values of precipitation and surface waters across the central cascades rise of the central cascades apparently occurred monotonically over the last 27 ma with a hiatus between v15 4 and 7 2 ma possibly related to eruption of the columbia river basalts progressive volcanic accumulation over tens of millions of years best explains the data rather than a short lived uplift event paleoseasonality as inferred from isotope zoning and intertooth variability decreased dramatically from 7 9x at 15 4 7 ma to v3x at 3 ma then increased to 6 8x today the cause of the decrease in seasonality at 3 ma may reflect either brief warming during the mid pliocene within the context of global tectonic reorganization or consumption by equids of water from an isotopically buffered lake idaho 2002 elsevier science b v all rights reserved

sedimentary and structural evolution of the eastern south korea plateau eskp east sea japan sea the east sea japan sea is a semi enclosed back arc basin that is thought to preserve a significant record of tectonic evolution and paleo climatic changes of eastern asia during the neogene we use here 2 d regional multi channel seismic reflection profiles and borehole data from expedition 346 of the integrated ocean drilling program iodp to provide new constraints on the geological history of the eastern south korea plateau eskp the eskp represents a structurally complex basement high in the southwestern east sea which formed during rifting of the back arc basin our new observations show that the eskp is composed of numerous horsts and grabens controlled by ne trending normal faults the acoustic basement is blanketed by oligocene to recent sediments that have preferentially accumulated in topographic lows up to 1 5 km thick and have been cored during expedition 346 at site u1430 close to the southern margin of the eskp seismic profiles in the eskp reveal three units separated by regional unconformities these seismic units closely correspond to iodp lithostratigraphic units defined at site u1430 where biostratigraphic data can be used to constrain the timing of three main evolutionary stages of the eskp stage 1 was related to rifting in the late oligocene and middle miocene terminated by a regional uplift leading to an erosional phase in the middle miocene stage 2 was associated with subsidence in the middle and late miocene and uplift and accompanying erosion or non deposition in the latest late miocene stage 3 pliocene to present recorded overall uniform hemipelagic pelagic subsidence of the eskp with short lived tectonically induced uplifts in the late middle miocene and latest miocene early pliocene the three stages of evolution of the eskp closely correlate to sedimentary changes since the oligocene and suggest a direct control of regional local tectonics on sedimentation patterns in the southwestern east sea with secondary influence of regional climatic and paleo oceanographic processes

change in tectonic force inferred from basin subsidence implications for the dynamical aspects of back arc rifting in the western mediterranean abstract a method has been developed that allows temporal changes in tectonic force during rift basin formation to be inferred from observed tectonic subsidence curves and has been applied to the gulf of lions the provencal basin and the valencia trough in order to gain some understanding of the dynamical aspects of back arc basin rifting in the western mediterranean sea two distinct tectonic force regimes active at different times during the evolution of each of these back arc basins are identified the first which can be seen in both basins is characterized by tensional forces that gradually abate with time to vanish some 20 my after the onset of rifting the magnitude of tectonic force required to initiate the rifting process is significantly greater in the valencia trough than in the provencal basin subsequently the dynamic development of these back arc basins differs in the provencal basin there is a renewal of force with extensional deformation concentrated in the central part of the rift whereas in the valencia trough the second tectonic force regime is inferred to be one that causes compression that subsequently relaxes such temporal patterns of tectonic force are interpreted to be related to the causative driving processes allowing constraints to be placed on the transient interaction between the overriding and subducting plates in a back arc setting the models also allow inferences to be made about the rheological structure of the lithosphere a significant variation of initial crustal thickness is inferred for the provencal basin but not for the valencia trough in both basins a wet rheology is required in order to initiate rifting given currently accepted bounds on tectonic force magnitudes adoption of a dry rheology leads to insufficiently high strain rates for significant lithosphere extension in both cases

tectonic evolution of the japanese islands as reflected in modal compositions of cenozoic forearc and backarc sand and sandstone cenozoic tectonic evolution of the japanese rifted continental arc trench system is reflected in the detrital modes of sand and sandstone deposited in forearc and backarc basins sampled by the deep sea drilling project at present the japan arc is divided into two segments along a complex plate boundary where the izu bonin ridge intersects the japan arc creating two triple junctions in front of and behind the ridge southwest of the izu bonin ridge quartzofeldspathic cretaceous forearc sediments were uplifted and recycled into tertiary forearc deposits in response to strike slip movement associated with backarc spreading in the shikoku basin quaternary forearc sections record the first major influx of volcanic detritus to southwest japan sites triple junction related deformation in central honshu has produced sand of mixed volcanic sedimentary provenance which is funneled by the suruga canyon into the nankai trough along the southwest japan margin north of the triple junction oligo miocene forearc sand compositions indicate oligocene forearc uplift and volcanism possibly related to initial backarc rifting and formation of the japan sea and subsequent miocene exposure of arc basement in contrast pliocene and quaternary forearc sand from northeast japan is primarily volcaniclastic and documents uninterrupted arc volcanism within the backarc region sand compositions vary from east to west across the japan sea the asian rifted continental margin and submerged remnants shed quartzofeldspathic sand into the western side of the basin whereas the japan arc sheds volcaniclastic sand into the eastern side of the basin

core and sediment physical property correlation of the second ulleung basin gas hydrate drilling expedition ubgh2 results in the east sea japan sea abstract we analyzed the data consist of core digital images and x rays core logs lwd logging while drilling and sediment grain size from the second ulleung basin gas hydrate expedition ubgh2 in the east sea core digital images and x rays were spliced as a complete composite core in meters below seafloor mbsf for five sites ubgh2 1 1 hole d 2 1 b 2 2 b 2 6 b and 2 10 c d and were correlated with the core log and lwd measurements showing that possible gas hydrate bearing layers are between the depths of about 60 180 mbsf at these sites bulk densities generally increase with depth from 1 3 to 2 0 g cm3 in lwd data and from 1 1 to 1 8 g cm3 onboard which measured lower than in situ gas hydrate bearing sediments respond with an increase of lwd densities 1 4 1 6 g cm3 and a decrease in core logs 1 1 1 4 g cm3 p wave velocity values of lwd increase 1400 to 1700 m s with depth for non reservoirs and are high 1500 and 2000 m s within the gas hydrate bearing intervals depending on the hydrate saturations resistivity values logged onboard range from less than 1 0 to over 10 0 m while lwd records are around 1 0 m and between 5 0 and 30 0 m in background sediments and possible gas hydrate reservoirs respectively high resistivity values were observed 5 0 30 0 m within coarse grained turbidites mean grain size between 2 9 and 5 1 laminated sandy mud or muddy sands medium resistivities were observed 5 0 m within the silt dominant hemi pelagic and turbiditic sediments 5 1 7 4 crudely laminated bioturbated homogeneous sand and disintegrated sand and sandy mud facies bearing pore filling gas hydrates or disseminated gas hydrates either formed in pores or small fractures of fine grained sediments core log measurements are highly fluctuating and sensitive but mostly lower e g density and resistivity than lwd records

comment tooth enamel mineralization in ungulates implications for recovering a primary isotopic time series by b h passey and t e cerling 2002 passey and cerling 2002 presented both direct measurement and a theoretical model that describe rates of tooth enamel mineralization in ungulates hoofed mammals and the retrievability of environmental time series their results are quite important because ungulate teeth are common in the fossil record and readily analyzed for stable isotope compositions which makes them outstanding archives of paleoecological and paleoclimate information e g koch 1998 because tooth enamel grows progressively isotopic zoning in enamel potentially encodes isotopic seasonality however passey and cerling show that enamel mineralization processes must cause records of isotopic seasonality to be damped relative to an environmental signal according to their model damping is strongly dependent on lengths corresponding to rates of enamel maturation lm and lengthwise growth t they measured lm but provided no values for t and in their models instead assumed various ratios of lm t unlike many comments the purpose of this note is not to challenge their results per se but rather to point out that published zoning profiles for several ungulates permit estimation of t this in turn provides broad discrimination of their model results and estimates for the degree of environmental damping likely present in tooth isotopic records

tectonic sedimentary and volcanic evolution of a back arc basin in the east sea sea of japan abstract this paper focuses on the tectonic sedimentary and volcanic evolution of a unique back arc basin ulleung basin in the southwestern part of the east sea sea of japan the basin consists of thick extended continental or transitional crust and an overlying sedimentary succession 4 8 km thick with interlayered volcanic flows and sills defining a number of seismic units of variable reflection characteristics the northern margin is bounded by faulted continental blocks south korea plateau with isolated basement lows and sub basins with intruded and extruded volcanics whereas the southern margin is underlain by deep seated basement with a thick 8 km thick sedimentary succession the western margin is bounded by a series of strike slip and normal faults produced by nnw sse directed dextral movements these structural features suggest a south southeastward drift of the southwestern japanese arc away from the south korea plateau during the early to middle miocene involving large scale right lateral strike slip deformation along the western margin akin to pull apart basin formation during the back arc opening the thinned continental crust was largely modified by intrusive volcanics under tensional stress regime the volcanics also extruded across the axis of extension as well as along the boundary faults on the west in the middle to late miocene major faults in the southern and western margins were inverted forming partial closure of the basin especially in the southern part although the plateau in the northern margin experienced continuous subsidence the ulleung basin thus provides an example of an immature back arc basin which experienced a rather brief episode of rifting and extension followed by closure due to tectonic inversion

infill history of the ulleung basin east sea sea of japan and implications on source rocks and hydrocarbons abstract the ulleung basin in the east sea sea of japan has experienced back arc opening in the miocene and partial closure since the middle miocene uplift along the southern basin margin caused by the back arc closure resulted in a series of anticlines and thrusts providing large volumes of sediments into the basin mass transport deposits dominated in the southern basin while turbidite and hemipelagic sedimentation prevailed in the northern basin one dimensional basin modeling shows that late postrift early late miocene marginal marine and prodeltaic sediments are buried too shallow to generate hydrocarbons the main phase of oil generation in the synrift lacustrine and early postrift marginal marine facies late oligocene early miocene in age beneath the southern basin margin occurred in the late early to early middle miocene predating the tectonic uplift this significantly reduces the chances of large oil accumulations in the southern basin margin the dominance of massive non uniform sediments in the southern basin together with the lack of preferred avenues such as faults are not favorable for the lateral migration of hydrocarbons sourced possibly from basinal muds in the north to the traps in the southern basin margin source rocks for the recently discovered gas in the southwestern shelf are probably the lacustrine and marginal marine sediments that have been expelling gas at least since the late middle miocene

alternate senses of displacement along the tsushima fault system during the neogene based on fracture analyses near the western margin of the japan sea abstract the western margin of the japan sea is characterized by the existence of a n20 e trending transcurrent fault system in the korea strait between korea and kyushu this fault system called here the tsushima fault system played a major role during the opening of the japan sea during the tertiary in order to understand its displacement history we analysed the deformation recorded by neogene rocks exposed on the korea strait islands tsushima goto and hirado islands a synthesis of published stratigraphical and structural data together with our field observations reveals that two tectonic events occurred in succession in the study area an early miocene nw se oriented extension event i and a middle miocene nw se oriented shortening event ii two distinct families of fractures with contrasted stratigraphic occurrences have been recognized in the neogene rocks exposed on the korea strait islands and allow us to define and date the stress fields characterizing each tectonic event stress field i is of intermediate type the vertical axis is either 1 or 2 with a n45 e hmax and n135 e hmin and was active between 22 and 16 ma stress field ii is compressional the vertical axis is 3 with a n135 e hmax and a n45 e hmin and was active between 15 and 10 ma the trends of stress field i principal axes imply that the displacement along the tsushima fault system was dextral during the early miocene conversely the trends of stress field ii principal axes imply that the displacement along the same fault system was sinistral during the second half of the middle miocene the inferred displacement history agrees with 1 a pull apart model for the opening of the japan sea during the early miocene and 2 transition from tensional to compressional stress fields in the japanese arc and back arc region at the end of the middle miocene

miocene pleistocene volcanism and tectonics in southern korea and their relationship to the opening of the japan sea abstract miocene pleistocene volcanism and tectonics in southern korea are discussed the miocene volcanism and related tectonics are represented by the eoil orogeny which occurred in the yangnam and pohang basins in the southeastern corner of the korean peninsula the yangnam and pohang basins represent the uplifted central part of the pohang ulsan graben which was rifted between the proto korean peninsula and paleo ulleung land probably in late oligocene early miocene times the eoil orogeny is correlated with the green tuff orogeny in japan evidence of pliocene volcanism is observed on ulleung island located in the western part of the central japan sea volcanic and tectonic events represented on ulleung island are in chronological order 1 volcanic eruption 2 subsidence and marine transgression 3 dome like uplift and 4 volcanic eruption evidence of pleistocene volcanism is present on cheju island located at the southwestern entrance to the korea tsushima strait volcanic and tectonic events represented on cheju island are in chronological order 1 volcanic eruption 2 subsidence and marine transgression 3 uplift and volcanic eruption and 4 doming and volcanic eruption three grabens namely the pohang ulsan graben the ulleung basin and the yamato basin were formed in the southern half of the japan sea which was above sea level in early miocene times paleo ulleung land was present between the pohang ulsan graben and the ulleung basin in miocene pliocene times these three grabens are active rifts and the tectonic events that occurred in this region originated from the action of rising magma the extension and deepening of the southern half of the japan sea resulted from the tectonic movements of these active rifts and their surrounding regions thus it is suggested that the opening of the japan sea progressed by diapiric tectogenesis

tectonic history of ulleung basin margin east sea sea of japan a geologic history analysis of an exploratory well drilled on the southern margin of the ulleung back arc basin east sea western part of the sea of japan reveals that tectonic force and sedimentary loading played a major role in the subsidence of the paleo ulleung basin where a thick clastic sequence was deposited during the neogene initial subsidence was most likely caused by a tectonic force related to the back arc rifting and spreading associated with convergent processes the southern margin underwent regional deformation uplift faulting and folding toward the late miocene this event was probably due to back arc deformation caused by changes both in plate motions and in subduction mode at the convergent zones

chronology of sanbagawa metamorphism by collating age data based on the fossil age of the protoliths radiometric dating of the metamorphic minerals and sedimentary records of erosion at the earth s surface the history of the sanbagawa metamorphism can be summarized as follows 1 the pre metamorphic sedimentary rocks carboniferous jurassic early cretaceous became mixed and formed a thickened packet in the vicinity of an ancient trench through a variety of subduction related tectono sedimentary processes probably in early cretaceous time c 130 120 ma 2 the subducted protoliths underwent progressive metamorphism reaching a maximum depth of c 30 km in late early cretaceous time c 116 10 ma 3 the high p t metamorphic rocks began to rise toward the surface during the interval 110 50 ma with minimum estimates for the average cooling rate around 9 12 c ma and an average uplift rate around 0 4 0 5 mm year 4 finally at some stage after reaching the erosional surface the high p t metamorphic rocks were covered unconformably by the middle eocene c 50 42 ma kuma group on the basis of the present chronological summary of the sanbagawa metamorphism the areal extent of the sanbagawa metamorphism is also discussed with respect to the weakly metamorphosed subduction accretion complex of the next tectonic belt to the south the northern chichibu belt

controls and evolution of fan delta systems in the miocene pohang basin se korea abstract the miocene pohang basin southeastern korea occurs in the eastern part of the ne sw trending yangsan fault which has experienced right lateral strike slip deformation since the eocene during the miocene however the strike slip movement was negligible and instead was under extensional regime large scale drainage systems were developed at the junction between the strike slip zone and the oblique transfer faults acting as major sources for coarse grained sediments high rate of sediment supply and rapid subsidence of the hanging wall resulted in the progradation of large scale gilbert type fan deltas doumsan duksung and gohyun systems which all show a radial distributional pattern along the steeply inclined footwall scarps created by ne sw trending faults the drainage systems were relatively small here low rate of sediment supply formed scree apron type malgol and yugye systems and steep faced slope type maesan system fan deltas based on variations in sedimentary facies and distribution architecture and overlapping patterns the fan delta systems in the pohang basin can be divided into four stages of evolution during the early stage early miocene alluvial fans prograded into shallow marine setting in the doumsan and duksung systems high rate of sediment supply and rapid rise of relative sea level resulted in the transformation of shoal water type to gilbert type foresets in the malgol and maesan systems rapid sea level rise accompanied with low rate of sediment supply caused transformation of alluvial fans to scree apron type and steep faced slope type fan deltas respectively in the second stage subsidence of the hanging wall formed large scale truncation surfaces in the doumsan and duksung fan deltas coarse grained sediments were continuously supplied in the doumsan system whereas only fine grained sediments were deposited in the duksung system in the malgol system sediment supply was almost terminated in this stage in the third stage middle miocene sediment supply rate of the doumsan fan delta decreased abruptly and the system was overlain by fine grained gilbert type deposits the duksung fan delta was overlain by the maesan and gohyun systems the maesan system prograded further basinward during the last stage late miocene sediment supply of the doumsan and maesan systems was also terminated and the entire basin was draped by fine grained biogenic materials mainly diatoms

shrimp u pb zircon dating of quartz bearing eclogite from the sanbagawa belt south west japan implications for metamorphic evolution of subducted protolith in order to decipher the origin of eclogite in the high p t sanbagawa metamorphic belt shrimp u pb ages of zircons from quartz bearing eclogite and associated quartz rich rock metasandstone were determined one zircon core of the quartz rich rock yields an extremely old provenance age of 1899 79 ma suggesting that the core is of detrital origin eight other core ages are in the 148 134 ma range and are older than the estimated age for trench sedimentation as indicated by the youngest radiolarian fossil age of 139 135 ma from the sanbagawa schists ages of metamorphic zircon rims 132 112 ma from the quartz rich rock are consistent with metamorphic zircon ages from the quartz bearing eclogite indicating that eclogite facies metamorphism peaked at 120 110 ma these new data are consistent with both the iratsu eclogite body and surrounding highest grade sanbagawa schists undergoing coeval subduction zone metamorphism and subsequent re equilibration under epidote amphibolite facies conditions during exhumation

seasonal stable isotope evidence for a strong asian monsoon throughout the past 10 7 m y o of wet season rainfall was signi cantly morenegative 29 5 smow prior to 7 5 ma than after 26 5 smow if this change is attributable to a lessening of the amounteffect in rainfall this agrees with oral and soil geochemical datathat indicate increasing aridity beginning at 7 5 ma keywords tibetan plateau monsoon stable isotopes paleohydrology seasonality introductionthe tibetan plateau is the engine that drives the modern asianmonsoon by generating a high altitude region of low pressure in thesummer as the plateau heats and a region of high pressure in the winteras the plateau cools hastenrath 1991 during the summer warm airrises from the plateau pulling moist air off the ocean across the indiansubcontinent and into the highlands this results in heavy summer rain fall on the subcontinent the opposite occurs in the winter resultingin cold dry air spilling off the plateau and effectively excluding rainfrom the subcontinent thus the presence of a strong wet season dry season alternation implies the presence of a plateau broad and highenough to drive the monsoon the timing of the uplift of the plateau remains a matter of con siderable debate because there are few direct indicators of paleotopog raphy in the geologic record consequently past workers in tibet re lying on indirect indicators of uplift have proposed dates ranging from40 to 3 4 ma on the basis of initiation of potassic volcanism chunget al 1998 turner et al 1993 or extension on the plateau harrisonet al 1995 coleman and hodges 1995 changes in marine sedimen tation rates burbank et al 1993 sediment types rea et al 1998 or biota nigrini and caulet 1992 kroon et al 1991 and changesin stable carbon isotope and palynological patterns on the indian sub continent quade et al 1989 chen 1981 although different areasof the plateau may have risen at different times many workers haveinferred rapid simultaneous uplift of large areas of the plateau at 7 8ma by a process such as lithospheric delamination molnar et al 1993 this inference was based on the following approximately coevalphenomena a major change in plant communities of the indian sub continent quade et al 1989 and shifts in marine upwelling patternsthat are linked to an intense monsoon kroon et al 1991 althoughthere is strong evidence for signi cant climate change at 7 8 ma it isunclear whether this is the onset of the monsoon the oral transitionseems to have been a global rather than local phenomenon cerling etal 1997 and monsoonally driven upwelling may have already beenpresent by 10 12 ma nigrini and caulet 1992 kroon et al 1991 because there is an intimate association between the intense sea sonality of the modern monsoon and a high tibetan plateau and be cause evaporation can be unambiguously recognized in the d

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

a seismic experiment in the ulleung basin tsushima basin southwestern japan sea east sea of korea understanding the crustal structure of the ulleung basin tsushima basin in the southwestern japan sea east sea of korea is important for reconstructing the opening tectonics of the japan sea a korea and russia collaborative seismic experiment was carried out in 1991 to investigate the crustal structure of this basin using ocean bottom seismometers obss and large capacity air guns the results of the experiment reveal that the ulleung basin is floored by distinctive upper and lower crustal layers with velocities typical of layers 2 and 3 the lower crust however is unusually thick 7 8 km and the moho lies flat at 15 16 km depths though similar to the yamato basin in crustal thickness the ulleung basin has a much thicker sedimentary sequence and a slightly thinner lower crust in the center geophysical evidence thus shows that the crust under the ulleung basin has velocity range and crustal layering falling closer to those of normal oceanic crust than the yamato basin the formation mechanism of the thicker than normal lower crust should be clarified to better understand the complex opening process in the southern japan sea

flexural isostasy and loading sequence of the dokdo seamounts on the ulleung basin in the east sea sea of japan abstract the isostatic compensation and loading sequence of the dokdo seamounts on the ulleung basin in the east sea are studied by a flexure model using gravity and bathymetric data the dokdo seamounts comprise dokdo dok island lying as a cluster of emerged small islets surmounting a large submerged volcanic edifice and two voluminous tablemounts simheungtaek and isabu in spite of their similarity in topographic expression a large difference of about 50 mgal between the observed gravity anomaly peaks over dokdo and the isabu tablemount implies different amounts of compensation a comparison between the observed and calculated gravity anomalies of the seamounts shows that the flexural compensation investigated in this study predicts well the observed data the flexure model suggests that the dokdo seamounts might be composed of high density volcanic rocks modeling results show that the flexural rigidity or effective elastic thickness of the lithosphere under dokdo is stronger or thicker than that under the isabu tablemount it implies that the age of lithosphere at the time of loading for isabu was younger than that for dokdo the effective elastic thicknesses associated with the dokdo seamounts approximately follow 200 400 c isotherms in the cooling plate model the results of this study and the former age dating of dokdo suggest that the isabu tablemount was formed first followed by dokdo after the opening of the east sea ceased

seismic reflection study of acoustic basement in the south korea plateau the ulleung interplain gap and the northern ulleung basin volcano tectonic implications for tertiary back arc evolution in the southern east sea abstract in order to understand the volcano tectonic evolution history of the east sea back arc basin this study focuses on the seismic characteristics of acoustic basement based on the multi channel seismic reflection data acquired from the south korea plateau the northern ulleung basin and the ulleung interplain gap according to the seismic reflection characteristics the acoustic basement in the study area can be classified into three types type a acoustic basement is a remnant of rifted continental crust comprising relatively shallow seated continental margin platforms elongated ridges and equidimensional blocks in the south korea plateau and its vicinities type b acoustic basement is volcanic sills flows sediments complexes infilling the rift controlled basement lows in the south korea plateau the ulleung interplain gap and the northern ulleung basin type c acoustic basement is a cluster or chain of volcanic edifices which shows internal facies variation from main body to apron slope facies volcanic activities identified in the types b and c acoustic basements can be classified into three stages based on the volcano stratigraphic correlation with the existing stratigraphic framework stage 1 volcanism is characterized by a fissure type eruption represented by scattering volcanic cones and mounds type c and volcanic sills and lava flows interlayering with syn rift sedimentary units type b early stage continental rifting prior to the middle miocene most likely controlled this volcanism stage 2 volcanism is characterized by ene wsw trending chain of volcanic edifices type c along the northern margin of the ulleung basin and ulleung interplain gap during the middle miocene the weakening of back arc extension might have resulted in limited volcanic eruption which formed elongate volcanic fields across the ulleung and yamato basins stage 3 volcanism is represented by highly peaked volcanic islands and seamounts type c showing vertically stacked apron slopes in seismic cross sections this vertical stacking pattern is indicative of multiple eruption events from a single eruption center at least from the late miocene to the quaternary expanded volcanic age control based on volcano stratigraphic and isotopic age dating reveals that the volcanic activities in the southwestern and southeastern east sea show similar spatio temporal variations this implies that the entire southern east sea has experienced almost same volcano tectonic evolution during the cenozoic back arc evolution especially the stage 2 volcanic chain along the northern ulleung basin and the yamato seamount chain in the yamato basin matches in their eruption timing ca 12 ma and geomorphic properties i e direction of the volcanic chains and distances from subduction zone which strongly suggests the existence of regional scale chain volcanism across the southern east sea considering the chemical properties of volcanic rock samples from the volcanic chain in association with the suggested tectonic frameworks during the tertiary the remnant magma source derived from the waning mantle convection most likely fed the volcanic chain in the terminal stage of back arc opening

pressure core based study of gas hydrates in the ulleung basin and implication for geomechanical controls on gas hydrate occurrence pressure coring technology enables the recovery of natural gas hydrate bearing sediments without pressure release and thus without gas hydrate dissociation a total of 21 pressure cores were successfully recovered from the ulleung basin east sea korea during the second gas hydrate drilling expedition in the ulleung basin ubgh2 recovered pressure core samples were utilized to characterize hydrate occurrences and formation mechanisms with non destructive physical property scans x ray ct scans and controlled degassing experiments findings include 1 the p wave velocity in mud rich sediments with grain displacing hydrate increases with decreasing bulk density since hydrate displaces sediment grains and lowers the bulk density 2 the p wave velocity in sand with pore filling hydrate is mostly affected by hydrate saturation rather than bulk density 3 the p wave velocity trend with hydrate saturations for pore filling hydrates follows pore filling model at low hydrate saturations and gradually deviates from pore filling model toward cementation model as hydrate saturation increases 4 gas recovery times during controlled core degassing experiments are proportional to both hydrate saturations and porosities 5 at site ubgh2 3 the thickness of both sub horizontal and sub vertical grain displacing hydrates decreases with depth while the number of sub vertical hydrates does not decrease with depth implying that the formation mechanisms of sub horizontal and sub vertical hydrates differ while growth mechanisms are similar to each other in different growth directions 6 the angle and thickness of grain displacing hydrate bearing fractures are a function of the overburden stress and the hydraulic conductivity but the main governing factor is the overburden stress

detection of microearthquakes and identification of their causative structures in the eastern offshore region of south korea abstract a matched filter has been applied to continuous seismic records from the eastern offshore region of south korea to identify small earthquakes undetected by routine processing the resulting density of the regional earthquake catalog has increased by a factor of five relative to the detections reported by the korea meteorological administration high precision locations of newly identified microearthquakes and previously located earthquakes cluster into streaks that delineate structures responsible for the seismicity associated with the hupo fault offshore of the southern korean peninsula microearthquakes in the northern and southern segments of the fault zone exhibit different behaviors earthquakes in the northern segment occur at a regular temporal interval while those in the southern segment occur in bursts the identified fault system dips steeply to the west at shallow

wave planation surfaces in the mid western east sea sea of japan indicators of subsidence history and paleogeographic evolution of back arc basin abstract this study focuses on revealing the origin of deep marine wave planation surfaces and its geomorphic and tectonic implications for the back arc evolution based on multi channel seismic reflection profiles acquired from the mid western east sea sea of japan on seismic reflection profiles the wave planation surfaces are recognized as continuous and high amplitude single reflectors outlining the flattened top of submarine terraces or isolated topographic highs the wave planation surfaces are classified into four types depending on the geomorphic characteristics and origins of substratal landmasses i e continental margin terrace type 1 rifted continental fragment type 2 volcanic edifices type 3 and uplifted sedimentary successions type 4 which have common origin of wave erosion near the sea level but different subsidence history the mean subsidence rate of wave planated substratum is calculated by dividing the maximum depth of a wave planation surface below modified datum sea level d e by the time elapsed since the onset of subsidence t information of local subsidence history enables reconstruction of paleogeographic evolution of mid western east sea during the neogene quaternary time 1 incipient continental rifting and onset of marine incursion ca 23 18 ma 2 progressive continental rifting and onset of wave planation ca 18 11 ma 3 final eruption of post rift volcanoes ca 11 ma 4 uplifting of shelf margin banks and onset of the pliocene holocene volcanic activities ca 11 2 5 ma 5 change in the locus of volcanic eruption and cessation of contractile uplifting in the basin margin ca 2 5 0 ma

paleogeographic and paleotectonic evolution of a basement controlled archean supracrustal sequence chibougamau caopatina quebec the 7 14 km thick archean volcano sedimentary sequence in the chibougamau caopatina region ccr composed of two mafic to felsic cycles and two thick essentially epiclastic successions is divided into a southern caopatina segment scs and northern chibougamau segment ncs the sedimentary units which evolved after cycle 1 volcanic rocks in the scs and after the combined cycles 1 and 2 in the ncs document a diachronous sedimentary basin evolution this criterion has been employed to distinguish an early evolutionary stage in the south and a late evolutionary stage in the north in each segment the basin episode represents a unique extensional event volcanism preceded the major sedimentary rifting event in both segments composition of sediments and sedimentary facies correlated with the interpreted basin margin faults support the interpretation of two phases of crustal extension volcanic construction and sill intrusion were the prevalent factors governing emergence of volcanic islands in the cc

comment on metamorphic p t time history of the sanbagawa belt in central shikoku japan and implications for retrograde metamorphism during exhumation by k aoki k kitajima h masago m nishizawa m terabayashi s omori t yokoyama n takahata y sano s maruyama lithos 113 2009 393 407 article history received 17 november 2009 accepted 24 january 2010 available online 6 february 2010 zones new zircon u pb age data presented by aoki et al 2009 of 85 6 3 0 ma are in good agreementwith relatively youngmetamorphism and rapid exhumation however aoki et al 2009 interpret these ages as recording the timing of retrograde metamorphism significantly later than the peak at around 120 ma in this comment we raise three points concerning the treatment of age data given by aoki et al 2009 we

depressurization experiment of pressure cores from the central ulleung basin east sea insights into gas chemistry abstract we performed depressurization experiments on pressure cores pcs recovered from holes ubgh1 10b and ubgh2 11b which were drilled during two separate expeditions in the ulleung basin ubgh1 and ubgh2 various lines of evidence such as convex curvature in the p v curves obtained by depressurization as well as x ray images and resistivity at bit rab data point to the presence of gas hydrates at these holes we estimated gas hydrate saturation sh at these holes to range from 5 23 based on the amount of gas released from pcs these sh values are in agreement with those reported at other high gas flux settings molecular c1 c2 and isotopic 13cch4 dch4 13cc2h6 indicators delineate a microbial source for the ch4 and c2h6 in core ubgh1 10b 5r the carbon isotopic fractionation factor between co2 and ch4 ec 13cco2 13cch4 was observed to increase from 50 to 68 as pressure was reduced during our experiments these changes illustrate the isotope fractionation that results from the preferential release of 13c depleted co2 during the early stages of depressurization the constant carbon isotope separation 10 20 between co2 in void gases and in the dissolved inorganic carbon dic pool shown in cores from the ulleung basin has also been observed in gas hydrate bearing sediments elsewhere it is important to consider this effect when using carbon isotopic data in carbon cycling models specifically when unraveling metabolic pathways of methane generation in situations where partial co2 degassing of a core is suspected we recommend the use of the carbon isotope ratio of dic instead of the gas measurements to best delineate the methane cycling pathways in marine systems

plate movements ductile deformation and geochronology of the sanbagawa belt sw japan tectonic significance of 89 88 ma lu hf eclogite ages prograde p t paths and thermal modelling suggest metamorphism in the sanbagawa belt represents unusually warm conditions for subduction type metamorphic belts and these likely reflect conditions of a convergent margin a few million years before the arrival of an active spreading ridge radiometric age data and kinematic indicators of ductile deformation suggest the sanbagawa belt formed in a cretaceous convergent margin associated with a plate movement vector that had a large sinistral oblique component with respect to the belt the east asian margin plate reconstructions for the cretaceous to tertiary for this region show that the only plausible plate compatible with such motion at this time is the izanagi plate these reconstructions also show that progressively younger sections of the izanagi plate were subducted beneath eastern asia i e a spreading ridge approached until 85 83 ma when the izanagi plate ceased to exist as an independent plate the major reorganization of plates and associated movements around this time is likely to be the age of major interaction between the ridge and convergent margin the ridge approach model for the sanbagawa metamorphism therefore predicts that peak metamorphism is a few million years older than this age range new lu hf dating of eclogite in the sanbagawa belt gives ages of 89 88 ma in excellent agreement with the prediction combining this estimate for the peak age of metamorphism with published p t t results implies vertical exhumation rates of greater than 2 5 cm yr 1 this high rate of exhumation can explain the lack of a significant thermal overprint in the sanbagawa belt during subduction of the ridge

regional seismic intensity anomalies in the korean peninsula and its implications for seismic hazard potentials the strength of seismic ground motion is a consequence of seismic source strength and medium response the dependence of seismic amplitudes and seismic intensity on regional geological structures and crustal properties in the stable intraplate region around the korean peninsula is investigated an instrumental seismic intensity scale based on spectral accelerations are proposed after calibrating with the reported macroseismic intensities a representative seismic intensity attenuation curve for the korean peninsula is given by i m text l l h 0 998 pm 0 222 1 72 pm 0 04 m text l 0 322 pm 0 027 text ln l 2 h 2 0 00608 pm 0 00049 sqrt l 2 h 2 where i m text l l h is the seismic intensity at an epicentral distance l in km for an earthquake with local magnitude m text l and focal depth h in km seismic intensities decay slowly with distance in the korean peninsula the observed decay rate for the korean peninsula is comparable with those for other stable intraplate regions while are lower than those for active regions the regional seismic intensity anomalies present a characteristic correlation with geological structures positive seismic intensity anomalies appear in the yeongnam massif okcheon belt and gyeongsang basin while negative seismic intensity anomalies in the gyeonggi massif the regional seismic intensity anomalies display positive correlations with crustal thicknesses crustal amplifications and seismicity density and negative correlations with heat flows positive seismic intensity anomalies are observed in the yeongnam massif and gyeongsang basin suggesting high seismic hazard potentials in the regions the regional crustal properties may provide useful information on potential seismic hazards

cenozoic deformation history of the area around yangnam yangbuk se korea and its tectonic significance abstract detailed mapping and structural analysis were carried out to establish the cenozoic deformation history of the yangnam yangbuk area se korea all structural elements were analyzed to establish the chronological sequence based on the classification of the fracture systems and the ages of the rocks two detailed grid maps represent the deformation history based on the cross cutting relationship between deformation fabrics we established the cenozoic deformation history in the studied area by synthesizing the analysis of structural elements in rocks of different ages and observing cross cutting relationships on grid maps results using these two approaches with two independent data sets are consistent the deformation history is comparable to that proposed from previous studies restoration of the structural elements suggests tilting and rotation in this area there is clear evidence of tectonic inversion which was observed in a previous trench study of the eupchon fault this implies that normal faults related to the right lateral yangsan fault associated with opening of the east sea japan sea may have been reactivated as thrust faults in the quaternary period

interpretation of the rupture history of a low slip rate active fault by analysis of progressive displacement accumulation an example from the quaternary eupcheon fault se korea abstract the eupcheon fault one of more than 20 identified quaternary faults recently reported in the area around the yangsan and ulsan faults se korean peninsula was discovered during the construction of a primary school in an area close to a nuclear power plant we analysed a trench excavated across the eupcheon fault with the aim of understanding its movement history and kinematics the eupcheon fault is a reverse fault strike dip n20 e 40 se that records 6 7 m of displacement 3 4 m vertical separation the fault consists of a series of branch faults associated fault related folds and rotated pebbles a previous study reported that the fault originally recorded normal slip but was reactivated during the quaternary as a reverse fault we identified four or five quaternary faulting events upon the fault based on an interpretation of the trench logs including an analysis of colluvial wedges and measurements of displacement distance d x relationships along the fault we used a quantitative analysis of d x relationships commonly used for consolidated sedimentary rocks to interpret the deformation history of the fault from this we estimated the amount of slip in the range of 0 7 1 8 m for each of the five identified faulting events and the earthquake magnitude in the range of m w 5 4 7 4 we propose two ideal d x profiles for syndepositional and post depositional faulting and a tectonic evolution model for the area around this fault this approach may be applicable to analyses of earthquake hazards and studies of fault evolution elsewhere

submarine geology and post opening tectonic movements in the southern region of the sea of japan abstract the submarine geologic structure of the southern region of the sea of japan was analyzed on the basis of seismic reflection profile data and bottom samples the seismic reflection patterns depict sedimentary layers with well developed onlap and toplap terminations and truncations by submarine erosion the planes marked by series of onlap toplap and erosional truncations enabled us to define three stratigraphic groups composed of six formations in this region they are the kasumioki group the hamasakaoki group and the tottorioki group in ascending order detailed analysis of the seismic reflection profiles reveals subtle structures of these sedimentary units the oldest kasumioki group is folded and faulted forming submarine ridges the hamasakaoki group mainly occurs in the depressions between these ridges the youngest tottorioki group covers widely both of the older formations with a pronounced marine onlap fossil evidence indicates that the depositional ages of the kasumioki group the hamasakaoki group and the tottorioki group are early miocene to earliest pliocene late early to late pliocene and late pliocene to holocene respectively these observations provide the basis to understand two main structural features in this region 1 e w trending folds and 2 northwestward tilting blocks the former construct a fold zone composed of two to four ranges of anticlines that have steeper southern flanks truncated by reverse faults the latter are shown by slightly inclined floors formed by submarine erosion step like asymmetric basins bounded by ne sw trending reverse faults and onlap toplap sedimentation patterns the lateral change in bed thickness sedimentation patterns and age of submarine sediments indicate that the e w trending folds were formed in the early middle or late miocene to the early pliocene by n s compression whereas the northwestward tilt blocks were formed in the late early to late pliocene by nw se compression the sedimentary records in this region dictate an abrupt change in tectonic setting in the late early pliocene this change is interpreted to show that the sea of japan has been closing since then due to either the reactivation of the amurian plate or the directional change of the philippine sea plate motion

back arc rifting initiated with a hot and wet continental lithosphere abstract how back arc rifting is initiated is studied by inferring the tectonic force and strain rate regimes from published subsidence data for nine back arc basins in the european tethyan belt and in the western pacific the results show that rifting only begins after some particular magnitude of tectonic force is reached this implies that subduction has already progressed to a point such that the total negative buoyancy of the slab becomes so large that the relevant tectonic force exceeds its bending strength once back arc rifting has been initiated the force required to maintain it gradually decays this indicates that the processes governing back arc extension are fast enough that lithosphere weakening due to an increase in geothermal gradient exceeds strengthening due to the thermal relaxation and crustal thinning this is achieved given currently accepted estimates for the maximum force 7 tn m if the thickness of the thermal lithosphere is significantly less than 125 km and if the lithosphere has a wet rheology meaning that a weak continental lithosphere is required for the initiation of back arc rifting the presence of significant strength in the uppermost mantle is not precluded but it is not required

u pb ages of detrital zircons from the sanbagawa belt in western shikoku additional evidence for the prevalence of late cretaceous protoliths of the sanbagawa metamorphics the sanbagawa metamorphic belt in japan is one of the best studied high pressure low temperature metamorphic belts recent work applying new dating techniques has challenged the previously accepted temporal framework for the evolution of the belt as it was shown that large parts of the belt contain detrital zircons of late cretaceous age younger than 100 ma i e they have protolith ages younger than the previously accepted age of metamorphism at ca 110 ma a 2000 m bore hole from north western shikoku provided an excellent opportunity to further evaluate the areal extent of late cretaceous protoliths as the drill hole was drilled in an area considered to be part of the jurassic to early cretaceous part of the sanbagawa belt dating of single zircon grains using the la icp ms u pb dating method shows that all but one sample contain zircons younger than 100 ma and thus the protoliths are younger than the previously accepted age of metamorphism of the sanbagawa belt the single sample that contains only zircons dated at 136 3 ma apparently is of volcanic origin and could be a clast representing the source of 130 140 ma zircons of the sample taken about 120 above this sample in addition three surface samples were analysed two of these also contain zircons younger than 100 ma whereas the third sample contains only zircons older than 159 ma the zircons from this sample also exhibit an age spectrum different from that exhibited by the other samples the exact significance of this sample is not clear as yet

paleoceanographic implications and cyclostratigraphy of variations in well log data from the western slope of the ulleung basin east sea cyclic variations of density and gamma ray logs achieved from the two drill sites of ubgh2 1 1 and ubgh2 1 2 in the western slope of the ulleung basin were investigated to reveal their paleoceanographic implications and establish cyclostratigraphy of the well logs integration of the core log and seismic data from the two sites indicates that the sediments of the drilled intervals mostly consist of hemipelagic muds with a few sporadic mass transport deposits intercalated only in the downslope site of ubgh2 1 1 comparison with variations in sediment composition suggests that ratios of terrigeneous to biogenic materials which were modulated by orbital scale climate changes should be responsible to the well log variations the established cyclostratigraphy of the well logs based on correlation with marine oxygen isotope records indicates such climatic modulation of the sedimentation in the western slope of the ulleung basin has persisted at least since 2 6 ma consistent with the variation reported from the oki ridge

not so deserted paleoecology and human subsistence in central iberia guadalajara spain around the last glacial maximum abstract in contrast to the coastal areas of the iberian peninsula the upper palaeolithic settlement of central iberia dominated by the spanish plateau is poorly known traditional models assume a total or virtual depopulation of the interior of the iberian peninsula during the last glacial in this paper we present a detailed investigation of human environment interactions through the first zooarchaeological taphonomic and isotopic study of the key site of pena capon a rock shelter located in the south eastern foothills of the central system range that contains a multi layered deposit dated to marine isotope stage 2 mis 2 analyses of the faunal assemblages of the proto solutrean 3 and middle solutrean 2 layers show that human preferentially hunted horse deer and iberian ibex living in the vicinity of the rock shelter isotope geochemistry of the animal remains of pena capon provides us with the first detailed intra tooth multi proxy analysis for this time period in south western europe providing estimates of climatic conditions seasonal flucturation of diet as well as patterns of seasonal mobility our results indicate that human presence at pena capon was apparently restricted to relatively warm intervals around the lgm or reflects the presence of an ecological refuge and provide us with evidence of recurrent human presence in the iberian interior during the upper paleolithic prior to the magdalenian