sequence stratigraphy and evolution history of the continental shelf of south sea korea since the last glacial maximum lgm abstract high resolution seismic data chirp and sparker profiles were used to investigate the sequence stratigraphy and evolution of the continental shelf of the south sea korea since the last glacial maximum lgm approximately 1950 km of chirp and sparker profiles were acquired along with seismic profiling 30 piston core samples were collected and two previous long drill cores ssdp 103 and 104 were tied to the seismic data our data show nine types of seismic facies on the basis of seafloor morphology and sub bottom acoustic characters based on the analysis of seismic profiles shelf deposits of the south sea accumulated after the onset of the lgm can be divided into five sedimentary units s1 to s5 from top to bottom correlation between sediment cores and seismic data suggests that unit s5 is an incised channel fill formed by fluvial or coastal sediments during the early transgressive stage accompanied by backstepping of the shoreline unit s4 is a transgressive sand layer reflecting the deposition of coarse sediments due to the strong currents and tides following the rapid retreat of the coastline unit s3 represents paleo channel and basin fill deposits formed in estuary or delta environments near the inner continental shelf unit s2 forms an inner shelf transgressive sand layer including sand ridges unit s1 is interpreted as the most recent mud formed during the sea level highstand stage when the sea level rise ended our results show that the sedimentary evolution of the continental shelf of the south sea since the lgm has been closely related to the sea level changes the distribution of paleo channels is associated with the paleo seomjin river local sediment supply and continental shelf erosion

depositional history of quaternary sediments on the continental shelf off the southeastern coast of korea korea strait abstract the depositional history of quaternary sediments on the continental shelf off the southeastern coast of korea korea strait was investigated by means of analysing high resolution seismic profiles and sediment samples quaternary sediments up to 50 m thick overlie the irregular surface of the acoustic basement in the inner shelf the sedimentary column is comprised of two main sequences separated by a mid reflector which is interpreted as the pre holocene surface the holocene sequence reaching up to 30 m in thickness with a depocenter near the present river mouth is characterized by deposition in a prodelta environment while the upper pleistocene sequence represents deposition in deltaic or shallow water environments during the late glacial period most of the shelf was subaerially eroded and deposition took place only in the trough region the present location of marine built terraces indicates that the lowest position of sea level was about 130 m below its present level the subsequent postglacial transgression reworked pleistocene sediments to form a thin veneer of transgressive facies sea level rose rapidly in the early stages of the postglacial transgression and approached the present level at approximately 7000 5000 yrs b p recent sedimentation the holocene sequence probably began at that time

seismic stratigraphy of the southeastern black sea shelf from high resolution seismic records abstract high resolution seismic reflection profiles obtained from the shelves off the samsun and trabzon coasts southeastern black sea have revealed the existence of two distinct reflectors r and t reflector r forms the boundary between the upper depositional sequence a and the lower depositional sequence b seismo stratigraphically upper sequence a is characterized by stratified simple complex and lenticular seismic reflection configurations which imply changing depositional systems and or conditions changes of source and supply of sediments due to the relative change of sea level additionally the observed onlapping pattern within this sequence denotes rising of sea level during the last post glacial transgression the mounded seismic facies beyond the steep gradients on the shelf area of trabzon imply slump masses the lower depositional sequence b on the samsun and trabzon shelves is commonly characterized by chaotic reflection configurations which are interpreted either as strata deposited in a variable relatively high energy setting or as initially continous strata that have been deformed additionally the presence of some parallel subparallel reflections within this sequence denotes its stratified character the upper boundary of sequence b reflector r reflects a pre holocene unconformity probably caused by falling sea level at the time of the last glacial maximum additionally toplap termination at the upper boundary of sequence b indicates a stillstand of sea level at 91 m depth during the last glacial maximum based on borehole data sequence b is composed of consolidated sand and gravel admixtures in the samsun area and basalt agglomerate tuff series in the trabzon area reflector t forms the boundary of a zone of anomalous reflections acoustic turbidity at that are interpreted to represent gas in the sediments of the upper depositional sequence a the gas accumulations tend to occur in blanket and curtain forms depending on their appearances on seismic records

seismic stratigraphic reconstruction of plio quaternary depositional sequences on the continental shelf of korea strait abstract the korea strait is a seaway connecting the east sea with the east china sea the plio quaternary stratigraphy and sedimentation on the korea strait shelf was studied using a dense network of high resolution single channel seismic reflection profiles the shelf sequences above the acoustic basement consist of seven depositional sequences separated by erosional unconformities corresponding to falls in sea level individual sequences are characterized by well stratified and complex sigmoid oblique prograding reflection configurations reflecting a history of upbuilding and outbuilding in response to repetitive transgressive and regressive events driven by sea level changes during the regression to lowstand of sea level lowstand prograding wedges were formed seaward along the present shelf margin whereas during the highstand of sea level as in the present condition highstand deposits were deposited in the inner shelf along the coast however as the subsequent regression began the inner shelf highstand deposits were severely eroded out and or formed a condensed section volumetrically the forced regressive and lowstand systems tracts are the most important components of the korea strait consequently the plio quaternary sequence in this area consists of a succession of stacked progradational lowstand wedges mainly formed during the regression and lowstand of sea level

recent sediment accumulation and origin of shelf mud deposits in the yellow and east china seas abstract modern last 100 yr accumulation rates of shelf mud deposits in the yellow and east china seas were investigated using the distribution of excess 210pb 210pbex in sediment core samples compilation and merger of new and previously published data helped clarify sediment accumulation in these seas the estimated accumulation rates together with data of suspended sediment concentrations provided findings on the sediment budget origin and transport pathway of the mud deposits the overall accumulation distribution in the yellow and east china sea shelf revealed a general cross shelf decreasing trend along the sediment dispersal system away from the rivers except for the south sea ssm and southeastern yellow sea seysm mud patches found along the korean coast notably 210pbex activity profiles within the ssm and the seysm yielded a relatively high accumulation rate of 2 5 mm yr implying a sedimentation rate of 4 15 107 tons per year in this coastal zone such an annual accumulation rate is about one order of magnitude greater than the total sediment discharge 6 20 106 tons yr from korean rivers suggesting an additional offshore source the distribution pattern of the well defined suspended plume clearly showed the possible transport and exchange of fine grained sediments between the ecs shelf and the coastal area of korea especially during winter such a high accumulation in korean coastal areas is attributable to the sediments supplied from the mud deposit of the ecs i e swcim with origins in chinese rivers therefore the korean coastal area may be an important sink for some of chinese river sediments being transported from the south by the yellow sea warm current

subglacial processes from drumlins in clew bay western ireland interpretation of subglacial processes and environments can be usefully informed by the stratigraphy and structures of sediments preserved within drumlins and the down ice variability of these sediments drumlins in clew bay western ireland were formed by westward late pleistocene ice flow onto the atlantic shelf but the depositional processes and environments of these sediments remain uncertain this study describes and interprets the drumlin stratigraphy and sediment properties and structures from two drumlins on the south side of clew bay drumlin sediments are dominated by massive to stratified diamicton deposited subglacially by deformation of flows of varying rheology folds shears and clastic dikes within the sediments suggest active subglacial water flow related to variations in ice flow and ice bed coupling the distal ends of the drumlins are dominated by stratified diamicton and gravel units with sandy interbeds these sediments reflect deposition in a leeside subglacial cavity formed coevally with bedform development a model is proposed that can account for sediment stratigraphic patterns and drumlin formation copyright 2015 john wiley sons ltd

arc continent collisions sediment recycling and the maintenance of the continental crust author posting geological society of london 2009 this is the author s version of the work it is posted here by permission of geological society of london for personal use not for redistribution the definitive version was published in geological society london special publications 318 2009 75 103 doi 10 1144 sp318 3

physical and acoustic properties of inner shelf sediments in the south sea korea abstract core sediment sampling has been conducted to investigate the physical and acoustic properties of inner shelf sediments in the south sea korea thirty two piston core samples were analyzed for sediment texture grain size as well as fractions of sand silt and clay physical properties porosity water content bulk density grain density and shear strength and acoustic properties compressional wave velocity and attenuation the sediments in the study area consist mostly of homogenous mud the study area can be divided into two different areas south of namhae island and southeast of naro island by texture and physical and acoustic properties the mean grain size generally decreases seaward from the mouth of yeosu sound and eastward in the southeast area of naro island the compressional wave velocity decreases southeastward from 1500 to 1480 m s and then increases to 1520 m s due to relict sediments deposited in mid shelf of the south sea porosity water content and bulk density show an inverse pattern to velocity the geoacoustic properties of the study area are generally similar to those of continental terrace sediment studied by hamilton in the north pacific the area south of namhae island area matches hamilton s model better than the area southeast of naro island this result is believed to be related to the higher silt and sand contents as well as lower clay content than southeast of naro island

sediment distribution dispersal and budget in the yellow sea abstract information on the surface sediment distribution in the yellow sea is newly compiled based on all available data produced by chinese and korean workers and is used to refine the dispersal patterns and budget of sediments derived from the adjoining landmass the central yellow sea is largely covered with fine grained sediments originating from the huanghe river 2 2 10 8 t yr about 20 of the total discharge thick sediment accumulation exceeding 5 mm yr occurs in the gulf of bohai and around the shandong peninsula about two thirds of the total huanghe river discharge the old huanghe delta suffers from reworking by strong tides and waves and forms a mud patch southwest of cheju island accumulation rate 2 10 7 t yr more than half of the sediments derived from the changjiang river are deposited along the coast of the east china sea the remainder accumulate on the inner shelf off the river mouth in the southeastern yellow sea the keum river dominates sediment discharge forming a holocene mud belt along the southwestern coast of korea accumulation rate 5 10 6 t yr turbid water plumes occur nearshore throughout the year and their suspended sediments are transported along the tip of the peninsula to the western coastal embayments in the south sea the nakdong river discharge of 1 10 7 t yr is responsible for the eastern nearshore mud of the south sea relict sands occur in the northern part of the yellow sea in the northern east china sea and in the korea strait

high resolution analysis of early diagenetic effects on magnetic minerals in post middle holocene continental shelf sediments from the korea strait 1 two studied sediment cores from the korea strait contain mud sequences 14 m and 32 62 m in thickness that were deposited during the last 6 000 years the sediments have uniform lithology and geochemical properties however marked down core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties an expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep sea sediments the studied sediments are divided into four descending intervals based on magnetic property variations interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite and the lowest solid phase sulfur contents interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations which suggest active reductive dissolution of detrital magnetic minerals interval 3 is marked by a progressive loss of hematite with depth and coincides with the minimum magnetite concentration interval 4 has an increasing down core enhancement of authigenic greigite which apparently formed at depths of 3 30 m below the sediment water interface due to arrested pyritization reactions these results indicate delays of thousands of years for acquisition of magnetizations carried by greigite which suggests that studies of geomagnetic field behavior from greigite bearing continental shelf sediments should be conducted with care also virtually complete destruction of detrital magnetic minerals at depth suggests that magnetic studies of rapidly deposited shelf sediments are unlikely to provide a meaningful signature associated with syn depositional environmental processes

seismic stratigraphy of late quaternary sediments of western mersin bay shelf ne mediterranean sea abstract high resolution shallow seismic reflection profiles obtained from the western mersin bay have revealed the existence of the two distinct depositional sequences c and b lying on a narrow and relatively steeply sloping continental shelf which mainly receives its sediments from the ephemeral rivers the upper holocene sedimentary sequence c is characterized by stratified simple to complex to chaotic reflection configurations produced by the development of a prograding wedge of terrigenous sediment particular occurrences of slope and front fill facies and the lack of a sharp boundary which has however been observed on the western shelf of this bay between the early holocene and latest pleistocene deposits are related to possible movement of underlying deposits due to local gravity mass movements or synsedimentary tectonics due to adjustment of the underlying evaporites in adjacent basin the maximum thickness of the topmost sequence c is associated with the tarsus seyhan delta which lies to the northeast of the area and is prograding along the shelf other variations in thickness 5 40 m of this topmost sequence are related to the variable sediment discharge along the coast and the distance from the coast it is at a maximum 40 m in the nearshore area just west of the lamas river mouth and at a minimum 5 15 m in the offshore area the lower depositional pre holocene sequence b is characterized by continuous to wavy reflection configurations and how some cyclicity suggesting coarse heterogeneous sediments deposited under high energy conditions fan deltas of plio pleistocene age the combined interpretation of seismic reflection profiles with the available bore hole data reveals the existence of a widespread miocene acoustic basement a off the susanoglu tirtar coasts and karapinar gilindirez rivers mouths unusual features in some profiles suggest the escape of coastal freshwater into the accumulating sediment

trace element constraints on the differentiation and crystal mush solidification in the skaergaard intrusion greenland new major and trace element analyses of plagioclase and clinopyroxene in gabbros from the skaergaard intrusion are used to understand the mechanisms of crystallization in the main magma body and in the crystal mush crystal cores show a continuous chemostratigraphic evolution in the layered series with compatible elements e g cr and ni in clinopyroxene being progressively depleted from the bottom up whereas incompatible elements e g sr ba ree in plagioclase and clinopyroxene become progressively enriched we performed numerical models and showed that these trends can be explained by a simple process of fractional crystallization except for the upper 20 of the intrusion where plagioclase and clinopyroxene trace element compositions depart from fractional crystallization trends at this stage of magma chamber solidification fractional crystallization becomes less efficient and is replaced by a major proportion of in situ equilibrium crystallization trace elements also show significant variations in interstitial overgrowths on plagioclase and clinopyroxene cumulus crystals they result from crystallization of the interstitial liquid in the liquid crystal mush however incompatible elements and especially ree show a degree of enrichment in plagioclase rims 20 ppm ce that strongly exceeds the highest concentrations observed in plagioclase cores up to 4 ppm ce at the top of the layered series such a strong enrichment is difficult to reconcile with a simple process of fractional crystallization of the interstitial liquid in the crystal mush but may be related to the development of silicate liquid immiscibility in the crystal mush or to delayed nucleation of apatite after the crystallization of plagioclase and clinopyroxene overgrowths diffusive re equilibration during a period of 0 1 0 25 myr significantly changed the original zoning profiles ce flux from clinopyroxene into the plagioclase lattice of adjacent crystals could also have contributed to the strong ce enrichment observed in plagioclase rims

distribution of suspended sediment in the korea strait and southeastern yellow sea onset of winter monsoons abstract high energy conditions in the yellow sea begin each year with the onset of monsoon winds in late october these transitional season surges of cold air initiate sediment resuspension vertical mixing of suspended sediments and a wind driven coastal current that flows to the south during the summer to winter transition suspended sediment concentrations in the southeastern yellow sea range from 5 100 mg l 1 at the surface and 5 500 mg l 1 at the bottom the highest concentrations occur off the southwest tip of the korean peninsula and the lowest occur in the central part of the korea strait the rate of transitional season destratification may depend on the timing and intensity of monsoonal surges whereas a late onset of monsoon winds allows waters to remain longer in their moderately stratified summer condition an early onset of monsoon winds tends to destratify the water column by mid november resulting in a nearly uniform high concentration of suspended sediments from surface to bottom the band of more turbid coastal water ends abruptly 25 50 km offshore as a turbidity front in waters 20 80 m deep a wind driven residual flow to the south appears to transport large volumes of this turbid water into the korea strait and perhaps as far as the sea of japan

stratigraphic evolution of the nakdong river valley in response to late quaternary sea level changes abstract sequence analysis using borehole samples and high resolution seismic data in the nakdong river valley yielded a good example of a river valley sequence influenced by the complex interplay between the bottom morphology of the steep paleo valley varying sediment supply and holocene sea level change associated with coastal currents the late quaternary stratigraphic sequence in the nakdong river estuary approximately 60 70 m thick forms a high frequency sequence consisting of a set of lowstand transgressive and highstand systems tracts that corresponds to a fifth order 20 ka sea level cycle four main depositional systems including ten sedimentary facies constitute these systems tracts fluvial estuarine coastal shoreface and deltaic the lowstand systems tract lst consisting of gravelly sand forms a fluvial depositional system unit i which fills the thalweg of river valley mainly developed before 12 ka the transgressive systems tract tst showing a succession of retrograding or backstepping depositional arrangements can be divided into two depositional systems unit ii and iii the riverine sediments were trapped within the paleo estuary forming an estuarine depositional system unit ii developed between 12 and 7 ka as the transgression continued the coarse sediments were deposited and redistributed by coastal processes resulting in coastal shoreface depositional system unit iii it is characterized by an isolated sand body and thin sand veneer the hst is composed of deltaic depositional system including delta plain delta front and prodelta unit iv during the delta progradation most coarse grained sands derived from the river were deposited in the lower delta plain and delta front forming sand bars and shoals less than 15 m deep the remaining fine grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth forming a subaqueous prodelta radiocarbon and optically stimulated luminescence osl dating suggest that the holocene deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea level rise and was then followed by a prograding clinoform after the highest sea level at approximately 7 ka

paleoenvironmental changes and depositional history of the korea tsushima strait since the lgm abstract two deep cores ssdp 102 and ssdp 105 from the southeastern inner shelves of korea were examined in order to reconstruct the paleoenvironmental history of the korea strait during postglacial sea level fluctuations the results of the lithofaces organic geochemical components foraminiferal assemblages and stable isotopes show that the korea strait was influenced in different ways by river discharges and open ocean currents according to their temporal and spatial variability the results of core ssdp 105 indicate that the southeastern coast of korea was probably a shallow coastal environment such as a shoreface or beach by about 17 5 cal ka the area remained a coastal environment that was affected by high energy conditions and partly by freshwater input during the transgressive period of 17 5 8 1 cal ka the area has changed to a modern type shelf environment influenced by the inflow of the tsushima current and by the high supply of fine grained sediments derived from the nakdong river since 8 1 cal ka meanwhile the results of core ssdp 102 taken from the nakdong river mouth reveal that the river mouth area was most likely a terrestrial or fluvial environment at least before 13 9 cal ka it then changed to the estuarine deltaic environment that was directly affected by the nakdong river between 13 9 and 7 0 cal ka and established a modern type shelf prodeltaic environment which is similar in many respects to the southeastern coast of korea after temporarily undergoing erosion between 7 0 and 6 1 cal ka

seismic stratigraphy and late quaternary sediments in inner and mid shelf areas of eastern mersin bay northeastern mediterranean sea abstract high resolution shallow seismic reflection uniboom profiles obtained in inner and mid shelf areas of eastern mersin bay turkey northeastern mediterranean show that the sedimentary column comprises two major and distinct lithological sequences c and b separated by a reflector r which is interpreted as the pre holocene surface the upper sedimentary sequence c is thought to represent roughtly the holocene and is characterized by parallel divergent to sigmoidal reflection patterns above unit 1 and sigmoidal obolique to disrupted wavy and hummocky reflection configurations below unit 2 this may reflect changes in relative sea level and or depositional conditions during the earlier and later stages of holocene the holocene sequence c reaches a maximum thickness of approximately 35 m about 500 600 m seaward of the mouth of seyhan river and thins in all directions away from this point adjacent shelf areas are characterized by thinner 10 15 m thick depositional sequences holocene sediment accumulation rates range from 1 to 3 5 m ka the lower sedimentary sequence b is marked by chaotic reflection configurations and is interpreted as having formed largely during the plio pleistocene the top of this sequence displays various channel onlap fills with parallel to oblique reflectors this record may represent the pre holocene surfaces produced by subaerial fluvial erosion of the pre existing shelf at least two or three orders of strong continuous reflectors similar to late pleistocene holocene unconformities are observed within sequence b and the repetitive pattern of the interfaces indicates cyclic sedimentation due to climatic fluctuations and oscillating sea level changes mostly in the pleistocene lithological logs from numerous soil borings on the adjacent coast suggest a significant increase in the thickness of the plio quaternary sequences from a few metres on the alluvial fan delta systems west of mersin to a few hundred metres on the fluvial plain delta system east of mersin climatic and sediment discharge fluctuations and coastal morphology controlled the temporal and spatial distributions of late pleistocene and holocene sediments in eastern mersin bay

factors determining the spatial distribution of gas charged sediments in the continental shelf off southeastern korea abstract a high resolution seismic survey piston coring and water column measurements were conducted on the continental shelf off southeastern korea to examine the gas charged sediments and gas seepage in the water column we examined the factors controlling the spatial distribution of the acoustic blanking zone in recent korea strait shelf mud kssm deposits along the southeastern shelf the molecular composition methane hydrogen and carbon dioxide isotope values of headspace gases and the geochemical composition of core sediments were measured in 11 piston cores dissolved methane concentrations in the water column were observed at 6 of the 11 coring sites acoustic blanking of the recent kssm deposits was limited to areas with water depths between 30 and 105 m along the continental shelf except line l 13 133 m depth the flanks of the acoustic blanking zone can be classified as distinct disturbed and step types based on their configurations the highest methane concentration in the headspace gases was about 2 7 2 4 m below the seafloor which matched the top of the acoustic blanking zone no obvious methane was found in piston cores obtained from the gas free zone the 13 c ch4 ranged from 56 5 to 106 3 relative to vienna pee dee belemnite v pdb and the d ch4 ranged from 194 to 207 relative to vienna standard mean ocean water v smow these isotope values show that methane is produced by the microbial reduction of co 2 ch 4 oxidation results in a significantly heavier carbon isotope fraction from 91 2 to 56 5 in the 2 m below the seafloor with constant 13 c co2 isotope fractionation no obvious differences were seen in the total carbon tc 2 438 3 378 total nitrogen tn 0 159 0 548 total organic carbon toc 1 139 2 078 or caco 3 2 825 15 258 in the continental shelf whereas the toc was high and the caco 3 low distant from the nakdong river distinct dissolved methane anomalies 21 87 ppm were seen in the water column in the acoustic blanking and gas seepage zones this level was about 15 times higher than the dissolved methane level 1 5 ppm in the water column in the gas free zone these results indicate that the acoustic blanking zone accumulates biogenic methane methane seepage was observed in the water column throughout the acoustic blanking zone of the continental shelf off southeastern korea

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

morphology and genesis of giant seafloor depressions on the southeastern continental shelf of the korean peninsula abstract we identify and describe five giant seafloor depressions from the southeastern continental shelf of the korean peninsula using multibeam bathymetry sub bottom profiler and multi channel seismic reflection data supplemented by piston cores multibeam bathymetry data from the shelf show four crescent shaped depressions sd1 to sd4 and one near circular depression sd5 within a group of nw se trending depressions the largest covering an area of about 7 km2 on the seafloor the depressions reach up to 4 5 km in width and 2 km in length and have asymmetric cross sections some have depths as large as 40 m below the surrounding seafloor with walls as steep as 45 the depressions are confined to water depths between 130 and 170 m and bounded on the north by a large submarine channel that was plausibly formed by fluvial or tidal processes during the last glacial maximum lgm sea level lowstand multi channel seismic and sub bottom profiler data reveal truncated depression walls and the presence of sediment drift deposits within the depressions indicating that both erosion and deposition are active processes flaser and lenticular bedding in the cored drift deposits along with variable grain size ranging between 2 6 phi and 4 3 phi are diagnostic features of the bottom currents influenced by tidal forces depressions sd1 to sd4 lack evidence of fluid or gas escape in contrast many features of depression sd5 are characteristic of gas escapes and blowouts including acoustic anomalies a 20 m high carbonate mound or carbonate encrusted mound and mud dikes and mud patches in cores based on the sd5 example we think it is likely that the other crescent shaped seafloor depressions formed originally as pockmarks by gas fluid venting and have since become inactive the pockmarks represent zones of weakened sediment that were eroded expanded and merged by bottom currents to form larger seafloor depressions modern currents are strong enough to transport shelf sediments and these currents were probably much stronger at lower sea levels when the korea strait was a more restricted passage between the east china sea and east sea

physical and acoustic properties of shelf sediments the south sea of korea abstract laboratory determinations of compressional wave velocity porosity density and sediment texture have been conducted on samples collected from the inner shelf holocene mud sediment in the south sea and southern part of the east sea of korea thirty five piston core samples were used for the measurement mean grain size decreases seaward reflecting the distance from source velocity decreases with increasing water depth porosity and clay content increase gradually with deepening bathymetry on the inner shelf the study area can be divided into three different areas namhae pusan and ulsan by sediment source texture and physical properties velocity increases from west to east namhae pusan ulsan porosity has a pattern that is inverse to that of velocity sediment texture mean grain size and clay content is a very important factor to determine physical and acoustic properties of sediment the geoacoustic properties of the three study areas generally coincide well with that of hamilton s 1970 north pacific continental terrace sediment ulsan area is a little different from the hamilton s model which has a relatively higher velocity at the same textural range the difference is believed to be related to the lowest clay content in ulsan area

ductile and brittle styles of subglacial sediment deformation an example from western ireland abstract in western ireland within a drumlin formed inside the margin of the late pleistocene ice sheet a range of different styles of ductile and brittle sediment deformation is observed within subglacial diamicton till and associated subglacial waterlain sediments at roonah point county mayo the structures associated with these different deformation styles include gravel clusters that have loaded subjacent sediments glacitectonic shears water escape structures and clastic dikes these structures are found for tens of metres laterally within the same diamicton units and the structures may cross cut or be superimposed upon one another based on these properties and geometric relationships the relative chronology and processes and patterns of subglacial deformation can be reconstructed including an evaluation of subglacial conditions and pore water pressure regimes this illustrates the relationship between glacitectonic forcing by ice bed coupling and the structural response within subglacial sediments to changing pore water pressure gradients

evolution and chronology of late pleistocene shelf perched lowstand wedges in the korea strait abstract detailed interpretation of high resolution seismic profiles from the korea strait has shown the existence of a complex of three stacked sedimentary sequences on the outer shelf the individual sequences consisting of prograding wedge are interpreted from internal structure and sediment data as a shelf perched lowstand wedge system related to alternating episodes of successive regression and transgression although the entire sequences have not been fully dated it is believed that the sequences were deposited during late pleistocene sea level lowstands repeated falls of sea level isotopic stages 8 6 and 2 resulted in the formation of lowstand sedimentary sequences during subsequent episodes of sea level rise isotopic stages 8 7 6 5 and 2 1 the sequences were reworked and draped by thin transgressive sands

transgressive sand ridges on the mid shelf of the southern sea of korea korea strait formation and development in high energy environments abstract the mid shelf of the southern sea of korea korea strait is covered by a series of shore parallel sand ridges up to 63 km long 3 9 km wide and 22 m thick the ridges are a moribund type but show well organized dipping strata indicating appreciable progradation the submerged paleo channel system the paleo seomjin river associated with the sand ridge field suggests that the ridges primarily originated from river mouth sandy shoals which subsequently developed into shore parallel linear sand bodies in high energy environments the combined effect of coastal tidal and longshore and offshore ocean currents was possibly responsible for shore parallel sediment transport and growth of the ridges 14c dates core lithology and sea level data suggest that the sand ridges mainly formed and developed during the middle period of the postglacial transgression they are postulated to have developed sequentially from offshore to onshore in response to sea level rise during that time very slow sea level rise and high sediment supply through the paleo channel system probably provided favorable conditions for forming the sand ridges the ridges became inactive during the late transgression period as a result of a substantial reduction of wave and current strength and remained on the mid shelf

late pleistocene holocene radiolarian and pollen records from sediments in the sea of okhotsk in two cores with oxygen isotope stratigraphy from the southern okhotsk sea marine pollen and siliceous microfauna record concurrent late glacial through holocene variations in regional terrestrial and marine environments glacial vegetation around the southern okhotsk basin which resembles the present tundra steppe of the northwest coast of this marginal sea yields to spruce dominated boreal forests during the glacial interglacial transition temperate forest components such as oak peak during the mid holocene decreasing oak accompanied by increasing spruce reflects the effect of global cooling on local vegetation during the last 4 kyr although the radiolarian fauna in the okhotsk sea samples is similar to that present in the northwest pacific the dominant species in both regions differ concentrations of radiolarians are low in latest glacial samples with higher concentrations occurring above and below this interval cycladophora davisiana the dominant radiolarian species in the majority of holocene okhotsk sea sediments is present at lower percentages in late glacial samples from our two sites thus this species holocene latest pleistocene abundance pattern in sea of okhotsk sediments is the reverse of that recorded in high latitude open ocean sites the combined marine pollen and radiolarian records indicate changes in the sea of okhotsk s physical oceanographic conditions and surrounding vegetation during the late glacial which were associated with this region s response to global climate change

evolution of fluvial sedimentation in the buntsandstein lower triassic of the eifel germany abstract the continental redbeds of the buntsandstein lower triassic in the western eifel germany are composed mainly of fluvial and aeolian sediments the terrestrial sequence reflects an evolution of fluvial depositional environments in the basisbildungen at the beginning of triassic sedimentation alluvial fans and mudflows distally intertounged with sandy braided rivers in local depressions of the pre triassic continent surface in the trifels schichten slow subsidence and rapid shifting of narrowly spaced channels in low sinuosity highly braided multi channel river systems often resulted in reworking of upper parts of cyclothems thus piling up thick sequences of stacked bar deposits in the rehberg schichten large flood plains developed due to increasing spacing and sinuosity of the channels and decreasing braiding of the river systems faster subsidence favoured preservations of predominantly complete cyclothems ideally terminated by thin aeolian sands in the karlstal schichten the climax of regional diversification of sedimentary environment matched the development of a large aeolian sand sea which was intersected by generally moderately braided rivers aeolian sands were deposited as barchanoid type dunes and interdune sheet sands and intertongued with fluvial channel and topstratum deposits at the top of the middle buntsandstein the violette grenzzone marks a hiatus in evolution resulting in recurrent change in fluvial style in the usch schichten coarse detritus accumulated in multi channel low sinuosity pebbly highly to moderately braided rivers rapid channel shifting and slow subsidence often led to erosion of topstratum deposits and palaeosols in the malbergweich schichten increase of channel spacing and sinuosity was accompanied by increasing subsidence sandy moderately to weakly braided streams and occasionally also meandering rivers deposited cyclic alluvial sediments at the beginning of the kyllburg schichten another minor recurrence interrupted the evolution channel braiding increased once more and rapid channel shifting accompanied by slower subsidence led to widespread erosion of overbank fines at the top of the kyllburg schichten sinuosity increased more and more and sandy moderately to weakly braided rivers graded into meandering streams in the voltziensandstein fluvial environment passed into a deltaic and or tidal milieu in front or at the margin of the prograding muschelkalk sea transgression of the shallow marine muschelkalk terminated the terrestrial period of the buntsandstein in the eifel evolution of fluvial sedimentary environment thus led in the middle buntsandstein from local alluvial fans via pebbly highly braided rivers to sandy moderately braided streams and finally to an intertonguing of aeolian dunes and multi channel rivers with regionally different degree of braiding tectonic activity in the source areas and climatic change at the beginning of the upper buntsandstein resulted in reversion to conditions existing in the inferior part of the middle

seismic stratigraphy of the mississippi alabama shelf and upper continental slope abstract the mississippi alabama shelf and upper continental slope contain relatively thin upper pleistocene and holocene deposits five stages of shelf evolution can be identified from the early wisconsinan to present the stages were controlled by glacioeustatic or relative sea level changes and are defined by the stratigraphic position of depositional and erosional episodes the stratigraphy was identified on seismic profiles by means of geomorphic pattern high angle clinoform progradational deposits buried stream entrenchments planar conformities and erosional unconformities the oldest stage stage 1 of evolution occurred during the early wisconsinan lowstand the subaerially exposed shelf was eroded to a smooth seaward sloping surface this paleosurface is overlain by a thin these upper quaternary shelf and slope deposits provide models for analogous deposits in the geologic record primarily they are examples of cyclic sedimentation caused by changes in sea level and may be useful in describing short term sandy depositional episodes in prograding shelf and slope sequences

shallow seismic stratigraphy and distribution pattern of late quaternary sediments in a macrotidal bay gunhung bay west coast of korea abstract the shallow seismic stratigraphy of late quaternary sediments in gunhung bay a macrotidal coastal embayment of western korea was investigated by means of analyzing high resolution seismic profiles and sediment samples late quaternary sediments up to 20 m thick overlie the irregular surface of the acoustic basement the sediments consist mainly of sands muddy sands and sandy muds and show a zonal facies distribution the distribution pattern appears to be largely controlled by the tidal currents in the bay the sedimentary column above the acoustic basement can be divided into two sequences by a relatively strong mid reflector which is interpreted as the erosional pre holocene surface formed during low sea level many v shaped erosional patterns in this reflector indicate the existence of old tidal channels the sediments underlying the mid reflector are interpreted to be semi consolidated pre holocene tidal deposits presumably deposited during the last interglacial period while the sediments overlying this reflector represent the late holocene tidal desposits deposition of the late holocene sediments began probably at about 5000 yrs b p when sea level approached its present level

occurence of the trace fossil beaconites antarcticus in the lower carboniferous fluviatile rocks of county mayo ireland abstract large straight curved or sinuous endichnial burrows with a meniscus pattern of infilling are described from lower carboniferous red beds of county mayo ireland the burrows have been identified as beaconites antarcticus the burrows show a strong facies association being concentrated in the upper parts of sandstones deposited during floods in shallow possibly ephemeral stream channels they appear to be absent from the overlying non red fluvial sandstones which show evidence for deeper more sinuous and more permanent channels it is suggested that burrowing was related to varying moisture content of the sediment the burrows were probably formed by locomotory back packing of arthropods or vertebrates but the precise nature of the producer remains unknown

high resolution seismic study as a tool for sequence stratigraphic evidence of high frequency sea level changes latest pleistocene holocene example from the korea strait abstract sequence stratigraphic analysis of high resolution seismic reflection profiles and sediment data reveals that the latest pleistocene holocene deposits in the korea strait shelf off the southeastern korean peninsula form a high frequency sequence consisting of a set of lowstand transgressive and highstand systems tracts that corresponds to a fifth order 20 kyr sea level cycle eight depositional systems each with different seismic facies constitute the systems tracts the lowstand systems tract consisting of sandy mud forms a deltaic wedge that pinches out updip near or at the relict shelf edge the transgressive systems tract consisting mainly of sands includes six depositional systems 1 inner shelf transgressive layer 2 transgressive estuarine deltaic complex 3 transgressive sand ridge 4 mid shelf transgressive layer 5 incised channel fill and 6 beach shoreface complex although the transgressive systems tract is widely distributed it is much thinner than the lowstand and highstand systems tracts the highstand systems tract is composed of a prodelta shelf complex consisting almost exclusively of holocene muds the distribution and geometry of the systems tracts in the latest pleistocene holocene sequence in the korea strait shelf is different from that of vail s model in that 1 the lowstand systems tract consists only of the lowstand deltaic wedge which forms an elongated sediment body along the paleoshelf edge and 2 the highstand systems tract is completely confined to the inner shelf and forms a nearshore belt parallel to the coastline high frequency 20 kyr high amplitude magnitude of about 130 m sea level change together with strong currents flowing northeastward along the southeastern coast of the korean peninsula and varying sediment supply have resulted in this rather unusual stratigraphic architecture

transgressive sand sheet covering the shelf and upper slope off sendai northeast japan abstract a thin sand sheet deposited during the last major transgression from 14 000 to 6000 yrs b p covers the shelf and upper slope off sendai northeast japan the sand sheet overlies the sediments deposited during the last low sea level stand and is partly overlain by modern offshore muds this sheet is regarded as palimpsest sediment formed during the transgression in water depths of 50 m the sand sheet is 50 150 cm thick and consists of alternations of poorly sorted thin sand layers and mud layers that are several millimeters to a few centimeters thick it bears mixed environment molluscan shells and small amounts of glauconite scour and fill structures are frequently found gravel with shell fragments is common near the base of the sheet

age and isotope geochemistry of magmatic rocks of the lohit plutonic complex eastern himalaya implications for the evolution of transhimalayan arc magmatism we present integrated in situ zircon u pb and hf isotope data along with whole rock sr nd isotope and geochemical data for plutonic rocks of the lohit plutonic complex of eastern himalaya to understand the age distribution and petrogenetic tectonic evolution of the transhimalayan batholiths in the eastern himalaya the plutonic rocks are gabbro diorite and quartz diorite in composition have calc alkaline signatures with metaluminous character and have an affinity with gangdese i type granitoids of southern tibet the enrichment of large ion lithophile elements with highly depleted negative nb anomalies is consistent with their origin in a subduction related environment our laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages suggest that two major stages of magmatic emplacement took place at c 145 ma early cretaceous for gabbro and c 100 90 ma early late cretaceous for diorite and quartz diorite the zircon hf isotopes in both the gabbro and diorite samples show high positive ehf t values between 11 and 20 suggesting crystallization from juvenile crust or depleted mantle derived melts as also constrained by the low initial 87sr 86sr ratios 0 7038 0 7045 and high positive end t values 2 9 to 5 9 results of ree modelling indicate that the source of these rocks is garnet lherzolite field observations and mineralogical and geochemical characteristics in conjunction with the isotopic database suggest that the transhimalayan magmatic rocks in eastern himalaya were generated by partial melting of the lithospheric mantle wedge and emplaced into the lower crust c 25 30 km during at least two major magmatic events that took place in the cretaceous period supplementary material la icp ms zircon u pb and hf isotope data are available at https doi org 10 6084 m9 figshare c 4665305

sediment properties of lithologic units and their correlation within the lower delta plain of the nakdong river delta southeast korea abstract multi proxy sediment properties reveal that three cores nd 01 nd 02 and nd 03 from the lower delta plain of the nakdong river delta southeast korea are characterized by the same stratigraphic lithologic successions consisting of a upper sand unit 10 15 m thick and 10 ka overlying weathered gravelly fluvial sediments and weathered bedrock the sediment properties of each lithologic unit are controlled by the balance between the marine influence from holocene sea level rise and the freshwater influence from nakdong river discharge in particular the middle mud unit is characterized by distinct peaks in caco3 content p t ratios the ratio of planktonic foraminifera to the sum of benthic and planktonic foraminifera total organic carbon and total nitrogen contents and 13corg values at 7 8 ka which indicates that the maximum marine forcing during the sea level rising and the greatest influence of the tsushima warm current during the evolution of the river mouth coastal depositional system from an estuarine to a deltaic environment although the vertical stacking of lithologic successions is stratigraphically consistent within the lower delta plain the precise temporal evaluation and comprehensive depositional evolution in the nakdong river delta including the upper delta plain and the prodelta zones remain a topic of future investigation

incised channel morphology and depositional fill of the paleo seomjin river in the continental shelf of the south sea korea this study is the first attempt at describing and interpreting incised channels on the continental shelf of the south sea korea the distribution pattern shape and infilling of submerged channels incised across the continental shelf of the south sea have been investigated based on approximately 1940 line km of chirp and sparker data the incised channel system of the paleo seomjin river on the continental shelf is approximately 109 km long 800 5000 m wide and is more than 890 km2 in area meandering and straight types of channel are dominant on the inner shelf with a change to straight and braided planforms on the mid to outer shelf sparker seismic data suggest the paleo channels formed under fluvial systems when the shelf was exposed during the last glacial maximum lgm channel fills are divided into five types based on erosional surfaces and internal seismic reflectors i transparent to semi transparent incised channel fill ii parallel to sub parallel incised channel fill iii complex incised channel fill iv divergent incised channel fill and v chaotic incised channel fill the acoustically transparent facies of the channel fill type type i suggest the presence of basin muddy deposits in a low energy environment which were dominant in the inner shelf these muddy sediments were likely during a period of higher sea level during the holocene transgression types ii iii and iv are characterized by onlap downlap and wave or tidal ravinement surfaces respectively indicating that they were deposited during a transgressive stage which type v represent basal incision surface the evolution of paleo seomjin river has been strongly controlled by sea level change and sediment transport processes since the lgm

depositional patterns of sand ridges in tide dominated shallow water environments yellow sea coast and south sea of korea abstract the continental shelf of the yellow sea and the korean south sea is a tide dominated shelf a number of sand ridges occur in this area which form bathymetric highs surveyed were one large sand ridge jangan satoe along the western yellow sea coast and a group of mid shelf sand ridges in the south sea to delineate their depositional pattern and probable origin in tide dominated shallow water environments analyses of sediment samples side scan sonographs and seismic profiles reveal that these ridges show regionally different characteristics in morphology bedforms and sediment the sand ridge in the yellow sea shows a composite form of various bedforms including sand waves and megaripples this ridge is interpreted to be in an accretional active stage maintained by strong tidal currents in contrast the sand ridges on the mid shelf of the south sea show rounded single forms without bedforms on them they are interpreted to represent moribund type sand ridges in the shelf environment which were formed near the shoreline during the holocene sea level transgression these ridges developed off the paleo seomjin river during a period of a stillstand or slow sea level rise approximately between 10 000 and 7000 yrs b p

partitioning and mass balance relations in lherzolites abstract the dependence of mineral composition on modal amounts in lherzolites is examined using mass balance equations coupled with inter phase partition coefficients the composition of clinopyroxene changes dramatically as its modal abundance approaches zero because clinopyroxene strongly concentrates incompatible elements compared with orthopyroxene and olivine compositional variables for clinopyroxene such as element concentrations la element ratios la yb and interpolated concentrations nb nb are not representative of bulk rock composition when clinopyroxene weight fraction

the terrestrial landscapes of tetrapod evolution in earliest carboniferous seasonal wetlands of se scotland abstract the lower mississippian tournaisian ballagan formation in se scotland yields tetrapod fossils that provide fresh insights into the critical period when these animals first moved onto land the key to understanding the palaeoenvironments where they lived is a detailed analysis of the sedimentary architecture of this formation one of the thickest and most completely documented examples of a coastal floodplain and marginal marine succession from this important transitional time anywhere in the world palaeosols are abundant providing a unique insight into the early carboniferous habitats and climate more than 200 separate palaeosols are described from three sections through the formation the palaeosols range in thickness from 0 02 to 1 85 m and are diverse most are entisols and inceptisols 63 indicating relatively brief periods of soil development gleyed inseptisols and vertisols are less common 37 vertisols are the thickest palaeosols up to 185 cm in the ballagan formation and have common vertic cracks roots are abundant through all the palaeosols from shallow mats and thin hair like traces to sporadic thicker root traces typical of arborescent lycopods geochemical isotope and clay mineralogical analyses of the palaeosols indicate a range in soil alkalinity and amount of water logging estimates of mean annual rainfall from palaeosol compositions are 1000 1500 mm per year the high mean annual rainfall and variable soil alkalinities contrast markedly with dry periods that developed deep penetrating cracks and evaporite deposits it is concluded that during the early carboniferous this region experienced a sharply contrasting seasonal climate and that the floodplain hosted a mosaic of closely juxtaposed but distinct habitats in which the tetrapods lived the diversification of coastal floodplain environments identified here may link to the evolution and movement of tetrapods into the terrestrial realm

regional spatial distribution of multiple elements in the surface sediments of the eastern tsushima strait southwestern sea of japan abstract a total of 402 coastal sea sediment samples were collected from the continental shelf slope and basin off tsushima island in the western sea of japan and were analyzed for 51 elements as part of a nationwide marine geochemical mapping project the samples were compared to potentially related sample sets and the results were considered from the viewpoint of the origin of marine surface sediments in the western sea of japan the spatial distribution of elemental concentrations in the coastal sea sediments correspond to texture grain size the presence of shells and foraminifera and the mud content of surface marine sediments most elemental concentrations increased with increasing mud content some samples located in littoral areas included sediment particles apparently supplied from nearby rivers but their contribution was limited overall the mean chemical compositions of clastic material in coastal sea sediments appear to differ from those of stream sediments in adjacent terrestrial areas in addition the geochemistry of the coastal sea sediments cannot be fully explained by the mixing of the material supplied from korean and chinese stream sediments which are the most feasible sources coastal sea sediments in the study area are well mixed by transportation processes therefore elemental abundances in these marine sediments may be homogenized to such an extent that it is not possible to determine their origin alternatively most of the clastics in the sediment may actually represent relict reworked material originally formed in the yellow sea and tsushima strait during the last glacial stage and subsequent transgression

late quaternary inner shelf deposits in response to late pleistocene holocene sea level changes nakdong river se korea abstract the high resolution seismic profiles from the inner shelf off the nakdong river in se korea can be directly correlated with the lithologic characteristics in the borehole data these correlations offer an opportunity to document the evolution of the inner shelf deposits with sediment supplies in response to the late quaternary sea level changes the inner shelf sequence in this area consists of four sedimentary units which comprise a set of lowstand transgressive and highstand systems tracts deposited since the last glacial maximum incised channel fill su1 estuary su2 sand veneer su3 and subaqueous delta su4 the lowermost unit su1 which overlies the sequence boundary is interpreted as fluvial deposits formed during the last glacial period and the early stage of transgression and belongs to the lowstand to transgressive systems tract the lower middle unit su2 lying below the ravinement surface represents a paralic component that consists of estuarine sandy mud or muddy sand developed between approximately 13 and 8 cal ka bp whereas the upper middle unit su3 above the ravinement surface corresponds to a marine component that consists of sand veneer produced by the shelf erosion during the ensuing sea level rise these two units su2 and su3 belong to the transgressive deposits the uppermost unit su4 regarded as the highstand systems tract formed the nakdong subaqueous delta including the proximal and distal systems developed after the highstand sea level at approximately 6 cal ka bp the lateral transition from the proximal to distal facies suggests a prograding delta system in the nakdong river

compositions of aqueous fluids in equilibrium with pyroxenes and olivines at mantle pressures and temperatures solubility experiments were performed at 30 kbars in the system mg2sio4 sio2 h2o and at 20 and 30 kbars on omphacitic pyroxene water mixtures they confirm that the solubility of the forsterite component in aqueous fluids remains rather low up to 5 wt whereas the solubility of the sio2 component from solids of appropriate sio2 rich compositions in the system mg2sio4 sio2 h2o increases with temperature up to some 75 at 1 100 c at this temperature a simplified harzburgite consisting of forsterite and enstatite coexists with a fluid containing about 35 mgo sio2 hydrous fluids coexisting with omphacitic clinopyroxenes leach sodium silicate component from the solid leaving less jadeitic pyroxenes behind most interestingly the amount of sodium leached at constant temperature increases with decreasing pressure comparison of the results with previous solubility studies in the system k2o mgo al2o3 sio2 h2o indicates that hydrous fluids in the mantle must be alkaline rather than silicanormative alkali metasomatism caused by such fluids would lead to potassium enrichment in deeper portions of the upper mantle and to sodium enrichment at shallower levels where amphiboles become stable this k na fractionation in the upper mantle may explain the generation of k rich or of na rich magmas through partial melting at different depths

a buried palaeosol and late pleistocene unconformity in coastal deposits of the eastern yellow sea east asia abstract deep drill core sampling with a high resolution seismic survey was carried out to identify a holocene late pleistocene boundary in the eastern coast of the yellow sea east asia analysis of core sections revealed the existence of an oxidized and desiccated sedimentary layer lying directly below a holocene horizon unit i and being developed at the top of a late pleistocene unit ii possibly last interglacial tidal deposit the buried oxidized sedimentary layer is characterized by semi consolidated yellowish sediments showing signs of desiccation and alteration such as periglacial cryogenic structures lithified trace fossils depletion of smectite and high geochemical weathering index ba sr ratio these features together with radiocarbon ages suggests that the layer defined as a palaeosol developed in marine sediments has formed as a result of prolonged subaerial exposure of unit ii sediments during the wisconsinan sea level lowstand producing a regional unconformity late pleistocene unconformity this unconformable bounding surface corresponds to a prominent near surface reflector r which is observed in seismic profiles obtained across the drilled core sections and further is traced ubiquitously across the yellow sea shelf consequently the buried palaeosol layer associated with the seismic reflector presents a key horizon for the understanding of late quaternary environmental changes and integrated stratigraphical correlation in the east asian marginal seas

supercritical fluids at subduction zones evidence formation condition and physicochemical properties abstract there is a general consensus that at subduction zones mass transfer from the subducted slab to the overlying mantle wedge is mediated by a hydrous mobile phase however it is under intense debate whether this phase is an aqueous fluid hydrous silicate melt or supercritical fluid with intermediate composition h 2 o concentration in the range of 30 wt 70 wt supercritical fluids with fluid like viscosity and melt like wetting and element carrying capability are an ideal agent for chemical transport at subduction zones after clarifying the phase relations of silicate h 2 o systems and the definition of supercritical fluids this contribution reviews existing evidence for the presence of supercritical fluids at subduction zones mostly from experimental investigation of phase relations of mineral h 2 o and rock h 2 o systems and the atomic structure and physicochemical properties of supercritical fluids h 2 o rich multi phase solid inclusions from continental subduction zones once their bulk water contents can be confirmed may provide a direct record of supercritical fluids experimental results generally indicate that supercritical fluids can derive from the slab at 160 km depth but there is still significant discrepancy between different studies on h 2 o saturated solidus fluid melt critical curve and the second critical end point scep some novel experimental methods are proposed to resolve the controversies over the formation condition of supercritical fluids the special physicochemical properties of supercritical fluids arise fundamentally from their intermediate composition and intermediate degree of polymerization that are distinctive from aqueous fluids or silicate melts probing the structure and properties of supercritical fluids which are required for understanding of their petrological and chemical behavior and geophysical characteristics relies mainly on in situ spectroscopy but first principles molecular dynamics is becoming a potentially powerful alternative approach

physical property characterization of quaternary sediments in the vicinity of the paleo seomjin river of the continental shelf of the south sea korea abstract thirty two core samples were collected from the continental shelf area of the south sea korea they have been used to characterize physical properties in relation to sedimentary units interpreted from seismic and core data and to interpret physical property variation as a function of burial depth the physical property data were readily classified into sedimentary units units s1 s2 s3 s4 and s5 in descending order the variations in physical properties reflect well the relative characteristics of sedimentary units equivalent to seismic units moreover the relationships between physical properties are well grouped by each sedimentary unit in addition the distributions of physical properties match well with the grain size distribution and bathymetry of the study area in particular the lithology e g grain size plays an important role in the variation of physical properties these results suggest that the physical properties of these sediments are mainly controlled by depositional processes in the vicinity of the paleo seomjin river and that sea level change specifically was a dominant sedimentary processes in the study area during the quaternary in particular the physical properties of unit s2 do not show transitional characteristics between units s1 and s3 although it belongs to the transition zone in sequence order this finding is attributed to the fact that compared with the sediments of units s1 and s3 unit s2 is composed of more coarse grained sediments with abundant shell fragments

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

the capacity of hydrous fluids to transport and fractionate incompatible elements and metals within the earth s mantle both silicate melts and aqueous fluids are thought to play critical roles in the chemical differentiation of the earth s crust and mantle yet their relative effects are poorly constrained we have addressed this issue by measuring partition coefficients for 50 trace and minor elements in experimentally produced aqueous fluids coexisting basanite melts and peridotite minerals the experiments were conducted at 1 0 4 0 gpa and 950 1200 c in single capsules containing either 40 or 50 wt h2o and trace element enriched basanite glass this allowed run products to be easily identified and analyzed by a combination of electron microprobe and lam icp ms fluid and melt compositions were reconstructed from mass balances and published solubility data for h2o in silicate melts relative to the basanite melt the solutes from h2o fluids are enriched in sio2 alkalis ba and pb but depleted in feo mgo cao and ree with increasing pressure the mutual solubility of fluids and melts increases rapidly with complete miscibility between h2o and basanitic melts occurring between 3 0 and 4 0 gpa at 1100 c although lree are favored over hree in the fluid phase they are less soluble than the hfse nb ta zr hf and ti thus the relative depletions of hfse that are characteristic of arc magmas must be due to a residual phase that concentrates hfse e g rutile otherwise h2o fluids have the capacity to impart many of the geochemical characteristics that distinguish some rocks and melts from the deep mantle lithosphere e g marid and lamproites

fluvial sedimentation in the lower carboniferous of clew bay county mayo ireland abstract a succession of about 300 m of fluvial sediments from the lower carboniferous of northwest ireland is described and interpreted a lower mainly red formation contains fluvial channel deposits dominated by flat laminated sandstone these are separated by interbedded sandstones and mudrocks with local caliche horizons and abundant mudcracks interpreted as levee and flood basin deposits an upper mainly non red formation contains fluvial channel deposits with common trough cross stratification and epsilon cross stratification also separated by interbedded sandstones and mudrocks evidence of desiccation is less common in the uppermost beds which pass transitionally upwards into marine sediments the change in fluvial channel style is interpreted as due to increasing sinuosity and permanence of flow which may have been partly temporally and partly spatially controlled the predominance of coarse sediments is thought to be largely controlled by limited subsidence the lower carboniferous transgression was the major overall control of alluviation

gamagyang bay southern coast of korea sedimentation on a tide dominated rocky embayment abstract layered up to 30 m thick sediment sequences overlie acoustic basement of cretaceous tuffs in the gamagyang bay a shallow post glacial embayment of approximately 150 km 2 in area on the southern coast of the korean peninsula sediments consisting mainly of terrigenous and bioturbated mud tend to accumulate at a rate of more than 134 cm 1000 yrs more in the central part of the bay than on the margins sedimentation has been influenced dominantly by strong tidal currents up to 2 5 knots resulting in numerous depressions or moats in the vicinity of islands and points the sedimentary sequences of the moats are either depositional or depositional erosional in origin acoustic basement lies deeper in the central axis of the bay following the buried paleovalleys here the thick sediments contain probable gas encountered on uniboom records characterized by the impedance of acoustic penetration the existence of mid reflectors above the acoustic basement suggests that the gamagyang bay was subaerially exposed during the last glacial period prior to about 4500 yrs b p

paleo tsushima water and its effect on surface water properties in the east sea during the last glacial maximum revisited abstract the semi enclosed deep marginal east sea is known by limited sill flow and low sea surface salinity during the last glacial maximum lgm when sea level was about 130 m lower than the present level although three straits the tsugaru the soya and the tartar with shallower than 130 m sills were completely closed the korea strait with a maximum sill depth of 140 m seems to have persisted as a partial connection to the east sea allowing a sill flow the volume transport at the korea strait during the lgm is estimated at approximately 0 3 1 1 1012 m3 yr by using bathymetry seismic reflection profiles and current data the low sea surface salinity has been explained by the east china sea coast water ecscw and high precipitation however the existing geological observations indicate that precipitation was reduced in the glacial east sea the high resolution numerical simulation results predict that evaporation 2 16 mm day exceeded precipitation 1 43 mm day further suggesting net evaporation evaporation minus precipitation rates 0 2 1012 m3 yr over the lgm east sea this signifies that the precipitation was not the factor lowering surface paleosalinity and that the paleo tsushima water carried a huge amount of freshwater from the ecscw than previously expected the calculated surplus evaporation 0 2 1012 m3 yr and sill flow 0 3 1 1 1012 m3 yr are not identical but they could be oceanographically considered as similar the comparison between both values implies that most of the throughflow ultimately escaped the east sea through the evaporation process during the lgm the regional sea level in the almost isolated east sea might be largely maintained by a rough balance between incoming throughflow and outgoing evaporation during the lgm the geographic restriction due to lowered sea level and lower surface salinity by limited vertical mixing in the glacial east sea are analogous to modern oceanographic features in the black sea

evolution of late quaternary deposits on the inner shelf of the south sea of korea abstract high resolution 3 5 khz seismic profiles and sediment samples were analysed to delineate the shallow seismic stratigraphy of late quaternary deposits in the central part of the korean south sea the stratigraphy above the acoustic basement is represented by three distinct sedimentary sequences separated by erosional boundaries the upper sequence a has an acoustically semi transparent signature usually without distinct internal reflectors and overlies the flat lying mid reflector r the sediments in this sequence consist of bioturbated terrigenous mud derived mainly from the seomijin river they have developed during the last 5000 yrs and have an accumulate rate of 10 40 cm 100 yrs reflector r represents the postglacial transgressive layer formed during the last stage of the holocene sea level rise approximately between 7000 yrs b p and 5000 yrs b p the middle sedimentary sequence b below r shows parallel to subparallel internal reflectors and prograding clinoforms that have formed largely during the last glacial period the top of this sequence displays various erosional channels and transparent fills produced by subaerial and fluvial erosion of the pre existing shelf the submerged channels indicate the existence of a paleochannel system presumambly the extension of the paleo seomijin river during the sea level lowstand the lower sequence c has an irregular erosional upper surface and an acoustically transparent subbottom it is interpreted as the erosional remnants of earlier pleistocene sediments formed in shallow water environments

late quaternary lowstand wedges on the shelf margin and trough region of the korea strait abstract high resolution sparker profiles collected from the korea strait reveal a distinct pattern of stacked progradational sedimentary wedges on the shelf margin and trough region these sedimentary wedges comprise a succession of three distinct units a lower b middle c upper unit bounded by erosional unconformities and their internal structures show well stratified complex sigmoid oblique types the isopach map shows that the wedges thicken seaward and their landward limit is in about 100 120 m water depth according to the internal structure distribution pattern and radiocarbon dates these sedimentary wedges are interpreted to have been formed during the glacioeustatic sea level lowstands multiple falls of sea level during the late quaternary coupled with high sediment discharge from the paleo nakdong river system resulted in the formation of thick lowstand wedges three intervals of wedge building are recorded the youngest one unit c is interpreted to mark the last glacial period while the middle one unit b represents the lowstand period before the last interstadial

development of a lake in a subsiding basin in front of a saalian ice sheet kleszczow graben central poland abstract relative movements of the substratum in a still active graben in central poland in combination with the n s advance of pleistocene ice masses largely determined the sedimentary conditions in front of the ice sheet during one of the saalian glacial phases the vertical successions and lateral facies transitions that formed under these extreme conditions which may include a forebulge of the ice in the ice front parallel graben show an order that can be logically explained by facies shifts four lithofacies associations with a total of eleven lithofacies have been distinguished they represent a transition from a glaciofluvial to a glaciolacustrine sedimentary environment with an extraglacial anastomosing river a partly submerged alluvial fan a lake both the margin and the central part and a delta slope the completeness of this sequence is probably due to continuous subsidence in the graben area the only interruption of the logical sequence is by a homogeneous mud layer which is explained as a result of reworking of a large volume of lacustrine mud possibly as a result of slope instability but more probably triggered by an earthquake during graben activity