late cretaceous volcanic rocks and associated granites in gyeongsang basin se korea their chronological ages and tectonic implications for cratonic destruction of the north china craton abstract the gyeongsang basin is the largest exclusively non marine sedimentary basin in korean peninsula located in southeastern part of the peninsula its sedimentary setting magma source tectonic nature and formation age are important to understand the mesozoic tectonic evolution of not only the sino korea craton but also the entire northeast asia the gyeongsang supergroup the basin fill is divided into the sindong hayang and yucheon groups in ascending order the sindong and hayang groups are composed of sandstone shale minor amounts of conglomerate and marl deposited in a non marine environment whereas the yucheon group is characterized by the dominance of volcanic rocks precise isotopic ages and geochemical analyses are scarce for the volcanic elements of this basin restricting our understanding of its geodynamic setting and evolution in this study we present new u pb zircon ages from the volcanic rocks of the yucheon group and associated granites in the gyeongsang basin thirteen volcanic samples yielded ages ranging from 94 4 to 78 4 ma and four granite samples give ages 72 ma these data confirm that a major magmatic event occurred during late cretaceous and the gyeongsang volcano sedimentary complex represents a rock association representing a late cretaceous island arc in comparison with the sambagawa metamorphic belt the jurassic chichibu accretionary complex ac with cretaceous strike slip basin sediments and the cretaceous shimanto melange zone in southwest japan it is likely that above motioned complexes constitute the trace of a continuous subduction related island arc system in se korea extending from sw japan although the peak ages of the magmatic rocks in the eastern part of the north china craton ncc are 130 10 ma indicating an important time of continental lithospheric thinning under the ncc the ages of the gyeongsang magmatic rocks are markedly younger late cretaceous magmatism was very weak in the eastern ncc therefore it is probable that early middle mesozoic lithospheric thinning beneath the eastern ncc is triggered by multiple tectonic factors not only by the subduction of the pacific plate suggested by some previous studies in addition 20 inherited xenocrystic zircons from these volcanic rocks give archean ages ranging from 2 5 to 2 6 ga suggesting the existence of late archean rocks in the yeongnam massif the yeongnam massif is predominated by the latest archean crustal growth at 2 50 ga consistent with the characteristics of the north china craton

an oceanic current against the wind how does taiwan island steer warm water into the east china sea abstract along the taiwan strait 100 m in depth a northeastward flow persists in all seasons despite the annually averaged wind stress that is strongly southwestward the forcing mechanism of this countercurrent is examined by using a simple ocean model the results from a suite of experiments demonstrate that it is the kuroshio that plays the deciding role for setting the flow direction along the taiwan strait the momentum balance along the strait is mainly between the wind stress friction and pressure gradient since both wind stress and friction act against the northward flow it is most likely the pressure gradient that forces the northward flow as noted in some previous studies what remains unknown is why there is a considerable pressure difference between the southern and northern strait the kuroshio flows along the east coast of taiwan and thus the western boundary current layer dynamics applies there integrating the momentum equation along taiwan s east coast shows that there must be a

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

spatial variability and the controlling mechanisms of surface sediments from nam co central tibetan plateau china abstract sixty six surface sediments were retrieved from nam co central tibetan plateau to evaluate the spatial variability of their distributions and controls across the entire lake grain size distribution total carbon total nitrogen total sulfur 210 pb and 137 cs activities and carbon and oxygen isotopes of carbonate of the bulk sediments were analyzed and the correlations among these variables as well as water depth were calculated the results showed distinct spatial variability for all variables the grain size distribution provides adequate information to reflect water energy levels within the lake based on these factors the accumulation zone of nam co was distinguished from the erosional and transportation zones the results indicate that the deep area 80 m of the central main basin and the centre of the eastern small basin serve as the accumulation zones in nam co water depth is the most important factor influencing the distribution of the surface sediments because all variables show different distribution patterns in shallow and deep areas additionally river input sediment focusing grain size effects and heterogeneous physicochemical features of the lake water as well as possible currents within the lake also play different roles that affect surface sediment characteristics water depth noticeably affects grain size and the 13 c and 18 o values of carbonate sediment implying that these proxies could be used as indicators of lake level change these findings are of significance for palaeoenvironmental interpretations when using these proxies

u pb ages of detrital zircons in lower cretaceous non marine successions of the gyeongsang basin northeast asia implications for sediment provenance abstract the cretaceous gyeongsang basin is the largest non marine mesozoic sedimentary basin of the korean peninsula the lower cretaceous successions of the gyeongsang basin are coevally correlated to those of the cretaceous gunsan basin in the yellow sea which is located far to the west of the gyeongsang basin this study presents u pb ages of detrital zircons to evaluate the sediment provenances of the gyeongsang basin the detrital zircon ages clearly show the different distributions between the northern uiseong area and southern jinju area areas of the gyeongsang basin the detrital zircons of the northern area have an age cluster in the jurassic or triassic whereas the detrital zircons of the southern area show a wide range of ages from early cretaceous to neoarchean in the gunsan basin detrital zircons from a core also yield ages ranging from early cretaceous to neoarchean the age distribution from the gunsan basin is similar to those of the southern gyeongsang basin except for the absence of jurassic detrital zircons the petrographic modal analysis of sandstones in the gyeongsang basin suggests a mixed provenance this study indicates that possible sediment provenances of the gyeongsang basin were shared with those of the gunsan basin we suggest that the sediment provenance of the northern gyeongsang basin was adjacent basement highs whereas sediments to the southern gyeongsang basin were probably derived from relatively distant source areas that possibly were located in the vicinity of the gunsan basin during the early cretaceous ca 113 ma

fate and distribution in sediments of carbon 14 added to canadian shield lakes of differing trophic state c was added to three lake basins of differing trophic state at the experimental lakes area in northwestern ontario in 1976 and 1978 to study primary production and gas exchange with the atmosphere this study was conducted to determine the long term fate of 14c and to use its observed distribution in sediments to evaluate the predictions of the mud depositional boundary depth mdbd model the eutrophic north basin of lake 226 initially retained 29 of the added 14c although mineralization reduced this to 20 within 2 yr sediment focusing redistributed 14c within the basin for 2 7 yr following the addition after 11 yr lake 226n retained 18 of the original 14c with 13 of that remaining in erosional areas of sediment and 87 in transitional or depositional areas although the mesotrophic south basin of lake 226 and oligotrophic lake 224 retained less each 7 of the initial 14c additions its distribution was similar to that in lake 226n the mdbd model which describes sediment sites as erosional transitional or depo sitional based on site exposure water depth and sediment slope correctly classifies the sediments of these lakes

diagenesis of the lower cretaceous kanmon group sandstones sw japan abstract the kanmon group lower cretaceous is a non marine sequence in the inner zone of southwest japan and is divided into the lower wakino lacustrine and the upper shimonoseki fluvial subgroups major diagenetic changes in this group are compaction iron oxide cementation calcite cementation and grain replacement quartz overgrowth and pore fill cementation illite authigenesis chlorite pore fill cementation and grain replacement albitization of feldspar and grain replacement by pyrite two subgroups of the kanmon group present no significant differences in general diagenetic features paragenetic sequence or the degree of diagenetic changes despite differences in depositional environments lacustrine vs fluvial and stratigraphic positions however some differences are recognized in the content and chemistry of authigenic minerals caused by different sandstone framework compositions the content of authigenic clay minerals is higher in sandstones of the shimonoseki subgroup containing abundant volcanic rock fragments in addition the composition of chlorite the most abundant authigenic clay mineral in kanmon sandstones is mg rich in the volcanoclastic shimonoseki sandstones compared to an fe rich variety in wakino sandstones the original sandstone composition played a significant role in pore water composition and diagenetic reactions the wakino sandstones lost most of its porosity by compaction whereas shimonoseki sandstones are only compacted in the vicinity of the basin bounding fault the weakly compacted shimonoseki sandstones instead were largely cemented by pore filling calcite during early diagenesis cementation prevented compaction during further burial the kanmon group sediments were heated to about 300 c based on illite crystallinity values

the influence of lake morphometry on sediment focusing sediment focusing is a process whereby water turbulence moves sedimented material from shallower to deeper zones of a lake sediment focusing occurs in lakes in both the erosional coarse grained sediments and the transportational zone with the latter characterized by discontinuous sedimentation and resuspension the zone of accumulation is diefined as the zone where sedimentation is final i e no resuspension and where there is no further sediment focusing a geochemical tracer pb was used to trace sediment focusing patterns in 12 lakes of different morphomctries the area occupied by the zone of accumulation is predicted from the mean basin slope a with 86 of the variance explained only in large exposed lakes in which turbulence from waves is more severe are the resulting sediment distributions more erratic this study is the first to provide a general model of sc diment focusing patterns among lakes the study of lake bottom dynamics has received attention in the contexts of sediment contaminant and eutrophication studies the fact that sediments are major depositories for contaminants and nutrients has made them a focus for research in limnology also because sediments provide a record of past events in lakes an understanding of the manner in whllch sediments accumulate is essential for hindcasting interpretations of the historical record in sediments will be confounded if the record has been obscured by sediment resuspension the term sediment focusing was coined by likens and davis 1975 to describe the resuspension of sediments in shallower zones by waves and water currents with subsequent transport to and settling in the deeper zones of lakes much of the work

holocene climatic events linked to environmental changes at lake komořany basin czech republic former lake komo any located in northwest bohemia in central europe provides multiple proxies pollen plant macrofossils diatoms chironomids and sediment chemistry that allowed reconstruction of the development of its aquatic environment and catchment throughout the holocene in order to reconstruct the climatic forcing of this development we performed a pollen based reconstruction of climate changes using the best modern analogue method the climate reconstruction was successful for the interval of 10 0 3 2 ka bp we demonstrate that shifts in climate were coupled with biotic changes within the lacustrine environment both processes were interconnected mainly through changes in the water level status of the lake the most significant climatic and environmental changes were recorded at 9 1 6 3 4 8 4 7 3 8 and 3 5 ka bp

modal composition and detrital clinopyroxene geochemistry of lithic sandstones from the new england fold belt east australia a paleozoic forearc terrane the new england fold belt of southeast australia is divided by the peel fault system into two time equivalent zones showing contrasting depositional structural and metamorphic histories these are inferred to represent a western magmatic arc frontal arc succession and an eastern subduction complex assemblage the composition of the early to middle paleozoic clastic rocks from both east and west of the peel fault system indicates derivation from an undissected volcanic arc detrital quartz is absent or present only in minor amounts and always as monocrystalline grains lithic fragments are almost exclusively volcanic and normally dominant over feldspar which is invariably plagioclase now largely albitized to the west of the fault the distribution of lathwork microlitic felsitic and vitric rock fragments as well as variation in the amount of detrital quartz indicates changes in provenance through time and two cycles of basaltic to silicic volcanic activity have been identified the composition of detrital calcic clinopyroxene grains particularly their low ti and al contents and their ti mn na ratios indicates that they crystallized mainly from subalkaline probably calc alkaline volcanic arc magmas the dominantly volcanogenic provenance of sandstone from east of the fault and the low ti content of most detrital clinopyroxene grains indicate that the volcanic chain that lay to the west of the peel fault was the most likely source for the major portion of the clastic debris in the eastern rocks however the presence of ti rich detrital clinopyroxenes identical in composition to those in the metabasalts of the subduction complex indicates that uplifted segments of the complex provided an additional sediment source

gregarious behaviour among non avian theropods inferred from trackways a case study from the cretaceous cenomanian candeleros formation of patagonia argentina abstract gregarious behaviour among dinosaurs has been inferred from several lines of evidence monospecific bonebeds skeletal morphology phylogenetic inferences comparison with modern ecosystems and parallel trackways with particular characteristics but is relatively poorly documented for non avian theropods here we report five parallel theropod trackways of large track size average length of 28 cm in the cretaceous cenomanian candeleros formation from northwestern patagonia argentina the tracks are provisionally assigned to aff asianopodus pulvinicalx and considering the autopod morphology of the theropod taxa documented in the candeleros formation abelisaurid theropods are suggested as trackmakers the trackways possess similar stride speed estimation direction and preservational features and track show uniform depth and do not overlap physical barriers i e large fluvial channels or perennial lake that could influence the direction of the theropod trackmaker gaits were not recognized in the section taking into account these considerations a gregarious behaviour for the abelisaurid theropod trackmakers is proposed the tracks are preserved as shallow undertracks in a medium grained sandstone bed deposited in a floodplain setting the tracking surface is interpreted as the overlaying layer of muddy siltstone the occurrence of swelling clays and microbial mats in the track bearing level could have contributed to the substrate stabilization and their role in the preservation is discussed

feldspar albitization in cretaceous non marine mudrocks gyeongsang basin korea plagioclases and k feldspars in the sandstones and mudrocks of the cretaceous non marine gyeongsang basin korea were partially to completely albitized the preservation of fresh plagioclase grains in early micrite cemented sandstones suggests the diagenetic origin of albite albitization textures in mudrocks were examined using backscattered electron images in contrast to completely albitized plagioclase grains in sandstones those in mudrocks are mostly partially albitized it suggests that mudrocks can be more useful for a provenance study than sandstones by preserving detrital minerals better k feldspar is unaltered to partially albitized in both sandstones and mudrocks in mudrocks albitization starts preferentially along microfractures cleavages and grain margins albitization along grain margins seems to be a characteristic feature in mudrocks where development of microfractures in silt sized feldspar grains by physical compaction is limited by clayey matrix as well as by overpressure the extent of albitization in mudrocks is mainly controlled by composition of the detrital plagioclase mudrocks containing calcic plagioclase grains tend to be more extensively albitized than those containing sodic varieties

observed wintertime tidal and subtidal currents over the continental shelf in the northern south china sea synthesis analyses were performed to examine characteristics of tidal and subtidal currents at eight mooring sites deployed over the northern south china sea nscs continental shelf in the 2006 2007 and 2009 2010 winters rotary spectra and harmonic analysis results showed that observed tidal currents in the nscs were dominated by baroclinic diurnal tides with phases varying both vertically and horizontally this feature was supported by the cc fvcom results which demonstrated that the diurnal tidal flow over this shelf was characterized by baroclinic kelvin waves with vertical phase differences varying in different flow zones the northeasterly wind induced southwestward flow prevailed over the nscs shelf during winter with episodic appearances of mesoscale eddies and a bottom intensified buoyancy driven slope water intrusion the moored current records captured a warm core anticyclonic eddy which originated from the southwestern coast of taiwan and propagated southwestward along the slope consistent with a combination of plane and topographic rossby waves the eddy was surface intensified with a swirl speed of 50 cm s and a vertical scale of 400 m in absence of eddies and onshore deep slope water intrusion the observed southwestward flow was highly coherent with the northeasterly wind stress observations did not support the existence of the permanent wintertime south china sea warm current scswc the definition of scswc which was based mainly on thermal wind calculations with assumed level of no motion at the bottom needs to be interpreted with caution since the observed circulation over the nscs shelf in winter included both barotropic and baroclinic components

tectonic and sedimentary evolution of a cretaceous continental arc backarc system in the korean peninsula new view abstract this paper focuses on the tectonic and sedimentary evolution of the cretaceous volcanic rocks and nonmarine successions in the southeastern part of the korean peninsula which constitute an ancient continental arc system the arc system gyeongsang arc system comprising an arc platform gyeongsang volcanic arc and a backarc basin gyeongsang backarc basin was a southwestward extension of the japanese arc formed by oblique northward subduction of the proto pacific izanagi plate under the asian continent the backarc basin was initiated in the southeastern part of the korean peninsula in the early cretaceous as a narrow ns trending trough the basin was bounded by a major fault in the northern part of the basin from which sediments largely emanated sediments were deposited in streamflow dominated alluvial fans adjacent to the fault bounded basin margin in the north and low gradient fluvial systems of braided channels that extended southward and southeastward for tens of kilometers sediments were also derived from the western highland margin draining precambrian to jurassic basement rocks the initially narrow trough progressively expanded toward the east resulting in eastward migration of depocenters that eventually generated a broad fluvio lacustrine plain fringing the volcanic arc platform the arc platform played an important role for the derivation of volcanogenic materials and accreted sediments into the backarc basin via extensive fluvial network pyroclastic density currents and landslides which originated from the arc platform also entered the basin in addition extrusion of basaltic volcanic rocks was continual within the basin during basin expansion the resultant succession of mixed sedimentary and volcanogenic rocks is generally indicative of a temporal increase in volcanic activity in the arc platform and in subsidence rate of the basin in the late cretaceous andesitic to rhyolitic volcanism became climactic in the arc platform producing a number of calderas or volcanotectonic depressions volcaniclastic aprons fringing the arc platform encroached upon the basin fill intraarc basins produced by sinistral shearing of the arc platform received sediments from active volcanoes and footwalls of contemporaneous faults forming small scale streamflow dominated alluvial fans and floodplains with later development of a deep lake overall the gyeongsang arc system formed under an extensional or transtensional sinistral strike slip stress regime suggesting that the subducting and the overriding plates were not strongly coupled both the volcanic arc and the backarc basin ceased to develop as volcanic activities shifted progressively eastward in the paleogene accompanied with rollback of the subduction of the izanagi plate

three dimensional hydrodynamic and sediment transport modeling to test the sediment focusing hypothesis in upland lakes palaeolimnological studies rely on assumptions regarding the distribution and completeness of lake deposits that are not always fully supported by observations in particular the assumption that focusing of suspended sediments leads to preferential deposition in the deepest part of a lake is not always justified especially in upland lakes subject to energetic wind forcing few studies have investigated the hydrodynamic controls on lake sediment focusing especially the importance of wind driven currents in deep water we combine a three dimensional numerical hydrodynamic and suspended sediment model fvcom with a semi empirical wind wave model to investigate the potential mobility of bottom sediments in a small oligotrophic upland lake llyn conwy north wales uk exploratory simulations of wave and current generated bottom stress and suspended sediment dynamics confirm the expected importance of wave generated bottom stresses in shallower waters 3 m depth around the shore field survey shows that lake sediments are largely absent from this zone this is consistent with peripheral wave action as a sediment focusing mechanism in deeper water wind driven currents become the dominant contributor to bottom stress strong wind forcing events drive an energetic circulation with peak bottom stresses that intermittently exceed any realistic erosion threshold over a large proportion of the lake at depths far below those at which waves can be effective the spatial distribution of lake sediments and the completeness of the sediment record is thus determined by a complex interaction between wind driven circulation and bathymetry rather than by bathymetry alone although our sediment dynamics simulations are purely exploratory the results are consisted with survey results that show a patchy distribution of deep water accumulation some implications of these results for the selection of sediment coring locations and the interpretation of sediment records are considered

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

sedimentation and evolution of the cretaceous gyeongsang basin southeastern korea the sedimentation and evolutionary history of the gyeongsang basin and their implications for plate tectonics are reviewed based mainly on sedimentological work on the gyeongsang strata and the regional geology of the japanese islands during the cretaceous e asia was characterized by an andean type continental margin formed by subduction of the kula plate and kula pacific ridge the marginal zone was subjected to precursory extensional tectonism of the magmatic arc so that fault bounded continental depressions developed including the proto gyeongsang basin the gyeongsang strata about 9 000 m thick consist in ascending order of the sindong the hayang with volcanic9 stics and volcanic yuchon groups during the sindong period extensional tectonism prevailed a the proto gyeongsang basin was a graben occupied by alluvial fan fluvial plain and lake environments from the margins to the centre of the basin streams flowed from the upthrown lip areas to the centre alluvial fans expanded periodically with rejuvenation of fault activity while the fluvial plaid lake boundary shifted in response to climatic changes during the hayang period the faults were no longer active and consequently the basin extended beyond them probably by back faulting the water level of the lake s at the basin centre fluctuated with changes of the evaporation precipitation ratio during parts of the period the marginal fluvial plain was drained by ephemeral streams which disappeared before reaching the lake s depositing fluvial sequences lacking channel sandstones localized volcanism formed volcanic terrains and supplied pyroclastics this volcanism was climactic during the yuchon period and terminated the sedimentation granitic plutons intruded all the gyeongsang strata at about the end of the cretaceous

kurosegawa zone and its bearing on the development of the japanese islands abstract the kurosegawa zone in southwest japan is a 600 km long serpentinite melange in the chichibu terrains it runs generally e w but is slightly oblique to the subparallel arrangement of the ryoke sanbagawa and chichibu belts of southwest japan a variety of geological units occurs in the kurosegawa zone 1 1 granodiorite gneiss and amphibolite of ca 400 ma 2 2 siluro devonian formations 3 3 upper carboniferous to jurassic formations 4 4 upper jurassic to lower cretaceous formations 5 5 serpentinite and 6 6 low to medium grade metamorphic rocks of various baric types ages 220 320 360 and 420 ma by k ar the most widespread is a high pressure intermediate group of metamorphic rocks serpentinite is emplaced along the faults between and within the constituent units rocks of the kurosegawa zone represent a mature orogenic belt along a continental margin or an island arc its original site as constrained by paleomagnetism was near the equatorial area here 400 ma old paired metamorphism and related magmatism took place the island arc or microcontinent migrated northward to collide with the eurasia plate during late jurassic thus consuming the intervening ocean

plume related sedimentary basins in east asia during the cretaceous abstract many cretaceous sedimentary basins of various sizes occur in east asia which are classified into four geotectonic settings forearc intra arc back arc and intra continental basins among these intra arc and back arc basins are characterized by rifting and pull apart origins and intra continental basins by rifting related to large scale magmatism or plume the pull apart basins in southwest japan are closely related to plate subduction magmatism the continental region rift basins in the early cretaceous however seem to have no direct relation to subduction controlled magmatisms because almost no accretionary prism was developed along the continental margin at that time this means that plume related magmatism played an important role in the eastern part of the asian continent due to return flow effects from the 670 km thermal boundary layer such a plume magmatism explains systematically the origin and development of varieties of rift basins in east asia in cretaceous time

spatial heterogeneity in lipid biomarker distributions in the catchment and sediments of a crater lake in central india the basin scale spatial variability in lipid biomarker proxies in lacustrine sediments which are established tools for studying continental environmental change has rarely been examined it is often implicitly assumed that a lake sediment core provides an average integral of catchment sources here we evaluated the distribution of lipid biomarkers in a modern ecosystem and compared it with the sedimentary record we analyzed lipid biomarkers in terrestrial and aquatic organisms and in lake surface sediments from 17 locations within the saline alkaline lonar crater lake in central india terrestrial vegetation and lake surface sediments were characterized by relatively high average chain length acl index values 29 6 32 8 of leaf wax n alkanes consistent with suggestions that plants in drier and warmer climates produce longer chain alkyl lipids than plants in cooler and humid areas a heterogeneous spatial distribution of acl values in lake surface sediments was found at locations away from the shore the values were highest 31 or more possibly indicating different sources and or transport of terrestrial biomarkers in floating benthic microbial mats and surface sediment n heptadecane carotenoids diploptene phytol and tetrahymanol occurred in large amounts interestingly these biomarkers of a unique bacterial community were found in substantially higher concentrations in nearshore sediment samples we suggest that human influence and subsequent nutrient supply resulted in increased primary productivity leading to an unusually high concentration of tetrahymanol in the nearshore sediments in summary the data showed that substantial heterogeneity existed within the lake but leaf wax n alkanes in a core from the center of the lake represented an integral of catchment conditions however lake level fluctuation may potentially affect aquatic lipid biomarker distributions in lacustrine sediments in addition to source changes

investigating the maximum resolution of µxrf core scanners a 1800 year storminess reconstruction from the outer hebrides scotland uk micro x ray fluorescence xrf core scanning is capable of measuring the elemental composition of lake sediment at sub millimetre resolution but bioturbation and physical mixing may degrade envir

provenance analysis of lower cretaceous sindong group sandstones in the gyeongsang basin korea using integrated petrography quartz sem cathodoluminescence and zircon zr hf analysis the sindong group aptian albian in southeastern korea is a 2 3 km thick fluvio lacustrine sedimentary package deposited in an elongated basin the nakdong trough which was formed by extension in an active continental margin setting the provenance of the sindong group was studied to understand spatial and temporal variation in composition in three different parts of the basin by using integrated data on petrography quartz sem cathodoluminescence cl analysis and zircon zr hf analysis although sindong group sandstones display wide variation in the composition of framework grains they generally have increasing amounts of feldspar and decreasing amounts of quartz up sequence significant amounts of volcanic rock fragments and volcanic quartz are observed in the late stage sediments metamorphic quartz is predominant in all sindong group sandstones indicative of the exposure of metamorphic rocks in the source terrane mostly from precambrian basement and triassic granites the occurrence of significant amounts of plutonic quartz from early stage sediments suggests that jurassic granites were widely exposed in the source terranes in addition the episodic increase in volume of plutonic quartz content in the sequence especially in the northern part of the basin suggests that episodic tectonic activity occurred in the catchment the increasing feldspar content up sequence could support the occurrence of tectonic activity in the catchments the zr hf analysis of detrital zircons revealed that the majority of zircons are of continental crust origin formed in orogenic settings but zircons in the lowest strata in the northern part of the basin were derived largely from anorogenic magmatic rocks of mantle origin our results demonstrate that source terranes for the sindong group have heterogeneous spatial and temporal distribution and were composed mainly of precambrian basement and triassic to jurassic granitic rocks with minor meta sedimentary rocks and syndepositional volcanic rocks the detritus derived from syndepositional volcanic rocks became significant in the late stage of basin filling representing the transition from extensional tectonism to continental arc magmatism the differences in characteristics of quartz sem cl and zircon zr hf ratios in different parts of the basin are best explained by deposition on different alluvial fans and river systems

key factors controlling mesozoic hydrocarbon accumulation in the southern east china sea basin abstract the east china sea basin is located on the southeastern edge of the eurasian plate since the mesozoic era the basin formation and evolution processes have been superimposed with the multi period oceanic subduction of the paleo pacific plate and multi structural systems interacting with the indo australian plate pacific plate and eurasian plate as previous studies have mainly focused on the cenozoic era the basin prototype tectono sedimentary characteristics and key factors controlling hydrocarbon accumulation during the mesozoic era have always been hotspots for research and scientific questions as part of a new horizon for oil and gas exploration in the east china sea basin based on the latest data from seismic drilling and onshore offshore comparison studies in the southern east china sea basin secsb this study explored the key factors controlling the oil and gas generation migration and accumulation and exploration direction of the mesozoic hydrocarbon accumulation by employing onshore offshore comparisons seismic stratigraphy and structural sedimentary evolutionary reconstruction the results showed that three regional unconformities and seven seismic sequences formed during the mesozoic period in the secsb the evolution since the mesozoic era included the formations of a basement by the passive continental margin before the late triassic the late triassic middle jurassic depression of the active continental margin and the cretaceous faulted basins at continental margins it is proposed that 1 the early basal ne trending structural framework controlled the structural pattern of the mesozoic basin and the macro hydrocarbon properties according to which the cretaceous should be dominated by oil and the upper triassic middle jurassic should be dominated by gas 2 two sets of source rocks i e upper triassic lower jurassic mud shale and lower cretaceous mudstone source rocks were deposited which formed the material basis for hydrocarbon accumulation and the source reservoir seal combinations during two stages of basin evolution in the mesozoic era 3 the east china sea basin has experienced at least seven tectonic movements since the mesozoic period including the keelung yushan yandang oujiang yuquan longjing and okinawa trough movements among which the keelung yushan and yandang movements dominated the formation and accumulation of early oil and gas and the adjustment transformation and re establishment of early reservoirs was accomplished by the longjing movement and 4 the minjiang slope and the taipei turning belt are the main petroleum exploration areas in the mesozoic basin in which the cretaceous should be the main target layer in the east of the basin and the upper triassic middle jurassic in the west

provenance of permian sandstones south kitakami terrane northeast japan implications for permian arc evolution abstract the sandstone petrography of the permian sequence of the south kitakami terrane skt suggests the disrupted development of a magmatic arc and subsequent scattering of the arc along the northern margin of the sino korea continent the skt in northeastern japan is a stratigraphic terrane with well developed coherent sequences of silurian to lower cretaceous extent on a pre silurian basement while most of the pre tertiary terranes of the japanese islands are regarded as accretionary in origin the permian deposits of the skt are particularly well developed and unconformably overlie carboniferous strata these permian deposits are overlain by lower triassic sediments and then upper triassic and jurassic sediments with local unconformities the permian system is divided into lower middle and upper permian units on the basis of lithofacies and fusulinid zonation the lower permian is composed of sandstone mudstone and limestone with a basal conglomerate the middle permian unit is subdivided into a lower sequence consisting of massive sandstone and an upper sequence of limestone or mudstone associated with thick conglomerates the upper permian unit is mainly composed of massive mudstone although sandstone and conglomerates are predominant near the top of the unit the provenance of the permian sandstones in the skt was investigated based on the petrography and chemical composition of detrital pyroxene grains the lower permian sandstones can be divided into two petrofacies based on petrographic character quartzose lithic sandstones derived from pre permian rocks and volcanolithic sandstones dominated by andesitic fragments suggestive of a magmatic arc provenance from the upper middle to upper permian the sandstone composition changes upwards from polymictic quartzofeldspathic to feldspathic detritus derived from the pre permian felsic volcanics and from contemporaneous magmatic arc volcanic plutonic rocks are mixed in various proportions and deposited as middle permian sediments the compositional variation within the permian sequence reflects progressive denudation from undissected to dissected magmatic arc the triassic to jurassic sandstones are derived from a continental provenance the permian jurassic sequences overall therefore records the transition of the tectonic setting of the skt from its development as an oceanic magmatic arc in the permian to its accretion with a continental block by the end of the triassic this tectonic history and paleobiogeographic data suggest that the skt may have originated as one of the terranes along the northern margin of the sino korea block

lake morphometry sediment mixing and the selection of sites for fine resolution palaeoecological studies abstract palaeoecologists are increasingly using close interval or continuous sampling of lake sediments to construct fine resolution records of environmental change the degree of temporal resolution sought in these studies is typically decades or years the use of lake sediments for such fine resolution reconstructions assumes that temporal mixing of the sediments is negligible in this paper we examine the physical and biological processes that cause sediment mixing in small lakes we use physical models and empirical data to develop a set of heuristics relating lake depth and area to sediment mixing by slumping waves currents and bioturbation we also develop a heuristic that allows information on lake depth and area to be used to determine if the sediments of a lake will likely be massive or annually laminated in general the degree of sediment mixing likely to occur in a small lake is directly related to the depth and surface area of the lake however each of the agents of mixing has a different critical relationship with lake depth and surface area we present a series of equations and a summarizing figure that based on lake surface area and maximum depth allows the type of thermal stratification polymictic dimictic or meromictic and the degree of sediment mixing present in the lake to be inferred

sedimentation resuspension and chemistry of particles in the northwest atlantic abstract sediment traps were deployed to sample vertical fluxes of particulate matter both immediately above and within the nepheloid layer on the continental slope and rise of the western north atlantic the data from the traps are used to estimate the settling flux of particles and to attempt to distinguish between the primary flux settling material from the upper water column and the resuspended flux settling material that has been resuspended from some region of the sea floor from these data and from measurements of the net nepheloid standing crop of particles estimates of the mean residence time for particles resuspended in the nepheloid layer are on the order of weeks to months from 15 to 500 m above bottom horizontal advection and diffusion are more important than vertical mixing in maintaining the upper portion of the nepheloid layer the estimated flux of al to the north atlantic as atmospheric dust is one to two orders of magnitude less than the primary flux of al measured just above the nepheloid layer yet the range of accumulation rates of al measured on the sea floor with radioisotopes is close to the values we define as the primary flux horizontal transport of al rich particles mostly aluminosilicates must therefore be significant even above the nepheloid layer the size of 80 90 of the particles collected in the traps both above and within the nepheloid layer was less than 63 m the mean size of particles trapped in the nepheloid layer was about 22 m and above the nepheloid layer 11 m the particles were probably in large aggregates when they encountered the traps but identifiable fecal pellets are only a small fraction of the material collected in the traps between 6 and 15 of the primary production of particulate organic carbon in the euphotic zone was collected in floating sediment traps at the 100 m depth indicating that most particulate organic carbon is recycled in the surface water only 2 3 of primary production of organic carbon was collected as primary flux 500 m above the sea floor from an intercomparison of the composition of particles falling rapidly collected in traps falling slowly or not at all collected in water bottles and resting on the sea floor from core tops it was found that elements associated with biogenic matter such as ca sr cu and i were carried preferentially by the rapidly falling particles once these particles reached the sea floor the concentration of those elements was decreased through decomposition respiration or dissolution dissolution appears to be rapid near or on the sea floor because radiolarians diatoms and juvenile foraminifera were rare in core samples even though abundant in all traps the dynamic nature of the nepheloid layer makes it possible for particles to be resuspended many times before they are finally buried enabling sediment to be carried long distances from its origin the recycling of particles near the sea floor may also increase dissolution of siliceous and carbonate matter

the horizontal distribution of major elements and organic matter in the sediment of esthwaite water england abstract a series of samples taken randomly from the surface sediment of esthwaite water were analysed for density dry solids content organic matter n c h carbonate si al fe mg ca na k ti mn and p the data and distribution maps for these determinands are given four main groups emerge the mineral associated measures the organic measures fe and mn ca si and carbonate the distribution of the mineral associated group is shown to be related to erosion accumulation effects fe and mn distributions are dominated by redox effects and the organic group is effected by differential bacterial oxidation in deep and shallow water sediment ca is remobilised from the hypolimnion by the increase in alkalinity in the bottom waters after stratification

playa lake and sheetflood deposits of the upper cretaceous jindong formation korea occurrences and palaeoenvironments abstract lake model of the upper cretaceous jindong formation in korea was established on the basis of sedimentological and palaeobiological records of the playa lake and sheetflood deposits and their palaeoenvironmental implications the playa lake and sheetflood deposits of the jindong formation are characterized by the common presence of traces of vanished evaporites complicated polygonal desiccation cracks and rainprints the pedogenic carbonate development and the preservation of invertebrate traces and dinosaur and bird tracks the traces of vanished evaporites including halite and sulphate evaporite occur as evaporite pseudopmorphs and moulds the occurrence of all of the evaporite minerals as traces suggests that flooding stages persisted much longer than evaporation and desiccation stages invertebrates birds and dinosaurs inhabited the playa lake environment of the upper cretaceous jindong lake the jindong lake formed by the combination of humid source area and arid depositional site due to an orographic effect in fault bounded basin extensive development of the playa lake and sheetflood deposits with evaporite mineral casts and very limited association of shoreline deposits in the jindong formation are characteristic of closed lake and the jindong lake is compared to a lake formed in partly drained closed basin the aggradation of mudflat deposits indicates continued subsidence of the basin and continuation of an underfilled lake basin the jindong lake expanded and stabilized as a playa lake surrounded by dry to saline mudflats and palaeoclimate and subsidence rates changed little throughout the period of the jindong lake development

seasonal controls on sediment transport and deposition in lake ohau south island new zealand implications for a high resolution holocene palaeoclimate reconstruction laminated sediments in lake ohau mackenzie basin new zealand offer a potential high resolution climate record for the past 17 kyr such records are particularly important due to the relative paucity of detailed palaeoclimate data from the southern hemisphere mid latitudes this paper presents outcomes of a study of the sedimentation processes of this temperate lake setting hydrometeorological limnological and sedimentological data were collected over a 14 month period between 2011 and 2013 these data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin wide scale sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy in contrast seasonal change in the lake system controls accumulation of light winter and dark summer laminations at the distal end of the lake resulting in the preservation of varves this study documents the key processes influencing sediment deposition throughout lake ohau and provides fundamental data for generating a high resolution palaeoclimate record from this temperate lake

a palaeoenvironmental assessment of human impact on wood lake okanagan valley british columbia canada abstract to ascertain the extent of recent impacts and to develop realistic goals for water quality improvement a palaeolimnological assessment of human impact on wood lake british columbia canada was initiated in 1992 geochemical and microfossil analyses on a series of short cores provided a detailed record of human impact since european settlement early post settlement sediments consisted of clastic materials rich in mg al fe p and associated metals an abrupt increase in marl deposition occurred about 1940 perhaps in response to diversion of inflowing water for irrigation and or an increase in algal productivity mo analyses provided a record of increasing hypolimnetic anoxia with eutrophication hg concentrations were highest in sediments deposited during the past decade microfossil analyses chironomids diatoms chrysophytes depicted the lake s progressive eutrophication and the disappearance of the profundal bottom fauna water quality improvements have been reported since 1975 but benthic invertebrate communities have recovered only slightly the diatoms may indicate a modest water quality improvement over the last 20 years wood lake was formerly an oligo mesotrophic lake with a well developed profundal fauna appropriate mitigative programmes could substantially improve water quality perhaps allowing re establishment of the natural oligo mesotrophic condition

influence of depth and mixing regime on sedimentation in a small fluctuating tropical soda lake the historical sediment record of lake sonachi kenya was used to study the influence of lake depth and mixing regime on patterns of sedimentation in a small fluctuating tropical soda lake lake sonachi last desiccated completely in the early nineteenth century and has fluctuated between 3 and 18 m lake depth over the past 115 yr a freeze core of offshore sediments describes recent lake history as a succession of meromictic episodes represented by varved or subannually laminated muds and holomictic episodes represented by more coarsely layered muds two interbedded horizons of colloidal amorphous silica dated to a period of rising lake level after a prolonged lowstand were deposited by abiogenic ph driven precipitation from the water column and represent the instantaneous sequestering of an estimated 63 mg liter 21 or possibly 50 of the lake s dissolved silica reservoir changes in offshore sedimentation and inferred bottom dynamics over time indicate that sediment resuspension and focusing in lake sonachi occur mostly during infrequent events of deep circulation between the average mud deposition boundary depth at 2 m and the chemocline depth at 4 5 m wind driven sediment redistribution across the lake floor is important only at lake depths of 3 m dry sediment accumulation has varied between 86 and 620 g m 22 yr 21 over the past 175 yr with no relationship to lake depth but on average lower rates during meromixis 199 6 90 g m 22 yr 21 than during holomixis 349 6 152 gm 22 yr 21 net organic carbon accumulation offshore varied between 0 and 92 g m 22 yr 21 with no significant relationship to either lake depth or mixing regime at the time of deposition sedimentary organic carbon content 5 7 26 9 is negatively correlated with bulk sediment accumulation 73 of this variation is accounted for by the clastic dilution of sedimented planktonic algal production with low organic littoral sediments redeposited offshore

anthropogenic inventories and historical and present accumulation rates of copper in great lakes sediments abstract sediment cores were collected from depositional basins in lakes michigan ontario and superior to assess spatial and temporal variations in cu accumulation rates and inventories sediment chronologies were determined via 210 pb dating and 210 pb inventories were used to correct for the effects of sediment focusing among the lakes studied cu loading histories generally decrease to the present signifying a regional reduction in the anthropogenic release of cu to the environment focusing corrected cu accumulation rates in surficial sediments vary significantly within lakes michigan and ontario suggesting that recent inputs of cu to these 2 lakes may have been dominated by localized sources variations in cu accumulation rates within lake superior are interpreted to be insignificant suggesting either that lake superior is well mixed with respect to copper inputs or that the lake is dominated by a single source for cu recent measurements of atmospheric fluxes of cu within the great lakes region generally indicate that the atmosphere accounts for less than 50 of the cu accumulating in surficial sediments historical cu accumulation rates from lake superior are poorly correlated with cu production associated with local smelters but favorably agree with national production rates trends in historical cu accumulation rates within all 3 lakes may indicate that recent declines in cu loading can be attributed to the enactment of stricter environmental regulations as well as changes in the use of cu focusing corrected cu inventories in lakes michigan ontario and superior are generally invariant within a given lake indicating that historically these lakes have been dominated either by a single source or were well mixed with respect to cu inputs the disparity between the results from recent accumulation rates and historical inventories may reflect differences in how the great lakes respond to contaminant loading on short e g years versus long e g decades timescales

relative importance of dust inputs and aquatic biological production as sources of lake sediments in an oligotrophic lake in a semi arid area the dustfall df and mass sedimentation rate msr in lake alchichica central mexico were studied from june 2006 to june 2008 df ranged between 0 11 0 93 g m 2 d 1 in the warm and rainy season and 0 54 1 21 g m 2 d 1 in the cold and dry season msr varied from 0 52 2 40 g m 2 d 1 in the stratification season to 1 14 5 07 g m 2 d 1 in the circulation season the timing of the highest fluxes of df and msr is most likely a product of several factors coinciding during the cold and dry season a availability of dust sources and the presence of strong winds 7 5 m s 1 in the df case and b the circulation period of the lake and the availability of nutrients in the msr case as expected the df in alchichica was high and similar to that found in other arid and semi arid areas however the msr was higher than that reported for other oligotrophic lakes particles captured in the aerial traps consisted mainly of detrital minerals in contrast particles found in the water traps were mostly biogenic and to a lesser extent detrital minerals the msr was one to seven times higher than the df in spite of the oligotrophic status of lake alchichica the large size of the settled phytoplankton autochthonous waterborne is what leads to the high msr which surpasses the df allochthonous airborne derived from whirlwinds originating in easily eroded terrains that are characteristic of arid semi arid areas our results indicate that caution must be taken in considering that the df amount measured through df collectors located at the lake shore does actually represent the df entering into the lake copyright 2010 john wiley sons ltd

provenance determination of volcaniclastic rocks the nature and tectonic significance of a cambrian conglomerate from the new england fold belt eastern australia abstract the murrawong creek and pipeclay creek formations of the new england fold belt of eastern australia provide one of the few records of middle cambrian early ordovician sedimentation along the eastern gondwana margin they comprise conglomerate sandstone siltstone and laminated argillite that accumulated in an inner submarine fan environment sandstones are quartz poor volcanolithic varieties conglomerate clasts are mainly andesite but range from basalt to rhyolite all these rocks are porphyritic with phenocrysts of feldspar albite after calcic plagioclase augite and uncommonly titanomagnetite the augite is a low tio2 variety and titanomagnetite has only a modest tio2 content alteration has modified the magmatic composition of the clasts but the ess mobile elements indicate they were derived from a low k orogenic suite in consonance with petrographic and mineralogical data a western source and the presence of lower paleozoic subduction complex rocks to the east of the cambrian ordovician units indicates that the latter accumulated in a forearc setting the distributive province may have been the precursor of the macquarie volcanic belt of the eastern lachlan fold belt in n s w or one of the cambrian oceanic island arcs preserved in the fragmented gondwana margin sequences in southeastern australia northern victoria land antarctica and new zealand

reactivation of an old plate interface as a strike slip fault in a slip partitioned system median tectonic line sw japan abstract in models for strain partitioning at obliquely convergent plate boundaries trench parallel slip occurs on a vertical fault trench parallel slip at the nankai subduction zone sw japan is mapped along the median tectonic line mtl which dips approximately 40 n to understand its structural context and how the mtl functions in this slip partitioned system we collected a set of three seismic profiles in the kii peninsula south of osaka using a multi scale acquisition strategy that provides increasingly fine resolution to understand its fault kinematics we analyzed microseismic activity in two locations on the fault using source data from japan s hi net monitoring network structural details suggest that the mtl functioned as a megathrust during subduction of the cretaceous sanbagawa hp metamorphic belt its current pattern of microseismicity shows that it behaves as a strike slip fault with no indication of a vertical fault at or around its surface trace thus trench parallel slip at the nankai is now accommodated on an inclined fault plane in an unusual form of partitioning this system appears to have developed out of a two phase tectonic history in which a thrust structure that formed under initial phase compressive stresses has been reactivated as a strike slip fault under subsequent phase shear stresses its unusual kinematics show that shear failure can occur on an existing non vertical fault plane at a regional scale in preference to the rupture of a new ideal vertical fault plane

horizontal sedimentation differences in a eutrophic swiss lake settling fluxes measured by means of sediment traps were 887 g dry wt m 2 yr i 113 g poc m 2 yr i and 2 6 g pp m 2 yr i in 1982 1983 at a central station in eutrophic lake hallwil switzerland nearshore settling rates were higher by a factor of 1 4 3 4 since particulate organic carbon poc particulate phosphorus pp and biomass concentration in the lake water showed vertical rather than horizontal differences this result was attributed to permanent bottom sediment resuspension and redeposition in the littoral zone horizontal sediment transport sediment focusing and sediment resuspension in the profundal zone in winter when wind and turbulence are increased accounted for only about 20 of the sedimentation rates because 70 80 of the total sedimentation for the year occurred during summer such processes are of minor importance in lake hallwil although a nepheloid layer with increased poc and pp concentrations 5 8 m above the bottom was present it is stressed that the mechanisms of sediment transport must be known to permit interpretation of trap results and to understand lake metabolism

on the dynamics of the south china sea warm current 1 the south china sea warm current scswc flows northeastward over the shelf and continental slope in the northern south china sea scs this current persists in its northeastward direction in all seasons despite the fact that the annually averaged wind stress is decisively southwestward against it two major mechanisms have been proposed in previous studies one attributing it directly to the wind stress forcing within the scs and the other to the kuroshio intrusion through the luzon strait in this study we use a simple model to demonstrate that neither of them is the leading forcing mechanism instead the scswc is a source and sink driven flow induced by the taiwan strait current tsc a year round northward flow through the taiwan strait the two previously suggested mechanisms are important but secondary the model simulations show that the local wind stress alone would force a current in the opposite direction to the scswc blocking the kuroshio intrusion through the luzon strait on the other hand only weakens the scswc the scswc vanishes when the taiwan strait is closed in the model

middle albian climate fluctuation recorded in the carbon isotope composition of terrestrial plant matter abstract this study presents the carbon isotopic record for terrestrial plant matter 13ctpm in the jinju formation gyeongsang basin korea during the middle albian the measured 13ctpm provides continuous high resolution temporal variations for reconstructing climate change during the middle albian which has previously been poorly understood we found that the 13ctpm variation mostly exceeds the isotopic variation of the contemporaneous atmospheric co2 indicating that the variation was primarily governed by climate change rather than atmospheric source the 13ctpm values corrected to modern atmospheric co2 show cyclic fluctuations 27 8 to 23 3 reflecting a temporal variation of water availability and or a related taxonomic turnover of plant communities in the hinterland of jinju lake based on a transfer function for estimating mean annual rainfall mar from the measured 13ctpm values the middle albian climate of the basin was found to vary from sub humid to humid conditions mar 500 1500 mm this variability suggests that albian climate change at middle latitudes occurred more frequently than previously interpreted the temporal increase in aridity observed in the basin 35 38 n has not been detected in the isotopic records of the cretaceous hokkaido section 42 45 n in japan this difference implies the possibility of a periodic northward shift or expansion of the northern hemisphere subtropical high pressure belt

sedimentation controls on the preservation and time resolution of climate proxy records from shallow fluctuating lakes lithological stratigraphies of 210pb dated sediment cores from four hydrologically interconnected fluctuating lake basins in kenya are used to investigate how differences in basin morphometry and physical limnology influence the preservation and time resolution of sedimentary climate proxy records the potential of lakes to accumulate an undisturbed sediment record is primarily determined by their relative depth the ratio between maximum depth and effective wind fetch chemically stratified crater lakes accumulate high quality climate proxy records because they complement great relative depth with topographical wind shelter resistance of density stratification to propagation of wind induced turbulence and absence of bioturbation in anoxic bottom waters the changes in water column circulation and bottom dynamics that accompany lake level fluctuations affect the time resolution of accumulating climate proxy signals and thus the apparent magnitude and frequency of inferred climatic events an episode of low lake level can be both over or underrepresented in the climate proxy record depending on the severity of the drawdown relative to the lake s critical depth of sediment accumulation decade scale hiatuses due to non deposition or erosion at low lake level may be difficult to recognize because mixing of unconsolidated muds deposited before and after the lowstand can obliterate evidence that the record has been truncated regional correlation of climate proxy records must consider both hydrology related differences in the climatic sensitivity of lakes and sedimentation related differences in the integrity of their climate history archives

sedimentation and palaeoenvironment in crater lake barombi mbo cameroon during the last 25 000 years lake barombi mbo is situated in a maar crater of the cameroon volcanic chain sediment cores were recovered with a livingstone corer this paper presents data on core bm6 23 5 m long from a water depth of 110 m the sediments are mainly organic matter rich clays 5 to 10 total organic carbon showing alternating brown and yellowish horizontal laminae on a cm scale the lower part of a couplet basal sublamina is rich in siliciclastic quartz mica grains sponge spicules and documents the deposition of flood detritus the upper unit upper sublamina is composed of grey to bluish clay which becomes green toward the top with frequently yellow layered concretions of siderite it corresponds to quiet conditions with settling of fine clayey particles from suspension the overall recurrence rate of these laminae is about 15 years this frequency is similar to present day large flood events in this intertropical zone from 14 000 to 20 000 yrs bp the sediment accumulation rate was quite low 15 30 g cm 2 10 3 yrs with less abundant precipitation pedogenic clay formed from mica family minerals from 12 000 yrs bp throughout the holocene the rate of accumulation increased 40 g cm 2 10 3 yrs and increasing precipitation favoured the pedogenic formation of kaolinites turbidity currents became less important to the overall sedimentation plankton production remained low documented by organic matter which is more of the exinite than the alginite type siderite concretions occur as early diagenetic products possibly related to alkalinity in anoxic waters at the sediment water interface which limited the formation of fe3 thin ash layers occur between 11 5 and 18 m depth in core bm6 bearing witness to several volcanic events during the late quaternary sediments are disturbed below 21 m with folded laminations and inverse ages these probably result from a slump glide of lower slope sediment but could also signal a possible gas event

cenozoic tectonic evolution of the east china sea shelf basin and its coupling relationships with the pacific plate subduction abstract the east china sea shelf basin is one of the mesozoic cenozoic basins located in the edge of eastern china continent whose formation and evolution are closely related to the subduction of the pacific plate however the underlying correlations between the tectonic evolution of the east china sea shelf basin and the pacific plate subduction 65 ma to present remain poorly understood in this paper the basin is divided into western and eastern depression groups to further study its tectonic evolution in combination with the characteristics of pacific plate subduction this paper performs a coupling analysis of the basin evolution regarding its migration direction and evolution rate the results of balanced section and deformation rate analyses reveal that the east china sea shelf basin experienced different regional activities during the cenozoic which could be summarized as four geologic periods and three tectonic evolution stages in this interpretation it is recognized that tectonic activity occurred in the western depression group and then shifted to depocenters of the eastern group in contrast the pacific plate subducted westwards beneath the eurasian plate over the same geologic time span surprisingly a slightly negative correlation between the intensity of the tectonic deformation of the east china sea shelf basin and the subduction rate of the pacific plate is demonstrated when the subduction rate is no more than 75 mm a however the basin deformation intensity increases with the plate subduction rate after 75 mm a the results of this work have implications for explaining the major role that the subduction of the pacific plate played in the formation and evolution of the eastern china basins

cooling history of the upper cretaceous palgongsan granite gyeongsang basin se korea and its tectonic implication for uplift on the active continental margin abstract apatite and zircon fission track analyses were carried out to reconstruct the cooling and inferred uplift history of the cretaceous palgongsan granite gyeongsang basin korea the palgongsan granite is one of the bulguksa intrusive rocks that formed by arc related plutonism during late cretaceous to early tertiary time fission track dating of the palgongsan granite yielded nearly concordant ages of 53 and 65 ma for apatite and zircon respectively the palgongsan granite also shows a simple cooling pattern which suggests that it has not been affected by any thermal event after emplacement the cooling history derived from fission track data combined with other thermochronometric data indicates that the palgongsan granite experienced relatively rapid cooling in earlier stage 30 c ma the initial rapid cooling rate during the late cretaceous has been caused by the large thermal contrast between the granite body and the country rocks after reaching thermal equilibrium with the surrounding country rocks the cooling rate of the palgongsan granite was abruptly decreased in late stage in this late stage the decelerated cooling rate is interpreted to have been controlled by uplift and erosion processes and the average exhumation rate is calculated to be ca 50 m my over the temperature range from 100 c to the surface temperature the cooling history of the palgongsan granite is in good agreement with that of the ryoke granitic belt in southwest japan as well as those of the taebaeksan range and other bulguksa intrusive rocks in the gyeongsang basin this suggests that such cooling was probably caused by regional uplift and exhumation processes on the east asian active continental margin compared with the uplift rates of the andes the uplift rates on the eastern pacific margin appear to be higher than those on the western pacific margin

effects of calculation procedure and sampling site on trap method estimates of sediment resuspension in a shallow lake resuspension estimates given by two different trap methods in a shallow lake were compared the sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored the methods were label method in which resuspension is estimated by determining the organic fraction of surface sediment suspended seston and trapped material and spim spm method where the relationship between settling particulate inorganic matter spim and total settling particulate matter spm is used during the whole 111 day study period according to the label method at a sheltered station 1949 g m 2 dry weight of sediment was resuspended whereas spim spm gave an estimate of 1815 g m 2 the difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods sensitivity analysis showed that of the two methods the label method was more sensitive to variations in the organic content of trapped material at a wind exposed station the total amounts of resuspended matter given by the label method and by the spim spm method were 4966 g m 2 and 4971 g m 2 respectively due to wind effects escape of trapped material took place which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods of the two methods the spim spm method seems thus more suitable for lakes where bacterial activity is high if cyanobacterial blooms take place the label method is probably more reliable providing that the exposure time of sediment traps is kept adequately short

sedimentation in a deep glacier fed lake lake tekapo new zealand surface sediments cores and seismic reflection profiling delineate sedimentary environments and processes of sedimentation in lake tekapo sedimentation is dominated by the godley river which forms an extensive delta in the northern third of the lake delta growth accounts for 55 of annual sediment deposition in winter sandy muds are deposited at the top of the delta slope where they may move under gravity as a surficial slide oversteepening of the upper slope also generates deep seated failures the entire 20 km2 of delta slope is subjected to rotational slumping which episodically reworks large volumes of sediment down the delta slope sedimentation rates decrease surface sediments get finer and varves become better developed in the lake basin sediments are parallel bedded varves which contain typical winter summer annual cycles as well as minor non annual flood varves annual varve thickness and semi annual varve frequency are determined by variations in the discharge of the godley river sedimentation in the basin accounts for 40 of the budget and sedimentation rates decrease with distance from the delta except at the distal end of the basin where turbid underflows are stopped by the rising lake floor beyond the basin sedimentation rates decrease abruptly coriolis deflection of inflowing river water increases sedimentation rates down the eastern shore the remaining 5 of the sediment is deposited on the lateral slopes and shoulders where sediments form a thin muddy veneer over basement which occasionally slumps to the basin floor

chlorophyll production degradation and sedimentation implications for paleolimnology1 chlorophyll a production degradation and sedimentation were studied simultaneously during summer stratification in three lakes with contrasting plankton communities pigment budgets showed that chlorophyll production and pigment resuspension were both major sources of water column pigments photodegradation rates were rapid and indicated that detritus particles that remained in the epilimnion for periods longer than about 3 days lost nearly all detectable pigments therefore only rapidly sinking detrital particles or those produced in deep layers at low light intensity could make appreciable contributions to sedimentary chlorophyll degradation products pheophorbide a a grazing indicator was the dominant chlorophyll a degradation product found in sediment traps pigment sedimentation increased significantly with mean size of cladocerans and omnivorous copepods in contrast sedimentation rates of chlorophyll degradation products did not increase with primary production in these lakes the deposition of chlorophyll degradation products in sediments depended primarily on the size and biomass of grazers

cenozoic basins in northern taiwan and tectonic implications for the development of the eastern asian continental margin abstract north of taiwan four offshore tertiary basins extend seaward from the inner shelf of the east china sea to the west of the okinawa trough these basins are characterized by rifting features with ne sw trending half grabens and fault blocks episodic rifting events have taken place from paleocene to early miocene with the eastward shift of depositional centers the paleogene rift basins are filled primarily with lacustrine to shallow marine sediments but also contain a slight amount of pyroclastics and basaltic flows regional subsidence has dominated during the late tertiary and these paleogene half grabens have united into a large marginal sea basin overlain by a neogene sedimentary wedge of shallow marine sediments a fifth basin the paleogene hsuehshan half graben trough in present day northern taiwan has been deformed into mountain ranges by the collision of the luzon arc with the eastern asian margin during the late cenozoic era the tectonic development of eastern asian margin in northern taiwan region has evolved into two phases first the eastward retreat of the west pacific subduction zone and accompanied rifting of continental crust occurred during late cretaceous to eocene times second as the intensity of rifting decreased thermal subsidence of eastern asian margin prevailed and subsequently caused a tilting seaward continental margin on which a large marginal sea basin rests collision of the luzon arc with the eastern asian margin in taiwan deformed the paleogene hseuhshan trough into mountain ranges late miocene to present

the effect of typhoon induced rainfall on settling fluxes of particles and organic carbon in yuanyang lake subtropical taiwan abstract a sediment trap monitoring program measured the fluxes of settling particles and organic carbon in yuanyang lake northern taiwan from july 2004 to july 2006 and assessed their relations to the amounts of normal monthly and typhoon event precipitation the flux of settling particles varied from 0 7 mg cm 2 month 1 to 14 7 mg cm 2 month 1 and the monthly precipitation ranged from 56 mm to 1218 mm during the survey period the contributions from typhoon event precipitation to monthly rainfall amounts were generally larger than 70 higher inputs of both particulate and organic carbon into the lake were found during typhoon seasons of the annual settling particle loading of 14 9 tons year 1 to the lake floor 69 occurred during the typhoon months and 62 of the annual organic carbon loading of 2 3 tons year 1 happened during the typhoon months these results show the importance of typhoon events on the fluxes of settling particles and organic carbon and their delivery to lakes

seasonal variability in phosphorus speciation and deposition in a calcareous eutrophic lake abstract settling particulate matter was collected in sediment traps from the major depositional basin of onondaga lake a calcareous eutrophic lake in syracuse new york u s a sediment traps were deployed at three depths from july to november and for a brief period under ice cover in february to investigate both vertical and seasonal variations in sedimentation a sequential chemical extraction fractionation method was applied to the collected material to quantify the following phosphorus p fractions or forms loosely bound p sorbed p caco3 associated p and fe and al bound p extractable biogenic p easily degradable organic p and biogenic inorganic poly phosphates calcium mineral p e g apatite and refractory organic p extractable biogenic p and refractory organic p were strongly correlated suggesting a common autochthonous origin in plankton calcium mineral p appears to be of terrigenous origin a dramatic increase in the loosely bound p content of the particulate matter was observed during fall turnover when dissolved fe2 which had accumulated in the anoxic hypolimnion mixed with the surface waters and oxidized with attendant adsorption of p we estimate that the labile or exchangeable p i e loosely bound and extractable biogenic p forms content of the settling particulates constitutes 50 of the total p influx to the sediments over the period of study the labile p flux over the july november study period was 11 mg p m 2 day 1 and the labile p flux estimated from sediment traps deployed under ice cover was 6 mg p m 2 day 1 from these values the annual average labile p flux to the sediments was estimated to be 9 mg p m 2 day 1 only slightly less than the estimated annual average sediment p release rate of 10 mg p m 2 day 1 this indicates that the sediments are approximately at steady state with respect to current external p loadings to the lake

provenance of the lower cretaceous hayang group gyeongsang basin southeastern korea implications for continental arc volcanism abstract provenance of the lower cretaceous hayang group in the gyeongsang basin korea was investigated using sandstone petrography and the composition of detrital plagioclase and clinopyroxene grains in sandstone and mudrock a magmatic arc tectonic setting is inferred for the source on the basis of sandstone composition detritus derived from granitic gneissic rock and incipient continental arc volcanic rock were mixed in a variable ratio in the hayang sedimentary rocks before deposition of the hayang group the source rock was composed mainly of granitic gneissic rocks this condition persisted in the north the euiseong subbasin during deposition of the lower part of the hayang group in the milyang subbasin the southern part of the gyeongsang basin source area volcanism occurred just before deposition of the hayang group compositions of detrital pyroxene and plagioclase revealed the source volcanic rock to be calc alkaline volcanic arc basaltic andesite to dacite later granitic gneissic rocks as well as volcanic rocks supplied detritus to both subbasins and the source volcanic rocks inferred from plagioclase composition might have been of silicic composition the hayang group was deposited in a transitional setting changing from strike slip movement with little volcanic activity to active subduction related volcanism in the eastern continental margin of asia during this transitional stage the source area was occupied by granitic gneissic rocks and within the source area intermediate to silicic volcanic rocks of dominantly calc alkaline affinity erupted sporadically

two hydrodynamically stable self suspended buoyant sediment traps abstract two self buoyant sediment traps using straight cylindrical sediment collection vessels have been designed and tested the constructions are hydrodynamically stable and the vertical alignment of the sediment collection vessels are retained both in laminar and moderately turbulent water currents with flow rates up to 40 cm s 1 for the nondisplacing and at least up to 45 cm s 1 for the displacing sediment trap type both constructions are simple and easily handled in the field

fossil wood diversity gradient and far east asia palaeoclimatology during the late triassic cretaceous interval abstract mesozoic fossil floras are distributed over eastern asia china mongolia siberia korea and japan according to a regular latitudinal pattern two floras are usually distinguished a northern type and a southern type the distribution of which oscillated during the mesozoic in japan this regular pattern is disrupted by a sharp inflexion of the boundary between the two floras two competing hypotheses have been proposed to explain this disruption one hypothesis advocates later tectonic motion clouding the original pattern while the other hypothesis proposes that a warm oceanic current allowed the southern flora to grow much further north in coastal areas we used fossil wood a biotic component that has not previously been used for a palaeobiogeographical study of the region the observed fossil wood diversity at the generic level does not fit with the hypothesis of a warm oceanic current unless this hypothesis is modified to include alternating warm northbound and cold southbound oceanic currents our results provide new evidence for the palaeoecology of the mesozoic continental biota in far east asia

horizontal and vertical variations in sedimentation and resuspension rates in a stratifying lake effects of internal seiches the temporal and spatial variations in the rate of sedimentation and sediment resuspension in lake rehtijarvi southern finland were studied by sediment traps deployed in the stratifying and non stratifying regions of the lake both the gross sedimentation rate and the resuspension rate recorded by near bottom traps were significantly higher in the stratifying region 20 m depth than in the shallow part of the lake 2 m depth these rate changes were caused by temporarily elevated hypolimnetic resuspension rates exceeding 40 g dry weight m 2 day 1 in july 2005 whereas in the shallow station no such peak was observed and the resuspension rate remained below 30 g dry weight m 2 day 1 throughout the study the elevated resuspension rate in the hypolimnion could not be attributed to surface wave action or sediment disturbance by fish but was due to the occurrence of internal seiches the seiche amplitude was on average the highest in july although the wind velocities were low this was because winds temporarily were blowing along the longitudinal axis of the lake due to the steep slopes the sediments of lake rehtijarvi are prone to redistribution and sediment focusing towards the accumulation areas also affected trap catches in the deep stations

the dominant processes of sediment distribution and focusing in a small eutrophic monomictic lake there is evidence for 10 mechanisms of sediment distribution in small lakes the sediment accumulation rates measured from a common horizon in cores from 64 sites on esthwaite water u k were used to determine the relative importance of these mechanisms on the distribution of sediment in the lake river inflows generally produced localized effects but there were indications of periodic turbidity flows to the deepest point of the lake from the major inflow active sediment focusing processes were the dominant distribution mechanisms a major resuspension of sediment at autumn overturn probably being the most important the remaining variance was much greater than observed in similar work elsewhere suggesting that redistribution of sediment by direct and indirect wave action may be taking placeall over the lakebcd during isothermal periods the relative contributions of the different processes were corroborated by analysis of previously published sediment trap data

effects of historical land use on sediment yield from a lacustrine watershed in central chile sediment yield in the san pedro lake watershed inferred from sedimentation in the lake can be related to land use changes shown on aerial photographs taken during the period 1943 1994 in this watershed which covers 4 5 km2 of mountainous terrain in san pedro county central chile the area of native forest species decreased from 70 per cent in 1943 to 13 per cent in 1994 during this same period the area of pine plantations increased from 4 to 46 per cent to study effects of these changes we took a core from the centre of the lake and estimated sedimentation rates by 210pb dating which we checked with 137cs and pine pollen the results show that sedimentation rate ranged from 5 mg cm 2 a 1 in the late 1800s to 60 mg cm 2 a 1 in the late 1960s these rates together with assumptions about the production and delivery of the sediment give corresponding figures for sediment yields with maximum values close to 1 t ha 1 a 1 sediment yield between 1955 and 1994 closely tracks the total land use change that can be detected irrespective of land use type on sets of aerial photographs taken four to 18 years apart however this measure of land use change while convenient and successful as a predictor of historical erosion may be unreliable because it probably excludes many changes that occurred in long intervals between successive photographs copyright 2001 john wiley sons ltd

multiproxy evidence for terrestrial and aquatic ecosystem responses during the 8 2 ka cold event as recorded at hojby so denmark abstract a sediment succession from hojby so a lake in eastern denmark covering the time period 9400 7400 cal yr bp was studied using high resolution geochemistry magnetic susceptibility pollen macrofossil diatom and algal pigment analysis to investigate responses of the terrestrial and aquatic ecosystems to the 8 2 ka cold event a reduced pollen production by thermophilous deciduous tree taxa in the period c 8250 8000 cal yr bp reveal that the forest ecosystem was affected by low temperatures during the summer and winter early spring seasons this finding is consistent with the timing of the 8 2 ka cold event as registered in the greenland ice cores at hojby so the climate anomaly appears to have started 200 250 yr earlier than the 8 2 ka cold event as the lake proxy data provide strong evidence for a precipitation induced distinct increase in catchment soil erosion beginning around 8500 cal yr bp alteration of the terrestrial environment then resulted in a major aquatic ecosystem change with nutrient enrichment of the lake and enhanced productivity which lasted until c 7900 cal yr bp

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

provenance history of a carboniferous gondwana margin forearc basin new england fold belt eastern australia modal and geochemical constraints abstract the visean stephanian myall trough eastern australia formed part of a forearc basin to the east of a magmatic arc situated along the palaeo pacific margin of gondwana petrographic modal whole rock geochemistry and mineral phase chemistry of sandstones siltstones conglomerates and associated igneous rocks provide a consistent and coherent data set which indicate sediment derivation from a magmatic arc of predominantly silicic volcanic composition the low quartz modes of the sandstones the largely volcanic origin of lithic fragments and the overall high sio 2 content of the siliciclastic sediments and igneous rocks require the arc source to be largely dacitic to rhyolitic in composition the predominance of vitric type highly siliceous volcanic rocks lithic fragments suggests a source composed largely of silicic pyroclastics the presence of potassium feldspar as well as the presence of biotite as the principal detrital ferromagnesian phase in the sandstones suggest a source of medium to high k tholeiite composition the high trace element abundances of relatively immobile elements such as zr la ce v nb y and th and corresponding high th u zr y la y la sm ratios and low zr th zr nb la th and ti zr ratios for both the igneous rocks and derived siliciclastic sediments in the myall trough also require a high k and or strongly medium k arc source a lack of temporal or spatial trends in the data indicate that the magmatic arc remained of uniform composition throughout the 25 ma interval of strata preserved within the trough the provenance history of the myall trough requires accumulation along an andean type continental margin rather than an intra oceanic arc outboard of the gondwana margin

deposition of serpentine bearing conglomerate and its implications for early cretaceous tectonics in northern japan abstract the discovery of serpentinite bearing conglomerate including detrital blue amphibole grains in cretaceous forearc basin sediments in the northern part of japan supports large tectonic movement in the forearc basin during the early cretaceous conglomerate and sandstone are intercalated in the lower cretaceous offshore mudstone sequence and contain serpentinite clasts chromian spinels blue amphiboles and oolitic grains with chromian spinel nuclei the conglomerate and sandstones were deposited as a debris flow consisting of an admixture of siliciclastic terrigenous sediments and calcareous biogenic material with serpentinite derived sediments the sandstones consist of feldspathic lithic arenites and wackes and their composition suggests that most of the terrigenous material was derived from the cretaceous volcanic terrane and the jurassic accretionary complex located to the west of the depositional basin however the serpentinite body correlated with the provenance of the sediments is not distributed in these terranes because the oolitic grains in the matrix of the conglomerate include only angular chromian spinels and serpentine clasts without quartz and feldspar grains most of the serpentinite derived sediments are considered to have been supplied primarily from a serpentinite body exposed along the shallow marine environments near the sedimentary basin therefore the serpentine derived sediments and feldspathic and lithic materials have essentially different sources thus we may infer that the examined sediments are due to large slope failure affecting a relatively wide area of shallow coast involving the place where the serpentine body was emplaced and the place where river fed terrigenous siliciclastic sediments accumulated the stratigraphic range of the serpentinite derived sediments which are sporadically distributed in the cretaceous forearc basin of northern japan suggests that the serpentinite derived material was actively supplied to the forearc basin in albian times recent tectono stratigraphy of the late mesozoic accretionary complex in japan reveals a strike slip movement in the subduction zone around northeastern asia large earthquakes affected by active strike slip motion of the oceanic plate are inferred to be the trigger of tectonic movement such as large slope failure following serpentine intrusion in the forearc region another possibility is that subduction of a large number of seamount on the oceanic plate might also cause a large change in basin morphology bringing about large slope failure

roles of mantle diapir and ductile lower crust on island arc tectonics abstract in order to examine the relationships between surface geological phenomena in island arcs and lower crustal and upper mantle dynamics crustal and upper mantle responses induced by upper mantle density heterogeneities with magnitudes expected from the seismic tomography beneath the northeastern japan arc have been evaluated according to the rheological model with a low viscosity lower crust and low viscosity uppermost mantle low density lower crustal material above mantle diapiric upwelling is mechanically dragged along by asthenospheric shear stresses and then lower crustal material flows from the back arc corner to the fore arc corner the surface subsidence for this process is about 300 m on a geological time scale of 5 50 my and the formation of a sedimentary basin with about the same lateral scale as the mantle diapir can be expected in the area above the mantle diapir stage s the subducted slab in island arc will operate as a barrier to the lateral movement of lower crustal material accumulation of low density lower crustal material may occur at the edge of the overriding plate during this process at a critical stage of the pressure in the mantle wedge of fore arc region high temperature lower crustal material may then be exposed along the tectonic line stage e as the result of discharging lower crustal material along the tectonic line the pressure in the lower crust will be decreased and accelerated subsidence accompanied by volcanism is expected in the sedimentary basin cretaceous geological phenomena in southwest japan may be explained by this physical mechanism its linked surface crustal movement and the flow of lower crustal material a relatively slow deposition in the period of about 140 120 ma observed in the kanmon sedimentary basin may be interpreted as the geological representation of stage s from about 110 ma the kanmon sedimentary basin was supplied with a large quantity of volcanic sediments and simultaneously expanded and suddenly subsided at about the same time low pressure high temperature metamorphism and granitic activity ryoke belt occurred along the areas to the south of the kanmon group it may be possible to interpret these geological phenomena along the median tectonic line mtl as the surface geological events corresponding to stage e it is however stressed that the time and spatial scale for this coupling is determined by the rheological structure of the lower crust and upper mantle and by the scale of mantle diapir

the fire history of danish heathland areas as reflected by pollen and charred particles in lake sediments sediments deposited during the last 5400 years in two danish closed oligotrophic lakes have been analysed for pollen dark coloured hyphae and microscopic charred particles chronologies are provided by numerous radiocarbon datings redundancy analysis is used to develop a model for the relationship between concentrations of sedimentary charred particles and pollen at lake solso the only pollen type which is significantly correlated with charred particles is calluna the model is used to predict charred particle concentrations in the sediments of lake skanso from the calluna concentrations and the predicted values are compared to the observed the results indicate that 1 the source area and the means of transportation for microscopic charred particles and pollen are approximately identical 2 charred particles and pollen may be focused differentially in a lake and 3 high fire intensities triggered heathland expansion and heaths were maintained by fires through millennia

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

flood stratigraphies in lake sediments a review abstract records of the frequency and magnitude of floods are needed on centennial or millennial timescales to place increases in their occurrence and intensity into a longer term context than is available from gauged river flow and historical records recent research has highlighted the potential for lake sediment sequences to act as a relatively untapped archive of high magnitude floods over these longer timescales abyssal lake sediments can record past floods in the form of coarser grained laminations that reflect the capacity for river flows with greater hydrodynamic energy to transport larger particles into the lake this paper presents a framework for investigating flood stratigraphies in lakes by reviewing the conditioning mechanisms in the lake and catchment outlining the key analytical techniques used to recover flood records and highlighting the importance of appropriate field site and methodology selection the processes of sediment movement from watershed to lake bed are complex meaning relationships between measureable sedimentary characteristics and associated river discharge are not always clear stratigraphical palaeoflood records are all affected to some degree by catchment conditioning fluvial connectivity sequencing of high flows delta dynamics as well as within lake processes including river plume dispersal sediment focussing re suspension and trapping efficiency with regard to analytical techniques the potential for direct e g laser granulometry and indirect e g geochemical elemental ratios measurements of particle size to reflect variations in river discharge is confirmed we recommend care when interpreting fine resolution geochemical data acquired via micro scale x ray fluorescence xrf core scanning due to variable down core water and organic matter content altering x ray attenuation we also recommend accounting for changes in sediment supply through time as new or differing sources of sediment release may affect the hydrodynamic relationship between particle size and or geochemistry with stream power where these processes are considered and suitable dating control is obtained discrete historical floods can be identified and characterised using palaeolimnological evidence we outline a protocol for selecting suitable lakes and coring sites that integrates environmental setting sediment transfer processes and depositional mechanisms to act as a rapid reference for future research into lacustrine palaeoflood records we also present an interpretational protocol illustrating the analytical techniques available to palaeoflood researchers to demonstrate their utility we review five case studies of palaeoflood reconstructions from lakes in geographically varied regions these show how lakes of different sizes and geomorphological contexts can produce comprehensive palaeoflood records these were achieved by consistently applying site validated direct and proxy grain size measurements well established chronologies validation of the proxy process interpretation and calibration of the palaeoflood record against instrumental or historical records