pseudotachylytes from corsica fossil earthquakes from a subduction complex subduction zones are the most seismically active tectonic environment on earth here we report fault rock evidence of palaeoearthquakes from a subduction complex pseudotachylyte veins formed by shear heating on faults at seismic strain rates contain dendrites spherulites and acicular minerals characteristic of blueschist facies conditions the veins have been found in both mantle peridotite and gabbro our discovery from corsica opens a new avenue of research towards understanding mechanisms related to subduction zone earthquakes and the conditions at which these are released

sedimentary facies and radiocarbon dates of the nam dinh 1 core from the song hong red river delta vietnam abstract the song hong red river delta which is located on the western coast of the gulf of bac bo gulf of tonkin in the south china sea is characterized by three morphological systems that are clearly distinguished spatially fluvial tidal and wave dominated we obtained a 70 m long core of sediments the nam dinh 1 core from the central part of the delta in 1999 this paper presents the first detailed description of sedimentary facies with high resolution radiocarbon dating for the latest pleistocene holocene sediments of the song hong delta the core sediments were divided into three units on the basis of the sediment facies in ascending order unit 1 fluvial sediments consisting of fining upward gravels to clay unit 2 coarsening upward marine clay to shelly sand and unit 3 coarsening upward marine clay and laminated sand twenty one radiocarbon dates showed that the core succession was deposited after the last glacial maximum lgm the ages were 15 11 cal kyr bp for unit 1 11 9 cal kyr bp for unit 2 and 8 0 cal kyr bp for unit 3 these data indicate that sediments were deposited in transgressive fluvial estuarine to regressive deltaic environments formed in the central delta plain of the song hong after the lgm in response to sea level changes

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

impact of relative sea level and rapid climate changes on the architecture and lithofacies of the holocene rhone subaqueous delta western mediterranean sea abstract the modern rhone delta in the gulf of lions nw mediterranean is a typical wave dominated delta that developed after the stabilization of relative sea level following the last deglacial sea level rise similar to most other deltas worldwide it displays several stacked parasequences and lobes that reflect the complex interaction between accommodation sediment supply and autogenic processes on the architecture of a wave dominated delta the interpretation of a large set of newly acquired very high resolution seismic and sedimentological data well constrained by 14c dates provides a refined three dimensional image of the detailed architecture seismic bounding surfaces sedimentary facies of the rhone subaqueous delta and allows us to propose a scenario for delta evolution during the last deglaciation and holocene the subaqueous delta consists of parasequence like depositional wedges a few metres to 20 30 m in thickness these wedges first back stepped inland toward the nw in response to combined global sea level rise and overall westward oceanic circulation at a time when sediment supply could not keep pace with rapid absolute eustatic sea level rise at the younger dryas preboreal transition more rapid sea level rise led to the formation of a major flooding surface equivalent to a wave ravinement surface after stabilization of global sea level in the mid holocene accommodation became the leading factor in controlling delta architecture an eastward shift of depocentres occurred probably favoured by higher subsidence rate within the thick messinian rhone valley fill the transition between transgressive backstepping geometry and regressive prograding geometry para sequences resulted in creation of a maximum flooding surface mfs that differs from a classical mfs described in the literature it consists of a coarse grained interval incorporating reworked shoreface material within a silty clay matrix this distinct lithofacies results from condensation erosion which appears as an important process even within supply dominated deltaic systems due to avulsion of distributaries the age of the mfs varies along strike between ca 7 8 and 5 6 kyr cal bp in relation to the position of depocentres and climatically controlled sediment supply the last rapid climate change of the holocene the little ice age 1250 1850 ad had a distinct stratigraphic influence on the architecture and lithofacies of the rhone subaqueous delta through the progradation of two deltaic lobes in response to changes in sediment supply linked to rapid climate changes and to anthropic factors the rhone delta evolved from wave dominated to fluvial dominated and then wave dominated again

lake sediment geochemistry reveals 1400 years of evolving extractive metallurgy at cerro de pasco peruvian andes the geochemical record preserved in lake sediments is a potentially powerful tool in archaeometallurgy here sediments from llamacocha a small lake in the central peruvian andes are used to reconstruct a 1400 year legacy of metal extraction from cerro de pasco once the largest silver mine in the world the earliest evidence for anthropogenic lead pb enrichment occurs ca a d 600 and is confi rmed by pb stable isotope ratios that match those of cerro de pasco ores early pb pollution is attributed to precolonial smelting for silver production which relied on galena based fl uxes following colonial control of the mine ca a d 1600 the switch to mercury hg amalgamation for winning silver resulted in atmospheric hg emissions as registered in llamacocha sediments both pb and hg deposition increased through the twentieth century attaining peak values in a d 1968 and 1942 respectively principal components analysis pca identifi es a gradient that differentiates anthropogenic from natural metals within the record confi rming that early smelting led to the volatilization of trace metals associated with local ore mineralogy these results represent the fi rst evidence for a major precolonial mining industry at cerro de pasco provide a chronological framework for evolving extractive technologies and are the fi rst to document widespread hg pollution associated with colonial hg amalgamation 80 w 70 w

mercury deposition through the permo triassic biotic crisis abstract a 6 7 million year record of marine sedimentation through the permo triassic biotic crisis shows notable shifts in mercury concentrations that varied over an order of magnitude 0 002 to 0 116 g g mercury concentrations correlate strongly with total organic carbon showing both parallel increasing and decreasing trends over geologic time scales results suggest that changes in bioproductivity strongly influence mercury sequestration into marine sediment this may provide insight to potential marine response to modern anthropogenic hg loading and supports models that suggest enhanced bioproductivity that due to recent climate has increased hg sequestration over time

deformation microstructures and magnetite texture development in synthetic shear zones abstract we present observations of deformation features in magnetite from synthetic magnetite bearing silicate aggregates deformed between 1000 c and 1200 c in transpressional shear experiments with strains of up to 300 anisotropy of magnetic susceptibility and shape preferred orientation spo analysis were combined with electron backscatter diffraction ebsd to characterize the magnetite deformation fabrics and intragrain microstructures crystallographic preferred orientation cpo in magnetite is very weak in all deformed samples and does not vary as a function of either temperature or shear strain magnetic anisotropy and spo increase strongly with both strain and deformation temperature and indicate that strain partitioning between magnetite and the plagioclase matrix decreases at higher temperatures ebsd orientation mapping of individual magnetite particles revealed substantial dispersions in intragrain orientation analogous to undulose extinction after deformation at 1000 and 1100 c indicating that dislocation creep processes were active in magnetite despite the lack of a well developed cpo geometrical analysis of crystallographic orientation dispersions from grain map data indicates that low angle grain boundary formation in magnetite could have been accommodated by slip on 110 or 100 planes but no evidence for dominant slip on the expected 111 planes was found evidence for activation of multiple slip systems was seen in some magnetite grains and could be partially responsible for the lack of cpo in magnetite these results suggest that at least in polyphase rocks crystallographic textures in magnetite may be inherently weak or slow to develop and cpo alone is not an adequate indicator of magnetite deformation mechanisms these results may aid in the interpretation of deformation textures in other spinel structured phases such as chromite and ringwoodite

holocene delta progradation into an epeiric sea in northeastern australia abstract progradation of the quaternary gilbert river megafan and holocene delta located in the low gradient intracratonic basin and epeiric sea of the gulf of carpentaria australia has been enhanced by the slight fall in sea level during the late holocene the monsoonal floods and channel avulsions on the megafan have controlled the rate of progradation and supply of sediment to the delta front the mixed influence delta can be classified as a tide dominated fluvially influenced and wave affected tfw delta palaeogeographic reconstruction of the gilbert river megafan delta and palaeoshorelines was created through gis analysis of beach and chenier ridges combined with field observations previous cross section data and radiocarbon and thermoluminescence dating progradation rates on the gilbert river delta are about 0 85 to 0 9 m yr in the northern and central parts of the delta and increase to 1 8 m yr in the southern part of the delta sedimentation rates vary from 0 2 to 1 0 mm yr with a total holocene delta volume of about 9 4 109 m3 and a sediment supply rate of 1 mm3 yr the low sediment supply rate is characteristic of most australian river systems but is about two orders of magnitude less than on many of the larger southeast asian deltas the low onshore and offshore accommodation space on the gilbert and mitchell river deltas is a function of the epeiric sea setting of these deltas and hence the thin succession of holocene sediments on these deltas also represent a significant difference from most southeast asian deltas

a hundred year record of industrial and urban development in french alps combining hg accumulation rates and isotope composition in sediment archives from lake luitel this study reconstructs the history of multiple industrial and urban mercury hg emissions recorded in the sediment archive of lake luitel france from ad similar to 1860 to ad 2011 for this purpose we provide a well constrained short lived radionuclides continuous age depth relationship of the sediment sequence mean accumulation rate of 5 18 0 28 mm yr 1 with hg accumulation rates hg ar hg isotopic composition and extensive historical data hg ar were stable around 45 mu g m 2 y 1 from 1860 to wwi and rose to reach their maximum at the end of wwii 250 mu g m 2 y 1 followed by a gradual decreased to reach about 90 mu g m 2 y 1 in the current period normalization to a terrigenous hg proxy highlighted the dominance of atmospheric hg inputs to the lake the combination of hg ar with isotopic signatures through the use of binary mixing delta hg 199 vs 1 hg ar models and isotopic plots and comparison to literature data allowed us to identify the main industrial and urban historical inputs the major outcome of this study is that the hg mass independent fractionation mif signature did not enable the identification of particular anthropogenic sources but reflected an integrated pool of industrial and urban emissions which tend to shift to less negative mif values mean 0 15 0 04 during their period of maximum emissions temporal mif and hg ar variations depict the rising hg emissions from the industrial revolution 1860 1910 to the modern industrial and urban development period 1950 1980 mass dependent fractionation mdf signatures enabled the identification of major contributors in relation to their relative intensities lying between two endmember pools i the combustion activities smelters cement factories and urban heating with more negative delta hg 202 values and ii the chemical and electrometallurgical activities electrochemistry chlor alkali with higher delta hg 202 values unconformities of mif and mdf signatures were observed during wwi wwii and interwar period and were attributed to drastic and rapid changes in regional industrial activities finally recent laws regarding hg emissions 1998 2011 prove their efficiency as hg ar decreased with a return to more negative mif and mdf signatures such as during the industrial revolution period our study highlights that the combination of hg isotopic data with hg ar in sediment archives is a useful tool for reconstructing the history of anthropogenic hg emissions and has the potential to identifiy their relative contributions c 2016 elsevier b v all rights reserved

holocene depositional history of the burdekin river delta of northeastern australia a model for a low accommodation highstand delta abstract the burdekin river of northeastern australia has constructed a substantial delta during the holocene delta plain area 1260 km2 the vertical succession through this delta comprises 1 a basal coarse grained transgressive lag overlying a continental omission surface overlain by 2 a mud interval deposited as the coastal region was inundated by the postglacially rising sea in turn overlain by 3 a generally sharp based sand unit deposited principally in channel and mouth bar environments with lesser volumes of floodplain and coastal facies the holocene burdekin delta was constructed as a series of at least thirteen discrete delta lobes formed as the river avulsed each lobe consists of a composite sand body typically 5 8 m thick the oldest lobes formed during the latter stages of the postglacial sea level rise 10 5 5 kyr bp are larger than those formed during the highstand 5 5 3 kyr bp which are in turn larger than those formed during the most recent slight sea level lowering and stillstand 3 0 kyr bp radiocarbon ages and other stratigraphic data indicate that inter avulsion period has decreased through time coincident with the decrease in delta lobe area the primary control on holocene delta architecture appears to have been a change from a pluvial climate known to characterize the region 12 4 kyr bp to the present drier enso dominated climate in addition to decreasing the sediment supply via lower rates of chemical weathering this change may have contributed to the shorter avulsion period by facilitating extreme variability of discharge more frequent avulsion may also have been facilitated by the lengthening of the delta plain channels as the system prograded seaward

understanding fine grained river sediment dispersal on continental margins studies of fine grained sediment dispersal in the marine environment have documented diversity in the behavior of depositional systems on continental margins with different oceanographic conditions and morphologies based on the pattern and nature of sediment accumulation for twenty three case studies we propose there are five basic types of dispersal systems and these are related to river wave tide and margin characteristics data suggest that the type of dispersal system on any margin can be predicted with knowledge of sediment load mean significant wave height tidal range and continental shelf width at a river mouth and from these a hierarchical decision tree is developed analysis of the dispersal system type of more than 100 river mouths reveals that proximal accumulation dominated pad and marine dispersal dominated mdd systems are most abundant but estuarine accumulation dominated ead systems also are anticipated to be numerous globally research quantifying marine sediment dynamics in these system types is needed although less common the size and nature of subaqueous delta clinoform sdc and canyon captured cc systems also warrant future attention to their study strong correlations between physical characteristics i e significant wave height and tidal range and the depth and distance to the nearest maximum shelf depocenter provide evidence that in reality a continuum exists between the system types the process related partitioning of sediment in the five different types of marine dispersal systems has important implications for understanding the stratigraphic record and the cycling of carbon

initiation of the mekong river delta at 8 ka evidence from the sedimentary succession in the cambodian lowland abstract modern deltas are understood to have initiated around 7 5 9 ka in response to the deceleration of sea level rise this episode of delta initiation is closely related to the last deglacial meltwater events and eustatic sea level rises the initial stage of the mekong river delta one of the world s largest deltas is well recorded in cambodian lowland sediments this paper integrates analyses of sedimentary facies diatom assemblages and radiocarbon dates for three drill cores from the lowland to demonstrate holocene sedimentary evolution in relation to sea level changes the cores are characterized by a tripartite succession 1 aggrading flood plain to natural levee and tidal fluvial channel during the postglacial sea level rise 10 8 4 ka 2 aggrading to prograding tidal flats and mangrove forests around and after the maximum flooding of the sea 8 4 6 3 ka and 3 a prograding fluvial system on the delta plain 6 3 ka to the present the maximum flooding of the sea occurred at 8 0 0 1 ka 2000 years before the mid holocene sea level highstand and tidal flats penetrated up to 20 50 km southeast of phnom penh after a period of abrupt 5 m sea level rise at 8 5 8 4 ka the delta progradation then initiated as a result of the sea level stillstand at around 8 7 5 ka another rapid sea level rise at 7 5 7 ka allowed thick mangrove peat to be widely deposited in the cambodian lowland and the peat accumulation endured until 6 3 ka since 6 3 ka a fluvial system has characterized the delta plain and the fluvial sediment discharge has contributed to rapid delta progradation the uppermost part of the sedimentary succession composed of flood plain to natural levee sediments reveals a sudden increase in sediment accumulation over the past 600 1000 years this increase might reflect an increase in the sediment yield due to human activities in the upper to middle reaches of the mekong as with other asian rivers

magnetite deformation mechanism maps for better prediction of strain partitioning 1 a meta analysis of existing experimental deformation data for magnetite and other spinel structured ferrites reveals that previously published flow laws are inadequate to describe the general deformation behavior of magnetite using updated rate equations for oxygen diffusion in magnetite we present new flow laws that closely predict creep rates similar to those found in deformation experiments and that can be used to predict strain partitioning between cubic fe oxides and other phases in the earth s crust new deformation mechanism maps for magnetite have been constructed as functions of temperature and grain size using the revised creep parameters estimates of strain partitioning between magnetite ilmenite and plagioclase indicate that concentrated zones of fe ti oxides in oceanic crust near slow spreading ridges could accommodate significant amounts of strain at moderate temperatures and may contribute to aseismic creep along spreading segment faults

deciphering viscous flow of frictional melts with the mini ams method abstract the anisotropy of magnetic susceptibility ams is widely used to analyze magmatic flow in intrusive igneous bodies including plutons sills and dikes this method owing its success to the rapid nature of measurements provides a proxy for the orientation of markers with shape anisotropy that flow and align in a viscous medium ams specimens typically are 25 mm diameter right cylinders or 20 mm on a side cubes representing a volume deemed statistically representative here we present new ams results based on significantly smaller cubic specimens which are 3 5 mm on a side hence 250 times volumetrically smaller than conventional specimens we show that in the case of frictional melts which inherently have an extremely small grain size this small volume is in most cases sufficient to characterize the pseudotachylyte fabric particularly when magnetite is present further we demonstrate that the mini ams method provides new opportunities to investigate the details of frictional melt flow in these coseismic miniature melt bodies this new method offers significant potential to investigate frictional melt flow in pseudotachylyte veins including contributions to the lubrication of faults at shallow to moderate depths

the palaeoenvironmental development of the northeastern vietnamese mekong river delta since the mid holocene three radiocarbon dated sediment cores from the northeastern vietnamese mekong river delta have been analysed with a multiproxy approach grain size pollen and spores macro charcoal carbon content to unravel the palaeoenvironmental history of the region since the mid holocene during the mid holocene sea level highstand a diverse zoned and widespread mangrove belt dominated by rhizophora covered the extended tidal flats the subsequent regression and coeval delta progradation led to the rapid development of a back mangrove community dominated by ceriops and bruguiera but also represented locally by e g kandelia excoecaria and phoenix along rivers this community seems to have endured even when the adjoining floodplain had already shifted to freshwater vegetation generally this freshwater vegetation has a strong swamp signature but locally arecaceae fabaceae moraceae urticaceae and myrsinaceae are important and mirror the geomorphological diversity of the delta plain the macro charcoal record

pseudotachylyte in the tananao metamorphic complex taiwan occurrence and dynamic phase changes of fossil earthquakes abstract pseudotachylyte veins and cataclasites were studied in the mylonitized granitic gneiss of the tananao metamorphic complex at hoping eastern taiwan the aphanitic pseudotachylyte veins vary in thickness ranging from millimeters to about 1 cm field and optical microscopic observations show that such pseudotachylyte veins cut across cataclasites which in turn transect the mylonitized granitic gneiss scanning electron microscopic images also show that both the pseudotachylyte veins and the cataclasites have been metasomatized by a k rich fluid resulting in the replacement of na plagioclase by k feldspar veins analytical electron microscopic observations reveal further details of physical and chemical changes mainly fragmentation dislocations cleaving healing with inclusions and relic voids and retention of high temperature albite of quartz and feldspar in crushed grains pseudotachylytes occur as dark veins having a higher content of chlorite biotite clinozoisite epidote and titanite fragments than cataclasites these veins coupled with hematite jarosite fe rich amorphous shell carbonaceous material indicate that crushing healing sintering and inhomogeneous melt fluid infiltration involving incipient and intermediate high temperature melt patches before and or contemporaneous with the metasomatic k rich fluid prevailed in a coupled or sequential manner in the faulting event to form nonequilibrium phase assemblage the chlorite biotite carbonaceous material and other nanoscale minerals could be vulnerable in future earthquakes under the influence of water the timing of the formation of these pseudotachylyte veins should be later than the area s age of mylonitization of granitic gneiss of approximately 4 1 3 0 ma wang et al 1998 the formation of pseudotachylytes registers the fossil earthquakes during early stages in the exhumation history of the uplifting taiwan mountain belt since the plio pleistocene arc continent collision

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

morphological change in the pearl river delta china morphological changes in the pearl river delta prd have been investigated using bathymetric charts underwater digital elevation models remote sensing data and geographic information systems water depths were extracted from digitized charts to explore the accretion erosion characteristics of three estuarine environments and to provide quantitative estimates of changes in sediment volumes multi temporal satellite images have been used in combination with topographical data to analyze the coastline changes prd has gained an abundant amount of sediment of almost 9 45 105 km3 above the 10 m isobath in the period roughly between 1970 and 2010 the average sedimentation rate was 3 15 104 km3 yr between 1976 and 2006 the coastline extended seaward by 579 2 m on average with a mean net extension rate of 19 3 m yr the results suggest that the prd experienced a major phase of accretion with net erosion only in some local zones coastline extension associated with major morphological changes has accelerated in recent decades changes in boundary conditions such as sea level rise seem to have relatively minor impacts on the dramatic changes in the morphology of the estuaries the seaward extension of the coastlines shows an increasing trend whereas the sediment supply from the delta displays a decreasing trend a detailed comparative analysis demonstrates that land reclamation in the prd is the most significant factor that progressively alters the delta morphology overwhelming the effects of subsidence and sediment supply

biogeochemical controls on mercury stable isotope compositions of world coal deposits a review abstract coal deposits were important natural hg sinks in the late paleozoic and middle late mesozoic coal combustion since the industrial revolution has emitted more than 35 000 t of hg into the atmosphere environmental geochemistry research on hg in coal is essential to understand the natural hg cycle throughout earth history and the present day hg cycle under human perturbation in this review we summarize the methods of hg isotope measurement in coals and compile recently published hg isotope data of 200 world coal samples according to their locations formation periods carboniferous permian jurassic cretaceous early middle cenozoic and ranks anthracite bituminous coal subbituminous coal lignite and illustrate the controls of sources and biogeochemical processes on hg isotope compositions in coal deposits up to 4 7 variation 3 90 to 0 77 in mass dependent fractionation mdf represented by 202 hg and 1 0 variation 0 63 to 0 34 in mass independent fractionation mif represented by 199 hg are observed in world coal deposit with an average value of 1 16 0 79 1sd and 0 11 0 18 1sd for 202 hg and 199 hg respectively we find that coal 202 hg and 199 hg are broadly controlled by two source materials terrestrial plants biogenic hg and crustal rocks geogenic hg accounting for 37 46 and 54 63 of hg in coals no clear trends are seen in neither 202 hg vs coal forming periods nor 202 hg vs coal ranks which we attribute to important overlapping of 202 hg in the source materials of different coal forming periods and the multidirectional hg mdf during coalification interestingly a step wise increase in total hg and a disappearance of 199 hg are observed along with increasing coal rank suggesting the addition of hydrothermal hg into high rank coals the hydrothermal fluids not only upgraded the coal ranks but also increased the hg concentrations and 199 hg of coals in addition the addition of hydrothermal hg into coal deposits was also partly responsible for the comparatively higher total hg and 199 hg in the late paleozoic coals relative to the mesozoic and cenozoic coals the co variation of atmospheric oxygen levels and 199 hg of coals at different coal forming time widows suggests that the removal of biogenic hg in response to widespread swamp fires may have increased the 199 hg in late paleozoic coals as well our study indicates that coal hg isotopes provide new insights into the biogeochemical cycle of hg in coal deposits and that 199 hg is a robust indicator to trace hg addition removal in coal deposits and biogeochemical processes magmatic intrusion hydrothermal fluids penetration burning of coal swamp occurring during coal deposition

stratigraphy and optically stimulated luminescence osl dating of a quaternary sequence along the dong nai river southern vietnam abstract the pre holocene cenozoic sequence outcrops in the terrestrial part of the eastern margin of the mekong basin however the stratigraphy of the sequence is still unclear its detailed stratigraphy and chronology were therefore studied along the dong nai river southern vietnam and the lithofacies and the relations among the formations were investigated from the outcrops the ages of the deposits were determined by using optically stimulated luminescence osl dating the ba mieu formation was deposited about 176 52 ka during marine isotope stage mis 7 6 the thu duc formation was deposited about 97 27 ka during mis 5 both the ba mieu and thu duc formations are composed of fluvial and tidally influenced coastal deposits the newly proposed nhon trach formation was originally an eolian blanket deposit but it has been partly reworked by fluvial processes the nhon trach formation was deposited about 10 9 4 7 ka in the last part of the pleistocene to the beginning of the holocene the osl ages for the ba mieu thu duc and nhon trach formations are younger than the ages previously assigned to these formations

late holocene evolution of the mekong subaqueous delta southern vietnam abstract as asia s third largest river with regard to sediment load the mekong river delivers approximately 160 million tons of sediment per year to the south china sea high resolution seismic profiling and coring during 2006 and 2007 cruises revealed a low gradient subaqueous delta system up to 20 m thick surrounding the modern mekong river delta mrd in the west of the south china sea based on clinoform structure grain size 210pb ams 14c and 13c results the subaqueous delta is divided into four zones defined by different sedimentary processes and depositional features over the past 3000 yr the evolution of the mrd has shown a morphological asymmetry indicated by a large down drift area and a rapid progradation around cape camau 200 km downstream from the river mouth this asymmetric feature is consistent with increased wave influence the strong southwestward coastal current strengthened by the strong ne monsoon plays an important role locally in longshore transport of resuspended sediments into the gulf of thailand a late holocene sediment budget for the mrd has been determined based on the area and thickness of deltaic sediment approximately 80 of mekong delivered sediment has been trapped within the delta area which together with a falling sea level resulted in a rapidly prograding mrd over the past 3000 yr

sedimentary processes on the mekong subaqueous delta clay mineral and geochemical analysis sedimentary processes on the inner mekong shelf were investigated by examining the characteristics of sediments sampled in gravity cores at 15 locations including grain size clay mineralogy sediment accumulation rates and the elemental and stable carbon isotopic composition of organic matter atomic c n ratios and delta c 13 deltaic deposits exhibit contrasting characteristics along different sides of the delta plain south china sea scs hereafter to the east and gulf of thailand got hereafter to the west as well as on and off the subaqueous deltaic system on one hand cores recovered from the subaqueous delta in the scs got are consisted of poorly well sorted sediments with similar different clay mineral assemblage with from mekong sediments excess pb 210 profiles supported by c 14 chronologies indicate either non steady scs side or rapid accumulation got side processes on the subaqueous delta the delta c 13 and c n ratio indicate a mixture of terrestrial and marine sourced organic matter in the deltaic sediment on the other hand cores recovered from areas with no deltaic deposits or seaward of the subaqueous delta show excess pb 210 profiles indicating steady state accumulation with a greater proportion of marine sourced organic matter core analysis s relevance with local depositional environment and previous acoustic profiling are discussed c 2012 elsevier ltd all rights reserved

fine sediment dynamics in the mekong river estuary vietnam field studies of fine sediment transport were carried out in the mekong river estuary vietnam in the high flow season of november 1993 in the freshwater region erosion and deposition of suspended sediment occurred at tidal frequency with a strong down river transport at a mean velocity of 1 m s 1and mean suspended solid concentration of about 250 mg l 1 also the suspended sediment was mostly fine silt and the clay fraction accounted for only 15 the suspended sediment was transported either as individual particles or agglomerated with organic detritus at the mouth of the estuary a salt wedge was present but was flushed out of the estuary at low tide flow reversal occurred across the pycnocline a turbidity maximum zone was present at the toe of the salt wedge at flood tide most of the suspended sediment was coagulated with little organic matter the bulk of the suspended sediment was exported to coastal waters but some sediment returned to the estuary in the salt wedge data for the low flow season are sparse but suggest that partially well mixed estuarine conditions prevail with salinity penetrating about 40 km inland carrying fine sediment up river to a turbidity maximum zone most of this sediment would have been deposited in shallow coastal waters in the previous high flow seasons the construction of large hydro electric dams further upstream on the mekong river may exacerbate siltation patterns in the estuary

process of magnetite fabric development during granite deformation this study evaluates the fabric defined by magnetite grains in a syntectonically deformed granite and deciphers the processes that led to magnetite fabric development anisotropy of anhysteretic re

tectonic controls on the stratigraphic development of the rifted taipei basin a late quaternary marine influenced inland half graben abstract we establish the three dimensional stratigraphic architecture of the taipei basin and its spatiotemporal palaeoenvironmental development during the past 50 kyr by analysing 36 borehole cores and 177 age dates we calculate the rates of basin subsidence from the borehole data at depths where radiocarbon age dates are available our results indicate that during the eustatic sea level falling period 35 20 ka low rates of sediment supply and or rapid basin subsidence controlled sedimentation leading to a change in the depositional environment from gravelly braided rivers through sandy braided rivers to meandering rivers with falling eustatic sea level during the early stage of eustatic sea level rise 20 10 2 ka balanced rates of sediment supply eustasy and basin subsidence maintained the meandering river environment rapid sea level rise led to the initial appearance of estuarine facies at 10 2 ka and widened the distribution of the estuarine environment after 8 5 ka however the coeval phases of rapid basin subsidence 10 6 10 2 ka and 9 8 5 ka promoted the first appearance and widening of the estuary respectively after 7 ka when the eustatic sea level and rate of basin subsidence remained relatively stable sufficient sediment supply gradually infilled the estuary the established stratigraphy improves our understanding of the factors controlling stratigraphic development in marine influenced inland half grabens specifically in the taipei basin with high rates of sediment supply accommodation space in the taipei basin was governed by eustatic fluctuations with modulations by basin subsidence and sediment supply since the last glacial period

magnetic and plagioclase linear fabric discrepancy in dykes a new way to define the flow vector using magnetic foliation in basaltic dykes the magnetic lineation k1 maximum magnetic susceptibility axis is generally taken to indicate the flow direction during solidification of the magma this assumption was tested in tertiary basaltic dykes from greenland displaying independent evidence of subhorizontal flow the digital processing of microphotographs from thin sections cut in k1 k2 planes yields the preferred linear orientation of plagioclase which apparently marks the magma flow lineation in up to 60 of cases the angular separation between k1 and the assumed flow direction is greater than 45 this suggests that the uncorroborated use of magnetic lineations in dykes is risky a simple geometrical method is proposed to infer the flow vector from ams in dykes based solely on magnetic foliations

siltation on a highly regulated estuarine system the magdalena river mouth case northwestern south america abstracts comparison of geo referred bathymetric datasets from 2000 to 2017 at different timescales allowed to analyze changes in the sedimentary balance and to determine patterns of morphological adjustment in the magdalena river south america the magdalena river has one of the highest sediment yields among the major rivers of the world in addition it is a laterally constrained river mouth due to a series of man made structures inhibiting its morphological response thus it provides an illustrative example to study siltation processes in a river mouth system where a low capacity of morphological response interacts with a high magnitude sediment transport regime the river mouth exhibited an overall slow pace deepening trend between 2000 and 2017 however it experienced cyclic shifts between erosive and siltation states both at interannual and intra annual scales the rates of erosion were 310 mm yr 1 on average during the erosional stages whereas sedimentation rates were 293 mm yr 1 on average during the sedimentation stages maximum rates of erosion and sedimentation were 1450 mm yr 1 and 2625 mm yr 1 respectively however intra annual rates of sedimentation erosion were of the same magnitude or larger compared with the interannual rates such high rates and the rapid changes in the sedimentary balance is the result of the cumulative effect of its limited morphological response capacity and its large suspended sediment load these rapid processes generate constraints and threats to navigation particularly at intra annual scales consequently innovative intervention proposals recognizing the rapid transitions and geomorphological adaptations are required for managing this type of river mouths

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

pseudotachylites in the eastern peninsular ranges of california abstract a continuous zone containing pseudotachylites in the eastern peninsular ranges of california extends over more than 15 km from deep canyon in the north to at least toro canyon in the south pseudotachylites are found in rocks of tonalitic to dioritic composition while the overall compositions of host rock and pseudotachylite veins are similar veins are characteristically enriched in fe and ti and depleted in si many veins are cataclastic and all contain fragments but a large number have a groundmass with skeletal and spherulitic microlites of calcic plagioclase an 40 50 biotite and ilmenite indicative of partial melting the pseudotachylites formed mainly during a late brittle event 56 62 ma and postdate the high strain ductile mylonitic deformation in the santa rosa mylonite zone 65 87 ma as ascertained by 40ar 39ar ages the size of veins ranges from less than 1 mm to more than 10 cm in thickness and aspect ratios display a broad log normal distribution three quarters of the veins are more or less parallel to the foliation the orientation of the veins is consistent with a top to the west displacement similar to that for the ductile mylonites from the sizes energies required for melting are estimated to range between 105 j for smaller veins and 1010 j for larger veins interestingly the energy distribution and geometry of these pseudotachylites correspond closely with energy distributions of current microseismic events along the san andreas fault at parkfield suggesting that basic mechanisms may be similar and due to intrinsic mechanical properties of rocks in particular these indicate that local stress concentrations rather than average crustal stresses are relevant for earthquakes

a lightweight extruder for accurate sectioning of soft bottom lake sediment cores in the field a new extrusion device is described for time efficient sectioning of high quality cores of soft bottom lake sediments in particular piston cores and core samples that include the undisturbed sediment water interface the instrument is lightweight versatile and easy to operate in the field while maintaining maximum accuracy in sectioning a sediment profile in predefined increments

sedimentary facies and holocene progradation rates of the changjiang yangtze delta china abstract the changjiang yangtze river one of the largest rivers in the world has formed a broad tide dominated delta at its mouth during the holocene sea level highstand three boreholes cm97 js98 and hq98 were obtained from the changjiang delta plain in 1997 1998 to clarify the characteristics of tide dominated delta sediments and architecture based on sediment composition and texture and faunal content core sediments were divided into six depositional units in ascending order they were interpreted as tidal sand ridge prodelta delta front subtidal to lower intertidal flat upper intertidal flat and surface soil deposits the deltaic sequence from the prodelta deposits to the delta front deposits showed an upward coarsening succession overlain by an upward fining succession from the uppermost part of the delta front deposits to the surface soil thinly interlaminated to thinly interbedded sand and mud sand mud couplets and bidirectional cross laminations in these deposits show that tide is the key factor affecting the formation of changjiang deltaic facies sediment facies and their succession combined with ams 14c dating revealed that isochron lines cross unit boundaries clearly and delta progradation has occurred since about 6000 to 7000 years bp when the rising sea level neared or reached its present position the average progradation rate of the delta front was approximately 50 km kyear over the last 5000 years the progradation rate however increased abruptly ca 2000 years bp going from 38 to 80 km kyear the possible causes for this active progradation could have been an increase in sediment production in the drainage basin due to widespread human interference and or decrease in deposition in the middle reaches related to the channel stability caused by human activity and climatic cooling after the mid holocene

early holocene initiation of the mekong river delta vietnam and the response to holocene sea level changes detected from dt1 core analyses abstract the early holocene initiation of the mekong river delta vietnam was investigated based on sedimentary facies microfossil analyses and radiocarbon dating of dt1 core taken from the upper delta plain the dt1 core 105 38 51 e 10 17 02 n elevation 2 m is 51 5 m long and located in fill of a buried incised valley this incised valley of the paleo mekong river formed during the last glacial maximum which is 20 30 km wide has been traced spatially from the cambodian border to the south china sea coast by compilation of existing core data the dt1 core records the history of the estuarine channel and delta systems of the mekong river during the early to middle holocene the sedimentary facies determined particularly from sedimentary structures diatom and foraminifera assemblages grain size variation and the accumulation rate clearly show an upward deepening succession in the lower part of the core from marsh or intertidal flat to subtidal inner bay facies and an overlying upward shallowing succession from prodelta to intertidal flat floodplain the boundary between the two successions indicating the maximum flooding surface occurred at approximately 8 0 ka at the time that the mekong river delta was initiated the delta initiation and sediment facies succession are closely linked to holocene sea level changes particularly a standstill from 8 0 to 7 5 ka after a rapid rise of sea level from 8 8 to 8 2 ka during the further sea level rise from 7 5 to 7 0 ka sediments aggraded forming topset sedimentary deposits

palaeogeography and dynamics of the deltaic wetland of save river mozambique abstract many mangrove wetland systems in deltaic environments are negatively affected by massive sedimentation from river inflows in this paper we use the example of the save river delta to assess the palaeogeographic distribution of mangrove wetlands and to analyze their dynamics to track past occurrences of mangrove wetlands in the study area we have integrated sedimentological data with siliceous microfossil analysis combined with ams radiocarbon and osl dating the results show a fine grained deposit with an approximate thickness of 2 m present at different sampling sites in the upper deltaic plain the deposit is interbedded between sand layers while in the lower deltaic plain the deposit occupies the uppermost stratigraphic position in most of the sampling sites the deposit shows a succession with brackish marine diatoms at the bottom of the sequence while the upper part shows only scattered occurrences based on sedimentological and microfossil characteristics we have interpreted the layer to represent a mangrove wetland deposit the development of the deposit in the study area is suggested to have been initiated around 3100 cal yr bp induced by sea level rise thereafter the development followed the combined effect of a sea level fall and delta progradation processes in some areas particularly in the proximal part of the delta the mangrove deposit has developed progressively on top of the delta front from around 1300 years ago osl onwards massive alluvial sedimentation impacted the mangrove ecosystem however the retreat of mangrove wetland coincided with a regional fall of sea level at the edges of the alluvial deposit the current mangrove ecosystem has reclaimed the habitat in some sectors where gully erosion has exposed the once extinct mangrove habitat

sedimentary facies diatom and foraminifer assemblages in a late pleistocene holocene incised valley sequence from the mekong river delta bentre province southern vietnam the bt2 core abstract a detailed description of sediment facies diatom mollusca and foraminifer assemblages and 14 c ages of the mekong river delta southern vietnam is presented in this paper a 71 m long core recovered in 1997 at the bentre province in the eastern part of the mekong river delta is divided into eight units and nine sediment facies on the basis of sedimentary properties diatom and foraminifer assemblages and 14 c ages these units show facies changes from transgression to regression in relation to the late pleistocene holocene sea level changes the postglacial transgression caused by a sea level rise led to infilling of the incised valley and formation of estuarine sediments and open bay muddy sediments in ascending order estuarine sediments consist of slightly oxidized yellowish grey silty sand and intercalated greenish grey and stiffly brownish grey sandy silt and silty clay the muddy facies 13 5 m thick is characterized by abundant marine planktonic diatoms and open sea foraminifers this facies indicates the maximum holocene marine influence was around 5300 cal yr bp at the bt2 site the regressive succession is composed of deltaic sediments from prodelta delta front sub to inter tidal flat and beach ridge in ascending order 14 c ages indicate that the delta front passed the core site at approximately 4000 3000 cal yr bp the coastal progradation rate was 17 18 m yr 1 during the 5300 3500 cal yr and decreased to 13 14 m yr 1 during the last 3500 cal yr

evaluation of arsenic sorption and mobility in stream sediment and hot spring deposit in three drainages of the tibetan plateau abstract enrichment of arsenic as in sediment 12 227 mg kg in the upstream tributaries of the indus and brahmaputra rivers originating from the tibetan plateau where hot springs were abundant has been found sandy sediment samples from the nu salween river lantsang mekong river and jinsha yangtze river also originating from the tibetan plateau were collected in july 2012 and were found to contain 6 8 mg kg to 30 5 mg kg as average17 3 6 5 mg kg n 12 deposits collected within 1 m of two hot springs in changdu tibet displayed significantly higher as levels 263 7 mg kg in ld 2 with 65 quartz and 101 8 mg kg in nud 1 with 82 calcite to evaluate the valence states of as and also the phases responsible for sorption x ray absorption spectroscopy xas was employed to analyze the two hot spring deposits and three river sediment samples coarse sand nud 6 as 14 6 mg kg fine sand nud 4 as 17 8 mg kg and silty sand ld 1 as 30 5 mg kg the x ray absorption near edge spectrum xanes data indicate that 70 of as from 3 samples in the nu salween river drainage nud 1 nud 4 and nud 6 is as v or arsenate with the rest being as 0 or as fe sulfides the proportion of as v is 90 for 2 samples in the lantsang mekong river drainage ld 1 and ld 2 linear combination fit of the iron extended x ray fine structure spectrum exafs show that 3 samples from the nu salween river contain 20 ferrihydrite and 10 goethite without any hematite being detected but 2 samples from the lantsang mekong river contain

early growth stage of a large delta transformation from estuarine platform to deltaic progradational conditions the northeastern mekong river delta vietnam abstract the initial growth stage of a river delta can be defined either as the beginning geomorphologic expansion of the river dominated coastal lowland or as the starting basinward directed progradation of the geological stratigraphic delta body differentiating between these two perspectives is necessary for understanding the sensitive reaction of a deltaic system to dynamic changes in sea level and sediment availability the holocene evolution of the northeastern part of the mekong river delta southern vietnam offers a great chance to depict these two different definitions and relate them genetically to each other since the transition between an old abrasion platform inner delta and the continental shelf basin outer delta is well developed in this marginal part of the delta the early stage of delta growth taking place during transgression related inundation between 8 cal ka bp maximum flooding and 5 7 6 0 4 8 cal ka bp sea level highstand was characterized by tide and saltwater influenced nearshore conditions allowing extensive mangrove and tidal flat deposits to aggradate on the wide abrasion platform with the onset of regression around 4 8 cal ka bp the depositional center shifted immediately beyond the seaward margin of this estuarine platform and thus true deltaic progradation could develop leading to rapid construction of a delta body and in addition to subsidence tilting of the inner delta zone directly at the transition of these two deposystems remains of shore related deposits indicate the sudden breakdown of the estuarine platform conditions around 4 6 cal ka bp

natural and anthropogenic trace metals in sediments of the ligurian sea northwestern mediterranean abstract the magnitude and the chronology of anthropogenic impregnation by hg and other trace metals of environmental concern v cr ni cu zn ag cd and pb including its stable isotopes in the sediments are determined at the dyfamed station a site in the ligurian sea northwestern mediterranean chosen for its supposed open sea characteristics the dyfamed site vd is located on the right levee of the var canyon turbidite system at the end of the middle valley in order to trace the influence of the gravity current coming from the canyon on trace metal distribution in the sediment we studied an additional sediment core va from a terrace of the var canyon and material collected in sediment traps at the both sites at 20 m above sea bottom the patterns of hg and other trace element distribution profiles are interpreted using stable pb isotope ratios as proxies for its sources taking into account the sedimentary context turbidites redox conditions and sedimentation rates major element distributions coupled with the stratigraphic examination of the sediment cores point out the high heterogeneity of the deposits at va and major turbiditic events at both sites at the dyfamed site we observed direct anthropogenic influence in the upper sediment layer according to the 210pbxs derived sedimentation rate at the dyfamed site 0 4 mm yr 1 the hg enriched layer of the top core corresponds to the sediment accumulation of the last 50 years which is the period of the highest increase in hg deposition on a global scale with the hypothesis of the absence of significant post depositional redistribution of hg the hg corg ratio changes between the surface and below are used to estimate the anthropogenic contribution to the hg flux accumulated in the sediment the hg enrichment from pre industrial to the present time is calculated to be around 60 consistent with estimations of global hg models however based on the chemical composition of the trapped material collected in sediment traps we calculated that epibenthic mobilization of hg would reach 73 conversely the cd corg ratio decreases in the upper 5 cm which may reflect the recent decrease of atmospheric cd inputs or losses due to diagenetic processes

reconstructing regional scale lead contamination of the atmosphere 1850 1980 in the united kingdom and ireland using lake sediments 1 a data set of 49 sediment cores from 41 lakes in the united kingdom and ireland was used to investigate how the variability of anthropogenic pb concentration and accumulation rate affects using lake sediments to reconstruct pb contamination of the atmosphere at the regional scale the anthropogenic pb concentration when averaged over six to eleven lakes in subregions was sufficient to isolate the trend in pb contamination of the atmosphere since 1850 from lake specific influences while the anthropogenic pb accumulation rate varied considerably within subregions as a result mainly of variable sediment focusing the results showed that the maximum focusing factor is typically 1 5 to 3 and rarely above 4 careful application of this finding may allow the history and geographical variation of pb deposition from the atmosphere at the regional and global scales to be described using lake sediments a model that relates anthropogenic pb concentration in lake sediment to pb flux from the atmosphere was developed and used to reconstruct pb flux from the atmosphere in three subregions the reconstructed flux varies from 2 7 0 9 to 18 9 5 2 mgpb m 2 yr 1 across the subregions in 1860 1870 to 7 4 2 1 to 34 5 6 0 mgpb m 2 yr 1 in 1940 1950

mesophotic coral buildups in a prodelta setting late eocene southern pyrenees spain a mixed carbonate siliciclastic system lower priabonian coral bioherms and biostromes encased in prodelta marls clays occur in the ainsa jaca piggyback basin in the south central pyrenean zone detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups coral lithosomes occur either isolated or amalgamated in larger buildups isolated lithosomes are 1 to 8 m thick and a few hundred metres wide clay content within coral colonies is significant stacked bioherms form low relief buildups commonly 20 to 30 m thick locally up to 50 m these bioherms are progressively younger to the west following progradation of the deltaic complex the lowermost skeletal rich beds consist of bryozoan floatstone with wackestone to packstone matrix in which planktonic foraminifera are abundant and light related organisms absent basal coral biostromes and the base of many bioherms consist of platy coral colonies floating in a fine grained matrix rich in branches of red algae corals with domal or massive shape locally mixed with branching corals and phaceloid coral colonies dominate buildup cores these corals are surrounded by matrix and lack organic framework the matrix consists of wackestone to packstone locally floatstone with conspicuous red algal and coral fragments along with bryozoans planktonic and benthonic foraminifera and locally sponges coral rudstone and skeletal packstone with wackestone to packstone matrix also occur as wedges abutting the buildup margins integrative analysis of rock textures skeletal components buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth the bathymetric position of the buildups has been constrained from the light dependent communities and lithofacies distribution within the buildups the process product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the late eocene and until the late miocene comparative analysis with some selected upper eocene coral buildups of the north mediterranean area show similarities in facies components and textures and suggest that they also grew in relatively low light mesophotic and low hydrodynamic conditions

holocene valley aggradation driven by river mouth progradation examples from australia since the end of the post glacial sea level rise 6800 years ago progradation of river mouths into estuaries has been a global phenomenon the responses of upstream alluvial river reaches to this progradation have received little attention here the links between river mouth progradation and holocene valley aggradation are examined for the macdonald and tuross rivers in south eastern australia optical and radiocarbon dating of floodplain sediments indicates that since the mid holocene sea level highstand 6800 years ago vertical floodplain aggradation along the two valleys has generally been consistent with the rate at which each river prograded into its estuary this link between river mouth progradation and alluvial aggradation drove floodplain aggradation for many tens of kilometres upstream of the estuarine limits both rivers have abandoned their main holocene floodplains over the last 2000 years and their channels have contracted a regional shift to smaller floods is inferred to be responsible for this change though a greater relative sea level fall experienced by the macdonald river since the mid holocene sea level highstand appears to have been an additional influence upon floodplain evolution in this valley copyright 2006 john wiley sons ltd

late holocene sedimentary and environmental development of the northern mekong river delta vietnam abstract a sedimentological and palynological study of three sediment cores from the northern mekong river delta shows the regional sedimentary and environmental development since the mid holocene sea level highstand a sub to intertidal flat deposit of mid holocene age is recorded in the northernmost core shoreline deposits in all three cores show descending ages from n to s documenting 1 the early stages of the late holocene regression and 2 the subsequent delta progradation the delta plain successions vary from floodplain deposits with swamp like elements to natural levee sediments the uppermost sediments in all cores show human disturbance to varying degrees the most intense alteration is recorded in the northernmost core where the palynological signal together with a charcoal peak indicates the profound change of the environment during the modern land reclamation the sediments from at least one of the three presented cores do not show a true delta facies succession but rather estuary like features as also observed in records from southern cambodia this absence is probably due to lack of accommodation space during the initial phase of rapid delta progradation which impeded the development of true delta successions as shown in cores from the southern mekong river delta

infilling and flooding of the mekong river incised valley during deglacial sea level rise the abrupt transition from fluvial to marine deposition of incised valley fill sediments retrieved from the southeast vietnamese shelf accurately records the postglacial transgression after 14 ka before present bp valley filling sediments consist of fluvial mud whereas sedimentation after the transgression is characterized by shallow marine carbonate sands this change in sediment composition is accurately marked in high resolution x ray fluorescence xrf core scanning records rapid aggradation of fluvial sediments at the river mouth nearly completely filled the mekong incised valley prior to flooding however accumulation rates strongly reduced in the valley after the river mouth system flooded and stepped back this also affected the sediment supply to deeper parts of the southeast vietnamese shelf comparison of the mekong valley filling with the east asian sea level history of sub and inter tidal sediment records shows that the transgressive surface preserved in the incised valley fill records is a robust sea level indicator the valley was nearly completely filled with fluvial sediments between 13 0 and 9 5 ka bp when sea level rose rather constantly with approximately 10 mm yr as indicated by the east asian sea level record at shallower parts of the shelf significant sediment reworking and the establishment of estuarine conditions at the final stage of infilling complicates accurate dating of the transgressive surface nevertheless incised valley fill records and land based drill sites indicate a vast and rapid flooding of the shelf from the location of the modern vietnamese coastline to the cambodian lowlands between 9 5 ka and 8 5 ka bp fast flooding of this part of the shelf is related with the low shelf gradient and a strong acceleration of the east asian sea level rise from 34 to 9 meter below modern sea level mbsl corresponding to the sea level jump of melt water pulse mwp 1c c 2010 elsevier ltd all rights reserved

modern and historic atmospheric mercury fluxes in both hemispheres global and regional mercury cycling implications 1 using two different natural archiving media from remote locations we have reconstructed the atmospheric deposition of mercury hg over the last 800 1000 years in both hemispheres this effort was designed 1 to quantify the historical variation and distributional patterns of atmospheric hg fluxes in the midlatitudes of north america at nova scotia n s and at a comparable midlatitude region in the southern hemisphere at new zealand n s 2 to identify and quantify the influence of anthropogenic and natural hg contributions to atmospheric hg fluxes 3 to further investigate the suitability and comparability of our two selected media lake sediments and ombrotrophic peat for hg depositional reconstructions and 4 to assess the relative importance of wet and dry deposition to the study areas significant findings from the study include the following 1 the lake sediments examined appear to faithfully record the contemporary flux of hg from the atmosphere e g 1997 n s lakes approximately 8 3 g m 2 yr 1 n s rain 8 g m 2 yr 1 the upper 10 cm approximately 10 yr of ombrotrophic peat cores from nova scotia were dated using a biological chronometer polytrichum and were also consistent with the flux data provided by current direct sampling of precipitation these observations place limits on the contribution of dry deposition 40 50 of wet flux unfortunately the peat samples could not be dated below 10 cm this was due to the apparent diagenetic mobility of the geochronological tracer 210pb 2 there is no evidence of a significant enhancement in the atmospheric hg flux as a result of preindustrial 1900 c e common era activities such as the extensive au and ag mining in the americas 3 a factor of 3 and 5x increase in the deposition of hg to the lake sediment archives was observed since the advent of the industrial revolution in new zealand and nova scotia respectively suggesting a worldwide increase in the atmospheric deposition of hg furthermore this increase is synchronous with increases in the release of co2 from combustion of fossil fuels on a global scale the magnitude of increase since industrialization appears larger in nova scotia than in new zealand this may be due to enhanced deposition of hg as a result of either regional emission of hg or enhanced regional oxidation of hg

mangrove bank sedimentation in a mesotidal environment with large sediment supply gulf of papua the most extensive mangrove forests on earth are associated with major river systems the indo pacific region has numerous large rivers that discharge onto broad continental shelves and mangroves occur widely along these coastlines in the gulf of papua gop alone there are 3350 km2 of mangrove forests the majority of which 2900 km2 are associated with the fly kikori and purari river deltas this study examines data from 28 vibracores to describe preserved sedimentary strata and to determine rates of sediment accumulation in this dynamic coastal environment the observations suggest a common stratigraphy is contained in prograding mangrove banks of the mesotidal western gop and that it is similar to mud dominated and physically stratified stratigraphy recorded by other intertidal areas with and without mangroves experiencing large tidal range 2 m and sediment supply e g ganges brahmaputra and yangtze river deltas grain size sedimentary structure radionuclide and remotely sensed data are analyzed and four stratigraphic facies are identified 1 supratidal to high tidal muds 2 mid tidal sandy muds 3 low tidal sand and mud and 4 subtidal channel sands supratidal and high tidal sediments of gop mangrove forests are typically muddy but can have high sand contents 30 in areas exposed regularly to ocean waves these muds can be homogenous but commonly have physical structures laminations and bedding probably reflecting high rates of sediment accumulation relative to bioturbation mangrove muds may have low water contents due to infrequent inundation and because of their cohesive nature and abundant roots can form steep intertidal banks and erosional scarps mid tidal and low tidal sediments are thinly laminated 2 mm laminations likely deposited from fluid mud transport channel sediments have thin and thick mud and sand laminations but are identified by thick 5 cm sand beds a conceptual model of mangrove bank progradation is created using sedimentological and radionuclide data maximum sediment accumulation rates were determined using steady state 210pb profiles and greatest mean rates are found in mid tidal areas 4 4 cm year 3 9 g cm2 year slower accumulation occurs in high tidal and low tidal areas 1 8 and 1 5 cm year respectively 1 2 and 1 0 g cm2 year respectively remotely sensed data indicate that areas of erosion and accretion co exist in the kikori purari region very large 210pb accumulation rates were measured in areas of significant accretion supporting the validity of the calculated rates in areas of rapid accretion cores can have non steady state or event related 210pb profiles reflecting episodic sedimentation or complex radionuclide scavenging dynamics most cores from the fly river delta are of this type sediment trapping in western gop mangroves is estimated to account for 2 14 of the total gop sediment load

changes in late pleistocene holocene sedimentary facies of the mekong river delta and the influence of sedimentary environment on geotechnical engineering properties abstract the aim of the study was to characterize a variety of sedimentary facies from the mekong river delta mrd and to determine their geotechnical properties the paper furthermore discusses the influences of sedimentary environment and conditions on geotechnical properties of the sedimentary facies a core at the vinhlong province mrd sufficiently presented the sedimentary facies of the area eight successive facies were identified based upon sedimentary properties characteristics of the unit showed development of sedimentary facies each sedimentary facies was formed under a different environment and revealed typical geotechnical properties estuarine channel estuarine marine delta front mouth bar and sub to inter tidal flat facies were formed under strong hydrodynamic conditions the sediments are from clay to coarse sand and even pebbles and the sedimentary structures are plentiful such as intercalated clay silt beddings and fine to coarse sand beddings with very different thicknesses strengths of these sedimentary facies vary significantly which can be observed by cone penetration test cptu results but not by standard penetration test spt the normalized values from cptu show saw tooth graphs with large variations especially delta front mouth bar and sub to inter tidal flat facies at shallower depth the soil behavior types determined from the normalized values are plentiful from cohesionless to cohesive soils as an example an estuarine channel facies experiencing a large consolidation pressure in relatively long time over 9920 yr bp has geotechnical properties with heavily overconsolidated conditions and high strength on the other hand marsh open bay pro delta and march flood plain facies which formed under relatively low hydrodynamic conditions have simple and homogenous sedimentary properties the sediments are commonly silt and clay and sedimentary structures are very faint interbedded clay and silt laminae and rarely very fine sand laminae strengths of these sedimentary facies increase linearly with depth the normalized values are all rather constant with depth and their soil behavior type is only normally consolidated clays from cptu results it could be said that the particular sedimentary conditions in the late pleistocene holocene deposits of mrd can be reasonably estimated by the cptu test

natural and anthropogenic variations in atmospheric mercury deposition during the holocene near quelccaya ice cap peru mercury hg is a toxic metal that is transported globally through the atmosphere the emission of hg from mineral reservoirs and subsequent recycling in surface reservoirs i e soil biomass ocean and atmosphere are fundamental to the modern global hg cycle yet past emissions from anthropogenic and natural sources are not fully constrained we use a sediment core from yanacocha a headwater lake in southeastern peru to study the anthropogenic and natural controls on atmospheric hg deposition during the holocene from 12 3 to 3 5 ka hg fluxes in the record are relatively constant mean 1 1 4 0 6 g m 2 a 1 n 189 past hg deposition does not correlate with changes in regional temperature and precipitation inferred from nearby paleoclimate records or with most large volcanic events that occurred regionally in the andean central volcanic zone 300 400 km from yanacocha and globally in b c 1450 3 4 ka hg fluxes abruptly increased and reached the holocene maximum flux 6 7 g m 2 a 1 in b c 1200 concurrent with a 100 year peak in fe and chalcophile metals as ag tl and the presence of framboidal pyrite continuously elevated hg fluxes from b c 1200 500 suggest a protracted mining dust source near yanacocha that is identical in timing to documented pre incan cinnabar mining in central peru during incan and colonial time a d 1450 1650 hg deposition remains elevated relative to background levels but lower relative to other hg records from sediment cores in central peru indicating a limited spatial extent of preindustrial hg emissions hg fluxes from a d 1980 to 2011 4 0 1 0 g m 2 a 1 n 5 are 3 0 1 5 times greater than pre anthropogenic fluxes and are similar to modern fluxes documented in remote lakes around the world

electrical resistivity tomography determines the spatial distribution of clay layer thickness and aquifer vulnerability kandal province cambodia despite being rich in water resources many areas of south east asia face difficulties in securing clean water supply this is particularly problematic in regions with a rapidly growing population in this study the spatial variability of the thickness of a clay layer controlling surface groundwater interactions that affect aquifer vulnerability was investigated using electrical resistivity tomography ert data were acquired along two transects showing significant differences in the imaged resistivities borehole samples were analyzed regarding particle density and composition and linked to their resistivity the obtained relationships were used to translate the field electrical resistivities into lithologies those revealed considerable variations in the thickness of the clay layer ranging from 0 m up to 25 m geochemical data highlighting zones of increased ingress of surface water into the groundwater confirmed areas of discontinuities in the clay layer which act as preferential flow paths the results may guide urban planning of the phnom penh city expansion in order to supply the growing population with safe water the presented approach of using geophysics to estimate groundwater availability accessibility and vulnerability is not only applicable to kandal province cambodia but also to many other areas of fast urbanization in south east asia and beyond

mobility and diagenesis of pb and 210pb in peat peatlands long have been considered to preserve the record of atmospheric deposition of anthropogenic contaminants such as pb in the past two decades sup 210 pb has been widely used to data recent strata of peat and to calculate accumulation rates the assumption that pb and sup 210 pb are immobile and not subject to diagenesis in peat has been questioned but not rigorously tested the authors attempted to determine if pb is mobile in peatlands and if pb profiles are altered by diagenic processes by constructing a mass balance for pb about a small peatland by comparing inventories concentrations and accumulation rates of pb and sup 210 pb in peatlands across northeastern north america and by examining the relationship between concentrations of pb in bog waters and peat in numerous sites the results clearly demonstrate that pb and sup 210 pb are mobilized by the organic rich waters of peatlands profiles of pb and sup 210 pb at depths below the water table do not preserve the record of atmospheric deposition and inventories of pb and sup 210 pb are depleted in peatland hollows concentrations of pb in bog waters are regulated by the concentration of pb in the peat and the concentration of dissolved organicmore carbon the mass balance for one bog indicated that over the specific three year period of study more than 30 of inputs of pb were not retained within the peat as a result of this mobility dates based on sup 210 pb can be biased and inaccurate by as much as 30 years dates based on sup 210 pb should be verified by other techniques especially when the inventory of sup 210 pb is less than that expected from local rates of deposition less

holocene variability of the kuroshio current in the okinawa trough northwestern pacific ocean abstract cores 255 and b 3gc from the southern and northern okinawa trough respectively were studied for determining the variability of the kuroshio current on centennial scales during the holocene based on detailed ams 14 c dates stable isotope and planktonic foraminiferal distribution the main flow of the kuroshio current was inferred to re enter the okinawa trough at 7 3 calendar cal kyr bp leading to abrupt changes in sedimentation rate remarkably increased abundance of the kuroshio current indicator pulleniatina obliquiloculata increased sea surface temperature sst and depth of thermocline dot during 4 6 2 7 cal kyr bp the abundance of p obliquiloculata sharply decreased corresponding to a decreases in sst and dot implying that the influence of the kuroshio current weakened at that time possibly as a result of the intensified winter monsoon significantly the kuroshio current proxies e g the difference in sst between the southern and northern okinawa trough display periodicities of 1500 yr and 700 800 yr ascribed to the second harmonic of the 1500 yr cycle in oceanic thermohaline circulation during the holocene the holocene events at 0 6 1 7 3 3 4 6 5 9 8 1 9 4 cal kyr bp in the okinawa trough appear to be the most recent manifestation of the millennial scale climate cycle recorded in the north atlantic arabian sea marine sediment cores and greenland ice cores suggesting global climatic tele connections

recent paleorecords document rising mercury contamination in lake tanganyika abstract recent lake tanganyika hg deposition records were derived using 14c and excess 210pb geochronometers in sediment cores collected from two contrasting depositional environments the kalya platform located mid lake and more removed from watershed impacts and the nyasanga kahama river delta region located close to the lake s shoreline north of kigoma at the kalya platform area pre industrial hg concentrations are 23 0 2 ng g increasing to 74 ng g in modern surface sediment and the hg accumulation rate has increased from 1 0 to 7 2 g m2 a from pre industrial to present which overall represents a 6 fold increase in hg concentration and accumulation at the nyasanga kahama delta region pre industrial hg concentrations are 20 3 ng g increasing to 46 ng g in surface sediment mercury accumulation rate has increased from 30 to 70 g m2 a at this site representing a 2 3 fold increase in hg concentration and accumulation there is a lack of correlation between charcoal abundance and hg accumulation rate in the sediment cores demonstrating that local biomass burning has little relationship with the observed hg concentration or hg accumulation rates examined using a sediment focusing corrected mass accumulation rate approach the cores have similar anthropogenic atmospheric hg deposition profiles suggesting that after accounting for background sediment concentrations the source of accumulating hg is predominantly atmospheric in origin in summary the data document an increase of hg flux to the lake tanganyika ecosystem that is consistent with increasing watershed sediment delivery with background level hg contamination and regional as well as global increases in atmospheric hg deposition

reply to comment by william shotyk on does within bog spatial variability of mercury and lead constrain reconstructions of absolute deposition rates from single peat records the example of store mosse sweden reply to comment by william shotyk on does within bog spatial variability of mercury and lead constrain reconstructions of absolute deposition rates from single peat records the example of store mosse sweden

mixed energy process interactions read from a compound clinoform delta paleo orinoco delta trinidad preservation of river and tide signals by mud induced wave damping

coseismic magnetization of fault pseudotachylytes 1 thermal demagnetization experiments fault pseudotachylytes form by quenching of silicate liquids produced through coseismic frictional melting here we show that in natural pseudotachylytes the main carrier of magnetic remanence blocked in during cooling of the frictional melt is fine grained magnetite this confirms previous studies on friction melt experiments stoichiometric magnetite produced during earthquakes by the breakdown of ferromagnesian silicates records the ambient magnetic field during seismic slip we find that most fault pseudotachylytes exposed in the santa rosa mountains southern california a classic pseudotachylyte locality acquired their natural remanent magnetization nrm upon cooling of the frictional melt through the range of magnetization blocking temperatures of the magnetite grains and this primarily constitutes a thermal remanent magnetization nrm intensities typical of most pseudotachylyte veins range from 1 to 60 10 4 am2 kg a few specimens however contain magnetizations significantly higher than that caused by the earth s field as well as magnetization directions that are highly variable over short distances other magnetization processes possibly related to coseismic electric currents may be involved during the seismogenic process to control nrm acquisition

sphagnum peatland distribution in north america and eurasia during the past 21 000 years the distribution and abundance of sphagnum spores in north america and eurasia are mapped for the past 21 ka the present day distribution of abundant sphagnum spores corresponds closely to areas with peatland development with maximum sphagnum abundance between 630 and 1300 mm annual precipitation and between 2 and 6 c mean annual air temperature during the wisconsin glaciation there were apparently not large areas of peatland in north america except in alaska high sphagnum spore percentages were found in eastern north america during deglaciation major peatland development occurred in boreal north america after 9 ka and there was a southward movement of high sphagnum spore abundance after 5 ka in the western great lakes region major peatland development began after 9 ka in europe and asia on the basis of maps of the area supporting peatlands carbon accumulation in peatlands is estimated to be low prior to 11 ka increased slightly between 11 and 5 ka and greatly increased during the past 5 ka

trace metal profiles in the varved sediment of an arctic lake abstract varved annually laminated sediments offer a rare and physically undisturbed archive of past trace metal deposition and limnological conditions here a high resolution 1 300 year record of metal accumulation is presented from a varved lake sediment on devon island in the canadian high arctic down core concentration profiles of cd cu and zn were positively correlated p

sediment facies and late holocene progradation of the mekong river delta in bentre province southern vietnam an example of evolution from a tide dominated to a tide and wave dominated delta abstract the mekong river delta southern vietnam is a typical mixed tide and wave energy delta with a wide delta plain formed during the last 6 ka and is one of the largest deltas in the world three cores were taken from bentre province in the lower delta plain with the objective to describe the sediment facies and to clarify the changes from tide dominated to tide wave dominated delta of the mekong river delta during the late holocene three cores bt1 bt2 and bt3 were obtained in 1997 holocene sediments in bt1 and bt3 with thickness ranging from 10 to 20 m were mainly composed of deltaic sediments unconformably overlying the late pleistocene sediments the bt2 core however consisted of transgressive estuarine sediments covered by deltaic sediments infilling the paleo mekong river incised valley which is more than 70 m deep and was formed during the last glacial period the deltaic sediment facies and succession in the bt2 and bt3 cores taken from the outer delta plain with beach ridges were different from those of the bt1 core taken from the inland delta plain the bt2 and bt3 cores provide a good example of tide and wave dominated delta sediments and were characterized by a coarsening upward delta front facies covered by a fining upward subtidal to intertidal flat facies followed by a coarsening upward foreshore dune facies these changes from the inland delta plain to the beach ridge delta plain were accompanied by changes in progradation rates and subaqueous delta topography caused by increased wave influence

ferrimagnetic resonance signal produced by frictional heating a new indicator of paleoseismicity 1 high speed fault slips during earthquakes may generate sufficient frictional heat to produce fused fault rocks such as pseudotachylyte we have carried out high speed slip tests using natural fault gouge to judge whether or not frictional heating universally occurs during seismic fault slips in our shearing tests natural fault gouge is put between two cylindrical silica glasses and sheared under a fixed axial stress of 0 61 mpa despite such a low stress near the earth s surface a darkened cohesive material resembling pseudotachylyte is made from the fault gouge along the edge of a circular shear plane when shearing at a high speed of 1500 rpm the maximum slip rate reaches 1 96 m s at the edge electron spin resonance measurements reveal that the darkened cohesive material has a strong ferrimagnetic resonance fmr signal which is derived from bulky trivalent iron ions in ferrimagnetic iron oxides fe2o3 the fmr signal is produced by the thermal dehydration of antiferromagnetic iron oxides feooh in the fault gouge this may be applicable to the detection of past heating during seismic fault slip we thus attempt to reconstruct the temperature of frictional heat generated on the nojima fault plane in the 1995 kobe earthquake m 7 3 by inversion using the fmr signal the computer simulation indicates that the frictional heat generated on the nojima fault plane at 390 m depth may have attained 390 c during the 1995 kobe earthquake the temperature in the fault plane may have returned to its initial state after 1 year this result suggests that a heat flow anomaly generated by faulting may be difficult to detect

preserved magnetic fabrics vs annealed microstructures in the syntectonic recrystallised george granite south africa the saldanian basement of the cape fold belt of south africa outcrops in the kaaimans inlier with granite plutons intruded in low grade pelitic and quartzitic metasediments around 535 ma new field data support a ubiquitous saldanian top to the north thrust kinematics coeval with granite emplacement with no substantial cape tectonic overprint the granites and their contact aureoles display both synkinematic and post kinematic fabrics this and the high strain zone commonly observed all along the contact between the kaaimans inlier and the cape fold belt suggest a structural decoupling between the basement and its cover microstructures in the kaaimans inlier and in the george pluton establish a post kinematic pervasive and thermal overprint of saldanian age granites and country rocks record a medium temperature high strain deformation phase followed by a strong low temperature static recrystallisation two sets of andalusite porphyroblasts occur systematically in the contact aureoles of the studied plutons and cannot be explained by successive magmatic pulses the granites studied by the anisotropy of magnetic susceptibility ams technique are paramagnetic 20 km 300 si biotite is mostly at the origin of the bulk rock susceptibility although minor contributions of tourmaline or ferromagnetic phases may occur the contribution of biotite alone to the bulk magnetic susceptibility is supported by two quantitative models based respectively on whole rock compositions curie weiss law and on intrinsic mineral susceptibilities the magnetic foliations and lineations are homogeneous throughout the george pluton and are consistent with field structures the ams results mainly from the magneto crystalline anisotropy of biotite and from its lattice preferred orientation lpo in the rock the magnetic fabric reveals the biotite subfabrics that had been acquired before static recrystallisation and which was not modified by the subsequent thermal metamorphic event the magnetic fabric therefore preserves the emplacement related deformation fabric

filter or conveyor establishing relationships between clinoform rollover trajectory sedimentary process regime and grain character within intrashelf clinothems offshore new jersey u s a abstract clinoform geometries and trajectories are widely used to predict the spatial and temporal evolution of sand distribution but most analytical approaches underplay the significance of topset and shelf process regime in determining how and when sediment is conveyed downdip or stored on the continental shelf we present an integrated study of clinoform rollover trajectory and detailed grain character analysis to assess the role of topset process regime in determining sand distribution and sediment character across clinothems this study targets the topset foreset and bottomset deposits of four successive miocene intrashelf clinothem sequences which represent deposition under either river dominated or wave dominated conditions seismic reflection data was combined with core analysis and grain character data derived from 664 samples collected from three cored research boreholes in river dominated clinothems the transfer of coarse grained sediment occurs under both rising and flat to falling clinoform rollover trajectories suggesting that process regime is more important in determining sediment delivery than clinoform trajectory river dominated systems are effective conveyors of sediment into deeper water wave dominated clinothems deposited exclusively under rising clinoform rollover trajectories largely retain sand within topset and foreset deposits wave dominated systems are effective sediment filters notably deposition under either river or wave dominated topset process regimes results in quantifiable differences in grain character attributes along clinoform profiles sediments in river dominated systems are coarser less well rounded and more poorly sorted and show greater intersequence and intrasequence variability than those in wave dominated systems prediction of sediment character is more challenging in river dominated systems this study highlights the need for caution when attempting to predict downdip sand distribution from clinoform trajectory alone and provides a novel perspective into downdip grain character profiles under end member topset process regime conditions the results of this study can be used to better constrain sediment grain size and grain shape distributions in process based forward models and have widespread applications in prediction of reservoir quality in both frontier and mature hydrocarbon basins

asymmetry in holocene river deltas patterns controls and stratigraphic effects abstract understanding controls on sediment distribution in river deltas is paramount to predicting facies relationships and stratal architecture most classifications of deltas have focused on subaerial plan morphology as a simplistic function of river tide and wave energy new work however is revealing the importance of subaqueous deposits and in particular shore parallel sediment redistribution in the shaping of delta planform delta asymmetry has emerged as an important characteristic reflective of patterns of alongshore sediment dispersal asymmetry has been described from onshore and offshore environments from several different types of modern deltas but aspects of asymmetry have not been fully documented and the degree to which these patterns are recorded in deltaic strata is not yet known this study is a comprehensive literature review of sediment distributions in modern deltas focusing on studies with high resolution geomorphic geophysical and geochronological datasets we reviewed 27 deltas using over 100 papers primarily from the past 15 20 years morphological facies and stratigraphic aspects were analyzed across the entire spectrum of deposits from the delta apex to the most distal muds of the prodelta we define quantifiable indices of asymmetry describing upcurrent vs downcurrent distribution of sediment volume sediment area sediment caliber and distributary channels most deltas are asymmetrical to some degree with respect to one or more of these parameters many deltas are increasingly skewed toward the downcurrent side from proximal to distal sub environments i e delta plain delta front prodelta some deltas are skewed toward the upcurrent side in one sub environment and toward the downcurrent side in another sub environment sand is preferentially deposited on the downcurrent side of most deltas but distributary channels tend to develop toward the upcurrent side the highest sand mud ratios are often on the upcurrent side in the lower delta plain but in the delta front these ratios are highest on the downcurrent side these complex patterns of asymmetry reflect different combinations of controls including discharge partitioning lobe abandonment and localized transgression plume deflection by coastal currents dominance of longshore current direction variable subsidence and other factors these processes may result in upcurrent downcurrent variations in clinoform geometry rates of progradation and stratal lapping relationships asymmetry has multiple aspects manifestations and controls even within a single delta but the long term preservation potential of these patterns likely varies depending on depositional setting and shoreline trajectory studies of ancient deltas will be better informed by recognizing the wide variety of controls on sediment distribution and avoiding the tendency toward a single model of delta asymmetry

late quaternary environmental change in oujiang delta along the northeastern zhe min uplift zone southeast china abstract we present a history of late quaternary coastal evolution based on the study of a 41 9 m long sediment core from the oujiang delta multiple analytical methods are employed including sedimentary facies analysis radiocarbon dating and the investigations of grain size elemental microfossil and pollen compositions two transgression regression sequences separated by a paleosol layer are identified several lines of evidence indicate that the lower sequence was deposited during the mid early mis 3 stage under a relatively warm and wet climate an elevated mis 3 highstand sea level higher than 24 m is observed the upper sequence was created after the paleosol was flooded during a marine transgression at 9 5 cal kyr bp seven weak east asian summer monsoon easm events are identified with central years of 8 4 7 7 6 3 5 7 4 7 2 8 and 1 8 cal kyr bp these coincide with those from the ecs sediment cores and the dongge cave 18o record indicating that easm precipitation is a major controlling factor of sedimentation rates in the region the oujiang delta is also subject to typhoon impacts and east asian winter monsoon eawm induced coastal currents active typhoons and a relatively enhanced eawm occurred during the weak easm period between 4 9 and 6 4 cal kyr bp producing high sedimentation rates in the middle holocene we emphasize the high sensitivity of small asian river deltas as archives of the easm eawm and typhoons such environments merit further as a means to understand past changes as well as future responses to projected climatic and sea level change

late holocene depositional environments and coastal evolution of the mekong river delta southern vietnam abstract the mekong river delta in southern vietnam is a tide dominated delta and has been formed by the mekong river system the sediments are dominantly fine grained and were deposited in the receiving basin with slight inclination of pre existing deposits in the south china sea and gulf of thailand around 6000 to 5000 yr bp maximum holocene transgression occurred and seawaves surrounded uplands of the late pleistocene terrace basement rock and weathered land in the northern parts of the delta double notches were undercut by seawaves on the limestone hill in hatien at about 4 5 and 2 5 m above present sea level marine deposits prevailed throughout the delta during the highstand and regressions of relative sea level over the last 4550 yr bp delta progradation has produced a great flat plain of 62 520 km 2 this extremely fast progradation could be due to a very high sediment supply depositing in the slight inclination of the receiving basin b neotectonic movements and relative sea level changes c widespread mangrove forests playing an important role to enhance sediment accumulation former mangrove marshy deposits were significantly developed in the plain of reeds and longxuyen quadrangle mangrove marshes have also been developing well in the camau peninsula and present coastlines moreover regressions over the last 4550 yr bp have produced many distinct sets of relict beach ridges which are useful in distinguishing the former coastlines and evolutionary history of the delta

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

holocene delta evolution and sediment discharge of the mekong river southern vietnam abstract evolutionary changes delta progradation and sediment discharge of the mekong river delta southern vietnam during the late holocene are presented based on detailed analyses of samples from six boreholes on the lower delta plain sedimentological and chronostratigraphic analyses indicate clearly that the last 3 kyr were characterized by delta progradation under increasing wave influence southeastward sediment dispersal decreasing progradation rates beach ridge formation and steepening of the face of the delta front estimated sediment discharge of the mekong river for the last 3 kyr based on sediment volume analysis was 144 36 million t yr 1 on average or almost the same as the present level the constant rate of delta front migration and stable sediment discharge during the last 3 kyr indicate that a dramatic increase in sediment discharge owing to human activities as has been suggested for the yellow river watershed did not occur although southeast asian rivers have been considered candidates for such dramatic increases in discharge during the last 2 kyr the mekong river example although it is a typical large river of this region does not support this hypothesis therefore estimates of the millennial scale global pristine sediment flux to the oceans must be revised

dynamic particle segregation and accumulation processes in time and space revealed in a modern river dominated delta a spatiotemporal record of the kiso river delta central japan abstract the holocene succession of the kiso river delta a sand rich river dominated delta in central japan was analyzed at high temporal and spatial resolution the results demonstrate how the spatiotemporal distribution of sedimentary facies gross sediment accumulation rates and accumulation rates of mud versus sand relate to the geomorphic development of the delta and the post glacial sea level history the centers of peak mud and sand accumulation have migrated seaward in parallel during a regressive stage from 6 5 ka to the present at the rate of 3 9 m y the mud and sand accumulation centers mark the bottom and top respectively of the delta front slope the sediments of the prograding delta show strong sorting and clear upward coarsening because of the steep slope of the delta front such internal topographic control redistributes and separates the coarse and fine fractions of the fluvial input during regression the topographic controlled sedimentary segregation constructs delta front topography in reverse therefore the proportion of sand to mud in the fluvial input controls the stability of the delta front morphology our modeling of the kiso river delta may have implications for prediction of coastal flooding adjacent to deltas in other parts of the world

viscosity determinations of some frictionally generated silicate melts implications for fault zone rheology at high strain rates analytical scanning electron microscopy has been used to determine the major element compositions of some natural and artificial silicate glasses and their microcrystalline equivalents derived by the frictional melting of intermediate to acid protoliths the data show that the matrices of the friction melts which cool to form pseudotachylytes are relatively basic and hydrous even when their protoliths are intermediate to acid this is because frictional fusion involves the selective comminution and nonequilibrium melting of minerals based on their individual mechanical properties and melting points not the formation of minimum melts through equilibrium mineral interaction this means that hydrous ferromagnesian minerals e g micas and amphiboles melt preferentially to form the liquid matrix while feldspars and especially quartz more readily survive as clasts pseudotachylytes generated by frictional melting are therefore not bulk melts and as clast melt suspensions they cannot be considered as simple newtonian fluids the calculated viscosities of the friction melts are low for example at 1200 c most friction melts possess zero shear suspension viscosities of 102 104 dpa s 1 dpa s 1 p this is equivalent to the viscosities of tholeiitic and alkaline basaltic magmas at the same temperature these viscosities are maximum determinations because as clast melt suspensions friction melts may undergo shear thinning and exhibit pseudoplasticity at high shear rates i e during slip on a fault surface contrary to earlier suggestions where the bulk melting of intermediate to acid protoliths was believed to result in the generation of viscous friction melts that could act to inhibit continued sliding this work shows that most pseudotachylytes are partial melts possessing low viscosities the formation of highly fluid suspensions during slip may have profound effects on the dissipation of stored strain energy in the rocks surrounding a fault interface lubrication could facilitate an increase in the slip rate and the rate of energy dissipation this would be manifest as an increase in high frequency seismic wave radiation and vibrational

mid holocene mangrove succession and its response to sea level change in the upper mekong river delta cambodia abstract middle holocene vegetation and mangrove successions are clearly evident in the palynological records of two cores from the upper mekong river delta in cambodia spanning from 9 4 to 6 3 cal ka bp the cores mainly record a transgressive sequence from floodplain freshwater marsh to tidal flat which was overlain by mangrove corresponding to the decelerated sea level rise at 8 3 cal ka bp pioneer mangrove species sonneratia alba and sonneratia caseolaris appeared in the sediments and then was replaced by regressive mangrove succession containing upward increasing abundances of rhizophora apiculata and bruguiera spp high salinity and flooding tolerant community s alba was developed at the western core site psg at 8 2 cal ka bp and the eastern core site pk at 7 5 cal ka bp the time difference of s alba appearance between the two sites might be resulted from the complexity of sedimentary environment where a higher sediment supply was provided to the western floodplain than to the eastern floodplain after 7 5 cal ka bp aggradational stacking of intertidal sediments of which the thickness is larger than the present maximum tidal range may have resulted from continuous sea level rise during 7 5 7 0 cal ka bp

huguangyan maar lake se china a solid record of atmospheric mercury pollution history in a non remote region abstract mercury is a highly toxic metal that can cause harm to environment and human health as atmospheric deposition is the main source of total hg input to aquatic system in remote and pristine regions almost all the studies on atmospheric hg pollution history concentrated in these areas while the studies in non remote areas are much limited especially for the long history records in this study huguangyan maar lake an undisturbed lake system at low altitude in china was selected to reconstruct the atmospheric mercury pollution history variation patterns of toc hg and non residual sr in the sediment core indicated that compared to the direct atmospheric hg deposition the effect of either hg scavenging from water column by algae or the catchment inputs of previously deposited hg on the hg accumulation in the lake sediment was limited the sediment hg content in huguangyan lake was mainly controlled by the atmospheric hg deposition and thus accurately reflected the atmospheric hg pollution history the hg a hg content from atmospheric deposition in huguangyan lake presented a comparable variation pattern to that in remote sites it had the same variation trend as the global atmospheric hg before 1950 ce which could be attributed to the industrial revolution after that it was mainly controlled by hg emissions from asian countries the variation of hg a also indicated that atmospheric hg deposition accelerated significantly since 2000 ce this study along with other investigations in remote sites in china showed that the sediment hg in huguangyan lake responded to the atmospheric hg pollution more sensitively than in the alpine regions it should be noted that the more intensive acceleration of hg deposition in huguangyan lake may imply that the south of china suffered from much more serious atmospheric hg pollution than previous studies revealed

cycling of trace metals and rare earth elements ree in acid sulfate soils in the plain of reeds vietnam abstract trace metals and rare earth elements ree are subject to intensive chemical cycling in acid sulfate soils the oxidation of pyrite bearing deposits and the subsequent acidification mobilizes a variety of trace metals and ree in this study solid phase and pore water data of three cores from the plain of reeds in the mekong river delta vietnam were analyzed distinct authigenic enrichments of trace metals and ree were observed in the solid phase of these cores thermodynamic modeling was employed to elucidate the controls on trace metal and ree mobility and the governing factors for the formation of these authigenic enrichments the formation of ree enrichments in these settings is clearly controlled by ph and the availability of potent sorbents under suitable conditions trace metals such as e g zinc nickel and cobalt are likely bound as trace metal monosulfides in the enrichment zones the solid phase and pore water data and the results of a thermodynamic model suggest a possible sequential precipitation of trace metal sulfides however the incorporation of trace metals into iron sulfides cannot be ruled out in the case of lead and arsenic the formation of pb as jarosite proved to be a further major sink these insights provide a better understanding of the controls and governing factors for trace metal and ree mobility in acid sulfate soils and will therefore help to assess impacts on soil and water

holocene evolution of the song hong red river delta system northern vietnam abstract the song hong red river delta located on the western coast of the gulf of bac bo tonkin in the south china sea formed as a result of the song hong sediment discharge throughout the holocene the river s sedimentary basin upstream from the delta plain is not large the delta plain comprises emerged tidal mangrove flats formed during the sea level highstand at 2 3 m 6 4 cal kyr bp and a beach ridge strandplain with straight to lobate beach ridges on the landward and seaward sides of the delta plain respectively the delta affords us the opportunity to examine river mouth morphodynamics comprehensively in relation to sediment discharge and sea level changes in this paper we describe the holocene evolution of the song hong delta system and the river mouth morphodynamics on the basis of seven sediment cores each 30 70 m long taken from the delta plain during 1999 2001 and 101 radiocarbon dates obtained from the core sediments sediments from the seven cores consisting of incised valley fills since the last glacial maximum can be divided in ascending order into fluvial sediments composed of gravelly sand and mottled clay tide influenced estuarine sediments containing shell and wood fragments and deltaic sediments composed of tide influenced sand and mud deposits in which the contents of sand and wood fragments increase upward by applying sequence stratigraphic concepts a transgressive surface can be identified at the gravelly sand mottled clay boundary and the maximum flooding surface can be identified at the estuarine deltaic sediments boundary the lowstand systems tract transgressive systems tract and highstand systems tract record 15 15 9 and 9 0 cal kyr bp respectively during the past 9 kyr the majority of the sediment discharged by the song hong accumulated in the incised valley and enhanced progradation at the river mouth the river mouth prograded from the bay head toward the gulf and its morphology changed from funnel shaped 9 6 cal kyr bp to straight 6 2 cal kyr bp and finally to lobate 2 0 cal kyr bp the morphological change from a funnel shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide dominated bay head setting to a wave influenced open coast setting the cessation of the sea level rise at 6 cal kyr bp may have played only a small role in the change of river mouth morphology because the progradation rate decelerated from 22 to 4 m yr instead of accelerating at that time the river mouth morphodynamic change from straight to lobate was largely caused by an increase in the song hong sediment discharge from 17 27 9 2 cal kyr bp to 49 million t yr 2 0 cal kyr bp as a result of anthropogenic deforestation along the upper reaches of the song hong

determination of low level mercury in coralline aragonite by calcination isotope dilution inductively coupled plasma mass spectrometry and its application to diploria specimens from castle harbour bermuda abstract we have developed a technique that combines a high temperature quartz furnace with inductively coupled plasma mass spectrometry for the determination of hg stored in the annual caco 3 bands found in coral skeletons substantial matrix effects presumably due to the discontinuous introduction of co 2 to the gas stream were corrected for by simultaneously supplying a stream of argon containing highly enriched elemental 202 hg o and observing peaks in the 200 hg 202 hg signal as the sample was decomposed primary signal calibration for hg was achieved using gas injections from a saturated vapor standard the absolute instrument detection limit was low about 0 2 fmol with a practical limit of detection 3 of blanks of 2 fmol reproducibility of samples was rsd 15 27 we applied this method to the determination of hg concentrations in two colonies of diploria labyrinthiformis collected from castle harbour bermuda at a site about to be buried under the municipal waste landfill the temporal reconstructions of castle harbour seawater hg concentrations implied by the coral record show a decline throughout the period of record 1949 2008 the coral archived no apparent signal associated with waste disposal practices in the harbour bulk waste land filling or since 1994 disposal of waste incinerator ash and mercury concentrations in the coral did not correlate to growth rate as assessed by linear extension there was however a large and nearly exponential decrease in apparent hg concentration in the harbour which circumstantially implicates the dredging and or landfilling operations associated with the construction of the airport on st david s island