paleoecology of mangroves along the sibun river belize abstract this study examines a sediment core sr 63 from a mangrove ecosystem along the sibun river in belize which is subject to both changes in sea level and in the characteristics of the river s drainage basin radiocarbon dates from the core show a decreased sedimentation rate from 6 ka to 1 cal ka bp and a marked change in lithology from primarily mangrove peat to fluvial derived material at 2 5 cal ka bp changes in the sedimentation rates observed in mangrove ecosystems offshore have previously been attributed to changes in relative sea level and the rate of sea level rise pollen analyses show a decreased abundance of rhizophora red mangrove pollen and an increased abundance of avicennia black mangrove pollen and non mangrove pollen coeval with the decreased sedimentation rates elemental ratios n c a and stable isotope analyses 15 n and 13 c show that changes in the composition of the organic material are also coeval with the change in lithology the decrease in sedimentation rate at the site of core sr 63 and at offshore sites supports the idea that regional changes in hydrology occurred during the holocene in belize influencing both mainland and offshore mangrove ecosystems

pollen distribution in marine sediments on the continental margin off northern california abstract pollen analysis of 84 samples from surface sediment of the continental margin off northern california between 38 and 39 n and 123 and 124 w shows that the composition of pollen assemblages in this part of the north pacific ocean reflects the regional vegetation of the russian river and other local drainage basins of the northern coast of california systematic trends in the quantitative and qualitative variations in these marine pollen assemblages show that fluvial and marine transport are important factors in determining the nature of pollen assemblages offshore these conclusions are supported by the analyses of pollen in rivers of the north coast of california and in particulate matter collected in a mid slope sediment trap

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

a holocene pollen record of vegetation and coastal environmental changes in the coastal swamp forest at batulicin south kalimantan indonesia abstract pollen analysis of a coastal peat swamp core representing 9100 bp from batulicin south kalimantan indonesia shows that mangrove forest with rhizophora as its main element has been established since the early holocene vegetation development in general and particularly mangrove forest was influenced by holocene environmental changes the highest value of rhizophora at ca 8200 bp indicates an early holocene sea level drop and implies sea level at ca 9 m subsequently mangrove forest was severely disrupted by rapid sea level rise at ca 6400 bp prior to the holocene maximum however it quickly recovered following a lower rate of sea level rise or subsequent sea level drop at ca 6000 bp and flourished until ca 1000 bp from ca 6000 bp the environmental setting around the site seems to have gradually become more terrestrial and changed from mangrove forest to peat swamp forest due to higher precipitation and intensive progradation human influence is recognized from ca 1600 bp

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

sea level changes in the tectonically stable malay thai peninsula abstract the malay thai peninsula is part of sundaland a geological region of relative crustal stability therefore the positions of old shorelines of the past 20 000 years or so can be considered to indicate positions of actual past sea levels over 200 shoreline indicators at positions below as well as above present sea level have been radiocarbon dated these dated positions indicate that prior to 6 ka the sea rose from at least 90 m below present sea level at rates that initially amounted to 15 mm year and later became 6 mm year at ca 6 ka the rising sea surpassed its current position and at ca 5 ka it reached 5 m during this maximum marine inundation the peninsula was narrower since the low coastal plains did not yet exist in the period following this maximum transgression the available shoreline data indicate that regional sea level subsided through a series of fluctuations that were characterized by amplitudes of 2 m and periods of about 2000 years the peaks and troughs of the fluctuations became progressively lower the latest peak was at about 1 7 m or 0 7 m above present high tide a few hundred years ago the cause of these fluctuations is not yet known but the trend suggests that in the near future regional sea level may subside at annual rates between 1 5 mm and 2 mm this rate of descent is 25 to 30 of the estimated rate of sea level rise that may result from global warming in other words for the malay thai peninsula the effect of sea level rise on account of manmade greenhouse gases will be partly compensated by actual subsidence of regional sea level

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

early holocene sea level record from submerged fossil reefs on the southeast florida margin massive fossil outlier reefs are preserved seaward of the modern shelf and reef tract along the southeast florida margin thermal ionization mass spectrometric tims u th dating of 16 pristine acropora palmata and head corals cored from two transects document early holocene reef growth from 8 9 to 5 0 ka from approximately 13 5 to 7 m msl mean sea level these samples fill a gap in the florida keys sea level database and clarify the timing of a significant decrease in the rate of sea level rise a portion of this interval represented by a gap in the caribbean record of a palmata reefs has been interpreted as reef drowning during an inferred catastrophic sea level rise event of 45 mm yr or a 6 5 m rise between 7 6 and 7 2 ka attributed to west antarctic ice sheet instability and changes in marine ice extent between 8 and 7 ka continuous in situ shallow water reef growth in florida during this interval precludes the occurrence of exceedingly rapid rates of sea level rise and is consistent with the north atlantic record of deglaciation from 9 to 7 ka gaps in the early holocene sea level records for florida and the caribbean are thus more likely to be artifacts of limited sampling and or core coverage and not necessarily a result of drowning

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

holocene development of the yellow river s subaqueous delta north yellow sea high resolution seismic profiles from the north yellow sea reveal a 20 40 m thick subaqueous clinoform delta that wraps around the eastern end of the shandong peninsula extending into the south yellow sea this complex sigmoidal oblique clinoform containing an estimated 400 km 3 of sediment overlies prominent relict transgressive surfaces the nearshore topset of the clinoform 50 m contain less than 1 m of holocene sediment with low sedimentation rates 1 mm year in contrast to other clinoforms the shandong clinoform appears to be a compound subaqueous deltaic system with what we interpret to be proximal and distal phases of clinoform development the underlying proximal sequence formed proximally between f11 and 9 2 ka in response to a temporary pause in the rapid postglacial sea level rise after the meltwater pulse 1b mwp 1b and increased discharge from the yellow river to the north yellow sea due to intensification of the summer monsoon a flooding surface appears to separate the proximal and distal phases corresponding to the next rapid sea level rise 9 5 9 2 ka bp mwp 1c since 9 2 ka bp an overlying distal sedimentary sequence has accumulated reflecting the backstepping and shifting river mouth westward to the gulf of bohai some inputs from coastal erosion and nearby small streams may be locally important along shore transport cross shelf advection and upwelling in the north yellow sea have reworked post lgm sediment and have helped maintain the morphology of the clinoform in the shandong mud wedge d 2004 elsevier b v all rights reserved

mangrove pollen of indonesia and its suitability as a sea level indicator we investigated the mangroves of southeast sulawesi indonesia to assess their potential as proxies for reconstructing sea level during the holocene initial investigations confirmed that the mangrove species demonstrate zonations parallel to the shoreline and are dominated by the family rhizophoraceae with avicennia heritiera and sonneratia also important constituents of the mangroves we investigated the vertical distributions of pollen assemblages at three sites partial cca analysis demonstrated that at all three sites elevation was a significant control on the distribution of pollen assemblages in surface samples we combined the three contemporary transects to develop a regional transfer function to explain the relationship between the surface assemblages and elevations using the maximum likelihood ml method the developed transfer function indicated mangrove pollen can be used as a precise indicator of past sea levels with an error of 0 22 m the transfer function was applied to two fossil cores from the wakatobi marine national park and evaluated using the modern analogue technique both cores showed similar patterns in changes of palaeo mangrove elevation and had modern analogues in the contemporary training set we conclude that mangrove pollen is a suitable proxy for reconstructing sea level in tropical environments

palynological records of holocene monsoon change from the gulf of tonkin beibuwan northwestern south china sea article i nfo article history received 2 september 2008 palynological records in cores c4 and b106 from the gulf of tonkin reveal signals of paleo monsoon and paleoenvironmental change during the late pleistocene and holocene before 13 4 cal kyr bp the gulf of tonkin was exposed to the atmosphere and covered by grassland starting at 11 7 cal kyr bp the gulf of tonkin was inundated by brackish water indicated by the appearance of the brackish algae cleisto sphaeridium sentusidinium and spiniferites a decrease of herb content and an increase of pinus after hainan island was completely separated from the leizhou peninsula by qiongzhou strait at 8 5 cal kyr bp a continuous marine sedimentary environment was found the current patterns were similar to those of the present with a general trend of current homogenization reflected by gradually decreasing quantities of quercus pollen and a narrowing gap between the palynological concentrations of the southern and northern parts of the region the data suggest that three short periods of strengthened winter monsoons and currents were centered at 6 0 cal kyr bp 2 7 cal kyr bp and 0 2 cal kyr bp and that two short periods of strengthened summer monsoons and currents were centered at 7 5 cal kyr bp and 3 4 cal kyr bp

pollen analysis of mangrove sediments as a sea level indicator assessment from tongatapu tonga increasing necessity for precision in holocene sea level records calls for definitive sea level indicators to be assessed these are reviewed by use of examples from the s w pacific and the technique of pollen analysis of mangrove sediments evaluated as a high resolution sea level indicator example is given how a fully calibrated sea level reconstruction can be gained from holocene mangrove peat units from tongatapu tonga by application of features established from a modern analogue of surface samples to interpret fossil pollen patterns

holocene evolution and anthropocene destruction of the krishna delta on the east coast of india delta lobe shifts human impacts and sea level history abstract the holocene evolution of the krishna delta was inferred using landform characteristics and 11 sediment cores with 59 accelerator mass spectrometry 14c dates the landform assemblages in a 5880 km2 area of the krishna delta indicate an upper landward river built fluvial plain and a lower seaward marine built beach ridge plain holocene sediment unconformably overlying a pleistocene basement consists of 11 sedimentary facies mainly shallowing upward and deltaic succession sea level indicators such as the basal mangrove peat layers above the pleistocene basement and the foreshore sediments indicate that the sea level rose from 9 m to 3 m during 8 3 6 3 cal ky bp and stabilised at the present level around 5 cal ky bp the 3539 km2 area of the krishna delta beach ridge plain developed in five major stages during the last 6 cal ky with distinct lateral and seaward migration of delta lobes depocentre shifts delta progradation accelerated in the last 500 years forming an out building lobate delta however predominant erosion along the sediment starved coast during the past five decades due to impoundment of riverine inputs at the burgeoning upstream dams has pushed the krishna delta into a persistent destruction phase

punctuated eustatic sea level rise in the early mid holocene whether eustatic sea level rise through the holocene has been punctuated or continuous has remained controversial for almost two decades resolving this debate has implications for predicting future responses of remaining ice sheets to climate change and also for understanding the drivers of human settlement and dispersal patterns through prehistory here we present a sea level curve for the past 8900 yr from singapore a tectonically stable location remote from ice loading effects we also present critical and unique sedimentation rate organic 13c and foraminiferal 13c proxy records of sea level change derived from a shallow marine sediment core from the same area over the same time interval the sea level curve corroborated by the independent proxy records suggests rapid rise at a rate of 1 8 m 100 yr until 8100 cal calibrated yr b p a near cessation in the rate of sea level rise between 7800 and 7400 cal yr b p followed by a renewed rise of 4 5 m that was complete by 6500 cal yr b p we suggest that this period of relatively stable sea level during the early to mid holocene enabled modern deltas to advance providing a highly productive environment for the establishment of coastal sedentary agriculture periods of rapid sea level rise before and after may have catalyzed significant postglacial episodes of human dispersal in coastal regions

studies on holocene mangrove ecosystem dynamics of the braganca peninsula in north eastern para brazil abstract three sediment cores from the braganca peninsula located in the coastal region in the north eastern portion of para state have been studied by pollen analysis to reconstruct holocene environmental changes and dynamics of the mangrove ecosystem the cores were taken from an avicennia forest bosque de avicennia bda a salt marsh area campo salgado cs and a rhizophora dominated area furo do chato pollen traps were installed in five different areas of the peninsula to study modern pollen deposition nine accelerator mass spectrometry radiocarbon dates provide time control and show that sediment deposits accumulated relatively undisturbed mangrove vegetation started to develop at different times at the three sites at 5120 14c yr bp at the cs site at 2170 14c yr bp at the bda site and at 1440 14c yr bp at the fdc site since mid holocene times the mangroves covered even the most elevated area on the peninsula which is today a salt marsh suggesting somewhat higher relative sea levels the pollen concentration in relatively undisturbed deposits seems to be an indicator for the frequency of inundation the tidal inundation frequency decreased probably related to lower sea levels during the late holocene around 1770 14c yr bp at bda around 910 14c yr bp at fdc and around 750 14c yr bp at cs the change from a mangrove ecosystem to a salt marsh on the higher elevation around 420 14c yr bp is probably natural and not due to an anthropogenic impact modern pollen rain from different mangrove types show different ratios between rhizophora and avicennia pollen which can be used to reconstruct past composition of the mangrove in spite of bioturbation and especially tidal inundation which change the local pollen deposition within the mangrove zone past mangrove dynamics can be reconstructed the pollen record for bda indicates a mixed rhizophora avicennia mangrove vegetation between 2170 and 1770 14c yr bp later rhizophora trees became more frequent and since ca 200 14c yr bp avicennia dominated in the forest

pollen distribution in marine sediments from the south eastern indonesian waters abstract pollen analysis on box core sediments from the south eastern indonesian waters provide information on trends in pollen transport and on pollen distribution in the marine surface sediments pollen and at a lower rate pteridophyta spore concentration values tend to decrease with increasing distance from the shoreline as a result pteridophyta percentages tend to increase with increasing distance from the shoreline mangrove pollen shows very little export from its distribution area while pollen from the mid upper montane group shows a substantial export from its onshore distribution area in general despite the complex nature of vegetation patterns and pollen transport in this region the onshore distribution of individual taxa and major vegetation types is well reflected in the pollen distribution in the marine sediments

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

the holocene history and development of the tonle sap cambodia abstract the tonle sap the great lake of central cambodia is the central component of wetland ecosystems in the lower mekong river basin and is of enormous conservation value the lake s unusual hydraulic relationship with the mekong river and its consequent sensitivity to monsoon variability makes the tonle sap sensitive to climate change exploring the dynamics and development of this system under different climate regimes of the past offers a perspective on possible future impacts which is critical for sound management biostratigraphic and sedimentological data derived from cores of lake sediment indicate that during the period 7000 to ca 5500 14 c years before present the lake was less variable than present in terms of depth during the annual cycle of flood and may have been strongly influenced by saline tidal waters associated with higher than present seas levels as regional environments became drier and more seasonal in the late holocene more sediment was re suspended during the increasingly marked dry season lake level minimum lowering the effective sediment accumulation rate contrary to current interpretations of the history of the lake and associated wetland ecosystems the data presented here imply that regional hydraulic connections between the lake and the mekong river existed from at least the early 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

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

palynological record of climate change during the last deglaciation from the song hong red river delta vietnam abstract the palynological sequence from core nd 1 on the song hong delta in the northern vietnam reveals the climate change during the last deglaciation the identified pollen in the core is dominated by castanopsis lithocarpus elaeocarpus ficus piperaceae and quercus high percentages of temperate taxa including the conifers dacrydium podocarpus pinus cupressaceae txodiaceae and cryptomeria and broad leaved taxa of carpinus alnus juglans carya ulmus fagus ilex castanea quercus which have a mainly upland distribution is possibly associated with a lowering of the montane vegetation boundary on the other hand intensified river influence can also result in an increase in the temperate allochthonous taxa after analyzing the magnitude of river influence on pollen assemblages during the sedimentary environment evolution we extracted the climate information and used this to reconstruct climate change during the last deglaciation a cooler climate during 14 5 10 9 cal kyr bp than at present is indicated by higher percentage of temperate types than at present under a similar river influence on the floodplain the younger dryas cooling event is recognized by widely developed grasslands between 12 9 and 11 6 cal kyr bp adding to the evidences for this period from both terrestrial and marine records in regions influenced by the east asian monsoon two other cooling periods 9 4 9 0 cal kyr bp and 6 5 5 2 cal kyr bp are indicated by increases of temperate pollen taxa such as cryptomeria alnus quercus and castanea

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

an early holocene sea level jump and delta initiation 1 early holocene sea level change controlled the evolution of clastic coastal depositional systems radiocarbon dated borehole cores obtained from three incised valley fill systems in asia changjiang song hong and kiso river record very similar depositional histories especially between about 9000 and 8500 cal bp sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period in addition large decreases in sediment accumulation rates occurred a sea level jump causes an estuarine system and its depocenter to move rapidly landward it is possible that the final collapse of the laurentide ice sheet accompanied by catastrophic drainage of glacial lakes at approximately 8500 cal bp caused such a jump the jump was followed immediately by a period of decelerated sea level rise that promoted delta initiation

depositional facies and radiocarbon ages of a drill core from the mekong river lowland near phnom penh cambodia evidence for tidal sedimentation at the time of holocene maximum flooding abstract the depositional facies and radiocarbon ages of a long holocene sediment core ks from cambodia are reported here to clarify the sedimentary environments of the mekong river delta system at the time of holocene maximum flooding by the sea the 30 7 m long ks core from the upper mekong river lowland about 20 km southeast of phnom penh penetrated five depositional facies a to e in ascending order facies a is cross laminated fluvial sand facies b is laminated very fine sand with mud drapes facies c to e are salt marsh flood plain and natural levee deposits characterized by a succession of peat organic clay and reddish brown silt facies b dates to 9 0 7 5 ka and is interpreted as aggradational tidal deposits 16 5 m thick deposited during a rapid rise of sea level these deposits became overlain by an accumulation of salt marsh and flood plain deposits during the subsequent period of slowly rising and then falling sea level the maximum flooding surface lies in the facies b interval the presence of tidal deposits implies that the core site about 230 km inland from the present river mouth was near the shoreline and experienced strong tidal influences during the early holocene

global meltwater discharge and the deglacial sea level record from northwest scotland quantitative models of earth ice sheet ocean interactions predict that periods of rapid eustatic sea level rise indicating enhanced meltwater discharge to the oceans should be manifest in the relative sea level histories from sites within the limits of late devensian ice sheets analysis of a record of relative sea level change for the last 16000 calendar years from northwest scotland constrains the magnitude and timing of two major pulses of meltwater ca 14000 and ca 11300 cal yr bp inferred from coral records the ca 14000 cal yr bp event saw a temporary doubling of the flux of meltwater but existence of the second major event at ca 11300 cal yr bp is not supported by the data from northwest scotland copyright 1999 john wiley sons ltd

mid holocene climate and land sea interaction along the southern coast of saurashtra western india abstract the relict mudflat from the southern saurashtra coast of gujarat was investigated using geochemical and palynological analyses supported by radiocarbon dating to understand whether climate fluctuations and sea level operated in tandem during mid holocene the study revealed that the saurashtra coast experienced relatively wet climatic conditions with simultaneous occurrence of marginally high sea level between 4710 and 2825 cal yr bp subsequently a gradual onset of aridity and lowering of the sea level was observed between 2825 and 1835 cal yr bp and further a slight decrease in aridity is observed after 1835 cal yr bp the present day coastal configuration was probably achieved after around 1500 cal yr bp considering the tectonic instability of saurashtra coast land level changes the effective mid holocene sea level was estimated to be 1 m higher than the present the study demonstrates that sea level changes climate variability and land level changes were coupled during the mid holocene

mangrove swamp stratigraphy and holocene transgression grand cayman island west indies abstract the island of grand cayman in the western caribbean has an extensive mangrove swamp vegetation numerous cores have been taken in and adjacent to these swamplands and these reveal that the swamps are generally underlain by a transgressive sequence of sediments the basal unit of this sequence consists of a laminated or non laminated crust formed in a subaerial environment locally these crusts are overlain by plastic mud deposited in seasonally flooded environments mangrove peat forms the upper unit of the transgression within most of the swamplands overlying the other units where these are found and reaching thicknesses of more than 4 m the final stage of marine incursion is recorded to the east of north sound where in water depths of 10 200 cm shelly mud occurs overlying mangrove peat in contrast to this to the west of north sound there is a regressive sequence in which shelly marl underlies a localised sea grass peat and mangrove peat this regressive sequence records local progradation of mangroves into marine environments the transgressive sedimentary sequence on grand cayman is similar to transgressive sedimentary sequences described from the florida everglades mangrove complex florida bay and the belize shelf on grand cayman however the stratigraphy is less complex because there are not extensive freshwater peat forming environments or intertidal and supratidal carbonate environments samples of mangrove peat were collected from the peat bedrock interface along a surveyed profile across barkers peninsula on grand cayman radiometric dating of these implies that sea level was approximately 185 cm below the present level at least 2100 years bp comparison of these dates with dates on mangrove peat from elsewhere suggests that submergence on grand cayman has taken place at a similar rate to that in florida

holocene sea levels and palaeoenvironments malay thai peninsula southeast asia sedimentological and palynological investigations of great songkhla lakes east coast of the malay thai peninsula southeast asia reveal sedimentary sequences rich in palynomorph assemblages dominated by pollen of mangroves and freshwater swamps compared with other regions in southeast asia the assemblages are of relatively low diversity geochronological data indicate that the great songkhla lakes record one of the earliest mangrove environments in southeast asia 8420 8190 cal yr bp which are subsequently replaced by a freshwater swamp at 7880 7680 cal yr bp owing to the decline of marine influence sea level observations from great songkhla lakes and other areas of the malay thai peninsula reveal an upward trend of holocene relative sea level from a minimum of 22 m at 9700 9250 cal yr bp to a mid holocene high stand of 4850 4450 cal yr bp which equates to a rise of c 5 5 mm yr the sea level fall from the high stand is steady at c 1 1 mm yr geophysical modelling shows that hydroisostasy

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

evidence for ca 7 ka maximum holocene transgression on the peninsular malaysia east coast in situ fossil coral and shelly marine deposits occur up to 50cm above mean sea level in north east peninsular malaysia the fossil reef comprises over 15 coral species and associated molluscs radiocarbon ages of corals range from 7238 to 6909 cal a bp the reef occurs adjacent to bedrock hills that formed a mainland peninsula when the coral was living abundant well preserved fossil molluscs with bivalves commonly articulated occur in ditch tailings from coastal plains flanking these hills landward a sand ridge represents part of the maximum transgression shoreline when alive the fossil coral reef required clear water and full marine conditions seaward of the peninsula the maximum transgression here occurred ca 7 ka with stable environmental conditions persisting long enough for diverse coral reef development assuming a similar tidal range to today relative sea level ca 7 ka would have been between 1 4 and 3m above present between then and ca 6 ka abundant sediment supply resulted in barrier beach construction seaward of the coral reef converting the area to a lagoonal environment unsuitable for coral and burial by muddy deposits assuming that regional relative sea level data indicate maximum holocene highstand up to 5m between 6 and 4 ka are correct then the maximum transgression preceded maximum sea level by at least 1000 years copyright 2014 john wiley sons ltd

origin and evolution of interdistributary delta plains insights from mekong river delta the geometry of river deltas is considered to refl ect the interplay of coastal processes river discharge and sediment supply as 25 of the world s population lives on deltaic lowlands prediction of delta growth is critical knowledge of processes responsible for delta geometries is not well established although such knowledge is critical for the risk management of land use and settlements on deltas the mekong river delta of southern vietnam is one of the largest deltas in the world and offers a unique opportunity to understand the sedimentary evolution of mixed tide and wave dominated large river deltas we constrained the three dimensional sedimentary evolution of the delta plains based on optically stimulated luminescence dating of beach ridges coupled with radiocarbon dated sediment cores results show that the beach shoreline in the lower delta plain initiated ca 3 5 ka by aggradation on basement shoals the delta plain propagated laterally during the late holocene evolving from bars that resulted in asymmetric bifurcation of the river mouth asymmetry was caused by the southwestward longshore sediment drift enhanced by the winter monsoon bars were successively formed on the wider side of the bifurcated river mouths and subsequently accreted seaward being stabilized by tide effects to result in shore perpendicular elongate delta plains our work based on the mekong delta demonstrates for the fi rst time that bar emergence is a key process in the long term evolution of mixed tide and wave dominated deltas

evidence for a rapid sea level rise 7600 yr ago dating the transgression and subsequent regression in marginal basins of the southeastern swedish baltic sea provides a new perspective of global ice volume changes and the isostatic adjustment of the mantle after the retreat of the scandinavian ice sheet from this area superimposed upon a smooth pattern of local sea level rise acceleration occurred ca 7600 calibrated cal yr b p evidenced as a nearly synchronous flooding in six elevated basins ranging from 3 0 to 7 2 m above present sea level we ascribe this rapid local sea level rise of similar to 4 5 m to a sudden increase in ocean mass most likely caused by the final decay of the labrador sector of the laurentide ice sheet the subsequent monotonic fall of local sea level from ca 6500 cal yr b p to the present is mainly an expression of the slow isostatic adjustment of the mantle less

mangrove sediment carbon stocks along an elevation gradient influence of the late holocene marine regression new caledonia abstract among blue carbon ecosystems mangroves are very efficient in storing carbon in their sediments over decadal to millennial time scales however this ability varies with numerous parameters including climate and sea level variations in new caledonia mangrove ecosystems develop in semi arid conditions with a typical zonation rhizophora spp colonize the seaward side of the intertidal area while avicennia marina develops at higher elevations just below the salt flat within this context we determined both the quantity organic carbon content and carbon stocks and the characteristics carbon over nitrogen ratios c n stable carbon and nitrogen isotopes radiocarbon age of the organic matter stored beneath each mangrove stands carbon stocks were determined down to different limits with depth approximate extension of the root systems one meter depth and the hard substrate within the extension of the root systems the sediment carbon stock was lower than 100 mgc ha 1 regardless of the mangrove species this low value resulted directly from the dry climate that limits mangrove productivity at depth beneath every zone a buried layer enriched in mangrove derived organic matter with c n values around 40 and 13c values around 26 was observed this layer likely resulted from a sea level high stand during the late holocene that allowed a long period of stability of the mangrove slowly accumulating organic matter within the sediment in this buried layer the carbon stock was higher than in the upper sediment and reached up to 665 255 and 300 mgc ha 1 in the salt flat zone the a marina stand and the r spp stand respectively the highest stock determined beneath the salt flat was suggested to be related to a period of sea level stability that lasted 3000 years whereas beneath the other zones which are at lower elevations mangrove colonization was more recent and the sea level was continuously decreasing till recently sea level variations and specifically current sea level rise may strongly influence mangrove development due to their migration along the tidal elevation gradient to maintain the biotic conditions needed for their development

closed basin modes of a dual basin harbour closed basin seiches have been studied in port kembla australia a compound harbour comprising two basins linked by a narrow channel despite the irregular geometry there are well defined closed basin resonances which may be excited by long waves incident on the harbour entrance the march 2011 japanese tsunami excited open basin modes but did not significantly excite closed basin modes this is attributed to the very low incident wave energy at those frequencies while the direct forcing of a closed basin mode has been extensively studied the indirect forcing via an independent open basin mode found here has not been extensively studied it was found that single basin modes are more readily excited than the higher dual basin harmonics and the role of the irregular geometry in inhibiting some modes is discussed the non linear generation of a higher frequency mode unrelated to the forcing mode is demonstrated

mangrove ecosystem changes during the holocene at spanish lookout cay belize abstract mangroves are halophytic plants living at the land sea interface and are therefore natural trackers of sea level multiple proxies of a continuous 8 m mangrove peat core bt 79 from spanish lookout cay belize illustrate mangrove ecosystem changes during the holocene radiocarbon measurements show this site was colonized by mangroves 8000 cal yrs bp with a significant decrease in the peat accumulation rate from 6000 to 1000 cal yrs bp stratigraphic characteristics of this peat core such as bulk density magnetic susceptibility and loss on ignition show relative uniformity inferring an uninterrupted mangrove ecosystem during a majority of the holocene this is supported by pollen data from bt 79 that show that the site has been consistently dominated by rhizophora mangle red mangrove with avicennia germinans black mangrove and laguncularia racemosa white mangrove present as well subfossil r mangle leaves are used for stable nitrogen carbon and oxygen isotope 15n 13c and 18o analyses 15n and 13c values provide a proxy of this plant s past physiology and stand structure showing that dwarf 15n

monsoon influenced variations in morphology and sediment of a mesotidal beach on the mekong river delta coast abstract a mesotidal beach on the mekong river delta coast exhibits unique patterns of river sediment discharge and experiences reversals of ocean wave directions in response to the summer and winter monsoons we analyzed long term changes of the shoreline since 1936 from past topographic maps and satellite images and short term changes in geomorphology and sedimentology by undertaking repeated field surveys between november 2005 and february 2008 along six shore normal beach transects the shoreline of the mekong river delta coast has changed asymmetrically over the last 70 years in response to net southwestward sediment transport related to dry northeasterly winter monsoons during the summer rainy season large volumes of sediments are discharged from the river at this time wave direction is reversed in response to the relatively weak southwesterly summer monsoon mud and very fine sand in the surface sediments of the northeastern updrift beach transects tend to be removed during winter suggesting that the sediment supplied from the river during summer is temporarily deposited near the river mouth and later transported southwestward during the winter monsoon the relief of intertidal bars on the beach increased during winter in response to higher waves however previous studies have suggested that higher waves flatten bars we hypothesize that the increase in relief that we observed is related to a wide and shallow subtidal delta front platform that attenuates ocean waves at all times other than at high tide the beach profile varies longshore the accreting to stable beach dips seaward at a gradient of about 1 80 with up to three longshore intertidal bars classified here as either slip face bars or low amplitude ridges in contrast the eroding beach profile is much steeper 1 20 1 40 and linear without intertidal bars and is similar in form to a low tide terrace because there is little variation of wave size and grain size within the study area we consider that the spatial variation of the beach profile is related to the availability of sediment accumulated on the beach

total volume and temporal variation of meltwater from last glacial maximum inferred from sea level observations at barbados and tahiti abstract it is very important to determine the temporal variation of meltwater volume from the last glacial maximum lgm for studying climate changes and for constraining mantle rheology sea level observations have been obtained at barbados at the lgm and in late glacial phase and tahiti in late glacial phase and suggest that two events of rapid sea level rise existed at about 14 000 and 11 000 calendar years before present we examine the total meltwater volume and temporal variation of meltwater volume by comparing sea level observations and predictions at barbados and tahiti comparison between observations and predictions for barbados indicates that the total meltwater volume from the lgm is 103 117 m for eustatic sea level rise the predicted sea level variations at tahiti based on the ice model satisfying observations for barbados are however inconsistent with late glacial sea level observations at tahiti thus two events of rapid sea level rise are not supported from the comparison between observations and predictions at tahiti more in situ observational data are required for the period from the lgm to late glacial phase in order to study the relationship between rapid sea level rise and climate change

holocene palynology and sea level change in two estuaries in southern irian jaya southern new guinea leads the continental australian plate into convergence to form the new guinea highlands extensive inter tidal deltas are typical of much of this low gradient equatorial coastline in two adjacent estuaries in irian jaya west papua this study uses present elevations of mangrove species zones as a finite indicator of holocene sea levels from pollen diagrams of estuarine cores all cores showed mangroves at levels well below the present tidal range with landward species zones being replaced over time by seaward zones results show tectonic subsidence in the recent period with late holocene relative sea level rise of 0 67 mm year 1

he ar n and c isotope compositions in tatun volcanic group tvg taiwan evidence for an important contribution of pelagic carbonates in the magmatic source abstract the tatun volcanic group tvg northeastern taiwan is considered to be the extension of the ryukyu arc and belongs to the post collisional collapse okinawa trough strong hydrothermal activity is concentrated along the chinshan fault and da you keng dyk represents the main fumarolic area where the most primitive isotopic and chemical composition is observed in this study we present chemical and he ar c and n isotopic compositions of fumaroles bubbling gas and water from hot springs sampled in 2012 and 2013 high 3 he 4 he ratios from dyk fumaroles 6 5 ra show a typical arc like setting whereas other sampling areas show a strong dependence of 3 he 4 he and ch 4 3 he ratios with the distance from the main active hydrothermal area dyk this could mean strong crustal contamination and thermal decomposition of organic matter from local sediments carbon isotope compositions of dyk range from 6 67 to 5 85 and indicate that carbon contribution comes mainly from pelagic carbonates from the slab limestone mantle and sediment contributions are 63 19 and 18 respectively this is consistent with the negative 15 n values 1 4 0 5 observed for dyk implying a strong nitrogen mantle contribution and an absence of contribution from nitrogen pelagic carbonates these results have important consequences related to the ryukyu subducted slab in fact the ryukyu margin presents little in off scraping the sedimentary cover to the subducting plate that does not permit any nitrogen contribution in magma from tvg

formation and fate of sedimentary depocentres on southeast asia s sunda shelf over the past sea level cycle and biogeographic implications abstract sea level variations are the major factor controlling sedimentation as well as the biogeographic patterns at continental margins over late quaternary times fluctuations on millennial time scales produce locally complex deposits in coasts and on shelves associated with short term influence on species development this article reviews the sedimentary and biogeographic history of the tropical siliciclastic sunda shelf as an end member of continental shelves regarding extreme width an enormous sediment supply and highest biodiversity in response to rapid sea level fluctuations we describe particular depositional segments as part of a genetic succession of zones from land to the deep sea based on literature data field observations and calculation of hydro isostatic adjustment effects on changing relative sea level these segments are characterized by individual sedimentary processes and deposits and by a specific potential for material storage and re mobilization long term regressive intervals led to overall sigmoidal promoting extremely thick and wide succeeding units in contrast rapid lateral shifts of defined depocentres over long distances took place in response to short term sea level fluctuations fully isolated small scale sediment bodies formed when sea level changed at exceptionally high rates as a result of the high availability of organic rich sediments mangrove and freshwater peats formed frequently over late quaternary times the appearance of thick massive and widespread peats is mainly linked to time intervals of a sea level rise at slow rates whilst organic matter appears much more dispersely in the sediments during episodes of rapidly changing sea level the preservation potential of the regressive units is generally high due to highest initial sediment supply stabilizing soil formation during exposure and rapid subsidence preservation of depositional elements from other periods is more exceptional and either restricted to local morphological depressions or to episodes of rapid sea level change besides complex channel incision an overall lowering of the sediment surface related to erosion as deep as 20 m or more over wide areas took place mainly during sea level lowering the final export of shelf material is documented by enormous mass wasting packages on the associated continental slope from a palaeogeographic perspective the rapid formation or disappearance of special habitat zones such as mangrove fringes and extended mud flats led to species establishment or truncation in distribution in addition the opening or closure of ocean passages as narrow bridges allowing limited species crossing or as fully colonized corridors had severe impact on eco fragmentation and the expansion or contraction of species independent of such particular conditions sea level changes have been too rapid over the past climatic cycle to allow full regeneration and mature development of coast related ecosystems

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

pollen distribution in hemipelagic surface sediments of the south china sea and its relation to modern vegetation distribution abstract this paper analyses the distribution of pollen in the surface sediments of the south china sea as recorded in 28 samples from the area 6 09 20 07 n and 112 05 119 45 e at water depths of 329 4307 m pollen concentrations range from 444 kgrains g dry wt on the lower part of the continental slope in the northeast to zero in the central basin below 4000 m water depth pollen distribution patterns in the concentration and percentage isopolls incorporating data from the literature reflect the routes and mechanisms of pollen transport pollen source areas and considerable systematic differences between north and south the northern scs is distinguished by very high concentrations due to the high production and effective long distance transport of pine pollen and fern spores the maximum of their concentration occurs in the north adjacent to the convergence of the bashi and taiwan straits rather than near the estuaries of big rivers and stretches as a saddle from ne to sw consistent with the direction of the ne winter monsoon and sea current this pattern implies that pine pollen and fern spores adapted to wind transport and water flotation come from the northeast through the straits borne on the winter monsoon and sea current forced by it their source areas should cover large regions probably including south and southeast china most pollen of tropical and subtropical broad leaved trees found in the northern part of the scs occur in low concentrations however these concentrations decrease uniformly offshore implying a fluvial discharge from nearby lowlands in south china in the southern part of the scs pollen of tropical and subtropical broad leaved trees predominate total pollen concentrations however are much lower only 1 10 of those of the northern part the greatest concentrations occur offshore north borneo and decrease toward deep water suggesting fluvial input from relatively local sources on the adjacent islands e g borneo

discovery of a submerged relic reef and shoreline off grand cayman further support for an early holocene jump in sea level abstract drilling close to the base of a submerged sea cliff on the terraced eastern shelf of grand cayman has revealed a relic acropora palmata reef at a depth of 21 m below msl ten cores from its crest are principally composed of cobble sized clasts of a palmata set in a matrix of cemented skeletal grainstone the clasts have a distinctive succession of encrusters that indicate rapid burial a photophilic association of crustose coralline algae foraminifera and vermetid gastropods superimposed by a cryptic association of sclerosponges foraminifera and serpulids in addition to rapid burial u th thermal ionization mass spectrometer tims dating of coral clasts within 1 m of the relic reef surface indicates minor temporal mixing with ages between 8 9 and 8 1 ka such mixing and rapid burial is consistent with a hurricane deposit and is identical to deposits found on the crests of modern reefs in relation to its age the preservation of a 18 5 m intertidal notch cut into the submerged sea cliff on the western shelf of grand cayman implies that the crest of the relic reef has been lowered 1 5 2 m by marine abrasion bioerosion at a rate of 0 25 mm yr 1 reconstructing this eroded section using average holocene accretion rates indicates that the reef likely ceased accreting at 7 6 ka at a depth of 19 m comparing these data with other relic reefs in the caribbean indicates that the relic reef on grand cayman died within 160 years of relic reefs on barbados st croix st thomas and north florida this narrow interval of reef demise also coincides with the time when modern reefs were establishing themselves some 4 9 m higher upslope a fact that can only be resolved by invoking a rapid 6 m jump in sea level 7 5 ka ago such a jump would also account for two unexplained events around this time the restricted interval of global delta initiation and the catastrophic flooding of the glacially lowered black sea

late quaternary peat formation and vegetation dynamics in a lowland tropical swamp nee soon singapore abstract cores of sediment from nee soon a peat forming freshwater swamp located in the perimarine zone of singapore have yielded a record of vegetation history that comprises parts of the last glacial and holocene periods the evidence includes two conventional and four ams radiocarbon dates the oldest of which is 23 050 330 b p uncalibrated radiocarbon years and variations in the abundances of sub fossil pollen and spores and charcoal the results of a study of the relationship between contemporary vegetation and modern pollen accumulation facilitated interpretation of sub fossil tree pollen data peat formation occurred at nee soon during the last glacial when sea levels on the sunda continental shelf were well below those at present the occurrence of montane pollen types notably podocarpaceae in sediment samples dated to the late glacial and early holocene suggests either temperatures substantially lower than those of the present and possibly humid conditions or cold seasonally dry climates and reduced levels of atmospheric co 2 the abundance of charcoal indicates the widespread occurrence of fires throughout the entire period represented by the cores for the mid holocene the evidence indicates an increased saline influence presumably as a result of relatively high sea levels falling sea levels during the late holocene appear to have preceded the onset of the most recent period of peat formation at nee soon the evidence confirms that long last glacial interglacial records of lowland vegetation history are available from terrestrial locations in the humid core of southeast asia and suggests that the complexity of perimarine swamp dynamics is not captured fully by anderson s model which assumes a close relationship between peat formation and sea level

an inflection in the rate of early mid holocene eustatic sea level rise a new sea level curve from singapore this study presents a sea level curve from 9500 to 6500 cal bp for the farfield location of singapore on the sunda shelf in southeast asia the curve is based on more than 50 radiocarbon dates from elevations of 1 43 m to 15 09 m representing sea level index points in intertidal mangrove and shallow marine sediments deposited by sea level rise accompanying deglaciation the results indicate that mean sea level rose rapidly from around 17 m at 9500 cal bp to around 3 m by 8000 cal bp after this time the data suggest but do not unequivocally prove that the rate of sea rise slowed for a period of 300 500 years centred on 7700 cal bp shortly after the cessation of meltwater input to the oceans from the northern hemisphere renewed sea level rise amounting to 3 5 m began around 7400 cal bp and was complete by 7000 cal bp the existence of an inflection in the rate of sea level rise with a slow down centred on 7700 cal bp is broadly consistent with other available sea level curves over this interval and is supported by evidence of stable shorelines and delta initiation elsewhere at this time as well as evidence of comparatively rapid retreat of the west antarctic ice sheet beginning around 7500 cal bp stepped sea level rise occurring shortly after 7500 cal bp and also earlier during deglaciation may have served to focus significant post glacial episodes of human maritime coastal dispersal into comparatively narrow time intervals

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

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

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

sediment trapping in deltas of small mountainous rivers of southwestern taiwan and its influence on east china sea sedimentation abstract taiwan s setting of high mountains steep gradients frequent earthquakes erodible lithology and heavy rainfall represents an ideal site to focus on sedimentary processes of the deltas of small mountainous rivers smrs several smrs in southwestern taiwan have deposited a thick sedimentary succession in the composite southwest taiwan delta swtd since the middle holocene evidence from the swtd can help to determine its trapping efficiency and assess the role of smrs in sediment transport to the sea we used historical nautical charts bathymetric data satellite radar data and 14c dates to calculate the sediment volume of the swtd on millennial and decadal scales the 14c dates of core samples indicate deposition of thick deltaic sediment in subsiding areas since the time of the maximum flooding surface about 7 cal ka bp the paleo shoreline changes of the swtd suggest a steady westward progradation since 7 cal ka bp in contrast the nautical charts suggest minor volume reduction of the offshore part of the swtd with a deepening trend and retreating shorelines during the last seven decades the results show that at least 201 72 13 90 km3 3 23 105 mt of sediment has been trapped in the swtd since 7 cal ka bp and that the delta has shifted to a destructive phase during the past seven decades as human influences such as construction of reservoirs dams and weirs in the hills have reduced the sediment supply the birth of the taiwan warm current and following continuous sediment supply from the western rivers of taiwan to the east china sea since 7 3 cal ka bp have played a crucial role in the sedimentation of the east china sea particularly in the okinawa trough and the japan sea through the tsushima warm current