post glacial sea level rise from a coral record at huon peninsula papua new guinea dating of coral reef terraces can provide a record of changes in sea level which should be pronounced during the transition between glacial and interglacial periods cores drilled from coral reefs at barbados in the equatorial west atlantic1have revealed the sea level changes that occurred during the younger dry as event at the end of the last glacial maximum 11 000 yr bp it has not been known however whether pacific coral reefs can grow at a rate sufficient to keep up with the rise in sea level during such a transition here we report results obtained from a 52 m drill core from the post glacial reef at huon peninsula papua new guinea spanning the interval from 7 000 to 11 000 14c yr bp which show that coral growth kept pace while the relative sea level rose by 50m although the tectonic environment is very different from that at barbados the two records compare well when corrections are made for local tectonic uplift showing that sea level rise was similar at both locations the rate of rise was greatest between 9 000 and 10 00014c yr bp corresponding to the time of the younger dryas

microbialite development patterns in the last deglacial reefs from tahiti french polynesia iodp expedition 310 implications on reef framework architecture abstract the widespread occurrence of microbialites in the last deglacial reef frameworks 16 6 ka bp implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea level variations and environmental changes the present study is based on the sedimentological and chronological analysis 14c ams dating of drill cores obtained during the iodp expedition 310 tahiti sea level on the successive terraces which typify the modern reef slopes from tahiti it provides a comprehensive data base to investigate the microbialite growth patterns i e growth rates and habitats to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea level rise the last deglacial reefs from tahiti are composed of two distinctive biological communities 1 the coralgal communities including seven assemblages characterized by various growth forms branching robust branching massive tabular and encrusting that form the initial frameworks and 2 the microbial communities developed in the primary cavities of those frameworks a few meters 1 5 to 6 m below the living coral reef surface where they heavily encrusted the coralgal assemblages to form microbialite crusts the dating results demonstrate the occurrence of two distinctive generations of microbialites the reefal microbialites which developed a few hundred years after coralgal communities in shallow water environments whereas the slope microbialites grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities the development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies the most widespread microbialite development occurred in frameworks dominated by branching thin encrusting tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity 50 in contrast their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity 30 and could not host a significant microbialite expansion

evidence from rare gases for magma chamber degassing of highly evolved mid ocean ridge basalt highly evolved lavas have been recovered from moderate to fast spreading centres along the mid ocean ridge system most commonly near propagating rifts and overlapping spreading centres1 7 their origin and occurrence are generally explained by extensive modification of a primary basalt magma by fractional crystallization at shallow levels in the oceanic crust model i 1 4 6 9 other crustal processes have also been invoked including periodic magma mixing of a highly fractionated liquid with multiple primary liquids model 2 10 11 and seawater interaction with the mantle derived magma model 3 12 14 here we report the first 4he and argon isotope data for several highly evolved mid ocean ridge basalts morbs and andesites the samples were recovered with the submersible alvin from a very limited section 8 km2 of the axial valley of the eastern galapagos rift between 85 52 and 85 50 w although they range in composition from moderately evolved normal n morb to ferrobasalts fe ti basalts and high silica andesites geochemical studies indicate that the suite is cogenetic facilitating interpretation of the data15 we find distinct differences in the rare gas data between the evolved and n morbs indicating that the evolved magmas have undergone pre eruption degassing in a process not common to the source magmas for normal morbs our data fit well with model 1 but provide no evidence for models 2 and 3

variations in pleistocene coral assemblages in space and time in southern and northern central ryukyu islands japan we studied the taxonomic and morphological compositions of pleistocene coral assemblages in 24 quadrats in okinawa jima southern central ryukyus and in 14 quadrats in kikai jima northern central ryukyus a total of 72 species belonging to 35 genera were identified in okinawa jima whereas 65 species coming under 33 genera were recorded in kikai jima cluster analysis of the bray curtis bc similarity coefficient produced 8 coral associations and 3 ungrouped taxa they correspond to a wide range of reef environments from shallow lagoon to lower reef slope settings the analysis of taxonomic similarities among quadrats leads to the identification of 7 clusters and 5 isolated quadrats the segregation of quadrats indicating a same reef zone into distinctive groups or single branches in the cluster diagram reflects the within reef slope variability in community structure specifically encrusting acropora palifera indicative of the upper reef slope zone shows a great variability of associated coral species and morphologies we also report differences in the geographic distribution of acropora palifera and platygyra contorta between present day and pleistocene reefs which may be linked to changes in sea surface temperature the decrease in the total species and generic richness recorded in modern reefs is not clearly detected in the fossil record in addition mds ordination of the bc similarities highlights patterns of reef zonation and geographic differences in taxonomic composition one way tests of similarity anosim show that differences in the composition of upper reef slope coral assemblages between okinawa jima and kikai jima are not larger than those observed between southern and central okinawa jima finally we report various types of coral successions sea level changes resulted in transitions from one reef zone to another whereas local disturbances are likely to have been responsible for the successions of distinctive coral assemblages with overlapping depth ranges which reflect the within reef zone variability

precise th u dating of small and heavily coated samples of deep sea corals marine carbonate skeletons like deep sea corals are frequently coated with iron and manganese oxides hydroxides which adsorb additional thorium and uranium out of the sea water a new cleaning procedure has been developed to reduce this contamination in this further cleaning step a solution of na2edta na2h2tb and ascorbic acid is used which composition is optimised especially for samples of 20 mg of weight it was first tested on aliquots of a reef building coral which had been artificially contaminated with powdered ferromanganese nodule applied on heavily contaminated deep sea corals scleractinia it reduced excess 230th by another order of magnitude in addition to usual cleaning procedures the measurement of at least three fractions of different contamination together with an additional standard correction for contaminated carbonates results in th u ages corrected for the authigenic component a good agreement between th u and 14c ages can be achieved even for extremely coated corals

paleobathymetric implications of microborings in tertiary strata of alaska usa abstract microboring algae bacteria and fungi that lived under non tropical conditions are abundantly present in four richly fossiliferous marine strata of paleocene to miocene age in alaska by comparing their boring trace communities with endolithic guide ichnocoenoses characterizing various photic zones which have been previously defined mainly in tropical and subtropical environments the alaska strata can be placed in bathymetric zones as follows the lower upper paleocene prince creek formation in the dysphotic zone the lower oligocene stepovak formation in the shallow euphotic zone shallow euphotic zone iii and the upper miocene tachilni formation in the deep euphotic zone these interpretations agree very well with bathymetric reconstructions inferred from other criteria a fourth formation the lower middle miocene narrow cape formation contains only heterotrophic microborers as if it had been deposited in the aphotic zone in contrast to previous reconstructions in this formation the periostracum of the mollusc shells is exceptionally well preserved this may explain the absence of boring algae because only heterotrophs can penetrate through organic shell layers the absolute depth ranges of these ichnocoenoses zones are inferred from their ranges in comparable latitudes of the modern north atlantic the most important features of bathymetrically controlled tropical and subtropical guide ichnocoenoses are also present at the non tropical alaskan sites although some boring algae that are widespread in tropical realms are absent

assessing subsidence rates and paleo water depths for tahiti reefs using u th chronology of altered corals we present uranium thorium chronology fora 102 m core through a pleistocene reef at tahiti french polynesia sampled during iodp expedition 310 tahiti sea level we employ total and partial dissolution procedures on the older coral samples to investigate the diagenetic overprint of the uranium thorium system although alteration of the u th system cannot be robustly corrected diagenetic trends in the u th data combined with sea level and subsidence constraints for the growth of the corals enables the age of critical samples to be constrained to marine isotope stage 9 we use the ages of the corals together with o based sea level histories to provide maximum constraints on possible paleo water depths these depth constraints are then compared to independent depth estimates based on algal and foraminiferal assemblages microbioerosion patterns and sedimentary facies confirming the accuracy of these paleo water depth estimates we also use the fact that corals could not have grown above sea level to place a maximum constraint on the subsidence rate of tahiti to be 0 39 m ka with the most likely rate being close to the existing minimum estimate of 0 25 m ka

variability in the uranium isotopic composition of the oceans over glacial interglacial timescales uranium series mass spectrometric analyses of corals from the uplifted last glacial terraces at huon peninsula papua new guinea that grew from 50 000 years ago to 30 000 years ago show systematically low values of 234u 238u at the time of coral growth compared with modern corals when combined with coral data from other studies a systematic trend emerges indicating shifts in the 234u 238u ratio at times of major glacial interglacial transitions that involve large variations in sea levels from last glacial to holocene the rate of change in 234u is approximately 1 per thousand years the variations in the u budget of the oceans appear to be due to accumulation of excess 234u in near shore areas in anoxic and suboxic sediments in salt marshes and mangroves in estuaries and in continental margins during periods of warm climate and high sea levels these near shore areas are exposed during periods of low sea level resulting in rapid oxidation of u into highly soluble phases the subsequent release of 234u enriched uranium into the oceans occurs over a sustained period in step with rising sea levels

u series dating of diagenetically altered fossil reef corals initial 234u 238u activity ratios higher than those expected from closed system evolution of seawater are an outstanding problem in u series dating of fossil reef corals the increased activity ratios are ascribed to post depositional diagenesis we analysed six last interglacial and one holocene coral of the genus porites collected near the northern end of the gulf of aqaba northern red sea together with three recent corals from this location as a modern reference while the values measured on the recent samples show no deviation from expected values the holocene and last interglacial corals display highly elevated 234u 238u activity ratios as well as increased 238u and 232th concentrations 234u 238u activity ratios are strongly correlated with 230th 238u and total uranium content a model assuming different degrees of uranium addition and subsequent loss in different sub samples of one coral produces straight lines isochrons on a 234u 238u 230th 238u plot and predicts that the true age of the coral can be calculated by intersecting this isochron with the seawater evolution curve we used the strong correlation detected in the aqaba corals to calculate isochron ages the isochron age of the holocene coral 3116 167 156 yr is concordant with its calibrated 14c age 2963 92 103 yr the ages of the last interglacial corals are between 121 6 7 5 3 and 121 9 7 0 6 3 kyr for a higher terrace 7 10 m asl and 106 4 8 9 8 1 and 117 1 19 7 15 3 kyr for a lower terrace 4 5 m asl one last interglacial coral with an aragonite content of 85 could not be dated the elevation and ages of the fossil terraces are consistent with existing sea level reconstructions from the red sea

impacts of light penetration on the bathymetry of reef microboring communities implications for the development of microendolithic trace assemblages abstract sediment samples recovered from three proximate reef environments in north jamaica characterised by different light penetration regimes reveal marked variations in the bathymetric range of sediment microboring communities in contrast to clear water environments assemblages developed in turbid water conditions undergo both bathymetric restriction and compression in their range in clear water sites the upper photic lower photic zone transition occurs between depths of 20 30 m this is marked by a shift from a predominance of cyanobacterial e g eurygonum nodosum scolecia filosa fasciculus frutex and fasciculus dactylus and chlorophyte e g rhopalia catenata fasciculus grandis reticulina elegans and scolecia botulifera traces to assemblages dominated by the traces e nodosum and s filosa cyanobacteria f grandis chlorophyte palaeoconchocelis starmarchii rhodophyte and orthogonum fusiferum and saccomorpha sphaerula fungi at sites characterised by intermediate levels of turbidity this same assemblage transition occurs at around 15 20 m depth and at the most turbid site at depths of only 5 10 m integration of assemblage data and light readings indicates that this transition occurs where percentages of surface light illumination are reduced to around 10 15 compression of the lower photic zone is so extreme at the most turbid site that microboring assemblages at only 30 m depth show evidence of a transition to an assemblage associated with dysphotic

holocene sea level record from corals reliability of paleodepth indicators at ishigaki island ryukyu islands japan abstract holocene sea level change provides direct evidence of the melting of ice sheets however our understanding of the timing and course of such change is limited by a lack of information regarding environmental condition of corals for example holocene sea level curves are compiled based on water depths estimated from the occurrence of a small number of coral species as species identification is difficult work the error associated with this method of estimating sea level exceeds 2 5 m in addition there generally occurs a difference in the living water depth of corals between high energy reefs and low to moderate energy reefs this difference in living water depth also results in an error in reconstructed sea level curves in the present study we analyzed drill core and recorded the vertical distribution of corals at the high energy ibaruma reef and low to moderate energy fukido reef ishigaki island ryukyu islands japan analyses of corymbose acropora a digitifera massive goniastrea g retiformis massive pocillopora p verrucosa massive platygyra p ryukyuensis and other corals enables the accurate reconstruction of a sea level curve because these species are distributed in a narrow range with a weighted mean m w error of between 0 5 and 2 5 m these observation data from ibaruma and fukido reefs can be used to reconstruct holocene sea level curves based on drill core data from ibaruma reef however the two reefs yield contrasting sea level curves the curve reconstructed based on data from fukido reef is several meters deeper than that reconstructed based on data from ibaruma reef this discrepancy reflects the different energy levels of the two reefs high energy at ibaruma reef and low to moderate energy at fukido reef therefore the accurate reconstruction of a holocene sea level curve requires the identification of species from drill core and observations of the vertical distribution of species at the present day reef at a location close to the drilling site the holocene sea level curve reconstructed based on drill core data from ibaruma reef reveals a rapid sea level rise of approximately 7 5 m kyr 1 between 8000 and 6000 cal years bp the rate of sea level rise decreased from 7 5 to 3 5 m kyr 1 between 6000 and 5000 cal years bp a mid holocene highstand occurred at around 5000 cal years bp at a level of approximately 3 2 5 m above the present mean sea level the increase in ocean volume corresponding to this sea level rise indicates that melting of the antarctic ice sheet continued beyond 6000 cal years bp as most of the northern hemisphere ice sheets had melted by 6000 cal years bp resulting in sea levels similar to those of the present day

the timing of sea level high stands during marine isotope stages 7 5 and 9 constraints from the uranium series dating of fossil corals from henderson island direct dating of fossil coral reefs using the u series chronometer provides an important independent test of the milankovitch orbital forcing theory of climate change however well dated fossil corals pre dating the last interglacial period 130 thousand years ago ka are scarce due to 1 a lack of sampling localities 2 insufficient analytical precision in u series dating methods and 3 diagenesis which acts to violate the assumption of closed system u series isotopic decay in fossil corals here we present 50 new high precision u series age determinations for fossil corals from henderson island an emergent coral atoll in the central south pacific u series age determinations associated with the marine isotope stage mis 9 interglacial and mis 7 5 interstadial periods are reported the fossil corals show relatively little open system u series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle however open system u series behaviour is still evident in most of the dated corals in particular percent level shifts in the 230th 238u act composition are observed leading to conventional u series ages that are significantly younger or older than the true sample age this open system u series behaviour is not accounted for by any of the open system u series models indicating that new models should be derived the new u series ages reported here support and extend earlier findings reported in stirling et al 2001 providing evidence of prolific coral reef development on henderson island at not vert similar320 ka most likely correlated with mis 9 3 and subsequent reef development at not vert similar307 ka during mis 9 1 while relative sea level was potentially not vert similar20 m lower than during mis 9 3 the u series ages for additional well preserved fossil corals are suggestive of minor reef development on henderson island during mis 7 5 245 230 ka at 240 3 0 8 and 234 7 1 3 ka all u series observations are consistent with the milankovitch theory of climate change in terms of the timing of onset and termination of the dated interglacial and interstadial periods the best preserved samples also suggest that the oceanic 234u 238u during mis 9 and mis 7 5 was within five permil of the modern open ocean composition

seawater 234 u 238 u during the last 800 thousand years abstract constraining the history of seawater 234u 238u is important because this ratio is used to assess the validity of u th ages and because it provides information about the past rate of physical weathering on the continents this study makes use of u rich slope sediments from the bahamas in an attempt to reconstruct seawater 234u 238u for the last 800 kyr for the last 360 kyr u th dating of these sediments provides ages and initial 234u 238u values sixty seven samples largely from marine highstands have initial 234u 238u which scatter somewhat about the modern seawater value 1 145 but neither this scatter nor the average value increases with age of sample these data contrast with published coral data and suggest that seawater 234u 238u has remained within 15 of the modern value for the last 360 kyr this confirms the rejection of coral u th ages where the initial 234u 238u is significantly different from modern seawater data from older highstands dated with 18o stratigraphy or by the presence of the brunhes matuyama b m reversal at 780 kyr allow seawater 234u 238u to be assessed prior to the range of the 230th chronometer unfortunately diagenetic scatter in the data between the b m reversal and 360 kyr is rather large probably relating to low u concentrations for these samples but there is no indication of a trend in seawater 234u 238u with age high u samples from close to the b m reversal show less diagenetic scatter and an initial 234u 238u that averages 1 102 this lower value can be explained by lower seawater 234u 238u at the time of the b m reversal or by progressive loss of 234u from the sediment by recoil a simple box model is presented to illustrate the response of seawater 234u 238u to variations in riverine input such as might be caused by changes in continental weathering comparison of the bahamas 234u 238u data with model results indicates that riverine 234u 238u has not varied by more than 65 for any 100 kyr period during the last 360 kyr it also indicates that the ratio of physical to chemical weathering on the continents has not been higher than at present for any extended period during the last 800 kyr

dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces abstract the sedimentation conditions and diagenetic processes of biogenic and inorganic carbonates are such that the assumptions of a closed system evolution and the absence of initial th invoked in classical 238 u 234 u 230 th dating methods are very often not fulfilled for such material this problem is of interest for all studies requiring accurate dating of corals or aragonite rich sediments as in palaeoclimatology or neotectonics extending the approach of henderson and slowey nature 404 2000 61 66 we propose a consistent model that takes into account possible initial 230 th excess and where continuous selective redistribution gain or loss of 234 u 234 th and 230 th is controlled by recoil processes this model applied to quaternary marine terraces in barbados marie galante lesser antilles arc and pacific islands is able to explain the large scatter in isotopic compositions observed in the series of cogenetic corals or sediments we show that recoil processes generally tend to increase the 234 u 238 u and 230 th 234 u ratios with time leading to an overestimation of the apparent ages calculated using classical methods on the basis of simple assumptions identical marine initial 234 u 238 u 0 and 230 th 232 th 0 ratios we propose a method for calculating a best estimate of the age of cogenetic series our model offers an alternative way to date old reef terraces where corals are almost systematically altered and where classical dating methods do not apply it may also explain the apparent variations of the 234 u 238 u seawater initial ratio estimated from corals formed in the last 300 ka and the apparent uncoupling between sea level highstands and high latitude northern hemisphere summer insolation our set of equations can be applied to all weathering processes where the mobility of u series isotopes is controlled by recoil

rapid fluctuations in sea level recorded at huon peninsula during the penultimate deglaciation about 140 000 years ago the breakup of large continental ice sheets initiated the last interglacial period sea level rose and peaked around 135 000 years ago about 14 meters below present levels a record of last interglacial sea levels between 116 000 years to 136 000 years ago is preserved at reef vii of the uplifted coral terraces of huon peninsula in papua new guinea however corals from a cave situated about 90 meters below the crest of reef vii are 130 000 2000 years old and appear to have grown in conditions that were 6 c cooler than those at present these observations imply a drop in sea level of 60 to 80 meters after 130 000 years sea level began rising again in response to the major insolation maximum at 126 000 to 128 000 years ago the early about 140 000 years ago start of the penultimate deglaciation well before the peak in insolation is consistent with the devils hole chronology

sea level reversal during termination ii the termination of the penultimate glacial period tii shows both similarities and differences to the last termination ti both terminations show significant cold reversals in the postglacial warming trend ti consists of a continuously increasing sea level trend whereas tii may demonstrate a sea level reduction midway through the termination we present a new continuous sea level record for tii derived from red sea 18 o records that supports the existence of the tii sea level reversal the record gives an unprecedented look at the structure of the tii sea level reversal which consists of an early highstand lasting several millennia in duration followed by a 30 12 m to 40 12 m reduction in sea level and a stillstand of several millennia before the final sea level rise to the marine oxygen isotope stage mis 5e interglacial we suggest that there is a link between the sea level reversal and internal millennial scale variability in the climate system

u th dating of carbonate platform and slope sediments absolute chronology of marine sediment beyond the 14c age range provides a test for models of climate change and has many other applications u th techniques have been used for such chronology by dating corals but extending these techniques to marine sediment is complicated by the presence of significant initial 230th both in detrital material and scavenged from seawater in this study we investigate four methods of solving the initial 230th problem for a particular type of marine sediment the aragonite rich sediments of carbonate platforms and slopes bulk sediment u th analyses can be corrected for initial th to yield ages with 2 to 3 kyr precision for highstand periods when sediment aragonite contents are particularly high uncertainty on the corrections causes inadequate precision for sediment from other periods however removal of scavenged th before analysis would enable a dramatic increase in this precision but has not proved successful despite a range of chemical leach approaches using heavy liquids to separate the various carbonate minerals found in bahamas sediment enables an isochron approach to correct for initial th but the presence of initial th from two sources requires correction or removal of one source of initial th before the other is deconvolved by the isochron quantitative removal of detrital material before isochron analysis proves a successful approach such isochron data demonstrate that although sediment remains closed to u th on a centimetre scale nuclides are moved from grain to grain by recoil such intergrain exchange is expected to be observed in all sediments containing mineral grains with different u concentrations measured 234u 238u allows the recoil movement to be corrected and results in isochron ages with precision sometimes as low as 3 kyr the accuracy of this approach has been proved by dating samples within the 14c age range sediments spanning the penultimate deglaciation have also been dated after a small correction for bioturbation the age for this event is found to be 135 2 3 5 ka this date is 8 kyr before the peak in northern hemisphere insolation and suggests that deglaciation is initiated by a mechanism in the southern hemisphere or tropics this isochron approach shows considerable promise for dating of sediments older than this event which will provide further information about the timing and mechanisms of global climate change

reef coralgal assemblages as recorders of paleobathymetry and sea level changes in the indo pacific province the coralgal framework within the outer reef margin of many indo pacific reefs exhibits three main shallow water communities the environmental significance of which can be inferred by comparison with their modern counterparts a community dominated by tabular acropora gr hyacinthus cytherea with branching pocillopora damicornis p eydouxi montipora digitata occasional domal faviids and mm thick crusts of the coralline algae lithophyllum and mesophyllum mainly typical of the 6 15 m paleodepth range a community including robust branching acropora gr danai robusta a humilis a digitifera and subordinate favia stelligera echinopora gemmacea associated to vermetid gastropods and thick coralline crusts of hydrolithon cf onkodes and neogoniolithon cf fosliei flourishing in depths less than 6 m in medium to high water energy settings a community composed of domal porites cf lutea and p cf lobata with occasional acropora gr danai robusta and cm thick crusts of coralline algae in sheltered habitats in depths less than 10 m these biological assemblages allow us to determine relationships between reef growth and paleobathymetry and consequently to reconstruct regional relative sea level curves high water energy reefal assemblages provide stronger evidence for reconstructing sea level curves than low energy buildups because they have generally been controlled by a keep up growth mode subsiding reef sites seem to be more reliable indicators of sea level variations because they usually present expanded reef sequences

sea level rise during termination ii inferred from large benthic foraminifers iodp expedition 310 tahiti sea level the course of sea level fluctuations during termination ii tii the penultimate deglaciation which is critical for understanding ice sheet dynamics and suborbital climate variability has yet to be established this is partly because most shallow water sequences encompassing tii were eroded during sea level lowstands of the last glacial period or were deposited below the present sea level here we report a new sequence recording sea level changes during tii in the pleistocene sequence at hole m0005d water depth 59 63 m below sea level mbsl off tahiti french polynesia which was drilled during integrated ocean drilling program expedition 310 lithofacies variations and stratigraphic changes in the taxonomic composition preservation states and intraspecific test morphology of large benthic foraminifers indicate a deepening upward sequence in the interval from core 310 m0005d 26r core depth 134 mbsl through 16r core depth 106 mbsl reconstruction of relative sea levels based on paleodepth estimations using large benthic foraminifers indicated a rise in sea level of about 90 m during this interval suggesting its correlation with one of the terminations assuming that this rise in sea level corresponds to that during tii after correcting for subsidence since the time of deposition a highstand sea level position would be 2 15 m above present sea level masl which is generally consistent with highstand sea level positions in mis 5e 4 2 masl if this rise in sea level corresponds to that during older terminations the subsidence corrected highstand sea level positions 30 15 masl for termination iii and 54 15 masl for termination iv are not consistent with reported ranges of interglacial sea level highstands 18 to 15 masl therefore the studied interval likely records the rise in sea level and associated environmental changes during tii in particular the intervening cored materials between the two episodes of sea level rise found in the studied interval might record the sea level reversal event during tii this conclusion is consistent with u th ages of around 133 ka which were obtained from slightly diagenetically altered i e 1 calcite in situ corals in the studied interval core 310 m0005d 20r core depth 118 mbsl this study also suggests that our inverse approach to correlate a stratigraphic interval with an approximate time frame could be useful as an independent check on the accuracy of uranium series dating which has been applied extensively to fossil corals in late quaternary sea level studies

volcano tectonic and geochemical evolution of an oceanic intra plate volcano tahiti nui french polynesia abstract geological mapping accurate k ar dating and geochemical analyses of lavas allow a detailed reconstruction of the geological history of tahiti nui island french polynesia the exposed volcanic activity is first characterized by the construction of a main shield from 1 4 ma to 870 ka with a maximum aerial eruptive rate around 2 km3 kyr lavas from this early building stage are alkaline slightly silica undersaturated with 87sr 86sr and 143nd 144nd compositions rather constant and close to the enriched mantle ii type vent locations were first concentrated along a main e w rift zone which was responsible for the lateral collapse of the northern and southern flanks of the main shield around 0 87 ma ago the subsequent activity was first restricted to the northern depression corresponding to an eruptive rate of about 5 km3 kyr in the period 850 760 ka significant variations in la sm 87sr 86sr and 143nd 144nd occur in lavas erupted immediately after the main northern landslide indicating a sudden increase in the extent of partial melting likely caused by the decompression subsequent to collapse however the later activity declined and the lavas exhibit a gradual change toward strongly silica undersaturated basanites likely indicating a decreasing extent of partial melting of the upper mantle the evolution of radiogenic isotope ratios over time indicates a change in the source toward more depleted compositions until around 500 ka post erosion volcanic activity following an apparent hiatus of 240 kyr exhibits similar major and trace element and isotope compositions the volcano structural and geochemical evolution of tahiti nui and the overall alkaline character of the lavas from other eruptive complexes of the society alignment suggest a relative weakness low temperature and low eruptive rate of the society plume compared to the hawaiian hot spot