u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

geochemical composition of tanzanian shelf sediments indicates holocene climatic and sea level changes we present a high resolution geochemical and grain size record from a holocene sediment core off the pangani river mouth tanzania elemental ratios between biogenic elements and al i e ca al mg al and sr al are mainly influenced by terrigenous dilution on carbonate concentration and or limitation of carbonate production as a result of variations in the supply of fine grained terrigenous sediments of the pangani river such elemental ratios increased significantly at the end of the mid holocene between 5 and 3 5 ka demonstrating a gradual transition from the humid early and mid holocene to the arid late holocene in east africa among the elemental ratios between terrigenous elements and al si al and k al ratios correlate to grain size variation indicating a change in sedimentation regime fe al and ti al ratios show that the sediment source area has shifted from the terrestrial volcanic region of tanzania fe ti rich to the coastal and inner shelf regions fe ti poor around 7 5 ka in response to arid climate and high sea level our geochemical results correspond with a sea surface temperature record derived from the same sediment core indicating that the end of the east african humid period could have been gradual and related to the cooling water in the western indian ocean

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

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

u pb zircon geochronology of silicic tuffs and chronostratigraphy of the earliest old red sandstone in the munster basin sw ireland

recognising the taghanic crisis in the devonian terrestrial environment and its implications for understanding land sea interactions the late mid devonian eday marl formation from the orcadian basin scotland is a terrestrial equivalent of the marine devonian taghanic crisis the eday marl from orkney contains a high resolution archive of climatic change controlled by the relative strength of the seasonal insolation this includes several distinct and discrete episodes of basin flooding as demonstrated by the deposition of lacustrine laminites bedded evaporites marginal sheet flood sands and marine influenced bioturbated sheet sands these flooding events are intercalated with intense and sustained episodes of aridity indicating that insolation was relatively weak and the monsoon climate was ineffective at drawing in seasonal rainfall recognition of these basin flooding events has enabled the definition of three new units the wha taing roeberry and berstane members the eday marl formation can be correlated offshore and also recognised within marginal facies as an aeolian intercalation an environmental hydrological and climatic interpretation is given for the different events recognised in the eday marl this sequence of events when combined with the palynological age dates enables a detailed correlation to be made with the marine tully formation of new york state this suggests that regressions forced by climatic aridity are significant for understanding the deposition of the shallow water carbonates of the tully formation in what is otherwise a clastic depositional system comparison with the pelagic marine record shows that the latter as yet gives only limited resolution of the taghanic crisis recognising the taghanic as a rapid alternation of cool arid and relatively hotter pluvial events provides a unifying explanation for the associated collapse in the terrestrial vegetation and the parallel faunal changes in the marine realm

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

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

late glacial to post glacial sea levels in the western indian ocean late glacial to post glacial sea level changes provide direct evidence of the progress of melting of large ice sheets during the last deglaciation but although the correlation between ice and ocean volumes is incontrovertible the causal link is commonly obscured local effects including tectonics isostatic and hydroisostatic responses and equatorial ocean syphoning impose additional signals that hide the true picture a detailed regional study of the western indian ocean based on the analysis of drill cores carried out through modern reefs in combination with observations and sampling of reef foreslopes and investigations of outcrops provides a comprehensive data base sites from a range of tectonic settings include the microcontinental margins of madagascar the granitic seychelles and the isolated volcanic islands of reunion mauritius and the comoros in which the effects of subsidence can be shown to be small these cover a range of latitudes and comparisons with adjacent sites on continental margins allow the construction of sea level curves that closely reflect the eustatic response and disengage this from the effects of other mechanisms the mayotte foreslope in the comoro islands provides the first coral reef record of sea level change during the early deglaciation in the indian ocean 110 115 m below present sea level between 18 000 and 17 000 yr bp two distinctive reef terraces at 90 and 60 m water depth are dated at 13 600 yr bp and partly attributed to the younger dryas period 12 700 11 600 cal yr bp reef drowning at around 13 500 yr bp may correspond to meltwater pulse 1a and although there were surges in the rate of sea level rise most notably between 11 950 and 11 350 yr bp there is little evidence to support a well defined meltwater pulse 1b reconstructed holocene sea level curves are in good agreement and reflect a rapid sea level rise of about 6 mm yr 1 between 10 000 and 7500 yr bp followed by a clear inflection around 7500 yr bp when the rate fell to 1 1 mm yr 1 modern reefs started to grow 8000 9000 years ago in the post glacial period the rate of sea level rise was 1 1 5 mm yr 1 before stabilization at its present level 3000 2500 years ago curves for the 10 000 6000 yr 1 bp interval correspond closely with those predicted by theoretical models but lie below these in the subsequent period in particular and with the exception of the margins of the madagascar microcontinent influenced by hydroisostatic processes they do not reflect predicted higher sea level stands during the late holocene

glacial rebound and sea level change an example of a relationship between mantle and surface processes lambeck k 1993 glacial rebound and sea level change an example of a relationship between mantle and surface processes in r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 15 37 the problem of glacial rebound provides an outstanding example of the relationship between surface and mantle processes on time scales of 103 to 105 years changes in surface loading of ice and melt water associated with the growth and decay of the great ice sheets deform the surface of the planet and induces flow in the mantle a measure of the earth s response to the changing surface loads and internal deformation is provided by observations of past sea levels relative to the present level and inversion of these observations provides constraints on both the models of the rheological response of the earth to loading and on models of the ice sheets constraints on ice sheet models include the total volume of the grounded ice at the time of maximum glaciation the global rates of melting of the ice sheets the thickness of the ice at maximum glaciation the extent of ice cover over shallow seas such as the north sea and the barents sea and the role of antarctica in the global ice balance constraints on mantle parameters include the effective lithospheric thickness and the effective viscosity of the mantle some recent results for both sets of parameters are discussed

plant assemblages from sw gondwana further evidence for high latitude vegetation in the devonian of argentina plant assemblages are described from the talacasto and punta negra formations san juan province the argentine precordillera a detailed facies study involving trace fossil assemblages indicates that the plants were buried in shallow low to high energy marine environments but not in turbidites as previously postulated apart from a single specimen resembling cooksonia from the lochkovian talacasto formation the abundant compression fossils consist of short lengths of smooth axes occasional defoliated lycopod stems and very rare isolated sporangia it is thus impossible to assign any to existing taxa with confidence nor are there sufficient distinguishing characters to erect new ones although the possible age of the formations in the precordillera remains conjectural the fossils themselves even preserved in such fragmentary states indicate much lower grades of organization than seen in coeval assemblages elsewhere particularly on the laurussian and south china palaeocontinents palaeocontinental reconstructions of gondwana indicate that the localities are within 30 of the palaeo south pole thus a global latitudinal gradient in vegetation is postulated for the early devonian with decreasing disparity and diversity at higher latitudes an explanation for the latter is explored in terms of light regime and temperature in highly stressed environments

crustal sources in lower palaeozoic rocks from nw iberia insights from laser ablation u pb ages of detrital zircons detrital zircons from greywackes belonging to an ordovician volcanosedimentary igneous complex in nw spain were dated using the laser ablation inductively coupled plasma mass spectrometry technique u pb results indicate the existence of three pre cambrian crustal sources in nw iberia the age grouping dated at c 590 620 ma confirms the presence of a cadomian avalonian basement in this zone the second age group c 1 1 1 2 ga is the first evidence for a grenvillean age crustal component in nw iberia the age grouping dated at c 1 9 2 0 ga corresponds to the age of the icartian igneous basement exposed in other areas of the european variscides

direct radiometric dating of the devonian mississippian time scale boundary using the re os black shale geochronometer many phanerozoic time scale boundaries are characterized by oceanic anoxia and mass extinction events with the deposition of black shale the re os isotope system in black shale can be used to provide depositional ages for these rocks thus yielding direct radiometric ages for time scale boundaries we demonstrate that the re os black shale geochronometer can yield precise ages useful for time scale research through study of the devonian mississippian boundary within the exshaw formation canada the re os date determined places the devonian mississippian boundary at 361 3 2 4 ma 2 including uncertainty model 1 mean square of weighted deviates 1 2 in accord with recent calibration interpolated from u pb zircon dates 360 7 0 7 ma for the hasselbachtal section germany

40ar 39ar dating of hydrothermal activity biota and gold mineralization in the rhynie hot spring system aberdeenshire scotland this study presents a new high precision 40ar 39ar age for the devonian hot spring system at rhynie hydrothermal k feldspar sampled from two veins that represent feeder conduits and a hydrothermally altered andesite wall rock date the hydrothermal activity the fossilised biota and syn k feldspar gold mineralization at 403 9 2 1 ma 2 oxygen isotope data for the parent fluid 4 to 2 show that the k feldspar was precipitated from a dominantly meteoric fluid which mixed with magmatic fluids from a degassing magma chamber the 40ar 39ar age 403 9 2 1 ma 2 when recalculated 407 1 2 2 ma 2 with respect to the astronomically tuned age for fish canyon sanidine 28 201 0 023 ma 1 also provides a robust marker for the polygonalis emsiensis spore assemblage biozone within the pragian earliest emsian furthermore the age identifies the devonian pull apart volcano sedimentary basins of the british and irish caledonides and their root zones as specific targets for future gold exploration

an eifelian u pb zircon date for the enagh tuff bed from the old red sandstone of the munster basin in nw iveragh sw ireland the first geochronological data from the minister basin sw ireland contradict the accepted biostratigraphical maximum age late givetian early frasnian of the oldest alluvium in the basin depocentre magmatic zircons from the enagh tuff bed a sub plinian air fall tuff within fluviatile old red sandstone of nw iveragh give a pb pb isotope age of 384 9 0 7 ma this confirms middle devonian probably eifelian sedimentation and allows possible early devonian basin initiation associated second cycle gravels suggest a pre 385 ma minimum age for the caherbla group of the dingle basin correlation with alluvium containing tetrapod trackways indicates a pre 385 ma age for the trace maker

holocene mangrove dynamics and relative sea level changes along the tanzanian coast east africa abstract there is continued uncertainty regarding the rate timing duration and direction of holocene sea level for the indian ocean and indeed the wider tropical realm we present the first synthesis and a new chronology for holocene relative sea level rsl using a range sediment cores retrieved from mangrove ecosystems in three locations along coastal tanzania this study applies the relationship of ratios between the key mangrove taxa of sonneratia bruguiera ceriops s bc ranging from 0 to 22 9 and sonneratia rhizophora s r ranging from 0 to 2 29 vegetation and altitude to interpret mangrove dynamics and refine the vertical errors associated with relative sea level change the variations in mangrove taxa ratios in the sediment cores obtained from each site shows mangrove development at different periods during the holocene from around 7900 cal yr bp an early to mid holocene rsl rise occurred from 7900 to 4600 cal yr bp that may have reached a higher level than present a lower rsl occurred after 4600 cal yr bp resulting in mangroves retreating seaward at all three study locations before a low magnitude rsl rise occurred between 4400 and 2000 cal yr bp another rsl rise is recorded at 500 cal yr bp before falling to a level lower than present at 100 cal yr bp there is evidence of a recent rsl rise recorded from mangrove ratios during the last century in addition the sedimentation rates among sites are relatively different due to different altitudinal ranges with freshwater input sediment supply and progradation having significantly more effect in the rufiji delta 2 1 10 9 mm cal yr 1 than at the zanzibar sites 0 3 6 6 mm cal yr 1

the numerical age of the devonian carboniferous boundary the shrimp ion microprobe has been used to date zircons in a 1 cm thick bentonite located in the hasselbachtal auxiliary global stratotype section through the devonian carboniferous boundary in germany and a tuff located at a similar biostratigraphic level in australia multiple replicate analyses have yielded indistinguishable ages and indicate 353 2 4 0 ma 2 as the age of the boundary obtaining an age for the boundary in the german reference section depended on the ability of shrimp to date a small sample and to target small areas of structurally complex zircons future refinements of the age of this boundary may depend on re analysis of this uniquely placed bentonite and this highlights the value of defining biostratigraphic stratotypes in the vicinity of known dateable horizons

possible two stage 87sr evolution in the stockdale rhyolite the rb sr total rock data for the stockdale rhyolite of significance for the palaeozoic time scale are more scattered about a single stage isochron than expected from experimental error two stage 87 sr evolution for several of the samples is explored to explain this as an alternative to variation in the initial 87 sr 86 sr which is customarily used in single stage dating models the deletion of certain samples having very high rb sr removes most of the excess scatter and leads to an estimate of 430 7 m y for the age of extrusion there is a younger alignment of rb sr data within each sampling site at 412 7 m y we suggest that the stockdale rhyolite is at least 430 m y old that its original range in rb sr was smaller than now observed and that it experienced a net loss in sr during later hydrothermal alteration at ca 412 m y

sea level changes and δ18o record for the past 34 000 yr from mayotte reef indian ocean new sea level and 18o curves for the past 34 000 yr based on uranium thorium chronology are proposed for the southwestern part of the indian ocean the archives include cores drilled from onshore coral reefs and submersed samples from foreslope corals of mayotte in the comoro islands the mayotte sea level curve shows a lowstand of 145 5 m below the present level during the last glacial maximum dated at 18 400 yr this lowstand is supported by the maximum18o enrichment in the coral colonies the residual signal 18o controlled by sea surface temperature changes indicates that surface waters 18 400 yr ago were approximately 5 c cooler than present the deglacial sea level rise is clearly recorded with a mean rate of about 1 7 cm yr 1between 18 400 and 10 000 yr ago the deglaciation phase is characterized by a strong18o depletion marked by two pulses related to meltwater discharges into the north atlantic ocean but also characterized by responses specific to the tropical indian ocean

response of reef coral communities to sea level rise a holocene model from mauritius western indian ocean the fringing reef at pointe au sable mauritius indian ocean was used to examine the effects of holocene sea level rise on coral growth this reef is about 1000 m wide and comprises a forereef slope 30 m maximum depth a narrow reef crest and a very shallow backreef 1 5 m maximum depth four major coral communities were recognized which developed within relatively narrow depth ranges a pachyseris oulophyllia community deeper than 20 m an acropora tabulate faviid community 20 6 m a robust branching acropora community less than 6 m and a pavona community less than 10m three high recovery cores show the holocene reef sequence is a maximum of 19 3 m thick and comprises four coral biofacies which are similar to counterparts identified in modern communities robust branching tabular branching robust branching domal and foliaceous coral facies a minimum sea level curve for the past 7500 years was constructed using distribution patterns of coral biofacies and radiocarbon dates from corals reconstruction of reef growth history indicates that both offshore and onshore reef zones were developing coevally aggrading at rates of 4 3 mm year 1 from 6900 years b p the reef caught up with sea level only after sea level stabilized changes in coral community and reef growth rates were driven principally by increasing water agitation due to the decrease in accommodation space based on the composition of the successive coral assemblages the reef appears to have grown through successive equilibrium stages

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian

sea level at the last glacial maximum evidence from northwestern australia to constrain ice volumes for oxygen isotope stage 2 new sea level information from the bonaparte gulf in northwestern australia is used to constrain the magnitude and rates of change of ice volumes during the last glacial maximum lgm the region is tectonically stable and far from the former ice covered regions the glacio hydro isostatic adjustment of the coast is therefore relatively small and the corrections for this evect are not sensitive to details of the rebound model microfossil analysis and ams radiocarbon dating of 11 gravity cores taken across the shelf and bonaparte gulf demonstrate that 1 the lgm sea levels were locally at 125 4 m 2 the lgm terminated abruptly at 19 000 cal yr bp with a rapid rise in sea level of about 15 m over the next 500 years and 3 the onset of the minimum sea levels occurred before 22 000 cal yr bp when corrected for the glacio hydro isostatic evects the increase of lgm ice volumes over the present day ice volume is 52 5 106 km3 the termination of the lgm is marked by a rapid ice discharge of 5 2 106 km3 2001 elsevier science b v all rights reserved

milankovitch cyclicity recorded from devonian non marine sediments hydrographically closed basins are sensitive to environmental change at all scales the influence of climate being particularly strong some devonian basins contain non marine successions which appear to represent the deposits of such basins climatic fluctuations may be recorded by sediments in the form of milankovitch band cyclicity two novel records of climatically related cyclicity are discussed well 12 13 1 in the north sea penetrates a fine grained old red sandstone succession which is thought to be comparable to the largely lacustrine middle devonian deposits of the orcadian basin which outcrop onshore the gamma ray log through the devonian interval reveals periodic large peaks which correlate with u rich fine grained intervals deposited during periods of greatest lake expansion the peaks are cyclical power spectrum of the gamma ray data reveal periodicities of c 8 and 40 m which are thought to correlate with the 21 000 yr precession and 100 000 yr eccentricity milankovitch cycles the sherkin sandstone formation of the munster basin sw ireland is a thick 1000 m succession of largely alluvial deposits which were deposited by a terminal fan network detailed analysis of channel body sandstones and sedimentary structures contained within them reveals a cyclical variation in the dimensions of the bedforms camed by the channels the same cyclicity is evident in the proportion of channel deposits this variation reflects fluctuations in palaeodischarge probably related to climatic variation the main cycles are approximately 130 m thick spectral analysis reveals two further strong periodicities at approximately 36 and 55 m estimated sediment accumulation rates suggest that the cycles represent periods of the order of lo4 years it is proposed that the longer cycles reflect the 412 000 yr orbital eccentricity cycle and that the shorter cycles are either harmonics or components of the 100 000 yr eccentricity cycle

palynology of the stonehaven group scotland evidence for a mid silurian age and its geological implications palynomorphs from the stonehaven group indicate a late wenlock to early ludlow age this is older than the currently accepted pridoli age based on fish and arthropods reasons for this discrepancy are discussed a previous correlative of the stonehaven group has been the old red sandstone of kerrera argyll however palynological assemblages from both kerrera and the adjacent succession at oban are in fact younger than that from stonehaven in being of latest silurian to earliest devonian age the palynomorphs from kerra and oban lie beneath the important geochronological tie point of the lorne lavas and suggest that the silurian devonian boundary is older than currently accepted

on postglacial geoid subsidence over the equatorial oceans we develop two new spectral formalisms for the gravitationally self consistent solution of the sea level equation which governs the redistribution of glacial meltwater on a visco elastic earth the first is a purely spectral technique based on an extension of theory outlined by dahlen 1976 for determining the equilibrium oceanic tide on an elastic planet using this technique with a feasible spherical harmonic truncation level l 30 we can obtain convergence in the computed sea level variations within the degree range l 10 we also develop a second pseudospectral technique however which permits the construction of gravitationally self consistent solutions to much higher degree and order l 100 the pseudospectral formalism is employed here to develop a comprehensive physical explanation for the global pattern of present day sea level variations due to ongoing glacial isostatic adjustment in particular we focus upon a mechanism which we term equatorial ocean syphoning that acts to draw water toward the oceanic portion of the collapsing peripheral bulge that encircles previously glaciated regions the collapse of the forebulge induces a flow of water which is required to maintain hydrostatic equilibrium the syphoning mechanism dominates the relative sea level rsl variation in oceans in the far field of the ice sheets that is beyond the peripheral bulge during periods such as the interglacial of the past 4000 years during which the volume of the ice sheets has not apparently changed appreciably while at the same time isostatic adjustment persists the rsl change in the near field is in contrast dominated by the local vertical displacement of the solid surface finally comparison of gravitationally self consistent predictions of rsl change in the far field with the observational data at small pacific island sites has provided an upper bound of 1 to 2 m for the eustatic sea level rise produced by any recent last 3000 years melting of the antarctic ice sheet

the laidlaw volcanics a late silurian point on the geological time scale mapping mineralogical and chemical studies of an area west and northwest of canberra southeastern australia have shownthat the laidlaw volcanics are unique in the region and that their age is tightly controlled stratigraphically as they lie both above and below early ludlow late silurian fossiliferous sediments k ar mineral analyses previously published rb sr mineral analyses and new rb sr wholerock and mineral analyses together give the laidlaw volcanics an age of 420 7 2 2 m y this result for the early ludlow is identical numerically with a recently published age of 421 3 m y for the ashgillian late ordovician stockdale rhyolite and suggests either that the time interval between the ashgill and ludlow does not exceed a few million yearsor that the age estimate for the stockdale rhyolite is too young

geochronology of late caledonian magmatism in northern britain rb sr k ar ar ar and sm nd isotopic data are presented for mineral separates and whole rock samples from old red sandstone ors lavas associated minor intrusions and 9newer granite9 intrusive complexes from the cheviot hills north to shetland these data yield 16 internally consistent rb sr mineral ages and one each of ar ar sm nd and k ar ages when considered with precise and reliable published data it is clear that there are systematic differences in the age of late caledonian magmatism through the geological regions of scotland in the grampian highlands and the scottish midland valley magmatism was concentrated during the period 423 to 410 ma ors volcanism in the highlands occurred around 420 ma with plutonism continuing to about 408 ma volcanism and plutonism in the midland valley took place between 415 and 410 ma in the southern uplands magmatism occurred earlier in the north with all magmatism close to the southern uplands fault dated around 408 ma and that close to the iapetus suture dated at around 394 ma as no evidence exists for ocean closure prior to c 400 ma the age of igneous activity north of the southern uplands fault is consistent with chemical evidence for a relationship to active nw directed subduction the younger magmatism of the s part of the southern uplands cannot be subduction related and the c 408 ma plutons nearer the southern uplands fault can only be subduction related if tectonic construction of the southern uplands was a two stage process

postglacial flooding history of mayotte lagoon comoro archipelago southwest indian ocean abstract four cores from the fringing reefs and five sediment cores from mayotte lagoon comoro archipelago southwest indian ocean which reached the pleistocene holocene boundary form the database of this study they offer the opportunity to reexamine and complete the postglacial sea level curve especially for the time interval between 11 6 to 8 kyr cal bp between 11 6 kyr cal bp until present the history of sea level rise showed the following steps 1 by about 19 mm yr between 11 6 and 9 6 kyr cal bp 2 by 9 mm yr between 9 6 and 8 kyr cal bp 3 by 3 mm yr between 8 and 7 kyr cal bp and 4 by 0 9 mm yr after 7 kyr cal bp until stabilisation at present level at 2 5 kyr cal bp in addition a decline in the rates of sea level rise or even a stillstand is observed between 13 to 11 6 kyr cal bp the flooding of the lagoon of mayotte was controlled by the depth of the reefal passages which were cut by rivers and or due to erosion during the time of emergence since the last interglacial the differences in the shape of the sea level curve from mayotte compared to those from other sites located far from the former glaciated regions are related to 1 the small size of the island 2 the rapid downward movement of this small volcanic island with the oceanic plate into the mantle due to hydro isostatic compensation after addition of meltwater and 3 the location between large continents

geomorphology and sedimentology of a modern isolated carbonate platform the glorieuses archipelago sw indian ocean abstract the study of modern carbonate systems commonly helps in improving facies interpretation in fossil reefs and in providing analogues of sediment distribution depending on the specific platform configuration i e rimmed shelves and isolated carbonate platforms this paper deals with a geomorphological and sedimentological study of the glorieuses archipelago an isolated carbonate platform located between the northern tip of madagascar and mayotte the dataset consists of digital terrain model satellite imagery and box sediment samples analyses of grain size and composition of carbonate grains are used to characterize the distribution and heterogeneity of sediment accumulated on the isolated platform main results show that the glorieuses archipelago is organized in distinctive morphological units including a reef flat developed along the windward side an apron and a semi enclosed 12 m and up to 15 m water depth the lack of carbonate mud in sediments deposited on the archipelago can be explained by the direct connection between the lagoon and the open ocean the main carbonate grains include halimeda segments coral fragments large benthic foraminifers red algae and molluscs according to the shape and the position of intertidal sandwaves the current arrangement of moderately sorted fine to medium sands appears to be strongly influenced by tidal currents the in situ sediment production accumulation and transport on the platform finally contribute to carbonate sand export to distinct deep marine areas depending on wind regimes and currents

holocene sea level determination relative to the australian continent u th tims and 14c ams dating of coral cores from the abrolhos islands u th tims and 14 c ams measurements are presented from two coral cores from the easter group of the houtman abrolhos islands between 28 s and 29 s on the western continental margin of australia the u th measurements on the morley core from morley island cover a depth interval from 0 2 m above present sea level to 24 4 m below present sea level and comprise eleven samples the ages vary between 6320 50 a at 0 2 m above sea level and 9809 95 a at 24 4 m below sea level all errors are 2 the mean growth rate is 7 1 0 9 m ka the 14 c dates of selected morley core corals show that the 14 c ages are 1000 a younger than their corresponding u th ages which agrees with previous results the main purpose of our 14 c measurements is to be able to compare them precisely with other coral cores where no u th measurements are available the u th measurements of the suomi core from suomi island cover a depth interval from 0 05 m to 14 2 m below present sea level and consist of four samples the ages vary between 4671 40 a at 0 05 m below sea level and 7102 82 a at 14 2 m below sea level with a mean growth rate of 5 8 0 2 m ka the growth history of both cores is explained by a simple model in which the growth rates of the morley core can be interpreted as reflecting local rates of sea level rise whereas the suomi core is interpreted as reflecting lateral growth during the past 6000 a our results indicate that sea level relative to the western margins of the australian continent was about 24 m lower than present at about 9800 a b p 14 c gives a date of 8500 a b p sea level then rose and reached a highstand slightly higher than the present position at about 6300 a b p 14c date 5500 a this highstand declined but was still higher than present at 4600 a b p this is in agreement with previous observations along the australian coastal margins and with observations from the huon peninsula papua new guinea our results are very similar to theoretical numerical models which take into consideration water loading and isostatic compensation and viscous mantle flow in contrast coral cores from barbados show that corals with a 14 c age of 5500 a b p are some 10 m b p s l we interpret the difference between the barbados core and the morley core as resulting from additional flooding of barbados by water redistribution due to changes in the earth s geoid but not reflecting global sea level rise or major addition of melt waters over the past 6000 a the difference in the geoid at barbados between 6000 a b p and the present will require a refinement in the geophysical models precise 230 th tims measurements on continental coasts will be required to provide an adequate data base for modelling deformation flow of mantle material and sea level height

late pleistocene evolution of the mixed siliciclastic and carbonate southwestern new caledonia continental shelf lagoon abstract the main island of new caledonia nc is surrounded by the second largest barrier reef in the world after the australian great barrier reef the upper pleistocene evolution of this barrier reef lagoon complex offers the opportunity to examine the response of a modern mixed tropical siliciclastic carbonate system to relative sea level changes and to better constrain the relative role of lagoon backfilling and paleo drainage system in sediment transfer across the shelf this paper mainly focuses on the results of chronostratigraphic and sedimentological interpretations of new seismic bathymetric and coring data collected in the sw nc lagoon several significant points are highlighted from this study and allow the construction of a refined model which includes the evolution of both the sw nc mixed shelf and lagoon new results show that the nc lagoon has not recorded a reciprocal sedimentation during glacial interglacial sea level cycles but a unique mixed regime strong contrasts are observed and these depend above all on the two lagoon domains the outer coral plateau and the inner lagoon depression corresponding to a semi closed proximal basin which is separated from the plateau by a basement ridge in the depression clastic sediments remain dominant from early flooding to highstand stages while carbonate sedimentation continued through time across the coral plateau this spatial contrast between terrigenous and carbonate deposits was maintained throughout various sea level cycles thus even if spatial segregation is also observed for other examples of mixed shelf environments the sw nc shelf appears quite unique in comparison to the other mixed systems when considering conceptual models of reciprocal sedimentation moreover the presence of a semi enclosed lagoon depression allows the preservation of larger volume of terrigenous deposits this semi filled geometry of the lagoon is assumed to be the result of several factors a significant subsidence that offers accommodation for aggrading deposits evacuation through channels of sediments mobilized during storm events the tidal currents and fairweather wave dynamics lastly the inherited morphologic and structures may explain the geomorphic evolution of the escarpment margin type of the sw nc rimmed shelf and its differentiation with the opposite se nc ramp type shelf

origins and development of holocene coral reefs a revisited model based on reef boreholes in the seychelles indian ocean until recently concepts of coral reef growth and accumulation have been predominantly based on a darwinian model in this the upwards and outwards growth of a reef core a coral framework takes place over a foreslope consisting of reef talus with the simultaneous filling of the back reef lagoon by reef derived debris the principal adaptations of this pattern relate to the influence of relative changes in sea level and commonly ignore oceanographic factors such as storm frequency and severity boreholes through the outer edge of a fringing reef in the seychelles western indian ocean reveal a record of holocene sediment accumulation first established approximately 8 ka ago faunal and floral associations show that growth of this body began in relatively deep water but that this shallowed to 5 m within 1 ka subsequent accumulation was of keep up style but as the rate of sea level rise slowed shoaling became more frequent and aggradation was limited by reducing accommodation space constructional facies are characterised either by massive corals including leptastrea porites and faviids or by branching corals typically acropora of the danai robusta group coral surfaces may be encrusted by red algae foraminifera and vermetids and are commonly bored by filamentous algae clionids and molluscs however detrital facies are volumetrically dominant and the paucity of a constructional framework requires a re evaluation of models of reef accretion new models relate the geometry of accretion to the interplay between extreme storm events and fairweather hydrodynamic conditions these suggest that a contiguous framework forms in areas of moderate fairweather energy without extreme storm events severe storms destroy the continuity of reef structures and generate increasing volumes of coarse detritus low storm severity coupled with low fairweather hydrodynamic energy may promote the accumulation of fine grained reef derived sediments that inhibit framework growth while ecology reflects year by year sea conditions lithology and structure are controlled by exceptional storms with the effects of changing sea level superimposed

seismic architecture and sediment distribution within the holocene barrier reef lagoon complex of mayotte comoro archipelago sw indian ocean twenty gravity cores and a large set of high resolution seismic profiles from various lagoonal settings were studied to determine the holocene sediment distribution and sequence architecture within the mayotte barrier reef lagoon complex the holocene seismic sequence comprises a type 1 sequence with lowstand transgressive and highstand systems tracts the lowstand systems tract consists of a paleosoil horizon formed during subaerial exposure the transgressive systems tract is composed of four depositional systems 1 inner transgressive layer 2 proximal and distal incised valley fills 3 mid lagoonal layer and 4 keep up or catch up fringing and barrier reef sequence the highstand systems tract comprises three depositional systems 1 of a proximal terrigenous wedge 2 mid lagoonal and distal carbonate sands or muds and 3 reefal carbonates our studies show that the nature of the holocene sequence is controlled by the rate and amplitude of sea level rise and environmental changes which are expressed by changes in clastic sediment supply and carbonate production the pre holocene topography and water dynamics steer the vertical and spatial sediment thickness distribution of the holocene additional important parameters are the proximity to a source area carbonate or terrigenous and the width of the depositional area climate dynamics are also of great importance while they determine carbonate production and terrigenous runoff sedimentation rates in the subtidal settings always lacked behind sea level rates thus a steep relief was created keeping most lagoonal parts within the deep subtidal realm in which sediment production was not efficient enough to fill up accommodation space in addition wave and or current energy might prevent the fill up of the lagoon this ultimately resulted in a typical empty bucket morphology only a high amplitude sea level fall would allow the subtidal lagoon to build up to base level unfilled accommodation space therefore must be a very common feature in the geologic record

basinwide stratigraphic synthesis and sequence stratigraphy upper pragian emsian and eifelian stages lower to middle devonian appalachian basin

mauritius since the last glacial environmental and climatic reconstruction of the last 38 000 years from kanaka crater a 10 m long peat core from the kanaka crater 20 25 s 57 31 e located at 560 m elevation in mauritius was analyzed for microfossils eight radiocarbon ages show the pollen record reflects environmental and climatic change of the last ca 38 cal ka bp the record shows that the island was continuously covered by forest with erica heath philippia in the uplands cyperaceous reedswamp with pandanus trees was abundant in the coastal lowlands as well as locally in the waterlogged crater the record shows changes in climatic humidity wet from 38 0 to 22 7 cal ka bp drier from 22 7 to 10 6 cal ka bp and wetter again from 10 6 cal ka bp to recent as the main response to climate change a high turnover in montane forest species is evidenced at 22 7 cal ka bp and at the start of the holocene the limited altitudinal ranges in the mountains of mauritius maximum altitude 828 m and changing humidity being more important than changing temperature suggests that in response to climate change a reassortment in taxonomic composition of montane forests might be equally important as displacement of forest types to new altitudinal intervals we found weak impact of the latitudinal migration of the intertropical convergence zone and data suggest that the indian ocean dipole is a more important driver for climatic change in the southwest indian ocean

calibration of the geologic time scale cenozoic and late cretaceous glauconite and nonglauconite dates compared revision of the 1982 time scale of harland et al has led to the compilation of 377 isotopic dates for calibration of the cenozoic to cretaceous time interval the results show that the ages of stage boundaries based on glauconite dates are on average about 2 m y younger than those based on nonglauconite dates but for many cenozoic and late cretaceous stages the differences are too small to require special consideration of glauconite dates future work may reveal an irreducible systematic difference between glauconite and nonglauconite time scales but the progress made so far in recognizing those glauconites likely to yield reliable dates for the cenozoic to late cretaceous interval may continue to provide useful time scale calibration points

the absolute age of the eifelian tioga ash bed pennsylvania the tioga ash bed bed b of the zeigler pit union county pennsylvania lies in the polygnathus costatus costatus zone of the eifelian stage of the middle devonian series the 27 5 cm thick bed contains igneous zircon and monazite crystals that have been dated by precise u pb techniques zircons are characterized by inherited pb that occurs as barely perceptible interior regions enriched in inclusions the zircons are discordant and do not reveal the igneous age of the bed in contrast high quality monazite crystals lack any evidence of inheritance or loss of pb and multiple analyses have overlapping 207 pb 235 u ages of 390 0 pm 0 5 ma the monazite analyses are concordant or very slightly reversely discordant the consistency of the monazite data provides a new precise estimate of age for the lower eifelian

the transient nature of the empty bucket model of reef sedimentation abstract the geometry of modern reefs has been likened to an empty bucket with the narrow reef rim comprising the container pail that encloses the water filled bucket while the analogy is valid the assumption that this constitutes a final geometry is not examples from the indian pacific and atlantic oceans individually and collectively demonstrate current filling of the lagoons by reef perimeter sand aprons since sea level only approximated its present position 3 to 6 ky ago it follows that the observed extent of modern highstand lagoon filling is minimal if the filling process was to continue unabated the result would be a flat topped bank but during the pleistocene low stands of sea level aborted the filling process extrapolating these relationships to the geologic record suggests that the empty bucket model of unfilled reef lagoon space is greatest during icehouse high frequency glacial fluctuations of sea level alternatively filled buckets in which cycle thickness approximates accommodation space are probably largely restricted to greenhouse time intervals the co occurrence of quaternary high amplitude frequency sea level changes with rapidly growing scleractinian corals probably enhanced the occurrence of empty bucket morphologies

a comparison of k ar and rb sr ages of rapidly cooled igneous rocks two points in the palaeozoic time scale re evaluated k ar and rb sr ages were measured on rapidly cooled igneous rocks from kinnekulle sweden ordovician bentonite the cerberean cauldron australia late devonian felsic volcanics mount dromedary australia cretaceous monzonite and cooma australia jurassic syenite no systematic bias was detected between the ages determined by the two techniques calculated using the constants recommended by the i u g s subcommission on geochronology the k ar and rb sr ages of the jurassic syenite also were indistinguishable from its zircon u pb age the kinnekulle a 1 bentonite gives a minimum age of 446 3 ma for the early caradocian diplograptus molestus zone the cerberean cauldron volcanics give a minimum age of 367 2 ma for the early frasnian these data are consistent with a small upwards revision of the ages in gale et al 9s 1979 time scale as proposed by gale et al 1980

chronometric calibration of mid ordovician to tournaisian conodont zones a compilation from recent graphic correlation and isotope studies three available graphic correlation analyses are used to calibrate mid palaeozoic conodont zonations sweet s scheme for the mid to upper ordovician kleffner s for the mid to upper silurian and murphy berry s for the lower and middle lower devonian the scheme of sweet is scaled by applying the high precision u pb zircon date of tucker and others for the rocklandian and linked with that of kleffner by scaling the graptolite sequence of the ordovician silurian global stratotype section to fit two similarly derived dates from this sequence the top of kleffner s scheme all of murphy berry s as well as standard zones to the frasnian are calibrated by using tie points of the latest cambridge bp time scale gts 89 however the recent microbeam zircon date by claoue long and others for the hasselbachtal devonian carboniferous auxiliary stratotype is used to calibrate the standard famennian zones also the similarly derived but preliminary determination reported by roberts and others from the isismurra formation of new south wales is tentatively taken as the top of the tournaisian and so used to calibrate tournaisian zones despite the considerable extrapolation required to compile these schemes and their inherent errors the resultant time scale closely agrees with other dates of tucker and others from the llanvirn as well as the gts 89 homerian gorstian tie point this suggests that stratigraphic methods can be usefully applied to geochronometry the llandovery appears to have lasted longer 16 m y than usually envisaged and the ordovician silurian boundary may need to be lowered to approximately 443 5 ma certainly chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high resolution dating for their calibration will be crucial to more accurate biochronometries

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

the leaking bucket of a maldives atoll implications for the understanding of carbonate platform drowning abstract seismic and multibeam data as well as sediment samples were acquired in the south male atoll in the maldives archipelago in 2011 to unravel the stratigraphy and facies of the lagoonal deposits multichannel seismic lines show that the sedimentary succession locally reaches a maximum thickness of 15 20 m above an unconformity interpreted as the emersion surface which developed during the last glacial sea level lowstand such depocenters are located in current protected areas flanking the reef rim of the atoll or in infillings of karst dolinas much of the 50 m deep sea floor in the lagoon interior is current swept and has no or very minor sediment cover erosive current moats line drowned patch reefs whereas other areas are characterized by nondeposition karst sink holes blue holes and karst valleys occur throughout the lagoon from its rim to its center lagoonal sediments are mostly carbonate rubble and coarse grained carbonate sands with frequent large benthic foraminifers halimeda flakes red algal nodules mollusks bioclasts and intraclasts some of them glauconitic as well as very minor ooids finer grained deposits locally are deposited in current protected areas behind elongated faros i e small atolls which are part of the rim of south male atoll the south male atoll is a current flushed atoll where water and sediment export with the open sea is facilitated by the multiple passes dissecting the atoll rim with an elevated reef rim and tower like reefs in the atoll interior it is an example of a leaky bucket atoll which shares characteristics of incipiently drowned carbonate banks or drowning sequences as known from the geological record

cyclic patterns in the paleozoic and mesozoic implications for time scale calibrations the analysis of both physical and biological data from the devonian strata of new york state reveals the existence of two robust cyclic patterns one cycle with a duration of 4 5 5 7 m y and a larger cycle of approximately twice this wavelength at 11 3 13 6 m y depending upon the absolute time scale used in the wavelength calculation the analysis of sedimentation rates from the jurassic likewise reveals a cycle with a temporal spacing of 4 to 6 m y a cycle with a periodicity virtually identical to the shorter cycle detected in the devonian the data further suggest the existence of cycles at 2 3 m y and 30 m y intervals though these periodicities approach the lower and upper limits of resolution of the data base the potential correlation of cyclic patterns has considerable implication for the development of new chronological time scales and global chronostratigraphic resolution current radiometric time scales have a resolution which is still above the stage level for most of the pre cenozoic in estimating the ages of stage boundaries most time scales are based on either the assumption of equal stage durations or the assumption of equal biostratigraphic zone durations and the subsequent linear interpolations between control tie points operating under the working hypothesis that a regular periodic signal exists in the data the above listed devonian cycles are brought into a more uniform periodicity by transforming the time scale itself yielding an alternatively calibrated timescale which is neither equal stage nor equal zone in structure

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

radiocarbon dating of mangrove sediments to constrain holocene relative sea level change on zanzibar in the southwest indian ocean mangrove sedimentary deposits are sensitive to changes in sea level and can be used to reconstruct mid to late holocene sea level fluctuations in intermediate and far field locations distant to t

sea level fluctuations imply that the younger dryas ice sheet expansion in western norway commenced during the allerod after the first emergence following deglaciation relative sea level rose by 10 m in western norway and culminated late in the younger dryas yd the relative sea level history reconstructed by dating deposits in isolation basins shows a sea level low stand between 13 640 and 13 080 cal yr bp a 10 m sea level rise between 13 080 and 11 790 cal yr bp and a sea level high stand between 11 790 and 11 550 cal yr bp shortly after the yd holocene boundary sea level fell abruptly by 37 m the shorelines formed during the sea level low stand in the mid allerod and during the sea level high stand in the yd have almost parallel tilts with a gradient of 1 3 m km 1 indicating that hardly any isostatic movement has taken place during this period of sea level rise we conclude that the transgression was caused by the major re advance of the scandinavian ice sheet that took place in western norway during the lateglacial the extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea our results show that the crust responded to the increased load well before the yd starting 12 900 cal yr bp with a sea level low stand at 13 640 cal yr bp and the subsequent yd transgression starting at 13 080 cal yr bp thus we conclude that the so called yd ice sheet advance in western norway started during the allerod possibly more than 600 years before the allerod yd transition r 2007 elsevier ltd all rights reserved

a new model evaluating holocene sediment dynamics insights from a mixed carbonate siliciclastic lagoon bora bora society islands french polynesia south pacific abstract mixed carbonate siliciclastic lagoons of barrier reefs provide great potential as sedimentary archives focusing on paleoenvironmental and paleoclimatic changes as well as on event deposition sediment sources include lagoonal carbonate production the marginal reef and the volcanic hinterland mixed carbonate siliciclastic continent attached coastal lagoons have been intensively studied however their isolated oceanic counterparts have been widely disregarded here we present a new model of holocene sediment dynamics in the barrier reef lagoon of bora bora based on sedimentological paleontological geochronological and geochemical data the lagoonal succession started with a pleistocene soil representing the lowstand systems tract as the rising holocene sea inundated the carbonate platform peat accumulated locally 10 650 9400 years bp mixed carbonate siliciclastic sedimentation started ca 8700 5500 years bp and represents the transgressive systems tract during that time sediments were characterized by relatively coarse grain size and contained high amounts of terrestrial material from the volcanic hinterland as well as carbonate sediments mainly produced within the lagoon siliciclastic content decreases throughout the holocene after the rising sea had reached its modern level sand aprons formed between reef crest and lagoon creating transport pathways for reef derived material leading to carbonate dominated sedimentation ca 6000 3000 years bp during the highstand systems tract however mainly fine material was transported and accumulated in the lagoon while coarser grains were retained on the prograding sand apron from ca 4500 500 years bp significant variations in grain size total organic carbon as indicator for primary productivity ca and cl element intensities as qualitative indicators for carbonate availability and lagoonal salinity are seen such patterns could indicate event re deposition and correlate with contemporaneous event deposits found in the lagoon of nearby tahaa which are supposed to be induced by elevated cyclone activity correspondingly enhanced erosion and run off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall increased amounts of coarse grained sediment from marginal reef areas would be transported into the lagoon however ti ca and fe ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid holocene also benthic foraminiferal faunas do not validate reef to lagoon transport of sediment alternatively the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher than present sea level which are supposed for the mid late holocene in the south pacific sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity we propose the shift towards coarser grained sedimentation patterns during the mid late holocene to reflect sediment load shedding of sand aprons due to oversteepening of slopes at sand apron lagoon edges during times of stronger trades and higher than present sea level of the highstand systems tract which led to redeposition of sediment even within the lagoon center modern conditions including a sea level fall to modern level were reached ca 1000 years bp and lagoonal infill has been determined to a large part by fine grained carbonate dominated sediments produced within the lagoon and derived from the marignal reef infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons contrary to the commonly supposed assumption that coarse grained sediment layers within fine grained lagoonal successions represent overwash events induced by storms or periods of higher storm activity we postulate a new model of long term lagoonal sediment dynamics including sea level climatic change and geomorphological variation of the barrier reef lagoon

continuous reef growth during the last 23 cal kyr bp in a tectonically active zone vanuatu southwest pacific abstract at urelapa island vanuatu sea level rise and a tectonic uplift of 3 mm yr 1 have controlled water depth and the colonization and reef development on a substrate from 23 until 6 cal kyr bp analysis of coralgal assemblages offers insights on the mode of reef growth and on water depth over the reef for the studied period those assemblages precisely dated by the 230 th 234 u method give valuable information on the rate and timing of sea level rise since the last glacial maximum the urelapa reef sequences are characterized by upwards replacement of reef frameworks which indicates changes in wave energy through time the sudden acceleration of sea level rise associated with meltwater pulse 1b at around 11 3 cal kyr bp is marked by a change in reef growth strategy from a keep up mode to a catch up mode we examine the delay in timing of the occurrence of suitable substrates the role of paleoceanographic factors and the influence of possible jumps in sea level

two new emsian early devonian u pb zircon ages from volcanic rocks of the rhenish massif germany implications for the devonian time scale so far only few biostratigraphically well constrained isotopic ages constitute the geochronological framework of the devonian period to expand this sparse dataset two new u pb isotope dilution thermal ionization mass spectrometry id tims zircon ages were obtained from volcanic rocks of the rhenish massif germany these rocks are interbedded in emsian lower devonian marine sedimentary successions that are well documented by index fossils given that the u pb zircon data represent primary crystallization and eruption ages they provide an important contribution to the devonian time scale the older sample a stratiform volcaniclastic layer hans platte is collected from bundenbach hunsruck the type locality of the lower emsian hunsruck slate a cluster of five coherent single zircon analyses obtained from this layer yielded a weighted mean 206 pb 238 u age of 407 7 0 7 ma which is regarded as the time of eruption of the pyroclastic rock biostratigraphically the layer can be assigned to the upper part of the polygnathus excavatus conodont zone the younger u pb age was obtained from the global stratotype section and stratigraphic point section at wetteldorf eifel where the k bentonite hercules i is intercalated 13 m below the lower middle devonian boundary in the uppermost part of the polygnathus costatus patulus conodont zone some of the 19 single zircon analyses obtained from this bentonite appear to document significant influences of inheritance the 13 youngest points are however concordant and form an elongated cluster along concordia with 206 pb 238 u ages between 392 2 and 407 7 ma given the risky assumption that this age scattering is exclusively caused by varying amounts of inheritance the youngest point of this cluster represents the analysis with the least or no inheritance in this case its 206 pb 238 u age of 392 2 1 5 ma should approach the eruptional age of the bentonite the ages presented here in combination with u pb id tims zircon and monazite ages from other workers allow a recalibration of the early emsian to early eifelian interval of the devonian time scale the result is a duration of the emsian stage excluding the basal emsian p kitabicus conodont zone of more than 17 2 ma and an emsian eifelian early middle devonian boundary age of 391 8 0 4 ma

devonian marine incursions into the orcadian basin scotland bp chevron well 14 6 1 drilled in the east orkney basin has penetrated devonian sedimentary rocks which can be dated palynologically as within the latest givetian to early frasnian interval this microflora contains the first substantiated record in western europe of archaeoperisaccus a spore hitherto regarded as restricted to northern laurasia three grey green intervals within the well contain marine microfossils which provide the first direct evidence for the movement of marine waters into the northern part of the old red sandstone continent onshore an eday marls section in the bay of berstane orkney contains a marine microfauna which demonstrates the presence of a marine incursion of mid late givetian age this is the first record of a devonian marine incursion in scotland combination of this palaeontological data with sedimentological studies of the eday marls and upper old red sandstone suggests that a wide flat sabkha plain extended eastwards from the onshore orcadian basin during the later stages of its infill and was subjected to episodic marine incursions these incursions are tentatively linked with marine transgressions into the argyll area of the central north sea two orders of cyclicity occur within the dated devonian interval of 14 6 1 and are interpreted as resulting from orbital cyclicity at periodicities of 39 5 and 413 9 ky this indicates that the control on the devonian sea level maxima may have been orbital cyclicity these marine incursions are speculatively correlated to high stands on the devonian sea level curve the bay of berstane marine incursion representing the taghanic onlap whilst those in 14 6 1 are the rhinestreet middlesex and genundewa transgressions reconsideration of the palaeogeography of the northern margin to the marine devonian indicates that the sea entered the orcadian basin from the east along the tornquist zone at the margin of the fenno scandian high