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

a high relative sea level stand in the middle holocene of southeastern tunisia abstract study of the marine holocene deposits in southeastern tunisia shows bioclastic beaches at elevations ranging between 0 and 100 cm above high tide level a h t l depending on the elevation of these fossilized shorelines the ages obtained are different the age of the older deposits ranges between 5900 and 4000 14cc yr b p 6400 4300 calendar yr b p there deposits consist of bioclastic beaches attaining an elevation of about 40 to 100 cm a h t l the younger deposit is dated at around 2100 14c years ago 1850 calendar yr b p and is found today at the same elevation as the present sea level this deposit also consists of bioclastic beach material and contains pottery fragments postglacial melting should not be responsible for this observed higher relative sea level stand because deglaciation ended about 7000 6000 14c years ago fairbanks 1989 furthermore the regularity of the paleobeach deposit elevation over a broad area in southeastern tunisia suggests that tectonics cannot explain the emergence the emergence of up to 1 m of marine deposits dating back to between 5900 and 4000 14c yr b p should rather be interpreted as the result in the region of a postglacial hydro isostatic rebound as predicted in the theological models of continental margins by for example clark et al 1978 and lambeck 1993 the present situation was reached 2100 14c years ago

responses of stable bay margin and barrier island systems to holocene sea level highstands western gulf of mexico abstract the microtidal wave dominated coast of the western gulf of mexico displays a variety of holocene geomorphic features indicating higher than present water levels that were previously attributed to storm processes while geoidal sea level was at its present position field and aerial photograph examinations of bay margins barrier islands and beach ridge plains following major hurricanes show that the elevated features are inundated periodically by high storm surge despite their inundation these highstand features are not modified by modern storm processes instead storm related erosion and deposition are always seaward of and lower than the highstand features and are always limited to the extant shorezone where elevations typically are less than 1 5 m above present sea level bay margin and lagoonal highstand indicators include raised marshes and subtidal flats wave cut benches abandoned wave cut scarps with fringing marshes and or beach ridges and accretionary islands and recurved spits other emergent marine features include abandoned compound flood tidal delta and washover fan complexes attached to barrier islands and anomalously high beach ridges within both the barrier island complexes and beach ridge plains the highest beach ridges raised marshes and flats and erosional scarps and benches are manifestations of one or more rising phases and highstands in sea level whereas the lower marshes and accretionary topography are mainly products of the falling phases and shoreface adjustment to present sea level different elevations of beach ridge sets discordant truncation of beach ridges and elevated marine and brackish water faunal assemblages preserved in beach ridges raised marshes and flats and natural levees are compelling evidence of sea level fluctuations of 1 to 1 5 m from about 5500 to 1200 cal yr bp independent evidence from studies of geodynamic climatic and glacio eustatic processes can explain the mid holocene highstands and late holocene lowering of sea level that is observed in tectonically stable coastal regions far from former centers of glaciation

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

mass balance model parameter transferability on a tropical glacier we explore the small scale spatial and temporal transferability of model parameters between two points in the ablation zone of tropical glaciar shallap cordillera blanca peru 9 s 77 w 4800 m a s l in order to provide a robust assessment of the performance of a process based glacier mass balance model relative surface height change is calculated at hourly time steps and cumulative values are compared to surface height measurements made at irregular intervals 14 64 days over the course of two continuous hydrological years august 2006 august 2008 best performing parameter combinations were determined for each point from the outcome of 1000 model simulations for which parameters were varied randomly within a defined range with these parameter combinations measurements for a specific location and time span are well reproduced transferring the parameter combination as optimized for one location to the other location in the ablation zone increases the errors of modeled cumulative mass balance by 5 1326 mm ice eq a 1 transferring the parameter combinations as optimized for one year to the other year increases the modeled errors in cumulative mass balance by 18 3179 mm ice eq a 1 model errors generally increase during periods with frequent snowfall and snow cover this could reflect either the inherent difficulty of modeling complex snow processes or the inability of the model to correctly capture the pattern of albedo evolution at this site the magnitude of errors associated with parameter transfer in space and time highlights the need for improving model performance for robust climatological and or hydrological analyses on tropical glaciers

new insights on the relative sea level change during holocene along the coasts of tunisia and western libya from archaeological and geomorphological markers new data of sea level changes for the mediterranean region along the coasts of northern africa are presented data are inferred from archaeological sites of punic roman age located along the coast of tunisia between tunis and jerba island and along the western coast of libya between sabratha and leptis magna data are based on precise measures of presently submerged archaeological markers that are good indicators of past sea level elevation nineteen selected archaeological sites were studied in tunisia and four in libya all aged between 2 0 and 1 5 ka bp the functional elevations of significant archaeological markers were measured with respect to the sea level at the time of measurements applying corrections for tide and atmospheric pressure values the functional elevations of specific architectural parts of the sites were interpreted related to sea level at the time of their construction providing data on the relative changes between land and sea observations were compared against sea level change predictions derived from the glacio hydro isostatic model associated with the last glacial cycle the results indicate that local relative sea level change along the coast of tunisia and libya has increased 0 2 0 5 m since the last 2 ka besides minor vertical tectonic movements of the land the observed changes are produced by eustatic and glacio hydro isostatic variations acting in the mediterranean basin since the end of the last glacial maximum

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

multiproxy assessment of holocene relative sea level changes in the western mediterranean sea level variability and improvements in the definition of the isostatic signal abstract a review of 917 relative sea level rsl data points has resulted in the first quality controlled database constraining the holocene sea level histories of the western mediterranean sea spain france italy slovenia croatia malta and tunisia we reviewed and standardized the geological rsl data points using a new multi proxy methodology based on 1 modern taxa assemblages in mediterranean lagoons and marshes 2 beachrock characteristics cement fabric and chemistry sedimentary structures and 3 the modern distribution of mediterranean fixed biological indicators these rsl data points were coupled with the large number of archaeological rsl indicators available for the western mediterranean we assessed the spatial variability of rsl histories for 22 regions and compared these with the ice 5g vm2 gia model in the western mediterranean rsl rose continuously for the whole holocene with a sudden slowdown at 7 5 ka bp and a further deceleration during the last 4 0 ka bp after which time observed rsl changes are mainly related to variability in isostatic adjustment the sole exception is southern tunisia where data show evidence of a mid holocene high stand compatible with the isostatic impacts of the melting history of the remote antarctic ice sheet our results indicate that late holocene sea level rise was significantly slower than the current one first estimates of gia contribution indicate that at least in the northwestern sector it accounts at least for the 25 30 of the ongoing sea level rise recorded by mediterranean tidal gauges such contribution is less constrained at lower latitudes due to the lower quality of the late holocene index points future applications of spatio temporal statistical techniques are required to better quantify the gradient of the isostatic contribution and to provide improved context for the assessment of 20th century acceleration of mediterranean sea level rise

quaternary raised coral reef terraces on sumba island indonesia a spectacular sequence of coral reef terraces six steps broader than 500 meters and many minor substeps is developed near cape laundi sumba island between an ancient patch reef 475 meters high and sea level several raised reefs have been dated with the electron spin resonance and the uranium series dating methods the uplift trend deduced from these reefs is 0 5 millimeter per year most terraces although polycyclic in origin appear to correspond to specific interglacial stages with the oldest terrace formed 1 million years ago this puts them among the longest and most complete mid quaternary terrace sequences

holocene aeolian morphogenetic phases in southern italy problems in 14c age determinations using terrestrial gastropods abstract radiocarbon age determination is one of the most important methods for dating holocene events in particular it has been used to reconstruct the sequence of aeolian morphogenetic phases along the apulia and basilicata coasts southern italy in these areas three main holocene morphogenetic phases have been recognized using radiocarbon data obtained from sub fossil terrestrial gastropods archaeological data and osl analyses those of the middle holocene period of the greek roman time and of the middle ages sub fossil terrestrial gastropods have been considered suitable indicators in the detecting holocene climate environmental changes however it is well known that they could show problems as chronological indicators mainly due to aging effects induced by i micro particles of calcite aragonite in the shell structure derived from the local substratum and ii a variation of co 2 content in the plants eaten in order to verify these hypotheses living terrestrial gastropods were collected from coastal areas and analysed using ams the results indicate that many living gastropods gave ages of 1500 years older than those expected thus confirming the aging effect as 14 c ages of middle and late holocene aeolian morphogenetic phases obtained from terrestrial gastropods seem to be confirmed by archaeological data and osl analyses the aim of this work is to verify if the age anomalies obtained from modern gastropods could be extended to the entire holocene period

recognition of electromagnetic overburden anomalies with horizontal loop electromagnetic survey data an analog modeling program was conducted to investigate the electromagnetic em response of nonuniform conductive overburden layers with the horizontal loop technique of geophysical prospecting several characteristics of the response that will help to differentiate between the em response of nonuniform overburden layers and the response of bedrock mineralized conductors are reported to recognize these characteristics survey data at several frequencies and coil separations are required it was observed that the response of a ramp like a ridge like and a valley like inhomogeneity in the overburden can be mistaken as caused by bedrock conductors in the case of the ramp and ridge inhomogeneities the migration of the negative peak anomaly observed in profiles surveyed at different coil separations was one of its more diagnostic characteristics prominent positive shoulders as well as an abnormal distance between crossovers of a given detected field anomaly might be the first indication of the presence

terminal antarctic melting inferred from a far field coastal site abstract the contribution of the antarctic ice sheet ais to deglacial sea level rise is poorly constrained this shortfall gives rise to concerns because incorrect ais estimates impact significantly on our ability to predict sea level change in the course of global warming given the scarcity of geological data and the complexity of the antarctic response to glacio isostatic adjustment processes there is a need for accurate data to constrain the timing of the ice sheet retreat here we provide such data on the holocene antarctic melting through an isolated geographic site on the northern hemisphere which we show is sensitive to the antarctic signal using both our site and other mid latitudinal relative sea level sites our model provides a consensus estimate that the ais released water corresponding to 5 m equivalent sea level at 8 ka and ceased melting at 6 ka this is different to most ais models which release an equal amount of water at 11 ka or after 6 ka our findings change model assumptions about the terminal ais melting and show that future holocene sea level research should focus on broad shelves and large coast embayments in the mid latitudes

biological evidence of sea level rise during the last 4500 years on the rocky coasts of continental southwestern france and corsica on the rocky coasts of the northwestern mediterranean basin biogenic littoral rims built by the coralline rhodophyte lithophyllum lichenoides develop whose remains may be preserved for millennia when submerged in a rising sea environment these remains can be used as biological indicators of recent sea level variations our survey of the continental coasts of var and bouches du rhone west of marseilles southern france and of northern corsica shows that relative sea level rose about 1 6 m in the study area during the last 4500 years without exceeding the present datum the rate of sea level rise was 0 4 mm per year between 4500 and 1500 yr b p and slowed down to 0 2 mm per year from 1500 yr b p to present time there are also morphological indications of an acceleration of the rate of sea level rise during the last century supporting the evidence of tide gauges regions at the periphery of the above zone alpes maritimes italian border zone and the french and spanish catalonia regions were also surveyed but a weaker development of lithophyllum rims and bad preservation of algal remains led to unconvincing dates which could also be linked to regional tectonic trends

tracing sea level changes during the mid holocene in the southern mediterranean coast an example from the gulf of gabes abstract mid holocene sea level emergence was recorded along a mid latitude coastal site in the gulf of gabes tunisia in beach rock deposits however the post emergence sea level curve and associated hydro sedimentary processes have rarely been documented this study presents new records of sea level changes along the tunisian coast since the mid holocene each phase of the sea level curve was evidenced and supported by lithostratigraphic morphological and archaeologic markers post emergence sea level fall due to postglacial isostatic rebound was recognized in regressive sequences which vary depending on available accommodation space from a small pocket beach to a well developed dune system sea level stabilization following isostatic rebound has promoted the end phase deposits of the regressive sequences however this stability was interrupted during the late holocene by a high energy storm event that accumulated a transgressive boulder unit at 2 m above present shape and disposition of the boulder ridge behind a prograding modern shoreline suggests that sea level has not changed during the late holocene the existence of a roman fish pond on the upper foreshore confirms stability of sea level during the last two millennia the combination of lithostratigraphic morphological and archaeologic markers represents a tool for improving the accuracy of dating of erosional and depositional periods in mid coastal sections

a mediterranean holocene restricted coastal lagoon under arid climate case of the sedimentary record of sabkha boujmel se tunisia abstract the holocene sedimentary record of sabkha boujmel se tunisia is expressed by a shallowing upward carbonate lagoon tidal flat cycle 2 3 m thick unconformably overlying continental silt sandy sediment late wurmian in age the sedimentary package of this cycle starts with transgressive marginal shallow marine intertidal to subtidal bioclastic sands grading upwards to black mudstone rich in organic matter t o c up to 1 3 deposited within a lagoon protected from the sea by upper pleistocene lithified sand spits the uppermost part of the cycle is represented by oobioclastic carbonate sands covered with dead biodegraded microbial mats and or reddish sands of aeolian origin deposited in intertidal to supratidal environments the facies arrangement particularly the spatial distribution of the ancient and the more recent microbial mats records the progressive infilling of the lagoon as well as the progradation of the shoreline during the last 2000 years the organic rich facies which provide an age varying between 4130 and 6800 yr b p were deposited when the boujmel lagoon started to be progressively separated from the mediterranean sea the main factors controlling the facies and the thickness variation are the local topographic sea floor irregularities most likely controlled by the inheritance morphology resulting from an important fluviatile digging that occurred during the last glacial maximum the relative sea level fluctuations the hydro isostatic rebound and the climate

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

u series evidence for two high last interglacial sea levels in southeastern tunisia abstract pleistocene raised marine deposits in southeastern tunisia consist of a siliciclastic unit that culminates at 3 m asl overlain by a carbonate rich unit with strombus bubonius that culminates at 5 m asl 234 u 238 u ratios on fossil ostraea shells from both units are compatible with a marine origin from the uranium incorporated into the shells and show narrowly clustered 230 th ages respectively between 147 and 110 ka and 141 and 100 ka the two units were therefore developed during marine isotopic substage 5e miss 5e last interglacial their heights are comparable to those of contemporaneous marine deposits found in many tectonically stable areas of the world such as in the bahamas and in bermuda and can therefore be used as indicators of eustatic changes during the last interglacial it is argued that on the basis of this evidence the last interglacial was characterised by two eustatic maxima

very high energy sedimentation supratidal hurricane deposits and mid holocene highstand on carbonate platforms andros bahamas an alternative view abstract twenty eight 14 c dates were obtained from 90 cores drilled through the tidal flats of western andros island a large area 2000 km 2 mostly covered by mangroves and stromatolitic deposits these dates are correlated with location of the samples sedimentological description position of the samples at the time of deposition and their present day sedimentological position measurements were made on bulk algal sediments and location of the relative paleo sea level is inferred from paleobathymetric reconstructions on the basis of 14 c dates i conclude that the whole area was flooded about 5000 years bp and then was covered by the subtidal greyish mud facies rich in peneroplids in the area of deep creek north of the study area pelican creek and wide opening southeast of the study area the level of this paleo great bahama bank sea continued to rise until 3500 years bp and then slowly fell asymptotically toward the present day level thick hurricane marks aragonitic lime mud with didemnids spicules several cm thick previously defined as hurricane trails can be observed throughout the cores from 2000 years bp onwards from 2000 years bp onwards it seems that the modern physiography was already established including tidal estuaries channels and stromatolite bearing swamps paleogeographic maps and sections have been drawn and accumulation rates calculated in the various sedimentological zones of the tidal flats of western andros these vary between 0 5 to 0 04 mm yr the modern topography of the tidal flats was established by 2000 years bp similarly the modern geological features controlled by a tropical climate strictly dependent on hurricanes were already established by 2000 years bp and seem to have been initiated between 2500 and 2000 years bp

bounds on the time history and holocene mass budget of antarctica from sea level records in se tunisia solving the sea level equation for a maxwell earth we analyze the sensitivity of holocene sea level records in se tunisia to the time history of remote ice sheets assuming that mantle viscosity increases moderately with depth we find that in this region the sea level variations driven by the northern hemisphere ice sheets cancel so that the late holocene sea level high stand suggested by the geological record merely reflects the melting history of antarctica new insight into the history of this ice sheet is obtained analyzing the information contained in a revised set of relative sea level observations for sites across the mediterranean covering the last 8 kyrs from a trial and error misfit analysis it holds true that in this region the match between model predictions and observations improves when the volume of water released from antarctica is well below the value imposed by the ice3g chronology and when a sudden meltwater pulse is allowed between 8 and 7 kyrs before present corresponding to the epoch of the catastrophic rise event known as cre3

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

catastrophic event recorded among holocene eolianites sidi salem formation se tunisia a high energy deposit cuts through the early holocene eolianites of the sidi salem formation which forms a ridge along the southeastern coast of tunisia the sedimentary structures as well as the paleo altitude and paleo location of the outcrop state for a subaqueous deposition by an unusually large catastrophic event regarding its age and the related uncertainties it could be either an exceptional storm or a landslide or impact triggered tsunami the mega tsunami of the 8000 bp collapse of the valle del bove valley etna volcano could be this event for its matching age and calculated run up height

lithospheric thickness antarctic deglaciation history and ocean basin discretization effects in a global model of postglacial sea level change a summary of some sources of nonuniqueness the global model of postglacial relative sea level variations that has been developed over the past decade is employed to investigate the constraints that it may be invoked to place on the timing of the deglaciation of west antarctica the analyses presented here confirm the suggestion of p wu and w r peltier 1983 geophysical journal of the royal astronomical society74 377 450 that the model of this event employed inj a clark and c s lingle 1979quaternary research11 279 298 may be simply modified to rectify the misfits between theory and observation that are otherwise obtained at southern hemisphere sites a large number of southern hemisphere relative sea level data are shown to require that the retreat of antarctic ice substantially lagged the retreat of northern hemisphere ice if the deglaciation of antarctica was abrupt the time of onset of antarctic deglaciation is thereby shown to coincide with the time of most rapid northern hemisphere deglaciation sensitivity tests are performed which demonstrate that this result is relatively insensitive to the discretization employed to represent the ocean basins the only exception to this general rule obtains at some coastal sites at which a trade off is revealed between the delay of west antarctic melting and the thickness of the lithosphere required to reconcile the observed local variations of relative sea level at such sites which are all in the far field of the ice sheets some attention must be paid to the accuracy of the local finite element representation of the oceans and to the details of the antarctic deglaciation history

mid holocene emergence of southern tunisian coasts abstract we present new sea level data from the coasts of southern tunisia between the gulf of gabes and the libyan border the work tests previously published evidence on holocene shorelines and confirmed that a distinct emergence has occurred in this area during this time the emergence peak lies at least 186 11 cm above present and is inferred from 1 ams radiocarbon dates of subtidal vermetids and boring shells collected in growth position and 2 careful assessment of tidal heights maximum emergence took place between about 6000 and 5000 14c years bp it cannot be ascribed to tectonics and is probably related to post glacial hydro isostatic effects it challenges the inference of a 3 m global sea level rise since 6000 years bp due to residual antarctic melting

palaeogeographical and palaeoenvironmental reconstruction of the medjerda delta tunisia during the holocene abstract the progradation of the medjerda delta has been the subject of many studies since the 19th century the scale and the rapidity of this phenomenon interested researchers in various fields early on such as geomorphology geology palaeogeography history archaeology or geoarchaeology indeed the delta prograded by around 10 km over 3 millennia at the time of its foundation supposedly at the end of the 12th century bc the phoenician city of utica was located on a promontory bathed by the sea but the sediments carried by the medjerda progressively sealed the bay leaving the tip of the utica promontory now 10 km inland this area is therefore an exception to the general pattern along the tunisian coast since as over the same period everywhere else there is a regression of the coastline owing to a sea level rise of several decimeters based on multi proxy analyses of two coring transects this paper aims to reconstruct the palaeoenvironments and the palaeogeography of the medjerda delta s progradation since the mid holocene some aspects of which are described in ancient sources the results highlight in particular an episode of high intensity flooding around the 4th century ad which is consistent with episodes of high floods and an increase in sedimentation rates recorded in the watershed at the end of the roman period the gradual abandonment of the city of utica can certainly be related to the activity of the medjerda river but our results show that it is because of an increase of fluvial sediment contribution in connection with an erosive crisis in the headwaters and not because of the change of course of the river which had occurred long before

pleistocene sea levels and tectonic uplift based on dating of corals from sumba island indonesia we collected and dated fossil corals from the uplifted reef tracts of sumba island mass spectrometry tims and ams was used to obtain reliable and precise radiochronological results it is possible to identify outcrops corresponding to major sea level high stands isotope stage 1 starting at 7 1 kyr bp 5a c a 86 kyr bp 5c c a 105 kyr bp 5e between 119 and 132 kyr bp and 9 c a 305 kyr bp the radiochronological data are thus broadly consistent with the timing of sea level fluctuations predicted by the astronomical theory of paleoclimates comparison with similar data from other terrace sequences and from benthic 18o records indicates that the average tectonic uplift rate at cape laundi sumba is on the order of 0 2 0 5m kyr the lowest values 0 3m kyr lead to the build up of polycyclic topographic terraces in which it is possible to find corals grown during different interstadial or even interglacial times

genesis and evolution of a beach ridge plain reflecting relative sea level rise a case study from trab el makhadha gulf of gabes southeastern tunisia abstract the trab el makhadha beach ridge plain presents a progradational shoreline feature on the gulf of gabes tunisia diachronic analysis coupled with a morpho sedimentary approach was applied to elucidate the genesis mode of the beach ridge plain its sedimentary sources and the climatic conditions responsible for the prograding trends in the gulf of gabes shapes dimensions sedimentologic compositions and other textural parameters of the sandy ridges have been analyzed therein we found that the trab el makhdha coast is made up of two distinctive categories of eolian beach ridge complex progradational sequences implying a significant change in climatic and hydrological conditions during the deposition of each ridge in the holocene sequence about 5600 14c years old the predominance of detrital material suggests an important contribution to sediment supply from continental input the preservation of the eolian beach ridge and its adjacent marine sediment has been favored by the postglacial hydro isostatic rebound today the paucity of rainfall is reflected by the decrease in input of terrigenous material therefore the modern sequence which has been emerging since 1987 is made mainly of bioclastic sand supplied by subaqueous shoals due to a rapid rise in sea level the observed decrease of sea level around 2100 14c yr b p largely contributed to the formation of the swale the formation of the beach ridge plain shows that since the middle holocene highstand the coastal segment of trab el makhadha has been governed by equilibrium of sediment abundance

chronology of early archaean granite greenstone evolution in the barberton mountain land south africa based on precise dating by single zircon evaporation abstract we report precise 207 pb 206 pb single zircon evaporation ages for low grade felsic metavolcanic rocks within the onverwacht and fig tree groups of the barberton greenstone belt bgb south africa and from granitoid plutons bordering the belt dacitic tuffs of the hooggenoeg formation in the upper part of the onverwacht group yield ages between 3445 3 and 3416 5 ma and contain older crustal components represented by a 3504 4 ma old zircon xenocryst fig tree dacitic tuffs and agglomerates have euhedral zircons between 3259 5 and 3225 3 ma in age which we interpret to reflect the time of crystallization a surprisingly complex xenocryst population in one sample documents ages from 3323 4 to 3522 4 ma we suspect that these xenocrysts were inherited during the passage of the felsic melts to the surface from various sources such as greenstones and granitoid rocks now exposed in the form of tonalite trondhjemite plutons along the southern and western margins of the bgb and units predating any of the exposed greenstone or intrusive rocks several of the granitoids along the southern margin of the belt have zircon populations with ages between 3490 and 3440 ma coeval with or slightly older than onverwacht felsic volcanism while the kaap valley pluton along the northwestern margin of the belt is coeval with fig tree dacitic volcanism these results emphasize the comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites some of the volcanic and plutonic units contain zircon xenocrysts older than any exposed rocks these indicate the existence of still older units possibly stratigraphically lower and older portions of the greenstone sequence itself older granitoid intrusive rocks or bodies of older unrelated crustal material our data show that the onverwacht and fig tree felsic units have distinctly different ages and therefore do not represent a single tectonically repeated unit as proposed by others unlike the late archaean abitibi greenstone belt in canada which formed over about 30 ma exposed rocks in the bgb formed over a period of at least 220 ma the complex zircon populations encountered in this study imply that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones a surprising similarity in rock types tectonic evolution and ages of the bgb in the kaapvaal craton of southern africa and greenstones in the pilbara block of western australia suggests that these two terrains may have been part of a larger crustal unit in early archaean times

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