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

reconstructing palaeo volcanic geometries using a geodynamic regression model grm application to deception island volcano south shetland islands antarctica abstract this article describes a reconstruction made of the palaeo volcanic edifice on deception island south shetland islands antarctica prior to the formation of its present caldera deception island is an active quaternary volcano located in the bransfield strait between the south shetland islands and the antarctic peninsula the morphology of the island has been influenced mainly by the volcanic activity but geodynamics and volcanic deformation have also contributed a volcanic reconstruction method the geodynamic regression model grm which includes a terrain deformation factor is proposed in the case of deception island the directions of this deformation are nw se and ne sw and match both the observed deformation of the bransfield strait and the volcanic deformation monitored over the last 20 years in the island using global navigation satellite system gnss techniques based on these data possible volcanic deformation values of 5 15 mm yr in these directions have been derived a possible coastline derived from a current bathymetry is transformed according to values for the chosen date to obtain the palaeo coastline of deception island of 100 k years ago topographic geomorphologic volcanological and geological data in a gis system have been considered for computation of the outside caldera slope palaeo coastline palaeo summit height and palaeo digital elevation model dem the result is a 3d palaeo geomorphological surface model of a volcano reaching 640 m in height with an increase of 4 km3 in volume compared to the current edifice covering 4 km2 more surface area and the method reveals the previous existence of parasite volcanoes two photorealistic images of the island are obtained by superposition of textures extracted from a current quick bird satellite image also this technique for reconstructing the terrain of an existing volcano could be useful for analysing the past and future geomorphology of this island and similar locations

deposits related to degradation processes on piton des neiges volcano reunion island overview and geological hazard abstract piton des neiges pn volcano on reunion island offers a rare opportunity to study deposits related to degradation processes in a deeply eroded oceanic shield volcano both the inner parts and flanks reveal a large amount of resedimented volcaniclastic material including extensive debris avalanche deposits pn litho structural units first studied by upton and wadsworth 1965 philos trans r soc lond a 271 pp 105 130 are re examined this review highlights the importance of long volcanic repose periods and erosion processes during pn history volcaniclastic deposits have been studied in the field in order to evaluate the spatial and temporal distribution of the three main types of pn degradation processes the deposits of these processes have been classified into 1 talus 2 mudflow and debris flow and 3 debris avalanche lithology frequency and estimated volumes of each deposit type imply that the structural evolution of pn can be considered in terms of the competition between the volcanic productivity and the degradation and erosion processes the occurrence of huge catastrophic avalanches produced by flank failure is convincingly linked to the basaltic activity of pn which implies a very low risk at present on the contrary mudflows and debris flows pose an important risk due to the high population density focussed around the basin outlets moreover if smaller debris avalanches can occur in the cirques of pn another major risk must be evaluated

drainage basin evolution in the rainfall erosion facility dependence on initial conditions four experiments in alluvial drainage basin evolution were carried out in the rainfall erosion facility ref at colorado state university to investigate the dependence of basin evolution on initial topography basins were initially undissected each experiment began with a unique initial condition representing various end members of relief and hypsometry drainage network development hillslope processes basin denudation and basin response to base level lowering all depended strongly on the initial topography no classic model of drainage network evolution was found to be generally applicable initially planar slopes first developed subparallel channels that extended headward dendritically during an early phase of extension channel incision occurred first in the interior of the basin where saturation overland flow was greatest not at the basin outlet as assumed in most classic models of network development channels widened over time initiating lateral migration and drainage capture in the downslope portion of the watershed before transferring lateral migration upslope planar basins of larger initial gradient grew headward more quickly and become more deeply entrenched inhibiting late stage lateral migration an experiment with initial relief concentrated at a plateau edge evolved in several unique ways a high ratio of subsurface to surface flow gave rise to mass movements at the plateau edge and outlet channels deep channels were quickly cut initially but did not extend far upslope because slope instability undermined channel head migration leaving the plateau undissected and hence very slow to erode these results suggest that the distribution of relief within a basin exerts an important control on drainage network pattern and basin denudation in addition erosional basins may evolve in several distinct modes characterized by particular combinations of hypsometry hillslope processes and mean denudation rate

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

inversion of relief a component of landscape evolution inversion of relief occurs when materials on valley floors are or become more resistant to erosion than the adjacent valley slopes as erosion proceeds the valley floor becomes a ridge bounded by newly formed valleys on each side areas of lava flows contain many examples of inversion of relief but it is also common in areas of duricrusts inversion of relief is so widespread in some areas that it should be regarded as a general component in a model of landscape evolution inversion of relief has some important implications drainage lines will shift significantly over time slope soil relationships catenas have to be reassessed because the regolith on the upper part of a hill slope may have developed under very different conditions from those existing at present the resulting catena is not a simple expression of soils and response to landscape position this also has important implications for geochemistry where present day ridge tops were once valley floors geochemical signatures will reflect lateral water movement in the old landscape rather than simple in situ weathering and vertical redistribution in the present landscape finally inversion of relief can produce erosion surfaces of very low relief that cannot be termed peneplains pediplains or etchplains because they have a very different genesis this underlines the importance of determining the complexities of landscape evolution before such genetic terms are applied to any landscape

lyttelton volcano banks peninsula new zealand primary volcanic landforms and eruptive centre identification abstract lyttelton volcano banks peninsula new zealand has historically been viewed as a simple volcanic cone this paper uses digital terrain models dtm and primary volcanic landforms to reinterpret lyttelton volcano as having multiple eruptive centres primary volcanic landforms are features produced during active volcanism classified as constructional hypabyssal and erosional volcanic features constructional volcanic features are lava flows scoria cones and domes hypabyssal volcanic features are dykes and sills and erosional volcanic features are valley and ridge patterns and orientations lava flow trends are recognised from aerial photograph analysis and supported by field observations highlighting radiating lava trends around specific locations within lyttelton harbour scoria cones and domes occur on the outer flanks of volcanic cones and are used as such in the identification of remnant cone surfaces dyke orientations are plotted and then projected to the interior of the volcano defining 13 zones of convergence the projected arrays of these orientations highlight defined regions along the erosional crater rim each indicating a radial dyke swarm from which the projected trends of the associated dykes indicate an eruptive centre valley and ridge orientations are projected from the longest valley or ridge segment towards the inner harbour radiating erosive patterns are incepted during the growth and degradation of a volcanic cone with the resulting trends orienting to the summit zones of convergence eruptive centres are identified from lava flow orientations onlapping lava sequences scoria cones and intrusive locations the summit of a volcanic edifice can be identified from the orientations of valleys and ridges while radial dyke systems determine whether this summit was a volcanic centre or simply a local topographic high volcanic landforms are used to identify cone sectors the preserved sector associated with a particular eruptive centre cone sector limits are defined by a basal footprint and an erosional crater rim with similar arcuate features remnant cone features being exposed in the interior of the volcano lyttelton volcano comprises fifteen volcanic cones with vent locations controlled by underlying fault lineaments the growth and erosion of each volcanic cone is reflected in primary volcanic landforms with the preserved features of cones confined to cone sectors and cone artefacts

reconstructing the architectural evolution of volcanic islands from combined k ar morphologic tectonic and magnetic data the faial island example azores the morpho structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass wasting processes we present here a multi disciplinary study of the successive stages of development of faial azores during the last 1 myr using high resolution digital elevation model dem and new k ar tectonic and magnetic data we reconstruct the rapidly evolving topography at successive stages in response to complex interactions between volcanic construction and mass wasting including the development of a graben we show that 1 sub aerial evolution of the island first involved the rapid growth of a large elongated volcano at ca 0 85 ma followed by its partial destruction over half a million years 2 beginning about 360 ka a new small edifice grew on the ne of the island and was subsequently cut by normal faults responsible for initiation of the graben 3 after an apparent pause of ca 250 kyr the large central volcano cv developed on the western side of the island at ca 120 ka accumulating a thick pile of lava flows in less than 20 kyr which were partly channelized within the graben 4 the period between 120 ka and 40 ka is marked by widespread deformation at the island scale including westward propagation of faulting and associated erosion of the graben walls which produced sedimentary deposits subsequent growth of the cv at 40 ka was then constrained within the graben with lava flowing onto the sediments up to the eastern shore 5 the island evolution during the holocene involves basaltic volcanic activity along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano tectonic depression we conclude that the whole evolution of faial island has been characterized by successive short volcanic pulses probably controlled by brief episodes of regional deformation each pulse has been separated by considerable periods of volcanic inactivity during which the faial graben gradually developed we propose that the volume loss associated with sudden magma extraction from a shallow reservoir in different episodes triggered incremental downward graben movement as observed historically when immediate vertical collapse of up to 2 m was observed along the western segments of the graben at the end of the capelinhos eruptive crises 1957 58

planetary waves kinematically forced by himalayan orography abstract an analysis is made of the planetary scale response of the atmosphere to the kinematic effects of orographic forcing by in particular the tibetan plateau himalayan mountain complex theoretical scaling arguments are used to deduce a critical mountain height hc beyond which the component of flow around will dominate that over the orography the hc is proportional to the meridional scale of the orography and depends on latitude for north south scales appropriate for the himalayas hc 1 5 km which is much less than the actual height of 3706 m when resolved with tour zonal planetary waves with the implication that the around component will dominate a steady state planetary wave model which has a full kinematic nonlinear lower boundary condition is used to simulate the response to the eastern orography whose height has been multiplied by factors ranging from 0 1 to 2 0 although the mountain configuration was fixed the locations of the simulated perturbation highs and lows change substantiall

east asian winter monsoon evolution since the late pliocene based on a pollen record from lake xingkai northeast asia a 328 58 m drill core xk12 was recovered from lacustrine alluvial sediments in the xingkai basin northeast china with the aim of obtaining a high resolution pollen record of east asian winter monsoon eawm evolution since 3 6 ma an index based on the pollen record of thermophilous trees and terrestrial herbs is used as an indicator of winter temperature conditions controlled by the eawm at the glacial interglacial scale primary age control was established based on lithostratigraphy and magnetostratigraphy and then the pollen index was correlated to the lr04 global benthic 18 o record and finally tuned to earth orbital obliquity to produce a high resolution astronomical time scale the pollen record indicates that the eawm underwent two stepwise enhancements at 2 8 and 1 6 ma these events are consistent with paleoclimatic records of mean quartz grain size from the chinese loess plateau and they are also in accord with the initiation and intensification of northern hemisphere glaciation our findings suggest that the variability of the eawm since 3 6 ma was primarily controlled by changes in global ice volume and climatic cooling

radiometric dates of uplifted marine fauna in greece implications for the interpretation of recent earthquake and tectonic histories using lithophagid dates n ad 365 a great mw n 8 earthquake lifted up western crete exposing a shoreline encrusted by marine organisms and up to 10 m of marine substrate beneath it radiocarbon ages determined for corals and bryozoans exposed between the paleo shoreline and present sea level are consistent within measurement error with each other and with the date of the earthquake but radiocarbon ages determined for the boring bivalve lithophaga lithophaga found on the same substrate are at least 350 years and up to 2000 years older than the date of the earthquake that lifted them above sea level these observations reveal two important effects that limit the use of radiocarbon lithophagid ages in tectonic and paleoseismological studies the first is that the exceptional preservation potential of lithophagids allows them to remain intact and in situ long after natural death while the substrate continues to be colonised until eventual uplift the second which we confirm with radiocarbon analysis of museum specimens of known age is the incorporation of old 14c free carbon into lithophagid shells from the limestone host rock into which the lithophagids bored the two effects are both significant in crete and central greece and can cause the radiocarbon lithophagid ages to be up to 2000 years older than the uplift event which exposed them understanding these effects is important because lithophagids are far more abundantly preserved and used to date uplift than most other marine organisms this study shows that they can rarely be used to distinguish uplift events or date them to better than 1000 years or even to distinguish whether observed uplift occurred in a single or in multiple events after taking account of these uncertainties the ages of the lithophagids are however consistent with the hypothesis that the highest prominent marine notches and exposed lithophagid holes within a few metres of sea level in greece formed when sea level became relatively stable 6000 years ago following rapid rise after the last glacial maximum

sea level during the penultimate interglacial period based on a submerged stalagmite from argentarola cave italy accurate constraints are presented for the absolute age duration and sea level for the highstand corresponding to marine isotope stage mis 7 1 our work is based on a stalagmite collected in a currently submerged cave from italy argentarola cave flooding of this coastal cave is clearly marked within the stalagmite by a thick marine overgrowth of serpulid worms precise uranium thorium u th ages measured by thermal ionization mass spectrometry suggest that the stalagmite growth varied in phase with climate during mis 7 2 and mis 6 the penultimate glacial period in addition the period of marine transgression is bracketed between 202 and 190 kyr bp defining a mis 7 1 duration of 11 2 kyr comparison with previous studies provides a new constraint on the sea level during mis 7 1 that has approximately remained between 318 and 39 m relative to present sea level the timing of the mis 7 1 highstand is in full agreement with the specmap chronology which contrasts with the growing body of evidence showing a significant phase difference for mis 5 5 a tempting conclusion is that second order sea level highstands such as mis 7 1 may be purely driven by astronomical changes in contrast with major terminations such as termination ii atmospheric co2 levels may partly explain this contrast since the two sea level transitions mis 7 2 7 1 and mis 6 5 5 are characterized by very different co2 rises 20 vs 100 ppm fl 2002 elsevier science b v all rights reserved

morpho structural evolution of a volcanic island developed inside an active oceanic rift s miguel island terceira rift azores the evolution of volcanic islands is generally marked by fast construction phases alternating with destruction by a variety of mass wasting processes more specifically volcanic islands located in areas of intense regional deformation can be particularly prone to gravitational destabilisation the island of s miguel azores has developed during the last 1 myr inside the active terceira rift a major tectonic structure materializing the present boundary between the eurasian and nubian lithospheric plates in this work we depict the evolution of the island based on high resolution dem data stratigraphic and structural analyses high precision k ar dating on separated mineral phases and offshore data bathymetry and seismic profiles the new results indicate that 1 the oldest volcanic complex nordeste composing the easternmost part of the island was dominantly active between ca 850 and 750 ka and was subsequently affected by a major south directed flank collapse 2 between at least 500 ka and 250 ka the landslide depression was massively filled by a thick lava succession erupted from volcanic cones and domes distributed along the main e w collapse scar 3 since 250 kyr the western part of this succession furnas area was affected by multiple vertical collapses associated plinian eruptions produced large pyroclastic deposits here dated at ca 60 ka and less than 25 ka 4 during the same period the eastern part of the landslide scar was enlarged by retrogressive erosion producing the large povoacao valley which was gradually filled by sediments and young volcanic products 5 the fogo volcano in the middle of s miguel is here dated between ca 270 and 17 ka and was affected by at least one southwards flank collapse 6 the sete cidades volcano in the western end of the island is here dated between ca 91 and 13 ka and experienced mutliple caldera collapses a landslide to the north is also suspected from the presence of a subtle morphologic scar covered by recent lava flows erupted from alignments of basaltic strombolian cones the predominance of the n150 and n75 trends in the island suggest that the tectonics of the terceira rift controlled the location and the distribution of the volcanism and to some extent the various destruction events

dem based reconstruction of southern basse terre volcanoes guadeloupe archipelago fwi contribution to the lesser antilles arc construction rates and magma production abstract we combine radiometric ages and geomorphologic investigations to quantify the relief creation of well preserved volcanic surfaces applied to the volcanoes of southern basse terre guadeloupe lesser antilles arc the last 650 ka volcanic evolution of this island has been modeled using ten main stages constrained by k ar ages previously obtained on lava flows and domes from the volcanic massifs of the axial chain 1000 435 ka and from the grande decouverte volcanic complex 250 ka present based on the construction of a 250 000 point database inferred from the analysis of the guadeloupe digital elevation model 3d reconstructions of the successive volcanic stage landforms were calculated and the correlated geochronological maps drawn using arcgis software volumes and rates of construction were computed for each time span separating these ten stages the average construction rates calculated here are 2 4 0 3 10 4 km 3 yr for the last million years 0 9 0 3 10 4 km 3 yr for the last 100 ka and 0 9 0 2 10 4 km 3 yr for the last 15 ka although basse terre volcanism is characterized by a marked dominance of effusive products our estimates should be considered as minimum values because the material that went into the sea during explosive events was not taken into account however we note that a relatively high construction rate of 4 5 1 3 10 4 km 3 yr has been obtained for the icaques volcano which was emplaced during the 630 600 ka time interval within the depression formed by the first large scale flank collapse having affected southern basse terre the sudden release of the lithostatic load induced by this mass wasting event could explain this value which is significantly higher than the average value of 0 8 0 1 10 4 km 3 yr obtained for the last 650 ka finally the comparison with other analogous volcanic massifs from islands and continental arcs points to a relatively low magmatic production for southern basse terre which could be tentatively related to the relatively slow subduction rate of the atlantic plate

geomorphic evolution of the piton des neiges volcano reunion island indian ocean competition between volcanic construction and erosion since 1 4 ma abstract reunion island indian ocean is a volcanic complex whose eruptive history was dominated by the activity of two main edifices piton des neiges pn and piton de la fournaise pf volcanoes the tropical climate induces erosion processes that permanently compete with volcanic constructional processes exposed to the trade winds and associated heavy rainfalls the northeastern part of the island exhibits the most complex morphological evolution geomorphological analysis performed on a 50 m dem and associated to new k ar ages has clarified the overall history of pn volcano each massif is assigned to one of the main building stages of the edifice in addition the arrangement of these different massifs reveals that the eruptive phases have led to successive relief inversions and successive excavations of large central depressions in the proximal area as a result the younger massifs are always located in more proximal parts of the volcano the youngest being close to the edifice center in distal areas early lava flows were channeled into valleys incised along the massif boundaries leading to a more complex geochronological organization quantitative study of the dissection of pn volcano allows us to propose a minimum eroded volume of 101 44 and 105 41 km3 for the mafate and cilaos cirques depressions respectively during the last 180 kyr and a minimum average long term erosion rate of 1 2 0 4 km3 ka this leads us to estimate the removed volume during the whole history of pn volcano 1000 km3 as equivalent to the volume of the deposits identified on the submarine flanks of piton des neiges volcano therefore as regressive erosion appears to be the prevailing geomorphic process during the whole pn history it questions the presence of major flank collapses younger than 1 4 ma on this volcano erosion processes have largely been neglected in recent models but our study emphasizes them as a key component of landscape development and a major process in the morphological evolution of reunion island that has to be fully integrated in future studies

have climate changes driven the diversity of a mediterranean coralligenous sponge assemblage on a millennial timescale abstract changes occurring over a pluri millennial span of time 6207 1767 yr b p within the sponge assemblages present in two coralligenous pillars about 60 cm high collected at 20 m depth inside the marine protected area of porto cesareo ionian sea mediterranean sea have been studied the sponge diversity has been analyzed at generic level using as a proxy the siliceous spicules trapped into the sediment present into the crevices of these bioherms in total 41 genera of ancient demosponges were identified the modern sponge fauna of these coralligenous pillars totals 31 genera 15 of them shared with the ancient assemblages the sponge biodiversity during the considered span of time showed critical changes with remarkably similar trends in both the considered pillars tentatively these changes were attributed to different climatic events that affected the mediterranean area during the studied time span the number of genera 6000 yr b p was low and increased between 5500 and 4000 yr b p during the late bronze age 4000 3000 yr b p a new decrease was recorded followed by a further increase around 2000 yr b p afterwards the bioherms stopped growing and no more siliceous spicules were trapped from a biogeographic point of view the wide presence of spiny microrhabdose microscleres belonging to the genus alveospongia heteroxyidae recently described from the tropical atlantic and still unknown in the mediterranean sea has to be underlined in addition the trends recorded over time in the ionian sea match with those already observed in the ligurian sea the comparison between the past periods and the modern one shows evident changes in biodiversity in both areas the sharp variations of the seawater temperature occurred in both the mediterranean regions could have driven the changes in genus richness using sponges to interpret the effects of climate changes can be a profitable strategy to unravel long term changes in biodiversity supporting future predictions

dendropoma lower intertidal reef formations and their palaeoclimatological significance nw sicily abstract most carbonate rocky shores of nw sicily are marked by a coalescence of shells of the gastropod dendropoma in a construction that is variably developed as a response to wave impact here we review all the available information on these constructions and find that the fossil reefs are reliable sea level indicators the thickness of the reef samples never exceeds 30 40 cm below sea level whereas all 14 c dates fall within a range of few centuries some small fragments ejected by violent sea storms date back to 2500 years cal bp no samples older than 6200 years cal bp have been detected so far the present distribution of mediterranean vermetid platforms should result from a northward migration related to the long term effect of the holocene sea surface temperature sst warming some consideration on the morphology of the reefs and the comparison with the available data point out that dendropoma reefs are excellent biological indicators of sea level fluctuations especially when detected and sampled in tectonically stable areas as those in nw sicily

comments on epiclastic deposits and horseshoe shaped caldeiras in tahiti society islands and ua huka marquesas archipelago french polynesia by clement et al 2003

fine tuning of age integrating magnetostratigraphy radiocarbon dating and carbonate cyclicity example of lacustrine sediments from heqing basin yunnan china covering the past 1 myr abstract high resolution magnetostratigraphy wavelength spectra of carbonate cyclicities and ams radiocarbon dating are integrated to establish an optimum age model for a 168 m long drill core of lacustrine sediments from heqing basin yunnan province southwestern china a 14c age of 51 62 2 42 1 85 kyr bp is obtained at a depth of 7 3 m remanent magnetization is carried by maghemite and partly in addition by magnetite both showing the same direction the polarity sequence clearly reveals the brunhes matuyama b m boundary at 141 5 m blake event is found between 16 3 and 17 5 m and the upper boundary of jaramillo is indicated at 167 0 m carbonate content and magnetic susceptibility were used for spectral analysis fourier analysis was done on the depth section for sliding windows with different window lengths the spectra within the range of window centers 30 140 m show a dominant long wavelength which changes from about 18 5 m in the lower part 65 m depth to about 14 5 m in the upper part

uplift events of the qinghai tibetan plateau and environmental evolution of the southwest monsoon since 2 7 ma recorded in a long lake sediment core from heqing china abstract the tectonic sedimentary cycles and environmental evolution in the southwest monsoon area since 2 7 ma were reconstructed based on the analysis of lithology grain size carbonate content loss on ignition loi and pollen in a 737 72 m sediment core from heqing basin china the results indicated that the lake basin was formed in about 2 7 ma continuous lacustrine sediment was preserved since 2 7 ma three stages of tectonic sedimentary cycle were revealed 2 7 1 5 ma 1 5 0 9 ma and 0 9 0 ma the environmental evolution in heqing area was influenced by the uplift of the qinghai tibetan plateau the resulting variation of southwest monsoon and the earth orbital scale periodicity

isotopic approach of rainfall and groundwater circulation in the volcanic structure of tahiti nui french polynesia abstract a chemical and isotopic study was conducted on rainfall river and spring waters from the northern half of tahiti nui tropical oceanic island in order to constrain a conceptual model of groundwater circulation within a discontinuous volcanic structure tahiti nui comprises a main shield cut by a huge landslide to the north this major flank collapse yielded the formation of a northern depression in which rapidly grew a second shield additional volcanic activity occurred along the rims of the depression as revealed by local concentrations of dykes the island is now volcanically inactive and is strongly dissected by erosion rainfall collected during a complete hydrological year at different altitudes are characterized by seasonal and altitude gradients in 18 o some of them have a deuterium excess upto 20 likely due to inland vapour recycling over the hydrological year non evaporated precipitation defines a mean annual altitude gradient of 0 7 km the mineralization and isotopic contents in river waters vary according to the geology rivers incising the main shield have low total mineral charges and are relatively enriched in stable isotopes 18 o around 3 vs vsmow whereas rivers in the northern post collapse in fill exhibit greater electrical conductivity and lower 18 o due to the contribution of more mineralized spring water springs sampled at different elevations along the nw rim of the n landslide depression have homogeneous stable isotopic compositions corresponding to signature of elevated rainfall recharge of these springs thus occurs on a localized area upto 1500 m above their altitude of emergence dominant infiltration occurs at or above the geological discontinuity between the thick impermeable base of the second shield and the late overlying fractured volcanic flows dykes from the peripheral part of the system are poorly active in terms of infiltration and water storage but likely connect the underground circulations the huge geological discontinuity between the main shield and the post collapse edifice may also concentrate the groundwater circulation this main resurgence likely occurs at a deep level of the northern submarine slope of tahiti nui

epiclastic deposits and horseshoe shaped calderas in tahiti society islands and ua huka marquesas archipelago french polynesia occurrences of debris avalanche deposits newly identified in tahiti society islands and ua huka marquesas archipelago are described and interpreted here in both islands the breccias are located within horseshoe shaped residual calderas in tahiti the epiclastic formations up to 500 m thick lie on the floor of the central depression and in the valley of the northwards running papenoo river in ua huka the breccias crop out within a depression limited by a semicircular crest in four bays along the southern coast their thickness is ca 100 m a few clasts collected in the tahitian breccias and some rocks forming their substratum have been dated k ar datings and analysed major and trace elements sr nd isotopes for this study using these data we show that the debris avalanche s occurred in tahiti nui at the end of the growth of the shield volcano between 570 000 and 390 000 years ago maybe in consequence of the emplacement of the plutonic body which occupies the central part of the caldera in ua huka the collapse took place nearly 3 ma ago between the construction of the shield volcano and that of the inner one the southwards orientation of the caldera like that of the neighbouring island nuku hiva might reflect a preferential direction of weakness in the substratum of the central marquesas 2002 elsevier science b v all rights reserved

non hawaiian lithostratigraphy of louisville seamounts and the formation of high latitude oceanic islands and guyots guyots are large seamounts with a flat summit that is generally believed to form due to constructional biogenic and or erosional processes during the formation of volcanic islands however despite their large abundance in the oceans there are still very few direct constraints on the nature and formation of guyots in particular those formed at high latitude that lack a thick cap of shallow marine carbonate rocks it is largely accepted based on geophysical constraints and surficial observations sampling that the summit platform of these guyots is shaped by wave abrasion during post volcanic subsidence of volcanic islands here we provide novel constraints on this hypothesis and the summit geology of guyots with a lithostratigraphic analysis of cores from three louisville seamounts south pacific collected during expedition 330 of the integrated ocean drilling program iodp thirteen lithofacies of sedimentary and volcanic deposits are described which include facies not previously recognized on the top of guyots and offer a new insight into the formation of high latitude oceanic islands on a fast moving plate our results reveal that the lithostratigraphy of louisville seamounts preserves a very consistent record of the formation and drowning of volcanic islands with from bottom to top i volcaniclastic sequences with abundant lava fed delta deposits ii submarine to subaerial shield lava flows iii post volcanic shallow to deeper marine sedimentary rocks lacking thick reef deposits iv post erosional rejuvenated volcanic rocks and v pelagic sediments recognition of erosional boundaries between subaerial lava flows and shallow marine sedimentary rocks provides novel support for post volcanic wave planation of guyots however the summit geology of louisville seamounts is dissimilar to that of high latitude hawaiian emperor guyots that have emplaced in a similar tectonic and environmental setting and that include thicker lava stacks with apparently little lava fed delta deposits to explain observed lithostratigraphic discrepancy we propose that louisville seamounts represent a distinct type of intraplate ocean volcano characterized by formation of a smaller island with a central shield volcano surrounded by extended shallow marine shelves formed by lava fed deltas in this interpretation the summit platform of louisville type guyots results from early syn volcanic subaerial to shallow marine constructional volcanic processes and marine erosion enhanced by later post volcanic wave planation this contrasts with larger hawaiian edifices that are capped by thicker shield volcanoes and that develop an extended wave planation surface during post volcanic subsidence in the absence of efficient coral growth the difference between hawaiian and louisville type volcanic islands and guyots can be explained by contrasted dynamic disequilibrium between magmatic growth erosion and subsidence during the island building stage unlike hawaiian type volcanoes louisville seamounts are characterized by alkaline magmatism that extends from the late seamount to island stages this supports more limited magmatic growth during the formation of louisville islands and we hypothesize that this promotes the formation of ephemeral shallow marine platforms and extended lava fed deltas hawaiian type volcanoes and guyots are unusually large in the population of intraplate ocean volcanoes louisville type guyots as defined in this study could therefore represent a very common but yet poorly documented mode of oceanic island formation in the pacific ocean and other similar fast moving plate settings

the palaeoenvironmental study of the alimini piccolo lake enables a reconstruction of holocene sea level changes in southeast italy based on multiproxy investigations of a 250 cm long sediment core ali1 a reconstruction of palaeoenvironmental dynamics for the alimini piccolo lake south adriatic coast of apulia italy is proposed our results indicate that shortly before 5500 cal yr bp a marsh environment established from 5400 cal bp the marsh progressively became a lagoon and did not change until 3320 cal bp when alimini piccolo evolved into a shallow sheltered freshwater basin around 1400 cal yr bp the basin became again a lagoon changes of the deposition environments and the chronological framework defined in the ali1 sequence allowed speculation about local relative sea level motions through the mid late holocene using proxy data molluscs foraminifers ostracods and plant macro remains as environment and bathymetry indicators we reconstruct the elevation of the basin bottom above or below sea level through time plant macro fossils have proved to be an especially reliable source of data for sea level reconstr

eruptive response of oceanic islands to giant landslides new insights from the geomorphologic evolution of the teide pico viejo volcanic complex tenerife canary large sector collapses are a major component of oceanic islands evolution here we show that voluminous events such as the icod landslide on tenerife canary islands cause dramatic changes on the magma feeding system and control the subsequent volcanic and geomorphologic evolution of the eruptive complex over a period of more than 150 kyr instantaneous unloading by the icod landslide is marked by the development of a large phonolitic explosive eruption dated at 175 3 ka and interpreted as reflecting the immediate emptying of a shallow pre existing magma chamber geochronological geomorphological and geochemical analyses carried out on the post landslide volcanic succession sampled in a 4 4 km long underground water recovery gallery provide further evidence for an enhanced extrusion of primitive lavas starting in the 10 kyr time interval following the failure rapid construction 40 kyr of a thick basaltic volcano in the landslide scar at high eruptive rates up to 8 km3 kyr 1 increased the lithostatic pressure which then favored the intermittent storage of basic magma under the edifice this resulted in more episodic construction evidenced by a significant decrease in output rates and the increasing occurrence of lavas with intermediate composition from 117 7 to 52 7 ka an apparent volcanic gap is observed between 52 7 and 18 1 ka after which highly differentiated lavas have been dominantly erupted we propose that part of the gap can be explained by the individualization of a shallow magma reservoir a few kilometers below the base of the teide volcano during recent periods vertical and lateral extrusions of trachytic and phonolitic viscous bodies from this storage area contributed to increase the slope of the main edifice up to 35 overall favoring its present day instability

erosion of the submarine flanks of the canary islands surveying with multibeam echo sounders around old 1 ma volcanic ocean islands reveals that their submarine flanks contain a strong downslope oriented ridge and valley corrugation which modifies the original volcanic morphology of lava terraces and cones by analogy with canyons in other settings this corrugation was probably caused by channel incision by erosive sedimentary mass flows such as turbidity currents and debris flows we adapt a method first used in subaerial geomorphology to isolate the erosion depth exhumation and apply it to the eroded flanks of the 6 8 ma anaga massif of tenerife the channels formed around this massif divert around local topographic highs these highs which are probably original volcanic cones are therefore preferentially preserved during erosion so that their elevations can be used to construct an artificial reference surface terrain depth was calculated by subtracting this reference surface from measured bathymetry comparison of the terrain depth of the old eroded submarine flank of anaga with that of the young mostly unaltered submarine flank of el hierro allows us to infer the mean depth of anaga s submarine erosion which is 100 m volcanic terrains can be dated by radiometric methods so they also provide a way of quantifying long term denudation rates we infer that submarine denudation of anaga has occurred at comparable rates to that of subaerial lowlands and much slower than denudation of highlands illustrated locally by the more extensive erosion of the subaerial anaga edifice

tyrrhenian holocene palaeoclimate trends from spelean serpulids abstract in tropical regions changes in sea level and sea surface temperature sst can be obtained from coral reefs in temperate seas such as the mediterranean where there are neither fossil nor actively growing coral reefs palaeoclimatic trends and associated sea level rise can be reconstructed through radiocarbon ages and the geochemical properties of serpulid calcite tubes from colonies that dwell in submerged caves in the present work we reconstructed holocene palaeoclimate trends for the tyrrhenian sea through the oxygen isotopic composition of marine polychaete serpulids that colonised continental speleothems when the sea invaded the caves which open along the italian coast the long term 18 o trend extracted from multiple serpulid skeletons of 0 7 per mil increase over the last 8 kyr can be interpreted in terms of temperature change but could also be due to long term changes in the salinity balance of the mediterranean if the 18 o trends recorded by serpulid calcite reflected changes in mediterranean sst starting at 8200 cal yr bp it would coincide with the cooling trend recorded in the tropics and in greenland ice cores spelean serpulids radiocarbon ages allowed us to reconstruct a tyrrhenian sea level curve comparable to that recorded along the french mediterranean coast spelean serpulid calcite therefore can be used as a useful tool to reconstruct paleoclimate and sea level changes in temperate coastal karst regions

offshore evidence for a huge landslide of the northern flank of tahiti nui french polynesia a bathymetric analysis of the flanks of tahiti nui french polynesia reveals the existence of a major catastrophic north directed landslide during its eruptive history the related debris avalanche da deposits extend north 70 km from the island shore and have a total volume of about 800 km3 two contrasted facies of the debris are recognized 1 relatively small sized material including a few blocks with well developed flow structures elongate downslope directed ridges and transversal pressure ridges and 2 a scattering of large kilometer sized individual blocks that form in part a prominent bathymetric hummock in the proximal central part of the landslide deposits bathymetric analyses suggest that the tahitian failure evolved through two main successive shots the da debris were rapidly overlain by subsequent volcanic material producing a smooth surface down to 1500 m below sea level the on land and offshore structures indicate a listric fault geometry for the landslide scar the volume removed by the landslide is thus estimated between 400 km3 and 450 km3 discrepancy in the volume of the scar and the debris derived from it is due in part to expansion of the debris to fragmentation of the avalanche and to incorporation of sediments comparison with a recently recognized southern tahitian landslide clouard et al 2001 and with landslides recognized around the hawaiian islands and the canary islands shows that the huge northern tahitian landslide described here has a reduced mobility in its central part perhaps the older tetiaroa eruptive complex to the north acted as a buttress to inhibit movement of the da products the northern and southern tahiti nui landslides moved in opposite directions away from the main central e w directed rift zone that served as the main magma feeding structure then the huge northern landslide strongly controlled the later volcano structural evolution by capturing subsequent volcanic activity to the north despite the northwestward displacement of the pacific plate over the society hot spot

growth and erosion rates of the east carpathians volcanoes constrained by numerical models tectonic and climatic implications abstract the east carpathian volcanic range experienced an along arc late miocene to quaternary migration of eruptive activity during its 11 ma long activity here a novel and complex methodology is presented that yields new geochronological and geomorphological constraints on the evolution of the 20 volcanic edifices new unspiked k ar ages either constrain their lifespan 6 79 0 10 6 47 0 09 ma for seaca t tarca 5 47 0 08 4 61 0 07 ma for v rghis or date the youngest volcanic activity central c limani in parallel numerical reconstructions of volcanic paleo topographies were performed to quantify their shape at the end of their construction stage the inferred initial volcano size shows a wide range 3 to 592 km3 making up the four main successive volcanic segments 910 880 279 and 165 km3 for c limani gurghiu north harghita and south harghita segment respectively totalizing 2200 km3 and an average growth rate of 200 km3 ma at range scale at the volcano scale with only consideration to their respective time spans i e avoiding repose periods growth rate is characterized by two major trends a moderate growth rate 137 km3 ma for the older volcanoes 11 3 6 ma followed by a lower growth rate 28 km3 ma obtained for the plio quaternary volcanoes comparing reconstructed and current topographies yielded a total eroded volume of 524 125 km3 defining averaged denudation of 22 and a 20 m ma erosion rate erosion rates for major climatic periods were computed which highlight the contrasting climatic contexts since 11 ma the highest erosion rate 38 m ma occurred during transitional moderate subtropical continental climate period 9 5 8 2 ma an intermediate erosion rate 14 m ma characterized a moderate continental climate period 8 2 6 8 ma when conditions became less humid the lowest erosion rate 7 m ma reflects the prevailing continental but occasionally semi arid climate 6 8 5 8 ma the highest erosion rate 28 m ma was obtained for plio quaternary times during the interglacial glacial cycles such a quantitative morphometric and geochronological approach demonstrates its efficiency to study volcanic dynamism including both constructional and erosional processes through time

nature and origin of toreva remnants and volcaniclastics from la palma canary islands abstract new data pertaining to the origin of volcaniclastic fan delta deposits the el time group and previously unreported toreva remnants intact landslide blocks are presented in terms of their relationships with the quaternary flank destruction of bejenado volcano on la palma canary islands bejenado volcano is the heavily dismantled relic of a stratocone which developed at the confluence of the cumbre nueva embayment and the caldera de taburiente collapse amphitheatre both of these giant landslide structures formed at around 0 55 ma after 0 2 ma of gravitational spreading on the western and eastern flanks of the taburiente cumbre nueva shield volcanic complex evidence is presented on the basis of stratigraphic photogeologic and geographic information system studies that both the toreva remnants and the el time group can be related to the sequential collapses of the north flank and summit region of bejenado inside the caldera de taburiente and the northernmost part of the adjoining cumbre nueva embayment the collapses probably occurred between 0 44 and 0 4 ma and they involved a volume of around 5 km3 the toreva remnants display a deformed volcanic architecture traversed by discontinuities which developed during impact and post collapse dislocation during slip they are composed of layer differentiated scoria with ancillary ankaramite and basanite tephrite lavas and occasional dikes they rest upon a thin veneer of sheared volcaniclastic deposits in relative proximity to the disfigured north flank of bejenado the collapse event s is distinguished by its extremely low mobility due to the deceleration of the debris avalanche mass within the confines of the caldera de taburiente the high friction coefficient h l 0 22 reflects this topographic factor reworking of the avalanche matrix gave rise to the accumulation and offshore progradation of the fan delta deposits at the sw base of bejenado contemporaneous fluvial sediments sourced by the retrogressive erosion of the pre bejenado collapse scarps were fed into the subaerial confines of the cumbre nueva embayment piecemeal scarp failure and the extrusion of substratum from beneath the scarps also contributed to the sediment budget the fluvial sedimentation rates subsequently increased with the onset of cumbre vieja volcanism prior to 0 125 ma these processes have contributed to the development of the flat floored submarine channels which extend onto the volcaniclastic apron west of la palma these new data give a fresh insight into the role of epiclastic processes landsliding and volcanism in the morphology and sediment mass balance of an oceanic island volcano system

an automatic orbital tuning method for paleoclimate records the recognized linkage of climatic events to the earth s orbital variations has provided the basis for establishing time scales of pleistocene climatic records most of the classic orbital tuning methods developed so far however need visual judgements to add new time control points into the climatic records thus being time consuming and hindering the construction of high resolution climatic time series in this study we propose to use the dynamic optimization method to overcome the shortcomings with this technique the additional time control points can be automatically added into the climatic records and a best age for each of the climatic data can be calculated results of a case study conducted on the baoji loess section show that the automatic orbital tuning method can lead to a much better agreement of climatic time series with theoretical changes in the orbital elements relative to the classic ones

magnetostratigraphy of the dali basin in yunnan and implications for late neogene rotation of the southeast margin of the tibetan plateau 1 the rotation pattern and fault activity in the southeast margin of the tibetan plateau semtp provide meaningful constraints on the geodynamic evolution of the plateau however the lack of cenozoic paleomagnetic studies and accurate age constraints on neogene sediments prevents a better understanding of the late cenozoic tectonic activity in this area to clarify the tectonic rotation pattern and deformation history of the semtp we report new magnetostratigraphic data from a late neogene sedimentary sequence in the dali basin northwestern yunnan province china rock magnetic analyses indicate that both magnetite and hematite are the main carriers of the characteristic remanent magnetizations chrms magnetostratigraphic results show that the sedimentary profile spans from chron c4n 1r to chron c2n the age of the sedimentary sequence in the dali basin can thus be paleomagnetically constrained to an interval from late miocene to early pleistocene the basal age of the sediments is 7 6 ma which indicates that the unroofing of diancang shan and activation of the dali fault system were initiated at this time the appearance of conglomerates and syntectonic sediments suggests the reactivation of the dali fault system at 2 5 ma moreover the overall mean chrm direction suggests that the dali basin experienced significant 4 4 2 5 but minor post late miocene rotation this indicates that most of the clockwise rotation demonstrated by previous paleomagnetic studies in the semtp occurred prior to late miocene and may be concentrated between eocene and miocene which is contemporaneous with the sinistral slip of the ailao shan red river fault

the morphology of insular shelves as a key for understanding the geological evolution of volcanic islands insights from terceira island azores shelves from volcanic ocean islands result from the competition between two main processes wave erosion that forms and enlarges them and volcanic progradation that reduces their dimension in places where erosion dominates over volcanism shelf width can be used as a proxy for the relative age of the subaerial volcanic edifices and reconstruction of their extents prior to erosion can be achieved in this study new multibeam bathymetry and high resolution seismic reflection profiles are exploited to characterize the morphology of the insular shelves adjacent to each volcanic edifice of terceira island in order to improve the understanding of its evolution subaerial morphological and geological stratigraphic data were also used to establish the connection between the onshore and offshore evolution shelf width contiguous to each main volcanic edifice is consistent with the known subaerial geological history of the island most of the older edifices have wider shelves than younger ones the shelf edge proved to be a very useful indicator in revealing the original extent of each volcanic edifice in plan view its depth was also used to reconstruct vertical movements showing that older edifices like serra do cume ribeirinha guilherme moniz and pico alto have subsided while more recent ones have not the morphology of the shelf namely the absence presence of fresh lava flow morphologies and several types of erosional depositional and tectonic features integrated with the analysis of the coastline morphology allowed us to better constrain previous geological interpretations of the island evolution

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

holocene sea level rise recorded by a radiocarbon dated mussel in a submerged speleothem beneath the mediterranean sea fossil shells of the boring mussellithophaga lithophagaprovide a means for dating changes in relative sea level these bivalves being among the first colonizers of bare calcareous substrates can mark the earliest stages of marine submergence of caves here we report data concerning the deepest submerged speleothem presently sampled in a temperate area at 48 m below present sea level off the west coast of italy mediterranean sea a fossil mussel shell beneath encrusting layers from later marine colonists gave an ams age of 9580 3514c yr b p 10 253 72 cal yr b p

geomorphological study of long term erosion on a tropical volcanic ocean island tahiti nui french polynesia abstract a quantitative geomorphological study has been made on 27 river basins in tahiti nui volcanic island french polynesia to reconstruct the erosional evolution of a young oceanic island subjected to heavy tropical rainfall tahiti nui is composed of a main shield volcano cut by two huge landslides on each side of a main e w rift zone the northern landslide depression was rapidly buried by the construction of a second shield the late activity of which overflowed the crest and then filled the southern landslide depression the island is now volcanically inactive and is deeply dissected by erosion the present geometries of the river basins are first compared using dimensionless parameters derived from a digital elevation model the original volcanic surfaces are then reconstructed to estimate the volumes removed by erosion and determine the average rates of long term erosion the basins developed on the flanks of the main shield are wider shallower and gentler than the basins incising the post landslide second shield indicating a higher degree of evolution rainfall concentration on the windward eastern side of the island also contributed to increase the vertical lowering of the volcanic relief and the enlargement of the valleys the magnitude of erosion however is neither directly linked with the age of the units incised nor with the differential amounts of rainfall erosion rates determined over the last 1 myr range between 10 3 km 3 kyr 1 and 0 25 km 3 kyr 1 the highest values occur in the basins incising the main e w rift zone and or the lateral rims of the northern and southern landslide depressions long term dissection has thus been enhanced along the geological discontinuities of the eruptive system deep erosion was first constrained along the axis of the main e w rift zone where numerous dykes compartmentalize the volcanic structure into large unstable blocks dykes most probably acted as mechanical discontinuities along which shallow gravitational landslides recurrently occurred such mass wasting episodes produced significant amounts of debris partly preserved as highly indurated sedimentary breccias of various ages exposed at various locations subsequent dissection of tahiti nui was enhanced to the north and to the south leading to the rapid evolution of the papenoo and taharuu drainage systems over the last 500 kyr long term dissection on tahiti nui has been responsible for the removal of at least 350 km 3 of volcanic material from the surface and for the partial exhumation of a shallow intrusive complex partly composed of coarse grained plutonic rocks gabbros and syenites in the central part of the eruptive system structurally controlled erosion is thus a key component of landscape evolution on such high relief oceanic tropical islands

palaeoclimatic changes over the past 1 million years derived from lacustrine sediments of heqing basin yunnan china abstract a 168 m long core of mostly fine grained lacustrine sediments was recovered from heqing basin yunnan province southwestern china the area is located at the south eastern margin of the tibetan plateau and is mainly affected by the sw monsoon magnetostratigraphy of this core indicates that it spans the last one million years spectral analysis of carbonate and magnetic susceptibility and a rough correlation of with the marine oxygen isotope record suggest that the climatic record of this area is consistent with the global climatic pattern pollen data from hq indicate alternations between temperate arid and cold humid climatic conditions as a typical regional palaeoclimatic pattern the highs and lows of can be related to warm and cold periods respectively maghemite and magnetite dominate the magnetic mineralogy maghemite is distributed throughout the whole core whereas magnetite occurs additionally in samples with higher deposited during arid periods the magnetic and non magnetic variations clearly show a change at 65 m corresponding to ca 410 ka indicating a change in the depositional system related to a climatic and or tectonic event

paleo sea level changes and relative sea level indicators precise measurements indicative meaning and glacial isostatic adjustment perspectives from mallorca western mediterranean abstract paleo relative sea level rsl indicators formed during the marine isotope stage mis 5e have been reported by a large number of studies worldwide despite this three main aspects are seldom reported 1 use of high precision survey techniques applied to mis 5e rsl indicators 2 application of modern analogs to understand the indicative meaning of mis 5e rsl indicators 3 estimates of the effects of glacial isostatic adjustment gia on the mis 5e records in this study we show how the three points above have been addressed in a focused study on last interglacial outcrops on the island of mallorca we measured the elevation of several rsl indicators with high accuracy differential gps vertical accuracies down to 0 1 m and we established the relationship between each rsl indicator and the paleo sea level through calculation of the indicative meaning for each rsl indicator in particular we present a novel technique to calculate the indicative meaning of fossil beach deposits with a phase averaged morphodynamic model cshore we show how this approach helps overcoming difficulties with the survey of the modern analogs for these indicators our results show that two paleo rsls are imprinted in mallorca at 2 9 0 8 m and 11 3 1 0 m we then compare our field based results with modelled paleo rsl calculated from the predictions of the ice earth coupled anice selen model using few different ice sheet melting scenarios during mis 5e we conclude that indicative ranges can be derived from relatively simple morphodynamic models and that the comparison of field derived and modelled rsl values is a good method to validate possible scenarios of mis 5e sea level variability especially in absence of precise dating

late pleistocene holocene sea level rise and the pattern of coastal karst inundation records from submerged speleothems along the eastern adriatic coast croatia in order to reconstruct the late pleistocene holocene sea level rise along the eastern adriatic coast eight speleothems were collected from three submerged caves along the croatian coast from depths of 38 5 to 17 m the marine biogenic overgrowth layer and the youngest and the oldest parts of the speleothems were dated by the 14c method their stable isotope 13c 12c and 18o 16o contents were also measured from the measured 14c activity of the marine overgrowth and using the model of alessio et al 1992 risultati preliminari relativi alla datazione di speleotemi sommersi nelle fasce costiere del tirreno centrale giornale di geologia ser 3 54 2 165 193 the start of overgrowth i e the time of flooding by seawater was determined to be 10 185 cal bp at 36 m 9160 cal bp at 34 m and 7920 cal bp at 23 m our results partially match the sea level curves reconstructed for adjacent areas tyrrhenian coast and french mediterranean coast however the start of the marine overgrowth on speleothems in pit caves indicates strong dependence on the steepness of the terrain on steep extensively karstified coasts marine overgrowths on speleothems coincided with the submersion of the speleothems due to the relatively short distance between the pit and the open sea and fast penetration of seawater into the pit in contrast marine overgrowths on speleothems in pits in the flat terrains occurred later because speleothem growth ceased due to flooding with fresh groundwater later the fresh water was replaced by seawater due to the greater distance of the inland pits to the former coast

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

late quaternary sea level changes along the tyrrhenian coast near orbetello tuscany central italy palaeoenvironmental reconstruction using ostracods abstract a multidisciplinary study has been carried out on a 51 m long core drilled on coastal lowlands near the albegna river tuscany central italy both sedimentological and faunal analyses ostracods and molluscs indicate a coastal lagoon environment repeatedly influenced both by the rising holocene sea and the albegna river alluvial inflow 13c 18o mg ca sr ca and 87sr 86sr analyses were performed on cyprideis torosa shells in order to detail the influence of albegna river freshwater on the coastal lagoon water the analytical data illustrate the difficulties of using geochemical proxies in marginal marine settings four radiocarbon dates provide a chronostratigraphy for the early holocene part of the core the data are used to reconstruct late pleistocene to early holocene palaeoenvironments along this part of the coast and show the development of freshwater environments followed by a coastal brackish lagoon formed in response to the initial holocene rapid rise in relative sea level an attempt is made to relate sediments and age data from the core to the relative sea level curve for the tyrrhenian sea

a giant landslide on the southern flank of tahiti island french polynesia we present evidence for an ancient and voluminous subaerial landslide of the southern flank of tahiti society islands during a marine geophysical survey in 1996 submarine mass wasting deposits were mapped as far as 60 km from the southern shore of the island acoustic imagery reveals a surface of 2950 km of debris avalanche and hummocky terrain based on bathymetric data the volume of the debris is estimated to be 1150 km in comparison with hawaiian and other oceanic island landslides it can be classified as a giant rapid and cataclysmic event tahiti morphology and the distribution of volcanic ages over the island strongly suggest that the slope failure initiated near the top of the southern island flank between 650 and 850 ka the landslide scar was subsequently filled by eruptions the estimated volume of the subaerial removed material exhibits a large discrepancy with the volume of the submarine deposits that can be explained by recurrent slide events

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

holocene evolution of the haifa bay area israel and its influence on ancient tell settlements the geographical evolution of haifa bay and zevulun plain israel from the late pleistocene to the holocene is based on detailed analysis of drilled cores at the beginning of the holocene the bay area was still under terrestrial conditions only about 9500 to 9000 cal yr bp when sea level rose to about 35 30 m below present sea level b s l did nile derived sand start to bypass the carmel headland and haifa bay come into existence as a morphological feature between 8000 and 7150 cal yr bp when sea level was 14 10 m b s l the invading sea crossed the present day coastline at about 6800 to 6600 cal yr bp sea level rose to about 5 m b s l and flooded the zevulun plain up to 2 km inland and the river qishon estuary up to 4 km inland it is still unknown exactly when the sea reached its maximum penetration inland but later about 4000 years ago the coastline in the research area was still east of the present day coast up to 3 km in the zevulun plain and 4 8 km in the river qishon estuary when the coastline started to retreat westward the reclamation was followed by intensive deposition of shallow marine sand and aeolian dunes while to the east different wetland conditions developed the archaeological data indicate that during the early bronze age i and early bronze age ii dated to between 5600 and 4700 cal yr bp and even later during the middle bronze age ii period about 4600 to 3500 cal yr bp the coastline was still east of the present day coast but it never actually reached the bases of most of the tells as has been suggested except for tel akko and tel abu hawam

diatom response to climatic and tectonic forcing of a palaeolake at the southeastern margin of the tibetan plateau during the late pleistocene between 140 and 35 ka bp abstract the heqing basin is located in yunnan province south western china near the southeastern edge of the tibetan plateau a region that is strongly influenced by the asian monsoon its long sedimentary record represents an archive of global importance for palaeoclimate research this study presents the results of diatom analysis of the last 140 35 ka of the record dated using ams 14 c and magnetostratigraphy diatoms are generally well preserved apart at the top of the sequence after 35 ka bp in which diatoms were too few to be counted the diatom data provide a detailed history of palaeoenvironmental changes during the late pleistocene and demonstrate the sensitivity of diatoms to changes in climate and hydrology in particular they provide proxy evidence for water depth and indirect evidence for temperature changes that are characterized by glacial interglacial shifts between planktonic and benthic diatoms and variations in the percentage of the warm water and eutrophic species aulacoseira granulata respectively in the heqing sequence remarkably high proportions of benthic diatoms coincide with warm and wet conditions suggesting that at this site the diatom signal is mediated by climate catchment vegetation processes such as the concentration of nutrient and runoff from the catchment from 132 ka bp however the tectonic uplift of the basin caused a change in the hydrological setting of the lake pollen and geochemical data are then used to help interpreting the diatom sequence and disentangle the direct effects of climate from those mediated by the conditions on the catchment such as the influence of glacier melt water

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

paleomagnetic record of the late pleistocene reef sequence of tahiti french polynesia a contribution to the chronology of the deposits abstract rock and paleomagnetic investigations were performed on the late pleistocene reef sequence of tahiti and take part of a multidisciplinary study of the holocene and pleistocene reef sequences carried out by the iodp integrated ocean drilling program expedition 310 the objectives were to characterize the natural remanent magnetization and its mineral carriers in order to identify high resolution magnetostratigraphic markers of the late brunhes chron a series of 85 specimens subsampled within a 79 m thick silty carbonate sequence cored at the maraa site sw of tahiti display a strong and stable natural remanent magnetization nrm carried by titanomagnetite inherited from the basalts which form the bulk of the island the average negative inclination is assignable to the field generated by the normal polarity axial dipole field at the site latitude a few specimens 103 119 m below modern sea level carry a reversed primary magnetization acquired in a weak excursional field based on subsidence rate estimates ranging from 0 25 to 0 4 m kyr this suggests the identification either the laschamp excursion 40 ka or the blake event 115 120 ka radiometric dates of 131 to 134 ka at 117 m below modern sea level confirm that these layers were deposited during the marine isotope stage 5 5 and recorded the direction and intensity anomaly associated with the blake event another sea level highstand reef unit occurring deeper in the pleistocene sequence has seemingly recorded another paleomagnetic intensity anomaly which is not yet definitely identified reef systems which developed around volcanic islands contain geological records of excursions but it is necessary to improve the understanding of nrm acquisition and the role of carbonate diagenesis in order to establish radiometrically dated records of geomagnetic excursions

the analysis of last interglacial mis 5e relative sea level indicators reconstructing sea level in a warmer world the last interglacial mis 5e 128 116 ka is among the most studied past periods in earth s history the climate at that time was warmer than today primarily due to different orbital conditions with smaller ice sheets and higher sea level field evidence for mis 5e sea level was reported from thousands of sites but often paleo shorelines were measured with low accuracy techniques and in some cases there are contrasting interpretations about paleo sea level reconstructions for this reason large uncertainties still surround both the maximum sea level attained as well as the pattern of sea level change throughout mis 5e such uncertainties are exacerbated by the lack of a uniform approach to measuring and interpreting the geological evidence of paleo sea levels in this review we discuss the characteristics of mis 5e field observations and we set the basis for a standardized approach to mis 5e paleo sea level reconstructions that is already successfully applied in holocene sea level research application of the standard definitions and methodologies described in this paper will enhance our ability to compare data from different research groups and different areas in order to gain deeper insights into mis 5e sea level changes improving estimates of last interglacial sea level is in turn a key to understanding the behavior of ice sheets in a warmer world

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

evidence for a persistent uplifting of la palma canary islands inferred from morphological and radiometric data abstract the morpho structural evolution of la palma canary islands is characterized by vertical movements responsible for or favoring large landslides in its northern part conglomerate terraces nowadays topographically hanged and re incised by the present day barranco de las angustias reveal a recent ongoing uplift process lava flows covered by this geological unit have been sampled and dated by the k ar cassignol technique at a mean age of 507 11 ka the minimum rate of uplift inferred of about 0 4 mm yr is similar to the one deduced from the abnormal elevation of the early submarine series staudigel and schmincke j geophys res 89 1984 11195 11215 this indicates that the northern shield may have experienced a global rise fairly constant throughout most of its geological history it probably results from the combination of regional atlas tectonic processes and the existence of a swell at the island scale this global rise together with the existence of a north south fault in the basement may have controlled triggering of the sw flank collapse of the northern shield and the subsequent concentration of magma along a southern still active topographic ridge the cumbre vieja cv morphological asymmetry of this structure may result from the destabilization of its distal western part favored by strong injections at the axis tilting processes along lateral listric faults can then explain the existence of slope break ups especially on the western side of the ridge such tectonic processes are likely responsible for local superimposed uplifting contributing to the genesis and development of huge western coastal cliffs even in sub historic and historic times we show that unlike many oceanic islands la palma island has experienced important positive vertical movements rather than subsidence

characterising the irregular coastlines of volcanic ocean islands volcanic ocean islands grow into irregular shapes because of eruption along radiating volcanic rift zones caldera collapse slope failure coalescence of adjacent volcanoes and marine and subaerial erosion with the aim of searching for variations with environmental parameters which might reflect variations in these processes this study calculates and analyses characteristics of island irregularity from the world vector shoreline database islands are idealised as flat plates bounded by the digitised shorelines from which perimeter distance elongation and moment of inertia are calculated to represent irregularity these characteristics are highly variable and do not correlate strongly with any of the parameters studied here reflecting the complexity of processes shaping island coastlines on closer scrutiny some weak variations with seafloor age and spreading rate are due to some highly irregular islands on old seafloor mostly formed at slow spreading ridges canaries cape verde comores molokai and madeira since most of these islands lie on the african plate which is slowly moving relative to the earth s mantle this may reflect a fortuitous superposition of adjacent volcanoes by stationary hot spots although their embayed outlines suggest that landslides are also important the analysis also resolves the orientations of islands with respect to the tectonic fabric of their underlying oceanic basement revealing that islands on seafloor originally created at slow spreading ridges are preferentially oriented perpendicular parallel and at 30 to the fabric and that islands on young seafloor show a slight tendency to be aligned fabric parallel

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

plio quaternary stepwise drying of asia evidence from a 3 ma pollen record from the chinese loess plateau abstract a 3 ma pollen record was obtained from a continuous red clay loess paleosol sequence at chaona in the central chinese loess plateau clp the record shows a permanent change of a domination of typical cupressaceae forest vegetation representative of an ecological environment with a relative warm and humid climate during 3 0 2 6 ma to largely steppe vegetation under dry climate conditions after 2 6 ma the later is further manifested itself as steppe to forest or forest steppe spruce forest mostly mesophilous herbs between 2 6 ma and 1 5 ma forest steppe pine grass between 1 5 ma and 0 95 ma open forest steppe mesophilous and xeromorphic herbs pine between 0 95 ma and 0 5 ma and steppe xeromorphic herbs after 0 5 ma suggesting a process of stepwise aridification in central asia at the late pliocene and the quaternary

diatom response to climate forcing of a deep alpine lake lugu hu yunnan sw china during the last glacial maximum and its implications for understanding regional monsoon variability abstract the yunnan plateau of southwest china is strongly influenced by the asian monsoon and is a critical area in terms of determining its development and variability since the last glacial maximum high resolution diatom analysis of a 14c dated sediment core retrieved from lugu lake yunnan provides a detailed history of palaeoenvironment changes from 30 000 to 10 000 cal yr bp a model of climate diatom interactions linking thermal stratification ice cover and catchment derived nutrients is proposed to explain the observed changes prior to 24 500 cal yr bp the dominance of the planktonic cyclotella rhomboideo elliptica indicates a period of stable stratification and low nutrient levels with a moderate change of temperature and precipitation in the southwest monsoon region during the lgm 24 500 14 500 cal yr bp the loss of the planktonic diatoms and a switch to small fragilaria spp suggest an altered thermal regime in the lake i e weaker stratification and possibly ice cover from 18 000 cal yr bp the expansion of planktonic taxa stephanodiscus and the asterionella formosa and increased toc are indicative of increased nutrient availability reflecting altered vegetation and soil processes due to rising regional temperatures after 14 500 cal yr bp a rapid reversal to dominance by planktonic diatoms indicates a further increase in temperature and continued development of catchment vegetation and soils the abrupt changes in diatom species composition around 24 500 and 14 500 cal yr bp suggest that the ecological status of the lake exceeded limnological thresholds interestingly however the younger dryas event is not clearly recognizable in either the diatom or pollen records in the lugu lake sediment record in a partial redundancy analysis 44 2 of the variability in the total diatom assemblages in the period 30 000 10 000 cal yr bp was accounted for by changes in summer solar radiation the relationships between the diatom assemblages and the c n and pollen data are further evidence of climate catchment vegetation interactions and their impact on lake functioning the composition of diatom assemblages in the lugu lake sediment core reflects direct and indirect i e via catchment processes climate forcing and in particular the strength of the southwest monsoon which in turn corresponds to orbitally induced variability in northern hemisphere summer solar insolation from 30 000 cal yr bp to 10 000 cal yr bp

foraminiferal record and high resolution seismic stratigraphy of the late holocene succession of the submerged ombrone river delta northern tyrrhenian sea italy abstract micropalaeontological data integrated with radiocarbon dates and seismic profiles allow for a reconstruction of the late holocene evolution of the ombrone river delta area during the last 6 0 ka seven cores collected in three distinct sectors of the submerged ombrone delta were studied the delta front cores nk7 nk8 bok5 and bok10 and prodelta slope core nk4 which are primarily affected by river input and the middle shelf cores nk2 and nk3 which is progressively less influenced by riverine impact seismostratigraphic interpretation indicated that the majority of the cores intercepted the most recent deposits of the late quaternary depositional sequence unit a whose base is dated at 2 8 100 ka bp the deepest and shallowest cores reveal a record of the ancient and the most recent evolution of the succession respectively although the most complete palaeoenvironmental evidence comes from the middle shelf core nk2 and prodelta slope core nk4 the oldest sedimentary phase is indicated by benthic foraminiferal assemblages and seismic profiles of the middle shelf core and correlates with the late transgressive systems tract unit b the following phase is attributed to the highstand systems tract unit a and spans the last 3 0 ka hierarchical cluster analysis hca q mode of the benthic foraminifera in the cores resulted in 10 foraminiferal assemblages that correspond to four distinct environments with various degrees of river influence

late pliocene and early pleistocene vegetation and climate change revealed by a pollen record from nihewan basin north china abstract the nihewan formation is an important early quaternary sedimentary formation in north china we conducted pollen analyses of 183 samples and 1611 modern surface samples to characterize the processes of vegetation succession and climate change during the pliocene pleistocene transition 2 89 2 34 ma in the nihewan basin the results show that pollen assemblages are dominated by arboreal pollen indicating that the vegetation in the study area was forest dominated and that the climate was more humid than today however the temperature varied substantially the most substantial vegetation and climate changes occurred at 2 8 ma when the pollen representation of warm and humid tolerant taxa such as evergreen quercus and carya disappeared and also broadleaved deciduous types such as ulmus deciduous quercus and betula decreased obviously on the contrary the pollen representation of cold and drought tolerant taxa increased substantially e g picea from generally less than 20 to more than 30 and chenopodiaceae from generally less than 10 to more than 20 the quantitative reconstructed results indicating that tann decreased by about 2 3 c and pann decreased by 150 mm compared to before 2 8 ma with a maximum decrease of 9 c for tann and 450 mm for pann another important vegetation and climate changes occurred at 2 6 ma which was the coldest and driest of the studied interval when the vegetation was substantially simplified with spruce generally above 80 as the dominated types

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