geothermobarometry of basaltic glasses from the tamu massif shatsky rise oceanic plateau 1 we present the results of a petrological study of core samples from tamu massif site u1347 recovered during the shatsky rise integrated ocean drilling program iodp expedition 324 the basaltic glasses from site u1347 are evolved tholeiitic basalts containing 5 2 6 8 wt mgo and are principally located within the compositional field of mid ocean ridge basalts morbs but they have systematically higher feo lower al2o3 sio2 and na2o concentrations and the cao al2o3 ratios are among the highest known for morbs in this sense glasses from site u1347 more closely resemble basaltic magmas from the ontong java plateau ojp although they still have lower sio2 concentrations in contrast to morb and similar to ojp our fractionation corrected values of na2o and cao al2o3 indicate more than 20 of partial melting of the mantle during the generation of the parental magmas of tamu massif the water contents in the glasses determined by midinfrared fourier transform infrared ftir spectroscopy are morb like and vary between 0 18 and 0 6 wt h2o the calculated pressure p temperature t conditions at which the natural glasses represent cotectic olivine plagioclase clinopyroxene compositions range from 0 1 to 240 mpa and 1100 to 1150 c reflecting magma storage at shallow depth the variation of the glass compositions and the modeled p t conditions in correlation with the relative ages indicate that there were at least two different magmatic cycles characterized by variations in eruptive styles massive flows or pillow lavas chemical compositions volatile contents and preeruptive p t conditions each magmatic cycle represents the progressive differentiation in course of polybaric crystallization after the injection of a more primitive magma batch magma crystallization and eruption episodes are followed by magmatic inactivity reflected in the core sequence by a sedimentary layer our data for tamu massif demonstrate that similar to ontong java ocean plateau the crystallization beneath shatsky rise occurs at different crustal levels

seismic structure of the mid atlantic ridge 8 9 s 1 the mid atlantic ridge at 8 9 s is characterized by a transition from axial valley to axial high and recent episodes of ridge jumping and ridge propagation we present constraints on the structure of 0 4 ma crust in this region on the basis of the analysis of wide angle seismic data from a grid of profiles across and parallel to the current and abandoned spreading centers a 350 800 m thick oceanic layer 2a interpreted as high porosity extrusive basalts is underlain by a 2 0 2 5 km layer 2b with velocities which increase with age and decrease in the vicinity of the pseudofaults layer 3 velocities are uniform across the area except for a possible localized anomaly at the ridge axis the crustal thickness varies from 6 7 km near the pseudofaults formed by ridge propagation to 9 10 km at the segment center of the recently 0 3 ma abandoned spreading center seismically determined crustal thickness and density variations and age related lithospheric cooling can plausibly account for all observed variations in gravity across the area and there is no requirement for the thicker crust at the segment center to be underlain by hot mantle the transition from axial valley to axial high occurs at a crustal thickness of 8 km

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

early oligocene dinoflagellate cysts from the upper rhine graben sw germany paleoenvironmental and paleoclimatic implications using principal component analysis and cyst diversity and equity trends we can recognize four distinct dinoflagellate cyst dinocyst assemblages from four rupelian early oligocene cores in the mainz embayment of the northern rhine graben sw germany these assemblages are the spiniferites ramosus pc1 thalassiphora pelagica pc2 homotryblium tenuispinosum pc3 and vozzhennikovia spinula pc4 assemblages the four cores provide an onshore offshore transect in the mainz embayment the h tenuispinosum assemblage shows high factor loadings in proximal to intermediate cores which is interpreted to reflect temporary high salinity conditions mean dinocyst diversity and equity increase with distance from the mid rupelian shoreline indicating increasingly stable paleoenvironmental conditions towards the center of the mainz embayment within individual cores changes in dinocyst assemblages through time are related to paleoenvironmental and paleoclimatological changes the three proximal to intermediate cores show dominance of the h tenuispinosum assemblage repeatedly alternating with high factor loadings of the t pelagica assemblage in both cases dinocyst diversity and equity tend to be reduced highest factor loadings of the s ramosus assemblage occur in intervals where neither of the above assemblages is dominant and tend to coincide with dinocyst diversity and equity maxima we interpret this distribution pattern to denote different paleoceanographic conditions reflecting drier and more humid phases in the early oligocene of central europe during relatively dry periods increased salinity conditions prevailed in proximal to intermediate settings of the mainz embayment as reflected by the dominance of the h tenuispinosum assemblage during more humid periods increased runoff led to higher nutrient availability and the formation of a pycnocline separating slightly less saline surface waters from higher saline deeper waters thus impeding vertical circulation these environmental conditions are documented in high loadings of the t pelagica assemblage which is indicative of increased eutrophication and or oxygen depleted bottom waters transitions between drier and more humid periods i e episodes of normal marine conditions are characterized by high loadings predominantly of the s ramosus assemblage as well as increased dinocyst diversity and equity values we propose that the alternations between drier and more humid phases may be related to variations in the ocean atmosphere moisture flux from the north atlantic into central europe bearing a high latitude climate signal 2002 elsevier science b v all rights reserved

crystal growth during dike injection of mor basaltic melts evidence from preservation of local sr disequilibria in plagioclase profiles of a total of 23 plagioclase crystals erupted within the 1982 1991 and 1993 flows of the coaxial segment of the juan de fuca ridge the 1996 flow of the north gorda ridge and from the western volcanic zone of the ultra slow spreading gakkel ridge have been studied for variations in major and trace element concentrations we derive equilibration times for the relatively rapidly diffusing sr in mid ocean ridge basalt morb plagioclase crystals of the order of months to a few years in each case all crystals preserve diffusive disequilibria of strontium and barium crystal residence times at morb magmatic temperatures are thus significantly shorter of the order of days to a few months at most precluding prolonged crystal storage in axial magma chambers and instead pointing to rapid crystal growth up to 10 8 cm s 1 and cooling up to 1 c h 1 shortly prior to eruption of these samples growth of these crystals is therefore inferred to occur almost entirely within oceanic layer 2 during dike injection crystals that grew at lower crustal levels or earlier in the differentiation sequence appear to have been excluded from the erupted magmas as might occur if most of the gabbroic rocks in oceanic layer 3 formed an interlocking crystal framework with viscosities that are too high to carry earlier formed crystals with the melt the vertical extent of eruptible crystal poor melt lenses within the gabbroic zone is constrained to 1 m or less by considering the width of local equilibrium growth zones equilibration times and crystal settling velocities this lengthscale is consistent with field evidence from ophiolites finally crystal aggregates within the gakkel ridge sample studied here are the result of synneusis within the propagating dike during melt ascent

an experimental investigation of the influence of water and oxygen fugacity on differentiation of morb at 200 mpa crystallization experiments were performed at 200mpa in the temperature range 1150 950 c at oxygen fugacities corresponding to the quartz fayalite magnetite qfm and mno mn3o4 buffers to assess the role of water and fo2 on phase relations and differentiation trends in mid ocean ridge basalt morb systems starting from a primitive mgo 9 8 wt and an evolved morb mgo 6 49 wt crystallization paths with four different water contents 0 35 4 7 wt h2o have been investigated in primitive morb olivine is the liquidus phase followed by plagioclase clinopyroxene amphibole is present only at water saturated conditions below 1000 c but not all fluid saturated runs contain amphibole magnetite and orthopyroxene are not stable at low fo2 qfm buffer residual liquids obtained at low fo2 show a tholeiitic differentiation trend the crystallization of magnetite at high fo2 mno mn3o4 buffer results in a decrease of melt feo mgo ratio causing a calc alkaline differentiation trend because the magnetite crystallization temperature is nearly independent of the h2o content in contrast to silicate minerals the calc alkaline differentiation trend is more pronounced at high water contents residual melts at 950 c in a primitive morb system have compositions approaching those of oceanic plagiogranites in terms of sio2 and k2o but have ca na ratios and feo contents that are too high compared with the natural rocks implying that fractionation processes are necessary to reach typical compositions of natural oceanic plagiogranites

experimental constraints on the low pressure evolution of transitional and mildly alkalic basalts the effect of fe ti oxide minerals and the origin of basaltic andesites one atmosphere melting experiments controlled at the fayalite magnetite quartz oxygen buffer on mildly alkalic and transitional basalts from iceland show that these begin to crystallize fe ti oxide minerals magnetite and or ilmenite at 1105 5 c apparently independently of bulk composition and the order of silicate and oxide mineral crystallization most samples crystalline plagioclase and olivine as the first two crystalline phases augite as the third phase and an fe ti oxide mineral as the fourth phase the main effects of fe ti oxide crystallization are a marked decrease in feo and tio2 in the liquid and a notable increase in sio2 and al2o3 and the minor oxides k2o and p2o5 with decreasing temperature the most silicic glasses are compositionally mugearitic and shoshonitic basaltic andesites because the smallest amount of glass that could be analyzed with the microprobe represents 20 55 percent liquid remaining it can be expected that more silicic liquids will occur at lower temperatures on normative pseudoternary projections the general effect of fe ti oxide crystallization for mildly alkalic and transitional basalts is a marked increase in normative quartz this is caused by a strong systematic convergence with the appearance of fe ti oxides of the bulk solid precipitates toward the liquid compositions as projected on the triangle plagioclase diopside olivine for alkalic basalts the bulk solid precipitate shows an increase in normative diopside with falling temperature and fe ti oxide crystallization this causes the liquids to move toward decreasing normative diopside and relatively little variation in nepheline the experimental observations imply that mildly alkalic and transitional magmas without stabilizing a fe ti oxide mineral will not evolve toward early silica saturation

climate and biomes in the west mediterranean area during the pliocene a new pollen derived method of climatic quantification based on the mutual climatic range of plant taxa has been applied to 17 pliocene pollen sequences in the west mediterranean area the latitudinal gradient observed in the pollen data was confirmed by the climatic reconstructions there is a gradient from north to south both for temperatures and precipitation at the beginning of the pliocene 5 32 5 ma the climate in the north mediterranean area was on average warmer and more humid than today respectively 1 4oc and 400 700 mm in the south mediterranean region the climate was both warmer and drier than today respectively equal to or 5oc higher and drier or equal humidity the pollen based climate estimates were then used to reconstruct biomes for the region the results show the occurrence of three biomes the broad leaved evergreen warm mixed forest the xerophytic woods scrub biome and the warm grass shrub biome these biomes are still represented today in the mediterranean region despite different thermic and water conditions

a multi proxy study of pliocene sediments from ile de france north east greenland abstract a multi technique approach has been used to study a pliocene shallow water marine deposit designated the ile de france formation in north east greenland the sequence is correlated on the basis of 87sr 86sr ratios in shells and palaeomagnetic studies with the gauss normal polarity chron which is dated to between 2 60 and 3 58 ma years bp this dating is in accordance with amino acid epimerisation and evidence from dinoflagellates foraminifers and molluscs sediments marine molluscs and foraminifers show that the sequence was deposited on the inner shelf below storm wave base seawater temperatures were much higher than today as demonstrated by the occurrence of a number of southern extra limital species the same applies to air temperature and the few remains of land plants may indicate a forested upland with picea and thuja a number of extinct taxa are present including nucula jensenii that is erected as a new species

large scale sediment underplating in the makran accretionary prism southwest pakistan field relations in the emergent part of the makran accretionary prism show that a mid miocene to early pliocene slope and shelf sedimentary sequence was deposited directly on abyssal plain turbidites without any detectable stratigraphic or structural discordance sedimentological evidence for rapid shoaling however indicates that the underlying sediment column was tectonically thickened by a factor of between two and three during this period this can be explained by large scale underthrusting and underplating of sediment a mode of accretion that is also favored by mass balance considerations the visible deformation in the coastal makran occurred when the region was 70 100 km north of the contemporary prism front

distinguishing climatic and current effects in mid pleistocene sediments of hatton and gardar drifts ne atlantic samples taken from dsdp sites 552 and 553 on hatton drift and site 611 on gardar drift in the northeast atlantic ocean were examined by analyses of carbonate content coarse fraction amount and composition fine fraction size and composition and oxygen isotope ratios the age of both sections is the mid pleistocene ranging from the end of the jaramillo normal event to the boundary between the matuyama and brunhes epochs about 0 77 0 96 ma records of this time show a change from a dominance of 23 ka to longer periodicity at about 0 818 ma this is marked at site 552 but less so at site 611 the grain size is mainly controlled by coccoliths foraminifera and ice rafted material all of which are related to glacial interglacial changes zones barren of and abundant in coccoliths are sensitive indicators of climatic effect carbonate increase lags behind foraminiferal oxygen isotope records of surface warming in several glacial to interglacial transitions at both drifts different types of carbonates oozes occur on hatton and gardar drifts of several possible factors influencing these bottom current effects seem more significant than others deduced from size analysis of the fine fraction sedimentological results in this study further confirm that sediment drifts in the ne atlantic have maintainted their basic characteristics at least since the mid pleistocene

dinoflagellate cyst paleoecology during the pliocene pleistocene climatic transition in the north atlantic dinoflagellate cysts dinocysts are widely used as tracers of sea surface conditions in late quaternary marine records however paleoenvironmental reconstructions across the pliocene pleistocene climatic transition and beyond are limited because the hydrologic conditions influencing assemblage compositions may not have a modern analogue and the ecological optima of extinct dinocyst species are not well known from a study of two cored sites in the central and eastern north atlantic we bypass these issues by statistically analyzing the variations in dinocyst assemblage composition and comparing the results directly to paleoecological parameters 18obulloides 18osalinity and geochemical proxies for sea surface temperature sst derived from the planktonic foraminifer globigerina bulloides recovered from the same samples as the dinocysts through canonical correspondence analysis we demonstrate the co variation of seasonality and dinocyst paleoproductivity we show that pyxidinopsis braboi is a cold tolerant species with an optimum sst between 12 and 14 c we extend the use of nematosphaeropsis labyrinthus as an indicator of transitional climatic conditions to the pliocene we offer evidence for the correlation of bitectatodinium tepikiense and filisphaera microornata to high seasonality and we reiterate an apparent link between spiniferites mirabilis and eastern north atlantic water masses finally we confirm that habibacysta tectata is cold tolerant rather than a strictly cold water indicator that operculodinium eirikianum is a cold intolerant species favoring outer neritic environments and that ataxiodinium confusum and invertocysta lacrymosa are both warm water species

dinoflagellate cysts and holocene oceanography of the northeastern atlantic ocean dinoflagellate cyst analysis of two sediment cores taken on the continental slope off the western coast of scotland has revealed new detail and complexity in the oceanography of the holocene changes in the dinoflagellate cyst assemblages suggest at least three fluctuations in the strength or disposition of the north atlantic current over the last 10 ka together with a consequent change in the oceanographic regime of the northeastern atlantic these changes based on comparison to well constrained data from the arctic include the first influx of the north atlantic current at about 10 ka together with some change in oceanography at between 8 and 6 ka and between 4 and 2 ka these oceanographic changes are based upon fluctuations in the numbers of dinoflagellate cysts per gram of sediment and by their relative proportions dinoflagellate cysts have therefore a significant role to play in reconstructing the complex history of holocene environmental change

morphology and tectonics of the mid atlantic ridge 7 12 s 1 we present swath bathymetric gravity and magnetic data from the mid atlantic ridge between the ascension and the bode verde fracture zones where significant ridge hot spot interaction has been inferred the ridge axis in this region may be divided into four segments the central two segments exhibit rifted axial highs while the northernmost and southernmost segments have deep rift valleys typical of slow spreading mid ocean ridges bathymetric and magnetic data indicate that both central segments have experienced ridge jumps since 1 ma mantle bouguer anomalies mbas derived from shipboard free air gravity and swath bathymetric data show deep subcircular lows centered on the new ridge axes suggesting that mantle flow has been established beneath the new spreading centers for at least 1 myr inversion of gravity data indicates that crustal thicknesses vary by 4 km along axis with the thickest crust occurring beneath a large axial volcanic edifice once the effects of lithospheric aging have been removed a model in which gravity variations are attributed entirely to crustal thickness variations is more consistent with data from an axis parallel seismic line than a model that includes additional along axis variations in mantle temperature both geophysical and geochemical data from the region may be explained by the melting of small 200 km mantle chemical heterogeneities rather than elevated temperatures therefore there may be no ascension circe plume index terms 1517 geomagnetism and paleomagnetism magnetic anomaly modeling 3010 marine geology and geophysics gravity 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158

recognition of cyclic and non cyclic environmental changes in the mediterranean pliocene a palynological approach the interval between 2 8 and 2 3 ma b p from the south italian singa section has been investigated for its dinoflagellate cyst and sporomorph contents in order to facilitate palaeoenvironmental interpretation the following curves are derived from the data the ratios sporomorphs dinoflagellate cysts protoperidinioid gonyaulacoid dinoflagellate cysts warm cold water indicating dinoflagellate cysts inner neritic oceanic dinoflagellate cysts outer neritic oceanic dinoflagellate cysts and the reworked dinoflagellate cysts per gram of sediment furthermore the already available 18o curve has been used calibration of changes in the sporomorph dinoflagellate ratio against the computed astronomical insolation curve leads to an improved age assessment for the section frequency analysis on the curves shows the 23 41 and 100 ka frequency components to be most important phase and amplitude differences between the filtered 23 41 and 100 ka frequency components are used for environmental interpretation the 23 ka frequency band is best explained by changes in runoff induced transport the 41 ka frequency components are classified in a group with short response time to orbital forcing and a group with longer response time those signals having a short response time are attributed to local precipitation induced changes in runoff those signals having a longer response time are mainly attributed to changes in global temperature and to a lesser extent to changes in global ice volume finally longer term cyclic and non cyclic changes are mainly attributed to temperature and sea level variation

depths of partial crystallization of h2o bearing morb phase equilibria simulations of basalts at the mar near ascension island 7 11 s phase equilibria simulations were performed on naturally quenched basaltic glasses to determine crystallization conditions prior to eruption of magmas at the mid atlantic ridge mar east of ascension island 7 11 s the results indicate that mid ocean ridge basalt morb magmas beneath different segments of the mar have crystallized over a wide range of pressures 100 900 mpa however each segment seems to have a specific crystallization history nearly isobaric crystallization conditions 100 300 mpa were obtained for the geochemically enriched morb magmas of the central segments whereas normal n morb magmas of the bounding segments are characterized by polybaric crystallization conditions 200 900 mpa in addition our results demonstrate close to anhydrous crystallization conditions of n morbs whereas geochemically enriched morbs were successfully modeled in the presence of 0 4 1 wt h2o in the parental melts these estimates are in agreement with direct fourier transform ir measurements of h2o abundances in basaltic glasses and melt inclusions for selected samples water contents determined in the parental melts are in the range 0 04 0 09 and 0 30 0 55 wt h2o for depleted and enriched morbs respectively our results are in general agreement within 200 mpa with previous approaches used to evaluate pressure estimates in morb however the determination of pre eruptive conditions of morbs including temperature and water content in addition to pressure requires the improvement of magma crystallization models to simulate liquid lines of descent in the presence of small amounts of water

differentiating glacio eustacy and tectonics a case study involving dinoflagellate cysts from the eocene oligocene transition of the pindos foreland basin nw greece in an attempt to discriminate between tectonically induced sea level changes and glacio eustacy the ekklissia and arakthos sections epirus nw greece are examined applying dinocyst palynology sedimentology and magnetostratigraphy the sections located in the pindos foreland basin both comprise the transition from pelagic limestones to hemipelagic silty clays and turbidite sandstones reflecting the onset of flysch sedimentation as a result of the pindos thrust activity despite an overall tectonic overprint relative changes of sea level can be reconstructed using i continental marine palynomorph ratios ii relative abundance of inshore and offshore dinoflagellate cysts and iii taxa indicative of relatively cold and warm sea surface temperature that can be calibrated against the global polarity time scale gpts increased fluxes of marginal marine and continental palynomorphs coincide with colder periods on a third order scale which thus appear to be related to glacio eustatic trends in sea level the larger scale is attributed to the increasing effect of tectonics and acts on a second order scale

pollen distribution in recent marine sediments eastern canada analysis of 90 samples from coastal and continental shelf areas off eastern canada between 42 and 69 n shows that quaternary pollen and spores are present in recent marine muds throughout this region pollen and spore concentrations range from 50 000 to 100 grains per cm3 and they decrease both offshore as a function of distance from vegetation sources and northwards as a function of lower vegetation density north of the summer arctic frontal zone isopercentage contours show that maximum relative abundances of most palynomorphs occur in marine sediments adjacent to their regions of highest vegetation representation onshore however pinus and picea pollen tend to increase in percentage abundance with distance offshore presence of these tree pollen in marine sediments off baffin island implies that wind transport is an important pathway by which bisaccate pollen types enter the ocean in addition to fluvial transport q mode factor analysis shows that four major factors account for 89 of the variance amo

an experimental study of the influence of oxygen fugacity on fe ti oxide stability phase relations and mineral melt equilibria in ferro basaltic systems

comparison of foraminiferal coccolithophorid and radiolarian paleotemperature equations assemblage coherency and estimate concordancy the imbrie kipp method of paleotemperature estimation is rigorously tested by comparing atlantic temperature equations independently derived from the microfossils of three biotic groups the foraminifera coccolithophorida and radiolaria this method consists of two steps factor analysis of the modern sea bed data of the individual groups which resolves discrete biogeographic assemblages and regression analysis of the modern assemblage data with observed sea surface temperature data to obtain paleotemperature equations assemblage biogeography shows a simple subdivision into warm low latitude and cold high latitude for all biotic groups between biotic groups there is greater similarity among high latitude assemblages than low latitude ones correlating the assemblage data with observed sea surface temperatures to produce temperature distribution patterns shows differences of less than 2 c in their optimum and critical temperatures regression analysis produced accurate temperature equations for each biotic group all with standard errors of estimate of less than or equal to 2 c multiple correlation coefficients were all greater than 0 970 applying these equations to two multiple biotic data sets the modern and ice age sea bed data and comparing their temperature estimates using the standard error pooled shows over 87 concordancy for both data sets unlike the modern data the discordancy among temperature estimates of the ice age data shows a distinct geographic distribution its cause is believed to be oceanographic a difference in the water mass structure between the modern and ice age ocean

controls of subduction geometry location of magmatic arcs and tectonics of arc and back arc regions most variation in geometry and angle of inclination of subducted oceanic lithosphere is caused by four interdependent factors combinations of 1 rapid absolute upper plate motion toward the trench and active overriding of the subducted plate 2 rapid relative plate convergence and 3 subduction of intraplate island seamount chains aseismic ridges and oceanic plateaus anomalously low density oceanic lithosphere cause low angle subduction under conditions of low angle subduction the upper surface of the subducted plate is in contact with the base of the overlying plate the wedge of low density asthenosphere is replaced by subducted lithosphere and the width of the arc trench gap either is significantly increased or a magmatic arc is not developed within the overlying plate the fourth factor is age of the subducting lithosphere subduction of young lithosphere produces two opposing tendencies 1 low angle subduction and increased arc trench distance owing to its low density and 2 decreased arc trench distance owing to its higher temperature two factors of secondary importance contribute to variation in subduction zone geometry and arc trench distance accretion of sediment in trenches depresses the upper portion of the subducting oceanic plate and causes the trench axis to migrate seaward prolonged subduction thickens the upper plate depresses the isotherms in the subducted plate and may create a broader arc both factors increase the arc trench gap the four primary factors also control development of other tectonic elements such as regional subsidence for example the amazon basin and a portion of the cretaceous interior seaway of western united states intra arc extension for example the basin and range province foreland fold and thrust belts and laramide style tectonics

evolution of the yukon tanana terrane evidence from southeastern yukon territory the yukon tanana terrane ytt in southeastern yukon consists predominantly of a mid paleozoic volcanic plutonic arc assemblage built on continental crust the ytt had experienced strong deformation and metamorphism by late triassic time by mid cretaceous the metamorphic complex and late triassic clastic rocks derived from it were imbricated with middle and upper paleozoic ophiolitic sheets the ytt differs markedly from adjacent parts of the north american continental margin in both its depositional and tectonic histories the composition and tectonic history of the ytt is comparable to that of the kootenay and barkerville terranes of southern and central british columbia from which the ytt may have been displaced

timing and progression of climatic tectonic and glacioeustatic influences on the messinian salinity crisis abstract new palynological analysis of the continuous upper neogene sequence from the rifian corridor at sale morocco permits the deconvolution of climatic tectonic and eustatic control on the messinian salinity crisis via two indices 1 a distance from shore index based on dinoflagellate cyst versus pollen distribution and 2 a land climate index based on detailed pollen analysis this new pollen analysis indicates that the messinian salinity crisis 6 8 ma to 5 3 ma was not associated with major climate change detailed analyses of dinoflagellate cyst ecology at sale correlated to the sale 18o record show that initial shoaling of the rifian corridor after 7 3 ma primarily resulted from tectonic uplift however from 6 5 ma to 5 4 ma the rifian corridor was sufficiently shallow to have experienced significant restriction of atlantic inflow during at least four small amplitude glacioeustatic lowstands at 5 4 ma abrupt increase in the ratio of continental versus marine derived palynomorphs indicates that restriction intensified as tectonic uplift significantly outpaced gradual glacioeustatic rise despite eustatic rise at 5 32 ma the sale palynological data show that the rifian corridor experienced a second major drop in relative sea level tectonic uplift or increased sedimentation therefore termination of the messinian salinity crisis was probably associated with a breach elsewhere along the gibraltar arc

upper oligocene to lowermost miocene strata of king george island south shetland islands antarctica stratigraphy facies analysis and implications for the glacial history of the antarctic peninsula the cape melville formation cmf exposed on southeastern king george island south shetland islands provides rare evidence of extensive earliest miocene glaciation in the antarctic peninsula region the formation records the presence of regional marine based grounded ice on the continental shelf it overlies disconformably the upper oligocene destruction bay formation which consists of sandstones recording nonglacial shallow marine conditions four units have been identified within the approximately 150 m thickness of the cmf the basal unit a consists of coarse glacigenic debris flow facies interbedded with glaciomarine mudstone and sandstone the overlying unit b is mainly fine grained this succession may represent relatively ice proximal deposition followed by glacial retreat and or relative sea level rise the upper cmf units c and d was deposited in an ice distal marine environment with intermittent input of coarse glacigenic debris mainly from ice rafting thin beds of pelagic carbonate ooze within unit c indicate periods of low terrigenous sediment input and high productivity lithologically diverse glacigenic gravel clasts mainly ice rafted debris in the cmf had a wide regional source area suggesting that ice cover was widespread regionally and included calving ice margins for a small proportion of clasts the nearest known source is the mountains fringing the southern weddell sea such clasts were presumably transported north in debris laden icebergs by a strong cold weddell sea surface current a temperate glacial setting is tentatively inferred from the cmf palynological results confirm and enhance the paleoenvironmental interpretation from the sedimentology and include the first early miocene dinoflagellate cyst assemblages recorded on the antarctic peninsula this reappraisal of the glacial record from the cmf provides valuable constraints on the antarctic cryosphere and regional paleoenvironments in the mid cenozoic

pliocene paleoclimatic reconstruction using dinoflagellate cysts comparison of methods the application of quantitative and semiquantitative methods to assemblage data from dinoflagellate cysts shows potential for interpreting past environments both in terms of paleotemperature estimates and in recognizing water masses and circulation patterns estimates of winter sea surface temperature wsst were produced by using the impagidinium index ii method and by applying a winter temperature transfer function tfw estimates of summer sea surface temperature ssst were produced by using a summer temperature transfer function tfs two methods based on a temperature distribution chart act and actpo and a method based on the ratio of gonyaulacoid protoperidinioid specimens g p wsst estimates from the ii and tfw methods are in close agreement except where impagidinium species are sparse ssst estimates from tfs are more variable the value of the g p ratio for the pliocene data in this paper is limited by the apparent sparsity of protoperidinioids which results in monotonous ssst estimates of 14 26 c the act methods show two biases for the pliocene data set taxonomic substitution may force matches yielding incorrect temperature estimates and the method is highly sensitive to the end points of species distributions dinocyst assemblage data were applied to reconstruct pliocene sea surface temperatures between 3 5 2 5 ma from dsdp hole 552a and odp holes 646b and 642b which are presently located beneath cold and cool temperate waters north of 56 n our initial results suggest that at 3 0 ma wssts were a few degrees c warmer than the present and that there was a somewhat reduced north south temperature gradient for all three sites it is likely that sssts were also warmer but by an unknown perhaps large amount past oceanic circulation in the north atlantic was probably different from the present

terrane motion by strike slip faulting of forearc slivers forearc slivers bounded by a trench and an active strike slip fault occur in about 50 of modern subduction zones analysis of earthquake slip vectors indicates that modern sliver terranes typically migrate at rates of 1 2 cm yr tertiary transport of some forearc slivers by 1000 km or more is therefore expected as a consequence of normal subduction active arc parallel strike slip faulting occurs whenever interplate coupling is strong and convergence is somewhat oblique strike slip rate increases with greater convergence obliquity

a new planktic foraminifer transfer function for estimating pliocene holocene paleoceanographic conditions in the north atlantic abstract a new planktic foraminifer transfer function gsf18 related 5 north atlantic assemblages to winter and summer sea surface temperature gsf18 based on recombined and simplified core top census data preserves most environmental information and reproduces modern north atlantic conditions with approximately the same accuracy as previous transfer functions but can be more readily applied to faunal samples ranging in age from pliocene to holocene transfer function gsf18 has been applied to faunal data from deep sea drilling project hole 552a to produce a 2 5 m y sea surface temperature sst time series estimates show several periods between 2 3 and 4 6 ma during which mean sst s were both several degrees warmer and several degrees cooler than modern conditions between 2 9 and 4 0 ma sst was generally warmer than modern except for a 250 k y interval centered at 3 3 ma maximum sst with respect to modern conditions occurred after the cool interval near 3 1 ma when sst was approximately 3 6 c warmer than present conditions comparison of sst estimates with stable isotope data suggest that after peak warming at 3 1 ma there was an overall surface water cooling with concomitant build up of global ice volume culminating in northern hemisphere glaciation this event is also indicated by the presence of ice rafted detritus in 552a sediments at about 2 45 ma

the role of polybaric crystallization in genesis of andesitic magmas phase equilibria simulations of the bezymianny volcanic subseries abstract using the updated comagmat model the crystallization sequences of a bezymianny volcano basaltic andesite kamchatka russia are simulated in a wide range of thermodynamic conditions p t f o 2 as a function of h 2 o concentration comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1 5 2 wt h 2 o stored under 490 520 mpa pressure in the magma plumbing system beneath bezymianny volcano the initial magma originates as a result of the polybaric evolution of mantle derived high mg basaltic magmas of the adjacent kliuchevskoi volcano the subsequent evolution of derivative hydrous and alumina rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of 12 mpa per 1 of crystallization in the course of polybaric crystallization compositions of pyroxene bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent however hornblende bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene bearing andesite formation they require high water contents and high pressures of crystallization in this case liquid composition should deviate from the chemical trend defined by the whole rock compositions

diking young volcanism and diffuse hydrothermal activity on the southern mid atlantic ridge the lilliput field at 9 33 s detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed at 9 degrees 33 s the presence of the southernmost active hydrothermal field known so far on the mid atlantic ridge the size of the hydrothermal field which we have named lilliput is about 1000 m x 250 m it lies in a water depth of 1500 m on a ridge segment segment a3 with considerably thickened crust of 11 km four relatively small diffuse vent sites occur on a large young estimated 100 years old lava flow partly covering the flow with hydrothermal fe oxide hydroxide sediments based on homogeneous major element compositions of ca 25 lava samples this flow covers an area of at least 5 km x 0 6 km the lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds the volcanic ridge probably represents the surface expression of an underlying dike which fed the flow several drained lava pond structures were observed within the flow but only one shows hydrothermal activity the hydrothermal venting and precipitation of abundant fe oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the lilliput field lie along and almost equidistant from the eastern flank of the supposed dike although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years 2005 and 2006 no high temperature venting associated with lilliput has been found in agreement with findings at other ridges with thick crust such as reykjanes high magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow spreading segments with thick crust whereas diffuse venting is abundant interestingly the fauna at the lilliput vents largely consists of small and apparently juvenile mussels bathymodiolus sp and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity

holocene history of bedford basin nova scotia foraminifera dinoflagellate and pollen records three piston cores from bedford basin a silled coastal inlet provide the basis for a micropaleontological study of postglacial to recent sediments five faunal units four foraminiferal one arcellacean are found in core 79 11 a surface assemblage followed by deep estuarine marginal marine transition and freshwater arcellacean assemblages the other cores contain only expanded marine sequences the top of the transition zone in core 79 11 has a c 14 age of 5830 230 years bp indicating a rise in sea level of at least 20 m the sill depth during the holocene four dinoflagellate assemblage zones are found in core 79 11 the first o centrocarpum b tepikiense is typical of a silled basin with marine water of near normal salinity the second p conicoides cyst c indicates a temperate marine environment with strong fluvial influence marginal marine the third p limbatum is dominated by freshwater cysts and the fourth dinocyst sp a is dominated by subarctic brackish water cysts fo

how likely was a green antarctic peninsula during warm pliocene interglacials a critical reassessment based on new palynofloras from james ross island the question of whether pliocene climate was warm enough to support a substantial vegetation cover on antarctica is of great significance to the ongoing and controversial debate on the stability or dynamism of antarctic ice sheets during warm periods with high atmospheric greenhouse gas concentrations here we present a systematic palynological comparison of pollen and dinoflagellate cyst assemblages from early pliocene diamictites and underlying late cretaceous sediments collected from james ross island northern antarctic peninsula the diamictites are dated using a combination of 40ar 39ar and 87sr 86sr isotope ages on interbedded lavas and pristine bivalves well preserved pectinid shells and cheilostome bryozoans suggest that the palynomorph bearing sediments were probably deposited during warmer pliocene interglacials and later amalgamated into a diamictite formed by a major ice advance during cold glacial cycle the palynological analyses presented herein do not identify any in situ pollen and spores which indicate the presence of a substantial vegetation cover our study suggests a local i e james ross island provenance for most of the diamictites whilst sediments from the western coast might have been delivered by ice sheets from the antarctic peninsula whilst the acritarch leiosphaeridia might imply the presence of sea ice and near modern climate conditions during the late neogene the presence of the dinoflagellate cyst bitectatodinium tepikiense at one location suggests that sea surface temperatures might have been substantially warmer during some interglacials the absence of in situ pollen and spores in the james ross island diamictites cannot be taken as proof of non existence of vegetation however the combined palynological and geological evidence presented in this paper makes the presence of a substantial pliocene vegetation cover on james ross island unlikely and supports previous reconstructions of a permanent ice sheet on the antarctic peninsula throughout the late neogene

multivariate analysis and quantitative paleoecology of benthic foraminifera in surface and late quaternary shelf sediments northern canada abstract benthic foraminifera in surface sediments from northeastern canada and the beaufort shelf were studied to determine the quantitative relationship between recent assemblage distributions and modern water depth temperature and salinity factor analysis shows that 7 factor assemblages account for 92 of the variance between samples multiple linear regression shows that different factors are significantly related to water depth august bottom water temperature or salinity multiple correlation coefficients for depth temperature and salinity are 0 94 0 72 and 0 92 respectively labrador fjords contain arenaceous faunas dominated by eithersaccammina atlantica andreophax fusiformis or byeggerella advena regression analysis shows that thesaccammina reophax factor is most strongly related to salinity theeggerella factor is related to depth and temperature a fauna dominated bytrochammina nana andbuliminella elegantissima is correlated with warm deep water in davis strait calcareous assemblages dominated byelphidium excavatum orcassidulina reniforme are found in arctic bays and shelf areas these factor assemblages are strongly related to temperature and depth cassidulina is also related to salinity anislandiella helenae fauna on the inner labrador shelf is strongly correlated with depth and salinity anonionellina labradorica fauna in deep shelf basins is closely related to salinity the multiple regression model for the sea bed data estimates water depth august bottom water temperature and salinity within confidence limits of 67 m 1 3 c and 1 0 paleoecological transfer functions were used to quantify environmental changes recorded by the foraminifera in two piston cores on a transect across the labrador shelf paleo depth estimates obtained from the core data produce relative sea level curves which are similar in shape to theoretical curves for this region paleo salinity and temperature estimates for offshore core 12 show that the change from a postglacialnonionellina fauna to a late glaciale excavatum fauna is accompanied by a decrease of about 2 in salinity and 4 c in temperature paleoecological estimates for fjord core 111 show that the change from a modernsaccammina reophax fauna to a mid holocenei helenae fauna corresponds to a salinity increase of 3 5 and temperature increase of 1 2 c

mid pliocene deep sea bottom water temperatures based on ostracode mg ca ratios abstract we studied magnesium calcium mg ca ratios in shells of the deep sea ostracode genus krithe from a short interval in the middle pliocene between 3 29 and 2 97 ma using deep sea drilling sites in the north and south atlantic in order to estimate bottom water temperatures bwt during a period of climatic warmth results from dsdp and odp sites 552a 610a 607 658a 659a 661a and 704 for the period ma reveal both depth and latitudinal gradients of mean mg ca values shallower sites 552a 610a and 607 have higher mean mg ca ratios 10 3 9 7 10 1 mmol mol than deeper sites 661a 6 3 mmol mol and high latitude north atlantic sites 552a 610a 607 have higher mg ca ratios than low latitude 658a 9 8 mmol mol 659a 7 7 mmol mol 661a 6 3 mmol mol and southern ocean 704 8 0 mmol mol sites converting mg ca ratios into estimated temperatures using the calibration of dwyer et al 1995 dwyer g s cronin t m baker p a raymo m e buzas j s correge t 1995 north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles science 270 1347 1351 suggests that mean middle pliocene bottom water temperatures at the study sites in the deep atlantic were about the same as modern temperatures however brief pulses of elevated bwt occurred several times between 3 29 and 2 97 ma in both the north and south atlantic ocean suggesting short term changes in deep ocean circulation

compositional variation and 226ra 230th model ages of axial lavas from the southern mid atlantic ridge 8 48 s we present geological observations and geochemical data for the youngest volcanic features on the slow spreading mid atlantic ridge at 8 48 s that shows seismic evidence for a thickened crust and excess magma formation young lava flows with high sonar reflectivity cover about 14 km2 in the axial rift and were probably erupted from two axial volcanic ridges each of about 3 km in length three different lava units occur along an about 11 km long portion of the ridge and lavas from the northern axial volcanic ridge differ from those of the southern axial volcanic ridge and surrounding lava flows basalts from the axial rift flanks and from a pillow mound within the young flows are more incompatible element depleted than those from the young volcanic field lavas from this volcanic area have 226ra 230th disequilibria model ages of 1 000 and 4 000 years whereas the older lavas from the rift flank and the pillow mound but also some of the lava field are older than 8 000 years glasses from the northern and southern ends of the southern lava unit indicate up to 100 c cooler magma temperatures than in the center and increased assimilation of hydrothermally altered material the compositional heterogeneity on a scale of 3 km suggests small magma batches rising vertically from the mantle to the surface without significant lateral flow and mixing the observations on the 8 48 s lava field support the model of low frequency eruptions from single ascending magma batches that has been developed for slow spreading ridges

the role of xenoliths and flow segregation in the genesis and evolution of the paleoproterozoic itapema granite a crustally derived magma of shoshonitic affinity from southern brazil abstract the paleoproterozoic itapema granite ig is a large granitic body that intrudes orthogneisses and amphibolites altogether representing part of the basement for neoproterozoic granitic magmatism in southern brazil it is composed of fine to medium grained hornblende biotite monzogranites to granodiorites that host abundant country rock xenoliths and irregularly distributed mafic aggregates interaction between magmatic flow and low flow velocity zones related to xenolith rich portions resulted in flow segregation and mineral fractionation as the main mechanisms that led to compositional and textural diversity expressed also in geochemical trends the geometry and distribution of flow foliation suggest that the itapema granite is a subhorizontal sheet like intrusion and that its emplacement was controlled by thrusting under upper amphibolite facies conditions many geochemical characteristics of the itapema granite are similar to those of shoshonitic granitoids however lower alkali contents lack of basic or intermediate associated rocks and intimate temporal association with high grade gneisses and migmatites suggest that it was crustally derived its origin is compatible with melting of amphibolitic orthogneisses derived from continental tholeiitic or shoshonitic sequences under high geothermal gradient conditions where temperatures reached at least 850 c

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

a method for climatic reconstruction of the mediterranean pliocene using pollen data pollen data from numerous sites around the mediterranean sea indicate that several important vegetation and climatic changes occurred during the pliocene these data are in good agreement with pollen records from northwest europe and with 18o curves from mediterranean and atlantic deep sea cores quantitative palaeoclimatic reconstructions from pliocene pollen data of the mediterranean region cannot be based on conventional modern analogue techniques as individual pliocene pollen spectra contain taxa representing temperate warm temperate and subtropical plants that do not grow together today instead we propose a new method that uses a climatic amplitude method modified to take partially into account the relative abundances of the taxa we applied this method to the pliocene garraf 1 palynological sequence from catalonia which provides a long continuous record of climatic change from 5 3 ma to the early pleistocene we estimate that annual temperatures were 1 to 5 c higher than today and the annual precipitation 400 to 1000 mm higher than today prior to the beginning of the late cenozoic glacial interglacial cycles in contrast temperature and precipitation both fell sharply during the glacial phases of the earliest glacial interglacial cycles

lead isotopic fingerprinting of tectono stratigraphic terranes east central alaska common lead isotopic compositions have been determined on feldspars from meta igneous rocks from nine tectono stratigraphic terranes or subterranes in east central alaska most of the terranes have distinct and well defined signatures in terms of isotopic composition thus most can be distinguished on conventional lead isotopic diagrams lead isotopic ratios provide evidence for 1 possible sources for the igneous rocks 2 time of metamorphism 3 correlation of terrane fragments and 4 delineation of juxtaposed terranes determination of lead isotopic ratios from igneous rocks can be useful in characterizing tectono stratigraphic terranes as to mantle or crustal origin and in correlation particularly where terrane relationships are enigmatic

correlating pleistocene sequences across the new jersey margin abstract the biostratigraphic ranges of palynomorphs as well as climatostratigraphic changes recorded by both marine and terrestrial palynomorphs provide one of the few means of dating and correlating neritic environments where calcareous microfossils are rare the transport of terrestrial palynomorphs to marine environments also allows for direct land sea correlation in addition palynological assemblages provide insights into sediment transport and sea levels over 500 m of upper pleistocene sediments were recovered in odp hole 1073a on the upper new jersey slope palynomorphs in this hole record rapid progradation during the late pleistocene a prominent unconformity pp3 s forms the upper boundary of this thick progradational sequence palynological analysis from odp sites 1072 and 1073 allows this surface to be correlated from the outer shelf to the upper slope and also suggests that it was generated during a sea level lowstand probably during oxygen isotope stage 12 450 425 ka both the atlantic coastal plain and odp site 1072 on the outer new jersey shelf appear to have become erosional during this progradational phase which began around the time that the magnitude of northern hemisphere ice accumulation increased this suggests that sediments prograded across the new jersey margin as accommodation in inner neritic and coastal environments decreased in response to amplified glacioeustatic fluctuation and substantially increased sediment availability supplied by glacial erosion erosion associated with the generation of unconformity pp3 s appears to have increased accommodation on the new jersey margin allowing sediments to aggrade on the continental shelf and even to accumulate on the atlantic coastal plain during interglacial highstands the upper pleistocene architecture of the new jersey margin appears to have been controlled by glacioeustatic fluctuations and the accompanying increase in sediment supply in contrast unconformable surface pp4 s is more complex and separates upper miocene sediments deposited between 7 4 and 5 9 ma from lower pleistocene sediments deposited prior to approximately 1 4 ma in hole 1072a whereas in hole 1073a pp4 s is in sediments of early pleistocene age between 1 6 and 1 3 ma these data suggest that unconformity pp4 s was generated during the early pleistocene but there is no clear palynological evidence that glacioeustasy was responsible for the generation of this unconformity

rates and processes of crystallization in on axis and off axis mor basaltic melts article i nfo residence times of olivine and plagioclase phenocrysts and xenocrysts in mid ocean ridge mor basaltic melts have been studied since the mid 1980s using geospeedometric techniques i e using diffusion of major and trace elements in order to constrain the processes of melt ascent and differentiation in this impor tant magmatic setting residence times range from a few hours to several years but potential links between these timescales and specific tectonomagmatic variables such as spreading rate and relative locations of eruption site and ridge axis have remained elusive here we demonstrate how incomplete chemical diffusion of sr within plagioclase crystals from mor basalts erupted in on and off axis settings on a number of ridges with variable spreading rates provide geospeedometric constraints we combine electron probe microanalyt ical crystal maps with detailed laser ablation profiles of almost 70 plagioclase crystals from the fast spreading east pacific rise epr at 9 10 n the intermediate spreading gorda and juan de fuca jdf ridges and the ultraslow spreading gakkel ridge to calculate crystal residence times these range from a few days to several months the scarcity of residence times exceeding years corroborates previous data indicating that most of the growth of plagioclase phenocrysts occurs within the conduit at the onset of and during eruption on the sea floor and extends this result to the fast spreading epr further statistical analysis is employed to show for the first time that residence times are systematically longer at slower spreading rates in off axis samples and samples sourced from laterally distal axial melt lenses plagioclase textures and residence time variations appear to be linked to differences in the dynamics of late stage pre eruptive magma storage and ascent in the different tectonomagmatic settings investigated in the future geospeedometric work on mor samples will be required to assess if the effect of spreading rate on crystallization timescales are globally applicable and to investigate potential variations in magma plumbing systems within individual ridge segments

taxonomic diversity and stratigraphic distribution of mediterranean pliocene bivalves abstract the mollusc disappearance extinction events throughout the mediterranean pliocene suggest the definition of four faunistic units mediterranean pliocene molluscan units mpmus the bivalve taxonomic diversity the paleobiogeographic significance and the chronological classification of each unit are analyzed in detail the boundaries of the mpmus approximate the major climatic changes of the northern hemisphere respectively at 3 0 2 5 and 2 1 ma on the whole the molluscan fauna changes 356 species of shallow water bivalves have been considered record the transition from a tropical unit mpmu1 to a biogeographic unit mpmu4 comparable with that of the recent mediterranean

neogene dinoflagellate cysts and acritarchs from the high northern latitudes and their relation to sea surface temperature organic walled dinoflagellate cysts and acritarchs are a vital tool for reconstructing past environmental change in particular in the neogene of the high northern latitudes where marine deposits are virtually barren of traditionally used calcareous microfossils yet only little is known about the paleoenvironmental value of fossil assemblages that do not have modern analogues so that reconstructions remain qualitative thus extracting their paleoecological signals still poses a major challenge in particular on pre quaternary timescales here we unravel the relationship between species relative abundance and sea surface temperature for extinct dinoflagellate cyst and acritarch taxa from the neogene of the iceland sea using palynological assemblages and organic geochemical alkenone data generated from the same set of samples the reconstructed temperatures for the miocene to pliocene sequence of ocean drilling program site 907 range from 3 to 26 c and our database consists of 68 dinoflagellate cyst and acritarch samples calibrated to alkenone data the temperature range of five extant species co occurring in the fossil assemblage agrees well with their present day distribution providing confidence to inferred temperature ranges for extinct taxa the 14 extinct dinoflagellate cyst and acritarch species clearly exhibit a temperature dependency in their occurrence throughout the analysed section the dinoflagellate cyst species batiacasphaera hirsuta labyrinthodinium truncatum cerebrocysta irregulare cordosphaeridium minimum impagidinium elongatum and operculodinium centrocarpum s s and the acritarch lavradosphaera elongatum which are confined to the miocene have highest relative abundances and restricted temperature ranges at the warm end of the reconstructed temperature spectrum the latter five species disappear when iceland sea surface temperatures permanently drop below 20 c thus indicating a distinct threshold on their occurrence in contrast species occurring in both the miocene and pliocene interval batiacasphaera micropapillata habibacysta tectata reticulatosphaera actinocoronata cymatiosphaera invaginata show a broader temperature range and a tolerance towards cooler conditions operculodinium eirikianum may have a lower limit on its occurrence at around 10 c the calibration of species relative abundance versus reconstructed sea surface temperature provides a quantitative assessment of temperature ranges for extinct miocene to pliocene species indicating that temperature is a decisive ecological factor for regional extinctions that may explain the frequently observed asynchronous highest occurrences across different ocean basins it demonstrates that qualitative assessments of ecological preferences solely based on paleo biogeographic distribution should be treated with caution in addition to enhancing knowledge on marine palynomorph paleoecology this study ultimately improves the application of palynomorphs for paleoenvironmental reconstructions in the neogene of the arctic and subarctic seas a region essential for understanding past global climate

ridge plume interactions or mantle heterogeneity near ascension island between the ascension and bode verde fracture zones an 200 km length of the axis of the mid atlantic ridge has a large positive residual depth anomaly and an axial high morphology that suggest a plume influence new wide angle seismic and gravity data from this area show that 1 the crustal thickness increases from 6 km at the propagating rift marking the northern limit of the anomalous zone to 10 km at the center of the zone and 2 the residual depth anomalies may be largely explained by airy isostatic support for these crustal thickness variations these observations combined with the lack of long wavelength gravity and residual depth anomalies associated with the proposed ascension plume suggest either the presence of a weak and intermittent plume or melting of a series of small mantle heterogeneities

elements d une climatostratigraphie du pleistocene moyen et tardif dans l est du canada par l analyse palynologique et isotopique du forage 84 030 003 mer du labrador the piston and gravity cores 84 030 003 collected in the southern labrador sea have been sampled for detailed palynological and isotopic analyses the 18o record on foraminifera neogloboquadrina pachyderma left coiling indicates a stratigraphy spanning isotopic stages 8 to 1 i e over ca 300 000 years the isotopic record allows the calculation of a mean sedimentation rate of approximately 5 cm ka the pollen and spore contents of the sediments are low the low pollen influxes generally less than 1 grain cm2 per year and the dominance of pinus suggest aeolian transport over long distances with southwest northeast to south southwest north northeast trends dinoflagellate cyst concentrations are relatively low indicating a low regional phytoplanktonic productivity the assemblages are however diversified they reflect influences from the north atlantic drift and from the labrador current the occurrence of warm temperate to tropical impagidinium species in deposits suggests an almost permanent

preferential rifting of continents a source of displaced terranes lithospheric rifting while prevalent in the continents rarely occurs in oceanic regions to explain this preferential rifting of continents we compare the total strength of different lithospheres by integrating the limits of lithospheric stress with depth comparisons of total strength indicate that continental lithosphere is weaker than oceanic lithosphere by about a factor of 3 also a thickened crust can halve the total strength of normal continental lithosphere because the weakest area acts as a stress guide any rifting close to an ocean continent boundary would prefer a continental pathway this results in the formation of small continental fragments or microplates that once accreted back to a continent during subduction are seen as displaced terranes in addition the large crustal thicknesses associated with suture zones would ironically make such areas likely locations for future rifting episodes this results in the tendency described as the wilson cycle of new oceans to open along the suture where a former ocean had closed

mid ocean ridge basalt generation along the slow spreading south mid atlantic ridge 5 11 s inferences from 238u 230th 226ra disequilibria u series disequilibria have provided important constraints on the physical processes of partial melting that produce basaltic magma beneath mid ocean ridges here we present the first 238u 230th 226ra isotope data for a suite of 83 basalts sampled between 5 s and 11 s along the south mid atlantic ridge this section of the ridge can be divided into 5 segments a0 a4 and the depths to the ridge axis span much of the global range varying from 1429 to 4514 m previous work has also demonstrated that strong trace element and radiogenic isotope heterogeneity existed in the source regions of these basalts accordingly this area provides an ideal location in which to investigate the effects of both inferred melt column length and recycled materials 226ra 230th disequilibria indicate that the majority of the basalts are less than a few millennia old such that their 230th values do not require any age correction the u th isotope data span a significant range from secular equilibrium up to 32 230th excess also similar to the global range and vary from segment to segment however the 230th 238u ratios are not negatively correlated with axial depth and the samples with the largest 230th excesses come from the deepest ridge segment a1 two sub parallel and positively sloped arrays for segments a0 2 and a3 and a4 between 230th 238u and th u ratios can be modelled in various ways as mixing between melts from peridotite and recycled mafic lithologies despite abundant evidence for source heterogeneity there is no simple correlation between 230th 238u and radiogenic isotope ratios suggesting that at least some of the trace element and radiogenic isotope variability may have been imparted to the source regions 350 kyr prior to partial melting to produce the basalts in our preferred model the two 230th 238u versus th u arrays can be explained by mixing of melts from one or more recycled mafic lithologies with melts derived from chemically heterogeneous peridotite source regions

orbital signatures in a late miocene dinoflagellate record from crete greece abstract a high resolution palynological study of the cyclically bedded faneromeni section upper tortonian lower messinian on crete greece is presented this study aims to recognize orbitally driven variations in the palynological record and to validate the age model based on the astronomical calibration of the sedimentary cycles four palynology based environmental proxies were utilised using interpretations of fossil dinoflagellate associations based on modern ecological characteristics cross spectral analysis between the proxy records and astronomical target curve the 65 n summer insolation yielded in most cases significant spectral power and coherence in the precession and or obliquity frequency bands precession controlled variations in the proxy records are related to lithology and indicate that maxima in continental input and minima in sea surface salinity coincide with sapropel formation the influence of obliquity is most clearly reflected in the index of continental versus marine palynomorphs s d the absence of a distinct time lag relative to obliquity indicates that the 41 kyr component in continental input is controlled by oscillations in regional mediterranean climate rather than by glacial cyclicity phase relations in the different astronomical frequency bands of the spectrum as compared with the mediterranean pliocene essentially confirm the validity of the miocene astronomical time scale finally a major non cyclic change in the palynological assemblage at 6 68 ma indicates enhanced salinity and decreased river discharge this shift coincides with a significant drop in sedimentation rate informally termed the early messinian sediment starvation event

a model for terrane accretion yukon tanana and slide mountain terranes northwest north america to date many north american cordilleran geologists employing the concept of suspect terranes have emphasized differences in lithology metamorphism styles of deformation and timing of these distinct tectonic units arguing that each evolved separately from its neighbors this practice of focusing on dissimilarity and nomenclature used in terrane analysis may be detrimental to our understanding of the evolutionary relationships between terranes i present a model in which the yukon tanana yt and slide mountain sm terranes which do exhibit certain lithotectonic disparities are correlated within a unifying tectonic framework in which each terrane represents a different crustal level of the same late paleozoic early mesozoic magmatic arc and west dipping subduction complex formed during plate convergence outboard of western north america the sm represents the upper crustal level of the arc and accretionary complex and the heterogeneously metamorphosed and ductilely deformed yt represents the deeper crustal level the teslin suture zone tsz the high p t portion of the yt formed the decollement between the yt sm composite terrane hanging wall and the descending north american plate tsz structural relations thus provide insight into the kinematic interaction of this composite terrane with north america prior to its late stage emplacement onto north america the present day collage of suspect terranes clearly comprises a multitude of structurally dismembered and dissimilar lithotectonic assemblages nonetheless it is possible to see order in the chaos to reassemble the pieces in a tectonically meaningful fashion the yt tsz sm association in yukon may serve as a model for tectonically coherent continental margin expansion

palaeoclimate of baffin bay from 300 000 year record of foraminifera dinoflagellates and pollen several different models1 5 have attempted to relate quaternary marine and terrestrial records of ice sheet growth in the north atlantic region the models are derived from either discontinuous terrestrial records including marine fossils in raised shorelines1 2 or from deep sea calcareous microfossils3 4 this study correlates arctic marine and terrestrial data directly by comparing 18o foraminiferal dinoflagellate and pollen records from a core taken in baffin bay the core contains an almost continuous sequence of sediments deposited during isotope stages 1 10 subarctic foraminifera and atlantic dinoflagellates in early isotope stages 2 4 6 and 8 show that subarctic water entered southern baffin bay before the glacial maxima boreal subarctic pollen suggest that atlantic air flowed into baffin bay during the ice sheet growth phases these data support models which postulate that open water in the labrador sea had an important role in supplying moisture to laurentide and greenland ice sheets

comments on the growth of accretionary wedges uplift within accretionary foreland wedges has been explained by the development of duplexes which provides a mechanism for underplating in submarine accretionary wedges with little deformation in the upper part of the wedge we interpret duplex development beneath the costa rica forearc a zone widely considered to be a prime example of nonaccretion because of the apparent absence of an imbricate fan of thrusts at the toe of the wedge large scale structural geometry of accretionary wedges is compatible with low angle trenchward dipping backstops in centrist to reverse angle backstops used commonly in models of return flow within wedges which have been invoked to explain the presence of high p t metamorphic rocks we suggest that emplacement of high p t metamorphic rocks are better explained in a collisional setting where known uplift rates are high than by flow within noncollisional accretionary wedges

paleoenvironmental changes in the norwegian sea and the northeast atlantic during the last 2 8 m y deep sea drilling project ocean drilling program sites 610 642 643 and 644 sedimentological isotopic and magnetostratigraphic investigations of ocean drilling program and deep sea drilling project sites 642 643 644 and 610 document the oceanographic and climatic evolution of the norwegian sea and the northeastern atlantic over the last 2 8 m y the results show that a major expansion of the scandinavian ice sheet to the coastal areas took place at about 2 56 ma relatively severe glacials appeared until about 2 ma the period 2 6 1 2 ma experienced in general cold surface water conditions with only a weak influx of temperate atlantic water as compared with late quaternary interglacials the norwegian sea was a sink of deep water through this period but deepwater ventilation was reduced and calcite dissolution was high compared with the holocene deep water formed by other mechanisms than it does today between 2 and 1 2 ma the glaciations in scandinavia were small a transition toward larger glacials took place during the period 1 2 to 0 6 ma corresponding to warmer interglacials and reduced calcite dissolution only during the last 0 6 m y has the oceanographic and climatic system of the norwegian sea varied in the manner described in previous studies of the late quaternary a strong thermal gradient was present between the norwegian sea and the northeastern atlantic during the matuyama 2 5 0 7 ma this is interpreted as a sign of a more zonal and less meridional climatic system over the region compared with the present situation