bottom simulating reflections and geothermal gradients across the western svalbard margin seismic reflection data reveal prominent bottom simulating reflections bsrs within the relatively young 0 78 ma sediments along the west svalbard continental margin the potential hydrate occurrence zone covers an area of c 1600 km2 the hydrate accumulation zone is bound by structural tectonic features knipovich ridge molloy transform fault vestnesa ridge and the presence of glacigenic debris lobes inhibiting hydrate formation upslope the thickness of the gas zone underneath the bsr varies laterally and reaches a maximum of c 150 ms using the bsr as an in situ temperature proxy geothermal gradients increase gradually from 70 to 115 c km 1 towards the molloy transform fault anomalies only occur in the immediate vicinity of normal faults where the bsr shoals indicating near vertical heat fluid flow within the fault zones amplitude analyses suggest that sub horizontal fluid migration also takes place along the stratigraphy as the faults are related to the northwards propagation of the knipovich ridge long term disturbance of hydrate stability appears related to incipient rifting processes

nd and sr isotopic variations in chinese eolian deposits during the past 8 ma implications for provenance change a record of changes in nd and sr isotopic composition of the eolian deposits from the central loess plateau has been determined for the past 8 ma the isotopic records of the silicate fraction of the quaternary and tertiary eolian deposits allow interpreting the interplay between the sr isotopic variations in the eolian deposits and the late cenozoic tectonic and climatic changes the results indicate that the temporal variations of nd and sr isotopes show remarkable changes around the beginning of the quaternary the lower values of the 143 nd 144 nd and the decreasing trend of the 87 sr 86 sr ratios after 2 58 ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late cenozoic uplift induced glacial grinding in the high orogenic belts in central asia in this context the substantial changes in climate and tectonics have modified dust sources significantly and the quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the tertiary red clay d 2005 elsevier b v all rights reserved

opening of the fram strait gateway a review of plate tectonic constraints abstract we have revised the regional crustal structure oceanic age distribution and conjugate margin segmentation in and around the lena trough the oceanic part of the fram strait between the norwegian greenland sea and the eurasia basin arctic ocean the lena trough started to open after eurasia greenland relative plate motions changed from right lateral shear to oblique divergence at chron 13 times 33 3 ma earliest oligocene a new bouguer gravity map supported by existing seismic data and aeromagnetic profiles has been applied to interpret the continent ocean transition and the influence of eocene shear structures on the timing of breakup and initial seafloor spreading assuming that the onset of deep water exchange depended on the formation of a narrow oceanic corridor the gateway formed during early miocene times 20 15 ma however if the initial lena trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep water circulation the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around chron 5 times 9 8 ma late miocene paleoceanographic changes at odp site 909 northern hovgard ridge are consistent with both hypotheses of gateway formation we cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the lena trough the gravity seismic and magnetic observations question the prevailing hypotheses on the yermak plateau and the morris jesup rise as eocene oceanic plateaus and the hovgard ridge as a microcontinent

a comparison of the nw european glaciated margin with other glaciated margins the present paper provides an overview of glacial related seabed features and sedimentary sequences found along the formerly glaciated nw european margin and compare it with those found on contemporary glaciated margins from both the southern and northern hemispheres a brief review of the seabed physiography and strata architecture of the margins under consideration is followed by comparison of the most relevant similarities and differences comparison of the present day bathymetric setting of both former and contemporary glaciated margins reveals no clear link to the effect of neither ice sheet or sediment load three different types of glacially eroded shelf transverse troughs have been identified while marginal troughs seem connected to similar geological settings everywhere beyond the shelf edge interaction between downslope and alongslope processes has occurred resulting amongst others in the formation of large sedimentary mounds on the rise more frequent large scale mass wasting occurs on the former glaciated nw european margin than the greenland and antarctic margins in the latest neogene to recent times a two stage evolution of the shelf prograding wedges is observed on all margins under consideration which may reflect a general development of an ice cover from an initial phase of non to restricted glaciation evolving to a mature stage of expansive glaciation

before the big chill a preliminary overview of arthropods from the middle miocene of iceland insecta crustacea abstract well preserved arthropods are reported from miocene sedimentary rocks of the skar sstrond mokollsdalur 9 8 ma and hre avatn stafholt 7 6 ma formations in iceland fossil remains of terrestrial and or freshwater animals have rarely been reported from the island before here we provide the first overview of the surprisingly rich tortonian fauna from the hrutagil locality and additional messinian aged trichopteran larval cases from the stafholt locality the hrutagil fauna includes representatives of cladocera crustacea branchiopoda and seven insect orders including several morphotypes of the orders plecoptera dermaptera hemiptera cercopoidea aphididae coleoptera hymenoptera trichoptera drusinae and diptera bibionidae previous studies on the miocene of iceland have been based principally on pollen analysis and the macrobotanical record with little attention paid to other aspects of the island s palaeontology this study provides the first comprehensive systematic description of miocene arthropods from the northern north atlantic region and offers the opportunity for a rare glimpse into the late cenozoic arthropod fauna of iceland in the context of transatlantic migration and palaeobiogeography and the onset of major global cooling events

the control of weathering processes on riverine and seawater hafnium isotope ratios hafnium 176 hf 177 hf isotope ratio variations in marine records are thought to reflect changes in continental weathering through time but the behavior of hf in rivers and during weathering is not well understood here we present 176 hf 177 hf data for rivers bedrock soils and leaching experiments for the moselle basin vosges france these data strongly suggest that the 176 hf 177 hf composition of river waters is controlled by prefer ential dissolution of accessory phases i e apatite sphene versus more resistant minerals e g k feldspar and linked to the intensity of silicate weathering estimates for the global isotopic composition of riverine hf suggest that the ocean hf budget may be dominated by river input and variations seen in marine records can be directly related to changes in silicate weathering intensity

impact of restriction of the atlantic mediterranean gateway on the mediterranean outflow water and eastern atlantic circulation during the messinian 1 messinian foraminiferal stable oxygen and carbon isotopes of the montemayor 1 core guadalquivir basin sw spain have been investigated this record is exceptional to study the mediterranean outflow water mow impact on the atlantic meridional overturning circulation amoc and global climate during the messinian because the core is near the guadalhorce corridor the last betic gateway to be closed during the early messinian our results allow dating accurately its closure at 6 18 ma constant benthic 18o values high difference between benthic and planktonic 18o and low sedimentation rates before 6 18 ma indicate the presence of a two layer water column with bottom winnowing due to an enhanced mediterranean outflow current the enhanced contribution of dense mow to the north atlantic ocean likely fostered the formation of north atlantic deep water nadw after 6 18 ma benthic 18o values parallel that of the global glacioeustatic curve the difference between benthic and planktonic 18o is low and sedimentation rates considerably increased this indicates a good vertical mixing of the water column interruption of the mow and a dominant glacioeustatic control on the isotopic signatures according to the role of mow in the modern atlantic thermohaline circulation the reduction of the mow after the closure of the guadalhorce corridor might have resulted in a decreased nadw formation rate between 6 0 and 5 5 ma weakening the amoc and promoting northern hemisphere cooling after the gibraltar strait opening the restoration of the mow and related salt export from the mediterranean could have promoted an enhanced nadw formation

marked ecological shifts during 6 2 2 4 ma revealed by a terrestrial molluscan record from the chinese red clay formation and implication for palaeoclimatic evolution abstract a new molluscan fossil record from the late miocene pliocene xifeng red clay sequence in the central loess plateau northern china reveals the process of ecological environmental changes during 6 2 2 4 ma three marked ecological shifts in mollusk assemblages occurred at about 5 4 4 5 and 3 4 ma which reflect changes in the east asian monsoon circulation a predominantly cold aridiphilous group reveals an extremely cold dry climate due to strengthened east asian winter monsoon during 6 2 5 4 ma a predominantly thermo humidiphilous group from 5 4 4 5 ma indicates a strengthening of the east asia summer monsoon circulation the marked occurrence of meso xerophilous taxa during 4 5 3 4 ma implies mild climatic conditions from 3 4 ma the cold aridiphilious species again became dominant in the fossil assemblages indicating that the winter monsoon was gradually intensifying towards the quaternary glaciations climate changes in this region were characterized by stepwise cooling from 5 4 to 2 4 ma with a 1 ma rhythmicity the cooling trend is in good agreement with the general global cooling trend during this period as documented by marine 18o records the formation and development of the northern hemisphere ice sheets during the late pliocene accelerated the climate deterioration towards the quaternary glaciations the history of environmental changes revealed by the red clay molluscan fossils is coupled in phase with the process of tibetan plateau uplift which may be the major cause and forcing mechanism of late miocene pliocene environmental changes in the loess plateau

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

late pliocene greenland glaciation controlled by a decline in atmospheric co2 levels it is thought that the northern hemisphere experienced only ephemeral glaciations from the late eocene to the early pliocene epochs about 38 to 4 million years ago and that the onset of extensive glaciations did not occur until about 3 million years ago several hypotheses have been proposed to explain this increase in northern hemisphere glaciation during the late pliocene here we use a fully coupled atmosphere ocean general circulation model and an ice sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the greenland ice sheet in particular we find that greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the late pliocene by contrast our model results suggest that climatic shifts associated with the tectonically driven closure of the panama seaway with the termination of a permanent el nino state or with tectonic uplift are not large enough to contribute significantly to the growth of the greenland ice sheet moreover we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the earth s orbit

magnetostratigraphy of the suerkuli basin indicates pliocene 3 2 ma activity of the middle altyn tagh fault northern tibetan plateau abstract the left lateral strike slip altyn tagh fault atf forming the northern boundary of the tibetan plateau accommodates parts of the overall convergence between the colliding indian and eurasian plates precise dating of the atf activity is essential for understanding possible mechanisms of tibetan plateau deformation and uplift here we report a magnetostratigraphic study of the suerkuli basin deposits recording depositional changes during the atf activity field investigations reveal a remarkable and widespread change in depositional environment in the suerkuli basin i e a transformation from low energy lacustrine deposits grayish green mud siltstone and brown mud siltstone into high energy alluviul fan deposits poorly sorted gray pebble and cobble conglomerates detailed magnetostratigraphy of the 390 m thick daban section at the southeastern margin of the suerkuli basin 38 43 09 n 90 58 84 e shows that this change in depositional facies occurred at 3 2 ma accompanied by a remarkable increase in sediment accumulation rate we attribute this depositional change to the piocene tectonic activity of the middle atf although the contribution of the pliocene global climate deterioration cannot be excluded

a 20 ma pollen record of east asian summer monsoon evolution from guyuan ningxia china abstract pollen analysis was conducted on the fluviolacustrine sediments from the east side of the liupan mountains a relatively monsoon sensitive region and provided for the first time a continuous evolutionary history of vegetation and climate in east china during the neogene the pollen record spanning the last 20 ma indicates that the vegetation and thus east asian summer monsoon evolution can be divided into three stages 20 13 14 25 ma 14 25 11 35 ma and 11 35 0 08 ma in spite of general dominance of steppe throughout the neogene during the period 20 13 14 25 ma the pollen assemblage was characterized by high abundance of artemisia and small amounts of temperate to subtropical deciduous broad leafed trees such as juglans carya quercus and betula suggesting that the east asian summer monsoon was generally strong the interval from 14 25 to 11 35 ma was marked by a significant decline in the east asian summer monsoon as indicated by artemisia gradually replaced by humulus and halophytic chenopodiaceae nitraria and ephedra also reached high values in this period since 11 35 ma ago percentages of halophytes dominated by chenopodiaceae and tamaricaceae maintained a high mean value of about 40 revealing a weak intensity of east asian summer monsoon the general weakening of the monsoon circulation during the neogene and the significant monsoon decline during the late middle miocene in particular might link with the global cooling trend probably through two mechanisms cooling and ice sheet expansion over the polar region caused an increase in meridional temperature gradients leading to the southward retreat of the monsoon circulation the global cooling may have also reduced the amount of water vapor held in the atmosphere and led to both additional cooling and further weakening of the east asian summer monsoon the cause for a short lived resumption during the period 1 0 0 8 ma is under investigation

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

late pliocene vegetation and climate of the lake baikal region southern east siberia reconstructed from palynological data abstract palynomorphs from a palaeomagnetically dated late pliocene sediment core 3 6 2 35 ma reflect highly variable climatic conditions and repeated expansion of steppe and boreo alpine vegetation mixed coniferous forests picea tsuga pinus with associated broadleaved taxa quercus corylus ulmus tilia were affected by dry and cold intervals already between 3 48 and 3 39 ma peak records of non arboreal pollen types and spores including subarctic boreo alpine selaginella selaginoides evidence advances of open vegetation which can be correlated to glacial marine oxygen isotope stages a cooling trend occurred from 3 15 ma to 2 5 ma documented by cold dry intervals and increased fluctuations of picea and pinus around 3 2 9 ma the palaeoclimate variation pattern shifted towards cold dry and warm moist oscillations cooling strengthened after 2 89 ma and severely restricted tsuga development cool and oligotrophic limnic conditions are documented by abundant gonyaulax dinoflagellate cysts in the interval 2 65 2 57 ma due to decreasing precipitation extensive areas with open steppe and rock steppe vegetation became permanently established after 2 62 ma dry conditions became a dominant environmental factor in the baikal region coeval in time with the red clay loess shift in northern china this climatic transition can be explained as a consequence of major intensification of northern hemisphere glaciation around 2 75 ma evidenced by marine records of ice rafted debris

messinian productivity changes in the northeastern atlantic and their relationship to the closure of the atlantic mediterranean gateway implications for neogene palaeoclimate and palaeoceanography the stable isotope composition of planktic and benthic foraminifera and the distribution of selected benthic foraminiferal species from a messinian record of the lower guadalquivir basin northeastern atlantic ocean show that regional productivity changes were linked to glacioeustatic fluctuations glacial periods were characterized by poorly ventilated bottom waters as a result of weak atlantic meridional overturning circulation amoc and by phases of high productivity related to intensified upwelling in contrast well ventilated bottom waters owing to strong amoc the presence of degraded organic matter in the upper slope and high input of degraded terrestrial organic matter derived from fluvial discharge to the outer shelf were recorded during interglacial periods before closure of the adjacent guadalhorce corridor at 6 18 ma which was the final active betic atlantic mediterranean gateway the study area was alternately influenced by well ventilated mediterranean outflow water mow and poorly ventilated atlantic upwelled water auw following closure of the corridor cessation of the mow reduced the amoc and promoted glacial conditions in the northern hemisphere resulting in the establishment of local upwelling cells

late pliocene sedimentation in lake baikal implications for climatic and tectonic change in se siberia abstract within the framework of the baikal drilling project bdp a 192 m long sediment core bdp 96 1 was recovered from the academician ridge a submerged topographic high between the north and central basins of lake baikal sedimentological clay mineralogical and geochemical investigations were carried out on the core interval between 90 and 124 m depth corresponding to ca 2 4 3 4 ma the aim was to reconstruct the climatic and tectonic history of the continental region during the intensification of northern hemisphere glaciation in late pliocene time a major climate change occurred in the lake baikal area at about 2 65 ma enhanced physical weathering in the catchment mirrored in the illite to smectite ratio and temporarily reduced bioproduction in the lake reflected by the diatom abundance evidence a change towards a colder and more arid climate probably associated with an intensification of the siberian high in addition the coincident onset of distinct fluctuations in these parameters and in the zr al ratio suggests the beginning of the late cenozoic high amplitude climate cycles at about 2 65 ma fluctuations in the zr al ratio are traced back to changes in the aeolian input with high values in warmer more humid phases due to a weaker siberian high assuming that the sand content in the sediment reflects tectonic pulses the lake baikal area was tectonically active during the entire investigated period but in particular around 2 65 ma tectonic movements have likely led to a gradual catchment change since about 3 15 ma from the western towards the eastern lake surroundings as indicated in the geochemistry and clay mineralogy of the sediments the strong coincidence between tectonic and climatic changes in the baikal area hints at the himalayan uplift being one of the triggers for the northern hemisphere glaciation

use of multiproxy records on the agulhas ridge southern ocean ocean drilling project leg 177 site 1090 to investigate sub antarctic hydrography from the oligocene to the early miocene 1 ocean drilling program odp site 1090 on the agulhas ridge in the south atlantic sector of the southern ocean is ideally located to capture changes in southern ocean circulation patterns using samples taken from cored sediments we construct multiproxy records of productivity biogenic barium baex opal and caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox conditions u and mn enrichments to investigate hydrographic conditions associated with climatic shifts from the oligocene through the early miocene orbitally induced cyclicity in u and mn enrichments 100 kyr suggests shifts in deepwater characteristics however caco3 dissolution coincident with low u and mn enrichments does not indicate low oxygen corrosive waters similar to modern conditions these observations indicate that a well developed modern type antarctic circumpolar current acc did not yet exist over the period from 30 to 20 ma with two potential consequences the southern ocean was not functioning as a silica trap permitting a broader distribution of silica that may have facilitated organic carbon burial in the ocean in general and the lack of a deeply mixing acc may have facilitated organic carbon burial in the southern ocean both the relative high opal mars coincident with low caco3 mars and absolute high pr mars burial of organic carbon suggest a powerful mechanism for pco2 drawdown

submarine glacigenic debris flows deep sea channels and past ice stream behaviour of the east greenland continental margin abstract former glacigenic debris flow gdf and deep sea channel build up is shown from side scan sonar seismic and sediment core data of the passive continental margin of the greenland sea the well developed deep sea channel systems cross gdf systems and point towards sediment laden meltwater production there is no indication for large scale submarine sliding such as observed on several locations on the norwegian margin where deep sea channels are far less frequent or do not exist whereas seabed erosion gdf stacking and trough mouth fans dominate the observed pattern on the east greenland margin reflects a contrast to the norwegian margin in paleo ice stream extent dynamics and type of sediment delivery a conceptual model for ice sheet behaviour on the continental margin of the greenland sea has been developed based on the characteristics distribution and morphology of gdfs and deep sea channels in four periods at ca 2 5 ma 1 5 ma 0 2 ma and 25 ka we argue that the erosional capabilities of ice streams on the ne greenland margin indicated by aggradation versus progradation were less then those of the fast flowing ice streams of the norwegian margin and that the ice streams in cross shelf troughs remained probably distal from the shelf break during the late weichselian

late neogene evolution of the east asian monsoon revealed by terrestrial mollusk record in western chinese loess plateau from winter to summer dominated sub regime article i nfo more and more evidence indicates that the onset of the east asian ea monsoon can be traced back to the oligocene miocene boundary at about 23 ma however the process of its evolution is still less well known until now here we investigate its late neogene evolution by analyzing a terrestrial mollusk sequence from the chinese loess plateau clp covering the period between 7 1 and 3 5 ma considering the modern ecological requirements of these organisms we were able to define two groups of cold aridiphilous ca and thermo humidiphilous th species representing the ea winter and summer monsoon variations respectively as previously defined in the quaternary glacial interglacial cycles variations in these two groups indicate two different monsoon dominated periods during 7 1 3 5 ma first between 7 1 and 5 5 ma the ea winter monsoon with a 100 kyr periodicity was dominant second between 5 1 and 4 ma the ea summer monsoon dominated with a 41 kyr periodicity furthermore our mollusk record yields valuable evidence for a late miocene pliocene transition of about 400 kyr from winter monsoon dominated towards summer monsoon dominated associated with a periodicity transition from weak 100 kyr to 41 kyr the strengthened winter monsoon interval with a 100 kyr periodicity is coeval with orbital scale global ice volume changes in conjunction with the uplift of the tibetan plateau which probably reinforced the winter monsoon sub regime conversely closures of the panama and indonesian seaways associated with changes in obliquity between 5 1 and 4 ma are probably major forcing factors for the observed dominant summer monsoon with 41 kyr frequency favoring heat and moisture transports between low and high latitudes to allow th mollusks to grow and develop in the clp

3d seismic analysis of the west shetland drift system implications for late neogene palaeoceanography of the ne atlantic abstract detailed seismic stratigraphic analysis of the west shetland drift located on the shetland margin of the faeroe shetland channel has been undertaken using commercial 3d seismic data emphasis was placed on the interpretation of a significant plastered contourite drift body the west shetland drift slope section with the aim of reconstructing the palaeoceanographic regime of the west shetland slope during the past 5 ma although limited in areal extent the west shetland drift slope section provides a key record of the depositional environment and bottom current activity on the west shetland slope during the late neogene the drift body was divided into three seismic stratigraphic units and depositional processes responsible for each unit were interpreted resulting in proposal of an evolutionary model in which a mixed downslope alongslope depositional system was succeeded by alongslope current derived contourite drift deposition during the early pliocene to mid pleistocene during this time sw flowing alongslope currents impinged upon the west shetland slope between the basin floor and a mid to upper slope position the final stage of deposition consisted of slope wedge progradation associated with mid to late pleistocene glaciation contourite deposition on the west shetland slope was punctuated by periods of glaciation activity during which alongslope current activity appears to have been disrupted suggesting a link between alongslope current activity and glaciation detailed mapping of key smaller scale features including a spectacular bottom current sediment wave field and iceberg ploughmarks both of which were identified for the first time during this study was instrumental in constraining the palaeocurrent regime and would not have been possible without the high spatial resolution of the 3d seismic data this study therefore highlights the efficacy of 3d seismic data as a tool for large scale spatial and temporal analysis of contourite drifts palaeoceanographic research

opal sedimentation shifts in the world ocean over the last 15 myr biogenic silica opal accumulation records were used to trace mechanisms consequence and geographic pattern of shifts in the main locus of opal deposition of the world ocean over the last 15 myr over this time interval the main opal sink seems to have moved from the north atlantic to the pacific equatorial pacific eastern equatorial pacific eastern boundary current upwelling systems california namibia peru and finally to the southern ocean the interplay between opal deposition and a series of climatic tectonic oceanographic and biologic events has been analyzed and discussed these events include the cenozoic global cooling trend intensified glaciation in antarctica late miocene early pliocene biogenic bloom development of northern hemisphere glaciation nhg closing of the panama seaway transition of the climate system from a monopolarto a bipolar glaciated world mid pleistocene revolution mpr nutrient availability evolution of diatoms and c4 plants and changes in continental weathering rates while the observed shifts are mostly traceable to oceanic reorganizations and global climatic evolution conditions favorable to opal deposition involve the above mentioned complex mix of processes for this reason the interpretation of opal deposition records might not always be straightforward we however believe that it can still provide clear indications of large scale oceanographic reorganizations in the geological past d 2004 elsevier b v all rights reserved

late cretaceous to early quaternary organic sedimentation in the eastern equatorial atlantic abstract reconstructing the long term evolution of organic sedimentation in the eastern equatorial atlantic odp leg 159 provides information about the history of the climate ocean system sediment accumulation and deposition of hydrocarbon prone rocks the recovery of a continuous 1200 m long sequence at odp site 959 covering sediments from albian to the present day about 120 ma makes this position a key location to study these aspects in a tropical oceanic setting new high resolution carbon and pyrolysis records identify three main periods of enhanced organic carbon accumulation in the eastern tropical atlantic i e the late cretaceous the eocene oligocene and the pliocene pleistocene formation of upper cretaceous black shales off west africa was closely related to the tectono sedimentary evolution of the semi isolated deep ivorian basin north of the cote d ivoire ghana transform margin their deposition was confined to certain intervals of the last two cretaceous anoxic events the early turonian oae2 and the coniacian santonian oae3 organic geochemical characteristics of laminated coniacian santonian shales reveal peak organic carbon concentrations of up to 17 and kerogen type i ii organic matter which qualify them as excellent hydrocarbon source rocks similar to those reported from other marginal and deep sea basins a middle to late eocene high productivity period occurred off equatorial west africa porcellanites deposited during that interval show enhanced total organic carbon toc accumulation and a good hydrocarbon potential associated with oil prone kerogen deposition of these toc rich beds was likely related to a reversal in the deep water circulation in the adjacent sierra leone basin accordingly outflow of old deep waters of southern ocean origin from the sierra leone basin into the northern gulf of guinea favored upwelling of nutrient enriched waters and simultaneously enhanced the preservation potential of sedimentary organic matter along the west african continental margin a pronounced cyclicity in the carbon record of oligocene lower miocene diatomite chalk interbeds indicates orbital forcing of paleoceanographic conditions in the eastern equatorial atlantic since the oligocene miocene transition a similar control may date back to the early oligocene but has to be confirmed by further studies latest miocene early pliocene organic carbon deposition was closely linked to the evolution of the african trade winds continental upwelling in the eastern equatorial atlantic ocean chemistry and eustatic sea level fluctuations reduction in carbonate carbon preservation associated with enhanced carbon dissolution is recorded in the uppermost miocene 5 82 5 2 ma section and suggests that the latest miocene carbon record of site 959 documents the influence of corrosive deep waters which formed in response to the messinian salinity crisis furthermore sea level related displacement of higher productive areas towards the west african shelf edge is indicated at 5 65 5 6 5 55 5 2 4 8 ma in view of humid conditions in tropical africa and a strong west african monsoonal system around the miocene pliocene transition the onset of pronounced toc cycles at about 5 6 ma marks the first establishment of upwelling cycles in the northern gulf of guinea an amplification in organic carbon deposition at 3 3 ma and 2 45 ma links organic sedimentation in the tropical eastern equatorial atlantic to the main steps of northern hemisphere glaciation and testifies to the late pliocene transition from humid to arid conditions in central and western african climate aridification of central africa around 2 8 ma is not clearly recorded at site 959 however decreased and highly fluctuating carbonate carbon concentrations are observed from 2 85 ma on that may relate to enhanced terrigenous eolian dilution from africa

late miocene early pliocene climatic evolution of the granada basin southern spain deduced from the paleoecology of the micromammal associations this paper analyses the relationship between the evolution of the late miocene and early pliocene rodent and insectivore assemblages from the granada basin southern spain and climate changes these climatic changes in terms of humidity and temperature fluctuations are inferred from variations of the relative abundances of taxons with definite ecological preferences there is a general tendency towards a temperature increase from the latest tortonian middle turolian to the messinian late turolian and towards a decrease from the mio pliocene boundary latest turolian earliest ruscinian to the end of the zanclean late ruscinian dry conditions predominate in the latest tortonian middle turolian at the beginning of the messinian late turolian there was a significant increase in humidity followed by an aridification throughout the end of the messinian and zanclean late turolian and ruscinian these climatic variations are in accordance with the sedimentary evolution of the basin and agree with the climatic interpretations inferred from the shallow marine carbonate sediments temperate tropical deposited in the marine basins of southeastern spain during the studied time interval

late weichselian local ice dome configuration and chronology in northwestern svalbard early thinning late retreat the chronology and configuration of the svalbard barents sea ice sheet sbsis during the late weichselian lw are based on few and geographically scattered data thus the timing and configuration of the sbsis has been a subject of extensive debate we present provenance data of erratic boulders and cosmogenic 10be ages of bedrock and boulders from northwest spitsbergen nws svalbard to determine the thickness configuration and chronology during the lw we sampled bedrock and boulders of mountain summits and summit slopes along with erratic boulders from coastal locations around nws we suggest that a local ice dome over central nws during lw drained radially in all directions provenance data from erratic boulders from northern coastal lowland reinsdyrflya suggest northeastward ice flow through liefdefjorden 10be ages of high elevation erratic boulders in central nws 687 836 m above sea level ranging from 18 3 1 3 ka to 21 7 1 4 ka indicate that the centre of a local ice dome was at least 300 m thicker than at present 10be ages of all high elevation erratics 400 m above sea level central and coastal locations indicate the onset of ice dome thinning at 25 20 ka 10be ages from erratic boulders on reinsdyrflya ranging from 11 1 0 8 ka to 21 4 1 7 ka indicate an ice cover over the entire reinsdyrflya during lw and a complete deglaciation prior to the holocene but apparently later than the thinning in the mountains lack of moraine deposits but the preservation of beach terraces suggest that the ice covering this peninsula possibly was cold based and that reinsdyrflya was part of an inter ice stream area covered by slow flowing ice as opposed to the adjacent fjord which possibly was filled by a fast flowing ice stream despite the early thinning of the ice sheet 25 20 ka we find a later timing of deglaciation of the fjords and the distal lowlands several bedrock samples 10be from vertical transects in the central mountains of nws pre date the lw and suggest either ice free or pervasive cold based ice conditions our reconstruction is aligned with the previously suggested hypothesis that a complex multi dome ice sheet configuration occupied svalbard and the barents sea during lw with numerous drainage basins feeding fast ice streams separated by slow flowing possibly cold based inter ice stream areas

post collisional sediment budget history of the alps tectonic versus climatic control based on the sediment budget of the eastern swiss and western alps since the oligocene the regional tectonic evolution has been identified as the dominant factor it is superimposed on the influence of both regional and global climate change and global sea level change during late pliocene and pleistocene times climate became the dominant factor because of cyclic glaciations the early post collisional history of the alps is characterized by a doubling of sediment discharge rates around the rupelian chattian boundary this increase is attributed to isostatic re adjustment either after large scale thermal reorganization of the lithosphere related to slab break off or to crustal thickening as continental crust became subducted from middle oligocene to late miocene times the overall trend of sediment discharge rates in the entire alps was modified only during relatively short lived phases these are characterized by an increase in aquitanian ca 23 21 ma and late burdigalian times ca 18 16 4 ma and a decrease in early to middle burdigalian 21 19 ma and langhian to serravalian times 16 4 12 ma an important still ongoing period of uplift reflected by rapidly increasing sediment discharge rates started in latest miocene times in the swiss and western alps and affected the eastern alps some 2 million years later the reason for this uplift is not clear but deep seated lithospheric processes appear to be likely

global miocene tectonics and the modern world abstract an amazing congruence of seemingly unrelated diverse global events began in the middle and upper miocene and established our modern world two global orogenic belts were active mostly in the middle and upper miocene while backarc basins formed along the eastern margin of asia coincident with these events global temperatures cooled in both the ocean and atmosphere desertification occurred from central asia into and across most of northern africa and also in australia and in southern south america coincident with the expansion of the antarctic ice cap at 14 ma there was initial widespread deep sea erosion and changes in patterns of deep sea sedimentation muddy pelagic sedimentation increased six fold in the north and central atlantic and pacific oceans and global changes in circulation lead to more diatomites in the pacific and fewer in the atlantic by the end of the miocene most of the mediterranean sea had evaporated broadly coincident with these events many old large river systems were destroyed and new ones formed as much of the world s landscape changed collectively these global on shore tectonic and ocean atmospheric events provide the foundation for our modern world a mixture of new and rejuvenated orogenic belts and their far field effects distant epiorogenic uplift rain shadow deserts large alluvial aprons and distant deltas as inherited gondwanan landscapes persisted remote from plate boundaries thus at the end of the miocene much of the world s landscape except for that changed by pleistocene continental glaciation would be recognizable to us today we argue that all of these events had the same ultimate common cause an internal earth engine that drove plate motions in two broad ways first the opening and closing of seven key gateways to deep water oceanic currents radically altered global heat transfer and changed a lingering greenhouse to an icehouse world secondly these events were in part coincident with renewed heat flow in the african and pacific superplumes that energized global plate motions in the middle and upper miocene we hope this global synthesis will stimulate more research on the many global events of the miocene to understand better both our modern world and earlier global orogenies

depositional environment and source rock potential of miocene strata from the central fram strait introduction of a new computing tool for simulating organic facies variations abstract organic rich sediments were recognized in early miocene strata from the norwegian greenland sea during odp leg 151 three organic geochemical subunits were distinguished in hole 909c using detailed organic geochemical and microscopic analyses toc up to 3 wt hi up to 200 mg hc g toc and 13corg values 24 26 indicate the predominance of terrestrial type iii organic matter in subunit 3 18 16 2 ma biomarker and vitrinite reflectance values r0 0 5 point to rather fresh immature terrestrial organic matter supplied by river discharge from adjacent vegetated coastal areas although the sediments of subunit 3 have a fair to good source rock potential they are insufficiently mature to generate significant amounts of oil or gas to test if the moderate generation potential and source rock quality of subunit 3 are applicable to the entire area the computer software of mod was applied several modelling runs testing the most probable depositional scenarios result even under conservative assumptions in the formation of good to excellent source rocks towards the basin margins

glacial interglacial variability in lower north atlantic deep water inference from silt grain size analysis and carbonate preservation in the western equatorial atlantic abstract grain size records of the terrigenous and calcareous silt fraction preservation of planktic foraminifera and benthic foraminiferal stable isotope data 13c 18o values of c wuellerstorfi at odp site 927 on the ceara rise 5 27 7 n 44 28 8 w are used to reconstruct variations in the history of bottom current strength ventilation and carbonate corrosiveness of deep waters during the time interval from 0 8 to 0 3 ma glacial periods are characterized by generally smaller mean sizes of the terrigenous sortable silt fraction mean ss lower 13c values and poorer preservation of planktic foraminifera compared to interglacials this indicates lower bottom current speeds larger nutrient contents and more corrosive deep water by contrast larger mean ss sizes higher 13c values and well preserved planktic foraminifera indicate strong circulation and a well ventilated deep water mass during interglacials the observed changes are most likely related to the weakening and strengthening of circulation of lower north atlantic deep water lnadw cross spectral analysis between the mean ss and benthic 18o records reveals that minima in mean ss occur about 7 6 k y after the maximum in ice volume this indicates a considerable lag time between ice shield induced changes in lnadw production and subsequent changes in the velocity of lnadw flow in the western equatorial atlantic striking changes in bottom current speed occur regularly during glacial to interglacial transitions extremely fine mean ss minima point to an almost complete shutdown of bottom current vigor in response to a cessation of lnadw production caused by an enhanced melt water release during the initial phases of deglaciation however each of the fine minima extremes is followed by a rapid shift to very high mean ss values that indicate strong bottom currents and hence vigorous lnadw flow during the early interglacials after the onset of glacial stage 12 generally poorer carbonate preservation and higher variability is registered this coincides with a global decrease in carbonate preservation during the mid brunhes mid brunhes dissolution event detailed grain size analysis of the calcareous fine fraction

estimation of seismic source functions of some explosions in the u s s r using ar method abstract autoregressive ar modelling of seismograms is used to estimate the high frequency slope of the source spectral variations of synthetic seismograms and of seismograms recorded at gauribidanur seismometer array gba india from explosions in the u s s r region analysis of synthetic seismograms shows that the ar method is able to reproduce the expected spectral variation for different t values and yields the analysis of explosions in central u s s r on 7 july 1980 4 april 1980 and 1 november 1980 shows a high frequency spectral variation 2 similar to the predicted variation by von seggern and blandford while eastern kazakh explosions on 29 june 1980 and 18 august 1980 show a 4 spectral falloff in the high frequency region as proposed in the source function model of haskell the recovered spectrum of western kazakh event on 14 july 1980 shows a 3 variation in the high frequency which could have occurred due to helmberger s type of source model or due to interference between p and pp

mountain building and the initiation of the greenland ice sheet the effects of a new hypothesis about mountain building in greenland on ice sheet initiation are investigated using an ice sheet model in combination with a climate model according to this hypothe

late cenozoic history of the polar north atlantic results from ocean drilling abstract dsdp odp drilling in the northern north atlantic reveals that so far the onset of northern hemisphere cooling deduced from the occurrence of ice rafted debris ird in deep sea sediments can be traced back to the middle miocene the greenland ice sheet has probably the longest history on the northern hemisphere leg 151 site 909 fram strait recovered a unique continuous sediment record dating from early middle miocene the composition of the coarse fraction indicates that the oldest ird pulses are documented around 14 ma in the fram strait site 909 and around 12 6 ma on the voring plateau leg 104 site 642 in the norwegian greenland sea fram strait site 909 indicates a further stepwise increase of northern hemisphere cooling by serveral ird pulses during late miocene between 10 8 and 8 6 ma around 7 2 6 8 and 6 3 ma which ultimately led to a drastic intensification of northern hemisphere glaciation during plio pleistocene the deep sea sediment records show that plio pleistocene strengthening of ird pulses have been observed since approximately 4 0 ma in the westernmost norwegian greenland sea and labrador sea by contrast strengthening of ird pulses are observed at approximately 3 2 2 7 ma on the eastern side of the norwegian greenland sea including the barents sea margin sediment composition and physical properties of the drilled mostly terrigenous sections reveal that orbital parameters have controlled major aspects of shallow and deep water environments with frequency domains related to 41 ka periods of obliquity dominant in the pre glacial miocene pliocene and early quaternary and to 100 ka periods of eccentricity dominant during the past 600 000 700 000 years the stratigraphy of ice rafted material reveals a frequently and rapidly changing history of the dynamics of various segments in ice sheets around the norwegian greenland sea it is particularly evident from the composition of the ice rafted material that the eurasian ice sheets delivered ird to the eastern part of the norwegian greenland sea whereas greenland source areas are represented in the drill sites of the east greenland continental margin and in the labrador sea the stratigraphic sequences on the yermak plateau suggest that the svalbard ice sheet may have extended far to the north prior to oxygen isope stage 16 but not since then invasions of temperate atlantic waters during interglacials can be observed as short lived and rather irregular events it never reached the area off eastern greenland except during the pliocene interval when tundra floras were able to develop on north eastern greenland and planktonic foraminifers suggesting the presence of temperate water masses in the fram strait as been documented in the drill sites from the yermak plateau

the andoya slide and the andoya canyon north eastern norwegian greenland sea based on gloria side scan sonar imagery echo sounder records 3 5 khz profiles multichannel seismics and gravity cores the andoya slide and andoya canyon north eastern norwegian greenland sea were mapped and interpreted the andoya slide covers an area of about 9700 km2 of which the slide scar area comprise ca 3600 km2 the slide has a total run out distance of about 190 km slope failure is inferred to have occurred during the holocene because the slide scar has prominent relief on the present sea floor the area of sediment removal is characterised by an irregular relief were relatively consolidated sediments are exposed at the sea floor little or no unconsolidated sediments overlies the slide deposits earthquake activity is inferred to have triggered the slide a holocene age of the andoya slide implies that three giant slides the storegga traenadjupet and andoya slides have occurred along the continental slope of norway during the last 10 000 years a large canyon the andoya canyon is located immediately south of the andoya slide on the upper slope the canyon has been incised about 1000 m in the bedrock and the maximum width at the bottom and between the canyon shoulders is 2 and 12 km respectively the andoya canyon represents the upper part of the lofoten basin channel based on analogy with other deep sea canyon channel systems the andoya canyon lofoten basin channel is possibly of pre quaternary age holocene sediments recovered from within the canyon and draping the flanking channel deposits indicate that the andoya canyon is not presently active and has probably not been active during the holocene during the holocene the canyon acted as a trap for sediments settling from the winnowing norwegian current

late cenozoic base level variations of the caspian sea a review of its history and proposed driving mechanisms abstract the caspian sea is characterized by significant variations in its base level during the late cenozoic and provides an important repository for long term records of both regional climate and tectonics due to its position within the interior of the eurasian continent and at the northern margin of the ongoing arabia eurasia collision zone the caspian also serves as an important moisture source for eastern eurasia including the northern tibetan plateau and thus the history of caspian base level variations represents an important and poorly understood constraint on paleoclimate reconstructions throughout eurasia prior work in the caspian region has largely focused on developing biostratigraphic age divisions and investigating the history of connection between the caspian black and mediterranean seas as well as the global ocean recent geochronologic work in the caspian and related basins has questioned previous correlations of hydrologic events in these different basins as a result prior estimates of the chronology and magnitude of caspian sea level variations may be incorrect here we synthesize previous work to develop a new caspian base level curve starting at the beginning of the meotian regional stage 7 ma we also present a new synthesis of potential driving mechanisms for the large variations in caspian base level and speculate on a possible cause for the enigmatic akchagyl transgression this synthesis highlights the dynamic range of caspian sea level which varied from 200 m above to in excess of 1000 m below its current level during the late cenozoic and provides a basis for future work investigating the tectonic and climatic drivers behind variations in caspian base level

the evolution of pco2 ice volume and climate during the middle miocene abstract the middle miocene climatic optimum 17 15 ma mco is a period of global warmth and relatively high co2 and is thought to be associated with a significant retreat of the antarctic ice sheet ais we present here a new planktic foraminiferal 11b record from 16 6 to 11 8 ma from two deep ocean sites currently in equilibrium with the atmosphere with respect to co2 these new data demonstrate that the evolution of global climate during the middle miocene as reflected by changes in the cyrosphere was well correlated to variations in the concentration of atmospheric co2 what is more within our sampling resolution 1 sample per 300 kyr there is no evidence of hysteresis in the response of ice volume to co2 forcing during the middle miocene contrary to what is understood about the antarctic ice sheet from ice sheet modelling studies in agreement with previous data we show that absolute levels of co2 during the mco were relatively modest 350 400 ppm and levels either side of the mco are similar or lower than the pre industrial 200 260 ppm these new data imply the presence of either a very dynamic ais at relatively low co2 during the middle miocene or the advance and retreat of significant northern hemisphere ice recent drilling on the antarctic margin and shore based studies indicate significant retreat and advance beyond the modern limits of the ais did occur during the middle miocene but the complete loss of the ais was unlikely consequently it seems that ice volume and climate variations during the middle miocene probably involved a more dynamic ais than the modern but also some component of land based ice in the northern hemisphere

hierarchical subdivision of the cenozoic era a venerable solution and a critique of current proposals abstract if tertiary and quaternary are to be formally defined and ranked then only one topology and two ranking options for the major subdivisions of the cenozoic era are consistent with the principles of hierarchical classification these are 1 for the tertiary and quaternary to be ranked as suberas with the paleogene and neogene ranked as periods of the tertiary or 2 for the tertiary and quaternary to be ranked as periods with the paleogene and neogene ranked as subperiods of the tertiary the first option would leave the period rank empty for quaternary time however so the second option is preferred here in neither case is an extension of the neogene to the present permitted if desired however early cenozoic and late cenozoic could be defined as formal unranked chrons with the latter term providing an unambiguous expression for the same concept as the extended neogene attempts to justify an extended neogene by reference to a statement arising from the 1948 international geological congress fail because they are based on a misinterpretation of that statement likewise an appeal to the alleged original meaning of the neogene fails because it is factually superficial and would also have unacceptable consequences if applied as a general principle to the rest of the time scale four arguments against a ranked tertiary and or quaternary involve the status of these names as parts of an obsolete classification the disparity in their durations an analogy between them and the unranked precambrian and their supposed ambiguity these arguments are readily refuted arguments in favor of a ranked tertiary and quaternary include the continuing widespread use of these names their practical relevance for geologic maps and their role in honoring the pioneers of stratigraphy a recent recommendation by the international commission on stratigraphy ics would decouple the beginning of the quaternary from the beginning of the pleistocene have the neogene and pliocene overlap the tertiary quaternary boundary and have the gelasian age belong to both the pliocene and the quaternary these results violate the existing guidelines of the ics this same proposal would also regard the quaternary as a subera within the neogene period the latter being extended to the present however this arrangement violates the most fundamental rule of hierarchical classification in that a unit of superior rank would be included entirely within a unit of inferior rank given these problems the international union of geological sciences iugs must reject the ics recommendation an improved version of the ics proposal with the quaternary ranked as a period and the paleogene and extended neogene ranked as suberas would still prohibit the tertiary from being ranked and would either violate simpson s rule or else require a new name for the traditional concept of the neogene because the classification of the cenozoic advocated here is strictly hierarchical violates none of the existing guidelines of the ics obeys simpson s rule requires no new names allows the tertiary quaternary paleogene and neogene to be formally ranked and has been in general use for more than a century it is to be preferred only two current options for defining the quaternary and pleistocene are valid namely to leave the beginnings of these units where they are now vrica gssp at 1 8 ma or to move both to the piacenzian gelasian boundary monte san nicola gssp at 2 6 ma the latter option is not prohibited by lyell s types of the older pliocene nor after 2008 by the existing guidelines of the ics but if enacted could jeopardize the stability of the rest of the standard global time scale

variations of north atlantic inflow to the central arctic ocean over the last 14 million years inferred from hafnium and neodymium isotopes the warm and saline north atlantic inflow to the arctic ocean is a major component of high northern latitude circulation and the main mechanism of deep water renewal in the arctic ocean knowledge of its past variability is critical for understanding the high latitude feedback mechanisms of the climate system here we present the first combined seawater hf and nd isotope compositions of past arctic intermediate water extracted from the authigenic fe mn oxyhydroxide fraction of two sediment cores recovered near the north pole to reconstruct changes in contributions from glacial brines of the eurasian shelf and past inflow of atlantic waters the hf and nd isotopic compositions obtained from leachates of the authigenic fraction show closely coupled and environmentally controlled variations over the past 14 million years an observed offset of these data from seawater ehf and end compositions from other ocean basins seawater array is interpreted as the result of continuously prevailing glacial weathering conditions on the high latitude eurasian continent in the late quaternary large amplitude hf and nd isotopic variations of arctic intermediate water aiw was characterized by more radiogenic isotope signatures generally prevailing under glacial conditions and less radiogenic values during interglacial periods on the basis of the close coupling between nd and hf isotopes we suggest that the evolution of hf isotope compositions of central arctic aiw has primarily been controlled by changes in ocean circulation and provenance of weathering inputs rather than changes in weathering regime

late miocene early pleistocene climate change in the mid latitude westerlies and their influence on asian monsoon as constrained by the k al ratio record from drill core ls2 in the tarim basin abstract in order to study the evolution of westerly mid latitude winds we analyzed k al records from lacustrine and fluvial sediments of drill core ls2 in the eastern tarim basin for which the sedimentary record is continuous and well dated back to the late miocene by magnetostratigraphy the k al ratio obtained from drill core ls2 may be a proxy index for precipitation amounts in the tarim basin k al ratios from drill core ls2 indicate that precipitation increased gradually in the tarim basin from 7 24 6 34 ma with a brief but rapid decrease from 6 708 6 702 ma climate became increasingly arid beginning at 5 68 ma we attribute these paleoclimatic changes in the tarim basin in western china to 1 global phenomena such as the expansion of global ice volume and 2 regional forcings such as the growth of the tibetan plateau and the retreat of the paratethys ocean expansion of global ice volume and uplift of the tibetan plateau migrated westerlies southward which results in the transport of moisture to the south and east of the plateau and enhanced the aridification of western china the retreat of the paratethys ocean may have further exacerbated the lack of water vapor the change of westerly winds in the late miocene early pliocene may have influenced east asian climate on the basis of comparison climatic indices from these two regions

comments on time functions appropriate for nuclear explosions by l j burdick and d v helmberger and seismic source functions and attenuation from local and teleseismic observations of the nts events jorum and handley by d v helmberger and d m hadley

geographic and temporal patterns in the late neogene 12 3 ma aridification of europe the use of small mammals as paleoprecipitation proxies abstract present day relations between small mammal community structure and rainfall are used to predict late neogene 12 3 ma precipitation patterns in europe and anatolia new proxy methods are developed which include regressions of mean annual and minimum monthly precipitation on diet invertivory index and locomotion habitat arboreality index a series of precipitation maps and a set of regional precipitation curves through time at 1 myr resolution are presented precipitation curves at a higher temporal resolution are constructed for the region of central spain the miocene results show the existence between 12 and 9 ma of a large wet 800 1200 mm yr zone extending from northern spain to the ukraine and characterized by the whole year penetration of large amounts of moisture far into the continent between 10 9 and 5 ma this european temperate wet zone etwz shrinks and or moves northward resulting in diachronous aridification a coeval northward migration of the subtropical high pressure zone shpz is hypothesized which is also consistent with the predicted onset of seasonal summer dryness between 10 and 8 ma the maximum extension of the etwz at 12 9 ma temporally correlates with northern hemisphere cooling suggesting that climate zonation rather than the global amount of atmospheric moisture controlled european climate at this time the main aridification at 9 8 ma could best be explained by a northward extension shifting of the subtropical high pressure zone and a transition towards less zonal circulation processes which ultimately could have been triggered by uplift of the tibetan plateau a temporary increase of precipitation at 7 6 ma is associated with renewed global cooling the lowest precipitation values less than 400 mm yr occur during the pliocene in southern and eastern europe uplift in eastern europe carpathians shrinking of the paratethys could well explain the aridification in this area and the associated sharpening of east west precipitation gradients across the continent

middle miocene to earliest pliocene sedimentological and geochemical records of climate change in the western qaidam basin on the ne tibetan plateau global cooling tibetan plateau uplift and the retreat of the para tethys sea have long been thought to be the key controls of the cenozoic climate change in the asian inland however due to the scarcity of long term palaeoclimate records it is not entirely clear which of these factors plays the major role here we present new sedimentological and geochemical proxy records toc carbonate so42 and cl from a 1040 m late cenozoic sedimentary sequence ca 17 to 5 0 ma from the western part of the qaidam basin the largest inland basin on the ne tibetan plateau geochemical records reveal an evident two stage change from ca 17 ma to 11 1 ma phase i the proxies show an upward decrease of carbonate content and toc concentration and a persistent increase in the concentration of the soluble anions so42 and cl even though superimposed high frequency fluctuations are evident from ca 11 1 ma to 5 0 ma phase ii the average concentrations of so42 and cl are higher than those from phase i and a sharp decrease in the carbonate content occurred the sedimentological and geochemical proxy records demonstrate that the qaidam basin has experienced increased aridity since ca 11 1 ma we suggest that the miocene global cooling exerted a significant influence on the drying of the qaidam basin by decreasing evaporation rates and water vapour concentrations in the atmosphere the mio pliocene episodic and persistent uplift of the ne tibetan plateau exerted an important influence superimposed upon this driving force while during ca 11 1 to 8 ma the rapid uplift of the altun shan might have played a key role in climate change of the qaidam basin c 2013 elsevier b v all rights reserved

anatomy of regional phases and source characterization of the soviet joint verification experiment underground nuclear explosion broadband data from the nrdc deployment of stations in kazakhstan at karkaralinsk kkl and bayanual bay are subjected to detailed waveform modeling to understand the nature of regional wave propagation and to determine the nature of the explosion time function and sources of low and high frequency tectonic release minor modification of a crustal model inferred from dss studies in the region is very effective in explaining the arrival times amplitudes and waveshapes of the pn and pmp arrivals at both stations the sh wave data are remarkable however for showing a large high frequency arrival after the expected and observed arrival of sms from the explosion source these secondary s arrivals imply a secondary source 1 to a few kilometers to the south of the shot point shear waves from this source dominate the seismic data at high frequency but are minor at low frequency where shear waves and surface waves from the inferred relaxation of the explosion cavity dominate the wave field the secondary s wave source is inferred to represent explosion driven faulting with no net moment significant overshoot in the rdp is required to match the p wave data it is found that von seggern blandford and haskell source functions are incapable of producing the observed overshoot however the mueller murphy source model is very effective in matching the clear overshoot effects seen in the p waves spall effects are also considered but appear to be minor and serve to require even more overshoot in the rdp the excitation and dispersion of rayleigh waves in the period band of 1 to 10 sec is seen to be a sensitive but nonunique function of both vs and vp in the upper crustal layer high poisson ratios in this layer are needed to explain the rayleigh waveform

new evidence for changes in plio pleistocene deep water circulation from southern ocean odp leg 177 site 1090 abstract changes in atlantic deep water circulation were reconstructed by comparing the benthic foraminiferal 13c record at odp site 1090 in the south atlantic with similar records from the north atlantic sites 982 607 925 929 and deep pacific site 849 oceans important deep water circulation changes occurred in the early pleistocene at 1 55 myr and during the mid pleistocene transition at 0 9 myr at 1 55 myr glacial 13c values in the southern ocean became significantly lower than those in the deep pacific establishing a pattern that persisted throughout the late pleistocene we propose that the lowering of 13c values of southern component water scw at this time resulted from expansion of sea ice and reduced ventilation of deep water during glacial periods after marine isotope stage 52 accompanying this change in southern ocean deep water circulation was enhanced interhemispheric coupling between the north and south atlantic after 1 55 myr at 0 9 myr the magnitude of glacial to interglacial variability in 13c increased and shifted to a longer frequency 100 kyr along with oceanic 18o ice volume calculation of percent northern component water ncw using site 1090 as the scw end member yielded 20 30 less reduction of ncw during glacial periods of the late pleistocene also a trend toward reduced glacial suppression of ncw during the past 400 kyr is not evident the apparent decoupling of ice volume and deep water circulation reported previously may be an artifact of using a pacific rather than a southern ocean carbon isotopic record to calculate past mixing ratios of ncw and scw

a late miocene climate model simulation with echam4 ml and its quantitative validation with terrestrial proxy data abstract for the tortonian late miocene 11 to 7 ma we present a model simulation using the atmospheric general circulation model agcm echam4 coupled to a mixed layer ml ocean model the tortonian simulation with echam4 ml includes an adjusted weaker than present ocean heat transport a generally lower palaeorography and an appropriate palaeovegetation we analyse the climatic differences between the tortonian run and the present day control experiment and we validate our tortonian model results for the mean annual temperature and the annual precipitation with quantitative terrestrial proxy data globally the tortonian run is slightly warmer 0 6 c and the global precipitation indicates more humid conditions 27 mm a than the pd control run particularly the northern high latitudes are warmer 3 5 c in the tortonian simulation which leads to a weaker meridional temperature gradient than today as well as to a reduction of polar sea ice we attribute the polar warming to the lowering of the greenland elevation 20 c in the miocene and to the effects of the palaeovegetation the reduced altitude of the tibetan plateau causes a warming 20 c as compared to today and leads to a weaker asian monsoon in the tortonian run for europe the mean annual temperature is almost unaffected as compared to today because a cooling effect of the weak palaeocean heat transport is compensated by the palaeovegetation when validating our model results we find that the tortonian run is largely consistent with quantitative proxy data however the high latitudes tend to be generally too cool in the palaeoclimate simulation and the equator to pole temperature gradient is too steep as compared to proxy data for europe the comparison with proxy data indicates that the tortonian simulation underestimates the mean annual temperatures but precipitation patterns are quite consistent between model results and proxy data overall the tortonian run is quite realistic and hence the model simulation contributes to a better understanding of the relevant climate processes in the miocene however the discrepancies to proxy data demonstrate that we still do not sufficiently understand the late miocene climate

high amplitude variations in north atlantic sea surface temperature during the early pliocene warm period 1 we provide the first continuous orbital resolution sea surface temperature sst record from the high latitude north atlantic a region critical to understanding the origin of the plio pleistocene ice ages and proximal to regions that became frequently glaciated after 2 7 ma we analyzed sediments from ocean drilling program site 982 over the last 4 ma for their alkenone unsaturation index and compared this surface water signal to a benthic 18o record obtained from the same section we find that while ocean surface temperatures were significantly warmer 6 c than modern temperatures during the early pliocene they were also as variable as those during the late pleistocene a surprising result in light of the subdued variance of oxygen isotopic time series during the interval of 3 5 ma we propose two possible explanations for the high orbital scale sst variability observed either that a strong high latitude feedback mechanism not involving large continental ice sheets alternately cooled and warmed a broad region of the northern high latitudes or that by virtue of its location near the northern margin of the north atlantic drift the site was unusually sensitive to obliquity driven climate shifts on supraorbital time scales a strong sustained cooling of north atlantic ssts 4 5 c occurred from 3 5 to 2 5 ma and was followed by an interval of more modest cooling an additional 1 5 c from 2 5 ma to the present evolutionary orbital scale phase relationships between north atlantic sst and benthic 18o show that sst began to lead 18o significantly coincident with the onset of strong cooling at site 982 3 5 ma we speculate that these changes were related to the growth and subsequent persistence of a greenland ice sheet of approximately modern size through interglacial states

variability of silt grain size and planktonic foraminiferal preservation in plio pleistocene sediments from the western equatorial atlantic and caribbean abstract records of mean sortable silt and planktonic foraminiferal preservation from the ceara rise western equatorial atlantic and from the caribbean are presented to analyze the pliocene 3 5 2 2 ma to pleistocene 1 6 0 3 ma evolution of near bottom current strength and the carbonate corrosiveness of deep water during the mid pleistocene climate transition 1 ma a drastic decrease in glacial bottom current strength and an increase in carbonate corrosiveness is registered demonstrating a substantial decrease in the glacial contribution of the lower north atlantic deep water lnadw to the atlantic ocean also an increased sensitivity to eccentricity orbital forcing is registered after the mpt by contrast carbonate preservation increases considerably in the deep caribbean in response to a strong and persistent stable contribution of upper north atlantic deep water unadw we found evidence for the strongest and most stable circulation within the lnadw cell during the northern hemisphere cooling period between 3 2 and 2 75 ma this is in agreement with the superconveyor model which postulates that the highest nadw production took place prior to 2 7 ma a considerable decrease in bottom current strength and planktonic foraminiferal preservation is observed synchronous with the first occurrence of large scale continental ice sheets in the northern hemisphere this documents the final termination of the superconveyor at ca 2 75 ma however our data do not support a superconveyor in the interval between 3 5 and 3 2 ma when high amplitude fluctuations in bottom current flow and preservation in planktonic foraminifera are observed because of the great sensitivity of nadw production to changes in surface water salinity we assume that the high amplitude fluctuations of lnadw circulation prior to 3 2 ma are linked to changes in the atlantic salinity budget after 2 75 ma they are primarily controlled by ice sheet forcing in contrast to the stepwise deterioration of planktonic foraminiferal preservation in the western deep atlantic a trend toward better preservation from the pliocene to pleistocene is observed in the deep caribbean this indicates a long term increase in the contribution of unadw to the atlantic ocean

paleoceanographic changes in the eastern equatorial pacific over the last 10 myr to examine the late neogene evolution of tropical pacific oceanography we determined multiple geochemical proxy records for temperature u 37 k and tex86h indices and primary productivity algal biomarkers and diol indices in sediments recovered at odp site 1241 in the east equatorial pacific eep spanning a record of the last 10 myr the tex86h temperatures are lower than those recorded by u 37 k indices exhibiting large fluctuations and suggesting strong warming during the mid pliocene warm period mpwp 4 5 3 2 ma and significantly colder temperature during the late miocene cooling period 7 5 ma and after the middle pliocene warm period mpwp such variations could reflect changes in the eep thermocline temperatures but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure a combination of temperature records inferred to represent different and likely varying depths in the water column as well as algal biomarker records for export production and ecosystem structure suggest that both productivity and inference upwelling were reduced in the eep during warmer periods such as the mpwp and prior to 7 ma in contrast stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 ma and for the past 3 myr both corresponding to globally cool intervals a further increase in eep productivity occurred at ca 1 8 ma coincident with the development of the e w pacific sst gradient these results confirm previous work that protracted el nino like conditions prevailed during warmer intervals of the pliocene before ultimately descending into the current climate state

new insights on arctic quaternary climate variability from palaeo records and numerical modelling terrestrial and marine geological archives in the arctic contain information on environmental change through quaternary interglacial glacial cycles the arctic palaeoclimate and its extremes apex scientific network aims to better understand the magnitude and frequency of past arctic climate variability with focus on the extreme versus the normal conditions of the climate system one important motivation for studying the amplitude of past natural environmental changes in the arctic is to better understand the role of this region in a global perspective and provide base line conditions against which to explore potential future changes in arctic climate under scenarios of global warming in this review we identify several areas that are distinct to the present programme and highlight some recent advances presented in this special issue concerning arctic palaeo records and natural variability including spatial and temporal variability of the greenland ice sheet arctic ocean sediment stratigraphy past ice shelves and marginal marine ice sheets and the cenozoic history of arctic ocean sea ice in general and holocene oscillations in sea ice concentrations in particular the combined sea ice data suggest that the seasonal arctic sea ice cover was strongly reduced during most of the early holocene and there appear to have been periods of ice free summers in the central arctic ocean this has important consequences for our understanding of the recent trend of declining sea ice and calls for further research on causal links between arctic climate and sea ice

late miocene washhouse climate in europe abstract we present two eight million year long proxy records of precipitation for southwest and central europe covering the middle to late miocene 5 3 13 ma at a temporal resolution of about 60 kyr and 150 kyr respectively the estimates of precipitation are based on the ecophysiological structure of herpetological assemblages amphibians and reptiles from 13 0 ma until about 9 ma both records show a similar trend evolving from a long dry period 13 11 ma into a washhouse climate 10 2 9 8 ma characterized by global warm conditions and several times more precipitation than present the transition from washhouse to a dryer climate between 9 7 and 9 5 ma and the concomitant cooling episode appear to have triggered a severe biotic event known as the vallesian crisis which included the extinction of hominoids in western europe a second washhouse period 9 0 8 5 ma coeval with a global warm episode was unprecedentedly intense in southwest europe but less pronounced in central europe from 8 ma onward a divergence in the two precipitation records is observed with southwest europe staying wetter and central europe becoming dryer than present both precipitation records are combined into a common run off curve as a measure of the relative intensity of the hydrological cycle for moderate latitudes of continental europe the run off curve shows a remarkable positive correlation with atlantic deep water temperatures from ceara rise by lear et al 2003 which are significantly higher up to 3 c during the two washhouse periods and show no other positive excursion of comparable magnitude we discuss potential links and the role of the coeval temporary restriction of the central american seaway on ocean and atmosphere circulation

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

magnitude of climate variability during middle pliocene warmth a palaeoclimate modelling study abstract the nature and magnitude of climatic variability during the period of middle pliocene warmth ca 3 29 2 97 ma is poorly understood we present a suite of palaeoclimate modelling experiments incorporating an advanced atmospheric general circulation model gcm coupled to a q flux ocean model for 3 29 3 12 and 2 97 ma bp astronomical solutions for the periods in question were derived from the berger and loutre bl2 astronomical solution boundary conditions excluding sea surface temperatures ssts which were predicted by the slab ocean model were provided from the usgs prism2 2 2 digital data set the model results indicate that little annual variation 0 5 c in ssts relative to a control experiment occurred during the middle pliocene in response to the altered orbital configurations annual surface air temperatures also displayed little variation seasonally surface air temperatures displayed a trend of cooler temperatures during december january and february and warmer temperatures during june july and august this pattern is consistent with altered seasonality resulting from the prescribed orbital configurations precipitation changes follow the seasonal trend observed for surface air temperature compared to present day surface wind strength and wind stress over the north atlantic north pacific and southern ocean remained greater in each of the pliocene experiments this suggests that wind driven gyral circulation may have been consistently greater during the middle pliocene the trend of climatic variability predicted by the gcm for the middle pliocene accords with geological data however it is unclear if the model correctly simulates the magnitude of the variation this uncertainty is derived from a the relative insensitivity of the gcm to perturbation in the imposed boundary conditions b a lack of detailed time series data concerning changes to terrestrial ice cover and greenhouse gas concentrations for the middle pliocene and c difficulties in representing the effects of climatic history in snap shot gcm experiments

deglaciation of the western margin of the barents sea ice sheet a swath bathymetric and sub bottom seismic study from the kveithola trough abstract kveithola trough an e w trending glacial trough in the nw barents sea was surveyed for the first time during the eglacom cruise of r v ogs explora in summer 2008 swath bathymetry shows that the seafloor is characterized by e w trending mega scale glacial lineations msgl that record a fast flowing ice stream draining the svalbard barents sea ice sheet sbis during the last glacial maximum lgm msgl are overprinted by transverse sediment ridges about 15 km apart which give rise to a staircase axial profile of the trough such transverse ridges are interpreted to be grounding zone wedges gzws formed by deposition of subglacial till during episodic ice stream retreat sub bottom chirp and multi channel reflection seismic data show that the present day morphology is largely inherited from the palaeo seafloor topography at the time of deposition of the transverse ridges overlain by a draping glaciomarine unit which in places is over 15 m thick our data allow the reconstruction of depositional processes which accompanied deglaciation of the spitsbergen bank area the sedimentary drape deposited on top of the gzws is suggested to have accumulated at a very high rate on average in the order of 1 1 5 m ka 1 and therefore may potentially preserve a high resolution palaeoclimatic record of deglaciation and post glacial conditions in this sector of the barents sea

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

late miocene global cooling and the rise of modern ecosystems a period of continental aridification and ecosystem change occurred about seven million years ago a global sea surface temperature reconstruction identifies cooling temperatures and a strengthened meridional temperature gradient at this time

chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations a chronostratigraphic framework has been established for upper neogene sediments from the northern netherlands offshore sector southern north sea data of dinoflagellate cysts pollen and foraminifers from eight boreholes are integrated and the resulting biostratigraphic events are connected to an additionally retrieved paleomagnetic record the sedimentary succession comprises at the base late to middle miocene sediments and spans the piacenzian to gelasian stages from 3 6 to 1 8 ma including the paleomagnetic gauss matuyama boundary and the olduvai subchron sedimentation rates vary between 30 cm kyr in the lower part of the succession and reach up to 84 cm kyr in the upper part these rates are high enough to record short paleomagnetic events and for the first time the presence of the so called x event has been recorded and dated at around 2 44 ma in a sedimentary setting the name north sea event is proposed here the paleoclimatic and paleoenvironmental information pictures the onset of northern hemisphere glaciation and the subsequent intensification of glacial conditions with its impact on the north sea sea region the paleoenvironmental changes are characterised by a stepwise development and five successive intervals are distinguished during the first interval a warm climate and an open marine setting prevailed the second interval is characterised by dominantly cold climatic conditions with occasional warmer periods during the third interval the environment became restricted marine and a stable freshwater layering occurred which facilitated the development of sea ice in the shallow sea within the fourth interval extreme cold arctic conditions were predominant and shallowing continued the fifth interval shows fluvial to deltaic paralic conditions from then on facies differences from the nearby delta system overruled the basin wide signals at the studied location 2006 elsevier b v all rights reserved

active gas venting through hydrate bearing sediments on the vestnesa ridge offshore w svalbard abstract gas hydrate systems offshore western svalbard are extensive and include the whole vestnesa ridge an elongated sediment drift north of the molloy transform and just east of the molloy ridge one of the shortest segments of the slow spreading north atlantic ridge system the crest of the vestnesa ridge at water depth between 1200 1300 m is pierced with fluid flow features seafloor pockmarks vary in size up to 700 m in diameter pockmarks are generally larger at the eastern start of the vestnesa ridge than at its western termination a recent cruise with r v jan mayen discovered methane flares in the water column above the pockmark field at the onset of the vestnesa ridge over a period of two days at least 3 pockmarks were continuously active and methane flares in the water column reached a height of approximately 800 m it is still unclear what has triggered the increase in gas expulsion from seafloor sediments high resolution 3d seismic data acquired in 2007 and 2010 show significant differences of the subseafloor expression of these fluid leakage systems at the western end of the vestnesa ridge sub seafloor fluid flow features resemble well described chimney structures however the seismic expression of the active fluid flow features is much broader much more chaotic dome shaped and is not very similar to a typical chimney structure the vestnesa ridge gas hydrate and free gas system occurs within few kilometers of a mid oceanic ridge and transform fault which makes this gas hydrate system unique on earth the close proximity to the spreading center and its hydrothermal circulation system affects the dynamics of the gas hydrate and free gas system the high heat flow together with the high tectonic activity of this region a thick sedimentary cover a shallow maturation window and an accelerated rate of biogenic and thermogenic gas production cause substantial disturbance to the free gas system leading to high variability in gas supply gas migration and gas hydrate build up and dissociation

arctic and antarctic submarine gullies a comparison of high latitude continental margins abstract submarine gullies are common features of high latitude continental slopes and over the last decade have been shown to play a key role in continental margin evolution submarine erosion downslope sediment transport slope deposits and the architecture of petroleum reservoirs however the processes that form these gullies the timescales over which they develop and the environmental controls influencing their morphology remain poorly constrained we present the first systematic and comparative analysis between arctic and antarctic gullies with the aim of identifying differences in slope character from which we infer differences in processes operating in these environments quantitative analysis of multibeam echosounder data along 2441 km of the continental shelf and upper slope and morphometric signatures of over 1450 gullies show that six geomorphically distinct gully types exist on high latitude continental margins we identify distinct differences between arctic and antarctic gully morphologies in the arctic data sets deep relief 30 m gully incision depth at 50 m below the shelf edge and shelf incising gullies are lacking these differences have implications for the timescales over which the gullies were formed and for the magnitude of the flows that formed them we consider two hypotheses for these differences 1 some antarctic gullies developed through several glacial cycles and 2 larger antarctic gullies were formed since the last glacial maximum as a result of erosive flows i e sediment laden subglacial meltwater being more abundant on parts of the antarctic margin over longer timescales a second difference is that unique gully signatures are observed on arctic and on antarctic margins environmental controls such as the oceanographic regime and geotechnical differences may lead to particular styles of gully erosion observed on arctic and antarctic margins

new evidence on the age of the taklimakan desert the taklimakan desert is the world s second largest shifting sand desert located in the rain shadow of the tibetan plateau the initiation of desert formation in the asian interior is one of the most prominent climate changes in the northern hemisphere during the cenozoic era dating the earliest formation of this desert is important for understanding the climatic effects of the uplifted tibetan plateau here we report 1071 m thick neogene deposits with inter calated eolian dune sands from the only outcrop in the central taklimakan desert based on paleo magnetic measurements biostratigraphic age control and previous electron spin resonance dating results the oldest in situ eolian dune sands were confi rmed to be ca 7 ma much older than the previous reported wind blown siltstone from the southern edge of the taklimakan desert this new result indicates that desert conditions initiated ca 7 ma in the center of the tarim basin we attribute this event to the late cenozoic climatic deterioration and or to the rain shadow effect caused by late miocene uplift of the northern tibetan margin

glacial inception and quaternary mountain glaciations in fennoscandia abstract the aim of this review is twofold first the role of the fennoscandian mountains as a nucleation center for glacial inception is investigated the second objective is to review glacial erosion by mountain glaciers throughout the quaternary all available field data and several modelling experiments show that the fennoscandian mountains seeded the last glaciation since the mountains seem to be of key importance for ice sheet inception it is reasonable to assume a similar inception pattern throughout most of the major pleistocene glaciations this pattern also implies prolonged periods of glacial ice in the fennoscandian mountains during late cenozoic time mountain based glaciers thus have had a long time to act on their substratum resulting in a profound geomorphological impact

changes in erosion and ocean circulation recorded in the hf isotopic compositions of north atlantic and indian ocean ferromanganese crusts abstract high resolution hf isotopic records are presented for hydrogenetic fe mn crusts from the north atlantic and indian oceans bm1969 from the western north atlantic has previously been shown to record systematically decreasing nd isotopic compositions from about 60 to 4 ma at which time both show a rapid decrease to unradiogenic nd composition thought to be related to the increasing influence of nadw or glaciation in the northern hemisphere during the oligocene north atlantic hf became progressively less radiogenic until in the mid miocene 15 ma it reached 1 it then shifted gradually back to an hf value of 3 at 4 ma since when it has decreased rapidly to about 1 at the present day the observed shifts in the hf isotopic composition were probably caused by variation in intensity of erosion as glaciation progressed in the northern hemisphere ferromanganese crusts ss663 and 109d are from about 5500 m depth in the indian ocean and are now separated by 2300 km across the mid indian ridge they display similar trends in hf isotopic composition from 20 to 5 ma with the more northern crust having a composition that is consistently more radiogenic by 2 hf units paradoxically during the last 20 ma the hf isotopic compositions of the two crusts have converged despite increased separation and subsidence relative to the ridge a correlatable negative excursion at 5 ma in the two records may reflect a short term increase in erosion caused by the activation of the himalayan main central thrust changes to unradiogenic hf in the central indian ocean after 5 ma may alternatively have been caused by the expanding influence of nadw into the mid indian basin via circum antarctic deep water or a reduction of pacific flow through the indonesian gateway in either case these results illustrate the utility of the hf isotope system as a tracer of paleoceanographic changes capable of responding to subtle changes in erosional regime not readily resolved using other isotope systems

neogene ice volume and ocean temperatures insights from infaunal foraminiferal mg ca paleothermometry antarctic continental scale glaciation is generally assumed to have initiated at the eocene oligocene transition yet its subsequent evolution is poorly constrained we reconstruct changes in bottom water temperature and global ice volume from 0 to 17 ma using 18o in conjunction with mg ca records of the infaunal benthic foraminifer o umbonatus from ocean drilling program odp site 806 equatorial pacific 2500 m considering uncertainties in core top calibrations and sensitivity to seawater mg ca mg ca sw we produce a range of mg ca temperature mg casw calibrations our favored exponential temperature calibration is mg ca 0 66 0 08 mg casw0 27 0 06 e 0 114 0 02 bwt and our favored linear temperature calibration is mg ca 1 21 0 04 0 12 0 004 bwt bottom water temperature mg casw 0 003 0 02 stated errors are 2 s e the equations are obtained by comparing o umbonatus mg ca for a paleocene eocene section from ocean drilling program odp site 690 weddell sea to 18o temperatures calculated assuming ice free conditions during this peak warmth period of the cenozoic this procedure suggests negligible effect of mg casw on the mg distribution coefficient dmg application of the new equations to the site 806 record leads to the suggestion that global ice volume was greater than today after the middle miocene climate transition 14 ma odp site 806 bottom waters cooled and freshened as the pacific zonal sea surface temperature gradient increased and climate cooled through the pliocene prior to the plio pleistocene glaciation of the northern hemisphere the records indicate a decoupling of deep water temperatures and global ice volume demonstrating the importance of thresholds in the evolution of the antarctic ice sheet

response of marine palynomorphs to neogene climate cooling in the iceland sea odp hole 907a abstract the present study on odp leg 151 hole 907a combines a detailed analysis of marine palynomorphs dinoflagellate cysts prasinophytes and acritarchs and a low resolution alkenone based sea surface temperature sst record for the interval between 14 5 and 2 5 ma and allows to investigate the relationship between palynomorph assemblages and the paleoenvironmental evolution of the iceland sea a high marine productivity is indicated in the middle miocene and palynomorphs and ssts both mirror the subsequent long term neogene climate deterioration the diverse middle miocene palynomorph assemblages clearly diminish towards the impoverished assemblages of the late pliocene parallel with a somewhat gradual decrease of ssts being as high as 20 c at 13 5 ma to around 8 c at 3 ma superimposed palynomorph assemblages not only reflect middle to late miocene climate variability partly coinciding with the short lived global miocene isotope events mi events but also the initiation of a proto thermohaline circulation across the middle miocene climate transition which led to increased meridionality in the nordic seas last occurrences of species cluster during three events in the late miocene to early pliocene and are ascribed to the progressive strengthening and freshening of the proto east greenland current towards modern conditions a significant high latitude cooling between 6 5 and 6 ma is depicted by the supraregional decahedrella event coeval with lowest miocene productivity and a sst decline in the early pliocene a transient warming is accompanied by surface water stratification and increased productivity that likely reflects a high latitude response to the global biogenic bloom the succeeding crash in palynomorph accumulation and a subsequent interval virtually barren of marine palynomorphs may be attributed to enhanced bottom water oxygenation and substantial sea ice cover and indicates that conditions seriously affecting marine productivity in the iceland sea were already established well before the marked expansion of the greenland ice sheet at 3 3 ma

geochemical evidence for magmatic fluids in porphyry copper mineralization part ii ion probe analysis of cu contents of mafic minerals koloula igneous complex

evidence of tectonic release in long period s waves from underground nuclear explosions at the novaya zemlya test sites abstract evidence of tectonic release produced by underground nuclear explosions at novaya zemlya is present in teleseismic long period s waves sh waveforms from representative events at the southern and northern novaya zemlya test sites were modeled to determine the sh radiation patterns long period p and sv waves were also investigated to further constrain the equivalent double couple orientation of the tectonic release events within each test site have similar faulting mechanisms but there are definite differences in the tectonic release orientation between the two sites the southern test site double couple orientation is either vertical strike slip or 45 dipping thrust while the northern test site has an oblique normal dip slip orientation the limited resolution of sh signals and complexity of the observed sv waveforms along with uncertainties in the absolute explosion source strengths and t prevent unique solutions for both test sites assuming a strike slip orientation the 27 october 1973 southern novaya zemlya event has the largest tectonic release moment 1 6 10 24 dyne cm and 14 october 1969 northern event has the smallest moment 0 9 10 23 dyne cm of the 12 events studied the ratio of tectonic release moment to explosion strength varies by as much as a factor of 3 at the northern test site and by a factor of 2 at the southern site the variability of the tectonic release orientation and strength at the two test sites allows us to address the question of whether tectonic release affects yield estimation