antarctic climate at the eocene oligocene boundary climate model sensitivity to high latitude vegetation type and comparisons with the palaeobotanical record abstract simulated climate for the antarctic continent using the genesis version 2 1 global climate model with 34 ma boundary conditions is shown to be highly sensitive to polar vegetation type six experiments were run using different levels of atmospheric co2 orbital configurations ice sheet geometries and vegetation types to assess model sensitivity to antarctica being covered with either a needle leaf evergreen forest or tundra simulations using 2 pre industrial levels of co2 combined mean annual temperature mat 19 c are about 7 c cooler than minimum estimates from the antarctic cenozoic plant record mat 12 to 15 c however simulations using 3 co2 mat 7 c are in good agreement with our empirical estimates of mean annual temperature with ice sheets and orbits set up to represent early oligocene interglacial conditions the tundra climate is significantly cooler than the evergreen forest climate with local austral summer averages up to 6 c cooler in non glaciated areas and continental averages 2 5 c cooler in the model this is mainly due to higher albedo and decreases in net radiation and sensible and latent heat flux especially during spring and summer feedbacks between coastal and continental cooling marginal sea surface temperatures and sea ice also appear to be significant a review of the late palaeocene to earliest miocene plant fossil record in the antarctic peninsula and ross sea regions shows that the vegetation was in transition 34 ma from a relatively diverse mainly evergreen forest to a tundra vegetation the modelled sensitivity of continental temperatures to a change from forest to tundra suggests vegetation climate feedbacks during the eocene oligocene transition played a significant role in the initial rapid glaciation of the continent

introduction pliocene climate processes and problems climate predictions produced by numerical climate models often referred to as general circulation models gcms suggest that by the end of the twenty first century global mean annual surface air temperatures will increase by 1 1 6 4 c trace gas records from ice cores indicate that atmospheric concentrations of co 2 are already higher than at any time during the last 650 000 years in the next 50 years atmospheric co 2 concentrations are expected to reach a level not encountered since an epoch of time known as the pliocene uniformitarianism is a key principle of geological science but can the past also be a guide to the future to what extent does an examination of the pliocene geological record enable us to successfully understand and interpret this guide how reliable are the retrodictions of pliocene climates produced by gcms and what does this tell us about the accuracy of model predictions for the future these questions provide the scientific rationale for this theme issue

deficiencies in the diatom evidence for a pliocene reduction of the east antarctic ice sheet evidence for pliocene reduction of the east antarctic ice sheet eais has been inferred from the presence of pliocene planktic marine diatoms in tills of the sirius group now exposed along the slopes of the transantarctic mountains we highlight deficiencies in this diatom evidence for a pliocene reduction of the eais first we examine what diatom habitats are left behind by a retreating ice sheet in this case the fennoscandian ice sheet fis and find that diatoms should occur in planktic and benthic marine brackish water freshwater and terrestrial habitats we expect that during former reexpansions these diverse diatom assemblages were picked up by the advancing fis and deposited in tills this is shown to be the case and diatoms found in tills from sweden and finland reflect the many habitats over which the fis passed if there was a reduction of the eais during the pliocene followed by renewed glaciation diatoms from many different habitats should be found in the resulting tills of the sirius group this is not the case only marine planktic diatoms and a few freshwater forms are reported similarly vertical downsection distribution of diatoms in sirius group and fennoscandian tills differ while in the sirius group diatoms appear restricted to surface and near surface sediments in fennoscandia they are found throughout the tills such data do not support a pliocene reduction model for the eais

neogene vegetation of the meyer desert formation sirius group transantarctic mountains antarctica a tundra vegetation consisting of at least 18 plant species is described from the meyer desert formation which outcrops along the beardmore glacier in the transantarctic mountains about 500 km from the south pole the fossils include pollen seeds fruits flowers leaves wood and in situ plants of which wood and leaves of nothofagus and a pollen assemblage had been previously reported the plants include a cryptogamic flora of mosses and liverworts conifers and angiosperms in the families gramineae cyperaceae nothofagaceae ranunculaceae hippuridaceae caryophyllaceae and chenopodiaceae or myrtaceae the plants grew in a weakly developed soil formed within a complex periglacial environment that included moraines glacial outwash streams well drained gravel ridges and poorly drained depressions in which peat and marl were being deposited d 2004 elsevier b v all rights reserved

geochronological evidence supporting antarctic deglaciation three million years ago the response of the antarctic ice sheets to increased global temperatures is an important unresolved issue in the assessment of future climate change in particular considerable controversy exists as to whether the east antarctic ice sheet suffered extensive deglaciation during the mid pliocene epoch 3 myr ago when temperatures were only slightly warmer than today although the ice sheet is widely assumed to have existed in something like its present form for the past 14 myr ref 1 marine diatoms eroded from the antarctic interior have been found in glacial till deposits high in the transantarctic mountains2 3 and have been bio stratigraphically dated at 3 myr before present this age has been disputed4 because it implies marine deposition in the antarctic interior and hence substantial deglaciation at a time when other evidence has been marshalled for the persistence of cold polar conditions4 here we report k ar and 40ar 39 ar ages for a volcanic ash bed in diatom bearing glaciomarine strata cored in ferrar fiord east antarctica by the ciros 2 drill hole5 which confirm the age of the diatoms at 3 myr and hence also confirm the mid pliocene deglaciation

formation of patterned ground and sublimation till over miocene glacier ice in beacon valley southern victoria land antarctica a thin glacial diamicton informally termed granite drift occupies the floor of central beacon valley in southern victoria land antarctica this drift is 40 ar 39 ar analyses of presumed in situ ash fall deposits that occur within granite drift at odds with the great age of this ice are high centered polygons that cut granite drift if polygon development has reworked and retransported ash fall deposits then they are untenable as chronostratigraphic markers and cannot be used to place a minimum age on the underlying glacier ice our results show that the surface of granite drift is stable at polygon centers and that enclosed ash fall deposits can be used to define the age of underlying glacier ice in our model for patterned ground development active regions lie only above polygon troughs where enhanced sublimation of underlying ice outlines high centered polygons the rate of sublimation is influenced by the development of porous gravel and cobble lag deposits that form above thermal contraction cracks in the underlying ice a negative feedback associated with the development of secondary ice lenses at the base of polygon troughs prevents runaway ice loss secondary ice lenses contrast markedly with glacial ice by lying on a d versus 18 o slope of 5 rather than a precipitation slope of 8 and by possessing a strongly negative deuterium excess the latter indicates that secondary ice lenses likely formed by melting downward percolation and subsequent refreezing of snow trapped preferentially in deep polygon troughs the internal stratigraphy of granite drift is related to the formation of surface polygons and surrounding troughs the drift is composed of two facies a nonweathered matrix supported diamicton that contains 25 striated clasts in the 16 mm fraction and a weathered clast supported diamicton with varnished and wind faceted gravels and cobbles the weathered facies is a coarse grained lag of granite drift that occurs at the base of polygon troughs and in lenses within the nonweathered facies the concentration of cosmogenic 3 he in dolerite cobbles from two profiles through the nonweathered drift facies exhibits steadily decreasing values and shows the drift to have formed by sublimation of underlying ice these profile patterns and the 3 he surface exposure ages of 1 18 0 08 ma and 0 18 0 01 ma atop these profiles indicate that churning of clasts by cryoturbation has not occurred at these sites in at least the past 10 5 and 10 6 yr although granite drift is stable at polygon centers low frequency slump events occur at the margin of active polygons slumping together with weathering of surface clasts creates the large range of cosmogenic nuclide surface exposure ages observed for granite drift maximum rates of sublimation near active thermal contraction cracks calculated by using the two 3 he depth profiles range from 5 m m y to 90 m m y sublimation rates are likely highest immediately following major slump events and decrease thereafter to values well below our maximum estimates nevertheless these rates are orders of magnitude lower than those computed on theoretical grounds during eruptions of the nearby mcmurdo group volcanic centers ash fall debris collects at the surface of granite drift either in open thermal contraction cracks or in deep troughs that lie above contraction cracks these deposits subsequently lower passively as the underlying glacier ice sublimes the fact that some regions of granite drift have escaped modification by patterned ground for at least 8 1 ma indicates long term geomorphic stability of individual polygons once established polygon toughs likely persist for as long as 10 5 10 6 yr our model of patterned ground formation which applies to the hyperarid cold desert polar climate of antarctica may also apply to similar sized polygons on mars that occur over buried ice in utopia planitia

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

on marine microfossil transport and pathways in antarctica during the late neogene evidence from the sirius group at mount fleming there are two extreme views of the evolution of the pliocene antarctic ice sheet dynamicists argue for ice sheet reduction and reexpansion on the basis of pliocene marine diatoms in a glacial deposit the sirius group that is widespread in the transantarctic mountains stabilists argue from other evidence that the antarctic cryosphere remained essentially constant in area and volume they propose marine diatom transport by eolian processes and emplacement into terrestrial glacial strata hence the inferred source area and transport mechanism of marine diatoms are of critical importance we tested the reduction hypothesis on an important outcrop of the sirius group at mount fleming south victoria land we observed very few unidentifiable marine diatom fragments in sirius group strata in contrast marine diatoms enclosed in a surface diamicton covering the sirius group were more abundant and identifiable our study further indicates that the sirius group at mount fleming was not deposited by the east antarctic ice sheet but rather by alpine ice originating on the transantarctic mountains on the basis of both data sets we infer that marine diatoms postdate sirius group deposition at mount fleming and that transport was by wind and we advance alternative scenarios for their source and transport pathways

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

crustal response to continental collisions between the tibet indian south china and north china blocks geochronological constraints from the songpan garze orogenic belt western china we report shrimp u th pb monazite conventional u pb titanite sm nd garnet and rb sr muscovite and biotite ages for metamorphic rocks from the danba domal metamorphic terrane in the eastern songpan garze orogenic belt eastern tibet plateau these ages are used to determine the timing of polyphase metamorphic events and the subsequent cooling history the oldest u th pb monazite and sm nd garnet ages constrain an early barrovian metamorphism m1 in the interval c 204 190 ma coincident with extensive indosinian granitic magmatism throughout the songpan garze orogenic belt a second higher grade sillimanite grade metamorphic event m2 recorded only in the northern part of the danba terrane was dated at c 168 158 ma by a combination of u th pb monazite and titanite and sm nd garnet ages it is suggested that m1 was a thermal event that affected the entire orogenic belt while m2 may represent a local thermal perturbation rb sr muscovite ages range from c 138 100 ma whereas rb sr biotite ages cluster at c 34 24 ma these ages document regional cooling at rates of c 2 3 c myr 1 following the m1 peak for most of the terrane however those parts of the terrane affected by the higher temperature m2 event e g the migmatite zone experienced initially more rapid c 8 c myr 1 cooling after peak m2 before joining the regional slow cooling path defined by the rest of the terrane at c 138 ma regional slow cooling between c 138 and c 30 ma is thought to be the result of post tectonic isostatic uplift after extensive crustal thickening caused by collision of the south and north china blocks the clustering of biotite rb sr ages marks the onset of rapid uplift across the entire terrane commencing at c 30 20 ma this cooling history is shared with many other regions of the tibet plateau suggesting that uplift of the tibet plateau including the songpan garze orogenic belt occurred predominantly in the last c 30 myr as a response to the continuing northwards collision of india with eurasia

vegetation and climate from two oligocene glacioeustatic sedimentary cycles 31 and 24 ma cored by the cape roberts project victoria land basin antarctica abstract the cape roberts project recovered over 1500 m of coastal glaciomarine sediments of oligocene and early miocene age off the ross sea margin of antarctica the strata are characterised by cyclic repetition of facies in a glaciomarine setting and are interpreted to be a record of glacial interglacial episodes involving significant changes in eustatic sea level on milankovitch frequencies we have undertaken a detailed study of pollen and spores miospores from an early oligocene 31 ma and a late oligocene 24 ma cycle although miospores are sparse in the core averaging only 1 grain per gram of sediment processed over 1200 cenozoic miospores were recovered for this study previous studies of miospores from ross sea sediments have encountered problems differentiating between reworked and in situ palynomorphs here only samples containing a low relative abundance of an eocene dinoflagellate cyst assemblage the transantarctic flora have been used to infer the contemporaneous oligocene miospore flora the flora of the early oligocene cycle is dominated by three species of nothofagidites and four types of podocarpidites the assemblage from the upper oligocene cycle is also dominated by nothofagidites and podocarpidites but with the addition of two distinctive taxa an angiosperm pollen and a bryophyte spore notwithstanding these additions there is a slight decrease in floral diversity between the two cycles while this study confirms that some floristic changes did occur between early and late oligocene time on the victoria land coast the present data suggest that the changes were not extensive it is likely that the vegetation of both cycles was a low diversity scrub of low stature consisting of mainly nothofagus podocarps and bryophytes modern analogues suggest that this vegetation was growing in a climate significantly warmer mean summer monthly temperature 4 12 c than is found on the present day victoria land msmt 5 c although colder that the temperate climate suggested by the diverse flora found in ross sea sediments of eocene age

carbon and nitrogen trends in soil chronosequences of the transantarctic mountains abstract determination of carbon and nitrogen levels in soils of ice free areas of the transantarctic mountains along with their origin may determine whether these soils serve as a source or sink of carbon with an increasingly warmer climate organic and inorganic forms of carbon and nitrogen were measured in five soil chronosequences in the transantarctic mountains using flash combustion and spectrometry accumulation of coal carbon was significant in the beardmore glacier area and was quantified using chemi thermal oxidation followed by flash combustion carbon levels decreased with drift age for two of the sequences decreases in carbon in the hatherton glacier sequence were due primarily to high levels of carbon in young ice cored drifts carbon content increased with drift age for the beardmore glacier sequence due to the presence of coal in older drifts nitrogen content increased with age for a majority of the soil chronosequences inorganic carbon and all forms of nitrogen were significantly and positively correlated with mean annual precipitation our results suggest that carbon levels in similar settings do not significantly change over time changes in temperature or moisture associated with microclimate likely play a much larger role in carbon and nitrogen levels

history of ice sheet elevation in east antarctica paleoclimatic implications abstract the multi disciplinary study of past ice surface elevations in the grove mountains of interior east antarctica provides direct land based data on the behavior of the east antarctic ice sheet since the pliocene the glacial geology the ages of cold desert soils the depositional environment of younger moraine sedimentary boulders and their spore pollen assemblages combine to imply a possible significant shrinkage of the ice sheet before the middle pliocene epoch with the ice sheet margin retreating south of the grove mountains 450 km south from its present coastal position exposure age measurements of bedrock indicate that the elevation of the ice surface in the grove mountains region subsequently rose at about mid pliocene to at least 200 m higher than today s levels the ice surface then progressively lowered with some minor fluctuations middle to late pleistocene exposure ages found on the lowest samples at the ice bedrock contact line indicate a long period with ice surface elevations kept at the current level or complex fluctuation history during the quaternary epoch

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

pliocene pleistocene diatoms in paleozoic and mesozoic sedimentary and igneous rocks from antarctica a sirius problem solved there are two competing scenarios on the behavior of the east antarctic ice sheet during the late tertiary in one scenario the ice sheet was very dynamic and underwent major drawdown and renewal as late as the pliocene in the other the ice sheet was relatively stable during the late neogene the presence of marine diatoms in sirius group sedimentary rocks in east antarctica is at the center of the disagreement one side regards the diatoms as the major piece of evidence to support the drawdown and renewal hypothesis and infers that they were introduced into the sirius during renewed glaciation of east antarctica others suggest that these diatoms were likely introduced into the sirius by atmospheric largely eolian processes we propose a simple test of the eolian hypothesis if diatoms were introduced into the sirius by eolian processes then they should also be present in older paleozoic and mesozoic sedimentary and igneous rocks samples from two units of the beacon supergroup devonian to jurassic from beacon valley east antarctica were analyzed the beacon heights orthoquartzite devonian and the feather conglomerate permian triassic also examined was sediment found in cracks of paleozoic and mesozoic devonian to cretaceous igneous rocks from marie byrd land west antarctica largely pliocene pleistocene planktonic marine diatoms were found in all sample sets because neither beacon supergroup sedimentary rocks nor igneous rocks from marie byrd land are pliocene pleistocene in age such findings strongly suggest that diatoms were introduced into them by eolian processes this same scenario can be applied to sirius group sedimentary rocks

direct measurement of over pressure of a volcanic blast on the june 1991 eruption at unzen volcano japan over pressure of a volcanic blast has been measured for the first time by a lead plate blastmeter at unzen volcano kyushu japan the over pressure of the volcanic blast on june 8 was 0 28 bar at 2700 m distance from the crater and that was less than 0 06 bar at 4400 m distance the estimated explosive yield of the explosion accompanied by the blast was 1 1 107 kg tnt 5 1020 erg calculated based on the over pressure and distribution of the blast effect the explosion energy is as much as 1 600 of that of the blast at mount st helens on 18 may 1980 the lead plate of the blastmeter at 2700 m has also recorded the collision with some accretionary lapillis the maximum particle velocity of the blast was estimated to be about 75 m sec based on the trace of the collision the significance of over pressure for the prediction of volcanic hazards is also discussed briefly

a case for sirius group alpine glaciation at mount fleming south victoria land antarctica a case against pliocene east antarctic ice sheet reduction the sirius group comprises a suite of consolidated glacial deposits that are widespread in the transantarctic mountains some of the deposits contain pliocene marine diatoms because of the interpretation that the sirius group tills and the marine diatoms were deposited by the east antarctic ice sheet it has been inferred that the east antarctic ice sheet was much reduced in area and volume during the pliocene these interpretations were evaluated by studying sirius group lodgment tills on mount fleming in the dry valleys sector of the transantarctic mountains we infer that the sirius group lodgment tills at mount fleming do not support the hypothesis that the east antarctic ice sheet was much reduced during the pliocene we demonstrate that sirius group lodgment tills on mount fleming were deposited by alpine ice this conclusion is founded on ice flow directions inferred from rattails gravel fabric and the orientation of bullet boulders as well as on sediment and gravel characteristics of the tills only a very few unidentifiable diatom fragments were recovered better preserved identifiable pliocene marine diatoms occur in moderate abundances in a 5 10 cm thick unconsolidated and discontinuous drift that caps the lodgment tills on the basis of the decline in diatom preservation with depth into the till we dismiss transport of the better preserved diatoms by the ice that deposited the underlying sirius group lodgment till instead we attribute diatom presence to eolian deposition and recycling into lodgment tills at a later stage

the last forests on antarctica reconstructing flora and temperature from the neogene sirius group transantarctic mountains abstract fossil bearing deposits in the transantarctic mountains antarctica indicate that despite the cold nature of the continent s climate a tundra ecosystem grew during periods of ice sheet retreat in the mid to late neogene 17 2 5 ma 480 km from the south pole to date palaeotemperature reconstruction has been based only on biological ranges thereby calling for a geochemical approach to understanding continental climate and environment there is contradictory evidence in the fossil record as to whether this flora was mixed angiosperm conifer vegetation or whether by this point conifers had disappeared from the continent in order to address these questions we have analysed for the first time in sediments of this age plant and bacterial biomarkers in terrestrial sediments from the transantarctic mountains to reconstruct past temperature and vegetation during a period of east antarctic ice sheet retreat from tetraether lipids mbt cbt palaeothermometer we conclude that the mean continental summer temperature was ca 5 c in agreement with previous reconstructions this was warm enough to have allowed woody vegetation to survive and reproduce even during the austral winter biomarkers from vascular plants indicate a low diversity and spatially variable flora consisting of higher plants moss and algal mats growing in microenvironments in a glacial outwash system abietane type compounds were abundant in some samples indicating that conifers most likely podocarpaceae grew on the antarctic continent well into the neogene this is supported by the palynological record but not the macrofossil record for the continent and has implications for the evolution of vegetation on antarctica

antarctic role in northern hemisphere glaciation earth s climate underwent a major transition from the warmth of the late pliocene when global surface temperatures were 2 to 3 c higher than today to extensive northern hemisphere glaciation nhg 2 73 million years ago ma we show that north pacific deep waters were substantially colder 4 c and probably fresher than the north atlantic deep water before the intensification of nhg at 2 73 ma the atlantic pacific temperature gradient was reduced to

fossil weevils coleoptera curculionidae from latitude 85 s antarctica two species of fossil listroderine weevils coleoptera curculionidae rhytirhinini listroderina are reported from the meyer desert formation at a locality on the beardmore glacier in the transantarctic mountains about 500 km from the south pole associated fossils include wood leaves and pollen of nothofagus stems and leaves of several species of mosses achenes of ranunculus shells of freshwater molluscs and a fish tooth the age of the fossiliferous strata is contentious but probably within the range of pliocene to mid miocene the fossils represent organisms that colonised the margins of a glacier at the head of a fjord during an interglaciation the autecology of the listroderine species indicates that temperatures during summer months averaged 5 c the mean annual temperature with winter temperatures constrained by 6 months of darkness is estimated to have been about 38 c compared to the 326 c estimated for sea level at latitude 85 s today the closest evolutionary link of the fossil listroderines is with south american rather than australian or new zealand taxa divergence of the taxa at least at the level of tribe had most probably occurred on gondwana before the continent broke apart the fossil species are considered to be the descendants of antarctic lineages which evolved on the continent in the late cretaceous or palaeogene and survived until the neogene extinction of the listroderines and most other antarctic terrestrial biota occurred with the growth of the polar ice sheets and the change to the polar desert climate 9 2003 elsevier science b v all rights reserved

provenance of the sirius group and related upper cenozoic glacial deposits from the transantarctic mountains antarctica relation to landscape evolution and ice sheet drainage abstract this study uses bulk x ray diffraction xrd heavy mineral analysis and analysis of detrital modes of the sirius group and related upper cenozoic deposits to evaluate their provenance the data suggest that deposition of the sirius group occurred as a result of long term glacial denudation of the transantarctic mountains such a conclusion is in contrast with the traditional view of deposition on a pre existing high relief glacial topography during one relatively short term phase of glacial expansion by the east antarctic ice sheet two petrofacies are distinguished which have different geomorphological settings and paleo ice flow directions one petrofacies includes much material from the higher elevated sedimentary sequences of the transantarctic mountains and represents overriding of the mountains and deposition of part of the sirius group during or after the late oligocene to early miocene the second petrofacies is characterized by a large input from crystalline basement sources and represents active erosion and deposition in glacial troughs during the neogene the second petrofacies of the sirius group shows similarities to the record from dry valley drilling project core 11 dvdp 11 which indicates that east antarctic ice was last flowing through the dry valleys in the late miocene to early pliocene

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

a marine and terrestrial sirius group succession middle beardmore glacier queen alexandra range transantarctic mountains antarctica a succession of sirius group glacigene sediments which crop out along the western margins of the beardmore valley between cherry icefall and hewson glacier below the cloudmaker is designated as the stratotype of the cloudmaker formation this new formation overlies a multiply glaciated pavement dominion erosion surface cut into the precambrian goldie formation and is disconformably overlain by the meyer desert formation sirius group the cloudmaker formation comprises bedded and massive diamictons bedded sands and silts and laminated clays assemblages of foraminifera occur throughout the cloudmaker formation and indicate that these basal sirius group sediments were deposited in brackish glacial marine environments the general absence of diatoms suggest these marine waters were ice covered similar marine assemblages are also present in basal sirius group sediments at oliver bluffs dominion range recycled marine diatom assemblages in the sirius group at the latter locality indicate that the host sediments have an age of 3 8 ma pliocene the cloudmaker formation is placed in the pliocene although a latest miocene age for the basal sediments cannot be ruled out stratigraphie sedimentologic and paleontologic evidence suggests that beardmore valley was occupied by a fjord and tidewater glacier system that extended at least 165 km through the transantarctic mountains from the southwestern ross sea the stratigraphy of the cloudmaker formation consists of a succession of members separated by disconformities it is hypothesised that these strata were deposited by a dynamic valley glacier system that underwent a history of glacier advance and grounding alternating with glacier retreat and flotation over a marine water column a combination of fjord basin sediment filling and sea level oscillations may also have influenced the pattern of glacier ice advance and retreat within beardmore paleofjord the marine cloudmaker formation is overlain by the terrestrial diamicton dominated meyer desert formation at oliver bluffs the meyer desert formation diamictons are interbedded with fluvial and lacustrine sediments successions that contain in situ vascular plant fossils principally the southern beech nothofagus mosses and beetle remains a magellanic type flora and fauna occupied the coastal margins of the beardmore paleofjord the vertical transition from the basal marine cloudmaker formation to terrestrial meyer desert formation provides a sea level datum that can be used to assess the extent of post sirius group tectonic uplift uplift rates at the cloudmaker section 90 km inland from the transantarctic mountain front or rift shoulder margin in the queen alexandra mountain block are determined to be 429 or 350 m myr this assumes a total uplift of 1331 m for the uppermost marine sediments of the cloudmaker formation and maximum diatom based ages for the sirius group of 3 1 ma or 3 8 ma gross similarities in stratigraphy and interpreted paleoenvironments are apparent between the cloudmaker succession beardmore paleofjord and the upper miocene pliocene successions at the mouth of taylor paleofjord 800 km to the north contrasting present day elevational settings for these two widely separated marine successions indicates the post sirius rate of tectonic uplift for the transantarctic mountains has been significantly greater in the queen alexandra block

archean granite greenstone tectonics at kolar south india interplay of diapirism and bulk inhomogeneous contraction during juvenile magmatic accretion 1 the structural study of the kolar greenstone belt and surrounding granite gneiss terrains combined with u pb dating reveals that the middle and lower crustal tectonoplutonic pattern of the eastern dharwar craton developed during a major magmatic accretion event between 2550 and 2530 ma the granite greenstone pattern resulted from the interference of gravity driven sagging of the greenstones i e diapirism e w bulk inhomogeneous shortening combined with horizontal n s stretching and syntectonic juvenile pluton emplacement bulk inhomogeneous contraction is accommodated by the synchronous development of a pervasive n s trending vertical foliation shallow stretching lineation and conjugate strike slip shear zone pattern within and outside the greenstone belt resulting in regional horizontal pure shear deformation the plutons around the greenstone belt record regional contraction by developing one set of strike slip c s fabrics of the shear zone pattern the development of the granite greenstone pattern was coeval and compatible with deformation during juvenile magmatic accretion melting and granulite metamorphism in the lower crust the kolar example points to a specific crustal rheology that allowed sagduction of the greenstones and regional distributed bulk inhomogeneous strain due to mechanical homogeneity and low viscosity provided by large scale melting during the accretion event this example further suggests specific boundary conditions to the craton that allowed e w inhomogeneous shortening to be accommodated by n s stretching and spreading of the crust without significant tectonic thickening such tectonoplutonic pattern is specific to the archean and may develop as a consequence of mantle plume activity in intracontinental settings

diatoms in south pole ice implications for eolian contamination of sirius group deposits marine and nonmarine diatoms occur throughout a south pole ice core spanning the past 2000 yr similar diatoms occur in east and west antarctica at siple and taylor domes because there are no local diatom sources at these locations diatoms must have been carried by winds from coastal or extra antarctic sites our data demonstrate widespread historical eolian transport of diatoms to the antarctic ice sheets supporting the view that sirius group sediments were contaminated by late neogene diatoms long after they were deposited if so there is no reason to postulate a pliocene deglaciation event in east antarctica

cretaceous patterns of floristic change in the antarctic peninsula cretaceous radiation of angiosperms from low to high palaeolatitudes coupled with the break up of gondwana played a major role in establishing and maintaining biogeographic patterns across the southern hemisphere uncertainties in details of plate reconstructions provide conflicting hypotheses about area relationships of gondwana fragments this has led to a number of competing proposals concerning angiosperm migration across gondwana central to this debate is the role of the antarctic peninsula a region that is often envisaged as providing the main connection between east and west gondwana the initial radiation of angiosperms into the antarctic peninsula region however postdates appearances elsewhere in east gondwana e g australia strongly suggesting that the antarctic peninsula was not the main gateway at least in the early stages of gondwana radiation a steep climatic gradient in this part of the world probably acted as an effective barrier to angiosperm radiation the peak of floristic replacement coincides with the peak of cretaceous warmth turonian which in turn suggests that climatic warming acted as a forcing mechanism by pushing latitudinal belts of vegetation southwards once into the southern high latitudes angiosperms diversified and as climates cooled during the late cretaceous a number of important groups seem to have their origins here recent investigations of antarctic macro and microfloras indicate progressive floristic replacement through the cretaceous bryophytes hepatophytes bennettites and other seed plants all show a rapid decline in diversity in contrast ferns initially decline then recover while conifers remain relatively stable the ecological preferences of the replaced groups imply that angiosperms initially occupied areas of disturbance and were understorey colonizers only later replacing fern thickets and becoming important in the overstorey this pattern is consistent with those observed elsewhere through the cretaceous

a tortonian late miocene 11 61 7 25 ma global vegetation reconstruction for the tortonian age of the miocene epoch 11 6 7 25 ma we present a global palaeobotanical and palaeoecologically based vegetation dataset combined with a best fit late miocene climate vegetation model experiment to create an advanced global data model hybrid biome reconstruction this new palaeoecological database and global vegetation reconstruction can be used both for the purposes of validating future palaeoclimate model simulations as well as a land cover dataset to initialise palaeoclimate modelling experiments our tortonian reconstruction shows significant changes in the distribution of vegetation compared to modern natural vegetation for example in contrast to the modern scenario in the northern hemisphere boreal forests reached 80 n and temperate forests were present above 60 n warm temperate forests covered much of europe coastal north america and south east asia our reconstruction shows a spread of temperate savanna in central usa the middle east and on the tibetan plateau evidence for arid deserts is sparse with the exception of the atacama region south america areas that exhibit arid desert today in the tortonian were instead covered by shrublands grasslands savannas and woodlands the extent of tropical forests in south america was likely reduced but expanded in the indian sub continent and east africa this pattern of global vegetation in the late miocene suggests a warmer and wetter world which is supported by the pattern of climate anomalies predicted by our best fit palaeoclimate vegetation model experiment global mean annual temperature may have been as much as 4 5 c higher than present day with many regions experiencing higher than modern amounts of precipitation over the annual cycle the pattern of temperature and precipitation change reconstructed palaeobotanically and predicted within our climate model experiment infers a global forcing agent on tortonian climate e g such as elevated concentrations of greenhouse gases to explain the observed and modelled climate anomalies this is in contrast to current proxy records of tortonian atmospheric co2 which range from last glacial maximum to mid 20th century levels

global middle pliocene biome reconstruction a data model synthesis 1 the middle pliocene warm interval ca 3 ma bp has been extensively studied however our knowledge concerning the global distribution of middle pliocene biomes remains far from complete this paper presents the results from a first attempt at simulating the distribution of different mid pliocene biomes using an advanced numerical general circulation climate model hadley centre atmospheric model version 3 and the biome 4 vegetation model the modeling indicates that during the middle pliocene the geographical coverage of tundra type biomes may have been significantly reduced compared with the present day in the northern hemisphere high latitude forests expand in the place of tundra forms of vegetation total area covered by forest increases for the pliocene case compared with the present day arid deserts become less prevalent in the pliocene scenario and are replaced by tropical xerophytic shrublands and savanna type vegetation these results compare favorably with geological data in general and with the u s geological survey s prism2 middle pliocene vegetation reconstruction although data model inconsistencies are apparent although some of these inconsistencies relate to the weaknesses of the climate and biome model employed others identify deficiencies in the extant geological data set or the interpretation of this data this modeled biome reconstruction will serve as a useful vehicle for aiding in future comparisons between geological data on middle pliocene biomes and model predictions

neogene glacial record from the sirius group of the shackleton glacier region central transantarctic mountains antarctica neogene glacigenic strata collectively referred to as the sirius group are widely distributed throughout the transantarctic mountains the group is particularly well exposed near the head of shackleton glacier 858109 to 858409s on roberts massif and at bennett platform these deposits are critical for examining the nature of former ice flow from the east antarctic ice sheet into the ross embayment the sirius group rests on a glacially grooved and striated pavement named herein the shackleton erosion surface the sub sirius group surface on roberts massif was of low relief and glaciogenic sediment was deposited on it as a sheet of uniform thickness at bennett platform stratigraphic sections attain a thickness of 110 m thick and are subdivided into the shackleton glacier formation maximum thickness 98 m and the overlying bennett platform formation 44 m separated by an unconformity a third older lithified diamictite containing wood fragments occurs as clasts within these formations and as boulders in the modern lateral moraines of shackleton glacier the dominant facies massive diamict is interpreted primarily as lodgement till other facies indicate glaciofluvial and glaciolacustrine deposition facies associations suggest deposition either by sliding temperate or by polythermal glaciers under much warmer conditions than those of today widespread large and small scale faulting has affected the sirius group and underlying rocks to the extent that inland exposures are over 500 m higher than those to the north over a distance of 30 km thus at the time of deposition of the sirius group the mountains were probably lower and the ice sheet was much thinner

the zedong window a record of superposed tertiary convergence in southeastern tibet determining the timing magnitude and location of deformation due to the indo asian collision is widely acknowledged as an important step in understanding how the lithosphere responds during continental collision a puzzling result of geological investigations of the lhasa block over the past 2 decades has been the apparent lack of significant tertiary deformation there perhaps the most important structural feature of the lhasa block is the south directed gangdese thrust system which developed along its southern edge the thrust system which separates the andean type batholith of southern asia from rocks of indian affinity is obscured at most locations across southeastern tibet by back thrusts of the younger north directed renbu zedong thrust system the best documented site where both thrusts are exposed occurs near zedong zedong window systematic geochronologic analyses were conducted in this area u pb zircon dating of three samples of a synkinematically to postkinematically deformed hanging wall granitoid the yaja granodiorite cut by the gangdese thrust indicates a crystallization age of 30 4 0 4 ma 2 thus placing an upper bound on the initiation of the thrust u pb zircon dating of granitoid samples structurally higher in the gangdese hanging wall yields emplacement ages of 42 5 1 0 ma and 48 9 0 8 ma 2 similar to other magmatic complexes within the gangdese arc geochemical results are consistent with these plutons forming in the same environment as precollisional intrusions within the gangdese batholith suggesting a significant post collisional input of juvenile heat the 40ar 39ar thermochronology of samples from a vertical section through the hanging wall within the yaja granodiorite coupled with results of a numerical thermal model indicate an average slip rate along the gangdese thrust of 7 mm yr between 30 and 23 ma and a minimum displacement of 50 km farther east in the zedong window thermal effects produced by later north directed thrust sheets of the renbu zedong system appear to have obscured thermal history signatures in the gangdese hanging wall related to earlier south directed thrusting thermochronological results from this region indicate that thermal overprinting related to the north directed thrusting occurred between 25 and 10 ma consistent with previous estimates

tundra environments in the neogene sirius group antarctica evidence from the geological record and coupled atmosphere vegetation models the neogene meyer desert formation sirius group at oliver bluffs in the transantarctic mountains contains a sequence of glacial deposits formed under a wet based glacial regime within this sequence fluvial deposits have yielded fossil plants that along with evidence from fossil insects invertebrates and palaeosols indicate the existence of tundra conditions at 85 s during the neogene mean annual temperatures of c 12 c are estimated with short summer seasons with temperatures up to 5 c the current published date for this formation is pliocene although this is hotly debated reconstructions produced by the triffid and biome 4 vegetation models utilizing a pliocene climatology derived from the hadam3 general circulation model running with prescribed boundary conditions from the us geological survey prism2 dataset also predict tundra type vegetation in antarctica the consistency of the model outputs with geological evidence demonstrates that a pliocene age for the meyer desert formation is consistent with proxy environmental reconstructions and numerical model reconstructions for the mid pliocene if so the east antarctic ice sheet has behaved in a dynamic manner in the recent geological past

late tertiary history of the antarctic ice sheet evidence from the dry valleys data from the dry valleys antarctica suggest that outlet glaciers of a local ice cap carved primary valley systems on both flanks of the transantarctic mountains while coeval alpine glaciers eroded exposed intervalley mountain ranges subsequently a thick ice sheet overrode the transantarctic mountains at least twice flowing northeastward across major pre existing valleys the youngest overriding episode postdated and the older episode antedated middle to early late miocene time we think that an extensive ice sheet covered east and west antarctica during overriding episodes

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

new grounds for reassessing palaeoclimate of the sirius group antarctica fossil nothofagus leaves from the meyer desert formation of the sirius group in the central transantarctic mountains have been found with recycled marine diatoms indicating that they are no older than 4 1 3 1 ma they have been interpreted as evidence for pliocene warming and diminution of the east antarctic ice cap in contrast plio pleistocene ice cap stability and sustained polar palaeoclimate has been argued from landforms in victoria land and isotopic data from the southern ocean new evidence on this question comes from fossil soils in the meyer desert formation one of these the siesta palaeosol has a gypsic horizon at a depth of 85 cm as in soils of polar deserts with a mean annual precipitation map of 120 220 mm clastic dykes from a 60 80 cm thick permafrost active layer in the palaeosols are evidence of a mean annual temperature mat of 3 to 11 c this is warmer and wetter than the dominion range today map 36 mm mat 39 c but still a periglacial climate cooler and drier than southern chilean moorland and krummholz map 600 7500 mm mat 5 8 c or subantarctic tundra map 400 2500 mm mat 5 to 5 c a pliocene age for the nothofagus fossils and siesta palaeosol is compatible with soil development on surfaces that bracket their enclosing deposits the dominion range was significantly warmer and wetter than it is today during pliocene c 3 5 ma growth of nothofagus and formation of the siesta palaeosol but the beardmore glacier was still large at that time surface soils and palaeosols of the meyer desert formation are evidence of another warmer and wetter episode earlier during the pliocene c 5 ma both warm intervals were separated by intervening times of glacial expansion and frigid palaeoclimate

late cenozoic denudation by large magnitude landslides in the eastern edge of tibetan plateau abstract eastern edge of the tibetan plateau is marked by the longmen shan which experienced pronounced denudation in late cenozoic and was previously attributed to river erosion our recent work however demonstrated that the landsliding must have played an important integral role in the surface processes various scale landslides are present in the peripheral zone of the southern longmen shan which were interpreted as overthrust related klippen in previous works we revisited these exotic blocks and demonstrated that they were actually gravity driven landslides in origin the landslides are composed mostly of thick bedded marine limestone and sandstone of paleozoic early triassic ages and were detached along some weak zones like lower silurian phyllite and unconformities three types of landslides can be categorized distributed stacked and coherent and their differential occurrence is considered to bear upon both uplift rates of the longmen shan and foreland topography outward flow of lower crustal materials from the tibetan plateau interior provides a feasible mechanism for initiating the uplift of its eastern flank in cenozoic positive feedbacks are believed to have existed between extrusion of lower crustal channel flow and surface denudation processes rapid denudation by large magnitude landslides in conjunction with coeval river erosion in the southern longmen shan might have led to predominant sub vertical extrusion of lower crustal flow channel as evidenced by nearly symmetric exhumation of the pengguan massif the northern longmen shan was comparatively less denuded with few basement rocks cropping out and landslides are absent in its front as well differential denudation between the southern and northern longmen shan might have in large part resulted from the lower crustal flow that presumably moved to the southeast and had less impact on the northern longmen shan

the mount feather diamicton of the sirius group an accumulation of indicators of neogene antarctic glacial and climatic history abstract a paucity of data from the antarctic continent has resulted in conflicting interpretations of neogene antarctic glacial history much of the debate centres on interpretations of the glacigene sirius group strata that crop out as discrete deposits along the length of the transantarctic mountains and in particular on its age and the origin of the siliceous microfossils it encloses pliocene marine diatoms enclosed within sirius group strata are inferred to indicate a dynamic east antarctic ice sheet that was much reduced compared with today in the early middle pliocene and then expanded again in the late pliocene however the geomorphology of the dry valleys region is interpreted to represent a relatively long lived middle miocene recent and stable polar climatic regime similar to that of today the mount feather diamicton infills a palaeovalley at ca 2500 m on the ne flank of mount feather in the dry valleys region and has been included within the sirius group we obtained four shallow cores comrac 8 9 10 and 11 from beneath the permafrost boundary in the mount feather diamicton in order to understand its origin and relationship with the surrounding landscape detailed studies of these cores stratigraphy sedimentology palaeontology micromorphology petrography and fabric have yielded new data that demonstrate a much more complex climatic and glacial history for the mount feather diamicton than in previous interpretations the data indicate that the mount feather diamicton was deposited beneath a wet based glacier fed from a larger ice sheet behind the transantarctic mountains it is however unlikely that this ice sheet overtopped mount feather 2985 m a near in situ non marine diatom assemblage was recovered from 90 cm depth in comrac 10 and indicates a maximum depositional age of late miocene for the mount feather diamicton a subsequent glacial episode has distributed a boulder blanket across the surface of the diamicton other post depositional processes include drying infilling of surface layers with aeolian sediment and the development of melt water runnels we interpret these combined data to indicate the persistence of more temperate climatic and glacial conditions in the vicinity of mount feather until at least the late miocene

exploring biological constraints on the glacial history of antarctica the evolutionary and biogeographic history of the contemporary antarctic terrestrial and marine biotas reveals many components of ancient origin for large elements of the terrestrial biota long term isolation over timescales from hundreds of thousands to tens of millions of years and thus persistence through multiple glacial cycles now appears to be the norm rather than the exception for the marine biota there are some parallels with benthic communities also including ancient components together with an incidence of species level endemism indicating long term isolation on the antarctic continental shelf although it has long been known that a few ice free terrestrial locations have existed in antarctica for up to 10 12 million years particularly in the dry valleys of victoria land along with certain nunataks and higher regions of large mountain ranges these do not provide potential refugia for the majority of terrestrial biota which occur mainly in coastal and or low lying locations and exhibit considerable biogeographic regionalisation within the continent current glacial models and reconstructions do not have the spatial resolution to detect unequivocally either the number or geographical distribution of these glacial refugia or areas of the continental shelf that have remained periodically free from ice scouring but do provide limits for their maximum spatial extent recent work on the evolution of the terrestrial biota indicates that refugia were much more widespread than has been recognised and it is now clear that terrestrial biology provides novel constraints for reconstructing the past glacial history of antarctica and new marine biological investigations of the antarctic shelf are starting to do likewise

mesozoic cooling across the yidun arc central eastern tibetan plateau a reconnaissance 40ar 39ar study abstract 40 ar 39 ar dating of hydrous minerals from igneous and metamorphic rocks was undertaken with the aim of characterizing the thermal history of the yidun arc eastern tibetan plateau regional metamorphism of palaeozoic rocks of the western yidun arc occurred during the early triassic collision with the qiangtang block along the jinsha jiang suture hornblende muscovite and biotite 40 ar 39 ar ages from syn tectonic igneous rocks within this collision zone suggest that the region had cooled to below 300 c by the late triassic muscovite samples from mica schists within this collision zone yield variably discordant age spectra with generally triassic 40 ar 39 ar ages consistent with cooling of the region to below muscovite closure temperatures by the close of the triassic hornblende and biotite 40 ar 39 ar ages from granite and granodiorite plutons in the eastern yidun arc suggest post emplacement cooling of these plutons occurred rapidly consistent with these granites being high level intrusions in sum these results suggest that by the beginning of the jurassic the yidun arc as a whole had cooled to below 300 c two cretaceous granites in the central yidun arc also experienced rapid cooling suggesting they too were emplaced at shallow crustal depths post triassic deformation of the region must have occurred at or below the brittle ductile transition within the crustal levels now exposed

geological record and reconstruction of the late pliocene impact of the eltanin asteroid in the southern ocean in 1995 an expedition on board the research vessel fs polarstern explored the impact site of the eltanin asteroid in the southern ocean the only known asteroidimpact into a deep ocean basin analyses of the geological record of the impact region place the event in the late pliocene 2 15 myr and constrain thesize of the asteroid to be 1 km the explosive force inferred for this event places it at the threshold of impacts believed to have global consequences and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events which are common on geological timescales

the million year evolution of the glacial trimline in the southernmost ellsworth mountains antarctica an elevated erosional trimline in the heart of west antarctica in the ellsworth mountains tells of thicker ice in the past and represents an important yet ambiguous stage in the evolution of the antarctic ice sheet here we analyse the geomorphology of massifs in the southernmost heritage range where the surfaces associated with the trimline are overlain by surficial deposits that have the potential to be dated through cosmogenic nuclide analysis analysis of 100 rock samples reveals that some clasts have been exposed on glacially moulded surfaces for 1 4 ma and perhaps more than 3 5 ma while others reflect fluctuations in thickness during quaternary glacial cycles modelling the age of the glacially moulded bedrock surface based on cosmogenic 10be 26al and 21ne concentrations from a depth profile indicates a minimum exposure age of 2 1 2 6 ma we conclude that the glacially eroded surfaces adjacent to the trimline predate the last glacial maximum and indeed the quaternary since erosion was by warm based ice near an ice sheet upper margin we suggest it first occurred during the early glaciations of antarctica before the stepped cooling of the mid miocene at 14 ma this was a time when the interior antarctic continent had summers warm enough for tundra vegetation to grow and for mountain glaciers to consist of ice at the pressure melting point during these milder conditions and subsequently erosion of glacial troughs is likely to have lowered the ice sheet surface in relation to the mountains this means that the range of orbitally induced cyclic fluctuations in ice thickness have progressively been confined to lower elevations

miocene to pleistocene glacial history of west antarctica inferred from nunatak geomorphology and cosmogenic nuclide measurements on bedrock surfaces we report geomorphic observations and cosmogenic nuclide measurements on bedrock surfaces from three isolated nunatak groups in west antarctica the pirrit hills and nash hills located in the weddell sea sector and the whitmore mountains located on the ross weddell divide the objectives of this paper are to i establish a chronology for landscape development at these sites and ii quantify the long term history of ice thickness variations in west antarctica these nunataks display relic alpine landscapes on which weathered bedrock surfaces are superimposed in the pirrit hills an erosional trimline is etched into alpine ridges and separates smooth crested ridges below from serrated ridges above below the trimline geomorphic evidence indicates repeated frozen based ice cover while above the trimline evidence for ice cover is entirely absent there is also no geomorphic evidence for thicker than present ice at the whitmore mountains cosmogenic nuclide concentrations in the oldest bedrock surfaces from the whitmore mountains and from above the pirrit hills trimline indicate uninterrupted exposure for 12 myr at extraordinarily low erosion rates this places a lower limit on the timing of the formation of alpine landscapes in west antarctica and we hypothesize that this occurred during the relatively warm climates prior to the mid miocene cooling the absence of evidence for thicker ice at the whitmore mountains is consistent with the hypothesis that the divide was typically thinner than present during pleistocene glacial periods due to reduced accumulation bedrock surfaces below the trimline have much lower nuclide concentrations and are most easily explained by a scenario of repeated frozen based ice cover and occasional subglacial plucking which is consistent with geomorphic observations bedrock surfaces near the modern ice level appear to have been covered more than half of the time while higher elevation surfaces indicate progressively less cover the trimline and associated geomorphic features are very similar to a prominent trimline in the ellsworth mountains and we conclude that these are in fact part of the same feature the ellsworth trimline is hypothesized to have formed during the mid miocene cooling and the transition from alpine to continental glaciation and our results are consistent with this hypothesis

soil formation in the transantarctic mountains from the middle paleozoic to the anthropocene abstract in the transantarctic mountains tams soils from the middle paleozoic and from the oligocene to the present have been examined soils representing other sections of the geologic column are missing probably because of the low proportion of ice free areas 0 35 in antarctica the evolution of soils in antarctica reflects changes in climate and geologic conditions as the continent became separated and increasingly isolated from gondwana a greenhouse climate existed during the middle paleozoic and an icehouse climate began in the early oligocene the climate of the tams has become increasingly hyper arid since the middle miocene humans have had a dramatic effect on the climate of the tams during the anthropocene the first forest soils under callixylon archaeopteris forest on earth identified as alfisols were discovered in antarctica and assigned to the middle devonian during the permian dicroidium forests covered entisols and inceptisols in the oligocene nothofagus podocarpaceae forests contained gelisols miocene aged soils enriched in silt are common in the tams but they tend to be poorly developed because they have been eroded a soil evolutionary sequence exists in the tams from the holocene through the pliocene that includes glacic haploturbels on ice cored holocene drift typic haploturbels on late pleistocene surfaces typic anhyorthels on middle pleistocene surfaces salic anhyorthels on early pleistocene surfaces and petrosalic anhyorthels on pliocene surfaces these changes reflect gradual sublimation of ice in ice cored drift and ice wedge polygons a recovery of the surface from cryoturbation accumulation of salts and eventual development of a salt pan soils of the tams are undergoing rapid change as the climate warms including loss of semi permanent snowbanks an expansion of the hyporheic zone flushing of salts from soils along valley walls and the development of thermokarst

evidence of pliocene nothofagus in antarctica from pliocene marine sedimentary deposits dsdp site 274 microfossil assemblages in pliocene sediments from dsdp site 274 68 59 81 s 173 25 64 e provide data on the age of the sediments and suggest the presence of nothofagus southern beech in antarctica during the pliocene a suite of 17 samples was collected in an interval from samples 28 274 6r 1 83 87 cm to 28 274 11r 4 73 77 cm 48 33 100 29 mbsf bio stratigraphic study of the abundant diatom assemblages combined with published radiolarian data indicates that the sample interval ranges in age from 5 0 to 2 2 ma with an apparent unconformity between about 3 8 and 3 2 ma nothofagidites the genus for fossil pollen referable to nothofagus occurs throughout the interval as well as pollen and spores with known stratigraphic ranges that unequivocally indicate reworking from older rocks species of nothofagidites recovered include n asperus n brachyspinulosus n flemingii n senectus and n sp cf n lachlaniae the latter form is previously known from the sirius group in the transantarctic mountains abundant palynomorphs were recovered in only three of the samples from site 274 samples 28 274 9r 2 15 19 cm 28 274 9r 2 48 52 cm and 28 274 9r 2 65 69 cm based on the diatom and radiolarian biostratigraphic data the ages of these samples range from 3 00 to 3 01 ma the relative abundance of n sp cf n lachlaniae in the three samples is an order of magnitude higher than relative abundances for the other species of nothofagidites in the same samples the significantly higher relative abundance of n sp cf n lachlaniae suggests that this pollen was derived from trees of nothofagus that were living in antarctica during the mid pliocene diatom assemblages from these three samples indicate that sediments in this interval were rapidly deposited as biogenic oozes in an open ocean setting relatively free of sea ice thus decreasing the possibility of reworking from a single source bed rich in n sp cf n lachlaniae clearly more detailed work in additional well dated cores from around antarctica is needed before a clear picture of the neogene history of antarctic terrestrial vegetation emerges

late neogene sirius group strata in reedy valley antarctica a multiple resolution record of climate ice sheet and sea level events late neogene sirius group strata from tillite spur and quartz hills in the reedy glacier area antarctica demonstrate the variability in sirius group facies and contrasts sirius group strata deposited at high and low paleo elevation respectively the tillite spur and quartz hills formations pliocene are formally defined here the tillite spur formation type section crops out on the edge of the wisconsin plateau overlooking tillite spur it comprises 32 m of alternating coarse gray conglomerate and muddy olive brown diamictites the quartz hills formation type section crops out above the western margin of reedy glacier in a pre existing cirque towards the southern end of the quartz hills it comprises c 100 m of alternating massive diamictites and rhythmically interbedded sandstone and laminated mudstones which were deposited close to sea level and subsequently rapidly uplifted 500 m myr 1 to their present elevation at c 1500 m three orders of paleoclimatic variability are recorded in the sirius group strata from reedy valley 1 recycled marine microfloras in glacial diamictites indicate intervals of marine incursion into the antarctic cratonic interior co occurring with reductions in the east antarctic ice sheet 2 an advancing and retreating paleo reedy glacier deposited a glacial interglacial sequence alternating on a 10 100 kyr scale 3 centimeter and millimeter stratification in strata of the quartz hills formation record annual kyr scale variability

denudational response to surface uplift in east tibet evidence from apatite fission track thermochronology east tibet preserves broad areas of low relief that occur at elevations 3000 m and are dissected by major strike slip faults that have been repeatedly reactivated since the late mesozoic apatite fission track samples from these low relief high elevation surfaces indicate cretaceous cooling ca 90 ma fast rock uplift of the 110 c isotherm and a fossilized partial annealing zone began in the plateau interior of east tibet in the miocene low denudation rates in the plateau interior during the cenozoic which are constrained by thermal history modeling and a consistency in ages from apatite fission tracks suggest that dip slip displacement on faults has been minor some localized areas have experienced the effects of structurally enhanced rock uplift and denudation or fault related hydrothermal reheating cooling ages in eocene sediments deposited on the older plateau surface suggest that rapid denudation occurred from the miocene to holocene other evidence of significant cenozoic denudation comes from river valleys in particular the yalong river valley where incision was initiated in the oligocene to miocene 28 12 ma estimated mean denudation in east tibet during the cenozoic was 1 2 km in the low relief high elevation plateau interior and at least 5 km at the high relief plateau margin in the longmen shan the region south of the longmen shan and the sichuan basin was not uplifted with the main tibetan plateau in the miocene but it has undergone enhanced denudation since the eocene due to an orographic effect most of the denudation in the east tibetan plateau interior has occurred in major river valleys incision in the major rivers of the longman shan occurred simultaneously and has kept pace with surface uplift that began in the middle late miocene 12 ma with acceleration of denudation rates in the late miocene 5 ma

an eocene magmatic belt across central tibet mantle subduction triggered by the indian collision mountain domes rising to 6600 m along tibet s tanggula range herald the eocene intrusion of calcalkaline granites into terranes accreted much earlier together with coeval cogenetic volcanics such intrusives which have similar crystallization and cooling ages may be part of an ese trending belt cutting central tibet in half this magmatic belt may have marked a former northern boundary of the plateau testifying to s directed subduction of the asian mantle such subduction would have developed soon after india s collision but long before the rise of the plateau s present rims along one of central tibet s mesozoic sutures

tree growth at polar latitudes based on fossil tree ring analysis permineralized trunks and mature wood samples with well preserved growth rings are described and analyzed from the upper permian and middle triassic of the central transantarctic mountains this fossil wood is unique in that the plants lived in an environment with no modern analogue and exhibited luxuriant tree growth above 75 s paleolatitude ring width averages 1 69 2 3 mm with maximum width of 6 83 9 9 mm an order of magnitude larger than ring widths produced at near polar latitudes today tree rings in both the permian and triassic woods show similar structure consisting almost entirely of earlywood spring wood with between 0 12 of each ring classified as latewood summer wood the small amount of latewood 0 6 cells indicates a very rapid transition to seasonal dormancy probably in response to decreasing light levels at these paleolatitudes in order to accurately delimit the earlywood latewood boundary a comparison was done of classical dendroclimatological techniques and alternative techniques utilized primarily by paleobotanists analyzing fossil woods we found that classical wood anatomy techniques provided a more accurate explanation of wood development and tree growth for these high latitude samples the suggested cool temperate late permian glossopteris flora from this area differs substantially from the warm temperate middle triassic corystosperm flora leaf type dicroidium and very different paleoclimates have been reconstructed for these two time periods ring structure and wood growth from both sites however are very similar indicating that these plants were responding to the environment in very similar ways the structure of the tree rings including a large number of earlywood tracheids and a very low number of latewood cells provides evidence that growth at these polar latitudes was limited by light levels rather than water and temperature as occurs in modern high latitude forests these fossil tree rings have important implications for understanding woody shoot growth and cambial function at high latitudes during periods of global warmth 2007 elsevier b v all rights reserved