interglacial collapse of crary trough mouth fan weddell sea antarctica implications for antarctic glacial history abstract in this study we investigate the stratigraphy of a trough mouth fan in the weddell sea to determine possible relationships between basin floor stratigraphy and glaciation on antarctica seismic data from the basin floor show a deep broad and elongate erosional channel filled by thick chaotic facies deposits basin floor fans and channel levee deposits from seismic stratigraphy analysis of basin floor stratigraphy we infer that this channel formed by large volume mass wasting sourced from poorly sorted glacial sediments from crary trough mouth fan and dronning maud land slopes correlation to odp leg 113 site 693 suggests that the mass wasting of the slopes occurred in the early pliocene we surmise that collapse occurred during an early pliocene interglacial and was related to major drawdown of the antarctic ice volume collapse was probably triggered by rebound and relative sea level fall a mathematically predicted geoidal effect related to antarctic ice volume reduction the record of this major ice volume reduction is not manifest in the trough mouth fan but rather is manifest in the basin floor stratigraphy as a major backfilled erosional channel which extends far beyond the trough mouth fan

the overdeepening hypothesis how erosional modification of the marine scape during the early pliocene altered glacial dynamics on the antarctic peninsula s pacific margin abstract a new synthesis of diatom assemblage data from ocean drilling program odp leg 178 suggests that the pacific margin of the antarctic peninsula underwent a transition from a shallow shelf to an overdeepened shelf in the early pliocene this modification of the marine scape was due to a relatively brief interval of erosion begun at 5 2 ma the erosion was caused by high frequency advances of a super inflated antarctic peninsula ice sheet apis the frequent advances of the higher elevation ice sheet were a consequence of abundant moisture delivered to the region as the polar front migrated southward by 5 12 ma ice streams incised foredeepened glacial troughs into basement on the inner shelf sediment eroded from the inner shelf was transported through cross shelf troughs and deposited in large trough mouth fan depocenters on the upper slope overdeepened shelf conditions became widespread as troughs widened and intra trough banks beveled by 4 25 ma trough mouth fan construction ceased and subsequent advances of the apis have been infrequent we propose that the reduced frequency of grounding events signaled the transition to a modern foredeepened and overdeepened shelf we hypothesize that a new glacial dynamic emerged in the early pliocene because overdeepening led to accelerated heat exchange between the ocean and apis in two ways firstly the overdeepened shelf required that a larger area of the grounded ice sheet s marine terminus be in contact with the ocean secondly erosional deepening of the outer shelf was equivalent to lowering a shelf edge sill that permitted frequent and voluminous intrusion of warm circumpolar deep waters that upwell in the region the resultant accelerated melting at the apis marine terminus caused the super inflated apis to deflate on the mainland which further decreased the possibility that grounded ice could advance on the overdeepened shelf

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

margin architecture reveals the transition to the modern antarctic ice sheet ca 3 ma seismic reflection data collected primarily on the continental slope of the pacific margin of the antarctic peninsula after drilling ocean drilling program odp leg 178 allow us to date a regional change in the style of margin accretion to ca 3 ma late pliocene deep erosion of continental shelf and slope which likely included the emplacement of a megadebris flow deposit was followed by prominent growth of steep relatively stable continental slope prograding wedges while the deep distal margin sedimentation rate was significantly reduced a review of the available stratigraphy from deep sea drilling project odp drilling and correlation with available seismic stratigraphic information allowed us to recognize comparable changes in terms of age and trends in continental margin evolution in several places around antarctica we argue that this late pliocene architectural change of the antarctic margin reflects a change in the texture and water content of the sediment delivered by the antarctic ice sheet following the transition from wet to dry based ice regimes this circum antarctic change coincides with the late pliocene ca 3 ma global cooling and is proposed as the marker event of the transition to the modern cold polar dry based antarctic ice sheet

seismic stratigraphy of the antarctic peninsula pacific margin a record of pliocene pleistocene ice volume and paleoclimate multichannel seismic profiles across the pacific margin of the antarctic peninsula show a series of oblique progradational sequences these sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum reflection events from deeper stratigraphic levels followed down the continental slope and onto the rise overlie ocean crust of known age showing that at least eight such glacial sequences have been deposited within the past 6 m y similar groundings have probably occurred on most antarctic margins but the depositional record is particularly well preserved at this margin because of pliocene pleistocene thermal subsidence neogene global sea level fluctuations have been attributed to changes in volume of continental ice sheets the depositional sequences on the pacific margin of the antarctic peninsula are thought to record west antarctic ice sheet fluctuations directly further investigation of these sequences would assess the relation between fluctuations in ice volume and the low latitude record of global sea level change

repeated advance and retreat of the east antarctic ice sheet on the continental shelf during the early pliocene warm period abstract diatom analysis of a sediment core recovered at iodp site u1358 on the continental shelf off the adelie coast indicated that the lower section of the core contained an assemblage dating back to the thalassiosira innura zone of the lower pliocene that ranges from 4 2 to 5 12 ma based on lithological descriptions at both a macro and micro scale of this early pliocene part of the core four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site facies 1a and 1b contain a distinct directional signal from the orientation of the a axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed facies 1c and 1d are finely laminated and were deposited in open marine conditions the four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the wilkes subglacial basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early pliocene the times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin this has significant implications because firstly it suggests a dynamic east antarctic ice sheet eais that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf it also has important implications for the future behaviour and sensitivity of the eais under present continuing warming conditions together with results from the rise this paper provides a crucial ice extent target for a new ice sheet model of this region during the pliocene

mineralisations pb zn sous inconformite des series de plates formes carbonatees exemple du gisement de treves gard france relations entre dolomitisations dissolutions et mineralisations le gisement zn pb de treves est situe dans le lias de la bordure orientale des causses sud est du massif central francais les concentrations principales constituent des amas stratoides portes par le lotharingien inferieur elles sont aureolees par des mineralisations fissurales ou disseminees reparties de l hettangien superieur a la base du domerien dans une serie entierement dolomitisee l analyse comparee de la serie calcaire peu transformee en bordure du gisement et de son equivalent lateral dolomitise remanie par dissolution et mineralise nous a permis de retracer l evolution paleographique et sedimentologique de l enveloppe des concentrations ainsi que le cheminement parallele des metaux cette reconstitution est resumee schematiquement par la figure 18 l etude gitologique montre que les phenomenes de dolomitisation dissolution et mineralisation s operent en relation avec une emersion qui se situe a la limite lotharingien inferieur lotharingien superieur et se developpent en milieu margino littoral de type mangrove les premiers indices sulfures apparaissent precocement dans les calcarenites du lotharingien inferieur avant leur dolomitisation puis vraisemblablement durant celle ci la mise en place des concentrations succede a la dolomitisation et s effectue parallelement au developpement de dissolutions l etude gitologique nous conduit en outre a envisager que le halo d indices qui cerne la mineralisation principale resulte de la remobilisation partielle de celle ci lors de recristallisations ulterieures en dolosparite blanche l etude de la distribution de pb zn cu et ba montre que le niveau porteur des concentrations principales succede a des formations deficitaires en zn pb et ba en interpretant ce deficit en termes de retenue a la source preconcentration continentale ou de mise en reserve dans les eaux connees on peut envisager une reutilisation ulterieure du stock metal correspondant l etude geochimique montre egalement que la dolomitisation s accompagne d un lessivage de zn ba et pb et n affecte pas cu les quantites mises en jeu ainsi que la concordance entre les elements lessives et la nature des accumulations qui succedent au lessivage nous ont amenes a opter pour un modele genetique dans lequel les metaux liberes par la dolomitisation contribuent pour une part importante aux concentrations principales

new insights on the post rift seismic stratigraphic architecture and sedimentary evolution of the antarctic peninsula margin central bransfield basin abstract a seismic stratigraphic study of the antarctic peninsula margin of the central bransfield basin was conducted using seismic and bathymetric data the study focused on seismic sequences and units deposited after the basin opened and yield a record of the evolution of the northern most antarctic peninsula ice sheet two seismic sequences compose the post rift stratigraphic succession on the central bransfield basin slope platforms both sequences are composed of seismic units that record glacial interglacial cycles and show evidence of the antarctic peninsula ice sheet having grounded on the continental shelf and slope platform on several occasions in the past this evidence includes glacial and glaciomarine related sedimentary and erosional features within the seismic units glacial unconformities glacial troughs till wedges prograded wedges trough mouth fans glaciomarine sheet deposits and moraines which are bounded by glacial unconformities the antarctic peninsula lower slope also registered in its eastern sector the deposition of gravity flow deposits during ice sheet retreat and interglacial stages the deposition of seismic units on the middle slope produced the present day step like profile of the margin composed of wide flat slope platforms and narrow and steep upper and lower slopes seismic units show changes in thickness and distribution that record the effect of the physiography and climatic changes on margin sedimentation these variations produced an overall change from more line sourced deposition to more point sourced deposition as ice streams evolved the stacking of units shows a change in the stratigraphic architecture through time from dominantly progradational s2 to progradational aggradational s1 this change is correlated with a change in the frequency of ice sheet grounding events which was probably driven by a higher rate of eustatic rise and fall in relation with the mid pleistocene global climatic change

piston core based biostratigraphic constraints on pleistocene oscillations of the west antarctic ice sheet in western ross sea between north basin and and 1b drill site abstract new diatom biostratigraphic age data derived from piston core were used to constrain the chronology for a seismic based interpretation of west antarctic ice sheet wais advance and retreat from the north basin outer shelf in western ross sea the data demonstrates that grounded ice occupied the outer shelf on at least ten occasions during the last 2 0 ma of the pleistocene although the biostratigraphic resolution is low the constraints permit correlations to coeval section recently drilled in south mcmurdo sound at the and 1b drill site our interpretation of regional scale correlations suggests that the pleistocene dynamics of the wais involved grounding line translations in excess of 600 km however the data also suggests that only two major advances of grounded ice occurred since 0 71 ma in other words several of the late pleistocene sediment cycles at and 1b must represent only minor advance and retreat of grounded ice to and from south mcmurdo sound the results prove false the long standing tacit assumption that the wais experienced major advances in association with peak glacials and eustatic lowstands during the last 700 ka of the pleistocene these results show that piston cores can be used to constrain the timing of pre holocene grounding events these data also highlight the need for regional scale correlations to distinguish between major versus minor grounding line translations of grounded ice in the marine setting

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

pleistocene collapse of the west antarctic ice sheet some glacial sediment samples recovered from beneath the west antarctic ice sheet at ice stream b contain quaternary diatoms and up to 108 atoms of beryllium 10 per gram other samples contain no quaternary diatoms and only background levels of beryllium 10 less than 10 6 atoms per gram the occurrence of young diatoms and high concentrations of beryllium 10 beneath grounded ice indicates that the ross embayment was an open marine environment after a late pleistocene collapse of the marine ice sheet

late cenozoic evolution of high gradient trough mouth fans and canyons on the glaciated continental margin offshore troms northern norway paleoclimatic implications and sediment yield trough mouth fans contain information about the evolution of high latitude continental margins including rates of glacial sedimentation and hinterland erosion here the late cenozoic evolution of high gradient trough mouth fans and canyons on the troms margin northern norway is reconstructed paleocanyons were active prior to the quaternary glaciations glaciomarine and glaciofluvial conditions prevailed between ca 2 7 ma and ca 1 5 ma and ice sheets possibly reached the paleo shelf break at least once the minimum average sedimentation rate of this period was 0 22 m k y from ca 1 5 ma to ca 0 7 ma the glaciations intensified and fast flowing ice streams reaching the shelf break were established in the cross shelf troughs subglacial deformation till was deposited at the outer shelf and later reworked by debris flows and turbidity currents the fennoscandian ice sheet started to route much of its ice mass to the north and south of the study area and so the troms margin possibly was a low ice flow sector from this time with a minimum average sedimentation rate of 0 15 m k y during the last ca 0 7 m y ice streams continued to traverse the troughs while sluggish flowing ice prevailed on the banks a minimum average sedimentation rate of 0 14 m k y is estimated for this period the minimum total erosion and erosion rate for the quaternary are 50 140 m and 0 02 0 05 m k y respectively compared with previous studies from other areas this implies up to one order of magnitude variation in average glacial erosion rates along the western sector of the fennoscandian barents sea ice sheets this is interpreted to be due to the size and bedrock composition of the catchment areas and the timing of ice growth and ice sheet dynamics in addition the steep preglacial continental slope promoted high sediment flow velocity for the glacigenic sediments causing much of the debris flows to transform into turbidity currents which efficiently transported sediments across the slope and thereby maintained its steep gradient

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

nature of the antarctic peninsula ice sheet during the pliocene geological evidence and modelling results compared abstract in this paper we examine the nature of the pliocene antarctic peninsula ice sheet by comparing the terrestrial and marine geological records of the antarctic peninsula and surrounding sea floor with estimated net snow accumulation in the region derived from numerical palaeoclimate model experiments pliocene geological data and our new modelling results are consistent and mutually supportive in suggesting that an ice sheet was present even during the warmest episodes of the pliocene the combined results suggest that the ice sheet in the antarctic peninsula is more robust to globally warmer conditions than is generally assumed at least up to the climatic limits examined in our study

seismic stratigraphy of the central basin in northwestern ross sea slope and rise antarctica clues to the late cenozoic ice sheet dynamics and bottom current activity abstract sedimentation processes influenced by late cenozoic ice sheet dynamics and bottom current activity can be extracted from the seismic stratigraphic record of the ross sea continental slope and rise where more continuous sedimentary successions are preserved compared to the continental shelf in this study we present a seismic stratigraphic analysis of the central basin that lies in the northwestern ross sea using newly acquired and existing legacy seismic reflection data that are correlated to adjacent scientific drill sites the chronostratigraphy of ross sea seismic sequences lying above the mid miocene sequence boundary rsu4 ca 16 5 15 5 ma is based on the former antarctic offshore stratigraphy antostrat project depth contour and isopach maps of sedimentary sequences bounded by two major unconformities of rsu4 and rsu2 the late pliocene boundary ca 4 0 2 8 ma and the present day seafloor were produced to illustrate the evolution of paleo seafloor morphology distribution of sediments and depocenter migration in the western ross sea outer margin the results of seismic stratigraphic analysis indicate that gravity sedimentation processes dominated the central basin infill up to the mid miocene and then downslope sediment supply gradually diminished through the late miocene and quaternary likely reflecting a shift toward a cooler less erosive glacial regime change since the late pliocene a topset truncated glacial prograding wedge developed in the upper continental slope at the mouth of the joides basin and the sediment depocenter was shifted from the basin floor to the upper slope suggesting the more persistent occurrence of grounded ice sheets on the outer continental shelf meanwhile persistent along slope bottom current processes formed contourites on the slope and over the crests of banks surrounding the central basin since the mid miocene in the late pliocene the contourites that formed off the joides basin mouth were overlain by glaciogenic debris flows while the growth of contourites continued over and along the flanks of banks farther to the north this suggests that along slope bottom current processes near the joides basin mouth were diminished or dominated by the glacial discharge to the continental shelf edge the sediment stacking patterns differ between the joides central basins and the drygalski adare basins located on the westernmost ross sea margin suggesting that distinctive glacial interglacial behavior of the former grounded ice streams and sediment supplies in the troughs feeding these basins were largely controlled by the paleo seafloor morphology of the western ross sea continental shelf

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

amundsen sea sediment drifts archives of modifications in oceanographic and climatic conditions abstract drift deposits document stages of particular dynamic bottom currents and associated sedimentary transport activities the analysis of seismic reflection data from the amundsen sea southern pacific ocean reveals sediment drift formation already in eocene oligocene times this observation indicates bottom current activity and hence a cold climate for the late palaeogene in an area which today lies under the influence of antarctic bottom water aabw originating in the ross sea the generation of sediment drifts is accompanied by the occurrence of mass transport deposits leading to the identification of a phase of strong ice sheet expansion 15 4 ma which due to a change in ice regime from wet to dry based was followed by less material input during the last 4 ma

did the antarctic ice sheets expand during the early pliocene seismic data show that glacial unconformities are located within lower pliocene strata on the antarctic continental shelves the glacial unconformities are significant because they provide direct evidence that the antarctic ice sheets advanced despite the generally warmer climates and elevated sea levels that characterized most of the early pliocene the magnitudes of peak eustatic lowstands and 18 o enrichments indicate that the ice volume on antarctica may have exceeded today9s ice volume by approximately 18 which suggests that the ice sheet grounding events on the shelves probably were associated with larger than present ice volumes on two to three occasions during the early pliocene

seismo stratigraphic analysis of the wilkes land continental margin east antarctica influence of glacially driven processes on the cenozoic deposition abstract multichannel seismic reflection data were collected from the wilkes land continental margin and particularly focusing on the lower rise area by the international wilkes basin glacial history wega project existing lower resolution seismic data also are used to understand the relationship between the basement and the sedimentary cover and to correlate the evolution of the rise and the shelf on the basis of the acoustic character and the internal geometry we recognise nine different sequences named wl s1 wl s9 from the deepest to the shallowest within the sedimentary section sequence wl s1 represents syn rift sediments deposited within tilted blocks of sedimentary crystalline and volcanic basement sequences wl s2 wl s9 represent the post rift sediments that show quite a complex architecture sequence wl s2 is a well developed wedge downlapping onto the break up unconformity sequences wl s3 wl s7 are parts of a margin prograding aggrading sequence during which large sediment ridges were deposited on the slope and rise in particular sequences wl s5 wl s7 began with the deposition of a turbidite fan system sequence wl s5 that developed in a braided channel levee complex wl s6 wl s7 dominated by downslope flows indirect correlation of the sequences wl s4 wl s6 with dsdp 269 about 600 km north of the study area suggests an early late miocene age sequences wl s8 and wl s9 represent the smoothing and filling of the pre existing morphology in a generally low energy environment with reduced bottom current activity during this time most of the sediment is deposited on the shelf and slope while the rise is generally starved differences in downslope current energy and in sediment load are interpreted to reflect variation of the terrigenous input from the shelf to the rise through time we suggest that channel levee systems on the rise reflect an increase in sediment supply from the continental shelf during the early miocene marking the growth of wet based temperate ice sheet on the near continent the youngest sequences on the rise and shelf reflect decreased sediment supply to the rise that may be related to the transition from a temperate to a polar glacial system

the permafrost regime in the mackenzie delta beaufort sea region n w t and its significance to the reconstruction of the palaeoclimatic history observed depths to the base of the ice bearing permafrost bpf as determined from geophysical well log and survey information in the mackenzie delta and offshore beaufort sea continental shelf show significant variation depths range from over 700m beneath the northeastern portion of richards island and the adjacent offshore region to the north to less than 100m in the modern mackenzie delta and offshore mackenzie bay regions along the tuktoyaktuk peninsula permafrost thicknesses exceed 600m but tend to thin to less than 100m in a southeasterly direction the wide variation in the thickness and distribution of permafrost is due in part to differences in the subsurface deltaic lithologies and to the complexity of the past surface temperature history exhibited for example by fluctuations of the mean annual ground temperature geological cross sections showing variation in the tertiary and upper cretaceous deltaic sequences indicate a good correlation with the permafrost distribution in particular where the sand and gravel units of the iperk and kugmallit sequences predominate permafrost is thick owing to the high thermal conductivities of the ice rich sediments conversely where the low thermal conductivity shales and mudstones of the richards sequence are present permafrost is accordingly thinner numerical models of permafrost aggradation in the mackenzie delta region suggest that early and late wisconsinan surface temperatures were of the order 18 c a mid wisconsinan rise in temperature to approximately 8 c similar to mean surface temperature today is also indicated this proposed palaeoclimate is sufficient to account for the observed maximum permafrost thicknesses in the region

high resolution sequence stratigraphy of clastic shelves iv high latitude settings abstract high frequency clastic shelf sequences deposited in high latitude settings display marked differences in term of facies and stratigraphic architecture with respect to their lower latitude counterparts this is due to the presence of ice which 1 leads to the accumulation of glacigenic and glacimarine deposits 2 provides an additional control on accommodation and 3 determines the position of the shoreline transgressions and regressions in glaciated settings are controlled respectively by the retreat and advance of the ice shoreline i e the water ice contact irrespective of relative sea level changes once the ice retreats across the land the traditional land shoreline is exposed and the control on sequence architecture is exerted by the interplay between relative sea level changes and sediment supply as in low and middle latitude settings a general model that includes both glacial and non glacial climatic regimes is provided by this paper in this frame the classic sequence stratigraphic model represents one ice free end member which is opposed to an ice permanent end member between these end members sequences may accumulate in part under ice free conditions and in part under conditions dominated by ice on the shelf the main implication of this is that the classic sequence stratigraphic model may be viewed as only a possible scenario in the stratigraphic record rather than the rule

an ice grounding line wedge from the ghaub glaciation 635 ma on the distal foreslope of the otavi carbonate platform namibia and its bearing on the snowball earth hypothesis our detailed examination of the ghaub formation possibly 635 ma on the distal foreslope of the otavi carbonate platform is part of a regional study of the congo paleocontinental margin in northwestern namibia detrital carbonates of the ghaub formation disconformably overlie the franni aus member of the ombaatjie formation a coarsening upward stack of carbonate turbidites and oolite clast debris flow breccias interpreted to be a glacioeustatic falling stand wedge within the main ghaub formation carbonate diamictites are interleaved with mesoscale laminated to cross laminated climbing rippled grainstones and mudstones and conglomeratic carbonates amalgamation of diamictite units is observed where interleaved facies grainstones mudstones are laterally discontinuous due to reactivation of erosion followed by renewed deposition the diamictite package is progradational overall and 80 m thick on average it is overlain by the 5 15 m thick bethanis member which is unique in its lateral continuity composite fining upward trend and distinctive interbedding of turbidite grainstones argillaceous siltstones climbing rippled mudstones and meter scale stromatolite dropstones dropstones are ubiquitous within the finer grained ghaub lithofacies and their presence along with the facies context for subglacial and near grounding line deposition indicates a glacigenic origin for the ghaub formation despite its subtropical paleolatitude and distal foreslope setting we infer a glacial maximum represented by the sub ghaub disconformity followed by the main ghaub interval when an ice grounding line on the distal foreslope experienced abrupt step backs and readvances of limited magnitude terminated by the bethanis episode of unusually widespread iceberg calving and slope instability the bethanis member is overlain conformably by the keilberg member of the maieberg formation reconstruction of the foreslope places the ghaub grounding line wedge 1 3 km vertically below the rim of the platform implying an enormous base level change upon deglaciation when the platform was drowned below wave base for a period far exceeding the time scale for isostatic adjustment the magnitude of base level change supports the pan glacial hypothesis that dynamic thick ice sheets existed simultaneously on virtually all continents the snowball hypothesis that the oceans were also covered by glacial ice sea glacier provides a simple explanation for the main ghaub to bethanis transition terminal deglaciation was triggered by collapse of the sea glacier

sea surface temperature control on the distribution of far traveled southern ocean ice rafted detritus during the pliocene the flux and provenance of ice rafted detritus ird deposited in the southern ocean can reveal information about the past instability of antarctica s ice sheets during different climatic conditions here we present a pliocene ird provenance record based on the 40ar 39ar ages of ice rafted hornblende grains from ocean drilling program site 1165 located near prydz bay in the indian ocean sector of the southern ocean along with the results of modeled sensitivity tests of iceberg trajectories and their spatial melting patterns under a range of sea surface temperatures ssts our provenance results reveal that ird and hence icebergs in the prydz bay area were mainly sourced from i the local prydz bay region and ii the remote wilkes land margin located at the mouth of the low lying aurora subglacial basin a series of ird pulses reaching up to 10 times background ird flux levels were previously identified at site 1165 between 3 3 and 3 0 ma our new results reveal that the average proportion of ird sourced from distal wilkes land margin doubles after 3 3 ma our iceberg trajectory melting models show that slower iceberg melting under cooling ssts over this middle pliocene interval allowed wilkes land icebergs to travel farther before melting hence declining ssts can account for a large part of the observed ird provenance record at site 1165 in early pliocene ird layers sampled at suborbital resolution around 4 6 ma we find evidence for significant increases in icebergs derived from wilkes land during very warm interglacials this is suggestive of large scale destabilization of the east antarctic ice sheet in the aurora subglacial basin as far traveled icebergs would have to overcome enhanced melting in warmer ssts our results highlight the importance of considering ssts when interpreting ird flux and provenance records in distal locations

morphology and acoustic character of the antarctic wilkes land turbidite systems ice sheet sourced versus river sourced fans the wilkes land continental slope contains an intricate network of submarine canyons that on the continental rise develop into a series of channel and overbank deposits of turbidite systems we can define upper fan middle fan and lower fan provinces the wilkes land upper fans are characterized by large channels with relief up to 900 m distances between levee crests up to 18 km and channel floor widths up to 6 km middle fan channels also have high relief 300 m and locally interchannel areas exhibit mounded contourite style deposits with high relief up to 490 m within middle fan sediment mounds there are acoustic facies of channel overbank deposits from turbidity currents and of sediment waves from contour current sedimentation the lower rise is characterized by small shallow channels 50 75 m relief and by interchannel areas of low relief both characteristic of a lower fan environment the wilkes land turbidite systems show the following significant morphological differences compared to most river sourced fans 1 multiple large tributary channels across the upper and middle fan 2 channel relief several times greater 900 m than typical relief 100 200 m for channels on fans less than 300 km in diameter and 3 steep middle fan and lower fan gradients we interpret the differences in channel network patterns channel size and middle fan and lower fan gradients between the wilkes land fans and other fans to result from the continental ice sheet feeding glacial ice streams that reached the outer continental shelf at times of glacial maxima the wilkes land canyon channel network patterns are comparable with the high latitude laurentian fan and labrador sea channels the laurentian fan also has large upper fan channels with larger relief 800 m than typical relief 200 300 m expected for fans that are 600 km in diameter both the labrador sea and laurentian fan are fed by continental ice sheets at the shelf edge

seaward growth of antarctic continental shelves since establishment of a continent wide ice sheet patterns and mechanisms abstract the location and setting of the continental shelf break along the antarctic continental shelves influences the paleoceanographic circulation patterns as well as sedimentation and ice sheet dynamics by evaluating the available multichannel seismic reflection data and drill core information we mapped the base of progradational features associated with the first advances of grounded ice sheet to the outer shelf the distance between the modern shelf edge and the pre glacial shelf edge varies from 200 km e g ross sea to

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

late neogene geomorphological and glacial reconstruction of the northern victoria land coast western ross sea antarctica abstract this study is a contribution to the reconstruction of the geomorphology and the glacial history of the northern victoria land coastal glaciers high resolution single channel reflection seismic lines were collected in 2002 within the framework of the italian antarctic programme pnra in wood bay and lady newnes bay north to cape washington western ross sea antarctica the data provide evidence of overdeepened marine subglacial valleys more than 1 km deep and 1 2 km wide formed along the seaward extension of the tinker aviator fitzgerald and icebreaker glaciers and converging into the major sw ne ice stream system the spatial distribution and the geometry of the seismic facies as well as the direct correlation with the seismic sequences in the northern basin are interpreted to document 1 the depositional activity of a coastal glacial system seaward of northern victoria land nvl after 18 ma based on the seismic correlation with the base of dsdp 273 and possibly in the early pliocene in coalescence with expanded ice streams coming from the south along the drygalski basin possibly draining from the wais as documented at and 1b in the mcmurdo sound naish et al 2007 2008 2009 followed by 2 the development of tam tidewater glaciers that carved sea valleys near the victoria land coast onto the shelf the transition from a dynamic thick ice sheet covering the coastal area of nvl to the nvl valley glaciers advancing and retreating up to about 100 km from the coast in the middle pliocene would represent a significant environmental change possibly from interglacial conditions more temperate than today and gradually cooling to a cold and dry coastal regime

seismic data from the northern basin ross sea record extreme expansions of the east antarctic ice sheet during the late neogene abstract approximately 3700 km of intermediate resolution single channel seismic data from the northern basin were analyzed to investigate the late neogene history of east antarctic ice sheet eais grounding events on the shelf and to evaluate how glacial unconformities on the shelf are manifested on the upper slope the northern basin was chosen as the site of this study because ice sheet reconstructions show that the basin received sediment by ice emanating from east antarctica in addition seismic correlations to dsdp site 273 suggest that a relatively thick late neogene section exists on the basin s outer shelf and upper slope on the northern basin shelf glacial unconformities exhibiting broad low angle relief topset truncation and cross cutting relationships reveal a dynamic history of expansions and contractions during which the eais was larger than present on at least eight occasions during the late neogene on the upper slope the correlative conformities of the glacial unconformities are indistinct reflections within thick trough mouth fan tmf depocenters at the mouths of drygalsky and joides basins the glacial unconformities and correlative conformities define tmf sequences and each tmf sequence contains several topset truncated prograding slope reflectors we infer that the correlative conformities on the continental slope correspond to the interface between prograding glaciogenic deposits glacial maximum and diatomaceous glacial marine sediments glacial minimum the seismic stratigraphic analysis and regional mapping indicate that the upper slope does not contain a more complete late neogene section than that which exists on the shelf we infer that diatomaceous glacial marine sediments on the slope may be relatively undisturbed and hence may provide a means of dating the tmf sequences it is hoped that these results will stimulate efforts to core the late neogene section in the northern basin tmfs to investigate how these eais expansions and contractions relate to other records of late neogene climate and eustasy

are antarctic peninsula ice sheet grounding events manifest in sedimentary cycles on the adjacent continental rise the direct record of late miocene early pliocene antarctic peninsula ice sheet expansions from a previously published seismostratigraphic study of the outer shelf at ocean drilling program site 1097 is compared to the glacial history we deduced from published proxy evidence within coeval sections on the adjacent continental rise the proxies are sedimentary structures laminated vs massive bioturbated facies and clay minerals predominantly smectite and chlorite contents from ocean drilling program site 1095 located on the distal part of a large drift the comparison shows that more sedimentary cycles are evident on the continental rise for three of the four diatom biozones we considered this indicates that the continental rise sedimentology may indeed be related to local or regional paleoenvironmental variability including antarctic peninsula ice sheet grounding events on the adjacent outer continental shelf if correct this would be a promising result because unlike the outer continental shelf sequences drilled thus far the continental rise record is relatively continuous and can be dated using paleomagnetic and biostratigraphic data however our study also shows that no objective criteria provide direct linkages between the glacial history we deduced from the two continental rise proxies and that previously derived from the continental shelf seismic stratigraphy furthermore the two sedimentologic proxies on the continental rise do not always provide a consistent picture of glacial history when compared against each other

a review of tertiary climate changes in southern south america and the antarctic peninsula part 2 continental conditions abstract climate changes in southern south america and the antarctic peninsula during the tertiary show a strong correlation with ocean warming and cooling events which are in turn related to tectonic processes during periods of accelerated sea floor spreading and mid ocean ridge activity sea levels rose so that parts of the continents were flooded and forests were destroyed however this was balanced by the large scale release of co2 during volcanic outgassing and carbonate precipitation on the continental shelves which caused rising air temperatures and the poleward expansion of sub tropical and temperate forests cooling episodes generally caused an increase in the north south thermal gradient because of an equatorward shift in climate belts so that the westerly winds intensified and brought higher rainfall to the lower latitudes an increase in wind blown dust caused temperatures to drop further by reflecting sunlight back into space the rising andes range had a marked influence on climate patterns up to the middle miocene it was still low enough to allow summer rainfall to reach central and north central chile but after about 14 ma it rose rapidly and effectively blocked the spill over of moisture from the atlantic ocean and amazon basin at this time the cold humboldt current was also established which together with the andes helped to create the arid diagonal of southern south america stretching from the atacama desert to the dry steppes of patagonia this caused the withdrawal of subtropical forests to south central chile and the expansion of sclerophytic vegetation to central chile however at the same time it intercepted more rain from the northeast causing the effect of the south american monsoon to intensify in northwestern argentina and southern bolivia where forest communities presently occur in patagonia glaciation started as early as 10 5 ma but by 7 ma had become a prominent feature of the landscape and continued apparently uninterruptedly into the pleistocene the antarctic peninsula saw its first mountain glaciation between 45 and 41 ma with major ice sheet expansion commencing at about 34 ma isolated stands of nothofagus forests were still present in low lying areas suggesting that the glaciers were initially wet based but dry based glaciers were established at around 8 ma although temperatures rose briefly during the messinian pliocene transition causing sub antarctic flora to retreat to higher elevations of the transantarctic mountains the present cold polar conditions were finally established by about 3 ma

depositional processes on the distal scoresby trough mouth fan odp site 987 implications for the pleistocene evolution of the scoresby sund sector of the greenland ice sheet accepted manuscript version licensed cc by nc nd 4 0 published version available at https doi org 10 1016 j margeo 2017 11 018

margin architecture reveals the transition to the modern antarctic ice sheet ca 3 ma comment and reply comment rebesco et al 2006 1 present multichannel seismic mcs reflection profiles showing a regional change in the style of margin accretion on the pacific margin of the antarctic peninsula pmap and estimate an age of ca 3 ma for this change by correlation with ocean drilling program odp site

coarse grained terrigenous sediment deposition on continental rise drifts a record of plio pleistocene glaciation on the antarctic peninsula sediment drifts on the continental rise are located proximal to the western side of the antarctic peninsula and recorded changes in glacial volume and thermal regime over the last ca 15 m y at ocean drilling program odp site 1101 leg 178 which recovered sediments back to 3 1 ma glacial interglacial cyclicity was identified based on the biogenic component and sedimentary structures observed in x radiographs magnetic susceptibility and lithofacies descriptions glacial intervals are dominated by fine grained laminated mud and interglacial units consist of bioturbated muds enriched in biogenic components from 2 2 to 0 76 ma planktonic foraminifera and calcareous nannofossils dominate in the interglacials suggesting a shift of the antarctic polar front apf to the south near the drifts prior to 2 2 ma cyclicity cannot be identified and diatoms dominate the biogenic component and high percent opal suggests warmer conditions south of the apf and reduced sea ice over the drifts analyses of the coarse grained terrigenous fraction pebbles and coarse sand from sites 1096 and 1101 record glaciers at sea level releasing iceberg rafted debris ird throughout the last 3 1 m y analyses of quartz sand grains in ird with the scanning electron microscope sem show an abrupt change in the frequency of occurrence of microtextures at similar to 1 35 ma during the late pliocene to early pleistocene the population of quartz grains included completely weathered grains and a low frequency of crushing and abrasion suggesting that glaciers were small and did not inundate the topography debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass through the glacier unmodified during glacial periods from 1 35 0 76 ma glaciers expanded in size the hid flux was very high and dropstones have diverse lithologies conditions resembling those at the last glacial maximum lgm have been episodically present on the antarctic peninsula since similar to 0 76 ma quartz sand grains show high relief fracture and abrasion common under thick ice and the ird flux is low with a more restricted range of dropstone lithologies

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures