origin and significance of calcium carbonate in soils of southwestern patagonia abstract a soil chronosequence spanning the last 0 76 1 0 ma shows a progressive increase in calcium carbonates based on 1 thickness of the bk bck horizons 2 maximum carbonate stage 3 profile accumulation of pedogenic carbonates and 4 mass flux of ca from a geochemical mass balance we favor a dust origin of the carbonates because 1 the till parent materials contain low amounts of caco3 2 there is minimal evidence for weathering of ca bearing minerals in the soil 3 the amount of caco3 in the profile is far in excess of what could be released by weathering 4 dust collected from the study area is enriched in caco3 and 5 a source area for the carbonates was identified although there likely were changes in dust deposition rates during the quaternary our calculations suggest that the current deposition rate of 0 18 g caco3 m 2 yr 1 is comparable to the long term profile accumulation rate of 0 16 g caco3 m 2 yr 1 230th u disequilibrium ages of carbonate pendants are consistent with cosmogenic surface exposure ages indicating that this method has potential for dating other geomorphic surfaces in patagonia cryogenic processes have affected many of the pedons particularly during the last glacial maximum

geological perspectives on the monte verde archeological site in chile and pre clovis coastal migration in the americas discovery of the monte verde archeological site in chile overturned the previous consensus that the first americans into the new world from asia were the makers of clovis projectile points and rejuvenated the hypothesis that migration through the americas occurred largely on portions of the pacific continental shelf exposed by pleistocene drawdown in eustatic sea level the postulate of travel along a paleoshoreline now hidden underwater is an attractive means to posit pre clovis human movement southward from beringia to chile without leaving traces of migration onshore geologic analyses of the pleistocene paleoenvironment at monte verde and of the morphology of the potential migration route along the continental shelf raise questions that have not been fully addressed the periglacial setting of monte verde may call its antiquity into question and the narrowness of the pacific continental shelf of the americas makes it unlikely that people could travel the length of the americas without impacting ground still onshore and no farther inland than monte verde itself geological perspectives on monte verde and coastal migration jointly suggest that the clovis first hypothesis for peopling the new world may have been abandoned prematurely

interhemispheric synchrony of late glacial climatic instability as recorded in proglacial lake mascardi argentina several high resolution continental records have been reported recently in sites in south america but the extent to which climatic variations were synchronous between the northern and southern hemispheres during the late glacial holocene transition and the causes of the climatic changes remain open questions previous investigations indicated that east of the andes the middle and high latitudes of south america warmed uniformly and rapidly from 13 000 14c yr bp with no indication of subsequent climate fluctuations equivalent for example to the younger dryas cooling here we present a multiproxy continuous record radiocarbon dated by accelerated mass spectroscopy from proglacial lake mascardi in argentina the results show that unstable climatic conditions comparable to those described from records obtained in the northern hemisphere dominated the late glacial holocene transition in argentina at this latitude furthermore a significant advance of the tronador ice cap which feeds lake mascardi occurred during the younger dryas chronozone this instability suggests a step wise climatic history reflecting a global rather than regional forcing mechanism the lake mascardi record therefore provides strong support for the hypothesis that ocean atmosphere interaction rather than global ocean circulation alone governed interhemispheric climate teleconnections during the last deglaciation 1997 john wiley sons ltd

submarine landforms in the fjords of southern chile implications for glacimarine processes and sedimentation in a mild glacier influenced environment abstract chilean fjords are the lowest latitude at which glaciers reach the sea today high accumulation and mass throughput sustain tidewater glacier margins in this relatively mild climatic and oceanographic setting 27 000 km 2 of swath bathymetry allow mapping of sea floor landforms and inferences on glacimarine sediments and sedimentation tidewater glaciers are present in several fjords beyond retreating tempano glacier a terminal moraine marks the limit of probable little ice age advance with smaller transverse ridges closer to the glacier beyond advancing pio xi glacier there are few signs of organised submarine landforms older moraine ridges along several fjords formed at still stands during deglaciation elsewhere meltwater fed braided rivers connect the glacial and marine sedimentary systems swath imagery shows glacifluvial and fluvial deltas with small channels and chutes that develop into long and sinuous turbidity current channels few iceberg ploughmarks and submarine slope failures were observed but several fields of pockmarks were present the fjords of chile are dominated by sediment delivery from turbid meltwater which distributes fine grained debris widely producing sorted and laminated fine grained ice proximal wedges and draping ice distal seismic architecture to give a predominantly smooth sea floor turbidity currents also transfer sediments to some ice distal environments the chilean fjordlands represent the mildest climatic and oceanographic end member of a continuum of glacier influenced marine settings similar to south east alaska in the northern hemisphere components of a landform assemblage model for climatically mild meltwater dominated fjords include ice contact moraine ridges glacifluvial and fluvial deltas and turbidity current channels full glacial and deglacial streamlined subglacial landforms are likely to have been buried in many areas by subsequent glacimarine sedimentation

the last glaciation in central magellan strait southernmost chile abstract glacial landforms and drift stratigraphy in central magellan strait southernmost chile document repeated fluctuations during the last glacial cycle of outlet lobes from an ice cap centered over the southern andes the lobes developed comparatively low gradient profiles because of low basal shear stresses over soft deformable beds and this made them sensitive to even small scale changes in the mass balance such low profiles and rapid calving in deep proglacial lakes during deglaciation may have made the magellan ice lobe particularly responsive to climatic fluctuations during the last glacial cycle and to advance and retreat over considerable distances study of the glacial landforms and drift stratigraphy has led to the identification of at least five glacier advances to limits at and south of the segunda angostura fragments of mollusc shells contained in basal till indicate marine incursions between some advances thus documenting extensive deglaciation a partial chronology based on amino acid studies and radiocarbon dating suggests that five of these advances occurred during the last glacial cycle the most extensive advances may have culminated during substages of marine isotope stage 5 substage 5b or 5d and or during stage 4 slightly less extensive advances occurred between ca 28 000 and 14 000 yr b p

postglacial vegetation fire and climate dynamics at central chilean patagonia lake shaman 44 s a 19 cal ka bp pollen and charcoal record from lake shaman 44 s 71 w chile was analyzed to establish vegetation fire and climate dynamics of the forest steppe ecotone in central chilean patagonia lake shaman record indicates that the upper rio cisnes valley was free of ice at around 19 cal ka bp from this date and until 14 8 cal ka bp a grass steppe with high proportions of shrubs associated to colder and drier conditions than present developed in this area a continuous increase of nothofagus accompanied by a decline in the steppe shrubs and sudden dominance of paludal over aquatic plants from 11 cal ka bp was associated to effective moisture increase but still under modern values the replacement of the cold dry grass shrub steppe by a similar than present forest steppe ecotone suggests an increase in temperature indicating the onset of the holocene at the same time moderate fire activity suggested by the charcoal record could be related to major fuel availability as consequence of nothofagus forest expansion between 8 and 3 cal ka bp the record indicates the easternmost position of the forest steppe ecotone suggesting the highest effective moisture with the establishment of seasonality between 5 and 3 cal ka bp from 3 cal ka bp the record indicates a retraction of the forest steppe ecotone accompanied by a high pollen record variability and an increased fire activity these late changes suggest decreased effective moisture associated with a high climatic variability at regional and extra regional scale climatic changes at lake shaman s record are mostly associated to changes latitudinal shifts and or strengthening weakening of past southern westerlies that were previously recorded along patagonia from the lateglacial to the mid holocene during the late holocene a regional pattern characterized by high record variability emerges throughout central chilean patagonia this variability would be related to 1 low magnitude southern westerlies changes probably associated to enso and or sam or 2 the complex relationships between vegetation fire and human occupations during the last 3 cal ka

structural tectonic and glaciological controls on the evolution of fjord landscapes abstract the fjord landscape of south america stretching 1500 km between golfo corcovado 43 s and tierra del fuego 56 s is the largest continuous fjord landscape on earth this paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models first order geological structures are represented by strike slip faults forming lineaments up to hundreds of kilometres long the strike slip faulting has been active since late cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to 10 km long a detailed analysis of these second order lineaments from digital image data was carried out in three sectors in sector 1 located northwest of the north patagonian icefield there are three distinct mean orientations characterized by a main nearly orogen parallel orientation az 145 and two orogen oblique secondary orientations az 20 and az 65 in sector 2 located west of the south patagonian icefield there are also three separate mean orientations with most of the lineaments concentrated between azimuths 0 and 80 mean at 36 and two other orogen oblique means at azimuth 122 and 163 in sector 3 around the cordillera darwin there is a single main orogen parallel mean at 100 115 in all three sectors mapped fjord orientations bear a striking similarity to the structural data with fjords orientated preferentially in the same direction as structural lineaments we infer that successive glaciations followed the same ice discharge routes widening and deepening pre existing geological structures at the expense of the surrounding terrain to create the fjord landscape this study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological

late quaternary vegetation and climate of southern tierra del fuego vegetation and climate over approximately the past 13 000 yr are reconstructed from fossil pollen in a 9 4 m mire section at caleta robalo on beagle channel isla navarino 54 56 s 67 38 w southern tierra del fuego fifty surface samples reflecting modern pollen dispersal serve to interpret the record chronologically controlled by nine radiocarbon dates fossil pollen assemblages are empetrum gramineae gunnera tubuliflorae zone 3b 13 000 11 850 yr b p gramineae empetrum assorted minor taxa zone 3a 11 850 10 000 yr b p nothofagus gramineae tubuliflorae polypodiaceae zone 2 10 000 5000 yr b p nothofagus empetrum zone 1b 5000 3000 yr b p and empetrum nothofagus zone 1a 3000 0 yr b p assemblages show tundra under a cold dry climate zone 3 followed by open woodland zone 2 as conditions became warmer and less dry and later with greater humidity and lower temperatures by closed forest and the spread of mires zone 1 comparisons drawn with records from antarctica new zealand tasmania and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar southern hemisphere the influences of continental and maritime antarctic air masses were apparently considerable in tierra del fuego during cold late glacial time whereas holocene climate was largely regulated by interplay between maritime polar and maritime tropical air

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

multiproxy record of late pleistocene holocene climate and vegetation changes from a peat bog in patagonia abstract pollen assemblage changes and stable hydrogen isotope analysis of mosses sphagnum magellanicum and drepanocladus s l from a bog in tierra del fuego argentina provided independent proxies for reconstructing changes in effective moisture and temperature over the past 16 000 cal yr b p a deterministic model was used to reconstruct the stable hydrogen isotope composition of meteoric water from the d h ratios of bog mosses over the last 16 000 years abrupt changes in temperature as recorded in d h ratios of moss cellulose were accompanied by synchronous changes in vegetation composition during the late pleistocene and early and middle holocene when moisture levels were lower than today in contrast temperature variability during the late holocene was not accompanied by comparable vegetation changes in particular grass pollen poaceae increased during periodic cold spells between 15 000 and 11 000 cal yr b p but a cold spell of similar magnitude ca 2000 cal yr b p did not appear to affect vegetation during the late pleistocene the isotopic record from the peat core shows variations similar to the d h ratios in the antarctic taylor dome ice core however the timing of the changes in the harberton record is more in line with the timing of other southern hemisphere records

deglacial pattern of circulation and marine productivity in the upwelling region off central south chile abstract a high resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36 s off central south chile geob 7165 1 36 33 s 73 40 w 797 m water depth core length 750 cm indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka comparative analysis of several cores along the chilean continental margin 30 41 s suggests that the onset and the pattern of deglacial warming was not uniform off central south chile due to the progressive southward migration of the southern westerlies and local variations in upwelling marine productivity augmented rather abruptly at 13 14 ka well after the oceanographic changes we suggest that the late deglacial increase in paleoproductivity off central south chile reflects the onset of an active upwelling system bringing nutrient rich oxygen poor equatorial subsurface water to the euphotic zone and a relatively higher nutrient load of the antarctic circumpolar current during the last glacial maximum when the southern westerlies were located further north productivity off central south chile in contrast to off northern chile was reduced due to direct onshore blowing winds that prevented coastal upwelling and export production

the glaciogenic origin of the pleistocene calcareous dust in argentina on the basis of field mineralogical textural and geochemical analyses calcareous dust occurs in argentina as layers and pockets closely associated with pleistocene deposits and periglacial features from southernmost patagonia to at least the mendoza precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper pleistocene deposits between 51 s and 33 s and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment all observations and analyses lead us to conclude that 1 the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic 2 the dust was carried by southeasterly antarctic winds and 3 it was deposited over most of southern and central argentina field observations geomorphic evidence and radiocarbon dates suggest that the dust was deposited during several pleistocene glacial episodes

dynamics of the millennial scale sea surface temperature and patagonian ice sheet fluctuations in southern chile during the last 70 kyr odp site 1233 abstract the ultra high sedimentation rates at odp site 1233 situated at 41 s off chile enabled the investigation of the millennial to multi centennial scale relationship and variability of the patagonian ice sheet pis extent as indicated by the fe relative concentration record and offshore sea surface temperatures sst during the last glacial period the close relationship of the fe record and the sst pattern as described previously for the 50 19 kyr time interval extends in the older part of the records 70 50 kyr during marine isotope stage mis 4 a delay of 500 yr of pis retreats relative to sst increases has been found similar to that described for the coldest part of mis 3 and 2 during early mis 3 60 56 kyr synchronous variability in both records resembles the deglacial to holocene time interval reflecting either a meltwater pulse or a dominant control of the fe input by rainfall changes related to a rather small pis results of spectral analysis on the detrended records show three main periodicity bands at 4 5 3 1 2 4 2 2 and 1 2 0 8 kyr the possible origins of these bands are discussed in terms of stochastic resonance and solar forcing

early deglaciation and paleolake history of rio cisnes glacier patagonian ice sheet 44 s the timing structure and landscape change during the patagonian ice sheet deglaciation remains unresolved in this article we provide a geomorphic stratigraphic and geochronological deglacial record of rio cisnes glacier at 44 s and also from the nearby rio nirehuao and rio el toqui valleys 45 s in chilean patagonia our 14 c 10 be and optically stimulated luminescence data indicate that after the last glacial maximum rio cisnes glacier experienced 100 km deglaciation between 19 0 and 12 3 ka accompanied by the formation of large glacial paleolakes deglaciation was interrupted by several ice readvances and by 16 9 0 3 ka rio cisnes glacier extended only 40 of its full glacial extent the deglaciation of rio cisnes glacier and other sensitive patagonian glaciers occurred at least 1 ka earlier than the ca 17 8 ka normally assumed for the local termination coincident with west antarctic isotope records this early deglaciation can be linked to an orbital forcing driven decline of southern ocean sea ice associated with a distinct atmospheric warming that is apparent for west antarctica through patagonia

the last glacial interglacial transition in patagonia argentina the stable isotope record of bulk sedimentary organic matter from laguna potrok aike abstract an investigation of stable isotope 13 c toc and 15 n tn and elemental parameters toc tn contents and toc tn ratios of bulk organic matter 13 c toc values toc tn contents and toc tn ratios indicate that the lake approached a new state with reduced primary productivity probably induced by unfavourable growing conditions for primary producers like strengthened winds and reduced nutrient availability the steady increase in 15 n tn values presumably suggests limitation of nitrate supply for growth of primary producers resulting from a nutrient shortage after the preceding phase with high productivity nitrate limitation and consequent decreased lacustrine primary productivity continued into the early holocene 10 970 8400 cal years bp as reflected by isotopic and elemental values

sources of dissolved silica to the fjords of northern patagonia 44 48 s the importance of volcanic ash soil distribution and weathering dissolved silica dsi plays an important biogeochemical role in the fjords of northern chilean patagonia 44 48 s where it drives high biogenic productivity and promotes carbon burial it is generally believed that the dsi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology climate topography vegetation and meltwater input in northern chilean patagonia several authors have proposed that the postglacial volcanic ash soils andosols may play a significant role in the high supply of dsi to the regional fjords to assess the influence of andosols on dsi concentrations in north patagonian rivers we mapped andosol thickness and compared our results with river chemistry the mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes the andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes i e high amounts of amorphous material plagioclase k feldspar and pyroxene down profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth resulting from weathering of the volcanic parent material for the five studied watersheds a highly positive correlation r2 0 98 was found between average andosol thickness and dsi concentrations suggesting that andosol thickness is the main parameter affecting dsi concentrations in north patagonian river systems on seasonal timescales increased precipitation winter and glacial meltwater summer input can significantly reduce dsi concentrations we argue that the weathering of andosols constitutes the most important source of dsi to the lakes and fjords of northern chilean patagonia explaining the particularly high regional rates of biogenic silica production copyright 2015 john wiley sons ltd

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

geomorphic records along the general carrera chile buenos aires argentina glacial lake 46 48 s climate inferences and glacial rebound for the past 7 9 ka a reply we present geomorphic stratigraphic and chronological data acquired along the general carrera buenos aires gcba glacial lake located along a major morphological incision across the andes complementing relevant available data relative chronology of morpho climatic records together with 18 10be cosmic ray exposure cre ages allow constraining the timing of the patagonian ice sheet fluctuations since the lgm it improves the knowledge of the patagonia climate evolution in the 46 48 s area and allows documenting the uplift rates glacial rebound for the past 7 9 ka the first major ice lobe retreat occurred after 17 3 0 6 ka and has likely continued during the acr from 12 9 to 14 5 ka between 12 9 ka and 10 9 1 3 ka the general carrera lake evolved as an endorheic basin terraces t4 to t1 top to bottom have recorded abrupt lake regressions likely controlled by rainfall deficit they have accumulated in the time interval 17 3 12 3 ka maximum limits two glacial re advances at 10 9 1 3 and 7 9 1 1 ka marked a major climate change that led the lake to be ice dammed again a major transgression occurred subsequently that have flooded the previously accumulated terraces since then a pervasive regression has steered the gcba lake to the situation at present the highest shoreline of the transgression is used as a passive marker in order to quantify the magnitude and character of the regional deformation at 72 30 w the gcba lake area uplifted glacial rebound at a rate between 15 to 33 5 mm yr 1 during the past 7 9 1 1 ka we infer that the high uplift rate mainly originates from the north patagonian icefield ice loss

timing and dynamics of the last deglaciation from european and north african δ13c stalagmite profiles comparison with chinese and south hemisphere stalagmites abstract the last deglaciation and its climatic events such as the bolling allerod ba and the younger dryas yd have been clearly recorded in the 13 c profiles of three stalagmites from caves from southern france to northern tunisia the three 13 c records dated by thermal ionization mass spectrometric uranium thorium method tims show great synchroneity and similarity in shape with the chinese cave 18 o records and with the marine tropical records leading to the hypothesis of an in phase between 15 5 and 16 ka 0 5 ka postglacial warming in the northern hemisphere up to at least 45 n the ba transition appears more gradual in the speleothem records than in the greenland records and the allerod seems warmer than the bolling showing here close similarities with other marine and continental archives a north south gradient is observed in the ba trend it cools in greenland and warms in our speleothem records several climatic events are clearly recognizable a cooler period at about 14 ka older dryas od the intra allerod cold period at about 13 3 ka the yd cooling onset between 12 7 and 12 9 0 3 ka similar to the ba the yd displays a gradual climate amelioration just after its onset at 12 75 0 25 ka up to the preboreal and is punctuated by a short climatic event at 12 15 ka even though the southern hemisphere stalagmite records seem to indicate that the postglacial warming started about 3 ka 1 8 ka earlier in new zealand 41 s and about 1 to 2 ka earlier in south africa 24 1 s large age uncertainties essentially due to slow growth rates make the comparison still perilous the overall 13 c speleothem record seems to follow a baseline temperature increase controlled by the increase in insolation and punctuated by cold events possibly due to the n america freshwater lake discharges

the last glacial maximum climatic conditions on easter island abstract the aim of this paper is to refine previous estimates of last glacial maximum lgm climatic conditions for easter island samples were analysed for fossil pollen from the lower half of a 13 40 m sediment core rra5 this part of the core includes a time span from ca 28 000 10 000 14 c bp the results show that during this period there were three different climatic conditions first a time span from ca 28 000 23 200 14 c bp with slightly cooler and probably drier conditions relative to present day second a more cool and dry climatic condition from ca 23 200 14 700 14 c bp the second time span had two peak points at ca 22 100 and 17 150 14 c bp it seems that the coolest and driest conditions occurred at 17 150 14 c bp third a warm and wet climate started at ca 15 000 14 c bp and continued until the end of the period studied 10 000 14 c bp in all the time covered in this study there was an inverse relationship between values of palmae and poaceae while poaceae and tubuliflorae shrubs show similar variations the temperature estimations that are presented by different authors based on oxygen isotopes are for approximately 4 c cooling at the lgm however the empirical values derived from the pollen evidence suggest only ca 1 9 c cooling this is in agreement with recently obtained values from tropical lowlands

modelling the inception of the patagonian icesheet abstract we use a coupled climate icesheet model to simulate the inception and growth of the patagonian icesheet assuming a temperature lowering of 6 c and a uniform pressure gradient driving windfields an icesheet builds up with dimensions and morphology similar to that of the last glacial maximum analysis of the stages of growth reveals the following conclusions different sectors of the 1800 km long icesheet behave differently as a result of latitudinal variations in mass balance the fastest growth occurs in latitudes 45 52 s where the north and south patagonian icefields merge and expand to the coast within 1500 model years the most favourable topography for glacier initiation is the presence of high elevation basins low elevation summits in the mountain chain take a long time to become covered by ice because of the delay in ice spreading along the main mountain axis feedback between the increasing elevation of the icesheet and increasing mass balance on its windward flank enhances the rate of migration of the icesheet towards the precipitation source there is a lee side effect whereby easterly mountains are glaciated early on but are then starved of snow as ice builds up to the windward such locations should hold an empirical record of the early stages of a glacial cycle

last glacial maximum environments in northwestern patagonia revealed by fossil small mammals abstract comparisons of historical and modern assemblages of mammals can yield important insights into patterns and processes of environmental change here we present the first analyses of small mammal assemblages present in northern patagonia during the last glacial maximum lgm using remains obtained from owl pellets excavated from an archeological cave site arroyo corral i levels vii v carbon dates of 22 400 21 530 cal yr bp we generate estimates of the minimum number of individuals for all species detected these estimates in turn are used to determine relative species abundances comparisons of these data with similar analyses of small mammal remains obtained from a second archeological site acoii levels iv v carbon dates of 10 010 9220 cal yr bp as well as from modern owl pellets reveal pronounced changes in relative species abundance since the lgm in particular euneomys chinchilloides and ctenomys sociabilis the predominant species during the lgm declined markedly suggesting a change from open bare habitat punctuated by patches of wet meadows and shrubs to the more densely vegetated mosaic of ecotone habitats found in this region today these data provide important new insights into the environmental changes that have occurred in northern patagonia over the last 20 000 years

trace element geochemistry and genesis of precambrian sub alkaline mafic dikes from the central indian craton evidence for mantle metasomatism abstract precambrian mafic dikes transect the archaean granite gneisses of the southern bastar craton central india on the basis of high field strength elements the bastar mafic dike swarms were sub divided into an earlier bd1 and a later bd2 system the bd1 set comprises amphibolites whereas the bd2 set consists of dolerites metadolerites on the basis of field relationships and available age data for enveloping granite rocks the bd1 dikes are regarded as middle archaean in age and bd2 dikes are paleoproterozoic 1 8 ga the silica and total alkalis contents of dikes of both swarms classified them mostly as sub alkaline basalts the bd1 dikes are low ti fe and high mg olivine to quartz normative rocks whereas the bd2 dikes are predominantly quartz normative with relatively high ti fe and low mg contents the high field strength element concentrations are relatively higher in the bd2 dikes than in the bd1 dikes for comparable values of mgo and or cr judging from the geochemical data these dikes probably were not contaminated by crustal components the geochemistry and field observations clearly suggest a continental rift environment for the emplacement of both bd1 and bd2 dikes rare earth element patterns and compatible incompatible trace element modelling suggest that the two swarms were derived from distinctly different sub alkaline basaltic magmas the middle archaean bd1 dikes were derived from 15 20 batch melting of a depleted lherzolite mantle source in contrast the paleoproterozoic bd2 dikes were derived from 7 10 batch melting of a relatively enriched mantle source a post archaean increase in the thickness of metasomatized mantle lithosphere is the probable cause of mantle enrichment

the chronology of the last glacial maximum and deglacial events in central argentine patagonia this paper evaluates the chronology of the last glacial cycle and deglaciation in the lago pueyrredon valley of central patagonia 47 5 s argentina the valley was a major outlet of the former patagonian ice sheet and the moraines that record its fluctuations are an important proxy record of climate change in southern south america such moraines are well preserved in the lago pueyrredon valley owing in part to the semi arid environment east of the mountain front here we provide the first direct chronology for the age of the rio blanco moraine system by utilizing cosmogenic nuclide surface exposure ages boulders on the moraines give 10be exposure ages that indicate the last glacial maximum lgm maximum extent occurred by 27 25 ka subsequent advances occurred at 23 22 ka 20 18 ka and ca 18 17 ka initial deglaciation began after ca 18 17 ka and was interrupted as evidenced by the lago columna moraines up valley subsequently the outlet glaciers occupying both the lago pueyrredon basin chilean name lago cochrane and the lago buenos aires basin chilean name lago general carrera to the north rapidly retreated more than 80 km at around 16 5 15 ka the timing of the lgm maximum extent and the onset of deglaciation occurred broadly synchronously throughout patagonia deglaciation resulted in a series of interconnected glacier dammed lakes in the region that initially drained toward the atlantic ocean and later drained to the pacific ocean as a consequence of disintegrating ice in the andes

pleistocene glaciation in the southern lake district of chile relative age criteria permit deposits of successive andean glacier advances in the southern lake district of chile to be divided into four mappable drift sheets the oldest two of which overlie tertiary bedrock along the eastern flank of the cordillera de la costa only the youngest drift llanquihue is datable by radiocarbon during the most extensive ice advance of the last glaciation the lago llanquihue glacier was about 95 km long and reached an estimated maximum thickness of between 1000 and 1300 m glacier equilibrium lines at that time lay about 1000 m below their present level and rose eastward with a gradient of about 5 m km successive ice advances in the lago llanquihue basin which resulted in construction of end moraines and associated outwash plains beyond the lake margin culminated sometime before about 20 000 yr ago and between 20 000 and 19 000 yr ago a later readvance inferred from the sedimentary record of lake level fluctuations in the basin had begun by about 15 000 yr ago and culminated shortly after 13 000 yr ago a comparable but less closely dated record of ice advances is found northwest of seno reloncavi and on isla chiloe deglaciation following the latest advance is likely to have been rapid for the major glacier lobes fronted on deep water bodies that would have promoted extensive calving

links between patagonian ice sheet fluctuations and antarctic dust variability during the last glacial period mis 4 2 abstract antarctic and greenland ice core records reveal large fluctuations of dust input on both orbital and millennial time scales with potential global climate implications at least during glacial periods the antarctic dust fluctuations appear to be largely controlled by environmental changes in southern south america we compare dust flux records from two antarctic ice cores to variations in the composition of the terrigenous supply at odp site 1233 located off southern chile and known to record fluctuations in the extent of the northern part of the patagonian ice sheet npis during the last glacial period marine isotope stage mis 4 to 2 within age uncertainties millennial scale glacial advances retreats of the npis correlate to antarctic dust maxima minima in turn npis fluctuations were closely related to offshore sea surface temperature sst changes this pattern suggests a causal link involving changes in temperature in rock flour availability in latitudinal extensions of the westerly winds and in foehn winds in the southern pampas and patagonia we further suggest that the long term trend of dust accumulation is partly linked to the sea level related changes in the size if the patagonian source area due to the particular morphology of the argentine shelf we suggest that sea level drops at the beginning of mis 4 and mis 2 were important for long term dust increases while changes in the patagonian dust source regions primarily control the early dust decrease during the mis 4 3 transition and termination 1

the geochemistry and sm nd isotopic systematics of precambrian mafic dykes and sills in the southern prince charles mountains east antarctica

the sedimentary record of glacial retreat marinelli fjord patagonia regional correlations and climate ties abstract the inland passage of chile comprises the most continuous latitudinal transect of ice fields ice caps and alpine glaciers in the southern hemisphere providing an excellent natural laboratory for the study of glacial response to climate change during the holocene here we report results from a marine geological investigation of marinelli fjord tierra del fuego 54 25 s 69 35 w and ainsworth fjord which merges with marinelli fjord data acquired during july 2005 onboard the rv ib nathaniel b palmer include high resolution seismic data multibeam swath bathymetry data and sediment cores post cruise analyses include detailed seismic facies and lithofacies analysis and radiocarbon dating the results indicate that a major transition in the glacimarine record from ice proximal facies to ice distal facies occurred in the outer basins of the fjord at 15 5 kyr to 12 5 kyr the ice proximal facies consists of pebbly mud with abundant laminations and is characterized by high average sedimentation rates 28 mm yr in contrast an ice distal facies is dominantly bioturbated mud with low average sedimentation rates 0 56 mm yr this transition marks the retreat of marinelli glacier from the outer basins with no evidence for glacial re advance subsequently during the mid to late holocene ainsworth glacier retreated and exposed ainsworth fjord our results are consistent with the climatic trends for southern south america where the final deglaciation of the region ended at 12 5 ka during the holocene stable ice conditions persisted until the mid 1960s when marinelli glacier began rapidly retreating to its modern day position

late glacial ice advances in the strait of magellan southern chile abstract during the last glacial cycle low gradient glaciers repeatedly drained north eastward into the strait of magellan and dammed extensive proglacial lakes in the central section of the strait this paper focuses on the two most recent glacial advances in the strait culminating over 150 and 80 km from the present ice limits the timing of the first of the two advances has up to now been ambiguous and depended on the interpretation of anomously older dates of 16 590 15 800 yr bp for deglaciation at puerto del hambre here we show there is evidence from seismic data and truncated shorelines that the puerto del hambre basin has been tectonically displaced and that the dates do not represent minimums for deglaciation several other dates show that the advance occurred sometime before 14 260 yr bp the timing of the second advance has been investigated using a refined tephrochronology for the region which has also enabled a palaeoshoreline and glaciolacustrine sediments to be linked to a moraine limit 14c dating of peat and a key tephra layer above and below the glaciolacustrine deposits respectively suggest that the advance culminated in the strait of magellan between 12 010 and 10 050 yr bp

the glaciovolcanic evolution of the copahue volcano andean southern volcanic zone argentina chile abstract glaciovolcanism produces distinctive features that are useful paleoclimate proxies for the distribution of past ice sheets and glacier extent the copahue volcano located in the andean southern volcanic zone argentina chile is an active composite volcano known to have glaciovolcanic features such as lava bodies with glassy margins and anomalous cooling fractures however the emplacement conditions of these products and the influence of pleistocene glaciations on the evolution of the copahue volcano remains poorly understood in this contribution we propose a model for glaciovolcanic evolution of the copahue volcano based on the analysis interpretation and mapping of its products ten lithofacies are described on the eastern flank of copahue volcano exhibiting several examples of glaciovolcanism the evolution of the copahue volcano can be divided into two main sequences the ancient sequence s1 and the young sequence s2 separated by a major erosive phase the s1 early middle pleistocene late pleistocene consists of an initial subaerial effusive stage followed by a major glaciovolcanic stage during which a thick ice cap existed and the edifice grew beneath an englacial lake with the eventual formation of a lava fed delta the s2 late pleistocene present is defined by mainly effusive activity during periods of glacial advance and retreat recorded by an alternation of unconfined subaerial lavas and ice confined lavas the evolution of the copahue volcano therefore indicates two glaciations in the copahue caviahue area during the late pleistocene in contrast to a single glaciation based on the glacial history in the area we associate the first glaciation with the end of marine isotope stage 3 57 29 ka and or the last glacial maximum period 26 5 19 0 ka and the second less extensive glacial period with the antarctic cold reversal 14 5 12 9 ka

mesozoic to quaternary continental margin dynamics in south central chile 36 42 s the apatite and zircon fission track perspective zircon and apatite fission track data provide constraints on the exhumation history fault activity and thermal evolution of the south central chilean active continental margin 36 s 42 s which we use to assess the tectonic and geomorphic response of the margin to the andean subduction regime several domains with different exhumation histories are identified the coastal cordillera is characterized by uniform and coherent exhumation between late triassic 200 ma and late miocene times with surprisingly slow average rates of 0 03 0 04 mm a thermal anomalies related to late cretaceous and early miocene magmatism have regionally modified fission track age patterns the upper cretaceous thermal overprint is of previously unrecognized significance and extent in the coastal cordillera south of 39 s with the exception of a local but distinct pliocene to recent exhumation period in the high relief cordillera nahuelbuta segment between 37 s and 38 s cenozoic overall exhumation in the coastal cordillera was very slow the sedimentary record shows that uplift and subsidence here was episodic with low amplitudes and durations this rules out large scale long term cenozoic accretion trench parallel tilting and tectonic erosion processes in the forearc the main andean cordillera shows markedly greater long term exhumation rates than the coastal cordillera and at 39 s a steep exhumation gradient to the south long term average pliocene to recent exhumation rates of 1 to 2 mm a in the liquine area 39 45 s are almost an order of magnitude more rapid than average paleogene to recent exhumation near lonquimay 38 30 s and farther north while no imprint of the intra arc liquine ofqui fault zone on the exhumation pattern is evident long term exhumation rates decrease from the crest of the andes toward the western foothills exhumation gradients correlate with climatic gradients suggesting a causal link to the variable intensity of late miocene to pleistocene glacial erosion

climatic inferences from glacial and palaeoecological evidence at the last glacial termination southern south america there is uncertainty about the interhemispheric timing of climatic changes during the last glacial interglacial transition different hypotheses relying on different lines of evidence point variously to the northern hemisphere leading the southern hemisphere and vice versa or to synchrony between the hemispheres southern south america is well placed to test the various alternatives using both glacial and palaeoecological evidence we argue here from a synthesis of key proxy records that there was a sudden rise in temperature that initiated deglaciation sychronously over 16 of latitude at 14 600 14 300 14 c yr bp 17 500 17 150 cal yr there was a second step of warming in the chilean lake district at 13 000 12 700 14 cy r bp 15 650 15 350 cal yr which saw temperatures rise to close to modern values a third warming step particularly clear in the south occurred at ca 10 000 14 c yr bp 11 400 cal yr the latter achieving holocene levels of warmth following the initial warming there was a lagged response in precipitation as the westerlies after a delay of ca 1600 yr migrated from their northern glacial location to their present latitude which was attained by 12 300 14 cy r bp 14 300 cal yr the latitudinal contrasts in the timing of maximum precipitation are reflected in regional contrasts in vegetation change and in glacier behaviour the large scale of a 80 km glacier advance in the strait of magellan at 12 700 10 300 14 c yr bp 15 350 12 250 cal yr which spans the antarctic cold reversal and the younger dryas was influenced by the return of the westerlies to southern latitudes the delay in the migration of the westerlies coincides with the heinrich 1 iceberg event in the north atlantic the suppressed global thermohaline circulation at the time may have affected sea surface temperatures in the south pacific and the return of the westerlies to their present southerly latitude only followed ocean reorganisation to its present interglacial mode copyright 2000 john wiley sons ltd

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

palaeoproterozoic assembly of the napier complex southern india and western australia implications for the evolution of the cuddapah basin abstract a detailed examination of lithostratigraphic tectonothermal geochronologic and palaeomagnetic database of the dharwar bastar cratons of south india the yilgarn craton of western australia and the east antarctic shield has shown broad similarity two palaeomagnetic key poles of 2400 ma age from the dharwar and yilgarn cratons suggest near neighbor positions matching patterns of craton outlines orientation of mafic dyke swarms and palaeo north direction for 2400 ma have established a continental assembly of siwa an acronym for south india si and western australia wa at 2400 ma in this assembly the yilgarn craton fits against the bastar craton and the singhbhum craton the available geological data from the napier complex of the eastern antarctica and the dharwar craton of south india were used to prepare the barcode style reconstruction of archaean tectonostratigraphic events of both the cratons the method of matching continental outlines the internal features of two continental blocks and the palaeomagnetic data demonstrate that the napier complex was also a part of siwa during the period 2200 1900 ma and was located at the position of the cuddapah basin of india adjacent to the dharwar craton and the yilgarn craton the separation of the napier complex from the south indian block led to the development of the cuddapah basin at 1950 ma

juxtaposition of india and antarctica during the precambrian inferences from geochemistry of mafic dykes abstract there are several geological geochemical and geophysical evidences which corroborate reconstruction of gondwanaland and juxtaposition of india and antarctica petrology of the precambrian mafic dykes of east antarctica and central east india also support juxtaposition of india and antarctica mafic dykes of different generations are emplaced in the archaean granite gneisses of these regions these dykes appear to be an important tool to support juxtaposition of india and antarctica geological and petrological data of the central east india precambrian mafic dykes suggest four episodes of mafic magmatism in the region three tholeiitic and one noritic similarly east antarctica also comprises four dyke suites emplaced during three distinct periods these suites are 2 4 ga meta tholeiites 2 4 ga high mg tholeiites 1 8 ga dolerites and 1 2 1 4 ga dolerites geochemical compositions of these mafic dykes are compared and they show good relationships with each other similarities in petrological and geochemical characteristics of precambrian mafic dykes of east antarctica and central east india strongly support juxtaposition of these two continents

fossil beetle evidence for climatic change 18 000 10 000 years b p in south central chile abstract cold adapted beetles colonized the lowlands of the lake region of south central chile following the retreat of glaciers from their maximum extent at about 19 500 yr b p the beetle fauna from 18 000 to 14 000 yr b p was characterized by species of moorland habitats this fauna was species poor compared to later faunas of the postglacial interval by 14 000 yr b p arboreal species were replacing species of open habitats reflecting a change toward a warmer climate by about 12 500 yr b p fossil beetle assemblages consisted entirely of rain forest species the fauna of the postglacial interval was about five times as species rich as that of the glacial interval the change in species composition and greater diversity of the beetle fauna was produced by an increase in mean annual temperature estimated to be about 4 5 c this was the last major climatic change to affect profoundly the biota of the middle latitudes of south america the fossil beetle assemblages do not imply a reversal to a colder climate at the time of the european younger dryas interval between 11 000 and 10 000 yr b p

the last glacial maximum and deglaciation in southern south america abstract this paper models the extent of the patagonian icesheet during the last glacial maximum lgm and its subsequent deglaciation it constrains a new coupled icesheet climate numerical model with empirical evidence and simulates the icesheet at the lgm and at stages of deglaciation under lgm conditions an icesheet with a modelled volume slightly in excess of 500 000 km3 builds up along the andes there is a marked contrast between the maritime and continental flanks of the modelled icesheet with positive mass balance exceeding 2 m in the west and declining tenfold to the east modelled ice velocities commonly reach 400 m yr 1 in the western fjords the model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6 c relative to present day temperatures with constant wind fields over the model domain assuming a stepped start to deglaciation modelled ice volumes declined sharply contributing 1 2 m to global sea level 80 of it within 2000 years the empirical record suggests that such a stepped warming occurred around 17 500 17 150 cal yr ago

tectonic control on rock uplift exhumation and topography above an oceanic ridge collision southern patagonian andes 47 s chile

volcanologic and petrologic evolution of antuco sierra velluda southern andes chile abstract the andean southern volcanic zone comprises 30 active arc front volcanoes that grew over periods of hundreds of thousands of years quantifying the rates at which these volcanoes grow is key to appreciating geological hazards clarifying petrologic evolution and exploring possible relationships between volcanism ice loading and climate the integration of precise geochronology and geologic mapping together with new lava compositions and volume estimates reveal the evolution of the antuco sierra velluda volcanic complex at 37 2 s thirty one new 40ar 39ar age determinations illuminate a punctuated eruptive history that spans at least 430 kyr sierra velluda comprises 130 km3 and began to grow prior to 426 8 ka a lacuna in the volcanic record between 343 5 and 150 4 ka coincides with glaciations associated with marine isotope stages mis 10 and 8 although shallow intrusions were emplaced at 207 0 and 190 0 ka antuco began to grow rapidly on the northeast flank of sierra velluda erupting 60 km3 of lava during three phases 1 an early phase that began at 150 4 ka 2 a post mis 2 phase between 16 3 and 6 2 ka and 3 a post sector collapse phase after 6 2 ka volcanism has been continuous during the last 100 kyr with an average rate of cone growth during this period of 0 46 km3 kyr that has accelerated by about 50 during the past 6 kyr whereas sierra velluda erupted basaltic andesitic to andesitic 53 5 to 58 7 wt sio2 lavas during the last expansion of glaciers between 130 and 17 ka early antuco erupted a wider spectrum of lavas ranging from basaltic andesite to dacite 52 0 to 64 5 wt sio2 notably eruptions following the last glacial termination at 17 ka produced basalts and basaltic andesites 50 9 53 7 sio2 and following the 6 2 ka cone collapse they have been exclusively olivine basalt 50 9 53 0 sio2 with 5 wt mgo thermodynamic and trace element modeling suggests that lavas from sierra velluda and early antuco reflect extensive fractional crystallization of parental basaltic magmas with low water content 1 wt at pressures between 0 9 and 1 5 kbar in contrast eruptions following rapid deglaciation tapped asthenospheric mantle derived basalt that has been extensively modified by assimilation of partial melts of lower crustal rocks

late quaternary chronology of the taitao peninsula southern chile six new radiocarbon ages and a pollen sequence are provided for laguna stibnite a small lake on the taitao peninsula chile latitude 46 25 s longitude 74 24 w the sediments record a late glacial to present sequence with a basal age of 14 335 145 yr bp q 2840 the radiocarbon ages provide the basis for a sound chronology in a region of chile where few palynological studies have been made and where previous radiocarbon ages are ambiguous the chronology from laguna stibnite supports the acceptance of a radiocarbon chronology based on wood fragments rather than bulk analysis at a site near puerto eden further south in the chilean channels 49 08 s these data from laguna stibnite provide evidence for an early deglaciation before 14 000 yr bp in this region of southern chile the sequence provides no evidence for a climatic reversal between 11 000 yr bp and 10 000 yr bp the so called younger dryas chron

reservoir analog studies using multimodel photogrammetry a new tool for the petroleum industry an advanced photogrammetric method called multimodel stereo restitution is a potential new tool for the petroleum industry when outcrop investigations are necessary such as in reservoir analog studies the method is based on very simple field photography techniques allowing the geologist to use his own standard small frame camera e g 24 36 or 60 60 mm formats it can be applied to geological studies of virtually any scale and outcrop mapping is significantly improved in detail accuracy and volume the method is especially useful when investigating poorly accessible exposures on steep mountain faces and canyon walls the use of multimodel photogrammetry is illustrated by a study of upper cretaceous deltaic sediments from the atane formation of west greenland detailed vertical cross sections of all outcrops in the area are measured and in addition horizontal maps of individual sand bodies are compiled on this basis data such as width thickness ratios sinuosity and the shapes of sand bodies and paleochannels crucial in reservoir analog studies are quantified and collected further potential applications of the method in petroleum explorations are discussed true scale mapping of lithologies in large continuous exposures can be used in understanding basin evolution and in seismic modeling close range applications can be used when modeling fault geometries and in studies of individual bed forms clay laminae cemented horizons and diagenetic fronts

radiocarbon chronology of the late glacial puerto bandera moraines southern patagonian icefield argentina abstract we report radiocarbon dates that constrain the timing of the deposition of the late glacial puerto bandera moraine system alongside the western reaches of lago argentino adjacent to the southern patagonian icefield close maximum limiting radiocarbon ages n 11 for glacier advance into the outer moraines with a mean value of 11 100 60 14 c yrs bp 12 990 80 cal yrs bp were obtained from wood in deformation soft till exposed beneath flow and lodgment till in bahia del quemado on the northeast side of brazo norte north branch of western lago argentino other exposures of this basal deformation till in bahia del quemado reveal incorporated clasts of peat along with larger inclusions of deformed glaciofluvial and lacustrine deposits radiocarbon dates of wood included in these reworked peat clasts range from 11 450 45 14 c yrs bp to 13 450 150 14 c yrs bp 13 315 60 to 16 440 340 cal yrs bp the implication is that during this interval glacier fronts were situated inboard of the puerto bandera moraines with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the puerto bandera advance minimum limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the puerto bandera moraines glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to 10 750 75 14 c yrs bp 12 660 70 cal yrs bp east of brazo rico 10 550 55 14 c yrs bp 12 490 80 cal yrs bp in peninsula avellaneda and 10 400 50 14 c yrs bp 12 280 110 cal yrs bp in bahia catalana in addition a radiocarbon date indicates that by 10 350 45 14 c yrs bp 12 220 110 cal yrs bp the brazo norte lobe or former upsala glacier had receded well up the northern branch of lago argentino to a position behind the herminita moraines furthermore glacier termini had receded to just outboard of the outer holocene moraines at lago frias and lago pearson anita prior to 10 400 40 14 c yrs bp 12 270 100 cal yrs bp and 9040 45 14 c yrs bp 10 210 50 cal yrs bp respectively the most extensive recession registered during the early holocene was in agassiz este valley where the upsala glacier had pulled back behind the outer holocene moraine reaching close to the present day glacier terminus before 8290 40 14 c yrs bp 9300 80 cal yrs bp the radiocarbon dated fluctuations of the lago argentino glacier in late glacial time given here are in accord with changes in ocean mixed layer properties predominately temperature derived from the isotopic record given here of odp core 1233 taken a short distance off shore of the chilean lake district it also matches recently published chronologies of late glacial moraines in the southern alps of new zealand on the opposite side of the pacific ocean from lago argentino finally the timing of the late glacial reversal of the lago argentino glacier fits the most recent chronology for the culmination of the antarctic cold reversal acr in the deuterium record of the epica dome c ice core from high on the east antarctic plateau therefore we conclude that the climate signature of the acr was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe

melting of the patagonian ice sheet and deglacial perturbations of the nitrogen cycle in the eastern south pacific local 230 th normalized biogenic vertical fluxes from the chilean continental margin they document in detail the sharp transition from relatively low wcd rates during the last glacial maximum lgm to high ones during the deglaciation and holocene but give no evidence that the glacial interglacial difference of wcd could have been caused by changes in local primary productivity furthermore we found no evidence that changes in ventilation due to samw formation could explain the nitrogen isotope record we present evidence for an alternative mechanism related to the melting of the patagonian ice sheet pis which is consistent with recent published proxy data and the regional physical oceanography

late quaternary tephrostratigraphy of southern chile and argentina abstract the southern and austral volcanic zones of the andes comprise 74 volcanic centres with known post glacial activity at least 21 of these have had one or more large explosive eruptions in the late quaternary dispersing tephra over vast areas these tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern chile and argentina a region that is particularly useful to study climate dynamics of the southern hemisphere however to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool here we review the existing post glacial tephrostratigraphic record of the southern and austral volcanic zones and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine marine peat and cave sediment records we address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area this study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes but also reveals the largely under utilised potential of tephra as a correlation tool in this region this is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections which are particularly important tephrostratigraphic records in southern chile and argentina due to the paucity of surface preservation

the mis 3 maximum of the torres del paine and ultima esperanza ice lobes in patagonia and the pacing of southern mountain glaciation abstract the timing structure and termination of the last southern mountain glaciation and its forcing remains unclear most studies have focused on the global last glacial maximum lgm 26 5 19 ka time period which is just part of the extensive time frame within the last glacial period including marine isotope stages 3 and 4 understanding the glacial fluctuations throughout the glacial period is a prerequisite for uncovering the cause and climate mechanism driving southern glaciation and the interhemispheric linkages of climate change here we present an extensive n 65 cosmogenic 10be glacier chronology derived from moraine belts marking the pre global lgm extent of the former patagonian ice sheet in southernmost south america our results show the mountain ice sheet reached its maximum extent at 48 0 1 8 ka during the local lgm but attained just half this extent at 21 5 1 8 ka during the global lgm this finding supported by nearby glacier chronologies indicates that at orbital time scales the southern mid latitude glaciers fluctuated out of phase with northern hemisphere ice sheets at millennial time scales our data suggest that patagonian and new zealand glaciers advanced in unison with cold antarctic stadials and reductions in southern ocean sea surface temperatures this implies a southern middle latitudes wide millennial rhythm of climate change throughout the last glacial period linked to the north atlantic by the bipolar seesaw we suggest that winter insolation acting alongside other drivers such as the strength and or position of the southern westerlies controlled the extents of major southern mountain glaciers such as those in southernmost south america

late quaternary glaciation history of isla de los estados southeasternmost south america isla de los estados is a mountainous island southeast of tierra del fuego in southernmost south america its central and eastern parts have an alpine topography transected by u shaped valleys small partly over deepened fjords and a multitude of abandoned cirques all associated with extensive former local glaciations traces of glacial erosion generally reach 400 450 m a s l and above that trimline a distinct sharp edged nunatak derived landscape is present the westernmost part of the island has a lower more subdued topography reflecting its softer geology but possibly also over running and erosion by mainland derived ice streams the present study concentrated on glacigenic sediment sequences exposed along coastal erosional cliffs a combination of osl and c 14 datings show that these sediments mostly date from the latest wisconsinan weichselian glacial cycle i e from the last ca 100 ka with the oldest glaciolacustrine deposits possibly as old as 90 80 ka the upper parts of overlying tills with associated lateral and terminal moraines from glaciers that expanded onto an eustatically exposed dry shelf north of the island date from the last global glacial maximum lgm radiocarbon ages of peat and lake sediments indicate that deglaciation began 17 16 cal ka bp c 2010 university of washington published by elsevier inc all rights reserved

can glacial erosion limit the extent of glaciation kaplan m r hein a s hubbard a 2009 can glacial erosion limit the extent of glaciation geomorphology 103 2 172 179

geomorphological and sedimentological evolution of a lake basin under strong volcano tectonic influence the seismic record of lago calafquen south central chile the chilean lake district is a geodynamically active area located at the foot of the andean cordillera and permanently influenced by the chilean active continental margin the study area is prone to steady mass movements that are triggered by active volcanism strong earthquakes and climatic forces on the glacial born lake lago calafquen high resolution seismic investigation was performed to select suitable coring sites for sedimentary analyses to revise the existing bathymetry and to integrate the lake bottom topography into the geomorphological context of the surroundings the sub bottom profiling reveals a complex structure of the lake floor which results in a division into an eastern and a central sub basin the eastern basin encompasses the deep basin plain which is a depositional area for dense suspension loaded underflows the morphology of the basement of the central sub basin is affected by large landslides large rock slope failures of debuttressed sidewalls fill the primary lake floor of the southern side covered by more than 40 m of sediment a high resolution seismic analysis of the sedimentary infill reveals deposits and structures of large mass movements and turbidites obviously triggered by strong earthquakes incidents related to rebound effects by isostatic uplift are also considered to provoke remarkable magnitudes that trigger mass movement processes in the central sub basin furthermore volcanic impact frequently interrupts normal lacustrine sedimentation of the sediment succession by deposition of tephra layers the serialized geodynamic impacts on lago calafquen cause severe damage to the sedimentary archive thus suitable coring sites for palaeoenvironmental reconstruction should be selected carefully

comment on the last glacial maximum and deglaciation in southern south america by n r j hulton r s purves r d mcculloch d e sugden m j bentley quaternary science reviews 21 2002 233 241

seismic facies changes along a nearly continuous 24 latitudinal transect the fjords of chile and the northern antarctic peninsula abstract high resolution seismic reflection profiles and piston cores from bays fjords and straits of the inland passage of chile and the northern antarctic peninsula region were used to examine changes in seismic facies along a nearly continuous 24 latitudinal transect that encompasses temperate subpolar and polar climatic regimes these climatic regimes are characterized by differences in seismic facies eight seismic facies are recognized on the basis of reflection character intensity of acoustic contrast at bounding surfaces and external shape of the unit the northern and central chilean fjord region is a temperate maritime setting characterized by thick ice proximal and ice distal glacial marine strata and a variety of morainal features the southern inland passage and the south shetland islands of antarctica represent transitional sub polar glacial marine settings these areas are characterized by relict ice proximal glacialmarine facies and relatively thin ice distal glacial marine facies morainal ridges occur in bays and fjords of chile the northern antarctic peninsula is a polar climatic setting the straits bays and fjords of the region have been virtually scraped clean of sediments a thin draping glacial marine unit occurs locally in these areas

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

the de correlation of westerly winds and westerly wind stress over the southern ocean during the last glacial maximum motivated by indications from paleo evidence this paper investigates the changes of the southern westerly winds sww and westerly wind stress between the last glacial maximum lgm and pre industrial in the pmip3 cmip5 simulations highlighting the role of antarctic sea ice in modulating the wind effect on ocean particularly a de correlation occurs between the changes in sww and westerly wind stress caused primarily by an equatorward expansion of winter antarctic sea ice that undermines the efficacy of wind in generating stress over the liquid ocean such de correlation may reflect the lgm condition in reality in view of the fact that the model which simulates this condition has most fidelity in simulating modern sww and antarctic sea ice therein two models stand out for their agreements with paleo evidence regarding the change of sww and the westerly wind stress they simulate strengthened and poleward migrated lgm sww in the atmosphere consistent with the indications from dust records whilst in the ocean they well capture an equatorward shifted pattern of the observed oceanic front shift with most pronounced equatorward shifted westerly wind stress during the lgm

chronostratigraphy and lake level changes of laguna cari laufquen rio negro argentina abstract evidence from shoreline and deep lake sediments show laguna cari laufquen located at 41 s in central argentina rose and fell repeatedly during the late quaternary our results show that a deep 38 m above modern lake level lake persisted from no later than 28 ka to 19 ka with the deepest lake phase from 27 to 22 ka no evidence of highstands is found after 19 ka until the lake rose briefly in the last millennia to 12 m above the modern lake before regressing to present levels laguna cari laufquen broadly matches other regional records in showing last glacial maximum lgm highstands but contrasts with sub tropical lake records in south america where the hydrologic maximum occurred during deglaciation 17 10 ka our lake record from cari laufquen mimics that of high latitude records from the northern hemisphere this points to a common cause for lake expansions likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the lgm

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

superimposed tectonic events at 2450 ma 2100 ma 900 ma and 500 ma in the north mawson escarpment antarctic prince charles mountains abstract the north mawson escarpment in antarctica s prince charles mountains forms part of a palaeoproterozoic crustal complex which separates archaean cratonic material to the south from early neoproterozoic and early palaeozoic metamorphic belts to the north it consists of nappe like masses of grey gneiss and metasupracrustal rocks that were subjected to repeated ductile deformation under upper amphibolite to lower granulite facies metamorphic conditions in this paper we report zircon u pb dating results that constrain the principal tectonothermal events to the periods 2490 2420 ma 2180 2080 ma 940 880 ma and 530 490 ma the magmatic precursors of volumetrically important grey gneiss were produced and reworked at least partly during the 2490 2420 ma and 2180 2080 ma events the superimposition of these events is clearly documented by u pb ages from several composite zircons the formation of associated metasupracrustals possibly in a passive margin setting occurred between the 2490 2420 ma and 940 880 ma events both grey gneiss and metasupracrustals were subsequently reworked during the 940 880 ma and 530 490 ma events corresponding to the superposition of both the rayner and prydz belts onto palaeoproterozoic lithosphere of the lambert complex transposition and peak metamorphism preceded the intrusion of leucogranite dykes at 905 ma and based on metamorphic zircon growth at around 930 ma in metapelitic schist are related to the rayner orogeny it is suggested that the north mawson escarpment was assembled to most coastal regions of the antarctic sector between 45 and 80 e by at least 900 m y ago

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

petrology of the precambrian mafic rocks of katekalyan area bastar district madhya pradesh india two types of mafic rocks are exposed around the katekalyan region viz amphibolites and dolerites and or meta dolerites amphibolites are further classified as volcanic amphibolites i e meta volcanics and plutonic amphibolites mainly dykes dolerites occur as small dykes middle proterozoic or older rock types of the area have been intruded by mafic rocks volcanic amphibolites show schistose texture whereas plutonic amphibolites exhibit either schistose or granoblastic textures porphyroblastic texture is also observed in some thin sections of both types dolerites and or meta dolerites show ophitic or sub ophitic texture geochemically all types of mafic rocks may be classified as sub alkaline high fe tholeiites and are enriched in rb k nb sr zr ti and y than the primitive mantle incompatible elements concentration suggest genetic links between all types of mafic rocks and are indicated to be emplaced in the within plate environment on the basis of petrological and geochemical data presented it is suggested that ferro tholeiitic magma has been emplaced at least twice one has been metamorphosed i e older emplacements amphibolitic types and another is fresh i e younger emplacements doleritic types it is also suggested that probably amphibolite dykes act as feeder dykes for volcanic amphibolites i e meta volcanics almost similar mafic rocks particularly dykes have been observed in the antarctic shield which supports the juxtaposition of india and antarctica and corroborates the views on reassembly of east gondwanaland

late pleistocene to holocene composite speleothem 18o and 13c chronologies from south island new zealand did a global younger dryas really exist oxygen and carbon data from eight stalagmites from northwest south island are combined to produce composite records of delta 18 o and delta 13 c from 23 4 ka to the present the chronology is anchored by 43 thermal ionization mass spectrometry tims uranium series ages delta o 18 values are interpreted as having a first order positive relationship to temperature but also to be influenced by precipitation in a complex manner delta c 13 is interpreted as responding negatively to increases in atmospheric co concentration biological activity and precipitation amount six climatic phases are recognized after adjustment of 1 2parts per thousand for the ice volume effect the delta 18 o record between 23 and 18 ka varies around 3 72parts per thousand compared to the holocene average of 3 17parts per thousand late glacial warming commenced between 18 2 and 17 8 ka and accelerated after 16 7 ka culminating in a positive excursion between 14 70 and 13 53 ka this was followed by a significant negative excursion between 13 53 and 11 14 ka of up to 0 55parts per thousand depth that overlapped the antarctic cold reversal acr and spanned the younger dryas yd positive delta 18 o excursions at 11 14 ka and 6 91 6 47 ka represent the warmest parts of the holocene the mid holocene from 6 to 2 ka was marked by negative excursions that coincide with increased glacial activity in the south island a short positive excursion from 0 71 to 0 57 ka was slightly later than the medieval warm period of europe delta c 13 values were high until 17 79 ka after which there was an abrupt decrease to 17 19 ka followed by a steady decline to a minimum at 10 97 ka then followed a general increase suggesting a drying trend to 3 23 ka followed by a further general decline the abrupt decrease in delta values after 17 79 ka probably corresponds to an increase in atmospheric co2 concentration biological activity and wetness at the end of the last glaciation but the reversal identified in the delta 18 o record from 13 53 to 11 14 ka was not reflected in delta 13 c changes the lowest delta 13 c values coincided with the early holocene climatic suboptimum when conditions were relatively wet as well as mild major trends in the delta 18 o c record are similar to the northern hemisphere but second order detail is often distinctly different consequently at the millennial scale a more convincing case can be made for asymmetric climatic response between the two hemispheres rather than synchronicity c 2004 elsevier b v all rights reserved

strontium isotopes trace biological activity in the critical zone along a climate and vegetation gradient abstract weathering and ecosystem nutrition are intimately linked through the supply of fresh mineral nutrients from regolith and bedrock the geogenic nutrient pathway however the prominence of this link is dependent on the efficiency of nutrient recycling from plant litter the organic nutrient cycle isotope ratios of strontium sr an element that behaves similarly to ca in ecosystems confer two types of information radiogenic sr isotopes inform as to the sources of sr and the degree of weathering while stable sr isotopes constrain partitioning between compartments of the critical zone bedrock water secondary solids and plants to date however neither the reactions nor the mass balance between compartments that fractionate sr isotopes nor the fractionation factors involved are well understood here we present geochemical budgets of sr using radiogenic and stable sr isotopes and ca sr ratios at four sites along a substantial climate and primary production gradient in the coastal mountains of chile we found that sr release through weathering is isotopically congruent and released sr is not strongly isotopically fractionated either during secondary mineral formation or transfer into the exchangeable pool despite this the 88sr 86sr ratio of bio available sr which should reflect the ratio of dissolved sr is higher than that of rock and regolith we propose that this offset is caused by plants while 88sr 86sr in plant organs at the four study sites systematically increased from roots towards their leaves whole plant sr isotope compositions indicate preferential uptake of light sr into plants with a fractionation of up to 0 3 relative to the bio available pool despite this strong biological fractionation 88sr 86sr ratios in bio available sr do not covary with biomass production across our study sites because with greater plant growth sr is recycled more times after release by weathering an isotope neutral process rather the loss of sr from the ecosystem in solid organic material sets the isotope ratio of dissolved or bio available sr organic solids thus appear to constitute a significant export path of elements released during weathering with the removal of solid plant debris reducing the recycling factor of sr and possibly that of other mineral nutrients too

tholeiitic and noritic magmatism during the precambrian in central east india and east antarctica implications for reconstruction of gondwanaland

geochemistry and geochronology of proterozoic tholeiite dykes of east antarctica evidence for mantle metasomatism two episodes of tholeiite dyke emplacement have been identified in archaean high grade metamorphics of the napier complex in enderby land middle proterozoic amundsen dykes are typical continental tholeiites and most of the chemical variation in individual suites can be explained in terms of different degrees of partial melting and low pressure crystal fractionation group i amundsen tholeiites were derived from a relatively homogeneous source region 1 190 200 m y ago whereas that of the group ii amundsen tholeiites was chemically and isotopically heterogeneous group ii dykes have various degrees of enrichment in incompatible elements and commonly show normalised trace element abundance patterns with negative nb anomalies these features imply variable metasomatism of the source region by a volatile rich fluid phase rather than a melt of any observed igneous composition enriched in k rb ba th and possibly la and ce early proterozoic 2 350 48 m y tholeiites were emplaced at considerable depths in the crust during the waning stages of granulite facies metamorphism and include a high mg suite of possible komatiitic affinity ranging in composition from hypersthene rich tholeiite norite to quartz rich tholeiite they tend to have higher ratios of highly to moderately incompatible elements e g k zr k ce and larger nb anomalies i e higher k nb compared with middle proterozoic tholeiites suggesting derivation from more enriched source regions isotopic data are not compatible with significant crustal contamination but constrain source metasomatism to a time immediately before emplacement metasomatism of the source region of the much younger group i tholeiites may have been contemporaneous with that of the high mg suite

fast flowing outlet glaciers of the last glacial maximum patagonian icefield abstract glacial geomorphology around the northern patagonian icefield indicates that a number of fast flowing outlet glaciers the continuation of ice streams further upglacier drained the icefield during the last glacial maximum these topographically controlled fast flowing glaciers may have dictated the overall pattern of last glacial maximum ice discharge lowered the ice surface profile and forced the ice divide westward the influence of the fast flowing outlet glaciers on icefield behavior also helps to explain why the configuration of the patagonian icefield at the last glacial maximum is not accurately represented in existing numerical ice sheet models fast flowing outlet glaciers would have strongly influenced ice discharge patterns and therefore partially decoupled the icefield from climatically induced changes in thickness and extent

superposed deformation and inherited structures in an ancient dilational step over zone post mortem of the rengali province india abstract in the eastern indian shield a dextral strike slip system juxtaposed the archaean singhbhum province against the proterozoic eastern ghats belt at 490 470 ma two wnw ese trending strands of the strike slip system enclose a multiply deformed d1 to d3 intervening domain called the rengali province with d3 representing dextral shearing in a granulite lens within the province an early fabric sgr was deformed by an amphibolite facies d1 d2 deformation continuum in the late archaean time forming cylindrical folds in the surrounding quartzofeldspathic gneisses quartzites and mica schists of the province superimposition of syn d3 shortening on d1 d2 folds generated complex non cylindrical geometries the granulites escaped d3 strain microstructures in the province bounding shear zones confirm that d3 deformation was associated with mylonitization dynamic recrystallization and greenschist facies metamorphism in the quartzites syn d3 folds can be correlated with rotation of d1 d2 structures through the shortening zone of bounding dextral shears since the province bounding shears form a step over zone the structural complexity within the rengali province arises from superposition of syn d3 shortening structures on initially asympathetically oriented inherited cylindrical d1 d2 folds hydrous fluid channeling causing greenschist facies metamorphism and quartz vein emplacement accompanied d3 as the step over zone was dilational in nature

on the differences between last glacial maximum and mid holocene climates in southern south america simulated by pmip3 models abstract differences between climate conditions during the last glacial maximum lgm and the mid holocene mh in southern south america inferred from the state of the art pmip3 paleoclimatic simulations are described for the first time in this paper the aim is to expose characteristics of past climate changes occurred without human influence in this context numerical simulations are an indispensable tool for inferring changes in near surface air temperature and precipitation in regions where proxy information is scarce or absent the analyzed pmip3 models describe mh temperatures significantly warmer than those of lgm with magnitudes of change depending on the season and the specific geographic region in addition models indicate that seasonal mean precipitation during mh increased with respect to lgm values in wide southern continental areas to the east of the andes cordillera whereas seasonal precipitation developed in areas to the west of patagonian andes reduced from lgm to mh

atmospheric scaling of cosmogenic nuclide production climate effect 1 absorption of cosmic rays by atmospheric mass varies temporally due to a redistribution of atmospheric pressure by ice sheets during glaciations the compression and expansion of the atmosphere due to cooling and warming and changes in katabatic winds near large ice masses these atmospheric processes can result in changes in production rates of cosmogenic nuclides which when integrated over long exposure durations may result in 0 to 5 adjustments in site production rates depending on location combining a ccm3 model with imbedded ice sheets for 20 ka we show that production rates changes relative to today are greatest at high elevations 6 7 at 5 km altitude due to atmospheric compression from decreased temperature production rates at specific times for sites near ice sheet margins can be reduced more than 10 due to a combination of katabatic winds draining off the ice sheet margins and atmospheric cooling nunatak settings may be significantly affected by the climate effect due to persistent glacial atmospheric conditions atmospheric variability may explain some of the disparities among cosmogenic nuclide production rate calibrations

regional mid pleistocene glaciation in central patagonia abstract southern south america contains a glacial geomorphological record that spans the past million years and has the potential to provide palaeoclimate information for several glacial periods in earth s history in central patagonia two major outlet glaciers of the former patagonian ice sheet carved deep basins 50 km wide and extending over 100 km into the andean plain east of the mountain front a succession of nested glacial moraines offers the possibility of determining when the ice lobes advanced and whether such advances occurred synchronously the existing chronology which was obtained using different methods in each valley indicates the penultimate moraines differ in age by a full glacial cycle here we test this hypothesis further using a uniform methodology that combines cosmogenic nuclide ages from moraine boulders moraine cobbles and outwash cobbles 10 be concentrations in eighteen outwash cobbles from the moreno outwash terrace in the lago buenos aires valley yield surface exposure ages of 169 269 ka we find 10 be inheritance is low and therefore use the oldest surface cobbles to date the deposit at 260 270 ka which is indistinguishable from the age obtained in the neighbouring lago pueyrredon valley this suggests a regionally significant glaciation during marine isotope stage 8 and broad interhemispheric synchrony of glacial maxima during the mid to late pleistocene finally we find the dated outwash terrace is 70 100 ka older than the associated moraines on the basis of geomorphological observations we suggest this difference can be explained by exhumation of moraine boulders

geochemistry of surface sediments from the fjords of northern chilean patagonia 44 47 s spatial variability and implications for paleoclimate reconstructions abstract the patagonian fjords have a clear potential to provide high resolution sedimentary and geochemical records of past climate and environmental change in the southern andes to improve our ability to interpret these proxy records we investigated the processes that control fjord sediment inorganic geochemistry through a geochemical mineralogical and sedimentological analysis of surface sediment samples from the fjords of northern chilean patagonia a simple terrestrial index based on measurements of salinity and fraction of terrestrial carbon was used to estimate the terrestrial input river discharge at each site our results demonstrate that under the cold climate conditions of patagonia chemical weathering is weak and the inorganic geochemical composition of the fjord sediments is primarily controlled by hydrodynamic mineralogical sorting i e the intensity of river discharge our results suggest that the distribution of fe ti and zr in surface sediments is controlled by their association with heavy and or coarse minerals whereas al is independent of hydrodynamic processes the elemental ratios fe al ti al and zr al are therefore well suited for estimating changes in the energy of terrestrial sediment supply into the fjords through time zr al is particularly sensitive in proximal environments while fe al is most useful in the outer fjords and on the continental margin in the most proximal environments however fe al is inversely related to hydrodynamic conditions caution should therefore be exercised when interpreting fe al ratios in terms of past river discharge the application of these proxies to long sediment cores from quitralco fjord and golfo elefantes validates our interpretations our results also emphasize the need to measure al based elemental ratios at high precision which can be achieved using simultaneous acquisition icp aes technology this study therefore constitutes a strong basis for the interpretation of sedimentary records from the chilean fjords

the eismint benchmarks for testing ice sheet models we present a series of benchmark experiments designed for testing and comparing numerical ice sheet models following the outcome of two eismintworkshops organized to intercompare large scale ice sheet models currently in operation model benchmark experiments are described for ice sheets underfixed and moving margin conditions these address both steady state and time dependent behavior under schematic boundary conditions and with prescribedphysics a comparison was made of each model s prediction of basic geophysical variables such as ice thickness velocity and temperature consensusachieved in the model intercomparison provides reference solutions against which the accuracy and consistency of ice sheet modeling codes can be assessed

middle pleistocene glaciation in patagonia dated by cosmogenic nuclide measurements on outwash gravels the well preserved glacial record in argentine patagonia offers a 1 ma archive of terrestrial climate extremes in southern south america these glacial deposits remain largely undated beyond the range of radiocarbon dating at ca 40 ka dating old glacial deposits several 105 a by cosmogenic surface exposure methods is problematic because of the uncertainty in moraine degradation and boulder erosion rates here we show that cobbles on outwash terraces can reliably date old glacial deposits in the lago pueyrredon valley 47 5 s argentina favorable environmental conditions e g aridity and strong winds have enabled continuous surface exposure of cobbles and preservation of outwash terraces the data demonstrate that nuclide inheritance is negligible and we therefore use the oldest surface cobbles to date the deposit 10be concentrations in outwash cobbles reveal a major glacial advance at ca 260 ka concurrent with marine isotope stage 8 mis 8 and dust peaks in antarctic ice cores a 10be concentration depth profile in the outwash terrace supports the age and suggests a low terrace erosion rate of ca 0 5 mm ka 1 we compare these data to exposure ages obtained from associated moraines and find that surface boulders underestimate the age of the glaciation by 100 ka thus the oldest boulders in this area do not date closely moraine deposition the 10be concentration in moraine cobbles help to constrain moraine degradation rates these data together with constraints from measured 26al 10be ratios suggest that all moraine boulders were likely exhumed after original deposition we determine the local last glacial maximum lgm occurred at 27 25 ka consistent with the maximum lgm in other parts of patagonia

glacier modeling and the climate of patagonia during the last glacial maximum ice cap modeling constrained by empirical studies provides an effective way of reconstructing past climates the former patagonian ice sheet is in a climatically significant location since it lies athwart the southern hemisphere westerlies and responds to the latitudinal migration of climatic belts during glacial cycles a numerical model of the patagonian ice cap for the last glacial maximum lgm is developed which is time dependent and driven by changing the mass balance altitude relationship it relies on a vertically integrated continuity model of ice mass solved over a finite difference grid the model is relatively insensitive to ice flow parameters but highly sensitive to mass balance the climatic input is adjusted to produce the best fit with the known limits of the ice cap at the lgm the ice cap extends 1800 km along the andes and has a volume of 440 000 km3 during the lgm the equilibrium line altitude ela was lower than at present by at least 560 m near latitude 40 s 160 m near latitude 50 s and 360 m near latitude 56 s the latitudinal variation in ela depression can be explained by an overall fall in temperature of about 3 0 c and the northward migration of precipitation belts by about 5 latitude annual precipitation totals may have decreased by about 0 7 m at latitude 50 s and increased by about 0 7 m at latitude 40 s the ela rises steeply by up to 4 m per kilometer from west to east as the westerlies cross the andes and this prevents ice growth to the east the limited decrease in temperature during the lgm could be related to the modest migration of the antarctic convergence between south america and the antarctic peninsula

glacial dynamics in southernmost south america during marine isotope stage 5e to the younger dryas chron a brief review with a focus on cosmogenic nuclide measurements the timing of major glacial changes between marine isotope stage mis 5e and the younger dryas chron yd in southern south america is reviewed focus is placed on studies that use cosmogenic nuclide measurements however other dated records and modelling results are also discussed to provide the broader glacial geological context limits on the state of glacial geologic knowledge are examined and suggestions are made as to how some of these can be addressed in future studies studies show that on the east side of the andes at lago buenos aires 45 s there is evidence indicating that following a mis 6 glaciation ice was less extensive during mis 4 than mis 2 in contrast on the west side of the andes in the chilean lake district area mis 4 ice may have been more extensive than during mis 2 although patagonia experienced an mis 2 glaciation broadly in phase with that in other areas around the globe there are differences in glacial histories between areas on millennial timescales climate reversals are evident in many records between ca 17 and 10 ka the timing of such lateglacial activity which included less extensive advances than during the local last glacial maximum lgm varies somewhat between areas this could be due to the relative influence of middle to high latitude climatic regimes at present chronological uncertainties prevent confident assignment of cosmogenic ages for glacial events at the millennial timescale and defining associated climate variability between different study areas copyright 2008 john wiley sons ltd

high resolution reconstruction of southwest atlantic sea ice and its role in the carbon cycle during marine isotope stages 3 and 2 1 recent modeling suggests that changes in southern ocean sea ice extent potentially regulated the exchange of co2release between the ocean and atmosphere during glacials unfortunately a lack of high resolution sea ice records from the southern ocean has prevented detailed testing of these model based hypotheses with field data here we present high resolution records of southern ocean sea ice for the period 35 15 cal ka bp derived from diatom assemblages measured in three glacial sediment cores forming an 8 transect across the scotia sea southwest atlantic chronological control was achieved through a novel combination of diatom abundance stratigraphy relative geomagnetic paleointensity data and down core magnetic susceptibility and ice core dust correlation results showed that the winter sea ice edge reached its maximum northward extent of 53 s at least 3 north of its modern limit between 25 and 23 5 cal ka bp predating the last glacial maximum lgm maximum northward expansion of the summer sea ice edge also pre dated the lgm advancing to at least 61 s and possibly as far north as 55 s between 31 and 23 5 cal ka bp a 12 advance from its modern position a clear shift in the seasonal sea ice zone is evident following summer sea ice edge retreat at 23 5 cal ka bp potentially related to austral insolation forcing this resulted in an expanded seasonal sea ice zone between 22 5 cal ka bp and deglaciation our field data confirm that southern ocean sea ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre formed nutrients our data indicates that southern ocean sea ice was most effective as a physical barrier between 31 and 23 5 cal ka bp and as a mechanism capable of reducing vertical mixing between 22 5 cal ka bp and deglaciation however poor correlations with atmospheric co2 variability recorded in ice cores particularly the lack of a co2response during a rapid sea ice meltback event recorded at our study sites at the same time as antarctic isotopic maximum 2 suggest that southern ocean sea ice in the scotia sea did not play a controlling role in atmospheric co2 variation during the glacial