climatic periodicity during the late pleistocene from a loess paleosol sequence in northwest argentina abstract a 42 m thick loess paleosol sequence was studied in the pre andean intramountain valley of tafi del valle 100 km west of the city of san miguel de tucuman at an elevation of 2280 m asl in northwest argentina the sequence contains 28 paleosols alternating with loess layers the loess layers are coarse loamy and have large hexagonal polyhedra the soil layers are restricted to bt horizons having fine loamy textures prismatic structures and organo argillans on the structural surfaces surface a and eluvial e horizons are absent from the whole sequence soil truncation is unlikely as no remains of these horizons or erosional unconformities were identified the dated part of the sequence encompasses a time span of 10 080 years from 17 580 bp at 5 2 m depth to 27 660 bp at 42 3 m depth the base of the exposed sequence the youngest strata are probably missing either because of a depositional hiatus or because of post depositional erosion as dated paleosols in adjacent areas indicate that loess deposition continued during at least the early holocene the 20 bt c couplets identified in the dated sequence correspond to 20 climatic oscillations in 10 080 years thus every 500 years on average there was a climatic change from dry cool conditions with loess deposition to moist warm conditions favouring soil development this might have been related to recurrent northward shifts of the polar front accompanied by weakening of the mid latitude south pacific anticyclone similar short term periodicity has been identified in the ice cap of greenland and in tropical lake level records so such frequent climatic changes during the late pleistocene seem to have been global in character

a 3 ma paleomagnetic record of coastal continental deposits in argentina abstract continental deposits of upper cenozoic age laid down under alternating depositional environments were subjected to paleomagnetic analyses the sequence was found to cover the last about 3 ma and to include the upper gauss the matuyama and brunhes epochs and the olduvai and jaramillo events the reversals are independent of stratigraphic boundaries the polarity changes are connected with low intensities and susceptibilities the reversals seem to form oblique vgp paths between approximately 90 w and 90 e longitude the magnetostratigraphy established may serve as a local south american magnetostratigraphic standard section

changes of mammal assemblages in the pampean region argentina and their relation with the plio pleistocene boundary abstract a gradual impoverishment of autochthonous mammals in the southeastern pampean region central eastern argentina during the late cenozoic is detected it is partially coeval to the gradual immigration of holarctic mammals and to important climatic changes we propose that the plio pleistocene boundary at around 2 5 ma in the area is located between the vorohue formations and the base of miramar formations

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

upper quaternary palaeoclimates of the mar chiquita area north pampa argentina abstract the mar chiquita shallow lake is the largest water body in argentina located in a quaternary tectonic depression 30 45 s and 62 30 w the southern margin of the depression is dominated by fluvial sediments transported by the rio segundo and aeolian deposits a 65 km wide alluvial fan is the most significant geological unit the sequence of climatic events in the area is i upper pleistocene dry period is4 development of a large sand sea ii complex upper pleistocene humid period is3 first phase of pedogenesis on the aeolian landforms and fluvial deposits marull sands general dissipation of the inherited relief carcarana fm and probable formation of the large alluvial fan lagunilla del plata fm second phase of pedogenesis in a flat landscape during this phase the mar chiquita lake acted as local base level iii late pleistocene dry period is2 lgm deposition of a loess mantle on the surface of the fan tezanos pinto fm iv a subhumid phase 16 000 yr bp redistribution of sand dunes lomita del indio fm and precipitation of pedogenic carbonates in the loess development of a fluvial terrace v younger dryas s l development of deflation hollows associated with lunettes vi hypsithermal humid period general pedogenesis rise of the lake level vii upper holocene dry period deposition of a loess sheet san guillermo fm formation of deflation hollows viii little ice age reduction of the lake surface area and formation of a dune field campo maare sands

a multi proxy approach to paleoenvironmental changes in the southwestern rio de la plata area argentina during late pleistocene abstract in the southwestern margin of the rio de la plata argentina mining works have uncovered deposits that correspond to the last glacio eustatic cycle

a magnetoclimatological investigation of pampean loess argentina summary magnetic susceptibility has proved to be a very useful tool for understanding northern hemisphere loess palaeosol sequences both for intersite correlation and for broad climatic interpretation however there are two competing magnetoclimatological models that predict completely opposite patterns of variability the so called wind vigour and pedogenic models in the former stronger winds during glacial intervals entrain larger quantities of dense magnetic particles than during interglacials glacial loess is therefore more magnetic than interglacial palaeosol e g kurtak siberia in the pedogenic model biological and or chemical processes lead to the neo formation of magnetic material so that palaeosols are more magnetic than pristine parent loess e g the chinese loess plateau we are currently extending our investigation of loess palaeosol sequences to the southern hemisphere starting with a new 13 m section in the el cristo quarry in the city of la plata buenos aires province argentina the magnetic susceptibility profile shows a clear sequence of maxima and minima that correspond to lithological variations but interpretation of these correlations is not straightforward in the top 4 m of the section parent material loess has high susceptibility whereas palaeosols have low values consistent with the wind vigour model the same pattern is seen for most of the remaining 9m of section but there are intervals where gleying has occurred particularly between depths of 8 and 10 m under the waterlogged conditions implied iron oxides are likely to be removed and any original magnetoclimatological signal is lost or at least strongly modified a further complication arises from the measured values of the frequency dependence of susceptibility which is usually taken to indicate the presence of ultrafine magnetic particles produced during pedogenesis the el cristo values fall squarely in between those observed in siberia and china an important consideration in attempting to understand the pampean loess is the fact that it differs markedly in mineralogical composition from its northern hemisphere counterparts being dominated by volcanic material we have therefore determined the appropriate magnetic properties of samples taken from an ash layer embedded in a typical argentinean loess sequence thermomagnetic analysis shows the ash to be magnetically indistinguishable from the el cristo deposits however its measured frequency dependence of susceptibility cannot explain the intermediate values found there the overall outcome is that neither of the existing magnetoclimatological models can adequately account for the complexities of the pampean loess

late pleistocene holocene eolian deposits of the southern buenos aires province argentina a preliminary model abstract the aim is to reconstruct the sedimentological history of the late pleistocene holocene eolian deposits of southern buenos aires province hence a preliminary model is proposed in order to analyze the different stages of the sedimentological cycle the deposits include sandy loess fine sand sheets and dunefields the southern buenos aires province represents the depositional area whereas the source and transport environments are located in the northern patagonian andes and northern extra andean patagonia according to the mineralogical characteristics of the material explosive volcanism is considered the predominant process of particle formation particularly as generator of pyroclastic deposits which were reworked by different erosive processes glacial fluvial eolian during the late glacial maximum and the holocene alluvial deposits which were mainly generated by fluvial erosion of volcaniclastic sedimentary units were deposited along the floodplains of the colorado and negro rivers including those distal segments located in the emerged offshore platform the fluvial regime depended upon the regime of the glaciers hence it reflected the major glacial fluctuations which took place in the andes floodplains were deflated by southwest winds transporting the material towards the southern buenos aires province sandy loess and loessial sands and to la pampa province dunefields

eolian depositional phases during the past 50 ka and inferred climate variability for the pampean sand sea western pampas argentina abstract the pampean sand sea which occurs from the argentinian pampas to the eastern andean piedmont hosts presently stabilized dune fields spanning the late quaternary this study integrates previous results and presents new geomorphic stratigraphic sedimentological and chronologic data for nineteen 2 m thick eolian successions for the san luis paleo dune field western pampas to better constrain the depositional history six eolian depositional phases are identified spanning the past 50 ka interposed with paleosols and or bounded by erosive surfaces age control was from 61 osl ages of small aliquots of quartz grains from eolian stratigraphic units the inferred timing of eolian phases are at ca 70 10 yr 190 20 yr 12 to 1 ka 22 to 17 ka 29 to 24 ka and 40 to 32 ka a maximum span for periods of pedogenesis at ca 12 to 17 ka 22 to 24 ka and 29 to 32 ka was provided by bounding osl ages which broadly overlap with high stands of pluvial lakes and glacier advances in the central andes we infer that the added precipitation may reflect expansion of the southern hemisphere monsoon associated with northern hemisphere heinrich events leading to episodes of significantly wetter conditions 350 mm map to at least 35 s most of the holocene 12 ka to 0 8 ka was characterized by sand sheet deposit under drier than present conditions 100 450 mm map associated with monte type vegetation shrub steppe the latest two eolian depositional phases occurred at ca 190 and 70 yr ago during the historic period with european settlement and are related to anthropogenic landscape disturbance though the youngest phase was concomitant with 1930s drought wet conditions dominated since ca ad 1970 with new lakes and rivers forming across this eolian terrain an incongruous environmental response in reference to drier conditions for most of the holocene

sedimentological maps of the typical loessic units in north pampa argentina abstract application of grain size data allowed the construction of maps of two typical loessic formations of north pampa a sand sea covering the central argentine plain and a peripheral loess belt to the northeast compose the pampean aeolian system a region of 20 000 km 2 in the loess belt santa fe and cordoba provinces was studied thick loess outcrops are located in this region the tezanos pinto loess upper pleistocene lower holocene in age and the san guillermo fm late holocene in age are analysed in this article the silt content has been taken as the main parameter for mapping in general the pattern of the isoplethic curves is similar in both maps these maps show that the silt content in both loessic units progressively increases from ssw to nne in the loess belt the silt content increases from 55 to 60 in the ssw at the transition belt to the sand sea up to 75 80 in the nne along a distance of 120 200 km other sedimentological data of the outcropping loess paleosols sequences are presented as complementary information

the present and past bottom current flow regime around the sediment drifts on the continental rise west of the antarctic peninsula throughout the last decade large sediment drifts located on the upper continental rise west of the antarctic peninsula were the target of oceanographic measurements bathymetric mapping seismic investigations shallow sediment coring and deep sea drilling by ocean drilling program odp leg 178 these studies concluded that for most of the late neogene and quaternary a generally sw ward directed bottom current affected the deposition on the drifts in particular during glacial periods the deposition was additionally influenced by nw ward directed transport of terrigenous detritus supplied by turbidity currents from the antarctic peninsula continental slope in a recent study however the palaeomagnetic signal of the drift sediments recovered at two odp leg 178 sites 1095 and 1101 was interpreted to provide spatial and directional information on the physical record of the ne ward flowing antarctic circumpolar current acc here we investigate the link between the clockwise flowing acc and the generally sw wards flowing near bottom contour current we show that at the odp leg 178 sites on the western antarctic peninsula continental margin the acc only affects the ocean circulation above ca 1000 m water depth therefore the signal of acc flow might only be archived in the ice rafted debris ird content of the drift sediments however the ird from the leg 178 sites accounts for only a small proportion of the drift sediments and is dominantly of local origin past variability of bottom water flow around the sediment drifts was reconstructed on the basis of seismic studies and clay mineralogical and grain size analyses these reconstructions provide useful information about both downstream direction and velocity changes of the bottom current and point to its sw ward flow along the upper rise during at least the last 9 4 ma

implications of loess and fluvial deposits on paleoclimatic conditions during an icehouse hothouse transition capitanian upper quanzijie low order cycle bogda mountains nw china abstract permian terrestrial sedimentary records provide important clues on paleoclimatic conditions and changes in a vegetated planet during the last icehouse hothouse transition seven stratigraphic sections of middle permian upper quanzijie low order cycle qzj lc in bogda mountains nw china are studied to interpret the depositional environments and paleoclimatic conditions within a multi order stratigraphic framework the upper qzj lc contains distinct laterally persistent thick and massive red mudrocks interbedded with laterally discontinuous conglomerates the mudrocks are interpreted as loess deposits on the basis of their massive structure uniform multi modal grain size distribution lateral extent mineral composition and uniform detrital zircon ages thin conglomerates with a low relief erosional base are interpreted as ephemeral braided stream deposits whereas thick conglomerates with a high relief base that display a clear fining upward trend as meandering stream deposits in tarlong taodonggou area in the south common protosols in loess deposits indicate dust accumulation under arid to semiarid conditions in dalongkou 70 km to the north argillic protosols indicate subhumid conditions alternating with arid semiarid episodes gleysols in the upper part in both areas indicate a change to subhumid humid conditions at the end of qzj time the results strongly suggest that persistent aridity eolian processes and dust trapping mechanisms had existed in ne pangea during capitanian time the gradual but dramatic climatic change from arid semiarid to subhumid humid conditions at the end of capitanian correlates to and is the result of the global demise of the late paleozoic ice age

geomorphology and shallow structure of a segment of the atlantic patagonian margin abstract we study an area little known of the atlantic patagonian margin from 44 30 s to 47 40 s and from 59 w to nearly 61 w the multi beam bathymetry coupled with high resolution seismic reflection profiles has provided details on the morphology and shallow acoustic structure on this area the main morphological characteristics of the seafloor features on the shelf and middle slope are described the atlantic patagonian continental shelf north of 45 40 s is located at a depth of 170 200 m south of this latitude the shelf edge is at 128 to 200 m the shelf surface is marred by circular depression and ridges oriented oblique to the shelf edge the upper slope and upper middle slope are plowing by icebergs from antarctica in pleistocene and local reefs of cold water coral further enhance the topography of the area in the middle slope there are two terraces the 20 to 60 km wide nagera and the 15 to 60 km wide perito moreno terraces showing moats hollows pot holes sediment drifts and sediment waves the terraces may have been formed in late miocene whereas the other forms are of pleistocene age other features are a sediment swell south of 47 s and seven submarine canyons on the middle slope these incipient canyons have been developed in the middle slope by retrogressive erosion some terminating on the upper middle slope and others on the upper slope and the canyon 6 breaching the shelf edge individual seafloor features existing on the atlantic patagonian margin have been classified into two main groups according to their origin along and across slope processes these primary agents were supplemented by endogenic processes such as expulsion of gas water diapirism of high pressure mud and folding faulting the results suggest that today down slope processes on the slope are practically non existent and that the morphology of the upper and middle slope is slowly being remolded by along slope bottom currents

factors affecting arsenic concentration in groundwaters from northwestern chaco pampean plain argentina the concentration of arsenic measured in groundwater from three aquifers in the study area located in the eastern tucuman province argentina mostly depends on the lithology but the spatial and temporal variations of concentrations seem to be also controlled by ph changes climatic factors and human perturbations the highest concentrations of as more than 1 000 g l 1 were found in the shallow aquifer made of as rich loess while the lowest concentrations were measured in the deep confined aquifer consisting of alternating layers of alluvial sands gravels and clays intermediate values were measured in the semiconfined aquifer made of the fluvial sediments deposited in the sali river valley that alternate in the upper part of the sedimentary sequence with layers of loess because most of as in the loess is considered to be adsorbed onto fe oxyhydroxide coatings the increase of ph in the flow direction west east leads to increasing arsenic concentrations towards the eastern border of the study area the decomposition of organic wastes poured into the sali river or associated with local and diffuse sources of contamination in the eastern part of the study area depletes dissolved oxygen which leads to the reductive dissolution of fe and mn oxyhydroxides and to the subsequent release of the adsorbed and co precipitated as this process mainly affects shallow groundwater and the upper part of the semiconfined aquifer geochemical and hydrological data also suggest that rising water table levels at the end of the wet season may also lead to reductive dissolution of as rich fe oxyhydroxides in the shallow aquifer

climatic interpretation of a 1 9 ma environmental magnetic record of loess deposition and soil formation in the central eastern pampas of buenos aires argentina abstract much of what we know about quaternary climate has been learned from sedimentary records from the world s oceans with the exception of the extensive studies of the chinese loess paleosol sequence and more recent studies of long lake records there are few long terrestrial climate records particularly from the southern hemisphere the loess record of argentina provides an important opportunity to further our understanding of climate change from a terrestrial environment but its complexity and discontinuity have led to difficulty in formulating a climatological model of depositional and pedogenic processes in this study we present one of the longest and most continuous loess loessoid records from the central eastern pampas of argentina our age model is based on optically stimulated luminescent dates and a paleomagnetic reversal stratigraphy and indicates a basal age around 1 9 ma within the age model uncertainties we characterize the environmental magnetic properties associated with loess deposition and soil formation with respect to wind patterns moisture availability and temperature major changes in magnetic grain size are linked to a differential northward shift of the subtropical high pressure cell during glacial periods we suggest that coarser finer magnetic grains correspond to weaker stronger glacial periods when the high pressure cell is located in a more southerly northerly position and the source region is more proximal distal to our study area an abrupt increase in the ultrafine grained magnetic material around 0 9 ma is related to an increase in moisture transport from the south atlantic driven by an increase in summer sea surface temperatures at the mid pleistocene transition 1 ma in addition to these grain size variations there is a relative decrease in the amount of goethite compared to hematite beginning around 0 5 ma which has been related to the temperature increase observed after the mid brunhes event 450 ka in the epica ice core temperature record a more detailed comparison to insolation indicates that for portions of the record ferrimagnetic minerals are depleted during periods of low insolation this result suggests that argentine loess deposition and soil formation follows a model more similar to the alaskan loess sequences than the chinese loess sequences although further work is needed to validate the models and mechanisms proposed in this study our record indicates that the mineral magnetic properties of the loess and paleosol deposits record major changes in deposition and soil formation and provide insight into possible mechanisms relating to global and or hemispheric climate change

aerosol deposited in east antarctica over the last glacial cycle detailed apportionment of continental and sea salt contributions 1 the major ions sodium na calcium ca2 and chloride cl deposited in central antarctica and preserved in ice cores originate from both marine and continental sources they provide important proxy records helping to reconstruct past climatic processes however it is difficult to clearly separate the individual contributions from the two sources particularly the continental one during glacial periods on the basis of na and ca2 records at an unprecedented resolution from the european project for ice coring in antarctica epica dome c ice core back to the penultimate glacial period mean ion mass ratios were deduced for the continental and the sea salt aerosol body over east antarctica the sea salt ion mass ratios are in the range predicted for both wind induced bubble bursting of breaking waves on the open ocean and sea ice brine derived aerosols respectively thus allowing no clear decision on the contribution of sea ice to the central antarctic sea salt aerosol the continental ion mass ratios point to a substantial contribution by halide aerosols which is in agreement with the source properties in southern south america although these ratios do not rule out the continental shelf exposed during glacial stages as an additional source while during cold glacial periods continental sources accounted for more than 90 of the total ca2 input this contribution was highly variable during the remaining glacial periods covarying with the antarctic warm events during the holocene it was less than 50 but it was significantly higher during the last interglacial period the sea salt aerosol contribution to the total na input which was mostly dominant and higher than 90 was reduced to only two thirds during the last two glacial maxima and the period around 60 ka thus the glacial continental na contribution appears to be more important than previously assumed implying that na records not corrected for continental na do not represent a pure marine signal at the east antarctic plateau during glacial times

control factors of the spatial distribution of arsenic and other associated elements in loess soils and waters of the southern pampa argentina abstract surface and groundwaters of el divisorio brook argentina have excessive as who usepa caa 10 g l 1 the rural population is at risk of arsenicism because groundwater is the only source of water for human consumption we analyse geoavailability of as and other associated elements ba br co cr fe and na in the solid phase inaa actlabs determine the association between as and other elements in the mineral suite and in waters quantify fe oxides fe ox mehra and jackson and interpret their relationship with as total fe fe total and na in the solid phase applying principal components pc to understand factors and processes that rule their incorporation into groundwaters and to identify areas at risk of elevated as in waters intrabasin variability of total as content range 5 80 20 70 mg kg 1 with the highest amounts towards the discharge areas and a more irregular vertical distribution particularly in the alluvial plain reflects differences in as bearer frequencies arsenic is slightly lower in the bw horizons compared with the a and c horizons and it increases in the bt horizon through clay illuviation more than 90 of sodium bicarbonated surface and groundwaters showed as 10 g l 1 range 10 to 114 g l 1 with the highest levels in the middle lower basin the highest contributions to pc1 were br 0 673 co 0 868 and na 0 769 as 0 814 and cr 0 686 were relevant to pc2 and ba 0 501 and fe 0 783 were relevant to pc3 in the upper basin a greater amount of na withheld in the solids promotes a less aggressive geochemical environment and prevents as from entering waters thus yielding lower as levels in the aquifer compared with the middle lower basin here alkalinity ph 7 up to 9 promotes weathering and liberation of as from volcanic glass and other carriers formation of as oxyanion species together with as desorption from charged clays and al fe mn sesquioxides and concentration up to unacceptable levels in solution landform configuration climate and pedoclimate the residence time of water and the local hydrogeochemical variables ph competition with other ions adsorption desorption control mobility and concentration of as in a dynamic equilibrium with the local chemistry evaporation subhumid to semiarid climate and oxyion competition reinforce as accumulation in the shallow aquifers

a review of late quaternary inland dune systems of south america east of the andes abstract inland dune systems of south america occur in a variety of environmental settings under different climatic conditions from humid subhumid to semiarid arid this contribution provides the state of the art on dune research of inland systems east of the andes tropical northern 10 n 10 s including the dune fields of llanos del orinoco and the amazonian basin are mainly formed from parabolic blowout or deflation basins and linear dunes developed on river floodplains aeolian activity was reported to occur near the late pleistocene holocene boundary in llanos del orinoco over the last 17 ka in the branco river basin and 32 6 ka in the negro river basin both in the amazonian region in general the attributed aeolian origin is controversial the morphology difficult to determine and the chronology still extremely limited and rather debatable in some cases the southern tropical region 10 s 22 s includes aeolian systems situated across the extensive lowlands of the gran chaco and those located in fluvial basins related to the cratonic brazilian shield sao francisco river pantanal and mato grosso the oldest barchanoid barchan ridges at the gran chaco were dated 36 33 ka and subsequent aeolian sand accumulation occurred at 18 ka 14 12 ka 10 9 ka and mid to late holocene times parabolic dunes at the sao francisco river floodplain show an oldest episode generated between 28 and 11 ka followed by eolian activity during the early to mid holocene no chronological data is available for the linear and lunette dunes described at the pantanal linear ridges were distinguished in the upper parana river mato grosso with associated sand accumulation at different intervals of the holocene the last reviewed region is the andean piedmont and western pampas at subtropical eastern south america comprising a large variety of dune morphologies barchan barchanoid linear parabolic transverse and lunette dunes deflation basins and sand sheets luminescence ages suggest the occurrence of aeolian activity intervals during late glacial times and the holocene the general understanding on the dynamic of south american dune systems is hampered by the paucity of chronological information and the representativeness of some dune records whether they reflect local or regional environmental conditions is still a matter of discussion in several areas that need further studies

depositional provinces dispersal and origin of terrigenous sediments along the se south american continental margin abstract continental margin sediments of se south america originate from various terrestrial sources each conveying specific magnetic and element signatures here we aim to identify the sources and transport characteristics of shelf and slope sediments deposited between east brazil and patagonia 20 48 s using enviromagnetic major element and grain size data a set of five source indicative parameters i e fd arm irm s0 3t sirm fe and fe k of 25 surface samples 16 1805 m water depth was analyzed by fuzzy c means clustering and non linear mapping to depict and unmix sediment province characteristics this multivariate approach yields three regionally coherent sediment provinces with petrologically and climatically distinct source regions the southernmost province is entirely restricted to the slope off the argentinean pampas and has been identified as relict andean sourced sands with coarse unaltered magnetite the direct transport to the slope was enabled by rio colorado and rio negro meltwaters during glacial and deglacial phases of low sea level the adjacent shelf province consists of coastal loessoidal sands highest hematite and goethite proportions delivered from the argentinean pampas by wave erosion and westerly winds the northernmost province includes the plata mudbelt and rio grande cone it contains tropically weathered clayey silts from the la plata drainage basin with pronounced proportions of fine magnetite which were distributed up to 24 s by the brazilian coastal current and admixed to coarser relict sediments of pampean loessoidal origin grain size analyses of all samples showed that sediment fractionation during transport and deposition had little impact on magnetic and element source characteristics this study corroborates the high potential of the chosen approach to access sediment origin in regions with contrasting sediment sources complex transport dynamics and large grain size variability

clay mineral composition of pampean loess argentina abstract this paper summarizes current knowledge on clay minerals on the pleistocene and holocene pampean loess detrital illite is the predominant clay mineral of the vitroclastic loess with minor amounts of montmorillonite and kaolinite minerals the illite with a small k content corresponds to a highly illitic illite smectite component in paleosols its crystallinity index decreases and there are more expandable interlayers as in the chinese loess

patagonian dust in antarctica abstract recent advances in the knowledge of antarctica have demonstrated that the atmospheric dust trapped in the west antarctica glaciers during is2 4 and 6 has a patagonian origin a climatic scenario is developed in this article in order to explain such a process patagonia is unique as it is the only sizable land mass located in the belt of westerlies in the southern hemisphere the westerlies are formed by cyclonic structures which normally elevate the air masses and aerosols to the upper troposphere there the phenomena of mass compensation occur with the antarctic anticyclone which as any anticyclone sinks air and aerosols to the surface large quantities of loose surficial sediments and atmospheric dust are typical of patagonia and can easily be picked up by the wind according to this scenario which is based on the general atmospheric circulation australia and southern africa are hindered in providing aerosols to antarctica because those territories are located in the subtropical high pressure belt

high frequency controls on alluvial successions an integrated sedimentological and palaeopedological approach to the plio pleistocene of argentina abstract plio pleistocene palaeosol bearing alluvial strata are continuously exposed along the marine cliffs of southeastern buenos aires province argentina the study interval was deposited by a mixed predominantly suspended load fluvial system outcrops are dominated by floodplain siltstones and mudstones that exhibit a cyclic alternation between calcic and vertic palaeosols this cyclicity is represented by meter scale alluvial cycles that show as a general trend a gradual increase in the proportion of channel fill deposits up section cyclic variations in palaeosols facies and architectural elements can be related to allogenic drivers such as climate and eustasy for the lower punta san andres alloformation the stratigraphic arrangement of the recognised palaeosols and the clay mineral distribution indicate that the palaeoclimate was subhumid average mean annual precipitation map 840 mm seasonal and temperate average mean annual temperature mat 7 85 c for at least 1 ma from ca 2 9 ma to ca 1 8 ma late pliocene early pleistocene with several intervals in which conditions became drier and probably colder even though climate was a major control on palaeosol development it is suggested here that it was not the main control on high frequency cycles variations in the orbital parameters more specifically in insolation were interpreted as having controlled the sedimentation and architectural evolution of the lower punta san andres alloformation depositional systems

mid latitude trans pacific reconstructions and comparisons of coupled glacial interglacial climate cycles based on soil stratigraphy of cover beds abstract south westland new zealand and southern chile are two narrow continental corridors effectively confined between the pacific ocean in the west and high mountain ranges in the east which impart significant influence over regional climate vegetation and soils in both these southern mid latitude regions evidence for extensive and repeated glaciations during cold phases of the quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants in south westland these variably aged glacial landforms are mantled by layered multisequal soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment these cover bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial warm and glacial cold climate during the quaternary in this study we recognise multisequal soils overlying glacial landforms in southern continental chile but unlike the spodic podzolic soil sequences of south westland these are of dominantly volcanigenic andic provenance and are very similar to multisequal soils of andic provenance that predominate in and adjacent to areas of rhyolitic to andesitic volcanism in north island new zealand here we develop a soil stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental chile based on proxy data from southern chile we propose that persistent vegetation cover and high precipitation on the western side of the andes during colder than present episodes tended to suppress the widespread production of glacially derived loessial materials despite the pervasive occurrence of glacial and glacio fluvial deposits that have frequently inundated large tracts of this landscape during the quaternary given the lack of loess cover beds that have traditionally assisted in the relative dating of glacial episodes prior to the late quaternary surface exposure dating techniques could provide another chronological alternative to address this issue however there have been two main obstacles to successfully apply this dating technique in patagonia first minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion although dating outwash plains is more robust second on the wet western side adjacent to the andes persistent vegetation cover during both glacial and post glacial times as well as widespread inundation by volcanic mass flows appear preventive we make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted andean sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified as already demonstrated by new zealand studies multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the quaternary on this basis similar sequences in northwest patagonia provide a relatively untapped archive to enable quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed

magnetostratigraphy and magnetic susceptibility of the las carreras loess paleosol sequence in valle de tafi tucuman nw argentina abstract stratigraphic studies on loess deposits in the intramontane basin of valle de tafi 27 s 66 w revealed up to 31 intercalated paleosols in order to clarify the chronostratigraphic position of the sediments we performed paleomagnetic investigations in the 50 m thick las carreras section the characteristic remanent magnetization chrm obtained after alternating field af demagnetization gives clear evidence of the matuyama brunhes boundary mbb at a profile depth of 26 7 m and of the jaramillo subchron at depths from 38 7 to 44 9 m we assign a minimum age of 1 15 ma to the onset of loess sedimentation which calls for a complete reassessment of the antiquity of loess in the region thus the las carreras sequence which is probably continuous and complete represents one of the longest quaternary terrestrial paleoclimatic records reported from the southern hemisphere the magnetic susceptibility signal follows the behavior known for argentinian eolian sediments though with certain restrictions and an overall weak correlation with pedostratigraphy this behavior is opposite to the pattern reported from the chinese loess plateau clp and seems to be influenced strongly by changing source materials contributing to the susceptibility signal in valle de tafi

a 3 3 ma impact in argentina and possible consequences enigmatic glassy materials escorias and red bricklike materials tierras cocidas occur at a restricted stratigraphic level the top of the chapadmalal formation materials from one locality near mar del plata are attributed to a mid pliocene impact event with a radiometric and magnetostratigraphic age of 3 3 million years ago ma an extinction of endemic fauna including the glyptodonts and flightless cariamid birds correlates with the unit containing the impact glasses moreover the age of the glasses is coincident within dating uncertainties with a pulselike change in the oxygen isotope marine record in the atlantic and pacific oceans just before the late pliocene deterioration of the climate

micromorphology and osl dating of the basal part of the loess paleosol sequence at la mesada in tucuman province northwest argentina abstract the basal part of the 42 m loess paleosol sequence at la mesada near tucuman in nw argentina reported by zinck and sayago j s am earth sci 12 1999 293 quat int 78 2001 11 is re examined here using a combination of micromorphology and optically stimulated luminescence osl dating depth distributions of microstructure clay coatings and secondary carbonate features enable the development of this part of the sequence to be reconstructed in terms of a series of pedosedimentary stages stage one involved accretionary pedogenesis with loess being modified by bioturbation and possibly leaching processes as it accumulated stage two was marked by a reduction in loess deposition and establishment of a relatively stable surface at which bioturbation leaching and clay translocation processes were dominant stage three represented a return to accretionary pedogenesis followed by establishment of a new relatively stable surface and vertical leaching and clay translocation processes with some welding of secondary carbonate features on the underlying older soil the three osl dates ranging from ca 150 to 195 ka bp suggest that the whole sequence is significantly older than indicated by the radiocarbon chronology ka bp reported in the works of zink and sayago cited above however assuming that the pedosedimentary changes reflect alternating periods of dry cool and moist warm conditions as suggested in the works of zink and sayago cited above the succession still potentially provides the highest resolution proxy climatic record so far reported in argentina

loess and the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap database abstract mineral dust is an important constituent of the solid load in earth s atmosphere the total atmospheric aerosol loading being both a function of and a factor affecting climatic change human actions have progressively enhanced atmospheric dust loading especially in the past century so that both natural and human induced effects of atmospheric dust on climatic change require more detailed research records of changing climate are preserved in cores from the ocean floors glaciers and ice sheets as well as in terrestrial sedimentary sections quantitative data on the present day distribution of atmospheric dust are sparse but simulation of dust transport and deposition has been modelled with some success the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap database was designed to serve as a global validation data set for use with earth system models of the palaeo dust cycle loess a wind borne silt deposited on the continents particularly in the past 2 6 myr is an important potential source of information on past atmospheric dust accumulation a recent initiative sought to improve the terrestrial data coverage within the existing dirtmap database by involving representatives from key loess regions in coordinating the data synthesis process so as to facilitate interaction between the dust modelling and the data collection communities the results are presented in this issue in order to compare past minerogenic dust records loess with those in ice and ocean cores mass accumulation rates mars have been calculated as fluxes in g m2 yr the loess regions covered include north and south america europe siberia eastern asia and australasia it is acknowledged that provision of age models for the calculation of realistic mar values depends upon a number of conditions most notably sound chronostratigraphy and realistic values of loess dry bulk densities the mar data sets presented here show some notable variation both within and between the studied regions regional mar coverage also varies reflecting differences in the availability of key data on loess from one world region to another loess facies vary according to specific site and source conditions as well as in response to post depositional re working of primary wind lain loess by surface geomorphic processes mean particle size consistently declines downwind and terrace valley and upland sites generally yield the highest mar values characteristics noted in all regions discussed here the loess accumulations in two major world regions central and eastern asia and the great plains region of north america differ in some important respects from loess elsewhere in that they lie peripheral to deserts and are remote from the former sites of major quaternary ice sheets it is concluded that the mars for terrestrial sites obtained from loess are consistently higher than those obtained from ocean and ice cores so that future climatic models designed to study the role of global atmospheric dust will have to take full account of the present and past dust records over the continents

a reply to relative sea level during the holocene in uruguay abstract martinez and rojas 2013 published a paper about the relative sea level during the holocene in uruguay the paper of martinez and rojas could be handled as an attempt to construct a sea level curve from data collected from different sources open ocean coast the rio de la plata coastline and the outlet of uruguay river in this sense several processes were involved storm effects at open ocean beaches the holocene enclosing of coastal lagoons storms within the funnel shaped estuary and the floods of the uruguay river however they included a series of omissions inaccuracies errors and critics to our work that need to be amended rectified and argued in response we present a historical background about the research on this issue in uruguay we refute the comments about the empirical framework used to construct the first sea level curve for uruguay bracco et al 2008 2011b we point out that the assumptions on which the curve proposed by martinez and rojas 2013 is based are mistaken in addition there are limitations of the performed statistical techniques and errors mainly systematic within their formulation we present evidence that the decrease in sea level from middle holocene would not have been constant instead a rapid sea level decrease would have taken place by 4300 yr bp finally we not only compare our sea level curve with that proposed by martinez and rojas but also we corrected the altimetry errors incurred in their formulation we conclude that the similarity supports the validity of our curve

loess in italy genesis characteristics and occurrence abstract there is currently a renewed interest in loess genesis and occurrence in italy well known loess profiles in northern italy have been re examined and previously unknown loess deposits in central and southern italy have been reported this work combines a meta analysis of published data with new data presented here for the first time to provide the state of the art on the spatial distribution characteristics genesis and deposition ages of loess in italy a database of 98 soil horizons from 91 soil profiles was created and made available it stores information on soils formed from loess or containing layers that show admixture of loess soil data include the source of information the topographic geomorphological and geological setting kind of parent material and land use main soil horizon properties as described in the field soil classification particle size distribution and chemical data loess is reported from almost all regions of italy it is generally pedogenized throughout the entire loess body and forms the parent material of deep and complex soil profiles the thickness of the loess deposits varies from a few decimeters to a few meters pedogenesis and local reworking partially change the original loess characteristics in this study we propose a set of parameters that help recognizing loess in soils particle size distribution and sorting geomorphological setting pedostratigraphic position shape of the grains under optical and scanning electron microscope sem and soil micromorphological characteristics the ages of the loess deposits range between 70 ka bp and 18 ka bp there are also a number of samples that have been dated to the holocene the meta analysis suggests that climate is not the only driver of loess deposition in italy geomorphological instability and human disturbance as well as the influence of saharan dust most likely played major roles too this study demonstrates that loess is much more widespread in italy than previously estimated yet further research on the spatial and temporal distribution of loess deposition across the mediterranean region is needed to better understand its genesis sources and trajectories periods of enhanced loess formation and the role of loess deposits in ecosystem functioning and resilience

changes in the as solid speciation during weathering of volcanic ashes a xas study on patagonian ashes and chacopampean loess abstract x ray absorption spectroscopy xas was used to determine the oxidation state of as local chemical coordination and the relative proportion of different as species in recent and ancient andean volcanic ashes as well as in chaco pampean loess as k edge xanes analysis indicates that in loess sediments the dominant species is as v i e 91 conversely as iii is dominant in all ash samples in the puyehue sample only as iii species were determined while in both the chaiten and the ancient tephra samples as iii species accounts for 66 of the total as the remaining 34 corresponds to as 1 in the chaiten sample and to as v in the weathered tephra the proposed exafs models fit well with the experimental data suggesting that in ancient and recent volcanic ashes as iii is likely related to as atoms present as impurities within the glass structure forming hydroxide species bound to the al si network in addition the identified as 1 species is related to arsenian pyrite while in the ancient volcanic ash as v was likely a product of incipient weathering in loess sediments the identified as v species represents arsenate ions adsorbed onto fe oxy hydr oxides forming inner sphere surface complexes in a bidentate binuclear configuration

sedimentological study of aeolian soil parent materials in the rio sauce grande basin buenos aires province argentina abstract sedimentological characteristics of aeolian soil parent materials in the rio sauce grande basin southern buenos aires province were analysed using grain size distributions transport mechanisms dynamics of the sedimentary process and the nature of calcareous layers samples were collected from c horizon of 13 profiles distributed over all the piedmont areas and plains calcium carbonate in these materials is either inherited from the parent material or was redistributed by pedogenic processes their amounts in ck horizons increase from the upper to the lower basin and are inversely related to the thickness of soil parent material to mean annual rainfall and to the calcrete depth the cumulative grain size plots show that the sediments were transported by both aeolian saltation and aeolian suspension most of them have coarser and more heterogeneous grain size distributions than typical loess of the northern hemisphere indicating a larger and more fluctuating wind energy than is required for the formation of typical loess deposits in the upper and middle basins were deposited in two main aeolian episodes which can be related to the dry periods of the late pleistocene and the late holocene recorded in southern buenos aires province in some thin profiles of the middle and lower basins the large clay content of the calcic c horizon was probably inherited from one or more previous pedogenic events there is a systematic increase of particle size towards the lower basin which may be related to an increase of energy towards the lower basin or to the influence of littoral dune fields along much of the atlantic coastal zone

the quaternary impact record from the pampas argentina abstract loess like deposits cover much of central argentina and preserve a rich record of impacts since the late miocene the present contribution focuses on two localities containing quaternary impact glasses along the coastal sequences near centinela del mar cdm and from near rio cuarto rc these highly vesicular glasses contain clear evidence for an impact origin including temperatures sufficient to melt most mineral constituents 1700 c and to leave unique quench products such as cristobolite the cdm glasses occur within a relatively narrow horizon just below a marine transgression expressed by a series of coastal paleo dunes and systematic changes in the underlying sediments high resolution 40ar 39ar dating methods yielded an age of 445 21 ka 2 glasses were also recovered from scattered occurrences lower in the section but were dated to 230 40 ka this inconsistency between stratigraphic and radiometric age is most likely related to a nearby outcrop of glass that had been exposed and locally re deposited in coastal lagoons during the last marine transgression at 125 ka sediments containing the original impact glass layer are now missing due to an unconformity perhaps related to subsequent marine transgressions after the impact 410 ka and 340 ka and hiatuses in deposition two different types of impact glasses from rc yield two distinct dates high resolution 40ar 39ar dating of fresher appearing glasses well preserved tachylitic sheen indicates an age of 6 2 ka 2 independent fission track analyses yielded a similar age of 2 3 1 6 ka 2 more weathered glasses however gave significantly older ages of 114 26 ka 2 consequently materials from two separate quaternary impacts have been recovered at rio cuarto the younger glasses are consistent with previously reported carbon dates for materials on the floor of one of the large elongate structures the depths of excavation for the rc and cdm impacts are very different while the rc glasses are largely derived from near surface materials the cdm glasses from the upper level contain added components consistent with miocene marine evaporites at a depth of about 400 500 m e g high cao and p2o5 the cdm glasses also incorporated older loess like sediments from depth based on the geochemistry several ratios of key trace and rare earth elements of sediments of different ages from the miocene to the holocene indicate a systematic compositional change through time such changes calibrate the observed differences in glass composition from their host sediments and further indicate incorporation of materials from depth consequently the argentine loess like sediments preserve evidence for at least four separate quaternary impacts based on foreign components in the glasses the cdm impact very likely produced a crater now buried or eroded once as large as 6 km in diameter the younger rc glasses however are consistent with shallower excavation consistent with an oblique impact

the argentine neotropical loess an overview abstract the neotropical loess primary and reworked covers a large part of argentina north of 30 s it is different in some ways from the loess of the pampa which is generally considered the typical argentine loess the mineralogical chemical and physical composition of the neotropical loess has been analyzed and is here compared with both pampean and northern hemisphere european and north american loess the distribution of neotropical loess is established following the former teruggi scheme and the bio stratigraphical data indicating a late pleistocene age is described the great climatic variability of this period is documented through description of a loess paleosol sequence that mantles the pre andean valleys the influence of loess influx upon the genesis of the paleosols and the stadial interstadial environmental changes are considered in relation to the generalized truncation of paleoedaphic sequences the migration of the polar front and the weakness of the pacific high pressure system are also analyzed in relation to south american environmental evolution during the upper quaternary in that sense the genesis of pre andean fluvial valleys and mega fans extending outward into the andean piedmont plains having sources on the eastern dry side of the andes would have been influenced by such a paleoclimatic situation

late pleistocene to recent climate change in cordoba province argentina geomorphological evidence abstract repeated episodes of climate change affected the cordoba plains during the late pleistocene and holocene many of the geomorphologic features of cordoba province were developed in response to climatic oscillations and their development can be correlated to changes in precipitation and hydrologic regimes alternating periods marked by dry climate and high evapotranspiration rates were interspersed with more humid intervals and can be correlated using stratigraphic and geomorphic evidence at the regional level the initial phase of the late pleistocene was characterized by significant loess deposition and the formation of large alluvial fans these sediments and landforms are representative of a dry climate the transition to the late pleistocene was marked by the initiation of a humid climate regime giving rise to enhanced fluvial activity and sedimentation expansion and integration of drainage networks and development of paludal areas and successions pedogenesis occurred in the interbasin areas involving precipitation of silica and sesquioxides during latest pleistocene early holocene time coinciding in part with the last glacial maximum a dry and cool climate resulted in widespread aeolian sand and loess deposition the early to mid holocene was characterized by humid subtropical conditions which became established throughout the region accompanied by pedogenic development of profiles with prominent bt horizons and further modification of drainage networks during the mid to late holocene these warm and humid conditions were replaced by a semiarid climate resulting in widespread aeolian deposition wind action formed deflation hollows and dune fields in several areas the climate reverted to subhumid and temperate conditions during the latter part of the late holocene and small areas of wetlands developed the little ice age was marked by climatic deterioration and the deposition of a thin layer of aeolian sediment the current climate of cordoba is subhumid and temperate

light acidification in n fertilized loess soils along a climosequence affected chemical and mineralogical properties in the short term some evidences indicate that n fertilization of crops decreased ph values of loess soils of the argentinean pampas in the last decades we analyzed the a horizons of four n fertilized f and non fertilized nf paired soils developed on similar parent materials within a climatic sequence ustic to udic water regimes and measured 1 the extent of ph changes 2 how these changes affected chemical and mineralogical soil properties and 3 how the soils according to their h buffering substances can react in the future if n fertilization and acidification continue results indicated that all f and nf soils were lightly acidified differences between phw and phkcl higher than 1 0 and that fertilization produced ph decreases in all studied soils but particularly in those with udic water regimes in agreement with their longer n fertilization histories fertilized ustic soils showed less crystalline illites and kaolinites and higher contents of amorphous al oxides than nf soils it remains unclear if the higher contents of amorphous al are related with the dissolution of phyllosilicates the transformation of the abundant volcanic glasses of these soils or both processes at the same time the cation exchange capacity cec and the percent of base saturation v did not change between f and nf soils probably due to the large influence of soil organic matter som in the studied soils if n fertilization and consequently ph decreases continue soils placed in both the moistest argiudolls and the driest extremes of the climosequence haplustolls would be the less affected this is because udic soils contain high som as well as illitic clays and silts while ustic soils contain free lime and high density charged clay minerals which have high h neutralization capacity the most affected soils by acidification should be those placed in the intermediate zone of the climosequence hapludolls which have low amounts of substances with high buffer capacity

isotopic constraints on the source of argentinian loess with implications for atmospheric circulation and the provenance of antarctic dust during recent glacial maxima we present rare earth element ree and sr nd isotopic data for argentinian loess 28 38 s with two aims 1 to examine the source regions of argentinian loess and the constraints that these put on palaeo wind directions 2 to further investigate the source of antarctic ice core dust and to test the hypothesis that some of it could be derived from a region to the north of patagonia into which the dry dusty westerly dominated patagonian climate expanded during quaternary glacial maxima sr nd isotopic data for argentinian loess from north of 37 s are distinct from patagonian loess compositions in that they have more radiogenic sr 87sr 86sr 0 7059 0 7123 and less radiogenic nd nd 0 8 to 6 4 ree patterns and sr nd isotopic values are relatively homogeneous for multiple samples taken from single loess sections but show significant differences between sections in general there is a northward change from patagonia like ree patterns and isotopic values away from volcanogenic signatures and towards those that are more like the continental crust the latitudinal nd isotopic pattern is remarkably similar to that for andean volcanic rocks and suggests derivation of loess from the andes by more or less direct westerly transport for loess sections in the north the data imply a contribution from palaeozoic gneisses to the northwest in the chilean altiplano sr nd data for extra patagonian argentinian loess north of 37 s do not support a significant role for this source region in supplying dust to antarctica at the last glacial maximum this conclusion contrasts with previous studies that suggest a significant northward shift in the climatic belts and in particular the westerlies and the antarctic polar front during quaternary glacial maxima very systematic relations between the sr nd isotopic composition of loess and their andean source highlights shifts in the sr isotopic composition of loess to more radiogenic values and strongly suggests that the slight offset between patagonian loess and ice core dust identified by previous workers is due to grain size differentiation effects

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

palaeoenvironmental evolution and sea level fluctuations along the southeastern pampa grasslands coast of argentina during the holocene holocene pollen and diatom analyses and complementary data from 18o and 13c malacology and sedimentology have provided a detailed record of vegetation history and palaeoenvironmental change at arroyo las brusquitas on the southeastern coast of the pampas of argentina especially in relation to past sea levels holocene palaeosalinity trends were estimated by detrended correspondence analysis and by salinity indexes based on pollen and diatom data as a consequence of sea level rise from the postglacial an extensive wave cut platform formed over which holocene infilling sequences were deposited unconformably in these sequences variation in pollen and diatom assemblages occurred in agreement with changes in mollusc diversity and abundance isotope values and sediment deposits between ca 6700 and 6190 14c yr bp 6279 6998 cal yr bp saline conditions predominated in an environment highly influenced by tides and salt water during the holocene sea level highstand between ca 6200 and 3900 14c yr bp 4235 4608 cal yr bp shallow brackish water bodies formed surrounded by saltmarsh vegetation that became more widespread from 5180 14c yr bp 5830 6173 cal yr bp to 3900 14c yr bp in relation to a sea level stabilisation period within the regression phase less saline conditions marked by frequent variations in salinity predominated between ca 3900 and 2040 yr 14c bp 1830 2160 cal yr bp the intertidal saltmarsh environment changed into a brackish marsh dominated by freshwater conditions and sporadic tidal influence halophytic vegetation increased towards ca 200014c yr bp indicating that saline conditions may be due to either desiccation or an unusually high tide range with rare frequency after ca 2000 14c yr bp the sedimentary sequences were buried by aeolian sand dunes changes in holocene vegetation and environments in las brusquitas area are in agreement with data obtained from various southeastern coastal sites of the pampa grasslands copyright 2005 john wiley sons ltd

pliocene pedosedimentary cycles in the southern pampas argentina well developed bt horizons of five palaeosols p1 p5 have been recorded previously within a 20 m thick succession of pliocene siltstones and clayey siltstones in the southern part of the buenos aires province of argentina this paper reports a detailed field and micromorphological thin section investigation of a 6 m portion of the sequence encompassing p2 and p3 large scale faunal burrow infillings occur throughout other bioturbation features in the form of channel and spongy microstructures are mainly confined to the siltstones the intervening clayey siltstones bt horizons have been affected more by shrink swell disruption as evidenced by slickensides and a range of striated b fabrics in thin sections clay coatings indicative of illuvial accumulation of clay translocated in suspension from overlying a or e horizons occur in both the siltstones and clayey siltstones the types microstratigraphic associations and depth functions of features are interpreted in terms of changing interactions balances and dominances between sedimentary pedogenic and erosional processes over time thus providing the basis for the pedosedimentary reconstruction of landscape evolution in the region during part of the pliocene represented by the whole p1 p5 sequence 4 5 ma bp it is envisaged that this period was dominated by aeolian deposition although fluvial and mass movement processes probably led to reworking and redistribution of some of the materials overall rates of subaerial deposition however were not substantial pedogenic processes were active throughout the balance between sedimentation and pedogenesis varying over time in a cyclical fashion phases of reduced deposition and establishment of relatively stable land surfaces were marked by the development of argillic soil profiles with clearly defined eluvial and illuvial horizons intervening periods of more rapid accumulation of coarser material were characterized by accretionary soil development and welding of new pedological features on existing soils as the surface accreted first transforming existing eluvial horizons into bct ae horizons siltstones and then encouraging the syndepositional upward extension of these complex horizons the primary basis of the alternating units of siltstones bct ae horizons and clayey siltstones bt horizons lies in the cyclical change in size of particles deposited although pedogenic translocation processes enhanced these textural differences the underlying driving mechanism behind the pedosedimentary cycle can only be speculated upon although it is tempting to relate the sedimentation pattern to climatic fluctuations linked to glacial advances and retreats in the patagonian andes during the pliocene

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

genesis of subtropical soils with stony horizons in ne argentina autochthony and polygenesis abstract deep red soils combining characteristics of highly weathered materials together with a significant degree of clay illuviation and with stony horizons close to the saprolite are found in the province of misiones northeastern argentina two basic types of stony horizons have been found which with the fine grained material above are together considered autochthonous the first one is a ferruginous nodular horizon composed mainly of in situ goethitic nodules of gravel size resulting from weathering and glaebulization processes of basalt the second are siliceous horizons which are also in situ derived from pre existing quartz veins within the basalt in contrast different analytical evidences particularly the vertical and geographical variations in the som stable carbon isotope ratios and the mineralogical composition of fine and coarse fractions suggest that these red subtropical soils are polygenetic being the result of a two fold process linked to paleoecological fluctuations in the framework of these results different interpretations about the origin of these soils and their parent materials and particularly the tropical loess theory are discussed

a multi proxy study of argentina loess marine oxygen isotope stage 4 and 5 environmental record from pedogenic hematite abstract a 12 m loess paleosol section la angostura from tafi del valle tucuman argentina was studied using rock magnetic measurements geochemistry mossbauer effect particle size and nd isotopes in order to elucidate changes in paleoenvironment at the site combining the results of these experiments allowed us to separate the effects of the two major controls parent material and pedogenesis on the measured parameters two behavior regimes were identified in the sediment 1 in the lower half of the section pedogenic processes though weak dominate the variation of the sediment s physical properties and 2 for the upper half of the section subtle changes in parent material control the majority of the measured parameters even those typically controlled by pedogenesis e g clay fraction applying rock magnetic mossbauer and bulk geochemistry measurements in concert we calculated an iron budget for the loess 80 of the iron in the sediment is in paramagnetic minerals 20 of the iron is in hematite 1 6 of the sediment s mass and 1 of the total iron is present as magnetite maghemite 0 1 of the sediment s total mass neither the pedogenic formation nor the depletion of ferrimagnetic material with increasing pedogenesis was consistently observed in this sediment throughout the entire section the concentration of hematite is argued to be sensitive to in situ alteration and it is further surmised to be sensitive to the available moisture at the site finally we present a curiosity within the error of our chronology the concentration of hematite seems to correlate with the coeval climate record from antarctica vostok it is possible that the sedimentary magnetic record from la angostura is a proxy for the strength of the south american summer monsoon

six millennia of atmospheric dust deposition in southern south america isla navarino chile to characterize dust deposition in southern south america for the holocene a 542 cm long core from a peat bog in southern chile oreste bog isla navarino was studied peat formation started 11 160 14c yr before present bp the titanium ti concentration in bulk peat combined with dry bulk density and peat accumulation rate were used to calculate the mineral accumulation rate mar in the oreste bog the distribution of calcium ca manganese mn and titanium ti showed that mineral accumulation for the last c 6000 yr was predominantly atmospheric with a record of effectively constant deposition 0 43 0 12 g m2 per yr similarly ti and zirconium zr concentrations in the acid insoluble ash aia were also effectively constant and agreed well with the mar for the last six millennia except at c 4200 cal yr bp where zr was enriched relative to ti here scanning electron microscope sem micrographs showed that the aia was dominated by volcanic particles 20 40 m with the mt burney

coherent composition of glacial dust on opposite sides of the east antarctic plateau inferred from the deep epica ice cores 1 the dust provenance identification through isotopic and geochemical tracers focused mostly on ice cores drilled in the pacific indian sector of antarctica where a common provenance of dust from southern south america during glacial ages was demonstrated conversely in other areas of the east antarctic plateau as dronning maud land provenance was deduced indirectly from back trajectory analyses and soluble chemistry records in this work we present the first comparison of major elemental composition of dust archived in two ice cores from opposite sides of antarctica in the framework of the epica project mineral particles extracted from the edc and edml cores date back to glacial mis 2 4 and 6 over the last 200 kyr results reveal a coherent geochemical dust composition at both locations providing experimental evidence of a common provenance over the wide area of east antarctica during glacials and key analytical constrains for atmospheric general circulation models

assessing links between late holocene climate change and paleolimnological development of pena lagoon using opal phytoliths physical and geochemical proxies abstract opal phytolith geochemical and sedimentological data from two cores taken in pena lagoon a small water body on the atlantic shore of uruguay are presented in this paper the choice of this specific sampling location aimed to obtain high resolution records to infer late holocene environmental and climatic changes in southeastern uruguay in order to improve previous models for early and middle holocene the combined record of two cores extends to 2500 14c bp with a sedimentation rate ranging between 0 6 and 2 mm y 1 a multiproxy approach allowed the identification of changes in dynamics particularly organic matter and sediment input variability from the watershed with this information differences in the amount and extent of environmental signals were evaluated and a comprehensive climate change model was generated especially for the last 1500 years three main climatic events were distinguished the oldest which lasted until 700 ad was characterized by temperate and humid conditions the second extended until 1200 ad and warmer and wetter conditions were inferred but also a colder and drier pulse was observed in between this second event was assigned to the warm medieval period wmp during the third event assigned to the little ice age lia which extended until the present a high variability in climate was observed but also three dry cold phases reaching their maxima by 1300 1600 and 1900 ad were inferred

rapid mineral surface weathering beneath the greenland ice sheet shown by radium and uranium isotopes abstract glaciated watersheds are regions of intense physical and chemical weathering in order to gain new insight on subglacial weathering processes we measured uranium and radium isotopes from a proglacial river draining the greenland ice sheet gris time series samples were collected from the spring to mid summer a time period during which subglacial drainage pathways are thought to transition from slow inefficient distributed to fast efficient channelized systems the 228ra 226ra activity ratio of the dissolved load varied from 5 2 0 9 16 9 3 6 which was significantly higher than the 228ra 226ra ratio of a suspended sediment load sample of 2 1 0 07 and crustal values of 1 the high 228ra 226ra in the dissolved load relative to the source rock material is indicative of mineral surface weathering induced by rapid and continuous flushing of the subglacial drainage network during the course of the melt season and those prior the 234u 238u ratio 234u varied between 33 and 106 with a discharge weighted mean of 67 the seasonal evolution of 234u did not correlate to geochemical indicators of subglacial meltwater storage time an experiment designed to measure changes in 234u with increasing meltwater storage times found that 234u in the dissolved phase decreased rapidly with increasing storage time similarly samples collected along a transect moving downstream from the ice sheet terminus had decreasing 234u values from 63 to 15 further indicating that with increased weathering the 234u of meltwater decreases coupled with the relatively low 234u and high 228ra 226ra u appears to be impacted by rapid chemical weathering of subglacial and suspended sediments the leverett river discharge weighted u concentration was 0 13 nm if this system is considered representative of the broader gris then the total dissolved u flux from the gris would be on the order of 6 4 104 mol y using a similar set of assumptions the dissolved 228ra and 226ra flux from the gris was 1 1 1014 dpm y and 5 5 1013 dpm y respectively these estimates suggest that the 226ra flux to the ocean from the gris is globally significant and that the 228ra flux in particular is larger than most river inputs

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

first data on volume and type of deflated sediment from southern puna plateau and its role as source of the chaco pampean loess abstract this paper presents the first attempt at qualitatively and quantitatively evaluating the sedimentary contribution of the puna plateau to the loess and soils of the argentinean pampas the origin of the pampean sediment has been traditionally ascribed to northern patagonia but new evidence supports a dual supply western central andes north patagonia and puna altiplano plateau three different lines of evidence show here that puna dust supply is active and produces significant sedimentary deposition up to places like buenos aires city the first evidence is meteorological and we show here one event related to an abnormal rainfall that deposited large quantities of a reddish brownish silt eroded out from the puna calling the attention of the environmental agency of buenos aires city the second evidence is the sampling of active wind transport collecting extremely coarse material carried out in the saltation layer suggesting the fine grained material escapes the area as fugitive dust this also demonstrates that observed gravel bearing bedforms of the puna are active and that the transport system seems to be activated by polar fronts only results show that the saltation curtain is abnormally thick and coarse suggesting that the kinetic energy peaks ca 7 10 times higher than for normal saltation while the transported grain size coincides with the lagged sediment in this basin composing different bedforms varying between sandy gravel and gravelly sand the third evidence is the quantification of the exported material by defining a reference surface as the initial time of evolution and the present day surface the initial surface is an alluvial surface of an estimated age of 11 12 ka bp volume balance was achieved by a detailed topographic stratigraphic and geophysical survey reconstructing old alluvial and present surfaces two gridding methods were used and more conservative results of the volume balance indicate a total erosion of ca 3 386 hm 3 of sediment in 72 ha spliced in 0 963 hm 3 of sediment that was left within the place forming gravel dunes while the remaining volume of ca 2 423 hm 3 is sediment truly exported from the surveyed area results imply a continuous blanket of ca 4 m thick of sediment exported out of this basin in the holocene these findings prove that the puna contribution to the chaco pampean plain is significant although not unique thus true proportions of sediment contribution to soils and loess from these multiple sources should be better evaluated in future studies

independent time markers validate pb 210 chronologies for two shallow argentine lakes in southern pampas abstract we report here the results of detailed 210pb analysis from two lake sediment cores collected from lagunas encadenadas del oeste leo located in the southern argentinean pampas 37 s 62 w non exponential and non monotonic 210pbuns depth profiles in the sedimentary record of these shallow lacustrine systems indicate the interaction of complex processes behind radionuclide fluxes and lake sedimentation the chronologies and sediment accumulation rates sar for the lake sediment sequences were modeled using different 210pb based mathematical models since modeled 210pb ages must be validated against independent stratigraphic markers of known age two chrono stratigraphic markers were selected to control the upper and lowermost parts of the 210pb dated sediments the younger stratigraphic marker of ad 1980 2 corresponds to an uppermost organic carbon rich mud accumulated by 1977 78 matching the most noticeable lake highstand occurred during the 20th century registered on instrumental and paleolimnological records across the pampean plains the oldest stratigraphic marker corresponds to ad 1878 10 matching with a high lake productivity and wet phase related to anomalously intense rainfall and flooding events in southeastern south america for ad 1877 1878 when comparing the resulting ages to the stratigraphic markers our results show that crs model constant rate of supply performs better than the other models thus these independent chronostratigraphic markers used along the sedimentary records were critical to validate 210pb derived ages and therefore to select the most appropriate model to establish the chronological framework of the recent sediments of the leo system the crs model appears to be an adequate technique for deriving ages and sar in the leo sedimentary record and other pampean lacustrine systems under strong hydrological variability

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

late quaternary vegetational and climatic changes in the pampa grassland of argentina abstract the vegetation and climate of the pampa grassland argentina during the late quaternary are reconstructed from pollen recovered from dated stratigraphic sections from arroyo walls and from archaelogical excavations prior to 10 500 yr b p herbaceous psammophytic steppe existed in the central part of the pampa grassland while xerophytic woodland associated with psammophytic and halophytic steppe occurred in the southwestern part of the pampa these types of vegetation and the continental conditions that prevailed in the area of the present day coast 38 s indicate subhumid dry climate and annual precipitation 100 mm lower than present a subsequent change toward a vegetation characteristic of ponds swamps and foodplains or toward environments with locally more effective moisture occurred ca 10 500 yr b p suggesting annual precipitation close to modern levels or a higher availability of water in the central part of the pampa grassland this type of vegetation existed until 8000 yr b p when it was replaced by grassland communities that lasted until 7000 yr b p in the southwestern part of the pampa grassland this vegetation developed before 7000 yr b p and persisted until ca 5000 yr b p sea level higher than the present ca 6200 yr b p is consistent with sharp modification of the vegetation and development of local halophytic communities dominant at 38 s a return to subhumid dry conditions occurred after 5000 yr b p the late holocene vegetation is characterized by pollen assemblages similar to the psammophytic and halophytic communities of the southern pampa grassland associated with communities with more edaphic conditions at the same time at 38 s a sea level regression is suggested by the dominance of fresh water pollen assemblages and micropaleontological remains the trend toward humid temperate conditions ca 1000 yr b p suggested by vertebrate remains characteristic of temperate and humid conditions as well as a very short but dry episode during the 18th century suggested by the geology are not clearly evidenced in the pollen sequences vegetational and climatic changes are explained by the latitudinal shifts and changes in intensity of the southern atmospheric circulation and changes in sea level

groundwater characteristics within loessic deposits the coastal springs of los acantilados mar del plata argentina the urban growth of the southern neighborhoods of mar del plata city provoked significant changes in the groundwater balance of the loessic sequences these regional loessic levels with a significant portion of volcanic ash layers were reported subject to fluoride and nitrate concentrations residential houses pump from sands located 70 m depth and withdraw the sewages to depths less than 5 m these effects cause significant local and seasonal summer increments of the water table outcropping via springs at certain unconformities of the coastal cliffs a mathematical model was applied to analyze the water level lowering at the productive levels while there is a decrease in the quality of the upper levels subject to waste discharges much of this groundwater flow is concentrated in unconformities between different types of sediments human activities have affected the aquifer dynamics increasing the groundwater pumping rates and the return velocity of the sewages this should be considered in the management strategies of coastal hydric resources

deep events in u k south western approaches summary apparently planar dipping events are observed in seismic data off south west britain within otherwise essentially transparent upper and middle crust these are believed to represent variscan thrusts some of which were re activated during the post carboniferous phase of extension that affected the southern u k they can be seen in two extensive commercial seismic surveys recorded to 6 s two way time twt and where laterally persistent they have been mapped to reveal their essentially planar nature commonly these dipping events are associated with deeper near horizontal or gently convex upwards events with which they often appear to converge where real these are thought to indicate a complex fault system or possibly the top of the reflective lower crust the thrusts are seen over the whole area except where granite is known to occur and commonly exert a major control on the position and subsequent deformation of overlying sedimentary basins

late quaternary aeolian and fluvial aeolian deposits from southwestern pampas of argentina southern south america abstract the central region of argentina southern south america is characterized by an extensive quaternary aeolian record in this context three locations from the southwestern pampas an andean foreland region bearing a rich fossil mammal record that contributed to the south america biostratigraphic scheme were selected to carry out a comprehensive sedimentological analysis of the late quaternary deposits the case studies are located at the transverse valleys of la pampa province chapalco quehue and utracan argentino valleys and exhibit a high resolution of the late quaternary in comparison with others areas of the southwestern pampas the toay locality 36 41 s 64 24 w records aeolian dominant activity since the end of the late pleistocene 30 ka onwards soil formation at some point during the holocene and early mid 20th century reactivation of aeolian process the arroyo quehue locality 37 04 s 64 42 w presents a late pleistocene holocene succession mostly related to an ephemeral endorheic fluvial system with an interval of relative surface stabilization and aeolian aggradation during the late holocene the utracan locality 37 17 s 64 35 w exhibits a prevailing aeolian and fluvial aeolian interaction succession developed in the mid to late holocene in a sand mud flat environment of a shallow saline lake the three studied cases are representative of aeolian aggradation in association with ephemeral fluvial shallow lake and pedogenic processes in a currently subhumid dry region numerical ages indicate sedimentation during the last 30 kyr they allow constraining and evaluating the paleoenvironmental conditions in this inland region of southern south america and provide age constraints for the regional databases of paleoclimatic proxies the results are in agreement with other late quaternary paleoclimatic paleoenvironmental archives of central argentina and show a fragile aeolian landscape that is susceptible to deterioration under extreme conditions including both aeolian reactivation during dry phases and erosion of sandy silty sediments during wet phases

climatic variations in the argentine plains during the last 18 000 years the last deglacial hemicycle was characterized by a general increase in temperature and precipitation in the region with a few significant departures from this general trend the present ne sw climatic gradient was maintained throughout the entire period except in the upper holocene the following sequence of events is apparent if the present climate is taken as a reference base 1 a 18 000 8500 yr b p arid and cool with aeolian sand ad loess deposition patagonian fauna climatic isolines temperature precipitation etc were located some 750 km northeast of their present positions 2 b 8500 3500 yr b p humid subtropical with brazilian fauna pedogenesis and fluvial dynamics climatic limits migrated about 800 900 km southwest of their former positions 3 c 3500 1000 yr b p dry subtropical aeolian dynamics the normal latitudinal climatic gradient was interrupted by the occurrence of an anticyclonic centre which stabilized the climate over an area of some 1 600 000 km2 4 d 1000 yr b p little ice age climate was similar to the present one over much of the plains but the northeastern extremity was warmer 5 e little ice age climatic deterioration in the southern belt was characterized by generalized aeolian activity and migration of isolines more than 150 km to the northeast in that area 6 f present climate 19th and 20th centuries subtropical humid in the east and dry in the west

geochemistry of a late quaternary loess paleosol sequence in central argentina implications for weathering sedimentary recycling and provenance abstract a loess paleosol sequence in the pampean plain central argentina was analyzed geochemically in order to evaluate the weathering signature and sedimentary recycling as well as to analyze the origin of these loessic sediments corralito i sequence is composed of three paleosols and a buried soil separated by loess layers the loess paleosol sequence shows a similar geochemical composition throughout suggesting that pedogenesis has not been intense enough to mask the chemical signature of the parent material weathering indices cia ciw pia and lwi elemental ratios rb sr cao tio2 and na2o tio2 and the a cn k ternary diagram indicate incipient chemical alteration for this sequence compatible with a weathering limited regime as expected paleosols cias 60 exhibit a slightly higher chemical alteration than loess layers cias 58 mass balance calculations reveal the losses of some major oxides i e cao na2o and sr in the buried soil and paleosols compared to its loess mantles reflecting the weathering of plagioclase besides the losses of k2o and ba in the buried soil and paleosols i and ii when compared to its loess layers suggest the chemical alteration of k feldspar the chemical alteration of volcanic glass is evidenced by the relative losses of as in almost all levels conversely the relative gains of fe2o3 and mgo reveal that pyroxenes and amphiboles or fe oxy hydroxides are concentrated in paleosols and the buried soil compared to its loess mantles the geochemical approach used to constrain the origin of these pampean plain loessic sediments indicates they derive mainly from the andean region conversely the pampean ranges the parana river basin and uruguayan precambrian outcrops which were pointed out as minor local sources do not contribute significantly to the loess deposits this work also shows that corralito i loess paleosol sequence and other loess samples from argentina do not evidence sedimentary recycling suggesting that these pampean plain loess deposits are mainly composed by young materials derived from undifferentiated volcanic rocks

discovery of a landscape wide drape of late glacial aeolian silt in the western northern calcareous alps austria first results and implications abstract aeolian deposits record palaeoenvironmental conditions and may coin soil properties whereas periglacial loess is extensively investigated for 200 years the study of the intramontane wind blown deposits of the alps has just stuttered along herein we describe a drape of polymictic siliciclastic silt interpreted as an aeolian deposit that veneers extensive areas in the western northern calcareous alps nca from kames terraces near valley floors up to last glacial nunataks the nca part of the eastern alps mountain range consist mainly of triassic carbonate rocks these are overlain by deposits of the last glacial maximum lgm and its deglacial paraglacial aftermath e g glacial tills fluvio lacustrine successions alluvial fans scree slopes and a regional drape of polymictic silt newly described herein the drape is typically a few decimeters in thickness and slightly modified by soil formation it consists mainly of well sorted silt of quartz feldspars phyllosilicates muscovite chlorite biotite amphiboles and rarely calcite or dolomite the drape is unrelated to the substrate it overlies carbonate bedrock and in lateral continuity abandoned deposystems such as colluvial slopes of redeposited till kames alluvial fans scree slopes and rock avalanche deposits the drape was spotted from near the present valley floors up to lgm nunataks over a vertical range of some 2000 m it is also present in catchments of the nca that were not overridden by far travelled ice streams and that lack metamorphic rock fragments two osl quartz ages of the drape from two distinct locations 18 77 1 55 ka 17 81 1 68 ka fall into the early alpine late glacial interval shortly after the collapse of pleniglacial ice streams this fits with geological and geomorphological evidence respectively that the drape should be of early late glacial age and that it accumulated during a specific interval of time in the nca localized minor deposition of aeolian dust is documented by other authors from plateaus deglaciated only during the late glacial to holocene no evidence however exists for another phase of similarly widespread aeolian deposition such as that which gave rise to the described regional drape of silt intense aeolian transport and deposition was probably a direct consequence of the liberation of huge amounts of unsorted sediment during deglacial ice collapse perhaps combined with climatic aridification this provides a hitherto unappreciated element of the deglacial to paraglacial phase intramontane dust storms because of its large extent and the availability to osl dating the aeolian drape provides an excellent geochronological marker level identified in terrestrial post glacial successions of the eastern alps because of its fine grained siliciclastic composition the drape gives rise to widespread development of atypical cambisols on carbonate bedrocks with comparatively high water storage capacity and nutrient supply

the record of miocene impacts in the argentine pampas argentine pampean sediments represent a nearly continuous record of deposition since the late miocene 10 ma previous studies described five localized concentrations of vesicular impact glasses from the holocene to late pliocene two more occurrences from the late miocene are reported here one near chasico ch with an 40ar 39ar age of 9 24 0 09 ma and the other near baha blanca bb with an age of 5 28 0 04 ma in contrast with andesitic and dacitic impact glasses from other localities in the pampas the ch and bb glasses are more mafic they also exhibit higher degrees of melting with relatively few xenoycrysts but extensive quench crystals in addition to evidence for extreme heating 1700 c shock features are observed e g planar deformation features pdfs and diaplectic quartz and feldspar in impact glasses from both deposits geochemical analyses reveal unusually high levels of ba 7700 ppm in some samples which is consistent with an interpretation that these impacts excavated marine sequences known to be at depth these two new impact glass occurrences raise to seven the number of late cenozoic impacts for which there is evidence preserved in the pampean sediments this seemingly high number of significant impacts over a 10 6 km 2 area in a time span of 10 myr is consistent with the number of bolides larger than 100 m expected to enter the atmosphere but is contrary to calculated survival rates following atmospheric disruption the pampean record suggests therefore that either atmospheric entry models need to be reconsidered or that the earth has received an enhanced flux of impactors during portions of the late cenozoic evidence for the resulting collisions may be best preserved and revealed in rare dissected regions of continuous low energy deposition such as the pampas additionally the rare earth element ree concentrations of the target sediments and impact melts associated with the chasic event resemble the hna k australites of similar age this suggests the possibility that those enigmatic tektites could have originated as high angle distal ejecta from an impact in argentina thereby accounting for their rarity and notable chemical and physical differences from other australasian impact glasses

new insights on sources contributing dust to the loess record of the western edge of the pampean plain during the transition from the late mis 2 to the early holocene high resolution studies of palaeorecords located closer to the dust source areas of south america are relevant for increasing the knowledge on past climatic conditions in the southern hemisphere i

upper quaternary geology of the lower carcarana basin north pampa argentina abstract the geological evolution of the lower carcarana basin reflects a sequence of dry and humid climates from a geomorphological point of view the area belongs to the pampean eolian system the geomorphological units comprise several fluvial geoforms partially masked by a loess carpet on which eolian erosive forms developed the sedimentary record is not simple the typical profile begins with a predominantly eolian unit composed of silty sand and including two pedogenic levels carcarana fm the formation is the result of the reworking of a dune field in the pampean sand sea is4 it is upper pleistocene in age is 3 another somewhat different climatic deterioration followed related to the begining of the last glacial maximum is 2 which caused the deposition of a loessic mantle tezanos pinto fm subsequent evolution of the climate involved a shift to humid conditions during the hypsithermal period generating a well developed soil at the top of the formation an upper holocene eolian layer san guillermo fm covers the whole sequence at the river margins of the basin the late pleistocene lower holocene eolian deposits are replaced by a complex silty clayey sequence mainly paludal with a soil complex in the middle of the section lucio lopez fm

soil forming rates and processes on quaternary moraines near lago buenos aires argentina thirty four pedons on four moraine groups spanning the last 1 myr are used to investigate mechanisms and rates of soil development in santa cruz province argentina all soils are coarse loamy mesic typic haplocalcids or calcic haploxerolls occurring under short grass shrub steppe in a semi arid climate the dominant soil forming processes are the accumulation of organic matter carbonate and clay sized particles organic carbon accumulates rapidly in these soils but significantly higher amounts in the oldest two moraine groups are likely the result of slight differences in soil forming environment or grazing practices accumulation rates of carbonate and clay decrease with age suggesting either decreased influx in the earliest part of the record or attainment of equilibrium between influx and loss there are no changes in soil redness and preservation of weatherable minerals in the oldest soils indicates there is little chemical weathering in this environment measured dust input explains the accumulation of both clay and carbonate we present a carbonate cycling model that describes potential sources and calcium mobility in this environment calibration of rates of soil formation creates a powerful correlation tool for comparing other glacial deposits in argentina to the well dated moraines at lago buenos aires

geochemical differentiation of quaternary sediments from the pampean region based on soil phosphorus contents as detected in the early 20th century abstract data obtained in the early 20th century on the total phosphorus tp content in soil materials from the pampean region have been processed and plotted on maps of the region approximately 1200 subsoil data and 1400 surface horizon data obtained using the same analytical method have been processed according to differences in phosphorus content several areas have been demarcated limits and characteristics of these areas have been correlated with data from the more recent literature regarding the p distribution and with both mineralogical and sedimentological information on surface materials results suggest that a confluence of sediments from different provenances i e the andean range the pampean hills and the brazilian shield is found in the argentine pampean region

implications for paleomobility studies of the effects of quaternary volcanism on bioavailable strontium a test case in north patagonia argentina abstract strontium isotopes 87sr 86sr are used as geochemical tracers for paleomobility studies because they display predictable and stable patterns in ecosystems primarily controlled by the underlying geological regimes while bedrock geology is stable over thousands of years geomorphological processes can influence the 87sr 86sr in ecosystems over archeologically relevant timescales among these geomorphological processes the deposition and reworking of volcanic sediments over quaternary timescales are little studied but could be an important control of 87sr 86sr variations in many archeological regions north patagonia is a key archeological region to address animal and human movements and an ideal location to test the influence of quaternary volcanism on 87sr 86sr variation as it is located downwind of major volcanic centers in this study we aim to assess the main environmental and geological controls of bioavailable 87sr 86sr and to build a high resolution isoscape using a machine learning regression framework for forthcoming paleomobility studies we sampled several locations and analyzed different types of samples n 94 the ratios show a limited range of variation which is not related to the bedrock geology rather bioavailable 87sr 86sr variations display a progressive increase going eastward away from the andes following dust aerosol deposition and elevation variations r2 0 71 rmse 0 00041 we argue that this trend relates to the deposition and reworking of unradiogenic volcanic sediments by aeolian fluvial and glacial erosion during the quaternary as most of this sediment reworking occurred during glacial periods the current bioavailable 87sr 86sr variations across the study area likely represent a long term average that varied little during the holocene consequently our isoscape provides a solid base for holocene paleomobility studies in north patagonia and underlines the importance of quaternary volcanism processes for interpreting 87sr 86sr data in paleomobility studies in volcanic regions

late quaternary palaeosol records from subtropical 38 s to tropical 16 s south america and palaeoclimatic implications abstract loess and palaeosols in the subtropical lowlands of south america 23 38 s have a large potential to serve as archives of late quaternary environmental and climate changes at present mean annual precipitation generally decreases from n to s and from e to w though with a complex seasonal pattern with austral summer rainfall related to the monsoonal circulation and with austral winter rainfall related to the se trades in this paper we present results of multiproxy geochemical analyses from three representative eolian alluvial soil profiles along a s n transect aiming at the reconstruction of past climate changes i profile chasico at the southern border of the subtropics 38 s ii d4 in misiones at the northern border of the subtropics 27 s and for comparison iii laguna sucuara in the savannas of the bolivian lowlands 16 s our results show that before 16 ka bp conditions were likely very cold and dry except for in d4 loess or soils are not preserved due to rather scarce vegetation cover and resultant deflation in chasico accumulation of sands directly overlying the tertiary starts only during the late glacial indicating increasing temperatures and increased monsoonal precipitation coinciding with the tauca wet phase on the altiplano in d4 a palaeosol is preserved below the late glacial sediments and the deflation hiatus this palaeosol is dated to 40 ka bp and documents an earlier but less intensive southward reaching phase of monsoonal precipitation inca huasi on the altiplano whereas the seasonality during the late glacial seems to have been very pronounced conditions for organic matter production and preservation became much more favourable at chasico and d4 during the early holocene we suggest that extra tropical winter precipitation played a more important role than before and than today between 7 5 and 3 ka bp the expansion of c4 plants along the s n transect suggests increasing aridity probably due to a weakening of the extra tropical circulation in combination with a relatively weak monsoonal circulation only after 3 ka bp climate became more humid again due to the re strengthening of the monsoon

paleosols in loess deposits of the argentine pampas abstract paleosol studies are in their first stages in argentina as far as we know the soil and paleosols correspond to buried alfisols and mollisols with hydromorphic and carbonatic features the paleosol sequences on loess are made up of a succession of b or c horizons which furthermore are polygenetic as a result of encroachment of each pedogenesis on the underlying loess mantle differences in mineral composition are scarce with the exception of increases in glass shards and phytoliths in some loess mantles the b fabric is mostly stipple speckled or mosaic speckled and microlaminated clay coatings are very common there are also amorphous features related to voids or to the soil matrix evidences of biological activity are present as an excremental fabric on which a fissure microstructure is superimposed the paleosol sequences consist of several loessoid mantles each corresponding to a depositional pulse followed by a quiescent pulse during which pedogenesis took place truncation is considered to be due to eolian fluviatile erosion also there probably are a horizons masked by alteration and pedogenesis a pedogenetic origin of the calcretes with redeposition in the buried paleosols is assumed

late quaternary paleoenvironments and paleoclimatic conditions in the distal andean piedmont southern mendoza argentina abstract the andean piedmont of mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology this paper is focused on the san rafael plain srp environment situated in the distal andean piedmont of mendoza 34 30 s and reports the sedimentology and osl chronology of two representative exposures of late quaternary deposits including their paleoenvironmental and paleoclimatic significance eleven facies including channel floodplain fluvio aeolian interaction and reworked pyroclastic and aeolian deposits were described and grouped into two facies associations fa1 and fa2 fa1 was formed by unconfined sheet flows minor channelized streams and fluvial aeolian interaction processes fa2 was interpreted as aeolian dune and sand sheet deposits osl chronology from the srp sedimentary record indicates that between ca 58 39 ka and ca 36 24 ka mis 3 aggradation was governed by ephemeral fluvial processes fa1 under generally semiarid conditions during mis 2 the last glacial maximum ca 24 12 ka a major climatic shift to more arid conditions is documented by significant aeolian activity fa2 that became the dominant sedimentation process north of the diamante atuel fluvial system the inferred paleoenvironmental conditions from the srp sections are in broad agreement with regional evidence

interaction of the south american monsoon system and the southern westerly wind belt during the last 14 kyr abstract surface currents and sediment distribution of the se south american upper continental margin are under the influence of the south american monsoon system sams and the southern westerly wind belt swwb both climatic systems determine the meridional position of the subtropical shelf front stsf and probably also of the brazil malvinas confluence bmc we reconstruct the changing impact of the sams and the swwb on sediment composition at the upper rio grande cone off southern brazil during the last 14 cal kyr bp combining sedimentological geochemical micropaleontological and rock magnetic proxies of marine sediment core geob 6211 2 sharp reciprocal changes in ferri and paramagnetic mineral content and prominent grain size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments our interpretations support the assumption that the sams over se south america was weaker than today during most of the late glacial and entire early holocene while the swwb was contracted to more southern latitudes resembling modern austral summer like conditions in consequence the stsf and the bmc were driven to more southern positions than today s favoring the deposition of fe rich but weakly magnetic la plata river silts at the rio grande cone during the mid holocene the northern boundary of the swwb migrated northward while the stsf reached its northernmost position of the last 14 cal kyr bp and the bmc most likely arrived at its modern position this shift enabled the transport of antarctic diatoms and more strongly magnetic argentinean shelf sands to the rio grande cone while sediment contributions from the la plata river became less important during the late holocene the modern el nino southern oscillation set in and the sams and the austral tradewinds intensified causing a southward shift of the stsf to its modern position this reinforced a significant deposition of la plata river silts at the rio grande cone these higher magnetic silts with intermediate fe contents mirror the modern more humid terrestrial climatic conditions over se south america

the continental uruguayan cenozoic an overview abstract although quaternary study in uruguay was started in the 1970s international diffusion of the results has been limited this contribution is an updating of the continental aeolian and fluvial cenozoic period reinterpreted mostly from a geomorphological perspective we discuss the limitations in the usage of chronostratigraphic generalizations in the cenozoic based on a lithostratigraphic interpretation the upper pleistocene and the holocene are reinterpreted through available 14 c dates presenting a comparative preliminary table with the geological formations found in the neighbouring argentine provinces of entre rios and corrientes

new late pleistocene megafaunal assemblage with well supported chronology from the pampas of southern south america abstract late pleistocene outcrops exposed in buenos aires province argentina represent one of the most informative sources about the paleoecology of south american megafauna however there are no records of an accurately dated carnivore herbivore taphocenosis this paper presents preliminary results of a recent excavation at the margins of the salado river on sediments attributed to the lujan formation late pleistocene early holocene the fossiliferous strata consist of greenish brown sandy clays deposited in a small paleopond environment that was filled by fluvial sediments exhibiting abundant organic matter gypsum and carbonate concretions fieldwork yielded an association of extinct large sized mammals that include the horse hippidion principale the saber tooth cat smilodon populator at least one adult and one juvenile associated specimen a giant ground sloth megatherium americanum and the glyptodont doedicurus clavicaudatus four 14 c dates were performed on organic matter 12 100 100 14 c bp a femur of s populator 13 400 200 14 c bp and a cervical vertebra of hippidion principale 12 860 120 14 c bp and a pelvis of d clavicaudatus 12 380 190 14 c bp situating the site within 12 500 and 13 500 years approximately remarkably some of the recovered specimens exhibit conspicuous bone modifications furrows pits punctures striations and crenulated margins attributed to the activity of a medium large carnivore the association between bones of herbivore mammals with conspicuous modifications produced by a large carnivore and the presence of cub and adult remains of smilodon link this felid with at least part of the excavated association

quaternary evolution of the cordillera frontal piedmont between c 33 and 34 s mendoza argentina fil zarate marcelo aristides consejo nacional de investigaciones cientificas y tecnicas instituto de ciencias de la tierra y ambientales de la pampa universidad nacional de la pampa facultad de ciencias exactas y naturales instituto de ciencias de la tierra y ambientales de la pampa argentina

chronology of late pleistocene pampa loess from the cordoba area in argentina in argentina loess palaeosol sequences were studied from the two sections at monte ralo and corralito located near to the city of cordoba in the east of the pampean ranges infrared optically stimulated luminescence irsl and thermoluminescence tl dating techniques were applied to set up a more reliable chronological framework for the upper pleistocene loess record irsl ages increase with depth and are stratigraphically consistent the oldest loess exposed correlates at least to the penultimate glaciation the luminescence dating study gives evidence for humid climate conditions with soil formation during the last interglacial period and the middle pleniglacial correlating to marine isotope stage mis 5 and 3 respectively three extended periods of soil formation are recorded in the loess palaeosol sequences at the corralito section these buried soils most likely correlate with the last interglacial and early last glacial period during the middle pleniglacial two palaeosols are intercalated in the loess successions in the cordoba area the periods of increased loess accumulation and deposition of loessic sediments correlate with more arid and glacial periods during the early pleniglacial the middle pleniglacial and the late glacial copyright 2009 john wiley sons ltd