Search

Fossil capybaras were long regarded as composed of numerous taxa, each one endemic to a particular area, a scenario completely different from the one shown by the living species. The interpretation of the record according to new criteria of ontogenetic change has demonstrated that they are useful for biocorrelation because their members have short biochrons with wide geographic distribution. The levels with capybaras of each locality would represent a short lapse within the bearing lithostratigraphic units. In turn, they would also represent short intervals within the temporal extension proposed for each Stage/ Age or SALMA. All the late MioceneePliocene records of capybaras were analyzed and a chronological scheme was built mainly for Argentina, where records are most abundant. Numerical ages and magnetostratigraphic studies contribute to correlate this scheme with the global time scale. The Chasicoan SALMA would be correlated with part of the Tortonian Stage/Age; the Huayquerian SALMA with the late Tortonian-Messinian, and it could even extend to the earliest Zanclean. The Montehermosan SALMA would be restricted to the Zanclean. The Chapadmalalan SALMA would be correlated with the late Zanclean-early Piacenzian. Fil: Deschamps, Cecilia Marcela. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina Fil: Vucetich, María Guiomar. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Montalvo, Claudia Inés. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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

Drought episodes during the early–mid 20th century were recognized and described in several places around the world, with extreme dry conditions and widespread landscape denudation, like during the famous ‘Dust Bowl’ in North America. However, there is scant documentation of droughts in southern South America, particularly from the Pampas, and none based on the geological record. In this article, we provide clear evidence of aeolian reactivation and sand deposition in some areas of La Pampa and San Luis provinces, western Pampas (Argentina), during early–mid 20th century in response to drier conditions, probably amplified, like historic droughts in North America, by anthropogenic factors (e.g. significant population increase and agriculture expansion into a fragile environment). Evidence includes widespread bare sand blowouts, extensive surfaces with active sand migration, steep dune lee slopes, and sharp crests covered by weak soil development (A/C profile), accompanied by historical documents. Optically stimulated luminescence (OSL) ages on aeolian beds confirm mobilization and sedimentation by wind processes c. 95–60 yr BP. Considering the dominant (over 70%) austral spring–summer precipitation, it is possible the rainfall deficit in western Pampas was linked to positive sea surface temperature (SST) anomalies in the western subtropical South Atlantic Ocean (20–30°S and 30–50° W), according to significant canonical correlation between the precipitation field in subtropical South America and the Atlantic Ocean SST anomalies. Fil: Tripaldi, Alfonsina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina Fil: Forman, Steven L.. University Of Chicago; Estados Unidos Fil: Badger, Timothy. University Of Chicago; Estados Unidos Fil: Doyle, Moira Evelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Ciccioli, Patricia Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina

In arid and semiarid regions of Central West Argentina, paleoenvironmental conditions and history of the Holocene vegetation is still scanty. This paper presents the analysis of palynological records of two Mid- to Late Holocene alluvial sequences (La Escala -LES- and Brazo Abandonado -BA-) in the fluvial basin of the Arroyo La Estacada (33°27'S and 69°03'W), placed in the Cordillera Frontal central piedmont of Mendoza province. Variations in pollen assemblages of the two sequences related to the environments developed in the floodplains of the arroyo allowed us to infer the evolution of local plant communities. Between the ca. 4000 and 3000 14C years BP and between ca. 500 and 400 14C years BP, a larger representation of hydrophytic communities related to environments with local water availability was inferred; and between ca. 3000 and 500 14C years BP an increase in shrubby xerophytic communities related to environments with lower water availability was detected. These results led us to propose that the Holocene pollen spectra fluctuations observed in the alluvial sedimentary sequences prove mainly changes in plant communities of the floodplain environment in response to the fluvial dynamics of the arroyo. Fil: Rojo, Leandro David. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología y Palinología; Argentina Fil: Mehl, Adriana Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. 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 Fil: Paez, Marta Mercedes. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología y Palinología; Argentina Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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

The geomorphological, sedimentary and pedological evidence related to the various glacial periods which took place in the Patagonian and Fuegian Andes between the Late Miocene and the Late Pleistocene are herein presented and discussed. The occurrence of basaltic flows interbedded with till and other glaciogenic deposits provides radiometric dating and paleomagnetic information for several Patagonian regions which may be applied to the related glacial episodes. The modern glacial chronology of the Patagonian terrestrial glacial record is basically supported by 40Ar/39Ar dating on volcanic rocks associated with glacial deposits, and cosmogenic isotope dating techniques on erratic boulders and glacial erosion surfaces. These sequences, chronologically calibrated, compared with 47 Marine 18O Isotope Stages (MIS) and constrained by global magnetostratigraphy, enable the interpretation of climatic changes over about seven million years in the Southern Hemisphere. In addition, the loess and loess-like record of southern South American extends back at least to the Late Miocene. These deposits cover the Chaco-Pampean region of central eastern Argentina, between 28–38° S, which formed a large continental sedimentary basin during the Neogene. The oldest glacial evidence is composed of till and glaciofluvial deposits interbedded with 5–7 Ma old basalts found in at least two areas, 38° and 46° S. It has been interpreted that the Pliocene–Pleistocene glaciations were of local ice cap and piedmont glacier type. These ancient glacial deposits have been also affected by Andean tectonics and deformation. At least parts of the Southern Andes were already covered by a local mountain ice sheet during the Late Pliocene. This statement is supported by the finding of glacial boulders in between basaltic flows at 41° S, lava flows overlying glacial and glaciofluvial units at 39° S, and glacial deposits interbedded with flows and till overlying basalt flows between latitude 46°–52° S. Whether the development of glaciers was promoted by climate deterioration, by tectonic forces, or both kinds of processes is still unknown. Thus, already during the Pliocene, local icefields would have been very extensive, covering part of the westernmost, extra-Andean tablelands all along Patagonia. A minimum of seven glaciations were recognized at Cerro del Fraile locality (50° S) during the Early Pleistocene and interpreted as repeated piedmont glaciations, synchronous to active volcanism. The most extensive glaciation recognized in many parts of Patagonia is known as The Great Patagonian Glaciation (GPG) and bracketed between 1.15–1.05 Ma. However, until precise chronology is available for all localities in which GPG has been found, GPG should be considered as a multiple-event glaciation. In several transversal Patagonian valleys three glacial advances took place after GPG and before Last Glacial Maximum (LGM). The absolute chronologies of these post-GPG events have not been closely defined yet though, based upon paleomagnetic data, all till deposits along the Atlantic coast of Tierra del Fuego would belong to the Brunhes epoch. The Last Glaciation is very well known in all Patagonian glacial valleys and coastal channels and fjords. The estimated ages of these deposits begin close to 60 ka, but full glacial times (LGM) have been dated between 25–20 ka. Correlation of all these glacial events with the Pampean loess units is possible, but more detailed studies and absolute dating is needed.

The Bogota basin and direct surroundings (eastern Andes in Colombia) holds a long sedimentary sequence that reaches from the present into the Miocene. Palaeo-botanical data indicates tectonic uplift by some 2,000 m during the Late Miocene–Pliocene that probably precluded sufficiently high enough terrain to support glaciers during the time period preceding the Quaternary. The first mountain glaciation as recorded by glaciofluvial sedimentation in the Bogota basin is dated by fission-track and magnetic polarity dating at ca. 2.6 Ma, whereas a shift towards more extensive glaciations occurred after ca. 0.8 Ma. Moraines preserved in the Bogota mountains record a series of glacial events for the time interval ca. 43 to 12.5 ka BP. Equilibrium Line Altitude (ELA) depression by ca. 1,300 m is reconstructed for the early Last Glacial Maximum (LGM; ca. 20 ka BP).

The loess/paleosol sequence of north central China is probably the most complete record of Quaternary climate change derived from terrestrial deposits in the world. Alternating loess units (utilizing grain-size differences) which indicate cold periods and paleosols which indicate warm periods, record 37 major climatic cycles over the past 2.6 Ma. The Eastern Hemisphere loess/paleosol climate records are compared to the Western Hemisphere glaciations in order to record similarities of climate change intervals over a wider area by comparing Marine Isotope Stage (MIS) records. Results indicate that even though there are many uncertainties in timing of glaciations, there are major equivalent synchronous climate intervals represented in both areas.

The best and oldest records of former glaciations are found in the mountainous areas of northwest Canada (Cordillera region) and Alaska, and the Arctic Islands and the northern Interior Plains. Evidence consists of multiple tills, loess units, stratified glacial deposits, nonglacial deposits, and paleosols. Paleomagnetic signals and radiometric dates although scarce, have aided in chronological control. Both mountain and continental glaciations have been recognized and are believed to be roughly synchronous. Two pre-Pleistocene, at least six Early Pleistocene, three Middle Pleistocene, and one Late Pleistocene glaciations have been recognized.

Comparison of North and South American glaciations is complicated because of incomplete records, lack of age estimates at high resolutions, the determination of what is synchronous and what is non synchronous, and the influence of local climate influences. The glaciations of the two continents are compared by placing their closest equivalents into cold periods determined by marine oxygen isotope records and then comparing them to the Chinese loess/paleosol record ( Chap. 5). The earlier glaciations, from about Late Miocene–Early Pliocene (Marine Isotope Stage, MIS >T2) to Early Pleistocene/Early Matuyama (MIS 76) show less equivalence than later glaciations, from about Early Pleistocene/Early Matuyama/Olduvai (MIS 70) to the Late Pleistocene (MIS 2) where several equivalent glaciations can be recognized.

Desde el objetivo de desarrollar estrategias de conocimiento proyectual alternativas de caracter sociofisicas dentro de un urbanismo focalizado sobre el ambiente del hombre, a partir de la premisa que considera a la ciudad como una compleja articulacion de lugares (en sentido antropologico), se ha investigado una articulacion estrategica entre las siguientes dimensiones esenciales del lugar: las practicas sociales relacionadas a determinados grupos humanos; las significaciones de esas practicas para los grupos que las desarrollan y para el resto de los grupos de un determinado lugar; los rasgos configurativos del escenario que hacen de soporte a las practicas sociales y la significacion con que estos y las practicas sociales estuvieran cargados. La hipotesis fundamental establece que: segun sea la configuracion del esquema socio-fisicosimbolico de articulacion de estos elementos, o esquema genetico del lugar, surgiran las claves para comprender si en un determinado lugar urbano estan dadas o no, las condiciones esenciales para desarrollar procesos participativos de planificacion urbana ambiental. A partir de esta hipotesis el trabajo fundamenta una respuesta posible sustentada en la articulacion estrategica entre: congruencias sociofisicas, (hacen referencia al nivel de adecuacion de un determinado escenario para el despliegue sustentable de determinadas practicas sociales), y correspondencias sociosimbolicas (hacen referencia a la coherencia entre las significaciones proyectadas desde distintos grupos humanos a partir de sus actividades asociadas a un escenario particular). SUMMARY Since the objective of developing alternative strategies of projectual knowledge of sociophysical character inside of an urban development focused on the environment of man, on the premise that considers the city as a complex articulation of places (in anthropological sense), a joint strategic between following essential dimensions of place, comes under investigation social practices relating to certain groups of humans; the meanings of these practices for the groups that develop and the rest of the groups of a particular place; features that form the stage make support to social practices and the significance that these and social practices were loaded. The basic hypothesis states that: depending on configuration schema socio-physical - symbolic of articulation of these elements, or genetic scheme in place, will emerge the keys to understand whether or not, are given in a particular urban place the preconditions for developing participatory processes of urban environmental planning. Beginning in this work hypothesis underlying a possible response based on the strategic joint between: socio-physical congruence (refer to the adequacy of a specific stage for sustainable social practices deployment level) and socio-symbolic correlation (refer to the coherence between the meaning projected from different human groups of activities associated with a particular stage).

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).

Archaeological sites in the pampean loess or loess-like deposits of southern Buenos Aires province are discussed. The focus in on site formation processes and the main characteristics acquired by the sites. Pedogenesis and faunal-turbation are considered the most important post-depositional processes which can generate transformations. The environmental conditions did not favor the preservation of organic remains, other than bones and shells. The poor preservation of archaeological features (i.e. floors and pits) is interpreted as a consequence of post-depositional processes, whereas the reduced amount of charcoal and hearths could result from environmental conditions.

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. Fil: Heil, Clifford W.. University of Rhode Island; Estados Unidos Fil: King, John W.. University of Rhode Island; Estados Unidos Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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 Fil: Schultz, Peter H.. Brown University; Estados Unidos

This paper reports the main sedimentary characteristics, soil micromorphology and optically-stimulated luminescence (OSL) ages, and details the pedosedimentary reconstruction, of the Hudson site situated in the northern Pampas of Buenos Aires province. It also provides the OSL chronology and a reinterpretation of previously reported micromorphological features for the nearby site of Gorina. Finally, the stratigraphic records of both sites are compared and the main environmental events discussed in a regional context. At Hudson, situated at a low altitude environment close to the coastal plain, the basal fine-grained paludal deposits were unconformably covered by coastal marine sediments with an OSL age of ca. 128 ka supporting its correlation with the high stand of sea level of marine isotope stage 5e. A paleosol developed on the marine deposits and the underlying paludal sediments. OSL ages suggest that soil development and its subsequent erosion occurred over some period between ca. 128 and 54 ka. Fine sediment accumulation in a paludal environment continued until prior to ca. 23 ka when the accumulation of the uppermost loess mantle started. It continued until the early Holocene when present soil development began. At Gorina, OSL ages suggest that the upper part of the pedocomplex formed at some stage between ca. 194 and 56 ka. Loess then accumulated followed by an erosional phase; loess deposition restarted by ca. 29 ka and continued until the beginning of the Holocene (ca. 9 ka) when the present land surface was established. The stratigraphic and paleoenvironmental differences exhibited by the Hudson and Gorina records result from their contrasting geomorphological settings. The OSL geochronology suggests that the last interglacial (MIS 5) at Hudson is marked by the accumulation of marine deposits (MIS 5e) and the subsequent development of a paleosol. The equivalent soil-forming interval at Gorina is represented by the upper part of the buried pedocomplex. Both at Gorina and Hudson, loess accumulation was dominant especially during MIS 2. Loess accumulation continued during MIS 1 until the early Holocene with apparently somewhat higher sedimentation rates in Hudson. Pedogenesis has been predominant during the rest of the Holocene, resulting in the formation of the surface soil profiles. Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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 Fil: Kemp, Rob. University of London; Reino Unido Fil: Toms, Phillip. University of Gloucestershire; Reino Unido

Cerro La China, within the Tandilia Range, has a long archaeological record in which three different human occupations were identified. The geoarchaeological approach allowed us to correlate the archaeosedimentary columns at Site 2 and Site 3 and place the local stratigraphy in a regional context. The archaeologically rich stratigraphic sequence is composed of three episodes of loess deposition. The first bears a 10,600 yr B.P. Paleoindian occupation with Fishtail or Fell's Cave Stemmed points. It is followed by a soil-forming interval which ended about 5000 yr B.P. with an erosive episode. The second event of loess deposition continued through an unknown span of time until a new soil-forming interval started; it includes triangular stemless medium size projectile points corresponding to a different human group. By the sixteenth century another erosive event interrupted the soil-forming interval. After this, the third short-term eolian episode occurred and bears the most recent archaeological occupation marked by small triangular stemless points.

Pedogenesis has played a major role in the evolution of the Pampean landscape which resulted in the common occurrence of pedogenic features in the stratigraphic successions, but has not been recognized in previous studies. The main problems facing paleopedological research are the identification of paleosol profiles, paleosol horizons and their interpretation. Paleosols have been traditionally interpreted as truncated profiles because A and E horizons were not recognized. This may be apparent or real. Erosion generally leaves supporting evidence such as a lag deposit, but superposed cycles of pedogenesis can obliterate original morphological properties, which alters the appearance of buried A and E horizons. Abrupt boundaries have always been interpreted as erosional surfaces because of an overgeneralization that all land surfaces are eroded. When paleosols are exposed in roadcuts and quarries, they acquire new morphological features such as induration and tension cracks, which have been misinterpreted as original properties. In the current view, the basic criteria for paleosol recognition in exposures are based on the vertical and lateral arrangements of soil morphological features within a detailed stratigraphic framework provided by sedimentary facies analysis. The framework can be verified by micromorphological studies of polygenetic horizons to determine the sequence of episodes of pedogenesis and to evaluate the effects of diagenesis following burial.

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 Chasicó (CH) with an 40Ar/39Ar age of 9.24 ± 0.09 Ma, and the other near Bahía 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 106 km2 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 econsidered 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 Chasicó 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.∼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 Chasicó (CH) with an 40Ar/39Ar age of 9.24 ± 0.09 Ma, and the other near Bahía 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 106 km2 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 econsidered 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 Chasicó 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. Fil: Schultz, Peter H.. Brown University; Estados Unidos Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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 Fil: Hames, Willis E.. Auburn Universty; Estados Unidos Fil: Harris, R. Scott. Brown University; Estados Unidos Fil: Bunch, T. E.. Northern Arizona University; Estados Unidos Fil: Koeberl, Christian. Universidad de Viena; Austria Fil: Renne, Paul. Berkeley Geochronology Center; Estados Unidos Fil: Wittke, James. Northern Arizona University; Estados Unidos

Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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 Fil: Neme, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Municipal de Historia Natural San Rafael - Unidad Asociada al CCT Mendoza; Argentina Fil: Gil, Adolfo Fabian. Museo Municipal de Historia Natural San Rafael - Unidad Asociada al CCT Mendoza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The synthesis of paleoclimatic archives provided by loess and alluvial sequences of central Argentina has been hindered by the lack of a cohesive lithostratigraphic framework extending across the Chaco-Pampean plains and catchments of the Rios Desaguadero, Colorado, and Negro. This condition originates in part from the dearth of absolute chronological controls. The occurrence of discrete tephra layers across this region may provide an opportunity to address this deficiency if a tephrochronological framework can be established. The potential of such a project is assessed within the context of a pilot study constrained within alluvial sequences of central western Argentina proximal to potential source vents in the Southern Volcanic Zone. The intersite discrimination and correlation of tephra layers on a geochemical basis is examined, with indirect chronological control for the eruption of each generated by optical dating. Alluvial sediments on either side of each of five tephra units at a type site were dated using the optically stimulated luminescence of fine-silt-sized quartz, thus providing an age control on each tephra (ca. 24,000, 30,000, 32,000, 39,000, and 48,000 yr). The geochemical composition of each tephra was derived. Using these data, tephra layers at other sites in the study area were geochemically analyzed and, in instances of statistical concordance in major oxide structure, correlated to the type site and therefore ascribed ages. This methodology identified a further sixth volcanic event between ca. 24,000 and 30,000 yr not registered by type-site tephras. The extension of this initial tephrochronological framework beyond the alluvial sequences of central western Argentina is encouraged by the occurrence of geochemically distinct tephra verified and dated in this study. Fil: Toms, Phillip S.. University of London; Reino Unido Fil: King, Matthew. University of London; Reino Unido Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Pampa; Argentina Fil: Kemp, Rob A.. University of London; Reino Unido Fil: Foit Jr., Franklin F.. Washington State University; Estados Unidos

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 Paraná 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 Tucumán, 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. Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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

A combined macromorphological and micromorphological approach was used to identify and differentiate paleosols at a representative exposure of the Pleistocene sedimentary succession in the northern Pampas of Buenos Aires (La Plata area). Five pedological units (Pu), which apparently represent four discrete paleosols plus the surface soil, were initially differentiated on the basis of field-scale morphological properties. The succession was divided into B and C horizon with an A horizon only clearly identified in the surface soil and a weak A horizon at depth. Micromorphology suggests a complex pedosedimentary history of welding, with some degree of water reworking indicated by fragments of sorted layers and the significant grain-size heterogeneity of the parent material. The micromorphological data do not support the field differentiation of Pu4, Pu3, and Pu2 into discrete paleosols. Pedological features (i.e. excrements, secondary carbonate coatings, illuvial clay coatings) occur throughout without any obvious breaks or patterns. Pu4, Pu3, and Pu2 are therefore interpreted as an accretionary and/or welded pedocomplex. The Gorina section does not conform to the simple classical model proposed by other authors in the region of alternating loess and paleosol units associated with arid (loess deposition) and wet (soil formation) intervals, respectively. Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. 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 Fil: Kemp, Rob A.. University of London; Reino Unido Fil: Blasi, Adriana. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentina

Publisher Summary This chapter deals with Eolian deposits, consisting of both dune and sheet sand in South and North America. Much of the loess present on both continents, which are derived from glacial outwash sources and deposited during the last glacial maximum. Cold, dry, windy conditions during the last glacial period have favored loess deposition from a variety of sources. Eolian sand is extensive on both the continents. Holocene eolian sand is abundant in the Pampas region of South America. Deep-sea sediment cores, ice cores, and soils contain long-term records of the dust flux. Deposition of loess and eolian sand, from multiple sources during the last glacial period, agrees with pollen records, lake records, and COHMAP (Cooperative Holocene Climate Mapping) climate simulations. In the Pampas region of South America, there is at least fair agreement between summer surface winds simulated by COHMAP and paleowinds as recorded by eolian sand and loess. In mid-continental North America, however, the presence of a strong glacial anticyclone centered over the Laurentide ice sheet generates northeasterly winds in the region immediately to the south of the ice sheet. Both eolian records and lacustrine records indicate that there are multiple periods of relatively dry climate during the late Holocene.

In southern South America the acquisition of high-quality Holocene paleoclimate data is a priority due to the paucity of complete, continuous and well dated records. Here we report preliminary results from a combined sedimentological and palynological study of an alluvial fan sequence and the laterally connected sedimentary deposits of the Vega de la Cueva profile at Agua Buena east of the Andes in central Argentina. The main geomorphological units of the area were identified and mapped based on satellite image analysis and multiple field surveys. The sedimentological and pollen results allowed us to reconstruct the development of some environments. The Agua Buena record corresponds to the distal facies of the Arroyo Bayo alluvial fan starting the aggradation process prior to ca. 4100 cal yr BP. The organic-rich levels found were formed during the development of wetlands (vegas) dominated by Cyperaceae, Juncaceae and Poaceae. These highly productive environments with almost permanent water saturation were important between 4100 and 2800 cal yr BP, indicating more stable conditions. After 2800 cal yr BP, the organic content was comparatively lower with increasing sedimentation rates that are indicative of higher fluvial discharges. This information is fundamental to interpret both the pollen and charcoal records of the area and to evaluate their representativeness and potential to reconstruct past local and/or regional vegetation.

The Late Pleistocene and Holocene loess deposits of the SE Buenos Aires province are composed of four allostratigraphic units that represent four episodes of loess deposition. The first and the second episodes occurred in Late Pleistocene times. The second episode was followed by a soil forming interval (Early Holocene to Mid-Holocene times). The third episode took place at about 5000 yr BP, after the Holocene sea-level maximum when marine regression began. The fourth episode constitutes a historical event of only local significance. Loess shows a fairly constant granulometric and mineralogical composition. The modal fraction consists of very fine sand and coarse silt (3 to 5 phi). They are classified as sandy silts or silty sands. Three grain-size subpopulations are differentiated: coarse, medium and fine. The medium-size subpopulation, which is the most important, consists of most of the very fine sand and coarse silt. It is thought to be transported by modified saltation and short-term suspension during local dust-storms. The mineralogical composition of loess consists of a volcaniclastic assemblage derived mainly from reworked pyroclastic deposits, primary tephras and volcaniclastic sediments. The source area of these materials was located in the lower Colorado river valley about 400 km SW of the studied area. There was also a direct supply by volcanic ash falls., Facultad de Ciencias Naturales y Museo

One of the key challenges in Global Change Research is the modelling of future changes in land use and land cover as a result of socio-economic and global climate change. Such changes are calculated dynamically in the Global Change decision support system for the Upper Danube (DANUBIA), thus helping to predict the effects of Global Change in this region. For any such spatially explicit modelling, land use/land cover is the key information layer which integrates all involved natural scientific and socio-economic process models. Land cover characterises the condition of the earth’s surface and hence the properties that most directly influence water and energy fluxes, whereas land use describes the type of anthropogenic use, thus being a key parameter for modelling socio-economic processes. In order to meet all model requirements, a new tailored land use/land cover map was created with a representative overall area approximation and localisation of land use and land cover classes on basin scale, using a combination of CORINE Land Cover (CLC) data, official agricultural statistics and rule-based GIS operations. The resulting land use/land cover map can be used as initial state for modelling in DANUBIA. A total of 27 unique land use/land cover categories are distinguished in DANUBIA. The top hierarchical level is used consistently in all models, whereas the additional levels (e.g. detailed arable land classes) are individually used depending on the information needed by each model.