Daniela Kröhling

Upper Quaternary geology of the lower Carcarañá 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).

The pedosedimentary evolution and chronology of Tortugas, a Late Quaternary type-site of the northern Pampa, Argentina

New micromorphological, magnetic susceptibility, geochemical and geochronological data have been collected from Tortugas, a key Late Quaternary type-site of the northern Pampa (Argentina), thus enabling the detailed reconstruction of the pedogenic and sedimentary history of this loess–paleosol sequence. Paleosols developed in the Ceres Formation and the overlying lower member of the Tezanos Pinto Formation retain evidence for leaching, bioturbation and particularly clay translocation processes being dominant. Both paleosols are truncated: evidence for water sorting and sediment reworking, as well as continued bioturbation and redistribution of carbonates, suggests that intervening depositional phases were complex. The previously recorded ‘Hypsithermal Soil’ developed in the upper member of the Tezanos Pinto Formation has similar characteristics to the buried paleosols, yet does not appear to have been truncated at this site and is only covered by a thin layer of sediment (San Guillermo Formation). This latter unit has been pedogenically welded onto the ‘Hypsithermal Soil’, thus creating the present-day surface soil (complex). A series of optically stimulated luminescence dates from throughout the sequence provide a stratigraphically consistent chronological framework (ca. 1–150 ka) for the pedosedimentary reconstruction, yet conflict with the previously reported thermoluminescence-based chronology for the site and region (ca. 1–90 ka).

The largest wind ripples on earth: REPLY

We thank [de Silva (2010)][1] for the opportunity to discuss the origin of the unique megaripples (MR) found on the Puna Plateau. Forman and Krohling were invited as co-authors of this Reply, because we produced new data supplied here. De Silva suggests that the genetic relationship inferred by [

Climate changes and solar cycles recorded at the Holocene Paraná Delta, and their impact on human population.

The Paraná delta, growing at a rate of c. 2 km2 yr−1 since 6,000 yrs, is one of the most complete records of the Late Holocene in southern South America. The evolution of this 17,400 km2 delta enclosed in Plata estuary, can be tracked by a series of 343 successive coastal-ridges showing a c.11 years period, in coincidence with sunspot cycle, also found in some North Hemisphere coastal-ridge successions. The Paraná delta shifted from fluvial, to wave-dominated, and back to the present fluvial-dominated delta, in response to climate changes associated with wind activity correlating with South American glacial cycles. The wave-dominated windy period coincides with the activation of the Pampean Sand Sea, suggesting desert conditions prevailed on the Pampas between 5,300 and 1,700 yrs, in coincidence with scarce or absent pre-historic aborigine remains (“archeological silence”). Further warmer and less windy conditions allowed human repopulation. Results suggest that aside the solar forcing, both short and medium term climate changes controlled delta evolution. An important learning is that a slight cooling would turn the highly productive pampas, into that unproductive desert and, given the lack of artificial irrigation systems, changing present-day warmhouse into a cooling cycle might be economically catastrophic for the region.

Leños Fósiles de la Formación el Palmar (Pleistoceno Tardío) en el Parque Nacional el Palmar, Entre Ríos, Argentina

Abstract. FOSSIL WOOD FROM EL PALMAR FORMATION (LATE PLEISTOCENE) IN THE EL PALMAR NATIONAL PARK, ENTRE RÍOS, ARGENTINA. This paper analyzes new fossil wood from El Palmar Formation (late Pleistocene) recovered from the El Palmar National Park, central-eastern Entre Ríos province, Argentina. Two new morphospecies of Beilschmiedioxylon Dupéron-Laudoueneix and Dupéron 2005 (Lauraceae) and other of Terminalioxylon Schönfeld 1947 (Combretaceae) are described, as well as Piptadenioxylon chimeloi Suguio and Mussa 1978 (Fabaceae-Mimosoideae) is cited for the first time in Pleistocene deposits of Argentina. This species was described from the ancient alluvial Tietê River “Porto de areia of Itaquaquecetuba”, São Paulo, Brazil. Wood anatomical characters suggest an affinity with the taxa Beilschmiedia taubertiana (Schw. and Mez) Kosterm., Terminalia australis Cambess, and Parapiptadenia Brenan respectively. The relationships and comparisons with the nearest living relatives were used to infer paleogeographic, paleoclimatic and paleoecological requirements. This fossil record suggests warm and humid climatic conditions for central-eastern of Entre Ríos, and during the period comprising the development of this geological formation. The fossil wood would correspond to components of riparian mixed forests (Lauraceae and Combretaceae) and semi-arid mixed forests (Fabaceae).

Planation Surfaces on the Paraná Basaltic Plateau, South America

SRTM data constituted a good resource for morphometrical analyses of the extensive Parana Basaltic Plateau (southern Brazil and northeastern Argentina, South America). The plateau is a stepped system of high-level surfaces separated by escarpments and with incised fluvial valleys, mainly belonging to the Upper Parana and the Upper Uruguay River basins. Palaeosurface remnants of such basins preserve attributes that have been identified in digital elevation models. Generation of hypsometric curves in six representative tributary basins of the Uruguay River basin and also in one tributary basin of the Parana River in the region permitted to identify, classify and map the main Cenozoic planation surfaces of the basaltic plateau. Other morphometric parameters such as longitudinal profiles and isobase lines were produced also to delimit such surfaces. Field geomorphological analyses were performed, also including the description of toposequences. Three groups of hypothetical hypsometric curves are deduced from proximal value sets for predicted base levels. Each mapped surface was considered between the minimum height for correlative surfaces in all of the subbasins and the minimum height of the next higher surface. Using that approach, which is based on the clustering from the modelled base level in the river mouth of the subbasins, three main palaeosurfaces were defined in northeastern Argentina. Complementarily, three intermediate or secondary surfaces also were identified based on morphometric analyses, taking into account that small flat remnants at the same level suggest that they could be remnants of a formerly extensive plain.

Primer registro de Cryptocaryoxylon Leisman, una Lauraceae de la Formación El Palmar (Pleistoceno tardío), Entre Ríos, Argentina

Este trabajo describe el primer registro de Cryptocaryoxylon Leisman del Pleistoceno tardio de Argentina. El ejemplar fue hallado en el Paraje Salto Grande (Cuenca del Rio Uruguay, Entre Rios, Argentina) en sedimentos fluviales de la Formacion El Palmar. Los caracteres diagnosticos son: Porosidad difusa a semicircular; vasos pequenos a medianos y numerosos, solitarios y multiples radiales cortos; tilosis abundante; puntuaciones radio-vasculares simples; parenquima axial vasicentrico, aliforme y confluente; radios heterocelulares, uniseriados, raros biseriados, altos; fibras no septadas con paredes gruesas y presencia de numerosas celulas oleiferas en los extremos de radios. Las caracteristicas anatomicas sugieren una relacion con Cryptocarya (Lauraceae). Las caracteristicas eco-anatomica son consistentes con un clima templado-calido y humedo durante este intervalo de tiempo.

ANÁLISIS FITOLÍTICO DE LA FORMACIÓN TEZANOS PINTO (PLEISTOCENO TARDÍO–HOLOCENO TEMPRANO) EN EL SECTOR SUDOESTE DE LA PROVINCIA DE ENTRE RÍOS (ARGENTINA)

Abstract. PHYTOLITH ANALYSIS OF TEZANOS PINTO FORMATION (LATE PLEISTOCENE-HOLOCENE) IN THE SOUTHWESTERN REGION OF ENTRE RÍOS PROVINCE (ARGENTINA). Loess deposits are the main component of the Late Quaternary sequences of the Pampa plains (South America). The Last Glacial Maximum loess represents a depositional unit of the Pampean Aeolian System that evidences the expansion of semiarid conditions to the northeast of the region. The Tezanos Pinto Formation is the typical loessic unit of the late Pleistocene—early Holocene of the northeastern Pampa region. Advances in the knowledge of the micropaleobotanical content of this geologic formation are presented in this work, especially the obtained results of the Southweastern area of Entre Ríos Province. The analyzed phytolith assemblages show a high homogeneity with some variations that allowed their quantitative differentiation across the analyzed sedimentary profiles. The presence of grass phytoliths jointly with palm, podostemoid and ciperoid elements allowed to make this characterization. The described phytolith assemblages, as previously observed in the northwestern part of the area covered by the loess in Entre Ríos, show high abundance of megathermic grasses, with a greater presence of xeric elements at lower levels, and with elements denoting warm-temperate episodes with major moisture principally in their middle and top sections. This is linked to the presence of a warm-temperate to temperate steppe with xeric conditions in the basal levels.