Fission-track dating of a tephra layer related to Poti-Malal and Seguro drifts in the Rio Grande basin, Mendoza, Argentina

Two old drift units called Poti-Malal and Seguro have been differentiated in the Rio Grande basin based on relative-age criteria, stratigraphical relationships, morphology and fission-track dating. A tephra dated at 0.226+/-0.025 Ma was deposited on the Poti-Malal drift and underlies the Seguro outwash, which is inferred to equate with marine oxygen isotope stage 6. The stratigraphical position and age suggest that the tephra post-dates the Poti-Malal glaciation and that it is older than the Seguro drift. The Poti-Malal glaciation must be at least as old as Early-Middle Pleistocene, and the Seguro glaciation is assigned to the penultimate glaciation. The tephra unit may have been deposited during marine oxygen isotope stage 7. Copyright (C) 2002 John Wiley Sons, Ltd.17878178

Pleistocene landscape entrenchment: a geomorphological mountain to foreland field case, the Las Tunas system, Argentina

The study of the Las Tunas River incisions, located in the eastern Andean foreland front (3320’ S in Argentina), provides new clues for the interpretation of deep piedmont entrenchments. Both the Las Tunas mountain catchment and its piedmont are strongly entrenched with maximal incision of over 100 m at the mountain front. Three main terrace levels are well exposed and are labelled T1, T2 and T3 from the youngest to the oldest. We combined geological and geomorphological field observations, kinematic GPS data, satellite data and aerial photos with geochronological 40 Ar/39 Ar and 10 Be analysis to provide a detailed description of terrace organization and a discussion of the evolution of the Las Tunas landscape. The surprisingly 10 Be constant concentrations in surface layers as deep as 1.5 m show that gently dipping alluvial surfaces can be continuously and deeply mixed. Our data show a first period of deposition (Mesones Fm) before 0.85 Myr (minimum T3 age), followed by deep erosion and a second sedimentation period (Las Tunas Fm) that includes a ca. 0.6 Myr ash deposit. T2 and T1 are inset in the Las Tunas Fm and were abandoned ca. 15–20 kyr ago. The similar ages for T2 and T1 show that post-20kyr entrenchment occurred very rapidly. Despite Quaternary deformation in the Las Tunas piedmont, terrace entrenchment is best explained by paleo-climatic changes. The terrace organization reveals that the erosion-sedimentation phases affected the entire system from the piedmont toe to 10 km upstream of the mountain front. Finally, contrary to the neighbouring more deeply incised Diamante River system, where late Quaternary piedmont uplift is more likely to have been a factor causing incision, the more stable Las Tunas system provides an incomplete geomorphological record of Pleistocene and Holocene climate variations. We suggest that climate variations are better recorded in uplifting piedmonts than in stable ones, where the magnitude of incision and sedimentation and the fact that they occur repeatedly at the same elevation can erase a large part of the record.Fil: Pepin, E.. Université de Toulouse. Geosciences Environnement Toulouse, OMP, UPS, CNRS, IRD; FranciaFil: Carrieter, S.. Université de Toulouse. Geosciences Environnement Toulouse, OMP, UPS, CNRS, IRD; FranciaFil: Hérail, G.. Université de Toulouse. Geosciences Environnement Toulouse, OMP, UPS, CNRS, IRD; FranciaFil: Regard, V.. Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas. Advanced Mining Technology Center (AMTC); Chile. Universidad Andres Bello. Facultad de Ingeniería. Escuela de Ciencias de la Tierra; ChileFil: Charrier, R. . Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas. Advanced Mining Technology Center (AMTC); Chile. Universidad Andres Bello. Facultad de Ingeniería. Escuela de Ciencias de la Tierra; ChileFil: Farías, M.. Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas. Advanced Mining Technology Center (AMTC); ChileFil: Garcia, Victor Hugo. Universidad Nacional de Río Negro. Instituto de Investigación en Paleobiología y Geología sede Alto Valle; Argentin

Summary of International Glacier Monitoring Summit

In the first week of September 2010, international experts on glacier monitoring convened in Zermatt, Switzerland, for two separate but related meetings. They discussed glacier data compiled over the past 150 years and how to improve this dataset to meet the challenges of the 21st century, pre- sented latest results from in situ and remotely sensed obser- vations, and came up with key tasks for the glacier moni- toring community for the coming decade