A ~1000 ka record of glacial and fluvial deposits: surface exposure dating (10Be) in Central Patagonia

CARLA M. TERRIZZANO; CHRISTL, MARCUS; JONATHAN TOBAL; MATIAS GHIGLIONE; ZECH, ROLAND; EZEQUIEL GARCÍA MORABITO; JULIAN STRUCK

Congreso; XV Chilean Geological Congress; 2018

Universidad de Concepcion

Theforeland of Patagonia provides a perfect setting to evaluate thelandscape response to tectonic and climatic forcing. There, thevalleys that were formerly occupied by glaciers often contain severalQuaternary moraine and terrace assemblages that have the potential toprovide paleoclimatic information extendingbeyond the last glacial cycle. Thispristine geomorphological record can also be used to evidence dynamictopographic uplift related to the openingof an asthenospheric window below the continent (Guillaumeet al. 2009). Surroundingthe Lago Buenos Aires (LBA), there are unusually well-preservedmoraine deposits, along with outwash and fluvial terraces that may beclimatic counterparts. In the last decade, surface exposure dating(SED) of glacially-transportedboulders andoutwash cobbles has been carried out(eg. Hein et al. 2017).Nevertheless, constraints on the ages of the oldest moraine andoutwash assemblages remain scarce, and surface exposure ages onterraces of the Rio Deseado system (RDS)are completely missing. To chronologically constrain the oldestmoraines (Deseado and Telken systems) and the fluvial sequence weapplied 10Be SED on moraines boulders, and on 6 outwash and fluvialterraces along the RD.Ourresults indicate:i)Arid climate in Central Patagonia favored the preservation of glacialand fluvial landforms allowing landscape and climate reconstructionsback to 1 Ma. ii)Exposure ages from moraine boulders are scattered,but there is some consistency in the age ranges and the oldest agesobtained for the Deseado I and III moraines. They reveal aconsistency between the Deseado and the Caracoles moraine system inthe LBA and Lago Pueyrredonvalleys respectively. These data indicate a regionally significantglacial advance during MIS 16. iii)Exposure ages from the Telken moraines reflect boulder exhumation asa consequence of moraine degradation. However, dating of cobbles onthe associated Telken outwash yield much older exposure ages of ~1000 ka. iv)10Beexposure ages of 15 outwash and fluvial cobbles fromthe RDterrace system yield stratigraphically consistent ages between 1000and 441 ka. They mark a generalized uplift in Central Patagoniathroughoutthe Quaternary.