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University of Cincinnati (2019)

36Cl Chronologies and ELA reconstructions from the northern boundary of the South American Arid Diagonal

Thornton, Rachel M

Titre : 36Cl Chronologies and ELA reconstructions from the northern boundary of the South American Arid Diagonal

Auteur : Thornton, Rachel M

Université de soutenance : University of Cincinnati

Grade : Master of Science (MS) 2019

Résumé
This study focused on glaciation in the South American Arid Diagonal (AD) climatic feature which intersects in the Andes mountain range at approximately 24°S. This NE-SW-trending zone of hyper-aridity separates the Atlantic-sourced Easterly moisture belt from the Pacific-sourced Westerly precipitation in the central Andes. We present new geomorphological maps of the landforms, particularly of glacial moraines across two mountain ranges within the Western Cordillera of the central Andes. Additionally, new 36Cl chronologies using surface exposure dating were produced from two sites near the northern boundary of the modern AD. One site is located in the Cordillera del Tatio at 21°S (Tatio field site), the other is the southernmost valley in a stratovolcano chain called the Cordon de Puntas Negras at 24°S (SPN field site). Paleo-ELAs were reconstructed utilizing a two-dimensional numerical model to simulate glaciers over a 90m digital elevation model of the upstream catchment. We find that four glacial stages were present at both field sites sampled. Glacial stabilizations from the El Tatio field site, once assumed Lateglacial in age are on the order of 10-20 thousand years older than previously published. Tatio ages ranged from 25 ka to as early as MIS 5. We also found that dated glacial stages from El Tatio and the Puntas Negras are not synchronous with lake highstands on the Altiplano, but projected ages of the younger glacial stages indicate both sites were glaciated during the Tauca phase. Regional comparison indicated the possibility of glacial occupation of the Tatio site into the Lateglacial during the Coipasa phase (12 ka) after rapid deglaciation of the SPN field site. Regional ELA comparisons supported the trend of moisture loss from the NE to SW portions of the climatic AD feature.

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