A Climate Perspective on Paleoelevation and Erosion Processes in the Andes.

Paleoclimate;Erosion;Andes;Geology and Earth Sciences;Science;Earth & Environmental Sciences

Jeffery, Mairi LouiseSheldon, Nathan Dale ;

University of Michigan

关键词: Paleoclimate;    Erosion;    Andes;    Geology and Earth Sciences;    Science;    Earth & Environmental Sciences;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/97894/louisej_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The topographic and climatic histories of the central Andes are closely coupled. As a result, geological evidence for the nature of past surface environments is commonly a record of both topographic and climatic changes. In order to understand tectonic, climate, and erosion mechanisms, the relative roles of climate and tectonics in changing surface environments must be resolved. This dissertation explores controls on Cenozoic climate change in the Andes, and the response of surface processes to those changes. To explore the factors controlling South American climate during the late Cenozoic uplift of the central Andes, several paleoclimate scenarios were simulated by a global climate model with isotope tracking capabilities. Results indicate that Andean topography is the strongest control on central Andean precipitation patterns and precipitation δ18O. Precipitation δ18O was also modified by global cooling (up to 8 ‰) and during late Miocene seaway incursions into the western Amazon basin (1-8 ‰). The response of surface processes to climate change as a result of Andean uplift is then quantified using a 1D river incision model embedded in a Monte Carlo search. The results indicate that increasing precipitation rates with increasing Andean elevation influenced the rate and timing of river incision on the Andean flanks. Quantitative analysis of the influence of climate on paleoelevation proxies indicates that a steady uplift since ~40 Ma is the simplest surface uplift model compatible with existing paleoelevation proxy records. To constrain the influence of climate on Andean surface processes further, a new analysis of satellite-based precipitation observations is presented and compared with topographic metrics in the central Andes. The dataset is used to identify which climate characteristics determine erosional efficiency at the orogen scale. Mean annual precipitation correlates strongly with mean hillslope gradients where an increase in mean annual precipitation causes an increase in vegetation cover. Where vegetation cover is fixed, mean precipitation intensity and mean interval duration are the dominant precipitation variables. Identification of the importance of vegetation to surface processes at the orogeny scale highlights a need for further research to constrain the role of vegetation changes in topographic development during mountain belt growth.