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Accueil du site → Doctorat → Allemagne → 2019 → Landscape and climate evolution in arid to hyperarid climates with special focus on the Atacama Desert

Universität zu Köln. (2019)

Landscape and climate evolution in arid to hyperarid climates with special focus on the Atacama Desert

Ritter, Benedikt

Titre : Landscape and climate evolution in arid to hyperarid climates with special focus on the Atacama Desert

Auteur : Ritter, Benedikt

Université de soutenance : Universität zu Köln.

Grade : Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Universität zu Köln 2019

The Atacama Desert of northern Chile and Peru is one of the driest places on Earth, with a modern hyperarid core, receiving less than 2 mm/yr of precipitation. The persistent arid climate in the Atacama Desert preserves evidences of earlier ‘wetter’ periods in the geological record. These evidences indicate that even during prolonged aridity, active geomorphological and biological processes existed. Arid conditions are controlled by several interconnected processes, such as atmospheric circulation, oceanic currents, and tectonic activity. Although the main factors forcing aridity have been identified, their timing and succession is still being debated. Most paleoclimate studies in the Atacama Desert have been carried out on the fringes of the extreme hyperarid zone (here, hyperarid regions are considered to be those displaying <2 mm/yr modern precipitation), in regions that still receive noticeable amounts of precipitation and/or runoff from the high Andes. From the different study areas and archives used contradictory views have emerged regarding the onset, duration and intensity of hyperaridity and the interspersed ‘wetter’ periods. This thesis presents geochronological, sedimentological and geomorphological investigations of endorheic basins, terrace-like features and alluvial fans preserved within the Coastal Cordillera and Central Depression of the Atacama Desert. The overall aim is to connect different dating techniques, archives and their interpretations to contribute to the ongoing discussion about the onset of hyperaridity and interspersed climate variability. The information obtained about episodes of surface activity and sedimentation are used for paleoenvironmental and climatological reconstructions in the respective study areas and subsequently synthesised to address the paleoclimate of the Atacama Desert at a broader scale. Situated in the southern Central Depression of the Atacama Desert, linear features, resembling shoreline terraces are found around Cerro Soledad and adjacent topographic highs. These were analysed and dated using terrestrial cosmogenic nuclide exposure dating (10Be, 26Al, 21Ne). The information obtained about the evolution and timing of shoreline formation reveals the chronology of lake phases and the related denudational history of the complex Quillagua-Llamara basin. Ancient, inactive, alluvial fan surfaces and other preserved fluvial features in the Coastal Cordillera south of the Río Loa were analysed and dated to reconstruct their age of abandonment. This part of the study contributes to the ongoing debate about the onset of hyperaridity, interspersed ‘wetter’ (still arid) episodes and the spatial heterogeneity, or gradients of aridity in the Atacama Desert. Paleoclimate records from the hyperarid core of the Atacama Desert are currently lacking. Endorheic sedimentary basins in the hyperarid Coastal Cordillera are capable of recording even subtle autochthonous changes in precipitation and surface modification. A 6 m long sediment core was analysed from an isolated basin, covering a sedimentary depositional record beginning 215 ka ago. This archive reveals that the persistent hyperarid climate witnessed episodes of somewhat ‘wetter’ climate, which led to minor amounts of surface modification and sedimentation in an endorheic basin within the Coastal Cordillera, coinciding with warmer sea-surface temperatures (SST) off Chile, imitating El Niño-like conditions. New data and interpretations from three individual publications, covering the above mentioned topics and collated in this thesis, were used to produce a synthesis of paleoenvironmental and climatological reconstructions for the Atacama Desert. As various archives and methods are used, an evaluation of these archives and methods is conducted within the scope of this thesis.


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