Pleistocene uplift, climate and morphological segmentation of the Northern Chile coasts (24°S–32°S): Insights from cosmogenic 10Be dating of paleoshorelines

• Published in: Geomorphology (Amsterdam, Netherlands) Netherlands), 2016-12, Vol.274, p.78-91
• Main Authors: Martinod, Joseph, Regard, Vincent, Riquelme, Rodrigo, Aguilar, German, Guillaume, Benjamin, Carretier, Sébastien, Cortés-Aranda, Joaquín, Leanni, Laetitia, Hérail, Gérard
• Format: Article
• Language: English
• Subjects: Age; Andes; Climate; Coastal morphology; Coasts; Cosmogenic nuclide; Earth Sciences; Elevation; Geomorphology; Morphology; Paleoshores; Sciences of the Universe; Tectonics; Terraces; Uplift
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2016.09.010

We present new cosmogenic (10Be) exposure ages obtained on Pleistocene marine abrasion shore terraces of Northern Chile between 24°S and 32°S in order to evaluate the temporal and spatial variability of uplift rates along the coastal forearc. Both the dispersion of cosmogenic concentrations in samples from the same terrace and data obtained in vertical profiles show that onshore erosion rates, following emergence of paleoshorelines, approached 1m/Myr. Therefore, minimum ages calculated without considering onshore erosion may be largely underestimated for Middle Pleistocene terraces. The elevation of the last interglacial (MIS-5) paleoshoreline is generally between 25 and 45m amsl, suggesting that the entire coast of the study area has been uplifting during the Upper Pleistocene at rates approaching 0.3mm/yr. Available ages for Middle Pleistocene terraces suggest similar uplift rates, except in the Altos de Talinay area where uplift may have been accelerated by the activity of the Puerto Aldea Fault. The maximum elevation of Pleistocene paleoshorelines is generally close to 250m and there is no higher older Neogene marine sediment, which implies that uplift accelerated during the Pleistocene following a period of coastal stability or subsidence. We observe that the coastal morphology largely depends on the latitudinal climatic variability. North of 26.75°S, the coast is characterized by the presence of a high scarp associated with small and poorly preserved paleoshorelines at its foot. The existence of the coastal scarp in the northern part of the study area is permitted by the hyper-arid climate of the Atacama Desert. This particular morphology may explain why paleoshorelines evidencing coastal uplift are poorly preserved between 26.75°S and 24°S despite Upper Pleistocene uplift rates being comparable with those prevailing in the southern part of the study area. •We date paleoshorelines in Chile between 24°S and 32°S using 10Be concentrations data.•Post-emergence erosion of abrasion shore terraces approaches 1m/Myr.•The coast has been uplifting at ~0.3mm/yr during the Upper Pleistocene.•Uplift velocity increased during the Pleistocene following a period of stability.•Paleoshorelines are poorly preserved beneath the northern coastal scarp.