Preprints
https://doi.org/10.5194/essd-2020-385
https://doi.org/10.5194/essd-2020-385

  18 Dec 2020

18 Dec 2020

Review status: a revised version of this preprint was accepted for the journal ESSD and is expected to appear here in due course.

Marine terraces of the last interglacial period along the Pacific coast of South America (1° N–40° S)

Roland Freisleben1, Julius Jara-Muñoz1, Daniel Melnick2,3, José Miguel Martínez2,3, and Manfred R. Strecker1 Roland Freisleben et al.
  • 1Institut für Geowissenschaften, Universität Potsdam, 14476 Potsdam, Germany
  • 2Instituto de Ciencias de la Tierra, TAQUACH, Universidad Austral de Chile, Valdivia, Chile
  • 3Millennium Nucleus The Seismic Cycle Along Subduction Zones, Valdivia, Chile

Abstract. Tectonically active coasts are dynamic environments characterized by the presence of multiple marine terraces formed by the combined effects of wave-erosion, tectonic uplift, and sea-level oscillations at glacial-cycle timescales. Well-preserved erosional terraces from the last interglacial sea-level highstand are ideal marker horizons for reconstructing past sea-level positions and calculating vertical displacement rates. We carried out an almost continuous mapping of the last interglacial marine terrace along ~5,000 km of the western coast of South America between 1° N and 40° S. We used quantitatively replicable approaches constrained by published terrace-age estimates to ultimately compare elevations and patterns of uplifted terraces with tectonic and climatic parameters in order to evaluate the controlling mechanisms for the formation and preservation of marine terraces, and crustal deformation. Uncertainties were estimated on the basis of measurement errors and the distance from referencing points. Overall, our results indicate a median elevation of 30.1 m, which would imply a median uplift rate of 0.22 m/ka averaged over the past ~125 ka. The patterns of terrace elevation and uplift rate display high-amplitude (~100–200 m) and long-wavelength (~102 km) structures at the Manta Peninsula (Ecuador), the San Juan de Marcona area (central Peru), and the Arauco Peninsula (south-central Chile). Medium-wavelength structures occur at the Mejillones Peninsula and Topocalma in Chile, while short-wavelength (< 10 km) features are for instance located near Los Vilos, Valparaíso, and Carranza, Chile. We interpret the long-wavelength deformation to be controlled by deep-seated processes at the plate interface such as the subduction of major bathymetric anomalies like the Nazca and Carnegie ridges. In contrast, short-wavelength deformation may be primarily controlled by sources in the upper plate such as crustal faulting, which, however, may also be associated with the subduction of topographically less pronounced bathymetric anomalies. Latitudinal differences in climate additionally control the formation and preservation of marine terraces. Based on our synopsis we propose that increasing wave height and tidal range result in enhanced erosion and morphologically well-defined marine terraces in south-central Chile. Our study emphasizes the importance of using systematic measurements and uniform, quantitative methodologies to characterize and correctly interpret marine terraces at regional scales, especially if they are used to unravel tectonic and climatic forcing mechanisms of their formation. This database is an integral part of the World Atlas of Last Interglacial Shorelines (WALIS), published online at http://doi.org/10.5281/zenodo.4309748 (Freisleben et al., 2020).

Roland Freisleben et al.

 
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Roland Freisleben et al.

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Marine terraces of the last interglacial period along the Pacific coast of South America (1°N-40°S) Roland Freisleben, Julius Jara-Muñoz, Daniel Melnick, José Miguel Martínez, and Manfred R. Strecker https://doi.org/10.5281/zenodo.4309748

Roland Freisleben et al.

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Short summary
Tectonically active coasts are dynamic environments that host densely-populated areas and associated infrastructure. We measured and described last interglacial marine terraces along 5000 km of the western South American coast. The pattern of terrace elevations displays short- to long-wavelength structures that may be controlled by crustal faults and the subduction of major bathymetric anomalies. Latitudinal climate characteristics may further influence their generation and preservation.