Comprehensive characterization of elevated coastal platforms in the north Iberian margin: A new template to quantify uplift rates and tectonic patterns

Abstract

The Cantabrian margin, at the northern Iberian Peninsula, shows elevated coastal platforms extending from west to east for >200 km. These erosional surfaces are several kilometers wide, and are bounded inland by a paleoshoreline, and towards the sea by the retreating current cliff. The origin and evolution of these geomorphologic markers remains controversial, one of the main challenges arising from the difficulties in correlating the patchy distribution of the platforms and their variable heights along the margin due to lithological differences, local tectonism, and varying degrees of preservation. With the aim of understanding recent coastal evolution, a systematic quantitative GIS analysis of LiDAR elevation models (5 m resolution) was carried out along 4.000 km2 of the Cantabrian coast between 4.15°W and 7.30°W longitude. The coastline runs parallel to the Cantabrian Mountains, which are supported by an orogenic root present only beneath the eastern half of the coastline under study. The integration on the GIS template of the crust-mantle boundary as a controlling factor of landscape development has helped in the understanding of the recent evolution of the coastal platforms, and in the interpretation of previously unexplained features of their distribution.The two main outcomes of this multiscale approach are: 1) the correlation of most of the fragmented rasas as part of an original unique coastal platform along the Cantabrian margin, and 2) the differentiation of two sectors separated by a highly tectonized area associated to the Ventaniella fault. The western sector has one main, continuous surface showing a 0.08° tilt towards the west, sometimes interrupted by local and recent minor faults with net slips of meters to tens of meters. The eastern sector has several steps of erosional surfaces spread out at various heights without tilt. The Ventaniella fault, separating both sectors, produces an apparent vertical offset of 50 m in the main erosional surface. Our study shows that this fault also separates two distinct evolutions in the elevation of the coastal platform: (1) the western coast, which has risen continuously, probably in response to a lateral gradient in crustal thickness; and (2) the eastern coast, where uplift is discontinuous over time since several of these surfaces formed below the main paleoshoreline. The Cantabrian coast captures the influence that crustal structure has on the expression and evolution of geomorphologic markers at the surface. And vice versa, landform features at the surface can be very sensitive to differential crustal thickness while responding to the same external and climatic forces. In the context of the western European framework, our work provides a regional template within which future absolute geochronological dating can be based to improve our knowledge of the recent evolution of the Atlantic margins.