Reconstitution of marine paleo-submersions (tsunamis and storms) along the North Atlantic coast of Morocco during the last millennia

• Main Author: Khalfaoui, Otmane
• Other Authors: Morphodynamique Continentale et Côtière (M2C), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU)-Centre National de la Recherche Scientifique (CNRS), Normandie Université, Laurent Dezileau
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2021
• Subjects: Marine paleo-submersions; Coast; Tsunamis; Storm surges; Risk; Morocco; Paléo-submersions marines; Littoral atlantique; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Tempêtes; North Atlantic
• Online Access: https://theses.hal.science/tel-03619449; https://theses.hal.science/tel-03619449/document; https://theses.hal.science/tel-03619449/file/sygal_fusion_31175-khalfaoui-otmane_623c691bc3570.pdf

The moroccan Atlantic coastline is vulnerable to marine submersion events, caused by storm surges and tsunamis, which are responsible for major human and economic losses. To reduce as much as possible the future damages related to these events, it is necessary to study their past behaviour, on a sufficiently long-time scale. This work seeks to identify geological evidences of marine submersion events that affected the moroccan Atlantic coast, using Holocene sedimentary archives, collected from the Tahaddart estuary. These archives are investigated using a multiproxy approach, combining granulometric, geochemical, microfaunal analyses of foraminifera and geochronological data (210Pb, 137Cs and 14C). The results show that the Tahaddart estuary evolved from a marine environment, between 6800 and 625 cal BP, characterized by very shell-like sandy facies, to an estuarine system, between 625 cal BP and the present, marked by mainly fluvial sedimentation. The archives collected in the area revealed the presence of sedimentary deposits belonging to marine submersion events. Two of them were identified in the marine phase of the cores, dated at ~3800 cal BP and ~2700 cal BP. They are chronologically similar to the tsunami deposits recognised on the Iberian Atlantic coasts, suggesting that they are regional events. In the fluvial phase of the cores, two events were detected for the first time on the moroccan coast. The first one is located around 625 cal BP. It probably corresponds to the tsunami of 1531 CE (419 cal BP). The second event is dated around 200 cal BP, which coincides with the tsunami of 1755 CE (195 cal BP). Le littoral Atlantique marocain est une zone vulnérable aux submersions marines, provoquées par des ondes de tempêtes et des tsunamis, et responsables de pertes humaines et économiques très importantes. Afin de réduire autant que possible les futurs dégâts provoqués par ces événements, il est nécessaire d’étudier leurs comportements dans le passé, sur une échelle de temps suffisamment longue. Ce ...