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Le Géosystème Dunaire Anthropisé d'Essaouira-Est (Maroc atlantique) : Dynamique et Paléoenvironnements.

Abstract : The holocene system of Essaouira is characterized by a significant aeolian activity which has formed a littoral sandy geosystem. Its significance is researched studying relations between biotic, abiotic components and anthropic factors who define its own features. Their description constitutes a first part, the second section shows the spatial dynamics of the geosystem and the third part develops its temporal dynamics at the upper Holocene scale from sedimentological and geo-historical analysis.
Two structuring geofacies are defined : a sandy geofacies and a lagoon geofacies extending in the west part in contact geosystem / urbanization. Horizontally, their spatial organization forms a mosaic where they interpenetrate. Vertically, the former is superimposed on the second which the silt-clayey lithomass constitutes the substratum. The top part of the last represents an erosion surface sanded and weathered by trade wind, notably in the main deflation gully (separate removal of sands and silt-clay amounts to 3 cm/year for 50 years). Also, diachronic aerial photogrammetry between 1953 and 1984 confirms this phenomenon showing a significant evolution of dunes spreading, density and shape surrounding the city. In a coherent way, mobility index according to Lancaster M = 160 underlines a very high instability on slopes and tops of dunes. In the sense that actual phytoliths assemblages are performed and graded on vegetation. Tree cover index, edaphic aridity index and climatic index (d/p = 0,5 ; Iph = 91 % and Ic = 27 %) show the actual arid and warm trend making more fragile the geosystem all the more since anthropic factors exert an high pressure involving main and secondary deflation gullies.
It is a fact that human setting has been marked by impact from the end of Neolithic and mutual links between nature and societies are punctuated with crises for five centuries at least. A drying up trend of climate is noted from 4 350 +/- 120 cal BP on a core sampling extracted from the silty-clayed substratum which continental paleo-synsedimentary particles are linked to the post-mellahian oceanic regression.
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Contributor : Yves Claude Simone <>
Submitted on : Wednesday, September 12, 2007 - 4:14:48 PM
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  • HAL Id : tel-00171576, version 1

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Yves Claude Simone. Le Géosystème Dunaire Anthropisé d'Essaouira-Est (Maroc atlantique) : Dynamique et Paléoenvironnements.. Géomorphologie. Université de Provence - Aix-Marseille I, 2000. Français. ⟨tel-00171576⟩

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