Aménagement, érosion et désertification sur les Hauts-Plateaux du Maroc oriental

In only a few decades, the ecological balance has been deeply endangered in the High-Plateaux of Eastern Morocco as a result of the excessive and irrational exploitation of soil and vegetation, which has been caused by the socio-spatial mutations of the XXth century relating to the colonialist economy. Several projects of intervention have succeeded in this area, which is pastoral by excellence. Studies have especially been concerned with the productivity of biotic resources and the socio-economic aspects of stock-breeding. The degradation of the ecosystems is approached essentially in its biocenotic context, while the processes, the forms and the extent of erosion and desertification are marginalized. Such a situation for such a sensitive and degraded environment entails the apprehension of those problems by systemic and largely pluridisciplinary approaches.En quelques décennies seulement, l'équilibre écologique a été profondément touché sur les Hauts-Plateaux du Maroc oriental, par le biais de l'exploitation irrationnelle et abusive du sol et de la végétation, suscitée parles mutations socio-spatiales du XXe siècle en rapport avec l'économie colonialiste. Plusieurs projets d'intervention se sont succédés dans cet espace pastoral par excellence. Les études ont surtout concerné la productivité des ressources biotiques et les aspects socio-économiques de l'élevage. La dégradation des écosystèmes est essentiellement abordée dans son contexte biocénotique, tandis que les processus, les formes et l'ampleur de l'érosion et de la désertification s'en trouvent marginalisés. Une telle situation pour un tel milieu sensible et dégradé suggère l'appréhension des problèmes posés par des approches systémiques et largement pluridisciplinaires.El Harradji Abderrahmane. Aménagement, érosion et désertification sur les Hauts-Plateaux du Maroc oriental. In: Méditerranée, tome 86, 1-2-1997. Impact anthropique en milieu méditerranéen. pp. 15-23

Transition climatique et culturelle à l'Holocène, la question du 8.2 ka event au Maroc oriental : durée, nature et impacts

International audienc

: Chronostratigraphy of travertines from lot of regions of Morocco and their relation with the paleoclimatic global context

We studied here travertines of Eastern Morocco. For this part of Africa, these concretions indicate ancient humidphases which are suspected to be linked with palaeo-monsoons and the precession cycle of 23,000 yrs. Ourprincipal aim is to precise the planetary configuration which is associated with the climatic conditions of theirconstruction and to determine the chronological frequency of the travertine deposits. In fact, travertines, likespeleothems, can be regarded as valuable archives of climatic conditions on the continent. The major differenceis that the formation of the speleothems is generally discontinuous and all the isotopic stages are not recorded,while the travertines are continuously recorded at least travertine sequences are very thicken and can cover hugegeological periods. However, erosion could unfortunately suppress a part of climatic information. The preliminary results show that in order to find the precession cycles of 23 000 yrs and to obtain a weak uncertainty for the periods comprised between 500,000 and 100,000 yrs., the development of mass-spectrometry by ICP-MS should to be used.Les travertins sont abondants au Maroc oriental, et correspondent à des formations largement développées auniveau des sources et des cascades au cours du Quaternaire. Les formations travertineuses soumises ici aux analyses radiochronologiques sont réparties dans différentes régions du Maroc (Errachidia, Lalla Mimouna,Debdou et Fès). On tente ainsi de définir le synchronisme des changements climatiques à une échelle continentale régionale et d'associer les périodes de forte humidité responsables des dépôts de travertins à des « paléo-moussons » issues de changements climatiques globaux, le terme « paléo-mousson » étant utilisé dans le sens anglo-saxon qui évoque le déplacement de masses d'air océanique vers le continent. Les travertins sont susceptibles d'avoir un enregistrement plus complet que ceux enregistrés dans les planchers stalagmitiques, maisl'érosion peut en supprimer une partie. Les résultats préliminaires montrent que pour essayer de retrouver descycles de précession de 23.000 ans responsables de ces paléo-moussons avec de faibles incertitudes durant lespériodes comprises entre 500.000 et 100.000 ans, la spectrométrie de masse (TIMS ou ICP-MS) devra êtreutilisée

First fluvial archive of the 8.2 and 7.6–7.3 ka events in North Africa (Charef River, High Plateaus, NE Morocco)

International audienceThe Early–Mid Holocene transition is a period of profound changes in climatic mechanisms and hydrological features in Europe and North Africa. The melting of the Laurentide ice sheet led to an oceanic and atmospheric reorganisation in the North Atlantic, while the Mediterranean underwent a major hydrological shift. The impacts on Mediterranean rivers remain unclear, as there are few records documenting responses to the 8.2 ka event (the main Holocene climatic degradation). We present a fluvial record from Eastern Morocco documenting detailed hydrological variations from 8200 to 7500 cal. BP and their climatic forcing. A major hydrogeomorphic evolution of the Charef River occurred at that time, marked by two major incision stages close in time, under hyper-arid conditions at 8200 and ca. 7500 cal. BP. The impacts of these phenomena on the alluvial plains and associated archaeological records during Neolithisation, a major process in human history, currently remain unidentified. This new record sheds light on the fluvial response to the 8.2 ka event in North Africa and why other records are missing. We also bring new insights into the hydrological disruption at the Early–Mid Holocene transition, which was driven by the end of deglaciation combined with insolation and solar forcing. Furthermore, centennial solar variability may have paced river activity in the Moulouya basin and arid regions of North Afric

First fluvial archive of the 8.2 and 7.6–7.3 ka events in North Africa (Charef River, High Plateaus, NE Morocco)

International audienceThe Early–Mid Holocene transition is a period of profound changes in climatic mechanisms and hydrological features in Europe and North Africa. The melting of the Laurentide ice sheet led to an oceanic and atmospheric reorganisation in the North Atlantic, while the Mediterranean underwent a major hydrological shift. The impacts on Mediterranean rivers remain unclear, as there are few records documenting responses to the 8.2 ka event (the main Holocene climatic degradation). We present a fluvial record from Eastern Morocco documenting detailed hydrological variations from 8200 to 7500 cal. BP and their climatic forcing. A major hydrogeomorphic evolution of the Charef River occurred at that time, marked by two major incision stages close in time, under hyper-arid conditions at 8200 and ca. 7500 cal. BP. The impacts of these phenomena on the alluvial plains and associated archaeological records during Neolithisation, a major process in human history, currently remain unidentified. This new record sheds light on the fluvial response to the 8.2 ka event in North Africa and why other records are missing. We also bring new insights into the hydrological disruption at the Early–Mid Holocene transition, which was driven by the end of deglaciation combined with insolation and solar forcing. Furthermore, centennial solar variability may have paced river activity in the Moulouya basin and arid regions of North Afric