Évolution holocène de la Tunisie saharienne et présaharienne

Abstract

On peut diviser l'Holocène de la Tunisie saharienne et présaharienne en quatre sous-périodes. L'Holocène inférieur (10 000 B.P. à environ 7 000 B.P.) est caractérisé par la croissance de l'humidité (fixation des dunes, réapparition de lacs, accumulation de la basse terrasse et élaboration du glacis holocène). Il se termine peut-être par une courte phase sèche vers 7 500 - 7 000 B.P. L'Holocène moyen ( 7 000 - 3 500 B.P.?) est probablement la sous-période de l'optimum climatique (fin de l'accumulation de la basse terrasse, épanouissement de la pédogenèse et de l'hydrographie). A l'Holocène supérieur préhistorique commence l'assèchement climatique progressif (entaille de la basse terrasse, développement de la déflation). L'Holocène supérieur historique, après une possible courte phase humide vers 2 400 B.P., se caractérise par l'accumulation de la très basse terrasse, puis son entaille et enfin par la désertification qui remobilise les sables éoliens.

The pleistocene alluvial formations of the Loir river in the Vendôme region (Loir-et-Cher, France) morphosedimentary context and ESR chronology [Les dépôts holocènes de la basse vallée de l'Oued Assaka, Sud-Maroc : résultats préliminaires.]

“…The morphology and the characteristic position of the Middle Rharbian terrace of the Assaka wadi valley are the same as those described by many authors in Morocco: Rohdenburg (1977), Sabelberg (1978), Weisrock (1980), Weisrock and Rognon (1977), Weisrock and Miskovsky (1988), Weisrock et al (1991), , Wengler (1993, and in Maghreb: Ballais (1991), Benazzouz (1994), Coudé-Gaussen et al (1983) and . Only one of the lower terraces of the Assaka has been dated.…”

“…However, the climate became drier during the Lower Holocene, sufficiently to denude the slopes, where during big stonns, gullies and run-off supplied the tributaries of the Assaka wadi with sandy silts and developed adjacent fans . Ballais (1991) and Ballais and Benazzouz (1994) have reached the same conclusion in Southern Tunisia and in Eastern Algeria. Thus in the Nemencha, the Lower Holocene reflects wetter conditions about 10 000 years BP.…”

“…These observations indicate that the climate at 280 ± 30 years BP was wetter than today. Effectively, nowadays, rainfall is very scarce with a significant annual irregular ity and comes from two main systems of atmospheric (1988), Weisrock et al (1991), , Wengler (1993 and, , and in Maghreb: Ballais (1991), Ballais and Benazzouz (1994), Coudé-Gaussen et al (1983) and . Only one of the lower terraces of the Assaka has been dated.…”

Enhanced Mediterranean water cycle explains increased humidity during MIS 3 in North Africa

“…Overall, there is therefore a striking mismatch between the apparent humidity of Africa between 23 and 32 • N in the empirical record (a zonally oriented belt ∼ 1000 km in width) and the climate models. This region encompasses southern Tunisia, in which multiple lines of evidence for distinct and widespread periods of increased humidity provide a highly secure basis for enhanced rainfall during Northern Hemisphere insolation maxima (Ballais, 1991;Petit-Maire et al, 1991), the Fezzan basin, in which compelling evidence for multiple lake highstands exists (Drake et al, 2011), and western Egypt, where large tufa deposits attest to higher past groundwater tables (Smith et al, 2004).…”

Enhanced Mediterranean water cycle explains increased humidity during MIS 3 in North Africa

“…Overall, there is therefore a striking mismatch between the apparent humidity of Africa between 23 and 32 o N in the empirical record (a zonally oriented belt ~1000 km in width) and the climate models. This region encompasses southern Tunisia, in which multiple lines of evidence for distinct and widespread periods of increased humidity provide a highly secure basis for enhanced rainfall during Northern Hemisphere insolation maxima (Ballais, 1991;PETIT-MAIRE et al, 1991), the Fezzan basin, in which compelling evidence for multiple lake highstands exists (Drake et al, 2011) and western Egypt, where large tufa deposits attest to higher past groundwater tables (Smith et al, 2004).…”