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ZusammenfassungKarstph~inomene und Kalkkrusten (Caliche) haben sich auf den Oberfl~chen der Gesteine des Mittelmioz~ins im Gebiet zwischen Quseir und Mersa Alam entlang der K~iste des Roten Meeres in )~gypten entwickelt. Eingehende Untersuchungen yon Kalkkrusten Profilen iassen unterschiedliche Strukturen und Gef~ige erkennen, die sowohi zyklische Bildung belegen aIs auch diagenetische Kristallisations-Differentiation und Deformation. Das Anftreten dieser Caliche-Bildungen legt nahe, dab die mittelmioziinen Gesteine im Untersuchnngsgebiet abwechselnd regenreichen Perioden und solchen mit starker Evaporation ausgesetzt waren. AbstractKarstified features and surficial calcareous crust (caliche) develop on the upper most surfaces of the Middle Miocene rocks in the area between Quseir and Mersa Alam along the Red Sea coast, Egypt. Detalied studies of the caliche profile revealed various textures and fabrics denoting a cyclicity in deposition as well as diagenetic differentiation crystallization and deformation. The occurrence of these caIiche deposits suggest that the Middle Miocene rocks in the study area have been subjected to alternating periods of rainfall and intense evaporation. R~sum~Des structures karstiques et des crofites calcaires superficielles (caliches), se sont form&s ~t la surface des roches du Mio&ne moyen dans la r6gion comprise entre Ouseir et Mersa Alam, le long de la c6te de la met Rouge, en Egypte. L'&ude d&aill& de profils de la caliche r&~le des structures varifies qui indiquent un dSp6t cyclique ainsi qu'une cristallisation diff6rentielle et une dSformation diag6n&ique. La prfsence de tels dSp6ts de caliche suggSre que les roches du Miocene moyen de cette rfgion ont &6 soumises alternativement ~t des p6riodes de pluie et d'&aporation intense. KpaTKOe coxep~aHHe

The Ras Shukeir sabkha, located along the Red Sea coastal plain is a siliciclastic sabkha enclosing some residual salinas, that are confined to localized depressions. A Holocene evaporite sequence at the southern edge of the area is considered to be an ancient equivalent to the present day sabkha-salina complex.A depositional model is proposed for the sabkha-salina showing the nature and distribution of the microfacies in three different zones: as subaerial sabkha deposits along the supratidal flat, and as subaqueous deposits along the margins and also within the salinas. The area is fed by resurging, mixed-source groundwater influx that fluctuates with the seasons, and this groundwater table is presently very shallow not exceeding one meter below the surface. The ground water regime, governed by replenishment in winter and evaporative depletion in summer, controls the mechanism of the evaporite deposition and the distribution of the different microfacies.A comparison of the recent deposits with the older Holocene evaporite sequence illustrates the similarities and differences between the two deposits and establishes the diagenetic alterations that affect the recent sabkha-salina deposits because they are clearly developed in the Holocene equivalent.

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