Paleoenvironmental Reconstruction from Palaeolake Sediments in the Area of Ouargla (Northern Sahara of Algeria)

Abstract

The hyper-arid climate of Ouargla area (Northern Sahara of Algeria) is important in the field of the paleoenvironmental reconstitution. This paper investigates the importance of palaeolake sediments as significant terrestrial archives for studying Quaternary climate changes. Through morphological and mainly micromorphological investigations of the studied sites (Sabkha of Ouargla and palaeolake of Mellala), we noted the fluctuation of climate between arid and more humid conditions during Quaternary. Some pedofeatures have recorded these environmental changes. The studied calcareous crusting has a lacustrine origin when precipitations were more important. The clay coatings around the quartz grains indicate an old origin and different geochemical conditions that led to their dissolution. Lenticular gypsum crystals were formed from groundwater saturated with Ca 2þ and SO 2À 4 ions. Calcite pseudomorphs after lenticular gypsum crystals indicate changes in local climatic parameters. Gypsum crusts can be explained by formation under wet climatic conditions in a lagoonal environment. Black and gray layers indicate evolution of organic matter at a wetter period. This paper highlights an unknown palaeolake which can be useful for the comprehension of the ecological past of the Sahara. The comparison between this palaeolake and other Saharan palaeolakes has allowed us to assign it to a probable active period between 10000 and 4000 years B.P. We are very grateful to Dr. Grillon François (center of materials Pierre-Marie Fourt, France) for the providing the SEM photomicrographs and to the Unité Environnement et Grandes Cultures (INRA-AgroPariTech, Paris-Grignon, France) for manufacturing soil thin sections. We would also like to give particular thanks to M. Belferrag Allaoua (University of Ouargla) for the constructive comments. We are also thankful to anonymous reviewers whose comments on an earlier version of this manuscript improved its quality substantially.

Lithic cyanobacterial communities in the polyextreme Sahara Desert: implications for the search for the limits of life

“…The climate of the studied area, the Ouargla and Oued Righ regions (Fig. 1) is of the hyperarid Mediterranean type (Youcef et al ., 2014; Youcef and Hamdi‐Aïssa, 2014) and is characterized by low rainfall, extremely high temperatures with strong thermal amplitudes, both between day and night (daily) and over a year (annual), and winds that contribute to the very high evaporation rates (Table S1). The low rainfall is accompanied by a marked irregularity and considerable variability depending on the month.…”

“…The surface of the soil is characterized by raised, bumpy areas on the order of 1 m in diameter and a half metre in height. The soil profile is characterized by petrogypsic/hypergypsic horizons where gypsum is well crystallized in large translucent crystals on the order of a decimetre in diameter (Youcef and Hamdi‐Aïssa, 2014). The gypsum crusts existing at the Sebkha Mallala site, characterized by pure gypsum crystals without sand, have a lagoon origin with a hydrogeochemical system dominated by SO 4 2− and Ca 2+ and must have formed in a less arid climate to allow the mobilization of these quantities of gypsum.…”