Geochemistry and Sedimentology Study of a Core From Chott Geuttar: Central Tunisia Climatic and Environmental Significance

Introduction

Water and air circulations around the planet change as the climate changes. Nonetheless, some regions immediately respond; others should wait a lapse of time to modify the record of their depositional environments. North Africa is climatically susceptible, and it is the first region in the Mediterranean basin to be affected by climate change. For academic and practical objectives, saline systems have been an important topic of study. Economically, they provide valuable evaporate minerals and brines (Tagorti et al., 2013; Ben Smida, 2016). Sedimentolgical, they give a lot of information about the sedimentary history and the depositional environment (Essefi et al., 2013). To climatologists, the sedimentary records of these systems could be a subject of paleoclimatic (Essefi et al., 2013; 2014; Mefteh et al., 2015) and cyclostratigraphic (Essefi et al., 2014) research.

Sebkhas or chott are considered wetlands. Sebkha is an Arabic word that refers to the salt lakes that are subject to periodic inundations. It is a depression occupied by a generally salty lake and where evaporites are deposited. Throughout human history, wetlands have been considered a valuable natural resource (Scholz and Lee, 2005). 'Wetlands are areas of marsh, fen, peatland, or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish, or salt, including areas of marine water the depth of which at low tide does not exceed six meters,' according to the Ramsar Convention, which brought wetlands to the attention of the international community (Goodwin, 2017). Wetlands are more prevalent in areas where precipitation exceeds water loss through evapotranspiration and surface runoff (Scholz and Lee, 2005). Moreover, ‘Wetlands are a halfway world between terrestrial and aquatic ecosystems and exhibit some of the characteristics of both,' says another, more succinct definition (Smith, 1980). In fact, chott El Geuttar is considered wetlands. It is endorheic system that never have a link to the sea due to the uplifted reliefs avoiding any contact with marine environments (Essefi et al., 2014).

Numerous saline systems have been established in Tunisia. Some of them are endorheic (Essefi, 2009; 2013; Bedoui, 2016; Bedoui et al., 2022); others are exoreic (Lakhdar, 2009). In this part, the studied systems will be introduced in terms of geographic, geologic, and climatic settings. These saline systems are candidates to record the climatic variability. Moreover, the studied saline systems will be introduced in their Mediterranean framework. Then, global phenomena and their effect on North Africa such as the Mediterranean Oscillation (MO), the North Atlantic Oscillation (NAO), and the Atlantic Multidecadal Oscillation (AMO) were introduced to understand the change in El Guettar saline systems with a global line of thinking.

As Complicated areas in which many factors can intervene, saline environments must be studied globally; that is to say that many specialties are involved. The study of saline environments is at the crossroads of many specialties. For this reason, the multidisciplinary study reveals vital in the case of the studied saline system. The study started from the field works to recuperate cores. Then, cores underwent nondestructive analyses such as facies identification and colors study. Once samples were taken from the cores, they underwent several destructive analyses such as geochemical (major elements), geophysical (magnetic susceptibility) and sedimentological (observations, grain size distribution). Statistical and mathematical techniques such as spectral analysis were used to treat the obtained data. The main objective of this study is to find with high resolution the climatic variability in the endorheic saline system.